Gallium arsenide optical phased array photonic integrated circuit.

A 16-channel optical phased array is fabricated on a gallium arsenide photonic integrated circuit platform with a low-complexity process. Tested with a 1064 nm external laser, the array demonstrates 0.92° beamwidth, 15.

Comparison of static and dynamic characteristics of 1550 nm quantum dash and quantum well lasers.

Compared to quantum well (QW) lasers, lower dimensional quantum dot (QD) or quantum dash (QDash) devices demonstrate superior performances, owing to their quantized energy levels and increased carrier confinement. Here, we report the systematic comparison of static and dynamic properties of long wavelength (1550 nm) QDash and QW lasers. For the QDash lasers, a higher maximum operating temperature and lower temperature dependence was achieved for long cavities, although the threshold current densities were larger than the QW reference devices.

Electrically driven, polarized, phosphor-free white semipolar (20-21) InGaN light-emitting diodes grown on semipolar bulk GaN substrate.

We demonstrate a simple method to fabricate efficient, electrically driven, polarized, and phosphor-free white semipolar (20-21) InGaN light-emitting diodes (LEDs) by adopting a top blue quantum well (QW) and a bottom yellow QW directly grown on (20-21) semipolar bulk GaN substrate. At an injection current of 20 mA, the fabricated 0.1 mm size regular LEDs show an output power of 0.

Indium Phosphide Photonic Integrated Circuits for Free Space Optical Links.

An indium phosphide (InP)-based photonic integrated circuit (PIC) transmitter for free space optical communications was demonstrated. The transmitter consists of a sampled grating distributed Bragg reflector (SGDBR) laser, a high-speed semiconductor optical amplifier (SOA), a Mach-Zehnder modulator, and a high-power output booster SOA. The SGDBR laser tunes from 1521 nm to 1565 nm with >45 dB side mode suppression ratio.

Low dark current III-V on silicon photodiodes by heteroepitaxy.

Top-illuminated PIN and modified uni-traveling carrier (MUTC) photodiodes based on InGaAs/InAlAs/InP were epitaxially grown on Si templates. Photodiodes with 30-μm diameter have dark currents as low as 10 nA at 3 V corresponding to a dark current density of only 0.8 mA/cm.

Strain-Compensated InGaAsP Superlattices for Defect Reduction of InP Grown on Exact-Oriented (001) Patterned Si Substrates by Metal Organic Chemical Vapor Deposition.

We report on the use of InGaAsP strain-compensated superlattices (SC-SLs) as a technique to reduce the defect density of Indium Phosphide (InP) grown on silicon (InP-on-Si) by Metal Organic Chemical Vapor Deposition (MOCVD). Initially, a 2 μm thick gallium arsenide (GaAs) layer was grown with very high uniformity on exact oriented (001) 300 mm Si wafers; which had been patterned in 90 nm V-grooved trenches separated by silicon dioxide (SiO₂) stripes and oriented along the [110] direction. Undercut at the Si/SiO₂ interface was used to reduce the propagation of defects into the III-V layers.

Towards chip-scale optical frequency synthesis based on optical heterodyne phase-locked loop.

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines.

3D integrated hybrid silicon laser.

Lasers were realized on silicon by flip-chip bonding of indium phosphide (InP) devices containing total internal reflection turning mirrors for surface emission. Light is coupled to the silicon waveguides through surface grating couplers. With this technique, InP lasers were integrated on silicon.

A 100-Gb/s noncoherent silicon receiver for PDM-DBPSK/DQPSK signals.

An integrated noncoherent silicon receiver for demodulation of 100-Gb/s polarization-division multiplexed differential quadrature phase-shift keying and polarization-division multiplexed differential binary phase-shift keying signals is demonstrated. The receiver consists of a 2D surface grating coupler, four Mach-Zehnder delay interferometers and four germanium balanced photodetectors.

Amplifier-free slab-coupled optical waveguide optoelectronic oscillator systems.

We demonstrate a free-running 3-GHz slab-coupled optical waveguide (SCOW) optoelectronic oscillator (OEO) with low phase-noise (<-120 dBc/Hz at 1-kHz offset) and ultra-low sidemode spurs. These sidemodes are indistinguishable from noise on a spectrum analyzer measurement (>88 dB down from carrier). The SCOW-OEO uses high-power low-noise SCOW components in a single-loop cavity employing 1.

Low-noise RF-amplifier-free slab-coupled optical waveguide coupled optoelectronic oscillators: physics and operation.

We demonstrate a 10-GHz RF-amplifier-free slab-coupled optical waveguide coupled optoelectronic oscillator (SCOW-COEO) system operating with low phase-noise (<-115 dBc/Hz at 1 kHz offset) and large sidemode suppression (>70 dB measurement-limited). The optical pulses generated by the SCOW-COEO exhibit 26.8-ps pulse width (post compression) with a corresponding spectral bandwidth of 0.

Versatile offset-free 16-QAM single dual-drive IQ modulator driven by binary signals.

A customized IQ modulator driven by equal-amplitude binary signals for generating offset-free 16-quadrature amplitude modulation (QAM) is proposed and validated through simulations. The incorporation of tunable splitters demonstrates the feasibility of the transmitter and enables more efficient constellations such as hexagonal 16-QAM.

Uni-traveling-carrier variable confinement waveguide photodiodes.

Uni-traveling-carrier waveguide photodiodes (PDs) with a variable optical confinement mode size transformer are demonstrated. The optical mode is large at the input for minimal front-end saturation and the mode transforms as the light propagates so that the absorption profile is optimized for both high-power and high-speed performance. Two differently designed PDs are presented.

Measurement of intermodulation distortion in high-linearity photodiodes.

Accurately characterizing third order intermodulation distortion (IMD3) in high-linearity photodiodes is challenging. Two measurement techniques are evaluated-a standard two-tone measurement and a more complicated three-tone measurement technique to measure IMD3. A model of the measurement system is developed and used to analyze the limitations of the two techniques in determining the distortion of highly linear photodiodes.

Compact beam splitters with deep gratings for miniature photonic integrated circuits: design and implementation aspects.

We present an extensive study of an ultracompact grating-based beam splitter suitable for photonic integrated circuits (PICs) that have stringent density requirements. The 10 microm long beam splitter exhibits equal splitting, low insertion loss, and also provides a high extinction ratio in an integrated coherent balanced receiver. We further present the design strategies for avoiding mode distortion in the beam splitter and discuss optimization of the widths of the detectors to improve insertion loss and extinction ratio of the coherent receiver circuit.

Selectively-undercut traveling-wave electroabsorption modulators incorporating a p-InGaAs contact layer.

A novel fabrication process has been developed for fabricating undercut-etched electroabsorption modulators that are compatible with tunable lasers. This process allows for the incorporation of highly doped p-type InGaAs above the upper cladding as an ohmic contact layer. The EAM demonstrates significant improvement in the microwave performance with little effect on modulation efficiency due to the undercut etching.

SOA gate array recirculating buffer with fiber delay loop.

We present a compact variable delay buffer for storage of 40 byte packets. The recirculating buffer is based on an InP SOA gate array two-by-two switch which provides greater than 40 dB of extinction, sub-nanosecond switching, and fiber-to-fiber gain. The switch is used with a fiber delay loop 450 centimeters, or 23 ns, in length.