JPH1168209A - Wavelength variable micro chip laser with electric field control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength variable micro chip laser wherein wavelength is changed in high-responsibility by electric field control. SOLUTION: A non-liner crystal 12 so configured that the index of refraction in each active direction is changed when electric field is applied, and a laser crystal 14, are provided. The non-liner crystal and the laser crystal comprise, respectively, plane interfaces 12a and 14a common to each other, and an outside end surface almost orthogonal to the interface. The outside end surface of the laser crystal is a total reflection surface 14b while that of the non-liner crystal is a partial reflection surface 12b, and the total reflection surface and the partial reflection surface constitute a Fabry-Perot type resonator. Further, by using polarizing crystal for the laser crystal, it can function as a double refraction filter on electric field control without incorporating in polarizing plate, the loss is reduced and wavelength is changed in high responsibility.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable microchip laser controlled by an electric field.

[0002]

2. Description of the Related Art FIG. 4 is a principle diagram of a conventional birefringent filter. This birefringent filter consists of several quartz wave plates of different thicknesses, each quartz plate having a cavity inside it so that the vertically polarized light in the cavity is not lost by reflection on the surface of the quartz plate. Is placed at Brewster's corner. Lossless conditions allow amplification of highly linearly polarized light within the cavity.

If the wavelength λ _{0 in} vacuum is d (n _slow −n
_fast ) = mλ ₀ (m is an integer), and when d satisfies the relationship that the light travels through the quartz plate, the quartz plate becomes a full-wavelength plate for vertically polarized light. The crystal axis of the quartz plate is oriented. For other wavelengths, the transmission of vertically polarized light through the quartz plate is elliptically polarized. After being reflected by the end mirror, this elliptically polarized light experiences a reflection loss the next time it meets the waveplate surface. This loss ensures that laser operation does not occur at wavelengths far different from those that satisfy the full wavelength condition.

[0004] Tuning of the laser is accomplished by rotating a plate mounted on a common platform about the plate normal, as shown in FIG. Since the plate is tilted with respect to the optical axis, the rotation effectively causes the slow axis refractive index to be n.
_{From slow} to n ′ _slow , the selected wavelength changes to λ ′ ₀ = d (n ′ _slow −n _fast ) / m. Therefore, by inserting the birefringent filter shown in FIG. 4 between the mirrors of the laser, it is possible to select and amplify only specific polarized light of wavelength λ ₀ .

FIG. 5 shows a configuration diagram (A) and a characteristic diagram (B) of another birefringent filter. In this figure, the birefringent filter is composed of three nonlinear crystals b _{1 and} b 3 having different thicknesses.
_2, consists of b ₃ and the polarizing plate P _1, P _2, P ₃ Prefecture. Of three nonlinear crystal b _1, b _2, a thickness of the b ₃ respectively d _1, is 2d _1, 4d _1, the polarizer P _1, P _2, P ₃ are α-axis, 45 ° with respect to β-axis
Is set to a polarization plane. In this case, the nonlinear crystal b ₁
And the transmittance of light passing through the combination of the polarizing plate P ₁ is
Similarly, the transmittance of light passing through the combination of the nonlinear crystal b ₂ and the polarizing plate P ₂ , and the transmittance of light passing through the combination of the nonlinear crystal b ₃ and the polarizing plate P ₄ are b and d in FIG. become that way.
Therefore, the whole of FIG. 5A can function as a very narrow band-pass filter like e in FIG. 5B. This birefringent filter is called “The Birefr
ingent Filter "(THE OPTICAL SOCIETYOF AMERICA, VOLU
ME 39, NUMBER3, MARCH, 1949).

[0006]

In the above-described conventional birefringent filter, it is necessary to select a wavelength by mechanically tilting and rotating the birefringent element such as a quartz plate or a mica plate using a fixed refractive index. There is. However, there has been a problem that it is difficult to apply to control of such a microminiature and precise device that is difficult to mechanically control, for example, a microchip laser or the like.

In the conventional monolithic microchip laser, the wavelength can be changed only by controlling the crystal temperature or the like. Therefore, in order to enable quick control, it is necessary to use a composite resonator and control the electrostrictive element. This has been done conventionally. However, even in this case, there is a problem that the response is low.

The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a wavelength tunable microchip laser capable of changing a wavelength with high response by electric field control.

[0009]

According to the present invention, there are provided a nonlinear crystal and a laser crystal, each of which is configured to change the refractive index in each crystal axis direction by applying an electric field. Each have a common plane boundary surface and an outer end surface substantially orthogonal to the boundary surface, the outer end surface of the laser crystal is a total reflection surface, the outer end surface of the nonlinear crystal is a partially reflection surface, A Fabry-Perot type resonator is constituted by a total reflection surface of a crystal and a partial reflection surface of a nonlinear crystal.

According to the configuration of the present invention, a crystal having a primary electro-optic effect (non-linear crystal) is used in an appropriate axial direction, and a normal birefringence element is mechanically operated by applying an electric field. Similar effects can be obtained. That is, in the complex resonance type microchip laser, as a means for controlling the oscillation wavelength, the primary electro-optic effect is used, and the optical length is changed by the change in the refractive index to control. Thereby, an improvement in operation speed can be expected as compared with electrostriction.

