The insertion loss of a fiber optical rotary joint depends on the mechanical misalignments of the collimating lenses. To achieve 3-dB or lees insetion loss, the lateral misalignment of the braded-index (GRIN) lenses should be less than 100μm, and the angular tilt of these lenses is limited to 0.1 deg. These requirements cause a high mechanical abrication and assembly cost. To solve this problem. We design a singlechannel optical rotary joint using a bulk optical detector. The requirement on lateral misalignment is relaxed to 500μm, and the angular tilting is relaxed to 2 deg. Using this method, the cost of the optical rotary joint can be dramatically reauced.

distributed polarization coupling in high birefringence fibres. Detailed theoretical analysis of the measurement accuracy of the testing system is presented. The main part is a Michelson interferometer with a scanning arm driven by a stepping motor. The minimum polarization coupling intensity detectable by this system is-77 dB. The maximum fibre length that can be tested under this design is more than 1 km, and the spatial resolution is better than 50mm. The influence of the opto-electro-mechanical devices on measurement accuracy has been analysed in order to improve the performance-to-cost ratio. This testing system can also be used in coherence division multiplexing optical fibre sensors.

A novel structure has been designed for bit synchronization in a terabit-per-second optical interconnection network with adjustable optical delay lines, The two-stage network consists of 1024 optical links connected to a central switching module. A distributed optical clock network is designed for bit synchronization at each node computer. Zero link setup time can be achieved by precisely atching the phases of each pair of clock and signal. The link-to-link switching time can be reduced to less than 20 ns in the two-stage network. Even in a three-stage network that can accommodate 32,768 optical links, the link switching time can be maintained below 30 ns. At the same time, a tetal bidirectional band width of 98.304 Tbit/s can be obtained. Since bit synchronization is achieved entirely in the optical domain, this structure is independent of link transmission rates.

The hardware and the communication protocol of a scalable optical ring have been designed. A hardware routing has been achieved on the network interface card to minimize data packet communication 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 usage of the data link layer bandwidth, a virtual multi-channel transmission mechanism has been achieved. The network supports a maximum of 16 virtual channels 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 multichannel ring is designed. Each sublayer network is connected to the ring with an access node (AN). which can transmit data at every wavelength with a tunable laser diode The data transmission speed at each wavelength is 1.25 Gbit/s. With eight waverengths, a total bandwidth of 10 Gbit/s can be obtained. With a bandpass filter, the desired 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 verified, if the data packet belongs to the local subnetwork, it is received. Otherwise, it is retransmitted to the next access node with a selected wavelength. So pipelining data transmission can be achieved among different wavelengths And this nelwork is a multipipelie structure. The data processing time is less than 3OO ns, and all of the pro cessing procedure is implemented via a field programmable gate array (FPGA). So the communication latency and communication overheads can be decreased. Meanwhile, the ring topology has good eatabillity More wavelengths can be adopted for a large-scale network with more access nodes.