JPH04219718A - Eight terminal optical circulator - Google Patents

Abstract

PURPOSE:To obtain an eight terminal optical circulator which is independent of polarization and has low loss and little dispersion of inserting loss. CONSTITUTION:The lower bottom faces of the first trapezoidal polarization beam splitters (4-1)-(4-8) which are integrated with polarization separating films (M-1)-(M-8) interposed between a rectangular prism 4a and a parallelogram prism 4b are provided with two nonhomologus antirotatory polarization elements (5-1)-(5-8) and (6-1)-(6-8) which rotate only one polarizing direction of linear polarizations mutually advancing in a reverse direction as much as 90 degrees, and the sides of these nonhomologus antirotatory polarization elements are separately provided on faces forming the right angle of each rectangular prism of a polarization beam splitter 7 which is integrated with polarization separating films (N-1)-(N-4) put between the each circumferential plane of a square prism 7b and the four oblique side planes of a rectangular prism 7a to form an eight terminal optical circulator being independent of polarization.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-loss eight-terminal polarization-independent optical circulator.

0002

[Prior art] A conventional polarization-independent optical circulator has four
There are no reports of optical circulators with other numbers of terminals. Therefore, conventionally, when an 8-terminal polarization-independent optical circulator is required, three 4-terminal polarization-independent optical circulators are connected to each other and used as shown in FIG. That is, terminals A, B, C,
Connecting the terminal C of the 4-terminal polarization-independent optical circulator 1-1 having D and the terminal E of the 4-terminal polarization-independent optical circulator 1-2 having terminals E, F, G, and H,
By connecting the terminal G of the 4-terminal polarization-independent optical circulator 1-2 and the terminal I of the 4-terminal polarization-independent optical circulator 1-3 having terminals I, J, K, and L, the terminal A
, terminal B, terminal F, terminal J, terminal K, terminal L, terminal H,
The light of terminal D and terminal A is coupled, that is, the operation of an eight-terminal polarization-independent optical circulator is performed.

0003

[Problems to be Solved by the Invention] However, such a method is not suitable for the four-terminal polarization-independent optical circulator 1-1.
, 1-2, 1-3 is effective only when the insertion loss is sufficiently small. The insertion loss of current general four-terminal polarization-independent optical circulators is low, about 1 dB, but it cannot be said to be sufficiently small to be applicable to such purposes. That is, as mentioned above, using the three 4-terminal polarization-independent optical circulators 1-1, 1-2, and 1-3,
When a terminal polarization independent optical circulator is constructed, the coupling from terminal B to terminal F, the coupling from terminal F to terminal J, the coupling from terminal L to terminal H, and the coupling from terminal H to terminal D have insertion losses. The insertion loss is 2 dB, and the other insertion loss is 1 dB. As described above, the conventional eight-terminal optical circulator has a problem in that the insertion loss of a particular coupling is large, and as a result, the variation in insertion loss is also large. Note that there is no prospect that the current insertion loss of 1 dB will decrease significantly in the future.

[0004] In view of these circumstances, the present invention
The purpose of the present invention is to realize an 8-terminal polarization-independent optical circulator that has a loss as low as that of a terminal optical circulator and has small variations in insertion loss.

[0005]

