JP2021056464A - Fabry-perot-etalon, wavelength variation detector using the same, and wavemeter - Google Patents

Abstract

To provide a wavelength locker module capable of accurate wavelength locking in a wide frequency range, a wavelength variation detector, a wave meter, and etalon used for the same.SOLUTION: Fabry-Perot-Etalon 2 has two partial reflection elements 31a, 31b having partial reflection surfaces for reflecting one portion of incident light and transmitting one portion, which are installed facing each other and in parallel, and has a phase plate 4 in between the two partial reflection elements. In addition, a wavelength locker module regarding another standpoint of the invention includes Fabry-Perot-Etalon having two partial reflection elements having partial reflection elements for reflecting one portion of the incident light and having one portion transmitted, which are installed facing each other and in parallel, a polarization type optical path separating element 5 separating light emitted from the Fabry-Perot-Etalon according to the polarization state, and two optical conversion elements 6a, 6b arranged to each emission surface side of the polarization type optical path separating element.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wavelength rocker module, a wavelength change amount detector, and a wavelength meter using Fabry-Perot Etalon (Etalon).

In recent years, in the field of spectroscopic measurement, a tunable light source capable of varying the wavelength of oscillating light has attracted attention. In a tunable light source, a wide band of the tunable wavelength range is required for the purpose of expanding the spectroscopic region, and temporal stabilization of the oscillation wavelength and wavelength change are required for the purpose of improving the reliability and quantitativeness of measurement. Higher accuracy of quantity is required.

By the way, a semiconductor laser (ECDL) using an external resonator is used as a tunable light source capable of tunable wavelength over a wide band, but ECDL has a property that its oscillation wavelength fluctuates due to disturbance such as temperature change. is there. Therefore, a wavelength rocker module that detects the output light of the ECDL and stabilizes its oscillation wavelength is required.

Further, the oscillation wavelength of ECDL is defined by the angle of the wavelength dispersion element constituting the external cavity, but always includes indefiniteness of several times (several to 10 GHz) of the external cavity mode, and the wavelength changes. At that time, a wavelength calibration module that serves as a scale for the amount of change is required.

By the way, in order to correct the wavelength fluctuation at a certain wavelength and stabilize the oscillation wavelength of the laser, it is common to use the transmission signal of an optical element (bandpass filter, etalon, etc.) whose transmittance changes with respect to the wavelength change. Is.

For example, the following Patent Document 1 discloses a method capable of stabilizing a wavelength with only one specific wavelength using a bandpass filter, and the following Patent Document 2 discloses a wide plurality of wavelengths using an etalon. A method capable of wavelength stabilization is described. In either method, the light A transmitted through the element whose transmittance changes and the output of the light B not incident on the element are received by the photoelectric conversion element (PD), and the difference between the two signals is used to obtain a specific light. It is characterized in that a signal that crosses 0 at a wavelength is generated, and the wavelength is stabilized by PID control using the signal as an error signal.

JP-A-10-209546 Japanese Patent Application Laid-Open No. 2003-204111

However, in the above-mentioned wavelength rocker module of the prior art, although it is possible to perform stable wavelength lock at a specific wavelength, there is a problem in supporting a wide wavelength band. For example, the method using the bandpass filter described in Patent Document 1 is effective only at a specific wavelength. Further, even with the method using etalon described in Patent Document 2, it is difficult to support a wide wavelength band. this is,
In the case of the method using the difference between the signal A that transmits the etalon and the signal B that does not enter the etalon, when the wavelength greatly changes beyond several tens of nm, the chromatic aberration and transmission characteristics of the etalon and its introduced optical system change. Since the intensity ratio of A and B and the amplitude of the etalon transmission signal change, it is necessary to trim the intensity ratio of the A and B signals at each wavelength for which wavelength locking is performed. This is not suitable for use with a light source that changes the wavelength over a wide band.

Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a wavelength rocker module capable of accurately locking a wavelength in a wide wavelength band and an etalon used therefor.

In the Fabry-Perot Etalon according to one aspect of the present invention that solves the above problems, two partially reflecting elements having a partially reflecting surface that reflects a part of the incident light and transmits a part of the incident light are installed facing each other and in parallel. It is a Fabry-Perot Etalon and is characterized by having a phase plate between the partial reflection elements.

