JP2005156634A - Wavelength transducer having cylindrical ferroelectric single crystal and light generator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength transducer of which the heat distribution is centro-symmetrical. <P>SOLUTION: The wavelength transducer is constructed with a cylindrical ferroelectric single crystal of which the cross section is essentially a perfect circle and which has a polarity reversal structure with a specified period in a direction vertical to a polarization direction. The cylindrical ferroelectric single crystal is selected from a group consisting of essentially stoichiometric lithium niobate, essentially stoichiometric lithium tantalate, essentially stoichiometric lithium niobate with doped impurities and essentially stoichiometric lithium tantalate with doped impurities. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wavelength conversion element in which heat distribution is centrosymmetric. The present invention also relates to a wavelength conversion element having a multi-grating whose heat distribution is centrally symmetric and free from damage propagation, and a light generator using the same.

In recent years, research on wavelength conversion elements using ferroelectric single crystals having excellent nonlinear optical constants and electro-optical constants has been actively conducted. In particular, the development of wavelength conversion elements employing a quasi-phase matching method has been remarkable due to improvements in manufacturing techniques of high-quality ferroelectric single crystals and polarization inversion forming techniques.
A wavelength conversion element utilizing a monolithic lithium tantalate single crystal has been developed (see, for example, Patent Document 1).

FIG. 11 is a diagram illustrating a wavelength conversion system according to the prior art.
The wavelength conversion system 1100 includes a wavelength tunable laser 1101, a lens 1102, and a wavelength conversion element 1103.
The wavelength conversion element 1103 is made of a lithium tantalate single crystal close to a stoichiometric composition having a thickness of 0.3 mm to 5 mm. The wavelength conversion element 1103 has a periodic polarization inversion structure with a period of 3 μm to 5 μm manufactured by a voltage application method.
In such a wavelength conversion system 1100, light (fundamental wave) emitted from the wavelength tunable laser 1101 enters the wavelength conversion element 1103 through the lens 1102. The fundamental wave that has entered the wavelength conversion element 1103 is phase-matched (pseudo-phase-matched) with the second harmonic of the fundamental wave by a periodically poled structure that is periodically repeated in the light guiding direction. In this way, the fundamental wave is converted into the second harmonic while propagating through the wavelength conversion element 1103.

  On the other hand, a wavelength conversion element that can be adjusted over a wide range of wavelengths using a lithium niobate single crystal (hereinafter simply referred to as tunability) has been developed (see, for example, Non-Patent Document 1).

FIG. 12 is a diagram showing a conventional multi-grating quasi phase matching (QPM) parametric oscillator (OPO).
The QPM OPO 1200 includes a wavelength conversion element 1201, a first mirror 1202, a second mirror 1203, and a moving unit 1204.
The wavelength conversion element 1201 is manufactured from a congruent lithium niobate (CLN) wafer. The wavelength conversion element 1201 has a thickness in the direction parallel to the polarization direction of the CLN wafer of 0.5 mm and an element length L of 26 mm. The wavelength conversion element 1201 has a plurality of polarization inversion structures (gratings) having different periods. The width W _{G of} each grating is 500 μm. The interval between each grating is 50 μm. The period of each grating is 26 to 36 μm. The grating period is arranged to be incremented by 0.25 μm. Such a grating is repeatedly manufactured by a lithography technique using a mask having a predetermined period for each grating and an electric field application method. In the figure, only a part of the multi-grating is shown.

The first mirror 1202 and the second mirror 1203 each have a curvature radius of 150 mm. The 1st mirror 1202 and the 2nd mirror 1203 are arrange | positioned through the wavelength conversion element 1201, and the space | interval is 30 mm.
The moving unit 1204 moves the wavelength conversion element 1201 in parallel.

Next, the operation of the QPM OPO 1200 will be described.
Pump laser light (first wavelength λ ₁ = 1.064 μm) generated from a Q-switched Nd: YAG laser (not shown) passes through the first mirror 1202 and passes through the first mirror 1202 at a given beam diameter. It is incident on a grating having a predetermined period. At this time, the moving unit 1204 moves the wavelength conversion element 1201 in advance so that the pump laser light is incident on a predetermined grating. Thereafter, the pump laser light having the first wavelength λ ₁ is converted into signal light having the second wavelength λ ₂ and idler light having the third wavelength λ ₃ according to the period of the wavelength conversion element 1201. . At this time, part of the signal light having a wavelength of 1.54 μm is reflected by the first mirror 1202 and the second mirror 1203. The signal light and idler light transmitted without being reflected by the second mirror 1203 are emitted from the QPM OPO 1200.

According to the QPM OPO 1200 designed in this way, when the first wavelength λ ₁ of the pump laser light is 1.064 μm and the period of the multi-grating is 26 μm to 32 μm, the wavelength conversion element 1201 is moved by the moving unit 1204. The second wavelength λ ₂ of the signal light is 1.36 μm to 1.98 μm, and the third wavelength λ ₃ of the idler light is 4.83 μm to 2.30 μm. Can be achieved.
JP 2002-90785 A L. E. Meyrs et al., “Multigrading quasi-phase-matched optical parametric oscillator in periodic polled LiNbO3”, OPTIC LETTERS, April 15, 1996. 21, no. 8, pp. 591-593

  For example, when the wavelength conversion element 1103 shown in FIG. 11 is irradiated with light emitted from the wavelength tunable laser 1101, heat distribution may occur in the wavelength conversion element 1103. When the heat distribution occurs, the thermal birefringence effect of the ferroelectric single crystal that is the material of the wavelength conversion element occurs. When the thermal birefringence effect occurs, there arises a problem that the polarization of light is disturbed (that is, the mode of light can be changed). Such deterioration of the polarization characteristic decreases the extinction ratio. In order to compensate for the thermal birefringence effect, an optical system such as a polarizer and a quarter-wave plate is required, which complicates the entire apparatus and makes it difficult to reduce the size.

  Further, due to the thermal birefringence effect caused by the heat distribution, a part of the phase matching condition in the wavelength conversion element 1103 may not be satisfied. As a result, conversion efficiency can be greatly reduced. Furthermore, the beam shape of the light emitted from the wavelength conversion element 1103 may be distorted (not circular) depending on the shape of the heat distribution.

  On the other hand, since the wavelength conversion element 1201 shown in FIG. 12 is manufactured from a single wafer, damage such as cracks generated in one grating due to irradiation of pump laser light easily propagates to other gratings. It has a drawback of being vulnerable to damage (damage propagation). In addition, the wavelength conversion element 1201 has a problem in that it costs because the entire element must be replaced when one grating is damaged.

When producing the multi-grating, if the wavelength conversion element 1201 fails to produce one grating (the polarization inversion part is bonded), the entire wafer must be discarded. Therefore, the yield is bad.
Furthermore, the wavelength conversion element 1201 can wavelength-convert only light having TM polarization. Therefore, when the wavelength of the pump laser light is TE polarized light, it is necessary to change the TE polarized light to TM polarized light. For this reason, an optical system such as a polarizer is required in accordance with the polarization of the pump laser light, which causes a problem that the entire QPM OPO becomes large.

Accordingly, an object of the present invention is to provide a wavelength conversion element whose heat distribution is centrally symmetric.
Another object of the present invention is to provide a wavelength conversion element having a multi-grating whose heat distribution is centrally symmetric and free from damage propagation, and a light generator using the same.
Still another object of the present invention is to provide a wavelength conversion element with improved yield and a light generator using the same.
Still another object of the present invention is to provide a wavelength conversion element having an improved degree of freedom with respect to the polarization of incident light and a light generator using the same.

The wavelength conversion element according to the present invention comprises a cylindrical ferroelectric single crystal having a substantially circular cross section, and the cylindrical ferroelectric single crystal has a predetermined period in a direction perpendicular to the polarization direction. It has a domain-inverted structure, thereby achieving the above object.
The columnar ferroelectric single crystal includes substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and impurities. May be selected from the group consisting of substantially constant ratio lithium tantalate doped with.

The predetermined period is such that the cylindrical ferroelectric single crystal transmits a _first light having a _first wavelength λ ₁ , a second light having a second wavelength λ _2, and a third wavelength λ ₃ . In the case of conversion into the third light having the relationship, the first wavelength λ ₁ , the second wavelength λ _2, and the third wavelength λ ₃ are related by the relationship 1 / λ ₁ = 1 / λ ₂ + 1 / λ. ₃ may be a period of quasi-phase matching so as to satisfy the relations λ ₁ <λ ₂ and λ ₁ <λ ₃ .

