Nonlinear semiconductor laser dynamics for wideband microwave time-frequency analysis

This paper introduces two time-frequency analysis schemes based on nonlinear semiconductor laser dynamics reported recently by us. The key to the two schemes is the nonlinear period-one (P1) semiconductor laser dynamics. By injecting an optical signal with linearly varying intensity over time into a semiconductor laser, a wideband frequency-sweep optical signal is generated via the P1 oscillation. Subsequently, the wideband frequency-sweep optical signal is modulated by the Signal Under Test (SUT), generating multiple frequency-sweep optical sidebands that are directly associated with the SUT frequency. Then, an optical narrowband filter is used to process these optical sidebands to implement the frequency-to-time mapping and the final time-frequency analysis. The narrow transmission peak in the notch of a phase-shifter fiber Bragg grating and the Stimulated Brillouin Scattering (SBS) gain spectrum are used as the optical narrowband filter, respectively. The former features a simple system structure and easy implementation but its bandwidth is hard to adjust. The latter, because its bandwidth is easy to manipulate, can meet the needs of performance optimization under different sweep chirp rates. To solve the problem of limited measurement resolution caused by the instability of P1 oscillation, an optoelectronic feedback loop is employed to stabilize the P1 oscillation to improve the stability and performance of the system. Furthermore, the nonlinearity of the generated frequency-sweep optical signal is compensated through pre-compensation or post-compensation. Using the proposed system, the time-frequency information of SUTs in a 4-GHz bandwidth is acquired.