**5. Acknowledgments**

This work has been financially supported by the *Ministerio de Ciencia e Innovación* and the *Generalitat Valenciana* of Spain (projects TEC2008-05490 and PROMETEO/2009/077, respectively). C. Cuadrado-Laborde acknowledges the *Secretaría de Estado de Universidades e Investigación del Ministerio de Ciencia e Innovación* (Spain) and ANPCyT (project PICT 2008- 1506, Argentina).

### **6. References**

632 Acoustic Waves – From Microdevices to Helioseismology

Perot cavity. Fully modulated *Q*-switched mode-locked trains of optical pulses were obtained for a wide range of pump powers and repetition rates. For a *Q*-switched repetition rate of 500 Hz and a pump power of 100 mW, the laser generates trains of 12–14 modelocked pulses of about 1 ns each, within an envelope of 550 ns, an overall energy of 0.65 μJ, and a peak power higher than 250 W for the central pulses of the train. Then, we discussed the construction of a mode-locked laser when the mode-locker is driven by travelling acoustic waves. In this case, the modulation frequency is half the frequency obtained when standing acoustic waves are used. Optical pulses were obtained of 530 mW peak power, 700 ps pulse width, at a repetition rate of 4.1 MHz. The variation of the pulses parameters under frequency detuning and applied voltage was also studied. Finally, we demonstrated that it is not necessary to modify the setup in order to reach double active *Q*-switching and modelocking, when travelling acoustic waves were used to drive the mode-locker. In this case the commutation between mode-locking and *Q*-switching mode-locking is remarkably simple; it just needs use of a different electrical signal to drive the piezoelectric of the mode-locker, i.e. from a sinusoidal to a burst-sinusoidal electrical signal. In this case, fully modulated 10–25 modelocked pulses around 700 ps each within a *Q*-switching envelope around 1 μs and a

In subsection 3.3 we shown another example of application of acousto-optic devices based on the interaction of longitudinal acoustic waves with fiber Bragg gratings in the shortwavelength regime. Thus, we carried out an experimental and theoretical study of the phase and group delay response of the acousto-optic supper-lattice modulator. The phase properties of the first sidebands permit the implementation of electrically-tuned photonic true-time delay line controlled by the AC voltage applied to the piezoelectric transducer that generates the acoustic wave. The proposed photonic true-time delay line permits to vary the

Finally, when the acoustic perturbation is not a harmonic wave but a single pulse, its passage through the FBG creates a defect which can be used to control the *Q*-factor in a DFB all-fiber laser, subsection 3.4. Thus, we shown a single-mode, transform-limited, actively *Q*switched distributed-feedback fiber laser. Optical pulses of 800 mW peak power, 32 ns temporal width, and up to 20 kHz repetition rates were obtained. The measured linewidth demonstrates that these pulses are transform limited: 6 MHz for a train of pulses of 10 kHz repetition rate, 80 ns temporal width, and 60 mW peak power. Efficient excitation of

In summary, photonic devices can benefit highly of a strictly all-fiber configuration which provides them a series of attractive advantages. Among all the proposed in-fiber solutions, devices controlled by acoustic waves have been by far the most employed, especially in mode-locked lasers, providing a broad range of alternatives. The recent advances in acoustically controlled photonic systems positioned them as a promising candidate for

This work has been financially supported by the *Ministerio de Ciencia e Innovación* and the *Generalitat Valenciana* of Spain (projects TEC2008-05490 and PROMETEO/2009/077, respectively). C. Cuadrado-Laborde acknowledges the *Secretaría de Estado de Universidades e Investigación del Ministerio de Ciencia e Innovación* (Spain) and ANPCyT (project PICT 2008-

maximum overall energy of 0.68 μJ were obtained.

spontaneous Brillouin scattering was demonstrated.

commercially available systems in the near future.

group delay up to 400 ps.

**5. Acknowledgments** 

1506, Argentina).

Agrawal, G. P. (2001). *Nonlinear Fiber Optics*, Academic Press, New York, 2001.


Applications of In–Fiber Acousto–Optic Devices 635

Italia, V.; Pisco, M.; Campopiano, S.; Cusano, A.; Cutolo, A. (2005). Chirped fiber Bragg

Jeon, M. Y.; Lee, H. K.; Kim, K. H.; Lee, E. H.; Oh, W. Y.; Kim, B. Y.; Lee, H. W.; Koh, Y. W.

Kee, H. H.; Lees, G. P.; Newson, T. P. (1998). Narrow linewidth CW and Q-switched erbiumdoped fibre loop laser. *Electronics Letters*, 34 (13): 1318-1319 Jun 25 1998. Kim, B. Y.; Blake, J. N.; Engan, H. E.; Shaw, H. J. (1986). All-fiber acoustooptic frequency

Kim, H. S.; Yun, S. H.; Kwang, I. K.; Kim, B. Y. (1997). All-fiber acousto-optic tunable notch

Kuizenga, D. J.; Siegman, A. E. (1970). FM and AM mode locking of homogeneous laser .1.