In the predetermined period, when the cylindrical columnar ferroelectric single crystal converts the first light having the first wavelength λ ₁ into the second light having the second wavelength λ ₂ , The period in which the phase λ ₁ and the second wavelength λ ₂ satisfy the relation λ ₁ = 2 × λ ₂ may be a period in which quasi-phase matching is performed.
In the predetermined period, the cylindrical ferroelectric single crystal generates a first light having a _first wavelength λ ₁ and a second light having a second wavelength λ _2, and a third wavelength λ _3. When the light is converted into the third light having the relationship, the first wavelength λ ₁ , the second wavelength λ _2, and the third wavelength λ ₃ are related by the relationship 1 / λ ₁ ± 1 / λ ₂ = 1 / The period may be a quasi-phase matching so as to satisfy λ ₃ .

  A wavelength conversion element according to the present invention includes a holder and a plurality of columnar ferroelectric single crystals disposed on the holder, and each of the plurality of columnar ferroelectric single crystals has a substantially circular cross section. Each of the plurality of cylindrical ferroelectric single crystals has a domain-inverted structure having a predetermined period in a direction perpendicular to the polarization direction, and the plurality of cylindrical ferroelectric single crystals are These are arranged so that the directions perpendicular to the polarization direction are the same, thereby achieving the above object.

The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and Each may be selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.
In the predetermined period, each of the plurality of columnar ferroelectric single crystals has a first light having a _first wavelength λ ₁ , a second light having a second wavelength λ _2, and a third light. when converting to the third light having a wavelength lambda _3, and the first said wavelength lambda ₁ and the second wavelength lambda ₂ and the third wavelength lambda ₃ is the relation 1 / lambda ₁ = 1 / lambda _The period may be quasi-phase matched so as to satisfy ₂ + 1 / λ ₃ , relationships λ ₁ <λ ₂ and λ ₁ <λ ₃ .

In the predetermined period, each of the plurality of cylindrical ferroelectric single crystals converts the first light having the first wavelength λ ₁ to the second light having the second wavelength λ ₂ . The first wavelength λ ₁ and the second wavelength λ ₂ may have a quasi-phase matching period so that the relationship λ ₁ = 2 × λ ₂ is satisfied.
In the predetermined period, each of the plurality of columnar ferroelectric single crystals includes a first light having a _first wavelength λ ₁ and a second light having a _second wavelength λ ₂ . when converting to a third light having a wavelength lambda _3, and the first said wavelength lambda ₁ and the second wavelength lambda ₂ and the third wavelength lambda ₃ is the relation 1 / lambda ₁ ± 1 / lambda _It may be a period for quasi-phase matching so as to satisfy ₂ = 1 / λ ₃ .

The holder may be formed from a thermally conductive material.
You may further include the temperature control element installed in the said holder, and the heat insulation flame | frame which surrounds the said holder and the said temperature control element.
A control unit for controlling the temperature control element may be further included.
The plurality of columnar ferroelectric single crystals may be arranged at a predetermined interval, and the predetermined interval may be filled with a heat conductive material.

The light generator according to the present invention includes a light source that emits a first light having a _first wavelength λ ₁ , a second light having a second wavelength λ _2, and a third wavelength λ. and a wavelength conversion element for converting into a third light having a _3, and a control unit for controlling the position of the wavelength conversion element, wherein the wavelength conversion element, holder and a plurality of cylindrical shape disposed in the holder Each of the plurality of columnar ferroelectric single crystals is substantially circular, and each of the plurality of columnar ferroelectric single crystals has a first wavelength. λ ₁ , the second wavelength λ _2, and the third wavelength λ ₃ satisfy the relationship 1 / λ ₁ = 1 / λ ₂ + 1 / λ ₃ and the relationship λ ₁ <λ ₂ and λ ₁ <λ ₃ A domain-inverted structure having a predetermined period of quasi-phase matching in a direction perpendicular to the polarization direction, and the plurality of columnar ferroelectric single units Crystal is arranged such that a direction perpendicular the same with respect to the polarization direction, thereby achieving the above object.

The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and Each may be selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.
The holder may be formed from a thermally conductive material.
The wavelength conversion element may further include a temperature control element installed in the holder, and a heat insulating frame surrounding the holder and the temperature control element.
The controller may further control the temperature of the temperature control element.
The plurality of columnar ferroelectric single crystals may be arranged at a predetermined interval, and the predetermined interval may be filled with a heat conductive material.

A light source that emits first light having a _first wavelength λ ₁ according to the present invention, a wavelength conversion element that converts the first light into second light having a _second wavelength λ ₂ , and the wavelength conversion element The wavelength conversion element includes a holder and a plurality of columnar ferroelectric single crystals arranged in the holder, and the plurality of columnar ferroelectric single crystals Each cross-section is substantially a perfect circle, and each of the plurality of cylindrical ferroelectric single crystals has a relationship of λ ₁ = 2 × λ ₂ between the first wavelength λ ₁ and the second wavelength λ _2. A plurality of cylindrical ferroelectric single crystals having a predetermined period of quasi-phase matching in a direction perpendicular to the polarization direction so as to satisfy the polarization direction; It arrange | positions so that a perpendicular direction may become the same, This achieves the said objective.

The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and Each may be selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.
The holder may be formed from a thermally conductive material.
The wavelength conversion element may further include a temperature control element installed in the holder, and a heat insulating frame surrounding the holder and the temperature control element.
The controller may further control the temperature of the temperature control element.
The plurality of columnar ferroelectric single crystals may be arranged at a predetermined interval, and the predetermined interval may be filled with a heat conductive material.

The light generator according to the present invention includes a first light source that emits a first light having a _first wavelength λ ₁ , a second light having a second wavelength λ ₂ incident from the first light and the outside. An optical system that couples light, a wavelength conversion element that converts the first light and the second light into third light having a _third wavelength λ ₃ , and control of the position of the wavelength conversion element The wavelength conversion element includes a holder and a plurality of columnar ferroelectric single crystals disposed in the holder, and each of the plurality of columnar ferroelectric single crystals has a cross-section Each of the plurality of cylindrical ferroelectric single crystals is substantially circular, and each of the first wavelength λ ₁ , the second wavelength λ _2, and the third wavelength λ ₃ has a relationship 1 / λ _1. A domain-inverted structure having a predetermined period that is quasi-phase matched in a direction perpendicular to the polarization direction so as to satisfy ± 1 / λ ₂ = 1 / λ ₃ The plurality of columnar ferroelectric single crystals are arranged so that the directions perpendicular to the polarization direction are the same, thereby achieving the above object.

The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and Each may be selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.
The holder may be formed from a thermally conductive material.
The wavelength conversion element may further include a temperature control element installed in the holder, and a heat insulating frame surrounding the holder and the temperature control element.
The controller may further control the temperature of the temperature control element.
The plurality of columnar ferroelectric single crystals may be arranged at a predetermined interval, and the predetermined interval may be filled with a heat conductive material.

  The wavelength conversion element of the present invention is composed of a cylindrical ferroelectric single crystal having a substantially circular cross section. A cylindrical ferroelectric single crystal has a domain-inverted structure having a predetermined period in a direction perpendicular to the polarization direction. Since the cylindrical ferroelectric single crystal has a substantially circular cross section, the heat distribution is always centrally symmetric even when the heat distribution is generated by the light applied to the wavelength conversion element. As a result, a high extinction ratio (that is, high linear polarization) can be maintained, and the shape of light emitted from the wavelength conversion element can be maintained circular.