According to a preferred embodiment of the present invention, the laser crystal is a polarizing crystal. With this configuration, it is possible to function as a birefringent filter by electric field control without incorporating a polarizing plate, reduce loss, and change the wavelength with high responsiveness. Preferably, the nonlinear axis of the nonlinear crystal is aligned with the optical axis of the laser. With this configuration, by applying an electric field to the crystal, the refractive index in the laser optical axis direction can be directly changed, the optical path length can be controlled, and the wavelength can be controlled. In addition, the responsiveness is improved as compared with the electrostrictive element, and the performance such as stabilization control is improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described.
Will be described with reference to the drawings. In addition, in each figure,
The same reference numerals are used for the portions to be used. FIG.
It is explanatory drawing of a linear crystal. As shown in this figure,
The crystal 12 is composed of two electrodes mounted on the sides facing each other.
13, a voltage is applied to this voltage.
The refractive index n in each crystal axis direction by the application of an electric field generated
_x,n _y,n_zAt least one of which has a changing property
You. Such a characteristic is also called a primary electro-optic effect. In addition,
BBO, LBO, etc. are known as such nonlinear crystals.
I have.

FIG. 2 is a configuration diagram of a wavelength tunable microchip laser according to the present invention. In this figure, (A) is a side view, and (B) is an end view. As shown in this figure,
The wavelength tunable microchip laser 10 by electric field control according to the present invention includes a nonlinear crystal 12 and a laser crystal 14.
Further, as shown in this figure, the nonlinear crystal 12 and the laser crystal 14 are respectively provided with common plane boundary surfaces 12a and 14a.
a and outer end faces 12b and 14b substantially orthogonal to the boundary faces 12a and 14a. Outer end face 1 of laser crystal 14
4b is a total reflection surface, and the outer end surface 12b of the nonlinear crystal 12
Is a partial reflection surface, and the total reflection surface 14b of this laser crystal
A so-called Fabry-Perot resonator (i.e., a composite resonance type microchip laser) is constituted by the above and the partial reflection surface 12b of the nonlinear crystal.

Further, in the example of FIG.
Is a crystal having a polarizing property such as Tm: YLF.
Further, in this example, each crystal axis c of the nonlinear crystal 12 is not aligned with the optical axis of the laser. With this configuration, the total reflection surface 14b of the laser crystal and the partial reflection surface 12b of the nonlinear crystal
When the laser beam is reflected back between the
Since the laser crystal 14 is a polarizing crystal, it functions as a birefringent filter by electric field control without incorporating a polarizing plate, and only the polarized light indicated by a double arrow in the figure is amplified, and the polarized laser light is partially reflected on the reflecting surface. 12b.

According to this structure, a crystal having the first-order electro-optic effect (non-linear crystal 12) is used in an appropriate axial direction, and a normal birefringent element is mechanically operated by applying an electric field. Similar effects can be obtained. In other words, in a complex-resonant microchip laser, the primary electro-optic effect is used as a means for controlling the oscillation wavelength, and the optical length is changed by the change in the refractive index to control the operation. Speed improvement can be expected.

FIG. 3 is a block diagram of another tunable microchip laser according to the present invention. In this figure, the nonlinear axis (for example, z axis) of the nonlinear crystal 12 is the optical axis Z of the laser.
Is consistent with In this example, the laser crystal 14
May be other than a polarizing crystal, for example, Tm: YLF, Tm
m: YAG or the like can be used. Other configurations are
It is the same as FIG.

With this configuration, by applying an electric field to the crystal, the refractive index in the laser optical axis direction can be directly changed, the optical path length can be controlled, and the wavelength can be controlled. In addition, the responsiveness is improved as compared with the electrostrictive element, and the performance such as stabilization control is improved.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0019]

As described above, the wavelength tunable microchip laser according to the present invention has an excellent effect that the wavelength can be changed with high responsiveness by controlling the electric field.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a nonlinear crystal.

FIG. 2 is a configuration diagram of a wavelength tunable microchip laser according to the present invention.

FIG. 3 is a configuration diagram of another tunable microchip laser according to the present invention.

FIG. 4 is a principle diagram of a conventional birefringent filter.

FIG. 5 is a principle diagram of another conventional birefringent filter.

[Explanation of symbols]

 Reference Signs List 10 wavelength-tunable microchip laser 12 nonlinear crystal 12a boundary surface 12b total reflection surface 13 electrode 14 laser crystal 14a boundary surface 14b partial reflection surface

Claims (3)

[Claims] 1. A non-linear crystal configured to change a refractive index in each crystal axis direction by application of an electric field, and a laser crystal. The non-linear crystal and the laser crystal each have a plane boundary surface common to each other. An outer end surface substantially orthogonal to the boundary surface, the outer end surface of the laser crystal is a total reflection surface, the outer end surface of the nonlinear crystal is a partial reflection surface, and a total reflection surface of the laser crystal and a portion of the nonlinear crystal. A wavelength tunable microchip laser controlled by an electric field, wherein a Fabry-Perot resonator is constituted by a reflection surface. 2. The laser chip according to claim 1, wherein said laser crystal is a crystal having a polarization property. 3. The tunable microchip laser according to claim 1, wherein a nonlinear axis of the nonlinear crystal is aligned with an optical axis of the laser.