JP2002323374A - Optical spectrum analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remote a cross talk by simplifying the structure of an incident part, in an optical spectrum analyzer constituted so as not to be influenced by polarization dependency of a diffraction grating. SOLUTION: In a first azimuth rotator 23 and a Faraday rotator 25 of a polarization conversion part 22, the polarization direction of light from a first optical path L1 toward a third optical path L3 is set in the direction perpendicular to a groove 28 of the diffraction grating 27, and the polarization direction of light from the third optical path L3 toward the first optical path L1 is set in the direction parallel to the groove 28 of the diffraction grating 27, and light is emitted to a polarization separation element 21. And in a second azimuth rotator 24 and the Faraday rotator 25, the polarization direction of light from a second optical path L2 toward a fourth optical path L4 is set in the direction perpendicular to the groove 28 of the diffraction grating 27, and the polarization direction of light from the fourth optical path L4 toward the second optical path L2 is set in the direction perpendicular to the groove 28 of the diffraction grating 27, light is emitted to the polarization separation element 21, and a light having a prescribed wavelength is emitted from an outgoing optical path L5 different from an input optical path L0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for facilitating separation of incident light and wavelength-selected light in an optical spectrum analyzer having a configuration for eliminating the influence of the polarization dependence of a diffraction grating. .

[0002]

2. Description of the Related Art An optical spectrum analyzer selectively receives each wavelength component contained in incident light by utilizing the diffraction effect of light by a diffraction grating.

However, it is known that the diffraction characteristics of the diffraction grating depend on the polarization direction of the incident light, and the polarization direction of the incident light has a large effect on the measurement result, and the reproducibility of the measurement is low. Become.

[0004] In order to eliminate the influence of the polarization dependence of the diffraction grating, in a conventional optical spectrum analyzer, as disclosed in, for example, US Pat. The light component is separated into a light component orthogonal to the inscribed line) and a light component parallel to the groove of the diffraction grating. , And selects light of a predetermined wavelength from the diffracted light of the diffraction grating with respect to the light incident through each optical path, and returns the selected light of the predetermined wavelength so that its polarization directions are orthogonal to each other. To receive the combined light.

Further, in such a conventional optical spectrum analyzer, an optical element for aligning the polarization directions of two light components whose polarization directions are orthogonal to each other with the direction orthogonal to the grooves of the diffraction grating is to enter the diffraction grating. The system and the optical system for returning the selected predetermined wavelength light so that the polarization directions thereof are orthogonal to each other are used, thereby simplifying the configuration of the entire apparatus.

FIGS. 7 (a) and 7 (b) show the configuration of an optical system of a conventional optical spectrum analyzer configured to eliminate the influence of polarization dependence as disclosed in the above-mentioned US Pat. No. 5,886,785. And a plan view of the operation.

This optical spectrum analyzer includes a polarization separation element 11, a polarization converter 12, and a wavelength selector 13.

[0008] The polarization splitting element 11 converts incident light A incident through an incident light path L0 parallel to a reference plane P (for example, the upper surface of a base (not shown)) of the optical system of the optical spectrum analyzer with respect to the reference plane P. Of the incident light A, the first light component Ai of which the polarization direction is parallel to the reference plane P is reflected by the reflection surface 11 parallel to the separation plane 11a.
b and parallel to the reference plane P and the incident optical path L0.
And the second light component Aj of which the polarization direction of the incident light A is orthogonal to the reference plane P is transmitted, and is emitted to the second optical path L2 parallel to the first optical path L1.

[0009] The polarization conversion unit 12 converts the first light emitted from the polarization separation element 11 into the first optical path L1 and the second optical path L2.
The polarization directions of the light component Ai and the second light component Aj are aligned so as to be parallel to the reference plane P, and the first optical path L
The light is emitted to a third optical path L3 and a fourth optical path L4 which are respectively continuous with the first and second optical paths L2.

Here, the polarization direction of the first light component Ai is parallel to the reference plane P, and the polarization direction of the second light component Aj is orthogonal to the reference plane P. Represents that the first light component Ai is emitted to the third optical path L3 as it is,
The polarization direction of the light component Aj of the
The light component Aj ′ rotated parallel to the reference plane P
Out of the optical path L4.

The light emitted from the polarization converter 12 to the third optical path L3 and the fourth optical path L4 enters the wavelength selector 13.

The wavelength selector 13 includes a diffraction grating 14 and a reflector 16. The diffraction grating 14 is provided with a plurality of parallel grooves (cut lines) 15 for diffracting light on one surface side. The grooves 15 are orthogonal to the reference plane P, and the third optical path L3 and the fourth Are arranged to receive light from the optical path L2.

The reflector 16 is composed of, for example, a corner mirror and has two reflecting surfaces 16a and 16b orthogonal to each other. The two reflecting surfaces 16a and 16b are
The light diffracted by the diffraction grating 14 is reflected to the diffraction grating 14 along a path shifted in parallel with the length direction of the groove 15 of the diffraction grating 14. I do.

