Idler Power Research Articles

Low Threshold, Dual-Wavelength, Mid-Infrared Optical Parametric Oscillator

In this letter, we demonstrated a dual-wavelength (DW) mid-infrared optical parametric oscillator (OPO) that was pumped by two independent fiber lasers fixed at 1018 nm and 1080 nm, and realized phase-matched signal beam coupling by tuning grating period of PPLN. Based on signal beam coupling, two interesting phenomena were observed for the first time. One is that the OPO threshold for 1018 nm and 1080 nm pump beams could be drastically lowered from 15.4 W to 266 mW and from 13.5 W to 1.38 W separately. The other is that the total idler power obtained when the OPO was simultaneously pumped by two fiber lasers was higher than sum of idler power obtained when the OPO was independently pumped by two fiber lasers, revealing obvious parametric gain enhancement. It also indicated that the two independent OPO processes became coherent when two signal beams were coupled. The results exhibit great potential in practical applications such as frequency down-conversion of some special near-infrared laser sources such as pulsed single-frequency sources, spectrum high-speed swept sources, and ultra-short pulse sources with low duty cycle.

Dual-Wavelength Mid-Infrared Generation Using Intracavity Stimulated Raman Scattering of PPLN

We report, to the best of our knowledge, the first demonstration of a continuous-wave, dual-wavelength (DW) mid-infrared optical parametric oscillator (OPO) based on the stimulated Raman scattering (SRS) effect of periodically poled lithium niobate (PPLN). The OPO was pumped by two independent fiber lasers, one being fixed at 1018 nm and the other being tunable. The high-power 1018-nm source built parametric oscillation, induced SRS effect in PPLN and generated 1495-nm signal beam as well as 1506-nm Raman beam. The tunable fiber laser was set at 1080 nm and the phase-matched difference frequency generation (DFG) occurred between the 1506-nm Raman beam and 1080-nm pump beam. Finally, DW idler beam located at 3189 and 3819 nm was obtained whose power ranged from 8.044 to 8.115 W, in which the 3189-nm idler power made up the majority of about 8 W and the maximum 3819-nm idler power reached 0.154 W. The slope and conversion efficiency of DFG and OPO processes was also discussed separately.

Frequency Down-Conversion of Dual-Wavelength Raman Fiber Laser in PPLN-Based Optical Parametric Oscillator

We report on frequency down-conversion of dual-wavelength (DW) Raman fiber laser in a periodically poled lithium niobate-based optical parametric oscillator. The DW pump source was fixed at 1060 and 1111 nm that was obtained based on stimulated Raman scattering effect by combining a home-made linearly polarized 1060-nm fiber laser and 137-m-long polarization-maintaining passive fiber. The total pump power went through three stages, in the latter two of which the 1111-nm wave appeared. In the entire experiment, the 1060-nm pump beam achieved parametric oscillation and generated 1626-nm signal beam and 3056-nm idler beam. The 1111-nm pump beam generated 3503-nm idler beam based on difference frequency generation (DFG) between itself and 1626-nm signal beam in the second stage. With power enhancement, it built independent parametric oscillation in the third stage and generated 1621-nm signal beam as well as 3530-nm idler beam. The DW idler power ranged from 3.94 to 7.78 W in the latter two stages. The power and efficiency characteristics in frequency conversion processes of 1060- and 1111-nm pump beams were also analyzed separately.

Tunable Dual-Wavelength, Continuous-Wave, Mid-Infrared Generation Using Intracavity Difference Frequency Mixing in PPLN-Based Optical Parametric Oscillator

We report on a widely tunable, dual-wavelength, continuous-wave, mid-infrared optical parametric oscillator (OPO), pumped by a dual-wavelength fiber source that was realized by combining two fiber lasers in series. The OPO was designed as a four-mirror singly resonant cavity, in which a periodically poled lithium niobate (PPLN) crystal was used as nonlinear crystal. Two idler emissions with different wavelengths were observed, one being basically fixed at 3140 nm and the other being tunable from 3227 to 3413 nm. Under the maximum pump power, the total idler power was over 6 W and the corresponding pump-to-idler slope efficiency reached 11.4%. The generated signal beam had just one central wavelength around 1600 nm. Through theoretical analysis and experimental verification, it was analyzed that two nonlinear processes, OPO and intracavity difference frequency generation (DFG), simultaneously occurred in the resonant cavity. The experimental phenomena revealed large widened DFG gain spectrum, which was in absolute contrast to simulation results based on classical DFG theory. It indicated great potential in practical application such ultra-wide nonlinear frequency conversion.

Continuous-wave, singly-resonant, intracavity optical parametric oscillator based on a single-mode-laser-diode-pumped Yb:KYW laser.

