JPS58130316A - Optical isolator - Google Patents

Abstract

PURPOSE:To reduce the weight of a titled isolator and to permit mass production thereof inexpensively by laminating a polarizing film on the surface of a 1/4 wavelength plate, and disposing the same in such a way that the film faces a light source and that the incident angle of the light to be made incident to the polarizing film attains a prescribed angle. CONSTITUTION:A 1/4 wavelength plate 9 laminated with a polarizing film 8 is so disposed in the optical path of the light to be emitted from a light source 1 that the angle alpha which said plate assumes to the normal N erected on the surface thereof attains 0<alpha<90 deg.. Then, the deviation of the phase difference between the extraordinary ray and ordinary ray from a desired value generated by the fluctuations in the incident angle alpha occurring in the variation in the wavelength of the light source and the variation in beam pattern is corrected extremely easily by fine adjustment of the incident angle alpha. Thus, the optical isolator is made light in weight and is mass produced easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical isolator, particularly an optical isolator used in optical systems, data transmission systems, and the like.

Conventionally, optical isolators have generally been constructed as shown in FIG.

That is, a beam splitter 2 sandwiched between two prisms 3 and 30 and a polarizing film 4 is placed on the optical path of the light emitted from the light source 1t, and the linearly polarized light that has passed through this is circularly transmitted through a 174 wavelength plate 9. The polarized light is reflected off the surface of the target 6, and the reflected light is again passed through the quarter-wave plate 5'f, reflected by the polarizing film 4 of the beam splitter 2, and guided to the detector 7.

At this time, the reflected light that has passed once through the 174-wave plate 5 cannot theoretically pass through the polarizing film 4 because its polarization state is perpendicular to that of the light that leaves the light source 1.

However, recently, optical isolators such as those described above often use semiconductor lasers as light sources, which are small and lightweight and have low power consumption. The pattern is oval.

For this reason, the 1/4 wavelength 415 and polarizing film 4, whose plate thickness and film thickness are designed for specific values of wavelength and incident angle, can fully exhibit their functions. A case may occur in which a polarized light component that can pass through the polarizing film 4 of the beam splitter 2 is included. When this return light enters the laser resonator, the laser oscillation light and the return light interfere with each other, causing so-called back talk in which the amount of oscillation light changes, and in the case of a video or audio player, the image quality and sound quality are affected. It will seriously harm the meeting.

To solve this problem, it is necessary to individually design and prepare quarter-wave plates and polarizing beam splitters according to the variations in the oscillation wavelength and emission beam pattern of the semiconductor laser, but this will reduce productivity. It is not something that can be implemented from the front.

Therefore, the optical system twI41i is used to minimize the amount of light returned to the light source, but since the beam splitter 2 and the quarter-wave plate 5 are arranged independently in the optical path, The adjustment was extremely troublesome.

Furthermore, the prism 3 used in the beam splitter 2 requires high precision in its prism angle and flatness, making it difficult and expensive to mass produce, and has many other defects.

The present invention has been made in order to solve the above-mentioned defects of conventional optical isolators. The configuration is simple and inexpensive by arranging the optical path of the light emitted from the light source at a predetermined angle α (0<α<900) with respect to the normal to the polarizing film surface of the 4-wave plate. It is an object of the present invention to provide an easily adjustable optical isolator that compensates for fluctuations in the wavelength of light emitted from the light source and minimizes the amount of light returned to the light source.

Hereinafter, the present invention will be explained in detail based on drawings showing embodiments.

FIG. 2 is a diagram showing the basic conversion of the optical isolator according to the present invention.

In this figure, for the optical path of light emitted from light source l, polarization m5
t-Normal N when the stacked quarter-wave plate 9 is erected on its surface
The arrows drawn on the optical path in the figure indicate changes in the polarization state of the light.

Under such conditions, the relationship that produces the desired phase difference Δ1#- between mutually orthogonal polarized components in the 1/4 wavelength plate of the incident light is as shown in FIG. If the optical axis C is inclined by an angle i (0<i<90°) with respect to the normal line N, the wavelength λ and the refractive index of the ordinary ray are 1 and n, respectively.