The wavelength selector 13 is a light source having a predetermined wavelength determined by the angle of incidence on the diffraction grating 14 and the angle of the reflector 16 with respect to the diffraction grating 14 among the light incident on the diffraction grating 14 from the third optical path L3. Is emitted to the fourth optical path L4, and of the light that has entered the diffraction grating 14 from the fourth optical path L4, the light having the predetermined wavelength is emitted to the third optical path L3.

In the optical spectrum analyzer having the above configuration, as shown in FIG. 7A, the light A incident from the incident optical path L0 is changed in polarization direction by the polarization separation element 11 to the reference plane P. , Ie, a first light component Ai orthogonal to the groove 15 of the diffraction grating 14, and a second light component Ai whose polarization direction is orthogonal to the reference plane P, ie,
Is separated into light components Aj. In addition, (a) of FIG.
In (b), the direction of the arrow in the circle indicates the polarization direction of each light as viewed from the polarization separation element 11 side.

The first light component Ai is transmitted from the first optical path L1 to the diffraction grating 14 of the wavelength selector 13 via the third optical path L3.
Is incident on.

On the other hand, the second light component Aj is the second light path L2
Is incident on the λ / 2 plate 12a of the polarization converter 12. Therefore, the light component Aj ′ obtained by rotating the polarization direction of the second light component Aj by 90 ° is incident on the diffraction grating 14 of the wavelength selector 13 via the fourth light path L4.

The diffraction grating 14 converts the diffracted light of the first light component Ai incident from the third optical path L3 into a reflector 16
Out toward one of the reflection surfaces 16a, and the fourth optical path L
The diffracted light with respect to the light component Aj ′ incident on the reflector 4 is emitted toward the other reflection surface 16 b of the reflector 16.

Of the light diffracted by the diffraction grating 14 and incident on one reflection surface 16a of the reflector 16, the diffraction grating 14
The light Bi of a predetermined wavelength (including light near that wavelength) determined by the angle of incidence with respect to the diffraction grating 14 and the angle of the reflector 16 with respect to the diffraction grating 14 as shown in FIG.
b, is reflected again by the reflection surface 16b, and is incident on the diffraction grating 14.

The reflector 1 is diffracted by the diffraction grating 14 and
6, the light Bj of the predetermined wavelength (including light near the wavelength) of the light incident on the other reflecting surface 16b is reflected by one reflecting surface 16a, and reflected again by this reflecting surface 16a. The light is incident on the diffraction grating 14.

The diffraction grating 14 reflects the light Bi from the reflector 16
Is diffracted again, and the light Ci of the predetermined wavelength is converted into a fourth optical path L.
4, the light Bj from the reflector 16 is diffracted again,
The light Cj having the predetermined wavelength is emitted to the third optical path L3.

Of the lights Ci and Cj of the predetermined wavelengths selected by the wavelength selector 13 as described above, the light Cj emitted to the third optical path L3 is transmitted to the polarization separation element 11 via the first optical path L1. Incident.

The light Ci emitted from the wavelength selector 13 to the fourth optical path is incident on the λ / 2 plate 12 a of the polarization converter 12, and the polarization direction of the light Ci coincides with the groove 15 of the diffraction grating 14. The light is converted into light Ci ′ in a parallel direction, and is incident on the polarization beam splitter 11 via the second optical path L2.

The polarization beam splitting element 11 passes through the first optical path L1.
Is incident on the reflection surface 11 of the polarization separation element 11.
The light beam Cj is reflected by b and travels toward the separation surface 11a. However, since the polarization direction of the light beam Cj is parallel to the reference surface P, the light beam Cj is reflected by the separation surface 11a and returns to the incident path L0.

The light Ci ′ incident on the polarization separation element 11 via the second optical path L2 and traveling to the separation surface 11a is
Since the polarization direction is orthogonal to the reference plane P, the light passes through the separation plane 11a and returns to the incident path L0.

Therefore, if the combined light D of the light Ci 'and Cj returning to the incident light path L0 is received by a light receiver (not shown), the level of light of a predetermined wavelength contained in the incident light A is
The detection can be performed accurately without being affected by the polarization state of the incident light A.

[0027]

However, in the above-mentioned conventional optical spectrum analyzer, the wavelength selector 1
Since the light D having the wavelength selected by 3 returns to the incident optical path L0 of the incident light A to be measured, a 3 dB coupler or light for separating the incident light A from the selected light D on the incident optical path L0. It is necessary to insert an optical path separating means such as a circulator, which complicates the configuration of the incident part.

In addition, since the light beams having the same polarization direction, that is, the light beam Ai and the light beam Cj and the light beam Aj and the light beam Ci 'reciprocate in the polarization separation element 11, the input and output may be crosstalk. .

An object of the present invention is to provide an optical spectrum analyzer which solves these problems.