Further, in the wavelength change amount detector according to another aspect of the present invention, two partially reflecting elements having a partially reflecting surface that reflects a part of the incident light and transmits a part of the incident light are installed facing each other and in parallel. Fabry-Perot Etalon having a phase plate between the two partially reflecting elements, a polarized light path separating element that separates the light emitted from the Fabry Perot Etalon according to the polarization state, and a polarized light path separating element, respectively. It is provided with two photoelectric conversion elements arranged on the emission surface side.

Further, in the wavelength change amount detector according to another aspect of the present invention, two partially reflecting elements having a partially reflecting surface that reflects a part of the incident light and transmits a part thereof are installed facing each other and in parallel. Fabric Perot Etalon having a λ / 16 wavelength plate between the partial reflecting elements and laser light having linearly polarized light at an angle of 45 degrees with respect to the delay axis of the λ / 16 wavelength plate are transmitted through Fabric Perot Etalon. A polarized light path branching element that separates the polarized light components parallel and orthogonal to the delay axis of the wavelength plate after reflection, and a signal corresponding to the amount of light of each polarized light component separated by the polarized light path branching element are output. It has a photoelectric conversion element for processing and a control device for processing the signal of the photoelectric conversion element, and can quantitatively detect a change in the oscillation wavelength of laser light using an output.

As described above, according to the present invention, it is possible to provide a wavelength rocker module capable of accurately locking a wavelength in a wide wavelength band and an etalon used therefor. As a result, the oscillation wavelength of the tunable light source can be stabilized for a long period of time, and the amount of wavelength change when the oscillation wavelength of the tunable laser is changed can be obtained with high accuracy. Further, according to the present invention, it is possible to provide a wavelength change amount detector capable of detecting a wavelength change amount with high accuracy, and further, a wavelength meter using the wavelength change amount detector.

It is a figure which shows the outline of the optical arrangement of Fabry-Perot Etalon which concerns on Embodiment 1. It is a figure which shows the wavelength dependence of the transmitted light obtained by Fabry-Perot Etalon which concerns on Embodiment 1. FIG. It is a figure which shows the example of the quotient of the sum and the difference in the intensity of transmitted light obtained by Fabry-Perot Etalon which concerns on Embodiment 1. FIG. It is a figure which shows the outline of the optical arrangement of Fabry-Perot Etalon which concerns on Embodiment 2. It is a figure which shows the outline of the wavelength change amount detector which concerns on Embodiment 3. It is a figure which shows the interference waveform of Fabry-Perot Etalon which concerns on Embodiment 3. It is a photograph figure of Fabry-Perot Etalon prepared in an Example. It is a graph which shows the value in the vicinity of 1060 nm of the output PDa of x-polarized light, and the output PDb of y-polarized light obtained by Fabry-Perot Etalon produced in the example. It is a figure which shows the error signal waveform obtained by the Fabry-Perot Etalon produced in an Example. It is a figure which shows the output of each of PDa and b from 990 nm to 80 nm obtained by Fabry-Perot Etalon produced in an Example. It is a figure which shows the output of each of PDa and b from 990 nm to 80 nm obtained by Fabry-Perot Etalon produced in an Example. It is a figure which shows the wavelength change when the wavelength is locked to 1064 nm in an Example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be implemented in many different forms, and is not limited to the description of the embodiments and application examples shown below.

(Embodiment 1)
FIG. 1 is a diagram showing an outline of an optical arrangement of a wavelength lock module (hereinafter referred to as “this module”) 1 using Fabry-Perot Etalon (hereinafter referred to as “this Etalon”; hereinafter referred to as “the present module”) according to the present embodiment. As shown in the figure, in the Etalon 2 in the Module 1, two partial reflection elements 3a and 3b having a partial reflection surface that reflects a part of the incident light and transmits a part of the incident light are installed facing each other and in parallel. The phase plate 4 is provided between the two partial reflection elements 3a and 3b.

Further, the Etalon 2 further includes a polarized optical path separating element 5 outside the pair of partial reflecting elements 3 and on the side opposite to the side on which light is incident, and further, the polarized optical path separating. It includes photoelectric conversion elements 6a and 6b that convert the amount of each light separated by the element 5 into an electric signal.

Further, the Etalon 2 includes a control device 7 electrically connected to the photoelectric conversion elements 6a and 6b, and can perform a predetermined process as described later and output the result to the outside.

