Circumvention of noise contributions in fiber laser based frequency combs

Abstract

We investigate the performance of an Er:fiber laser based femtosecond frequency comb for precision metrological applications. Instead of an active stabilization of the comb, the fluctuations of the carrier-envelope offset phase, the repetition phase, and the phase of the beat from a comb line with an optical reference are synchronously detected. We show that these fluctuations can be effectively eliminated by exploiting their known correlation. In our experimental scheme, we utilize two identically constructed frequency combs for the measurement of the fluctuations, rejecting the influence of a shared optical reference. From measuring a white frequency noise level, we demonstrate that a fractional frequency instability better than 1.4 x 10(-14) for 1 s averaging time can be achieved in frequency metrology applications using the Er:fiber based frequency comb.

Self-referencable frequency comb from a 170-fs, 1.5-μm solid-state laser oscillator

“…Even at quantum-limited noise performance, fiber lasers can easily exhibit significant timingjitter, which is a challenge for stable frequency comb generation [16]. It is therefore important to implement efficient noise suppression schemes [17][18][19][20]. Furthermore, repetition rate scaling in fundamentally mode-locked fiber lasers is challenging.…”

Optical Frequency Comb Generation based on Erbium Fiber Lasers

“…2: (1) the offset frequency, fceo, and the comb tooth spacing given by the repetition rate, frep, which stabilizes the comb to an rf reference [1,2], (2) the offset frequency, fceo, and the frequency of a single optical comb tooth, f n0 , that stabilize the comb to an optical reference [6] or (3) the frequency of two widely spaced optical comb teeth, f n0 and f n1 [79][80][81], that effectively stabilize the comb to their frequency difference. Any noise is then canceled either through active feedback to the oscillator or through signal processing [32,38,82,83]. The method of noise cancelation-(direct feedback, signal processing, or a combination)-is a matter of experimental choice.…”

“…Specifically, nearly any noise source affects frep, even those commonly viewed as impacting fceo. An alternative description of the comb known as the elastic tape model, introduced by Telle and coworkers [82,83], is more useful and captures the correlations across the comb spectrum [31,32]. In this description, a given noise process or actuator will cause a comb tooth to expand or contract about a stationary point in frequency space known as the fixed point, f x .…”

“…However, one could argue that this is a misconception. First, the free-running linewidth of the detected offset frequency can be reduced by an order of magnitude through the use of a lower noise pump laser and by minimizing the cavity dispersion [27][28][29][30][31][32][33]. Second, this free-running phase noise is well-behaved in the sense that the basic comb structure is always preserved.…”

Broadband phase noise suppression in a Yb-fiber frequency comb

“…Changes in the pump diode output lead to changes in both the gain and pulse parameters of the oscillator, which affect both f rep and f 0 via a variety of nonlinear mechanisms [12]. However, in practical terms, the action of pump diode RIN and other noise terms is best described by the fixed-point formalism [13], where a given perturbation leads to changes in f rep and f 0 such that the spacing between comb teeth breathe about a fixed frequency at which the changes due to f rep and f 0 cancel. Due to this coupled action, error signals derived from f rep or f 0 alone do not directly address the action of the perturbation and are less effective at minimizing the broadband noise in the optical domain compared to error signals derived directly from the RIN.…”