Abstract: A wavelength of pump is set to an anomalous dispersion area of an optical fiber for wavelength conversion and pump power is set to be larger than a predetermined threshold of MI so that wavelength conversion capable of flattening conversion efficiency spectrum within a wide bandwidth is permitted. A pumping source can oscillate a lightwave having a wavelength in the anomalous dispersion region of the optical fiber for wavelength conversion and intensity which can flatten the conversion efficiency spectrum over the wide bandwidth.

Abstract: An optical wavelength converter that includes an optical sum frequency generator (SFG) and an optical difference frequency generator (DFG). The SFG receives part of both an input beam and a continuous-wave (CW) beam. The DFG receives part of the input beam as well as the output of the SFG. The output of the DFG represents the signal of the input beam modulated or carried on a beam having the frequency of the CW beam. Both single-channel and multi-channel configurations are integrally realized in similar numbers of components.

Abstract: A wavelength converter for converting wavelength of a signal beam combined to a pump beam. The wavelength converter comprises a mode converting region for converting mode of the pump beam; a direction combining region for combining the signal beam to the pump beam; and wavelength converting region for converting the wavelength of the signal beam combined to the pump beam. The mode converting region and the wavelength converting region are formed as integrated by nonlinear polymeric material to construct a polymeric waveguide extended along propagation direction. The wavelength converting region includes the nonlinear polymer poled to a predetermined direction. According to the present invention, a DFG device, a cascade wavelength converting device, and second harmonic generation device of higher energy converting efficiency can be developed.

Abstract: A compensated nonlinear optical frequency mixer for compensating the walk-off produced by group velocity mismatch (GVM) between interaction waves. The compensated mixer has a first mixing region in which the interaction waves participate in a non-linear optical mixing process and where walk-off occurs between the interaction waves due to GVM. The compensated mixer is equipped with a frequency selective coupling and time delay structure located after the first mixing region for eliminating the walk-off produced between the interaction waves in the first mixing region by guiding the waves in arms whose lengths differ by a re-synchronization length. A second mixing region is located after the frequency-selective coupling and time delay structure, such that when the waves emerge in phase from the frequency selective coupling and time delay structure they continue to interact efficiently in the second mixing region.

Abstract: An optical parametric device for broadband parametric processes involving first and second frequencies &ohgr;1 and &ohgr;2. The device comprises an optical fiber comprising a core and a cladding, the cladding being microstructured with holes for providing waveguiding confinement of at least one optical mode in the core. The optical fiber is poled lengthwise with a non-linearity profile having a period that satisfies a quasi phase matching (QPM) condition including the first and second frequencies. Through the use of a poled holey fiber of suitable hole structure, it is possible to increase the second harmonic (SH) efficiency in comparison with poled conventional (non-holey) fiber. This is achieved by a combination of a low mode overlap area between the fundamental and SH waves, a low absolute value of the mode area, and a large SH bandwidth per unit length of the fiber, all of which can be provided together in a poled holey fiber.

Abstract: An optical wavelength converter converts an optical input signal having a first wavelength into an optical output signal having a second wavelength. The wavelength converter includes a saturable absorber switch having a control beam waveguide and an input waveguide. The converter further includes a first input coupled to the control beam waveguide and adapted to receive the optical input signal, and a second input coupled to the input waveguide and adapted to receive a second optical signal having the second wavelength from an optical source.

Abstract: An Optical Frequency Shifter (Shifter) enables all-optical frequency translation to be imparted on a data-carrying Input Optical Signal (Input Signal). The Shifter includes a first difference-frequency-mixer for achieving quasi-phase-matching between a first pump channel, the Input Signal and an Intermediate Signal. A second difference-frequency-mixer is employed for achieving quasi-phase-matching between a second pump signal, the intermediate signal and a converted signal. A frequency shift discriminates the input signal from the output signal wherein the value of the frequency shift is proportional to the difference in frequencies of the first pump signal and the second pump signal. In this fashion, the value of the frequency shift in independent of the frequency of the input signal.

Abstract: An optical waveguide device includes a dielectric substrate; and an optical waveguide formed in the dielectric substrate, the optical waveguide having a longitudinal axis and an outgoing surface disposed at an angle other than a right angle relative to a plane perpendicular to the longitudinal axis.