[Means for Solving the Problems] An 8-terminal optical circulator according to the present invention that achieves the above object is an 8-terminal optical circulator that operates independently of the polarization state of input light, and includes a right-angle prism and a right-angle prism. By using a parallelogram prism consisting of a pair of flat surfaces corresponding to the hypotenuse surface and a pair of flat surfaces corresponding to the surfaces forming a right angle of the right angle prism, the hypotenuse surface of the right angle prism and the right angle of the parallelogram prism are used. a first polarizing beam splitter that is integrated with one of a pair of planes corresponding to the hypotenuse surface of the prism so as to sandwich the polarization separation film and has a trapezoidal outer shape; When linearly polarized light passes from the second surface to the first surface, its polarization direction is rotated by 90 degrees, but when the linearly polarized light passes from the second surface to the first surface, its polarization direction is not rotated. using a non-reciprocal optical rotation element, the first non-reciprocal optical rotation element is set so that its second surface faces the half surface opposite to the upper bottom surface of the lower bottom surface of the first polarization beam splitter, and the By setting the second non-reciprocal optical rotation element so that its first surface faces the other half of the bottom surface of the first polarization beam splitter, the top surface of the first polarization beam splitter is First, third, fifth, and seventh optical circulator terminals are configured as input/output sections, and the first polarizing beam splitter is provided on a half surface opposite to the upper bottom surface of the lower bottom surface of the first polarizing beam splitter. The non-reciprocal optical rotation element is set so that its first surface faces, and the second
By setting the non-reciprocal optical rotation elements such that the second surface thereof faces, the second, fourth, sixth and eighth polarizing beam splitters are set such that the upper bottom surface of the first polarizing beam splitter serves as the input/output portion of light. constitutes an optical circulator terminal, and on the other hand, four right-angle prisms each having a pair of right-angled planes corresponding to the bottom surface of the first polarizing beam splitter; A second square prism having a square outer shape is used, and each peripheral plane of the square prism and the hypotenuse surface of the right-angled prism are integrated so as to sandwich a polarization separation film. A polarizing beam splitter is configured, and the first optical circulator terminal is set in half of an arbitrary surface of the second polarizing beam splitter so that the first and second non-reciprocal optical rotation elements thereof are directed. , the first and second non-reciprocal optical rotation elements face the second optical circulator terminal on a half surface of the second polarizing beam splitter that faces the surface on which the first optical circulator terminal is set, and first and second non-reciprocal optical rotation elements of the first optical circulator terminal;
The first and second non-reciprocal optical rotation elements of the optical circulator terminal of the optical circulator terminal are set so that they are arranged at opposing positions, and the third optical circulator terminal is set so that the second optical circulator terminal is set. the first and second non-reciprocal optical rotation elements face another surface forming a right angle with the plane of the right-angle prism, and the third optical circulator terminal side of the second optical circulator terminal The non-reciprocal optical rotation element and the non-reciprocal optical rotation element on the second optical circulator terminal side of the third optical circulator terminal are set to be different types, and the fourth optical circulator terminal is connected to the second optical circulator terminal. On the half surface of the polarizing beam splitter opposite to the surface on which the third optical circulator terminal is set, the first
and a second non-reciprocal optical rotation element, and the first and second non-reciprocal optical rotation elements of the third optical circulator terminal and the first and second non-reciprocal optical rotation elements of the fourth optical circulator terminal. are arranged at opposite positions, and the fifth optical circulator terminal is paired with the plane of the right-angle prism on which the fourth optical circulator terminal is set to form a right angle. The first and second non-reciprocal optical rotation elements face the plane of the fourth optical circulator terminal, and the non-reciprocal optical rotation element on the fifth optical circulator terminal side of the fourth optical circulator terminal The nonreciprocal optical rotation element on the optical circulator terminal side is set to be of a different type, and the sixth optical circulator terminal is
The first and second non-reciprocal optical rotation elements face a half surface of the second polarizing beam splitter opposite to the surface on which the fifth optical circulator terminal is set, and The first and second non-reciprocal optical rotation elements and the fourth optical circulator terminal are set to be disposed at opposing positions, respectively, and the seventh optical circulator terminal is arranged so that the sixth optical circulator terminal is arranged so as to face each other. The first and second non-reciprocal optical rotation elements are oriented to another plane that forms a right angle with the plane of the set right-angle prism,
and the non-reciprocal optical rotation element on the seventh optical circulator terminal side of the sixth optical circulator terminal and the non-reciprocal optical rotation element on the sixth optical circulator terminal side of the seventh optical circulator terminal are of different types. and the first and second non-reciprocal optical rotation elements are placed on a half surface of the second polarizing beam splitter opposite to the surface on which the seventh optical circulator terminal is set. and the first and second non-reciprocal optical rotation elements of the seventh optical circulator terminal and the first and second non-reciprocal optical rotation elements of the eighth optical circulator terminal are arranged at opposing positions, respectively. It is characterized by being set so that

[0006]

