Many infrared sensing and communication systems (3-5, 8-12 µm) have very weak signals, where optical pre-amplifiers (OPAs) can significantly extend the receiver sensitivity. System considerations require OPAs to be compact, efficient, integratable with detectors, as well as having low noise and broadband capability that can accommodate wavelength-agile/multi-spectral systems. Small-signal pre-amplification does not need high saturation power, but is mainly concerned with gain, amplified spontaneous emission (ASE) noise, and gain amplitude noise. From this perspective, mid-IR semiconductor OPAs based on either quantum cascade (QC) or Sb are attractive. The main components of a free-space-coupled OPA include input/output couplers, signal isolator, gain segment, and ASE filter. Except for isolators, semiconductors are amenable to compact micro-integration of these elements.

© 2003 Optical Society of America

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