Trevor K. Chan

Retroreflecting optical modulator using an MEMS deformable micromirror array

A modulating corner-cube reflector with one microelectromechanical-system (MEMS) mirror that deforms from a flat into a hexagonal array of concave reflective microlenses to disperse the retroreflected wavefront is demonstrated. It is shown that such retromodulators can operate under a wide range of wavelength and angle illumination using Huygens-Fresnel propagation analysis, and this analysis is verified using devices fabricated by surface micromachining. A gold-coated silicon-nitride membrane suspended over 1-mm-diameter circular cavities had a resonant frequency of 160 kHz and 0.55-/spl mu/m maximum deformation with 79 V applied. While this deflection was only 2/3 of the design value of 0.8 /spl mu/m, we measured an up to 7:1 modulation contrast ratio from a prototype retromodulator, which achieved 100-kHz modulation over a 100-nm optical bandwidth, a 35/spl deg/ range of incident angles, and temperatures ranging from 20 to 100/spl deg/C.

2-Dimensional beamsteering using dispersive deflectors and wavelength tuning

We introduce a 2D beamscanner which is controlled by wavelength tuning. Two passive dispersive devices are aligned orthogonally to deflect the optical beam in two dimensions. We provide a proof of principle demonstration by combining an arrayed waveguide grating with a free space optical grating and using various input sources to characterize the beamscanner. This achieved a discrete 10.3 degrees by 11 degrees output field of view with attainable angles existing on an 8 by 6 grid of directions. The entire range was reached by scanning over a 40 nm wavelength range. We also analyze an improved system combining a virtually imaged phased array with a diffraction grating. This device is much more compact and produces a continuous output scan in one direction while being discrete in the other.

1092 Channel 2-D Array Demultiplexer for Ultralarge Data Bandwidth

We demonstrate 1 times 1092 channel wavelength demultiplexing with 50-GHz channel pitch and a 600-nm total bandwidth. Outputs from 1 times 40 channel arrayed waveguide gratings operating with multiple orders enter a free-space optical grating demultiplexer which separates the orders into a 2-D spot array, where the light can be coupled into discrete output fibers or operated on by a surface normal device (i.e., microelectromechanical system switch or detector array). Supercontinuum source input from 1140 to 1750 nm produced a 28 times 39 spot array at the output plane. The insertion loss for light is coupled into a single mode fiber ranged from 7 to 18 dB with less than 10-dB loss in channels between 1300 and 1750 nm. Bit-error-rate measurements show a negligible 0.1-dB power penalty at 10 GB/s

Integrated diffractive shearing interferometry for adaptive wavefront sensing

We present theory, design, and preliminary experimental studies for a compact wavefront sensor based on lateral shearing interferometry using a binary phase grating, image sensor, and Fourier-based processing. The integrated system places a diffractive element directly onto an image sensor to generate interference fringes within overlapping diffraction orders. The shearing ratio and the interferogram signal-to-noise ratio directly affect the reconstruction accuracy of wavefronts with differing spatial variations. Optimal shearing parameters associated with the autocorrelation of the input encourage placing a spatial light modulator as the diffractive element allowing adaptive wavefront sensing. Experimental results from a fixed-grating system are presented as well as requirements for next-generation adaptive systems.

2-D array wavelength demultiplexing by hybrid waveguide and free-space optics

We demonstrate wavelength demultiplexing into a raster-scanned 8/spl times/9 array by combining a 1/spl times/8 arrayed waveguide grating with a free-space grating multiplexer. 9 diffraction orders from each AWG output are separated onto a 2D array on an InGaAs camera or coupled into a scanned output fiber. This first proof-of-principle device had 0.2 nm channel -20 dB width, >35 dB spectral extinction and 15 to 25 dB insertion loss over the 70 nm operating range.

Short-haul transmission links based on 25- and 56-Gbaud PAM4 modulation

In this paper, we review our experimental and simulation work on 28- and 56-Gbaud PAM4-based 100Gbps and 400Gbps short-haul links, including 10, 40, and 80km transmission distances. We also discuss the system performances, limitations, and areas of improvement for these links and their future applications.

Fourier-Based Diffractive Shearing Interferometer for Wavefront Sensing

We propose a simple and compact wavefront sensor using a phase transmission grating attached to a CMOS image sensor. We present experimental results using a binary phase grating. An adaptive grating displayed by a phase modulator can extend sensor dynamic range.

Fast, Two-Dimensional Optical Beamscanning by Wavelength Switching

We introduce a passive (stationary) 2-dimensional beamscanner which scans by wavelength tuning. Our prototype system demonstrated discrete 0.2 ms switching over a 11.0deg times 10.3deg scanning range. 100 nanosecond switching is possible using existing tunable lasers.

Data transmission through a 1014-channel two-dimensional array wavelength demultiplexer

We demonstrate a 1/spl times/1014 channel wavelength demultiplexer with 50 GHz pitch and a 594 nm total bandwidth. The hybrid AWG/grating produced a 26/spl times/39 array of wavelength-demultiplexed spots measured by an InGaAs camera and by a scanned output fiber used to sample the output. Insertion loss was <10 dB for all channels measured within the 1270 nm to 1700 nm operating range (700 total channels). BER measurements show a 0.1 dB power penalty at 10 GB/s.

Deformable MEMS micromirror array for wavelength and angle insensitive retroreflecting modulators

We demonstrate a large-aperture, angle-insensitive MEMS modulator that switches from flat to a reflective microlens array. We measure 10 dB contrast with 0.55 /spl mu/m sag, and calculate 0.8 /spl mu/m sag will produce 20 dB contrast.