JP2012004514A - Wavelength-variable laser light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength-variable laser light source capable of high-speed wavelength sweeping and stable laser oscillation.SOLUTION: One embodiment of the wavelength-variable laser light source includes: a laser medium having a gain with respect to a laser oscillation wavelength; variable-focus lens means provided on the optical axis of the output side of the laser medium; a first mirror provided on the optical axis of the output side of the variable-focus lens means; and a second mirror provided at a position opposing the first mirror and constituting a resonator containing the laser medium. The variable-focus lens means can vary the focal distance of the light passing through the electro-optic materials and, based on the focal distance having wavelength dependency, selects the wavelength of the laser oscillation light in the resonator containing the laser medium.

Description

  The present invention relates to a wavelength tunable laser light source, and more particularly to a wavelength tunable laser light source in which a variable focus lens having wavelength dispersion is disposed in a resonator.

  The wavelength tunable laser light source is used in the field of optical communication such as DWDM (Dense Wavelength Division Multiplexing) optical transmission, an analyzer that irradiates a measurement target with laser light, and analyzes transmission and reflection.

  When a tunable laser light source is used as a light source for an analyzer, it is necessary to change the wavelength at high speed and to narrow the width of the oscillation spectrum. For example, if high-speed wavelength scanning becomes available in optical coherence tomography (OCT: Optical Coherence Tomography), dynamic analysis such as high-speed image processing, blood flow observation, and oxygen saturation concentration changes becomes possible. Such a laser light source is required.

  FIG. 1 shows a conventional Littrow tunable laser light source. It is an example of an external resonator type wavelength tunable laser light source (for example, refer nonpatent literature 1). The wavelength tunable laser light source includes a laser medium 11, a collimating lens 12 disposed on the optical axis on the output side, and a diffraction grating 13. The output light from the laser medium 11 is collimated by the collimator lens 12 and is incident on the diffraction grating 13 as incident light 14 to generate first-order diffracted light 15 and zero-order diffracted light (laser output light) 16. The first-order diffracted light 15 is fed back to the laser medium 11 and forms a resonator between the high reflection mirror 11 a provided on the laser medium end face of the laser medium 11 and the diffraction grating 13.

  At this time, the direction (diffraction angle) in which the 1st-order diffracted light 15 and the 0th-order diffracted light (laser output light) 16 are emitted has wavelength dependency. Accordingly, the first-order diffracted light 15 having a wavelength component directed from the diffraction grating 13 in the direction opposite to the incident light 14 is laser-oscillated in the resonator. By rotating the diffraction grating 13, the wavelength of the first-order diffracted light 15 toward the incident light 14 is changed, and the wavelength of the laser output light is changed.

L. Ricci, et.al., ‘‘ A compact grating-stabilized diode laser system for atomic physics, ’’ Optics Communications, Vol.117, Issues 5-6, 15 June 1995, p. 541-549 J. E. Geusic, et.al., ‘‘ ELECTRO-OPTIC PROPERTIES OF SOME ABO3 PEROVSKITES IN THE PARAELECTRIC PHASE, ’’ Appl. Phys. Lett. Vol.4, No.8, p.141-143 (1964) F. S. Chen, et.al., ‘‘ Light Modulation and Beam Deflection with Potassium Tantalate-Niobate Crystals, ’’ J. Appl. Phys. Vol.37, No.1, p.388-398 (1966)

  However, since the conventional Littrow tunable laser light source mechanically rotates the diffraction grating to sweep the wavelength, there is a limit to the speed required to change the output wavelength, and the wide wavelength range can be swept at high speed. There was a problem that could not. In addition, although precise oscillation length control is necessary for laser oscillation, there is a problem in continuously realizing stable laser oscillation because it includes a mechanically movable part.

  The present invention has been made in view of such problems, and it is an object of the present invention to provide a tunable laser light source capable of performing high-speed wavelength sweeping and obtaining stable laser oscillation.

