Kuldeep Amarnath

InP-based optical waveguide MEMS switches with evanescent coupling mechanism

An optical waveguide MEMS switch fabricated on an indium phosphide (InP) substrate for operation at 1550 nm wavelength is presented. Compared to other MEMS optical switches, which typically use relatively large mirrors or long end-coupled waveguides, our device uses a parallel switching mechanism. The device utilizes evanescent coupling between two closely-spaced waveguides fabricated side by side. Coupling is controlled by changing the gap and the coupling length between the two waveguides via electrostatic pull-in. This enables both optical switching and variable optical coupling at voltages below 10 V. Channel isolation as high as -47 dB and coupling efficiencies of up to 66% were obtained with switching losses of less than 0.5 dB. We also demonstrate voltage-controlled variable optical coupling over a 17.4 dB dynamic range. The devices are compact with 2 /spl mu/m/spl times/2 /spl mu/m core cross section and active area as small as 500 /spl mu/m/spl times/5 /spl mu/m. Due to the small travel range of the waveguides, fast operation is obtained with switching times as short as 4 /spl mu/s. Future devices can be scaled down to less than 1 /spl mu/m/spl times/1 /spl mu/m waveguide cross-sectional area and device length less than 100 /spl mu/m without significant change in device design.

Monolithic suspended optical waveguides for InP MEMS

We present a novel waveguide design for InP microelecromechanical systems. The substrate is removed from underneath the waveguide by sacrificial etching, and the suspended waveguide is supported by lateral tethers. This allows segments of the waveguide to be moved and prevents substrate leakage loss in the fixed segments of the waveguides. A single-mask fabrication process is developed that can be extended to more complex devices employing electrostatic actuation. Fabricated suspended waveguides exhibit a loss of 2.2 dB/cm and tether pairs exhibit 0.25-dB additional loss.

Laterally coupled InP-based single-mode microracetrack notch filter

We demonstrate an InP-based microracetrack notch filter with >25-dB extinction and 19-nm free-spectral range at 1550 nm. The curved section of the resonator has a radius of 2.25 /spl mu/m. To our knowledge, this represents the best extinction and the smallest radius of curvature for such a device to date.

End-coupled optical waveguide MEMS devices in the indium phosphide material system

We demonstrate electrostatically actuated end-coupled optical waveguide devices in the indium phosphide (InP) material system. The design of a suitable layer structure and fabrication process for actuated InP-based waveguide micro-electro-mechanical systems (MEMS) is reviewed. Critical issues for optical design, such as coupling losses, are discussed and their effect on device performance is evaluated. Several end-coupled waveguide devices are demonstrated, including 1 × 2 optical switches and resonant sensors with integrated optical readout. The 1 × 2 optical switches exhibit low-voltage operation (<7 V), low crosstalk (−26 dB), reasonable loss (3.2 dB) and switching speed suitable for network restoration applications (140 µs, 2 ms settling time). Experimental characterization of the integrated cantilever waveguide resonant sensors shows high repeatability and accuracy, with a standard deviation as low as σ = 50 Hz (0.027%) for fresonant = 184.969 kHz. By performing focused-ion beam (FIB) milling on a sensor, a mass sensitivity of Δm/Δf = 5.3 × 10−15 g Hz−1 was measured, which is competitive with other sensors. Resonant frequencies as high as f = 1.061 MHz (Qeffective = 159.7) have been measured in air with calculated sensitivity Δm/Δf = 1.1 × 10−16 g Hz−1. Electrostatic tuning of the resonator sensors was also examined. The prospect of developing InP MEMS devices monolithically integrated with active optical components (lasers, LEDs, photodetectors) is discussed.

Electrically pumped InGaAsP-InP microring optical amplifiers and lasers with surface passivation

Vertically coupled electrically pumped InGaAsP microring optical amplifiers providing gain at 1550 nm are demonstrated. The microrings provide up to 10 dB of gain at the through-port in pulsed mode. The bias current is used to control the loss in the ring and, hence, the region of operation (under-coupled, critically coupled, transparency, and gain). Sulfur passivation is used to reduce carrier loss due to surface recombination in the active region. The amplifiers are designed for application in cascaded microring optical logic gates in photonic logic circuits.

Wavelength-selective integrated optical MEMS filter in InP

This paper presents a low-power, electrostatically-actuated integrated optical filter on an InP MEMS platform. The micromachined filter achieves a resonant wavelength shift of 12nm (1513-1525nm) at a low operating voltage (7V). The filter consists of a half-wavelength long resonant cavity bound by two highly reflective distributed Bragg reflector (DBR) mirrors fabricated by lithography and dry-etching. The filter is integrated monolithically with a doubly-clamped suspended-beam capacitive microactuator and optical waveguides. This paper discusses the fabrication as well as experimental results, showing good agreement between the measured and simulated performance of the filter. The novelty of the device lies in its in-plane MEMS actuation scheme enabling easy integration with other waveguide-based planar integrated optical active and passive components on an InP optoelectronic chip.

Micromechanical resonators with integrated optical waveguides for sensing applications

Low-power indium phosphide microelectromechanical systems (MEMS) cantilever resonators with integrated optical waveguides for bio-chemical sensing are presented. Resonant frequencies up to 168.8 kHz (Q=26.5) have been measured in air and mass detection of 510 fg/100 Hz is possible.

Tunable optical filters for in-plane integration on InP MEMS platform

We have demonstrated a planar waveguide-based tunable integrated optical filter in indium phosphide (InP) with on-chip micro-electro-mechanical (MEMS) actuation. An air-gap Fabry-Perot resonant microcavity is formed between two waveguides, whose facets have monolithically integrated high-reflectivity multilayer InP/air Distributed Bragg Reflector (DBR) mirrors. A suspended beam electrostatic microactuator attached to one of the DBR mirrors modulates the microcavity length, resulting in a tunable filter. The DBR mirrors provide a broad high-reflectivity spectrum, within which the transmission wavelength can be tuned. The in-plane configuration of the filter enables easy integration with other active and passive waveguide-based optoelectronic devices on a chip and simplifies fiber alignment. Experimental results from the first generation of tunable optical filters are presented. The microfabricated filter exhibited a resonant wavelength shift of 12nm (1513-1525nm) at a low operating voltage of 7V. A full-width-half-maximum (FWHM) of 33 nm was experimentally observed, and the quality factor was calculated to be 46. Several improvements of the MEMS actuator, waveguide, and optical cavity design for the future devices are discussed.

All-Optical Non-Linear Switching in Active Microdisks

We demonstrate all-optical pump-probe switching in electrically-pumped microdisks fabricated on InGaAsP/InP using gain-saturation optical non-linearity to achieve switching at lower powers than in passive devices. A pseudo-microdisk design combines the best of microrings and disks.