Integrated self-referenced frequency-comb laser based on a combination of fiber and waveguide technology

Abstract

An optically integrated self-referenced frequency comb laser is demonstrated. The system consists of a passively-modelocked Er-fiber laser, a butt-coupled periodically poled lithium niobate (PPLN) waveguide phase-sensor and an electronic feedback loop for carrier-envelope-offset (CEO) phase stabilization. The fceo-beat-signal has a linewidth of 62 kHz and is detected with a S/N-ratio of 40 dB, with greatly reduced pulse energy requirements compared to bulk crystal phase-sensors. To our knowledge this is the first self-referenced frequency-comb system entirely based on guided-wave technology.

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

“…This is to our knowledge the narrowest CEO frequency linewidth of a freerunning laser in the 1.5-µm regime. A state-of-the-art amplified fiber oscillator system is presented by Hartl et al in [14]. Its free-running CEO frequency distribution fits well to a Lorentzian function, not a squared-Lorentzian function as observed in our measurements.…”

“…The main peak at 75 MHz is the pulse repetition rate, and the CEO frequency appears as sidebands around DC and the first harmonic of the pulse train signal. The signal-to-noise ratio (SNR) is 49 dB in a 100-kHz resolution bandwidth (RB), which is significantly better than typically obtained by fiber oscillators [8][9][10][11][12][13][14], and substantially higher than the typical 30 dB required for standard stabilization electronics. Even more important is the bandwidth of the CEO frequency variations since it reflects the intrinsic stability of the underlying laser oscillator.…”

“…It is common to stabilize optical frequency combs by active feedback from a phase-locked loop (PLL), which reduces their linewidth by orders of magnitude [14]. The presented system has not yet been stabilized, but considering the high intrinsic stability and the excellent signal strength we expect that stabilization will be straightforward.…”

“…However, noise suppression and operation at multi-gigahertz repetition rates are more challenging than for Ti:Sapphire systems. Femtosecond fiber oscillators can show a considerable amount of excess noise [8][9][10][11][12][13][14], which arises from the spontaneous emission, the low cavity quality factor, and large intracavity nonlinearities [15]. Even at quantum-limited noise performance, fiber lasers can easily exhibit significant timingjitter, which is a challenge for stable frequency comb generation [16].…”

Optical Frequency Comb Generation based on Erbium Fiber Lasers

“…In fiber combs, a collinear all-fiber-based f -to-2f interferometer is usually used, which avoids losses from freespace coupling as well as non-common mode noise seen in non-collinear interferometers [25]. Furthermore, compact and efficient commercial fiber-coupled periodically-poled lithium-niobate waveguide frequency doublers are available, which greatly simplifies and improves the fceo detection [102]. To stabilize the comb without "phase slips", the SNR of the detected fceo signal should exceed~30 dB within a 300 kHz bandwidth and SNRs of 40 dB or more are now routinely achieved [25,70,102].…”