We demonstrate here a compact optical parametric oscillator module for mid-infrared generation via nonlinear frequency conversion. This module weighs only 2.5 kg and fits within a small volume of 220 × 60 × 55 mm³. The module can be easily aligned to various pump laser sources, and here we use a 50 W ytterbium (Yb)-doped fiber laser as an example. With a two-channel MgO-doped periodically poled lithium niobate crystal (MgO:PPLN), our module covers a tuning range of 2416.17–2932.25 nm and 3142.18–3452.15 nm. The highest output power exceeds 10.4 W at 2.7 μm, corresponding to a conversion efficiency of 24%. The measured power stability is 2.13% Root Meat Square (RMS) for a 10 h duration under outdoor conditions.

We demonstrate a compact, high efficiency and widely tunable intracavity singly resonant optical parametric oscillator (IC-OPO) based on multichannel periodically poled lithium niobate (PPLN). The IC-OPO is composed of 808 nm pump laser diode (LD), Nd:YVO₄ laser and linear OPO. The continuous-wave (CW) mid-infrared (MIR) output laser is tunable from 2.25 to 4.79 μm. The maximum output power exceeds 1.08 W at 3.189 μm at 9.1 W LD pump power and the conversion efficiency is 11.88%. We also build up a prototype with volume of 145 × 85 × 42.5 mm³ and its total weight is less than 2 kg. The measured power stability is 1.3% Root Meat Square (RMS) for a 3 h duration under simulated high temperature conditions of 40 °C. RMS is 2.6% for a 4 h duration when simulated temperature is − 40 °C.

We demonstrate a tunable optical parametric oscillator in a periodically poled congruently grown lithium tantalite whispering gallery mode resonator. The resonator is mechanically polished to millimeter size, and the quality factor is approximately 107 at 1064 nm. Our experiments show that this kind of resonator is capable of reaching a very low threshold and having a wide tuning range. Combined with its narrow resonant linewidth, it is potentially used as a compact, widely tunable, and narrow-linewidth infrared to mid-infrared laser source.

High-power and widely tunable continuous-wave optical parametric oscillators (cw OPOs), as mature radiation sources in the mid-infrared range, are limited by their frequency fluctuation. We built a cw OPO working at the near- and mid-infrared ranges and discuss the extent to which its frequency stability is affected by the mechanical temperature and the air pressure of the cavity. In addition, we artificially provoked mode hops by changing the above two factors to analyze the thermal-induced refractive index variation of the crystal. An inequality between the spacing of the hops and the free spectrum range (FSR) was observed. The wavelength stability of the cw OPO was guaranteed passively, and the longest mode-hopping-free time exceeded 13 h through sealing the cavity and thermal control. Further analysis of factors affecting frequency drift is critically essential for the reliability of cw OPO, particularly in environments outside the laboratory, and may provide a new method for high-precision tuning wavelengths.

High-power optical parametric oscillators (OPOs), as mature radiation sources in mid-infrared (MIR), degenerate gradually with wavelength increase, mainly above 3700 nm. Using a periodically poled magnesium-oxide-doped lithium niobate (MgO:PPLN) as the nonlinear crystal, we build a high-power signal-resonant OPO pumped by ytterbium-doped fiber laser (YDFL). To improve the OPO’s output power at ~3.8 μm, the parameters, such as the pump beam’s waist diameter and location, the curvature radius of the output coupler and the length of MgO:PPLN, are discussed in detail. When pump power is 79 ± 4 W with a repetition rate of 200 kHz, the OPO provides up to 8 ± 0.4 W average power in beam quality with M² factors of ~1.84 and ~1.69 in the two axes. Under the highest output power, the center wavelength of the idler beam is 3768.4 nm with a full-width at half-maximum (FWHM) bandwidth of ~18.6 nm. When the output power reaches ~6.3 W, its power stability is 1.6% root mean square (RMS) over 7 h. Further analysis of the factors affecting OPO’s performance and simple structure are critically essential for compact OPO prototypes with a capacity of high output power.

A two-dimensional binary phase grating is proposed in this paper. Unlike a conventional transmission grating, in theory, the proposed phase grating can simultaneously eliminate the zero- and high-order diffraction along certain axes on the image plane, forming a pure sinusoidal transmission modulation that leaves only the first-order diffraction. The first-ever, to the best of our knowledge, theoretical model for achieving sinusoidal transmission modulation is suggested in this paper; then the theoretical calculation and experiment results are displayed to investigate the physical mechanism of the proposed grating. Moreover, the manipulation on the arrangement of grating design can disperse or concentrate the diffraction energy at a specific axis. Finally, almost first-order-only diffraction is achieved on a single axis by introducing random changes to certain geometrical parameters of the two-dimensional binary phase grating. Our work provides potential applications in optical science and engineering fields.