JPS6319846B2 - - Google Patents

Description

Detailed Description of the Invention The present invention employs a pair of beam splitters for polarization separation and a crystal element having an electro-optic effect, for example, a crystal element having a secondary electro-optic effect, as an optical path switching element to reduce the total amount of incident light. The present invention relates to an optical path switching switch capable of emitting 100% of the linearly polarized beams 1a and 1b (both linearly polarized beams 1a and 1b) onto a first switching optical path and a second switching optical path.

FIG. 1 shows the principle of an optical path switching switch using a beam splitter 5' for polarization separation and a crystal element 3' having an electro-optic effect as optical path switching elements for comparison with the present invention.

As is known, the light beam 1 consists of two linearly polarized beams 1a and 1b whose polarization directions are orthogonal to each other. The polarizing beam splitter 5' has a function of separating the incident light beam into two different directions according to the polarization direction thereof and outputting the separated light beams. For example, one of the linearly polarized beams 1a, which is a component of the incident light beam 1, is emitted in a direction perpendicular to the direction of incidence, and the other linearly polarized beam 1b is emitted in the same direction.

Therefore, by setting the light beam incident on the polarized beam splitter 5' to either the linearly polarized beam 1a or 1b, the output direction can be changed, that is, a switch operation can be obtained.

The polarization direction of the light beam incident on the polarized beam splitter 5' is set to the linearly polarized beam 1a or 1.
A crystal element 3' having an electro-optic effect as described above is used for selective conversion to b. The electro-optic effect is a phenomenon in which the refractive index of a crystal changes when a voltage is applied to the crystal. Crystal bodies with such properties include single crystal LiNbO ₃ and transparent ceramic PLZT. In particular, transparent ceramic, which is a crystalline material having a secondary electro-optic effect, is considered to be promising as an element for optical path switching because it has a large electro-optic effect and can be driven at a low voltage.

A crystal element having an electro-optic effect as described above has the function of converting a passing light beam into a different polarization direction when a voltage is applied (ON), and the polarization direction cannot be changed when the voltage application is removed (OFF). Allow passage without.

Polarizing beam splitter 5' having the above action
The optical path switching switch using the electro-optic crystal element 3' will be described in detail with reference to FIGS. 1a and 1b.

As mentioned above, the incident light beam 1 is a circularly polarized beam, and two linearly polarized beams 1 whose polarization directions are orthogonal are formed.
The components are a and 1b. This incident light beam 1
A linearly polarized beam 1a with one polarization direction is placed on the optical path of
A polarizing element 2' for light selection, which allows only the light to pass through, is disposed on the optical path of the linearly polarized beam 1a that has passed through the polarizing element 2'. A beam splitter for polarization separation that includes a secondary electro-optic crystal element 3', and emits the polarized beam that has passed through the element 3' on the optical path in a perpendicular direction or a rectilinear direction depending on the polarization direction of the light beam. Tsuta 5' is arranged.

According to the above, the incident light beam 1 is incident on the polarizing element 2', and the linearly polarized light beam 1a in one polarization direction is
Only the light is allowed to pass and enters the electro-optic crystal element 3'.

The electro-optic crystal element 3' is provided with electrodes on two opposing surfaces parallel to the optical path, and is connected to a power source 4'. The electrode plane is inclined at 45° to the polarization direction of the light beam passing through it.

As shown in FIG. 1a, when no voltage is applied to the electro-optic crystal element 3', the light beam 1a passes through the electro-optic crystal element 3' without having its polarization direction changed, and the polarizing beam splitter 5 ′. As described above, the polarizing beam splitter 5' has the function of emitting a light beam in a straight direction or a perpendicular direction depending on its polarization direction, and is therefore selected as a polarizing element 2' as shown in FIG. The linearly polarized beam 1a that has passed through the electro-optic crystal element 3' is reflected from the polarizing beam splitter 5' in a perpendicular direction depending on its polarization direction and exits.

On the other hand, when a predetermined half-wave voltage is applied to the electro-optic crystal element 3' as shown in FIG.
The polarization direction is rotated by 90 degrees and converted into a linearly polarized beam 1b, which enters a polarizing beam splitter 5'. Therefore, this linearly polarized beam 1b is emitted in a straight direction without being reflected by the beam splitter 5'. In the figure, 1a' indicates scattered light emitted in the right angle direction when the electro-optic crystal element 3' is turned on.

