Tunable 300 W single-frequency 2 micron fiber amplifier

Abstract

We present an all-fiber design for a Tm-based fiber amplifier that can tune over 1992-2065 nm with 300-350 W single-frequency (<100 kHz) output. Over 180 W is achieved out to 2085 nm with <10% ASE content without utilizing ASE spectral filters. The amplifier employs both Tm- and Tm/Ho-doped gain fibers in two preamplifier stages in addition to longer sections of Tm fiber to extend the bandwidth of the Tm-based high-power amplifier to longer wavelengths (>2050 nm). Efficiencies of 55% are realized across the full bandwidth. Roll-off occurs beyond 2085 nm where ASE becomes intractable. The amplifier has an average M^2 value of 1.39 at high-power due to the presence of light guided within the fiber pedestal. Estimates of the pedestal light and higher-order mode contents are provided.

Figures (6)

• Figure 1: Schematic of the TDFA. TFB: tapered-fiber bundle pump/signal combiner; MFA: mode-field adapter; OSA: optical spectrum analyzer; HP: high power.
• Figure 2: Maximum output power of the signal, efficiency, and ASE % of the MOPA from 1992-2096.75 nm.
• Figure 3: Output vs pump power curves for 2015-2065, with y-axis being output power of the signal wavelength. Each is linearly fit to calculate slope efficiency.
• Figure 4: Output spectra from 1992-2085 nm at each wavelength's maximum achieved output power. All spectra have been normalized so that peak values are at 0 dB.
• Figure 5: (a) Electronic spectrum analyzer trace of the seed at 2040 nm measured by a 10 GHz amplified photodetector. The magnitude of the signal has been calibrated to calculate the SMSR of the seed as a function of frequency spacing from the fundamental longitudinal mode. (b) Lineshape of the seed, as measured via heterodyning with a stabilized frequency comb, with curve-fitting applied to calculate the -3 dB linewidth.