FSK heterodyne transmission experiments at 560 Mbit/s and 1 Gbit/s

Optical frequency-shift-keying (FSK) signals are obtained from directly modulated distributed feedback (DFB) semiconductor lasers. Experimental studies of the direct frequency modulation (FM) characteristics of the DFB lasers show a nonuniform FM response due to the competing effects of thermal modulation of the laser active region and carrier density modulation. Equalization of the signal current to the laser is employed to produce a flat FM response from 30 kHz to 1 GHz. Optical FSK transmission and heterodyne detection experiments at 560-Mbit/s and 1-Gbit/s are conducted at a wavelength of 1497 nm. Receiver sensitivities of -39 dBm at 560 Mbit/s and -37 dBm at 1 Gbit/s are obtained. Transmission through 100 km of single-mode fiber at 1 Gbit/s is achieved with no degradation in receiver sensitivity.     

Performance of directly modulated DFB lasers in 10-Gb/s ASK, FSK,and DPSK lightwave systems

A comparison is presented of the performance of amplitude-shift-keying (ASK), frequency-shift keying (FSK), and differential-phase-shift-keying (DPSK) lightwave systems which operate at 10 Gb/s with directly modulated 1550-nm distributed feedback (DFB) laser transmitters and conventional 1310-nm dispersion-optimized fiber. Computer modeling techniques were used to accurately simulate the amplitude modulation response and the frequency modulation response of DBF lasers. The system performance is evaluated from simulated eye patterns for both direct and heterodyne detection. With the narrow-optical spectral widths of these signal formats, fiber chromatic dispersion limits up to 70 km were obtained for transmission at 1550-nm using conventional 1310-nm optimized fiber     

Submicron silicon bipolar master-slave D-type flip-flop for use as 8.1 Gbit/s decision circuit and 11.2 Gbit/s demultiplexer

The authors have designed and implemented a submicron silicon bipolar master-slave D-type flip-flop integrated circuit which can be used either as a decision circuit or a demultiplexer, operating at data rates as high as 8.1 and 11.2 Gbit/s, respectively. The circuit was fabricated using a 0.6 mu m, nonpolysilicon emitter technology, occupying an area of 0.8 mm*0.9 mm, and dissipating 410 mW of power.<>     

Effects of phase-to-intensity noise conversion by multiplereflections on gigabit-per-second DFB laser transmission systems

Large power penalties and bit-error-rate floors have been observed in some Gb/s systems using distributed feedback (DFB) lasers, which could be attributed to interferometric conversion of laser phase noise to intensity noise by multiple reflections at connectors and splices. The authors calculated the power spectral density of the interferometric noise and its impact on system performance as a function of both the magnitude and number of reflections, and they compare the theoretical predictions with experimental results. Their studies indicate that connectors and splices with return losses of more than about 25 dB are required for the reliable operation of Gb/s fiber transmission systems, even if optical isolators are used     

Ultralow error rate and dispersion-free transmission of 2.5 Gbit/s SONET for gigabit networks

It is demonstrated that for an NRZ modulated 1310 nm optical transmitter, dispersion-free transmission can be achieved up to approximately 250 km using dispersion-shifted singlemode fibre (DS-SMF) and optical pulse compression. This result implies that DS-SMFs have a potential advantage over standard SMFs for dual-window (1310/1550 nm) multigigabit per second transmission systems. Results on the long-term error performance of experimental prototype 2.5 Gbit/s SONET optical transmission systems are presented with measured error rates smaller than 10/sup -15/.<>     

Sensitivity penalty in multichannel coherent optical communications

The error rates and sensitivity penalties for multichannel coherent optical communications systems are evaluated for amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) modulation, taking into account adjacent channel interference. Both time-domain and frequency-domain analysis are used, the latter being based on a Gaussian approximation. Both techniques yield similar results for sensitivity penalties below 1 dB. For FSK systems, larger values of the modulation index Δ do not necessarily lead to larger channel spacings. ASK and PSK systems both require larger channel spacings than FSK systems with Δ=1. The study was conducted for sources with linewidths narrow enough so that phase noise does not degrade the performance of receivers with matched filter demodulators     

High-performance monolithic dual-MSM photodetector for long-wavelength coherent receivers

A high-speed AlInAs/GaInAs monolithic dual-MSM photodetector has been demonstrated for long-wavelength coherent receiver applications. It exhibits a very low leakage current (<2 nA at 8 V), attains extremely high electrical isolation (>1000 M Omega ), and shows strong suppression to local oscillator laser intensity noise (>16 dB up to 5 GHz). This device has been fabricated using FET planar process technology to obtain a high-performance balanced mixer receiver for high-density wavelength-division-multiplexed systems.<>     

Use of "Activity" Classes in Adaptive Transform Image Coding

The weighted sum of the absolute values of the transform coefficients, defined herein as the activity index, is proposed as an objective measure of scene busyness (i.e., the density of significant scene detail). For an image divided into subpictures, it is possible to classify each subpicture into a finite number (say four) of categories according to its computed activity index. A different coding scheme, involving different truncation and quantization rules and hence a different number of bits, is used for each activity category. Data compression is efficiently achieved by assigning more bits to code those portions of the image showing the most detail.     

1 Gbit/s optical FSK heterodyne transmission experiment over 100 km of single-mode fibre

A 1 Gbit/s optical FSK modulation/heterodyne detection transmission experiment has been conducted at a wavelength of 1497 nm. The receiver sensitivity is ?37dBm and no degradation is observed after transmission through 100 km of single-mode fibre.     

Transmission experiments at 560 Mbit/s and 140 Mbit/s using single-mode fibre and 1300 nm LEDs

Transmission at 560 Mbit/s has been demonstrated using single-mode fibre and LEDs at 1300 nm. Surface-emitting, edge-emitting and super-radiant LEDs were used to transmit over maximum distances of 4.5 km, 15 km and 25 km, respectively. At 140 Mbit/s, the corresponding distances achieved with the same set of LEDs are 7.5, 35 and 50 km. respectively.