An optical second-harmonic generator (or spontaneous parametric down-converter) includes a microresonator formed of a nonlinear optical medium. The microresonator supports at least two modes that can be phase matched at different frequencies so that light can be converted between them: A first resonant mode having substantially radial polarization and a second resonant mode having substantially vertical polarization. The first and second modes have the same radial order. The thickness of the nonlinear medium is less than one-half the pump wavelength within the medium.

According to examples, a tunable visible light source may include a periodically poled lithium niobate (PPLN) waveguide and a control mechanism to optimize the phase-matching of the PPLN waveguide in response to an input signal with a varied wavelength. The control mechanism may include an electro-optic (EO) tuning mechanism, a microheater-based thermo-optic (TO) control mechanism, and/or an acousto-optic (AO) control mechanism. The control mechanisms may, respectively, generate an electric field, heat, or an acoustic wave to affect a change in refractive index of the PPLN waveguide and thereby optimize the conversion efficiency to maximize the output power of the output wavelength of the PPLN waveguide as the input wavelength is tuned.

A sensor including a resonator comprising a nonlinear material comprising a nonlinear susceptibility configured to convert a pump electromagnetic wave (EM) wave to a signal EM wave and an idler EM wave, wherein at least one of the pump EM wave, the signal EM wave and/or the idler EM wave is fed back through the nonlinear material to form one or more resonant EM waves. An actuator coupled to the resonator or a pump path to the resonator, controls at least one of a pump power of the pump EM wave, a detuning of the frequency modes of the resonator relative to one or more frequencies of the resonant EM waves, or a phase matching of the nonlinear material. An output of the resonator outputs one or more output EM waves comprising information about a sample coupled to the resonator.

An optical-frequency shift device to shift a first optical-signal of a first optical-frequency to a second optical-signal of a second optical-frequency, including a splitter to split the first optical-signal to optical-signals of first and second polarizations, orthogonal each other, a generator to generate first and fourth controlled-light of the first polarization, and second and third controlled-light of the second polarization, each of frequency differences between the first and second controlled-light and between the third and fourth controlled-light having a spacing equal to a difference between the first and second optical-frequencies, a nonlinear optical-medium in which idler light of the second and first polarization are created by causing cross phase modulation of the optical-signals of the first and second polarizations, the first and third controlled-light, and the second and fourth controlled-light, respectively, and an optical-combiner to combine the idler light of the second and first polarization.

A frequency converter system includes a source that emits a beam having a wide spectral band; and a frequency conversion cell including 1) a birefringent nonlinear crystal having a first phase-matching wavelength, with an input face that receives the beam, an output face that emits at least one frequency-converted beam, and at least two parallel faces different from the input and output faces; 2) means for applying an external mechanical force to at least one of said two parallel faces, resulting in a variation in the birefringence of the nonlinear crystal, the value of the applied external mechanical force being determined so as to obtain phase matching at a second phase-matching wavelength different from the first phase-matching wavelength; and 3) means for adjusting the external mechanical force for wavelength tunability in the frequency conversion cell.

A laser apparatus generating frequency converted light. Embodiments of the laser apparatus described herein apply a cascade of nonlinear frequency mixer for sum frequency generation (SFG) or difference frequency generation (DFG) between two frequency components of a spectrally combined laser beam with at least two spectral components originating from two respective laser sources, SFG of two frequency components beams offers up to a factor of four amplification of output power over SHG of a single laser beam.

An OPO with very fast and accurate tuning. The angle of the crystals in the OPO is controlled by converting the linear motion of a voice coil into rotational motion. In preferred embodiments one or two OPO crystals are mounted as a crystal unit that can rotate around an axis such that the angle of the crystals with respect to the beams' direction can be varied to generate the desired wavelengths. The crystal unit has a lever that is connected to the shaft of the voice coil such that as the shaft extend or retracts the level is pulled or pushed and the linear motion of the shaft is converted to an angular motion of the crystal unit. The position of the voice-coil shaft is controlled in a close-loop based on a built-in encoder. The relation between the reading of the encoder and the crystals' angle is recorded and provides the calibration of the unit. Preferably calibration is done by measuring the output wavelength of the OPO as a function of the encoder position.

A microwave-to-optical photon transducer is provided for generating coupling between a microwave signal (S.sub.in2) and an optical signal (S.sub.pi_in1, S.sub.pi_out1). The transducer comprises: a first input port; a second input port; a first output port for outputting the optical signal (S.sub.pi_out1) and one or more optical sideband signals (S.sub.out1, S.sub.out11, S.sub.out12); a first waveguide disposed between the first input port and the first output port to allow the optical signal (S.sub.pi_in1) and the one or more optical sideband signals (S.sub.out1, S.sub.out11, S.sub.out12) to propagate in the first waveguide; a second waveguide connected to the second input port, and extending in the transducer adjacent to the first waveguide to allow the microwave signal (S.sub.in2) to propagate in the second waveguide; a phase-matching arrangement to cause at least the optical signal (S.sub.pi_in1) and the microwave signal (S.sub.in2) to be phase-matched or quasi-phase-matched.

According to one aspect, the invention relates to a frequency conversion cell (10) comprising: a birefringent nonlinear crystal (12) characterized by a first phase-matching wavelength, having an input face (121.sub.A) for receiving at least one incident beam, an output face (121.sub.B) for emitting at least one frequency-converted beam, and at least two parallel faces (120.sub.A, 120.sub.B) different from the input and output faces; means (14, 14.sub.A) for applying an external mechanical force to at least one of said parallel faces (120.sub.A), called a force application face, resulting in a variation in the birefringence of the nonlinear crystal, the value of the applied external mechanical force being determined so as to obtain phase matching in the nonlinear crystal at a second phase-matching wavelength different from the first phase-matching wavelength.

A terahertz-wave generating element includes a waveguide including an electro-optic crystal; an optical coupling member that extracts a terahertz wave, which is generated from the electro-optic crystal as a result of light propagating through the waveguide, to a space; and at least two electrodes that cause a first-order electro-optic effect in the electro-optic crystal by applying an electric field to the waveguide so as to change a propagation state of the light propagating through the waveguide. A crystal axis of the electro-optic crystal of the waveguide is set such that the terahertz wave generated by a second-order nonlinear optical process and the light propagating through the waveguide are phase-matched.