N. Chubun

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

Efficiency of cathodoluminescent phosphors for a field-emission light source application

The efficiency of major types of cathodoluminescent phosphors has been investigated at high-brightness (up to 30 000 cd/m2) operational conditions using thermionic electron source. The accelerating voltage was varied from 4 to 14 kV and electron beam current density was independently varied from 2 to 50 μA/cm2. Under those conditions both thermal quenching and current saturation of the phosphors were observed. Due to combined influence of those factors, it was found that the best way to characterize the phosphor is plotting the efficiency (in lm/W) versus the specific power density (in mW/cm2) graph. The resulting plots show the integrated influence of current loading and elevated temperature on the phosphor efficiency. The best efficiencies at 200 mW/cm2 and 10 kV were measured for a green color phosphor −55 lm/W, for a blue one—10 lm/W, and for a red—13 lm/W.

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.

Field emission characterization of silicon tip arrays coated with GaN and diamond nanoparticle clusters

Wide band-gap materials show promise for applications in coating of field emission tips. Recently nanocrystalline hexagonal GaN crystallites as small as 12 nm average diameter have been formed using reactive laser ablation of gallium metal in nitrogenating ambient [T. J. Goodwin et al., Appl. Phys. Lett. 70, 3122 (1997)]. In this article we investigated the performance of ungated emitters with and without surface coating. Silicon tip arrays are coated by dielectrophoresis of gallium nitride nanoparticles or nanocrystalline diamond clusters from an ethanol suspension. The emitters were evaluated and compared before and after the surface treatment using SEM image and I–V measurements in the diode configuration. The results suggest that the emitters benefit from coating the surface with nanocrystalline diamond clusters in terms of reduction in the turn on voltage by 100 V and increase uniformity in emission during low voltage operation. The long-term emission stability for both types of the coated cathodes w...

Fabrication and characterization of singly addressable arrays of polysilicon field-emission cathodes

Abstract Polysilicon is a viable candidate material for field-emission microelectronics devices. It can be competitive for large size, cost-sensitive applications such as flat-panel displays and micro electro-mechanical systems. Singly addressable arrays of field-emission cells were fabricated in a matrix configuration using a subtractive process on polysilicon-on-insulator substrates. Matrix rows were fabricated as insulated polycrystalline silicon stripes with sharp emission tips; and matrix columns were deposited as gold thin film electrodes with round gate openings. Ion implantation has been used to provide the required conductivity of the polysilicon layer. To reduce radius of curvature of the polysilicon tips, an oxidation sharpening process was used. The final device had polysilicon emission tips with end radii smaller than 15 nm, surrounded by gate apertures of 0.4 μm in diameter. Field emission properties of the cathodes were measured at a pressure of about 10−8 Torr, to emulate vacuum conditions available in sealed vacuum microelectronics devices. It was found that an emission current of 1 nA appears at a gate voltage of 25 V and can be increased up to 1 μA at 70 V. Over this range of current, no “semiconductor” deviation from the Fowler–Nordheim equation was observed. I–V characteristics measured in cells of a 10×10 matrix, with a cell spacing of 50 μm demonstrated reasonable uniformity and reproducibility.

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

Phase characterization of an InP based optical-CDMA encoder using frequency-resolved optical gating (FROG)

We demonstrate the optical phase characterization of a monolithically integrated InP optical-CDMA encoder/decoder chip using frequency-resolved optical gating.

A monolithic ultra-compact InP O-CDMA encoder with planarization by HVPE regrowth

We report a monolithic, ultra-compact optical-CDMA encoder/decoder photonic chip in InP with surface planarization by low-pressure hydride-vapor-phase-epitaxy regrowth. The chip consists of an AWG pair and eight electro-optic phase shifters and demonstrated excellent encoding operation.