Core-pumped single-frequency fiber amplifier with an output power of 158 W

Over 250 W low noise core-pumped single-frequency all-fiber amplifier

A high-power linearly-polarized all-fiber single-frequency amplifier at 1 µm based on tandem core-pumping is demonstrated by using a large-mode-area Ytterbium-doped fiber with a core diameter of 20 µm, which nicely balances the stimulated Brillouin scattering effect, thermal load, and output beam quality. A maximum output power of more than 250 W with a corresponding slope efficiency of >85% is achieved at the operating wavelength of 1064 nm without being constrained by the saturation and nonlinear effects. Meanwhile, a comparable amplification performance is realized with a lower injection signal power of the wavelength near the peak gain of the Yb-doped fiber. The polarization extinction ratio and the M² factor of the amplifier are respectively measured to be >17 dB and 1.15 under the maximal output power. In addition, by virtue of the single-mode 1018 nm pump laser, the intensity noise of the amplifier under maximal output power is measured to be comparable to that of the single-frequency seed laser at frequencies higher than 2 kHz, except for the emergence of parasitic peaks that can be eliminated by optimizing the driving electronics of the pump lasers, while the deterioration of the amplification process to the frequency noise and linewidth of the laser is negligible. To the best of our knowledge, this is the highest output power of a single-frequency all-fiber amplifier based on the core-pumping scheme.

550 W single frequency fiber amplifiers emitting at 1030 nm based on a tapered Yb-doped fiber

In this paper, we report a high power single frequency 1030 nm fiber laser with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). The T-YDF has advantages of effectively suppressing stimulated Brillouin scattering (SBS) while maintaining good beam quality. As a result, a record output power of 379 W single frequency, linearly polarized, nearly single-mode fiber amplifier operating at 1030 nm is demonstrated. The polarization extinction ratio is as high as 16.3 dB, and the M² is measured to be 1.12. Further, the dependence of the thermal-induced mode instability (TMI) threshold on the polarization state of an input signal laser is investigated for the first time. By changing the polarization state of the injected seed laser, the output power can increase to 550 W while the beam quality can be maintained well (M²=1.47). The slope efficiency of the whole amplifier is about 80%. No sign of SBS appears even at the highest output power and the further brightness scaling of both situations is limited by the TMI effect. To the best of our knowledge, this result is the highest output power of all-fiberized single frequency fiber amplifiers.

55 W kilohertz-linewidth core- and in-band-pumped linearly polarized single-frequency fiber laser at 1950 nm

Based on core- and in-band-pumped polarization-maintaining ${{\rm Tm}^{3 + }}$Tm³⁺-doped single-cladding fiber (PM-TSF, the core diameter is 9 µm) by a 1610 nm fiber laser and a distributed Bragg reflector seed laser, a linearly polarized single-frequency fiber laser (LP-SFFL) at 1950 nm with an output power of 55.3 W and a laser linewidth of 6.95 kHz is demonstrated. The output beam qualities of ${M}_x^2$Mx2 and ${ M}_y^2$My2 are measured to be 1.01 and 1.03, respectively. The slope efficiency with respect to the launched pump power is 71.0%, in comparison with a theoretical quantum efficiency of 82.6%. A polarization-extinction ratio of 19 dB and an optical signal-to-noise ratio of 58 dB are obtained from the 1950 nm LP-SFFL. To the best of our knowledge, to date, this is the highest power of 2.0 µm SFFL output directly from a strict single-mode active fiber. Our experiment offers a promising solution to the current limitations of the high-performance fiber lasers at 2.0 µm, which is particularly essential for coherent detection.

Narrow-linewidth fiber amplifier for gravitational-wave detectors

We report on the design and noise performance of a narrow-linewidth Yb-doped fiber amplifier emitting up to 178 W at 1064 nm for possible use in gravitational-wave (GW) interferometric detectors. The novel design utilizes a specialty large-mode-area gain fiber with confined-core doping and depressed cladding, followed by a smaller-core passive fiber to improve output beam quality. We show that the free-running noise of the system is equal to or better than current Advanced LIGO noise requirements. Finally, we discuss potential improvements for long-term use in GW detectors.

All-fiber, single-frequency, and single-mode Er3+:Yb3+ fiber amplifier at 1556 nm core-pumped at 1018 nm

Emerging applications, such as gravitational wave astronomy, demand single-frequency lasers with diffraction-limited emission at 1.5 μm. Fiber amplifiers have greatly evolved to fulfill these requirements. Hundreds of watts are feasible using large-mode-area and specialty fibers. However, their application in a few watts to tens of watts in monolithic systems is unnecessarily complex due to the poor commercial availability of fiber components and standard integration procedures. In this Letter we propose and experimentally demonstrate a novel and simple method to amplify single-frequency signals at 1.5 μm up to tens of watts by core-pumping single-mode Er³⁺:Yb³⁺ fiber amplifiers at 1018 nm. The proof-of-principle system is tested with different active fibers, lengths, and seed power levels. Over 11 W with an efficiency of more than 48% versus launched power is achieved. Additionally, performance degradation during operation was observed for which photodarkening due to P1 defects might be an explanation.

25 W single-frequency, low noise fiber MOPA at 1120 nm

This Letter reports on the development of a 25 W single-frequency, all-fiber master oscillator power amplifier (MOPA) operating at 1120 nm. By heating the gain fiber at 75°C, an output power of 25.3 W is achieved with an optical-to-optical efficiency of 53.5%. The output shows no sign of stimulated Brillouin scattering and the signal to amplified spontaneous emission ratio is close to 40 dB. A M² value of 1.15 and a polarization extinction ratio of 17 dB are measured. The relative intensity noise of the output is also characterized, reaching -155  dBc/Hz at 10 MHz at the maximum output power. The study of the noise dynamics highlights, for the first time to the best of our knowledge, an unpredicted behavior due to the strong backward amplified spontaneous emission.

Cascaded Kerr photon-blockade soruces and applications in quantum key distribution

To raise the repetition rate, a single-photon source based on Kerr quantum blockade in a cascaded quantum system is studied. Using the quantum trajectory method, we calculate and simulate the photon number distributions out of a two-cavity system. A high quality single-photon source can be achieved through optimizing parameters. The designed photon source is further applied to the decoy state quantum key distribution (QKD). With and without statistical fluctuation, the key rate can be both raised drastically.