Bright entangled photon sources including an alignment-free, fiber-based, mechanically-rugged and generic interferometric module are disclosed. The inherent phase-stability of a Sagnac interferometer is deployed. High down-conversion efficiency of periodically poled nonlinear-waveguides is combined with the optical gain of semiconductor optical amplifiers and immunity of fiber optics. A single compact interferometric engine combines these attributes, allowing highly stable, integrable and bright polarization entangled-photon sources operating at room temperature. Using a minimum number of in-line optical parts, the compact module is based on a novel method that enhances the long-term stability and efficiency without compromising the entanglement quality. Besides energy entanglement, polarization entanglement is presented and set through the operational conditions. An optional periodically poled nonlinear waveguide can be hosted to achieve the desired spectral bandwidth and photons generation rate. The result is a zero-maintenance, lightweight, low-power consumption engine of compact and fully-integrable bright polarization-entangled photon sources.

A system for resonantly enhanced frequency conversion includes a nonlinear crystal for frequency converting a pump laser beam, and mirrors forming a ring resonator for the pump laser beam such that a closed propagation path of the pump laser beam, inside the ring resonator, passes through the nonlinear crystal. The mirrors include an adaptive mirror, a curved-mirror pair positioned in a first segment of the propagation path spanning between the adaptive mirror and the nonlinear crystal, and an input coupler for coupling the pump laser beam into the ring resonator. The curved-mirror pair forms an imaging system having conjugate planes at the adaptive mirror and the nonlinear crystal. The input coupler is positioned in a second segment of the propagation path that spans between the adaptive mirror and the nonlinear crystal and does not include deflection by the curved-mirror pair.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is Hz, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), H.sub.2Te (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is Hz, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), HzTe (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is H.sub.2, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), H.sub.2Te (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.

A nonlinear optical crystal of guanidinium tetrafluoroborate has a chemical formula of [C(NH.sub.2).sub.3]BF.sub.4 and a molecular weight of 146.89, belongs to the trigonal crystal system, has a space group of R3m; has lattice parameters of a=7.4634(10)Å, b=7.4634(10)Å, c=9.1216(19) (6)Å, and Z=3; has an ultraviolet cutoff edge of 200 nm; and has a frequency-multiplication response that is 4-5 times that of the commercialized nonlinear optical crystal KDP. A hydrothermal method, a room-temperature solution method, an evaporation method or a solvothermal method is used to grow the crystal in a centimeter-scaled size. The crystal can produce frequency-doubling, frequency-tripling, frequency-quadrupling, frequency-quintupling or frequency-sextupling harmonic light output from the fundamental frequency light of 1064 nm generated by a Nd:YAG laser, and/or can produce ultraviolet and deep-ultraviolet frequency-multiplication light output below 200 nm.

Devices, systems, and methods for generating ultraviolet lasers are disclosed. Schematics and arrangements of a combination structure implementation that often uses an intra-cavity second harmonic generation (SHG) element and a UV extractor often with a birefringent crystal (BC) to extract the UV light are described and disclosed. A Nonlinear crystal (NLC) may serve as the SHG element and volume Bragg gating (VBG) may be included to control pump light characteristics.

An optical element includes Strontium tetraborate SrB.sub.4O.sub.7 (SBO) crystal plates that are cooperatively configured to create a periodic structure for quasi-phase-matching (QPM) is used in the final frequency converting stage of a laser assembly to generate laser output light having a wavelength in the range of 125 nm to 183 nm. One or more fundamental light beams having fundamental wavelengths between 1 and 1.1 μm are doubled and/or summed using multiple intermediate frequency conversion stages to generate one or more intermediate light beam frequencies (e.g., second through eighth harmonics, or sums thereof), and then the final frequency converting stage utilizes the optical element to either double a single intermediate light beam frequency or to sum two intermediate light beam frequencies to generate the desired laser output light at high power and photon energy levels. A method and inspection system incorporating the laser assembly is also described.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is Hz, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), H.sub.2Te (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.

Improved efficiency for nonlinear optical interactions is provided by using strongly confining waveguides for simultaneous imposition of dispersion design constraints at two or more dispersion orders. Quasi-phase-matching allows for phase-matching to be accomplished independently of the waveguide design, which helps provide sufficient design freedom for the dispersion design.