JP2005010734A - Compound type etalon element and laser apparatus using compound type etalon element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound type etalon element of a lamination type which can prevent the deterioration of optical characteristics, has no dependency on polarized light, is excellent in temperature stability, and can be miniaturized. <P>SOLUTION: The compound type etalon element 18 has HR films 31 and 32 on an incident surface and exit surface of a transparent body, and utilizes the multiple reflections of light within the transparent body, in which the transparent body is formed by laminating a plurality of transparent thin body sheets 10 and 20 from the incident surface toward the exit surface and the transparent body thin sheets 10 and 20 are joined through an AR film 40. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a composite type etalon element and a laser apparatus using the composite type etalon element, and more particularly to a composite type etalon element for a wavelength selective filter used as an optical component for optical communication such as optical fiber communication and the composite type etalon element. The present invention relates to the laser apparatus used.

  There is a wavelength division multiplexing method as a method for transmitting a large amount of signals at high speed in optical communication. In this wavelength division multiplexing system, it is possible to increase the amount of information transmitted at a time by storing as many signals with different carrier wavelengths as possible in a narrow band.

  For this reason, the wavelengths of different channels with different carrier wavelengths are very close to each other. For this reason, in order to correctly transmit and receive signals of channels having wavelengths close to each other, it is necessary that the characteristics of the optical filter used in the optical communication network be stable with respect to the wavelength. The quality of optical signal transmission / reception will deteriorate. Therefore, the optical filter is required to have stable characteristics such as wavelength (frequency) characteristics and temperature stability.

  As a technique for improving temperature stability in a solid type etalon optical element that is an optical filter, at least one side of a transparent plate having a reflective film on both sides is made of a material different from this transparent plate and There is also known a technique for forming an optical element by closely contacting a plate-like body having a large linear expansion coefficient (see, for example, Patent Document 1).

  According to this technique, the change in the product of the thickness of the transparent plate and the refractive index (that is, the optical distance) caused by the temperature change is offset by the volume change caused by the temperature change of the plate-like body, and the optical distance is reduced. It can be kept approximately invariant. However, in the configuration of the optical element as described above, when the transparent plate is thick, it is difficult for the volume change to occur due to the temperature change of the plate-like body, and the optical distance cannot be kept unchanged with respect to the temperature change. There was an inconvenience.

As another technique, as a technique for selecting a material having high temperature stability for the transparent plate of the optical element, a coefficient (1 / n · dn / dt) obtained by dividing the temperature change of the refractive index of the transparent plate by the refractive index. ) And a linear expansion coefficient α (hereinafter referred to as a characteristic index) is selected (for example, see Patent Documents 1 and 2). Examples of such a material include PMMA, AgCl, LiCaAlF ₆ , LiO ₃ , CaCO ₃ , CaWO _{4, and the} like, and when these are used for a transparent plate to form an optical element, the temperature at the central wavelength (1550 nm). The amount of change with respect to is about 0.8 to 3.6 pm / K, and has high temperature stability.

As described above, when an optical element is configured by selecting a material having high temperature stability for the transparent body plate, considering reliability, workability, stability, etc. of the material (for example, PMMA as a polymer material is sufficient as reliability) However, among the above materials, LiCaAlF ₆ is considered to be practical. When LiCaAlF ₆ is used, the amount of change with respect to temperature at the center wavelength (1550 nm) is about −3.6 pm / K.

In order to transmit more signals at once, it is desirable that the FSR value is small. For example, when the FSR is set to 25 GHz and LiCaAlF ₆ (refractive index n = 1.386) is selected, the incident angle is approximately 0. In the case of the degree, the thickness of the optical element is about 4.3 mm.

  Another technique for improving the temperature stability of optical elements is to use a material that has a positive characteristic index value in the crystal axis direction and a negative characteristic index value in the other crystal axis direction. There is a technique in which the characteristic index is substantially zero at the incident angle by tilting the angle to a predetermined angle with respect to the optical axis (see, for example, Patent Document 3).

Further, as another technique for improving the temperature stability of the optical element, there is a technique in which a transparent plate is formed by bonding a material having a positive characteristic index and a material having a negative characteristic index (for example, patents). Reference 1 and Patent Reference 3). According to this technology, since a composite optical element is configured by bonding materials having positive and negative characteristic indexes, one material has a longer optical distance due to temperature change, and the other material has a shorter optical distance. . Therefore, the temperature stability of the optical element can be improved by setting the thicknesses of both materials so as to cancel out the change in the optical distance due to the temperature change.
Japanese Patent No. 3294986 (page 3-7, FIG. 1-6) JP 2001-324702 A (Page 5-9) US Pat. No. 6,452,725 (pages 5-8, FIGS. 1-7)

  In order to send and receive many signals at a time, it is necessary to set the FSR to be small. However, when the FSR is set to 25 GHz, the thickness of the transparent plate is larger than when the FSR is set to 50 GHz and 100 GHz, for example. The thickness is twice and four times, respectively.

When LiCaAlF ₆ is used as a technique for improving the temperature stability of the optical element by selecting a material having high temperature stability for the transparent plate, the amount of change with respect to the temperature at the center wavelength (1550 nm) is about −3.6 pm / K. When the FSR is set to 25 GHz, the thickness is about 4.3 mm, and the structure can be excellent in temperature stability and contribute to downsizing.

However, although optical elements using LiCaAlF ₆ have been downsized, there is a market demand for further downsizing of the optical elements. At the same time, since there is a demand for higher temperature stability, an optical element using LiCaAlF ₆ has a problem that it is not sufficient from the viewpoint of temperature stability and size.

  In addition, the technique of tilting the crystal axis of the optical element and making the characteristic index substantially zero for light incident at a predetermined angle uses the tilt of the crystal axis, resulting in polarization dependence and incident. There was a problem that the direction of polarization of the light beam was limited.

In the case of a bonded (composite) optical element, there is an advantage that the temperature stability can be further improved, but the reflection of the optical joint surface of the bonded transparent plate is used as an optical element. In addition, there has been a problem that the optical characteristics are disturbed with respect to a necessary wavelength band. Moreover, in the said prior art, the combination of BK7 and NaCl is illustrated as two types of materials. However, when BK7 and NaCl are used as materials, it cannot be said that the reliability of the materials is sufficient.
Further, in a laser device such as a laser module using a conventional etalon element, a cooling device or a control device for maintaining the etalon element at a predetermined temperature is required, or the size of the etalon element is not limited to the provision of the cooling device. Since it is necessary to use a large air gap type etalon element, there is a disadvantage that the laser device itself is increased in size and power consumption is large.

