FMCW Generation with Large Time-Bandwidth Product by Semiconductor Laser Cavity Tuning

Project: Research

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In high-frequency electronic systems, a constant-amplitude sinusoid with a predefined time-varying frequency is referred to as a signal of frequency-modulated continuous-wave (FMCW), which is often applied for deducing time-of-flight information in ranging and imaging applications. Performances such as spatial and temporal resolutions are related to the high center frequencies, large sweep ranges, and fast sweep rates of FMCW signals, where the time-bandwidth product (TBWP) is considered a useful metric. Although FMCW generators have been realized electronically, photonic approaches were rapidly developed over the past decade, exploiting the broadband optoelectronic devices and long low-loss fibers. These photonic approaches include optical frequency sweeping in fiber lasers and dispersive wavelength-to-time mapping by spectral shaping mode-locked pulses. With a relative ease of adjusting the FMCW parameters, nonlinear dynamics of lasers was also investigated, where TBWP recently reached 14,000. The spectral purity of individual frequency comb components was controlled by optoelectronic feedback via external modulators or high-speed connectorizations of the lasers. However, the limited practical lengths of the feedback paths put constraints on the maximal sweep period and the associated TBWP. In this proposal, FMCW generation of high TBWP is considered using semiconductor laser with various forms of cavity tuning. Cavity tuning by adiabatic variation is responsible for long-period frequency sweep for increasing TBWP, while microwave locking to an external stable electronic source is proposed for maintaining spectral purity, thereby removing the need for excessively long feedback paths. The adiabatic cavity tuning will be considered by varying the bias current, injection power, and injection detuning frequency. The microwave locking will be introduced via bias current modulation, optical amplitude modulation, and optical phase modulation that is derived from a single-frequency electronic source. First, the optimization between the frequency sweep range and the spectral purity will be examined, as the external locking of frequency component inherently competes with the modulation of frequency, where FMCW with TBWP of greater than 10 million will be examined. Second, the signal generation will be incorporated by inherent on-off switching for ensuring power efficiency, where the switching in the form of square-wave modulation is based on feedback dynamics. Third, the properties of the switched FMCW will be examined through ambiguity function analysis, where the potential application for range and velocity detection is evaluated. Numerical stochastic modeling will be carried out before the respective experimental investigations. The project will in general extend the applications of signals generated by the fast responses of semiconductor lasers. 


Project number9043310
Grant typeGRF
Effective start/end date1/01/23 → …