JPS6145219A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain an optical isolator superior in light transmission efficiency by projecting laser light through a half-wavelength plate and a birefringent tapered plate, and reflecting totally backward light or a rutile surface by the refraction of the birefringent tapered plate. CONSTITUTION:Laser projection light which is emitted by an oscillator 1 and has a 0.67 beam diameter ratio and a 23.9 deg. total reflection angle is incident on the rutile part 4 of an optical isolator 3 at a Brewster angle through a convex lens 2. This incident light enters the rutile part 4 without being reflected and light refracted by the rutile part 4 is incident on a 45 deg. Faraday rotator 5. This rotator 5 rotates the plane of polarization of the light by 45 deg. and increases the beam ratio to 1.65, the half-wavelength plate 6 further rotates the plane of polarization by 45 deg., and the birefringent tapered plate 7 decreases the beam diameter ratio to 1.00, so that the light is incident on a convex lens 8. Therefore, the light incident on the rutile part 4 is projected from the birefringent tapered plate 7 without any loss as laser light (extraordinary light) having the plane of polarization by 90 deg. and circular plane of polarization with 1.00 beam diameter.

Description

Detailed Description of the Invention (1) Technical Field of the Invention The present invention relates to an optical isolator, and in particular to an optical isolator that uses rutile (titanium dioxide) to completely reflect backward laser light so that the laser light returns to the oscillator side. The present invention relates to an optical isorter that prevents.

(2) Background of the invention In recent years, it has been used in laser application equipment such as optical fibers.

An optical isolator is used to prevent the operation of the device from becoming unstable if some of the laser light reflected from the elements in the transmission path returns to the oscillator side.

(3) Prior art and problems In general, an optical isolator has a polarizer that converts laser light into linearly polarized laser light and a Faraday element to which a magnetic field is applied in a fixed direction. It is set at 45°.

When a laser beam is incident on a polarizer, the transmitted linearly polarized light from the polarizer is rotated by 45° within the Faraday element,
Since the direction of the magnetic field applied to the Faraday element is constant and the direction of rotation of the light is unrelated to the direction in which the light travels, light once emitted from the Faraday element is reflected back from other elements. In this case, when the light is rotated by 45° within the Faraday element, it becomes light whose polarization plane is shifted by 45° with respect to the polarizer.

For this reason, the laser beam cannot return to the oscillator side again.
It is possible to eliminate reflected light returning to the oscillator side.

A conventional optical isolator laser module using YIG uses, for example, a birefringent flat plate as a polarizer. Therefore, the light traveling in the opposite direction returned near the two oscillators, and sufficient isolation could not be obtained.

(4) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention provides an optical isolator with excellent light transmission efficiency by using rutile as the optical isolator and injecting a laser beam into the rutile at the Brewster angle. The purpose is to

(5) Summary of the Invention The above objects are 9. According to the present invention, in an optical isolator provided on the front surface of a laser oscillator, a rutile portion on which a laser beam is incident at Brewster's angle and a rutile portion on which the laser beam transmitted through the rutile portion are incident. a 45° Faraday rotator, and a half-wave plate and a birefringent taper plate into which the laser beam that has passed through the 45° Faraday rotator is incident, and the laser beam is transmitted through the half-wave plate and the birefringent taper slope. This is achieved by providing an optical isolator characterized in that the laser beam is then emitted with a circular beam shape, and the retrograde ordinary light is totally reflected on the rutile surface by refraction by the birefringent tapered plate. .

(6) Examples of the invention Hereinafter, nine embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 1(a) and 1(bl) are block diagrams of an optical fiber device including an optical isolator of the present invention, with FIG. 1(a) showing a front view of the device and FIG. 1(b) showing a plan view of the device. Also, the same figure (
The beam waveform A shown in a) and (b) is elliptical, and the beam waveform B is circular.

In the figure, an oscillator 1 that oscillates a laser beam is a laser diode using a semiconductor device, and the laser beam generated from the oscillator 1 enters a convex lens 2. The laser beam converted into parallel light by the convex lens 2 enters the rutile portion 4 of the optical isolator 3 of the present invention. The laser beam incident on the rutile section 4 is transmitted through a 45° Faraday rotator 5. Half-wave plate6. The light enters a convex lens 8 through a birefringent tapered plate 7, and enters a fiber 9 located on the focal length of the convex lens 8.

FIG. 2 shows a detailed configuration diagram of the optical isolator 3 of the present invention used in the above configuration.

Rutile section 4. 45° Faraday rotator 5. half-wave plate 6,
The birefringent taper plate 7 is provided in close contact with each other, the rutile portion 4 acts as a prism for the laser beam input from the convex lens 2, and the 45° Faraday rotator 5 is made of yttrium iron garnet (YIG). The half-wave plate 6 shifts the phase of the incident light by half a wavelength and rotates the plane of polarization by 45 degrees, and the birefringent taper plate 7 is a prism that refracts and emits the incident light in two directions.

