JPH11326048A - Optical spectrum analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wavelength selectivity characteristics. SOLUTION: A total reflection mirror 34 is arranged in the zero-step diffraction direction of a diffraction lattice 33 relative to incident light, and a resonator is formed by an optical path from the total reflection mirror 34 through the diffraction lattice 33 to a half mirror 35. The half mirror 35, a condenser 36 and a light receiver 37 on a rotary stage 38 are rotatively moved in a body around the axis, which is positioned on a prescribed point on a plane formed by extending a diffraction face of the diffraction lattice 33, and which is parallel to the graduation direction of the diffraction lattice 33, and the length of the resonator and the angle of the half mirror 35 against the diffraction lattice 33 are made cooperatingly variable, to make the wavelength of the light received in the light receiver 37 variable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical spectrum analyzer for measuring the spectrum of light contained in light to be measured.

[0002]

2. Description of the Related Art An optical spectrum analyzer is used to measure a wavelength component contained in light to be measured.

An optical spectrum analyzer selectively receives a wavelength component contained in light to be measured by using an optical filter having high wavelength selectivity and capable of changing the selected wavelength.

FIG. 9 shows a schematic configuration of a conventional optical spectrum analyzer using such a principle.

In this optical spectrum analyzer, the light to be measured incident from the light incident part 11 is converted into parallel light by the collimator 12, and the first light is split into the first beam splitter 13 and the second light.
And enters the diffraction surface of the diffraction grating 15 via the beam splitter 14.

[0006] Part of the diffracted light from the diffraction grating 15 passes through the second beam splitter 14, is reflected by the total reflection mirror 16, and returns to the diffraction grating 15. A part of the diffracted light is converted by the second beam splitter 14 into the first beam splitter 1.
The light is reflected to the third side, passes through the first beam splitter 13, enters the light collector 17, and is incident on the light receiver 18 from the light collector 17.

In this optical spectrum analyzer, the measurement wavelength is continuously set by linking a resonator length determined by an optical path length from the diffraction grating 15 to the total reflection mirror 16 and a selected wavelength determined by an incident angle of light on the diffraction grating 15. It is variable.

That is, the diffraction grating 15 is fixed on a rotating stage 19 for changing the incident angle of light on the diffraction grating 15, and the rotating stage 19 is
Is rotatably supported on a rectilinear stage 20 for approaching or moving away from the total reflection mirror 16. The rectilinear stage 20 is driven by a driving device 21. One end of a slide bar 22 having a predetermined length is attached to the rotary stage 20, and the other end of the slide bar 22 contacts a guide surface 23 a of a slide guide 23 extending in a direction orthogonal to the direction of movement of the rectilinear stage 20. In contact.

Therefore, when the rectilinear stage 20 is moved by the driving device 21 to change the resonator length, the contact position between the other end of the slide bar 22 and the guide 23 changes,
As the rotation stage 19 rotates, the angle of incidence of light on the diffraction grating 15 also changes.

And a wavelength determined by the length of the resonator;
The measurement wavelength of the optical spectrum analyzer is continuously varied by setting the dimensions and angles of the respective parts in advance so that the wavelength determined by the incident angle of the light on the diffraction grating 15 and the diffraction angle match. Thus, of the light included in the measured light, only the light having this measurement wavelength can be received by the light receiver 18.

Therefore, with the light to be measured incident,
By moving the rectilinear stage 20 in a certain direction by the driving device 21, the intensity of each wavelength of the light included in the measured light can be measured by the output of the light receiver 18.

[0012]

However, in the above-mentioned conventional optical spectrum analyzer, the diffraction grating 15
There is a problem that the beam splitter 14 is required between the mirror and the total reflection mirror 16, and the beam splitter 14 causes light loss.