  In an embodiment of the present invention, in order to achieve such an object, an embodiment of a wavelength tunable laser light source is provided on a laser medium having a gain with respect to a laser oscillation wavelength and an optical axis on an output side of the laser medium. A variable focus lens means, a first mirror provided on the optical axis on the output side of the variable focus lens means, and a resonator provided at a position facing the first mirror and including the laser medium. And the variable focus lens means includes an electro-optic material having inversion symmetry, and two or more electrodes for applying an electric field inside the electro-optic material, By changing the voltage applied to the electrodes, the focal length of the light transmitted through the electro-optic material can be varied, and the focal length has a wavelength dependence, so that a laser in a resonator including the laser medium can be used. Wherein the can select the wavelength of oscillation light.

  The varifocal lens means has the electrode formed on a light incident surface and a light exit surface of the electro-optic material, and enters the light from a gap where the electrode on the incident surface is not formed, and emits the light. An optical axis is set so as to emit from a gap where no surface electrode is formed, and a part of electric lines of force from the electrode on the incident surface to the electrode on the emission surface is bent in the gap, and the optical axis The focal point of the light transmitted through the electro-optic material is varied by changing the electric field of the portion through which the light is transmitted centering on and changing the applied voltage between the electrode on the entrance surface and the electrode on the exit surface It is characterized by that.

  The variable focus lens means is formed on a first surface formed on the first surface of the electro-optic material, and on a second surface opposite to the first surface, and the first anode Formed on the second surface, a first cathode formed on the first surface, a second cathode formed on the first surface, and spaced from the first anode And a second anode formed at a position facing the second cathode and spaced from the first cathode, and light from a third surface orthogonal to the first surface. Is transmitted between the first electrode pair composed of the first anode and the first cathode, and then the second electrode pair composed of the second anode and the second cathode. And an optical axis is set so that light is emitted from a fourth surface opposite to the third surface. By varying the voltage applied between the second electrode pair, characterized by varying the focus of light emitted from the fourth surface of the electro-optical material.

  As described above, according to the present invention, it is possible to obtain a much faster response speed than the conventional variable focus lens by using the electro-optic effect. Further, since there are no movable parts such as a rotating diffraction grating in the laser resonator, stable laser oscillation can be obtained.

It is a figure which shows the conventional Littrow type | mold wavelength variable laser light source. It is a figure which shows the structure of the wavelength tunable laser light source concerning the 1st Embodiment of this invention. It is a figure which shows the structure of the variable focus lens concerning the 1st Embodiment of this invention. It is a figure which shows the wavelength dependence of the refractive index of a KTN crystal | crystallization. It is a figure which shows the wavelength dependence of the focal distance of the variable focus lens concerning 1st Embodiment. It is a figure which shows the structure of the variable focus lens concerning the 2nd Embodiment of this invention. It is a figure which shows the structure of the wavelength tunable laser light source concerning the 2nd Embodiment of this invention. It is a figure which shows the structure of the wavelength tunable laser light source concerning the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 shows a configuration of a wavelength tunable laser light source according to the first embodiment of the present invention. The tunable laser light source includes a laser medium 21, a first varifocal lens 22 disposed on the output optical axis, a half-wave plate 23, a second varifocal lens 24, and an output mirror 25 (first mirror). 1 mirror). The first variable focus lens 22 can change the focus in the x-axis direction with respect to the polarization in the x-axis direction, and the second variable focus lens 24 in the y-axis direction with respect to the polarization in the y-axis direction. The focus can be varied. A lens for shaping the light beam may be disposed between the laser medium 21 and the first variable focus lens 22 or one or both of the second variable focus lens 24 and the output mirror 25. .

  The output light 26 from the laser medium 21 is input to the output mirror 25 via two variable focus lenses, a part of the light becomes reflected light 27 in the direction of the laser medium 21, and the remaining light is the laser output light 28. Become. The reflected light 27 reciprocates in the resonator formed between the high reflection mirror 21 a (second mirror) provided on the end face of the laser medium 21 and the output mirror 25. Note that the second mirror may be arranged at a position away from the end face of the laser medium 21 instead of the high reflection mirror 21a. It suffices if a resonator including the laser medium 21 can be formed between the first mirror and the second mirror provided at the opposed position.

