Synchronously Pumped Optical Parametric Oscillator Research Articles

Brewster mirror ultrafast optical parametric oscillator with high precision wavelength tuning.

We demonstrate a synchronously-pumped optical parametric oscillator (OPO) with a cavity formed from high refractive index inverted prisms, also known as Brewster mirrors. Exploiting a single total internal reflection, this is the simplest device capable of deviating a laser beam by 180∘. The OPO produced a chirped signal output tunable from 1060-1570nm with a maximum power of 114 mW. We investigate the geometric properties of ideal and imperfect Brewster mirror prisms and find the latter can provide ∼1000 × finer control of the signal wavelength when compared to cavity length tuning.

Effect of spatial walk-off on squeezing properties of quantum optical frequency combs

Quantum optical frequency combs are of great significance in the fields of quantum computing, quantum information, and high precision quantum measurement, which can be produced by using a degenerate type-I synchronously pumped optical parametric oscillator (SPOPO). When anisotropic crystal is used as a nonlinear medium in the SPOPO, the spatial walk-off effect will occur due to the birefringence effect, which cannot be ignored and will adversely affect the generation of squeezed state. In this work, we investigate the influence of spatial walk-off effect on the squeezing level of quantum optical frequency combs both theoretically and experimentally. A Ti∶sapphire mode-locked femtosecond pulsed laser which produces 130 fs pulse trains at 815 nm with a repetition rate of 76 MHz is utilized as a fundamental source. Its second harmonic at 407.5 nm is used to pump the collinear BiB<sub>3</sub>O<sub>6</sub> (BIBO) crystal for generating the squeezed vacuum frequency comb. It is indicated that as the crystal length increases, the area of interaction between pump light and signal light decreases gradually. Thus the enhancement of squeezing is eventually limited by the spatial walk-off effect. According to the simulations, the squeezing level reaches a maximum value when the crystal length is 1.49 mm. The quantum properties of squeezed vacuum optical frequency combs obtained for four crystal lengths (0.5, 1.0, 1.5 and 2.0 mm) are subsequently measured experimentally. When the length of BIBO is 1.5 mm, the maximum vacuum squeezing of (3.6±0.2) dB is obtained, which is (7.0±0.2) dB after being corrected for detection loss. The experimental results are consistent with the numerical simulations. This study demonstrates that the spatial walk-off effect in nonlinear crystal is a significant factor affecting the quantum optical frequency comb, and the theoretical model presented in this paper can be used to provide a guideline for optimizing the experimental implementation.

Widely-tunable mid-infrared (2.6–5 μm) picosecond vortex laser

We report on a widely-tunable mid-infrared picosecond optical vortex laser source that employs a synchronously-pumped optical parametric oscillator optimized for mid-infrared emission up to 5 μm. Vortex output with a continuously-tunable wavelength range of 2.6–5 μm could be obtained simply by translating the MgO:PPLN crystal. At the maximum pump power of 15 W, the maximum idler output powers were measured as 3.7, 1.7, and 0.165 W at the wavelengths of 2.6, 3.8, and 5 μm, respectively. The corresponding photon conversion efficiencies were estimated to be 60% at 2.6 μm, 40% at 3.8 μm, and 5.2% at 5 μm.

Femtosecond optical parametric oscillator with 3D-printed polymeric parts

A synchronously-pumped optical parametric oscillator (SPOPO) based on a periodically-poled, MgO-doped lithium niobate (MgO:PPLN) crystal was realized exploiting additive manufacturing technology for the pump and focusing section of the cavity, where careful predesign of the tightly-packed mounts and optics can be very helpful in view of a more traditional mechanical realization. Surprisingly, the 3D-printed plastic parts ensured long-term stability of the (quite sensitive, in principle) femtosecond SPOPO.

Ultrashort-pulsed optical parametric oscillator employing Brewster angle prism retroreflectors.

