John A. Neff

Characterization of Dupont photopolymers in infrared light for free-space optical interconnects

Dupont photopolymer as a potential holographic material for an optical interconnect system was studied. The optimized conditions of recording plane-wave holograms with ∼99% effective diffraction efficiency for infrared reconstruction were obtained by testing different Dupont photopolymers and different copying parameters. The scattering ratios of the holograms recorded with Dupont photopolymers HRF600-10, HRF600-20, and HRF600-38 were measured and compared.

Analysis of vertical-cavity surface-emitting laser multimode behavior

This paper investigates problems associated with multimode oscillation in vertical-cavity surface-emitting lasers (VCSELs). The multimode rate equations for transverse mode were formulated. These equations take into account carrier diffusion and gain nonuniformity in the lateral direction. It was shown that multimode transverse mode excitation is due to carrier spatial hole burning, but many factors affect the number of lasing modes. The role of gain nonuniformity distribution, carrier diffusion, and modal loss compared with mirror loss in a cavity were demonstrated by numerical solution of the multimode rate equations.

VCSEL/CMOS smart pixel arrays for free-space optical interconnects

This paper describes a VCSEL-Si smart pixel array technology, developed at the University of Colorado, and reports on an optoelectronic processor that is based on these hybrid SPAs. This effort is unique in the processing complexity of the pixels, in the bidirectionary of the optical interconnects, and in the thermosonic bonding of the VCSEL and silicon chips.

A multi-component solder self-assembled micromirror ☆

Solder self-assembled micromirrors have the advantages of rigid electrical and structural connections to the substrate as well as compact assembly mechanisms. In addition solder assembly allows a structure to be rotated to any angle desired. This work presents a design process that uses these advantages to produce a novel electrostatic micromirror that can stably rotate ±10° from its assembled position in a rotation range that does not include the plane of the substrate. The compact solder mechanism allows each of three mirror components to be assembled independently to individual angles. A lumped parameter model based on a torque balance between the electrostatic force on the mirror and the restoring torque of the torsion beams is used to create the mirror design. After fabrication and assembly the design is statically tested and compared to the predicted model performance.

Analysis of a three-dimensional computer optical scheme based on bidirectional free-space optical interconnects

We describe the optical design of an optoelectronic 3-D system that is being developed by the Optoelectronic Computing Systems Center at the University of Colorado to prove the utility and viability of 3-D computers that use free-space optical interconnects to achieve a high degree of global connectivity among the PEs of a fine-grained parallel computer. The features of the VCSEL array as a source of coherent emission for hologram reconstruction and the CGH design procedure are discussed. An optical design in paraxial approximation of the 3-D computer with bidirectional 8 x 8 holographic interconnects is presented. The effect of VCSEL wavelength variation on diftraction crosstalk is estimated. The aberration in optical system based on the shelf objective is calculated, and a distortion compensation procedure is proposed.

Tolerance analysis for three‐dimensional optoelectronic systems packaging

A series of optoelectronic processing systems is under development at the Optoelectronic Computing System Center (OCSC) at the University of Colorado. The demonstrations consist of two facing optoelectronic modules that communicate with each other using bidirectional free-space optical channels. An analysis of the fabrication tolerances required for correct operation of these systems is presented. An overview of the system and the techniques used for fabrication is given, along with the tolerances achieved in practice. A comparison with theoretical results indicates the critical alignments within the system. Methods to obtain the alignments required for larger systems are discussed.

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.

Assembly of VCSEL based smart pixel arrays

Several applications of VCSEL-based SPA systems are being developed at the Optoelectronic Computing Systems Center (OCSC). These include a crosspoint switch, an FFT processor and an ATM switch. All of these applications are based on 8/spl times/8 VCSEL and detector arrays forming a bi-directional free space optical interconnect between two planes of processors. Two identical optoelectronic modules are placed at the front and back focal planes of a Fourier transform lens. Each module has 64 smart pixels with optical input (detectors) and output (VCSELs), electrical connections to nearest neighbors and a processing element.

Digitally positioned micromirror for open-loop controlled applications

The power consumption and complexity of the close-loop control electronics are the major barriers that limit the applications of optical switches, beam steering devices and other micromirrors. To eliminate or lower the barriers, it is desirable to have a micromirror with precise, digitally positioned angles. This paper reports the first investigation to design a digitally positioned micromirror and characterize its precision levels. From the experimental results, very encouraging results have been reported for the first designed digital micromirror: +/-0.01/spl deg/ position precision has been achieved with the mirrors fabricated in the same batch but operated sporadically over a 3-month period. In order to reduce the number of the electrical drives for the mirror and increase the maximum tilting angle, an improved device was designed and tested. 0.02/spl deg//V precision has been demonstrated in the digital levels via experimental testing and +/-0.03/spl deg/ position precision of repeatability has been achieved within the angle range +/-3.5/spl deg/. The electrical-mechanical performance of the mirror is discussed here. Standard deviation of average angle and angle variance per driving voltage within the digital levels are identified to characterize the digital behavior of the mirror.

A solder self-assembled large angular displacement torsional electrostatic micromirror

Solder self-assembled micromirrors have the advantages of rigid electrical and structural connections to the substrate as well as compact assembly mechanisms. In addition solder assembly allows a structure to be rotated to any angle desired. In this work, these advantages are used to produce a novel electrostatic micromirror that can stably rotate /spl plusmn/10/spl deg/ from its assembled position. The compact solder mechanism allows each of three mirror components to be assembled independently to individual angles. After assembly the design is statically tested and compared to both analytical and finite element (FE) model results.