  First, selection of the laser output wavelength by the variable focus lens will be described. In order to perform laser oscillation in the above-described resonator, the output light 26 may be converted into parallel light and reach the output mirror 25, and the reflected light 27 may be converted into parallel light and folded back to the variable focus lens. Therefore, the output mirror 25 is a plane mirror. When the focal point of the variable focus lens having the output light 26 as parallel light has wavelength dependence, only a specific wavelength becomes parallel light, and laser oscillation occurs in the resonator. The light 29 having other wavelengths does not become parallel light and is not folded back to the variable focus lens, and therefore does not oscillate. By changing the focal length of the varifocal lens, the wavelength of the parallel light changes, so the wavelength of the light that is laser-oscillated in the resonator can be selected.

  The first variable focus lens 22 has a condensing function only in the x axis direction with respect to the polarized light in the x axis direction, and the second variable focus lens 24 is only in the y axis direction with respect to the polarized light in the y axis direction. Has a light condensing effect. The half-wave plate 23 converts the polarized light in the x-axis direction into the polarized light in the y-axis direction. Functions as a lens. For the variable focus lens, an electro-optic crystal having a wavelength dependence on the electro-optic effect is used. It will be explained that the focal length of the varifocal lens has wavelength dependence when an electro-optic crystal having wavelength dependence is used for the refractive index and the electro-optic effect.

  FIG. 3 shows the configuration of the variable focus lens according to the first embodiment of the present invention. A pair of entrance surface electrodes 32a and 32b and exit surface electrodes 33a and 34b are respectively formed on the upper surface (light incident surface) and the lower surface (light exit surface) of the substrate 31 obtained by processing the electro-optic material into a plate shape. Yes. The entrance surface electrodes 32a and 32b are set to the same potential, and the exit surface electrodes 33a and 33b are set to the same potential. The optical axis is set in the z-axis direction so that the incident light 34 passes through the gap between the pair of electrodes having the same potential and is transmitted as the outgoing light 35.

  Each of the entrance surface electrodes 32a and 32b is formed so that the sides facing each other across the gap through which light passes are parallel to the y-axis. The emission surface electrodes 33a and 33b are also formed such that opposite sides across a gap through which light passes are parallel to the y-axis. The positions of the opposing sides of the exit surface electrodes 33a and 33b are the same as the opposing sides of the entrance surface electrodes 32a and 32b in the x-axis direction, that is, the substrate 31 is sandwiched. A voltage can be applied from the entrance surface electrode 32 to the exit surface electrode pair 33 or vice versa.

In the variable focus lens of the present embodiment, among the electro-optic effects, a material having a secondary electro-optic effect (Kerr effect) in which refractive index modulation proportional to the square of the electric field occurs is preferable. For Kerr effect, a refractive index distribution [Delta] n _x in the x-axis direction does not depend on the sign of the electric field component E _x, because becomes suitable symmetrical shape as a lens. On the other hand, in the case of the Pockels effect, refractive index modulation is proportional to the first power of the electric field, the refractive index change due to the electric field component E _x is not symmetrical, it does not work well as a lens.

  Many electro-optic materials do not have inversion symmetry and develop a Pockels effect. On the other hand, some electro-optic materials have inversion symmetry, do not exhibit the Pockels effect, and the Kerr effect is dominant. Therefore, it is important to use a material having inversion symmetry as the electro-optic material of this embodiment.

As the electro-optical material having inversion symmetry, a single crystal material having a perovskite crystal structure is suitable. This is because the perovskite type single crystal material has a cubic phase in use when the use temperature is appropriately selected, and the Kerr effect in this cubic phase is large. For example, a single crystal material mainly composed of potassium tantalate niobate (KTa _1-x Nb _x O ₃ , hereinafter referred to as KTN) has more preferable characteristics. For KTN, the phase transition temperature can be selected mainly by the composition ratio of tantalum and niobium. Thereby, the phase transition temperature can be set near room temperature. In order to use the Kerr effect in KTN, it is necessary to set the operating temperature to a temperature higher than the phase transition temperature and use it in a cubic phase state. Even in the same cubic phase, the electro-optic effect becomes overwhelmingly closer to the phase transition temperature. For this reason, setting the phase transition temperature around room temperature is very important for easily realizing a large Kerr effect.