Abstract: A method of creating a varying second order non-linearity profile along a waveguide, comprising: providing a waveguide structure with a waveguiding core and a surface adjacent to the waveguiding core; structuring the surface to produce a structured surface defining a varying distance between the structured surface and the waveguiding core along the waveguide; and thermally poling the waveguide structure to generate a varying second order non-linearity profile along the waveguide—derived from the varying distance between the structured surface and the waveguiding core. By the surface structuring the modulation of the second order non-linearly induced by the thermal poling can be enhanced. The waveguide structures can be used for making a variety of quasi-phase-matched (QPM) devices.

Abstract: A wavelength converter with a monolithically integrated delay loop in a delayed interference configuration that needs only one SOA, only one in and one output fiber. Unlike prior-art hybrid wavelength converters, our inventive device has a monolithically integrated delay loop utilizing an asymmetric splitting ratio.

Abstract: The present invention relates to a semiconductor optical amplifier system integrated within a semiconductor waveguide structure. The semiconductor optical amplifier system comprises a first semiconductor optical amplifier having a first spectral response and a second semiconductor optical amplifier having a second other spectral response. The second semiconductor optical amplifier is coupled to the first semiconductor optical amplifier for optically receiving an amplified optical signal from the first semiconductor optical amplifier.

Abstract: A two-dimensional second order nonlinear lattice formed in a lattice body is utilized for performing a one-step optical carrier wavelength interchange between pairs of input optical signals. The lattice body includes sensitized regions arranged in a two-dimensional array in a matrix material with the sensitized regions differing from the matrix material in the sign of the second order susceptibility. When an optical pump signal is coupled to the lattice body at a frequency corresponding to the sum of the frequencies of the two input signals, nonlinear interactions in the lattice body produce wavelength interchange between the input signals, resulting in angularly deflected optical signals exiting the lattice body in which the signal information on the input signals is interchanged between the carrier frequencies of the two input signals.

Abstract: A method of manufacturing a polymer film having second order non-linear optical properties which has excellent stability of orientated molecules and does not become disorientated, and a polymer film and a non-linear optical element are provided. A polymer solution is placed between two substrates, which are disposed substantially perpendicular with respect to a rotating stand and substantially symmetrical with respect to a rotation axis of the rotating stand, and the rotating stand is rotated. A polymer film having second order non-linear optical properties is formed by the centrifugal force generated at the polymer solution.

Abstract: The present invention relates to a wavelength converter apparatus for ultra-high speed optical signal process. So, the present invention (a)embodies a wavelength converter which does not need an outer pump light by composing a semiconductor optical amplifier-ring type laser and (b)provides a wavelength converter apparatus for ultra-high speed optical signal process which embodies to be always operated wavelength conversion to be always possible within the amplifying bandwidth(about 40 mm) of SOA by a wavelength-tunable optical band pass filter deposited in a laser resonator.

Abstract: Employed as a structure of a highly nonlinear optical fiber (nonlinear optical fiber) is a double-cladding structure in which a first cladding region 20 and a second cladding region 30 are disposed on the outer periphery of a core region 10. Since the double-cladding structure is employed, the cutoff wavelength &lgr;c can sufficiently be shortened even when, in order to increase the nonlinear coefficient &ggr;, the concentration of GeO2 added into the core is enhanced so as to raise the nonlinear refractive index, or the relative refractive index difference between the core and cladding is increased so as to reduce the effective area Aeff. This realizes an optical fiber or nonlinear optical fiber shortening its cutoff wavelength while having a sufficient nonlinearity, an optical amplifier and wavelength converter using the same, and a method of making an optical fiber.

Abstract: A wavelength converting element is provided in which a fundamental wave with respect to an optical crystal substrate and a peak of a vertical transverse mode of a second harmonic are made to coincide, the converting efficiency is good, and a beam shape which enables good joining to a lens or an optical fiber is obtained. Given that an angle formed by a surface of the optical crystal substrate and a C axis of the optical crystal substrate is &thgr;, a period at which inverted domains are formed is p, and a distance from a distal end of a comb-shaped electrode for forming the inverted domain to a central position of a waveguide is G, in the ion implantation, a concentration peak of the ion implantation is formed at a distance of substantially (G·tan &thgr;+p/4) from the surface of the optical crystal substrate.

Abstract: A device for spatially separating components of frequency in a primary radiation beam comprising means for separating the primary radiation beam into a plurality of secondary radiation beams, a plurality of electrically biasable waveguides forming a waveguide array, each for transmitting a secondary radiation beam to an output, wherein each waveguide has an associated optical delay line having a corresponding optical delay time, wherein each of the optical delay times is different. The device also comprises means for applying a variable electric field across each of the waveguides such that the phase of the secondary radiation beams transmitted through each may be varied by varying the electric field. The secondary radiation beams output from each of the waveguides interfere in a propagation region with a secondary radiation beam output from at least one of the other waveguides so as to form an interference pattern comprising one or more maximum at various positions in the propagation region.