[0030]

In order to achieve the above object, an optical spectrum analyzer according to claim 1 of the present invention comprises:
The incident light to be measured is divided into a first light component whose polarization direction is parallel to a predetermined reference plane and a second light component whose polarization direction is orthogonal to the reference plane.
And polarized light that emits the first light component to a first optical path (L1) and emits the second light component to a second optical path (L2) different from the first optical path. Separating element (2
1), a first light component emitted from the polarization separation element to the first optical path, and a second light component emitted to the second optical path.
The polarization directions of the light components are aligned so as to be parallel to the reference plane, and the polarization directions respectively emitted to a third optical path (L3) and a fourth optical path (L4) that are parallel to each other and parallel to the reference plane. A wave conversion part (22) and a diffraction grating (27) provided with a plurality of parallel grooves (28) orthogonal to the reference plane on one surface side
And 45 each perpendicular to the reference plane with respect to the reference plane.
And a reflector (29) having a reflecting surface at an angle of ° and reflecting the light diffracted by the diffraction grating to the diffraction grating on a path shifted parallel to the length direction of the groove. The light having a predetermined wavelength determined by an incident angle with respect to the diffraction grating and an angle of the reflector with respect to the diffraction grating among the light incident on the diffraction grating from the conversion unit via the third optical path is converted into the fourth light. The light having the predetermined wavelength is emitted through the third optical path, out of the light emitted from the polarization conversion section through the fourth optical path, and emitted to the polarization conversion section through an optical path. A wavelength selector (26) that emits light to the polarization converter side; and the third optical path and the fourth
In the optical spectrum analyzer which converts the light of the predetermined wavelength emitted to the optical path by the polarization conversion unit so that the polarization directions are orthogonal to each other and receives the combined light, the polarization conversion unit includes the first The direction of polarization of light traveling from the optical path to the third optical path is rotated by 45 ° around a predetermined direction, and the direction of polarization of light traveling from the third optical path to the first optical path is opposite to the predetermined direction. First to rotate 45 ° around the direction
And the polarization direction of light traveling from the second optical path toward the fourth optical path is rotated by 45 ° around a direction opposite to the predetermined direction, and the second optical path is rotated from the fourth optical path to the second optical path. A second optical rotator (24) for rotating the polarization direction of light traveling toward the optical path by 45 ° in the predetermined direction, and a light traveling from the first optical path to the third optical path and from the second optical path to the second optical rotator. 4th
The direction of polarization of light traveling toward the optical path is rotated by 45 ° around a direction opposite to the predetermined direction, and the light traveling from the third optical path toward the first optical path and the light traveling from the fourth optical path to the second optical path And a Faraday rotator (25) for rotating the polarization direction of the light traveling toward by 45 ° around the direction opposite to the predetermined direction.

The optical spectrum analyzer according to a second aspect of the present invention receives an incident light to be measured on a specific side surface and separates the incident light into a first light and a second light whose polarization directions are orthogonal to each other. Polarization separation means (21) having a separation surface for transmitting and outputting the second light and a reflection surface for reflecting the first light separated by the separation surface and outputting the first light in parallel with the second light; A diffraction grating (27) for receiving light from a third optical path and a fourth optical path parallel to each other and outputting respective diffracted lights; and receiving each of the diffracted lights from the diffraction grating, a cutting line direction of the diffraction grating. And returns the light to the diffraction grating again to output the diffracted light by the light from the third optical path as the third light to the fourth optical path by the diffraction grating, and the fourth optical path And outputs the diffracted light from the light as fourth light to the third optical path. A reflector (29), provided between the polarization splitting means and the diffraction grating, receives the first light and the second light from the polarization splitting means, and receives the first light and the second light. The light is transmitted to the third optical path and the fourth optical path so that the polarization direction of the light is also perpendicular to the score line of the diffraction grating, and the third light output from the diffraction grating is also output. Receiving the light, outputs light orthogonal to the polarization direction of the second light to the separation surface of the polarization separation means, and receives the fourth light and outputs the first light to the reflection surface of the polarization separation means.
By outputting light orthogonal to the polarization direction of the light,
A polarization conversion unit (22) configured to combine the light input to the separation surface and the reflection surface with the polarization separation unit and output the light from another surface different from the specific side surface. .

[0032]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an overall configuration of an optical spectrum analyzer 20 to which the present invention is applied.
FIG. 3 is a diagram three-dimensionally showing the configuration of the optical system of the optical spectrum analyzer 20. FIG.
FIG. 3 is a diagram showing the optical system in a plan view and explaining its operation.

In these figures, the optical spectrum analyzer 20 includes a polarization splitter 21 and a polarization converter 2.
2. It has a wavelength selection unit 26, a light receiving unit 35, and a signal processing unit 40.

Polarization separating element 21 as polarization separating means
Consists of, for example, a polarizing beam splitter (PBS),
The reference plane P of the optical system of the optical spectrum analyzer 20
(For example, an incident optical path L0 parallel to the upper surface of a base (not shown)).
Is separated into a first light component Ai whose polarization direction is parallel to the reference plane P and a second light component Aj whose polarization direction is orthogonal to the reference plane P. , The first light component A
i is emitted to a first optical path L1 parallel to the reference plane P, and the second light component Aj is emitted to a second optical path L2 parallel to the first optical path L1.