Further, as a single crystal material related to KTN, the main component of the crystal is composed of periodic group Ia group and Va group, group Ia is potassium, and group Va includes at least one of niobium and tantalum. Materials can be used. Moreover, 1 or multiple types of periodic table group Ia except potassium as an additional impurity, for example, lithium, or IIa group can also be included. For example, a cubic phase KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ , 0 <x <1, 0 <y <1) crystal may be used.

In the configuration of FIG. 3, the direction of the optical electric field is the x-axis direction for polarized light. The characteristic of the lens is expressed by optical path length modulation that the light receives by passing through the substrate 31. The optical path length modulation Δs is obtained by integrating the refractive index modulation over the path through the electro-optic material. _{Let the} refractive index modulation be Δnx. Since the variable focus lens according to the present embodiment propagates light in the z-axis direction, the optical path length modulation Δs is

Thus, it is a function of only x without depending on z. That is, it changes only in the x-axis direction where light is concentrated, and does not change in the y-axis direction. When the direction of the optical electric field in the x-axis direction, a refractive index modulation [Delta] n _x which light feel,

It is. Here, n ₀ is a refractive index when no voltage is applied. s ₁₁ and s ₁₂ are second-order electro-optic coefficients, and E _x and E _z are the x component and z component of the electric field generated by the applied voltage.

  In the varifocal lens shown in FIG. 3, when a voltage is applied to the electrodes, part of the electric lines of force connecting the electrodes are bent inside the electro-optic material, so that the electric field of the portion through which light is transmitted changes. Be made. The electric field due to the applied voltage is strong in the vicinity of the electrode and becomes weaker as the distance from the electrode increases. That is, the refractive index changes greatly near the electrode, and the refractive index change near the center of the crystal becomes relatively small. When KTN is used as the electro-optic material, the refractive index changes so as to decrease, so that the optical path length when the optical electric field is directed in the x-axis direction is shorter near the electrode than near the crystal center. . That is, it functions as a convex lens.

Non-Patent Document 2 describes the wavelength dependence of g ₁₁ and g ₁₂ . Here, between s _ij and g _ij , when the dielectric constant in the cubic phase is ε,
s _ij = g _ij ε ²
There is a relationship. Non-Patent Document 3 describes the wavelength dependence of n ₀ . Therefore, in equation (2), n ₀ , s ₁₁ , and s ₁₂ have wavelength dependence, so that the optical path length modulation Δs has wavelength dependence.

FIG. 4 shows the wavelength dependence of the refractive index of the KTN crystal. The wavelength dependence of the refractive index of the KTN crystal described in Non-Patent Document 3 is shown in the wavelength range of 1.2 to 1.4 μm. The KTN crystal shows that the refractive index decreases as the wavelength increases. Also, Non-Patent Document 2 describes that s ₁₁ and s ₁₂ are similarly reduced as the wavelength increases. Therefore, the optical path length modulation Δs increases as the wavelength increases. The focal length f of the variable focus lens according to the present embodiment can be obtained in correspondence with the optical path length modulation distribution of a general lens by fitting the optical path length modulation distribution with a quadratic curve. If the absolute value of the optical path length modulation Δs is large and the change in the optical path length modulation distribution is steep, the focal length f of the lens becomes short. In this embodiment, since the optical path length modulation Δs is negative, the absolute value of Δs decreases as the wavelength increases, and the focal length f of the lens increases.

  FIG. 5 shows the wavelength dependence of the focal length of the variable focus lens according to the first embodiment. In the wavelength range of 1.2 to 1.4 μm, the focal length is shown normalized. If the light having a wavelength with a focal length of 1 is the output light 26 of the tunable laser light source shown in FIG. 2, it becomes parallel light through the variable focus lens and can resonate in the resonator. When the voltage applied to the electrode pair of the variable focus lens is V1, the variable focus lens converts only light having a specific wavelength of 1.2 μm into parallel light, and only this wavelength resonates in the resonator. When the applied voltage is V1, the light of other wavelengths has a longer focal length, and therefore does not become parallel light and cannot resonate.

