IFOG and IORG Gyros: A Study of Comparative Performance

*Ramón José Pérez Menéndez*

### **Abstract**

In this revision work, firstly classical structure and main performance parameters of interferometric fiber-optic gyroscope (IFOG) and integrated optics passive resonator gyroscope (IORG) are reviewed. Then, the main advanced models and performance parameters of these two types of rotation-rate inertial sensors are described, and finally the design trends of both types are analyzed. Taking as reference the performance parameters analyzed above, a comparative analysis between manufactured IFOG and IORG units of close geometrical dimensions is realized. This analysis leads ranking these devices into six classical levels of inertial performance: strategic grade, navigation grade, high-end tactical grade, tactical grade, industrial low-end tactical grade, and consumer grade. This classification allows to deduce the main application areas of both kinds of devices. This way, the impact of these sensors in applications such as aeronautics, aerospace navigation, mechanical micro-fabrication, tactical weapons, or, more recently, robotics can be disclosed.

**Keywords:** interferometric fiber-optic gyroscope (IFOG), integrated optics passive resonator gyroscope (IORG), optical passive ring resonator interferometer, single-mode fiber (SMF), silicon wire waveguide

#### **1. Introduction**

Applications as guidance, navigation, and control systems in aircrafts, spacecrafts, and attitude systems in terrestrial vehicles, to give some examples, require compact, low cost, and reliable inertial navigation systems (INSs), which are equipped with increasingly accurate gyroscopes. For this reason, gyroscopes (in what follows from here, gyros) are key elements, which are essential to obtain the desired sensitivity for all above applications. Gyros having a dynamic range up to 1500°/s are required in both space and terrestrial vehicle navigation inertial measurement units (IMUs). Attitude and heading systems in aircraft and precisionspacecraft INSs require a gyro resolution typically on the order of 1°/h and 0.01– 0.001°/h, respectively. Optical gyros based on Sagnac effect are the key components of IMUs which are widely used in the above mentioned applications [1, 2]. Currently, the most widely used gyro technology for high-performance gyro systems is the optical fiber-based technology, specifically the technology based on interferometric fiber-optic gyro (IFOG). However, the counterpart of the IFOG made entirely in silicon wire waveguides on silicon-on-insulator (SOI) platform, called photonic integrated circuits (PICs) and, specifically, the integrated optics passive

**4**

2011

*Gyroscopes - Principles and Applications*

[1] Toys Invented in Ancient China. Classroom. Available from: https:// classroom.synonym.com/toys-inventedancient-china-10930.html [Accessed: 18 [9] Fang J, Qin J. Advances in atomic gyroscopes: A view from inertial navigation applications. Sensors.

[10] Zhuang X, Chen B, Wang X, et al. Microscale polysilicon hemispherical shell resonating gyroscopes with integrated three-dimensional curved electrodes. Journal of Physics: Conference Series. 2018;**986**:012022

[11] Oh H, Lee KJ, Lee K, et al.

2015;**3**(1):1

Gyroscopes based on surface acoustic waves. Micro and Nano Systems Letters.

[12] Armenise MN. Emerging gyroscope technologies. In: Advances in Gyroscope Technologies. Berlin, Heidelberg: Springer; 2010. pp. 103-108

2012;**12**(5):6331-6346

[2] Gyroscope. Available from: http:// physics.kenyon.edu/EarlyApparatus/ Mechanics/Gyroscope/Gyroscope.html

[3] Gyroscopes have a huge variety of uses, find out how they work in our latest Tech Explained. Tech Explained: Gyroscopes. Available from: https:// www.springwise.com/tech-explainedgyroscopes/ [Accessed: 20 November

[4] Shamir A. An Overview of Optical Gyroscopes Theory, Practical Aspects, Applications and Future Trends: Technical paper: Adi Shammir; 2006

[5] Ring Laser Gyroscope Market-Snapshot. Transparency Market Research. available from: https://www. transparencymarketresearch.com/ringlaser-gyroscope-market.html [Accessed:

[6] Fiber Optics Gyroscope Market. Markets and Markets. Available from: https://www.marketsandmarkets.com/ Market-Reports/fiber-optic-gyroscopemarket-99825571.html [Accessed: 14

[7] Trusov AA. Overview of MEMS Gyroscopes: History, Principles of Operations, Types of Measurements. Irvine, USA: University of California;

[8] MEMS Gyroscope Market - Growth, Trends and Forecast (2020-2025). Mordor Telligence. Available from: https://www.mordorintelligence.com/ industry-reports/mems-gyroscopemarket [Accessed: 15 March 2020]

15 March 2020]

March 2020]

[Accessed: 18 March 2020]

March 2020]

2018]

resonator gyro (IORG), has many advantages such as high robustness, theoretical sensitivity, and superior reliability due to its inherent characteristics of miniaturized structure, all-solid-state, and the combination between integrated optics and well-known CMOS fabrication technology [3, 4]. Thus, IORG has been considered as the next generation of resonant micro-optical gyros (RMOG) and a promising candidate in the field of inertial navigation [3, 5]. In particular, IORGs are very promising in terms of performance parameters such as low cost, compactness, light weight, and high reliability.

For a fixed length *L* by fixing the coil diameter *D*, the sensitivity of the sensor can be improved by increasing the total coil length *L* by adding a high number of turns *N* taking into account an upper limit due to the fiber attenuation. Also working at 1310 nm wavelength instead of 1550 nm could help to improve the sensitivity of the sensor. From **Figure 1** it can be clearly seen that IFOG has a passive configuration because the laser source is located externally to the sensing coil. In this system, the two counter-propagating light beams travel through the core of a single-mode optical fiber (SMF) under the total internal reflection phenomenon. As the core diameter of such an optical fiber is only about 8 μm, the spot size of the interference signal can only be coupled to a small area at the end of the fiber loop, for example, on the small detection area of a photodetector. So that, this interference signal affects only one or two interference fringes whose intensity can

where *I*<sup>0</sup> is the amplitude of each of the two counter-propagating beams and *ϕ* is the optical phase difference between them. **Figure 2** represents the variation of light

*I*ð Þ¼ *ϕ I*0ð Þ 1 þ cos *ϕ* (2)

be evaluated by the following expression:

*IFOG and IORG Gyros: A Study of Comparative Performance*

*DOI: http://dx.doi.org/10.5772/intechopen.89957*

**Figure 1.**

**Figure 2.**

**7**

*Two-beam interference response curve as a function of ϕ (phase difference).*

*Basic structure of the IFOG.*

Both of them (IFOGs and IORGs) are based on Sagnac effect, which generates a phase or frequency difference proportional to the angular rate when two counterpropagating light beams in an optical resonant cavity suffer a rotation. Sagnac effect has also been demonstrated in semiconductor ring laser gyros (SRLGs) [1, 6]. Passive optical resonators with the laser source external to the ring resonator are particularly attractive because they show high performance and overcome some issues of active devices, mainly lock-in effect and mode competition. So far, best demonstrated resolution for the IFOG is 0.0002°/h [IXSea, FOG Marins] for a strategic-grade unit with 5 km length and 200 mm fiber coil diameter [7], while for the IORG, the best value achieved is 1°/h [IntelliSense Corp., VIGOR] for a temperature-compensated high-end tactical-grade unit with weight < 100 g and volume < 5 cc. made on a silicon wire waveguide ring resonator [8].