As explained above, according to the above comparison example, it is possible to provide an optical path switching switch that can accurately switch the optical path of an incident light beam in two directions by combining the polarizing beam splitter 5' and the electro-optic crystal element 3'. However, in the optical path switching method described above, the light beam component used is always a linearly polarized beam 1a or 1 having a vertical or horizontal polarization direction.
If either one of the linearly polarized beams b is not present, the desired optical path switching cannot be achieved, and therefore the other linearly polarized beam must be cut from the incident light and used (in the above comparative example, the linearly polarized beam 1b is cut and the linearly polarized beam 1b is (using polarized beam 1a).

In this way, in the above-mentioned optical path switching switch, the light beam emitted onto each switching optical path can always utilize only one half of the total amount of incident light, and only 50%
The biggest problem is that the optical loss is unavoidable.

Therefore, as in the comparative example above, the present invention includes a beam splitter for polarization separation as an optical path switching element,
While adopting a crystal element with electro-optic effect,
This was developed to fundamentally solve the problem of optical loss, which is the problem in the above comparison example. That is, the present invention includes a first polarizing beam splitter that is shared by the incident light element and the light output element for the first switching optical path, and a second polarizing beam splitter that is applied to the light output element for the second switching optical path. The optical path switching switch comprises a first switch of the first polarizing beam splitter to convert two linearly polarized beams incident on the first polarizing beam splitter and separated by cooperation with a crystal element having an electro-optic effect. Substantially the entire amount of the incident light is emitted from the first polarizing beam by superimposing it onto the optical path or the second switching optical path of the second polarizing beam splitter.
Alternatively, it is an object of the present invention to provide a highly reliable, highly sensitive, and highly accurate optical path switching switch which guides the light onto each of the second switching optical paths to obtain an optical switching operation.

Hereinafter, the present invention will be explained in detail based on FIGS. 2a and 2b.

In the figure, A indicates the incident optical path in the optical path switching switch, A ₁ indicates the first switching optical path, and A ₂ indicates the second switching optical path. 4 and 5 are polarizing beam splitters that separate the incident light beam into a linearly polarized beam whose polarization direction is perpendicular to the plane of the paper and a linearly polarized beam whose polarization direction is parallel to the plane of the paper, as described above; Polarizing beam splitter, 5 to 2nd
It is called a polarizing beam splitter.

The first and second polarized beam splitters 4 and 5 are arranged side by side so that their polarized beam splitting surfaces inclined at 45 degrees are parallel to each other and are oriented in the same direction on the extension of the optical axis of the incident light beam 1, and the first polarized beam splitter The splitter 4 is used as a light emitting element that guides the output light beam 2 onto the first switching optical path A1 that is perpendicular to the input optical path _A , and the second polarizing beam splitter 5 is used as a light output element that guides the output light beam 2 onto the first switching optical path A1 that is perpendicular to the input optical path A. The light output element is used as a light emitting element that guides the output light beam 3 onto the second switching optical path _A2 that is perpendicular to the first switching optical path _A1 , and at the same time, the first polarizing beam splitter 4 is used to direct the input light beam 1 into the second switching optical path A2. It is also used as a light input element to separate polarized light.

6 is a linearly polarized beam 1 which is polarized by the first polarized beam splitter 4 and emitted in a perpendicular direction.
a first reflecting mirror that further reflects a in the right angle direction;
is a second reflecting mirror that further reflects the light beam reflected by the first reflecting mirror 6 in the right angle direction and makes it incident on the second polarizing beam splitter 5.

9 to 12 are the first elements that rotate the plane of polarization by 90°;
to a fourth electro-optic crystal element, for example, a secondary electro-optic crystal element PLZT, each crystal element 9 to 12
is provided with electrodes on two opposing surfaces parallel to the optical path (the electrode surfaces are inclined at 45 degrees with respect to the polarization direction of the light beam passing through) and a pair of crystal elements 9 and 12, and the same 10,
The 11 sets are connected to the power supply 18 so that they can be switched alternately by the switching terminals S ₁ and S _2.As mentioned above, when no voltage is applied to the crystal element (OFF), the light beam has a polarization direction. The light beam passes through this without being converted, and when a voltage is applied to the crystal element (ON), the polarization direction of the light beam is changed when passing through this and is emitted. Turn on the same crystal element 9,
In order to distinguish the OFF state in the drawing, the same crystal element in the ON state is shown with diagonal lines, and the same crystal element in the OFF state is shown in white.

