Clement Romano

• PhD
• Fraunhofer Institute of Optronics, System Technologies and Image Exploitation

In this study, an efficient hybrid fiber and solid-state master oscillator power amplifier (MOPA) system is introduced. This system is composed of an actively pulse-shaped Ho³⁺- and Tm³⁺-doped silica fiber MOPA at 2048 nm. A subsequent Ho³⁺:YAG power amplifier stage enables the efficient scaling of the pulse energy. By utilizing a novel cascaded cr...

This paper presents the results of experimental and theoretical studies of the influence of temperature and pump modulation on an erbium:ytterbium co-doped fiber laser in context for an optimized size, weight, and power (SWaP) integration. The fiber laser setup including the active fiber and pump diode lasers are heated up or cooled down for rangin...

We report on an all-fiber Master Oscillator Power Amplifier (MOPA) laser at a signal wavelength of 2048 nm, designed for pumping an Optical Parametric Oscillator (OPO). This setup offers the benefit of miniaturization while being rugged and thereby suite the demands for mobile counter measures. By utilizing the MOPA structure to design suitable OPO...

The demand for high-power lasers in the 2 μm region is growing across various applications. Thulium-Doped Fiber Lasers (TDFL) lead with 50-60 % slope efficiencies and over 1 kW of output power. Thulium:Holmium-co-Doped Fiber Lasers (THDFL) show lower slope efficiencies but operate beyond 2.1 μm, beneficial for atmospheric applications. The latter l...

A nanosecond-pulsed Tm-doped fiber laser (TDFL) operating at 2050 nm is reported based on a flexible photonic crystal fiber with a core diameter of 50 μm. The TDFL delivers gaussian-shaped pulses with a maximum pulse energy of 1.9 mJ, corresponding to a peak power of 15.4 kW and a pulse width of 116 ns. The average output power of the pulsed TDFL i...

We report our latest results in nonlinear mid-infrared frequency conversion using a fiber-based single-oscillator pumping a ZGP-based OPO. To minimize absorption in the ZGP crystal a simplified Q-switched Tm3+:Ho3+-codoped fiber laser was realized, emitting at 2.1 μm. Based on this pump source, mid-infrared output powers up to 12.2 W were achieved...

Erbium:ytterbium-codoped fibre lasers (EYDFL) are used in many industrial and defence applications such as free-space communication, range finding and LIDAR. These applications benefit from a low atmospheric absorption and improved eye-safety. They are supported by widely available matured fibre components that simplify the realization of the EYDFL...

Developing a device to retrieve the full Stokes’ vector at high-speed requires a careful design. We present an analysis of the measurement error of a polarimeter as a function of all optical component defects.

Ho³⁺:YAG amplifiers are able to efficiently scale pulse energy at wavelengths far shorter than the main emission peak. For 24 W input power at 2048 nm a signal output power of 81.6 W is reached, resulting in 5.3 dB gain.

A nanosecond-pulsed diode-pumped Tm³⁺-doped fiber laser (TDFL) operating at 2050 nm is reported based on a flexible photonic crystal fiber (PCF) with a core diameter of 50 µm. Analytical evaluation of reabsorption effects and optimization of the fiber length allow enhanced pulse energy extraction at long wavelengths. This enables the generation of...

We report on the mode field adaption of an active thulium-doped fiber by using the thermally-diffused expanded-core technique. The fiber core diffusion is analyzed by splice transmission measurements and visually from side view images. The obtained heating parameters are used to build a thulium-doped fiber laser emitting at 2036nm that is core-pump...

Exceeding the multi-kW power level with thulium-doped fiber lasers has not been achieved using a single thulium-doped fiber laser. One solution to overcome this limit is the coherent beam combination. We focus on an active phase control with tiled aperture configuration. The setup consists in an amplified seed laser split in three channels. These c...

In this work we propose a simulation tool to analyze the case of conduction-driven thermal blooming and compare the results with measurements at the 2055 nm absorption line of CO2. Using a split-step beam propagation method and incorporating the spatial refractive index change related to the absorption-driven radial temperature gradient resulting f...

We report on the scaling of a polarization-maintaining MOPA at a signal wavelength of 2048 nm, designed for pumping an optical parametric oscillator (OPO). By utilizing the MOPA structure to design suitable OPO pump pulses the overall mid-IR conversion efficiency is enhanced enabling the scaling of the mid-IR average power. 60 W of average power is...

An actively Q-switched diode-pumped Tm3+-doped fiber laser (TDFL) operating at 2050 nm is reported based on a flexible Photonic Crystal Fiber (PCF) with a core diamter of 50 μm. Using a fiber length of 3 m, the TDFL delivers gaussian shaped pulses with a maximum pulse energy of 1.5 mJ, corresponding to a peak power of 16 kW and a pulse width of 88...

