Abstract: A method for preparing a periodically poled structure according to this aspect of the present invention comprises the steps of providing a ferroelectric substrate and performing a poling process by applying a poling current to at least one portion of the ferroelectric substrate according to a current waveform. The current waveform include a major phase and a tailed phase accompanying the major phase; the major phase has at least one peak current (Ip) and terminates when the current drops substantially equal to Ip/e, and the charge delivered to the portion of the ferroelectric substrate during the major phase is larger than that delivered during the tailed phase. The nucleation phase is configured to generate nucleation sites in the portion of the ferroelectric substrate and the spreading phase is configured to increase the size of the nucleation sites.

Abstract: A method for preparing a poled structure comprises the steps of forming a ferroelectric substrate having a top surface and a bottom surface, performing a doping process to form at least one inhibition block in the ferroelectric substrate, forming an electrode structure including a first electrode and a second electrode on the top surface and a third electrode on the bottom surface and applying a predetermined voltage to the electrode structure to form a plurality of inverted domains outside of the inhibition block in the ferroelectric substrate. The ferroelectric substrate has a first polarization direction and a first crystal structure, the inhibition block has a second crystal structure different from the first crystal structure, and the inverted domains have a second polarization direction substantially opposite to the first polarization direction.

Abstract: A periodic poling structure comprises a ferroelectric substrate including a plurality of tunnels, a plurality of first domains positioned in the ferroelectric substrate between the tunnels and a plurality of second domains interleaved between the first domains in the ferroelectric substrate. Each first domain has a first polarization direction, and each second domain has a second polarization direction different from the first polarization direction. The tunnels are disposed on a top surface and on a bottom surface of the ferroelectric substrate in an equal interval manner or in a variant interval manner. Particularly, the second polarization direction is opposite to the first polarization direction. The periodic poling structure further comprises a plurality of conductive blocks covering the entire base surfaces of the tunnels, or separated from the sidewalls of the tunnels by insulation gaps such that the conductive blocks cover only a portion of the base surfaces of the tunnels.

Abstract: A poled structure comprises a ferroelectric substrate having a top surface and a bottom surface, at least one inhibition block positioned in the ferroelectric substrate, an electrode structure including a first electrode and a second electrode on the top surface and a third electrode in a portion of the bottom surface between the first electrode and the second electrode and a plurality of inverted domains positioned outside of the inhibition block in the ferroelectric substrate. The ferroelectric substrate has a first polarization direction and a first crystal structure, the inhibition block has a second crystal structure different from the first crystal structure, and the inverted domains has a second polarization direction substantially opposite to the first polarization direction.

Abstract: A method for preparing a periodically poled structure according to this aspect of the present invention comprises the steps of providing a ferroelectric substrate and performing a poling process by applying a poling current to at least one portion of the ferroelectric substrate according to a current waveform. The current waveform include a major phase and a tailed phase accompanying the major phase; the major phase has at least one peak current (Ip) and terminates when the current drops substantially equal to Ip/e, and the charge delivered to the portion of the ferroelectric substrate during the major phase is larger than that delivered during the tailed phase. The nucleation phase is configured to generate nucleation sites in the portion of the ferroelectric substrate and the spreading phase is configured to increase the size of the nucleation sites.

Abstract: A method for preparing a periodically poled structure comprises the steps of providing a ferroelectric substrate having an upper surface and a bottom surface, forming an upper electrode including at least one first block and at least one second block on the upper surface, forming a bottom electrode including at least one third block and at least one fourth block on the bottom surface and performing a plurality of poling processes to form at least one first domain and at least one second domain in the ferroelectric substrate, wherein the first domain is formed between the first block and the third block, and the second domain is formed between the second block and the fourth block.

Abstract: A method for preparing a periodically poled structure comprises the steps of providing a ferroelectric substrate having an upper surface and a bottom surface, forming an upper electrode including at least one first block and at least one second block on the upper surface, forming a bottom electrode including at least one third block and at least one fourth block on the bottom surface and performing a plurality of poling processes to form at least one first domain and at least one second domain in the ferroelectric substrate, wherein the first domain is formed between the first block and the third block, and the second domain is formed between the second block and the fourth block.