As shown in FIG. 2a, the first and fourth secondary electro-optic crystal elements 9, 12 converge the linearly polarized beams 1a, 1b onto the first polarized beam splitter 4.
These are the same crystal elements that are turned on when superimposed on the switching optical path _{A1 and} emitted, and as shown in Figure b, the second and third secondary electro-optic crystal elements 10 and 11 are the second polarizing beam splitter. Linearly polarized beam 1a, 1 to 5
This crystal element turns on when condensing the light beam b and superimposing it onto the second switching optical path _A2 and emitting it.

The first secondary electro-optic crystal element 9 is provided between the first and second polarizing beam splitters 4 and 5, that is, the linearly polarized light is polarized by the first polarizing beam splitter 4 and travels straight to the second polarizing beam splitter 5. The second secondary electro-optic crystal element 10 is arranged on the optical path of the beam 1b, and the polarization direction of the second electro-optic crystal element 10 is not changed by the first secondary electro-optic crystal element 9 and is incident on the second polarizing beam splitter 5 and goes straight. linearly polarized beam 1
The third secondary electro-optic crystal element 11 is polarized by the first polarizing beam splitter 4 and emitted in a perpendicular direction, and is emitted from the mirrors 6 and 7.
The fourth secondary electro-optic crystal element 12 is disposed on the optical path of the linearly polarized beam 1a heading towards the second polarized beam splitter 5 through the 3. On the optical path of the linearly polarized beam 1a, which is incident on the second polarized beam splitter 5 without having its polarization direction converted by the secondary electro-optic crystal element 11, is reflected in the right angle direction, and heads toward the first polarized beam splitter 4. Allotted.

Reference numeral 8 denotes a second polarized beam splitter 5 which converts the polarization direction in the second secondary electro-optic crystal element 10 and makes a U-turn on the emitted linearly polarized beam 1a.
A rectangular prism 13 is used to convert the polarization direction of the light into the fourth secondary electro-optic crystal element 12.
A half-wave plate 14 is provided on the optical path of the linearly polarized beam 1b heading toward the polarizing beam splitter 4, and the polarization direction is converted by the first secondary electro-optic crystal element 9, and then directed to the right angle direction by the second polarizing beam splitter 5. It is a half-wave plate disposed on the optical path of the linearly polarized beam 1a that is reflected and emitted and goes to the first polarized beam splitter 4 via mirrors 7 and 6, and both half-wave plates 1
3 and 14 have the function of converting the polarization direction of the light beam passing through them (when the linearly polarized beam passing therethrough is 1a, it is converted to 1b, and when it is 1b, it is converted to 1a).

Further, a polarizing element 15 is disposed on the output optical path of the second electro-optic crystal element 10 to block scattered light emitted when the first electro-optic crystal element 9 is turned on, and a polarizing element 15 is arranged on the output optical path of the second electro-optic crystal element 10. Another polarizing element 16 is arranged on the output optical path of the half-wave plate 13 disposed on the output light side to block the scattered light emitted when the fourth electro-optic crystal element 12 is turned on. It is a polarizing element that has a function. That is, this polarizing element 1
5 and 16 allow passage of only either the linearly polarized beam 1a or 1b in the direction perpendicular or horizontal to the plane of the paper. In other words, the passage of light beams other than the light beams in one of the polarization directions is blocked.

The present invention will be further described in detail along with an explanation of its operation as follows.

As already mentioned, FIG.
8, a predetermined voltage is applied to the first polarizing beam splitter 4 as a light emitting element, and the first switching optical path A _{1 is} set.
This shows an operating state in which linearly polarized beams 1a and 1b are superimposed and output as an output light beam 2.

In the figure, an incident light beam 1 first enters a first polarized beam splitter 4 from an incident optical path A, and is split by the beam splitter 4 into two linearly polarized beams 1a and 1b, one in a straight direction and one in a perpendicular direction.

The linearly polarized beam 1a emitted in the orthogonal direction passes through the mirrors 6 and 7 without being changed in polarization direction by the third secondary electro-optic crystal element 11 to which no voltage is applied, and is sent to the second polarized beam splitter. The light is incident on the twine 5, is emitted in a perpendicular direction depending on its polarization direction, and is incident on the fourth secondary electro-optic crystal element 12. A voltage is applied to this crystal element 12.
Since it is in the ON state, the linearly polarized beam 1a
The polarization direction of the beam is changed and the beam is emitted as a linearly polarized beam 1b. When this polarized beam 1b further passes through the half-wave plate 13, its polarization direction is converted again to the original linearly polarized beam 1a, which passes through the polarizing element 16 and enters the first polarized beam splitter 4.

