The results from a low cost 622 Mb/s, free-space laser communication link operating at 850 nm for short distance commercial applications is presented. The test results demonstrate the use of a free-space laser communications transceiver for building to building applications such as LAN, WAN and ATM operations, etc. This illustrates the potential for wide-use commercial computer network applications. The transceiver is constructed of commercial off-the-shelf materials for the development of a low-cost laser communications data link. The test system configuration utilizes standard Personal Computers with network cards and signal conversion cards for the copper to optical medical conversion. These tests precede the development of an increased data rate device operating at 2.5 Gb/s.
KEYWORDS: Semiconductor lasers, Commercial off the shelf technology, Avalanche photodetectors, Free space optical communications, High power lasers, Diodes, Receivers, Telecommunications, Quantum wells, Transmitters
In our Photonics West 98 paper, we presented our study results on using commercially available 860 nm high power laser diodes and high-speed laser driver for free-space laser communication terminal application. We demonstrated the feasibility of a free space laser communication link using a junction-up 860 nm high power laser diode driven by a high current laser driver from Hytek Microsystems up to 622 Mb/s. Recent development in high speed InGaAs/GaAs strained layer quantum well (SLQW) laser at 980 nm has provided an additional design option for a laser communication terminal. The advantages of using the 980 nm laser are: (1) WDM market in the telecom industry has created a volume demand for the 980 nm pump lasers. The future cost of 980 nm lasers is expected to be lower due to the economy of scale. (2) In our previous publications, we have demonstrated CW operation of strained layer QW laser at temperature higher than 200 degree(s)C. There is a potential for this type of laser diode to operate in a much harsher and higher temperature environment, and (3) 980 nm pump laser has output power comparable to high power 860 nm laser diodes. In this paper, we will present the high data rate characteristics of a high-speed 980 nm (SLQW) pump laser. Using commercial-off-the-shelf laser drivers we will demonstrate the laser transmitter system characteristics from 622 Mb/s to 3 Gb/s. Detail experimental results on bit- error-rate measurement for a 980 nm device will be presented.
KEYWORDS: Semiconductor lasers, Diodes, Commercial off the shelf technology, High power lasers, Transmitters, Free space optical communications, Avalanche photodetectors, Capacitance, Modulation, Laser applications
Recently, there has been strong interest in the application of commercial-off-the-shelf (COTS) electronic and optoelectronic (O/E) components for free space laser communication application. Besides the space qualified packaging issues, the main problems of using COTS O/E transmitter are: (1) Telecom grade laser transmitters do not have sufficient power to meet the free space laser communication requirements; (2) COTS laser diode transmitter driver circuits have limited peak drive current, usually below 100 mA, which is too low for driving high power laser diodes; and (3) COTS high power laser diodes are usually not used for high data rate applications since the high speed performance of the laser/driver combination is usually inadequate. In this paper we will present our latest study results on the SDL 5430 and SDL 580 high power laser diodes driven by high current laser drivers at data rates from 600 Mb/s to over 1 Gb/s. Several models from the HY6000 family of high current and high speed laser diode drivers from Hytek Microsystems Inc., designed for free space laser communication applications, have been tested with the SDL high power laser diodes. Using direct drive technique with NRZ modulation, average output power over 100 mW at 622 Mb/s were obtained with these low cost Hytek drivers. For data rates over 1 Gb/s, the parasitic associated with the laser diode becomes an important limitation factor. We have measured the capacitance of the SDL 5430 and the new junction up SDL 580 laser diodes, an equivalent circuit model is developed to examine the effect of these parasitics on the speed of the laser diode. The results are consistent with our experimental observations.
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