We report a continuous-wave (cw), intracavity, singly resonant optical parametric oscillator (ICSRO) based on an Yb:KYW laser pumped by a single-mode laser diode (LD). Pumping the ICSRO by a low-noise single-mode LD, combined with the reduced heat generation due to the lower quantum defect of the Yb:KYW laser system, effectively eliminated the onset of relaxation oscillations, which have been a long-standing problem in previous multimode-LD-pumped ICSROs, and resulted in a cw ICSRO being operated free of relaxation oscillations. At an LD power of 515mW, the generated idler power was 21mW at ∼3500 nm. To the best of our knowledge, this is the first demonstration of a single-mode-LD-pumped ICSRO.

Phase-stabilized 100\xa0mW frequency comb near 10\xa0\u03bcm

Long-wavelength mid-infrared (MIR) frequency combs with high power and flexible tunability are highly desired for molecular spectroscopy, including investigation of large molecules such as C60. We present a high power, phase-stabilized frequency comb near 10 μm, generated by a synchronously pumped, singly resonant optical parametric oscillator (OPO) based on AgGaSe2. The OPO can be continuously tuned from 8.4 to 9.5 μm, with a maximum average idler power of 100 mW at the center wavelength of 8.5 μm. Both the repetition rate (frep) and the carrier-envelope offset frequency (fceo) of the idler wave are phase-locked to microwave signals referenced to a Cs clock. We describe the detailed design and construction of the frequency comb, and discuss potential applications for precise and sensitive direct frequency comb spectroscopy.

Polarization-Insensitive Four-Wave-Mixing-Based Wavelength Conversion in Few-Mode Optical Fibers

We report theoretical and experimental results on a wavelength converter based on intermodal phase matching in a graded index three-mode elliptical-core fiber. Here, two copolarized pump waves propagate in one spatial mode, whereas a signal and the corresponding generated idler propagate in another mode. We demonstrate that the idler power is independent of the signal polarization in both a 1 km and a 50 m long fiber. We attribute this polarization insensitivity to the fast random birefringence of the fiber under investigation in combination with the copolarized pump configuration.

Yb-fiber-pumped mid-infrared picosecond optical parametric oscillator tunable across 6.2–6.7 µm

We report a high-average-power picosecond optical parametric oscillator (OPO) tunable in the mid-infrared (mid-IR) based on CdSiP2 synchronously pumped by an Yb-fiber laser at ~ 80 MHz repetition rate. Successful operation of this high-repetition-rate singly-resonant picosecond OPO has been enabled by the improved CSP crystal quality over a long interaction length. The OPO can be tuned across 1264–1284 nm in the near-IR signal and 6205–6724 nm in the mid-IR idler by temperature tuning the CSP crystal over 39–134 °C. By deploying a 5% output coupler for the resonant signal, we have extracted up to 44 mW of average power in the near-IR and up to 95 mW of non-resonant idler power at 6205 nm at 6.3% total conversion efficiency, with > 50 mW over > 55% of the mid-IR tuning range. We have investigated temperature-tuning characteristics of the OPO and compared the data with the theoretical calculations using the recent Sellmeier and thermo-optic coefficients for CdSiP2. The signal pulses from the OPO exhibit a Gaussian pulse duration of 19 ps centered at 1284 nm. We have also studied the output power stability of the OPO, resulting in a passive stability better than 1.9% rms for the near-IR signal and 2.4% rms for the mid-IR idler, measured over > 17 h, with both beams in high spatial quality.

Continuous-Wave 3.1–3.6 μm Difference-Frequency Generation of Dual Wavelength-Tunable Fiber Sources in PPMgLN-Based Rapid-Tuning Design

We report on a single-frequency continuous wave (CW) difference-frequency generation (DFG) source based on single-frequency wavelength-tunable polarization-maintaining ytterbium- and erbium-doped fiber master oscillator–power amplifiers (MOPAs), acting as the pump and signal source, respectively, and a 40-mm long periodically poled MgO-doped LiNbO3 (PPMgLN) crystal. Owing to the dual wavelength-tuning of the MOPAs, the generated idler light reaches a wavelength-tuning range of close to 500 nm, from ∼3117.2 to ∼3598.8 nm, only by tuning the launched pump and signal wavelengths from 1040 to 1084.6 nm and from 1545.2 to 1561.4 nm, respectively, without any change of temperature or grating period of the PPMgLN. Compared to temperature-based idler-wavelength-tuning, this method is potentially faster in speed. The maximum idler power exceeds 60 mW, which is the highest reported power for a wavelength-tunable single-frequency CW DFG source. A rapidly wideband-tunable DFG source with tens of milliwatts of output power in a narrow line can be a practical tool for mid-infrared molecular spectroscopy, detection, and sensing at high measurement rates.