[Operation] In the above configuration, the light incident from the optical input/output part of the first optical circulator terminal is divided into two types of linearly polarized light by the first polarizing beam splitter, but both of them pass through the second polarizing beam splitter. The light is then emitted from the light input/output section of the second optical circulator terminal. On the other hand, the light incident from the optical input/output part of the second optical circulator terminal is divided into two types of linearly polarized light by the first polarizing beam splitter, but both of them are separated by the first polarization separating film of the second polarizing beam splitter. The light is reflected and exits from the light input/output section of the third optical circulator terminal. Similarly, the light incident from the optical input/output part of the third optical circulator terminal is transmitted from the optical input/output part of the fourth optical circulator terminal, and the light incident from the optical input/output part of the fourth optical circulator terminal is transmitted from the optical input/output part of the fourth optical circulator terminal. The light incident from the optical input/output part of the fifth optical circulator terminal is transmitted from the optical input/output part of the sixth optical circulator terminal to the optical input/output part of the sixth optical circulator terminal. The light incident from the output section is transmitted from the optical input/output section of the seventh optical circulator terminal, and the light incident from the optical input/output section of the seventh optical circulator terminal is transmitted from the optical input/output section of the eighth optical circulator terminal. The light incident from the optical input/output section of the optical circulator terminal No. 8 is output from the optical input/output section of the first optical circulator terminal. Note that if the first non-reciprocal optical rotation element and the second non-reciprocal optical rotation element in each optical circulator terminal are replaced, an eight-terminal optical circulator with reverse rotation will be obtained.

[0007]

[Example] The present invention will be explained below based on an example.

FIG. 1 is a block diagram of an 8-terminal polarization-independent optical circulator according to an embodiment of the present invention, and in the figure, 2-1
~2-8 (hereinafter also referred to as 2-i) is an optical fiber, 3-
1 to 3-8 (hereinafter also referred to as 3-i) are lenses, 4-1
-4-8 (hereinafter also referred to as 4-i) are polarizing beam splitters, 5-1 to 5-8 (hereinafter also referred to as 5-i) are non-reciprocal optical rotation elements, and 6-1 to 6-8 (hereinafter also referred to as (Also referred to as 6-i)
is a non-reciprocal optical rotation element, 7 is a polarizing beam splitter, 8-1
8-8 (hereinafter also referred to as 8-i) are optical circulator terminals.

Here, the polarizing beam splitters 4-1 to 4
-8 respectively denote a right-angle prism 4a, and a parallelogram prism 4b composed of a pair of planes corresponding to the hypotenuse surface of the right-angle prism 4a and a pair of planes corresponding to the right-angled surfaces of the right-angle prism. using the above-mentioned right angle prism 4a.
The polarization separation films M-1 to M-8 are integrated so as to be sandwiched between the hypotenuse surface of the parallelogram prism 4b and one of the pair of planes corresponding to the hypotenuse surface of the right angle prism 4a of the parallelogram prism 4b. The outer shape is trapezoidal. Further, the polarizing beam splitter 7 includes polarizing beam splitters 4-1 to 4-1.
Four rectangular prisms 7a having a pair of right-angled planes corresponding to the lower bottom surface of the rectangular prisms 7a, and a square prism 7b whose surrounding plane is a plane corresponding to the hypotenuse surface of the rectangular prisms 7a are used. Polarization separation films N-1 to N-8 are formed on each peripheral plane of the square prism 7b and the hypotenuse surface of the right angle prism.
It is integrated in such a way that it is sandwiched between the two, and its outer shape is a square. In addition, if the square prism 7b is a prism with a square outer shape, for example, a right angle prism can be used as a square prism.
Needless to say, it may be one piece or a combination of four pieces.

[0010] The polarizing beam splitters 4-1 to 4-8
are arranged at a position where their respective lower bottom faces face one of the perpendicular planes of each rectangular prism 7a constituting the polarizing beam splitter 7, and a first One non-reciprocal optical rotation element 5-i and one non-reciprocal optical rotation element 6-i are arranged. More specifically, the non-reciprocal optical rotation elements 5-1, 5-3, 5-5, 5-7 are
Polarizing beam splitter 4-1, 4-3, 4-5 respectively
, 4-7 is set on the half side opposite to the top bottom surface,
The non-reciprocal optical rotation elements 5-2, 5-4, 5-6, 5-8 are polarized beam splitters 4-2, 4-4, 4-6, respectively.
It is set on the half side that does not face the upper bottom surface of 4-8. On the other hand, the non-reciprocal optical rotation elements 6-1 to 6-8 are set in the remaining half. The polarizing beam splitter 4-i, non-reciprocal optical rotation element 5-i, and non-reciprocal optical rotation element 6-i arranged in this manner constitute each optical circulator terminal 8-i. Note that each lens 3-i and the optical fiber 2-i coupled to the lens 3-i are connected to each polarizing beam splitter 4.
-i is connected to the upper bottom part which becomes the optical input/output part.