We demonstrate a synchronously-pumped optical parametric oscillator (OPO) cavity in which traditional dielectric mirrors are replaced by all-planar Brewster angle prism retroreflectors, also known as Pellin-Broca prisms. Exploiting total internal reflection, these prisms form a cavity supporting >350-fs chirped signal pulses that were externally compressible to sub-150-fs durations. This simple architecture produces wavelengths tuneable across 1100 - 1350 nm, suitable for basic multi-photon applications.

Broadband operation of a synchronously pumped optical parametric oscillator with a spatially dispersed beam

We demonstrate the broadband operation of a synchronously pumped optical parametric oscillator (SPOPO) with a spatially dispersed beam and a fan-out type MgO-doped periodically poled LiTaO3 (MgO:PPLT). Spatial dispersion was generated using a glass prism placed in the SPOPO cavity. The poling period was designed to match the spatial dispersion and phase matching in MgO:PPLT, and the spectral dispersion in the cavity was compensated for using a fused silica plate, which had a negative dispersion at a signal wavelength of 1500-1600 nm. We succeeded in generating signal pulses with a pulse length of 81 fs, which was approximately 1/5 of the pump pulse length.

Theoretical investigation of pulse-to-pulse instabilities in a synchronously pumped femtosecond optical parametric oscillator

A singly resonant synchronously pumped optical parametric oscillator (SPOPO) based on the experimental setup of J. Opt. Soc. Am. B 36, 131 (2019)JOBPDE0740-322410.1364/JOSAB.36.000131 is studied theoretically. Stable, oscillatory, and chaotic operation modes of the SPOPO are investigated. The need of the self- and cross-phase modulation terms in the theoretical model for the explanation of the instabilities is demonstrated. The theoretical values of the wavelengths of the signal spectrum maxima are found. The evidence of chaos by the calculation of the Lyapunov exponent is provided. The possibilities to avoid the instabilities are discussed.

啁啾脉冲光学参量振荡器及宽谱中红外激光的产生（特邀）

Mid-infrared laser sources with broad instantaneous-bandwidth are critical for many applications, including infrared micro-spectroscopy, environmental monitoring, medical diagnosis, and ultra-short pulse generation. In this article, the output spectrum bandwidth from synchronously pumped optical parametric oscillator (SPOPO) was focused on and a scheme, chirped-pulse optical parametric oscillator (CPOPO) was proposed to achieve broadband output beyond the limitation of pump pulse width. The CPOPO with self-phase modulation (SPM) or chirped quasi-phase matching (CQPM) were studied and achieved through period-poled lithium niobate (PPLN) based SPOPO. The outputs covered 2.9-3.9 μm (~27 THz) with power up to 92 mW and 2.9-5.0 μm (~44 THz) with 64 mw, respectively.

Temporal characteristics of a synchronously pumped optical parametric oscillator at different conditions of cavity losses

We present detailed experimental data and numerical simulation results obtained during the investigation of temporal characteristics of a synchronously pumped optical parametric oscillator (SPOPO) based on a periodically poled potassium titanyl phosphate crystal. A femtosecond Yb:KGW laser was used for SPOPO pumping, and signal pulse durations were measured in the 1.49–1.82 µm spectral range at three different conditions of cavity losses. The experimental investigation and numerical modeling showed strong SPOPO signal pulse duration dependency on the transmission of the output coupler. We also used external group delay dispersion compensation to achieve shorter SPOPO signal pulses.

Tunable visible frequency combs from a Yb-fiber-laser-pumped optical parametric oscillator

We present a 100 MHz repetition rate Yb-fiber-laser-pumped synchronously pumped optical parametric oscillator (SPOPO) delivering tunable frequency combs covering almost the entire visible spectral range. By intracavity doubling both the signal and idler combs and using collinear residual pump light, nearly continuous tuning over the range of 420-700 nm is achieved with only small gaps near the OPO degeneracy condition. Output powers range from 10 mW to 200 mW, depending on wavelength, with pulse durations below 150 fs without external compression. Frequency locking of all three collinearly outcoupled combs (pump, doubled signal, and doubled idler) to a femtosecond enhancement cavity facilitates direct comparison of their optical phase noise and phase modulation transfer functions. In the singly-resonant OPO, optical phase modulation of the pump comb is transferred nearly completely to the non-resonant idler comb. This results in a resonant signal comb with reduced optical phase noise and also enables high-bandwidth modulation on the idler comb via phase modulation of the pump.

