Ranging with a frequency-shifted feedback laser using frequency-comb driven phase modulation of injected radiation

Abstract

Theoretical and experimental data is presented for the application of an injection-seeded frequency-shifted feedback (FSF) laser for high accuracy ranging. Previous work discussed such a ranging scheme with a phase-modulated single-frequency laser where the phase modulation is done by an electro-optical modulator driven by a single frequency $\Omega$ which is swept over a certain bandwidth depending on the given experimental situation. In the present theoretical and experimental work, the phase modulation of the injection laser is done by a frequency comb with temporally fixed frequency components at intervals $\Omega_d$ spanning a bandwidth adapted to the geometry of the object to be measured. It is shown that the superposition of such FSF radiation returning from the object and a reference surface on a detector leads to a train of sinusoidal pulses with an instantaneous frequency $\Omega_{inst}$ in the radio-frequency range. The repetition rate of these pulses is $\Omega_d$ and their duration is $< 2\pi / \Omega_d$. The central result of this work is the observation that the path length difference between reference and object surface can be deduced from $\Omega_{inst}$, e.g. by frequency counting. The benefit of this approach lies in the fact that active frequency variation is not needed; all features of the entire system (FSF laser plus phase-modulated injected radiation) are constant in time. Proof-of-concept results using an FSF-laser ranging scheme based on a semiconductor laser are presented.

Generation of dual and quad-optical frequency combs in the injected radiation free mode-locked frequency-shifted feedback laser

“…Previous studies have shown that despite certain features of FSF lasers operation, they are able to generate pico- and femto-second pulses with characteristics suitable for various practical applications: high-resolution distance ranging [ 31 , 41 – 43 ], atomic cooling and slowing [ 44 ], efficient optical pumping of atoms [ 45 ], dispersion measurement [ 46 ].…”