**4. Advanced FP architecture**

In this last section, we present two advanced architecture of FP cavity based on cylindrical 1D photonic crystal vertically etched in silicon. The first architecture is based on cylindrical Bragg mirrors to focus light beam along one transverse beam. SEM Photo of a device based on single silicon layer is presented in Fig. 21. The measured characteristic is shown in Fig. 22 pertain to three different spacing between the injection fiber and the input mirror. Numerical modeling confirms the measurements and reveals that the device exhibits selective excitation of transverse modes TEM20. For more details, the interested reader may refer to [Malak et al. Transducers 2011] [Malak et al. JMEMS 2011]. The second architecture however, aims to focus the light beam in both transverse planes to reduce losses introduced by Gaussian beam expansion as well. For this purpose, the cylindrical Bragg is combined with a fiber rod lens to focus the light beam in the other transverse plane. Since the second architecture is not common, a stability model has been devised to enable the design of stable resonator [Malak el al. JMST 2011]. Photo of the realized device and corresponding response is shown in Fig. 23. This architecture provides a high quality factor (~9000) for a Bragg mirror based on four silicon layers. It has a strong potential for spectroscopic applications.

Fig. 21. SEM photo of the FP cavity with single cylindrical silicon layer measured with cleaved fibers.

Tuning is achieved either by rotating the cavity further or by controlling its gap *g*, as shown in Figs. 20a and 20b. Tuning range of 30 nm is shown as the result of gap tuning of 150 nm. The increase in the separation distance *L* doesn't affect the peak position as

In this last section, we present two advanced architecture of FP cavity based on cylindrical 1D photonic crystal vertically etched in silicon. The first architecture is based on cylindrical Bragg mirrors to focus light beam along one transverse beam. SEM Photo of a device based on single silicon layer is presented in Fig. 21. The measured characteristic is shown in Fig. 22 pertain to three different spacing between the injection fiber and the input mirror. Numerical modeling confirms the measurements and reveals that the device exhibits selective excitation of transverse modes TEM20. For more details, the interested reader may refer to [Malak et al. Transducers 2011] [Malak et al. JMEMS 2011]. The second architecture however, aims to focus the light beam in both transverse planes to reduce losses introduced by Gaussian beam expansion as well. For this purpose, the cylindrical Bragg is combined with a fiber rod lens to focus the light beam in the other transverse plane. Since the second architecture is not common, a stability model has been devised to enable the design of stable resonator [Malak el al. JMST 2011]. Photo of the realized device and corresponding response is shown in Fig. 23. This architecture provides a high quality factor (~9000) for a Bragg mirror based on four silicon layers. It has a strong potential for

Fig. 21. SEM photo of the FP cavity with single cylindrical silicon layer measured with

shown in Fig. 20c.

**4. Advanced FP architecture** 

spectroscopic applications.

cleaved fibers.

Fig. 22. Highlights on "Wavelength selective switching" and "Mode selective filtering" of the curved FP cavity (a) Recorded spectral response of the cavity, measured with lensed fiber while varying the fiber-to-cavity distance D. The quasi-periodic pattern of the curve reveals selective excitation of the resonant transverse modes TEM20 around 1532 nm in addition to the fundamental Gaussian mode TEM00. Varying the distance D leads to different levels for mode TEM20 with an extinction ratio of 7:1, the maximum amplitude was at D=150 µm. (b) Ideal intensity distribution of TEM00 and TEM20 modes. (c) Measured intensity profiles (of modes TEM00 and TEM20) obtained by lateral in-plane scanning of the detection fiber.

MEMS Based Deep 1D Photonic Crystal 111

modeling, fabrication technology, common applications and a brief introduction to an

Lipson, A. & Yeatman, E.M. (2005). Free-Space MEMS tunable optical filter on (110) silicon,

Lipson, A. & E. Yeatman, E. M. (2007). A 1-D Photonic Band Gap Tunable Optical Filter

Malak, M.; Pavy, N.; Marty, F.; Peter, Y.-A.; Liu, A. Q. & Bourouina, T. (2011).