Depending on its polarization direction, this linearly polarized beam 1a is reflected from the beam splitter 4 in a perpendicular direction and is emitted onto the first switching optical path _A1 .

Scattered light 1b' generated by turning on the fourth secondary electro-optic crystal element 12 is completely blocked by the polarizing element 16.

In addition, in Figure 2a, the light beam is switched to the first switching optical path.
If you only intend to output the light onto the optical path A ₁ and ignore the emission of the scattered light onto the same optical path A ₁ in FIG. Without using the plate 13 or the polarizing element 16, the linearly polarized beam 1a reflected by the second beam splitter 5 and emitted in the perpendicular direction is incident on the first polarized beam splitter 4 without reconverting the polarization direction. Even if the light beam is used, it can be emitted onto the optical path _A1 .

On the other hand, in Figure a, the linearly polarized beam 1b split in the straight direction by the first polarized beam splitter 4 changes its polarization direction by passing through the first secondary electro-optic crystal element 9 which is in the ON state. is converted into a linearly polarized beam 1a, which is incident on the second polarizing beam splitter 5. Depending on the polarization direction, it is emitted from the beam splitter 5 in a perpendicular direction, passes through mirrors 7 and 6, and enters the half-wave plate 14. The polarization direction of the light is changed by passing through the half-wave plate 14, and the light beam becomes a linearly polarized beam 1b and enters the first polarized beam splitter 4. Therefore, depending on its polarization direction, this polarized beam 1b travels straight through the first polarized beam splitter 4 and is superimposed on the linearly polarized beam 1a, and becomes the first output beam 2.
The light is emitted to the switching optical path _A1 .

At this time, when passing through the first secondary electro-optic crystal element 9 which is in the ON state, the generated scattered light 1b' passes straight through the second polarizing beam splitter 5, and passes through the second secondary electro-optic crystal element 9 which is in the OFF state. Although it reaches the polarizing element 15 through the element 10 and the right-angle prism 8, this completely blocks the scattered light from entering the second polarizing beam splitter 5 and outputting it onto the second switching optical path _A2 , which will be described later. It can be avoided.

As described above, the two linearly polarized beams 1a and 1b which enter the first polarized beam splitter 4 from the incident optical path A and are separated become second polarized beams in cooperation with the secondary electro-optic crystal elements 9 and 12. Via the beam splitter 5, it is refocused on the first polarizing beam splitter 4, and can be superimposed and emitted onto the first switching optical path _A1 , so that approximately 100% ( (there is an optical loss due to scattered light) can be used for optical path switching.

Furthermore, in FIG. 2b, the first and fourth secondary electro-optic crystal elements 9 and 12 are used, contrary to the case in FIG. 1a.
Turn off the second and third secondary electro-optic crystal elements 1
0 and 11 are turned on, and the second polarized beam splitter 5 is used as a light emitting element to superimpose both linearly polarized beams 1a and 1b onto the second switching optical path _A2 to output an output light beam 3.
This shows the switching operation status output as .

Similarly to the above, the incident light beam 1 from the incident optical path A is converted into linearly polarized beams 1a and 1b in the direction perpendicular to the straight direction by the first polarized beam splitter 4.
It is separated and emitted.

First, the linearly polarized beam 1a emitted from the first polarized beam splitter 4 in the perpendicular direction is sent to the mirror 6,
Secondary electro-optic crystal element 1 in ON state after 7
1, its polarization direction is changed as it passes through, and it becomes a linearly polarized beam 1b and enters the second polarized beam splitter 5.

According to its polarization direction, this light beam 1b travels straight through the second polarized beam splitter 5, and
The light beam is emitted to the switching optical path _A2 as a half beam of the emitted light beam 3. At this time, the scattered light 1a' generated by the third secondary electro-optic crystal element 11 which is in the ON state is reflected by the second polarizing beam splitter 5.
Fourth secondary electro-optic crystal element 12 in OFF state
and passes through the half-wave plate 13 (becomes scattered light 1b')
The light reaches the polarizing element 16, where it is completely blocked.