In the Etalon 2, the partial reflection elements 3a and 3b have partial reflection surfaces 31a and 31b that reflect a part of the incident light and transmit a part of the incident light as described above. In the present etalon 2, the partial reflection elements 3a and 3b are installed so that the partial reflection surfaces 31a and 31b face each other and face each other to form a hollow Fabry-Perot etalon. Examples of the partial reflection elements 3a and 3b are not limited as long as they have the above functions, and examples thereof include a half mirror, a beam splitter, and a beam sampler.

Further, in the present etalon 2, it is desirable that the back surfaces 32a and 32b of the partially reflective surfaces 31a and 31b have at least one of a non-reflective coated surface and a wedge. By doing so, it is possible to prevent the light once emitted from the outside of the pair of partial reflection elements 31a and 31b from entering the pair of partial reflection elements 31a and 31b again.

Further, in the phase plates 3a and 3b of the etalon 2, the distance between the partially reflecting surfaces 31a and 31b is not limited as long as the effect of the etalon 2 can be obtained, and can be adjusted as appropriate.

Further, the material of the partial reflection members 3a and 3b in the Etalon 2 is not particularly limited as long as it has the above functions, but it is desirable that the material is defined by a thermally stable material, for example, Super Invar. Etc. are suitable.

Further, in the present etalon 1, the phase plate 4 is a member capable of giving a change to the phase of the incident light, and by utilizing this phase change, the effects of the present etalon described above and described later can be achieved. Can be done.

Specifically, in the present Etalon 2, the phase plate 4 has a finite difference in the free spectral range (FSR) with respect to the light of the polarization component parallel to the delay axis of the phase plate 4 and the polarization component orthogonal to the delay axis. Is preferable. Here, "having a finite difference" means that the spectral responses of the incident light are different, that is, the wavelengths at which the strengthening / weakening interference occurs are different.

Further, in the etalon 2, the phase plate 4 is preferably a λ / 8 wave plate that delays polarization parallel to the delay axis by 1/8 wavelength. The effect of this will be described later.

Further, in the present etalon 2, the delay axis of the wave plate 4 is preferably installed orthogonally or parallel to the incident surface of the polarized optical path separating element 5. In this figure, for convenience, the delay axis of the wave plate is described so as to be in the y direction.

Further, in the present module 1, the polarized light path separating element 5 is a member capable of separating light by changing the traveling direction of the light according to the polarization state of the incident light. The configuration of the polarized optical path separating element 5 is not limited as long as it has the above functions, and examples thereof include a polarizing beam splitter, a beam displacer, and Gran Thomson.

Further, in the present module 1, it is preferable that the incident surface of the polarizing type optical path separating element 5 is arranged parallel or perpendicular to the delay axis of the phase plate 3. By doing so, it is possible to more reliably separate the light that has undergone the phase change as different polarized light.

Further, the module 1 further includes photoelectric conversion elements 6a and 6b that convert the amount of light into an electric signal for each of the lights separated by the polarization type optical path separation element 5. The photoelectric conversion elements 6a and 6b are not limited as long as they have this function, but for example, a photodiode is preferable.

Further, the light (incident light) 8 incident on the Etalon 2 of the module 1 is a laser beam and is linearly polarized light that forms an angle of 45 degrees with the incident surface of the polarized optical path separating element 5. preferable. By doing so, the intensities of the respective lights reaching the photoelectric conversion elements 6a and 6b after being separated by the polarizing type separation element 5 become 1: 1, the influence of noise is minimized, and signal processing is simplified. become. Light that has never been reflected by the partial reflection surfaces 31a and 31b of the partial reflection elements 3a and 3b and transmitted light and light that has been reflected once each are separated into x and y polarization components by the polarization type optical path separation element 5 and then photoelectric. The conversion elements 6a and 6b interfere with each other to generate an etalon transmission waveform. At this time, since the optical path length of the etalon with respect to the polarization component along the delay axis of the wave plate is λ / 4 longer than the optical path length of the polarization component perpendicular to the delay axis, it can be obtained by the photoelectric conversion elements 6a and 6b. The wavelength dependence of the transmitted light is relatively shifted by half FSR as shown in FIG. Then, since the quotient of the difference between the signals and the sum is a signal that crosses 0 as shown in FIG. 3, PID control by negative feedback becomes possible.