  In view of the above problems, an object of the present invention is to prevent degradation of optical characteristics in a bonded composite etalon element, and has no polarization dependency, excellent temperature stability, and downsizing. It is an object of the present invention to provide a composite etalon element that can be used and a laser device using the composite etalon element.

  According to the composite etalon element of claim 1, the subject is a composite etalon having a reflective film on the entrance surface and the exit surface of the transparent body, and utilizing multiple reflection of light inside the transparent body. In the element, the transparent body is formed by laminating a plurality of transparent body thin plates from the entrance surface to the exit surface, and the transparent body thin plate is bonded to the adjacent transparent body thin plate via an antireflection film. Is done.

  As described above, the composite type etalon element of the present invention is formed by laminating a transparent body in which a reflection film is formed on the incident surface and the exit surface, by laminating a plurality of transparent thin plates from the entrance surface to the exit surface, and the transparent body. The thin plates are joined via an antireflection film. By comprising in this way, it can reduce that the light ray which injected in the composite type | mold etalon element will be reflected in the joining interface of transparent body thin plates.

  Thereby, it is possible to suppress the change in the spectral transmittance (optical characteristics) of the composite etalon element from being disturbed by the reflection, and it is possible to maintain the change in the spectral transmittance periodically. In addition, it is possible to align the values of the maximum values of the periodic changes in the spectral transmittance, and to make the interval between the wavelengths at which the maximum values are obtained substantially constant. Therefore, in the composite type etalon element of the present invention, it is possible to effectively prevent the deterioration of the optical characteristics caused by bonding the transparent thin plates.

  In addition, as described in claim 2, it is preferable that the antireflection film has a reflectance of 0.3% or less with respect to light having a wavelength to be used. When the transparent thin plates are joined without an antireflection film, several percent of reflection occurs at the joining interface. However, it is possible to effectively prevent the deterioration of the optical characteristics caused by laminating the transparent thin plates by setting the reflectance to 0.3% or less for the light of the wavelength used as in the present invention. It becomes.

  In addition, as described in claim 3, the antireflection film can be composed of a single layer or a plurality of layers. In addition, as described in claim 4, it is preferable that the antireflection film is formed by being laminated on one of adjacent transparent thin plates and bonded to the other of the adjacent transparent thin plates by optical adhesion. . In this way, by joining the transparent thin plates through the antireflection film by optical adhesion, for example, the deterioration of the optical characteristics without causing attenuation, reflection or the like at the adhesion interface like adhesion by an organic substance or the like. The influence can be reduced.

Further, according to the composite etalon element of claim 5, the subject is a composite having a reflection film on the incident surface and the emission surface of the transparent body, and utilizing multiple reflection of light inside the transparent body. In the type etalon element, the transparent body is formed by laminating a plurality of transparent body thin plates from the entrance surface to the exit surface, and the transparent body thin plate has a refractive index difference of 0.160 or less from an adjacent transparent body thin plate. It is solved by setting to.
Such a simple configuration can reduce the reflection at the joint interface of the light beam incident on the composite etalon element, thereby suppressing the change in the spectral transmittance, and reducing the change in the spectral transmittance. It becomes possible to keep it periodic. Thereby, it is possible to effectively prevent the deterioration of the optical characteristics caused by pasting the transparent thin plates.

  In addition, as described in claim 6, the transparent body is suitable if the sum of the product of the thickness and refractive index of each transparent body thin plate is kept approximately unchanged with respect to temperature change. By appropriately selecting the transparent thin plate, if the sum of the product of the thickness and refractive index of each transparent thin plate is kept approximately unchanged with respect to the temperature change, the optical distance in the composite etalon element is Therefore, it becomes possible to obtain a composite etalon element having excellent temperature stability.

  In addition, as described in claim 7, the transparent body includes a transparent thin plate having a positive coefficient that increases a product of thickness and refractive index with respect to a temperature change, and a product of thickness and refractive index with respect to a temperature change. The positive and negative coefficients so that the sum of the product of the thickness and refractive index of each transparent sheet is approximately invariant to temperature changes. It is preferable if the ratio of the thicknesses of the transparent thin plates having a thickness is set.

  Thus, as a material for the transparent thin plate, a material having a property of decreasing an optical distance with respect to a temperature change (that is, having a negative coefficient) and a property of increasing an optical distance with respect to a temperature change ( In other words, if the material having a positive coefficient is selected and the ratio of the thicknesses of these materials is set to an optimum value in consideration of the magnitude of the positive and negative coefficients, the optical in the composite etalon element Since the distance can be made constant regardless of the temperature, it is possible to obtain a composite etalon element having excellent temperature stability.

In addition, as described in claim 8, the transparent thin plate having the negative coefficient can be made of any one of SrTiO ₃ , TiO ₂ , and LiCaAlF ₆ . SrTiO ₃ is an optical crystal having isotropic properties, and TiO ₂ is an optical crystal having no isotropic properties. TiO ₂ is an optical crystal having no isotropic property, but can be regarded as optically isotropic when a light beam is incident parallel to the optical axis. TiO ₂ is a crystal having a negative coefficient when incident on a light beam as described above. Therefore, even when an optical crystal having no isotropic property is used for a transparent thin plate having a negative coefficient, it is possible to obtain a composite etalon element having extremely little polarization dependency. Since these materials have a refractive index higher than that of optical glass, the size of the composite etalon element can be reduced by using these materials. LiCaAlF ₆ is a material having a refractive index close to that of optical glass.

  In addition, as described in claim 9, the transparent body can be configured to include a transparent thin plate made of optical glass and a transparent thin plate made of optical crystal. In addition, as described in claim 10, the transparent body can be constituted by a transparent thin plate made of an optical crystal.

  In addition, as described in claim 11, the transparent body is made of the optical crystal so that the sum of the product of the thickness and refractive index of the transparent body thin plate is kept approximately unchanged with respect to temperature change. The composite etalon element can also be configured by setting the direction of the optical crystal axis of the transparent thin plate so as to form a predetermined angle with respect to the direction from the incident surface toward the reflecting surface.