Li, Y. H.; Lou, C. Y.; Han, M.; Gao, Y. Z. (2001). Detuning characteristics of the AM modelocked fiber laser. *Optical and Quantum Electronics*, 33 (6): 589-597 Jun 2001. Li, Y. Q.; Zhang, F. C.; Yoshino, T. (2003). Wide-range temperature dependence of Brillouin

Li, X. W.; Peng, L. M.; Wang, S. B.; Kim, Y. C.; Chen, J. P. (2007). A novel kind of

Liu, W. F.; Russell, P. S. J.; Dong, L. (1997). Acousto-optic superlattice modulator using a

Liu, W. F.; Russell, P. S. J.; Dong, L. (1998). 100% efficient narrow-band acoustooptic tunable

Liu, Y. Q.; Yang, J. L.; Yao, J. P. (2002). Continuous true-time-delay beamforming for phased

Liu, Y. Q.; Yao, J. P.; Yang, J. L. (2003). Wideband true-time-delay beam former that employs

Myren, N.; Margulis, W. (2005). All-fiber electrooptical mode-locking and tuning. *IEEE* 

Ortega, B.; Cruz, J. L.; Capmany, J.; Andres, M. V.; Pastor, D. (2000). Analysis of a

Parker, T. R.; Farhadiroushan, M.; Feced, R.; Handerek, V. A.; Rogers, A. J. (1998).

Pérez-Millán, P.; Torres-Peiró, S.; Mora, J.; Díez, A.; Cruz, J. L.; Andres, M. V. (2004). Electronic

single optical carrier. *Optics Communications*, 238 (4-6): 277-280 Aug 15 2004.

fiber Bragg grating. *Optics Letters*, 22 (19): 1515-1517 Oct 1 1997.

Theory. *IEEE Journal of Quantum Electronics*, QE 6 (11): 694-& 1970.

filter with electronically controllable spectral profile. *Optics Letters*, 22 (19): 1476-

shift in a dispersion-shifted fiber and its annealing effect. *Journal of Lightwave* 

programmable 3(n) feed-forward optical fiber true delay line based on SOA. *Optics* 

reflector using fiber Bragg grating. *Journal of Lightwave Technology*, 16 (11): 2006-

array antenna using a tunable chirped fiber grating delay line. IEEE *Photonics* 

a tunable chirped fiber grating prism. *Applied Optics*, 42 (13): 2273-2277 May 1 2003.

microwave time delay line based on a perturbed uniform fiber Bragg grating operating at constant wavelength. *Journal of Lightwave Technology*, 18 (3): 430-436

Simultaneous distributed measurement of strain and temperature from noiseinitiated Brillouin scattering in optical fibers. *IEEE Journal of Quantum Electronics*, 34

tuning of delay lines based on chirped fiber gratings for phased arrays powered by a

*Quantum Electronics*, 11 (2): 408-416 Mar-Apr 2005.

shifter. *Optics Letters*, 11 (6): 389-391 Jun 1986.

*Technology*, 21 (7): 1663-1667 Jul 2003.

*Express*, 15 (25): 16760-16766 Dec 10 2007.

*Technology Letters*, 14 (8): 1172-1174 Aug 2002.

*Photonics Technology Letters*, 17 (10): 2047-2049 Oct 2005.

312-316 Apr 15 1998.

1478 Oct 1 1997.

2009 Nov 1998.

Mar 2000.

(4): 645-659 Apr 1998.

gratings for electrically tunable time delay lines. *IEEE Journal of Selected Topics in* 

(1998). Harmonically mode-locked fiber laser with an acousto-optic modulator in a Sagnac loop and Faraday rotating mirror cavity. *Optics Communications*, 149 (4-6):


Cuadrado-Laborde, C.; Perez-Millán, P.; Andres, M. V.; Díez, A.; Cruz, J. L.; Barmenkov, Y.

Cuadrado-Laborde, C.; Diez, A.; Cruz, J. L.; Andres, M. V. (2009b). Doubly active Q

Cuadrado-Laborde, C.; Diez, A.; Cruz, J. L.; Andres, M. V. (2010a). Experimental study of an

Cuadrado-Laborde, C.; Diez, A.; Cruz, J. L.; Andres, M. V. (2010b). Actively Q-switched and modelocked all-fiber lasers. *Laser Physics Letters*, 7 (12): 870-875 Dec 2010. Culverhouse, D. O.; Farahi, F.; Pannell, C. N.; Jackson, D. A. (1989a). Potential of stimulated

Culverhouse, D. O.; Farahi, F.; Pannell, C. N.; Jackson, D. A. (1989b). Stimulated Brillouin-

Culverhouse, D. O.; Richardson, D. J.; Birks, T. A.; Russell, P. S. J. (1995). All-fiber slidingfrequency Er3+/Yb3+ soliton laser. *Optics Letters*, 20 (23): 2381-2383 Dec 1 1995. Delgado-Pinar, M.; Zalvidea, D.; Diez, A.; Perez-Millan, P.; Andres, M. V. (2006). *Q*-

Delgado-Pinar, M.; Diez, A.; Cruz, J. L.; Andres, M. V. (2007). Single-frequency active Q-

Erdogan, T. (1997). Fiber crating spectra. *Journal of Lightwave Technology*, 15 (8): 1277-1294

French, P. M. W. (1995). The generation of ultrashort laser pulses. *Reports on Progress in* 

Galtarossa, A.; Nava, E.; Valentini, G. (1993). *Single-Mode Optical Fiber Measurement:* 

Geister, G.; Ulrich, R. (1988). Neodymium-fiber laser with integrated-optic mode locker.

