In this paper, we demonstrate high peak power mid-infrared tunable Raman soliton generation in a large-core diameter short-length fluorotellurite fiber. The pump source uses a tunable Raman soliton generated in a large mode area (LMA) silica fiber with a narrowest pulsewidth of 78 fs, a pulse energy of up to 104 nJ, and a peak power of up to 1.3 MW. Subsequently, a Raman soliton at 3.7 μm was obtained using this Raman soliton pulse as a pump source to further pump a 25 μm core diameter fluorotelluride fiber. The peak power of the Raman soliton in the mid-infrared was tested to be about 0.52 MW, with a pulse energy of 40 nJ and a pulsewidth of about 77 fs. These output parameters validate the great potential of fluorotellurite fibers as a nonlinear frequency-shifting medium for obtaining ultrashort pulses in the mid-infrared region
An all-fiber polarization maintaining laser system of wavelength tunable from 1.76 to 1.84 μm based on the Raman-induced soliton self-frequency shift in an erbium-doped amplifier is demonstrated. The system only includes oscillator and two-stage amplifiers which are built entirely based on commercial silica fibers and devices. The ultra-short pulse achieved by oscillator and first amplifier stage by the method of nonlinear compression is delivered into second amplifier stage which is designed as both Raman shifter and amplifier. Within the pump power range of 16-25 W, tunable Raman soliton can be obtained with the average power gradually increases from ~180 mW to ~250 mW as the center wavelength of the soliton shifts towards the longer wavelength direction within the range of 1.76 to 1.84 μm. The system delivers Raman soliton from an entirely fiberized, fusion spliced system without any free-space optics, which can provide robust and stable soliton generation. To our knowledge, this tunable soliton source is the highest output power demonstrated within 1.7-1.8 μm wavelength range from an all-fiber polarization maintaining laser. Our experiment provides a feasible femtosecond source for multiphoton microscopy.
KEYWORDS: Microwave radiation, Frequency combs, Four wave mixing, Fiber lasers, Signal to noise ratio, Optical filters, Signal generators, Nonlinear filtering
In this work, a multiband microwave waveforms transmitting system was demonstrated based on all-optical dual fiber combs. Two optical fiber frequency combs via cascaded four waves mixing process ensure the coherence of the system by sharing the pump light. The high-speed frequency tuning of the pump laser will be transferred to each newly generated comb line through the nonlinear effect in the fiber. The comb pairs of the same order obtained through filtering transform the frequency chirp in the optical domain to the frequency chirp in the electrical domain after being beat on the PD. By changing the parameters of the control signal, the center frequency, bandwidth, PRF and envelope of the multi band microwave signal can be flexibly reconfigurable. Thanks to the coherence of dual optical frequency combs, microwave signals all show excellent line-type, high signal to noise ratio and no burrs. As a result, the chirped microwave signals of triangle wave, sine wave and sawtooth wave types are obtained at the repetition rate of 500 Hz. Overall, multi-band chirped microwave generation system based on all-optical system provides a practical device for transmitting and receiving multi band radar.
KEYWORDS: Microwave radiation, Fiber lasers, Radio optics, Optical filters, Frequency combs, Signal to noise ratio, Signal generators, Optical coherence, Microwave photonics
A scheme for the photonic generation of Multi-band Reconfigurable Microwave Waveforms (MRMWs) is proposed and demonstrated based on dual-correlated chirped fiber combs. In the proposed system, the output of master laser is split into two paths, and then respectively coupled with another a single-frequency fiber laser and amplified for the generation of dual combs, which also acts as the reference frequency. During various formats wavelength sweeping operation, one of the single-frequency lasers can flexibly manipulate the repetition-rate difference of the dual-comb. Meanwhile, the chirp from a pump laser is transferred to all spectral comb teeth through the intra-cavity cascaded four-wave mixing process at once. After optical filtering, by beating the paired comb lines of the same order at a high-speed photodetector (PD), the bandwidth, central frequency and repetition rate of the chirped microwave waveforms are obtained. This system has a compact structure without electro-optical modulators and takes into account mutual coherence.