This work is structured as follows: Sections 2 and 3 deal with the main structure and configurations of IFOG and IORG, respectively. Section 4 examines the performance-grade classification and parameters of IFOG and IORG. Section 5 collects the main performance parameters of IFOG and IORG units made or designed by the most important world manufacturers and laboratories, respectively, enabling a comparative study between them. Section 6 presents the main design advances, trends, and optimization issues in the IFOG and IORG cuttingedge engineering. Finally, Section 7 is devoted to extract the main conclusions of this work.

#### **2. IFOG: basic structure and configurations**

The interferometric fiber-optic gyro is to date a mature technology and was originally designed as a low-cost alternative to the ring laser gyro (RLG). Surprisingly, today IFOG can substitute the RLG both in terms of manufacturing costs and that of performance, gaining prominence in a series of military and commercial applications [9–12]. The studies provide that the developments in solidstate optics and fiber-optic technology could lead up to 0.0001°/h ultimate value in resolution performance for IFOG units even for small-size designs. The IFOG is based on the Sagnac effect within an open optical path realized by a N-turn fiberoptic coil when two independent counter-propagating light modes are externally introduced from a broadband laser source through its two ends, respectively (see **Figure 1**). This causes an interference pattern between the CW and CCW light beams to be collected in a photodetector with a phase shift given by the following equation:

$$
\phi\_{\rm S} = \frac{2\pi LD}{\lambda\_0 \ c\_0} \,\Omega \tag{1}
$$

where *L* and *D* are length and diameter of fiber-optic sensing coil, respectively; λ<sup>0</sup> and *c0* are wavelength and speed of light source in vacuum, respectively; and Ω is the rotation rate.

*IFOG and IORG Gyros: A Study of Comparative Performance DOI: http://dx.doi.org/10.5772/intechopen.89957*

resonator gyro (IORG), has many advantages such as high robustness, theoretical sensitivity, and superior reliability due to its inherent characteristics of miniaturized structure, all-solid-state, and the combination between integrated optics and well-known CMOS fabrication technology [3, 4]. Thus, IORG has been considered as the next generation of resonant micro-optical gyros (RMOG) and a promising candidate in the field of inertial navigation [3, 5]. In particular, IORGs are very promising in terms of performance parameters such as low cost, compactness, light

Both of them (IFOGs and IORGs) are based on Sagnac effect, which generates a phase or frequency difference proportional to the angular rate when two counterpropagating light beams in an optical resonant cavity suffer a rotation. Sagnac effect has also been demonstrated in semiconductor ring laser gyros (SRLGs) [1, 6]. Passive optical resonators with the laser source external to the ring resonator are particularly attractive because they show high performance and overcome some issues of active devices, mainly lock-in effect and mode competition. So far, best demonstrated resolution for the IFOG is 0.0002°/h [IXSea, FOG Marins] for a strategic-grade unit with 5 km length and 200 mm fiber coil diameter [7], while for

This work is structured as follows: Sections 2 and 3 deal with the main structure

The interferometric fiber-optic gyro is to date a mature technology and was

Surprisingly, today IFOG can substitute the RLG both in terms of manufacturing costs and that of performance, gaining prominence in a series of military and commercial applications [9–12]. The studies provide that the developments in solidstate optics and fiber-optic technology could lead up to 0.0001°/h ultimate value in resolution performance for IFOG units even for small-size designs. The IFOG is based on the Sagnac effect within an open optical path realized by a N-turn fiberoptic coil when two independent counter-propagating light modes are externally introduced from a broadband laser source through its two ends, respectively (see **Figure 1**). This causes an interference pattern between the CW and CCW light beams to be collected in a photodetector with a phase shift given by the following

> *<sup>ϕ</sup><sup>S</sup>* <sup>¼</sup> <sup>2</sup>*πLD λ*<sup>0</sup> *c*<sup>0</sup>

where *L* and *D* are length and diameter of fiber-optic sensing coil, respectively; λ<sup>0</sup> and *c0* are wavelength and speed of light source in vacuum, respectively; and Ω is

Ω (1)

originally designed as a low-cost alternative to the ring laser gyro (RLG).

the IORG, the best value achieved is 1°/h [IntelliSense Corp., VIGOR] for a temperature-compensated high-end tactical-grade unit with weight < 100 g and

and configurations of IFOG and IORG, respectively. Section 4 examines the performance-grade classification and parameters of IFOG and IORG. Section 5 collects the main performance parameters of IFOG and IORG units made or designed by the most important world manufacturers and laboratories, respectively, enabling a comparative study between them. Section 6 presents the main design advances, trends, and optimization issues in the IFOG and IORG cuttingedge engineering. Finally, Section 7 is devoted to extract the main conclusions of

volume < 5 cc. made on a silicon wire waveguide ring resonator [8].

**2. IFOG: basic structure and configurations**

weight, and high reliability.

*Gyroscopes - Principles and Applications*

this work.

equation:

**6**

the rotation rate.

For a fixed length *L* by fixing the coil diameter *D*, the sensitivity of the sensor can be improved by increasing the total coil length *L* by adding a high number of turns *N* taking into account an upper limit due to the fiber attenuation. Also working at 1310 nm wavelength instead of 1550 nm could help to improve the sensitivity of the sensor. From **Figure 1** it can be clearly seen that IFOG has a passive configuration because the laser source is located externally to the sensing coil. In this system, the two counter-propagating light beams travel through the core of a single-mode optical fiber (SMF) under the total internal reflection phenomenon. As the core diameter of such an optical fiber is only about 8 μm, the spot size of the interference signal can only be coupled to a small area at the end of the fiber loop, for example, on the small detection area of a photodetector. So that, this interference signal affects only one or two interference fringes whose intensity can be evaluated by the following expression:

$$I(\phi) = I\_0(\mathbf{1} + \cos \phi) \tag{2}$$

where *I*<sup>0</sup> is the amplitude of each of the two counter-propagating beams and *ϕ* is the optical phase difference between them. **Figure 2** represents the variation of light

**Figure 2.** *Two-beam interference response curve as a function of ϕ (phase difference).*

intensity along a single interference fringe as a function of *ϕ*. Notice the output intensity noise produced when the phase difference is detected with a phase error Δ*ϕ*. Phase noise sources and their influence are treated in Ref. [13].

reciprocity condition as exactly as possible. Optical light source used is a broadband laser source to reduce the noise signal due to Rayleigh scattering within the fiber. As fiber sensing coil, either standard or rare-earth doped optical fiber can be used, but polarization-maintaining fiber is needed in both cases to ensure that just one polarization mode exists within it. The optical round trip experienced by the two counter-propagating beams is as follows. The light beam from source is collimated and coupled into an optical straight path and, then, passes through an optical system composed of one beam splitter, one linear polarizer, and a filter between two convergent lenses to select only one propagated mode within the fiber coil. The second beam splitter is used to split the original beam from the source and create two counter-propagated CW and CCW beams into the fiber coil. Then, after having traveled through the fiber loop, the CW and CCW beams recombine into the interferometer after passing again through the polarizer and reflecting onto the second face of splitter. Then, the photodetector collects the produced interferomet-

ric signal. The phase modulator is used to apply a sinusoidal or square-wave dynamic phase bias to light path, thus increasing the sensitivity of the sensor [15]. When modulation frequency of phase bias is high enough, electronic noise is avoided. Finally, an electronic demodulation circuit is needed to extract the magnitude and sign of rotation rate. Main advantages for the open-loop IFOG scheme are a few number of optical and electronic components and, hence, low price, good sensitivity, long lifetime, high reliability, and low power consumption. The main disadvantages of this configuration are high fiber coil length (100–3000 m) to increase sensitivity, electronic drift of analogical components, and disturbing influ-

A more advanced design is achieved by closing the measurement loop by means of a feedback signal becoming into the so-called IFOG closed-loop configuration. The general scheme of a closed-loop IFOG is depicted in **Figure 5**. Very high performance was obtained for closed-loop IFOG configuration with respect the open-loop one [16]. In this scheme, the output signal of demodulator circuit passes through a servo amplifier which drives a phase transducer placed in the interferometer path. The total phase shift becomes equal to zero because the phase transducer introduces a nonreciprocal phase shift that is equal, by in the opposite sign, to that generated by Sagnac phase shift induced by rotation. The output of the system is then the output of the phase transducer. The main advantage of this configuration is the insensitivity to the laser source amplitude variations and the electronic circuitry gain because the system is always operated at zero total phase shift. This

ence of temperature and environmental conditions.

