**3. Description of the realized system**

In this section we concretely present a realization. We apply the principle detailed in the previous section to settle a phase noise optoelectronic system. For the demonstration, we characterize a frequency synthesizer as a DUT. It presents advantage to check different fre‐ quencies in X-band. System is shown on Figure 2.

**Figure 2.** Picture of the phase noise measurement system.

The system is composed from different parts. We see on Figure 2, that we use a frequency synthesizer to check if the system works properly in X-band. On the picture we see the results of the phase noise characterization (inserted on the left of the picture) for a +3 dBm, 10 GHz signal. On the top of the picture we see the double channels Fast Fourier Transform ana‐ lyzer used for this purpose (*Hewlett-Packard* HP3561A). £(f) expressed in dBc/Hz is deduced from the data provided by the FFT analyzer are given in V²/Hz.

Figure 3 shows the picture of the *Hewlett-Packard* HP3561A FFT analyzer. Note that the data are expressed in V²/Hz. It is necessary to use a program to get the expected quantity £(f) in dBc/Hz. It is developed in the next section of this chapter.

**Figure 3.** Picture of the double channels *Hewlett-Packard* HP3561A FFT analyzer.

### **4. Validation of the performances**

£( *f* )= *V* ²*out* ( *f* ) ⋅ / ⋅ 2*K*²*<sup>φ</sup>* .│*Hφ*( *jf* )│²*G*²*DC* ⋅ *B* (4)

Such instruments has been recently introduced [3,9,10]. In section 3, we present concretely a

In this section we concretely present a realization. We apply the principle detailed in the previous section to settle a phase noise optoelectronic system. For the demonstration, we characterize a frequency synthesizer as a DUT. It presents advantage to check different fre‐

The system is composed from different parts. We see on Figure 2, that we use a frequency synthesizer to check if the system works properly in X-band. On the picture we see the results of the phase noise characterization (inserted on the left of the picture) for a +3 dBm, 10 GHz signal. On the top of the picture we see the double channels Fast Fourier Transform ana‐ lyzer used for this purpose (*Hewlett-Packard* HP3561A). £(f) expressed in dBc/Hz is deduced

Figure 3 shows the picture of the *Hewlett-Packard* HP3561A FFT analyzer. Note that the data are expressed in V²/Hz. It is necessary to use a program to get the expected quantity £(f) in

realized optoelectronic phase noise measurement system.

**3. Description of the realized system**

340 Optoelectronics - Advanced Materials and Devices

quencies in X-band. System is shown on Figure 2.

**Figure 2.** Picture of the phase noise measurement system.

from the data provided by the FFT analyzer are given in V²/Hz.

dBc/Hz. It is developed in the next section of this chapter.

The measured phase noise includes the DUT noise and the instrument background. The cross correlation method allows to decrease the cross spectrum terms of uncommon phase noise as √(1/m), where m is the average number. Thereby uncorrelated noise is removed and sensitivity of measure is improved. To validate the measure of our phase noise bench, we need to compare data sheet of the commercial frequency synthesizer Anritsu/Wiltron 69000B [11] with the phase noise we measure using our system.

**Figure 4.** Phase noise (dBc/Hz) of the synthesizer measured at 10 GHz with Kφ=425 mV/rad and GDC= 40dB versus Fourier Frequency between 10 Hz and 100 kHz.

Figure 4 shows the result of this measure. We can see that our bandwidth is limited to 100 kHz (τ = 10 μs) and the measured phase noise corresponds to the data sheet.

One can note that the use of a shorter delay line in a optoelectronic phase noise measure‐ ment system working in X-band, allow a characterization of the phase noise far from the car‐

delay line in addition of a 2 km optical fiber [12]. As the Fast Fourier Transform (FFT) ana‐ lyzer (*Hewlett-Packard* 3562A) used for characterizing the noise up to 100 kHz from the carri‐ er is not operating for higher frequencies, it is necessary to use another FFT such as an

On Figure 6, we check that the two different FFT systems provide the same results for Fouri‐

Note that our results are as expected with the data sheet of a 10 GHz phase noise spectrum for an *Wiltron* 69000B series. Our bandwidth is limited to 100 kHz (τ = 10 μs) and the meas‐ ured phase noise corresponds to the data sheet. Figure 6 then gives the noise floor of the in‐ strument versus Fourier frequencies. The noise floor is respectively better than – 90 and –

The introduction of a 100 m short fiber in addition to the 2 km fiber allows to characterize

**Figure 7.** Spectral density of phase noise floor £(f) expressed in dBc/Hz versus Fourier frequencies (in Hz) for the devel‐

in X-band (8.2 – 12.4 GHz) especially for those delivered by optoelectronic oscillators. We see on Figure 7 that the noise floor of the system is in the range of –165 dBc/Hz at 5. 106 Hz

to 2x106 Hz from the carrier. This system works for any microwave signal

Hz from the carrier.

phase noise of oscillators with an optoelectronic phase noise measurement system.

to 2x106

Optoelectronic Oscillators Phase Noise and Stability Measurements

Hz by introducing a 100 m

http://dx.doi.org/10.5772/3463

343

Hz limit due to the 2 km fiber can be

rier. Fourier frequency analysis can be extended from 105

*Agilent* 89600 for instance.

