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We report on low-loss, alignment-tolerant coupling between a single-quantum-well (SQW) GaAs-AlGaAs laser and a cleaved single-mode fiber. The laser was fabricated using conventional growth and processing techniques, and did not involve any regrowth. The mode size in the transverse direction was expanded by using a diluted waveguide structure. A butt-coupling efficiency of 66% was achieved against a theoretically possible 78% (which does not correct for Fresnel losses). In addition, large alignment tolerances for a 1-dB excess loss of /spl plusmn/2.0 pm and /spl plusmn/1.0 /spl mu/m were measured in the lateral and the transverse directions, respectively.

We have used a combination of experimental techniques and a numerical method based on a waveguide model to demonstrate low-modal reflectivity antireflection coatings on semiconductor lasers. Our approach does not require a detailed knowledge of the laser layer structure. We have modeled the experimental spectral reflectivities for single- and two-layer antireflection coatings using this approach. This is the first time that a detailed comparison between theory and experiment has been made for two-layer antireflection coatings.

Wavelength conversion from 830 nm to 837 nm of a 250 Mb/s NRZ optical signal has been demonstrated at 10/sup -9/ bit-error rate and a detector sensitivity of -29 dBm using a semiconductor power amplifier monolithically integrated at 90/spl deg/ with a GaAs-AlGaAs SQW semiconductor laser. This device offers a high degree of isolation between the input and the output and has the potential for high-speed operation with a wide continuous-wavelength conversion range.

The paper summarizes on the development of a fiber Bragg grating sensor for the detection of small changes of index of refraction of the medium surrounding the fiber. The etched fiber Bragg grating sensor can detect changes of the index of refraction of a liquid as small as a few parts in 10/sup -5/.

The reliability testing methodology of 1550 nm, sub-200 nm broadly tunable InP-based laser chips for external cavity lasers is discussed. The article summarizes FIT rate achieved and degradation observed with multiple manufactured lots.

A higher level of functionality in semiconductor optical amplifiers is demonstrated through hybrid and monolithic integration. A booster optical amplifier (BOA) is packaged with input and output power monitoring capability. A fiberto-fiber gain of 14.6 dB is achieved. Saturation power of 20 dBm is demonstrated in the package. An optical bench is used to position different optical components, including the SOA chip. lenses, optical isolators, beam splitters, monitoring input and output detectors, in a common package. The optical components are attached using laser-welding technique in a flux free process. Design of a booster optical amplifier monolithically integrated with input and output power monitoring taps is also presented.

A semiconductor booster optical amplifier chip with a saturation power of 20.2 dBm has been demonstrated to operate over the whole C-band. This booster amplifier was used in 10 Gb/s propagation experiment over 80 km of single mode fiber.

We study the spectral optical properties of vertical-cavity surface-emitting lasers (VCSEL's) in the presence of strong optical feedback from an external reflecting surface. When the feedback strength exceeds 1%, multicompound-cavity-longitudinal-modes are observed. The output spectral width increases significantly as the feedback increases. Besides the normal compound-cavity modes, high-loss compound-cavity modes are also observed for the first time. The experimental observations are well explained by a compound-cavity laser theory. >

Ridge-waveguide lasers emitting at /spl sim/1.9 /spl mu/m have been fabricated from a multiple-quantum-well heterostructure with an active region consisting of five GaInAsSb wells and six AlGaAsSb barriers. At room temperature, single-ended cw output power as high as 100 mW has been obtained. The maximum cw operating temperature is 130/spl deg/C, with a characteristic temperature of 85 K between 20 and 80/spl deg/C. >

Summary form only given. Ultrahigh-speed single stream optical time division multiplexed (OTDM) networks operating at data rates of 100 Gb/s or higher can offer advantages over wavelength division multiplexed (WDM) networks providing the same aggregate capacity. A key element for such systems is a packet header generator, capable of taking header information at a low rate and imposing this bit pattern on a high-speed optical stream. In this letter we describe a new concept for the generation of high bit rate optical signals using a programmable pattern generator. The concept involves the formation of an arbitrary spatial pattern of gain and loss along an optical waveguide which contains the information that needs to be converted to a high bit rate optical signal. This process is controlled electronically and can be performed at word or packet rates. A single optical control pulse is used to transcribe the entire spatial pattern onto a counter-propagating optical beam by sequentially saturating the gain and absorption in the active waveguide. With proper spectral filtering following the waveguide, high bit rate RZ and NRZ data patterns can be generated.

