Off-axis refractive mass-transported gallium-phosphide microlens array for the reduction of distortion in an optical interconnect system

Mass-transport smoothing has been used to fabricate an array of off-axis gallium-phosphide microlenses for use in an optical interconnection system employing a single macroscopic lens to image an array of vertical-cavity surface-emitting lasers (VCSEL's) onto a detector array. Steering the individual VCSEL beams through the center of the relay lens creates an optical system with low distortion.     

Narrow-linewidth vertical-cavity surface-emitting lasers for oxygen detection

The use of vertical-cavity surface-emitting lasers (VCSEL's) for optical detection of atmospheric oxygen is described. The VCSEL's were custom designed for single-mode emission in the 763-nm wavelength range, with low noise and narrow optical linewidth. Using standard wavelength modulation spectroscopy and a second-harmonic detection scheme with a 1-m air path, we determined an oxygen concentration resolution of 0.2%. Because of its small size, low power dissipation, and good tunability characteristics, the VCSEL promises to be an attractive light source for use in compact, low-cost optical sensor microsystems for trace gas detection.     

Wavelength-division multiplexing free-space optical interconnect networks for massively parallel processing systems

Wavelength-division multiplexing (WDM) techniques provide many advantages for building optical interconnect networks for massively parallel processing (MPP) systems. A design for a 1024-channel network for MPP systems based on the interconnection-cached network with vertical-cavity surface-emitting laser (VCSEL) arrays with one wavelength is described. We then show how a WDM version with four different wavelengths can increase the channel density. We also show how a WDM system can reduce the fan-in loss by a factor of 4. All the VCSEL's in each array are of the same wavelength, while different arrays use different wavelengths. We describe our experimental WDM subsystem containing four VCSEL arrays, operating at wavelengths of 843, 950, 970, and 980 nm, and three different WDM filters for multiplexing-demultiplexing. We present the operational results of the subsystem at 1 Gbit/s per channel.     

Cross talk and ghost talk in a microbeam free-space optical interconnect system with vertical-cavity surface-emitting lasers, microlenses, and metal-semiconductor-metal detectors

A diffraction-based beam-propagation model is used to study optical cross talk in microbeam free-space optical interconnection (FSOI) systems. The system consists of VCSEL's, microlenses, and metal-semiconductor-metal (MSM) detectors, with the detectors modeled as amplitude gratings with low contrast ratio (based on experimental results). Different possible cross-talk sources are studied. Results show that, in an optimized system, the cross talk caused by diffractive scattering is not an issue. However, in such systems the principal reflection from a MSM detector surface creates two problems: VCSEL coupling and ghost talk. The coupling of the reflected beam into the VCSEL's may cause power oscillation (and increase the bit error rate), whereas ghost talk will limit the distance-bandwidth product of the interconnect system. This optical system is also abstracted in hspice together with the laser driver and receiver circuits to analyze ghost talk in this system. Results show that at high speed (1 Gbit/s or more) these effects negatively affect system performance.     

Trade-offs between lens complexity and real estate utilization in a free-space multichip global interconnection module

The FAST-Net (Free-space Accelerator for Switching Terabit Networks) concept uses an array of wide-field-of-view imaging lenses to realize a high-density shuffle interconnect pattern across an array of smart-pixel integrated circuits. To simplify the optics we evaluated the efficiency gained in replacing spherical surfaces with aspherical surfaces by exploiting the large disparity between narrow vertical cavity surface emitting laser (VCSEL) beams and the wide field of view of the imaging optics. We then analyzed trade-offs between lens complexity and chip real estate utilization and determined that there exists an optimal numerical aperture for VCSELs that maximizes their area density. The results provide a general framework for the design of wide-field-of-view free-space interconnection systems that incorporate high-density VCSEL arrays.     

Performance comparison between multiple-quantum-well modulator-based and vertical-cavity-surface-emitting laser-based smart pixels

We compared multiple-quantum-well modulator-based smart pixels and vertical-cavity-surface-emitting laser (VCSEL) based smart pixels in terms of optical switching power, switching speed, and electric-power consumption. Optoelectronic circuits integrating GaAs field-effect transistors are designed for smart pixels of both types under the condition that each pixel has an optical threshold and gain. It is shown that both types perform maximum throughput of ~3 Tbps/cm(2). In regard to design flexibility, the modulator type is advantageous because switching time can be reduced by supplying large electric power, whereas switching time and electric-power consumption are limited to larger than certain values in the VCSEL type. In contrast, in regard to optical implementation, the VCSEL type is advantageous because it does not need an external bias-light source, whereas the modulator type needs bias-light arrays that must be precisely located because the small modulator diameter, <10 μm, is essential to high-speed operation. A bias-light source that increases the total power consumption of the system may offset the advantages of the modulator type.     

