Double-pass Amplifier Research Articles

Depolarization compensation with a spatially variable wave plate in a 116 W, 441 fs, 1 MHz Yb:YAG double-pass laser amplifier.

A subpicosecond laser system featuring a fiber chirped pulse amplification-based seed laser and a double-pass end-pumped Yb:YAG crystal power amplifier was investigated. The key novelty of the system was the application of depolarization compensation using a specially designed spatially variable wave plate. To the best of our knowledge, this method was applied for the first time. The presented laser system produced pulses of 441 fs duration, 116 µJ pulse energy at 116 W average power with a beam quality of M2∼2.1, featured optical-to-optical efficiency of 32% at room temperature (T=20∘C), and had residual depolarization level of 2.7%.

1 kHz, 430 mJ, sub-nanosecond MOPA laser system.

We demonstrate a sub-nanosecond MOPA system with a pulse repetition frequency of 1 kHz at 1.06 µm, based on an integrated seed source with pulse energy of 6.2 mJ and two conductively cooled end-pumped Nd:YAG slab gain modules. After a 4-pass amplification stage and a double-pass amplification stage with amplification factors of 12.6 dB and 5.84 dB, respectively, maximum pulse energy of 434 mJ with pulse duration of 691 ps was obtained, corresponding to a peak power of 628 MW. Via adjusting the pump distribution to compensate the static wavefront distortion of the signal laser, the beam quality, at the maximum pulse energy, was optimized to be 2.5 mm·mrad and 2.2 mm·mrad respectively in the vertical and transverse directions. The results benefit a variety of applications including material processing, nonlinear frequency conversion, and lidars.

Double-pass pre-chirp managed amplification with high gain and high average power.

We demonstrate, to the best of our knowledge, the first double-pass pre-chirp managed fiber amplifier. The double-pass fiber amplifier exhibits high gain allowing us to amplify chirped picosecond pulses from 20 mW to 113 W in a rod-type Yb-fiber corresponding to 38 dB gain. We study the dependence of static mode degradation (SMD) on the nonlinear phase shift (NPS) accumulated by the amplified pulse. Our results indicate that a larger nonlinear phase shift results in stronger nonlinear polarization evolution of the fundamental mode and leads to a lower threshold for SMD. After optimization, our pre-chirp managed amplifier seeded by 80 mW pulses delivers 102 W amplified power from the main output. The amplified pulses are compressed to 37 (55) fs with 90 (100) W average power by a grating pair (chirped mirrors). The double-pass configuration significantly simplifies the implementation of pre-chirp managed fiber amplifiers leading to an extremely compact system.

Dual-wavelength mode-locked Er-doped fiber laser in a spectral filter free cavity

We present the experimental investigation of a dual-wavelength passively mode-locked Er-doped fiber laser with strict polarization control. The configuration includes a double-pass amplifier with a Faraday mirror and twisted fiber. We observe that including double-twist fiber cancels circular and linear birefringence and allows obtaining dual-wavelength emission varying the losses in the cavity. In contrast, results including single-twist fiber which only emits single-wavelength due to large circular birefringence.

Performance analysis on double-pass thulium-doped fiber amplifier for 16-channel WDM system at S-band

Abstract In this paper, the performance of single and double-pass thulium-doped fiber amplifiers (SD-TDFA and DP-TDFA) is analyzed in the short wavelength (S-band) region. The effect of thulium-doped fiber (TDF) length, input signal power, and input pumping power on the amplifier’s performance is comprehensively investigated on basis of gain and noise figure (NF). DP-TDFA showed a higher gain compared to single-pass configuration and that is due to double-propagation of the forwarded and amplified spontaneous emission (ASE) signal into the TDF which maximizes the achievable gain in the S-band region. At a gain medium length of 8 m, the proposed DP-TDFA showed higher gain enhancement over SP-TDFA at an input power of −20 dB compared to −40 and 0 dB input signal powers. The gain enhancement at 1470 nm is 5.6 dB, while the maximum recorded gain with the proposed double-pass configuration is 14.7 dB.