On the other hand, in Figure b, the linearly polarized beam 1b emitted from the first polarized beam splitter 4 in the straight direction passes through the first polarized beam splitter 9, which is in the OFF state, without undergoing any change in polarization direction, and passes through the second polarized beam splitter 9 without undergoing any change in polarization direction. The light enters the polarization beam splitter 5, and is emitted in a straight direction depending on the polarization direction, and enters the second secondary electro-optic crystal element 10 which is in the ON state.
0, it is converted into a linearly polarized beam 1a, is U-turned by a right angle prism 8, passes through a polarizing element 15, and enters a second polarized beam splitter 5.

According to its polarization direction, this light beam 1a is reflected by the second polarization beam splitter 5 and is superimposed on the linearly polarized light beam 1b, resulting in an output light beam 2.
As a result, the light is emitted to the second switching optical path _A2 .

At this time, the scattered light 15' generated by the second secondary electro-optic crystal element 10 which is in the ON state is completely blocked by the polarizing element 15 before the second polarizing beam splitter 5.

As described above, the two linearly polarized beams 1a and 1b that enter the first polarized beam splitter 4 from the incident optical path A and are separated into two directions are split in cooperation with the secondary electro-optic crystal elements 10 and 11. The light is refocused onto the second polarized beam splitter 5 and sent to the second switching optical path.
It can be superimposed onto A ₂ and emitted, and approximately 100% of the light beam 1 incident from the optical path A can be used for optical path switching.

The present invention cleverly employs the secondary electro-optic effect of a secondary electro-optic crystal element that is suitable as an optical path switching element and the polarization separation effect of a polarizing beam splitter, and uses the first polarizing beam splitter as a first switching optical path. The two sets of electro-optic crystal elements are alternately used so that the light output element and the second polarized beam splitter are used as the light output element for the second switching optical path, and the first polarized beam splitter is also used as the input optical element.
The present invention provides for the first time an optical path switching switch which outputs the entire amount of the incident light beam onto each of the first and second switching optical paths by turning it on and off.

As shown in the comparison, an optical path switching switch that uses an electro-optic crystal element and a polarizing beam splitter alternately converts the polarization direction of a linearly polarized beam having one polarization direction and uses it for optical path switching. The basic idea is that it is impossible to avoid an increase in crosstalk due to light scattering and a light loss of 50% of the amount of incident light when the electro-optic crystal element is ON. Each of the two polarizing beam splitters is used as an exit window for the two switching optical paths, and one is used as a window for the input optical path, and by combining this with an electro-optic crystal element, the problem of the above comparison example is solved. Another object of the present invention is to provide a highly sensitive and highly reliable optical path switching switch which, as described above, guides substantially the entire amount of the incident light beam onto each of the first or second switching optical paths to obtain optical switching operation. .

In the conventional method of outputting a light beam from a single polarizing beam splitter to the first switching optical path and the second switching optical path, an element is installed to prevent the scattered light from being removed due to its structure (of course, it is not possible to remove the scattered light). If the light path is placed on the optical path of the light beam), it may be possible to switch one optical path, but if the other optical path is switched, the normal light beam that is originally required will be blocked, making it impossible to accomplish the purpose of switching the optical path, resulting in scattering. Since light cannot be removed, it has been considered almost impossible to prevent crosstalk caused by this.

Therefore, the present invention includes a dedicated first polarized beam splitter 4 as an element for combining and outputting the linearly polarized beams 1a and 1b onto the first switching optical path _A1 , and also provides a first polarizing beam splitter 4 on the second switching optical path _A2 . An optical switching method is adopted in which a dedicated second polarized beam splitter 5 is provided as an element for combining and outputting the linearly polarized beams 1a and 1b, and the optical beams 2 and 3 used for optical path switching are emitted from separate elements. Since the basic configuration is adopted, the path for guiding the light beams 1a and _1b to the first switching optical path A1 and the path for guiding the light beams _1a and 1b to the second switching optical path A2 are separate paths. Therefore, when the light beam 2 is emitted from the first polarizing beam splitter 4 onto the first switching optical path _A1 , the scattered light is transmitted in the path before reaching the second polarizing beam splitter 5. Similarly, when the light beam 3 is emitted from the second polarizing beam splitter 5 onto the second switching optical path _A2 , the scattered light is blocked by the path before reaching the first polarizing beam splitter 4. For example, as illustrated in FIG.
It has now become possible to realize an optical path switching switch that can effectively prevent crosstalk caused by light scattering, which has been considered a fatal drawback in optical path switching switches.

