Generation of a 660–2100 nm laser frequency comb based on an erbium fiber laser

Abstract

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXXWe present a multibranch laser frequency comb based upon a 250 MHz mode-locked erbium-doped fiber laser that spans more than 300 terahertz of bandwidth, from 660 nm to 2000 nm. Light from a mode-locked Er:fiber laser is amplified and then broadened in highly-nonlinear fiber to produce substantial power at ~1050 nm. This light is subsequently amplified in Yb:fiber to produce 1.2 nJ, 73 fs pulses at 1040 nm. Extension of the frequency comb into the visible is achieved by supercontinuum generation from the 1040 nm light. Comb coherence is verified with cascaded f-2f interferometry and comparison to a frequency stabilized laser.OCIS Codes: 190.7110, 060.2320 The Er:fiber-based laser frequency comb is a technologically mature tool for precision metrology with benefits of long-term reliability and relatively low cost. However, in some applications, such as direct frequency comb spectroscopy [1, 2] Here, we present a technique for generating a visible light frequency comb from a mode-locked erbium laser that is self-referenced and frequency-stabilized using established techniques. In nonlinear fiber we shift significant pulse energy to the 1 μm region, where it is amplified with a core-pumped Yb:fiber amplifier [7,8,9,10,11]. The amplifier output is then compressed to provide a 73 fs pulse, which is spectrally broadened to below 650 nm using microstructured fiber. Significantly, we verify that the coherence of the original Er:fiber source is transfered to the amplified 1040 nm pulses, and that with subsequent nonlinear broadening the system provides a multibranch LFC with nearly two octaves of bandwidth from 660 nm to beyond 2000 nm.Intense ultrashort pulses at 1.04 μm are generated from a 250 MHz mode-locked Er:fiber laser [12] using a series of amplifiers and nonlinear fibers, shown in Fig. 1. One third (35 mW) of the light produced by the Er:fiber laser is amplified in a core-pumped Er:fiber amplifier to an average power of 450 mW. Dispersion management and nonlinear pulse-shortening are achieved by carefully trimming the length of standard anomalous-dispersion single-mode fiber (SMF) between the laser and the gain fiber and by making use of a normal-dispersion Er:doped fiber [13] (nLight Er80 4/125). After recompressing the amplified pulses in SMF, a pulse duration of ~ 70 fs at 1580 nm is achieved as measured using second-harmonic generation frequency-resolved optical gating (SHG-FROG) [14].The erbium amplifier output is fusion spliced to a 5 cm long piece of solid-core highly nonlinear fiber (HNLF) [15] with dispersion of 7.7 (ps/nm)/km at 1600 nm, which is in turn coupled out by splicing to a length of SMF. This generates a supercontinuum with ~ 8 % of the 240 mW power coupled into the SMF falling between 1000 nm and 1100 nm. Within that range, the placement of the spectral peak can be refined by tuning the polarization state of light entering the Er:fiber amplifier and the HNL...

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