Long-span optical FSK heterodyne single-filter detection transmission experiment using a phase-tunable DFB laser diode

High receiver sensitivity (?51.9 dBm) and long span (243 km) transmission expriments have been achieved with a 140 Mbit/s optical FSK heterodyne single-filter detection system, using a phase-tunable DFB laser diode as a transmitter. This has enabled direct FSK modulation without waveform distortion. Also, a 280 Mbit/s 204 km transmission experiment has been carried out successfully.     

An optical FSK heterodyne dual filter detection system for takingadvantage of DFB LD applications

An optimum system configuration for an optical frequency-shift keying (FSK) heterodyne dual-filter detection system with distributed feedback laser diodes (DFB LDs) is investigated, taking into consideration LD phase noise influence. Experimental and theoretical examination show that an IF filter bandwidth greater than 10 times the beat spectral linewidth is necessary to avoid LD phase noise influence. A 301-km long-span transmission experiment has been successfully carried out with an optimum configuration for 34 Mb/s. High receiver sensitivity, -61.8 dBm with more than 10 dB improvement over the direct detection system, has also been achieved. Experimental results at higher bit rates of 140, 200, and 280 Mb/s indicate that a modulation index greater than two is desirable to avoid cross talk between mark and space signals. With sufficient frequency deviations, high receiver sensitivities of -54.7 dBm (140 Mb/s) and -52.5 dBm (200 Mb/s) have been achieved. These represent 9.6- and 9-dB sensitivity improvement, respectively, over direct detection systems. A guide for FSK dual-filter detection system design is derived from the experimental and theoretical results. Potential application regions for a dual-filter detection system with DFB LDs are determined     

Consideration on influence of directly modulated DFB LD spectralspread and fiber dispersion in multigigabit-per-second long-spanoptical-fiber transmission systems

The relation between optical-fiber dispersion and directly modulated distributed-feedback laser diode (DFB LD) spectral spread in multigigabit-per-second long-span transmission systems is discussed. It is observed that two peak spectra at the leading edge of the pulse induce spectral spread in directly modulated DFB LDs. Specifications for the difference between the DFB LD oscillation wavelength and the optical-fiber zero-dispersion wavelength in a multigigabit-per-second long-span transmission system, considering these two peak spectra, are predicted. Experimental confirmation was provided by 2-Gb/s-140-km and 5-Gb/s-100-km transmission experiments, using 1.5-μm zero-dispersion shifted optical fiber     

High-speed digital-signal transmission experiments by optical wavelength-division multiplexing

The letter reports results obtained with laboratory transmission experiments on high-speed digital signals by optical wavelength-division multiplexing, using a newly developed optical multiplexer and demultiplexer, as well as other high-performance optical devices and fibres.     

Reduction of nitric oxide with ammonia on silica-supported vanadium oxide catalysts

Highly active catalysts for the reduction of nitric oxide with ammonia can be obtained by supporting vanadium oxide, more than 15% by weight, on a silica gel with micropores of a mean diameter larger than 10 nm, followed by calcining it in the temperature range from 250 to 350°C. Both pre-impregnation with a small amount of titania and addition of ammonium bromide increased the activity markedly. The catalyst gave an NO conversion level of 100% at 150°C. A series of life tests of the catalysts, which was performed at 230°C using a simulated flue gas containing 700 parts/10⁶ of sulphur dioxide, demonstrated that their activities were stable for more than 300 h. Little irreversible change in the catalyst properties was observed after the test.     

Stabilisation of heterodyne receiver sensitivity with automatic polarisation control system

A low-insertion-loss automatic optical fibre polarisation control system with low driving voltage and low monitoring power has achieved stabilisation of the receiver sensitivity within the fluctuation range of less than 0.4 dB in an optical FSK heterodyne 280 Mbit/s, 141 km transmission experiment.     

Oxidation of toluene to benzoic acid over modified V2O5-TiO2 catalyst with SeO2, TeO2 and Sb2O3

It was found that the addition of SeO₂, TeO₂ or Sb₂O₃ to a V₂O₅/TiO₂ catalyst greatly improved the catalytic activity in the vapor phase oxidation of toluene to selectively form benzoic acid.     

Novel optical FSK heterodyne single filter detection system using a directly modulated DFB-laser diode

A novel optical FSK heterodyne single filter detection system, which can use direct modulation and can tolerate the relatively large spectral width of a laser diode, is proposed. The receiver sensitivity improvement, as much as 8 dB over direct detection using a Ge APD, has been achieved after 105 km transmission at 100 Mbit/s.     

High-efficiency laser-to-fibre coupling circuit using a combination of a cylindrical lens and a selfoc lens

A new efficient coupling circuit, using a combination of a cylindrical lens and a Selfoc lens, which can be mounted in a laser package, has attained a coupling loss nearly as low as 0·6 dB.     

Random access optical heterodyne receiver for coherent FDM broadcasting systems

A random access optical heterodyne receiver for a coherent FDM broadcasting system has been developed, using a wavelength tunable local DBR LD, polarisation diversity technique and a random access automatic frequency controller. In a 10-channel FDM experimental system, 114 GHz capture range, 80 GHz lock range and arbitrary channel selection within less than 1 ms were realised.<>