The polarization separation element 21 has a separation surface 21a at an angle of 45 ° with respect to the incident optical path L0 and a reflection surface 21b parallel to the separation surface 21a, and is orthogonal to the reference plane P. Out of the incident light A input from a specific side surface, the first light component Ai whose polarization direction is parallel to the reference plane P is reflected from the separation plane 21a to the reflection plane 21b, and the first light path L1
, And transmits the second light component Aj whose polarization direction is orthogonal to the reference plane P, and exits along the second optical path L2 that is continuous with the incident optical path L0.

The polarization converter 22 is disposed between the polarization splitter 21 and the wavelength selector 26, and is configured to polarize the first light component Ai and the second light component Aj emitted from the polarization splitter 21. The direction is aligned with a direction orthogonal to a groove (cut line) 28 of a diffraction grating 27 described later, and the light is emitted to a third optical path L3 and a fourth optical path L4 parallel to the reference plane P, respectively. It is composed of one optical rotator 23, a second optical rotator 24, and a Faraday rotator 25.

The first optical rotator 23 is composed of, for example, a λ / 2 plate, and rotates the polarization direction of light traveling from the first optical path L1 to the third optical path L3 in a predetermined direction (for example, as viewed from the polarization separation element 21 side). The light is rotated 45 ° clockwise, and the polarization direction of the light traveling from the third optical path L3 to the first optical path L1 is rotated 45 degrees around the direction opposite to the predetermined direction (for example, counterclockwise as viewed from the polarization separation element 21 side). Rotate °.

The second optical rotator 24 is formed of, for example, a λ / 2 plate, and changes the polarization direction of light traveling from the second optical path L2 to the fourth optical path L4 in a direction opposite to the predetermined direction (for example, polarization separation). 45 ° counterclockwise as viewed from the element 21 side,
The polarization direction of light traveling from the optical path L4 to the second optical path L2 is rotated by 45 ° in the predetermined direction (for example, clockwise as viewed from the polarization separation element 21).

The Faraday rotator 25 is made of, for example, a Bi (bismuth) -substituted rare earth iron garnet single crystal or the like, and transmits light from the first optical path L1 to the third optical path L3 and the second optical path L3.
The direction of polarization of light traveling from the optical path L2 to the fourth optical path L4 is around a direction opposite to the predetermined direction (for example, the polarization separation element 21).
45 ° in the counterclockwise direction as viewed from the side, and the third optical path L3
The polarization directions of the light traveling from the first optical path L1 to the first optical path L1 and the light traveling from the fourth optical path L4 to the second optical path L2 are rotated in a direction opposite to the predetermined direction (for example, counterclockwise as viewed from the polarization separating element 21). Rotate 45 °.

That is, the polarization converter 22 receives the first light component Ai and the second light component Aj from the polarization splitter 21 and receives the first light component Ai and the second light component Aj. Are transmitted to the third optical path L3 and the fourth optical path L4, respectively, so that the polarization direction of the light beam is also perpendicular to the grooves (cut lines) of the diffraction grating 27. Upon receiving the third light of a predetermined wavelength output to the optical path L4, the third light having a predetermined wavelength is output to the separation surface 21a of the polarization separation element 21 and the light orthogonal to the polarization direction of the second light component Aj is output. Upon receiving the third light of a predetermined wavelength output to the third optical path L3, the third light is transmitted to the reflection surface 21b of the polarization splitting element 21 by the first light.
By outputting light orthogonal to the polarization direction of the light component Ai, the light input to the separation surface 21a and the reflection surface 21b is combined with the polarization separation element 21 so that the other surface different from the specific side surface Output from.

The wavelength selector 26 includes a diffraction grating 27, a reflector 29 and angle varying means 31.

The diffraction grating 27 has a large number of parallel grooves (cut lines) 28 for diffracting light on one surface thereof. The grooves 28 on one surface are orthogonal to the reference plane P, and It is arranged so that light input from the optical path L3 and the fourth optical path L4 can be received on one surface side.

The reflector 29 is composed of, for example, a corner mirror and has two reflection surfaces 29a and 29b orthogonal to each other. The two reflection surfaces 29a and 29b are
The light diffracted by the diffraction grating 27 is reflected by the diffraction grating 27 along a path shifted in parallel to the length direction of the groove 28 of the diffraction grating 27. .

In other words, this reflector 29 is
, And is turned back in the direction of the groove (cut line) 28 and sent back to the diffraction grating 27, so that the light is diffracted by the light from the third optical path L 3 through the third diffraction path L 3. The light is output to the fourth optical path L4, and the fourth optical path L
The third light path L is a light diffracted by the light from the fourth light 4 as the fourth light.
3 output.

The angle varying means 31 relatively varies the angle of the reflector 29 with respect to the diffraction grating 27.

The wavelength selector 26 converts the light having a predetermined wavelength, which is determined by the angle of incidence on the diffraction grating 27 and the angle of the reflector 29 with respect to the diffraction grating 27, from the light incident on the diffraction grating 27 from the third optical path L3. The light having the predetermined wavelength out of the light emitted to the fourth optical path L4 and incident on the diffraction grating 27 from the fourth optical path L4 is emitted to the third optical path L3.

The light receiving section 35 receives the light of the wavelength selected by the wavelength selecting section 26 and outputs an electric signal corresponding to the intensity of the light.