We present our latest results in power scaling of Midwave-Infrared (MWIR) Optical Parametric Oscillators (OPOs) based on a Zinc Germanium Phosphide (ZGP) crystal, utilizing a single oscillator fiber laser as pump source. To obtain a compact and complexity-reduced pump source emitting at ≥ 2.09 μm, a Q-switched Tm3+:Ho3+- codoped fiber laser was dev...

Thulium-Doped Fiber Lasers (TDFL) emitting at 2 μm wavelength are used in various applications such as imaging, telecommunication and optical countermeasures. Many of these applications require highly integrated and passively cooled lasers with low SWaP (size, weight, and power) architecture that can work in harsh environment at different temperatu...

This study investigated the perforation time of polyamide 6.6 using fiber lasers at two different wavelengths: 1070 and 1943 nm. The novelty of this research lies in the comparison of perforation times at equivalent laser irradiances on the polymer sample with two different colors of polyamide 6.6: natural and black. The results revealed that, at c...

We investigate the temperature dependence of an in-band core-pumped thulium-doped fiber laser with a low SWaP (size, weight, and power) architecture. The temperature investigation is carried out both experimentally and numerically by a simulation model. We demonstrate experimentally that the investigated setup is resistant for temperatures till 353...

This study discusses the limitations for pulse energy extraction in nanosecond-pulsed rare-earth-doped fiber lasers. Optimization of the fiber length considering reabsorption effects leads to the demonstration of pulse energies of 1.9 mJ at an average output power of 114 W and an emission wavelength of 2050 nm from a Tm ³⁺ -doped flexible photonic...

Ho ³⁺ :YAG amplifiers are able to efficiently scale the pulse energy at wavelengths as short as 2048 nm. While maintaining 5.3 dB gain, an output power of 81.6 W and a slope efficiency of 68 % is achieved.

A compact, high-power 1931 nm diode-pumped, all-fiber MOPA laser with up to 100 W of output power and narrow linewidth is demonstrated. The laser achieves a slope efficiency as high as 59 %.

We present a study of perforation time for a polymer material. Two different colors of the same polymer were investigated: natural and black. The study compares two different fiber laser wavelengths: 1 μm and 2 μm. The beam diameter on the polymer material was kept the same to provide a fair comparison between wavelengths. The irradiance was varied...

We investigated the temperature dependence of a multi-watt thulium-doped fiber laser. For high-power laser operation, thulium-doped fiber lasers are often pumped in the cladding by diode lasers operating at 793 nm to take advantage of the cross-relaxation effect. However, these diode lasers have to be temperature stabilized since the 3H4 absorption...

We present our latest results in power scaling of thulium-doped fiber lasers in the 2 μm region based on coherent beam combination with tiled aperture technique. The investigation of a high-power laser system based on coherent beam combination was divided into three individual experiments. First a MOPA architecture was studied with focus on power s...

We present a Tm3+:Ho3+- codoped all-fiber laser emitting at 2120 nm relying on an FBG-based single oscillator cavity. The fiber laser delivers 160 W of output with a slope efficiency of 46.6 %.

We demonstrate a pulsed three-stage master oscillator power amplifier (MOPA) at a wavelength of 2047 nm and its application for mid-IR generation via pumping a ZnGeP2 (ZGP) optical parametric oscillator (OPO). A maximum MOPA output power of 19.8 W is reached while achieving a diffraction limited beam quality M² <1.1. By applying the MOPA setup to p...

An all-fiber laser system is presented with a simple MOPA configuration composed of a seed laser followed by a one-stage high-power amplifier. The seed delivers 10 W of output power at 2036 nm. The high-power amplifier operates with a high slope efficiency of 59 %. An output power of 937 W is demonstrated with a close to diffraction limited beam qu...

A Q-switched 2050 nm Tm ³⁺ -doped flexible photonic crystal fiber laser is reported with maximum pulse energy of 1.5 mJ, pulse width of 89 ns, average output power of 19.7 W, and 3-dB-linewidth of 100 pm.

A pulsed Tm ³⁺ and Ho ³⁺ -doped all-in-fiber single-mode MOPA with 50.9 W average power at 2047 nm is presented. 50 ns square pulses with >10 kW peak-power and 509 µJ pulse energy were obtained.

A Tm³⁺:Ho³⁺-codoped free-space single-oscillator fiber laser is under investigation with special focus on the power scalability of emission wavelengths from 2.1 µm to 2.2 µm. Using a tunable diffraction grating, a 200-nm tunable laser source is built. Laser output powers above 10 W are delivered from 1990 nm up to 2190 nm, demonstrating the range f...

