Khaled Hassan

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.

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.

In-Line Optical MEMS Phase Modulator and Application in Ring Laser Frequency Modulation

Optical phase modulators are essential building components in a wide range of applications, for instance, optical communication systems, tunable lasers, optical phase locked loops, and optical sensors. The production of in-plane MEMS-based optical phase modulator with self-aligned mirrors, actuator, and fiber grooves enables the low cost and easy integration with fiber-based lasers and sensors or photonic microsystems. In this paper, we report an in-plane transmission type MEMS-based optical phase modulator fabricated by deep reactive ion etching technology on a silicon-on-insulator (SOI) substrate. Detailed optical analysis of the MEMS phase modulator considering the diffraction of the single-mode fiber output beam, the asymmetric truncation of the beam by the limited aperture of the micromirrors and the tilt angle of the deeply etched mirrors is presented. The device layer height of the fabricated SOI wafer is 100 μm, and the sidewalls are etched with verticality that is better than 89.98°. The micromechanical system is characterized experimentally using electrical technique, and the resonance frequency and quality factor are 11.3 kHz and 163, respectively. The MEMS device is integrated into fiber ring laser (FRL) enabling the achievement of low- and high-frequency modulation indices. The frequency modulation of the FRL using the presented phase modulator is supported with numerical analysis and experimental results.

High-throughput deeply-etched scanning Michelson interferometer on-chip

A miniaturized scanning Michelson interferometer is demonstrated on-chip using a deep-etching process. Etching depths larger 300 μm were obtained with side-wall angle better than 0.1 degree and scalloping depth smaller than 60 nm. Multi-mode optical fibers with core diameters of 62.5 μm and 200 μm were used for delivering the white light to SOI chips with device layer heights of 90 μm and 200 μm for evaluating the improvement with larger depth. The resulting interferograms were compared showing 12-dB increase in the signal, which is a significant boost for the signal-to-noise ratio. The presented interferometer opens the door for the use of miniaturized instruments in practical applications.

Thermal stability of multi-longitudinal mode laser beating frequencies in hybrid semiconductor-fiber ring lasers

The temperature dependence of the beating frequencies in multi-longitudinal mode hybrid semiconductor-fiber based ring lasers is studied theoretically and experimentally. The variation of the beating frequency with temperature is found to be smaller for larger cavity length and lower beating order. Measured frequency variation as low as -0.24 Hz/°C is obtained for cavity length of 2.7 km. The stability of the frequency is evaluated using the Allan variance technique. The measurement is carried out for different beating frequency orders. The lowest order beating frequency has about 20x better long-term frequency stability than the beating frequency of the 100th order.

Straight multimode interference phased array structure using periodic segmented waveguide phase array

A new design of a multimode interference (MMI) phased array structure is proposed. This design is based on replacing the arrayed delay arms between the first MMI power splitter and the second MMI combiner by periodic segmented waveguides. This allows a straight structure without curved waveguides and thus reduces greatly the size of the structure. A design example of an 8 channel multiplexer is presented showing a size reduction by a factor of 23 when compared with conventional design, while keeping nearly the same performance.

MEMS-based frequency modulation of fiber ring laser

Fiber lasers are gaining wide attention nowadays due to their high stability, high reliability, low cost and compactness. Frequency modulation of the laser system has many applications such as wavelength tuning, active mode locking, generation of optical frequency combs and fiber sensors in general. In this work, we report frequency modulation of fiber ring laser system using transmission-type corner cube in-plane MEMS phase modulator fabricated by DRIE technology on an SOI substrate. The fiber-coupled MEMS-based phase modulator is inserted in a multilongitudinal mode fiber ring laser, which has a free spectral range of 345 kHz. By varying the applied voltage on the MEMS device, a wide range of the frequency modulation index can be achieved.

MEMS corner-cube transmission-type optical phase modulator in DRIE technology

In this work we report an in-line, transmission-type corner-cube optical Phase Modulator (PM) fabricated by DRIE technology on an SOI substrate. The PM has a resonance frequency of 11.2 kHz and a maximum travel range of 5.5 μm. The structure is tested using single-mode fibers in a Mach-Zehnder interferometer configuration at the wavelength of 1550 nm demonstrating the capability of producing both low and high modulation indices by varying the applied voltage.

Ultra-compact MEMS FTIR spectrometer

Portable and handheld spectrometers are being developed and commercialized in the late few years leveraging the rapidly-progressing technology and triggering new markets in the field of on-site spectroscopic analysis. Although handheld devices were commercialized for the near-infrared spectroscopy (NIRS), their size and cost stand as an obstacle against the deployment of the spectrometer as spectral sensing components needed for the smart phone industry and the IoT applications. In this work we report a chip-sized microelectromechanical system (MEMS)-based FTIR spectrometer. The core optical engine of the solution is built using a passive-alignment integration technique for a selfaligned MEMS chip; self-aligned microoptics and a single detector in a tiny package sized about 1 cm3. The MEMS chip is a monolithic, high-throughput scanning Michelson interferometer fabricated using deep reactive ion etching technology of silicon-on-insulator substrate. The micro-optical part is used for conditioning the input/output light to/from the MEMS and for further light direction to the detector. Thanks to the all-reflective design of the conditioning microoptics, the performance is free of chromatic aberration. Complemented by the excellent transmission properties of the silicon in the infrared region, the integrated solution allows very wide spectral range of operation. The reported sensor’s spectral resolution is about 33 cm-1 and working in the range of 1270 nm to 2700 nm; upper limited by the extended InGaAs detector. The presented solution provides a low cost, low power, tiny size, wide wavelength range NIR spectral sensor that can be manufactured with extremely high volumes. All these features promise the compatibility of this technology with the forthcoming demand of smart portable and IoT devices.

Deeply-etched 1 micron-thick silicon layers enabling 170-NM bandwidth highly-reflective Bragg mirrors

Deeply-etched distributed Bragg reflectors are demonstrated experimentally on silicon with mirror bandwidth that is larger than 170 nm. The reflector is realized by two layers of silicon 1-μm thick separated by a 1.95-μm air gap. Etching depth of 80 μm was obtained with side-wall angle better than 0.05 degree and scalloping peak-to-peak roughness of 15 nm. An optical filter was formed by two reflectors separated by a filter gap of 7 μm and the corresponding measured linewidth is 5 nm around 1550 nm wavelength. The estimated reflectivity of the mirror is larger than 96%. The reported micromirrors and filter enable the realization of on-chip wideband systems.