In addition, since the cross section of the cylindrical ferroelectric single crystal is substantially a circle, it is possible to easily cope with the polarization of incident light simply by changing the arrangement angle of the cylindrical ferroelectric single crystal. Therefore, since an optical system such as a polarizer is unnecessary, the entire system can be reduced in size.
Further, since the cylindrical ferroelectric single crystal does not have corners, there is no possibility that unnecessary cracks caused by the lack of corners are generated in the crystal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiment, a substantially single crystal lithium tantalate single crystal (MgSLT) doped with Mg is used as the ferroelectric single crystal. In the present specification, substantially “stoichiometric composition” means that the molar fraction of Li ₂ O / (Nb ₂ O ₅ + Li ₂ O) is not completely 0.50, but is more than the congruent composition. It has a composition close to the stoichiometric ratio (Mole fraction of Li ₂ O / (Nb ₂ O ₅ + Li ₂ O) = 0.490 to 0.5), and the deterioration of the device characteristics due to the composition It means that it does not become a problem in normal device design. Such MgSLT can be produced, for example, by the Czochralski method using a double crucible described in JP-A-2000-344595. MgSLT is merely an example of a ferroelectric single crystal, and lithium niobate (SLN) having a substantially stoichiometric composition, lithium tantalate (SLT) having a substantially stoichiometric composition, impurities (for example, Mg, Zn, Note that any ferroelectric single crystal such as SLN or SLT doped with Sc, In, etc. may be used.
In the figure, similar elements are denoted by the same reference numerals, and description thereof is omitted.

(Embodiment 1)
FIG. 1 is a diagram showing the polarization inversion period dependence of idler light and signal light oscillation wavelengths of substantially constant composition lithium tantalate (MgSLT) doped with 1 mol% of MgO.
In the figure, the horizontal axis represents the polarization inversion period, and the vertical axis represents the oscillation wavelengths of idler light and signal light, respectively. FIG. 1 shows the polarization inversion period dependence of the wavelength of idler light and signal light generated when pump light having a wavelength of 1.064 μm is incident on MgSLT having various periods and parametrically oscillates. From FIG. 1, it can be seen that when MgSLT is used for a parametric oscillator, the oscillation wavelength of idler light has a tunability of 2.9 μm to 3.7 μm in a polarization inversion period of 29.5 μm to 32 μm. Similarly, it can be seen that the wavelength of the signal light has a tunability of 1.5 μm to 1.7 μm. Although not shown in the figure, when the polarization inversion period is in the range of 26 μm to 33 μm, the idler oscillation wavelength of the MgSLT described above has a tunability of 2.5 μm to 4.0 μm, and the signal light oscillation wavelength is 1. It has been found to have a tunability of 45 μm to 1.85 μm.

FIG. 2 is a perspective view of a wavelength conversion element made of a cylindrical ferroelectric single crystal according to Embodiment 1 of the present invention.
The columnar ferroelectric single crystal 200 is, for example, MgSLT in FIG. The diameter of the cross section of the cylindrical ferroelectric single crystal 200 is, for example, 1.5 mm. The cylindrical ferroelectric single crystal 200 has a periodically poled structure 201 having a predetermined period in a direction perpendicular to the polarization direction. That is, one columnar ferroelectric single crystal 200 has a single grating. In the figure, the cross section shows a plane parallel to the polarization direction of the cylindrical ferroelectric single crystal 200, but the present invention is not limited to this.

The predetermined cycle will be described. When parametric oscillation is performed using the cylindrical ferroelectric single crystal 200, the wavelength of light incident on the cylindrical ferroelectric single crystal 200 is λ _1, and the wavelength of light emitted from the cylindrical ferroelectric single crystal 200 is Assuming that λ ₂ and λ ₃ are satisfied, the range of the polarization inversion period to be quasi-phase matched is such that the relationship 1 / λ ₁ = 1 / λ ₂ + 1 / λ ₃ and the relationship λ ₁ <λ ₂ and λ ₁ <λ ₃ are satisfied. It is determined. Similarly, when second harmonic generation is performed using the cylindrical ferroelectric single crystal 200, the wavelength of light incident on the cylindrical ferroelectric single crystal 200 is λ ₁ , and the cylindrical ferroelectric single crystal 200 is When the wavelength of the emitted light is λ ₂ , the range of the polarization inversion period for quasi phase matching is determined so as to satisfy the relationship λ ₁ = 2 × λ ₂ . Similarly, when the difference frequency generation or the sum frequency generation is performed using the cylindrical ferroelectric single crystal 200, the wavelengths of light incident on the cylindrical ferroelectric single crystal 200 are λ ₁ and λ ₂ , and the cylindrical ferroelectric is generated. When the wavelength of light emitted from the body single crystal 200 is λ ₃ , the polarization inversion period for quasi-phase matching is determined so as to satisfy the relationship 1 / λ ₁ ± 1 / λ ₂ = 1 / λ ₃ . When the cylindrical ferroelectric single crystal 200 is MgSLT, the parametric oscillation polarization inversion period is selected from the range of 26 μm to 33 μm, and the second harmonic polarization inversion period is selected from the range of 1 μm to 10 μm. In the case of difference frequency generation, an arbitrary polarization inversion period is adopted according to the wavelength of λ ₂ . It should be noted that such a polarization inversion period is inherent to the ferroelectric single crystal.

The length L in the direction perpendicular to the polarization direction of the cylindrical ferroelectric single crystal 200 is, for example, 35 mm. The diameter D (for example, in the Z-axis direction) at an arbitrary position in the cross section of the cylindrical ferroelectric single crystal 200 is 1.5 mm. Note that these lengths L and diameters D are only examples and are not limited to these values.
For example, the columnar ferroelectric single crystal 200 is first cut out of a prismatic ferroelectric single crystal. Next, the periodic domain-inverted structure 201 can be formed on a prismatic ferroelectric single crystal cut out using any method such as a voltage application method, an electron beam scanning irradiation method, and a proton exchange heat treatment method. Thereafter, the prismatic ferroelectric single crystal is punched out using a predetermined mold (for example, a hollow body). However, the manufacturing method of the cylindrical ferroelectric single crystal 200 is not limited to this. Further, an orientation flat may be provided at a predetermined position so that the Z-axis direction can be understood. A reflective film may be provided on the end face of the columnar ferroelectric single crystal 200.

The cross section of the cylindrical ferroelectric single crystal 200 of the present invention is substantially a perfect circle. A substantially perfect circle means that the ratio of the diameters at arbitrary positions having different cross-sections is not necessarily 1, but the deterioration of device characteristics caused by using such a cylindrical ferroelectric single crystal 200 is normal. It means that it is not a problem in device design.
Thus, since the cross section of the cylindrical ferroelectric single crystal 200 is substantially a perfect circle, the arrangement of the cylindrical ferroelectric single crystal 200 can be changed according to the polarization of incident light. That is, the cylindrical ferroelectric single crystal 200 can convert the wavelength of light having an arbitrary polarization only by changing the arrangement angle.

The operation of the wavelength conversion element 200 when generating the second harmonic using the wavelength conversion element 200 shown in FIG. 2 will be described.
The wavelength conversion element 200 can be used together with a light source (not shown) and a condensing optical system (not shown). The light source can be, for example, a semiconductor laser that emits first light (fundamental wave) having a _first wavelength λ ₁ of 780 nm, but is not limited thereto. Any light source can be used as long as it is coherent. The condensing optical system may be any optical system that functions to collect the first light and make it incident on the wavelength conversion element 200.

The first light emitted from the light source enters the wavelength conversion element 200 via the condensing optical system. The periodically poled structure 201 is periodically repeated in the propagation direction of the first light (fundamental wave) of the light source. With such a periodically poled structure 201, the fundamental wave and its second harmonic are phase matched (pseudo phase matched). In this way, the fundamental wave is converted into the second light (second harmonic) having the second wavelength λ ₂ of 390 nm while propagating through the wavelength conversion element 200. The wavelength conversion element 200 may function as a resonator by providing reflection films on the incident surface and the emission surface of the fundamental wave of the wavelength conversion element 200.

  As described above, since the wavelength conversion element 200 is made of a cylindrical ferroelectric single crystal, the arrangement angle of the cylindrical ferroelectric single crystal can be changed in accordance with the polarization of the first light. That is, the wavelength conversion element 200 can convert the wavelength of light having arbitrary polarization. Thereby, since the freedom degree with respect to the polarization of a light source improves, arbitrary light sources can be used. The change in the arrangement angle of the cylindrical ferroelectric single crystal may be performed manually or by machine control.

  Even if a heat distribution is generated in the wavelength conversion element 200 by the irradiation of the first light, the heat distribution is centrally symmetric because the cross section of the wavelength conversion element 200 is substantially a perfect circle. At this time, it should be noted that the first light is applied to the center of the wavelength conversion element 200. Therefore, since the thermal birefringence is reduced because the heat distribution is centrally symmetric, it is possible to maintain a high extinction ratio (that is, high linear polarization) of the light propagating through the wavelength conversion element 200, and the wavelength conversion element The shape of the light emitted from 200 is maintained in a circular shape without distortion.