*IFOG and IORG Gyros: A Study of Comparative Performance*

*DOI: http://dx.doi.org/10.5772/intechopen.89957*

**Figure 5.**

**9**

*Typical closed-loop IFOG configuration.*

**Figure 3** shows the minimal open-loop IFOG unit configuration. This configuration includes apart fiber sensing coil, a superluminescent (SLD) broadband light source, two (2 input 2 output) directional couplers, one linear polarizer, one photodetector, and one electro-optic phase modulator made of piezo ceramic tube (PZT) or lithium-niobate electrodes. The function of electro-optical phase modulator is to provide a controlled phase shift which adds to the Sagnac phase shift produced by the rotation onto the system.

This way, the signal detected by photodetector can be demodulated with some ease to recover by electronic means the Ω rotation-rate value which affects the whole system. A reduced minimal configuration fiber-optic gyro for land navigation applications can be found in Ref. [14]. Then two main options can be adopted for IFOG: open-loop configuration and closed-loop configuration. **Figure 4** represents one typical bulk optics open-loop IFOG configuration, the dotted block being usually made on an integrated optical chip (IOC). In this configuration, the rotationrate information is recovered by the electrical output signal of photodetector after a previous demodulation process.

This configuration guarantees the reciprocity of the system. This implies that the two counter-propagating beams have exactly equal amplitude and phase at output when no rotation affects the system. However an error phase shift can be present on interferometric signal collected by the photodetector. So to reduce phase difference error and increase the resolution of the sensor, it is necessary to reach the

#### **Figure 3.**

*Minimal open-loop IFOG unit configuration.*

**Figure 4.** *Typical bulk optics IFOG open-loop configuration.*

#### *IFOG and IORG Gyros: A Study of Comparative Performance DOI: http://dx.doi.org/10.5772/intechopen.89957*

intensity along a single interference fringe as a function of *ϕ*. Notice the output intensity noise produced when the phase difference is detected with a phase error

**Figure 3** shows the minimal open-loop IFOG unit configuration. This configuration includes apart fiber sensing coil, a superluminescent (SLD) broadband light source, two (2 input 2 output) directional couplers, one linear polarizer, one photodetector, and one electro-optic phase modulator made of piezo ceramic tube (PZT) or lithium-niobate electrodes. The function of electro-optical phase modulator is to provide a controlled phase shift which adds to the Sagnac phase shift

This way, the signal detected by photodetector can be demodulated with some ease to recover by electronic means the Ω rotation-rate value which affects the whole system. A reduced minimal configuration fiber-optic gyro for land navigation applications can be found in Ref. [14]. Then two main options can be adopted for IFOG: open-loop configuration and closed-loop configuration. **Figure 4** represents one typical bulk optics open-loop IFOG configuration, the dotted block being usually made on an integrated optical chip (IOC). In this configuration, the rotationrate information is recovered by the electrical output signal of photodetector after a

This configuration guarantees the reciprocity of the system. This implies that the two counter-propagating beams have exactly equal amplitude and phase at output when no rotation affects the system. However an error phase shift can be present on interferometric signal collected by the photodetector. So to reduce phase difference

error and increase the resolution of the sensor, it is necessary to reach the

Δ*ϕ*. Phase noise sources and their influence are treated in Ref. [13].

produced by the rotation onto the system.

*Gyroscopes - Principles and Applications*

previous demodulation process.

*Minimal open-loop IFOG unit configuration.*

*Typical bulk optics IFOG open-loop configuration.*

**Figure 3.**

**Figure 4.**

**8**

reciprocity condition as exactly as possible. Optical light source used is a broadband laser source to reduce the noise signal due to Rayleigh scattering within the fiber. As fiber sensing coil, either standard or rare-earth doped optical fiber can be used, but polarization-maintaining fiber is needed in both cases to ensure that just one polarization mode exists within it. The optical round trip experienced by the two counter-propagating beams is as follows. The light beam from source is collimated and coupled into an optical straight path and, then, passes through an optical system composed of one beam splitter, one linear polarizer, and a filter between two convergent lenses to select only one propagated mode within the fiber coil. The second beam splitter is used to split the original beam from the source and create two counter-propagated CW and CCW beams into the fiber coil. Then, after having traveled through the fiber loop, the CW and CCW beams recombine into the interferometer after passing again through the polarizer and reflecting onto the second face of splitter. Then, the photodetector collects the produced interferometric signal. The phase modulator is used to apply a sinusoidal or square-wave dynamic phase bias to light path, thus increasing the sensitivity of the sensor [15]. When modulation frequency of phase bias is high enough, electronic noise is avoided. Finally, an electronic demodulation circuit is needed to extract the magnitude and sign of rotation rate. Main advantages for the open-loop IFOG scheme are a few number of optical and electronic components and, hence, low price, good sensitivity, long lifetime, high reliability, and low power consumption. The main disadvantages of this configuration are high fiber coil length (100–3000 m) to increase sensitivity, electronic drift of analogical components, and disturbing influence of temperature and environmental conditions.

A more advanced design is achieved by closing the measurement loop by means of a feedback signal becoming into the so-called IFOG closed-loop configuration. The general scheme of a closed-loop IFOG is depicted in **Figure 5**. Very high performance was obtained for closed-loop IFOG configuration with respect the open-loop one [16]. In this scheme, the output signal of demodulator circuit passes through a servo amplifier which drives a phase transducer placed in the interferometer path. The total phase shift becomes equal to zero because the phase transducer introduces a nonreciprocal phase shift that is equal, by in the opposite sign, to that generated by Sagnac phase shift induced by rotation. The output of the system is then the output of the phase transducer. The main advantage of this configuration is the insensitivity to the laser source amplitude variations and the electronic circuitry gain because the system is always operated at zero total phase shift. This

**Figure 5.** *Typical closed-loop IFOG configuration.*

brings very small drift, from 0.001°/h up to 0.01°/h On the other hand, the output scale factor linearity and stability depends only on the phase transducer accuracy.

Eq. (3) allows the calculation of photon-shot-noise photocurrent at photodetector (*Isn*), which is the minimum photodetector output current corresponding to a given level of optical input power:

$$I\_{sn} = \sqrt{\frac{e^2 \eta \lambda}{hc} P\_{\text{max}} \Delta f} \tag{3}$$

*<sup>δ</sup>*<sup>Ω</sup> <sup>¼</sup> <sup>1</sup>

*IFOG and IORG Gyros: A Study of Comparative Performance*

*DOI: http://dx.doi.org/10.5772/intechopen.89957*

Sagnac effect to be applied.

possible with very reduced tolerance.

