This paper presented an optical intercormection multiple PC system connected by a ring network. This multiple PC system uses Linux Operating system, and the standard communication protocol of complying with Ethemet specification This paper studied the factors that influence the intereomection performance among multiple computers, including the effect of the buffer size of OLI on the bandwidth of network layer, and the effect of retransmission method on the performance. The results of ping-pong test show that optical fiber link is able to provide high-bandwidth and low-latency communication for a multi-PCs system. We found that the performance of the interoonneetion network can be improved by improving the interface match between the optical fiber link and computer bus input/oatput. Besides, the development of a chip to implement network interface and a part of network protocol, such as developing with FPGA device in this paper, could result in the higher performance of the interconnection.

The nmnerieal aperurc (NA3 of the double beam thterferometers (DBD can affect the acotrate measurement of surface profiles. Based on the double beam interference microscope imaging theory, the fringe spacing will vary wide nonlinearly with the increasing of numerical aperture. The double beam interferometers require oblique incidence illmnination, including Miehelson, Mirth and Linnik lypes. The intensity distribution of the ilumination across its slop is constant so the correction factor depends mainly on the NA in the Michelson and Linnik interferometers. The correction factor expression is derived in the Miehelson interferometer. The reference surface is a central obscnration in the beam, which will reduec the effective mnnerical aperture in the Miran interferometer. At the same mumerical aperatre, larger central obscuration has a much effect on the correction factor. The correction factor expression is determined by considering the influence of central obseuration and oblique incidence in the Mirau interferometer.

The hardware and the communimtion protocol of a statable optical ring have been designed. A hoxdware routing has been achieved on the network interface card to minimize data paeket communieation latency and a simplified communication protocol has been designed to reduce communication overheads. To reduce the data packet bilking probability and have a more efficient umgn of the data link layer bandwidth, a virtuaI multi channel transmimion mechanism has been achieved. The network supports a maximum of 16 virtual channds for each physical data link, Time slots can be dynamically assigned to each virtual channel. Zero wait time has been achieved for the switching between different virtual channels.

A mugichannel ring is designed. Each sublayer network is connected to the dng with an access node (AN), which can transmit data at every wavelength with a tunable laser diode. The data transmission speed at each wavmength is 1.25Gbit/s. With eight wavelengths, a total bandwidth of 10Gbg/s can be obtained With a bandpass filter, the de-sired optical signal can be dropped down at the access node On receiving a data packet, the optical signal is split into two parts. One part is converted to an electrical signal and its destination address is extracted and vedtied. If the data packet belongs to the local subnatwork, it is received. Otherwise. it is retransmitted to the next access node with a selected wavelength. So pipelining data transmlssien can be achieved among different wavelengths. And this natwodt is a multipipeline structure. The data processing time is less than 30Ons, and all of the processing procedure is implemented via a fieid programmable gate array (FPGA). So the communication latency and communication overheads can be decreased. Meanwhile, the ring topology has good sca/ability. More wavelengths can he adopted for a large-scale network with more access nodes.

A new structure for bit synchronization in a tera-bit/s optical interconnection network has been designed using micro-electro-mechanical system (MEMS) technique. Link multiplexing has been adopted to reduce data packet communication latency. To eliminate link set-up time, adjustable optical delay lines (AODLs) have been adopted to shift the phases of the distributed optical clock signals for bit synchronization. By changing the optical path distance of the optical clock signal, the phase of the clock signal can be shifted at a very high resolution. A phase-shift resolution of 0.1ps can be easily achieved with 30-μm alternation of the optical path length in vacuum.