Watt-level widely tunable femtosecond mid-infrared KTiOAsO4 optical parametric oscillator pumped by a 1.03 μm Yb:KGW laser.

A high-power, high-repetition-rate, broadband tunable femtosecond optical parametric oscillator (OPO) is constructed based on KTiOAsO4 crystal, pumped by a 75.5MHz mode-locked Yb:KGW laser. With 7W pump power, the OPO generates as much as 2.32W of signal power at 1.55μm and 1.31W of idler power at 3.05μm, corresponding to a total conversion efficiency of 51.8%. Operating at 151MHz repetition rate, the wavelength of the signal covers 1.41-1.71μm with a tunable idler range of 2.61-3.84μm. The idler bandwidth is more than 180nm over the entire mid-infrared range. By compensating intracavity dispersion, the signal pulse has a nearly Fourier transform-limited duration of 129fs at 1.52μm.

Tunable, high-repetition-rate, dual-signal-wavelength femtosecond optical parametric oscillator based on BiB3O6

We have demonstrated a high-repetition-rate tunable femtosecond dual-signal-wavelength optical parametric oscillator (OPO) based on BiB3O6 (BiBO) crystal, synchronously pumped by a frequency-doubled mode-locked Yb:KGW laser. The cavity is simple since no dispersion compensators are used in the cavity. The wavelength range of dual-signal is widely tunable from 710 to 1000 nm. Tuning is accomplished by rotating phase-matching angle of BiBO, and optimizing cavity length and output coupler. Using a 3.75 W pump laser, the maximum average dual-signal output power is 760 mW at 707 and 750 nm, leading to a conversion efficiency of 20.3% not taking into account the idler power. Our experimental results show a non-critical phase-matching configuration pumped by a high peak power laser source. The operation of the dual-signal benefits from the balance of phase matching and group velocity mismatching between the two signals.

Crosstalk Mitigation in Multichannel Optical Parametric Sampling via Raman Amplification

We propose to use backward Raman amplification to mitigate the crosstalk in multichannel optical parametric sampling. The performances of multichannel sampling based on four-wave mixing (FWM) have been experimentally compared with different Raman pump powers. Optical crosstalk is suppressed by lowering the input signal power so that the depletion of the parametric pump and higher order FWM products are reduced. Meanwhile, Raman amplification compensates the parametric pump power and improves the conversion efficiency, thus maintaining the output idler power. A 12.2- and 13.6-dB reduction of crosstalk-induced frequency components has been achieved in two output channels. We also analyze bandwidth broadening resulting from the self-phase modulation of the pulsed parametric pump for the two cases when it is amplified by an erbium-doped fiber amplifier and by the Raman pump.

Widely tunable and narrow-bandwidth pulsed mid-IR PPMgLN-OPO by self-seeding dual etalon-coupled cavities.

Integrating narrow-bandwidth and wavelength tunability together is crucially important in upgrading the applications of optical parametric oscillators (OPO). Here, we have demonstrated a widely tunable, narrow-bandwidth and efficient mid-IR OPO pumped by a single-longitudinal-mode pulsed Yb-fiber laser. By restricting the bandwidth of the oscillated signal via self-seeding dual etalon-coupled cavities, the bandwidth of the idler can be suppressed to about 0.35 nm, with a wide tunable range of 2.85-3.05 μm, which can be achieved by synergistically adjusting the temperatures of PPMgLN crystal and one of the etalons. The maximum idler power at 3.031 μm is 2.67 W with an optical-to-optical conversion efficiency of 17.4%.

Optical parametric generation in orientation-patterned gallium phosphide.

We report an optical parametric generator (OPG) based on the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched nanosecond Nd:YAG laser at 1064nm with 25kHz pulse repetition rate, the OPG can be tuned across 1721-1850nm in the signal and 2504-2787nm in the idler. Using a 40-mm-long crystal in single-pass configuration, we have generated a total average output power of up to ∼18 mW, with ∼5 mW of idler power at 2670nm, for 2W of input pump power. The OPG exhibits a passive stability in total output power better than 0.87% rms over 1h, at a crystal temperature of 120°C, compared to 0.14% rms for the input pump. The output signal pulses, recorded at 1769nm, have duration of 5.9ns for input pump pulses of 9ns. Temperature-dependent loss measurements for the pump polarization along the [100] axis in the OP-GaP crystal have also been performed, for the first time, indicating a drop in transmission from 28.8% at 50°C to 19.4% at 160°C.

Room-temperature, rapidly tunable, green-pumped continuous-wave optical parametric oscillator.