Malak, M.; Pavy, N.; Marty F. & Bourouina, T. (2011). Mode-Selective Optical Filtering And

Malak, M.; Pavy,N.; Marty, F.; Peter, Y.-A.; Liu, A. Q. & Bourouina, T. Cylindrical Surfaces

Malak, M.; Pavy,N.; Marty, F.; Richalot, E.; Liu, A. Q. & Bourouina, T. (2011) Design,

Marty, F.; Rousseau, L.; Saadany, B.; Mercier, B.; Français, O.; Mita, Y. & Bourouina, T.

Pruessner, M.W.; Stievater, T.H. & Rabinovich, W.S. (2008). Reconfigurable Filters Using

Saadany, B.; Malak, M.; Kubota, M.; Marty, F.; Mita, Y.; Khalil, D. & Bourouina, T. (2006).

Yun, S. & Lee, J. (2003). A Micromachined In-Plane Tunable Optical Filter Using the

Yun, S-S; You, S-K & Lee, J-H (2006). Fabrication of vertical optical plane using DRIE and

Song, I.-H. ; Peter, Y.-A. & Meunier, M. (2007). Smoothing dry-etched microstructure

*Micromechanics and Microengineering*, vol. 17, pp.1593-1597.

Macleod, H. A. (2001). *Thin Film Optical Filters*, ISBN 0 7503 0688 2, London, UK

high quality factor, *Applied Physics Letters*, vol 98, 211113/1-3.

*Journal of Microsystem Technologies*, vol 17, no 4, pp. 543-552

Nano-Structures, *Microelectronics Journal*, vol. 36, pp. 673-677.

*Microsystems (TRANSDUCERS),* pp. 534-537.

*Microengineering*, vol. 13, pp.721-725.

*IEEE/LEOS International Conference on Optical MEMs and Their Applications*, Oulu,

in (110) Silicon, *Journal of Microelectromechanical Systems*, vol. 16, no.3, pp. 521-

Micromachined Fabry–Perot resonator combining submillimeter cavity length and

Wavelength-Selective Switching Through Fabry-Perot Cavity With Cylindrical Reflectors, *16th International Conference on Solid-State Sensors, Actuators and* 

Enable Wavelength-Selective Extinction and Sub-0.2 nm Linewidth in 250 µm-Gap Silicon Fabry-Pérot Cavities, submitted to the *Journal of Microelectromechanical* 

modeling and characterization of stable, high Q-factor curved Fabry–Perot cavities,

(2005). Advanced Etching of Silicon Based On Deep Reactive Ion Etching For Silicon High Aspect Ratio Micro Structures And Three-Dimensional Micro- And

MEMS Resonators and Integrated Optical Microcavities, *IEEE MEMS conference*,

Free-space Tunable and Drop Optical Filters Using Vertical Bragg Mirrors on Silicon, *IEEE Journal of Selected Topics in Quantum Electronics*, vol 12, no. 6, pp.1480-

Thermo-optic Effect of Crystalline Silicon, *Journal of Micromechanics and* 

KOH crystalline etching of (110) silicon wafer, *Sensors Actuators A*, vol. 128, pp.

sidewalls using focused ion beam milling for optical applications, *Journal of* 

advanced application: The curved FP cavity.

Finland, 1-4 August pp. 73-74

**6. References** 

527.

*systems.* 

pp.766-769.

1488.

387–394.

(a)

Fig. 23. (a) Top view of the curved FP cavity with the fiber rod lens (b) Typical response obtained from such device

#### **5. Concluding remarks**

1D photonic crystal structure acquired a high interest long ago due to the application domain they touch. As outlined in this chapter, they constitute a basic building block in many devices like FP resonators, multilayered coating. The attractiveness in them comes from their easy design and modeling based on multilayered stack theory and the affordable fabrication process, thanks to the advance in the fabrication processes, in particular, the advance in the DRIE process which helped producing vertical Bragg on silicon. In this context, this chapter focused on specific issues concerning 1D photonic crystal: design and modeling, fabrication technology, common applications and a brief introduction to an advanced application: The curved FP cavity.