  Further, according to the laser device of the twelfth aspect of the present invention, the laser device according to claim 12 receives the laser beam branched in one direction at the branching unit that branches the incident laser beam in two directions, and receives the laser beam. An intensity detector that detects the intensity of the light; the composite etalon element that selectively transmits laser light having a predetermined wavelength among the laser light branched in the other direction by the spectroscopic section; and the composite etalon element. This is solved by including a wavelength detection unit that receives the transmitted laser beam having a predetermined wavelength and detects the intensity of the laser beam having the predetermined wavelength. By providing the above composite type etalon element, a device for cooling to keep the etalon element at a predetermined temperature is not required as in the prior art, so that the laser device itself can be made compact and manufactured. Cost can be reduced.

  The composite type etalon element of the present invention has a structure in which a transparent thin plate is attached by optical adhesion through an antireflection film, so that reflection and loss at the joint surface are reduced, and includes the wavelength of the light beam to be used. The change in the spectral transmittance of the composite etalon element can be made periodic in a wide wavelength range, and the wavelength interval at which the maximum value of the change can be made substantially constant and the maximum value can be made uniform.

  Further, the composite etalon element of the present invention has a transparent thin plate made of an optical material having a positive coefficient that increases the optical distance with respect to a temperature change, and a negative coefficient that decreases the optical distance with respect to a temperature change. Since the transparent thin plate made of the optical material provided is laminated and these thicknesses are set so that the change in the optical distance with respect to the temperature change cancels each other, stable optical characteristics can be obtained regardless of the temperature. Have.

  Further, by selecting an optical material having a high refractive index, it is possible to obtain a more compact composite type etalon element. Furthermore, when an optical crystal is used as the optical material, it has become possible to form a composite etalon element without tilting the crystal axis direction.

  As described above, according to the present invention, in a bonded composite etalon element, optical characteristics can be prevented from being deteriorated, and there is no dependence on polarization, temperature stability is excellent, and miniaturization is achieved. It is possible to provide a composite etalon element that can be used. Further, by using the composite etalon of the present invention for a laser device, the laser device can be made compact and the manufacturing cost can be reduced.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 to FIG. 21 are examples relating to a combination of SrTiO ₃ and optical glass (S-TIH53), and FIG. 1 is a cross-sectional explanatory view of a composite type etalon element having a single-layer antireflection film of the example. 2 is a graph showing the spectral reflectance characteristics of the single-layer antireflection film of the example, FIG. 3 is an enlarged view of FIG. 2, and FIG. 4 is a graph showing the spectral reflectance characteristics of the single-layer antireflection film of another example. It is. FIGS. 5 and 7 are cross-sectional explanatory views of the composite type etalon element having the two-layer and three-layer antireflection films of the embodiment, respectively, and FIGS. It is a graph showing a spectral reflectance characteristic.
9 to 18 show examples in which the reflectance of the highly reflective film is changed, and FIGS. 9, 11, 13, 15, and 17 show the spectral transmittance characteristics of the composite type etalon element of the embodiment. FIG. 10, FIG. 12, FIG. 14, FIG. 16, and FIG. 18 are graphs showing the spectral transmittance characteristics when the antireflection film is not formed in the composite type etalon element of the example.
FIG. 19 is a graph showing the spectral transmittance characteristics when the reflectance of the antireflection film of the example is varied, and FIG. 20 shows the spectral transmittance characteristics when the antireflection film is not formed in the composite type etalon element of the example. FIG. 21 is a graph showing the spectral transmittance characteristics when the antireflection film is formed and not formed in the composite etalon element of the example.

FIGS. 22 to 32 show an embodiment relating to a combination of SrTiO ₃ and quartz. FIG. 22 shows a single-layer antireflection film, FIG. 23 shows a two-layer antireflection film, and FIG. 24 shows a three-layer antireflection film. It is a graph showing the spectral reflectance characteristic of an Example. 25 to 32 are examples in which the reflectance of the highly reflective film is changed, and FIGS. 25, 27, 29, and 31 are graphs showing the spectral transmittance characteristics of the composite type etalon element of the embodiment. 26, 28, 30, and 32 are graphs showing the spectral transmittance characteristics when the antireflection film is not formed in the composite type etalon element of the example.

FIGS. 33 to 44 show an embodiment relating to a combination of LiCAF and optical glass (S-BAH32). FIG. 33 is a single-layer antireflection film, FIG. 34 is a two-layer antireflection film, and FIG. It is a graph showing the spectral reflectance characteristic of the Example of this anti-reflective film. 36 to 39, FIG. 41 and FIG. 42 are examples when the reflectance of the high reflection film is changed, and FIG. 36, FIG. 38 and FIG. 41 are spectral transmittance characteristics of the composite type etalon element of the embodiment. 37, FIG. 39, and FIG. 42 are graphs showing the spectral transmittance characteristics when the antireflection film is not formed in the composite type etalon element of the example.
FIG. 40 is a graph showing spectral transmittance characteristics when an antireflection film is formed and not formed in the composite etalon element of the example, and FIG. 43 is a spectrum when the reflectance of the antireflection film of the example is varied. FIG. 44 is a graph showing the spectral transmittance characteristics when the antireflection film is not formed in the composite type etalon element of the example.

45 to 50 are examples relating to the combination of LiCAF and optical glass (S-FSL5), and FIG. 45 is a graph showing the spectral reflectance characteristics of an example of a single-layer antireflection film. 46 to 49 show examples in which the reflectivity of the high reflection film is changed, and FIGS. 46 and 48 are graphs showing the spectral transmittance characteristics of the composite type etalon element of the example, and FIGS. 47 and 49. These are graphs showing the spectral transmittance characteristics when the antireflection film is not formed in the composite type etalon element of the example. FIG. 40 is a graph showing spectral transmittance characteristics when an antireflection film is formed and not formed in the composite type etalon element of the example.
51 to 54 are graphs showing temperature characteristics of the composite type etalon element of the embodiment, and FIG. 55 is a configuration diagram of the laser apparatus. Note that the configurations and the like described below are not intended to limit the present invention, and various modifications can be made according to the spirit of the present invention.

  The composite etalon element 1 of the present invention is an etalon optical filter as a wavelength selective filter for optical communication. The composite etalon element 1 is a Fabry-Perot optical element that multi-reflects light incident on the inside of the transparent body 2 by reflection films formed on both side surfaces of the transparent body 2 in parallel. The composite etalon element 1 of the present invention is characterized by having stable optical characteristics (spectral transmittance characteristics) regardless of wavelength (frequency) and temperature. First, it will be described that the composite etalon element 1 of the present invention has stable optical characteristics (spectral transmittance characteristics) regardless of wavelength (frequency).

