Transformation of the frequency-modulated continuous-wave field into a train of short pulses by resonant filters

TL;DR

This paper proposes a resonant filtering method to convert frequency-modulated continuous-wave light into short pulse trains in the optical domain, utilizing interference effects and resonant filter tuning.

Contribution

It introduces a novel resonant filtering technique for pulse generation from FM fields, requiring significantly thinner filters than traditional dispersive methods.

Findings

Effective pulse train formation through resonant filter tuning.

Optimal filter thickness is much smaller than dispersive filter requirements.

Interference of scattered and comb components explains pulse formation.

Abstract

The resonant filtering method transforming frequency modulated radiation field into a train of short pulses is proposed to apply in optical domain. Effective frequency modulation can be achieved by electro-optic modulator or by resonant frequency modulation of the filter with a narrow absorption line. Due to frequency modulation narrow-spectrum CW radiation field is seen by the resonant filter as a comb of equidistant spectral components separated by the modulation frequency. Tuning narrow-bandwidth filter in resonance with $n$-th spectral component of the comb transforms the radiation field into bunches of pulses with $n$ pulses in each bunch. The transformation is explained by the interference of the coherently scattered resonant component of the field with the whole comb. Constructive interference results in formation of pulses, while destructive interference is seen as dark windows between pulses. It is found that the optimal thickness of the resonant filter is several orders of magnitude smaller than the necessary thickness of the dispersive filters used before in optical domain to produce short pulses from the frequency modulated field.