An optical circuit was designed and built to facilitate the testing of a free-space optical interconnect. Details of the optical design are presented. The interconnect was based on a hybrid CMOS/GaAs chip which had a 16 X 16 array of detectors on a 250 micrometers pitch interlaced with a 16 X 16 array of modulators. The optomechanics enabled two such chips, bonded to printed circuit boards, to be mounted, positioned and aligned relative to each other. The operating wavelength of the devices was 827 nm. The optical system worked successfully and alignment could be achieved across the array with ease and high precision.
Electronically switchable Bragg gratings (ESBG) based on holographic polymerized polymer/liquid crystal composites have been described by Sutherland et al. We present an overview of potential applications to waveguide based fiber optic NXN crossconnect and waveguide selective (WDM) crossconnect devices. Various proposed waveguide grating devices are described, and silicon and glass/polymer fabrication paths are outlined. Recent experimental results are summarized. ESBGs are a promising new technology for efficient, large N scalable, moderate speed reconfigurration switches for fiber optic networks.
A new photo-lithographic imaging (PLI) method to produce high efficiency volume phase-only CGH has been developed. PLI technique utilizes Du Pont proprietary materials and processes to replicate a binary intensity CGH, recorded on a chrome photomask-master, into a dry photopolymer. By changing the refractive index of the photopolymer in the imaged areas the intensity modulated pattern in the chrome photomask-master is converted into a volume phase modulated pattern with a single lithographic step. This technique was used to fabricate a variety of computer generated holographic optical element (CGHOE), such as on-axis and off- axis Fresnel zone plates and array illuminators. Diffraction efficiencies up to 98% were observed for a CGHOE consisting of a 10 X 10 array of off-axis Fresnel zone plates. Such CGHOEs can be fabricated on a variety of substrates and in different configurations, providing substantial technological and economical advantages over existing conventional manufacturing techniques for diffractive binary CGHOEs.
Computer generated holograms (CGH) and holographic optical elements (HOE) were fabricated onto thick photopolymer(Du Pont HRF films) to demonstrate interconnects architectures based on the hypercube and perfect shuffle designs. A 16element CGH Fresnel lens array was used to fabricate the multifacet holograms which are recorded as phase modulation because of the exposuredependent refractive index change of the photopolymer. The recording method can be applied to other holographic elements to be used for spacevariant optical interconnect configurations. I NTRODUCTI ON The need to overcome the interconnect bottleneck in massive parallel computing architectures has been the subject of much discussion. Free space optical interconnects based on CGH''s and HOE''s can potentially provide a practical solution to this problem. They provide the possibility of implementing an arbitrary mapping using a single optical element. such a space variant interconnects topology can result in high degree of flexibility and interconnects density. One such an approach involves a 2D input array of processing elements(PE''s) each drives a semiconductor laser its beam is directed onto a HOE that images it into one or more photodetector located on an output array of PE''s. [4Similarly the system can be coherent when the input array is spatial light modulator illuminated by a laser. This paper deals with the design and fabrication of transmission HOE''s for free space optical interconnects in two specific examples the hypercube and the perfect shuffle architectures.
A method for recording volume computer-generated holograms on photopolymer layers is described. The method provides high diffraction efficiency, fabrication simplicity and flexibility. In addition, this technique makes it possible to introduce spatial filtering during the recording process, thus providing the ability to combine into the volume hologram additional functions not originally existing in the CGH.