Abstract
We show the generation of a tunable linearly chirped microwave waveform (LCMW) with an ultra-large time-bandwidth product (TBWP) based on a hybrid Fourier-domain mode-locked (FDML) laser. The key device in the hybrid FDML laser is a silicon photonic integrated micro-disk resonator (MDR) which functions as an optical bandpass filter, to have strong wavelength selectivity and fast frequency tunability. By incorporating the integrated MDR in the fiber-based ring cavity to perform frequency-domain mode locking, an FDML laser is realized and a broadband frequency-chirped optical pulse is generated. By beating the frequency-chirped optical pulse with an optical carrier from a laser diode (LD) at a photodetector (PD), an LCMW is generated. The bandwidth of the LCMW is over 50 GHz and the temporal duration is over 30 µs, with an ultra-large TBWP of 1.5 × 106. Thanks to the strong tunability of the MDR in the FDML laser, the generated LCMW is fully tunable in terms of bandwidth, temporal duration, chirp rate, and center frequency.
Highlights
We show the generation of a tunable linearly chirped microwave waveform (LCMW) with an ultra-large time-bandwidth product (TBWP) based on a hybrid Fourier-domain mode-locked (FDML) laser
The generated linearly frequency-chirped optical pulse is sent to a high-speed PD together with an optical carrier from an laser diode (LD), to generate an LCMW due to heterodyne beating at the PD
When the driving signal applied to the microdisk resonator (MDR) is tuned, the frequency-chirped optical pulse from the FDML laser can be tuned in terms of bandwidth, temporal duration, chirp rate, and center frequency, leading to the generation of a fully tunable LCMW
Summary
We show the generation of a tunable linearly chirped microwave waveform (LCMW) with an ultra-large time-bandwidth product (TBWP) based on a hybrid Fourier-domain mode-locked (FDML) laser. In the past few years, different photonics approaches have been proposed and demonstrated for LCMW generation, including direct space-to-time (STM) pulse shaping[17,18,19], spectral shaping and wavelength-totime (SS-WTT) mapping[20,21,22,23], optical heterodyne detection[24,25,26] and Fourier-domain mode-locked (FDML) optoelectronic oscillation (OEO)[27]. Among these approaches, the STM technique is the one that can be implemented. The implementation of such a hybrid FDML laser with a silicon photonic integrated MDR for highly tunable LCMW generation with an ultra-large TBWP paves the way toward practical applications of FDML lasers for generating large TBWP microwave waveforms for highresolution microwave imaging and sensing
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