Fiber-based optical parametric oscillator with flexible repetition rates by rational harmonic pumping.

We demonstrated a fiber-based synchronously pumped optical parametric oscillator (SPOPO) with flexible repetition rates while retaining the cavity length. In contrast to conventional free-space SPOPO, the repetition rate of output signal pulses was solely determined by the repetition rate of the pump source in harmonic, fractional and rational operations. The relevant mechanism relies on synchronous pumping and intrinsic losses in our fiber resonator. The novel scheme enabled us to flexibly tune the repetition rate from 0.5 to 6.0 MHz without altering the resonator configuration. The resulting pulse properties were systematically analyzed at various operation conditions, and particularly showed that a wavelength tuning range of 157 nm was obtained. Such rational harmonic resonance implemented in our SPOPO provides not only a simple yet effective way to tune the repetition rate, but also a feasible approach to narrow down the spectral bandwidth. The presented SPOPO could be useful in nonlinear biomedical imaging by offering a convenient approach to optimize the pulse repetition rate for different biomedical samples with minimum photodamage.

Dual-channel operation in a synchronously pumped optical parametric oscillator for the generation of broadband mid-infrared coherent light sources.

We report, to the best of our knowledge, a novel approach for generating broadband mid-infrared (mid-IR) light by implementing a dual-channel scheme in a synchronously pumped optical parametric oscillator (SPOPO). Two-channel operation was achieved by inserting a prism pair and two reflection mirrors inside an optical parametric oscillator (OPO) cavity. Pumped by a Yb-fiber laser, the OPO generated an idler wave at ∼3150 nm with a -10 dB bandwidth of ∼13.2 THz, which was twice as much as that of the pump source. This scheme represents a promising technical route to transform conventional SPOPOs into a device capable of generating mid-IR light with very broad instantaneous bandwidth.

Characteristics of optical parametric oscillator synchronously pumped by Yb:KGW laser and based on periodically poled potassium titanyl phosphate crystal

We present experimental data and numerical simulation results obtained during investigation of synchronously pumped optical parametric oscillator (SPOPO) pumped by femtosecond Yb:KGW laser (central wavelength at 1033 nm). The nonlinear medium for parametric generation was periodically poled potassium titanyl phosphate crystal (PPKTP). Maximum parametric light conversion efficiency from pump power to signal power was more than 37.5% at λs=1530 nm wavelength, whereas the achieved signal wave continuous tuning range was from 1470 nm to 1970 nm with signal pulse durations ranging from 91 fs to roughly 280 fs. We demonstrated wavelength tuning by changing cavity length and PPKTP crystal grating period and also discussed net cavity group delay dispersion (GDD) influence on SPOPO output radiation characteristics. The achieved high pump to signal conversion efficiency and easy wavelength tuning make this device a very promising alternative to Ti:sapphire based SPOPOs as a source of continuously tunable femtosecond laser radiation in the near and mid-IR range.

Noiseless signal shaping and cluster-state generation with a quantum memory cell

In this article, we employ multimode radiation of a synchronously pumped optical parametric oscillator (SPOPO) to build a cluster state through a conversion on the base of quantum memory cell. We demonstrate that by choosing an appropriate driving field we can ensure the effective writing of the only one supermode from the entire set of the SPOPO squeezed supermodes. Further, by changing the driving field profile at the readout, we convert the time profile of the retrieved signal while maintaining its quantum state. We demonstrate the possibilities of using the presented scheme by the example of creating a four-mode linear cluster state of light.