**Figure 6.**

**11**

*Q D* ffiffiffiffiffiffiffi *Ppd* p

here *Q* is the *Q* factor of the cavity, *D* is its diameter, *Ppd* is the input optical power incident on photodetector, *τ* is the integration time, and *h*, *c*, *λ*, and *η* are the same as in Eq. (4). A new step to achieve the miniaturization of the gyro is to perform the passive ring resonator by means of an integrated optical waveguide made of high-index-contrast materials like silica-on-silicon, silicon-on-insulator, III–V semiconductors (InP), or silicon nitride (Si3N4). Then, this solution gets to what is called the IORG. Thus, an IORG can be formed by a ring resonator that includes an optical waveguide having a ring shape and one or two straight bus waveguides (see **Figure 6**). The bus and the ring waveguides are coupled by the evanescent field. When the ring is used for rotation sensing, it is necessary to launch two input signals (CW, CCW) simultaneously in the bus waveguides to excite the ring resonator cavity for both the CW and CCW propagation directions for the

If a two-bus waveguide approach is used, the two input beams can be launched

The conventional configuration of an IORG includes a narrow linewidth laser source, a high *Q* factor ring resonator, an optoelectronic processing unit, two pho-

manufactured by using hybrid or monolithic photonic integration. Hybrid integration has as main problems the optical alignment of all components and the high value of optical power losses. Monolithic integration has the advantages of the absence of optical alignment issues, the higher robustness and compactness, the

todetectors, and an electronic readout unit (**Figure 7**). The sensor can be

*Integrated ring resonator coupled with one (c) or two (a), (b) waveguides (sensing element of IORG).*

minor dimensionality, and the lower optical power consumption.

in two different bus waveguides or in the two opposite ends of the same bus waveguide. Consequently there are two possible configurations for the excitation of the cavity and resonance frequency measurement. In the first case, output ports are called through ports (**Figure 6(a)** and **(c)**), whereas in the second one, output ports are the drop ports (**Figure 6(b)**). Using a one-bus waveguide architecture, each end of the bus can be utilized either as input or output port. In this case, two circulators or switches have to be used at both ends of the bus to excite the resonator in CW and CCW directions and to monitor the spectral response at the respective through port (**Figure 6(c)**). To minimize the bias drift of the gyro, the two beams coupled to the resonator must have the same optical power amplitude or as similar as

ffiffiffiffiffiffiffiffiffiffi 2*h c*<sup>3</sup> *λητ* s

(6)

Here, *P*max is the maximum optical power incident at photodetector, Δ *f* is the minimum bandwidth detectable by the photodetector, and *e*, *η*, *λ*, *h*, and *c* are the electron charge, the quantum efficiency of photodetector, the operating vacuum wavelength, the Planck constant, and the vacuum speed of light, respectively. This way, in accordance with photon-shot-noise photodetector current, the *δ*Ω threshold sensitivity of gyro sensor (that is to say, the minimum rotation rate which this gyro is able to measure) can be calculated by Eq. (4):

$$
\delta \Omega\_{\parallel} = \left(\frac{hc^2}{\pi e \,\eta L D P\_{\text{max}}}\right) I\_{\text{sn}} \tag{4}
$$

where *L* and *D* are the length and diameter of sensing fiber coil, respectively, and the other parameters are the same as in Eq. (3). From this expression it can be clearly seen that the greater the product L � D, the better the sensitivity of the detector. Thus, typical performance reported for open-loop and closed-loop IFOG configurations are �100°/hr [17–21]. dynamic range, bias drift between 0.001°/h and 0.2°/h with drift stability between 0.0005°/h and 0.01°/h, angle random walk (ARW) between 0.004°/ ffiffiffiffiffi hr <sup>p</sup> and 0.04°/ ffiffiffiffiffi hr <sup>p</sup> , and bandwidth from 20 to 100 Hz. Those IFOGs have long been used for land navigation applications mainly due to their extreme robustness, and also they are also commercially available for use in space applications due to their high reliability and cost-effectiveness.

#### **3. IORG: fundamentals and main configurations**

The usage of RFOGs instead of IFOGs is the first step that allows to reduce the fiber-optic coil length, thus leading to lower dimensions. Then, in the era of miniaturization, the possibility of integrating optical waveguides different than optical fibers leads to even smaller geometrical dimensions. Thus, RMOG is a promising candidate for applications requiring small, light, and robust gyros. The first design of an RFOG was made by S. Ezekiel and S.R. Balsamo at M.I.T. in 1977. In this design, the difference Δ *f* between CW and CCW frequency resonances of the cavity is given by the following equation [22, 23]:

$$
\Delta f = \left(\frac{4A}{\lambda P}\right) \Omega \tag{5}
$$

where *A* is the area enclosed by the cavity, *P* is the perimeter of the cavity, *λ* is the vacuum wavelength, and Ω is the rotation rate affecting the system. The precision with which Δ*f* can be measured depends on the *Q* factor of the cavity. This way, the minimum rotation rate that this gyro is able to measure can be calculated by Eq. (6):

*IFOG and IORG Gyros: A Study of Comparative Performance DOI: http://dx.doi.org/10.5772/intechopen.89957*

brings very small drift, from 0.001°/h up to 0.01°/h On the other hand, the output scale factor linearity and stability depends only on the phase transducer

r

*<sup>δ</sup>*<sup>Ω</sup> <sup>¼</sup> *h c*<sup>2</sup>

*Isn* ¼

Eq. (3) allows the calculation of photon-shot-noise photocurrent at photodetector (*Isn*), which is the minimum photodetector output current corresponding to a

Here, *P*max is the maximum optical power incident at photodetector, Δ *f* is the minimum bandwidth detectable by the photodetector, and *e*, *η*, *λ*, *h*, and *c* are the electron charge, the quantum efficiency of photodetector, the operating vacuum wavelength, the Planck constant, and the vacuum speed of light, respectively. This way, in accordance with photon-shot-noise photodetector current, the *δ*Ω threshold sensitivity of gyro sensor (that is to say, the minimum rotation rate which this gyro

> *π e ηLDP*max � �

where *L* and *D* are the length and diameter of sensing fiber coil, respectively, and the other parameters are the same as in Eq. (3). From this expression it can be clearly seen that the greater the product L � D, the better the sensitivity of the detector. Thus, typical performance reported for open-loop and closed-loop IFOG configurations are �100°/hr [17–21]. dynamic range, bias drift between 0.001°/h and 0.2°/h with drift stability between 0.0005°/h and 0.01°/h, angle

hr

The usage of RFOGs instead of IFOGs is the first step that allows to reduce the fiber-optic coil length, thus leading to lower dimensions. Then, in the era of miniaturization, the possibility of integrating optical waveguides different than optical fibers leads to even smaller geometrical dimensions. Thus, RMOG is a promising candidate for applications requiring small, light, and robust gyros. The first design of an RFOG was made by S. Ezekiel and S.R. Balsamo at M.I.T. in 1977. In this design, the difference Δ *f* between CW and CCW frequency resonances of the

> <sup>Δ</sup>*<sup>f</sup>* <sup>¼</sup> <sup>4</sup>*<sup>A</sup> λP* � �

where *A* is the area enclosed by the cavity, *P* is the perimeter of the cavity, *λ* is the vacuum wavelength, and Ω is the rotation rate affecting the system. The precision with which Δ*f* can be measured depends on the *Q* factor of the cavity. This way, the minimum rotation rate that this gyro is able to measure can be calculated

