An important aspect of coherent optical satellite communication technology is the power consumption of the employed laser systems. Therefore, an enhanced wall-plug efficiency of the optical amplifiers is required. We present the prototype design (technology readiness level 4, TRL) and optical characterization of a 10-channel amplifier system for the use in WDM optical communication infrastructures operating at 1 μm wavelength. Combining the experience of in-house manufactured fiber components and laser systems, an all-fiber amplifier solution was designed to realize an overall wall-plug efficiency of around 30%. All ten input channels were simultaneously amplified up to a combined power of 100W.
We present the development of a fiber-based high-efficiency laser amplifier (HELA) as a demonstrator for future high throughput satellite communication systems operating in the 1µm wavelength range. The work is conducted in the context of ESA’s ARTES ScyLight framework programme (SeCure and Laser Communication Technology) and more specifically within its HydRON project. Combining the experiences of in-house manufactured optical fiber components and of laser developments for space applications, an all-fiber amplifier solution was designed. The realized laboratory testbed simultaneously amplifies a 10-channel seed input from the mW-level up to a total output power of 100W. Leveraging the benefits of advanced fiber technology, an enhanced wall-plug efficiency of about 29% has been achieved.
The power consumption of the laser systems is an important aspect of optical satellite communication technology. We present an optical amplifier for a WDM optical communication system with a simultaneous multichannel amplification in a single fiber in the 1 μm wavelength range. The desired enhanced wall-plug efficiency of ∼30% can only be achieved through fiber technology. Combining the experiences of in-house manufactured optical fiber components and of laser developments for space applications, an all-fiber amplifier solution was designed. Each of the 10 channels can be efficiently amplified up to a total power level of 100W.
Specialty fibers such as chirally-coupled-core fibers (3C®-fiber) show a high potential for further power scaling of single-frequency fiber amplifiers. Especially, the application of gravitational wave detectors requires a high optical output power at low noise characteristics. The output power of fiber-based single-frequency amplifiers is typically limited by nonlinear effects (e.g. stimulated Brillouin scattering). In general, to reduce the impact of nonlinearities, the mode area of the fiber core is enlarged and 3C®-fibers have been specifically designed to enable single-mode operation with a large mode area core. This fiber type consists of a step-index fiber structure, whose signal core is additionally chirally surrounded by one or more satellite cores. Because of the phase matching and the helical geometry, the higher order modes are pulled out of the signal core, which allows a high-purity modal content in the core. The development of compact all-fiber lasers in conjunction with specialty fibers combines the advantages of both techniques. For the first time, we demonstrate a spliceless all-fiber amplifier, where all optical components are directly integrated in a single Yb3+-doped 3C®-fiber. Such a spliceless laser design allows a compact and robust architecture using specialty fibers, while maintaining excellent beam properties. At an output power of 336 W, a fundamental mode content of 90.4% was demonstrated. This work emphasizes the suitability of 3C®-fibers in high-power laser and amplifier systems and the potential as laser sources for the next generation of gravitational wave detectors.
We present the development of an all-fiber side-fused signal-pump-combiner based on an integrated 3C R feedthrough fiber. This specialty fiber uses a 34 μm single-mode core and shows great potential to enable further output power scaling while maintaining high beam quality. The side-fusing technique has the advantage of an uninterrupted signal core and can be used in co- and counter-pumped fiber lasers and amplifiers. The signal-pump-combiner was operated up to an input power of 600W from four pump fibers and coupling efficiencies of 79% were achieved. The component was additionally investigated by computer tomography imaging, which revealed that the cladding structure of this specialty fiber prevented the required level of glass fusion of the 3C R fiber with the pump fibers. The investigation will help to further increase the pump coupling efficiency of the signal-pump-combiners. This represents the first step of developing all-fiber and high power capable laser systems based on the 3C R fiber.
The output power of fiber-based single-frequency amplifiers, e.g. for gravitational wave detectors, is typically limited by nonlinear effects (e.g. stimulated Brillouin scattering). In addition to a high output power, long-term stable and less complex laser systems are required. It has been shown that all-fiber amplifier systems can be a suitable option to avoid power scaling problems of single-frequency solid-state lasers with injection locking. Chirally-coupled-core (3C®) fibers have been specifically designed to enable single-mode operation with a large mode area core to overcome these limitations. 3C®-fibers consist of a step-index fiber structure, whose signal core is additionally chirally surrounded by one or more satellite cores. For this purpose, the all-solid design of 3C®-fibers allows a manufacturing process of fiber-based components. We present various optical components based on 3C®-fibers for the realization of a single-frequency all-fiber amplifier. These amplifiers typically consist of a mode field adapter (MFA), cladding light stripper (CLS) and pump combiner (PC) to minimize the excitation of higher order modes, remove residual pump light and optimize the coupling efficiency of the pump light in the 3C®-fibers. The components have been specifically designed for the first time with 3C®-fibers and tested according to their performance. As a first prototype, a robust and monolithic fiber amplifier with an ytterbiumdoped 3C®-fiber in combination with commercially available standard fibers was developed. Overall, the fiber amplifier achieves an optical output power of 165W in a linearly polarized TEM00-mode. This work emphasizes the high potential of amplifiers based on 3C®-fibers as laser sources for the next generation of gravitational wave detectors and demonstrates that compact and robust amplifiers can be realized using 3C®-fibers.
