Low resistance ohmic contacts have been successfully fabricated on n-GaSb layers grown by MBE on semi-insulating (SI) GaAs substrates using the Interfacial Misfit Dislocation (IMF) technique. Although intended for photovoltaic applications, the results are applicable to many antimonide-based devices. The IMF technique enables the growth of epitaxial GaSb layers on semi-insulating GaAs substrates resulting in vertical current confinement not possible on unintentionally doped ~ 1e17 cm-3 p-doped bulk GaSb. Results for low resistance ohmic contacts using NiGeAu, PdGeAu, GeAuNi and GeAuPd metallizations for various temperatures are reported. Specific transfer resistances down to 0.12 Ω-mm and specific contact resistances of < 2e-6 Ω-cm2 have been observed.
In this paper, we investigate the dynamics of a nonlinear delay differential equation model for passive mode-locking in
semiconductor lasers, when the delay model is seeded with parameters extracted from the gain and loss spectra of a
quantum dot laser. The approach used relies on narrowing the parameter space of the model by constraining the values of
most of the model parameters to values extracted from gain and loss measurements at threshold. The impact of the free
parameters, namely, the linewidth enhancement factors that are not available from the gain and loss measurements, on
the device output is then analyzed using the results of direct integration of the delay model. In addition to predicting
experimentally observed trends such as pulse trimming with applied absorber bias, the simulation results offer insight
into the range of values of the linewidth enhancement factors in the gain and absorber sections permissible for stable
mode-locking near threshold. Further, the simulations show that this range of permissible values progressively decreases
with increasing bias voltage on the absorber section. This is important for telecomm and datacom applications where
such devices are sought as pulsed sources, as well as in military RF photonic applications, where mode-locked diode
lasers are used as low noise clocks for sampling.
Design details and performance data are presented for (Al,Ga)As and polymeric monolithic tapered rib waveguides achieving modal spot-size transformation for mode-matching from a variety of devices to single-mode optical fiber. 2D expanded output modes of waveguide modulators and lasers are achieved using 1D and 2D tapers between non-critical initial and final widths well suited for optical lithography.
Several thousand glass optical fibers fused together is routinely used as fiber image guides for medical and other image remoting applications. Fiber image guides also offer possibility for flexible optical interconnect links with potentially thousands of bi-directional parallel channels with data rates as high as 10 Gbps per channel, leading to more than Tera bits per second aggregate data transfer rates. A fair number of fiber image guide based link demonstrations using vertical cavity surface emitting lasers have been reported. However, little is known about designable parameters and optimization paradigms for applications to massively parallel optical interconnects. This paper discusses critical optical parameters that characterize a massively parallel link. Experimental characterizations were carried out to explore some of the fundamental interactions between single-mode 850 nm VCSELs and fiber image guides having different numerical apertures, 0.25, 0.55 and 1.00. Preliminary optical simulation results are given. Finally, potential directions for further experimental and analytical explorations, and for applicability into designable link systems are suggested.
New methods for integration of dissimilar components and optical inputs/outputs are expected to mass-produce photonic micro-systems at reduced levels of difficulty and therefore reduced cost. These methods involve monolithic and hybrid approaches, the latter at both wafer-to-wafer and chip-to- wafer levels. Broadly, these are called 'heterogeneous integration' and encompass technologies as diverse as wafer- fusion and DNA-assisted micro-assembly. This review summarizes the associated micro-assembly techniques and discusses their possible influence upon cost- and yield-benefits to industry.
High optical loss due to mode mismatch at the interfaces of different components in a hybrid photonic integrated circuit (PIC) poses a major challenge in the implementation of such devices. Increased coupling efficiency can be achieved by incorporating an optical mode converter at the interface. This converter basically consists of a tapered waveguide section adapting different modal spot-sizes. Optimized coupling requires total control of the transverse optical field. This can be achieved by the ability to shape both the vertical as well as the lateral waveguide dimension. We present design, simulations, and fabrication considerations for a 3D tapered waveguide structure for low loss mode conversion. Our mode converter concept is based on polymeric optical waveguides on silicon substrate. A gradually deeper trench is formed in the silicon substrate, using diffusion limited wet etching with a laterally tapered mask pattern. The structure is then planarized with a polymer and patterned laterally. Our method thus allows control of both the lateral and vertical waveguide dimensions. The concept is consistent with low-loss coupling to singlemode fibers as well as between laser and amplifier arrays and single mode waveguides in a low-cost hybrid PIC solution.
Optical interconnects at the cabinet-to-cabinet, board-to-board, and multichip module-to- multichip module levels will enable future avionics systems requirements to be met by eliminating undesirable compromises associated with electrical interconnects. Fiber optics is the well established medium of choice for cabinet-to-cabinet applications, while planar polymeric interconnects are required at the backplane level. Significant advances have been made in demonstrating practical polymer interconnects compatible with existing board fabrication principles, however both waveguide loss and interfaces to optoelectronic components require further improvement before the technology is broadly applicable.
Integrated optical time-shift networks consisting of cascaded pairs of 2 x 2 linear electrooptic switches and optical delay lines in GaAs waveguides at 1.32 micron are investigated for true-time optical beam forming in phased array antennas. We report new state-of-the-art results in curved waveguide and corner bend insertion loss, and preliminary results from 2-bit time delay generators (TDGs) constructed in the form of GaAs-based photonic integrated circuits utilizing these components. These results represent significant progress in our longer-term goal of demonstrating a 7-bit TDG with a loss matching monolithic microwave integrated circuit (MMIC) delay line techniques, while providing very wide bandwidth unmatched by MMIC technology.
Optical modulators based on electrooptically-induced lateral mode interference in multimode AlGaAs/GaAs waveguides at lambda = 1.32 micron are investigated for high-frequency linear applications. The key design issue is achieving higher slope efficiency while maintaining significant linearity improvements over sinusoidal interference-based modulator designs. We report experimental results which demonstrate indirectly a reduction in intermodulation distortion of 48 dB compared to an ideal Mach-Zehnder interferometer.
Approaches for future 'mixed application' monolithic integrated circuits (ICs) employing optical receive/transmit, RF amplification and modulation and digital control functions are discussed. We focus on compatibility of the photonic component fabrication with conventional RF and digital IC technologies. Recent progress at Honeywell in integrating several parts of the desired RF/digital/photonic circuit integration suite required for construction of a future millimeter-wave optically-controlled phased-array element are illustrated.
A new design of GaAs/AlGaAs waveguide amplitude modulator intended for array applications at 830nm wavelength is reported. The device is based on polarization rotation and has bandwidths in excess of 1 GHz and an extinction ratio of 1 7dB. Mach-Zehnder modulators with 23dB have also been fabricated and arrays with 20 microns device separation fabricated. The arrays have crosstalk less than -20dB and feature electrical interconnection compatible with standard packaging techniques.
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