Abstract: The present invention provides a method of fabricating an electro-optically active fiber segment comprising the steps, in any order, of inducing a second-order nonlinearity in the fiber segment, and placing a portion of the fiber segment between and in contact with two electrodes. Also, the present invention provides an electro-optically active fiber segment comprising a second-order nonlinearity induced within the fiber segment, and a portion of the fiber segment being between and in contact with a first electrode and a second electrode.

Abstract: A wavelength converting element having improved wavelength converting efficiency and having a beam shape which facilitates coupling to a fiber or the like, is manufactured at low cost. After a waveguide is formed by carrying out proton exchange at a lower substrate in which inverted domains are formed, an upper substrate is laminated to the lower substrate so as to oppose the waveguide. Thereafter, a heat treatment is carried out and protons diffuse into the upper substrate and the lower substrate such that the waveguide is made to be a waveguide whose refractive index distribution is symmetrical, and simultaneously, the upper substrate and the lower substrate are joined by the heat treatment.

Abstract: An optical waveguide element has a substrate made of a lithium tantalate single crystal or a lithium niobate-lithium tantalate solid solution single crystal and a bulky optical waveguide made of a lithium niobate single crystal directly joined the substrate. The c-axis of the single crystal to constitute the substrate is tilted from the surface of the substrate to be joined preferably by 17-37 degrees.

Abstract: Conventional short pulse optical parametric oscillator systems have relatively low repetition rates and cannot be pumped by continuous-wave lasers. The invention describes passively mode locked parametric oscillators, consisting of a continuous-wave laser pump source, an optical resonator which is resonant for only one of the two parametrically generated waves, a non-linear medium, and a saturable absorber or a medium for formation of a Kerr lens and an aperture. The repetition rate of such an oscillator system can be selected within a large range through selection of the resonator length. Fields of use are measuring technology and optical spectroscopy.

Abstract: Methods for fabricating a non-linear optical (NLO) film and a NLO film structure produced thereby are provided. The methods include depositing an alignment layer material on at least one surface of a substrate, aligning the molecules of the alignment layer material in a substantially uniaxial direction, and depositing a NLO film on the alignment layer material. The methods may be advantageous in that they tend to produce NLO films having relatively strong NLO properties. The methods may be further advantageous in that they are relatively simple and may be applied to a wide range of organic NLO materials.

Abstract: A photonic crystal comprises a plurality of elongated elements formed of a first dielectric material and arranged in a two-dimensional periodic honeycomb lattice. A second dielectric material surrounds the elongated elements and extending between them. The a second dielectric material defines between the elongated elements a plurality of spaces filled with a third dielectric material. The first dielectric material has permittivity that is greater than permittivity of the second dielectric material and permittivity of the third dielectric material.

Abstract: An optical wavelength converter, including first and second semiconductor optical amplifiers, in which an input optical pulse signal having a first wavelength &lgr;1 and a non-modulated optical signal having a second wavelength &lgr;2 are made incident upon the first semiconductor optical amplifier. Propagation constants of the first and second semiconductor optical amplifiers are determined such that a propagation constant difference &Dgr;&bgr; between the first and the second semiconductor optical amplifiers when only the optical signal having the second wavelength &lgr;2 propagates along the first semiconductor optical amplifier is smaller than a propagation constant difference &Dgr;&bgr; when both the input optical pulse signal and non-modulated optical signal propagate along the first semiconductor optical amplifier.

Abstract: An electrically controllable grating is provided by forming regions 4 and 5 of different refractive index within an electro-optic material. Electrodes are provided so that a readily controllable electric field may be applied to the index grating formed by the alternating regions such that the refractive index of the regions may be varied electrically to form a controllable grating. The grating may be used as an electrically controllable distributed Bragg reflector to allow variable wavelength feedback within a laser cavity. The grating may be used to perform wavelength division multiplexing and/or frequency modulation.

Abstract: A method for forming a ferroelectric domain-inverted structure, having the steps of joining at least two kinds of ferroelectric material which have different spontaneous polarizations, and ferroelectric domain-inverting one of the ferroelectric materials and thereby ferroelectric domain-inverting the other ferroelectric material joined thereto.