  By changing the voltage applied to the electrodes, the wavelength at which the focal length becomes 1 changes, so that the wavelength of light that is converted into parallel light and resonates in the resonator can be changed. Since the focal length of the varifocal lens becomes longer as the wavelength becomes longer, by applying a higher voltage, light having a longer wavelength can be converted into parallel light and resonated. When selecting the wavelength by changing the applied voltage and changing the focal length, the response time is 1 μs or less, which is much faster than the conventional configuration using moving parts. Further, it is possible to avoid a variation in the resonator length, which is a problem when including a movable part.

  When a high voltage is applied to the electro-optic material, charges are injected from the electrodes, and space charges can be generated in the crystal. This space charge causes a gradient in the magnitude of the electric field in the direction in which the voltage is applied. Therefore, in order to obtain a desired refractive index distribution for causing the electro-optic material to function as a lens, or to prevent light transmitted through the electro-optic material from being deflected, when a voltage is applied to the substrate 1, It is better that no space charge is formed inside the substrate 1.

  Since the amount of space charge depends on the carrier injection efficiency, the carrier injection efficiency injected from the electrode should be small. When the carriers contributing to electric conduction in the electro-optic material are electrons, as the work function of the electrode material increases, the electrode and the substrate approach a Schottky junction, and the carrier injection efficiency decreases. Therefore, the electrode is preferably a material that forms a Schottky junction with the electro-optic material. Specifically, when the carrier contributing to electrical conduction in the electro-optic crystal is an electron, the work function of the electrode material is preferably 5.0 eV or more. For example, as an electrode material having a work function of 5.0 eV or more, Co (5.0), Ge (5.0), Au (5.1), Pd (5.12), Ni (5.15), Ir (5.27), Pt (5.65), Se (5.9) can be used. The parentheses indicate work functions, and the unit is eV.

  On the other hand, when the carriers contributing to electrical conduction in the electro-optic crystal are holes, the work function of the electrode material is preferably less than 5.0 eV in order to suppress the injection of holes. For example, Ti (3.84) or the like can be used as an electrode material having a work function of less than 5.0 eV. Since the Ti single-layer electrode is oxidized and becomes high resistance, generally, the Ti layer and the electro-optic material are bonded using an electrode in which Ti / Pt / Au are sequentially laminated. Furthermore, transparent electrodes such as ITO (Indium Tin Oxide) and ZnO can also be used.

  FIG. 6 shows the configuration of a variable focus lens according to the second embodiment of the present invention. Four strip-shaped electrodes are formed on the upper surface (first surface) and the lower surface (second surface) of the substrate 41 obtained by processing the electro-optic material into a plate shape. An anode 42 (first anode) is disposed as an upper electrode on the light incident side, and a cathode 43 (first cathode) is disposed as a lower electrode across the substrate 41. Further, another pair of electrodes is arranged on the light emission side with a space from these electrode pairs, the upper electrode is the cathode 44 (second cathode), and the lower electrode is the anode 45 (second anode). It is. The four strip-shaped electrodes have a shape in which all the sides in the longitudinal direction are parallel.

  Light is incident from a surface (third surface) orthogonal to the surface on which the electrodes are arranged, travels in the x-axis direction inside the substrate 41, and between the anode 42 and the cathode 43, the longitudinal direction of these strip electrodes Transmits in the vertical direction. Next, after passing between the cathode 44 and the anode 45, the light is emitted from the surface (fourth surface) opposite to the incident surface into the air.

  In such a configuration, a voltage is applied between the anode and the cathode. The direction of applying a voltage (z-axis direction) is opposite between the light incident side electrode pair and the light emission side electrode pair. The potentials of the anode 42 and the anode 45 may be different, and the potentials of the cathode 43 and the cathode 44 are the same. The lower potential of the anodes 42 and 45 is set to be higher than the higher potential of the cathodes 43 and 44.