The error signal corresponds to obtaining the difference between the transmitted signals of two etalons having FSRs different by λ / 4. It goes without saying that this is economical and space-saving because this is achieved by inserting a wave plate into one etalon. Further, since the same optical axis is shared until just before the polarization type optical path separation element 5 branches, the changes due to disturbances such as heat and vibration are exactly the same, and the wavelength dependence of each optic is also the same. Therefore, stable wavelength lock and wavelength calibration are possible.

The above signal processing can be realized by the above control device 7. Examples of the control device 7 are not limited as long as the above processing can be performed, but for example, an information processing device such as a computer equipped with a CPU, a hard disk, a memory, etc., an IC capable of performing the above processing, and the like can be used. A laminated dedicated device or the like is suitable.

(Embodiment 2)
The present embodiment is almost the same as the first embodiment, but the direction of the light emitted from the Fabry-Perot Etalon and the optical arrangement for the same are different. The differences will be mainly described below. The part where the description is omitted is the same as that of the first embodiment.

FIG. 4 shows the optical system of the wavelength lock module 1 according to the present embodiment. As shown in this figure, this module includes two partial reflection elements 3a and 3b having partial reflection surfaces 31a and 31b and a phase plate 4 arranged between them, as described in the first embodiment. A hollow Fabry-Perot Etalon, an unpolarized optical path separating element 9 provided outside the Fabry-Pérot Etalon, a polarized optical path separating element 5, and photoelectric conversion elements 6a and 6b for converting the amount of light into an electric signal are included. It is composed. Similar to the first embodiment, the partial reflection elements 3a and 3b are installed so that the partial reflection surfaces 31a and 31b face each other and face each other.

Further, in this lock module, an unpolarized light path separating element 9 is provided on the side where light is incident, and the light emitted from this etalon is reflected by the unpolarized light path separating element (on the side). The point that the polarized light path separating element 5 is provided is significantly different from the above-described first embodiment.

Further, in the present module 1, similarly to the above, the control device 7 is connected to the photoelectric conversion elements 6a and 6b, performs a predetermined process, and then is output as a signal.

Further, in the present module 1, it is preferable that the polarization of the incident light 8 with respect to the incident surface of the polarized optical path separating element 5 and the delay axis of the wave plate 2 have the same relationship as in the first embodiment.

Further, the phase plate 4 is preferably a λ / 8 wave plate that delays polarization parallel to the delay axis by 1/8 wavelength, as in the first embodiment.

In this module 1, the incident light 8 is once incident on the unpolarized optical path separating element 9 before being incident on the etalon 2. Then, the light reflected by the partially reflecting surface of one partial reflecting element 3a and the light reflected by the partially reflecting surface of the other partially reflecting element 2b are separated from the incident optical axis by the unpolarized light path separating element 9. After being branched into x and y polarized components by the polarized light path separating element 5, they interfere with each other on the photoelectric conversion elements 5a and 5b to generate an etalon transmission waveform.

That is, in the present embodiment, the wavelength dependence of the transmitted light obtained by the photoelectric conversion elements 5a and 5b is relatively shifted by half FSR as shown in FIG. 2 as in the first embodiment. Since the quotient of the signal difference and the sum is a signal that crosses 0 as shown in FIG. 3, PID control by negative feedback is possible.

Since etalon reflected light is used in this arrangement, it is possible to make the dark part of the interference waveform zero regardless of the reflectance of the partially reflecting surface. Therefore, by using an uncoated surface or the like having a reflectance of about 4% as a partially reflecting surface, it is possible to obtain an error signal that approximates a sine curve. As a result, even if the wavelength is locked at either the rising or falling slope of the error signal, the wavelength can be locked at equal intervals, so that the same effect as when the etalon having twice the length is used can be obtained.

(Embodiment 3)
This embodiment is an embodiment relating to a wavelength change amount detector that detects a wavelength change amount. FIG. 5 shows a layout diagram of the wavelength change amount detector (hereinafter referred to as “the present detector”) 1 according to the present embodiment. However, the configuration of this detector is generally the same as that of the above embodiment, and the differences will be mainly described below. The part where the description is omitted is the same as that of the first embodiment.

In the present embodiment, the pair of partial reflection elements 3a and 3b are installed so that the partial reflection surfaces 31a and 31b face each other and face each other. The phase plate 4 arranged between them is a λ / 16 wave plate that delays polarized light parallel to the delay axis by 1/16 wavelength.