The output power of fiber-based single-frequency amplifiers, e.g. for gravitational wave detectors, is typically limited by nonlinear effects (e.g. stimulated Brillouin scattering). In general, to reduce the impact of nonlinearities, the mode area of the fiber core is enlarged. Chirally-coupled-core (3C®) fibers have been specifically designed to enable single-mode operation with a large mode area core. 3C®-fibers consist of a step-index fiber structure, whose signal core is additionally chirally surrounded by one ore more satellite cores. Because of the phase matching and the helical geometry, the higher order modes are pulled out of the signal core, which enables a high-purity modal content in the core. We present a robust and monolithic fiber amplifier based on an ytterbium-doped 3C®-fiber in combination with commercially available standard fibers. For the realization of such a monolithic system, a mode field adapter (MFA) was designed and installed between a standard polarization-maintaining fiber and an active 3C®-fiber for the first time. The MFA was tested regarding the guided modal content by means of a S2-system. Overall, the fiber amplifier achieves a polarization extinction ratio of 17.6 dB and an optical output power of 100.1W in a linearly polarized TEM00-mode. To our knowledge, the fundamental mode content of 98.9% is the highest TEM00-mode content of fiber amplifiers reported at this power level. This work emphasizes the high potential of fiber amplifiers based on 3C®-fibers as laser sources for the next generation of gravitational wave detectors and demonstrates that compact and robust amplifiers can be realized using 3C®-fibers.
Fiber-based single-frequency amplifiers, e.g. for gravitational wave detectors, are typically limited by the nonlinear effect of the stimulated Brillouin scattering (SBS). In addition to a decreasing output power level, SBS also initiates a broadband intensity noise in a frequency regime up to several MHz. Several published theories provide models to explain this excess intensity noise. Here, we report new theoretical and experimental studies, which suggest the conversion from phase to intensity noise by an asymmetric Brillouin gain spectrum.
Due to the asymmetric Brillouin gain profile, upper and lower frequency sidebands experience a frequency-dependent gain-factor and a differential non-zero phase shift. Thus, the sidebands do not cancel each other out and the differential non-zero phase shifts provides an additional contribution to the intensity noise. Using a measured asymmetric Brillouin gain spectrum and the 1/f-frequency noise characteristics of the pump source, we are able to reconstruct the shape of the excess intensity noise fairly well.
In addition, further evidence for an asymmetric SBS gain profile has been observed. Due to small back reflections at the fiber end faces corresponding resonances are evident in the intensity noise spectrum. Through the asymmetry of the SBS gain profile and the differential non-zero phase shift, the conditions for the resonator eigenfrequencies are influenced. Therefore, the beat frequency between the upper and lower eigenfrequencies with the carrier are not equal anymore, which becomes noticeable in a splitting of resonances in the intensity noise spectrum.
Single-frequency Yb3+ and Er3+:Yb3+ fiber amplifiers (YDFA/EYDFA) in MOPA configuration operating at 1064 nm and around 1550 nm are promising candidates to fulfill the challenging requirements on laser sources for the next generation of interferometric gravitational wave detectors (GWDs). They offer high beam quality, long-term stability and allow for excellent thermal management. We developed an engineering fiber amplifier prototype at 1064 nm emitting around 200W of linearly-polarized light in the TEM00 mode. The system consists of three modules: the seed source, the pre-amplifier and the main amplifier. The modular design ensures reliable long-term operation, decreases system complexity and simplifies maintenance procedures and repair. In addition, commercial available fibers increase the flexibility of the entire system. We also developed and characterized a fiber amplifier prototype at 1556 nm that emits 100W of linearly-polarized light in the TEM00 mode. The EYDFA is pumped off-resonantly at 940 nm to enhance the Yb3+-to-Er3+ energy transfer efficiency and enable a higher amplified spontaneous emission (ASE) threshold. In addition to that, we performed measurements to study phase to intensity noise coupling via the Kramers-Kronig relation above the stimulated Brillouin scattering (SBS) threshold, as it was proposed based on numerical simulations. This effect is based on an asymmetric gain spectrum, which we measured experimentally and used for the reconstruction of the broadband excess intensity noise.
Single-frequency fiber amplifiers in MOPA configuration operating at 1064 nm (Yb3+) and around 1550 nm (Er3+ or Er3+:Yb3+) are promising candidates to fulfill the challenging requirements of laser sources of the next generation of interferometric gravitational wave detectors (GWDs). Most probably, the next generation of GWDs is going to operate not only at 1064 nm but also at 1550 nm to cover a broader range of frequencies in which gravitational waves are detectable. We developed an engineering fiber amplifier prototype at 1064 nm emitting 215 W of linearly-polarized light in the TEM00 mode. The system consists of three modules: the seed source, the pre-amplifier, and the main amplifier. The modular design ensures reliable long-term operation, decreases system complexity and simplifies repairing and maintenance procedures. It also allows for the future integration of upgraded fiber amplifier systems without excessive downtimes. We also developed and characterized a fiber amplifier prototype at around 1550 nm that emits 100 W of linearly-polarized light in the TEM00 mode. This prototype uses an Er3+:Yb3+ codoped fiber that is pumped off-resonant at 940 nm. The off-resonant pumping scheme improves the Yb3+-to-Er3+ energy transfer and prevents excessive generation of Yb3+-ASE.
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