R.G. Broeke

Monolithically integrated InP-based photonic chip development for O-CDMA systems

This work discusses photonic integration efforts toward developing an InP-based monolithically integrated photonic chip for optical code-division multiple-access (O-CDMA) system applications. The chip design includes the colliding pulsed mode (CPM) locked laser, the Mach-Zehnder interferometer-based threshold detector (MZI), and the monolithic O-CDMA encoder/decoder chip based on array-waveguide-gratings and phase modulator arrays. The compact 4 /spl times/ 1 cm monolithic chip can replace a complex and large O-CDMA setup based on bulk optics. The integration technique involves active-passive integration using dry etching, metal organic chemical vapor deposition growth, and lateral hydride vapor phase epitaxy regrowth technologies. The fabricated CPM showed stable 1.54 ps modelocked laser output, the MZI showed excellent O-CDMA threshold detection, and the O-CDMA encoder showed Walsh-code O-CDMA encoding. Further, the fabricated devices showed excellent planarity, which accelerate our progress toward monolithic integration of O-CDMA systems.

Demonstration of Spectral Phase O-CDMA Encoding and Decoding in Monolithically Integrated Arrayed-Waveguide-Grating-Based Encoder

We report on successful spectral phase encoding and decoding operation in a pair of monolithically integrated InP encoder chips, each consisting of an arrayed waveguide grating (AWG) pair and an eight-channel electrooptic phase shifter array. The monolithic fabrication process includes anisotropic reactive ion etching and planarizing hydride-vapor-phase-epitaxy lateral regrowth to realize buried hetero-waveguide structures in AWGs and phase shifters. Electrooptical modulation in the phase shifter arrays in the encoder chip achieved Walsh-code-based optical code-division multiple access (O-CDMA) encoding and decoding. The matched-code encoding-decoding operation resulted in error-free performance in the presence of an interferer, indicating good potential for O-CDMA network applications

Synchronized transform-limited operation of 10-GHz colliding pulse mode-locked laser

We report a 10-GHz colliding pulse mode-locked laser fabricated with integrated active-passive waveguides. The laser fabrication adopted a deep reactive ion etching and single-step metal-organic vapor phase epitaxy regrowth process for forming the buried heterostructure waveguide. Clean output pulses resulted from laterally tilting the active-passive interface and effectively suppressing residual back-reflections at the interface. Hybrid mode-locking resulted in a synchronized transform-limited sech2optical waveform. Pulsewidth, chirp, timing jitter, and frequency-locking range were investigated through systematic device biasing condition optimization

Optical-CDMA in InP

This paper describes the InP platforms for photonic integration and the development on these platforms of an optical code division multiple access (O-CDMA) system for local area networks. We demonstrate three building blocks of this system: an optical pulse source, an encoder/decoder pair, and a threshold detector. The optical pulse source consists of an integrated colliding pulse-mode laser with nearly transform-limited 10 Gb/s pulses and optical injection locking to an external clock for synchronization. The encoder/decoder pair is based on arrayed waveguide gratings. Bit-error-rate measurements involving six users at 10 Gb/s showed error-free transmission, while O-CDMA codes were calibrated using frequency resolved optical gating. For threshold detection after the decoder, we compared two Mach--Zehnder interferometer (MZI)-based optical thresholding schemes and present results on a new type of electroabsorber-based MZI.

A Monolithic InP-based Photonic Integrated Circuit for Optical Arbitrary Waveform Generation

We demonstrate a compact monolithically-integrated InP optical arbitrary waveform generator, consisting of an arrayed waveguide grating pair with 10 GHz channel spacing, 10 high-speed optical amplitude modulators, and 10 high-speed optical phase modulators.

10-GHz and 20-GHz Channel Spacing High-Resolution AWGs on InP

This letter reports on 10-GHz and 20-GHz channel-spacing arrayed waveguide gratings (AWGs) based on InP technology. The dimensions of the AWGs are 6.8 times 8.2 mm2 and 5.0 times 6.0 mm2, respectively, and the devices show crosstalk levels of -12 dB for the 10-GHz and -17 dB for the 20-GHz AWG without any compensation for the phase errors in the arrayed waveguides. The root-mean-square phase errors for the center arrayed waveguides were characterized by using an optical vector network analyzer, and are 18deg for the 10-GHz AWG and 28deg for the 10-GHz AWG.

80.8-km BOSSNET SPECTS O-CDMA Field Trial Using Subpicosecond Pulses and a Fully Integrated, Compact AWG-Based Encoder/Decoder

We successfully demonstrate a spectral phase-encoded time-spreading (SPECTS) optical code-division multiple-access (O-CDMA) field trial on an 80.8-km link within the Boston-South Network (BOSSNET) using a fully-integrated, polarization-independent arrayed-waveguide grating (AWG)-based encoder/decoder. The subpicosecond pulse source is based on an ultrastable optical frequency comb generator employing dispersion-decreasing fiber. A novel tunable dispersion-slope compensator enables the use of subpicosecond pulses without extensive characterization of the field-deployed fiber. Bit-error rate (BER) and Ethernet traffic statistics are presented.

Electrical subharmonic hybrid mode locking of a colliding pulse mode-locked laser at 28 GHz

This letter discusses electrical subharmonic hybrid mode locking (SHML) of a colliding pulse mode-locked (CPM) laser in InP. The CPM laser fabrication adopts a simple wet etching process and bisbenzocyclobutene planarization process for realizing planarized low-capacitance devices. The experimental results show, for the first time to our knowledge, stable emission of nearly transform-limited pulses at 28 GHz of a CPM laser synchronized to a clock source by SHML. We further describe careful optimization steps of dc and radio-frequency biasing conditions which lead to minimal output pulsewidth of 1.4 ps, limited by the saturable absorber dimension.

InP-Based Arrayed-Waveguide Grating with a Channel Spacing of 10 GHz

We realize a high-precision 10-channel InP-based arrayed-waveguide grating (AWG) with a 10-GHz channel spacing. The AWG showed approximately 10 dB excess-loss, 10 dB crosstalk, and 8.2 × 6.8 mm2 dimensions.

Error-free spectral encoding and decoding operation of InP O-CDMA encoder

We report error-free spectral encoding and decoding operation of an InP monolithic, ultra-compact optical-CDMA encoder/decoder photonic chip pair. The experimental results demonstrate the strong potential for realizing high performance O-CDMA networks with InP micro-systems