Single-frequency Fiber Laser Research Articles

310-W Single Frequency Tm-Doped All-Fiber MOPA

We present a high-power single frequency (SF) Tm-doped fiber amplifier employing all-fiber master oscillator power amplifier (MOPA) configuration. An SF fiber laser with ultrashort cavity and output power of ~40 mW was used as the seed laser of the MOPA, and the central wavelength located at ~1971 nm. The final output power of the MOPA reaches 310 W with slope efficiency of 0.56, and no amplified spontaneous emission or parasitic lasing is observed. The stimulated Brillouin scattering threshold is not reached yet, and the output power is only pump limited. This is the first demonstration, to the best of our knowledge, on an SF Tm-doped all-fiber MOPA with output power exceeding 300 W.

105 W ultra-narrowband nanosecond pulsed laser at 2 μm based on monolithic Tm-doped fiber MOPA.

We present a high power ultra-narrowband pulsed fiber amplifier at 2 μm. A single frequency fiber laser was modulated by a phase modulator and an intensity modulator to serve as the ultra-narrowband pulsed seed laser with a bandwidth of 307 MHz. The pulsed seed laser was amplified by a monolithic Tm-doped fiber master oscillator power amplifier (MOPA). The average output power reaches 105 W with a slope efficiency of 0.41. The output pulse train has a repetition rate of 1 MHz and a pulse width of 66 ns. The output power is limited by the onset of stimulated Brillouin scattering. Higher output power can be achieved by further broadening the linewidth or narrowing the pulse width to several nanoseconds. To the best of our knowledge, this is the first demonstration on a monolithic ultra-narrowband nanosecond pulsed MOPA at 2 μm with an average power exceeding 100 W.

Fiber lasers and their applications [Invited

Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

Dual-wavelength single-frequency fiber laser based on FP-LD injection locking for millimeter-wave generation

We propose and successfully demonstrate a dual-wavelength single-frequency fiber laser based on two cascaded Fabry Pérot laser diodes (FP-LDs) and a WaveShaper. Both the cascaded FP-LDs and the WaveShaper perform the dual-wavelength selection. Injection locking of the FP-LDs in laser cavity and narrow bandwidth filtering effect of the WaveShaper guarantee single-frequency operation of the laser. By adjustment of the drive currents of the two FP-LDs and the filtering characteristic of the WaveShaper, dual-wavelength single-frequency output with switchable wavelength spacing can be obtained, which can be used for switchable millimeter-wave generation.

A switchable and wavelength-spacing tunable single-frequency and single-polarization dual-wavelength erbium-doped fiber laser based on a compound-cavity structure

A switchable and wavelength-spacing tunable single-frequency and single-polarization dual-wavelength erbium-doped fiber laser is proposed and demonstrated experimentally. The fiber laser is composed of a main linear cavity and two subring cavities. In dual-wavelength operation, the wavelength spacing can be tuned from 0.430 nm to 4.487 nm, showing that the fiber laser can be used for photonic generation of a microwave signal with a tunable frequency range from 54 GHz to 563 GHz; in single-wavelength operation, the fiber laser can either work at a fixed wavelength of 1544.108 nm or work at a wavelength with a tunable range of 4.057 nm, from 1544.538 nm to 1548.595 nm. The linewidths of two wavelengths are approximately 760 Hz and 810 Hz respectively. The polarization-extinction ratios of the laser outputs, both in dual- and single-wavelength operation, are higher than 30 dB.

Experimental and Numerical Investigation of Single Frequency Amplifier with Photonic Bandgap Fiber at 1178 nm

A single frequency photonic bandgap fiber amplifier at 1178 nm is investigated experimentally and numerically. With a pump power of 81 W, a single frequency 1178 nm fiber laser of 10.3 W is obtained with a 3W seed laser and a 20 m gain fiber. Numerical simulation is conducted with a rate equation model taking amplified spontaneous emission and stimulated Brillouin scattering (SBS) into consideration. Temperature distribution along the fiber is applied for SBS suppression, more than 50 W single frequency fiber laser at 1178 nm is predicted theoretically with a 5W seed laser and a 40 m long gain fiber with five temperature steps.

A fiber ring interferometer for measuring spectral widths of emission lines of single-frequency lasers

A fiber ring multipass scanning interferometer has been designed for measuring spectral widths of emission lines of single-frequency fiber lasers at a wavelength of 1.55 μm in a range of 5 kHz to 1 MHz with a signal level of 0.5 mW and higher.

