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Optics Letters

30 W-class tunable single-frequency thulium-doped fiber amplifier at 1730–1762 nm with low intensity noise

Kentin Poncelet, Thomas Dubé, Coline Lavit, Ruizhe Gu, Saïd Hamdi, Roopa Prakash, Nicholas Traynor, Adèle Hilico, Germain Guiraud, Giorgio Santarelli

Published Mar 31, 2026• 0 citations
Publisher

Abstract

We report a fully fibered, polarization-maintaining, single-frequency thulium-doped fiber amplifier operating between 1730 and 1762 nm and delivering more than 30 W of output power. Relative intensity noise is preserved after amplification, with a noise floor of -158 dBc/Hz between 100 kHz and 4 MHz. These results demonstrate the suitability of this source for quantum technology, including direct operation within the tuning range at 1762 nm for barium ion excitation or a possible nonlinear frequency conversion toward 813 nm for strontium atom trapping.

DOI
10.1364/ol.597210

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We report a fully fibered, polarization-maintaining, single-frequency thulium-doped fiber amplifier operating between 1730 and 1762 nm and delivering more than 30 W of output power. Relative intensity noise is preserved after amplification, with a noise floor of -158 dBc/Hz between 100 kHz and 4 MHz. These results demonstrate the suitability of this source for quantum technology, including direct operation within the tuning range at 1762 nm for barium ion excitation or a possible nonlinear frequency conversion toward 813 nm for strontium atom trapping.
Quantum processors based on ion traps (171Yb+,88Sr+,43Ca+or133Ba+) are one of the key components in the emergence of quantum technologies and have seen their interest explode in the last decade [1]. Although171Yb+ions are commonly used as qubits, a new alternative is based on133Ba+offering several key advantages in terms of lifetime, speed, fidelity and performance. The readout of the qubit is made by shelving the133Ba+ion directly to the metastable 5D5/2 state using a 1762 nm single-frequency laser radiation [2]. For quantum computing and optical qubit manipulation low noise and high-power laser at this wavelength is highly recommended. Thulium doped fiber amplifiers (TDFAs) with broad emission between 1600–2100 nm and high-power capabilities are one of the best candidates for this application. Walasik et al demonstrated a 3W-1762 nm single-frequency TDFA but phase and intensity noise weren't investigated [3].
We report the optical architecture, experimental performance, and simulated performance of polarization- maintaining CW and pulsed single clad Tm-doped fiber amplifiers designed to operate over a wavelength span of 1760—1960 nm. We highlight the potential applications of these amplifiers to quantum computing and quantum qubit experiments using 1762 nm light. Our amplifier exhibits 3 W CW output power and 20 W peak pulsed output power (2 MHz rep. rate, 10% duty cycle) at 1762 nm. Measurements of the wavelength response of the TDFA yield an experimental operating bandwidth extending from < 1750 nm to > 1920 nm. Simulations of the amplifier bandwidth indicate a 3 dB (50% FWHM) wavelength span of 1745 nm to 1980 nm (135 nm). Experimental output power and bandwidth results agree well with the simulations. The external noise figure for this amplifier ranges from 7.5 dB to 9.5 dB. No linewidth broadening was observed in a typical TDFA output when using a single frequency input laser source with a linewidth of 10 kHz. We discuss suitability and applications of the TDFA to 1762 nm enabled manipulation of optical qubits in trapped 133Ba+ ions.
A complete experimental and theoretical study of rare earth doped fiber-optic amplifiers for the first tele-communication window has been made. The thulium doped fluoride fiber amplifier is shown to provide amplification in the 800nm-820nm signal region. A complete steady state theoretical model has been presented and the model has been experimentally verified. The model predicts the gain, noise figure and the amplified spontaneous emission in the 800nm, 1470nm, 1900nm and 2300nm bands. The effect of population trapping at the sp3Fsb4\\sp3F\\sb4sp3Fsb4 energy level of thulium ion is also shown with the help of the model. It has been shown that about 5-15%o of the population is trapped at the sp3Fsb4\\sp3F\\sb4sp3Fsb4 energy level. We have also shown theoretically, the expected gain and noise performance of Thulium doped fluoride fiber amplifiers pumped in the 680nm absorption band. The maximum gain at 806nm is slightly lower than with comparable 780 nm pumping. The gain bandwidth is however found to increase with 680nm pumping. The higher ASE at shorter wavelengths ($<$806nm) reduces the gain at the peak wavelength (806nm). This is a result of the better inversion with three level pumping at 680nm as compared to two level resonant pumping at 780nm. We report an efficient single mode erbium doped flouride fiber amplifier in the 850nm signal band for the first time. The amplification is through an up-conversion process. The erbium doped flouride fiber amplifier was pumped with an estimated pump power of 35mW at 792nm. We have also considered a theoretical model for a single mode erbium doped fluoride fiber amplifier. Efficient amplification occurs because of the strong excited state absorption at the pump wavelength from the sp4Isb13/2\\sp4I\\sb{13/2}sp4Isb13/2 energy level.