High-energy, high-repetition-rate ultraviolet pulses from an efficiency-enhanced, frequency-tripled laser

Abstract In this study, a high-energy, temporally shaped picosecond ultraviolet (UV) laser running at 100 Hz is demonstrated, with its pulses boosted to 120 mJ by cascaded regenerative and double-pass amplifiers, resulting in a gain of more than 108. With precise manipulation and optimization, the amplified laser pulses were flat-top in the temporal and spatial domains to maintain high filling factors, which significantly improved the conversion efficiency of the subsequent third harmonic generation (THG). Finally, 91 mJ, 470 ps pulses were obtained at 355 nm, corresponding to a conversion efficiency as high as 76%, which, as far as we are aware of, is the highest THG efficiency for a high-repetition-rate picosecond laser. In addition, the energy stability of the UV laser is better than 1.07% (root mean square), which makes this laser an attractive source for a variety of fields including laser conditioning and micro-fabrication.

Performance Analysis on Single- and Double-Pass Ytterbium-Doped Fiber Amplifier in the 1 µm Region

ABSTRACT In this work, single- and double-pass configurations of ytterbium-doped optical fiber amplifiers (YDFAs) have been investigated. This low quantum defect rare-earth dopant and their performance near 1 µm region has been comprehensively investigated on the basis of gain and noise figure in relation with input signal power and input pump power. The obtained results showed that at an input pump power of 100 mW, the gain was proportionally increased with ytterbium-doped fiber (YDF) length for both proposed configurations, but double-pass regime scored higher gain. This is due to the double-propagation of the forwarded and amplified spontaneous emission (ASE) signal into the active medium and hence will maximize the attainable gain near the 1 µm wavelength region. At YDF length of 5 m, the double-pass technique showed better amplification performance at a lower input signal power of −20 dB compared to the higher input signal power of 0 dB. The maximum gain and optical signal-to-noise ratio (OSNR) attained by double-pass configuration were 24.6 dB and 53.4 dB, respectively. Double-pass amplification at input signal power of −20 dB has increased the gain by 11.2 dB in comparison with the single-pass technique.

High-Brightness 100 Hz/363 mJ Picosecond Nd:YAG Laser System for Ultra-Remote Laser Ranging

A high pulse energy and high beam quality Nd:YAG laser system with extremely high brightness of 105 PW/sr·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is reported. The system is based on a master oscillator power amplifier scheme containing a Nd:YVO4 mode-locked oscillator, laser diode end-pumped Nd:YAG regenerative amplifier, Ø6.35-mm double-pass amplifier, and two Ø15-mm double-pass amplifiers. Laser pulses with energy of 363 mJ and pulse duration of 63 ps were obtained at a repetition rate of 100 Hz, corresponding to a peak power of ~5.76 GW. A near-Gaussian beam with M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <; 2.2 and a narrow bandwidth with 0.17 nm were achieved, which make this laser system an attractive light source for ultra-remote laser ranging.

Gain-control technique in double-pass parallel hybrid fiber amplifier

In this paper, the effect of gain control technique in double pass parallel hybrid fiber amplifier in terms of gain level as well as pump powers optimization are simulated using Optisystem and experimentally validated. An average gain level of 22.8 dB and overall gain variation of 3 dB within C and L band regions are achieved. The gain flatness bandwidth of 60 nm from 1530 to 1590 nm are obtained. A comparison with a single pass parallel hybrid fiber amplifier is presented. This comparison showed an average gain level of 38.5% higher than single pass-structure utilizing only 650 mW of Raman pump which is 18.7% lower.

Double pass remotely pumped L-band EDFA with the integration of Raman amplification using multiwavelength dispersion compensator

We demonstrate a remotely pumped L-band erbium-doped fiber amplifier for long-haul transmission system that consists of a multiwavelength dispersion compensator. In this proposed amplifier, the L-band signals experience double pass amplification using the multiwavelength dispersion compensator as signal reflector. In addition, the distributed Raman amplification helps to improve the gain flatness of the propagated signals that is pumped by a 1497 nm fiber laser. High average transmission gain of 20.64 dB with low gain flatness of 2.64 dB is attained when the input signal power is at 0 dB m with wavelength ranging from 1570.45 to 1604.92 nm. The proposed amplifier structure offers better transmission gain flatness for multiwavelength systems.