  At this time, an electric field distribution is generated between these electrodes, and the refractive index is modulated by the electro-optic effect of the substrate 41. When light is transmitted through the refractive index modulated portion, the light is bent by this refractive index distribution, and as a result, the light is condensed or diverged. When condensed, according to the structure of FIG. 6, it functions as a cylindrical convex lens, and when diverged, it functions as a cylindrical concave lens. Further, since the degree of bending of light changes depending on the applied voltage, the focal length can be controlled by the voltage.

  Such a variable focus lens can be used as the first variable focus lens 22 and the second variable focus lens 24 of the wavelength variable laser light source shown in FIG.

  FIG. 7 shows a configuration of a wavelength tunable laser light source according to the second embodiment of the present invention. The wavelength tunable laser light source of FIG. 7A includes a laser medium 51, a first variable focus lens 52 disposed on the optical axis on the output side, a half-wave plate 53, and a second variable focus lens 54. And an output mirror 55. The first variable focus lens 52 can change the focus in the x-axis direction with respect to the polarization in the x-axis direction, and the second variable focus lens 54 in the y-axis direction with respect to the polarization in the y-axis direction. The focus can be varied. The output light 56 from the laser medium 51 is output from the first variable focus lens 52 and then spreads without becoming parallel light in the x-axis direction. Similarly, the light traveling from the second variable focus lens 54 toward the output mirror 55 spreads without becoming parallel light with respect to the y-axis direction. Further, as in the first embodiment, the half-wave plate 53 converts polarized light in the x-axis (y-axis) direction into polarized light in the y-axis (x-axis) direction. The variable focus lens described in FIG. 3 or FIG. 6 can be used.

  The output mirror 55 (first mirror) is a concave mirror, and has a function of a concave lens with respect to reflected light. The output light 56 from the laser medium 51 is input to the output mirror 55 through two variable focus lenses, a part of the light becomes reflected light 57 in the direction of the laser medium 51, and the remaining light is the laser output light 58. Become. As described above, the resonator including the laser medium 51 is formed between the first mirror and the second mirror provided at the opposed position. In the present embodiment, a high reflection mirror is formed on the end surface of the laser medium 51. If the focal length of the variable focus lens is adjusted so that the reflected light 57 returns to the laser medium 51 via the same path as that of the output light 56, the wavelength of the light oscillated in the resonator can be changed.

  The wavelength tunable laser light source of FIG. 7B includes a laser medium 61, a first variable focus lens 62 disposed on the optical axis on the output side, a half-wave plate 63, and a second variable focus lens 64. And an output mirror 65. The output light from the laser medium 61 is output from the first variable focus lens 62 and then converges without becoming parallel light in the x-axis direction. Similarly, the light from the second variable focus lens 64 toward the output mirror 65 converges without becoming parallel light with respect to the y-axis direction. The output mirror 65 is a convex mirror and has a function of a convex lens with respect to the reflected light. Similar to the wavelength tunable laser light source in FIG. 7A, the wavelength of the laser-oscillated light can be changed by changing the focal length of the variable focus lens.

  FIG. 8 shows the configuration of a wavelength tunable laser light source according to the third embodiment of the present invention. FIG. 8A shows a configuration viewed from the yz plane, and FIG. 8B shows a configuration viewed from the xz plane. The wavelength tunable laser light source includes a laser medium 71, a first variable focus lens 72 arranged on the optical axis on the output side, and an output mirror 75. The first variable focus lens 72 can change the focus in the y-axis direction with respect to the polarization in the y-axis direction. The variable focus lens described in FIG. 3 or FIG. 6 can be used. The output mirror 75 is a cylindrical mirror and has a focal point with respect to the x-axis direction. Similar to the wavelength tunable laser light source of FIG. 7, the focal length of the variable focus lens is changed so that the light reflected by the output mirror 75 returns to the laser medium 71 through the same path as the light incident on the output mirror 75. Thus, the wavelength of the laser-oscillated light can be changed.

