Widely tunable difference frequency generation around 3.4 μm using index dispersion property of PPLN

In this paper, the wide difference frequency generation (DFG) tuning characteristics around 3.4 μm are investigated by using the index dispersion property of PPLN. With a ytterbium doped fiber laser (YDFL) and an erbium doped fiber laser (EDFL) as the fundamental light sources, our simulation results show that the quasi-phase matching (QPM) wavelength acceptance bandwidth (BW) for the pump is much larger than that for the signal. Although the positions of the broadened QPM pump bands vary with the poling period and the signal wavelength, the corresponding idler tuning ranges center around 3.4 μm. With a signal wavelength of 1.57 μm, an idler tuning range of greater than 170 nm is experimentally obtained in the 30 uniform grating PPLN. When the signal wavelength and the poling period are respectively changed to 1.55 and 29.50 μm, wide DFG tuning operations around 3.4 μm are also achieved with the crystal temperature adjusted to adapt the change.     

基于光纤激光器的中红外差频多波长激光产生

针对由YDFL和EDFL作为基频光源的QPM-DFG激光系统,利用PPMgLN晶体的色散关系及其温度特性,有效拓宽了QPM波长接受带宽.模拟结果表明,当采用1550和1060 nm波段的EDFL和YDFL分别作为DFG的信号和抽运光源时,对于相同的中红外波段,满足QPM条件所允许的抽运光波长变化范围远大于信号光波长变化范围.当固定信号光波长为1560 nm时,对于给定的晶体温度,1060 nm波段抽运光的QPM接受带宽超过17 nm,对应于中红外差频光带宽可约180 nm.采用多波长YDFL作为抽运源,单 关键词： 差频产生 准相位匹配 多波长中红外 光纤激光器     

Widely tunable mid-IR difference-frequency generation based on fiber lasers

A wide tuning technique for mid-IR difference-frequency generation (DFG) with uniform grating periodically poled LiNbO(3) (PPLN) is presented. Based on the dispersion property of the PPLN, the quasi-phase matching (QPM) band for the pump can evolve to two separate bands, and the spacing between them can be increased with the decrease of the crystal temperature. Two such separate QPM bands can be used for increasing the idler tuning range when the crystal temperature is set to adapt the pump tuning. With the technique, an idler tuning range of 690nm is experimentally achieved with fiber laser fundamental lights.     

Difference-frequency generation by mixing dual-wavelength pulses emitting from an electronically tuned Ti:sapphire laser

Broadly tunable difference-frequency generation (DFG) in AgGaS₂ was achieved by mixing dual-wavelength oscillating pulses from an electronically tuned Ti:sapphire laser with a two-frequency-driven acousto-optic device. Continuous tuning from 6.5 to 8.5 μm was achieved by simultaneous dual-wavelength-tuned DFG without crystal rotation. In the dual-pulse oscillation, the shorter and longer wavelength pulses were tuned from 700 to 775 nm and from 763 to 880 nm, respectively, while keeping the phase-matching relationship for DFG. When crystal rotation was adopted, however, the tunable output range was extended from 5.3 to 12 μm by tuning the longer wavelength pump pulse, while the shorter wavelength pulse was fixed. Received: 18 November 1998 / Revised version: 5 February 1999 / Published online: 26 May 1999     

High-Power,high-repetition-rate operation of a period-continuously-tunable optical parametric oscillator at 3.78–4.62 μm based on a fan-out periodically poled MgO-doped lithium niobate

We present a period-continuously-tunable optical parametric oscillator based on a fan-out MgO:PPLN with a grating period range from 26.9 to 29.5 μm. The OPO was pumped by a Q-switched Nd:YAG laser with a repetition of 10 kHz. With a grating period of 29.3 μm and 22.0 W pump power, the idler output power at 3.78 μm arrived at 3.40 W. With a period of 27.1 μm and 13.5 W pump, the idler output at 4.58 μm arrived at 0.36 W. This is, to our best knowledge, the highest average power for pulsed OPO operating near 4.5 μm based on PPLN or MgO:PPLN. By translating the fan-out MgO:PPLN, the idler wavelength was tuned continuously from 3.78 to 4.62 μm.     

Influences of gain broadening on multiwavelength oscillations in YDFLs and EDFLs

We report the comparisons of the influences of gain broadening on multiwavelength oscillations in YDFL and EDFL with typical commercial ytterbium- and erbium-doped Al/Ge silica fibers. Our experimental results show that both the YDF and the EDF exhibit inhomogeneous gain broadening, which allows the lasing lines to increase with the increase of the pump, however, multiwavelength oscillations of the EDFL are more stable than those of the YDFL, in particular, when the wavelength spacing is small. Moreover, the minimum wavelength spacing for stable multiwavelength operations of the YDFL and the EDFL are observed to be 1.0 and 0.8 nm at room temperature, and 0.8 and 0.25 nm at 77 K, respectively. This show that the inhomogeneous gain broadening of the EDF may be stronger than that of the YDF.     

