JPS60203914A - Variable wavelength filter - Google Patents

Abstract

PURPOSE:To eliminate the need for mechanical operation and to attain speedy wavelength tuning with high precision by applying a magnetic field which has optional intensity to a material which is arranged between polarizers and exhibits magnetic birefringent operation, and selecting the wavelength of passing light. CONSTITUTION:Assuming that the polarizers 2 and 3 are equal in angle of polarization, light L2 incident on the material which provides magnetic birefringent operation is equal in intensity to light L4 projected from the polarizer 3 when the phase difference /2pi is an integer. In other cases, the intensity of the light L4 decreases according to the curve of the square of the cosine. Therefore, when the material 4 has constant thickness, the wavelength of the light L3 transmitted through the material 4 is set optionally by controlling the intensity of the magnetic field applied to the material 4 and the temperature. Then, the light L3 with desired wavelength is passed through the polarizer L3 to obtain the light L4 having a prescribed plane of polarization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wavelength tunable filter for obtaining light of a desired wavelength.

[Technical background of the invention and its problems]

For example, when obtaining laser light of a desired wavelength in a laser oscillator, the variable wavelength filter is required. As such a wavelength tunable filter, the Japanese Patent Publication No. 53-99
In this known example, a filter is used to narrow the wavelength of an external optical oscillator such as a dye laser or to make the output of an optical oscillator resonate. . A birefringent plate having an ordinary refractive index and an extraordinary refractive index is used as this filter, and this birefringent plate is provided so as to be tilted at an optical oscillator angle, and is rotated to select a desired output wavelength. I try to get it.

However, with filters that use such birefringent plates, the birefringent plate must be rotated by mechanical means, so unless sufficient rotational precision is achieved, the output wavelength will not be stable. A drawback arises. Moreover,
Since the wavelength tuning is done mechanically, there is also the drawback that it is difficult to do it at high speeds.

[Purpose of the invention]

The object of the present invention is to provide a wavelength tunable filter that can perform inter-wavelength IM using electrical means and can perform wavelength tuning of 1 ml in a stable state and at high speed.

[Summary of the invention]

This invention involves arranging a pair of polarizers facing each other and disposing a substance exhibiting magnetic birefringence between these polarizers (2
, it is possible to apply a magnetic field of arbitrary strength to this material, and to select the wavelength of light that passes through the material.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 1f. The wavelength β-variable filter 1 shown in Figure 1 is a first polarizer 2.
and a second polarizer 3 which is spaced apart and opposed to the first polarizer 2 in parallel.

Between these pair of polarizers 2.3, a substance 4 exhibiting magnetic birefringence is arranged at 6°. This substance 4 is, for example, nitrobenzene contained in a transparent container, and by controlling the magnetic field H and temperature T applied thereto, the wavelength λ of the transmitted light can be selectively controlled as described later.

Next, the operation of the wavelength tunable filter 10 will be explained. The light L8 passing through the first polarizer 2 becomes light whose polarization plane is determined by the first polarizer 2, and becomes an object a.
4.

When a magnetic field H is applied perpendicularly to the direction of propagation of light, this material 4 has a magnetic field l() with a different refractive index n for polarized light parallel to the magnetic field H and a refractive index n for polarized light perpendicular to the magnetic field H. Artificial optical anisotropy occurs such that the direction is the optical axis.The difference in the refractive index of these two components depends on the strength of the magnetic field H, and is expressed by the following equation: n, -n, = KH' ・・・・・・・・・・・・
- Equation (1) Here, K is a proportionality constant, and in the case of a paramagnetic material, this K can be approximated by the following equation. Rei Tsuma, K-C
/T11 ・・・・・・・・・・・・・・・・・・(2
1 where C is a constant due to the substance "4, T is an absolute warm temperature,
λ is the wavelength.

Also, the phase difference Δ between the two polarized lights is Δ= C'l/
T I H”・・・・・・・・・・・・・・・・・・(
3) It can be expressed by the following equation. Here, l is the optical path length of the substance 4, that is, the thickness.

In the wavelength tunable filter 1, if the polarization angles of the first polarizer 2 and the second polarizer 3 are made equal, then the light L! which is incident on the substance 4 when '/2□ is the negative value! and the intensity of the light L4 emitted from the second polarizer 3 are equal; otherwise)
The intensity of tt'4 decreases approximately according to a squared cosine curve. Therefore, from the above equation i1+31, when l is constant, by controlling the strength of the magnetic field H and the temperature T, it is possible to arbitrarily set the wavelength λ of the light L3 passing through the earthenware 4. Then, the light L3 with the desired wavelength λ passes through the second polarizer 3, and becomes the light L3 whose plane of polarization is determined.
It becomes 4.

In addition, when obtaining the rumored light of wavelength λ.

Although either the magnetic field H or the temperature T may be controlled, the temperature T
Since there is a time delay, it is performed using the magnetic field H.
In other words, electrical control is more effective. Also %1st
Even if the polarization angles of the polarizer 2 and the second polarizer 3 are not the same, the phase difference Δ is set to an appropriate value by the magnetic field H and the temperature T, and the polarization angle of the light L3 is changed to the polarization angle of the second polarizer 3. By matching the plane of polarization, the light L4 can be efficiently emitted from the second polarizer 3.

The wavelength tunable filter 1 described above can be used in a laser oscillator 11 as shown in FIG. That is, in the figure, 12 is a reflection law mirror forming a resonator, and 13 is also an output side mirror.

Between these mirrors 12 and 13, a laser medium 14 that is optically excited i1e by excitation light P and the wavelength variable filter 1 are arranged optically in series.

According to the laser oscillator 11 of this type, when the light generated by the laser medium 14 being optically excited is amplified between the pair of mirrors 12 and 13, the magnetic field applied to the substance 4 of the wavelength tunable filter 1 is The wavelength λ of light passing through this substance 4 is determined by the intensity of H. Therefore, only the light of the desired wavelength λ is amplified between the pair of mirrors 12 and 13 and is emitted from the output mirror 13. Laser light with a desired wavelength λ can be emitted from the output side mirror 13.

〔Effect of the invention〕

As described above, the present invention is achieved by arranging a pair of polarizers facing each other at a distance, arranging a substance exhibiting magnetic birefringence between these light particles, and applying a magnetic field of arbitrary strength to this substance. The wavelength that passes through the material can now be selected. Therefore, since the strength of the magnetic field that applies light of the desired wavelength to the material can be obtained by mechanical means, no mechanical operation is required, and the synchronization of the flood length can be carried out with precision and speed. Ru.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a wavelength tunable filter showing an embodiment of the present invention, and FIG. 2 is a block diagram of a laser oscillator using the wavelength tunable filter. 2...First polarizer, 3...Second (fi+I photon)4...Substance exhibiting magnetic birefringence action Fig. 1 Fig. 2

Claims (1)

[Claims] A pair of polarizers are placed facing each other, a substance exhibiting a magnetic birefringence effect is placed between the pair of polarizers, and the above object is used to select the wavelength of light that passes through this substance. A wavelength tunable filter characterized by comprising: means for applying a magnetic field of desired strength.