Offset-free broadband Yb:fiber optical frequency comb for optical clocks

Abstract

We demonstrate a passively offset-frequency stabilized optical frequency comb centered at 1060 nm. The offset-free comb was achieved through difference frequency generation (DFG) between two portions of a supercontinuum based on a Yb:fiber laser. As the DFG comb had only one degree of freedom, repetition frequency, full stabilization was achieved via locking one of the modes to an ultra-stable continuous wave (CW) laser. The DFG comb provided sufficient average power to enable further amplification, using Yb-doped fiber amplifier, and spectral broadening. The spectrum spanned from 690 nm to 1300 nm and the average power was of several hundred mW, which could be ideal for the comparison of optical clocks, such as optical lattice clocks operated with Sr (698 nm) and Hg (1063 nm) reference atoms.

Free-running performance and full control of a passively phase-stable Er:fiber frequency comb

“…Inherent stability of the CEP is especially appealing for space-based applications [17,18] and high-power fiber systems aiming at sensitive experiments in extreme nonlinear optics [19]. Very recently, a DFG comb from an Yb:fiber oscillator mode locked via nonlinear polarization rotation was stabilized to a linewidth of 1 kHz by coupling to an external reference cavity [20].…”

Noise Characterization of an Optical Frequency Comb Using Offline Cross-Correlation

“…Passive mode-locking [16] of an Erbium fiber laser at 1550 nm generates femtosecond pulses which are the basis of the OFC. After spectral broadening in a photonic crystal fiber [17] and DFG [5], [6], [7], which both preserve the phase relationship between all modes, a super-continuum light spanning from 1450 nm to 1625 nm is obtained. It is composed by equally spaced modes separated by the repetition frequency f rep without offset frequency, mode N has a frequency f N = N ×f rep .…”

“…Frequency combs that emit at telecommunication wavelengths are especially attractive for microwavephotonics and radio-over-fibre communication systems in order to generate millimetre wave and low-phase-noise carriers which can hugely increase communication data rates [3], [4]. Recently, offset-free OFCs have been introduced in which the carrier-envelope offset (CEO) frequency, f 0 , cancels out in a non-linear process of difference frequency generation (DFG) [5], [6], [7]. Ultimate performances on all OFC modes can be reached by locking the OFC to an ultra-stable frequency reference [8] by means of a single parameter, the repetition frequency f rep .…”

Optical Frequency Comb Generation based on Erbium Fiber Lasers

“…Though not technically an actuator, difference frequency generation (DFG) in a nonlinear crystal can be used to simply force fceo to zero [160][161][162]. In the DFG, fceo drops out of the final comb due to the subtraction.…”