In this work, a high-power all-fiber mid-infrared (MIR) supercontinuum (SC) laser source was generated in a short piece of centimeter level germania-doped fiber (GDF). The MIR SC generation in GDF was pumped by a 2 μm chirped pulse amplification (CPA) system. The seed source was a passively mode-locked oscillator by semiconductor saturable absorber mirror (SESAM) with a pulse width of 29.7 ps, a spectrum width of 0.3 nm and a fundamental repetition rate of 44.31 MHz. A high-power pump source with a spectral coverage of 1.9~2.2 μm was obtained in thulium-doped fiber amplifier (TDFA). Adopted by 19 cm-long 64 mol. % GDF, we obtained a broadband SC source spanning from 1850 to 3000 nm. The generated SC had a maximum output power of 31.2W with a pump slope efficiency from 56.2% to 30.9%. By optimizing fusion-spliced parameters, a high optical coupling efficiency was obtained between single-mode fiber (SMF) and GDF. In addition, we measured the pulse characteristics of SC laser source in different peak power of pumping source and different length of GDF. It paved the way for further realization of high power and wide spectrum MIR SC laser source.
All-polarization-maintaining (PM) fiber oscillator based on nonlinear amplifying loop mirror (NALM) modelocking has important applications for chirped pulse amplification systems. In this paper, we report an all-PM-fiberintegrated femtosecond chirped pulse amplification (CPA) system operating at 1030 nm, which consists of a NALM oscillator, an ytterbium-doped amplifier and a chirped volume Bragg grating (CVBG) compressor. The laser produces linearly polarized, linearly chirped pulses that can be recompressed down to 711 fs, corresponding to 95% compression efficiency. All-PM NALM fiber oscillator combined with CVBG compressor is a promising method for CPA system due to its extremely compact and robust architecture.
In this letter, we report a high-power all-fiber mid-infrared (MIR) supercontinuum (SC) laser source based on a short piece of centimeter level germania-core fiber (GCF). The pump source at the wavelength of 2 μm was directly generated from a single-mode fiber laser. The all-fiber seed oscillator was passively mode-locked by a SESAM to generate pulse duration of 62 ps at a fundamental repetition rate of 44.31 MHz in a linear cavity. After all-fiber thulium-doped fiber amplifier (TDFA), we obtained a high-power pump source with a spectral coverage of 1.9~2.2 μm. We only use 12 cm long 94 mol. % GCF for spectral broadening pumped by TDFA. In addition, we measured the spectral broadening after 12 cm GCF in different length of dispersion compensation fibers (DCF) corresponding to different pulse width and peak power. As a result, we obtained a broadband SC source based on 12 cm 94 mol. % GCF extending from 1630 to 3205 nm and a maximum output average power of 15.07 W with a slope efficiency of 34.2%. The 20 dB spectral bandwidth was over 1000 nm spanning from 1.89 to 2.92 μm. To the best of our knowledge, this is the first demonstration of 15-W level SC laser based on germania-core fiber with long wavelength edge extending beyond 3.2μm. Further broadening of spectrum is limited to pump power.
In this paper, the physical model of the coherent polarization beam combination (CPBC) system is established by using Jones-matrix mathematics, and then the coherent-adding mechanisms between the sub-beams in temporal, spatial and spectral domains are analyzed. The intrinsic relationship between optical-field coherence decay and beam misalignment is established from temporal domain (optical-path deviation, phase-locking residual), spatial domain (beam-pointing deviation, spot-overlapping deviation, spot-width error) and spectral domain (B-integral imbalance, dispersion imbalance, central-wavelength drift, spectrum-width error) respectively. Furthermore, the dependence between the combining efficiency and the individual experimentally-measurable misalignment is quantified using numerical simulation, and the error tolerance of the each factor is calibrated separately for efficient combination, which provides quantitative guidance for the practical system. The results of this paper can be applied to the analysis of cascade extended array CPBC system after proper mathematical extension. In addition, this study also provides a feasible quantitative analysis method for the degradation of optical-field coherence between coherent beams, which can be applied to other research fields that require optical coherence management.
In this paper, we report a simpler and efficient hybrid laser amplification system, which delivers a single pulse energy of 20 mJ at 500 Hz with a pulse width of 278 ps. This hybrid amplification system mainly consists of a hundred-picosecond all-fiber structure seeder, a regenerative amplifier and a single-pass amplifier. The hundred-picosecond laser pulse from the fiber seed is first amplified to 4 mJ by a regeneration amplifier with a normally doped Nd:YAG rod. For the improvement of the laser energy, the QCW side-pumped Nd:YAG single-pass amplifier has been adopted at the second stage of solid-state amplifiers. To reduce the serious thermal effect, the bonded composite YAG-Nd:YAG-YAG rod crystal is used as the gain medium, which possesses 6 mm in diameter and 85 mm in effective pumped length, and a doping concentration of 0.8%. Finally, 20 mJ output energy and 278 ps pulse duration are obtained with a peak power of 72 MW, and its beam quality factor is 1.7. In addition, this laser amplifier is confirmed by latter theoretical simulations of laser-induced plasma in silicon-based photodiode. The high-energy amplification of the hundred-picosecond pulse is realized in this hybrid amplifier system, which will be used as laser irradiation source in laser-induced damage application.