We report a high-power, single-frequency, green-pumped continuous-wave optical parametric oscillator (OPO) capable of providing rapid and continuous tuning across a wide spectral range in the near-infrared at room temperature. By exploiting the nonlinear crystal of MgO:sPPLT in a fan-out grating design pumped at 532nm in the green, the OPO can be tuned continuously across 1097-2100nm in the idler, with corresponding signal tuning over 712-1033nm using simple mechanical translation of the crystal at fixed temperature. The device can deliver hundreds of milliwatts of idler power across the complete tuning range, with as much as 2.2W at 1097nm for 9W of input pump power at 77% pump depletion. The passive power stability of the generated idler at 1110nm, measured at 6.8W of pump power, is better than 1%rms over 30min. The signal frequency stability, measured at 837nm, is 518MHz over 2min, with an instantaneous linewidth of 6.9MHz, in high beam quality.

Compact KTA-Based Optical Parametric Oscillator Driven by a Passively Q-Switched YVO<sub>4</sub>/Nd:YVO<sub>4</sub> Laser

A compact passively Q-switched YVO4/Nd:YVO4/KTA intracavity optical parametric oscillator (OPO) is realized. With an end-pumping diode power of 16.6 W, output signal power of 932 mW and idler power of 415 mW are obtained at a pulse repetition rate of 101 kHz. The pulse widths and the beam quality factors are also analyzed for both signal and idler lasers.

A fiber laser pumped dual-wavelength mid-infrared laser based on optical parametric oscillation and intracavity difference frequency generation

We report a dual-wavelength mid-infrared laser based on intracavity difference frequency generation (DFG) in an MgO-doped periodically poled LiNbO3, which was pumped by a dual-wavelength fiber MOPA consisting of two parts: a dual-wavelength seed and a power amplifier. The maximum pump power was 74.1 W and the wavelengths were 1060 nm and 1090 nm. The wavelengths of the mid-infrared output were 3.1 µm and 3.4 µm under maximum pump power with a total idler power of 6.57 W. The corresponding pump-to-idler slope efficiency reached 12%. The contrast for the peak intensity of the emissions for the two idlers was 0.6. A power preamplifier was added in a further experiment to enhance the contrast. The idler output reached 4.45 W under the maximum pump power of 70 W, which was lower than before. However, the contrast for the idler emission peak intensity was increased to 1.18. The signal wave generated in the experiment only had a single wavelength around 1.6 µm, indicating that two kinds of nonlinear processes occurred in the experiment, namely optical parametric oscillation and intracavity DFG.

Pump-tuned deep-infrared femtosecond optical parametric oscillator across 6-7 μm based on CdSiP2.

We report on a high-power femtosecond optical parametric oscillator (OPO) at 80 MHz repetition rate, tunable across 6318-7061 nm in the deep-infrared (deep-IR) using pump wavelength tuning. The OPO, based on CdSiP2 (CSP), is synchronously pumped by a commercial Ti:sapphire-pumped femtosecond OPO in the near-IR, enabling rapid static tuning of the CSP OPO with minimal adjustments to its cavity length. The deep-IR CSP OPO provides as much as 32 mW of average idler power at 6808 nm with spectral bandwidth >1000 nm (at -10 dB level) across the tuning range. By implementing intracavity dispersion control, near-transform-limited signal pulses of ∼100 fs duration with smooth single-peak spectrum are achieved at 1264 nm, corresponding to an idler wavelength at 6440 nm. To the best of our knowledge, this is the first time such practical idler powers in the deep-IR have been generated from a dispersion-compensated CSP femtosecond OPO at sub-100 MHz repetition rate.

Four-wave mixing and nonlinear losses in thick silicon waveguides.

We experimentally investigate four-wave mixing and nonlinear losses in low-loss 3μm thick silicon strip waveguides. Adiabatic bends allow for single-mode operation in an ultra-compact 35cm long spiral. The waveguides exhibited reduced nonlinear losses due to the large mode area of 2.75 μm2. The nonlinear coefficient γ was measured as 5.5 m-1 W-1. These features, along with the low propagation loss of 0.17dB/cm, enable large idler power generation at 1550nm.

Ti:sapphire-pumped deep-infrared femtosecond optical parametric oscillator based on CdSiP_2

We report on a femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on the Kerr-lens-mode-locked Ti:sapphire laser as the pump source. By deploying a novel cascaded intracavity arrangement, comprising a femtosecond OPO based on the nonlinear crystal, CdSiP2, synchronously pumped internal to a MgO:PPLN femtosecond OPO, we have generated broadly tunable radiation across 5958-8117 nm using rapid static cavity delay tuning, with a maximum power of 64 μW at 6791 nm, limited by the absorption in mirror substrates as well as polarization-dependent intracavity losses. The deep-IR idler power exhibits excellent passive stability of better than 1.1% rms over 2 h, with a spectral bandwidth as large as ∼650 nm at ∼6800 nm. The demonstrated concept is generic and can be similarly deployed in other operating time scales and wavelength regions, also using different laser pump sources and nonlinear materials.