Henry E. Garrett

Less than 5-ns wavelength switching with an SG-DBR laser

We achieve fast wavelength switching between all channel combinations of a 64-channel sampled-grating distributed Bragg reflector laser in less than 5 ns. The laser was designed to have low tuning currents and efficient heat extraction in order to reduce parasitic thermal effects. We also report on the behavior of the front and back mirror pre-emphasis amplitudes required for the fast switching

Multiwavelength parallel optical interconnects for massively parallel processing

We describe a multiwavelength, multifiber (parallel) optical interconnect based on multimode fiber ribbon cables with applications in massively parallel processing systems. By combining the benefits of parallel optics and coarse wavelength division multiplexing high aggregate throughputs are possible in a broadcast and select architecture that provides a single hop to all nodes. We identify the key components needed for such a system and report on our component development efforts for multiwavelength parallel optical interconnects. System components reported herein include a four-wavelength bit-parallel transmitter using a silicon optical bench and hybrid packaging, and two-port and three-port wavelength selective filter modules packaged to be compatible with mechanically transferable ferrule terminated ribbon cables. The transmitters were modulated up to 1.25 Gb/s with a bit-error rate better than 10/sup -12/ and no measurable power penalty due to multiple wavelength bit parallel operation. The filters exhibited insertion losses of between 1 and 2 dB and would support 10 nm spaced channels at -23-dB crosstalk.

Multi-mode fiber coarse WDM grating router using broadband add/drop filters for wavelength re-use

We demonstrate a grating-router with 37 nm channel spacing and 6 nm FWHM in the 800-900 nm range for WDM over multimode fiber. Broadband thin-film add/drop filters provide wavelength re-use enabling N/spl times/N fully non-blocking interconnection with N wavelengths.

Characterization of Lithium Niobate Electro-Optic Modulators at Cryogenic Temperatures

This paper reports on the operation of lithium niobate electro-optic waveguide modulators at temperatures down to 15 degree(s)K. Commercial and laboratory fiber pigtailed devices have successfully been cooled without any increases in insertion loss from temperature induced stresses in device packaging. Three x-cut devices exhibited a linear increase in Vpi voltage of 8% +/- 1% when cooled from room temperature to approximately 20 degree(s)K. The broadband frequency response improved at lower temperatures. A velocity-matched experimental modulator has shown increased bandwidth when cooled to liquid nitrogen temperature.

1.3-μm optoelectronic devices on GaAs using group III-nitride-arsenides

Group III-Nitride-Arsenides are promising materials for 1.3 micron opto-electronic devices grown on GaAs substrates, allowing AlAs/GaAs distributed Bragg reflector (DBR) mirrors and integration with GaAs electronics. Nitrogen decreases the GaAs bandgap dramatically, and the smaller GaN lattice constant results in less strain in GaInNAs compared to InGaAs. However, the anneal necessary to achieve device quality material shifts the emission peak to shorter wavelengths. Secondary ion mass spectroscopy (SIMS) depth profiling on GaInNAs quantum wells shows that nitrogen diffusion exceeds indium diffusion during anneal. We have demonstrated broad-area lasers, pulsed lasers, and CW VCSELs. However, due to nitrogen out-diffusion from the QWs, the operating wavelength of these initial devices was shorter than 1.23µm. Subsequent use of GaNAs barriers surrounding the QWs reduced the shift of the emission peak during anneal, as the GaAsN diffused nitrogen into the QW. This also resulted in longer wavelength emission due to decreased electron confinement energy and compensted overall strain. This new active region resulted in devices emitting at 1.3 micron. The new design also improved laser characteristic temperature T0 from 105K to 146K for similar devices.

Multiwavelength VCSEL transmitter for WDM parallel optical fiber interconnects

We employ a combination of direct fiber coupling and broad-band add/drop filtering to demonstrate a 4-wavelength by 10-fiber VCSEL-based transmitter in a PGA package with MT-connectorized optical output. This is the first demonstration to our knowledge of a multiwavelength VCSEL-based parallel optical fiber transmitter. Such a device is useful for future high-bandwidth low-cost data communications applications. The use of a hybrid packaging scheme employing a fiber-ribbon-guided add/drop filter enables ten fibers by four wavelengths with a wide (>10 nm) channel spacing; more wavelengths should be achievable either by using additional filters and/or by combining this approach with monolithic techniques of achieving multiple wavelengths per VCSEL die.

Transient radiation effects in annealed proton-exchange LiNbO3 and LiTaO3 waveguides

We have measured optical attenuation in LiNbO3 and LiTaO3 waveguides due to exposure to an approximately 3 ns pulse of approximately 400 KeV electrons. The LiNbO3 operated at 810 nm and the LiTaO3 at 1309 nm. Both waveguides were formed using the annealed proton exchange method. Transient attenuation and recovery was observed for a series of pulse doses. To the accuracy of the measurements, total recovery was observed within 1 sec after exposure for both waveguides. Results from these waveguides were compared to earlier measurements of a titanium-indiffused LiNbO3 waveguide.

Monolithic Tunable Interferometric Transmitter (TunIT) in Indium Phosphide

Tunable chip-scale optical transmitter devices have revolutionized the pluggable module telecom market, by enabling excellent performance with great cost and size reduction. In this paper, we report on a novel patented tunable transmitter device, based on a dual-output tunable laser, and a pair of modulators, which are interferometrically combined (Tunable Interferometric Transmitter, TunIT). The dual-output laser is based on a Y-branch device architecture, and it utilizes high-reflectivity coating on the back facet. This device exhibits 50-nm tuning range and >40-dB side mode suppression ratio, as well as allows for chirp control. Transmission experiments at 10 Gbps through 75 km of SMF-28 fiber validate its performance. A tunable optical subassembly module with the TunIT device has also been demonstrated.

Glass, plastic, and semiconductors: packaging techniques for miniature optoelectronic components

At Lawrence Livermore National Laboratory, we have extensive experience with the design and development of miniature photonic systems which require novel packaging schemes. Over the years we have developed silicon micro-optical benches to serve as a stable platform for precision mounting of optical and electronic components. We have developed glass ball lenses that can be fabricated in-situ on the microbench substrate. We have modified commercially available molded plastic fiber ribbon connectors (MT) and added thin film multilayer semiconductor coatings to create potentially low-cost wavelength combiners and wavelength selective filters. We have fabricated both vertical-cavity and in-plane semiconductor lasers and amplifiers, and have packaged these and other components into several miniature photonics systems. For example, we have combined the silicon optical bench with standard electronic packaging techniques and our custom-made wavelength-selective filters to develop a four-wavelength wavelength-division-multiplexing transmitter module mounted in a standard 120-pin ceramic PGA package that couples light from several vertical-cavity-surface-emitting-laser arrays into one multimode fiber-ribbon array. The coupling loss can be as low as 2 dB, and the transmitters can be operated at over 1.25 GHz. While these systems were not designed for biomedical or environmental applications, the concepts and techniques are general and widely applicable.