Abstract: A high gain optical parametric amplifier is implemented in a LiNbO3 waveguide fabricated by a combination of periodic electric field poling and proton exchange techniques. The device is capable of amplification in the whole transmission window of silica optical fibers with gains up to 90 dB. The high nonlinearity and resultant high gain of the waveguide-amplifier permits the use of essentially standard power (milliwatt to 10 watt) fiber laser pump sources.

Abstract: A wavelength converter with a monolithically integrated delay loop in a delayed interference configuration that needs only one SOA or other non-linear optical element coupled to the input fiber, a first coupler to arranged to split the output of the SOA or other non-linear optical amplifying element into two paths having controllable delay and phase shift characteristics, and at least one output coupler to combine the signals present on the two paths to provide the converter output. Unlike prior-art hybrid wavelength converters, one embodiment of the invention has a monolithically integrated delay loop utilizing an asymmetric coupler that can be either the first coupler or the second coupler, or both. Another embodiment of the invention has a coupler that does not require an asymmetric splitting ratio, and has either a gain element in one of the paths, an attenuation element in one of the paths, or both.

Abstract: An all-optical switch for outputting output light by transmitting/interrupting second input light with a second wavelength synchronizing with first input light with a first wavelength. The all-optical switch has: an optical interferometer to which the first and second input lights are input and which is composed of a non-linear semiconductor waveguide; a supervisory laser light source which supplies supervisory light with a third wavelength to the optical interferometer; and a controller to which supervisory light output from the optical interferometer is input as output supervisory light and which controls the phase bias of the interferometer according to the output supervisory light.

Abstract: An optical waveguide element is disclosed, which includes a three-dimensional optical waveguide of a bulky non-linear optical crystal, a substrate, and a joining layer made of an amorphous material through which the substrate is joined to the optical waveguide.

Abstract: A multiple-wavelength ultrashort-pulse laser system includes a laser generator producing ultrashort pulses at a fixed wavelength, and at least one and preferably a plurality of wavelength-conversion channels. Preferably, a fiber laser system is used for generating single-wavelength, ultrashort pulses. An optical split switch matrix directs the pulses from the laser generator into at least one of the wavelength conversion channels. An optical combining switch matrix is disposed downstream of the wavelength-conversion channels and combines outputs from separate wavelength-conversion channels into a single output channel. Preferably, waveguides formed in a ferroelectric substrate by titanium indiffusion (TI) and/or proton exchange (PE) form the wavelength-conversion channels and the splitting and combining matrices. Use of the waveguide allows efficient optical parametric generation to occur in the wavelength-conversion channels at pulse energies achievable with a mode-locked laser source.

Abstract: A wavelength conversion apparatus and method uses four wave mixing of a first wavelength and a control wavelength in an optical fiber to convert the first wavelength to a desired wavelength. Four wave mixing is produced by operating the optical fiber at a predetermined input power density and by using a fiber length which provides substantial Raman gain. The first wavelength is converted to a higher wavelength by using the higher wavelength four wave mixing signal and converted to a lower wavelength by using the lower wavelength four wave mixing signal.

Abstract: To a first nonlinear waveguide and a second nonlinear waveguide each having a refractive index which varies in response to the input of an optical signal, input optical signal pulses are inputted together with continuous light of a predetermined wave length said input optical signal pulses being caused to have a time delay corresponding to 0.6˜1.2 times the pulse width of said input optical signal pulses. Then, the phase of an optical signal outputted from the second nonlinear waveguide is adjusted to a predetermined amount with respect to the phase of an optical signal outputted from the first nonlinear waveguide, and the optical signal outputted from the first nonlinear waveguide and an output signal outputted from the second nonlinear waveguide are coupled, whereafter a wavelength component of the input optical signal pulse is removed from the coupled optical signal.

Abstract: An optical waveguide device includes a dielectric substrate; and an optical waveguide formed in the dielectric substrate, the optical waveguide having a longitudinal axis and an outgoing surface disposed at an angle other than a right angle relative to a plane perpendicular to the longitudinal axis.

Abstract: An ultra-compact, room-temperature, continuous-wave infrared source that can rapidly tune over a very wide spectral range. The targeted spectral overages are 3 &mgr;m to 4 &mgr;m, 4 &mgr;m to 6 &mgr;m, 6 &mgr;m to 8 &mgr;m, and 8 &mgr;m to 12 &mgr;m. The spectral width of the infrared idler is expected to be ˜10 MHz. In particular, the invention is a monolithically integrated device which requires no external pump lasers or bulk optics for its operation. The invention uses difference-frequency-generation in a highly nonlinear optical semiconductor waveguide with which high power semiconductor lasers are integrated to internally provide the tunable pump and signal waves.