High gain in a dual-pass rod-type fiber amplifier

Single-pass amplification using rod-type fibers has become a common route to pulsed laser sources around 1030 nm with high average and peak power. Average-power scaling is currently limited by the dynamic thermo-optic phenomenon of “transverse mode instability.” In comparison, double-pass amplifier configurations have not been extensively studied. Recent theoretical and experimental work has shown both static and dynamic mode degradation phenomena, including an unexpected nonlinear polarization rotation effect. Here we present new results obtained with a modified setup using polarization filtering between the first and the second pass. We obtain up to 113 W output power, i.e., more than 40 dB of amplification from a single amplifier module seeded by 10 mW of 20 ps/20 MHz/1030 nm pulses. We observe excellent beam quality and polarization extinction ratio. Finally, we investigate a wide range of seed powers and report a strong increase in the static mode deformation threshold with decreasing seed power. The experimental results are corroborated by numerical simulations.

Half-open-cavity multiwavelength Brillouin-erbium random fiber laser with improved performance

Half-open-cavity multiwavelength Brillouin-erbium random fiber lasers (RFLs) with improved performance in terms of the generated Stokes order number and wavelength tuning range have been proposed and demonstrated. Our contrastive experiments reveal that the position of the used erbium-doped fiber (EDF) gain is crucial for the performance improvement of the Brillouin-erbium RFLs with half-open-cavity configuration. When the EDF is incorporated in the double-pass port of the circulator used, eighteen Stokes orders have been generated, which demonstrates the highest order obtained from Brillouin-erbium RFLs to the best of our knowledge. The Brillouin order enhancement is attributed to the sufficient gain for the randomly reflected Stokes wavelengths with the double-pass amplification. The broadest wavelength tunability of 54 nm is achieved in the case with the EDF located at the port 1 of the circulator, owing to its strongest suppression ability for self-lasing cavity modes. The significant performance upgrade that is obtained with these RFLs, whilst maintaining a simple structure, gives rise to promising potential applications in optical communications, microwave photonics, precision metrology and fiber-optic sensing.

Laser with 1.2 ps, 20 mJ pulses at 100 Hz based on CPA with a low doping level Yb:YAG rods for seeding and pumping of OPCPA

We report on a picosecond two-stage double-pass chirped pulse amplifier based on a low doping level Yb:YAG rods. After compression, it provides output pulses with a pulsewidth of 1.15 ps and an energy of more than 20 mJ at a repetition rate of 100 Hz with a beam quality of M2 ∼1.05. These pulses were frequency doubled in a two-cascaded second harmonic converter based on LBO and BBO crystals with an output energy of 12 mJ and 5 mJ at 515 nm, suitable for simultaneously pumping OPCPA cascades.

30 mJ, 1 kHz sub-nanosecond burst-mode Nd:YAG laser MOPA system.

We demonstrated a sub-nanosecond burst-mode MOPA Nd:YAG laser at 1.06 µm that consists of a cavity-dumped Q-switched master oscillator and a double-pass side-pumped amplification system. During the 1 kHz burst-mode operation, outputs with the single pulse energy of 29.8 mJ were obtained within the burst duration of 100 ms. The pulse width was 900 ps, which resulted in a peak power of 33.1 MW. During the 10 Hz operation, the single pulse energy reached 81 mJ with a pulse width of 900 ps, which resulted in a peak power of 90 MW.

Double-pass amplification of picosecond pulses with a tapered semiconductor amplifier.

Double-pass amplification of picosecond pulses is demonstrated and compared with single-pass amplification. This was achieved using a two-section tapered semiconductor optical amplifier with a chirped quantum-dot active region and a mode-locked laser diode as a seed. Across the range of biasing conditions common to both configurations, an enhancement in signal gain of up to 7 dB and output power by a factor of 4.1 was seen in the double-pass amplifier, compared to the single-pass. Only marginal increases in pulse duration were observed in the double-pass regime compared to the single-pass amplifier, meaning that enhancements in output power were well translated into peak power. Furthermore, the two-section contact layout of the SOA allowed the pulse duration to be optimised for a given fixed output power, giving additional flexibility to the amplifier. These results demonstrate the suitability of this simple and versatile technique, which could become the new standard in amplification of ultrashort pulses.

