80-ps and 4-ns pulse-pumped gains in a GaP-AlGaP semiconductor Raman amplifier

The characteristic of 80-ps mode-locked (ML) pulse-pumped gain, which results in a decline that changes from a linear gradient to a square-root gradient at introduced pump densities exceeding 10 dB, makes it difficult to develop pulse-pumped gains for high efficiency amplification. To overcome this disadvantage with pumping, we compared an 80-ps ML pulse and 4-ns Q-switched pulse in a straight waveguide. The amplification of the 4-ns pulse was linear and had a maximum gain of 23.3 dB at an introduced pump density of 1.4 W/μm² in a straight waveguide. The gain was more efficient than with the 80-ps pulse, which was limited by the optical damage threshold of the input antireflective coating (1.6 W/μm²). These high-gain operations should enable semiconductor Raman amplifiers to be used for detecting signals from chemical or biological materials, in addition to infrared light frequency selective amplification with wavelength-division multiplexing in optical communications.