In this embodiment, the non-reciprocal optical rotation element 5-i does not change the direction of the linearly polarized light passing from the polarizing beam splitter 4-i to the polarizing beam splitter 7, but it changes the direction of the linearly polarized light passing from the polarizing beam splitter 7 to the polarizing beam splitter 4-i. On the other hand, the non-reciprocal optical rotation element 6-i rotates the direction of the linearly polarized light passing from the polarizing beam splitter 4-i to the polarizing beam splitter 7 by 90 degrees.
Although it is rotated by 0 degrees, the direction of the linearly polarized light passing from the polarizing beam splitter 7 to the polarizing beam splitter 4-i remains unchanged.

In such a configuration, the optical fiber 2-
The optical path of light emitted from 1 is shown in FIG. As shown in the figure, this light is converted into a parallel light beam by a lens 3-1, and a linearly polarized light (linear The light beam is separated into a polarized light beam (referred to as a polarized beam Q) and a linearly polarized light (referred to as a linearly polarized beam R) that is vertically reflected by the polarization separation film M-1. After the linearly polarized beam Q passes through the polarizing beam splitter 4-1, it travels through the non-reciprocal optical rotation element 5-1 toward the polarizing beam splitter 7, so the polarization direction remains unchanged. On the other hand, the linearly polarized beam R is transmitted to the polarizing beam splitter 4-1.
After being reflected by the polarization separation film M-1 and the hypotenuse surface, the light travels through the non-reciprocal optical rotation element 6-1 toward the polarization beam splitter 7, so that the polarization direction is rotated by 90 degrees and the light enters the polarization beam splitter 7. That is, since both the linearly polarized beam Q and the linearly polarized beam R enter the polarizing beam splitter 7 as linearly polarized light whose electric field vibration plane is parallel to the plane of the paper, the polarizing beam splitting films N-1 and N-2 of the polarizing beam splitter 7 are pass. Since the linearly polarized beam Q travels through the non-reciprocal optical rotation element 5-2 toward the polarizing beam splitter 4-2, the polarization direction is rotated by 90 degrees, and the polarized beam Q travels through the non-reciprocal optical rotation element 5-2 toward the polarizing beam splitter 4-2. It is reflected and coupled to the optical fiber 2-2. On the other hand, the linearly polarized beam R is transmitted through the non-reciprocal optical rotation element 6-
2 proceeds toward the polarizing beam splitter 4-2, so its polarization direction remains unchanged and the polarizing beam splitter 4
-2, and is coupled to the optical fiber 2-2 via the lens 3-2. In this way, the light emitted from the optical fiber 2-1 is coupled to the optical fiber 2-2.

FIG. 3 shows the optical path of light emitted from the optical fiber 2-2. As shown in the figure, this light is transmitted through lens 3-
2 into a parallel light beam, and a polarizing beam splitter 4-2
Therefore, the vibration plane of the electric field is parallel to the plane of the paper, and the polarization separation film M-2
The linearly polarized light (referred to as a linearly polarized beam S) that passes through the polarization separation film M-2 and the linearly polarized light that is vertically reflected by the polarization separation film M-2 (referred to as a linearly polarized beam T). After passing through the polarization separation film M-2 of the polarization beam splitter 4-2, the linearly polarized beam S travels through the nonreciprocal optical rotation element 6-2 toward the polarization beam splitter 7, so that the polarization direction is rotated by 90 degrees. The light enters the polarizing beam splitter 7. On the other hand, the linearly polarized beam T is reflected by the polarization separation film M-2 and the hypotenuse surface of the polarization beam splitter 4-2, and then travels through the non-reciprocal optical rotation element 5-2 toward the polarization beam splitter 7, so that the polarization direction changes. do not have. That is, since both the linearly polarized beam S and the linearly polarized beam T enter the polarizing beam splitter 7 as linearly polarized light whose electric field vibration plane is perpendicular to the plane of the paper, they are reflected by the polarizing separation film N-2 of the polarizing beam splitter 7, and the light is It heads toward the circulator terminal 8-3. Since the linearly polarized beam S travels through the non-reciprocal optical rotation element 6-3 toward the polarizing beam splitter 4-3, the polarization direction remains unchanged and is reflected by the hypotenuse surface of the polarizing beam splitter 4-3 and the polarization separation film M-3. ,
It is coupled to the optical fiber 2-3 via the lens 3-2. On the other hand, the linearly polarized beam T travels through the nonreciprocal optical rotation element 5-3 toward the polarizing beam splitter 4-3, so its polarization direction is rotated by 90 degrees, passes through the polarizing beam splitter 4-3, and then passes through the lens 2- 3 to the optical fiber 2-3. In this way, the light emitted from the optical fiber 2-2 is coupled to the optical fiber 2-3.