[Brief explanation of the drawing]

Figures 1a and 1b are perspective views showing the principle of an optical path switching switch in comparison with the present invention using element arrangement, and Figure 1a shows optical path switching when no voltage is applied to the electro-optic crystal element. Figure b shows the optical path switching state when the same voltage is applied. Figure 2a,
Figure b is a perspective view showing the principle of an optical path switching switch according to an embodiment of the present invention using an element arrangement;
The figure shows an optical path switching state when a light beam is emitted from the first polarizing beam splitter onto the first switching optical path by applying a voltage to one of two sets of secondary electro-optic crystal elements. , and Figure b shows an optical path switching state in which the light beam is emitted from the second polarizing beam splitter onto the second switching optical path by applying a voltage to the same crystal element of the other set. A...Incoming optical path, _A1 ...First output optical path, _A2 ...
...Second output optical path, 1...Incoming light beam (input),
1a, 1b...Linearly polarized beam, 2... Outgoing light beam (output) to the first outgoing optical path, 3... Outgoing light beam to the second outgoing optical path, 4... Light input element of the incoming optical path, and A first polarizing beam splitter that shares a light emitting element to the first emitting optical path, 5... A second polarizing beam splitter that serves as a light emitting element to the second emitting optical path, 6, 7... Reflecting mirror, 8 ...Right angle prism, 9, 14...First and fourth secondary electro-optic crystal elements that are turned on when switching the optical path to the first switching optical path, 11, 12... Optical path to the second switching optical path Second and third secondary electro-optic crystal elements, 13, 14, which are in the ON state when switching is performed, half-wave plate, 1
5, 16...Polarizing element, 18...Power source.

Claims (1)

[Claims] 1 A first polarizing beam splitter and a second polarizing beam splitter are arranged side by side on the same optical axis so that their respective polarization separation planes are parallel to each other, and the first polarizing beam splitter is connected to a first switching optical path. The second polarized beam splitter is used as a light output element for the second switching optical path, and the first polarized beam splitter is also used as a light input element, and the first polarized beam splitter is used as a light input element for the second switching optical path. The two linearly polarized beams incident on the first polarized beam splitter and separated between the incident optical paths are refocused on the first polarized beam splitter via the second polarized beam splitter. A first path that superimposes light onto the switching optical path and emits the light, and a second path that focuses the light onto a second polarizing beam splitter, superimposes it onto the second switching optical path, and emits the light, and a first and a fourth electro-optic crystal element which is an element for rotating the plane of polarization by 90 degrees on the second path; second and third electro-optic crystal elements which are elements for rotating the plane of polarization by 90 degrees on the second path; 1. An electro-optic crystal element is provided between the first and second polarizing beam splitters, and the light of the linearly polarized beam on the first path is separated by the first polarizing beam splitter and goes straight to the second polarizing beam splitter. The second electro-optic crystal element is placed on the road, and the second electro-optic crystal element is placed on the road.
The electro-optic crystal element is disposed on the optical path of the linearly polarized beam of the second path which enters the second polarizing beam splitter and travels straight without its polarization direction being changed, and the third electro-optic crystal element The fourth electro-optic crystal element is disposed on the optical path of the linearly polarized beam of the second path, which is polarized by the polarizing beam splitter and emitted in the right angle direction and heads toward the second polarized beam splitter. The above polarized beam splitter between the first polarized beam splitters is incident on the second polarized beam splitter without having its polarization direction converted by the third electro-optic crystal element, is reflected in a perpendicular direction, and is directed toward the first polarized beam splitter. It is placed on the optical path of the linearly polarized beam of the first path, and the polarization direction is further converted by the fourth electro-optic crystal element.
A half-wave plate is disposed on the optical path of the linearly polarized beam on the first path toward the polarizing beam splitter, and the polarization direction is converted by the first electro-optic crystal element and reflected in a perpendicular direction by the second polarizing beam splitter. A half-wave plate is disposed on the optical path of the linearly polarized beam of the first path which is emitted from the polarized beam and heads toward the first polarized beam splitter, and a first electro-optic crystal is further disposed on the optical path of the linearly polarized beam of the second electro-optic crystal element. Element ON
A polarizing element for blocking scattered light emitted by the fourth electro-optic crystal element is disposed on the output optical path of the half-wave plate disposed on the output light side of the fourth electro-optic crystal element. A polarizing element is arranged to block the scattered light emitted by the first and fourth
An optical path switching switch characterized in that the two paths are switched by alternately turning on and off a set of electro-optic crystal elements and a set of second and third electro-optic crystal elements.