, crystal plate pressure @1 and straight = 2K (M + k) (1) Here, M is an integer and k is the wave plate constant, which is 1 in the case of a 174 wave plate. /4.

Also, as shown in FIG. 4, when the optical axis C exists in a plane perpendicular to the normal N on the surface of the crystal plate 9, let the refraction angles of the extraordinary ray e and the ordinary ray 0 be β and r, respectively. = 2 K (M-L-k) ・・・・−・・・・
−...Given by (2).

In the above relational expression (1), from Snell's law, sin α=
It is nesiII (i+β)! Since β is constant, β is a function of α, and the above relational expression t! (1), (2)
Kyodo rays, abnormal lines of force. ga, difference Ao, kakuga. .

You can see that it is a number.

Therefore, [Fig. 3 or 4] Regardless of which type of wave plate is used to construct an optical isolator as shown in Fig. 2, variations in the angle of incidence α due to variations in the wavelength of the light source and variations in the beam pattern Abnormalities caused by jt, the position of the line and the ordinary light line, 5-GO, □1.
Now the corner.

It can be corrected very easily by making fine adjustments.

This means that even if the light s1 is a semiconductor laser and the individual oscillation wavelengths vary, the optical isolator according to the present invention can be adjusted to the optimum state with minimal return light to the light source by simply adjusting the incident angle α. It means scales.

On the other hand, the optical isolator according to the present invention constitutes 1/4
It goes without saying that artificial quartz is currently the best choice for long plates a, but w, two-plate quartz is best for the crystal plates shown in Figure 3, and #iy for the crystal plates shown in Figure 4. It may be advisable to use element material cut from rod or X-plate crystal.

Further, the polarizing film 8 laminated on the surface of the wavelength plate 9 is, for example, 8i.
02. It can be constructed from a stack of ten layers with a low refractive index and a high refractive index like Ti01. II has a very small influence on the extinction ratio due to variations in the wavelength of the light source and the angle of incidence, as compared to a quarter-wave plate.

However, if it is necessary to take into consideration the aging characteristics of the surface of the polarizing film 8 exposed to the atmosphere, the polarizing film 8t - the quarter wavelength plate 9 and the glass plate 10 may be combined as shown in Figure 1g5.
It may be sandwiched between the prism 11 and the prism 11 as shown in FIG.

However, as shown in the WJs diagram, there is polarized light WI between the glass plate lO and
If B is sandwiched, the angle of incidence of the light beam on the polarizing film 8 changes, which may cause problems in the design of the polarizing film, but in such a case, a mechanism for adjusting the incident optical path may be added.

Furthermore, as shown in FIG. 7, if a lens 12 having an appropriate focal length is attached to the back surface of the 1/4 wavelength plate 9, the spot of light incident on the detector 7 can be narrowed down to a desired size. becomes.

Since the present invention is constructed as described above, it is not only possible to mass-produce the present invention in a smaller size, lighter weight, and at lower cost than conventional optical isolators. By finely adjusting the angle of incidence, it is possible to limit the amount of light returning to the light source, so when applied to optical pickups of optical video or audio players, it has a significant effect on mass production or -1. This makes it possible to achieve significant cost reductions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a modification I of an optical isolator showing the configuration of a conventional optical isolator.

Claims (2)

[Claims] (1) A polarizing film is laminated on the surface of a 1/4 wavelength plate made of a crystal 1iK having both 1m refractive property or refractive property and optical rotation property, and the polarizing film is made to face the light source and the surface of the crystal plate is 9. An isolator characterized in that the isolator is arranged so that the incident angle α of light incident on the polarizing film is expressed as a predetermined angle (0×α<90°). (2) The optical axis of the crystal plate makes a predetermined angle i (0<i, (90°)) with respect to the normal line oriented to the surface of the crystal plate. Nine isolators.