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The recently proposed nonlinear optical processing method named Optical Dynamic Range Compression (ODRC) has been shown to reduce the burden on the dynamic range in photodetection and data acquisition and enhance the signal-to-noise ratio. Signals with a large dynamic range are compressed by the analog optical dynamic range compressor through a logarithmic-like transform before the photodetection and digitization and then recovered digitally. This powerful idea enables a larger detectable range, optical non-uniform quantization and signal statistics redistribution.
To compress the high-dynamic-range optical signals, ODRC devices should have a nonlinear gain/loss that decreases /increases as input amplitudes increase, and is able to respond to the instantaneous power change. In this work, we explore the extension of this idea to create an optical limiter that harvests the optical power that would otherwise be wasted by the action of the limiter.
In silicon nano-scale waveguide, two-photon absorption (TPA) and the induced free-carrier absorption (FCA) generate nonlinear absorption and limit the output power when the input power increases. The limiting curve can be sharpened to take effect at lower input power by introducing saturated Raman amplification in the forward propagation direction. Through the two-photon photovoltaic effect, the free carriers generated through the two-photon absorption are recycled so the optical energy lost in the compression is harvested as electrical power. The limiting transform can be tuned with the input pump power and the biasing voltage to best fit the statistics of the input signal.
In applications where the device bandwidth is a concern, we showed that the carrier lifetime can be significantly reduced to tens pico-second through the carrier sweep-out with reverse bias.
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