Integrated optoelectronics for optical interconnections and optical processing

Integrated optoelectronics using III–V compound semiconductor technology has so far shown exciting advances for application in optical telecommunication systems. New applications of this technology are in optical interconnections and signal processing systems. The technology is expected to be very effective in solving the wiring limit in data transmission within electronic systems, using the advantages of optical techniques such as high data transmission rate and high parallelism, and thus improve the performance of overall systems. Optical interconnection devices currently being developed aim both at multiplexing vast amounts of data and exhibiting flexible interconnection functions using the advantageous characteristics of light. Future research is expected to explore new techniques such as that for multiplexing and processing data in the wavelength division as well as for integrating functional devices in two-dimensions. Synergetic collaboration among materials and processing, design and fabrication, and packaging areas is extremely important and this will lead to practical optical interconnections and signal processing systems.     

高速850/980 nm垂直腔面发射激光器的研究进展

垂直腔面发射激光器(VCSEL)具有低损耗、 光束质量好、 光纤耦合效率高、 调制速率高且易于与其他光电子器件集成等优势,在光互连、 光存储、 高速传输和通讯等领域得到了迅猛发展.随着大数据时代的到来,对建立高带宽、 低损耗的高速光通讯网络提出了更高的要求.因此,近年来VCSEL在面向高速数据通讯中提高调制速率、 降低...     

Analysis of a vertical-cavity surface-emitting laser-based bidirectional free-space optical interconnect

The design of a bidirectional free-space optical interconnect system is presented. Vertical-cavity surface-emitting laser (VCSEL) arrays as a coherent light source and VCSEL beam collimation are described. Hologram array design and a way to improve the diffraction efficiency by use of a copying technique utilizing Dupont photopolymers are presented. Scattering from the hologram as a noise source is measured. An optical model for the design of system parameters such as the VCSEL beam diameter, size and apodization of the hologram, and size of the detector is given on the basis of cross-talk analysis of the system. The effect of VCSEL wavelength variation on system design is considered. Aberrations caused by the Fourier lens in the system are calculated, and ways for correction of the aberrations are discussed.     

Design Approaches for VCSEL's and VCSEL-Based Smart Pixels Toward Parallel Optoelectronic Processing Systems

The technical issues involved in applying vertical-cavitysurface-emitting lasers (VCSEL's) to parallel opticalinterconnection systems are discussed from the viewpoint of theirapplication to asynchronous transfer mode switching and parallelcomputer systems. We also discuss approaches to designing a VCSELarray structure for high-speed modulation and the effect ofpixel-performance homogeneity on the transmission bandwidth and powerconsumption. We review monolithic and hybrid integrationtechnologies for VCSEL-based smart-pixel arrays, and we estimate themaximum pixel number and input-output throughput allowed in a chip, considering the power consumption and pixel homogeneity. We showthat a one-chip optoelectronic parallel processing system comprisingmore than 1000 processor elements is possible when smart-pixel arraysare fabricated under the 0.25-mum complementary metal-oxide semiconductor design rule.     

Discrete correlation processor as a building core of a digital optical computing system: architecture and optoelectronic embodiment

In this paper we present a general-purpose discrete correlation processor (DCP) expected to be the building core block of a digital optical computing system. The DCP-1 is embodied by optoelectronic devices such as a VCSEL and a complementary metal-oxide silicon photodetector. The application targets of the DCP-1 are optical interconnection and various types of digital optical computing. It is expected that digital optical computing techniques coupled with the optoelectronic technology will provide large capability and flexibility in information processing. Introduction of a processing scheme of optical array logic enlarges the applicable field of the DCP-1 as well as its processing capability. With the experimental DCP-1 a bit error rate smaller than 10(-9) was obtained for A . B? operation under a 500-kHz clock rate.     

Database filter: optoelectronic design and implementation

The results of a successful demonstration of the selection module of an optoelectronic parallel-processing database filter is presented. The module utilizes 4 x 4 arrays of AND and XOR logic gates that respectively perform the functions of reducing the data fields and determining a match between the input data and a selection argument. The logic arrays were fabricated with InGaP/GaAs heterojunction phototransistors that drive vertical-cavity surface-emitting lasers (VCSEL's). The VCSEL's provide the free-space optical interconnection between stages. The design of the system and the optical power budget are discussed.     