Example 1 (combination of SrTiO ₃ and optical glass)
As shown in FIG. 1, the transparent body 2 of the composite etalon element 1 is configured by laminating transparent thin plates 10 and 20 and an AR film (antireflection film) 40. The transparent thin plates 10 and 20 are laminated and disposed in close contact with each other via an AR film (antireflection film) 40, and the transparent thin plates 10 and 20 are provided with an HR film (high incidence surface) on the outer side surfaces (incident and outgoing surfaces, respectively). Reflective films) 31 and 32 are provided. The transparent thin plates 10 and 20 of this example are composed of SrTiO ₃ that is an optical crystal and S-TIH53 (optical glass manufactured by OHARA INC.) That is an optical glass, respectively.

The refractive index n ₁ of SrTiO ₃ is 2.279, the refractive index n ₂ of S-TIH 53 is 1.800, the thickness D ₁ of the transparent thin plate 10 is 292.27 μm, and the thickness D ₂ of the transparent thin plate 20. Is formed to 443.91 μm. Therefore, the total thickness of the composite etalon element 1 is about 0.736 mm. In the composite etalon element 1 of the present embodiment, the thicknesses D ₁ and D ₂ are not set in consideration of temperature characteristics described later. In the present invention, the thickness refers to the thickness of the material in the direction from the incident surface to the emission surface.

  The joining surfaces of the transparent thin plates 10 and 20 are polished and polished with extremely high surface accuracy to form an optical flat. The AR film 40 is formed by being laminated on the bonding surface of the transparent thin plate 10 or 20 so as to have a predetermined thickness by, for example, a vacuum deposition method, a sputtering method, an ion assist deposition method, an ion plating method or the like.

  The transparent thin plates 10 and 20 are integrally connected to each other at the bonding interface by an optical contact without using an organic material or the like with the AR film 40 interposed therebetween. Thereby, it can reduce that the light ray which passes the adhesion interface attenuates and reflects by the adhesion interface.

The AR film 40 is provided in order to further reduce reflection at the bonding interface between the transparent thin plate 10 and the transparent thin plate 20. 2 shows the reflectance characteristics of the AR film 40 (line a in the figure) when SrTiO ₃ and S-TIH 53 are selected as the transparent thin plates 10 and 20, respectively, and the reflectance characteristics when the AR film 40 is not formed (FIG. 2). The middle line b) is shown. The AR40 film is formed as a single layer film using an optical material having a refractive index n of 2.025 so that the optical film thickness is 0.25λ (λ = 1550 nm). FIG. 3 is an enlarged view of the vertical axis (reflectance) of FIG.

  By forming the AR film 40 in this way, the reflectance can be made substantially zero% at the center wavelength of 1550 nm (see the line a in the figure). In addition, the reflectance can be suppressed to an extremely low level of 0.02% or less in the S, C, and L bands (1460 nm to 1625 nm) used in optical fiber communication, centering on the wavelength of 1550 nm. Even when manufacturing errors are taken into consideration, at least the reflectance can be suppressed to 0.3% or less. In the case where the AR film 40 is not provided at the interface, the reflectance increases to about 1.38% (see line b in the figure).

  FIG. 4 shows a case where a material having a refractive index n of 1.900, 1.950, 2.100, 2.150 is used as a material of the AR film 40 in addition to a material having a refractive index n of 2.025. Reflectance characteristics are shown. Each thickness d is set to satisfy nd = 0.25λ. In the figure, the refractive index n of the line a is 2.025, the refractive index n of the line b is 1.950, the refractive index n of the line c is 1.900, the refractive index n of the line d is 2.100, and the linear e is This represents a change in reflectance when the refractive index n is 2.150.

As described above, the material used for the AR film 40 is most preferably a material having a refractive index n of 2.025. However, if the refractive index n is near 2.025, a wavelength of 1460 nm to 1625 nm centering on a wavelength of 1550 nm is used. In the wavelength range, the reflectance can be suppressed to 0.3% or less. As such an optical material, for example, Ta ₂ O ₅ , HfO ₂ or the like can be used.

2 to 4 show an example in which the AR film 40 is a single layer film, the present invention is not limited to this, and the AR film 40 may be formed of two or more layers. FIG. 5 is a cross-sectional explanatory view of the composite etalon element 1 when the AR film 40 is formed in a two-layer film. The AR film 40 in FIG. 5 includes two layers composed of films 40a and 40b formed by laminating materials having _a refractive index n _a (n _a = 1.45) and a refractive index n _b (n _b = 2.10). It is a membrane. The film 40a is formed so that the thickness d _a is n _a d _a = 0.025λ, and the film 40b is formed so that the thickness d _b is n _b d _b = 0.155λ.

  FIG. 6 shows the reflectance characteristics of the AR film 40 thus configured. As shown in FIG. 6, the reflectance characteristic is substantially zero% at the center wavelength of 1550 nm, and is suppressed to 0.02% or less in the wavelength range of about 1460 nm to 1625 nm. Therefore, the reflectance can be suppressed to 0.3% or less in the wavelength range of 1460 nm to 1625 nm even when manufacturing errors are taken into consideration.

FIG. 7 is an explanatory cross-sectional view of the composite etalon element 1 when the AR film 40 is formed of three layers. The AR film 40 in FIG. 7 is made of materials having a refractive index n _a (n _a = 1.45), a refractive index n _b (n _b = 2.10), and a refractive index n _c (n _c = 1.70). It is a three-layer film composed of films 40a, 40b, and 40c formed by stacking. The films 40a, 40b, and 40c are formed such that the thicknesses d _a , d _b , and d _c are n _a d _a = 0.025λ, n _b d _b = 0.155λ, and n _c d _c = 0.50λ, respectively. Has been.

  FIG. 8 shows the reflectance characteristics of the AR film 40 configured as described above. As shown in FIG. 8, the reflectance characteristic is substantially zero% at the center wavelength of 1550 nm, and the reflectance can be suppressed to substantially zero even in the wavelength range of about 1460 nm to 1625 nm. Therefore, the reflectance can be suppressed to 0.3% or less in the wavelength range of 1460 nm to 1625 nm even when manufacturing errors are taken into consideration.

  As described above, by forming the AR film 40 in a single layer or a plurality of layers, a low reflectance can be achieved in a wide wavelength range centering on the wavelength of 1550 nm. In addition, the reflectance can be suppressed to 0.3% or less in a wavelength range of at least about 1460 nm to 1625 nm. In the above embodiment, the AR film 40 has an example of a single-layer, two-layer, or three-layer film configuration, but is not limited to this and may have a four-layer film configuration or more.