The signal processing section 40 drives the angle varying means 31 of the wavelength selecting section 26 so that the wavelength selecting section 26 selects light having a desired wavelength. At this time, the electric signal output from the light receiving section 35 And perform the necessary processing for analysis.

In the optical spectrum analyzer 20 having the above configuration, as shown in FIG. 3A, the incident light A incident along the incident optical path L0 is polarized by the polarization separation element 21 in the polarization direction. Are parallel to the reference plane P, that is, the first light component Ai orthogonal to the groove 28 of the diffraction grating 27, and the second light component whose polarization direction is orthogonal to the reference plane P, that is, parallel to the groove 28 of the diffraction grating 27. Ai, the first light component Ai is emitted to the first optical path L1, and the second light component Aj is emitted to the second optical path L2. 3A and 3B, the directions of the arrows in the circles indicate the polarization directions of the respective lights as viewed from the polarization separation element 21 side.

The first light component Ai that has entered the polarization converter 22 from the first optical path L 1 is rotated by a first direction by the first optical rotator 23 in a predetermined direction (for example, clockwise as viewed from the polarization separation element 21 side). In addition, the Faraday rotator 25 receives a 45 ° polarization rotation in a direction opposite to a predetermined direction (for example, counterclockwise as viewed from the polarization separation element 21 side).

For this reason, a light component having the same polarization direction as the light component Ai (with the same sign Ai) is emitted from the polarization converter 22 to the third light path L3.

The second optical path L2 passes through the polarization converter 22.
Is subjected to a 45 ° polarization rotation around the predetermined direction (for example, counterclockwise as viewed from the polarization separation element 21) by the second optical rotator 24, and further Faraday rotation The element 25 undergoes a 45 ° polarization rotation around the direction opposite to the predetermined direction (for example, counterclockwise as viewed from the polarization separation element 21 side).

Therefore, the polarization direction of the light component Aj is rotated by 90 ° from the polarization converter 22 to the fourth optical path L4, and the light component Aj is converted to a direction orthogonal to the groove 28 of the diffraction grating 27. 'Is emitted.

The diffraction grating 27 of the wavelength selector 26 emits the diffracted light of the light component Ai incident from the third optical path L3 toward one reflecting surface 29a of the reflector 29, and outputs the fourth optical path L1. The diffracted light with respect to the light component Aj ′ incident from the reflector 29 is emitted toward the other reflection surface 29 b of the reflector 29.

Of the light diffracted by the diffraction grating 27 and incident on one reflection surface 29a of the reflector 29, the diffraction grating 27
The light Bi of a predetermined wavelength (including light near the wavelength) determined by the incident angle with respect to the diffraction grating 27 and the angle of the reflector 29 with respect to the diffraction grating 27, as shown in FIG.
b, is reflected again by the reflection surface 29b and is incident on the diffraction grating 27.

The reflector 2 diffracted by the diffraction grating 27
9 of the light incident on the other reflection surface 29b, the incident angle with respect to the diffraction grating 27 and the reflector 2 with respect to the diffraction grating 27
Light Bj having a predetermined wavelength determined by the angle 9 (including light near that wavelength) is reflected by one reflection surface 29a, reflected again by this reflection surface 29a, and incident on the diffraction grating 27.

The diffraction grating 27 diffracts the light Bi incident from the reflector 29 again to convert the light Ci of the predetermined wavelength into a fourth light.
Bj emitted from the reflector 29 to the optical path L4
Is diffracted again, and the light Cj of the predetermined wavelength is converted into a third optical path L
Emitted to 3.

The lights Ci and Cj of the predetermined wavelengths selected by the wavelength selector 26 are incident on the polarization converter 22 via the third optical path L3 and the fourth optical path L4.

The light Cj of a predetermined wavelength that has entered the polarization converter 22 from the wavelength selector 26 via the third optical path L3 is
The Faraday rotator 25 receives a polarization rotation of 45 ° in a direction opposite to a predetermined direction (for example, counterclockwise as viewed from the polarization separation element 21 side), and further rotates in a direction opposite to the predetermined direction by the first optical rotator 23 (for example, It receives a 45 ° polarization rotation counterclockwise when viewed from the polarization separation element 21 side.

For this reason, the polarization direction of the incident light Cj is rotated by 90 ° from the polarization converter 22 to the first optical path L 1 to be orthogonal to the reference plane P, that is, the groove 28 of the diffraction grating 27.
The light Cj 'converted in parallel is emitted.

The fourth optical path L from the wavelength selector 22 side
The light C having a predetermined wavelength incident on the polarization converter 22 through
i is 45 around the direction opposite to the predetermined direction by the Faraday rotator 25 (for example, counterclockwise as viewed from the polarization separation element 21 side).
In addition, the second optical rotator 24 receives a 45 ° polarization rotation around the predetermined direction (for example, clockwise as viewed from the polarization separation element 21 side).

For this reason, the polarization direction from the polarization converter 22 to the second optical path L 2 is the same as the incident light Ci and the polarization direction is parallel to the reference plane P, that is, orthogonal to the groove 28 of the diffraction grating 27. Light Ci is emitted.