InGaAsP-InP based injection laser diodes operating at 1.55 /spl mu/m are very attractive for optical communication systems. The most common Al containing material used in InP based system is Al/sub y/In/sub 1-y/As which is lattice matched to InP for y values near 0.48. Due to this low Al concentration, the oxidation rate for this material is very slow. As a result, the advantages of selectively oxidized structures can not be easily transferred to devices based on InP substrates. We propose using a short period InAs-AlAs superlattice layer as the buried oxidation layer. A short-period superlattice consisting of 2 monolayers of AlAs and 2 monolayers of InAs are grown right above the active region.

Summary form only given. The performance of multiple quantum well (MQW) electroabsorption (EA) waveguide modulators based on the quantum confined Stark effect (QCSE) shows considerable promise due to the low drive voltage, enhanced excitonic absorption, and high-speed operation. Our approach uses a unique quantum well design that incorporates two thin highly tensile strained GaAs-strain layers in order to provide separate confinement, and effective well widths denoted L/sub lh/ and L/sub hh/, for the LH1 and HH1 wavefunctions respectively. This design maintains the degeneracy of the LH1 and HH1 energy levels, for polarization independent transmission, for potentially larger values of the electric field as compared to other approaches.

We have demonstrated an ultra-compact, highly efficient mode transformation between a highly confined active waveguide and a well-confined passive waveguide using conventional fabrication and single epitaxial growth. The mode is transformed over a taper 100 /spl mu/m long and with a low round trip mode transformation loss of 0.3 dB. This scheme provides an attractive platform technology for monolithic integration of various active and passive devices, like splitters with amplifiers, Mach-Zehnder interferometers etc.

We report the measurement of the frequency response of nearly degenerate four‐wave mixing in a vertical‐cavity surface‐emitting laser. High efficiency conjugate signal generation is demonstrated. A superlinear dependence between the square of relaxation oscillation frequency and the output power is observed. The experimental observation is well described by present theories.

We present simulation results, based on a one-dimensional p-i-n photodetector model, to explain the reductions in photodetector response observed at high optical powers. The nonlinear effects are attributed to the redistribution of the internal electric field due to space-charge effects created by the photocarriers. The corresponding modification of the position-dependent charge velocities results in high-frequency response reduction, roll-off reduction, and pulse narrowing. Electric field redistribution leads to two dimensional effects, which must be included for accurate modeling of milliampere photocurrents. >

We report a study of the effects of external optical feedback on the threshold and spectral characteristics of VCSELs with feedback levels in the range from /spl minus/25 dB to 0 dB. A large threshold current reduction and multi-extended-cavity-mode operation have been observed. The experimental results are in good agreement with the theoretical calculations based on a compound cavity laser model. >

Nearly degenerate four-wave mixing (NDFWM) in semiconductor lasers has been studied extensively. As we will demonstrate, the frequency dependence of FWM signals can be used to extract the intrinsic AlGaAs-GaAs semiconductor laser parameters since the FWM process is free of electrical parasitic effects. Through a quantitative fit to the NDFWM data, we were able to extract some basic semiconductor laser parameters, including the relaxation oscillation frequency, damping rate, nonlinear gain parameter, linewidth enhancement factor and optical confinement factor. >

Summary form only given. GaAs-AlGaAs GRINSCH single quantum well tapered semiconductor optical amplifier characterisation and fabrication. We demonstrated 6 mW of coupled input power, and more than 4.5 W of pulsed output power. >

The investigation of the importance of optical feedback on the optical properties of vertical-cavity surface emitting lasers (VCSELs) is important because of their potential applications in optical signal processing and light-wave communications. We report on the study of strong feedback effects on the threshold and spectral characteristics of a GaAs-AlGaAs VCSEL. Such studies have not yet been reported for VCSELs. >