  The HR films 31 and 32 are formed by being laminated on the outer side surfaces of the transparent thin plates 10 and 20 by a vacuum deposition method or the like, respectively. Since the composite type etalon element 1 of the present embodiment is configured by laminating transparent thin plates 10 and 20 made of different materials, if the HR films 31 and 32 have the same film configuration, the reflectance differs on each side surface. End up. Therefore, in the composite type etalon element 1 of the present embodiment, the HR films 31 and 32 are formed in different film configurations, and the reflectances on the respective side surfaces are matched.

  Next, FIG. 9 shows optical characteristics (spectral transmittance characteristics) of the composite etalon element 1 in the configuration of FIG. The HR films 31 and 32 both have a reflectance of about 5%. The AR film 40 uses the single layer film shown in FIG. As can be seen from FIG. 9, when the AR film 40 is interposed at the bonding interface, the optical characteristics of the composite etalon element 1 maintain a substantially constant period in proportion to the wavelength, and the maximum and minimum values are uniform. A regular spectral transmission waveform can be obtained. In addition, it is possible to obtain a composite etalon element 1 having local maximum values of approximately 100% and low loss.

  On the other hand, FIG. 10 shows optical characteristics of the composite etalon element 1 when the AR film 40 is not interposed in the composite etalon element 1 of FIG. The HR films 31 and 32 have the same reflectance of about 5%. As apparent from FIG. 10, when the reflection at the bonding interface is as large as about 1.38%, it can be seen from the Fabry-Perot principle that the change in the optical characteristics has an irregular period. That is, in FIG. 10, the absence of the AR film 40 causes reflection at the bonding interface, and the change in optical characteristics is disturbed by this reflection. For this reason, the change in the optical characteristics does not have a constant periodicity, and the maximum value and the minimum value are not uniform, and the composite etalon element 1 generates a loss.

  As described above, in the composite etalon element 1 of this example, the AR film 40 is interposed between the transparent thin plate 10 and the transparent thin plate 20 to reduce reflection at the bonding interface, so that it is approximately proportional to the wavelength. It became possible to obtain optical characteristics having a constant period and to reduce loss.

  FIG. 11 shows optical characteristics when the reflectance of the HR films 31 and 32 is set to about 18% in the composite etalon element 1 of FIG. The AR film 40 uses the single layer film shown in FIG. As described above, even in the case of the composite etalon element 1 having a side reflectance of about 18%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value.

  On the other hand, in the composite etalon element 1 of FIG. 1, the optical characteristics of the composite etalon element 1 when the reflectivity of the HR films 31 and 32 is set to about 18% and the AR film 40 is not interposed are shown in FIG. Indicates. As is apparent from FIG. 12, when the reflection at the interface is large, the change in the optical characteristics has an irregular period, and the maximum value and the minimum value are not uniform, resulting in loss.

  Similarly, FIG. 13 shows optical characteristics when the reflectivity of the HR films 31 and 32 is set to about 36% in the composite etalon element 1 of FIG. The AR film 40 uses the single layer film shown in FIG. As described above, even in the case of the composite type etalon element 1 in which the reflectance of the side surface is about 36%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value.

  On the other hand, in the composite etalon element 1 of FIG. 1, the optical characteristics of the composite etalon element 1 when the reflectivity of the HR films 31 and 32 is set to about 36% and the AR film 40 is not formed are shown in FIG. Indicates. As is apparent from FIG. 14, when the reflection at the interface is large, the change in the optical characteristics has an irregular period, and the maximum value and the minimum value are not uniform, resulting in loss.

  Further, FIG. 15 shows optical characteristics when the reflectivity of the HR films 31 and 32 is set to about 79% in the composite etalon element 1 of FIG. The AR film 40 uses the single layer film shown in FIG. As described above, even in the case of the composite type etalon element 1 having a side surface reflectance of about 79%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value.

  On the other hand, in the composite etalon element 1 of FIG. 1, the optical characteristics of the composite etalon element 1 when the reflectivity of the HR films 31 and 32 is set to about 79% and the AR film 40 is not formed are shown in FIG. Indicates. At first glance, when the reflectivity of the HR films 31 and 32 is increased, it appears that the effect of the antireflection effect of the AR film 40 at the bonding interface on the optical characteristics of the composite etalon element 1 is reduced. However, it is clear from FIG. 16 that the local maximum values are uneven and the periodicity of the wavelength at which the local maximum values are not constant.

  FIG. 17 shows optical characteristics of the composite etalon element 1 when the HR films 31 and 32 are not formed in the composite etalon element 1 of FIG. The AR film 40 uses the single layer film shown in FIG. As can be seen from FIG. 17, when the HR films 31 and 32 are not formed, the change in the optical characteristics is close to a sine wave having a substantially constant regularity, and the maximum value and the minimum value are substantially aligned. However, since the transmittance at all local maximum values is not 100%, a loss of several percent occurs in the light beam that passes through the composite etalon element 1.

  On the other hand, FIG. 18 shows optical characteristics of the composite etalon element 1 when the HR films 31 and 32 are not formed and the AR film 40 is not formed in the composite etalon element 1 of FIG. As can be seen from FIG. 18, when the reflection at the interface is large, the change in the optical characteristics has an irregular period, and the maximum value and the minimum value are not uniform, resulting in loss.

  As described above, the antireflection effect of the AR film 40 at the bonding interface is not affected by the reflectivity of the HR films 31 and 32, but the periodicity of the change in the optical characteristics of the composite etalon element 1 and the wavelength that takes the maximum value. It can be seen that it is extremely effective in ensuring the uniformity of the interval.

  Next, FIG. 19 shows optical characteristics of the composite etalon element 1 when the reflectance of the AR film 40 is about 0.01% and about 0.35% in the composite etalon element 1 of FIG. The reflectivity of the HR films 31 and 32 is set to about 5%. The horizontal axis (wavelength) indicates a range of 1548 nm to 1552 nm, and the vertical axis (transmittance) indicates a range of 50% to 100%. In the figure, lines a and b represent changes in optical characteristics when the reflectance of the AR film 40 is set to about 0.01% and about 0.35%, respectively. FIG. 20 shows optical characteristics of the composite etalon element 1 when the AR film 40 is not formed in the composite etalon element 1 of FIG. The reflectivity of the HR films 31 and 32 is set to about 5% as in FIG.