Further, in the present embodiment, an optical path separation element 9 is provided on the outside of the Fabry-Perot Etalon 2 to separate the light emitted from the Fabry-Perot Etalon 2. The optical path separating element 9 may be a non-polarized type, but may be a polarized type. Further, one of the lights separated from the optical path separation element 9 is incident on the photoelectric conversion element 6c, and the other is incident on the other optical path separation element 5, and is incident on the photoelectric conversion elements 6a and 6b, respectively, and is converted into an electric signal. Will be done.

In the present embodiment, the wavelength dependence of the transmitted light obtained by the photoelectric conversion elements 6a and 6b is an etalon interference waveform that is relatively deviated by a quarter of the FSR as shown in FIG. Assuming that the wavelength that gives one maximum point of the 6a output is λ ₀ and the frequency change from that point is Δν, the 6a, 6b and 7 outputs are represented by the following equations.

Output of 4a: X = 2Acos (θ / 2) ^ 2 = A (1 + cosθ)
Output of 4b: Y = 2Acos (θ / 2-λ / 8) ^ 2
= A (1 + cos (θ-λ / 4))
= A (1 + sinθ)
6c output: A

At this time, θ is θ = Δν / FSR × 2π, where FSR is the fringe interval of etalon. Then, by calculating these outputs as follows, the frequency difference from _{λ 0 can be obtained in the range of ± FSR / 4.}

x = XA = Acosθ
y = YA = Asinθ
arctan (y / x) = θ = Δν / FSR × 2π

If the frequency change of the incident laser is sufficiently continuous with respect to the FSR (as a guide, if the change is smaller than one tenth of the FSR), even if the frequency changes in the range exceeding ± FSR / 4. , ± FSR / 4 can be added / subtracted to expand the frequency range and capture frequency changes.

In the arrangement of the second embodiment, the amount of wavelength change can be quantitatively obtained by the fringe interval (FSR) of etalon, but in this arrangement, the resolution can be quantitatively evaluated to about 1/100 of the FSR. It is possible.

Further, the wavelength change amount of the present embodiment can be used as a wavelength meter by combining with a reference light source. Specifically, this wavelength change detector is combined with a reference light source that outputs a known wavelength, and the wavelength of the incident laser light is calculated based on the wavelength of the reference light source and the output of the wavelength change detector. By doing so, it can function as a wavelength meter. Alternatively, a wavelength change detector according to the present embodiment and a wavelength detector capable of detecting an absolute wavelength for one or more specific wavelengths are combined, and the wavelength of the incident laser light is determined to be the absolute wavelength and the wavelength change amount detector. It can function as a wavelength meter by calculating based on the output of.

Here, the Fabry-Perrot Etalon according to the above-described embodiment was actually prepared and its effect was confirmed. In this example, the optical arrangement described in the second embodiment was produced.

FIG. 7 shows a photograph of the example. A λ-Master 1040 manufactured by Spectra Quest Lab was used as the target laser for the wavelength lock, and the linearly polarized light output was introduced into the wavelength rocker module system by the polarization plane preservation fiber.

A beam sampler BSF05-B manufactured by Thorlabs was used as a partial reflection element, and an etalon was constructed with an uncoated surface (reflectance 4%) as a partial reflection surface. The distance between the etalons was defined by a lens barrel using a super-invar wire rod, which is a low thermal expansion material. The distance between the partially reflecting surfaces of Etalon is about 15 cm, and the FSR at this time is 1 GHz (3.3 pm).

A 1/8 wave plate was used as the phase plate 2, and a 1040 nm zero-order wave plate was custom-ordered and used by CRYSLAR of China.

A polarization-independent half-beam splitter cube BS014 manufactured by Thorlabs was used as a polarization-independent optical path branching optical element.

As the polarized optical path branching optical element, a wideband polarized beam splitter cube CCM5-PBS203 manufactured by Thorlabs was used.

Then, the amount of light was detected using a photodetector PDA100A manufactured by Thorlabs, an error signal was calculated by a dedicated circuit or the like, and feedback control was performed on the oscillation wavelength of λ-Master 1040, which is a wavelength lock target. The λ-Master 1040 has an external modulation function for the LD current value, and feedback control can be easily performed by adding an appropriate gain to the error signal.

FIG. 8 shows the values of the x-polarized output PDa and the y-polarized output PDb near 1060 nm. The wavelength dependence of PDa and b is shifted by half a peak in the same period, and it can be seen that the λ / 8 wave plate causes a finite difference in FSR.

