Effect of the Coherence Time of the Semiconductor Laser Emitter on the Quality of Radio Signal Processing in the Optoelectronic Delay-Line Processor

The effect of the coherence time of the semiconductor laser emitter incorporated in the most commonly used optoelectronic radio signal processor (OERSP) based on a multitapped optical delay circuit (ODC) on the transmission gain and signal-to-noise ratio at the device output is studied by computer simulation in a widely used optoelectronic CAD tool. It is found that efficient operation of a practical device implies that its coherence time should be shorter than the duration of the processed radio-frequency signal at least by an order of magnitude. Measurements of coherence times of three most commonly used modern emitters: the external-cavity-based laser, distributed feedback laser, and Fabry—Perot laser show that only the latter type can be efficiently used as a part of the studied OERSP with a four-tapped ODC based on 7-core optical fiber.