New developments in LIDAR and atmospheric sensing experiments highlight the need for studies of the optical bandwidth and wavelength dependence of multi-watt, large bandwidth, high dynamic range polarization-maintaining optical amplifiers in the 2—2.1 μm band. Recently we have demonstrated a hybrid single clad-double clad Tm-doped fiber amplifier with greater than 20 W output and a dynamic range of <20 dB in the 2 μm band, and a <25W output PM hybrid HDFA/TDFA with a dynamic range of 34 dB. Both demonstrations were carried out at a single input wavelength of 2051 nm. In this paper we extend our experimental studies to the signal wavelength dependence of a PM hybrid HDFA/TDFA with a single clad Hodoped preamplifier [4-7] and a double clad Tm-doped power amplifier. We have studied the performance of the amplifier from 2004 to 2108 nm, and in this paper, we report first experimental results for this wavelength region. We find that our hybrid Ho-Tm-doped design provides a PM fiber amplifier with a combination of large output optical signal-to-noise ratio, broad operating bandwidth, and high P<sub>out</sub> of 28.5 W at λs = 2069 nm.
Current developments in LIDAR and atmospheric sensing experiments highlight the need for multi-watt, large bandwidth, high dynamic range polarization-maintaining optical amplifiers in the eye safe 1.9—2.15 μm band. So far, as an illustration of the previous state of the art for high power devices, multi-watt Tm-doped fiber amplifiers (TDFAs) have been demonstrated by Goodno et al. with an output power of 608 W at a signal wavelength of 2040 nm. As for Ho-doped fiber amplifiers (HDFAs) Hemming et al. have reported output powers of 265 W at 2110 nm. For this HDFA, a double clad Ho-doped fiber pumped by high power fiber lasers made the configuration complex and yielded an optical slope efficiency of 41%. Both of these achievements were with standard (non-polarization-maintaining) fiber.
We present a kW level pulsed laser based on a master oscillator power amplifier (MOPA) configuration. The directly modulated single frequency laser at 1952 nm was pulsed in the nanosecond regime with a repetition rate frequency from 10 kHz to 2 MHz. The MOPA topology was based on a two stage amplifier using single clad Thulium-doped fiber: it consisted of a pre-amplifier stage followed by a booster stage. We investigated the performance of this pulsed laser for two different TDFs with different saturating energies in the booster stage. The direct modulation allowed us to demonstrate more than 1 kW of output peak power over pulse repetition frequencies from 10 kHz to 500 kHz. For a pulse duration of 21 ns, we measured output energy of 13 μJ and 29 μJ for booster fiber saturating energies of 15 μJ and 30 μJ, respectively.
We report the experimental performance and simulation of a multiwatt two-stage TDFA using an L-band (1567 nm) shared pump source. We focus on the behavior of the amplifier for the parameters of output power P<sub>out</sub>, gain G, noise figure NF, signal wavelength λ<sub>s</sub>, and dynamic range. We measure the spectral performance of the TDFA for three specific wavelengths (λ<sub>s</sub>= 1909, 1952, and 2004 nm) chosen to cover the low-, mid-, and upper-wavelength operating regions of the wideband amplifier. We also compare the performance of the two-stage shared pump TDFA with a one stage shared pump amplifier. Experimental results are in good agreement with simulation.
We report the performance of a two stage single clad (SC) Thulium-doped fiber amplifier (TDFA), delivering an output power of 5 W at 1952 nm without stimulated Brillouin scattering (SBS) for a single-frequency input signal. A slope efficiency greater than 60 %, a signal gain greater than 60 dB and an input dynamic range > 30 dB are achieved. The amplifier topology was optimized with a modelization tool of the SC TDFA performance: experimental results and simulations are in good agreement.
A simple engineering design is important for achieving high Thulium-doped amplifier (TDFA) performance such as good power conversion, low noise figure (NF), scalable output power, high gain, and stable operation over a large dynamic range. In this paper we report the design, performance, and simulation of two stage high-power 1952 nm hybrid single and double clad TDFAs. The first stage of our hybrid amplifier is a single clad design, and the second stage is a double clad design. We demonstrate TDFAs with an output power greater than 20 W with single-frequency narrow linewidth (i.e. MHz) input signals at both 1952 and 2004 nm. An optical 10 dB bandwidth of 80 nm is derived from the ASE spectrum. The power stage is constructed with 10 μm core active fibers showing a maximum optical slope efficiency greater than 50 %. The experimental results lead to a 1 dB agreement with our simulation tool developed for single clad and double clad TDFAs. Overall this hybrid amplifier offers versatile features with the potential of much higher output power.
We report the design, experimental performance, and simulation of a single stage, co- and counter-pumped Tmdoped fiber amplifier (TDFA) in the 2 μm signal wavelength band with an optimized 1567 nm shared pump source. We investigate the dependence of output power, gain, and efficiency on pump coupling ratio and signal wavelength. Small signal gains of >50 dB, an output power of 2 W, and small signal noise figures of <3.5 dB are demonstrated. Simulations of TDFA performance agree well with the experimental data. We also discuss performance tradeoffs with respect to amplifier topology for this simple and efficient TDFA.
A careful comparison of experiment and theory is important both for basic research and systematic engineering design of Thulium fiber amplifiers operating in the 2 μm region for applications such as LIDAR or spectroscopy (e.g. CO<sub>2</sub> atmospheric absorption at 2051.4 nm). In this paper we report the design and performance of a multistage high-power PM Tm-doped fiber amplifier, cladding pumped at 793 nm. The design is the result of a careful comparison of numerical simulation, based on a three level model including ion-ion interactions, and experiment. Our simulation model is based on precise measurements of the cross sections and other parameters for both 6 and 10 μm core diameter fibers. Good agreement for several single and multistage amplifier topologies and operating conditions will be presented. Origins of the difference between theory and experiment are discussed, with emphasis on the accuracy of the cross sections and the cross relaxation parameters. Finally based on our simulation tool, we will demonstrate a design with an output power greater than 10 W for a multistage amplifier with a single-frequency signal at 2050 nm. The power stage was constructed with a 6 μm active fiber showing a 64 % optical slope efficiency. The output power is found to be within 5 % of the simulated results and is limited only by the available launched pump power of ~24 W. No stimulated Brillouin scattering is observed at the highest output power level for an active fiber well thermalized.