A polarization-maintaining (PM) pulsed three-stage master oscillator power amplifier (MOPA) emitting at 2047nm is reported, generating 19.8W of output power (396 µJ pulse energy) for a 50 ns pulse width at a repetition rate of 50 kHz. The output signal is linearly polarized and a diffraction limited beam quality is achieved. This MOPA laser is used...

A Q-switched polarization-maintaining (PM) Thulium (Tm³⁺):Holmium (Ho³⁺)-codoped triple-clad fiber (THTF) laser is under investigation with special focus on important optical parameters enabling efficient frequency conversion into mid-infrared (mid-IR). An active fiber of 5 m length is used in a single-oscillator free-space cavity arrangement and o...

A single-frequency polarization-maintaining holmium-doped fiber master oscillator power amplifier operating at signal wavelengths of $2054\;{\rm nm}$ and $2090\;{\rm nm}$ is presented. The two-stage setup delivers up to $240\;{\rm W}$ peak power and $6.7\;\unicode{x00B5} {\rm J}$ pulse energy for a pulse width of $30.2\;{\rm ns}$ at a repetition ra...

A diode-pumped actively Q-switched polarization-maintaining Tm³⁺-doped fiber laser is reported generating pulse energies of 630 μJ, minimum pulse widths of 42 ns, and a maximum peak power of 13.9 kW with linear polarized output and diffraction-limited beam quality at a wavelength of 2044 nm. The unpolarized fiber laser even reaches pulse energies o...

A mid-infrared ${{\rm ZnGeP}_2}$ optical parametric oscillator pumped by a ${{\rm Tm}^{3 +}}$ -doped fiber laser is reported, providing pulse energies of $230 \;\unicode{x00B5}{\rm J}$ , pulse widths of 40 ns, and peak powers of ${\sim}6\;{\rm kW} $ with excellent efficiency and beam quality. The pump source is an actively $Q$ -switched single osci...

We present the performance of a thulium:holmium-codoped fiber amplifier operating at 2050 and 2090 nm signal wavelength. This amplifier is built with polarization-maintaining fibers and is clad-pumped at 793 nm. We demonstrate more than a watt of signal power for both signal wavelengths. We compare the performance of this amplifier with a previousl...

We report the design and performance of Holmium-doped fiber amplifiers (HDFAs) with novel alternative in-band pump wavelengths in the 1720—2000 nm spectral region. We demonstrate through simulations that pump wavelengths of 1840—1860 nm can yield significantly improved output power (3—6 dB), gain (8—10 dB) , and optical-optical conversion efficienc...

A diode-pumped actively Q-switched Tm3+-doped fiber laser is reported generating pulse energies of 800 μJ, pulse widths of 43 ns and peak powers of 17.5 kW. By using the single-oscillator as a pump source for nonlinear frequency conversion, mid-IR pulse energies of 230 μJ are extracted from a ZnGeP2 (ZGP) optical parametric oscillator (OPO).

We report on current advances in polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser. First fundamental studies were performed in a continuous-wave (CW) regime. A fiber laser with a 7 m active fiber delivered high output powers of up to 180 W for an emission wavelength centered at ~2050 nm. In addition...

We report on the development of a pulsed MOPA laser as a pump source for nonlinear fibers, for supercontinuum generation, or optical parametric generation in the mid-IR. The master oscillator is a directly modulated semiconductor laser, while the power amplifier is a two-stage polarization-maintaining fiber amplifier. Such a laser setup allows a fl...

We report the design and performance of a packaged broadband PM hybrid HDFA/TDFA in the 2000—2100 nm band using all-single-clad doped fibers. Internal small signal G = 49.1 dB, small signal NF = 6.5 dB, and Pout = 3.54 W are achieved at ${\lambda_{s}}$ = 2051 nm. The simulated 3 dB output power bandwidth is 98 nm. Comparisons of experimental data...

We report on the development of a nanosecond pulsed laser based on external modulation and polarization-maintaining Holmium amplifiers operating at 2050 & 2090 nm. We demonstrate peak power greater than 120 W at 10 kHz repetition rate for a pulse width of 30 ns.

Efficient high-power 2 µm fiber laser sources play a growing role in direct pumping of nonlinear crystals for frequency conversion into to mid-IR. There is an ongoing progress in fiber development and cavity improvement achieving outstanding laser performance for an efficient optical parametric generation. In this paper, we report on the investigat...

We report on the first polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser. First fundamental studies were done in a CW regime and showed highly promising results as a high power pump source for frequency conversion in ZGP crystals. For an unpolarized output, the fiber laser delivered up to 145 W. Swit...