Total reflection angle 2 with beam diameter ratio of 0.67 emitted from oscillator 1
Laser emitted light (hereinafter referred to as ordinary light) having an angle of 3.9° enters the rutile portion 4 of the optical isolator 3 via the convex lens 2 with a Brewster angle. Ordinary light that has entered the rutile section 4 with a pre-Aster angle enters the rutile section 4 without reflection, and the ordinary light that has been refracted at the rutile section 4 enters the 45° Faraday rotator 5.

In the 45° Faraday rotator 5, the plane of polarization of ordinary light is 4
The beam rotates by 5°, the beam diameter ratio becomes 1.65, and the plane of polarization is further rotated by 45° by the half-wave plate 6, and the beam enters the convex lens 8 via the birefringent taper plate 7 with a beam diameter ratio of 1.00.
For example, ordinary light that has passed through the rutile part 4 at an angle of 22.1° with respect to the normal direction of the interface in contact with the outside of the rutile part 4 is aligned with the normal direction of the interface in contact with the outside of the birefringent tapered plate 7. The light is emitted from the birefringent tapered plate 7 at an angle of 54.68°. Therefore, the ordinary light incident on the rutile portion 4 is completely lost and is treated as laser light (hereinafter referred to as extraordinary light) whose polarization plane has been rotated by 90 degrees.

A birefringent tapered plate 7 having a circular polarization plane with a beam diameter of 1
It is emitted from. Here, the rutile portion 4 is constructed in such a shape that the negative side is more curved than the other side, as shown in the plan view (Fig. 1). The birefringent tapered plate 7 is formed to be thicker than one side corresponding to the thinner portion of the rutile portion. In addition, the rutile part has a n e of 2.721°nc and a n of 2.463.

On the other hand, when the extraordinary light emitted from the birefringent tapered plate 7 is reflected by some element and enters the tapered plate 7 again, it passes through the optical path opposite to that described above and is totally reflected in the direction shown by the dotted arrow in the rutile part 4. do.

Further, as shown in FIG. 3, when ordinary light enters the birefringent tapered plate 7 for some reason, the plane of polarization is rotated by 6 degrees by the half-wave plate 6, and the plane of polarization is further rotated by 6 degrees by the 45 degrees Faraday rotator 5. It rotates and enters the rutile section 4. Ordinary light traveling inside the rutile portion 4 toward the convex lens z side is totally reflected at the interface of the rutile portion 4 in contact with the outside, and does not travel toward the convex lens 2 side. For example, ordinary light that enters at an angle of 54.68° with the normal direction of the birefringent taper plate 7 is refracted at the interface with the outside of the birefringent taper plate 7 and forms an angle of 19.35° with the normal direction. The rutile section 4 is connected through a half-wave plate 6 and a 45° Faraday rotator 5.
It is totally reflected at the interface with the outside at an angle of 24° with respect to the normal direction of the interface.

24'"r*mN""-Pa5"ゝAJIt L&R'g
%4.1. Neither light returns to the convex lens 2 side, that is, to the oscillator 1 side.

Furthermore, the beam shape of the light shown in FIG. 1 can be changed from an elliptical shape A before entering the optical isolator 3 to a circular shape B after exiting from the optical isolator by adjusting the refraction angle of the birefringent tapered plate 7. . Therefore, since the input cross section of the fiber 9 is circular, light having a circular beam shape efficiently enters the fiber 9 via the convex lens 8.

As described above, the present invention allows all laser light incident on the optical isolator 3 in the forward direction to pass through, while completely blocking laser light (ordinary light, extraordinary light) incident on the optical isolator 3 from the opposite direction.

The present invention is not limited to the above embodiments, and the half-wave plate 6
, replace the 45° Faraday rotator 6.

The same effect can be achieved by placing the half-wave plate 6 in close contact with the rutile portion 4 and placing the 45° Faraday rotator 5 in close contact with the birefringent tapered plate 7.

(7) Efficiency of the Invention As explained in detail above, according to the present invention, the laser beam incident on the rutile part can be completely emitted from the birefringent tapered plate, and furthermore, the laser beam emitted from the birefringent tapered plate The beam shape is circular.

When transmitting the output length of an optical isolator via an optical fiber, it is efficient (has the effect of allowing laser light to enter the optical fiber).

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical device including an optical isolator according to the present invention, FIG. 2 is a block diagram of an optical isolator according to the present invention, and FIG. FIG. 3 is a configuration diagram illustrating a passing optical path. 3-・・・・-Optical isolator, 4・・・・−
1---Rutile part, 5-・-・-・-45゛Faraday rotator. 6・−・−・−・−half wave plate, 7・−・・−・
- Birefringent tapered plate.

Claims (2)

[Claims] (1) In the optical isolator provided on the front side of the laser oscillator, there is a rutile part where the laser light is incident at Brewster's angle and a 45° angle where the laser light that has passed through the rutile part is incident.
It has a Faraday rotator and a half-wave plate and a birefringent taper plate into which the laser beam transmitted through the 45° Faraday rotator is incident, and the laser beam is emitted through the half-wave plate and the birefringent taper plate. At the same time, the optical isolator is characterized in that the retrograde light is totally reflected on the rutile surface by refraction by the birefringent tapered plate. (2) The optical isolator according to claim 1, wherein the emitted laser beam has a circular shape.