Simultaneous quasi-phase-matching of two nonlinear interactions within a single orientation-patterned GaAs (OP-GaAs) grating was experimentally demonstrated for the first time, to the best of our knowledge. When pumped by the signal (2.74 μm) and idler (8.77 μm) output beams of a ZGP-based optical parametric oscillator, the designed aperiodic OP-GaAs grating produces a 2.09-μm and a 3.99-µm output with power levels of several milliwatts via the sum-frequency generation and difference-frequency generation, respectively, of the beams involved. This research opens up new possibilities for the development of engineered single OP-GaAs gratings, which can simultaneously produce multiple wavelengths in the whole infrared spectrum.

Time-multiplexed networks of degenerate optical parametric oscillators have demonstrated remarkable success in simulating coupled Ising spins, thus providing a promising route to solving complex combinatorial optimization problems. In these systems, referred to as coherent Ising machines, spins are encoded in the oscillator phases, and measured at the system output using phase-sensitive techniques, making intricate phase stabilization necessary. Here, we introduce an optical Ising machine based on spontaneous polarization symmetry breaking in a coherently driven fiber Kerr nonlinear resonator. In our architecture, the spins are encoded in the polarization state, allowing robust, all-intensity readout with off-the-shelf telecom components. By operating in a newly-discovered regime where nonlinearity and topology lock the system's symmetry, we eliminate drift and bias, enabling uninterrupted Ising trials at optical speeds for over an hour, without manual intervention. This all-fiber platform not only simplifies the hardware but also opens a path to more stable, high-throughput coherent optical optimization devices for applications from finance to drug design and beyond.

Dispersion engineering is pivotal for nonlinear optics, yet it often faces challenges posed by material and structural limitations. Here, we establish rotational symmetry breaking as the guiding principle for dispersion engineering in optical microcavities. Through boundary deformation, multi-branch global dispersion emerges in island modes, and local dispersion is controlled via resonance-assisted tunneling between quasi-whispering gallery modes. Enabled by the global dispersion, the optical parametric oscillation is predicted in blue-violet light spectrum with high efficiency (>55%) and large frequency separation (>180 THz). Using the local dispersion engineering, the doubly-resonant enhancement of second-harmonic generation is regulated by the resonance-assisted tunneling.

An all-solid-state single-frequency 248 nm deep-ultraviolet (DUV) source with watt-level (~1.2 W) average power was realized by sum-frequency generation (SFG) between 355 nm and 827 nm lasers, which is nearly one order-of-magnitude higher than our previous result [Opt. Lett.50, 1881 (2025)10.1364/OL.553247]. For this advancement, pulsed pumping was employed to increase the pulse energy of the 1064-nm fundamental driver. Meanwhile, simulation-guided optimization on the length of the LBO crystal was performed to maximize the conversion efficiency of the 827-nm optical parametric oscillator (OPO). Benefiting from both, the conversion efficiency from 1064 nm to 248 nm source was improved from 1.41% to 3.93% at 4 kHz. The beam quality factors M2 in the x and y directions were measured to be 1.61 and 1.10, respectively, and the linewidth was estimated to be ~270 MHz. To the best of our knowledge, this is the first watt-level output reported for all-solid-state single-frequency 248 nm source.

High optical nonlinearity can enable classical and quantum functionalities in all-fibre laser systems. However, despite long-standing efforts to exploit second-order optical nonlinearity in conventional all-fibre systems, nonlinear optical conversion efficiencies remain modest. Here we demonstrate all-fibre integration of twist-phase-matched rhombohedral boron nitride (rBN) flakes on the end facet of optical fibres for second-harmonic generation (SHG) and spontaneous parametric downconversion (SPDC). We provide local and global optimization of the interflake twist angles for phase-matching design, achieving an SHG conversion efficiency of ~4.1% and an SPDC coincidence rate of ~90 in van der Waals crystals integrated on optical fibre devices. Finally, we design an all-fibre frequency-doubling ultrafast laser by integrating a multifunctional nonlinear crystal of a graphene/rBN heterostructure to simultaneously generate mode-locked pulses and intracavity SHG emission. This work establishes a route for developing high-efficiency, second-order nonlinear functionalities, such as optical parametric oscillators, optical modulators and entangled photon sources, in all-fibre lasers.