Similarly, it should be understood that the wavelength conversion element 200 can be used to generate parametric oscillation and difference frequency.
FIG. 3 is a diagram showing the temperature dependence of idler light and signal light oscillation wavelengths of lithium tantalate (MgSLT) having a substantially stoichiometric composition doped with 1 mol% of MgO.
In the figure, the horizontal axis represents the polarization inversion period, and the vertical axis represents the oscillation wavelengths of idler light and signal light. FIG. 3 shows the polarization inversion period dependence of the oscillation wavelength of idler light and signal light generated when pump light having a wavelength of 1.064 μm is incident on MgSLT having various periods and parametrically oscillated at various temperatures. Showing gender. In the figure, the result of MgSLT at room temperature (30 ° C.) and the result of heating MgSLT to 70 ° C., 110 ° C., 150 ° C. and 190 ° C. are shown. From FIG. 3, it was found that when MgSLT is used for a parametric oscillator, for example, the idler oscillation wavelength has a tunability with a temperature of about 0.4 μm in the same polarization inversion period. In addition to controlling the period of the domain-inverted structure, controlling the temperature of the cylindrical ferroelectric single crystal 200 can achieve a tunability controlled with higher accuracy.

FIG. 4 is a perspective view of another wavelength conversion element made of a cylindrical ferroelectric single crystal according to Embodiment 1 of the present invention.
A wavelength conversion element 400 shown in FIG. 4 is the same as the wavelength conversion element 200 shown in FIG. 2 except that it includes a temperature control element 401 and a frame 402 that covers the temperature control element 401. As described with reference to FIG. 3, for example, the cylindrical ferroelectric single crystal made of MgSLT has tunability depending on the temperature. Therefore, by installing the temperature control element 401 in the wavelength conversion element 200, A more precisely controlled tunability can be achieved. Further, the frame 402 is formed of a heat insulating material so as to surround the temperature control element 401. Thereby, the heat dissipation of the temperature control element 401 can be prevented, the cylindrical ferroelectric single crystal 200 can be heated uniformly, and the user can be prevented from being injured by the heat of the temperature control element 401. In the figure, the temperature control element 401 covers the entire columnar ferroelectric single crystal 200, but any temperature control element can be used as long as the temperature of the columnar ferroelectric single crystal 200 can be made uniform. Can do. The temperature control element 401 can be, for example, a Peltier element.

  The wavelength conversion element 400 may further include a control unit (not shown) in order to control the temperature control element 401. Such a control unit has the temperature dependence of the emission wavelength unique to the ferroelectric single crystal as shown in FIG. 3, and the cylindrical ferroelectric single crystal 200 has an appropriate temperature using this information. You may control so that it may become. In addition to controlling the temperature, the control unit obtains information related to the polarization of the light incident on the wavelength conversion element 400, and controls to change the angular arrangement of the wavelength conversion element 400 according to the polarization of the incident light. May be.

  As described above with reference to FIGS. 2 and 4, the wavelength conversion element made of the cylindrical ferroelectric single crystals 200 and 400 according to the present invention has a substantially circular cross section. Even if the heat distribution is generated by the light applied to the conversion element, the heat distribution is always centrally symmetric. As a result, a high extinction ratio of light (that is, high linear polarization) can be maintained, and the shape of light emitted from the wavelength conversion elements 200 and 400 is maintained in a circular shape.

In addition, since the cross section of the cylindrical ferroelectric single crystal is substantially a circle, it is possible to easily cope with the polarization of incident light simply by changing the arrangement angle of the cylindrical ferroelectric single crystal. Therefore, since an optical system such as a polarizer is unnecessary, the entire system can be reduced in size. Moreover, arbitrary light sources can be used.
Further, since the cylindrical ferroelectric single crystal does not have corners, there is no possibility that unnecessary cracks caused by the lack of corners are generated in the crystal.

(Embodiment 2)
FIG. 5 is a perspective view of the wavelength conversion element according to the second embodiment of the present invention.
The wavelength conversion element 500 includes a holder 501 and a plurality of cylindrical ferroelectric single crystals 502.
The holder 501 accommodates a plurality of cylindrical ferroelectric single crystals 502. The size (length, width, thickness) of the holder 501 can be changed according to the number of cylindrical ferroelectric single crystals 200 accommodated and the arrangement of the plurality of cylindrical ferroelectric single crystals 502. In the figure, the holder 501 includes a bottom portion and a lid portion imitating a semicircle, but the configuration of the holder 501 is not limited to such a configuration. For example, a rectangular tube may be used.

  The holder 501 is preferably formed from a thermally conductive material such as copper. As described in the first embodiment, in the plurality of columnar ferroelectric single crystals 502, the heat distribution due to the irradiation of incident light is always centrally symmetric. For this reason, even if heat distribution occurs in the cylindrical ferroelectric single crystal 200, a high extinction ratio of light (that is, high linear polarization) can be maintained. However, if the holder 501 is a heat conductive material, heat due to irradiation of incident light can be easily dissipated, so that occurrence of heat distribution can be reduced.

  The plurality of columnar ferroelectric single crystals 502 are arranged so that the directions perpendicular to the respective polarization directions are the same. Thereby, multi-grating can be easily achieved. In the figure, for simplicity, five cylindrical ferroelectric single crystals 502 are arranged in a planar shape so that their polarization directions are the same. However, the number and arrangement of the cylindrical ferroelectric single crystals 200 are arbitrary as long as the directions perpendicular to the polarization directions of the cylindrical ferroelectric single crystals 200 are the same. The polarization inversion period of each of the plurality of cylindrical ferroelectric single crystals 502 corresponds to the user's needs from the predetermined period range for achieving parametric oscillation, second harmonic generation or difference frequency generation described in the first embodiment. Selected. The polarization inversion periods of the plurality of columnar ferroelectric single crystals 502 are different.

  Thus, the wavelength conversion element 500 according to the present invention achieves multi-grating by arbitrarily combining a single cylindrical ferroelectric single crystal 200 having a single grating. Thus, when any one of the plurality of cylindrical ferroelectric single crystals (multi-grating) 502 is damaged when the wavelength conversion element 500 is manufactured, the damaged cylindrical ferroelectric single crystal is damaged. Since only the crystals need to be exchanged, the yield can be improved. Further, even if a crack is generated in one cylindrical ferroelectric single crystal when the wavelength conversion element 500 is used, the crack does not propagate to the adjacent cylindrical ferroelectric single crystal. Therefore, it is only necessary to replace the cylindrical ferroelectric single crystal in which the crack has occurred, so that the cost on the user side can be reduced.

Next, the operation of the wavelength conversion element 500 will be described.
Light (incident light) from the outside (for example, a light source) of the wavelength conversion element 500 has a specific polarization inversion period among the plurality of cylindrical ferroelectric single crystals 502 so as to be converted into light having a desired wavelength. Incident to a cylindrical ferroelectric single crystal. Depending on the polarization inversion period of the wavelength conversion element 500, the incident light is wavelength-converted based on parametric oscillation, second harmonic generation, or difference frequency generation. Thereafter, the light is emitted from the wavelength conversion element 500 as emitted light. For example, in the case of parametric oscillation, when the wavelength of the pump light (incident light) is 1.064 μm and the specific polarization inversion period is 31.8 μm, the wavelengths of the idler light and the signal light (emitted light) are respectively 2.5 μm and 1.85 μm. Thus, the tunability can be improved by moving the wavelength conversion element 500 manually or using mechanical control so that incident light irradiates a cylindrical ferroelectric single crystal having a specific polarization inversion period. Can be achieved.

  In addition, since the wavelength conversion element 500 includes the plurality of cylindrical ferroelectric single crystals 502, the arrangement angle of each of the plurality of cylindrical ferroelectric single crystals can be changed in accordance with the polarization of incident light. That is, the wavelength conversion element 200 can convert the wavelength of light having arbitrary polarization. Thereby, since the freedom degree with respect to the polarization of a light source improves, arbitrary light sources can be used. The change of the arrangement angle of each of the plurality of columnar ferroelectric single crystals may be performed manually or may be performed by machine control.

  Thus, by making each cross section of the plurality of cylindrical ferroelectric single crystals 502 substantially circular, the incident light can be transmitted regardless of whether the polarization mode of the incident light is the TE mode or the TM mode. Wavelength conversion can be performed without providing an optical system such as a polarizer between a light source (not shown) and the wavelength conversion element 500. Therefore, the entire system can be reduced in size.