Picosecond near- to mid-infrared optical parametric oscillator using KTiOAsO4

The operation and characterization of a high-repetition-rate singly-resonant picosecond optical parametric oscillator based on the non-linear material KTiOAsO4 and synchronously pumped by a Kerr-lens-mode-locked Ti:sapphire laser at 81 MHz is described. By utilizing non-critical type II phase-matching in a 10 mm crystal, average near-infrared output powers of 403 mW have been generated at 31% extraction efficiency. The oscillator exhibits a pump power threshold of 230 mW and with the available mirror set can provide signal tuning over 1.116–1.281 μm and idler tuning over 2.260–3.160 μm by tuning the pump wavelength over 770–896 nm. Without dispersion compensation, near-transform-limited signal pulses with durations of 1.01–1.03 ps and idler pulses with 1.61–2.91 ps duration have been obtained for 1.2 ps input pump pulses. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fiber-laser-pumped continuous-wave singly resonant optical parametric oscillator

We report on what is to our knowledge the first continuous-wave (cw) optical parametric oscillator (OPO) that is pumped by a tunable fiber laser. The OPO is singly resonant for the signal wave and consists of a 40-mm-long periodically poled LiNbO(3) crystal in a four-mirror ring cavity. At a pump power of 8.3 W provided by the wavelength-tunable Yb-doped fiber laser, the singly resonant OPO generates 1.9 W of 3200-nm cw idler radiation. The singly resonant OPO was tuned from 1515 to 1633 nm (signal) and from 3057 to 3574 nm (idler) by means of the crystal temperature and poling period. We obtained a wide idler tuning range, from 2980 to 3700 mn, by tuning the wavelength of the fiber laser from 1032 to 1095 nm.     

Widely tunable narrow-linewidth nanosecond optical parametric generator with self-injection seeding

This paper reports a widely tunable narrow-linewidth nanosecond optical parametric generator (OPG) with a pulse-repetition rate of 10 kHz. The OPG consists of a 55-mm-long periodically poled lithium niobate crystal with a domain period of 29.5 m. At an average pump power of 2.0 W the OPG emitted 0.33 W of signal power and 0.17 W of idler power. The wavelength and spectral width of the OPG are controlled by self-injection seeding. For this purpose, a small fraction of the OPGs pulsed signal radiation is used as seed radiation for the next OPG pulse. In order to overlap in time the seed pulse with the succeeding pump pulse, the seed pulse is delayed by a 22-km-long single-mode fiber. For narrowing the spectrum of the seeded OPG output, the seed radiation is spectrally filtered by a tunable fiber Fabry–Perot interferometer (FFPI). The OPG signal radiation could be tuned from 1547 to 1605 nm by changing the OPGs crystal temperature and by tuning simultaneously the FFPI. The corresponding idler wave tuned from 3157 to 3413 nm. Within the whole tuning range, the linewidth of the signal wave was less than 185 MHz. Compared to the 240-GHz linewidth of the free-running OPG, the linewidth of the seeded OPG is thus narrowed by more than three orders of magnitude. By tuning the FFPI, continuous wavelength tuning has been demonstrated within the gain spectrum of the OPG over a range of 820 GHz. PACS 42.65.Yj; 42.79.Nv; 42.79.Qx     

Few‐cycle,broadband, mid‐infrared optical parametric oscillator pumped by a 20‐fs Ti:sapphire laser

A few‐cycle, broadband, singly‐resonant optical parametric oscillator (OPO) for the mid‐infrared based on MgO‐doped periodically‐poled LiNbO₃ (MgO:PPLN), synchronously pumped by a 20‐fs Ti:sapphire laser is reported. By using crystal interaction lengths as short as 250 µm, and careful dispersion management of input pump pulses and the OPO resonator, near‐transform‐limited, few‐cycle idler pulses tunable across the mid‐infrared have been generated, with as few as 3.7 optical cycles at 2682 nm. The OPO can be continuously tuned over 2179‐3732 nm (4589‐2680 cm^‐1) by cavity delay tuning, providing up to 33 mW of output power at 3723 nm. The idler spectra exhibit stable broadband profiles with bandwidths spanning over 422 nm (FWHM) recorded at 3732 nm. The effect of crystal length on spectral bandwidth and pulse duration is investigated at a fixed wavelength, confirming near‐transform‐limited idler pulses for all grating interaction lengths. By locking the repetition frequency of the pump laser to a radio‐frequency reference, and without active stabilization of the OPO cavity length, an idler power stability better than 1.6% rms over >2.75 hours is obtained when operating at maximum output power, in excellent spatial beam quality with TEM₀₀ mode profile. Photograph shows a multigrating MgO:PPLN crystal used as a nonlinear gain medium in the few‐cycle femtosecond mid‐IR OPO. The visible light is the result of non‐phase‐matched sum‐frequency mixing between the interacting beams.     

