Diaa Khalil

Free-Space Tunable and Drop Optical Filters Using Vertical Bragg Mirrors on Silicon

Vertical Bragg grating mirrors are realized by the anisotropic etching of Si using deep reactive ion etching (DRIE), thus producing multiple vertical interfaces between Si and air. The Bragg mirrors are used to realize two optical filter configurations. The first is a tunable Fabry-Peacuterot cavity composed of two mirrors, where tuning is achieved by moving one of the mirrors using silicon-on-insulator (SOI) electrostatic microelectromechanical system (MEMS) actuation. The second is a drop filter, where a tilted Bragg mirror acts as a wavelength selective reflector. The enhanced etching process involving a mix of cryogenic and Bosch DRIE processes is presented. The realized structures, fabrication process, as well as measured performance are also presented

Integrated wide-angle scanner based on translating a curved mirror of acylindrical shape

A wide angle microscanning architecture is presented in which the angular deflection is achieved by displacing the principle axis of a curved silicon micromirror of acylindrical shape, with respect to the incident beam optical axis. The micromirror curvature is designed to overcome the possible deformation of the scanned beam spot size during scanning. In the presented architecture, the optical axis of the beam lays in-plane with respect to the substrate opening the door for a completely integrated and self-aligned miniaturized scanner. A micro-optical bench scanning device, based on translating a 200 μm focal length micromirror by an electrostatic comb-drive actuator, is implemented on a silicon chip. The microelectromechanical system has a resonance frequency of 329 Hz and a quality factor of 22. A single-mode optical fiber is used as the optical source and inserted into a micromachined groove fabricated and lithographically aligned with the microbench. Optical deflection angles up to 110 degrees are demonstrated.

A MEMS-based VOA with very low PDL

In this letter, we study the optical performance of a microelectromechanical system reflection-type variable optical attenuator (VOA). Experimental results of packaged VOA devices show that the proposed architecture exhibits very low polarization dependence within the entire attenuation range (polarization-dependent loss (PDL)<0.1 dB at 30-dB attenuation level).

An exact simplified method for the normalization of radiation modes in planar multilayer structures

Abstract We present an exact simplified method for the power normalization of the radiation modes in planar multilayer or graded index structures. The method depends mainly on the physical understanding of the radiation mode as a superposition of plane waves. The technique proposed simplifies greatly the required calculations and gives exactly the same analytical results obtained by the classical integration technique. Beside its physical point of view, this technique could be integrated in a more general computer program for the analysis of integrated optical discontinuities.

Fully Integrated Mach-Zhender MEMS Interferometer With Two Complementary Outputs

In this paper, a novel Mach-Zhender interferometer for spectroscopy applications is presented. The interferometer is fully integrated on an silicon on insulator wafer using deep reactive ion etching technology, the moving mirror is coupled to a comb drive microelectromechanical systems (MEMS) actuator. Optical propagation inside the MEMS structure is modeled and the diffraction effect is studied. Practical results show the complementary nature of the two outputs and a resolution of 25 nm at 1.55 μm is reported when using the interferometer as an Fourier transform infrared spectrometer. The complementary nature of the interferometer can be further used for source noise reduction.

Deeply-Etched Optical MEMS Tunable Filter for Swept Laser Source Applications

In this letter, we report a wide tuning range MEMS-based swept laser source using deep reactive ion etching on an SoI substrate. A MEMS Fabry-Pérot filter with a free-spectral range and a tuning range wider than 94 nm is presented. The measured transmission loss of the filter is between -10.2 and -13.6 dB. This filter is used to construct a swept laser source with 85 nm tuning range. These results represent the widest tuning range reported in literature for an in-plane SoI-MEMS based swept laser source using deeply-etched free-standing distributed-Bragg-reflection mirrors. The recorded tuning range enables the use of the in-plane MEMS filter in optical coherence tomography applications.

Rigorous spectral analysis of leaky structures : application to the prism coupling problem

Abstract This work presents a rigorous spectral analysis of the leakage phenomenon in integrated optical structures. We first show that the “leaky mode” of a dielectric waveguide actually represents a group of radiation modes around a central component satisfying the transverse resonance of the structure. Then we give a rigorous integral formulation for the calculation of the coupled power in structures like the prism coupling structure. The approximations for the case of weak coupling are then analysed to show their limits of validity. With these approximations we get the same formula existing in the literature.

Two-dimensional multimode interference in integrated optical structures

In this work we study the two-dimensional (2D) multimode interference and self-imaging in a dielectric optical waveguide. The studied waveguide is assumed to be multimode in both the transverse directions x and y. The conditions required for single and multiple image formations are developed. New types of image are also found. The obtained results are verified using a three-dimensional FDBPM technique. Applications of the 2D interference in waveguides for 2D optical power splitting are also investigated.

Design of strip-loaded weak-guiding multimode interference structure for an optical router

We introduce a new multimode interference structure that can be used as an integrated optical router. This structure is based on the existence of a first cross state in weakly guiding multimode waveguides. Such a cross image, not expected by the self-imaging technique, is tested by rigorous modal analysis as well as the nonmodal beam propagation method. We show that the quality of this image could be enhanced by strip loading the multimode section of the structure. Making use of this image, we propose a new optical router based on the large nonlinearity associated with the blockaded reservoir and quantum-well electron transfer structure.

All-optical networks as microwave and millimeter-wave circuits

In this work we study the use of optical fiber networks to perform microwave processing functions. Theoretical and experimental results are presented in the case of a Mach-Zehnder interferometer network, a Fabry-Perot network, and a combination of the two previous networks. All of these networks are realized with single-mode fiber elements. The use of optical scattering parameters and the graphical representation technique was introduced in our model, which greatly simplified the analysis. A good agreement between modeling and experiment as well as good performances from the microwave point of view are observed. >