All-fiber broadband frequency comb source at 2050 nm center wavelength

Summary form only given. In the last decade, laser development based on Tm and Ho doped materials in the mid-IR has made a significant progress, especially in fiber technology [1-2]. Current work focusses on Tm doped fiber broadband amplifiers at the central wavelength toward 1.95 μm with high average power and pulse duration of 141 fs [3]. Whereas purely Tm doped fibers are well suited for a center wavelength in the 1.9-2 μm range, the co-doping with Ho ions shifts the gain region to 2-2.15 μm in the water transparency window. Up to our knowledge, no broadband fiber based amplifier has been demonstrated using the advantage of Tm/Ho co-doping.Here we present an all polarization maintaining (PM) fiber system emitting pulses with a broadband spectrum centered at 2050 nm. The output average power is 670 mW and the spectrum spans 1950 nm to 2200 nm corresponding to a transform limited pulse duration of 63 fs. The fiber system consists of an all PM Erbium oscillator running at 100 MHz repetition rate, followed by an all PM Er doped fiber amplifier (EDFA) amplifying 70 fs pulses at 1560 nm center wavelength with 550 mW output average power. This output is then directly pumping a 23 cm HNLF, generating a coherent supercontinuum spanning over more than one octave from 900 nm to 2300 nm. An 8 cm unpumped Tm/Ho codoped fiber has been spliced after the supercontinuum stage in order to self-amplify the 2 μm region [4]. The pulses are further amplified in a 3 m PM double clad Tm/Ho co-doped fiber pumped with one 4W pump diode at 793 nm.The slope efficiency at room temperature is about 22%, as shown in Fig. 1 (left) with the evolution of the average output power as function of the pump power. The amplified spectrum with a FWHM bandwidth of about 126 nm at maximum output power is shown in Fig. 1 (right). To conclude, we have developed a robust all-PM fiber system including a broadband amplifier at 2050 nm center wavelength able to support 63 fs TL - ulses. The average output power of 670 mW was achieved at 100 MHz repetition rate corresponding to 6.7 nJ pulse energy. The system is scalable to higher average output power and offers high potential for many applications such as spectroscopy in the 2 μm region or seeding high power Ho doped free space amplifiers. This work was supported by the CCQED European Program through its Marie Curie ITN FP7 (project 264666).