Temperature-tuned difference-frequency mixing in periodically poled KTiOPO4

4 (PPKTP). We generated 12 μW of radiation tunable around 1.6 μm by difference-frequency mixing of the outputs of a frequency-doubled Nd:YLF laser at 523 nm (240 mW) and a tunable Ti:sapphire laser near 760 nm (340 mW). A temperature tuning rate of 0.73 nm/°C for the generated wavelength and a FWHM temperature acceptance bandwidth of 6.9 °C cm was observed. The effective d₃₃ coefficient was estimated to be ∼5 pm/V. Received: 02 September 1998     

High-conversion-efficiency and tunable phase-stabilized infrared parametric laser source

High-conversion-efficiency and tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With a 1 kHz repetition rate 800 nm pump source, the output idler pulses are tunable from 1.2 to 2.4 μm, and the maximum output average power of the idler pulses is >2 W with the total 7.4 W pump power, and the maximum parametric conversion efficiency in the final optical parametric amplifier is near 60%. Due to the differential frequency process, the output idler pulses is self-phase-stabilized, the phase fluctuation can reach 0.374 rad (rms).     

12 W mid-infrared output,singly resonant,continuous-wave optical parametric oscillator pumped by a Yb<Superscript>3+</Superscript>-doped fiber amplifier

We report a continuous-wave singly resonant optical parametric oscillator (SRO) with more than 12 W of idler power at 3414 nm when it was operated at 30°C. The SRO was directly pumped by a single-frequency, ytterbium-doped fiber laser with 49 W linear polarization pump powers, and based on 50 mm long periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity with 30.5 μm grating period. It’s pump power at threshold was 5.4 W. The slope-efficiency and quantum-limited performance reached 26 and 79.2%, respectively. The beam polarization matched the e → e + e interaction in crystal. The idler waves were temperature tuned in the range of 3654 to 3811 nm and 3248 to 3414 nm based on two 50 mm long PPMgLN with 29.5 and 30.5 μm grating period. To the best of our knowledge, this is the highest continuouswave mid-IR output obtained for a fiber laser pumped optical parametric oscillator (OPO).     

Mid-infrared ZGP OPO pumped by near-degenerate narrowband type-I PPKTP parametric oscillator

The total pulse energy of the signal and idler in a near-degenerate type-I periodically poled KTiOPO₄ (PPKTP) optical parametrical oscillator (OPO) was spectrally confined within a 2 nm spectral bandwidth at 2.13 μm. This was achieved by using a volume Bragg grating as the output coupler. Both the signal and the idler from the PPKTP OPO were then simultaneously used to pump a mid-infrared ZnGeP₂ (ZGP) OPO. The 2 nm bandwidth was narrower than the ZGP crystal acceptance bandwidth and, thus, made efficient conversion in the second OPO possible. A total slope efficiency of 10% from 1.06 μm to the 3.5–5 μm region was demonstrated, generating 250 μJ in the mid-IR with only 3.6 mJ of 1.06 μm pump energy. This corresponds to a Nd:YAG pump to mid-IR conversion efficiency of 7%. PACS 42.65.Yj; 42.72.Ai; 42.40.Eq     

Long-wave IR chemical sensing based on difference frequency generation in orientation-patterned GaAs

The combination of continuous-wave difference frequency generation based on quasi-phase-matched (QPM) gallium arsenide with cavity ring-down spectroscopy is explored for use in spectroscopic and chemical sensing applications. The advent of QPM materials based on orientation-patterned GaAs (OP-GaAs) offers a significant advantage over traditional ferroelectric QPM materials of extended wavelength coverage into the spectroscopically important 8–12 μm region. In this work, the outputs from two tunable, external cavity diode lasers covering the 1.3 μm and 1.5 μm telecom bands were amplified then mixed in an orientation-patterned GaAs crystal, producing several microwatts of tunable radiation in the 7–9 μm region. We also evaluate the use of a low-power DFG source for use in cavity ring-down spectroscopy. PACS 82.80.Gk; 42.62.Fi; 42.70.Hj; 42.65.Ky     

A 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator with cw diode laser injection seeding