We report the first observation of bistable polarization switching in a vertical cavity surface-emitting GaAs/AlGaAs laser (VCSEL) under optical injection. Input wavelength dependence of the switching is studied. Polarization switching at frequencies up to 6 GHz is obtained. We believe this polarization switching is achieved through injection locking where both the wavelength and the polarization of the VCSEL are locked by the injected optical signal. Because of the high switching speed and the low switching energy, the polarization bistable switching in VCSELs opens new possibilities in optical storage and the area of smart pixels for optical processing and interconnects. >

High-sensitivity, high-speed optical receivers are important components for both high-bit rate and microwave modulated optical systems. Optically preamplified receivers circumvent the gain-bandwidth limitation of APD receivers and have demonstrated improved receiver sensitivity in optical fiber systems at data rates up to 10 Gbit/s. In order to obtain maximum sensitivity, an optically preamplified receiver must be optical amplifier noise limited rather than thermal noise limited. Operation in this regime is more difficult to achieve at higher frequencies, however, due to reduced detector quantum efficiency and higher electronic receiver noise. We demonstrate an optically preamplified receiver comprised of a semiconductor optical amplifier (SOA) and 25 GHz Schottky InGaAs photodiode operating at the SOA noise limit. Because of the broadband, low-responsivity of this photodiode, these results apply over its entire spectral range (400-1600 nm), subject to SOA availability, as well as to operation at frequencies up to 120 GHz.

This report gives the preliminary results of using a three monolayer GaAs layer in a lattice matched InGaAs quantum well. Referring to earlier work on thin strained layers, we choose to call this a delta-strained quantum well structure. One of the important advantages of this novel structure is the ease of MBE growth.

Summary form only given. Tapered semiconductor amplifiers have successfully demonstrated high-power diffraction-limited emission. So far, all these amplifiers had normal incidence facets coated with antireflection (AR) coating to prevent self-oscillation. In this work, an angled-facet high-power diffraction-limited tapered GaAs-AlGaAs QW semiconductor amplifier operating at 809-nm was realized. Due to the angled facet structure, any residual reflection from the facets is fed back at a small angle with the signal propagation direction.

Fiber Bragg grating semiconductor lasers (FGSLs) are interesting laser sources for WDM and many other applications. Dispersive fiber grating together with a laser diode chip form a complex cavity and can lead to many interesting phenomena. We have found that a discrete mode hop associated with an increase of the injection current can lead to a decrease of the relaxation oscillation frequency. The experimental observation and the theoretical explanation are reported in this paper.

We report a novel semionductor optical amplifier device design that incorporates delta-strained quantum wells to achieve polarization insensitivity at a wavelength of 1.55 /spl mu/m. Solid source molecular beam epitaxy (MBE) was used to grow a GaInAsP-InP separate confinement heterostructure (SCH) with six lattice matched GaInAs quantum wells, each containing three thin, highly tensile strained GaAs layers.

The 1.55 /spl mu/m wavelength window is important for future WDM systems, and hence there has been considerable interest in realizing mode expanded lasers at this wavelength. Here, we present a mode expanded laser based on a tapered ridge design, which was grown in a single epitaxial step, and required only conventional lithography and etching techniques. This device showed reduced far-field divergence angles and high coupling efficiencies to a standard cleaved single mode fiber (3.7 dB loss). To our knowledge, this is the lowest loss demonstrated in longer wavelength devices fabricated without using regrowth.

We have developed a general method for rapidly bonding semiconductor laser arrays, optical traveling wave amplifier arrays, and other optoelectronic devices to silicon waferboards or submounts. Our method uses octagonal electrodeposited copper bosses to physically register with precision etched inverted pyramidal receptacles in the silicon. Flip-chip bonding of semiconductor laser diode arrays is significantly faster with this method than with a commercial precision flip chip bonder which images the die and the substrate simultaneously (i.e. with the "vision servo" method). The pre-bond die placement window we obtained is compatible with certain standard flip chip bonders. The post-bond positioning accuracy that we have demonstrated is essential for minimizing the worst-case temperature rise in high power semiconductor lasers and high gain traveling wave amplifiers (TWAs) operating at high levels of current injection.

550 mW quasi-CW output power with 85% of the power in the central lobe is obtained from a 1.55 /spl mu/m wavelength InGaAsP/InP MQW tapered unstable resonator. This power was found to be emitted in a near-diffraction-limited beam.