20 to 100 Hz. Those IFOGs have long been used for land navigation applications mainly due to their extreme robustness, and also they are also commercially available for use in space applications due to their high reliability and

<sup>p</sup> and 0.04°/ ffiffiffiffiffi

hr

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi *e*2*ηλ*

*h c <sup>P</sup>*max <sup>Δ</sup>*<sup>f</sup>*

(3)

*Isn* (4)

<sup>p</sup> , and bandwidth from

Ω (5)

accuracy.

given level of optical input power:

*Gyroscopes - Principles and Applications*

is able to measure) can be calculated by Eq. (4):

random walk (ARW) between 0.004°/ ffiffiffiffiffi

**3. IORG: fundamentals and main configurations**

cavity is given by the following equation [22, 23]:

cost-effectiveness.

by Eq. (6):

**10**

$$
\delta\Omega \,\,=\,\frac{1}{Q D \sqrt{P\_{pd}}} \sqrt{\frac{2hc^3}{\lambda \eta \,\,\tau}}\,\,\tag{6}
$$

here *Q* is the *Q* factor of the cavity, *D* is its diameter, *Ppd* is the input optical power incident on photodetector, *τ* is the integration time, and *h*, *c*, *λ*, and *η* are the same as in Eq. (4). A new step to achieve the miniaturization of the gyro is to perform the passive ring resonator by means of an integrated optical waveguide made of high-index-contrast materials like silica-on-silicon, silicon-on-insulator, III–V semiconductors (InP), or silicon nitride (Si3N4). Then, this solution gets to what is called the IORG. Thus, an IORG can be formed by a ring resonator that includes an optical waveguide having a ring shape and one or two straight bus waveguides (see **Figure 6**). The bus and the ring waveguides are coupled by the evanescent field. When the ring is used for rotation sensing, it is necessary to launch two input signals (CW, CCW) simultaneously in the bus waveguides to excite the ring resonator cavity for both the CW and CCW propagation directions for the Sagnac effect to be applied.

If a two-bus waveguide approach is used, the two input beams can be launched in two different bus waveguides or in the two opposite ends of the same bus waveguide. Consequently there are two possible configurations for the excitation of the cavity and resonance frequency measurement. In the first case, output ports are called through ports (**Figure 6(a)** and **(c)**), whereas in the second one, output ports are the drop ports (**Figure 6(b)**). Using a one-bus waveguide architecture, each end of the bus can be utilized either as input or output port. In this case, two circulators or switches have to be used at both ends of the bus to excite the resonator in CW and CCW directions and to monitor the spectral response at the respective through port (**Figure 6(c)**). To minimize the bias drift of the gyro, the two beams coupled to the resonator must have the same optical power amplitude or as similar as possible with very reduced tolerance.

The conventional configuration of an IORG includes a narrow linewidth laser source, a high *Q* factor ring resonator, an optoelectronic processing unit, two photodetectors, and an electronic readout unit (**Figure 7**). The sensor can be manufactured by using hybrid or monolithic photonic integration. Hybrid integration has as main problems the optical alignment of all components and the high value of optical power losses. Monolithic integration has the advantages of the absence of optical alignment issues, the higher robustness and compactness, the minor dimensionality, and the lower optical power consumption.

emission noise. Then, with this ring resonator configuration, an IORG unit

*IFOG and IORG Gyros: A Study of Comparative Performance*

*DOI: http://dx.doi.org/10.5772/intechopen.89957*

**4. IFOG and IORG: performance grade and parameters**

of application are detailed on the right column.

mance parameters, the reader should consult [26].

and (2) the short-term bias drift, say 1 s.

Consumer 30–1000°

Industrial and low-end tactical 1–30°

Tactical 0.1–30°

High-end tactical 0.1–1°

Navigation 0.01–0.1°

Strategic 0.0001–0.01°

*IFOG and IORG: performance-grade classification and respective applications.*

**4.2 Scale factor linearity**

(parts-per-cent).

**Table 1.**

**13**

of 10°/h.

**4.1 Bias stability**

exhibiting 10°/h bias drift was achieved. A spiral resonator having a total length of 42 cm and a footprint of 20 cm<sup>2</sup> was designed in 2012 by Ciminelli et al. with an estimated bias drift equal to 0.2°/h, which is the best value reached to date for this kind of IORG [25]. A new trend of design over InP waveguide technology is emerging to improve the scale of integration of IORG, to come to make a true gyro-on-a-chip (GoC). However, substantial improvements have to be found in this technology because the best value calculated so far reaches a resolution

**Table 1** collects the six levels of gyro performance-grade classification together with its characteristic rotation-rate resolution. As it can be seen, each performance level includes scales by two orders of magnitude. For each of them, the main areas

What follows next is a concise description of each gyro performance parameter.

Bias instability is the measurement of bias offset at any constant temperature and ideal environment. It can be measured using the Allan variance technique. Bias instability introduces errors that may not be easy to calibrate. Its influence is greater on longer measurement periods, so that bias instability is one of the most critical parameters in the gyro selection process for applications that require excellent accuracy over long time. Therefore, two values of bias stability are usually considered: (1) the long-term bias drift for long integration time values, say 1 min or 1 h,

The linearity of the scale factor is the maximum separation with respect to the linear variation of the rotation rate expressed in ppm (parts-per-million) or %

/h Motion interface

/h Platform stabilization

/h Aeronautics navigation

/h Submarine navigation

/h Missile navigation

/h Ammunitions and rocket guidance

**Performance grade/bias stability range Applications**

Four main gyro performance parameters will be considered here, namely, bias stability, scale factor linearity, angle random walk, and dynamic range. For one more deep analysis and exhaustive information about the definition of gyro perfor-

#### **Figure 7.**

*Conventional configuration of an IORG, including a narrow linewidth laser source, an optical isolator, optoelectronic components for demodulation processing, a waveguide ring resonator, two detectors, and electronics readout unit.*

#### **Figure 8.**

*Two SOAs are incorporated within ring resonator to compensate propagation loss.*

The dimensions of the integrated passive resonator influence gyro scale factor, and, in time, the cavity *Q* factor depends on loss and resonator length. This way, to achieve *δ*Ω < 5°/h and ARW < 0.02°/ ffiffiffi h <sup>p</sup> , a *<sup>Q</sup>* factor around 10<sup>6</sup> and a resonator length in the range of centimeters are at least required [24].

Maximum achieved *<sup>Q</sup>* factor in SOI ring resonators is around 1.5 � <sup>10</sup><sup>5</sup> . This limitation in *Q* factor makes very difficult to realize a passive integrated optical gyroscope having *δ*Ω < 5°/h by using a SOI ring resonator. On the other hand, silicaon-silicon technology allows very low loss (<0.1 dB/cm) operating at 1.55 μm, so that waveguides made on this technology are more suitable for IORG engineering. Propagation losses around 0.02–0.03 dB/cm have been achieved for low-index contrast silica-on-silicon waveguides (Δ < 1%). As bending loss suffered by these waveguides exponentially decreases with curvature radius, to achieve negligible bending loss, a curvature radius larger than a few millimeters is required. Some ring resonators employing a 5 μm � 5 μm squared core having a very large quality Q factor (2.4 � <sup>10</sup><sup>7</sup> ) and operating at 1.55 μm wavelength have been fabricated in silica-on-silicon technology. To further enhance the *Q* factor of resonators in silicaon-silicon technology, the hybrid integration of two semiconductor optical amplifiers (SOAs) within a silica-on-silicon ring resonator was proposed (**Figure 8**).

