A shallow-etched, distributed grating is proposed as a wavelength demultiplexer. The distributed grating constitutes a
structure with completely decoupled reflective and diffractive properties. The theory behind the layout of the distributed
grating is presented. The structure is modeled using RCWA and FDTD. Modeling results predict up to 79% efficiency
over a 60nm wavelength range. Device fabrication results are presented. Early optical characterization of a test
structure confirms the expected behavior for the device.
Diffraction gratings are often used in fiber-optic telecommunication, especially as wavelength (de)multiplexers and three-dimensional micro-optical coupling devices. The use of diffraction gratings made out of anisotropic materials is particularly attractive when trying to design high efficiency, polarization insensitive components. We show that by incorporating perpendicular grating structures of subwavelength dimensions, it is possible to enhance or reduce the polarization dependence of a traditional grating structure. This three-dimensional, form birefringent structure is analyzed with the use of rigorous coupled wave analysis (RCWA) and effective medium theory (EMT). The application of other analytical techniques, such as the coordinate transformation method and the classical differential method, are discussed, in the context of this particular type of grating structure. We present grating structures in which it is possible to enhance or reduce the polarization dependence of the diffraction efficiency, in a given wavelength range.
A wide variety of integration strategies for micro-optical systems have been employed. Here we review some of these and comment on their relative strengths and weaknesses. In particular we compare approaches that are based on monolithic fabrication with those that make use of discrete components. As applications we consider free-space optical interconnects, telecommunications optical space switches and radiation mode interconnects for optical waveguides.
Board to board free-space optical interconnects can deliver high bandwidth with no physical contact but suffer from poor tolerances to misalignment. In order to obtain high misalignment tolerances, we propose the use of an active alignment scheme in conjunction with an optimized optical design. The active alignment scheme uses a redundant set of optical links and the active selection of the best link. The optical design maximizes the alignment tolerances between the two boards.
A novel board-to-board free space optical interconnect which operates on the principle of redundancy is described. Tolerance to misalignment is achieved through the use of 2D arrays of lasers and detectors together with an adaptive alignment algorithm based on redundant transceivers and a defocused optical interconnect. In this system, four 1.25 Gb/s data channels are supported by transmitter modules and receiver modules (2 per board) which contain 3 X 3 VCSEL and 3 X 3 photodiode arrays, respectively. The system was designed to have lateral misalignment tolerance of +/- 1 mm and angular tolerance of +/- 1 degree(s).
This paper presents the design of a receiver used in a self- aligning optical interconnect. We have made use of spatial redundancy to increase the misalignment tolerance of a system of four 1 Gb/s free-space optical links. The receiver for this system is a rapidly re-configurable array that accepts nine low-amplitude, high-speed photocurrents, selects one of them, and then outputs that signal as a digital differential positive emitter coupled logic signal. The selection of which channel to amplify is based on received power, and is performed off-chip. Preliminary results indicate that the receiver performs with a low bit error rate up to 750 Mb/s.
In order to provide a reliable optical link, the emitters and detectors within a free-space optical interconnect need to be aligned to each other within tight tolerances. Typical methods to achieve this alignment involve the use of precision optomechanics or active steering elements. An alternative approach to the alignment problem is to use spatial redundancy. One way to accomplish this is by increasing the number of possible optical links and using only a subset of those links to provide reliable high-speed channels. This paper presents the design and testing of a high speed transmitter chip developed for an adaptive redundant optical interconnect system. Optoelectronic design and device packaging will also be described.