170 dBc/Hz at 103

er frequencies between 10 Hz and 100 kHz.

and 5x106

oped system when using the 100 meters delay lines.

from the X-band microwave signal.

extended from 105

100 m fiber corresponds to a 500 ns delay. So the 105

**Figure 5.** Phase noise floor (dBc/Hz) of the bench measured at 10 GHz with Anritsu synthesizer (500 averages) versus Fourier Frequency between 10 Hz and 100 kHz.

Figure 5 represents the background phase noise of the bench after performing 500 aver‐ aged with cross-correlation method, when removing the 2 km optical delay line. In this case, phase noise of the 10 GHz synthesizer is rejected. The solid curve shows noise floor (with‐ out optical transfer function) respectively better than -150 and -170 dBc/Hz at 10<sup>1</sup> and 104 Hz from the 10 GHz carrier. Dotted curve is the noise floor when optical fiber is introduced.

**Figure 6.** Spectral density of phase noise floor £(f) expressed in dBc/Hz versus Fourier frequencies (in Hz) between 10 Hz and 100 kHz for a commercial synthesizer measured with our bench with Kφ = 425 mV/rad and GDC = 40 dB for two different FFT analyzing system : *Hewlett-Packard* 3562A and *Agilent* 89600.

One can note that the use of a shorter delay line in a optoelectronic phase noise measure‐ ment system working in X-band, allow a characterization of the phase noise far from the car‐ rier. Fourier frequency analysis can be extended from 105 to 2x106 Hz by introducing a 100 m delay line in addition of a 2 km optical fiber [12]. As the Fast Fourier Transform (FFT) ana‐ lyzer (*Hewlett-Packard* 3562A) used for characterizing the noise up to 100 kHz from the carri‐ er is not operating for higher frequencies, it is necessary to use another FFT such as an *Agilent* 89600 for instance.

Figure 4 shows the result of this measure. We can see that our bandwidth is limited to 100

**Figure 5.** Phase noise floor (dBc/Hz) of the bench measured at 10 GHz with Anritsu synthesizer (500 averages) versus

Figure 5 represents the background phase noise of the bench after performing 500 aver‐ aged with cross-correlation method, when removing the 2 km optical delay line. In this case, phase noise of the 10 GHz synthesizer is rejected. The solid curve shows noise floor (with‐

from the 10 GHz carrier. Dotted curve is the noise floor when optical fiber is introduced.

**Figure 6.** Spectral density of phase noise floor £(f) expressed in dBc/Hz versus Fourier frequencies (in Hz) between 10 Hz and 100 kHz for a commercial synthesizer measured with our bench with Kφ = 425 mV/rad and GDC = 40 dB for

two different FFT analyzing system : *Hewlett-Packard* 3562A and *Agilent* 89600.

and 104

Hz

out optical transfer function) respectively better than -150 and -170 dBc/Hz at 10<sup>1</sup>

Fourier Frequency between 10 Hz and 100 kHz.

342 Optoelectronics - Advanced Materials and Devices

kHz (τ = 10 μs) and the measured phase noise corresponds to the data sheet.

On Figure 6, we check that the two different FFT systems provide the same results for Fouri‐ er frequencies between 10 Hz and 100 kHz.

Note that our results are as expected with the data sheet of a 10 GHz phase noise spectrum for an *Wiltron* 69000B series. Our bandwidth is limited to 100 kHz (τ = 10 μs) and the meas‐ ured phase noise corresponds to the data sheet. Figure 6 then gives the noise floor of the in‐ strument versus Fourier frequencies. The noise floor is respectively better than – 90 and – 170 dBc/Hz at 103 and 5x106 Hz from the carrier.

The introduction of a 100 m short fiber in addition to the 2 km fiber allows to characterize phase noise of oscillators with an optoelectronic phase noise measurement system.

**Figure 7.** Spectral density of phase noise floor £(f) expressed in dBc/Hz versus Fourier frequencies (in Hz) for the devel‐ oped system when using the 100 meters delay lines.

100 m fiber corresponds to a 500 ns delay. So the 105 Hz limit due to the 2 km fiber can be extended from 105 to 2x106 Hz from the carrier. This system works for any microwave signal in X-band (8.2 – 12.4 GHz) especially for those delivered by optoelectronic oscillators. We see on Figure 7 that the noise floor of the system is in the range of –165 dBc/Hz at 5. 106 Hz from the X-band microwave signal.