Feasibility study of a scalable optical interconnection network for massively parallel processing systems

The theoretical modeling of a novel topology for scalable optical interconnection networks, called optical multimesh hypercube (OMMH), is developed to predict size, bit rate, bit-error rate, power budget, noise, efficiency, interconnect distance, pixel density, and misalignment sensitivity. The numerical predictions are validated with experimental data from commercially available products to assess the effects of various thermal, system, and geometric parameters on the behavior of the sample model. OMMH is a scalable network architecture that combines positive features of the hypercube (small diameter, regular, symmetric, and fault tolerant) and the mesh (constant node degree and size scalability). The OMMH is implemented by a free-space imaging system incorporated with a space-invariant hologram for the hypercube links and fiber optics to provide the mesh connectivity. The results of this work show that the free-space links can operate at 368 Mbits/s and the fiber-based links at 228 Mbits/s for a bit-error rate of 10(-17) per channel. The predicted system size for 32 nodes in the OMMH is 4.16 mm × 4.16 mm × 3.38 cm. Using 16-bit, bit-parallel transmission per node, the system can operate at a bit rate of up to 5.88 Gbits/s for a size of 1.04 cm × 1.04 cm × 3.38 cm.     

GaAs VCSEL／MISS混合集成光子开关

报道了ＭＢＥ生长的ＧａＡｓ材料ＶＣＳＥＬ与ＭＩＳＳ混合集成构成的光子开关。将ＭＢＥ生长的超薄ＡｌＡｓ层氧化为ＡｘＯｙ层用作ＭＩＳＳ器件的超薄半绝缘层，从而解决了该半绝缘层厚度的精密控制以及与ＶＣＳＥ工艺相容的问题。该集成器件除光子开关功能外，还能实现光放大功能，并可用于自由空间光互连。     

Analysis of a hybrid micro/macro-optical method for distortion removal in free-space optical interconnections

Eikonal analyses are applied to a hybrid micro/macro-optical shuffle interconnection approach that minimizes distortion in a multichip smart-pixel shuffle interconnection system. The optical system uses off-axis imaging elements to link clusters of dense arrays of vertical-cavity surface-emitting laser (VCSEL) sources to matching clusters within arrays of detectors. A critical requirement for such a system is that the images of the two-dimensional arrays of the VCSELs must be registered on their associated detector arrays with a precision of the order of 10 microm across the entire multichip array. The hybrid approach exploits the typical narrow-beam cone angles of VCSELs by use of beam-deflecting micro-optics to create a distortion-canceling symmetry about a central aperture in the optical system for each VCSEL-detector link. The second- and third-order aberrations of the plane-symmetric system created by the global off-axis imaging system are analyzed. The results prove that the hybrid concept cancels distortion and minimizes the spot size at the detector array plane.     

Long-wavelength vertical-cavity surface-emitting lasers for high-speed applications and gas sensing

Long-wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers (LW-VCSELs) covering the wavelength range from 1.3 to 2.3 mum are presented. Furthermore, these lasers can be fabricated in a novel high-speed design-reducing parasitics to enable bandwidths in excess of 11 GHz at 1.55 mum. To the best of the authors' knowledge, this is the fastest 1.55 mum VCSEL ever presented. As a proof-of-concept one- and two-dimensional arrays have been fabricated with high yield. All devices use a buried tunnel junction for current confinement and a dielectric backside reflector with integrated electroplated gold-heatsink. This concept enables CW operation at room temperature with typical single-mode output powers above 1 mW. Both, wavelength range and modulation performance, together with VCSEL features such as operation voltage around IV and power consumption as low as 10-20 mW enable applications in tunable diode laser spectroscopy (TDLS) and optical data transmission. Error-free data transmission at 10 Gbit/s over 22 km which can be readily applied in uncooled coarse wavelength division multiplex passive optical networks is presented. A laser hygrometer using a 1.84 mum VCSEL demonstrates the functionality of TDLS systems with VCSELs.     

Demonstration and architectural analysis of complementary metal-oxide semiconductor /multiple-quantum-well smart-pixel array cellular logic processors for single-instruction multiple-data parallel-pipeline processing

We present an optoelectronic-VLSI system that integrates complementary metal-oxide semiconductor/multiple-quantum-well smart pixels for high-throughput computation and signal processing. The system uses 5 x 10 cellular smart-pixel arrays with intrachip electrical mesh interconnections and interchip optical point-to-point interconnections. Each smart pixel is a fine grain microprocessor that executes binary image algebra instructions. There is one dual-rail optical modulator output and one dual-rail optical detector input in each pixel. These optical input-output arrays provide chip-to-chip optical interconnects. Cascading these smart-pixel array chips permits direct transfer of two-dimensional data or images in parallel. We present laboratory demonstrations of the system for digital image edge detection and digital video motion estimation. We also analyze the performance of the system compared with that of conventional single-instruction-multiple-data processors.     