The light incident from the optical fiber 2-3, the light incident from the optical fiber 2-5, and the light incident from the optical fiber 2-7 can be considered in the same way as the light incident from the optical fiber 2-1. Although the explanation will be omitted since it is possible, they are coupled to the optical fiber 2-4, the optical fiber 2-6, and the optical fiber 2-8, respectively. Furthermore, the light incident from the optical fiber 2-4, the light incident from the optical fiber 2-6, and the light incident from the optical fiber 2-8 can be considered in the same way as the light incident from the optical fiber 2-2. Therefore, the explanation will be omitted, but optical fiber 2-5 and optical fiber 2
-7, coupled to optical fiber 2-1. Therefore, Figure 1
With the configuration shown in FIG.
-4, terminal 8-5, terminal 8-6, terminal 8-7, terminal 8-
8. It is clear that the operation of an 8-terminal polarization-independent optical circulator in which light is coupled to the terminal 8-1 is performed.

If the positions of the non-reciprocal optical rotation element 5-i and the non-reciprocal optical rotation element 6-i are reversed to those in the embodiment shown in FIG. 1, a circulator will be created in which light is coupled in a direction opposite to that described above. In addition, optical fibers 2-1 to 2-8 and lenses 3-1 to 3-
It will be clear that 8 is necessary for the optical circulator to function for optical fibers and is not essential for the operation of the optical circulator.

In the present invention, the configuration is devised so that the optical path lengths from the input light to the output light are approximately equal for the mutually orthogonal polarized lights into which the input lights are separated, and the terminals that are coupled to each other are The distance between the lenses can be divided into two groups, but by appropriately designing the lens system, it is possible to reduce the variation with considerably low loss. Incidentally, in the conventional configuration in which three 4-terminal polarization-independent optical circulators are connected, the insertion loss of the 4-terminal polarization-independent optical circulator is sufficient for coupling across two 4-terminal polarization-independent optical circulators. Unless it is small, the loss will be larger than others, and the insertion loss of the 8-terminal polarization-independent optical circulator will vary widely.

[0017]

As explained above, in the present invention, the function of an 8-terminal optical circulator is realized by the circuit configuration, and the optical path length from input light to output light is determined by the separation of each input light. The configuration is devised so that the polarizations perpendicular to each other are almost equal, and the distance between the lenses of the terminals that are coupled to each other is divided into two groups.
By appropriately designing the lens system, it is possible to perform coupling with considerably low loss and small variation, and as a result, an eight-terminal polarization-independent optical circulator with low insertion loss and small variation can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an 8-terminal polarization-independent optical circulator according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation of the embodiment.

FIG. 3 is an explanatory diagram of the operation of the embodiment.

FIG. 4 is a configuration diagram of a conventional 8-terminal polarization-independent optical circulator.

[Explanation of symbols]

2-1 to 2-8 Optical fibers 3-1 to 3-8 Lenses 4-1 to 4-8 Polarizing beam splitters 5-1 to 5-
8 Non-reciprocal optical rotation elements 6-1 to 6-8 Non-reciprocal optical rotation element 7 Polarization beam splitter

Claims (1)