For a ring radius of 10 mm and a cross-coupling coefficient of 0.001 between, a *<sup>Q</sup>* factor as high as 2.9 � <sup>10</sup><sup>8</sup> was calculated, neglecting the effect of spontaneous

*IFOG and IORG Gyros: A Study of Comparative Performance DOI: http://dx.doi.org/10.5772/intechopen.89957*

emission noise. Then, with this ring resonator configuration, an IORG unit exhibiting 10°/h bias drift was achieved. A spiral resonator having a total length of 42 cm and a footprint of 20 cm<sup>2</sup> was designed in 2012 by Ciminelli et al. with an estimated bias drift equal to 0.2°/h, which is the best value reached to date for this kind of IORG [25]. A new trend of design over InP waveguide technology is emerging to improve the scale of integration of IORG, to come to make a true gyro-on-a-chip (GoC). However, substantial improvements have to be found in this technology because the best value calculated so far reaches a resolution of 10°/h.

### **4. IFOG and IORG: performance grade and parameters**

**Table 1** collects the six levels of gyro performance-grade classification together with its characteristic rotation-rate resolution. As it can be seen, each performance level includes scales by two orders of magnitude. For each of them, the main areas of application are detailed on the right column.

What follows next is a concise description of each gyro performance parameter. Four main gyro performance parameters will be considered here, namely, bias stability, scale factor linearity, angle random walk, and dynamic range. For one more deep analysis and exhaustive information about the definition of gyro performance parameters, the reader should consult [26].

#### **4.1 Bias stability**

Bias instability is the measurement of bias offset at any constant temperature and ideal environment. It can be measured using the Allan variance technique. Bias instability introduces errors that may not be easy to calibrate. Its influence is greater on longer measurement periods, so that bias instability is one of the most critical parameters in the gyro selection process for applications that require excellent accuracy over long time. Therefore, two values of bias stability are usually considered: (1) the long-term bias drift for long integration time values, say 1 min or 1 h, and (2) the short-term bias drift, say 1 s.

#### **4.2 Scale factor linearity**

The linearity of the scale factor is the maximum separation with respect to the linear variation of the rotation rate expressed in ppm (parts-per-million) or % (parts-per-cent).


**Table 1.**

*IFOG and IORG: performance-grade classification and respective applications.*

The dimensions of the integrated passive resonator influence gyro scale factor, and, in time, the cavity *Q* factor depends on loss and resonator length. This way, to

) and operating at 1.55 μm wavelength have been fabricated in

silica-on-silicon technology. To further enhance the *Q* factor of resonators in silicaon-silicon technology, the hybrid integration of two semiconductor optical amplifiers (SOAs) within a silica-on-silicon ring resonator was proposed (**Figure 8**).

For a ring radius of 10 mm and a cross-coupling coefficient of 0.001 between, a *<sup>Q</sup>* factor as high as 2.9 � <sup>10</sup><sup>8</sup> was calculated, neglecting the effect of spontaneous

<sup>p</sup> , a *<sup>Q</sup>* factor around 10<sup>6</sup> and a resonator

. This

h

Maximum achieved *<sup>Q</sup>* factor in SOI ring resonators is around 1.5 � <sup>10</sup><sup>5</sup>

*Conventional configuration of an IORG, including a narrow linewidth laser source, an optical isolator, optoelectronic components for demodulation processing, a waveguide ring resonator, two detectors, and*

limitation in *Q* factor makes very difficult to realize a passive integrated optical gyroscope having *δ*Ω < 5°/h by using a SOI ring resonator. On the other hand, silicaon-silicon technology allows very low loss (<0.1 dB/cm) operating at 1.55 μm, so that waveguides made on this technology are more suitable for IORG engineering. Propagation losses around 0.02–0.03 dB/cm have been achieved for low-index contrast silica-on-silicon waveguides (Δ < 1%). As bending loss suffered by these waveguides exponentially decreases with curvature radius, to achieve negligible bending loss, a curvature radius larger than a few millimeters is required. Some ring resonators employing a 5 μm � 5 μm squared core having a very large quality Q

achieve *δ*Ω < 5°/h and ARW < 0.02°/ ffiffiffi

factor (2.4 � <sup>10</sup><sup>7</sup>

**12**

**Figure 7.**

**Figure 8.**

*electronics readout unit.*

*Gyroscopes - Principles and Applications*

length in the range of centimeters are at least required [24].

*Two SOAs are incorporated within ring resonator to compensate propagation loss.*

#### **4.3 Angle random walk (ARW)**

In the output of a gyro, there is always a broadband white noise element. Angle random walk describes the error resulting from this noise element and can be evaluated using the Allan variance technique. Active elements of the gyro are the major contributors to random noise (laser diode and photodiode for optical gyroscopes and the vibrating beam and detection electronics for MEMS). Noise is one of the most important differences between optical and MEMS gyro performance, resulting in different precision and accuracy in measurements.

#### **4.4 Dynamic range**

Dynamic range is the maximum excursion of rotation rate that the gyro is able to measure with a maximum error specified by the rotation-rate drift (bias stability).

#### **5. IFOG and IORG performance parameters: a comparative analysis**

Next, in **Table 2**, the performance parameters of 33 IFOG, RFOG, RLG, or IORG gyros are collected for comparison purposes. Five gyro performance parameters are considered here: bias stability, scale factor linearity, ARW, dynamic range, and dimensions/weight/response time. For each type of gyro unit, either manufactured or designed, the manufacturer and the main areas of application are also specified. In the case of the units manufactured, the performance parameters were obtained from the technical manufacturer data sheets, while for the units designed and tested in the laboratory, the data have been obtained from the referenced scientific publication.

#### **6. IFOG and IORG: advanced design, trends, and optimization**

In recent years, several groups of researchers throughout the world are devoting great effort in the development of high-performance resonant micro-optical gyros (RMOG). All of these RMOG designs are based on a waveguide/ring resonator structure acting as the sensor element of rotation rate. The main variants of this design are focused either on ultrahigh Q silica-on-silicon (Q = 1.5 <sup>10</sup><sup>6</sup> ) or InP (Q ≥ 10<sup>6</sup> ) ring resonators or on Si waveguide/photonic crystal (PhC) ring resonator (Q = 7 <sup>10</sup><sup>8</sup> ). More explicitly, the very promising research field of IORGs aiming at the development of optoelectronic ultracompact and high-performance gyros compliant with the requirements of aerospace and defense industry is recently focused onto five technological approaches that are being explored: (1) SRLGs, (2) RMOGs based on ultrahigh Q silica resonators, (3) InP gyro-on-a-chip, (4) the gyro configuration based on the ring cavity with a Bragg grating in the resonant path, and (5) the multi-ring-cavity gyro. For all of them, main efforts focus on design improvement, efficient modulation technique, and resolution enhancement. It is expected that a gyroscope on-a-chip prototype will be developed soon. If the characterization of that prototype will be successful, it is expected that the gyro-on-a-chip will have a very notably impact on the aerospace and defense navigation applications.