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

[0014]

In order to achieve the above object, an optical spectrum analyzer according to a first aspect of the present invention comprises a light incident portion (31) for receiving a light to be measured, and an incident light from the light incident portion. A collimator (32) for converting the converted light into parallel light, a diffraction grating (33) for receiving light emitted from the collimator at a diffraction surface at a predetermined incident angle, and entering the diffraction surface of the diffraction grating from the collimator. Total reflection mirror (3) which is arranged in the 0th-order diffraction direction of the light to be reflected and reflects the 0th-order diffraction light from the diffraction grating to the diffraction surface of the diffraction grating.
And 4) disposing the diffracted light from the collimator in a diffraction direction different from the zero-order diffraction direction of the light incident on the diffraction surface of the diffraction grating, and reflecting a part of the diffracted light from the diffraction grating to the diffraction surface of the diffraction grating. The half mirror (35) transmitting at least the remaining part, the light receiver (37) receiving the light transmitted through the half mirror, and the half mirror and the light receiver are not changed in relative position to each other. At a predetermined point on a plane obtained by extending the diffraction surface of the diffraction grating, that is, a line passing through the reflection surface of the total reflection mirror and parallel to a plane including the incident optical axis and the diffraction optical axis of the diffraction grating; A predetermined point including an intersection of a line parallel to the plane including the diffraction optical axis and the incident optical axis of the diffraction grating passing through the diffraction surface of the diffraction grating, and integrated around an axis parallel to the cutting line direction of the diffraction grating; Pivotally move from the total reflection mirror forward. Measurement in which the length of a resonator formed in an optical path to the half mirror via a diffraction grating and the angle of the half mirror with respect to the diffraction grating are interlocked and changed, and the wavelength of light received by the light receiver is changed. Wavelength changing means (38, 39).

According to a second aspect of the present invention, there is provided an optical spectrum analyzer, comprising: a light incident portion for receiving the light to be measured; and a collimator for converting the light incident from the light incident portion into parallel light. 32), a first half mirror (51) that transmits a part of the light emitted from the collimator and reflects at least a part of the remaining light, and transmits the light transmitted through the first half mirror at a predetermined incidence. A diffraction grating (33) received on a diffraction surface at an angle, and a diffraction grating arranged in a direction different from an incident direction of light incident on the diffraction surface of the diffraction grating from the first half mirror. A second half mirror (35) for reflecting a portion on a diffraction surface of the diffraction grating and transmitting at least a part of the remaining portion;
(37) for receiving light transmitted through half mirror
And the second half mirror and the photodetector are positioned at predetermined points on a plane obtained by extending the diffraction surface of the diffraction grating without changing their relative positions, that is, the reflection surface of the first half mirror. The intersection of a line parallel to a plane including the incident optical axis and the diffraction optical axis of the diffraction grating and a line passing through the diffraction surface of the diffraction grating and parallel to the plane including the incident optical axis and the diffraction optical axis of the diffraction grating At a predetermined point including the axis and parallel to an axis parallel to the cutting line direction of the diffraction grating, and the second half is rotated from the first half mirror via the diffraction grating. The length of the resonator formed by the optical path to the mirror,
Measurement wavelength varying means (38, 39) for interlockingly varying the angle of the second half mirror with respect to the diffraction grating and varying the wavelength of light received by the light receiver.

According to a third aspect of the present invention, there is provided an optical spectrum analyzer, comprising: a light incident portion for receiving the light to be measured; and a collimator for converting the light incident from the light incident portion into parallel light. 32), a first half mirror (51) that transmits a part of the light emitted from the collimator and reflects at least a part of the remaining light, and transmits the light transmitted through the first half mirror at a predetermined incidence. A diffraction grating (33) received on a diffraction surface at an angle, and a diffraction grating arranged in a direction different from an incident direction of light incident on the diffraction surface of the diffraction grating from the first half mirror. A second half mirror (35) for reflecting a portion on a diffraction surface of the diffraction grating and transmitting at least a part of the remaining portion;
(37) for receiving light transmitted through half mirror
A predetermined point on a plane obtained by extending the diffraction surface of the diffraction grating without changing the relative positions of the light incident portion, the collimator, and the first half mirror;
A line parallel to a plane including the incident optical axis and the diffraction optical axis of the diffraction grating passing through the reflection surface of the half mirror, and a plane passing the diffraction plane of the diffraction grating and including the incident optical axis and the diffraction optical axis of the diffraction grating At a predetermined point including an intersection with a line parallel to the diffraction grating, and integrally rotates about an axis parallel to the cutting line direction of the diffraction grating to pass through the diffraction grating from the first half mirror. Then, the length of the resonator formed by the optical path leading to the second half mirror and the angle of the first half mirror with respect to the diffraction grating are interlocked to change the wavelength of the light received by the light receiver. Measuring wavelength variable means (38, 39)
And

The optical spectrum analyzer according to a fourth aspect of the present invention is the optical spectrum analyzer according to the first to third aspects, wherein an optical isolator (71) is arranged between the light incident part and the collimator. I have.