Abstract: A wavelength converter structure according to one aspect of the present invention comprises a ferroelectric substrate, a ridge positioned on the ferroelectric substrate, a plurality of first domains positioned in the ridge and a plurality of second domains interleaved between the first domains in the ridge. The first domains have a first polarization direction and the second domains have a second polarization direction opposite to the first polarization direction. The refraction index of the ferroelectric substrate is different from the refraction index of the ridge. The ridge may include a rectangular portion, a taper portion, or a taper portion and a rectangular portion connected to the taper portion.

Abstract: A method for preparing a periodically poled structure comprises the steps of applying a predetermined voltage to first conductive blocks on a ferroelectric substrate such that a plurality of first domains having a first polarization direction are formed in the ferroelectric substrate and applying the predetermined voltage to second conductive blocks on the ferroelectric substrate such that a plurality of second domains having the first polarization direction are formed in the ferroelectric substrate between the first domains. In addition, the method may further comprises a step of applying the predetermined voltage to a third conductive blocks between the first conductive blocks and the second conductive blocks such that a plurality of third domains having the first polarization direction are formed in the ferroelectric substrate between the first domains and the second domains.

Abstract: A wavelength converter structure according to one aspect of the present invention comprises a ferroelectric substrate, a ridge positioned on the ferroelectric substrate, a plurality of first domains positioned in the ridge and a plurality of second domains interleaved between the first domains in the ridge. The first domains have a first polarization direction and the second domains have a second polarization direction opposite to the first polarization direction. The refraction index of the ferroelectric substrate is different from the refraction index of the ridge. The ridge may include a rectangular portion, a taper portion, or a taper portion and a rectangular portion connected to the taper portion.

Abstract: A periodic poling structure comprises a ferroelectric substrate including a plurality of tunnels, a plurality of first domains positioned in the ferroelectric substrate between the tunnels and a plurality of second domains interleaved between the first domains in the ferroelectric substrate. Each first domain has a first polarization direction, and each second domain has a second polarization direction different from the first polarization direction. The tunnels are disposed on a top surface and on a bottom surface of the ferroelectric substrate in an equal interval manner or in a variant interval manner. Particularly, the second polarization direction is opposite to the first polarization direction. The periodic poling structure further comprises a plurality of conductive blocks covering the entire base surfaces of the tunnels, or separated from the sidewalls of the tunnels by insulation gaps such that the conductive blocks cover only a portion of the base surfaces of the tunnels.

Abstract: An optical frequency mixer according to one embodiment of the present invention comprises a V-shaped resonant cavity including a first reflective surface, a second reflective surface and an output coupler, a pumping unit configured to emit a pumping wave to the laser gain medium to generate a resonating wave in the resonant cavity, a nonlinear crystal positioned on an optical path of the resonating wave in the resonant cavity, and an input interface configured to emit a mixing wave into the resonant cavity. Preferably, the output coupler can be a plano-concave lens having a concave surface configured to reflect the resonating wave and to focus the resonating wave such that the spot size of the resonating wave is matched the spot size of the pumping wave. Particularly, the nonlinear crystal is positioned between the output coupler and the input interface.

Abstract: An optical frequency mixer according to one embodiment of the present invention comprises a V-shaped resonant cavity including a first reflective surface, a second reflective surface and an output coupler, a pumping unit configured to emit a pumping wave to the laser gain medium to generate a resonating wave in the resonant cavity, a nonlinear crystal positioned on an optical path of the resonating wave in the resonant cavity, and an input interface configured to emit a mixing wave into the resonant cavity. Preferably, the output coupler can be a plano-concave lens having a concave surface configured to reflect the resonating wave and to focus the resonating wave such that the spot size of the resonating wave is matched the spot size of the pumping wave. Particularly, the nonlinear crystal is positioned between the output coupler and the input interface.