Further, FIG. 9 shows an error signal that is actually calculated and output as (PDa-PDb) / (PDa + PDb). An error signal that swings positively or negatively with respect to zero is obtained, and it is easy to lock the wavelength by feedback using this signal. Further, by using the 4% reflecting surface as the partial reflecting surface, a signal similar to a sine curve is obtained, and the wavelengths crossing zero are aligned at equal intervals regardless of the up / down slope. This makes it possible to lock wavelengths at equal intervals with twice the wavelength pitch.

Further, FIGS. 10 and 11 show the outputs of PDa and b from 990 nm to 1080 nm, respectively. Both show almost the same wavelength dependence, and wavelength lock is possible over the entire oscillation wavelength of the λ-Master 1040 without the need for gain adjustment of each of the PDa and b. The intensity fluctuation observed in the period of about 1 nm, which is larger than Etalon's FSR 3.3 pm, is due to the interference of beam splitters, etc., but since it shows exactly the same dependence on PDa and b, it is offset by the error signal calculation and the wavelength lock. Does not cause any trouble.

Further, FIG. 12 shows a wavelength change when the wavelength is locked to 1064 nm by using this wavelength rocker module. The wavelength change was measured using a wavelength meter A771 (wavelength accuracy: 60 MHz) manufactured by Bristol. The solid black line shows the data when the wavelength is locked, and the gray solid line shows the data without the wavelength lock. Without the lock, the output wavelength drifts due to changes in the outside air temperature, etc., but the wavelength lock provides a stable oscillation wavelength within the accuracy range of the wavemeter.

As described above, the effect of the present invention could be confirmed by this example.

The present invention has industrial applicability as Fabry-Perot Etalon and a wavelength rocker module using the same. In addition, it has industrial applicability as a wavelength change detector using this Fabry-Perot Etalon and as a wavelength meter.

Claims (8)

A Fabry-Perot Etalon in which two partial-reflecting elements having a partial-reflecting surface that reflects a part of incident light and transmits a part of the incident light are installed facing each other and in parallel, and a phase plate is provided between the two partial-reflecting elements. The Fabry-Perot Etalon according to claim 1, wherein the phase plate has a finite difference in free spectral range (FSR) with respect to light of a polarized light component parallel to the delay axis and a polarized light component orthogonal to the delay axis. The Fabry-Perot Etalon according to claim 1, wherein the phase plate is a λ / 16 wave plate. Two partial reflection elements having a partial reflection surface that reflects a part of the incident light and transmits a part of the incident light are installed facing each other and in parallel, and a Fabry-Perot Etalon having a phase plate between the two partial reflection elements. ,
A polarized optical path separating element that separates the light emitted from the Fabry-Perot Etalon according to the polarization state, and
A wavelength change amount detector including two photoelectric conversion elements arranged on the emission surface side of each of the polarization type optical path separation elements. The wavelength change amount detector according to claim 4, further comprising a control device connected to each of the two photoelectric conversion elements and performing output signal processing of the two photoelectric conversion elements. Fabry-Perot Etalon with two partial-reflecting elements with partial-reflecting surfaces that reflect and transmit part of the incident light, facing each other and in parallel, with a λ / 16 wave plate between the partial-reflecting elements. When,
Polarized light parallel and orthogonal to the delay axis of the wave plate after the laser beam having linear polarization at an angle of 45 degrees with respect to the delay axis of the λ / 16 wave plate passes through or reflects the Fabry-Perot Etalon. Polarized light path branching element that separates each component,
A photoelectric conversion element that outputs a signal corresponding to the amount of light of each polarization component separated by the polarization type optical path branching element, and
It has a control device for processing the signal of the photoelectric conversion element, and has.
A wavelength change amount detector capable of quantitatively detecting a change in the oscillation wavelength of the laser beam using the output. The wavelength change amount detector according to claim 6 and
Has a reference light source that outputs a known wavelength,
A wavemeter that calculates the wavelength of the incident laser light based on the wavelength of the reference light source and the output of the wavelength change amount detector. The wavelength change amount detector according to claim 6 and
It has a wavelength detector that can detect absolute wavelengths for one or more specific wavelengths.
A wavemeter that calculates the wavelength of the incident laser light based on the absolute wavelength and the output of the wavelength change amount detector.

Images