JPS6256923A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain an excellent splitting function without reference to an ellipticity angle by providing a Faraday element which rotates a plane of polarization by 45 deg. and a phase plate which has a phase difference in specific relation with the ellipticity angle. CONSTITUTION:Incident light L1 is passed through a polarizer 16 to become linear polarized light, which is incident on a Faraday rotator 10; and its plane of polarization is rotated by 45 deg. to obtain elliptic polarized light having an ellipticity angle X, which is transmitted through the phase plate 14 having a phase difference delta having relation sindelta>=sin2X with the angle X to becomes linear polarized light, which is transmitted through an analyzer 18 to obtain light L2. Return light L3 obtained by its reflection is passed through an analyzer 18 and the phase plate 14 and made into linear polarized light by the rotator 10, but it crosses the polarization direction of the polarizer 16 and is cut off by the polarizer 16. Thus, the splitting function if made invariably excellent without reference to the ellipticity angle X.

Description

[Detailed description of the invention] (Technical field) The present invention relates to optical isolators.

(Prior art) In magneto-optical disk heads, linearly polarized light is applied to the disk.
Generally, an optical isolator using a Faraday element is used because of the need for irradiation.

By the way, the Faraday element has a polarization '/l in1';x
It has the ability to rotate and simultaneously convert linearly polarized light into elliptically polarized light. If a Faraday element that greatly increases the ellipse and difference of the Ift circularly polarized light is used in an optical isolator, the separation function (isolaire: In) will deteriorate, causing an increase in noise.

For this reason, in the past, a Faraday element with an ellipticity angle X as large as possible was required, and there was limited room for selecting the material of the Faraday element.

(Purpose) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a novel method with excellent separation function regardless of the ellipticity angle X()O). Providing optical isolators.

(composition) The present invention will be explained below.

The optical isolator of the present invention includes a Faraday element and a phase plate.

The Faraday rotation angle of the Faraday element is set to rotate the plane of polarization by 45 degrees.

The phase plate has a phase difference δ, and this phase shifter δ satisfies the relationship sin δ≧sin 2X with respect to X, where X is the ellipse half angle provided by the Faraday element.

The linearly polarized light is incident on the Faraday element of the optical isolator.

Then, the light transmitted through the optical isolator has its plane of polarization rotated by 45 degrees and becomes elliptically polarized light having an ellipticity angle X. This elliptically polarized light then passes through a phase plate.

The relationship sin between the phase difference δ of the phase plate and the above ellipticity angle X
From δ≧5in2XK, phase plate? The transmitted light becomes linearly polarized light again.

Description will be given below with reference to the drawings.

J□ Figure 1 shows one of the optical isolators implementing the present invention.
Example f/Illustrated diagrammatically.

This optical isolator includes a Faraday rotator 10, permanent magnets 12A and 12B serving as magnetic field generating means, a phase plate 14, a polarizer 16, and an analyzer 18.

Faraday rotator 10 and permanent magnets 12A and 12B
constitutes a Faraday element.

As the Faraday rotation angle 10, for example, a single crystal of bismuth-substituted gadolinium iron garnet polished so that the Faraday rotation angle becomes 45 degrees can be used. Moreover, as the permanent magnets 12A and 12B, Sm
Co magnets are preferred. When the above-mentioned single crystal is used as the Faraday rotator 10, an extreme Oersted magnetic field is applied to the Faraday rotator 10.

As the phase plate 18, one made by laminating two crystal plates together can be used. Of course, the phase difference δ has the relationship sin δ with respect to the ellipticity angle XVc given by the Faraday element.
≧5in2X must be satisfied.

In addition, polarizer 16. As the analyzer 18, a dichroic polarizing filter can be used.

From the left side of the optical isolator in Figure 1,
When the light L1 is incident, this light L1 passes through the polarizer 16, becomes linearly polarized light, and is transferred to the Faraday rotator 10.
When the light is incident on and transmitted through it, the plane of polarization is rotated by 45 degrees, and at the same time it becomes elliptically polarized light with an ellipticity angle of X. This elliptically polarized light then passes through the phase plate 14 and becomes linearly polarized light again. That is, the angle of the phase plate 140 is adjusted so that the light emitted to the right from the phase plate 14 becomes linearly polarized light. At this time, the angle ψ between the optical axis direction of the phase plate 14 and the major axis direction of the elliptically polarized light of the incident elliptically polarized light is sib 2cp = sin
The relationship 2X/sin δ is satisfied.

The linearly polarized light thus obtained is incident on the analyzer 18Vc.

The analyzer 18 has its polarization direction aligned in the direction of the polarization plane of this incident linearly polarized light, and therefore, the linearly polarized light becomes light L2 and tentatively pivots to the right of the optical isolator. .