### **6. References**

110 Photonic Crystals – Introduction, Applications and Theory

**Fiber Rod Lens**

(a)

1555.5 1556 1556.5 1557 1557.5

(b) Fig. 23. (a) Top view of the curved FP cavity with the fiber rod lens (b) Typical response

1D photonic crystal structure acquired a high interest long ago due to the application domain they touch. As outlined in this chapter, they constitute a basic building block in many devices like FP resonators, multilayered coating. The attractiveness in them comes from their easy design and modeling based on multilayered stack theory and the affordable fabrication process, thanks to the advance in the fabrication processes, in particular, the advance in the DRIE process which helped producing vertical Bragg on silicon. In this context, this chapter focused on specific issues concerning 1D photonic crystal: design and

Wavelength in nm

**Fiber Rod Lens**

OUTPUT fiber groove

1556.2 1556.3 1556.4

3-dB = 0.177 nm


INPUT fiber groove


obtained from such device

**5. Concluding remarks**

Transmitted Power in dB

Curved Bragg reflector


**6** 

*Italy* 

Alessandro Massaro

*Italian Institute of Technology IIT* 

*Center for Bio-Molecular Nanotecnology, Arnesano, Lecce* 

**Photonic Crystal Waveguides and Bio-Sensors** 

Photonic crystals (PCs) are actually implemented as biosensors [Ganesh et al., 2007], optical resonators [Karnutsch et al., 2007] and wavelength filters [D'Orazio et al., 2008; Pierantoni et al., 2006]. Other kinds of photonic crystals can be implemented by considering a periodic structure with defect line and/or central cavities. Several architectures of micro-cavities (see examples in Fig. 1 (a), (b)and (c)) have been studied in the past by using triangular and square lattices layouts [Joannopoulos, 1995] oriented on optoelectronic technology. Optoelectronic technologies are often affected by cost and space problems that prevent them from being used even more widely. The development and implementation of photonic integrated circuits (PICs) could provide a solution to these two major obstacles. Couplers such as tapered waveguides and photonic crystal (PhC) devices can be integrated in the same chip in order to reduce the space, especially concerning complex optical switch systems, and, to provide high transmitted power and high efficiency of the PICs. For example, the use of tapered waveguides is necessary in order couple the light into a W1 PhC waveguide (illustrated in Fig. 1 (a)). This kind of W1 PhC waveguide is object of much interest because of its potential for controlling and manipulating the propagation of light. In particular, sharp bends, junctions, couplers, cavities, add-drop filters, and multiplexers have been experimentally demonstrated or theoretically predicted, thus making these devices very attractive for highly integrated photonic circuits [Mekis et al., 2008; Pottier et al., 2003; Johnson et al., 2002; Sanchis et al., 2002; Chau et al., 2004; Chietera et al., 2004; Xing et al., 2005; Camargo et al., 2004; Talneau et al., 2004; Marki et al., 2005; Camargo et al., 2004; Sanchis et al.,2004; Khoo et al.,2006]. The in-plane coupling of W1 PhC is also an important issue for bio-sensors implemented by micro- and nanofabrication technologies. In fact, the development of micro- and nanofabrication technologies, biomolecular patterning and micro-electromechanical systems (MEMS), has greatly contributed to the realization of miniaturized laboratories applied to genomic and proteomic analysis. The application fields of these biochips are extremely broad, and they have been referred as several different terms (gene-chip, gene-array, DNA microarray, protein chip, and lab-on-chip). Essentially, these chips, developed both in simple stand-alone configurations and integrated devices/architectures, consist of planar structures, realized on several substrates such as glass or plastic materials, where (bio)molecules (such as DNA, proteins or cells, which selectively conjugate with target molecules) can be immobilized on them through chemical surface modification or in situ synthesis [Fan et al., 2006] as happens DNA sensors. These chips require the use of suitable micro-reactors and/or capillary systems, and the

**1. Introduction** 

Zandi, K.; Wong, B.; Zou, J.; Kruzelecky, R. V.; Jamroz W. & Peter, Y.-A. (2010). In-Plane Silicon-On-Insulator Optical MEMS Accelerometer Using Waveguide Fabry-Perot Microcavity With Silicon/Air Bragg Mirrors, *in Proc. 23rd IEEE Int. Conf. Micro Electro Mech. Syst.,* pp. 839-842.