According to a fifth aspect of the present invention, there is provided an optical spectrum analyzer according to the first to third aspects, wherein λ / 4 is provided in an optical path forming the resonator.
A plate (72) is arranged.

According to a sixth aspect of the present invention, there is provided an optical spectrum analyzer according to the first to third aspects, wherein a part of the light incident on the incident part or the part of the light emitted from the collimator is branched. And a second light receiver (83, 92) for receiving the light branched by the light branching means.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an optical spectrum analyzer 30 according to the embodiment of the present invention.

In FIG. 1, a light incident portion 31 is for receiving light to be measured, and is constituted by, for example, a connection terminal of an optical fiber.

The light to be measured incident on the light incident part 31 is converted into parallel light by the collimator 32 and
At a predetermined angle of incidence.

A total reflection mirror 34 is arranged in the zero-order diffraction direction (specular reflection direction) of the diffraction grating 33 with respect to the incident light from the collimator 32.

The total reflection mirror 34 reflects the 0th-order diffracted light (specular reflection light) of the light incident on the diffraction surface of the diffraction grating 33 from the collimator 32 and enters the diffraction surface of the diffraction grating 33.

The half mirror 35 is disposed so as to face the diffraction direction different from the zero-order diffraction direction of the diffraction grating 33. The half mirror 35 reflects a part of the light diffracted by the diffraction grating 33 to the diffraction surface 33a of the diffraction grating 33, and transmits the remaining light except for the loss.

The light transmitted through the half mirror 35 is condensed on a light receiver 37 by a light collector 36 and is converted into an electric signal by the light receiver 37.

The half mirror 35, the light collector 36 and the light receiver 37 are fixed on a rotary stage 38.

The rotary stage 38, together with the driving device 39, forms the measurement wavelength varying means of this embodiment, and passes through the diffraction surface 33a of the diffraction grating 33 and
A straight line A passing through a plane including the incident optical axis and the diffractive optical axis of No. 3 and a diffraction grating 33
Axis which is at the intersection J with the straight line B passing through the plane including the incident optical axis and the diffractive optical axis and is parallel to the scribe line of the diffractive surface of the diffraction grating 33, that is, the predetermined The diffraction grating 33 rotates along a plane including the incident optical axis and the diffracted optical axis with respect to an axis which is at a point and is parallel to an inscribed line of the diffraction surface of the diffraction grating 33.

The reflecting surface 35a of the half mirror 35 on the rotating stage 38 has a straight line C passing through the reflecting surface 35a and passing through a plane including the incident optical axis and the diffractive optical axis of the diffraction grating 33. In the direction crossing the center of rotation J,
It faces the diffraction surface 33 a of the diffraction grating 33.

The driving device 39 pushes and pulls the rotary stage 38 from the side to drive it to rotate. The rotary stage 38 is urged toward the drive device 39 by a spring 39a.

Therefore, when the rotary stage 38 is rotated by the driving device 39, the half mirror 35, the light collector 3
6. The light receiver 37 rotates integrally about the rotation center J of the rotary stage 38 without changing the relative position, and the optical path length from the diffraction grating 33 to the half mirror 35 and the diffraction of the diffraction grating 33 The angle of the reflection surface 35a of the half mirror 35 with respect to the surface 33a changes simultaneously.

That is, as shown in FIG. 2A, when the rotary stage 38 is driven to rotate counterclockwise, the half mirror 35 moves away from the diffraction grating 33 and the half mirror 35 with respect to the diffraction surface of the diffraction grating 33. The angle of the normal line 35, that is, the angle of the diffraction optical axis becomes large.

As shown in FIG. 2B, when the rotary stage 38 is driven to rotate clockwise, the half mirror 3 is rotated.
As 5 approaches the diffraction grating 33, the angle of the normal of the half mirror 35 to the diffraction surface of the diffraction grating 33, that is, the angle of the diffraction optical axis decreases.