Generating sub-50 fs laser pulses in the near-IR using nonlinear down-conversion is challenging due to the fundamental tradeoff between amplification bandwidth and gain. Conventionally, such ultrashort pulses in the near-IR are generated by optical parametric oscillators (OPOs)/optical parametric amplification (OPA) or OPO/OPA combinations, but the aforementioned challenges and the additional complexity remain, often requiring even several OPA stages. An elegant solution to circumvent this added complexity of an additional OPO is a continuous-wave (cw)-seeded OPA. However, such a setup usually encompasses a complex combination of multiple OPA stages. To avoid these problems, we here utilize our recently introduced compact multipass OPA technology to demonstrate a cw-seeded, extremely compact and simple, low-noise sub-50 fs watt-scale OPA that is tunable in the near-IR from 1.5 to 1.7 µm.

133 % Overall photon efficiency from 793 nm to mid-infrared 3.82 μm based on a compact optical parametric oscillator

Widely tunable mid-infrared BaGa2GeS6 optical parametric oscillator pumped at 1064 nm by Nd:YAG laser

A three-wavelength narrow-linewidth mid-infrared optical parametric oscillator based on secondary-pumping tandem MgO:PPLN double crystals

Exploring high-order Hermite-Gaussian modes generation from pump-wave off-axis pumped optical parametric oscillator for adjustable wavelength-versatile optical vortex sources

Optimization of optical parametric oscillator performance through active temporal pulse shaping

ABSTRACT We demonstrate a femtosecond optical parametric oscillator (OPO) based on using a temperature‐chirped LBO crystal as the parametric gain medium. The temperature‐chirp along the long LBO crystal is obtained by separately heating several points along the crystal. We achieve a wavelength‐tuning range over 660–945 nm for the signal wave by simply scanning the OPO cavity length, without the need to re‐align the OPO cavity. The tuning speed is only limited by the rate of scanning the cavity length. Experimentally, we have achieved a wavelength tuning speed of 124 nm ms −1 , which, to the best of our knowledge, represents the highest tuning speed that has been demonstrated for green‐pumped femtosecond OPOs. Moreover, by altering the temperature profile along the crystal, the OPO can generate chirp‐free pulses or chirped pulses over the wavelength‐tuning range. Our work provides a scheme to break the tuning‐speed limitation of conventional femtosecond OPOs based on temperature‐tuned crystals, which will benefit many applications, including biological imaging and Raman microscopy.

We demonstrate a compact, cavity-free approach to generate high-energy, few-picosecond (<5 ps), high beam quality near and mid-infrared (NIR-MIR) sources. This approach overcomes the size limitation of conventional synchronously pumped optical parametric oscillator (SPOPO). By using a mode self-reproduction periodic array of four KTA crystals pumped by a 1 MHz Nd:YVO4 MOPA system, we produce microjoule-level pulses from a tens centimeter-scale device. The device delivers 3 ps pulses with 2.6 μJ of energy at 1535 nm (signal light) and 0.8 μJ at 3467 nm (idler light).

The study examines two LBO phase-matched (PM) configurations for near-infrared optical parametric oscillators (OPOs) pumped by a 532 nm laser. The type-I PM LBO OPO generated an 1118 nm idler with an 11.4 ns pulse duration and an output power of 635 mW. The conversion efficiency was 27.6%, and the spectral linewidth was ∼23.2nm. The temperature tuning range was 3.5°C, corresponding to an average wavelength tuning rate of ∼22nm/ ∘ C. The beam quality factor M 2 was measured to be about 3.05. The type-II PM LBO OPO generated an 1116 nm idler with an 8.0 ns pulse duration and an output power of 424 mW, achieving an 18.4% conversion efficiency and a spectral linewidth of ∼1.3nm. The temperature tuning range was 130°C, corresponding to an average wavelength tuning rate of ∼0.77nm/ ∘ C, and the beam quality factor M 2 was measured to be about 2.50. The experiments reported in this paper indicate that type-I PM LBO OPOs offer higher efficiency and a broader wavelength tuning range than type-II configurations, whereas the type-II PM LBO OPO may be more favorable for achieving narrower spectral linewidths.

Abstract A dual-frequency, wavelength-tunable blue-green laser system is demonstrated. The system utilizes a high-energy 532 nm green laser to pump a KTiOPO 4 (67.8°, 0°) optical parametric oscillator followed by a LiB 3 O 5 (90°, 22.5°) second harmonic generator, generating blue laser light tunable from 447.6 to 459.7 nm with an overall frequency conversion efficiency of 4.2%. Both the residual green laser and the tunable blue laser can be emitted simultaneously, with respectively energies of 11.24 mJ and 0.92 mJ . The beam quality factors M 2 of the green and blue lasers are M 2 (x,y) = (18.7, 12.6) and M 2 (x,y) = (29.5, 11.0), respectively, with corresponding energy stabilities of 6.1% and 13.9%. The blue laser pulse width is 6.84 ns, yielding a peak power of 134 kW. This laser system offers potential for various undersea applications where adaptable wavelength tuning is essential.