Watt-level short-length holmium-doped ZBLAN fiber lasers at 12 μm

In-band core-pumped Ho3+-doped ZBLAN fiber lasers at the 1.2 μm region were investigated with different gain fiber lengths. A 2.4 W 1190 nm all-fiber laser with a slope efficiency of 42% was achieved by using a 10 cm long gain fiber pumped at a maximum available 1150 nm pump power of 5.9 W. A 1178 nm all-fiber laser was demonstrated with an output power of 350 mW and a slope efficiency of 6.5%. High Ho3+ doping in ZBLAN is shown to be effective in producing single-frequency fiber lasers and short-length fiber amplifiers immune from stimulated Brillouin scattering.

Kilowatt high average power narrow-linewidth nanosecond all-fiber laser

AbstractA high power narrow-linewidth nanosecond all-fiber laser based on the master oscillator power amplifier (MOPA) configuration is demonstrated. A pulsed seed with high repetition rate of 10 MHz was generated by modulating a continuous-wave (CW) single-frequency fiber laser at $\sim $1064 nm by using an electro-optic intensity modulator (EOIM). After multi-stage cascaded power amplification, the average power was boosted to be kilowatt level. The pulses from the main amplifier had a pulse width of $\sim $3 ns and an average/peak power of 913 W/28.6 kW. Further power scaling of the pulses was limited by stimulated Raman scattering (SRS) for the moment, method for SRS suppression and further power scaling was briefly discussed.

820 Hz linewidth short-linear-cavity single-frequency fiber laser at 1.5 μm

We proposed a short-linear-cavity fiber laser with a virtual-folded-ring configuration, which combines the advantages of ring lasers and short-linear-cavity lasers. An all-fiber quarter-wave plate was used inside the cavity to introduce polarization retardation. By retarding the polarization of the travelling waves, the spatial-hole-burning effect was weakened and the efficient cavity length was extended to nearly twice its physical length. As a result, a single-frequency laser output with a linewidth of less than 820 Hz was obtained from the free-running fiber laser. The relaxation oscillation frequency was observed to be around 280 kHz and the signal to noise ratio of the laser output was >72 dB.

Modal instability-suppressing, single-frequency photonic crystal fiber amplifier with 811 W output power

An acoustic- and gain-tailored Yb-doped polarization-maintaining photonic crystal fiber is used to demonstrate 811 W single-frequency output power with near diffraction-limited beam quality. The fiber core is composed of 7 individually doped segments arranged to create three distinct transverse acoustic regions; including one region that is Yb-free. The utility of the Yb-free region is to reduce coupling between the LP01 and LP11 modes to mitigate the modal instability. The application of thermal gradients is utilized in conjunction with the transverse acoustic tailoring to suppress stimulated Brillouin scattering. To the best of our knowledge, the 811 W output represents the highest power ever reported from a near diffraction-limited single-frequency fiber laser.

Intensity noise analysis of a fibre laser after passing through an optical mode cleaner

The intensity noise in a 1560 nm single frequency fiber laser after passing through an optical mode cleaner is analyzed both theoretically and experimentally. Experimental measurement shows that in addition to the evident suppression of intensity noise by the mode cleaner, there exist induced observable periodic fluctuations in the analyzing frequency range of 2 to 12 MHz, as well as the amplification of the intensity noise at low frequencies. The above results cannot be explained by the present mode cleaner model for noise suppression. In this paper, we propose a new theoretical model, in which the mode cleaner is considered equivalent to a delay line and through it the phase-noise of the fiber laser is partially converted to the intensity noise. The phase-induced relative intensity noise (RIN) amplitude is jointly determined by the laser linewidth, the mode cleaner linewidth, and the analyzing frequency. The theoretical analysis shows a very good agreement with the experimental results. The noise suppression effect of the acoustic optical modulator is further analyzed by inserting it into the setup and providing a frequency modulation for it. We have observed an evident improvement of the mode cleaner locking, while the bandwidth of the laser is slightly suppressed from 26 to 16kHz, and the degradation of the measured intensity noise after the mode cleaner is also moderate. The theoretical analysis according to our proposed model fits well with this result. This result further confirms that the phase-induced intensity noise has no direct connection to the mode cleaner locking quality. Through the above analysis, a complete theoretical mode for analyzing the noise suppression by a mode cleaner is built.

51.5 W monolithic single frequency 1.97 m Tm-doped fiber amplifier

AbstractWe demonstrate a monolithic single frequency Tm-doped fiber amplifier with output power of 51.5 W. A single frequency fiber laser at 1.97 $\mathrm {\mu} $m is amplified by a cascaded master oscillator power amplifier (MOPA) system with all-fiber configuration. The optical-to-optical conversion efficiency of the main fiber amplifier is 45%. No amplified spontaneous emission (ASE) or stimulated Brillouin scattering (SBS) effect is observed in the fiber amplifier. The output power could be further scaled by launching more pump power.

