Phase locking of a mode-locked titanium–sapphire laser-based optical frequency comb to a reference laser using a fast piezoelectric actuator

Abstract

We phase lock an octave-spanning optical frequency comb, generated using a mode-locked titanium-sapphire laser and a photonic-crystal fiber, to a continuous-wave laser line-narrowed to a reference cavity. To phase lock the pulse-repetition frequency, the cavity length of the mode-locked laser is controlled by using a fast piezoelectric-actuated mirror of a servo bandwidth up to 80 kHz. The residual phase noise is 0.35 rad, and 89% of the power is concentrated to the carrier. To apply the system to optical frequency-ratio measurements and to evaluate the phase locking, a simultaneous frequency measurement of the beat between the other mode of the comb and another laser line-narrowed to a different resonance of the common reference cavity is demonstrated.

Phase-locking of octave-spanning optical frequency comb based on Kerr-lens mode-locked Yb:KYW laser to reference laser

“…This was caused by the drift of the resonance frequency of the high-finesse cavity in which the ECLD at 871 nm was line-narrowed because the temperature of the high-finesse cavity was not adjusted to that of the zero thermal expansion coefficient. Although this value was 4-16 times as large as the previous measurements, 21,33) it can be understood from a possible temperature change.…”

“…In this paper, we describe the phase locking of a LD-pumped Kerr-lens mode-locked Yb:KYW laser to a reference laser by controlling the mode frequency using a fast piezoelectricactuated mirror on a lead-filled mount. We obtained a wider servo-bandwidth than that in our previous measurement, 21) and a better residual phase noise than that measured in a previous study on an OFC based on a mode-locked Yb:KYW laser. 26) The mode frequency 𝑓 (𝑛) of an OFC can be described as follows:…”

“…The servo-oscillation frequency was higher than that obtained in our previous study, i.e., 80 kHz, using an OFC based on a mode-locked Ti:sapphire laser. 21) This is caused by the use of a lighter mirror. The residual phase noise and the power concentration were better than those measured in a previous study using an OFC based on a mode-locked Yb:KYW laser, where the residual integrated phase noise was measured to be 0.4 rad by the integration between 0.1 Hz and 0.5 MHz.…”

“…We supposed that the residual linewidth and phase noises were caused by problems in the servo electronics for the line-narrowing of the reference lasers or the phase noise generation in the fibers used for beam transport. 21) The results of the simultaneous measurement of 𝑓 beat1 , 𝑓 CEO , 𝑓 beat2 , and 𝑓 rep are shown in Fig. 5.…”

“…20) We achieved a tight phase locking of the mode frequency of an OFC based on a mode-locked titanium-sapphire (Ti:sapphire) laser using a piezoelectric-actuated mirror on a lead-filled mount. 21) For a long continuous operation, OFCs based on mode-locked fiber lasers have been developed. 22,23) Although OFCs based on mode-locked fiber lasers had a relatively large phase noise at the early stage of development, new techniques have been invented to overcome this problem.…”