  19 and 20, when the reflectance at the bonding interface increases, the cycle of the transmitted light amount in the change in the optical characteristics (spectral transmittance) of the composite etalon element 1 is disturbed, and the interval between the wavelengths having the maximum value does not become constant. I understand. Therefore, keeping the reflectance of the AR film 40 low is effective for ensuring the periodicity of the change in optical characteristics of the composite etalon element 1.

  It will be described with reference to FIG. 21 that the reflectivity of the bonding interface affects the periodicity of the wavelength interval at which the maximum value is obtained. 21 shows a change in optical characteristics when the single layer film shown in FIG. 2 is used as the AR film 40 when the reflectivity of the HR films 31 and 32 of the composite etalon element 1 of FIG. (Line a) and changes in optical characteristics (line b) when the AR film 40 is not formed are shown.

In the figure, W _{a1 to} W _a4 represent the wavelength intervals at which the line a has a maximum value, and W _{b1 to} W _b3 represent the wavelength intervals at which the line b has a maximum value. W _{a1 to} W _a4 have a value of about 0.819 nm, and the interval between the maximum values is kept substantially constant. Further, W _{b1 to} W _b3 take values of 0.870 nm, 0.758 nm, and 0.881 nm, respectively, and the interval between the maximum values is not constant. This is presumably because the resonance length of the Fabry-Perot changes depending on the presence or absence of the AR film 40 at the bonding interface, and the interval between the maximum values changes without being kept constant.

  As described above, in the composite etalon element 1 of the present embodiment, the AR film 40 is provided between the transparent thin plate 10 and the transparent thin plate 20, thereby maximizing the transmittance in the transmittance characteristic of the composite etalon element 1. Since the interval between the taking wavelengths is kept constant and optical characteristics that change periodically can be obtained, a certain quality can be ensured regardless of the wavelength (frequency).

Example 2 (combination of SrTiO ₃ and optical glass)
Next, the composite etalon element 1 in the case where SrTiO ₃ which is an optical crystal is used as the transparent thin plate 10 and quartz which is a general optical material is used as the transparent thin plate 20 will be described. Quartz has a refractive index of 1.444. Composite etalon device 1 of this embodiment, the thickness _{D 1} of the transparent body thin plate 10 is 292.27Myuemu, the thickness _{D 2} of the transparent body thin plate 20 are formed on 553.35Myuemu. In the composite etalon element 1 of the present embodiment, the thicknesses D ₁ and D ₂ are not set in consideration of temperature characteristics described later. Further, the composite etalon element 1 of this embodiment also has an FSR of 100 GHz.

FIG. 22 shows the reflectance characteristics of the AR film 40 when SrTiO ₃ and quartz are selected as the transparent thin plates 10 and 20, respectively. The AR film 40 is formed as a single layer film using an optical material having a refractive index n of 1.81 so that the optical film thickness is 0.25λ (λ = 1550 nm). By forming a single-layer film in this way, the reflectance can be reduced to approximately 0% at the center wavelength of 1550 nm. Further, the reflectance can be suppressed to 0.05% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center.

  FIG. 23 shows the reflectance characteristics of the AR film 40 when the AR film 40 has a two-layer structure as in FIG. The AR film 40 uses optical materials having a refractive index of 1.45 and a refractive index of 2.10, and the product of the thickness and the refractive index of each optical material is 0.071λ and 0.103λ (where λ is 1550 nm). It is formed so as to be laminated. By forming the two-layer film in this way, the reflectance can be reduced to approximately 0% at the center wavelength of 1550 nm. Further, the reflectance can be suppressed to 0.08% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center.

  FIG. 24 shows the reflectance characteristics of the AR film 40 when the AR film 40 has a three-layer film structure as in FIG. The AR film 40 uses optical materials having a refractive index of 1.45, a refractive index of 2.10, and a refractive index of 1.38, and the product of the thickness and refractive index of each optical material is 0.071λ, 0.103λ, The layers are laminated so as to be 0.50λ (wherein λ is 1550 nm). By forming the three-layer film in this way, the reflectance can be made substantially zero% at the center wavelength of 1550 nm. Further, the reflectance can be suppressed to 0.03% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center.

Next, FIG. 25 shows optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. The HR films 31 and 32 both have a reflectance of about 5%. The AR film 40 uses the single layer film shown in FIG. As is apparent from FIG. 25, when the AR film 40 is interposed at the bonding interface, the optical characteristics of the composite etalon element 1 maintain a substantially constant period in proportion to the wavelength, and have a maximum value and a minimum value. A regular spectral transmission waveform can be obtained. In addition, it is possible to obtain a composite etalon element 1 having local maximum values of approximately 100% and low loss.

On the other hand, FIG. 26 shows optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. 1 and the AR film 40 is not formed. The HR films 31 and 32 have the same reflectance of about 5%. As is clear from FIG. 26, the change in the optical characteristics has an irregular cycle. That is, in FIG. 26, the change in the optical characteristics does not have a constant periodicity, and the maximum value and the minimum value are not uniform, resulting in loss.

  Thus, also in the composite type etalon element 1 of this embodiment, the AR film 40 is interposed between the transparent thin plate 10 and the transparent thin plate 20 to reduce the reflection at the bonding interface, thereby being proportional to the wavelength. Optical characteristics having a substantially constant period can be obtained, and loss can be reduced.

FIG. 27 shows the optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. The reflectance of the HR films 31 and 32 is set to about 18%. The AR film 40 uses the single layer film shown in FIG. As described above, even in the case of the composite etalon element 1 having a side reflectance of about 18%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value.

On the other hand, FIG. 28 shows optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. 1 and the AR film 40 is not formed. The reflectance of the HR films 31 and 32 is set to about 18%. As is apparent from FIG. 28, when the reflection at the interface is large, the change in the optical characteristics has an irregular period, and the maximum value and the minimum value are not uniform, resulting in loss.

Similarly, FIG. 29 shows the optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. The reflectivity of the HR films 31 and 32 is set to about 36%. The AR film 40 uses the single layer film shown in FIG. As described above, even in the case of the composite type etalon element 1 having a side surface reflectance of about 36%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value.

On the other hand, FIG. 30 shows the optical characteristics of the composite type etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. 1 and the AR film 40 is not formed. The reflectivity of the HR films 31 and 32 is set to about 36%. As is clear from FIG. 30, when the reflection at the interface is large, the change in the optical characteristics has an irregular period, and the maximum value and the minimum value are not uniform, resulting in loss.