**IFOG/**

**15**

**Performance**

 **grade/bias**

**IFOG/IORG**

 **parameters** **Dimensions/weight/response**

**ARW**

 **Dynamic**

**range**

**time**

**Manufacturer**

**Applications**

**[model]/**

**researcher**

 **ref.**

**[X]**

**stability range**

**Bias**

**Scale factor**

**stability**

**linearity**

**IORG gyro** **technology**

IFOG

IFOG

IFOG

IFOG

RLG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

 Tactical

 0.1–30°/h

≤3°/h

<500 ppm

 L = 125 m, D = 58.42 mm/no

data

≤0.10°

/

h

p

ffiffiffi

�100°/s

KVH

Platform stabilization

[DSP3000analog]

 Tactical

 0.1–30°/h

≤5°/h

≤1000 ppm L = 75 m, D = 58.42 mm/≤3 ms

 Strategic

0.0001–0.01°/h

≤0.0002°/h

≤15 ppm

 L = 5000 m, D = 370 mm/no

data

≤0.00017°

≤0.14°

/

h

p

ffiffiffi

�204°/s

KVH

Platform stabilization

[DSP1500digital]

/

h

p

ffiffiffi

�15°/s

 IXSea [FOG

Submarine navigation

MarinsM3]

 Strategic

0.0001–0.01°/h

≤0.0005°/h

≤30 ppm

 L = 2000 m, D = 330 mm/no

data

≤0.00021°

/

h

p

ffiffiffi

�15°/s

 IXSpace

Space navigation

[ASTRIX200]

 Strategic

0.0001–0.01°/h

≤0.0007°/h

≤15 ppm

 L = 1500 m, D = 180 mm /no

data

≤0.00022°

/

h

p

ffiffiffi

�30°/s

 IXSea [FOG180]

 Aeronautics

navigation

 Strategic

0.0001–0.01°/h

≤0.0003°/h

≤1 ppm

 L = 4000 m, D = no data/no

data

≤0.00010°

/

h

No data

 Honeywell

Space navigation

[HPFOG]

p

ffiffiffi

 High-end

0.1–1°/h

≤1°/h

≤1 ppm

 Volume = 541 cm3/900 g

≤0.125°

/

h

p

ffiffiffi

�358°/s up to

Honeywell

Missile navigation

[HG1700IMU]

�1620°/s

tactical

 Strategic

0.0001–0.01°/h

≤0.0009°/h

≤10 ppm

 L = 1000 m, D = 76 mm/750 g

≤0.0009°

/

h

p

ffiffiffi

�250°/s

 Litton guidance

Space navigation

> and control

systems [7]

 Navigation

 0.01–0.1°/h

≤0.04°/h

≤100 ppm

 210.8 � 119.9 � 79.8

(L � W �

H)/1950 g

≤0.002°

/

h

p

ffiffiffi

�300°/s

 Northrop

Image and platform

*IFOG and IORG Gyros: A Study of Comparative Performance*

stabilization

Grumman LITEF

[LR-240]

 Navigation

 0.01–0.1°/h

≤0.07°/h

≤100 ppm

 L = 200 m, D = 88.9 mm/

≤0.056°

/

h

p

ffiffiffi

�11.46°/s

 Litton [LN-200]

 Aeronautics

*DOI: http://dx.doi.org/10.5772/intechopen.89957*

navigation

750 g/no data

 High-end

0.1–1°/h

≤1°/h

≤10,000 ppm 18.8mm � 19.1 mm � 24.6 mm

(L � W � H)/25 g

≤0.05°

/

h

p

ffiffiffi

�200°/s

 Northrop

Missile and platform

stabilization

Grumman LITEF

[G-2000]

tactical


#### *IFOG and IORG Gyros: A Study of Comparative Performance DOI: http://dx.doi.org/10.5772/intechopen.89957*

**4.3 Angle random walk (ARW)**

*Gyroscopes - Principles and Applications*

measurements.

(bias stability).

publication.

(Q ≥ 10<sup>6</sup>

**14**

resonator (Q = 7 <sup>10</sup><sup>8</sup>

navigation applications.

**4.4 Dynamic range**

In the output of a gyro, there is always a broadband white noise element. Angle random walk describes the error resulting from this noise element and can be evaluated using the Allan variance technique. Active elements of the gyro are the major contributors to random noise (laser diode and photodiode for optical gyroscopes and the vibrating beam and detection electronics for MEMS). Noise is one of the most important differences between optical and MEMS gyro performance, resulting in different precision and accuracy in

Dynamic range is the maximum excursion of rotation rate that the gyro is able to measure with a maximum error specified by the rotation-rate drift

**5. IFOG and IORG performance parameters: a comparative analysis**

**6. IFOG and IORG: advanced design, trends, and optimization**

design are focused either on ultrahigh Q silica-on-silicon (Q = 1.5 <sup>10</sup><sup>6</sup>

Next, in **Table 2**, the performance parameters of 33 IFOG, RFOG, RLG, or IORG gyros are collected for comparison purposes. Five gyro performance parameters are considered here: bias stability, scale factor linearity, ARW, dynamic range, and dimensions/weight/response time. For each type of gyro unit, either manufactured or designed, the manufacturer and the main areas of application are also specified. In the case of the units manufactured, the performance parameters were obtained from the technical manufacturer data sheets, while for the units designed and tested in the laboratory, the data have been obtained from the referenced scientific

In recent years, several groups of researchers throughout the world are devoting great effort in the development of high-performance resonant micro-optical gyros (RMOG). All of these RMOG designs are based on a waveguide/ring resonator structure acting as the sensor element of rotation rate. The main variants of this

) ring resonators or on Si waveguide/photonic crystal (PhC) ring

aiming at the development of optoelectronic ultracompact and high-performance gyros compliant with the requirements of aerospace and defense industry is recently focused onto five technological approaches that are being explored: (1) SRLGs, (2) RMOGs based on ultrahigh Q silica resonators, (3) InP gyro-on-a-chip, (4) the gyro configuration based on the ring cavity with a Bragg grating in the resonant path, and (5) the multi-ring-cavity gyro. For all of them, main efforts focus on design improvement, efficient modulation technique, and resolution enhancement. It is expected that a gyroscope on-a-chip prototype will be developed soon. If the characterization of that prototype will be successful, it is expected that the gyro-on-a-chip will have a very notably impact on the aerospace and defense

). More explicitly, the very promising research field of IORGs

) or InP


**IFOG/**

**17**

**Performance**

 **grade/bias**

**IFOG/IORG**

 **parameters** **Dimensions/weight/response**

**ARW**

 **Dynamic**

**range**

**time**

**Manufacturer**

**Applications**

**[model]/**

**researcher**

 **ref.**

**[X]**

**stability range**

**Bias**

**Scale factor**

**stability**

**linearity**

**IORG gyro** **technology**

IFOG

IFOG

RFOG

IORG

IORG

IFOG

IFOG

IFOG

IFOG

 Navigation

 0.01–0.1°/h

<

0.02°/h

<150 ppm

 Ø2.7" � 2″ (11.5 in.)/0.8 lb.

