We here present our holmium-doped fiber amplifier developed for research on topics on a future third-generation gravitational wave detector for the ETpathfinder research facility. For lasers to be used in gravitational wave detectors, there are not only highest demands on typical laser parameters, such as linewidth, spectral purity, and polarization, but especially on the Relative Intensity Noise (RIN) properties. Our developed laser system consists of a compactly packaged holmium-doped fiber amplifier, which is pumped by a thulium-doped fiber amplifier. By setting up both fiber amplifiers in the same, thermally stabilized and compactly engineered laser housing, we aim to achieve highest output power stabilities. With our current setup, we achieve an output power of app. 450 mW with linear polarization and a low linewidth of app. 2 MHz at a wavelength of 2095 nm. To analyze the RIN, we use our in-house developed measurement setup. We present the achieved RIN results in the frequency range from 10-3 to 104 Hz, and for example at a frequency of 100 Hz, we achieve a RIN of app. 10-6 1/Hz0.5, which shows the suitability of our concept to achieve highest power stabilities.
In this publication, we present a linearly polarized MOFPA (Master Oscillator Fiber Power Amplifier) setup for generating and amplifying short pulses in the ps- to ns-regime at wavelengths around 2 μm to ⪆20 W of average power. The Master Oscillator consists of a directly gain-switched seed diode laser at a center wavelength of approx. 1950 nm which is capable to generate pulses with durations down to 50-70 ps by separating the gain spike and suppressing the trailing edge by using specially designed driver electronics. The subsequent fiber amplifier is formed by three cascaded amplifier stages based on polarization-maintaining Thulium-doped active fibers pumped by multimode pump laser diodes around 800 nm. The realized setup achieves a total gain of ⪆60 dB, which leads to a spectrally filtered output power of ⪆20 W with slightly broadened pulse durations ⪅350 ps due to nonlinear effects, for example when an input pulse duration of 222 ps is used. Since our fully monolithic fiber amplifier system consists of single-mode and LMA fibers, the output beam quality is nearly diffraction limited. Due to the separately variable pulse durations and pulse repetition rates, our here presented approach offers technical and economic advantages over commercially available laser systems with comparable pulse durations, which are largely based on mode-locked oscillators.
Within the context of the E-TEST (Einstein Telescope EMR Site & Technology) project, Fraunhofer ILT develops thulium- and holmium-based seed sources and fiber lasers at app. 2 μm wavelength with highest demands on linewidth and stability for usage in a third-generation gravitational wave detector, the Einstein telescope. To fulfill the requirements, we develop a seed laser and a multi-stage fiber amplifier, consisting of holmium-doped fibers. Within this paper, we present our current laser concept and the first results of our dual-stage holmium-doped fiber amplifier stage. We achieve a low linewidth (< 2 MHz) output power of more than 5 W at a wavelength of 2095 nm. By using our in-house developed fiber laser simulation, we show that the efficiency of our amplifier is currently limited by pair induced quenching and the potential for further power scaling.
In single-mode fiber lasers, power scaling is typically limited by effects such as stimulated Raman-scattering and transverse mode instabilities. However, in highly multi-mode fibers, these two effects are usually negligible due to the high number of transverse modes and therefore, higher optical powers can be achieved. To further decrease the complexity, increase the robustness and reliability of multi-mode fiber resonators, we develop highly reflective multi mode Fiber Bragg Gratings (FBGs) in active doped fibers, which is challenging e.g. due to the required homogeneity of the FBG within the fiber. Here, we present a proof of concept of a fiber-integrated multi-mode resonator using a highly reflective multi-mode FBG for spectral stabilization in a fiber with a rectangular core of 20 x 60 µm² and a numerical aperture of 0.1. More than 60 modes can be guided within this fiber, which can result in a homogeneous near-field beam profile. In our experimental verification, we build up a fiber resonator and achieve an optical-optical efficiency of 50 % and stable wavelength operation at 1072 nm. 10 % of the power is emitted as ASE at a wavelength of 1030 nm, which can be removed by using longer fiber lengths to further improve the efficiency. Approximately 12 % of the signal power is propagating through the HR-FBG, which leads to an FBG-reflectivity of 70-80 % based on our simulations. As a next step, we plan to transfer the HR-FBG concept to round-core XLMA-fibers to improve our earlier demonstrated setups and realize full in-fiber multimode resonators.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.