As shown in FIG. 1, the driving device 39 is controlled by the measurement processing unit 40. The measurement processing unit 40 controls the driving device 39 to digitize the output of the light receiver 37 while rotating the rotary stage 38 in an arbitrary range, stores the digitized output in a memory, and outputs the received light output with respect to the angular position of the rotary stage 38. The display 41 displays the spectrum waveform of the light included in the measured light.

Next, conditions for continuously varying the measurement wavelength of the optical spectrum analyzer will be described.

As shown in FIG. 3A, the optical path length La from the diffraction grating 33 to the total reflection mirror 34 is constant irrespective of the rotation of the rotary stage 38, and the optical path length La and the diffraction grating The sum of the optical path length Lb from 33 to the half mirror 35 is the resonator length L.

Here, the optical path length Lb is determined from the incident position of light on the grating surface of the diffraction grating 33 by the rotation center J of the rotating stage 38.
Until the length and L _0, if the grating surface and the reflecting surface of the half mirror 35 of the diffraction grating 33 is an angle between _{α, Lb = L 0 · sin} α , and the resonator length L is, L = La + L ₀ · sin α.

If the light of wavelength λ resonates at the resonance mode order q of the resonator, it is necessary to satisfy the relationship of q · λ = 2L. Therefore, the resonance mode order q is q = 2L / Λ = 2 (La + L ₀ · sin α) / λ (1)

On the other hand, as shown in FIG. 3B, when the incident angle from the total reflection mirror 34 to the diffraction grating 33 is i and the diffraction angle to the half mirror 35 is β, the light having a wavelength λ Are diffracted by setting the diffraction order of the diffraction grating 33 to m,
Assuming that the lattice constant is d, λ = d · (sin i + sin β) / m, and the diffraction angle β of the diffraction grating 33 is equal to the angle α between the diffraction surface 33a and the reflection surface 35a of the half mirror 35. = D · (sin i + sin α) / m (2)

From equation (2), sin α = (m · λ / d) −sin i. By substituting this into equation (1), q = 2 ｛La + L ₀ [(m · λ / d) −sin i ｝ / Λ Here, L ₀ = La / sin i. By substituting this into the above equation and rearranging, q = 2 · La · m / (d · sin i) (3)

In equation (3), the diffraction order m of the diffraction grating 33 and the diffraction constant d of the diffraction grating 33 are both constant, and the incident angle i of the diffraction grating 33 is also constant. La is a fixed value that can be set arbitrarily.

Accordingly, one resonance mode order q is obtained irrespective of the rotation of the mirror, and the measurement wavelength can be continuously varied while maintaining this one resonance mode order.

By satisfying the above relationship, the measurement wavelength is continuously set by rotating the rotary stage 38 in a state where the wavelength determined by the resonator length and the wavelength determined by the incident angle and the diffraction angle of the diffraction grating coincide. Variable.

Therefore, the relationship between the angular position of the rotary stage 38 and the measurement wavelength is determined in advance, and the measurement processing unit 40
If the output of the light receiver 37 for each measurement wavelength is stored while driving the rotation stage 38 while the light to be measured is incident, spectrum data of light included in the light to be measured can be obtained. If this is displayed on the screen of the display 41, the spectrum waveform can be observed.

As described above, in the optical spectrum analyzer 30, since the resonator is formed by the optical path from the total reflection mirror 34 to the half mirror 35 via the diffraction grating 33, the wavelength selection characteristics of the diffraction grating are reduced. As a result, it is possible to separate and measure even spectra having similar wavelengths.

In the optical spectrum analyzer 30 of this embodiment, the light to be measured is specularly reflected by the diffraction grating 33 and is incident on the total reflection mirror 34, and the reflected light is reflected by the diffraction grating 3.
Since the light is incident on the light source 3, there is an advantage that the loss can be reduced and the components can be configured with a small number of components.