Tunable laser sources capable of controlling the spatial structure of light fields are of great significance for multimodal laser physics and structured beam studies. To achieve efficient and flexible mode switching, we for the first time, to the best of our knowledge, propose and demonstrate an electro-optic Q-switching Nd:YAG laser oscillator capable of switching between Gaussian and vortex beams through spot-defect modulation. By introducing a spot-defect on the surface of a quarter-wave plate and adjusting its rotation angle, rapid switching between Gaussian and vortex beams is realized within the stable Q-switching operation region, yielding pulse energies of 4.08 mJ and 4.10 mJ for the Gaussian and vortex beams, respectively, at a repetition rate of 1 kHz. Furthermore, when employed as the pump source for a KTiOAsO4-based optical parametric oscillator (OPO), the system maintains consistent mode-switching behavior and excellent output performance in the mid-infrared region (∼3.5 µm).

We demonstrate a high-power wavelength-tunable nanosecond mid-infrared (MIR, 3-5 μm) vortex laser based on a singly resonant optical parametric oscillator (OPO). With a MgO:PPLN crystal pumped by a first-order vortex at 1064 nm, efficient orbital angular momentum (OAM) transfer was achieved from the pump to the idler, while the signal remained a Gaussian-like profile without OAM. By varying the crystal temperature, the idler wavelength was tuned from 3142 to 3442 nm. At 3442 nm, the idler delivered a record vortex output of 3.87 W with 0.84% root-mean-square (RMS) fluctuation over one hour. To our knowledge, this is the highest reported vortex power beyond 3 µm among oxide-based OPOs, providing a stable and practical source for MIR applications such as spectroscopy, imaging, and material processing.

Stabilization of Frequency-Doubled Synchronously Pumped Optical Parametric Oscillators Using an Optimized Parasitic Wavelength

Our previous studies demonstrated that a prototype photoacoustic (PA) and ultrasound (US) imaging catheter can differentiate intestinal inflammation and fibrosis. However, its compatibility with clinical endoscopic procedures has not been validated. Here, we present a translational PA-US dual-modality imaging catheter with a reduced diameter to fit the biopsy channel of standard adult colonoscopes and therapeutic upper endoscopes (∼3.7 mm). The catheter integrates an angle-tipped optical fiber (600-µm core) for PA illumination and a miniaturized 48-element ultrasound array operating at a center frequency of ∼9 MHz for signal reception. These components are enclosed in a hydrostatic balloon (12 mm diameter, 15 mm length when fully inflated) to ensure acoustic coupling with the intestinal lumen. The system was upgraded from our previous setup by incorporating a more portable optical parametric oscillator (OPO) laser and a Verasonics imaging platform. The imaging catheter was positioned at the disease locations in a pig model of esophageal fibrosis induced by argon plasma coagulation (APC). Multi-wavelength PA imaging and US imaging were performed to resolve the tissue components. The results demonstrate the catheter’s ability to assess inflammation and fibrosis in the gastrointestinal tract during a standard clinical endoscopy procedure.

In this work a quantum imaging setup based on undetected squeezed photons is employed for metrological applications such as sensitive phase measurement and quantum imaging. Unlike traditional quantum imaging with undetected photons, as introduced by A. Zeilinger et al., the proposed setup incorporates a homodyne detection system and enhances the brightness of the quantum light using optical parametric oscillators (OPOs). The inclusion of OPOs may challenge the validity of the low-gain approximation, necessitating the development of a new theoretical framework that extends beyond this approximation. The results demonstrate a higher signal-to-noise ratio, which serves as a key metric for both image quality and phase-measurement accuracy. Furthermore, an imaging protocol is introduced to effectively suppress background noise. Notably, this protocol enables the extraction of image information encoded in quantum fluctuations (noise), paving the way for non-disruptive imaging. This is particularly significant in the field of bio-imaging, since the object (a sensitive living cell) is interrogated by longer-wavelength idler light while detection is applied at optical frequency in which the sensors are less noisy and has more quantum efficiency.