The light Cj ′ incident on the polarization beam splitter 21 from the polarization conversion section 22 via the first optical path L1 is reflected by the reflection surface 21b and travels toward the separation surface 21a.
Since the polarization direction of j 'is orthogonal to the reference plane P, the separation plane 21a
And is emitted to an emission optical path L5 orthogonal to the incident optical path L0.

The second optical path L from the polarization converter 22 side
The light Ci incident on the polarization separation element 21 via the light source 2 goes to the separation surface 21a, and the polarization direction of the light Ci is changed to the reference plane P.
Therefore, the light is reflected by the separation surface 21a and emitted to the emission optical path L5 orthogonal to the incident optical path L0 like the light Cj '.

Therefore, if the combined light D of the lights Ci and Cj ′ emitted to the emission optical path L5 of the polarization splitting element 21 is received by the light receiving section 35, the light of the predetermined wavelength contained in the incident light A An electric signal corresponding to the intensity can be obtained without being affected by the polarization dependence of the diffraction grating 27.

As described above, in the optical spectrum analyzer 20 of the embodiment, the polarization separation element 21 and the wavelength selection section 26
The polarization converter 22 disposed between the first optical path L1 and the third optical path L3 rotates the polarization direction of the light traveling from the third optical path L3 to the first optical path L3 by 45 ° around a predetermined direction. Optical path L1
A first optical rotator 23 for rotating the polarization direction of the light traveling toward by 45 ° around a direction opposite to the predetermined direction, and a second optical path L2
From the fourth optical path L4 to the fourth optical path L4, the polarization direction of the light traveling from the fourth optical path L4 to the second optical path L2 is changed to the predetermined direction. Second optical rotator 24, which is rotated by 45 °, and a first optical path L
Light traveling from 1 to the third optical path L3 and the second optical path L2
From the third optical path L3 to the first optical path L1 and the second optical axis from the fourth optical path L4 to the second optical path from the third optical path L3 to the second optical path.
And a Faraday rotator 25 that rotates the polarization direction of light traveling toward the optical path L2 by 45 ° around a direction opposite to the predetermined direction.

For this reason, the polarized light separating element 21 itself can separate the incident light and the wavelength-selected light, and the light of the predetermined wavelength selected by the wavelength selecting section 26 can be used without using a 3 dB coupler or an optical circulator on the incident optical path. The light can be emitted from an emission optical path L5 different from the incident optical path L0 of the polarization splitting element 21, and the spectrum analysis of the light can be performed without being affected by the polarization dependence of the diffraction grating 27.

Further, since light having the same polarization direction does not reciprocate in the same path in the polarization splitting element 21, there is no possibility that crosstalk will occur between input and output.

In the optical spectrum analyzer 20 described above, the optical system of the wavelength selecting section 26 is constituted by the diffraction grating 27 and one reflector 29, but as shown in FIG.
It is also possible to use the wavelength selector 26 in which the auxiliary reflector 30 is provided to increase the number of times of diffraction by the diffraction grating 27 to further improve the wavelength selectivity.

In the wavelength selector 26, the polarization converter 22
The first diffraction of the light incident through the third optical path L3 and the fourth optical path L4 from the side is performed by the diffraction grating 27, and the diffracted light is received by one reflection surface 29b of the reflector 29 and the other is received. And the second diffraction is performed by reflecting the light from the reflection surface 29a to the diffraction grating 27, and the diffracted light is reflected by the two reflection surfaces 26 of the auxiliary reflector 30.
a and 26b, the reflection paths are exchanged with each other, reflected on the diffraction grating 27 and the third diffraction is performed, and the diffracted light is reflected on the diffraction grating 27 by the reflector 29 and the fourth diffraction is performed. The diffracted light is emitted to the third optical path L3 and the fourth optical path L4.

In the polarization converter 22, the first optical rotator 23 and the second optical rotator 24
And the Faraday rotator 25 is arranged on the wavelength selection unit 26 side. However, like the polarization conversion unit 22 shown in FIG.
A Faraday rotator 25 is arranged on the polarization separation element 21 side,
The first optical rotator 23 and the second optical rotator 2 on the wavelength selection unit 26 side
4 may be arranged, and a first optical rotator 23 and a second optical rotator are provided on both sides of a Faraday rotator 25, as in a polarization converter 22 shown in FIGS. 6 (a) and 6 (b). 24 may be arranged respectively.

In this embodiment, the polarization separation element 2
Reference numeral 1 denotes a first light component whose incident light A is orthogonal to the groove 28 of the diffraction grating 27 (parallel to the reference plane P) and a diffraction grating 2
Although the second light component parallel to the groove 28 (perpendicular to the reference plane P) is separated and incident on the polarization converter 22, the first light component and the second light component whose polarization directions are orthogonal to each other are separated. In the case where the polarization directions of the two light components are not orthogonal and parallel to the grooves 28 of the diffraction grating 27, respectively, the polarization rotation angles of the respective components of the polarization converter 22 are changed by the deviation angle. can do.

