Comb Offset Frequency Detection & Stabilization

Dual Frequency Comb

Comb Offset Frequency Detection & Stabilization

We utilize the Octave Photonics Comb-Offset-Stabilization Module (COSMO) to detect the carrier-envelope-offset frequency (fCEO) of a Menhir Photonics 1 GHz, 1550 nm oscillator with less than 140 pJ of pulse energy (<140 mW average power). A Vescent Photonics SLICE-OPL offset-phase-lock controller provides the feedback signal to the oscillator and establishes a tight lock with only 0.26 radians of residual phase noise. Together, this demonstrates a simple method for building compact and reliable frequency comb sources at GHz repetition rates. 

Figure 1. The experimental setup for carrier-envelope offset frequency (fCEO) stabilization of a 1 GHz 1550 nm oscillator. The Menhir Photonics oscillator generates a 1 GHz pulse train at 1550 nm, which is fed into an erbium-doped fiber amplifier to increase the pulse energy. The amplified pulse train passes through a short section of dispersion compensating fiber and then enters the Octave Photonics Comb-Offset-Stabilization Module (COSMO) where fCEO is detected. The fCEO signal is then amplified, filtered, and fed into the Vescent SLICE-OPL, which provides a feedback signal to the laser. The locked fCEO signal with coherent spike is seen on the RF spectrum analyzer

Laser frequency combs are essential optical-to-microwave converters for applications
such as optical atomic clocks and high-resolution dual-comb spectroscopy. Frequency combs are based on femtosecond mode-locked lasers that have their repetition rate (frep) and carrier-envelope-offset frequency (fCEO) stabilized. The repetition rate can easily be stabilized by detecting the pulse train with a photodetector and providing feedback to the laser oscillator. Detecting fCEO is more difficult and is typically accomplished through f-2f self-referencing, where the spectrum is broadened to at least one
octave via supercontinuum generation. The low frequency side of the spectrum is then frequency doubled in a second-harmonic-generation material and overlapped in time with the high-frequency spectrum on a photodetector, detecting the microwave fCEO.

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