[0047]

[Other Embodiments] In the above embodiment, the light to be measured is reflected by the diffraction surface of the diffraction grating 33 and is incident on the total reflection mirror 34 arranged in the zero-order diffraction direction. Like the spectrum analyzer 50, the light incident from the light incident part 31 may be converted into parallel light by the collimator 32 and incident on the half mirror 51, and the light transmitted through the half mirror 51 may be incident on the diffraction grating 33.

When the light to be measured is incident through the half mirror 51 as described above, the light incident part 31, the collimator 32 and the half mirror 51 are connected to the rotating stage 38 as in a spectrum analyzer 60 shown in FIG. The input and output paths may be reversed.

Further, as in an optical spectrum analyzer 70 shown in FIG. 6, an optical isolator 71 may be inserted between the light incident part 31 and the collimator 32. By inserting the optical isolator 71, it is possible to prevent return light from the diffraction grating 33 side from being emitted to the light source side of the measured light via the light incident part 31.

The optical spectrum analyzer 7 shown in FIG.
As in the case of 0, a λ / 4 plate 72 of an arbitrary wavelength may be inserted between the total reflection mirror 34 and the diffraction grating 33 (or between the half mirror 35 and the diffraction grating 33). By inserting the λ / 4 plate 72, the influence of the polarization dependence of the diffraction grating 33 on the measurement can be reduced.

Also, as in an optical spectrum analyzer 80 shown in FIG. 7, the light emitted from the collimator 32 is branched in two directions by a light branching means 81, one of which is incident on the diffraction grating 33 and the other is condensed. Detector 82 by the detector 82
3, and the power of the measured light may be measured by the output of the light receiver 83.

Also, as in an optical spectrum analyzer 90 shown in FIG. 9, the light incident on the light incident section 31 is branched in two directions by an optical branching means 91 such as an optical coupler, and one of the light is incident on a collimator 32. Alternatively, the other may be made incident on the light receiver 92 so that the power of the measured light can be measured by the output of the light receiver 92.

The optical isolator 71 shown in FIG.
The λ / 4 plate 72 can also be provided in the optical spectrum analyzers of FIGS. 4, 5, 7, and 8 described above.
The power measurement functions shown in FIGS. 7 and 8 can also be provided in the optical spectrum analyzers of FIGS.

[0054]

As described above, according to the first aspect of the present invention,
In the optical spectrum analyzer, the resonator is formed by the optical path from the total reflection mirror for inputting the measured light to the half mirror via the diffraction grating, so that the loss is small and the wavelength selection characteristics by the diffraction grating are low. Get better,
Even a spectrum having a short wavelength can be measured separately.

In the optical spectrum analyzer according to the second and third aspects, the resonator is formed by an optical path from the first half mirror through which the light to be measured is incident to the second half mirror via the diffraction grating. Since it is formed, the loss is small, the wavelength selection characteristic of the diffraction grating is improved, and even a spectrum with a close wavelength can be measured separately.

By arranging an optical isolator between the light incident portion and the collimator, it is possible to prevent the light to be measured from returning to the light source side.

Further, by disposing a λ / 4 plate having an arbitrary wavelength in the optical path forming the resonator, the influence on the measurement due to the polarization dependence of the diffraction grating can be reduced.

In an optical spectrum analyzer in which light incident on a light incident portion or light emitted from a collimator is split by an optical splitter and the split light is received by a second light receiver, the power of the light to be measured is Can be measured together with the spectrum.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the embodiment;

FIG. 3 is a diagram for examining conditions for continuously varying a measurement wavelength.

FIG. 4 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a conventional apparatus.

[Explanation of symbols]

30, 50, 60, 70, 80, 90 Optical spectrum analyzer 31 Light incidence unit 32 Collimator 33 Diffraction grating 34 Total reflection mirror 35 Half mirror 36 Condenser 37 Receiver 38 Rotation stage 39 Drive unit 40 Measurement processing unit 41 Display Reference Signs List 51 half mirror 71 optical isolator 72 λ / 4 plate 81, 91 light branching means 82 light collector 83, 92 light receiver

[Procedure amendment]

[Submission date] June 16, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 4

FIG. 5

FIG. 3

FIG. 6

FIG. 7

FIG. 8

FIG. 9

Claims (6)