<0.0022°

/

h

� 360°/s

 Lockheed Martin

(IFOS) [G5-G7-

G8-G9

prototypes]

p

ffiffiffi

(362.87 g)/>40 kHz

(short-term)

<

0.20°/h

(long-term)

 High-end

0.1–1°/h

≤0.05°/h

<50 ppm

 90 mm � 90 mm � 88 mm/

<0.012°

/

h

� 490°/s

 Advanced Navigation

[SPATIAL FOG]

p

ffiffiffi

655 g/440 Hz

tactical

 Low-end

1–30°/h

≤1.00°/h

<2000 ppm

 60 mm � 60 mm � 19.5 mm

(L � W � H)/85 g

tactical

 Consumer

 30–1000°/h

≤180°/h

≤2000 ppm

 No data/no data/50 Hz

≤0.04°

<0.1°

/

h

p

ffiffiffi

�300°/s

 Lockheed Martin

AHRS aircraft, ground

(NEDAERO)

vehicles, robotics, platform stabilization

(antennas)

Surveying

applications,

navigation,

vehicle positioning

Aeronautics

navigation

 ground

 robot

[FOG-60, FOG-

80]

/

h

p

ffiffiffi

�60°/s

 Hitachi Cable

[HOFG-1]

 Low-end

1–30°/h

 1.432°/h

 344.71 ppm

 60 mm ring resonator Ø/no

data/76 μs

tactical

 Low-end

1–30°/h

 10°/h

<

volume < 5 cm3/weight

<0.1°

0.8°

/

h

p

ffiffiffi

�300°/s

 Feng et al. [31]

rocket guidance

Robotics

Ammunitions

 and

/

h

p

ffiffiffi

�100°/s

 IntelliSense [VIGOR], [8]

< 100 g/no data

10,000 ppm

tactical

 Low-end

0.1–1°/h

 0.10°/h

No data

 L = 100 m, D = 50.8 mm/no

data

≤0.029°

/

h

No data

 Honeywell

Commercial

navigation

*IFOG and IORG Gyros: A Study of Comparative Performance*

Ammunitions

rocket guidance

 and

[RFOG], [30]

p

ffiffiffi

(RMS)

tactical

 High-end

0.1–1°/h

 0.10°/h

100 ppm

 L = 200 m, D = 160 mm/320 g

(RMS)

tactical

 High-end

0.1–30°/h

 1.00°/h

100 ppm

 L = 150 m, D = 129 mm/280 g

≤0.015°

≤0.007°

/

h

p

ffiffiffi

�60°/s

 Fizoptika

Missile navigation

*DOI: http://dx.doi.org/10.5772/intechopen.89957*

[VG951]/ [29]

/

h

p

ffiffiffi

�60°/s

 Fizoptika

Platform stabilization

[VG035Q]/

 [29]

(RMS)

tactical

*Gyroscopes - Principles and Applications*


#### *IFOG and IORG Gyros: A Study of Comparative Performance DOI: http://dx.doi.org/10.5772/intechopen.89957*

**IFOG/**

**16**

**Performance**

 **grade/bias**

**IFOG/IORG**

 **parameters** **Dimensions/weight/response**

**ARW**

 **Dynamic**

**range**

**time**

**Manufacturer**

**Applications**

**[model]/**

**researcher**

 **ref.**

**[X]**

**stability range**

**Bias**

**Scale factor**

**stability**

**linearity**

**IORG gyro** **technology**

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

IFOG

 Tactical

 0.1–30°/h

 10°/h (RMS)

 100 ppm

 L = 125 m, D = 82 mm/120 g/<

20 ms

 Tactical

 0.1–30°/h

 20°/h (RMS)

 100 ppm

 L = 100 m, D = 60 mm/45 g/

10 ms

 Tactical

 0.1–30°/h

 30°/h (RMS)

 100 ppm

 L = 75 m, D = 24 mm/30 g/

20 ms

 Strategic

0.0001–0.01°/h

 0.00008°/h

≤10 ppm

 L = 5000 m, D = 250 mm/

2500 g

 Strategic

0.0001–0.01°/h

 0.00024°/h

≤30 ppm

 L = 2000 m, D = 250 mm/

1700 g

≤0.00026°

<0.000069°

ffiffiffi

h

p

≤0.090°

≤0.040°

≤0.015°

/

h

p

ffiffiffi

�250°/s

 Fizoptika

Platform stabilization

[VG095M]/

 [29]

/

h

p

ffiffiffi

�300°/s

 Fizoptika

Platform stabilization

[VG949P]/[29]

/

h

p

ffiffiffi

�300°/s

 Fizoptika

Platform stabilization

[VG091A]/[29]

/

�12°/s

Optolink [SRS-5000]/[28]

Space navigation

�550°/s

/

h

p

ffiffiffi

�30°/s

 Optolink [SRS-2000]/[28]

Space navigation

 Strategic

0.0001–0.01°/h

 0.0006°/h

≤100 ppm L = 1000 m, D = 150 mm/900 g

 Strategic

0.0001–0.01°/h

 0.0011°/h

≤200 ppm

 L = 500 m, D = 100 mm/350 g

 Strategic

0.0001–.01°/h

 0.0060°/h

≤300 ppm

 L = 200 m, D = 78 mm/200 g

≤ 0.015°

≤0.003°

≤0.0005°

/

h

p

ffiffiffi

�550°/s

 Optolink [SRS-1001]/[28]

Submarine navigation

/

h

p

ffiffiffi

�250°/s

Optolink [SRS-501]/[28]

Submarine navigation

�1000°/s

/

h

� 550°/s

 Optolink [SRS-200]/[28]

Submarine navigation

p

ffiffiffi

 Strategic

0.0001–0.01°/h

 0.005°/h

25 ppm

 L = 200 m, D = 83.8 mm/230 g

(RMS)

 Navigation

 0.01–0.1°/h

 0.10°/h

50 ppm

 L = 200 m, D = 81.2 mm/220 g

(RMS)

 Navigation

 0.01–0.1°/h

≤0.05°/h

≤500 ppm

 L = 500 m, D = 45.97 mm/≤

1.3 ms

 Tactical

 0.1–30°/h

≤1°/h

<500 ppm

 L = 300 m, D = 58.42 mm/no

data

≤0.067°

≤0.013°

≤0.015°

≤0.002°

/

h

p

ffiffiffi

�1000°/s

 Emcore [EMP-

1.2 k]

/

h

p

ffiffiffi

�1000°/s

 Emcore [EMP-1]

 Aeronautics

navigation

Aeronautics/aviation

/

h

p

ffiffiffi

�490°/s

 KVH [DSP1750]

 Aeronautics

*Gyroscopes - Principles and Applications*

navigation

/

h

p

ffiffiffi

�375°/s

 KVH [DSP3000

Platform stabilization

digital]


 *IFOG and IORG gyro technology comparison in terms of performance parameters.* **7. Conclusions**

resolution and 0.00075°/ ffiffiffiffiffi

**Acknowledgements**

**Author details**

**19**

Ramón José Pérez Menéndez UNED-Spain, Lugo, Spain

provided the original work is properly cited.

\*Address all correspondence to: ramonjose.perez@lugo.uned.es

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

realize a significant impact on the market.

provided in the realization of this work.

IFOGs have higher resolution performance than RFOG and IORG gyros. There-

eral prototypes of RMOGs based on silica resonators have been already theoretically engineered, but the experimentally demonstrated performance is still at least one order of magnitude worse than that one demanded by aerospace and defense navigation applications. Therefore, an improvement of those kinds of gyros is needed to

The author wishes to thank the UNED-Spain for technical support and assistance

hr <sup>p</sup> ARW, respectively. As already mentioned above, sev-

fore, IFOG technology is the best option for strategic-grade (0.0001°/hr), navigation-grade (0.001°/hr), or high-end tactical-grade (0.01°/hr) applications. Best RFOG designs reach high-end tactical-grade (0.01°/hr) or tactical-grade (0.1°/ hr) performance, and they constitute a mature and tested technology for a large set of applications ranging from aircraft navigation up to platform stabilization. On the other hand, IORG technology is not yet mature, and over the last decade, it has experienced a vigorous development and refinement. Best results obtained experimentally in the laboratory for the performance of IORG prototypes are of 0.20°/h

*IFOG and IORG Gyros: A Study of Comparative Performance*

*DOI: http://dx.doi.org/10.5772/intechopen.89957*