In this paper, we propose and demonstrate a simple GaAs-AlGaAs SQW laser employing conventional growth and processing techniques. In this laser, the transverse spot size has been increased by the use of a diluted waveguide (Al mole fractions are graded from 30% in the core to 31% in the cladding). This laser butt-couples into a cleaved single mode fiber with only -2.8 dB loss, and has a -3 dB excess loss misalignment tolerance of /spl plusmn/3.4 /spl mu/m in the lateral and /spl plusmn/1.6 /spl mu/m in the transverse directions. The laser showed a T/sub 0/ of 112 K, indicating that the leakage of carriers is not very significant.

In summary, we have demonstrated filter-free, polarization insensitive, wavelength conversion using a T-gate semiconductor laser. Wavelength conversion of a 250 Mb/s NRZ optical signal has been achieved with a 2.1 dB power penalty at 10/sup -9/ BER and a detector sensitivity of -29 dBm. Future work in our laboratory will be conducted at 1.55 /spl mu/m to ensure compatibility of the T-gate device with present high-speed optical communication system.

We have developed a reliable, high yield, void-free method for soldering high power semiconductor laser diodes epitaxy-side down. We have consistently obtained absolute thermal resistances as low at 1.5/spl deg/C/Watt and specific thermal resistances of 4/spl middot/10/sup -3/ K/spl middot/cm/sup 2//Watt on oxygen-free high conductivity (OFHC) copper heatsinks. This method has very wide process margins (75/spl deg/C), exhibits excellent repeatability (4%), and is suitable for laser die attach to diamond submounts.

LIGHTNING is a scalable distributed shared memory computation system based on powerful workstations interconnected together via a high speed WDM optical bus with direct access to the memory of the workstations. This system supports high-performance I/O-both interprocessor communication and remote filesystem access-by using a high speed WDM optical backbone. The optical interconnections combine wavelength, space, and time-multiplexing techniques. The chosen interconnection architecture is hierarchical and achieves low latency and high throughput. Wavelengths are re-used at each level of the hierarchy through spatial multiplexing by adaptable wavelength routers. The system is dynamically reconfigurable through the wavelength routers and therefore can dynamically vary the bandwidth allocated to different levels of the hierarchy. Single-hop communication is achieved through allowing a packet to remain in the optical form from source to destination, without requiring cross-dimensional intermediate routing.

In order to enable the monitoring method to work for thin film systems with a large number of layers, the value of the target reflectivity should be dynamically adjusted. We report a new monitoring technique to solve problems related to the current method: necessity of change of witness samples, poor dynamic range and sensitivity, applicability to nonquarter-wave layers, limitation of light source, and restriction of incident angle, etc. In our scheme, only one witness sample is used for multiple layers by the direct in-situ monitoring with a shifted monitor wavelength to avoid the DBR effective range. Furthermore, the target point is dynamically adjusted by controlling the phase thickness of each layer instead of its physical thickness, which is insensitive to the index fluctuation. With a proper calibration, the method gives us a considerable flexibility to be adaptive to arbitrary chamber size and layout.

Polarization self‐modulation at frequencies up to 6 GHz is observed in a vertical‐cavity surface‐emitting laser. This self‐oscillation is observed when a portion of the laser output power is injected back into the laser after having rotated its polarization by 90° with respect to the initial laser polarization state. Our experiment demonstrates a simple technique for generating an ultrahigh frequency optical clock. New applications in optical storage are also envisioned.

We report the observation of bistable polarization switching in a vertical‐cavity surface‐emitting laser under optical injection. The wavelength dependence of the switching is measured. It is found that this polarization switching is achieved through injection locking where both the wavelength and the polarization of the vertical‐cavity laser are locked to the injected optical signal.

We present a first direct experimental observation of dynamic frequency chirp associated with the turn‐on spike in the output of a Fabry–Perot semiconductor laser amplifier. Such a frequency chirp exists because of the change in the refractive index at the onset of light injection due to carrier saturation. The experimental observation is made by using a novel technique to optically isolate the turn‐on spike from the steady‐state response level. Using this technique, we have also successfully demonstrated conversion of a high duty‐cycle data stream to a low duty‐cycle data stream of the same frequency, which could have potential applications in optical time division multiplexing.