The linewidth of a laser plays a pivotal role in ensuring the high fidelity of ion trap quantum processors and optical clocks. As quantum computing endeavors scale up in qubit number, the demand for higher laser power with ultra-narrow linewidth becomes imperative, and leveraging fiber amplifiers emerges as a promising approach to meet these requirements. This study explores the effectiveness of thulium-doped fiber amplifiers (TDFAs) as a viable solution for addressing optical qubit transitions in trapped barium ion qubits. We demonstrate that by performing high-fidelity gates on the qubit while introducing minimal intensity noise, TDFAs do not significantly broaden the linewidth of the seed lasers. We employed a Voigt fitting scheme in conjunction with a delayed self-heterodyne method to accurately measure the linewidth independently, corroborating our findings through quadrupole spectroscopy with trapped barium ions. Our results show linewidth values of 160 ± 15 Hz and 156 ± 16 Hz, respectively, using these two methods, underscoring the reliability of our measurement techniques. The slight variation within the error-bars of the two methods can be attributed to factors such as amplified spontaneous emission in the TDFA or the influence of 1/f noise within the heterodyne setup delay line. These contribute to advancing our understanding of laser linewidth control in the context of ion trap quantum computing as well as stretching the availability of narrow linewidth, high-power tunable lasers beyond the C-band.
We describe a fiber Raman amplifier for nanosecond and sub-nanosecond pulses centered around 1260 nm. The amplification takes place inside a 4.5-m-long polarization-maintaining phosphorus-doped fiber, pumped at 1080 nm by 3-ns-long pulses with a repetition rate of 200 kHz and up to 1.75 kW peak power. The input seed pulses are of sub-mW peak-power and minimal duration of 0.25 ns, carved out of a continuous-wave laser with sub-MHz linewidth. We obtain linearly polarized output pulses with peak powers of up to 1.4 kW, corresponding to peak-power conversion efficiency of over 80%. An ultrahigh small signal gain of 90 dB is achieved, and the signal-to-noise ratio 3 dB below the saturation power is above 20 dB. No significant temporal and spectral broadening is observed for output pulses up to 400 W peak power, and broadening at higher powers can be reduced by phase modulation of the seed pulse. Thus, nearly-transform-limited pulses with peak power up to 1 kW are obtained. Finally, we demonstrate the generation of pulses with controllable frequency chirp, pulses with variable width, and double pulses. This amplifier is thus suitable for coherent control of narrow atomic resonances, especially for the fast and coherent excitation of rubidium atoms to Rydberg states. These abilities open the way towards several important applications in quantum non-linear optics.
We developed a fiber-laser-pumped Ti:sapphire laser system designed for quantum precision measurement applications. By employing a 35 W single-frequency 532 nm fiber laser as the pump source, the system delivered continuous-wave output powers of 4.12 W at 770.108 nm (D 1 line, K), 4.72 W at 780.244 nm (D 2 line, Rb), and 5.29 W at 794.982 nm (D 1 line, Rb), thereby fulfilling the requirements for optical pumping and probing of alkali atoms. To enhance frequency stability, saturated absorption spectroscopy was used to lock the laser frequency, resulting in frequency drifts below 1 MHz over two hours. Furthermore, since low-frequency intensity noise (DC-100 Hz) critically affects spin-relaxation-free quantum sensing, we carried out a theoretical analysis which identified the pump laser as the dominant noise source. By implementing feedback control to the pump source as well as an external noise suppression, both methods achieved over 30 dB of intensity noise suppression within the DC-4kHz frequency range. In addition, improved beam pointing stability further reduced noise below 3 Hz. These results collectively demonstrate the system’s strong potential for quantum sensing applications.