Capacity upgrade in short-reach optical fibre networks: simultaneous 4-PAM 20 Gbps data and polarization-modulated PPS clock signal using a single VCSEL carrier

In this work, a four-level pulse amplitude modulation (4-PAM) format with a polarization-modulated pulse per second (PPS) clock signal using a single vertical cavity surface emitting laser (VCSEL) carrier is for the first time experimentally demonstrated. We propose uncomplex alternative technique for increasing capacity and flexibility in short-reach optical communication links through multi-signal modulation onto a single VCSEL carrier. A 20 Gbps 4-PAM data signal is directly modulated onto a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm, therefore, doubling the network bit rate. Carrier spectral efficiency is further maximized by exploiting the inherent orthogonal polarization switching of the VCSEL carrier with changing bias in transmission of a PPS clock signal. We, therefore, simultaneously transmit a 20 Gbps 4-PAM data signal and a polarization-based PPS clock signal using a single VCSEL carrier. It is the first time a signal VCSEL carrier is reported to simultaneously transmit a directly modulated 20 Gbps 4-PAM data signal and a polarization-based PPS clock signal. We further demonstrate on the design of a software-defined digital signal processing (DSP)-assisted receiver as an alternative to costly receiver hardware. Experimental results show that a 3.21 km fibre transmission with simultaneous 20 Gbps 4-PAM data signal and polarization-based PPS clock signal introduced a penalty of 3.76 dB. The contribution of polarization-based PPS clock signal to this penalty was found out to be 0.41 dB. Simultaneous distribution of data and timing clock signals over shared network infrastructure significantly increases the aggregated data rate at different optical network units (ONUs), without costly investment.     

Experimental demonstration of the optical multi-mesh hypercube: scaleable interconnection network for multiprocessors and multicomputers

A prototype of a novel topology for scaleable optical interconnection networks called the optical multi-mesh hypercube (OMMH) is experimentally demonstrated to as high as a 150-Mbit/s data rate (2(7) - 1 nonreturn-to-zero pseudo-random data pattern) at a bit error rate of 10(-13)/link by the use of commercially available devices. OMMH is a scaleable network [Appl. Opt. 33, 7558 (1994); J. Lightwave Technol. 12, 704 (1994)] architecture that combines the positive features of the hypercube (small diameter, connectivity, symmetry, simple routing, and fault tolerance) and the mesh (constant node degree and size scaleability). The optical implementation method is divided into two levels: high-density local connections for the hypercube modules, and high-bit-rate, low-density, long connections for the mesh links connecting the hypercube modules. Free-space imaging systems utilizing vertical-cavity surface-emitting laser (VCSEL) arrays, lenslet arrays, space-invariant holographic techniques, and photodiode arrays are demonstrated for the local connections. Optobus fiber interconnects from Motorola are used for the long-distance connections. The OMMH was optimized to operate at the data rate of Motorola's Optobus (10-bit-wide, VCSEL-based bidirectional data interconnects at 150 Mbits/s). Difficulties encountered included the varying fan-out efficiencies of the different orders of the hologram, misalignment sensitivity of the free-space links, low power (1 mW) of the individual VCSEL's, and noise.     

A CMOS smart pixel for active 3-D vision applications

A CMOS smart pixel aimed at three-dimensional vision applications is introduced. It is suitable for scannerless laser ranging systems which employ the indirect time-of-flight measuring technique to recover distance information. The pixel is operated with trains of light pulses generated by an external source to illuminate the scene and contains most of the processing electronics to perform signal accumulation and noise reduction operations. The smart pixel architecture includes an N-well photodiode plus a self-biasing voltage amplifier and a switched-capacitor fully differential stage. The pixel is fabricated in standard CMOS 0.6 /spl mu/m technology and measures 180/spl times/160 /spl mu/m/sup 2/ (including the photodiode) with a fill factor of 14%. Electrooptical test results confirm the smart pixel functionality in a range of distance from 3 m to 9 m, and the accuracy achieved for preliminary distance measurements is 15 cm. Both the accuracy and the extension of the range of distance are supposed to be improved by reducing setup and environmental noise contributions that limit the pixel performance.