Abstract: A method is provided for forming a waveguide region within a periodically domain reversed ferroelectric crystal wherein the waveguide region has a refractive index profile that is vertically and horizontally symmetric. The symmetric profile produces effective overlapping between quasi-phasematched waves, a corresponding high rate of energy transfer between the waves and a symmetric cross-section of the radiated wave. The symmetric refractive index profile is produced by a method that combines the use of a diluted proton exchange medium at a high temperature which produces a region of high index relatively deeply beneath the crystal surface, followed by a reversed proton exchange which restores the original crystal index of refraction immediately beneath the crystal surface.

Abstract: A method for forming uniform, sharply defined periodic regions of reversed polarization within a unidirectionally polarized ferroelectric material proceeds as a two-step process. First, alignment keys are formed on upper and lower planar surfaces of a unidirectionally polarized ferroelectric material by producing a spaced pair of alignment key shaped domain reversed regions and etching alignment key shaped notches in the upper and lower surfaces where the domain reversed regions intersect the surface planes. These notches, being vertically aligned between the upper and lower surfaces, are then used to align photomasks over a surface coating of photoresist formed directly on the material surface or on SiO2 layers coating the material surface.

Abstract: A method for forming uniform, sharply defined periodic regions of reversed polarization within a unidirectionally polarized ferroelectric material proceeds as a two-step process. First, alignment keys are formed on upper and lower planar surfaces of a unidirectionally polarized ferroelectric material by producing a spaced pair of alignment key shaped domain reversed regions and etching alignment key shaped notches in the upper and lower surfaces where the domain reversed regions intersect the surface planes. These notches, being vertically aligned between the upper and lower surfaces, are then used to align photomasks over a surface coating of photoresist formed directly on the material surface or on SiO2 layers coating the material surface.

Abstract: A multi-channel optical frequency mixer for all-optical signal processing and a method for engineering the same. The multi-channel mixer uses a nonlinear optical material exhibiting an effective nonlinearity deff whose spatial distribution is defined by a quasi-phase-matching grating, e.g., a QPM grating. The spatial distribution is defined such that its Fourier transform to the spatial frequency domain defines at least two wavelength channels which are quasi-phase-matched for performing optical frequency mixing. The wavelength channels correspond to dominant Fourier components and the Fourier transform is appropriately adjusted using grating parameters such as grating periods, phase reversal sequences and duty cycles to include an odd or even number of dominant Fourier components. The multi-channel mixer can perform frequency mixing operations such as second harmonic generation (SHG), difference frequency generation (DFG), sum frequency generation (SFG), and parametric amplification.

Abstract: A method is provided for forming a waveguide region within a periodically domain reversed ferroelectric crystal wherein the waveguide region has a refractive index profile that is vertically and horizontally symmetric. The symmetric profile produces effective overlapping between quasi-phasematched waves, a corresponding high rate of energy transfer between the waves and a symmetric cross-section of the radiated wave. The symmetric refractive index profile is produced by a method that combines the use of a diluted proton exchange medium at a high temperature which produces a region of high index relatively deeply beneath the crystal surface, followed by a reversed proton exchange which restores the original crystal index of refraction immediately beneath the crystal surface.

Abstract: A multi-channel optical frequency mixer for all-optical signal processing and a method for engineering the same. The multi-channel mixer uses a nonlinear optical material exhibiting an effective nonlinearity deff whose spatial distribution is defined by a quasi-phase-matching grating, e.g., a QPM grating. The spatial distribution is defined such that its Fourier transform to the spatial frequency domain defines at least two wavelength channels which are quasi-phase-matched for performing optical frequency mixing. The wavelength channels correspond to dominant Fourier components and the Fourier transform is appropriately adjusted using grating parameters such as grating periods, phase reversal sequences and duty cycles to include an odd or even number of dominant Fourier components. The multi-channel mixer can perform frequency mixing operations such as second harmonic generation (SHG), difference frequency generation (DFG), sum frequency generation (SFG), and parametric amplification.

Abstract: A method of patterning and fabricating poled dielectric microstructures in dielectric materials comprising the following steps. A poled dielectric microstructure within a dielectric material is provided. The poled dielectric microstructure is then segmented into a plurality of independent sub-structures. The poled dielectric microstructures are then fabricated within each of the plurality of independent sub-structures. Additional processes and a novel poling setup for improving and implementing this patterning and fabrication method are also disclosed.