[Claims] Claim 1: An eight-terminal optical circulator that operates independently of the polarization state of input light, comprising: a right-angle prism; a pair of planes corresponding to the hypotenuse surface of the right-angle prism; polarization separation between the hypotenuse surface of the right angle prism and one of the pair of planes of the parallelogram prism corresponding to the hypotenuse surface of the right angle prism. A first polarizing beam splitter is integrated so as to sandwich the film and has a trapezoidal outer shape, and a polarizing beam splitter that rotates the polarization direction by 90 degrees when linearly polarized light passes from the first surface to the second surface. , using first and second non-reciprocal optical rotation elements that do not rotate the polarization direction of linearly polarized light when it passes from the second surface to the first surface, The first non-reciprocal optical rotation element is set on the half surface opposite to the upper bottom surface so that its second surface faces, and the second non-reciprocal optical rotation element is set on the other half surface of the lower bottom surface of the first polarizing beam splitter. By setting the reciprocal optical rotation element so that its first surface faces, the first, third, fifth, and seventh beams with the upper bottom surface of the first polarization beam splitter serving as the input/output portion of the light are generated. It constitutes a circulator terminal, and the first
The first non-reciprocal optical rotation element is set so that its first surface faces the half surface opposite to the top surface of the bottom surface of the polarization beam splitter, and the remainder of the bottom surface of the first polarization beam splitter. By setting the second non-reciprocal optical rotation element so that its second surface faces one half of the polarizing beam splitter, the upper bottom surface of the first polarizing beam splitter serves as a light input/output part. , sixth and eighth optical circulator terminals, and four right-angle prisms having a pair of right-angled planes corresponding to the bottom surface of the first polarizing beam splitter, and a hypotenuse surface of the right-angle prisms. and a square prism whose surrounding planes correspond to the planes of the rectangular prism, and integrate the polarized light separating film between each surrounding plane of the square prism and the hypotenuse surface of the rectangular prism, thereby changing its outer shape. constitutes a second polarizing beam splitter having a square shape, the first optical circulator terminal is connected to half of an arbitrary surface of the second polarizing beam splitter, and the first and second non-reciprocal optical rotation elements thereof The second optical circulator terminal is placed on the half surface of the second polarizing beam splitter opposite to the surface on which the first optical circulator terminal is set, and the first and second non-reciprocal a position in which the optical rotation element is oriented and the first and second non-reciprocal optical rotation elements of the first optical circulator terminal and the first and second non-reciprocal optical rotation elements of the second optical circulator terminal face each other; The third optical circulator terminal is placed on another surface forming a right angle with the plane of the right-angle prism on which the second optical circulator terminal is set. The first and second non-reciprocal optical rotation elements are oriented, and the non-reciprocal optical rotation element on the third optical circulator terminal side of the second optical circulator terminal and the second optical circulator terminal side of the third optical circulator terminal and the non-reciprocal optical rotation element is set to be of a different type, and the fourth optical circulator terminal is placed on the half surface of the second polarization beam splitter that faces the surface on which the third optical circulator terminal is set, the first and second non-reciprocal optical rotation elements are oriented, and the first
and a second non-reciprocal optical rotation element and the first and second non-reciprocal optical rotation elements of the fourth optical circulator terminal are arranged at opposing positions, respectively, and the fifth optical circulator terminal , the first and second non-reciprocal optical rotation elements face another plane forming a right angle with the plane of the rectangular prism in which the fourth optical circulator terminal is set, and the fourth The non-reciprocal optical rotation element on the fifth optical circulator terminal side of the optical circulator terminal and the non-reciprocal optical rotation element on the fourth optical circulator terminal side of the fifth optical circulator terminal are set to be of different types, and The first and second non-reciprocal optical rotation elements face the sixth optical circulator terminal on the half surface of the second polarizing beam splitter that is opposite to the surface on which the fifth optical circulator terminal is set, and The first and second non-reciprocal optical rotation elements of the fifth optical circulator terminal and the fourth optical circulator terminal are set to be arranged in opposing positions, and the seventh optical circulator terminal is The first and second non-reciprocal optical rotation elements face another plane forming a right angle with the plane of the rectangular prism in which the sixth optical circulator terminal is set, and The non-reciprocal optical rotation element on the seventh optical circulator terminal side of the circulator terminal and the non-reciprocal optical rotation element on the sixth optical circulator terminal side of the seventh optical circulator terminal are set to be different types, and the optical circulator terminal of the second polarizing beam splitter, the first and second non-reciprocal optical rotation elements thereof are directed to the half surface opposite to the surface on which the seventh optical circulator terminal of the second polarizing beam splitter is set, and The first and second non-reciprocal optical rotation elements of the optical circulator terminal and the first and second non-reciprocal optical rotation elements of the eighth optical circulator terminal are set to be arranged at opposing positions, respectively. An 8-terminal optical circulator characterized by: