Optical polarisation control utilising an optical heterodyne detection scheme

An optical polarisation control scheme utilising optical heterodyne detection for coherent transmission is proposed and demonstrated at a wavelength of 1.5 ?m. It converts an arbitrary polarisation state to a linear state at a received optical power level of less than ?70 dBm.     

Optical FDM transmission technique

This paper surveys the present state of optical frequency-division multiplexing (optical FDM) technologies. Utilizing a broad optical frequency bandwidth up to several hundred terahertz, optical FDM is expected to find applications in large-capacity trunking and local distribution networks. The present state of the related technologies and the future prospects for these applications are discussed.     

Tunable optical multi/demultiplexer for optical FDM transmission system

An optical multi/demultiplexer with spectrum selectivity of gigahertz order is proposed. It consists of a Mach-Zehnder interferometer and a feedback control circuit. Its feasibility was experimentally demonstrated.     

A 100-channel optical FDM transmission/distribution at 622 Mb/sover 50 km

A 100-channel optical frequency-division multiplexing (FDM) transmission/distribution experiment at 622 Mb/s is demonstrated for a fiber length of 50 km. The feasibility of a polarization-insensitive waveguide frequency selection switch for 10-GHz intervals and a frequency-shift-keying (FSK) direct-detection scheme employing a Mach-Zehnder filter is verified. The demodulation circuit employs a Mach-Zehnder filter and a balanced receiver, which utilizes optical power more efficiently than the Fabry-Perot filter. No receiver sensitivity degradation is observed due to interchannel crosstalk of the 128-channel tunable waveguide frequency selection switch (FS-SW) or fiber four-wave mixing for transmissions over a 50-km-long nondispersion-shifted (NDS) fiber and a 26-km-long dispersion-shifted (DS) fiber     

Optical multi/demultiplexers for single-mode fiber transmission

This paper describes two types of optical multi/demultiplexers using a single-mode fiber for a two-way transmission system. One type, the filter type, consists of four bandpass filters and a short wavelength pass filter or a long wavelength pass filter. The other, the filter-grating type, consists of two bandpass filters and a grating. The present multi/demultiplexers have four channels with 1.05, 1.15, 1.3, and 1.5 μm wavelengths. Total insertion losses are less than 2.3 and 3.2 dB for the filter type and the filter-grating type, respectively. Cross-talk between channels is less than -40 dB.     

A Field Trial of Fiber Optic Subscriber Loop Systems Utilizing Wavelength-Division Multiplexers

Future subscriber loops will provide various services including broad-band video. Fiber optic technology is the key for introducing these services. The Electrical Communication Laboratories (ECL) of Nippon Telegraph and Telephone Public Corporation (NTT) have been promoting research and development on basic technology of fiber optic subscriber loops, and studying the ways to use fiber optic subscriber loops for new services. As one of the programs, a field trial of fiber optic subscriber loops was planned and conducted in the Yokosuka area from April 1980 until May 1981. This paper first describes fiber optic transmission technologies for subscriber loops. Then, the system configuration and experimental results of the Yokosuka field trial are presented.     

16-channel optical FDM distribution/transmission experiment utilising Er/sup 3+/-doped fibre amplifier

A 16-channel optical FDM distribution/transmission experiment at around 1534 nm wavelength is demonstrated utilising an Er/sup 3+/-doped fibre amplifier. 16 intensity-modulated optical signals at 622 Mbit/s were amplified simultaneously at a gain of 15.2-18.5 dB. One of the amplified signals is selected using the waveguide frequency selection switch and directly detected with a receiver sensitivity of -38 dBm (P/sub e/=10/sup -9/).<>     

5 GHz-spaced, eight-channel optical FDM transmission experimentusing guided-wave tunable demultiplexer

A 5 GHz-spaced, eight-channel optical FDM transmission experiment using a guided-wave tunable demultiplexer is presented. 400 Mbit/s intensity-modulated optical carriers are multiplexed and transmitted through 13 km single-mode fibre. One of the carriers is selected by the tunable demultiplexer and directly detected     

Design consideration on a DBR-laser transmitter for fastfrequency-switching in an optical FDM cross-connect system

The design of a laser transmitter for fast frequency switching in an optical frequency-division-multiplexing (FDM) cross-connect system that uses tunable laser diodes and passive frequency-channel selection filters is considered. Small-signal analysis of the laser rate equation is used to estimate laser switching time. The results show that the frequency switching time depends on the allowable frequency detuning as well as the frequency spacing and the carrier lifetime. Frequency switching time is obtained from the calculation of power penalty due to the frequency detuning at the receiver section with ASK and FSK direct detection schemes. To achieve frequency switching without bit loss in the cross-connect module, switching times of 4-200 ns are required to change frequencies of 500 GHz. This suggests that a duplex transmitter configuration using two laser diodes must be employed to perform fast frequency switching and bit-error-free operation in a cross-connect system. The thermally induced frequency drift is experimentally evaluated. The feasibility of the duplex transmitter configuration is experimentally verified with a 156 Mb/s cross-connect unit     

Transmission limitations due to fiber nonlinearities in optical FDMsystems

Transmission limitations due to stimulated Brillouin scattering and four-wave mixing processes are investigated for optical frequency division multiplexing (FDM) systems. The applicability of the dispersion-shifted (DS) and nondispersion-shifted (NDS) fibers is discussed, taking account of channel frequency separation, total channel numbers, input signal power, transmission length, and receiver sensitivity degradation. Experimental results on Brillouin gain spectra and the wave generation efficiency in four-wave mixing processes are also presented to discuss the applicability of the two types of single-node fiber. It was found that NDS fibers operated at a wavelength of 1550 nm can be widely deployed in multichannel systems both for the long-haul and information distribution transmissions, if the signal waveform distortion due to fiber chromatic dispersion is precluded. The delay equalizer will be useful for a high-speed system employing bit rates over 10 Gb/s and repeaterless spans over 300 km. For such an application, DS fiber is preferable. Concerning information distribution network applications, the NDS fiber should be more attractive as a transmission medium for FDM system applications