Optical apparatus for performing a frequency-conversion operation on laser-radiation includes three elongated optically nonlinear crystals arranged end-to-end on a propagation-axis of the laser-radiation. Each of the crystals is arranged to perform the same frequency-conversion operation. The length of the crystals is made progressively shorter in the propagation-axis direction.

The present application discloses a single-frequency continuous-wave optical parametric oscillator, comprising a pumping source, a focusing lens, a resonant cavity, an optical parametric down-conversion crystal, and a birefringent crystal. The resonant cavity comprises a concave-convex lens, an output planoconcave lens, and at least two transitional planoconcave lenses; and a waist spot of pump light obtained through the focusing lens is located between the concave-convex lens and a first transitional planoconcave lens adjacent to the concave-convex lens on a light path. The center of the optical parametric down-conversion crystal coincides with a waist spot of the pump light; the birefringent crystal is located at the beam waist between the output planoconcave lens and the second transitional planoconcave lens adjacent to the output planoconcave lens on the light path; and the birefringent crystal adopts a critical phase matching or non-critical phase matching mode.

A nonlinear optical device includes two coupling systems. A coupling coefficient between the two coupling systems is regulated and controlled. During operation, the pump light input from a straight waveguide is coupled into the second coupling system through the first coupling system and obtains great resonance enhancement in the second coupling system, so it is ensured that the second coupling system is in a high energy state. For signal light input from the same end of the straight waveguide, the signal light enters a resonator of the second coupling system through the coupling between the first and second coupling systems. A nonlinear effect of the system mainly occurs in the resonator of the second coupling system because in the resonator of the second coupling system, the pump light is in a great resonance enhancement. The entire resonator is in a high energy state.

A system for conversion or amplification using quasi-phase matched nonlinear optical wave-mixing includes a first radiation source for providing a pump radiation beam, a second radiation source for providing a signal radiation beam, a bent structure for receiving the pump radiation beam and the signal radiation beam, and an outcoupling radiation propagation portion for coupling out an idler radiation beam generated in the bent structure. A radiation propagation portion of the bent structure is made of a uniform three-dimensional material at least partly covered by a two-dimensional or quasi-two-dimensional material layer and has a dimension taking into account the spatial variation of the nonlinear optical susceptibility along the radiation propagation portion as experienced by radiation traveling along the bent structure for obtaining quasi-phase matched nonlinear optical wave-mixing in the radiation propagation portion. The dimension thereby is substantially inverse proportional with the linear phase mismatch for the nonlinear optical process.

An extra cavity harmonic generator system may produce a round, non-astigmatic third harmonic output beam from a nominally round, non-astigmatic, diffraction limited input fundamental beam. The system may include a second harmonic generation crystal. An input fundamental beam size is expanded in a non-walkoff direction for the SHG crystal at the SHG crystal input face. A higher harmonic generation crystal has an output face oriented at an oblique angle of incidence in a non-walkoff direction for the HHG crystal such that an output higher harmonic beam size is contracted in this direction. Expansion of the input fundamental beam at the SHG crystal input face exceeds reduction of third harmonic beam at the HHG crystal output face.

A steerable laser transmitter and situational awareness sensor uses a liquid crystal waveguide (LCWG) to steer a spot-beam onto a conical mirror, which in turn redirects the spot-beam to scan a FOV. The spot-beam passes through one or more annular sections of non-linearly material (NLM) formed along the axis and around the conical mirror. Each NLM section converts the wavelength of the spot-beam to a different wavelength while preserving the steering of the spot-beam. The LCWG may shape or move the spot-beam along the axis of the conic mirror to sequentially, time or time and spatially multiplex the spot-beam between the original and different wavelengths. This provides multispectral capability from a single laser source. The transmitter also supports steering the spot-beam at a wavelength at which the LCWG cannot steer directly.

A laser system includes a seed source optically coupled to an extra cavity harmonic generator system may produce a round, non-astigmatic third harmonic output beam from a nominally round, non-astigmatic, diffraction limited input fundamental beam from the seed source. The system may include a second harmonic generation crystal. An input fundamental beam size is expanded in a non-walkoff direction for the SHG crystal at the SHG crystal input face. A higher harmonic generation crystal has an output face oriented at an oblique angle of incidence in a non-walkoff direction for the HHG crystal such that an output higher harmonic beam size is contracted in this direction. Expansion of the input fundamental beam at the SHG crystal input face exceeds reduction of third harmonic beam at the HHG crystal output face.

A second harmonic generator may include a combiner to combine a fundamental optical beam with a residual fundamental optical beam. The second harmonic generator may include a second harmonic crystal, coupled to the combiner, to generate a second harmonic optical beam from the fundamental optical beam and the residual fundamental optical beam. Upon generation of the second harmonic optical beam, the residual fundamental optical beam may exit the second harmonic crystal.

An optical output coupler includes an uncoated plano-concave lens having a planar side and a concave side. An optical axis of the plano-concave lens is tilted at or near a Brewster angle relative to a beam axis. A first optical element is configured to focus a beam of radiation emerging from the planar side of the plano-concave lens along a first axis that is perpendicular to the beam axis. The first optical element is disposed between the planar side of the plano-concave lens and a second optical element. The second optical element is configured to focus a beam of radiation emerging from the planar side of the plano-concave lens along a second axis that is perpendicular to the beam axis, wherein the second axis is different from the first axis.

An optical filter for attenuating higher-order modes in an optical waveguide includes a shoulder slab formed of a first material having a first index of refraction and disposed on a second material having a second index of refraction, the first index of refraction being higher than the second index of refraction. The shoulder slab defines a near end having a first width, an intermediate section, adjacent to the first end section, and a far end section, adjacent to the intermediate section and opposite the first end section along a direction of beam propagation. The optical filter also includes a waveguide ridge, formed of the first material and disposed atop the shoulder slab, that traverses the shoulder slab, and is configured to guide light of a fundamental mode along the direction of beam propagation from the near end section to the far end section.