Haitham Omran

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.

MEMS tunable Michelson interferometer with robust beam splitting architecture

A new beam splitter [1] is proposed to realize a completely integrated Michelson interferometer, where a single medium interface (Si/Air) is used for optical beam splitting. This offers a stable splitting ratio over a very wide spectral range. Using this technique on SOI wafers, with a moving mirror, a highly robust and tunable interferometer is fabricated. The tunable interferometer is tested experimentally by measuring optical interference versus mirror displacement.

Wideband Subwavelength Deeply Etched Multilayer Silicon Mirrors for Tunable Optical Filters and SS-OCT Applications

In this paper, we report subwavelength deeply etched 1000-nm-thick silicon layers using deep etching on an SOI substrate. The subwavelength silicon layers are used to construct wideband multilayer Bragg mirrors showing more than 220-nm 3-dB bandwidth. The mirror reflectivity and effect of silicon layers etching errors are estimated using optical measurements. The deeply etched mirrors are used to realize a 125-nm-tuning range Fabry-Perot tunable with a free spectral range of 130 nm enabled by the MEMS technology. The filter has input/output fibers inserted into micromachined grooves with in-plane axis aligned with the filter mirrors. The filter is utilized in a ring laser swept source configuration with a semiconductor optical amplifier. The swept source has 100-nm tuning range and 0.13-nm 3-dB linewidth.

Miniaturized tunable integrated Mach-Zehnder MEMS interferometer for spectrometer applications

In this work a novel miniaturized Mach-Zehnder MZ interferometer fabricated by Deep Reactive Ion Etching DRIE technology on an SOI wafer is presented. The new structure is based on the use of two Si/Air beam splitters, and two metallic mirrors fabricated monolithically in a small footprint measuring 1 mm × 2 mm on the die. By moving the mirrors using an integrated comb drive actuator, the structure is tested as an FTIR spectrometer and the two wavelengths 1550 nm and 1575 nm have been successfully identified using it. The successful implementation of this 4 elements interferometer in an integrated form opens the door for more complicated optical structures self aligned and fabricated in a one step lithography process

Characterization of MEMS FTIR spectrometer

In this work we present the full characterization of an optical MEMS Fourier Transform Infra Red FTIR spectrometer fabricated by Deep Reactive Ion Etching DRIE Technology on Silicon substrate. Both electrical and optical properties of the spectrometer are measured. The presented techniques allows to build an engineering model for the spectrometer and to predict its main specifications taking into account the specificity of the MEMS technology used in the spectrometer fabrication.

Intrinsic improvement of diffraction-limited resolution in optical MEMS fourier-transform spectrometers

High resolution MEMS FTIR spectrometers are now of growing interest on both the academic and industrial levels. Such spectrometers are characterized by their small compact size, high speed of response and the use of optical fiber coupling. The main optical MEMS engine of the spectrometer is an interferometer with a moving mirror displaced using a MEMS actuator. The resolution of the FTIR spectrometer is related to the travel distance of the moving mirror but with a lower limit restricted by the divergence angle of the input light to the spectrometer; an effect called self-apodization. In this work, we analyze this effect within the MEMS systems, in which the size of the optical components is in the order of 50-300 μm limited by the microfarbication technology. We show analytically and experimentally that the resolution is intrinsically improved 5-10 times relative to the values directly predicted by the input light divergence angle.

Linewidth of swept laser source

In this work we study the factors affecting the linewidth of a swept laser source. A ring fiber laser source based on EDFA and a Fabry-Perort resonator is used for this purpose. With this setup a swept source with a linewidth of better than 0.1 nm is obtained over a tuning range of about 47 nm limited by the spectral gain of the EDFA amplifier used. The factors affecting the source linewidth are then examined by modeling the EFDA amplifier and the swept source and then compared to the practical measured results of an EDFA swept laser source. The measurements and simulations both show that the swept laser linewidth is about 10 times narrower than the Fabry-Perot filter 3dB linewidth.

Mach-Zehnder MEMS interferometer with two Si/Air beam splitters

In this work we present a novel MEMS interferometer based on the Mach-Zehnder (MZ) architecture. The interferometer is fabricated by deep reactive ion etching (DRIE) technology on an SOI wafer. The new structure is based on the use of two Si/Air beam splitters [1] and two metallic mirrors, integrated with a comb drive actuator on a single die. The whole structure is integrated on one chip and no parts are assembled from outside the structure. By moving the mirrors using the integrated comb drive actuator, the structure is tested as an FTIR spectrometer. The two wavelengths 1525 nm and 1575 nm have been successfully identified using it.

Accessing Rapidly Scanning Swept Laser Source Instantaneous Spectral Width Using a Multimode Rate Equation Model

In this paper, we present a multimode rate equation model for rapidly scanning swept laser source. The model accounts for the dynamics of a semiconductor-based swept laser source in a ring configuration. The instantaneous spectral width of the laser during sweeping is calculated through wavelength- and time-dependent cavity loss model. The various factors affecting the instantaneous spectral width are studied including the effect of the semiconductor optical amplifier gain spectrum and the filter scanning speed. The model also allows monitoring the evolution of the cavity modes in the time domain as the filter scans. It shows that the instantaneous spectral width is a multifolded property affected by the filter scanning speed and spectral width, the SOA gain spectrum, and other parameters.