21, 51, 61, 71 Laser medium 22, 52, 62, 72 First variable focus lens 23, 53, 63 Half-wave plate 24, 54, 64 Second variable focus lens 25, 55, 65, 75 Output mirror

Claims (12)

A laser medium having a gain with respect to a lasing wavelength;
Varifocal lens means provided on the optical axis on the output side of the laser medium;
A first mirror provided on the output optical axis of the varifocal lens means;
A second mirror provided at a position facing the first mirror and constituting a resonator including the laser medium;
The varifocal lens means includes an electro-optic material having reversal symmetry and two or more electrodes for applying an electric field inside the electro-optic material, and by changing a voltage applied to the electrodes, The focal length of light transmitted through the electro-optic material can be varied,
A wavelength tunable laser light source characterized in that, since the focal length has wavelength dependence, the wavelength of light that oscillates in a resonator including the laser medium can be selected.   2. The variable focus lens unit includes a first variable focus lens capable of changing a focal point with respect to polarized light in a uniaxial direction, and the first mirror is a cylindrical mirror. The tunable laser light source described.   The varifocal lens means includes a first varifocal lens capable of changing a focal point with respect to a polarized light in a first axial direction, and a polarized light in a second axial direction orthogonal to the first axis. A second variable focus lens capable of changing a focus; and a half-wave plate inserted between the first variable focus lens and the second variable focus lens; The tunable laser light source according to claim 1, wherein the tunable laser light source is a concave mirror or a convex mirror.   The varifocal lens means converts either the first axial direction or the second axial direction into parallel light, and the first mirror is a cylindrical mirror instead of a concave mirror or a convex mirror. The tunable laser light source according to claim 3.   The variable focus lens means converts parallel light into the first axial direction and the second axial direction, and the first mirror is a flat mirror instead of a concave mirror or a convex mirror. The tunable laser light source according to claim 3. The variable focus lens means has the electrodes formed on a light incident surface and a light output surface of the electro-optic material,
The optical axis is set so that the light is incident from a gap where the electrode on the incident surface is not formed, and is emitted from the gap where the electrode on the emission surface is not formed,
A portion of the lines of electric force directed from the electrode on the incident surface to the electrode on the output surface is bent in the gap, and the electric field of the portion through which the light is transmitted around the optical axis is changed,
5. The focus of light transmitted through the electro-optic material is varied by changing an applied voltage between the electrode on the incident surface and the electrode on the exit surface. 6. Tunable laser light source. The variable focus lens means includes:
A first anode formed on a first surface of the electro-optic material;
A first cathode formed on a second surface opposite to the first surface and formed at a position facing the first anode;
A second cathode formed on the first surface and spaced from the first anode;
A second anode formed on the second surface, facing the second cathode, and spaced apart from the first cathode;
When light is incident from a third surface orthogonal to the first surface, the light passes through the first electrode pair composed of the first anode and the first cathode, and then the second The optical axis is set so that light passes through a second electrode pair consisting of an anode and the second cathode, and light is emitted from the fourth surface facing the third surface,
5. The focus of light emitted from the fourth surface of the electro-optic material is varied by changing an applied voltage between the first and second electrode pairs. The tunable laser light source according to any one of the above.   8. The wavelength tunable laser light source according to claim 1, wherein the electro-optic material is a perovskite single crystal material. The electro-optical material, a wavelength tunable laser light source according to claim 8, characterized in that the potassium tantalate niobate _{(KTa 1-x Nb x O} 3).   The electro-optic material is characterized in that the main component of the crystal is composed of groups Ia and Va in the periodic table, group Ia is potassium, and group Va includes at least one of niobium and tantalum. The wavelength tunable laser light source according to claim 8.   11. The wavelength tunable laser light source according to claim 10, wherein the electro-optical material further includes one or more members of Group Ia of the periodic table excluding potassium as an additive impurity, for example, lithium or Group IIa.   12. The wavelength tunable laser light source according to claim 8, wherein the electrode is a material that forms a Schottky junction with the electro-optic material.

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