Haus, H. A. (2000). Mode-locking of lasers. *IEEE Journal of Selected Topics in Quantum* 

Huang, D. W.; Liu, W. F.; Yang, C. C. (2000). *Q*-switched all-fiber laser with an acoustically

Hudson, D. D.; Holman, K. W.; Jones, R. J.; Cundiff, S. T.; Ye, J.; Jones, D. J. (2005). Mode-

Imai, T.; Komukai, T.; Yamamoto, T.; Nakazawa, M. (1997). A wavelength tunable Q-

modulated fiber attenuator. *IEEE Photonics Technology Letters*, 12 (9): 1153-1155 Sep

locked fiber laser frequency-controlled with an intracavity electro-optic modulator.

switched fiber laser using fiber Bragg gratings. *Electronics and Communications in* 

*Characterization and Sensing*, Ed. G. Cancellieri, Artech Pub. 1993.

*Optics Communications*, 68 (3): 187-189 Oct 1 1988.

*Electronics*, 6 (6): 1173-1185 Nov-Dec 2000.

*Optics Letters*, 30 (21): 2948-2950 Nov 1 2005.

*Japan Part II-Electronics*, 80 (11): 12-21 Nov 1997.

temperature sensor. *Electronics Letters*, 25 (14): 915-916 Jul 6 1989.

*Applied Physics B-Lasers and Optics*, 99 (1-2): 95-99 Apr 2010.

*Electronics Letters*, 25 (14): 913-915 Jul 6 1989.

*Optics Express*, 14 (3): 1106-1112 Feb 6 2006.

(17): Art. No. 171110 Apr 23 2007.

*Physics* 58 (2): 169-267 Feb 1995.

Aug 1997.

2000.

distributed fiber laser. *Optics Letters*, 33 (22): 2590-2592 Nov 15 2008. Cuadrado-Laborde, C.; Díez, A.; Delgado-Pinar, M.; Cruz, J. L.; Andres, M. V. (2009a). Mode

34 (7): 1111-1113 Apr 1 2009.

Sep 15 2009.

O. (2008). Transform-limited pulses generated by an actively Q-switched

locking of an all-fiber laser by acousto-optic superlattice modulation. *Optics Letters*,

switching and mode locking of an all-fiber laser. *Optics Letters*, 34 (18): 2709-2711

all-fiber laser actively mode-locked by standing-wave acousto-optic modulation.

Brillouin-scattering as sensing mechanism for distributed temperature sensors.

scattering - a means to realize tunable microwave generator or distributed

switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating.

switched distributed fiber laser using acoustic waves. *Applied Physics Letters*, 90


**28** 

*U.S.A.* 

**Surface Acoustic Waves and** 

*Department of Electrical and Computer Engineering* 

Dustin J. Kreft and Robert H. Blick *University of Wisconsin – Madison* 

**Nano–Electromechanical Systems** 

Surface acoustic waves (SAW) follow the industrial trend of reducing the size, enhancing the speed, while enhancing the efficiency of energy coupling. Integrating this with microelectromechanical systems (MEMS) and nano-electromechanical systems (NEMS) offers a wide variety of applications such as touch screens, gas and biological sensors, and embedded RFID devices. With modern lithographic techniques, allowing the fabrication of smaller SAW devices, we now use SAWs to probe the mechanical interactions of nano structures. In particular, SAWs can be used to actuate NEMS which gives rise to many interesting phenomena including anomalous acoustoelectric currents, shock waves in suspended devices, and few electron transport, to only name a few, (Beil et al., 2008; Talyanskii et al., 1997). Today, SAWs are also used to generate a quantized current for use as a current standard. In practice two counter-propagating SAWs are used to observe a quantized acoustoelectric current. This leads to population and depopulation of discrete states (Kataoka et al., 2007). In the following we want to give an overview of the state of the art of applying SAWs to nanomechanical devices. We will also give a brief introduction to recent nanoelectromechanical systems with integrated low-dimensional electron gases,

which have the potential to reveal insights into quantized acoustoelectric states.

acoustic impedance matching of IDTs to nanomechanical devices.

The main equation to consider when designing an IDT is:

**2.1 Interdigitated Transducer Design** 

The focus for generating SAWs in this chapter will involve the fabrication of interdigitated transducers (IDT). An IDT is simple in concept but can be very involved when fine tuning a structure for engineering applications. Such topics as electronic impedance matching to RF lines, effects of bulk waves in contrast to SAWs, and increasing bandwidth will not be covered; though, this is simply a shortened list of things to consider when designing a proper IDT for engineering applications, they do fall outside the scope of this chapter. Nevertheless, another fabrication step we will consider is the use of acoustic waveguides for

**1. Introduction** 

**2. Fabrication** 