Further, FIG. 31 shows optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are respectively used for the transparent thin plates 10 and 20 in the configuration of FIG. The reflectivity of the HR films 31 and 32 is set to about 79%. The AR film 40 uses the single layer film shown in FIG. As described above, even in the case of the composite type etalon element 1 with the side surface reflectance of about 79%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value.

On the other hand, FIG. 32 shows the optical characteristics of the composite etalon element 1 when SrTiO ₃ and quartz are used for the transparent thin plates 10 and 20 in the configuration of FIG. 1 and the AR film 40 is not formed. The reflectivity of the HR films 31 and 32 is set to about 79%. From FIG. 32, it can be seen that even in the case of the composite type etalon element 1 in which the reflectance of the side surface is about 79%, the maximum values are not uniform, and the periodicity of the wavelength at which the maximum values are obtained is not constant.

As described above, even when the composite etalon element 1 is configured by using SrTiO ₃ and quartz for the transparent thin plates 10 and 20, respectively, the antireflection effect of the AR film 40 at the bonding interface is the same as that of the HR films 31 and 32. It can be seen that the composite etalon element 1 is extremely effective in ensuring the periodicity of optical characteristics and the constantness of the maximum value regardless of the reflectivity.

Example 3 (combination of LiCaAlF ₆ and optical glass)
Next, LiCaAlF ₆ (hereinafter referred to as “LiCAF”) which is an optical crystal is used as the transparent thin plate 10, and S-BAH32 (optical glass manufactured by OHARA INC.) Which is an optical glass is used as the transparent thin plate 20. The composite etalon element 1 will be described. The refractive indexes of LiCAF and S-BAH32 are 1.386 and 1.644, respectively. Composite etalon device 1 of this embodiment, the thickness _{D 1} of the transparent body thin plate 10 is 869.15Myuemu, the thickness _{D 2} of the transparent body thin plate 20 are formed on 172.96Myuemu. In the composite etalon element 1 of the present embodiment, the thicknesses D ₁ and D ₂ are not set in consideration of temperature characteristics described later. Further, the composite etalon element 1 of this embodiment also has an FSR of 100 GHz.

  FIG. 33 shows the reflectance characteristics of the AR film 40 when LiCAF and S-BAH32 are selected as the transparent thin plates 10 and 20, respectively. The AR film 40 is formed as a single layer film using an optical material having a refractive index n of 1.51 so that the optical film thickness is 0.25λ (λ = 1550 nm). By forming a single-layer film in this way, the reflectance can be reduced to approximately 0% at the center wavelength of 1550 nm. In addition, the reflectance can be suppressed to 0.01% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center. In the absence of the AR film 40, reflection of about 0.73% occurs.

  FIG. 34 shows the reflectance characteristics of the AR film 40 when the AR film 40 has a two-layer structure as in FIG. The AR film 40 uses an optical material having a refractive index of 2.10 and a refractive index of 1.45, and the product of the thickness and the refractive index of each optical material is 0.025λ and 0.135λ (where λ is 1550 nm). It is formed so as to be laminated. By forming the two-layer film in this way, the reflectance can be reduced to approximately 0% at the center wavelength of 1550 nm. In addition, the reflectance can be suppressed to 0.01% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center.

  FIG. 35 shows the reflectance characteristics of the AR film 40 when the AR film 40 has a three-layer film structure as in FIG. The AR film 40 uses an optical material having a refractive index of 2.10, a refractive index of 1.45, and a refractive index of 1.70, and the product of the thickness and refractive index of each optical material is 0.025λ, 0.135λ, The layers are laminated so as to be 0.50λ (wherein λ is 1550 nm). By forming the three-layer film in this way, the reflectance can be made substantially zero% at the center wavelength of 1550 nm. In addition, the reflectance can be suppressed to 0.01% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center.

Next, FIG. 36 shows optical characteristics of the composite etalon element 1 when LiCAF and S-BAH32 are used for the transparent thin plates 10 and 20 in the configuration of FIG. The AR film 40 uses the single layer film shown in FIG. On the other hand, FIG. 37 shows optical characteristics when the AR film 40 is not formed. Note that the reflectivity of both the HR films 31 and 32 is set to about 5%. As can be seen from FIGS. 36 and 37, when the AR film 40 is interposed at the bonding interface, the optical characteristics of the composite etalon element 1 maintain a substantially constant period proportional to the wavelength, and have a maximum value and a minimum value. It is possible to obtain a regular spectral transmission waveform with a uniform number. In addition, it is possible to obtain a composite etalon element 1 having local maximum values of approximately 100% and low loss. However, when the AR film 40 is not interposed at the bonding interface, the change in the optical characteristics does not have a constant periodicity, and the maximum value and the minimum value are not uniform, resulting in loss.
Thus, also in the composite type etalon element 1 of this embodiment, the AR film 40 is interposed between the transparent thin plate 10 and the transparent thin plate 20 to reduce the reflection at the bonding interface, thereby being proportional to the wavelength. Optical characteristics having a substantially constant period can be obtained, and loss can be reduced.

38 shows the optical characteristics of the composite etalon element 1 when LiCAF and S-BAH32 are used for the transparent thin plates 10 and 20 respectively in the configuration of FIG. 1 and the reflectivity of the HR films 31 and 32 is set to about 80%. Show the characteristics. The AR film 40 uses the single layer film shown in FIG. On the other hand, FIG. 39 shows optical characteristics when the AR film 40 is not formed. The reflectivity of the HR films 31 and 32 is set to about 80% as in FIG. FIG. 40 shows the optical characteristic curves (lines a and b, respectively) in FIGS. 38 and 39 at wavelengths from 1548 nm to 1552 nm.
As can be seen from FIGS. 38 and 39, in the case of the composite etalon element 1 having a side surface reflectance of about 80%, it is possible to obtain high-quality optical characteristics that are regular and have a maximum value and a minimum value. In addition, even when the reflection at the interface is large, it seems that the optical characteristics are such that the change is a regular cycle and the maximum value and the minimum value are aligned.
However, more specifically, from FIG. 40, W _{a1 to} W _a4 take a value of approximately 0.806 nm, and the interval between the maximum values is kept substantially constant, but W _{b1 to} W _b4 are each 0.818 nm. , 0.831 nm, 0.805 nm, and 0.781 nm, and the interval between the maximum values is not constant.

