Coherent optical detection: a thousand calls on one circuit

Article Abstract:

Coherent detection of laser signals is a promising technology. Laboratories all over the world report coherent transmission at increasing bit rates. A coherent system works through homodyne detection, where a beam splitter combines the incoming optical wave with the much stronger wave from a local oscillator. The combined waves then illuminate a photodetector. The number of photoelectrons produced by the detector during each bit time is compared with a threshold value to determine whether a binary 0 or a one has been transmitted. Detection in all the experiments with semiconductor lasers has thus far been by heterodyning; before trying homodyne detection with semiconductor lasers, engineers must achieve phase-locking for the local laser to the incoming signal. The Optical Fiber Conference is a forum for those working on this technology.

Detection equipment, Detectors

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Optical Preamplifiers: Promising Only at High Data Rates

Article Abstract:

Practical considerations involved in incorporating semiconductor optical amplifiers into fiber-optic systems include excess noise factors, external filter requirements, polarization effects, transmitting laser stability, and input coupling losses. Because of some of these, such amplifiers could be used only in transmission systems with stabilized single-frequency diode laser sources. Traveling-wave amplifiers are better for practical preamplifiers than Fabry-Perot devices. Graphs illustrate the performances of such devices.

Fiber optics, LEDs, Optoelectronic devices, Optics, Amplifiers, Light-Emitting Diodes

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Optical Memory Is a Reality

Article Abstract:

The 7600 Optical Storage Subsystem from Storage Technology Corp. is a very high-capacity optical memory system for data processing. The system stores four gigabytes of data on a single fourteen-inch optical platter. Data are written onto the disk with infrared output of a semiconductor laser diode and are read when reflected light from individual data marks are detected by photodiodes.

Optical Memory, Data Processing, Mass Memory, Auxiliary Memory, 7600 Optical Storage Subsystem

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