Stabilization of femtosecond optical parametric oscillators for infrared frequency comb generation.

A synchronously pumped optical parametric oscillator (SP-OPO) is one of the most common techniques to generate femtosecond frequency combs in the mid-infrared region. Stable long-term operation of an SP-OPO requires active locking of the OPO resonator round-trip time to the pump pulse interval. A simple modulation-free locking method based on stabilization of narrow-band frequency-doubled power of the SP-OPO output comb is demonstrated in this Letter. The method relies on the strong dependency of frequency-doubled power on spectral shape of the comb, leading to better stability of the comb envelope spectrum than the commonly used dither-and-lock method.

Preservation of quantum correlations in a femtosecond light pulse train within an atomic ensemble

In this paper, we examined a possibility of preservation of a substantially multimode radiation in a single cell of quantum memory. As a light source we considered a synchronously pumped optical parametric oscillator (SPOPO). As it was shown in [1-4], SPOPO radiation has a large number of the correlated modes making it attractive for the purposes of the quantum communication and computing. We showed that these correlations can be mapped on the longitudinal spin waves of the memory cell and be restored later in the readout light. The efficiencies of the writing and readout depend on the mode structure of the memory determined by a mechanism of the light-matter interaction under consideration (the non-resonance Raman interaction) and by the profile of the driving light field. We showed that like the initial light pulse train, the restored one can be represented by a set of squeezed supermodes. The mapping of the quantum multimode correlations on the material medium offers opportunities to manipulate the quantum states within the memory cell followed by the reading of the transformed state.

Reduced models and design principles for half-harmonic generation in synchronously pumped optical parametric oscillators

We develop reduced models that describe half-harmonic generation in a synchronously-pumped optical parametric oscillator above threshold, where nonlinearity, dispersion, and group-velocity mismatch are all relevant. These models are based on (1) an eigenmode expansion for low pump powers, (2) a simulton-like sech-pulse ansatz for intermediate powers, and (3) dispersionless box-shaped pulses for high powers. Analytic formulas for pulse compression, degenerate vs. nondegenerate operation, and stability are derived and compared to numerical and experimental results.

Frequency comb metrology with an optical parametric oscillator.

We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser.

Tuning characteristics of femtosecond optical parametric oscillator with broadband chirped mirrors

We present the investigation of a synchronously pumped optical parametric oscillator (SPOPO) based on beta barium borate (BBO) nonlinear crystal with broadband complementary chirped mirror pairs (CMPs). Three SPOPO cavity configurations with slightly different intracavity dispersion were explored. Dispersion properties of cavity mirrors were characterized using a white light interferometer and found to be the key factor determining the gap-free tuning range as well as simultaneous multiwavelength generation. The SPOPO is pumped by the second harmonic of a Yb:KGW oscillator and provides signal pulses tunable over a spectral range from 625 to 980 nm. Signal pulse duration ranges from 102 to 268 fs in various intracavity dispersion regimes. In addition, signal beam power in excess of 500 mW is demonstrated, corresponding to 27% conversion efficiency from pump to signal wave.

Pulse compression effects of passive mode locker in ultrafast optical parametric oscillator

The pulse compression effects of passive mode locker, such as graphene and Kerr lens medium, which has been inserted into a synchronously-pumped optical parametric oscillator (SPOPO) pumped by pulse laser, and a continuous-wave (cw) pumped actively mode-locked OPO has been studied theoretically. By solving the nonlinear coupled-wave equations in the plane-wave approximation, we simulate the relations of the pulse width and peak power of the signal pulses to the normalized aperture radius, the nonlinear crystal length and the beam radius on the nonlinear crystal. The numerical results indicate that the Kerr lens medium and graphene are both favorable for the pulse compression in the SPOPO, and each of them has different advantages. Whereas in the actively mode locked OPO, the Kerr lens medium may be a better alternative for the pulse compression.