Willie W. Ng

Holographic interference lithography for integrated optics

In this paper, some of our recent work in the use of holographic interference lithography and various material removal techniques to corrugate thin-film optical waveguides are reviewed. The specific applications of these periodic thin-film devices in the distributed feedback and distributed Bragg reflector semiconductor laser, and as output grating couplers, are described. Recent results in the use and fabrication of chirped and curved-line gratings are also summarized.

Demonstration of a Large Stretch-Ratio

We report the demonstration of a time-stretch photonic analog-to-digital conversion (ADC) system with a stretch ratio of . By stretching a 10-GHz modulation envelope to 242 MHz via optical dispersion, we demonstrated, for the first time, an ADC resolution that is better than 8 effective number of bits for a 10-GHz input-signal bandwidth.

({\rm M}=41)

Room-temperature operation of GaAs distributed Bragg reflector lasers is reported. The diodes are fabricated from conventional double heterostructures involving only a single step of liquid-phase epitaxy. For gratings with a period of 3700 A, the diodes lased at 8770 A, which corresponds to the high-absorption side of the spontaneous emission spectrum. Thresholds as low as 6 kA/cm^2 have been realized.

Photonic Analog-to-Digital Converter With 8 ENOB for an Input Signal Bandwidth of 10 GHz

Optical surface waves propagating along the surface of a multilayer stack have been observed. The multilayer stack is grown by liquid phase epitaxy. The transverse intensity distribution measured is found to agree with our theoretical calculation.

Room‐temperature operation of GaAs Bragg‐mirror lasers

Highly collimated laser beams have been observed to be coupled out by second‐order Bragg scattering from GaAs distributed Bragg reflector lasers. The beams are perpendicular to the waveguide plane and have an angular width of less than 1°. The diodes have a separate confinement structure and operate at room temperature with thresholds as low as 1.4 kA/cm2.

Optical surface waves in periodic layered medium grown by liquid phase epitaxy

We report the fabrication and characterization of the two-bit monolithic optical time-delay network on GaAs. GaAs rib-waveguides and InGaAs waveguide-coupled MSM detectors serve respectively as delay-lines and optoelectronic switches on the photonic integrated circuit. From the linear RF differential phase observed between 1 and 11 GHz, we estimate that the measured time-delays are within 4 psec of their designed values.<<ETX>>

Highly collimated broadside emission from room‐temperature GaAs distributed Bragg reflector lasers

Abstract An equivalent cavity approach is used to derive the oscillation condition of a distributed Bragg reflector laser. The oscillation frequencies and thresholds are determined graphically. The effect of lossy reflectors is discussed. Several advantages and potential applications of distributed Bragg reflector structures are pointed out. Experimental results on optically pumped GaAs lasers are presented.

High-precision detector-switched monolithic GaAs time-delay network for the optical control of phased arrays

A RF photonic link selectively attenuates strong interference components in a composite RF signal while passing the weaker desired frequency components. This self-adapting limiter makes use of seeded stimulated brillouin scattering in the optical fiber and covers a wide range of interference and signal frequencies.

GaAs distributed Bragg reflector lasers

We compare the GaAs and Silica-based approaches for realizing integrated time-shift networks. The performance of a fully functional 2-cm X 2-cm monolithic GaAs circuit is reviewed in detail. In addition, we describe the design of an optoelectronic- switched network that uses Silica-based star-couplers and waveguide arrays.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Self adapting limiter

The design and fabrication of a 1.3- mu m waveguide-coupled strained-layer In/sub x/Ga/sub 1-x/As/GaAs MSM detector with an optimized active layer thickness is reported. For 100- mu m-long devices, a responsivity of 0.58 mA/mW is observed. Using the detector as an optoelectronic switch, on/off ratios better than 40 dB were achieved at L and X band.<<ETX>>