The imaging systems are widespread observation tools used in the national defense, industry and a number of aspects in science and technology. The CMOS image sensors which serve as the core part of optical imaging systems and detecting systems, are highly susceptible to laser interference and destruction. Therefore, it is of great theoretical and practical significance to study the damage characteristics of CMOS image sensor. There are many researches on the damage phenomena of CMOS image sensors irradiated by continuous laser, ns-laser, ms-laser and fs-laser, but the damage effects of CMOS irradiated by the hundred picoseconds fiber laser are few investigated. In this work, we used an all-fiber MOPA ps-pulsed laser system which generates pulse width of 226.5 ps and average power of 20 W with high beam quality and pulse stability to irradiate the CMOS at repetition rate of 9.6 MHz and 2.4 MHz. The experimental results showed that with the increase of laser power density, the phenomena of over saturation effect, saturated crosstalk effect, black line damage and black lines semi-cross damage appeared at different repetition rates. And the measured threshold and damage mechanism of CMOS were studied. Besides, based on the hydrodynamics theory, the laser-induced plasma density and temperature distribution of various materials (aluminum, copper and silicon) irradiated by the ps-laser were simulated, which provide a theoretical basis for the interaction of metals and semiconductors by the hundred picoseconds fiber laser
We report a high-power 10 ps level ultrashort pulsed polarization maintaining (PM) supercontinuum source (SCS) fiber amplifier based on a typical Master Oscillator Pulse Amplification (MOPA) configuration. At the pulse width of 12.1 ps, an average output power of 35.45 W is achieved with the single pulse energy of 2.2 μJ. The output wide spectrum ranging from 1020 nm to 1700 nm has been obtained directly from the Yb-doped fiber amplification (YDFA). But the nonlinear effects in this amplification system are too strong to enhance the average power due to the high peak power of 184 kW. Thus an improved high-power picosecond pulsed PM fiber amplifier is achieved based on a chirped pulse amplification (CPA) configuration. The pulse width is stretched to hundred picosecond scale to reduce the high nonlinear effects and the high peak power by a PM single mode fiber (SMF) stretcher. Only 0.9 m-long PM highly Yb-doped fiber is used in the main-stage amplifier. High average output power of 100.8 W is achieved with repetition rate of 16.68 MHz and pulse width of 280 ps. The central wavelength of the output laser is 1064 nm with 3 dB bandwidth of 2.32 nm. The peak power is 21.58 kW and the single pulse energy is 6.04 μJ, respectively. In addition, the pulse trains are stable without serious distortion and pulse splitting which ensure that the high power PM pulse laser can be used in both fundamental research and industrial fields.
Through simulation calculations and experiments, the two popular methods of generating nanosecond (ns) pulsed laser were studied respectively. A new method for generating a ns pulsed laser with high power and ultra-high repetition frequency by using dispersive fiber after SESAM mode-locked oscillator was proposed. In the simulation calculation of the mode-locked ns pulsed laser, the time-frequency evolution characteristics of the laser formation process were analyzed. The variation process of the stimulated Raman scattering (SRS) effect was obtained at different injection powers. In the simulation calculation of the extracavity modulation ns pulsed laser, the threshold of the stimulated Brillouin scattering (SBS) effect was obtained in the 4-stage fiber amplification experiment. Then, the nonlinear dynamics model of the ns pulsed fiber laser was established by considering various nonlinear effects. The results showed the theoretical models were consistent with the experimental investigations. This provided a new way to further optimize the parameter of ns pulsed fiber lasers and also contribute to solve nonlinear damage problems in such lasers.
We report on a nanosecond all-fiber MOPA with ultra-high repetition rate (tens of MHz), which is seeded by a semiconductor saturable absorber mirror (SESAM) mode-locking fiber oscillator at 1064 nm. Ultra-high repetition rate of tens of MHz is realized by reducing fiber length in laser cavity. By using single-mode fiber stretcher with total length of 16 km, pulse width of mode locking laser pulse can be broadened from 28 ps to 1~7 ns. The maximum average power is achieved to be 54 W with pulse duration of 1.3 ns and repetition rate of 27.7 MHz. To the best of our knowledge, this is the first demonstration on an ultra-high repetition-rate (tens of MHz) nanosecond all-fiber MOPA based on a SESAM passively mode-locking fiber oscillator.
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