When the reflected light L6 of the light L2 enters the optical isolator from the right, this light passes through the analyzer 18.
, passes through the phase plate 14, becomes elliptically polarized light, and enters the Faraday rotator 10. Then, when it passes through 10 Faraday rotators to the left, it becomes linearly polarized light, but the polarization direction is
The direction is perpendicular to the polarization direction of the polarizer 16, and therefore, this returned light is blocked by the polarizer 16 and will not be tentatively oriented to the left of the optical isolator.

Incidentally, the essential elements for the optical isolator of the present invention are a Faraday element and a phase plate. 1・1
In the embodiment shown in the figure, a polarizer and an analyzer are also added at l.

Hereinafter, it will be explained that it is possible to function as an optical isolator even without the polarizer and analyzer described above.

Regarding the analyzer 18, in the embodiment shown in Figure 3.1, the analyzer 18 rotates the polarization plane of the return light L6 from the direction of the polarization plane of the light L2 due to magneto-optical effects. In such cases, it is used to block the rotated component and to eliminate the influence of other optical elements on polarization. Since such components and influences are weak in general VC, this analyzer is not necessary if very high accuracy is not required.

Next, looking at the polarizer 16, this polarizer 16 has the function of linearly polarizing the light L1 incident on the Faraday rotator 10, and blocking the returning light L6.
Optical isolator prevents propagation to the left (has a surface function).

By the way, in the general usage of optical isolators,
Optical isolators are used for semiconductor lasers to prevent returning light from entering the semiconductor laser and acting as noise on laser oscillation.

However, as is well known, in the songle mode semiconductor laser, the emitted light is a direct @ 1ii6 light from the beginning.
Moreover, even if a polarized light component in a direction perpendicular to this emitted light is incident, the laser oscillation is not affected by the shadow -pl. Therefore, light W
An uninvented optical isolator along with a solid semiconductor laser? When used, even if the polarizer 16 is removed, it is only semi-dedicated! /-The return light that enters the laser is the same as the emitted light of the same laser if
The two sides intersect in the same direction and have no effect on laser oscillation.

Therefore, when used in conjunction with a single mode semiconductor laser, an optical isolator consisting only of a Faraday element and a phase plate can sufficiently function as an optical isolator.

]・Figure 2 shows the optical M using the optical isolator of the present invention.
The main parts of the M air disk head are shown in an explanatory diagram.

Laser light emitted from a semiconductor laser 20 serving as a light source is collimated by a collimator lens 22, and passes through a beam splitter 26 and a total reflection mirror 28 to an objective lens 6.
The light is incident on the magneto-optical disk 1uU and focused by the same lens 30VC toward the recording surface of the magneto-optical disk 1uU.

The light reflected by the magneto-optical disk 100 is reflected by the objective lens 60.
．． It goes through the total reflection mirror 2B and enters the beam splitter 26, and a part of the light is returned to the beam splitter 26? Although the light passes through and enters the optical eye inflator 24, due to the action of the optical isolator 24, the laser oscillation of the semiconductor L/-f-20 is not affected.

The light reflected downward from the beam splitter 26vc in Figures 3 and 2 is split into two by the beam splitter 32vc, and one enters the splitting photodiode 50 via the condenser lens 46 and the knife lens 48,
The output of 0 is amplified by an amplifier 5 to become a focusing signal F. An actuator (not shown) servo-drives the objective lens 60 in the optical axis direction based on the focusing signal FK to perform a focusing operation.

On the other hand, the light transmitted through the beam splitter 32 passes through an analyzer 34 and a condensing lens 66 and enters a two-split photodiode (4uVC) at a temperature of 4 uV. amplifier 44g
Therefore, the tracking signals T and R are each subjected to width processing.
The F signal becomes RF.

(Effects) As described above, according to the present invention, a novel optical isolator can be provided. Since this optical isolator is constructed as described above, regardless of the ellipticity angle X of the Faraday element, it can always provide a good separation function. Therefore, a wide range of freedom in material selection is provided for the Faraday rotator.

Furthermore, does the optical isolator of this invention use an electromagnet as a magnetic field generation means? It should be noted that it can also be used as an optical switch.

[Brief explanation of the drawing]

Is Figure 3.1 an embodiment of the present invention? Figure 1 for explanation.
FIG. M-2 is a diagram showing only the essential parts of an example of a hennode for a magneto-optical disk using the original inulator of the present invention. 10... Faraday rotator, 14... Phase plate, 12
A.

Claims (1)

[Claims] A Faraday element that rotates the plane of polarization by 45 degrees, and sin δ≧si for the ellipticity angle X given by this Faraday element.
An optical isolator comprising: a phase plate having a phase difference δ that satisfies the relationship n2X, and linearly polarized light is incident from the Faraday element side.