We report on an injection-seeded 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator (OPG) based on a 55 mm long crystal of periodically poled lithium niobate (PPLN) with a quasi-phase-matching (QPM) grating period of 29.75 μm. The OPG is excited by a continuously diode pumped mode-locked picosecond Nd:YVO₄ oscillator-amplifier system. The laser system generates 7 ps pulses with a repetition rate of 82.3 MHz and an average power of 24 W. Without injection-seeding the total average output power of the OPG is 8.9 W, which corresponds to an internal conversion efficiency of 50%. The wavelengths of the signal and idler waves were tuned in the range 1.57–1.64 μm and 3.03–3.3 μm, respectively, by changing the crystal temperature from 150 °C to 250 °C. Injection seeding of the OPG at 1.58 μm with 4 mW of single frequency continuous-wave radiation of a distributed-feedback (DFB) diode laser increases the OPG output to 9.5 W (53% conversion efficiency). The injection seeding increases the pulse duration and reduces the spectral bandwidth. When pumped by 10 W of 1.06 μm laser radiation, the duration of the signal pulses increased from 3.6 ps to 5.5 ps while the spectral bandwidth is reduced from 4.5 nm to 0.85 nm. Seeding thus improved the time-bandwidth product from 1.98 to a value of 0.56, much closer to the Fourier limit. Received: 29 April 2002 / Published online: 8 August 2002     

Widely tunable PPLN/IOPO driven by a diode-end-pumped Q-switched Nd:YVO<Subscript>4</Subscript> laser

This paper reported a broadband tuning intracavity optical parametric oscillator (IOPO), based on the multiple grating periodical poled lithium niobate (PPLN) pumped by a acoustic-optical (AO) Q-switched Nd:YVO₄ laser. The widely tunable OPO output signal wavelength range from 1390 to 1605 nm, which was obtained by changing PPLN poling period from 27.8 to 31.6 μm at a certain temperature of 46°C, while the continuous tuning range was measured from 1475 to 1592 nm with the PPLN poling period of 30 μm by varying the temperature of nonlinear crystal PPLN from 50 to 120°C. The maximum output power of 0.92 W at 1534 nm with the minimum pulse width of 5.17 ns was generated under the incident pump power of 9.6 W at 808 nm. The corresponding peak power and single pulse energy were calculated to be 5.94 kW and 30.7 μJ, respectively. The M ₂-factor was measured to be 2.01 at the signal power of 0.4 W.     

Wavelength Tuning of Double-Cavity Micromachined Filter with Electrical and Thermal Actuations

We demonstrate double-cavity micromachined tunable filters with electrical actuations for both blue and red wavelength tuning. Electrical actuations for both shifts can be achieved by combining electrostatic and electro-thermal actuations below and above the breakdown voltage of p-n junctions in the micromachined cantilevers. The measured tuning range with the actuation is 8 nm for both tuning sides and the micromachined filter with a cantilever length of 80 μm exhibits a switching time of less than 115 μs for both turn-on and turn-off states. We also present the theoretical and measured temperature dependence of fabricated micromachined filters at various cantilever lengths, which experimentally gives us a temperature dependence of 0.14 nm/K for a cantilever length of 100 μm.     

光纤型宽带可调连续波差频产生中红外激光器转换效率的研究

以掺镱光纤激光器为抽运源、掺铒光纤激光器后接掺铒光纤放大器为信号源,利用周期极化掺镁铌酸锂晶体,研究了全光纤化差频产生中红外激光器的转换效率特性。结果表明,抽运光和信号光偏振态影响差频产生过程的转换效率,利用偏振控制器,可将抽运光和信号光偏振方向调节到与晶体光轴方向平行,以获得高的转换效率。抽运光和信号光的光束质量既影响差频产生过程的转换效率,又决定晶体纵向位置的容限,当聚焦系统由自聚焦透镜和焦距100mm平凸透镜组成时,相对转换效率达0.717mW-2,晶体纵向位置容限为44mm。此外,差频光在3126.36~3529.6nm范围内调谐时,转换效率基本保持不变。     

一种热光可调谐级联微环滤波器的理论分析

根据Vernier效应可大幅度提高滤波器自由光谱范围和调谐范围,设计了一种热光可调谐级联微环滤波器. 利用传输矩阵方法和有限元方法从理论上计算了对于第一级微环半径为48 μm,第二级半径为50 μm的级联微环滤波器的自由光谱范围和调谐范围可以达到75.6 nm,而功耗仅为103.1 mW,这是目前为止我们 所知的基于微环谐振腔的硅基热光可调谐滤波器中最大的自由光谱范围和在如此低功耗下最大的调谐范围. 利用有限元方法,还计算了半径为50 μm微环的热光调谐响应时间,上升沿时间为3.5 μs,下降沿时间仅为0.8 μs.