2-μm fiber laser sources for sensing

2-μm fiber lasers have become a research topic with an increased emphasis due to a variety of applications including eye-safe LIDAR, spectroscopy, remote sensing, and mid-infrared (mid-IR) frequency generation. We review our latest development on various 2-μm fiber laser sources, including single-frequency fiber lasers, Q-switched fiber lasers, mode-locked fiber lasers, and mid-IR supercontinuum fiber sources. All these fiber laser sources are based on thulium and holmium ions using our proprietary glass fiber technology. Potential applications of these fiber laser sources for sensing are also briefly discussed.

Research progress of 1.5 μm-band CW single-frequency fiber laser

Continuous-wave (CW) single-frequency fiber lasers have been widely used in optical fiber communication systems, optical fiber sensors, gravitational wave detection, laser LIDAR, nonlinear frequency conversion, and spectroscopy. In the past two decades, 1.5 μm-band single-frequency fiber lasers were greatly improved, such as laser linewidth from MHz to kHz, laser power scaling from several milliwatts level to a few hundred watts level. However, the noise suppression, linewidth as well as the output power of the single-frequency fiber laser need further research. This article reviews the key technologies of single-frequency fiber laser, and introduces the output performance and amplified characteristics of our home-made 1.5 μm-band single-frequency fiber laser, based on the DBR cavity constructed by the high-gain Er3+/Yb3+ co-doped phosphate glass fiber.

195 μm kHz-linewidth single-frequency fiber laser using self-developed heavily Tm^3+-doped germanate glass fiber

We demonstrated a kHz-linewidth single-frequency laser at 1.95 μm using the self-developed heavily Tm(3+)-doped single-mode germanate glass fiber with the net gain coefficient of 2.3 dB per centimeter. The maximum output power of the stable single longitudinal mode continuous wave laser is over 200 mW. The slope efficiency measured versus the absorbed pump power is 34.8%, the signal-to-noise ratio is higher than 68 dB and laser linewidth is less than 7 kHz. A wavelength-tuning from 1949.55 to 1951.23 nm was also demonstrated based on changing the tension on the fiber Bragg grating outside the cavity.

Single-frequency fiber laser operating at 29 μm

We report the demonstration of a single-longitudinal-mode fiber laser operating at 2914 nm, which exhibits a spectrometer-limited linewidth of <0.4 nm, in a 49 mm long holmium/praseodymium co-doped ZBLAN fiber. Narrow-linewidth feedback is provided by a fiber Bragg grating inscribed directly in the ZBLAN fiber using the femtosecond laser point-by-point technique. Measurements of the temporal stability and coherence confirm that the laser is operating on a single longitudinal mode.

A linearly frequency modulated narrow linewidth single-frequency fiber laser

A novel linearly frequency modulated narrow linewidth single-frequency phosphate fiber laser has been demonstrated. The output power of the laser is more than 40 mW. A maximum frequency excursion of more than 700 MHz at the modulating bandwidth of 1 kHz has been achieved. Single longitudinal mode operation under modulation is confirmed and the linewidth of the laser is measured to be less than 2 kHz. This type of laser source shows real promise for applications in coherent optical frequency domain reflectometry.

Tunable single frequency fiber laser based on FP-LD injection locking

We propose and demonstrate a tunable single frequency fiber laser based on Fabry Pérot laser diode (FP-LD) injection locking. The single frequency operation principle is based on the fact that the output from a FP-LD injection locked by a multi-longitudinal-mode (MLM) light can have fewer longitudinal-modes number and narrower linewidth. By inserting a FP-LD in a fiber ring laser cavity, single frequency operation can be possibly achieved when stable laser oscillation established after many roundtrips through the FP-LD. Wavelength switchable single frequency lasing can be achieved by adjusting the tunable optical filter (TOF) in the cavity to coincide with different mode of the FP-LD. By adjustment of the drive current of the FP-LD, the lasing modes would shift and wavelength tunable operation can be obtained. In experiment, a wavelength tunable range of 32.4 nm has been obtained by adjustment of the drive current of the FP-LD and a tunable filter in the ring cavity. Each wavelength has a side-mode suppression ratio (SMSR) of at least 41 dB and a linewidth of about 13 kHz.

A 1014 nm linearly polarized low noise narrow-linewidth single-frequency fiber laser

We present the demonstration of a compact linearly polarized low noise narrow-linewidth single-frequency fiber laser at 1014 nm. The compact fiber laser is based on a 5-mm-long homemade Yb(3+)-doped phosphate fiber. Over 164 mW stable continuous-wave single transverse and longitudinal mode lasing at 1014 nm has been achieved. The measured relative intensity noise is less than -135 dB/Hz at frequencies of over 2.5 MHz. The signal-to-noise ratio of the laser is larger than 70 dB, and the linewidth is less than 7 kHz, while the obtained linear polarization extinction ratio is higher than 30 dB.