We report on a novel scheme to implement a high‐performance optically addressable generalized optical crossbar switch based on Fabry–Perot nonlinear diode laser amplifiers. This approach permits fast, parallel optical reconfiguration and a potentially large switch size. By using discrete components, we have demonstrated a 1×3 optical crossbar switch with an aggregate throughput rate of 4.2 Gbit/s, and a reconfiguration time of less than 1 ns. In addition, we demonstrate wavelength conversion at bit rates up to 1.5 Gbit/s, with a facet‐to‐facet usable gain of 9.6 dB.

Very strict requirements need to be met for producing a high-quality single-layer antireflection coating on a traveling-wave laser amplifier facet. In order to obtain a facet reflectivity of 10/sup -4/ or less, the index of refraction and the layer thickness of single-layer coatings have to be controlled to better than 0.03 and 30 AA, respectively. An innovative approach to highly controlled antireflection layer deposition based on in situ real-time ellipsometry is presented. Index control within +or-0.01 and a facet reflectivity on the order of 10/sup -4/ are reproducibly obtained. >

There is a need for integrating various active and passive devices on a single substrate to increase the functionality of optical modules [1-4]. One of the methods is to use regrowth for creating a low-loss passive waveguide butt-coupled to the active waveguide [1]. Besides being a complex technology, issues like low-loss coupling over multiple runs is still a challenge. A second technique used for integration is selective area growth [2]. In general, this technology does not allow for freedom in the design of the various layer thickness and bandgaps of the integrated waveguides. Quantum well interdiffusion [3] has also been used for integration by altering the bandgaps of the waveguides but also suffers from a lack of freedom in waveguide design and in the selection of the proper bandgaps.

BER measurements at 2.5 Gbit/s on wavelength converted signals using double pump FWM in a semiconductor optical amplifier have been performed experimentally for both single- and multiple-input wavelengths. These results were presented at an OSA sponsored conference entitled: Advanced Semiconductor Lasers and their applications" and the results have appeared in print in Trends in Optics and Photonics.

A free-space integrated optoelectronic interconnect was built to explore parallel data transmission and processing. This interconnect comprises an 8 X 8 substrate-emitting 980-nm InGaAs/GaAs quantum-well vertical-cavity surface- emitting laser (VCSEL) array and an 8 X 8 InGaAs/InP P-I- N photodetector array. Both VCSEL and detector arrays were flip-chip bonded onto the complimentary metal-oxide- semiconductor (CMOS) circuitry, packaged in pin-grid array packages, and mounted on customized printed circuit boards. Individual data rates as high as 1.2 Gb/s on the VCSEL/CMOS transmitter array were measured. After the optical alignment, we carried out serial and parallel transmissions of digital data and live video scenes through this interconnect between two computers. Images captured by CCD camera were digitized to 8-bit data signals and transferred in serial bit-stream through multiple channels in this parallel VCSEL-detector optical interconnect. A data processing algorithm of edge detection was attempted during the data transfer. Final images were reconstructed back from optically transmitted and processed digital data. Although the transmitter and detector offered much higher data rates, we found that the overall image transfer rate was limited by the CMOS receiver circuits. A new design for the receiver circuitry was accomplished and submitted for fabrication.

The presentation gives an overview of the ongoing Army Research Laboratory (ARL)/University of Maryland research effort on vertical-cavity-surface-emitting-laser (VCSEL) interconnects and OE processing and why this technology is of interest. ARL is conducting a research and development effort to develop VCSELs, VCSEL arrays, and their hybridization with complimentary metal-oxide-semiconductor (CMOS) electronics and microwave monolithic integrated circuits (MMICs). ARL is also very active in the design, modeling, and development of diffractive optical elements (DOEs). VCSEL-CMOS flip-chip optoelectronic circuits and DOEs are of interest together with detector-CMOS flip-chip circuits to provide digital and analog optoelectronic interconnects in optoelectronic processing architectures. Such optoelectronic architectures show promise of relieving some of the information flow bottlenecks that are emerging in conventional digital electronic processing as the electronic state of the art advances at a rapid pace and the electronic interconnects become a significant limitation. Such optoelectronic interconnects are also of interest in the development of analog optoelectronic processing architectures that are very difficult to implement in conventional electronic circuitry due to the incorporation of dense arrays of interconnects between electronic elements. VCSEL-MMIC- detector flip-chip circuits are of interest for the incorporation of optoelectronic interconnects into analog RF systems where the optoelectronic interconnect offers advantages of size, weight, bandwidth, and power consumption. VCSEL-MMIC interconnects may also play a role in future high- speed digital optoelectronic processing.

