Dataset for "Microwave noise downconversion in interband cascade laser frequency combs"

Chip-scale semiconductor laser frequency combs offer remarkable prospects for compact and power efficient optical sensors. However, to fully unlock their application capabilities, the degree of coherence must first be assessed from a microwave self-mixing signal. Unfortunately, such a measurement involves the use of scarcely available fast photodetectors with multi-GHz bandwidths and radio-frequency electronics. In this work, we demonstrate the relation between easily-accessible MHz frequency (baseband) noise and multi-GHz frequency intermode beat note in an interband cascade laser emitting near 3.25 μm that simplifies comb coherence assessment. Intrinsic downconversion of microwave noise to near-DC frequencies is found to originate from the laser which simultaneously acts as a frequency mixer due to electrical nonlinearities, and phase-to-amplitude noise converter due to a linewidth enhancement factor. Correlation between the electrical signals is explored in both frequency and time domains. A potentially universal character of this phenomenon creates a new opportunity for frequency comb characterization in semiconductor lasers and is of particular importance in wavelength regions where fast photodetectors are not available.