However, even in this case, the polarization converter 22
As described above, upon receiving the first light component Ai and the second light component Aj from the polarization separation element 21, the polarization directions of the first light component Ai and the second light component Aj are the same as those of the diffraction grating. 27
Are transmitted to the third optical path L3 and the fourth optical path L4, respectively, at a right angle to the groove (notched line), and a predetermined wavelength outputted from the diffraction grating 27 to be described later to the fourth optical path L4. Receiving the third light of the polarization separation element 21
And outputs the light orthogonal to the polarization direction of the second light component Aj to the separation surface 21a, and receives the third light of a predetermined wavelength output from the diffraction grating 27 to the third optical path L3 to be polarized. By outputting light orthogonal to the polarization direction of the first light component Ai to the reflection surface 21b of the separation element 21, the polarization separation element 21
Is combined with the light input to the separation surface 21a and the reflection surface 21b to output the light from another surface different from the specific side surface.

[0074]

As described above, the optical spectrum analyzer of the present invention converts the incident light to be measured into the first light component whose polarization direction is orthogonal to a predetermined reference plane and the polarization direction of the reference light. The light is separated into a second light component parallel to the plane, the first light component is emitted to a first light path (L1), and the second light component is separated from a second light path (L1) different from the first light path (L1). L2), a polarized light separating element (21), a first light component emitted from the polarized light separating element to the first optical path, and a polarized light of the second light component emitted to the second optical path. A third optical path (L3) and a fourth optical path (L4) parallel to each other and orthogonal to the reference plane, with the wave directions aligned to be parallel to the reference plane.
And a diffraction grating (27) provided with a plurality of parallel grooves (28) on one surface side orthogonal to the reference plane, and a polarization conversion unit (22) respectively emitting light to the reference plane. A reflector for reflecting light diffracted by the diffraction grating to the diffraction grating along a path deviated parallel to the longitudinal direction of the groove, the reflecting surface having a reflecting surface forming an angle of 45 ° each other;
Out of the light incident on the diffraction grating from the polarization conversion section via the third optical path, the light having a predetermined wavelength determined by the angle between the diffraction grating and the reflector is transmitted to the fourth optical path. Out of the polarization conversion unit through the fourth optical path, and the light of the predetermined wavelength out of the light emitted from the polarization conversion unit through the fourth optical path through the third optical path. A wavelength selector that emits light toward the wave conversion unit side, and light of a predetermined wavelength emitted from the wavelength selector to the third optical path and the fourth optical path is mutually polarized by the polarization conversion unit. In an optical spectrum analyzer that converts the wave directions to be orthogonal to each other and receives the synthesized light, the polarization conversion unit rotates the polarization direction of light traveling from the first optical path to the third optical path in a predetermined direction. At 45 ° from the third optical path to the first optical path. Cormorants first rotator the polarization direction of the light is rotated 45 ° in the direction about said predetermined direction opposite (23)
And rotating the polarization direction of light traveling from the second optical path to the fourth optical path by 45 ° around a direction opposite to the predetermined direction, and changing the direction of light traveling from the fourth optical path to the second optical path. A second optical rotator (24) for rotating the polarization direction by 45 ° in the predetermined direction, light traveling from the first optical path to the third optical path, and traveling from the second optical path to the fourth optical path. The polarization direction of the light is rotated by 45 ° around the direction opposite to the predetermined direction, and the light traveling from the third optical path toward the first optical path and the light traveling from the fourth optical path toward the second optical path are A Faraday rotator (25) for rotating the polarization direction by 45 ° around a direction opposite to the predetermined direction.

The optical spectrum analyzer according to the second aspect of the present invention receives incident light to be measured on a specific side surface and separates the incident light into a first light and a second light whose polarization directions are orthogonal to each other. Polarization separation means (21) having a separation surface for transmitting and outputting the second light and a reflection surface for reflecting the first light separated by the separation surface and outputting the first light in parallel with the second light; A diffraction grating (27) for receiving light from a third optical path and a fourth optical path parallel to each other and outputting respective diffracted lights; and receiving each of the diffracted lights from the diffraction grating, a cutting line direction of the diffraction grating. And returns the light to the diffraction grating again to output the diffracted light by the light from the third optical path as the third light to the fourth optical path by the diffraction grating, and the fourth optical path And outputs the diffracted light from the light as fourth light to the third optical path. A reflector (29), provided between the polarization splitting means and the diffraction grating, receives the first light and the second light from the polarization splitting means, and receives the first light and the second light. The light is transmitted to the third optical path and the fourth optical path so that the polarization direction of the light is also perpendicular to the score line of the diffraction grating, and the third light output from the diffraction grating is also output. Receiving the light, outputs light orthogonal to the polarization direction of the second light to the separation surface of the polarization separation means, and receives the fourth light and outputs the first light to the reflection surface of the polarization separation means.
By outputting light orthogonal to the polarization direction of the light,
A polarization conversion unit (22) configured to combine the light input to the separation surface and the reflection surface with the polarization separation unit and output the light from another surface different from the specific side surface. .

For this reason, a polarization separation element (polarization separation means)
The incident light itself and the wavelength-selected light can be separated by itself, and the light of the selected predetermined wavelength is emitted from an exit optical path different from the incident optical path of the polarization separation element without using a 3 dB coupler or an optical circulator on the incident optical path. The light spectrum can be analyzed without being affected by the polarization dependence of the diffraction grating.