FIG. 6 is a perspective view of still another wavelength conversion element according to the second embodiment of the present invention.
A wavelength conversion element 600 shown in FIG. 6A is the same as the wavelength conversion element 500 described with reference to FIG. 5 except that it includes a temperature control element 601. As described with reference to FIG. 3, for example, a cylindrical ferroelectric single crystal made of MgSLT has tunability depending on temperature, and therefore, by installing a temperature control element 601 in the wavelength conversion element 500, A more precisely controlled tunability can be achieved. In the figure, the temperature control element 601 has a sheet shape, but any temperature control element may be used as the temperature control element 601 as long as the temperatures of the plurality of columnar ferroelectric single crystals 502 can be made uniform. it can. The temperature control element 601 can be, for example, a Peltier element.

  A wavelength conversion element 610 illustrated in FIG. 6B includes a frame 602 that surrounds the temperature control element 601. The frame 602 is made of a heat insulating material. In this way, by surrounding the holder 501 and the temperature control element 601 with the heat insulating frame 602, heat dissipation of the temperature control element 601 is prevented, and a plurality of cylindrical ferroelectric single crystals 502 are uniformly heated. In addition, the user can be prevented from being injured by the heat of the temperature control element 601.

  The wavelength conversion element 600 or 610 may further include a control unit (not shown) in order to control the temperature control element 601. Such a control unit has a polarization inversion period dependency of the emission wavelength unique to the ferroelectric single crystal material as shown in FIG. 1 and / or the emission wavelength unique to the ferroelectric single crystal as shown in FIG. The temperature control element 601 may be controlled so that the wavelength conversion element 600 or 610 has an appropriate temperature by using these relationships. In addition to controlling the temperature, the control unit obtains information on the polarization of light incident on the wavelength conversion element 600 or 610, and changes the angular arrangement of the wavelength conversion element 600 or 610 according to the polarization of the incident light. You may control as follows.

FIG. 7 is a perspective view of still another wavelength conversion element according to the second embodiment of the present invention.
The wavelength conversion element 700 is a holder 701 in which a plurality of cylindrical ferroelectric single crystals are arranged at a predetermined interval, and a thermally conductive material is filled at a predetermined interval with reference to FIG. This is the same as the wavelength conversion element 500 described. In this way, by filling a thermally conductive material between the ferroelectric single crystals on each cylinder, the heat that can be generated in the cylindrical ferroelectric single crystal by the incident light is dissipated to reduce the occurrence of heat distribution. can do. As a result, since the birefringence effect due to heat is reduced, the polarization mode of light propagating through the wavelength conversion element 700 is maintained, and the conversion efficiency can be kept constant. The predetermined interval is, for example, 50 μm, but is not limited to this interval. In this case, the example in which the heat conductive material and the holder are integrated is shown, but may be separate.

  As described above, by combining the cylindrical ferroelectric single crystals each having a domain-inverted structure having a predetermined period and forming a wavelength conversion element having a multi-grating, the tunability of the conversion wavelength can be easily achieved. Achieve. Since the cross section of the cylindrical ferroelectric single crystal is substantially perfect, it does not depend on the polarization direction of incident light. Therefore, the degree of freedom of the incident light source is increased and the entire optical system can be miniaturized. In addition, since the heat distribution due to the irradiation of incident light is centrally symmetric, a high extinction ratio (that is, high linear polarization) of light can be achieved even if the heat distribution occurs.

  Since the wavelength conversion element according to the present invention is formed by combining cylindrical ferroelectric single crystals, it is only necessary to discard the cylindrical ferroelectric single crystals damaged at the time of manufacturing, thereby improving the yield. Furthermore, at the time of use, it is only necessary to replace the damaged columnar ferroelectric single crystal, which reduces the cost on the user side. Since the wavelength conversion element according to the present invention is formed by arbitrarily combining cylindrical ferroelectric single crystals, it can be adjusted according to the needs of the user.

  In the second embodiment, an example of a wavelength conversion element using the MgSLT columnar ferroelectric single crystal 200 described with reference to FIG. 2 has been shown. It should be understood that these are merely examples. If any ferroelectric single crystal material is used, and a plurality of cylindrical ferroelectric single crystals having at least a cross-sectional diameter of 2 mm and a substantially circular cross-section are used, the above effect can be obtained. it can.

(Embodiment 3)
FIG. 8 is a diagram showing a light generation apparatus using parametric oscillation according to Embodiment 3 of the present invention.
The light generation device 800 includes a light source 801, a wavelength conversion element 802, and a control unit 803.
The light source 801 emits first light (pump light) having a _first wavelength λ ₁ . According to the present invention, the polarization of the first light may be TM mode or TE mode. The light source 801 is, for example, a Q-switched Nd: YAG laser having a _first wavelength λ ₁ = 1.064 μm. A tunable light source may be used as the light source 801.

The wavelength conversion element 802 is one of the wavelength conversion elements 500, 600, 610, and 700 described in the second embodiment, or a modification thereof. The wavelength conversion element 802 converts the first light received from the light source 801 into the second light (signal light) having the second wavelength λ ₂ and the third light (idler light) having the third wavelength λ _3. ) And wavelength conversion. At this time, each of the plurality of cylindrical ferroelectric single crystals in the wavelength conversion element 802 has a relationship 1 /, a first wavelength λ ₁ , a second wavelength λ _2, and a third wavelength λ _3. A domain-inverted structure having a predetermined period in which quasi-phase matching is performed in a direction perpendicular to the polarization direction so as to satisfy λ ₁ = 1 / λ ₂ + 1 / λ ₃ , relations λ ₁ <λ ₂ and λ ₁ <λ ₃ Have When MgSLT shown in FIGS. 1 and 3 is used for the cylindrical ferroelectric single crystal, the polarization inversion period of the cylindrical ferroelectric single crystal is selected from the range of 26 μm to 33 μm. The columnar ferroelectric single crystal is not limited to MgSLT.

  The control unit 803 controls the position of the wavelength conversion element 802. Specifically, the control unit 803 obtains information (for example, wavelength and polarization) of the first light from the light source 801, and controls the position of the wavelength conversion element 802 based on the obtained information. In this specification, the control of the position of the wavelength conversion element 802 means that the control unit 803 has a plurality of cylindrical strengths of the wavelength conversion element 802 based on the polarization mode among the information of the first light from the light source 801. Controlling the respective arrangement angles of the dielectric single crystals so as to correspond to the polarization mode of the first light, and / or the control unit 803 to the wavelength of the information of the first light from the light source 801 Based on this, it means that the position of the wavelength conversion element 802 is controlled so that the first light emitted from the light source 801 irradiates a predetermined cylindrical ferroelectric single crystal of the wavelength conversion element 802. The control unit 803 stores, for example, the cycle-dependent data of the idler light and the signal light and the temperature-dependent data of the cylindrical ferroelectric single crystal shown in FIGS. 1 and 6, and based on these data. The position of the wavelength conversion element 802 may be controlled.

  The light generation device 800 may function as a resonator by providing reflection mirrors (not shown) between the light source 801 and the wavelength conversion element 802 and on the emission side of the wavelength conversion element 802.

Next, the operation of the light generator 800 will be described.
The light source 801 emits first light having a _first wavelength λ ₁ = 1.064 μm to the wavelength conversion element 802. The control unit 803 controls the position of the wavelength conversion element 802 based on information (wavelength and polarization) of the first light so that light with a wavelength desired by the user can be obtained. For example, when the user desires the third light (idler light) having the third wavelength λ ₃ = 3.62 μm, the control unit 803 has a cylindrical strong intensity in which the first light has a polarization inversion period of 30 μm. The position of the wavelength conversion element 802 is controlled so as to be incident on the dielectric single crystal.

The first light incident on the predetermined cylindrical ferroelectric single crystal of the wavelength conversion element 802 satisfies the above relational expression, and the second light (signal light) having the second wavelength λ ₂ = 1.507 μm. ) And a third wavelength (idler light) having a _third wavelength λ ₃ = 3.62 μm.
Since the second light wavelength-converted in this manner is in the wavelength band of optical communication, it can be used in optical communication. Since the third light is a wavelength band effective for gas spectroscopy, it can be used for chemical analysis.

  The light generating device 800 according to the present invention includes a wavelength conversion element 802 having a multi-grating in which cylindrical ferroelectric single crystals having a predetermined period are combined. Thereby, the tunability of the conversion wavelength is easily achieved. As described in the first embodiment, since the cylindrical ferroelectric single crystal has a substantially circular cross section in the same direction as the polarization direction, the cylindrical ferroelectric single crystal is irradiated with the light irradiated to the wavelength conversion element 802. Even if heat distribution occurs in the body single crystal, the heat distribution is always centrally symmetric. As a result, a high extinction ratio of light (that is, high linear polarization) can be maintained, and the shape of the light (second light and third light) emitted from the wavelength conversion element 802 is maintained in a circular shape. Is done. Furthermore, there is no dependency on the polarization direction of incident light. Therefore, the degree of freedom of the incident light source is increased and the entire optical system can be miniaturized.

  Since the wavelength conversion element 802 of the light generating device 800 according to the present invention is formed by combining cylindrical ferroelectric single crystals, it is only necessary to discard the cylindrical ferroelectric single crystals damaged at the time of manufacturing, thereby improving the yield. Let Furthermore, at the time of use, it is only necessary to replace the damaged columnar ferroelectric single crystal, which reduces the cost on the user side. Since the wavelength conversion element 802 of the light generator 800 according to the present invention is formed by arbitrarily combining cylindrical ferroelectric single crystals, it can be adjusted according to the needs of the user.

(Embodiment 4)
FIG. 9 is a diagram showing a light generation apparatus using second harmonic generation according to Embodiment 4 of the present invention.
The light generation device 900 includes a light source 901, a wavelength conversion element 902, and a control unit 903.
The light source 901 emits first light (fundamental wave) having a _first wavelength λ ₁ . According to the present invention, the polarization of the first light may be TM mode or TE mode. The light source 901 can be a tunable semiconductor laser (wavelength tunable laser) that emits coherent first light.
The wavelength conversion element 902 is one of the wavelength conversion elements 500, 600, 610, and 700 described in the second embodiment, or a modification thereof. The wavelength conversion element 902 converts the wavelength of the first light received from the light source 901 into second light (second harmonic) having the second wavelength λ ₂ . At this time, in each of the plurality of cylindrical ferroelectric single crystals in the wavelength conversion element 902, the first wavelength λ ₁ and the second wavelength λ ₂ satisfy the relationship λ ₁ = 2 × λ _2. And a domain-inverted structure having a predetermined period that is quasi-phase matched in a direction perpendicular to the polarization direction. When MgSLT is used for the cylindrical ferroelectric single crystal, the polarization inversion period of the cylindrical ferroelectric single crystal is selected from the range of 1 μm to 10 μm. The columnar ferroelectric single crystal is not limited to MgSLT.

The control unit 903 controls the position of the wavelength conversion element 902. Specifically, the control unit 903 obtains information (for example, wavelength and polarization) of the first light from the light source 901, and controls the position of the wavelength conversion element 902 based on the obtained information. In this specification, the control of the position of the wavelength conversion element 902 means that the control unit 903 has a plurality of columnar strengths of the wavelength conversion element 902 based on the polarization mode among the information of the first light from the light source 901. Controlling the respective arrangement angles of the dielectric single crystals so as to correspond to the polarization mode of the first light, and / or the control unit 903 to the wavelength of the information held by the first light from the light source 901 Based on this, it means that the position of the wavelength conversion element 902 is controlled such that the first light emitted from the light source 901 is irradiated to a predetermined cylindrical ferroelectric single crystal of the wavelength conversion element 902. The control unit 903 stores, for example, period-dependent data of the second harmonic of the cylindrical ferroelectric single crystal and temperature-dependent data, and controls the position of the wavelength conversion element 902 based on these data. May be. The control unit 903 may control the light source 901 so as to set the first wavelength λ ₁ emitted by the light source 901 so that light having a wavelength desired by the user can be obtained.
The light generation apparatus 900 may function as a resonator by providing reflection mirrors (not shown) between the light source 901 and the wavelength conversion element 902 and on the emission side of the wavelength conversion element 902, respectively.

Next, the operation of the light generator 900 will be described.
For example, when the user desires the second light having the second wavelength λ ₂ = 0.39 μm, the control unit 903 causes the light source 901 to have the first wavelength λ ₁ = 0.78 μm. The light source 901 is controlled to emit. Next, the control unit 903 controls the position of the wavelength conversion element 902 based on information (wavelength and polarization) of the first light. In this case, the control unit 903 controls the position of the wavelength conversion element 902 so that the first light is incident on the cylindrical ferroelectric single crystal having a polarization inversion period of 3 μm. The first light incident on the predetermined cylindrical ferroelectric single crystal of the wavelength conversion element 902 satisfies the above relational expression, and the second light (second light having the second wavelength λ ₂ = 0.39 μm). Wavelength conversion to harmonics).

  The light generation apparatus 900 according to the fourth embodiment includes a wavelength conversion element 902 having a multi-grating in which cylindrical ferroelectric single crystals each having a polarization inversion structure having a predetermined period are combined. This makes it possible to generate second harmonics that are always phase-matched to the tunable light source 901 that emits the fundamental wave (that is, to easily achieve the tunability of the light source 901). As described in the first embodiment, since the cylindrical ferroelectric single crystal has a substantially circular cross section in the same direction as the polarization direction, the cylindrical ferroelectric single crystal is irradiated with light irradiated to the wavelength conversion element 902. Even if heat distribution occurs in the body single crystal, the heat distribution is always centrally symmetric. As a result, a high extinction ratio of light (that is, high linear polarization) can be maintained, and the shape of the light (second light) emitted from the wavelength conversion element 902 is maintained in a circular shape. Furthermore, there is no dependency on the polarization direction of incident light. Therefore, the degree of freedom of the incident light source is increased and the entire optical system can be miniaturized.

  Since the wavelength conversion element 902 of the light generating device 900 according to the present invention is formed by combining cylindrical ferroelectric single crystals, only the cylindrical ferroelectric single crystals damaged at the time of manufacturing need be discarded, and the yield is improved. Let Furthermore, at the time of use, it is only necessary to replace the damaged columnar ferroelectric single crystal, which reduces the cost on the user side. Since the wavelength conversion element 902 of the light generator 900 according to the present invention is formed by arbitrarily combining cylindrical ferroelectric single crystals, it can be adjusted according to the needs of the user.

(Embodiment 5)
FIG. 10 is a diagram showing a light generation apparatus using difference frequency generation according to Embodiment 5 of the present invention.
The light generation apparatus 1000 includes a light source 1001, a coupling optical system 1002, a wavelength conversion element 1003, and a control unit 1004.
The light source 1001 emits first light (pump light) having a _first wavelength λ ₁ . According to the present invention, the polarization of the first light may be TM mode or TE mode. The light source 1001 can be, for example, a semiconductor laser having a _first wavelength λ ₁ = 0.78 μm. A tunable light source may be used as the light source 1001.
The coupling optical system 1002 is an arbitrary optical system that couples the first light from the light source 1001 and the second light (signal light) having the second wavelength λ ₂ . The second light is, for example, light in a C band (1.53 μm to 1.57 μm), which is a typical communication band in wavelength domain multiplexing (WDM). The first wavelength λ ₁ and the second wavelength λ ₂ satisfy the relationship λ ₁ <λ ₂ .

The wavelength conversion element 1003 is one of the wavelength conversion elements 500, 600, 610, and 700 described in the second embodiment, or a modification thereof. The wavelength conversion element 1003 converts the wavelength of the first light and the second light coupled by the coupling optical system 1002 into third light (output light) having the third wavelength λ ₃ . At this time, each of the plurality of cylindrical ferroelectric single crystal of the wavelength conversion element 1003, the first wavelength lambda _1, the second wavelength lambda _2, and the third wavelength lambda _3, the relationship 1 / In order to satisfy λ ₁ −1 / λ ₂ = 1 / λ ₃ , the polarization inversion structure has a predetermined period in which a quasi-phase matching is performed in a direction perpendicular to the polarization direction. The columnar ferroelectric single crystal is not limited to MgSLT.

The control unit 1004 controls the position of the wavelength conversion element 1003. Specifically, the control unit 1004 obtains information (for example, wavelength and polarization) of the first light and information (for example, wavelength and polarization) of the second light from the light source 1001, and based on the obtained information. Then, the position of the wavelength conversion element 1003 is controlled. In this specification, controlling the position of the wavelength conversion element 1003 means that the control unit 1003 is based on the polarization of the information included in the first light from the light source 1001 and the polarization of the information included in the second light. And / or controlling the arrangement angles of the plurality of cylindrical ferroelectric single crystals of the wavelength conversion element 1003 so as to correspond to the polarization mode of the first light and the polarization of the second light. Based on the wavelength of the information of the first light from the light source 1001 and the wavelength of the information of the second light, the unit 1004 has a predetermined cylindrical ferroelectric single crystal in the wavelength conversion element 1003 This means that the position of the wavelength conversion element 1003 is controlled so that the first light and the second light coupled by the coupling optical system 1002 are irradiated. The control unit 1004 stores, for example, data on the period dependence of signal light and outgoing light of a cylindrical ferroelectric single crystal and data on temperature dependence, and the position of the wavelength conversion element 1003 is determined based on these data. You may control.
The light generation apparatus 1000 may function as a resonator by providing reflection mirrors (not shown) between the coupling optical system 1002 and the wavelength conversion element 1003 and on the emission side of the wavelength conversion element 1003.

Next, the operation of the light generator 1000 will be described.
For example, when the user desires to convert the second light (C band band) having the second wavelength λ ₂ = 1.55 μm into the third light having the wavelength of the L band band, the control unit 1004 Controls the position of the wavelength conversion element 1003 based on information (wavelength and polarization) of the first light, information (wavelength and polarization) of the second light, and the like. In this case, the control unit 1004 converts the wavelength so that the first light and the second light coupled by the coupling optical system 1002 enter a columnar ferroelectric single crystal having a polarization inversion period of 17 μm, for example. The position of the element 1003 is controlled. The first light and the second light incident on the predetermined columnar ferroelectric single crystal of the wavelength conversion element 1003 satisfy the above relational expression and have the third wavelength λ ₃ = 1.57 μm. Wavelength converted to light. The third wavelength λ ₃ converted in this way is an L band band (1.57 μm to 1.62 μm) which is a typical communication band in wavelength domain multiplexing (WDM).

The light generation apparatus 1000 according to the fifth embodiment includes a wavelength conversion element 905 having a multi-grating in which cylindrical ferroelectric single crystals having a predetermined period are combined. Accordingly, if the light source 1001 is a tunable light source, the wavelength of the fixed C band (second wavelength λ ₂ of the second light) is changed to the wavelength of the L band (third wavelength λ ₃ ). Tunable. Further, when the light source 1001 is a light source that emits a single wavelength, if the wavelength of the C band (second wavelength λ ₂ of the second light) is made variable, the wavelength of the L band (third wavelength λ) ₃ ) can be adjusted tunable. In this way, CL band conversion can be performed in a tunable manner. As described in the first embodiment, since the cylindrical ferroelectric single crystal has a substantially circular cross section in the same direction as the polarization direction, the cylindrical ferroelectric single crystal is irradiated with light irradiated to the wavelength conversion element 902. Even when heat distribution occurs in the body single crystal, the heat distribution is always centrally symmetric, so that a high extinction ratio of light (that is, high linear polarization) can be maintained, and the wavelength conversion element 1003 The shape of the emitted light (third light) is maintained in a circular shape. Furthermore, there is no dependency on the polarization direction of incident light. Therefore, the degree of freedom of the incident light source is increased and the entire optical system can be miniaturized.

  Since the wavelength conversion element 1003 of the light generating device 1000 according to the present invention is formed by combining cylindrical ferroelectric single crystals, it is only necessary to discard the cylindrical ferroelectric single crystals damaged at the time of manufacturing, thereby improving the yield. Let Furthermore, at the time of use, it is only necessary to replace the damaged columnar ferroelectric single crystal, which reduces the cost on the user side. Since the wavelength conversion element 1003 of the light generation apparatus 1000 according to the present invention is formed by arbitrarily combining cylindrical ferroelectric single crystals, it can be adjusted according to the needs of the user.

Although the case where the difference frequency is generated using the light generator 1000 shown in FIG. 10 has been described, it should be noted that the sum frequency can also be generated using the light generator 1000. In this case, each of the plurality of cylindrical ferroelectric single crystal of the wavelength conversion element 1003, the first wavelength lambda _1, the second wavelength lambda _2, and the third wavelength lambda ₃ is the relation 1 / so as to satisfy _{λ 1 + 1 / λ 2 =} 1 / λ 3, may have a polarization inversion structure having a predetermined period of quasi phase matching in a direction perpendicular to the polarization direction.

As described above, the wavelength conversion element of the present invention is composed of a cylindrical ferroelectric single crystal having a substantially circular cross section. A cylindrical ferroelectric single crystal has a domain-inverted structure having a predetermined period in a direction perpendicular to the polarization direction. Since the cylindrical ferroelectric single crystal has a substantially circular cross section, the heat distribution is always centrally symmetric even when the heat distribution is generated by the light applied to the wavelength conversion element. As a result, a high extinction ratio of light (that is, high linear polarization) can be maintained, and the shape of light emitted from the wavelength conversion element can be maintained circular.
In addition, since the cross section of the cylindrical ferroelectric single crystal is substantially a circle, it is possible to easily cope with the polarization of incident light simply by changing the arrangement angle of the cylindrical ferroelectric single crystal. Therefore, since an optical system such as a polarizer is unnecessary, the entire system can be reduced in size.

Further, since the cylindrical ferroelectric single crystal does not have corners, there is no possibility that unnecessary cracks caused by the lack of corners are generated in the crystal.
Tunability of the conversion wavelength is easily achieved by combining the cylindrical ferroelectric single crystals each having a domain-inverted structure having a predetermined period to form a wavelength conversion element having a multi-grating. Such a wavelength conversion element can be used for chemical analysis, communication, and the like.

The figure which shows the polarization inversion period dependence of the idler light and signal light oscillation wavelength of lithium tantalate (MgSLT) of substantially stoichiometric composition doped with 1 mol% of MgO The perspective view of the wavelength conversion element which consists of a cylindrical ferroelectric single crystal by Embodiment 1 of this invention The figure which shows the temperature dependence of the idler light and signal light oscillation wavelength of lithium tantalate (MgSLT) of substantially stoichiometric composition doped with 1 mol% of MgO The perspective view of another wavelength conversion element which consists of a cylindrical ferroelectric single crystal by Embodiment 1 of this invention The perspective view of the wavelength conversion element by Embodiment 2 of this invention The perspective view of another wavelength conversion element by Embodiment 2 of this invention The perspective view of another wavelength conversion element by Embodiment 2 of this invention The figure which shows the light generator using the parametric oscillation by Embodiment 3 of this invention The figure which shows the light generator using the 2nd harmonic generation by Embodiment 4 of this invention The figure which shows the light generator using the difference frequency generation by Embodiment 5 of this invention Diagram showing wavelength conversion system according to prior art A diagram showing a multi-grating quasi phase matching (QPM) parametric oscillator (OPO) according to the prior art.

Explanation of symbols

200, 400, 500, 600, 610, 700, 802, 902, 1003 Wavelength conversion element 201 Periodic polarization inversion structure 501, 701 Holder 502 Multiple cylindrical ferroelectric single crystals 401, 601 Temperature control element 402, 602 Frame 801 , 901, 1001 Light source 803, 903, 1004 Control unit 1002 Combined optical system

Claims (32)

  A wavelength conversion element comprising a columnar ferroelectric single crystal having a substantially circular cross section, wherein the columnar ferroelectric single crystal has a polarization reversal structure having a predetermined period in a direction perpendicular to the polarization direction. .   The columnar ferroelectric single crystal includes substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and impurities. The wavelength conversion element according to claim 1, wherein the wavelength conversion element is selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with tantalum. The predetermined period is such that the cylindrical ferroelectric single crystal transmits a _first light having a _first wavelength λ ₁ , a second light having a second wavelength λ _2, and a third wavelength λ ₃ . In the case of conversion into the third light having the relationship, the first wavelength λ ₁ , the second wavelength λ _2, and the third wavelength λ ₃ are related by the relationship 1 / λ ₁ = 1 / λ ₂ + 1 / λ. _3. The wavelength conversion element according to claim 1, wherein the wavelength conversion element has a quasi-phase matching period so as to satisfy the relationships λ ₁ <λ ₂ and λ ₁ <λ ₃ . In the predetermined period, when the cylindrical columnar ferroelectric single crystal converts the first light having the first wavelength λ ₁ into the second light having the second wavelength λ ₂ , 2. The wavelength conversion element according to claim ₁ , wherein the wavelength λ ₁ and the second wavelength λ ₂ have a quasi-phase matching period so as to satisfy the relationship λ ₁ = 2 × λ ₂ . In the predetermined period, the cylindrical ferroelectric single crystal generates a first light having a _first wavelength λ ₁ and a second light having a second wavelength λ _2, and a third wavelength λ _3. When the light is converted into the third light having the relationship, the first wavelength λ ₁ , the second wavelength λ _2, and the third wavelength λ ₃ are related by the relationship 1 / λ ₁ ± 1 / λ ₂ = 1 / The wavelength conversion element according to claim 1, wherein the wavelength conversion element has a quasi-phase matching period so as to satisfy λ ₃ . With a holder,
A wavelength conversion element comprising a plurality of cylindrical ferroelectric single crystals arranged in the holder,
Each of the plurality of cylindrical ferroelectric single crystals has a substantially circular cross section, and each of the plurality of cylindrical ferroelectric single crystals has a predetermined period in a direction perpendicular to the polarization direction. A wavelength conversion element having a domain-inverted structure, wherein the plurality of cylindrical ferroelectric single crystals are arranged so that directions perpendicular to the polarization direction are the same.   The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and The wavelength conversion element according to claim 6, wherein the wavelength conversion element is selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities. In the predetermined period, each of the plurality of columnar ferroelectric single crystals has a first light having a _first wavelength λ ₁ , a second light having a second wavelength λ _2, and a third light. when converting to the third light having a wavelength lambda _3, and the first said wavelength lambda ₁ and the second wavelength lambda ₂ and the third wavelength lambda ₃ is the relation 1 / lambda ₁ = 1 / lambda The wavelength conversion element according to claim 6, wherein the wavelength conversion element has a period for quasi-phase matching so as to satisfy ₂ + 1 / λ ₃ and relationships λ ₁ <λ ₂ and λ ₁ <λ ₃ . In the predetermined period, each of the plurality of cylindrical ferroelectric single crystals converts the first light having the first wavelength λ ₁ to the second light having the second wavelength λ ₂ . The wavelength conversion element according to claim 6, wherein the first wavelength λ ₁ and the second wavelength λ ₂ have a quasi-phase matching period so as to satisfy the relationship λ ₁ = 2 × λ ₂ . In the predetermined period, each of the plurality of columnar ferroelectric single crystals includes a first light having a _first wavelength λ ₁ and a second light having a _second wavelength λ ₂ . when converting to a third light having a wavelength lambda _3, and the first said wavelength lambda ₁ and the second wavelength lambda ₂ and the third wavelength lambda ₃ is the relation 1 / lambda ₁ ± 1 / lambda The wavelength conversion element according to claim 6, which has a period for quasi-phase matching so as to satisfy ₂ = 1 / λ ₃ .   The wavelength conversion element according to claim 6, wherein the holder is made of a heat conductive material. A temperature control element installed in the holder;
The wavelength conversion element according to claim 6, further comprising: a heat insulating frame surrounding the holder and the temperature control element.   The wavelength conversion element according to claim 12, further comprising a control unit that controls the temperature control element.   The wavelength conversion element according to claim 6, wherein the plurality of columnar ferroelectric single crystals are arranged at a predetermined interval, and the predetermined interval is filled with a heat conductive material. A light source emitting a first light having a _first wavelength λ ₁ ;
A wavelength conversion element that converts the first light into a second light having a second wavelength λ ₂ and a third light having a _third wavelength λ ₃ ;
A light generating device including a control unit that controls a position of the wavelength conversion element, wherein the wavelength conversion element includes a holder and a plurality of cylindrical ferroelectric single crystals arranged in the holder, Each of the plurality of cylindrical ferroelectric single crystals has a substantially circular cross section, and each of the plurality of cylindrical ferroelectric single crystals has a first wavelength λ ₁ and a second wavelength λ ₂ . a third wavelength lambda ₃ is the relation _{1 / λ 1 = 1 / λ} 2 + 1 / λ 3, so as to satisfy the relation λ ₁ <λ ₂ and lambda ₁ <lambda _3, a direction perpendicular to the polarization direction The plurality of cylindrical ferroelectric single crystals are arranged so that the directions perpendicular to the polarization direction are the same. , Light generator.   The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and The light generating device according to claim 15, wherein the light generating device is selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.   The light generation device according to claim 15, wherein the holder is formed of a heat conductive material. The wavelength conversion element is:
A temperature control element installed in the holder;
The light generation device according to claim 15, further comprising: a heat insulating frame surrounding the holder and the temperature control element.   The light generation apparatus according to claim 18, wherein the control unit further controls the temperature of the temperature control element.   The light generating device according to claim 15, wherein the plurality of cylindrical ferroelectric single crystals are arranged at a predetermined interval, and the predetermined interval is filled with a heat conductive material. A light source emitting a first light having a _first wavelength λ ₁ ;
A wavelength conversion element that converts the first light into second light having a _second wavelength λ ₂ ;
A light generating device including a control unit that controls a position of the wavelength conversion element, wherein the wavelength conversion element includes a holder and a plurality of cylindrical ferroelectric single crystals arranged in the holder, Each of the plurality of cylindrical ferroelectric single crystals has a substantially circular cross section, and each of the plurality of cylindrical ferroelectric single crystals has a first wavelength λ ₁ and a second wavelength λ ₂ . Has a domain-inverted structure having a predetermined period of quasi-phase matching in a direction perpendicular to the polarization direction so that the relationship λ ₁ = 2 × λ ₂ is satisfied, and the plurality of columnar ferroelectrics The light generating device, wherein the single crystals are arranged so that a direction perpendicular to the polarization direction is the same.   The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and The light generating device according to claim 21, wherein the light generating device is selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.   24. The light generator of claim 21, wherein the holder is formed from a thermally conductive material. The wavelength conversion element is:
A temperature control element installed in the holder;
The light generation device according to claim 21, further comprising: a heat insulating frame surrounding the holder and the temperature control element.   The light generation device according to claim 24, wherein the control unit further controls the temperature of the temperature control element.   The light generator according to claim 21, wherein the plurality of cylindrical ferroelectric single crystals are arranged at a predetermined interval, and the predetermined interval is filled with a heat conductive material. A first light source that emits first light having a _first wavelength λ ₁ ;
An optical system for combining the first light and a second light having a _second wavelength λ ₂ incident from the outside;
A wavelength conversion element that converts the first light and the second light into a third light having a _third wavelength λ ₃ ;
A light generating device including a control unit that controls a position of the wavelength conversion element, wherein the wavelength conversion element includes a holder and a plurality of cylindrical ferroelectric single crystals arranged in the holder, Each of the plurality of cylindrical ferroelectric single crystals has a substantially circular cross section, and each of the plurality of cylindrical ferroelectric single crystals has a first wavelength λ ₁ and a second wavelength λ ₂ . Polarization reversal having a predetermined period in which the third wavelength λ ₃ satisfies the relationship 1 / λ ₁ ± 1 / λ ₂ = 1 / λ ₃ in a quasi-phase-matched direction perpendicular to the polarization direction. A light generator having a structure, wherein the plurality of columnar ferroelectric single crystals are arranged so that directions perpendicular to the polarization direction are the same.   The plurality of cylindrical ferroelectric single crystals include substantially stoichiometric lithium niobate, substantially stoichiometric lithium tantalate, substantially doped stoichiometric lithium niobate doped with impurities, and 28. The light generating device according to claim 27, each selected from the group consisting of lithium tantalate having a substantially stoichiometric composition doped with impurities.   28. The light generator of claim 27, wherein the holder is formed from a thermally conductive material. The wavelength conversion element is:
A temperature control element installed in the holder;
The light generation device according to claim 27, further comprising: a heat insulating frame surrounding the holder and the temperature control element.   The light generation device according to claim 30, wherein the control unit further controls the temperature of the temperature control element. 28. The light generator according to claim 27, wherein the plurality of columnar ferroelectric single crystals are arranged at a predetermined interval, and the predetermined interval is filled with a heat conductive material.