We report on mid-IR supercontinuum generation in an all-silica nanosecond pulsed fiber laser. The laser topology is a master oscillator power amplifier which consists of a two stage Thulium-doped fiber amplifier seeded with a directly modulated semiconductor laser at 1952 nm. The supercontinuum performance is investigated for repetition rate freque...

We report on a polarized MOPA operating at 2050 nm or 2090 nm delivering pulses in the nanosecond regime from 10 kHz to 1 MHz. Peak powers greater than 1 kW are demonstrated.

We report the broadband spectral performance of a three-stage, high gain, single mode, high output power (25 W) polarization-maintaining (PM) hybrid Ho-doped and Tm-doped fiber amplifier at signal wavelengths of $\lambda _{\text{s}}$ = 2004—2108 nm. The three-stage amplifier consists of a two stage high gain Ho-doped PM single clad preamplifier s...

We report the design, evaluation, and performance of a polarization-maintaining (PM) fiber amplifier with a CW output power of at 2051 nm and a high input signal dynamic range of 34 dB at 25 W. To improve both the output power and dynamic range performance of previous amplifiers, we propose a PM hybrid design with a single-clad Ho-doped preamplifie...

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 w...

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 b...

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 consi...

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...

We propose and report the experimental demonstration of a shared pump architecture for a two-stage, broadband, high-gain polarization-maintaining Ho-doped fiber amplifier (HDFA). The gain as high as 59 dB, a noise figure of 10 dB, a dynamic range of >43 dB, and an output power of 4.1 W are achieved at a signal wavelength $\lambda _{ {s}}$ of 2051...

We report the experimental demonstration and record performance of two-stage broadband, high gain polarization-maintaining (PM) Ho-doped fiber amplifiers (HDFAs) at a signal wavelength of λ_s = 2051 nm. We begin by presenting a new PM Ho-doped fiber with core diameter 8 μm, a PANDA structure, a cutoff wavelength of 1650 nm, and a peak a...

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 were achieved. The amp...

We report measurements of absorption, gain, and the lifetime of the transition 3H6 – 3F4 for three commercially available thulium-doped single clad silica fibers. These measurements are used in a steady-state simulation of thulium-doped fiber amplifiers (TDFAs). Comparison of simulation and experimental results yield good agreement for a single sta...

We report measurements of absorption, gain, and the lifetime of the transition ³H6 – ³F4 for three commercially available thulium-doped single clad silica fibers. These measurements are used in a steady-state simulation of thulium-doped fiber amplifiers (TDFAs). Comparison of simulation and experimental results yield good agreement for a single sta...

We report the performance of a robust and compact two stage single clad TDFA delivering an output power of 8 W at 1952 nm, with slope efficiency of 70 % and input dynamic range > 30 dB.

We report the first experimental demonstration and record performance of broadband, high gain PM HDFAs at λs = 2051 nm. We achieve G = 60 dB, BW = 100 nm, η = 80%, and Pout = 6.7 W.

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 , gain , noise figure NF, signal wavelength , and dynamic range. We measure the spectral performance of the TDFA for three specific wavelengths...

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 am...

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 Pout, gain G, noise figure NF, signal wavelength λs, and dynamic range. We measure the spectral performance of the TDFA for three specific wave...

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...

We report the design, experimental performance, and simulation of a single stage, co- and counter-pumped Tm-doped 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...

We report the design, experimental performance, and simulation of a single stage, co- and counter-pumped Tm-doped 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...

We report experimental and simulated performance of a tandem (dual-stage) Tm-doped silica fiber amplifier with a high signal output power of 2.6 W in the 2 μm band. Combined high dynamic range, high gain, low noise figure, and high OSNR are achieved with our design.

We report the performance of one- and two-stage single clad polarization-maintaining (PM) Ho-doped fiber amplifiers (HDFAs) at λs = 2051 nm, pumped at λp ≈ 1950 nm. We show that the Ho-doped fiber has a slope efficiency η = 70 %, and demonstrate an output power Pout of 3.5 W and a gain G = 43 dB.

We report measurements of absorption, gain and lifetime for two commercially available Tm-doped single clad silica fibres for the transition 3 H6-3 F4. Comparison of simulation and experimental results for a single stage amplifier at 1952 nm yields good agreement.

We report experimental and simulated performance of a tandem Tm-doped silica fibre amplifier with a high signal output power of 2.6 W in the 2 µm band. Combined high dynamic range, high gain, low noise figure, and high OSNR are achieved with our design.

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. CO2 atmospheric absorption at 2051.4 nm). In this paper we report the design and performance of a multistage high-power PM...

This work focuses on the influence of stress-rods on bending losses of polarization modes in microstructured optical fibers with large mode area. We perform detailed numerical simulations with a modal solver based on the finite element method that takes into account the stress distribution. We show that such fibers, in addition to guide a single-mo...