[Claims] A light incident portion for receiving light to be measured;
1); a collimator (32) for converting light incident from the light incident portion into parallel light; a diffraction grating (33) for receiving light emitted from the collimator on a diffraction surface at a predetermined incident angle; A total reflection mirror (34) arranged in a zero-order diffraction direction of light incident on the diffraction surface of the diffraction grating from the collimator, and reflecting the zero-order diffraction light from the diffraction grating to the diffraction surface of the diffraction grating; Are arranged in a diffraction direction different from the 0th-order diffraction direction of light incident on the diffraction surface of the diffraction grating, and a part of the diffraction light from the diffraction grating is reflected on the diffraction surface of the diffraction grating, and at least one of the remaining light is reflected. A half mirror (35) for transmitting light through the section, and a light receiver (3) for receiving light transmitted through the half mirror.
7) and, without changing the relative positions of the half mirror and the photodetector, at a predetermined point on a plane obtained by extending the diffraction surface of the diffraction grating, the half mirror and the photodetector are parallel to the cutting line direction of the diffraction grating. The length of a resonator formed by an optical path from the total reflection mirror to the half mirror via the diffraction grating by rotating integrally about an axis, and the angle of the half mirror with respect to the diffraction grating Measurement wavelength variable means (38, 38) that varies the wavelength of light received by the light receiver
39) An optical spectrum analyzer comprising: 2. A light incident part (3) for receiving a light to be measured.
1), a collimator (32) for converting the light incident from the light incident portion into parallel light, and a first which transmits a part of the light emitted from the collimator and reflects at least a part of the remaining light. Half mirror (5
1), a diffraction grating (33) receiving light transmitted through the first half mirror at a diffraction surface at a predetermined incident angle, and light incident on the diffraction surface of the diffraction grating from the first half mirror. A second half mirror (35) that is arranged in a direction different from the incident direction, reflects a part of the diffracted light from the diffraction grating to a diffraction surface of the diffraction grating, and transmits at least a part of the remaining light; A light receiver (37) for receiving light transmitted through the second half mirror; and a second half mirror and the light receiver arranged on a plane extending the diffraction surface of the diffraction grating without changing their relative positions. At a predetermined point, and integrally rotating about an axis parallel to the cutting line direction of the diffraction grating, from the first half mirror via the diffraction grating to the second half mirror Formed by the optical path leading to An optical spectrum analyzer comprising measurement wavelength varying means (38, 39) for interlockingly varying the length of the second half mirror with respect to the diffraction grating and varying the wavelength of light received by the light receiver. . 3. A light incident portion (3) for receiving light to be measured.
1), a collimator (32) for converting the light incident from the light incident portion into parallel light, and a first which transmits a part of the light emitted from the collimator and reflects at least a part of the remaining light. Half mirror (5
1), a diffraction grating (33) that receives the light transmitted through the first half mirror at a diffraction surface at a predetermined incident angle, and a light incident on the diffraction surface of the diffraction grating from the first half mirror. A second half mirror (35) that is arranged in a direction different from the incident direction, reflects a part of the diffracted light from the diffraction grating on a diffraction surface of the diffraction grating, and transmits at least a part of the remaining light; A light receiver (37) for receiving the light transmitted through the second half mirror; and a light incident portion, the collimator, and the first half mirror, the diffraction surface of the diffraction grating being changed without changing their relative positions. At a predetermined point on an extended plane, the diffraction grating is integrally rotated around an axis parallel to the cutting line direction of the diffraction grating, and is moved from the first half mirror via the diffraction grating to the second half mirror. Depending on the optical path to the second half mirror Measurement wavelength varying means (38, 39) for interlockingly varying the length of the resonator formed and the angle of the first half mirror with respect to the diffraction grating to vary the wavelength of light received by the light receiver.
An optical spectrum analyzer comprising: 4. An optical spectrum analyzer according to claim 1, wherein an optical isolator (71) is arranged between said light incident part and said collimator. 5. The optical spectrum analyzer according to claim 1, wherein a λ / 4 plate (72) is arranged in an optical path forming the resonator. 6. A light splitting means (81, 91) for splitting a part of light incident on the incident part or light emitted from the collimator, and a second light receiving means for receiving the light split by the light splitting means. The optical spectrum analyzer according to claim 1, further comprising: a light receiver (83, 92).