Subramaniam Kanakaraju

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.

A tunable GaInAsP-InP optical microring notch filter

The authors demonstrate an ultracompact tunable GaInAsP-InP microring notch filter. The core of the device is a quantum-well superlattice and forms the intrinsic region in a p-n structure. The device has curved sections of radius 2.25 /spl mu/m and straight sections of length 1 /spl mu/m, making it the smallest microring filter ever reported. They obtain 0.8 nm (100 GHz) of tuning by reverse-biasing the diode structure over 8 V using the quadratic electrooptic effect.

Low-loss suspended quantum well waveguides.

We have used surface micromachining to fabricate suspended InGaAs/InGaAsP quantum well waveguides that are supported by lateral tethers. The average measured TE propagation loss in our samples is 4.1 dB/cm, and the average measured TE loss per tether pair is 0.21 dB. These measurements are performed at wavelengths in the optical L-band, just 125 nm below the quantum well band gap.

Conversion of RZ-OOK to RZ-BPSK by XPM in a Passive AlGaAs Waveguide

The conversion of data modulation format from 10-Gb/s return-to-zero on-off keying (RZ-OOK) to 10-Gb/s RZ binary phase-shift keying (RZ-BPSK) has been successfully carried out for the first time utilizing cross-phase modulation (XPM) in a passive AlGaAs waveguide. A 10-9-bit-error-rate (BER) preamplified receiver sensitivity gain of ≈ 1 dB was measured for the converted RZ-BPSK relative to baseline RZ-OOK, whereas a penalty of ≈ 2.7 dB relative to baseline RZ-BPSK is explained to be due to cross-absorption modulation induced by nondegenerate two-photon absorption (ND-TPA), as well as to an insufficient nonlinear phase shift.

Indium Phosphide MEMS Cantilever Resonator Sensors Utilizing a Pentacene Absorption Layer

We report a microelectromechanical system cantilever waveguide resonator sensing platform utilizing a novel optical readout scheme and the organic semiconductor pentacene as a surface absorbing layer. In this paper, the measurement of isopropyl alcohol and ethanol vapors by way of mass induced frequency shift using a cantilever microbalance is demonstrated. Vapor was introduced to the system through a custom built environmental chamber. A frequency shift due to a mass absorption of 65 Hz was measured, corresponding to a measurement of 6.92 ±1.1 ×10-14 g with a minimum detectable mass of 5.09 ×10-15 g for the devices presented. The pentacene absorbing layer in this paper shows it for the first time, functioning as a mass absorbing layer. These results are also the first demonstration of repeatable mass sensing performed using the integrated indium phosphide cantilever waveguide sensor platform.

Enhanced Electro-Optic Phase Shifts in Suspended Waveguides

We demonstrate enhanced electro-optic phase shifts in suspended InGaAs/InGaAsP quantum well waveguides compared to attached waveguides. The enhancement stems from an improved overlap between the optical mode and the multiple quantum well layers in thin waveguides when the semiconductor material beneath the waveguide is selectively etched. The measured voltage length product is 0.41 V-cm and the measured propagation loss is 2.3 +/- 0.7 dB/cm for the TE mode in the optical L-band.

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.

A microelectromechanically tunable asymmetric Fabry-Perot quantum well modulator at 1.55 µm

We experimentally demonstrate an InP-based microelectromechanically tunable asymmetric Fabry-Perot quantum well modulator that operates in the optical C-band. The device exhibits contrast ratios over 20 (13 dB) with less than 8 volts bias.

Indium phosphide-based monolithically integrated PIN waveguide photodiode readout for resonant cantilever sensors

An integrated photodiode displacement readout scheme for a microelectromechanical cantilever waveguide resonator sensing platform is presented. III-V semiconductors are used to enable the monolithic integration of passive waveguides with active optical components. This work builds upon previously demonstrated results by measuring the displacement of cantilever waveguide resonators with on-chip waveguide PIN photodiodes. The on-chip integration of the readout provides an additional 70% improvement in mass sensitivity compared to off-chip photodetector designs due to measurement stability and minimized coupling loss. In addition to increased measurement stability, reduced packaging complexity is achieved due to the simplicity of the readout design. We have fabricated cantilever waveguides with integrated photodetectors and experimentally characterized these cantilever sensors with monolithically integrated PIN photodiodes.