Abstract: An optical fiber communication system according to the present invention has, for example, first and second phase conjugators. The first phase conjugator converts a signal beam from a first optical fiber into a first phase conjugate beam. The first phase conjugate beam is supplied to the second phase conjugator by a second optical fiber. The second phase conjugator converts the first phase conjugate beam into a second phase conjugate beam. The second phase conjugate beam is transmitted by a third optical fiber. The second optical fiber is composed of a first portion located between the first phase conjugator and a system midpoint and a second portion located between the system midpoint and the second phase conjugator. The total dispersion of the first optical fiber substantially coincides with the total dispersion of the first portion, and the total dispersion of the second portion substantially coincides with the total dispersion of the third optical fiber.

Abstract: An optical parametric circuit for separating an input signal light and a wavelength-converted light even when the wavelength difference is small is provided. The optical parametric circuit includes: a nonlinear Mach-Zehnder interferometer which includes a first optical path and a second optical path; optical dispersive mediums and second-order optical nonlinear mediums provided in the first and second optical paths; wherein optical dispersive medium and second-order optical nonlinear medium in the first optical path are placed in the reverse order of optical dispersive medium and second-order optical nonlinear medium in the second optical path.

Abstract: A multi quantum well layer has a lamination of first and second quantum well layers each sandwiched between barrier layers and defining a quantum well. The band gap of the second quantum well layer is larger than the band gap of the first quantum well layer. Current is flowed through the multi quantum well layer from a pair of electrodes. A first optical system input inputting a signal light wave to the multi quantum well layer via an input plane of the multi quantum well layer. A second optical system propagates an output light wave output from an output plane of the multi quantum well layer. A wavelength converting device is provided which can suppress the conversion efficiency from being lowered at a large detuning angular and obtain a relatively high conversion efficiency even at a negative detuning angular frequency.

Abstract: A wavelength converter is provided. The wavelength converter includes a substrate; first and second semiconductor optical amplifiers (SOAs) provided in parallel on the substrate, each of the SOAs including a first portion which passes light at one end, and a second portion which passes light at the opposite end; a first waveguide connected to the second portions of the first and second SOAs; a second waveguide connected to the first portion of the first SOA; and a third waveguide connected to the first portions of the first and second SOAs. The first through third waveguides are arranged on one side of the substrate in the vicinity of the first portions of the first and second SOAs. The first waveguide is connected to the second portions of the first and second SOAs through a unit for changing an optical progressing path.

Abstract: A wavelength converter which has a simple configuration and can be easily controlled and stably operated, used for a long-distance mass optical communication, it comprises a waveguide 5 for causing a change of a nonlinear refractive index, a delay interference circuit 6 having two optical paths 62 and 63 of different optical path lengths, and a CW light source 1 and the like, wherein a coherent length (&Dgr;LC=vg/&Dgr;&ngr;:vg is a traveling speed of the CW light in the delay interaction circuit 6) determined by a spectral line width (&Dgr;&ngr;) of CW light output from the CW light source 1 is longer than an optical path difference (&Dgr;Ld) between the two optical paths in the delay interference circuit 6 (&Dgr;LC>&Dgr;Ld).

Abstract: A wavelength converter which has simple configuration and can be easily controlled and operated with stability, and used for a long-distance mass optical communication, comprises a waveguide for causing a change of a nonlinear refractive index. The converter includes a delay interference circuit having two optical paths and of different optical path lengths. A CW light source is input into the waveguide. A coherent length determined by a spectral line width of CW light output from the CW light source is longer than an optical path difference between the two optical paths in the delay interference circuit.

Abstract: A tunable photonic band-gap device is disclosed which utilizes photoresponsive materials and is tunable over a range of wavelengths with the application of light. The device comprises a structure having a plurality of photoresponsive regions arranged in a matrix whereby the behavior of the device in preventing electromagnetic radiation from propagating through the structure may be modified by applying light to the photoresponsive regions. In one embodiment, a photonic band-gap transistor has a light propagation path defined by a plurality of dielectric and photoresponsive rods disposed in a substrate for the routing of a signal through the structure from an inlet to an outlet. The path comprises an input signal path beginning at the inlet, an output signal path terminating at the outlet, and a control signal path which merges with the input signal path to be joined with the output signal path at a common intersection point.

Abstract: An active structure in the semiconductor die of an amplifier or converter includes a plurality of stacked active layers with different compositions. The different compositions lead to a spectral offset between the respective gain bands of the layers which widens the gain band of the amplifier or the optical bandwidth of the converter. Applications include fiber optic telecommunication networks.