Further, since lights having the same polarization direction do not reciprocate along the same path in the polarization splitting element, there is no possibility that crosstalk will occur between input and output.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a diagram three-dimensionally showing a main part of the embodiment of the present invention.

FIG. 3 is a plan view showing a main part and operation of the embodiment of the present invention.

FIG. 4 is a diagram showing a modification of the main part of the embodiment of the present invention.

FIG. 5 is a diagram showing a modification of the main part of the embodiment of the present invention.

FIG. 6 is a diagram showing a modification of the main part of the embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a conventional device.

[Explanation of symbols]

 Reference Signs List 20 optical spectrum analyzer 21 polarization splitter 22 polarization converter 23 first optical rotator 24 second optical rotator 25 Faraday rotator 26 wavelength selector 27 diffraction grating 28 groove 29, 30 reflector 31 angle varying unit 35 light receiving unit 40 signal processing unit

Claims (2)

[Claims] 1. An incident light to be measured is separated into a first light component whose polarization direction is parallel to a predetermined reference plane and a second light component whose polarization direction is orthogonal to the reference plane, The first light component is emitted to a first optical path (L1), and the second light component is emitted to the first light path (L1).
A polarization splitting element (21) that emits to a second optical path (L2) different from the optical path of the first element, and a first light that is emitted from the polarization separation element to the first optical path.
And a third optical path parallel to each other and parallel to the reference plane, with the polarization directions of the light component and the second light component emitted to the second optical path being aligned so as to be parallel to the reference plane. (L3)
And a polarization converter (22) for emitting to the fourth optical path (L4), a diffraction grating (27) having a plurality of parallel grooves (28) orthogonal to the reference plane provided on one surface side, A reflection surface that has a reflecting surface that is orthogonal and forms an angle of 45 ° with respect to the reference surface, and that reflects light diffracted by the diffraction grating to the diffraction grating along a path that is displaced parallel to the length direction of the groove. A light incident on the diffraction grating from the polarization conversion unit via the third optical path, and an angle of incidence on the diffraction grating and an angle of the reflector with respect to the diffraction grating. Out of the light having a predetermined wavelength determined by the fourth optical path to the polarization conversion unit side, out of the light emitted from the polarization conversion unit through the fourth optical path, the light of the predetermined wavelength The light exits through the third optical path to the polarization converter. A wavelength selecting unit (26) that performs predetermined wavelengths emitted from the wavelength selecting unit to the third optical path and the fourth optical path so that the polarization directions are orthogonal to each other by the polarization conversion unit. In the optical spectrum analyzer that receives the combined light after the conversion, the polarization conversion unit rotates the polarization direction of the light from the first optical path toward the third optical path by 45 ° around a predetermined direction, A first optical rotator (2) that rotates the polarization direction of light from the third optical path toward the first optical path by 45 ° around a direction opposite to the predetermined direction.
3) rotating the polarization direction of the light from the second optical path toward the fourth optical path by 45 ° around the direction opposite to the predetermined direction, and heading from the fourth optical path to the second optical path. A second optical rotator (2) for rotating the polarization direction of light by 45 ° in the predetermined direction.
4) rotating the polarization directions of the light traveling from the first optical path to the third optical path and the light traveling from the second optical path to the fourth optical path by 45 ° around a direction opposite to the predetermined direction. Faraday rotating the polarization directions of the light traveling from the third optical path to the first optical path and the light traveling from the fourth optical path to the second optical path by 45 ° around a direction opposite to the predetermined direction. An optical spectrum analyzer comprising a rotator (25). 2. Receiving incident light of a measuring object on a specific side surface,
A separation surface that separates the first light and the second light whose polarization directions are orthogonal to each other and transmits and outputs the second light, and a second light that reflects the first light separated by the separation surface. A polarization splitting means (21) having a reflecting surface for outputting light in parallel with the third light path and a diffraction grating (27) for receiving light from a third optical path and a fourth optical path parallel to each other and outputting respective diffracted lights; Receiving each diffracted light from the diffraction grating, turning the diffraction grating in the direction of the scribe line of the diffraction grating, and sending the reflected light back to the diffraction grating. To the fourth optical path as a third light,
A reflector (29) for outputting diffracted light by the light from the fourth optical path as fourth light to the third optical path; and a reflector (29) provided between the polarization splitting means and the diffraction grating; Receiving the first light and the second light from the separation means,
And the second light are transmitted to the third optical path and the fourth optical path, respectively, such that the polarization directions of the second light and the second light are also perpendicular to the engraved line of the diffraction grating, and output from the diffraction grating. Receiving the third light, and outputting light orthogonal to the polarization direction of the second light to the separation surface of the polarization separation means, and receiving the fourth light and controlling the polarization separation means. By outputting light orthogonal to the polarization direction of the first light to the reflection surface, the polarization splitting means is combined with the light input to the separation surface and the reflection surface to be different from the specific side surface. Polarization conversion unit (2
2) An optical spectrum analyzer comprising: