We report a single-end forward-pumped fiber laser with a record high output power of 3 kW. The laser is assembled exclusively from commercially widespread components such as the Yb-doped fiber with core/cladding diameter of 20/400 µm, pump laser diodes at an emission wavelength of 915 nm, and a signal and pump fiber combiner that serves as the pump recycler. The record high power arises from the combination of the 915 nm pumping and pump recycler with an effective reflectivity of 78%, increasing simultaneously the thresholds for stimulated Raman scattering and transverse mode instability (TMI). The length of the oscillator was also varied experimentally from 20 m to 5 m, showing a contrast of up to 19% in the TMI threshold. This shows the importance of accurately partitioning the Yb-doped fiber length in between the oscillator and amplifier sections to minimize the impact of TMI.
We demonstrate the first single-mode optical fiber couplers made with ZBLAN optical fiber. Couplers are fabricated using a controlled tapering procedure enabling high reproducibility while limiting glass crystallization. A coupling ratio of up to 41%/59% in cross/through ports with an excess loss of 2.5 dB is obtained at a wavelength of 2.73 µm. In addition, the stability of a coupler with traces of surface crystallization is tested at ambient atmosphere over a period of more than 90 days.
We demonstrate chalcogenide optical fiber couplers with a power-dependent coupling coefficient. The couplers are designed and fabricated using an As2Se3 fiber and characterized at a wavelength of 1938 nm, leading to a critical power of 126 W, the lowest ever reported for any optical fiber coupler. These nonlinear couplers enable all-optical switching and will be useful for passive mode-locking over a wide wavelength range from the telecommunication band to the mid-infrared.
We report an effective pump recycler for industrial kilowatt fiber lasers. The pump recycler is a (6+1)×1 tapered fiber bundle, with signal ports of Ge-doped fiber (GDF) with core/cladding diameters of 20/400 µm and pump fiber ports (PFPs) with core/cladding diameters of 135/155 µm. By splicing PFPs in pairs, 77.9% of the residual pump light reaching the pump recycler is sent back to the cladding of the GDF. The insertion of a pump recycler increases the power conversion efficiency (PCE) of a fiber laser using an Yb-doped fiber (YDF) from 61.0% to 70.5%, with a maximum output power of 2.78 kW. The laser with a 20 m long YDF and pump recycler compares well to another laser using a 40 m long YDF without pump recycler. In both cases, the PCE is comparable but the laser with a 20 m long YDF and pump recycler benefits from reduced stimulated Raman scattering (SRS), thus enabling an 80% increase in Raman threshold. By giving access to short YDF length, the tapered fiber bundle represents an effective pump recycler since it enables reducing SRS while keeping a large PCE.
Fiber optical parametric oscillators (FOPOs) are compact optical sources of coherent and broadly tunable light compatible with operation in unconventional spectral bands. Highly nonlinear silica fibers have enabled the development of FOPOs in the telecommunication wavelength band, but the strong material absorption of silica glass at wavelengths >2â µm limits its applicability in the mid-infrared (MIR) spectral range. In this work, we overcome this issue and report a FOPO designed entirely out of soft glass fiber. For this purpose, we combine an As2Se3 single-mode fiber coupler, an As2Se3 parametric gain medium, and a low-loss ZBLAN delay fiber to build the first all-fiber laser cavity made of soft glass. Two proof-of-concept FOPOs are presented, one driven by pure parametric gain leading to wavelength-tunable Stokes emission within the range 2.088-2.139â µm, and the other driven by Raman-assisted parametric gain leading to Stokes emission within the range 2.023-2.048â µm. This demonstration is a promising first step toward the development of fully fiberized MIR light sources.
We demonstrate a thulium-doped fiber laser that is mode-locked thanks to nonlinear polarization rotation (NPR) in a chalcogenide tapered fiber. The high nonlinearity of the tapered fiber leads to a combined reduction in mode-locking threshold power and cavity length compared to any all-silica NPR based mode-locked lasers. In the continuous wave mode-locking regime, the laser generates stable, tunable solitons pulses. In the Q-switched mode-locked regime, it allows single and multiwavelength pulses, tunable central wavelength and tunable multiwavelength separation.
Emerging applications in the mid-infrared (MIR) stimulate the growth and development of novel optical light sources. Soliton self-frequency shift (SSFS) in soft glass fiber currently shows great potential as an efficient approach toward the generation of broadly tunable femtosecond pulses in the MIR. In this work, we demonstrate a highly efficient tunable soliton source based on SSFS in chalcogenide glass. We show a simple and fully fiberized system to generate these continuously tunable Raman solitons over a broad spectral range of 2.047-2.667 µm, which consumes no more than 87 pJ per pulse. The spectral measurements suggest that the generated pulses are as short as 62 fs with a maximum power conversion efficiency of 43%. This result is realized thanks to an 8 cm long As2S3 microstructure optical fiber tapered into a microwire. Thanks to their broad transparency, their high nonlinearity, and their adjustable chromatic dispersion, chalcogenide microwires are promising components for the development of compact and highly efficient MIR optical sources with low power consumption.
The polarization-maintaining performance of the traditional Panda-type polarization-maintaining fiber (PMF) coil is significantly affected by winding stress and temperature. Here, we present an elliptical core Panda-type PMF coil based on a fiber that employs both geometric and stress birefringence. The extinction ratio of the elliptical core PMF coil was found to be 20.13 dB at a temperature of 20°C, corresponding to an increase of 3.71 dB compared to the traditional Panda-type PMF coil. In addition, results from distributed polarization cross talk and gyroscope output tests also revealed a low sensitivity of the fiber to stress caused by the winding process and temperature. In summary, the proposed fiber coil has better polarization-maintaining ability compared to conventional coil and is promising for applications in high-precision optical fiber sensors.
We report the effective suppression of Raman emission in a monolithic ytterbium-doped fiber laser by the insertion of a chirped and tilted fiber Bragg grating (CTFBG) directly within the gain fiber of the laser. In comparison with a non-compensated filtered laser cavity for which the Raman threshold occurs at an output power of 1.54 kW, the insertion of a CTFBG within the gain medium leads to an increase in the Raman threshold by 260 W. We also demonstrate that the insertion of a CTFBG in between a laser cavity and a passive beam delivery fiber leads to an increase in the Raman threshold by 100 W with respect to the non-compensated case.
We demonstrate an all-fiber wavelength conversion system from the C-band to the wavelength range of 2.30-2.64 µm of the mid-infrared (MIR). A series of nonlinear processes is used to perform this spectral shift in excess of 80 THz; from optical pulses in the C-band, self-phase modulation spectral broadening and offset filtering generate probe pulses in the C- and L-band. In parallel to this, Raman-induced soliton self-frequency shift converts pulses from the C-band into pump pulses in the 2 µm wavelength band. The resulting synchronized probe and pump pulses interact via degenerate four-wave mixing to produce wavelength-converted idler pulses in the MIR. Silica fiber is used for nonlinear processes at wavelengths $ {\lt} 2\;{\unicode{x00B5}{\rm m}}$<2µm whereas chalcogenide glass is used for nonlinear processes at wavelengths $ {\ge} 2\;{\unicode{x00B5}{\rm m}}$≥2µm. This system is a major step toward the development of compact MIR optical sources generated from widespread pump lasers of the C-band.
We demonstrate the fabrication of all chalcogenide single-mode optical fiber couplers including broadband couplers, wavelength division multiplexers, and polarization beamsplitters. The functionality of each coupler is engineered with a careful design of geometry. As a result, broadband couplers can be set to any arbitrary coupling ratio. Wavelength division multiplexers provide a coupling extinction ratio up to 35 dB, and polarization beamsplitters provide a polarization extinction ratio up to 18 dB.
We demonstrate an in situ approach for the fabrication of all-fiber wavelength converters with a wavelength offset that is both far-detuned and precisely engineered. Such wavelength converters are fabricated using the parametric gain of A2Se3 microwires and finely tuned from successive adjustments of microwire diameter along with real-time monitoring. Wavelength conversion is achieved from a pump at a wavelength of 1.938 µm to any far-detuned idler within the spectral range of 2.347-2.481 µm, resulting in a detuning of 27.0-33.9 THz with a wavelength offset precision within 3.1 THz.
We present a real-time dual-comb spectrometer operated from a bidirectional mode-locked fiber laser in the wavelength range of 1.9 µm. Two pulsed signals emitted from a common cavity ensure mutual coherence and common mode noise rejection. The resulting spectrometer operates without any complex electronic feedback system.
We report, to the best of our knowledge, the first all-fiber frequency-resolved optical gating (FROG) device based on cross-phase modulation in chalcogenide glass. The amplitude and phase of pulses as short as 390 fs at femtojoule energy levels are accurately characterized without direction-of-time ambiguity in the retrieved pulse. A measurement sensitivity of 18 mW2 is achieved from the strong nonlinearity of a 10 cm long chalcogenide microwire.
We report a bidirectional mode-locked thulium-doped fiber laser. Mode-locking is enabled by the combination of semiconductor saturable absorption and nonlinear polarization rotation. Two stable mode-locked picosecond pulse trains in opposite directions are generated with a fundamental repetition rate of â¼16.57 MHz. Output wavelengths are tunable over 35 nm.
We report, to the best of our knowledge, the first all-fiber frequency-resolved optical gating device from nonlinear processing in chalcogenide glass. The strong four-wave mixing efficiency of an 11 cm long chalcogenide microwire enables a high sensitivity characterization of pulses in the 2 µm wavelength band. The amplitude and phase of chirped and unchirped picosecond pulses are accurately characterized with a high sensitivity of 0.16 mW2.
We demonstrate the operation of a Fourier transform spectrometer that operates by sweeping the pulse repetition frequency of an electro-optic frequency comb. Incorporating a length-imbalanced interferometer, this single-comb system is analogous to a conventional dual-comb system, but with a greatly simplified design. The functionality of the spectrometer is demonstrated via the high-resolution spectrum measurement of an H13C14N reference gas cell.
We demonstrate an optical comb source that generates 550 ultra-narrow spectral lines with a spectral linewidth of 1.5-3 kHz, spanning over the C-band. The source originates from a single-mode Brillouin laser processed with phase modulation, pulse compression, and four-wave mixing. As a result, the narrow linewidth of the Brillouin laser improves the phase noise of every spectral line of the frequency comb.
We demonstrate all-fiber far-detuned and widely tunable mid-infrared wavelength conversion using As2Se3 microwires. In a first experiment, an idler is generated and tuned from 2.351 to >2.500 µm from four-wave mixing in a 0.5 cm long microwire. In a second experiment, tunable parametric sidebands are generated via modulation instability in a 10 cm long microwire. The resulting parametric frequency conversion reaches up to 49.3 THz, the largest ever reported in soft glass materials.
Dual-band fiber lasers are emerging as a promising technology to penetrate new industrial and medical applications from their dual-band properties, in addition to providing compactness and environmental robustness from the waveguide structure. Here, we demonstrate the use of a common graphene saturable absorber and a single gain medium (Tm3+:ZBLAN fiber) to implement (1) a dual-band fiber ring laser with synchronized Q-switched pulses at wavelengths of 1480 nm and 1840 nm, and (2) a dual-band fiber linear laser with synchronized mode-locked pulses at wavelengths of 1480 nm and 1845 nm. Q-switched operation at 1480 nm and 1840 nm is achieved with a synchronized repetition rate from 20 kHz to 40.5 kHz. For synchronous mode-locked operation, pulses with full-width at half maximum durations of 610 fs and 1.68 ps at wavelengths of 1480 nm and 1845 nm, respectively, are obtained at a repetition rate of 12.3 MHz. These dual-band pulsed sources with an ultra-broadband wavelength separation of ~360 nm will add new capabilities in applications including optical sensing, spectroscopy, and communications.
