April 2019
Spotlight Summary by Fritz Riehle
Optical phase-locking of two extended-cavity diode lasers by serrodyne modulation
Oscillators in the optical frequency domain can produce pure sinusoidal oscillations that are superior by orders of magnitude to oscillators in any other spectral range with respect to their phase stability. To make the best use of such a stability for various scientific and commercial applications often requires that this ultra-stable optical frequency can be shifted accurately by several gigahertz with a similar modulation bandwidth. Such requirements appear, e.g., in optical atomic clocks, atom-optical interferometers, highest resolution atom spectroscopy, or coherent optical communication. Serrodyne modulation in an electro-optical modulator, where the phase of the optical carrier is modulated by a sawtooth radio frequency signal, results in a single sideband and is currently one of the most promising approaches for such a challenge.
Sin Hyuk Yim and colleagues have used two extended-cavity diode lasers, one of them frequency stabilized to a spectroscopic line in rubidium, with the other one phase locked to the first one by means of serrodyne modulation. The sawtooth signal was generated by a nonlinear transmission line where the propagation speed of the electronic signal depends on its amplitude and, hence, results in a steepening of the input signal. The authors demonstrated with the beat note between the two lasers servo bumps close to 10 GHz, indicating a similar bandwidth of the phase-locking loop. From the measured phase noise spectral density, the authors calculated the sensitivity limit for an atom interferometic gravitational acceleration measurement based on their stabilization system. This sensitivity surpassed the conventional locking scheme with the same lasers by about a factor of two, promising the possibility of improved performance in atom interferometric precision measurements.
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Sin Hyuk Yim and colleagues have used two extended-cavity diode lasers, one of them frequency stabilized to a spectroscopic line in rubidium, with the other one phase locked to the first one by means of serrodyne modulation. The sawtooth signal was generated by a nonlinear transmission line where the propagation speed of the electronic signal depends on its amplitude and, hence, results in a steepening of the input signal. The authors demonstrated with the beat note between the two lasers servo bumps close to 10 GHz, indicating a similar bandwidth of the phase-locking loop. From the measured phase noise spectral density, the authors calculated the sensitivity limit for an atom interferometic gravitational acceleration measurement based on their stabilization system. This sensitivity surpassed the conventional locking scheme with the same lasers by about a factor of two, promising the possibility of improved performance in atom interferometric precision measurements.
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Article Information
Optical phase-locking of two extended-cavity diode lasers by serrodyne modulation
Sin Hyuk Yim, Sang-Bum Lee, Taeg Yong Kwon, Kyu Min Shim, and Sang Eon Park
Appl. Opt. 58(10) 2481-2484 (2019) View: HTML | PDF