Improvement of Noise and Gain Characteristics of Low-Repetition-Rate Double-Pass Fiber Amplifiers

The noise and gain characteristics of pulsed double-pass (DP) amplifiers operating at low repetition rates are analyzed theoretically and experimentally. The Frantz–Nodvik equations are extended to realize rapid calculation of signal gain in DP fiber amplifiers. At the same time, the rate equations are used to compute the evolution of amplified spontaneous emission (ASE) noise. The effects of the pump scheme, the input energy, and the insertion loss on the gain and noise characteristics are discussed. Based on the simulation results, a new structure Yb-doped DP amplifier is proposed. The experimental results show that the small-signal gain of the DP amplifier can exceed 50 dB. In particular, the average ASE background of the DP amplifier at high-energy output is lower than that of the single-pass amplifier at the same output. This result is quite different from continuous-wave fiber amplifiers.

40 dB gain all fiber bismuth-doped amplifier operating in the O-band

In this Letter, we investigate and compare the gain and noise figure characteristics of bismuth (Bi)-doped fiber amplifiers configured in both single and double signal pass implementations. A maximum gain of 25dB and a noise figure of 4dB is measured at 1360nm in the single pass configuration for -23 dBm input signal power, whereas in the double pass configuration the gain of the amplifier is improved significantly by 14dB allowing us to achieve a gain of 39dB with a noise figure of 5dB. To the best of our knowledge, this is the highest gain reported to date using Bi-doped fiber as a gain medium. Furthermore, we also study the gain and noise figure dependency on pump power, signal power, and pump wavelength for the double pass amplifier configuration. We observed similar gain and noise figure performance in the double pass configuration to that of the single pass configuration but with the benefit of less pump power and a shorter length of the Bi-doped fiber.

Direct Amplification of High Energy Pulsed Laser in Fiber-Single Crystal Fiber with High Average Power

A laser master oscillator power amplifier (MOPA) system consisting of a fiber amplifier and a two-stage Yb:YAG single crystal fiber (SCF) is experimentally studied. The nonlinear stimulated Raman scattering (SRS) is avoided by limiting the output power of the fiber preamplifier to 600 mW. Due to the benefit from the low nonlinearity and high amplification gain of the SCF, a laser pulse duration of 16.95 ps and a high average power of 41.7 W at a repetition rate of 250 kHz are obtained by using a two-stage polarization controlled double-pass amplification of Yb:YAG SCF, corresponding to an output energy of 166.8 μJ and a peak power of 9.84 MW, respectively. The polarization controlled SCF amplification scheme achieved a gain as high as more than 69 times. During the amplification, the spectra gain narrowing effect and the polarization controlled four-pass amplification setup are also studied. The laser spectrum is narrowed from over 10 nm to less than 3 nm, and the pulse width is also compressed to hundreds of femtosecond by dechirping the laser pulse. This compact-sized, cost-effective laser source can be used in laser micromachining, or as the seeder source for generating much higher power and energy laser for scientific research. For some applications which need femtosecond laser, this laser source can also be compressed to femtosecond regime.

500-kHz Level High Energy Double-Pass Nd:YVO4 Picosecond Amplifier with Optic–Optic Efficiency of 51%

We have demonstrated a high pulse energy and high optic–optic efficiency double-pass picosecond (ps) master oscillator power amplifier system of 1064 nm at a pulse repetition rate of 500 kHz. A 500 kHz, 7.68 μJ picosecond laser is used as the seed laser. Through one stage double-pass traveling-wave amplifier, a maximum output power of 16.19 W at a pump power of 31.7 W is generated with the optic–optic efficiency of 51.07%. The output pulse duration is 17.6 ps, corresponding to the pulse energy of 32.38 μJ. The beam quality factor M 2 were measured to be 1.28 and 1.17 along the x, y axis direction, respectively.

Amplified spontaneous emission suppression of a saturable absorber in a nanosecond double-pass laser amplifier

We propose the insertion of a saturable absorber (SA) in a nanosecond double-pass laser amplifier as an amplified spontaneous emission (ASE) suppressor. To analyze the influence of the SA, a theoretical model is developed. One-dimensional simulation results show reasonable agreement with measurements in terms of the output energy and temporal pulse shape. For our amplifier parameters, when an SA of initial transmission 0.5 is inserted, the simulation anticipates the ASE to be reduced by a factor of 0.37 while the output pulse energy is maintained.