Summary form only given.There is a need for integrating various active and passive devices on a single substrate to increase the functionality of optical modules. In our previous work, we had proposed and demonstrated a platform technology for this purpose called the passive active resonant coupler (PARC). We have integrated a mode expander to the PARC platform by incorporating three waveguides in the vertical direction. The top waveguide is the active waveguide (AW) optimized for gain at 1.55 /spl mu/m. The middle waveguide is a confined passive waveguide (CPW) optimized for passive devices like splitters etc. The bottom waveguide is a large loosely confined passive waveguide ILPW) optimized for high coupling efficiency to a cleaved standard single-mode fiber. The mode is coupled between respective waveguides using resonant coupling over a taper.

A platform technology for monolithic integration called Passive Active Resonant Coupler (PARC) is utilized for vertical resonant coupling from an active to a passive waveguide over a taper. The effect of reducing the taper length on the coupling loss between the two waveguides is studied. We experimentally demonstrate that tapers as short as 40 um can be used to couple optical power between the two waveguides with 1 dB coupling loss. As the PARC uses single epitaxial growth and conventional fabrication schemes, it offers an attractive option for monolithic integration of optical devices.

We demonstrate an optoelectronic interconnect based on an 8 by 8 array of vertical-cavity surface-emitting lasers, an 8 by 8 array of photodetectors, and a single compound lens. The substrate-emitting VCSEL array and back-illuminated photodetector array were flip-chip bonded to a CMOS driver circuit and a Si fan-out pad array, respectively. The CMOS driver provides laser addressing, signal conditioning and modulation current.In this paper we will describe the interconnect configuration, device structures and characteristics, and CMOS driver circuits. We then discuss the system operation and performance.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present results of investigations into optical focus and edge detection algorithms relevant to overlay metrology. We compare gradient energy, standard deviation, contrast and summed intensity of acquired images as focus metrics for bright-field, scanning confocal, and confocal microscopy. For our purposes, gradient energy calculated via Sobel filtering was found to be the best criterion for an autofocus algorithm. We predict, based on theoretical results, that all of the focus algorithm we considered will focus in different heights relative to the object depending on the material properties of the object. Edge detection is accomplished via a window and spline technique for whole image data, and by application of a multiple line regression algorithm for single scan data. Measurements accomplished through these techniques are compared to state of the art scattering and analysis models.

Expanded mode alignment tolerant optical structures will play an important role in low-cost, large-scale packaging of optoelectronic devices. In this paper, we present two expanded mode structures for operation at 1.55 micrometers . Our devices use single epitaxial growth and conventional fabrication schemes. High butt-coupling efficiencies (> 40%) to a single mode fiber with relaxed alignment tolerances were achieved. The first of our devices uses adiabatic transformation over 500 micrometers . The second device uses resonant coupling over a much shorter region of 200 micrometers . The second scheme offers an interesting possibility for monolithic integration of active-passive components. We present the design and simulation results of such an integrated device.

This paper reviews performance of hybrid and monolithically integrated WDM transmitter arrays based on directly modulated 2.5Gbps lasers, with a focus on the wavelength accuracy and stability under normal operating conditions. We also consider power stability, chromatic dispersion penalties, and the channel cross-talk. Large numbers of four-wavelength devices were obtained and evaluated under a program designed to provide university-based system researchers with advanced WDM components We show that multi-wavelength laser arrays capable of high-performance out-of-the-box operation can be now produced for research-type WDM systems.

Bit error rate measurement at 2.5Gbit/s on single and multiple input wavelength converted signals using double pump four wave mixing in a semiconductor optical amplifier has been performed. It is found that the wavelength converted signal can be made wavelength insensitive for single input for detuning from -30nm to 15nm. Multiple-input wavelength conversion using low pump powers has also been demonstrated for the first time with a low penalty of about 1.5 dB.