A multichannel bidirectional dynamic data transmission system (DDTS) through a rotary interface with one fiber is designed based on a fabricated single pass fiber optic rotary joint. The feasibility of transmission system is tested at both 1310-and 1550-nm wavelength bands. The performance of this DDTS was measured using optical spectrum analyzer and lightwave multimeter. The insertion losses of DDTS were 1.55 and 1.20 dB at 1310-and 1550-nm wavelength bands, respectively. The total bandwidth of the DDTS is more than 170 nm.With the rapid development of communication, a highspeed, rotating-to-fixed dynamic data transmission system ͑DDTS͒ is needed in some fields. Usually, a fiber optic rotary joint ͑FORJ͒ can be used to transmit both analog and digital signals through a rotating interface. Compared with electrical slip rings, FORJ is immune to electromagnetic interferences, 1 but has the disadvantage of high manufacturing and assembly cost.To ensure that the optical signal is efficiently transmitted, both ends of the single-mode fiber are required to be held very closely and in proximity so that a minimal amount of light is lost in the gap. 2 In this letter, a singlechannel FORJ was designed using C-lenses, the working principle and structure of which are similar to those of graded-refracted-index ͑GRIN͒ lenses. 3 Compared with GRIN lenses, the insertion loss of C-lenses is better when the working distance is longer than 50 mm. 4 Through precise mechanical design, the insertion loss of single channel FORJ is less than 2 dB at either the 1310-or 1550-nm wavelength. To enhance the capability of the FORJ, a wavelength division multiplexing ͑WDM͒ technique was adopted to increase the signal transmission capacity. 5 The working principle of DDTS is shown in Fig. 1. The wavelengths 1 , 2 ,..., n are first sent to WDM multiplexer 1 ͑MUX 1͒ where the input signals are combined into an optical single-mode ͑SM͒ fiber. Then they are sent to an isolator where the input signals are isolated from the output signals from the FORJ to reduce the noise of the dynamic transmission system. The optical signals arrive at the FORJ through the connector and are transferred across a rotating interface. Finally the received light is demultiplexed and sent into the output channels. In this way, multichannel signals from a rotary platform can be transferred to the stationary platform. At the same time, the wavelengths nϩ1 , nϩ2 ,..., 2n at the other end of DDTS are transmitted to MUX 2 and the input optical signals arrive at the FORJ. Then the input optical signals pass the rotating interface through the optical isolator and connector. Finally the nϩ1 , nϩ2 ,..., 2n are transmitted into the output channels by DEMUX 1. Because the optical components including the FORJ are all bidirectionally operable and passive components, the DDTS supports bidirectional optical transmission as well as a data transfer rate of hundreds of Gbps.To test the feasibility of the multichannel bidirectional DDTS, an optical signal transmission system on both 1310-a...