Abstract: There is provided an optical wavelength converter which allows the rapid and efficient shifting of information modulated on a light signal of one wavelength to a light signal of a second wavelength without the negative effects of noise and other disturbances which have proven to be problems in the prior art. The device splits a CW probe signal of a first wavelength into two components, which propagate with opposite orientations through a Kerr leg. Also propagating in the Kerr leg is a modulated drive signal at a second wavelength. These signals interact in the Kerr leg, and are recombined at an output coupler so as to create interference between the two probe components. An intensity modulated probe signal is output.

Abstract: A first polarizer separates an input light of the wavelength &lgr;2 into an X polarized wave and a Y polarized wave normal to each other. The input light of wavelength &lgr;2 is a linearly polarized wave. The X polarized wave is input to the second polarizer after passing through a semiconductor optical amplifier. The Y polarized wave is led by a reflecting device to the second polarizer. The refractive index of a waveguide of the semiconductor amplifier changes depending on the intensity of an input light. A signal light which is intensity-modulated according to a transmission signal and has the wavelength &lgr;1 is input to the semiconductor optical amplifier. The second polarizer couples the X and Y polarized waves. The third polarizer receives and outputs an output light from the second polarizer.

Abstract: A wavelength converting device for converting a wavelength of a light is provided. The wavelength control device including: a waveguide layer for guiding the light; a substrate having a lattice constant is different from a lattice constant of the waveguide layer; and a buffer layer which is disposed between the waveguide layer and the substrate and which has a lattice constant between the lattice constant of the waveguide layer and the lattice constant of the substrate.

Abstract: The component comprises structures, achieved in integrated optics, exerting predetermined stresses on a light wave guiding waveguide so as to maintain or modify in predetermined manner the polarization state of an incident light wave. These structures are formed by at least one segmented plane waveguide arranged laterally with respect to the light wave guiding waveguide and formed by parallel lateral waveguides perpendicular to the longitudinal axis of the light wave guiding waveguide. These structures are achieved at the same time as the light wave guiding waveguide, the segmented plane waveguides having refractive indexes lower than or equal to those of the light wave guiding waveguide. Such structures can be arranged symmetrically or asymmetrically, alternately on each side of the light wave guiding waveguide.

Abstract: A wavelength converter incorporating an on-chip integrated laser for use in an optical system. The converter includes a first port for receiving an optical input signal such as a WDM signal and providing it to an interferometer, and an output port for outputting a signal which is a wavelength-converted version of the input signal. An optical source or laser is fabricated on the chip substrate on which the interferometer is formed for providing operating power to the interferometer. Power levels of the input signal are maintained by adjusting an on-chip semiconductor optical amplifier that receives the optical input signal and provides the amplified signal to the interferometer. In an alternative embodiment, the on-chip optical source is replaced by an on-chip pre-amplifier for an external laser source.

Abstract: Disclosed is a wavelength converter that is appropriate for long-distance large-capacity optical communication, a wavelength converter according to the present invention includes: waveguides 1 and 2 for producing nonlinear changes in refractive indices; light interaction circuits 3 and 4; and light delay circuits 9 and 10. When an input signal pulse interval is denoted by To and a speed at which signal pulse light proceeds through a delay circuit is denoted by vg, a difference &Dgr;Ld for optical paths in the light delay circuits satisfies a relation &Dgr;Ld=vgTo/2. As a result, when there is an interaction involving two sequential light beams, the phases of which are demodulated by the input signal pulse, the wavelength chirping affecting the light beams is canceled out.

Abstract: A second harmonic wave-generating element for generating a second harmonic wave from a fundamental wave, having an optical waveguide layer made of first epitaxial material having a fundamental composition of K3Li2−x(Nb1−YTaY)5+XO15+Z, an underclad part made of second epitaxial material having a fundamental composition of K3Li2−X+A(Nb1−Y−BTaY+B)5+X−AO15+Z, an overclad part made of third epitaxial material having a fundamental composition of K3Li2−X+C(Nb1−Y−DTaY+D)5+X−CO15+Z and formed on and contacting the optical waveguide layer, wherein X=0.006 to 0.5, Y=0.00 to 0.05, A=0.006 to 0.12, B=0.005 to 0.5, C=0.006 to 0.12, D=0.005 to 0.5, X−A≦0, X−C≧0, |A−C|≦0.006, and |B−D|≦0.005).