  FIG. 41 shows optical characteristics of the composite etalon element 1 when the HR films 31 and 32 are not formed in the composite etalon element 1 of FIG. The AR film 40 uses the single layer film shown in FIG. On the other hand, FIG. 42 shows optical characteristics when the HR films 31 and 32 are not formed and the AR film 40 is not formed. As can be seen from FIGS. 41 and 42, when the HR films 31 and 32 are not formed, the change in the optical characteristics is close to a sine wave having a substantially constant regularity, and the maximum value and the minimum value are substantially aligned. It becomes. However, since the transmittance at all local maximum values is not 100%, a loss of several percent occurs in the light beam that passes through the composite etalon element 1. In addition, when the reflection at the interface is large, the change in the optical characteristics has an irregular cycle, and the maximum value and the minimum value are not uniform, resulting in loss.

  Next, FIG. 43 shows optical characteristics of the composite type etalon element 1 when the reflectance of the AR film 40 is about 0.01% and about 0.29% in the composite type etalon element 1 of FIG. The reflectivity of the HR films 31 and 32 is set to about 5%. In the figure, lines a and b represent changes in optical characteristics when the reflectance of the AR film 40 is set to about 0.01% and about 0.29%, respectively. FIG. 44 shows optical characteristics of the composite etalon element 1 when the AR film 40 is not formed in the composite etalon element 1 of FIG. The reflectivity of the HR films 31 and 32 is set to about 5% as in FIG.

  In FIG. 43, the line b is slightly shifted from the line a. That is, it can be seen from FIGS. 43 and 44 that when the reflectance at the bonding interface increases, the cycle of the transmitted light amount in the change in the optical characteristics (spectral transmittance) is disturbed, and the interval between the wavelengths having the maximum value is not constant. Therefore, keeping the reflectance of the AR film 40 low is effective for ensuring the periodicity of the change in optical characteristics of the composite etalon element 1.

  As described above, even when the composite etalon element 1 is configured using LiCAF and S-BAH32 for the transparent thin plates 10 and 20, respectively, the antireflection effect of the AR film 40 at the bonding interface is the HR film 31, Regardless of the reflectance of 32, it can be seen that the composite type etalon element 1 is extremely effective in ensuring the periodicity of optical characteristics and the constantness of the maximum value.

Example 4 (combination of LiCaAlF ₆ and optical glass)
The composite etalon element 1 when LiCAF is used as the transparent thin plate 10 and S-FSL5 (optical glass manufactured by OHARA INC.), Which is optical glass, is used as the transparent thin plate 20 will be described. The refractive index of S-FSL5 is 1.473. This example is a combination example of LiCAF (refractive index n = 1.386) and a material having a similar refractive index. That is, the refractive index n was 1.644 in the above-described embodiment (in combination with S-BAH32), but in this example (in combination with S-FSL5), the refractive index n was 1.473, and the refractive index. The difference is 0.087. Moreover, the refractive index of the material of the transparent body thin plate 10 and the transparent body thin plate 20 is a value close | similar compared with another Example.
Composite etalon device 1 of this embodiment, the thickness _{D 1} of the transparent body thin plate 10 is 863.44Myuemu, the thickness _{D 2} of the transparent body thin plate 20 are formed on 198.59Myuemu. In the composite etalon element 1 of the present embodiment, the thicknesses D ₁ and D ₂ are not set in consideration of temperature characteristics described later. Further, the composite etalon element 1 of this embodiment also has an FSR of 100 GHz.

  45 shows the reflectance characteristics of the AR film 40 (line a in the figure) when LiCAF and S-FSL5 are selected as the transparent thin plates 10 and 20, respectively, and the reflectance characteristics when the AR film 40 is not formed (FIG. 45). The middle line b) is shown. The AR film 40 is formed as a single layer film using an optical material having a refractive index n of 1.43 so that the optical film thickness is 0.25λ (λ = 1550 nm). By forming a single layer film in this way, the reflectance can be made substantially zero% at the center wavelength of 1550 nm (see line a in the figure). In addition, the reflectance can be suppressed to 0.01% or less in the wavelength range of about 1460 nm to 1625 nm with the wavelength of 1550 nm as the center. As shown in FIG. 45, even when the AR film 40 is not provided, the reflectance is as low as about 0.09% (see line b in the figure).

  Next, FIG. 46 shows optical characteristics of the composite etalon element 1 when LiCAF and S-FSL5 are used for the transparent thin plates 10 and 20 in the configuration of FIG. The AR film 40 uses the single layer film shown in FIG. On the other hand, FIG. 47 shows optical characteristics when the AR film 40 is not formed. Note that the reflectivity of both the HR films 31 and 32 is set to about 5%. As can be seen from FIGS. 46 and 47, when the AR film 40 is interposed at the bonding interface, the optical characteristics of the composite etalon element 1 maintain a substantially constant period proportional to the wavelength, and have a maximum value and a minimum value. It is possible to obtain a regular spectral transmission waveform with a uniform number. In addition, it is possible to obtain a composite etalon element 1 having local maximum values of approximately 100% and low loss. However, in the case where the AR film 40 is not interposed at the bonding interface, even if the interface reflectance is as small as about 0.09% as shown in FIG. Although the local maximum is approximately 100%, the local minimum does not take a constant value.

48 shows the optical characteristics of the composite etalon element 1 when LiCAF and S-FSL5 are used for the transparent thin plates 10 and 20 in the configuration of FIG. 1 and the reflectivity of the HR films 31 and 32 is set to about 80%. Show properties. The AR film 40 uses the single layer film shown in FIG. On the other hand, FIG. 49 shows optical characteristics when the AR film 40 is not formed. The reflectance of the HR films 31 and 32 is set to about 80% as in the case of FIG. FIG. 50 shows the optical characteristic curves (line a and line b, respectively) of FIGS. 48 and 49 at wavelengths from 1548 nm to 1552 nm.
As can be seen from FIGS. 48 and 49, even in the case of the composite type etalon element 1 in which the reflectance of the side surface is about 80%, it is possible to obtain high-quality optical characteristics with regular and uniform maximum and minimum values. . Even if the AR film 40 is not formed, the waveform of the change in optical characteristics becomes substantially constant and becomes substantially periodic.
More specifically, from FIG. 50, W _{a1 to} W _a4 have a value of approximately 0.806 nm, and the interval between the maximum values is kept substantially constant. Further, W _{b1 to} W _b4 have values of 0.808 nm, 0.801 nm, 0.801 nm, and 0.805 nm, respectively, and the intervals between the maximum values are substantially constant although there are slight variations. As described above, in this embodiment, when the AR film 40 is not interposed, at least the wavelength having the maximum value has a substantially constant periodicity.

  When the composite type etalon element 1 is configured using LiCAF and S-FSL5 for the transparent thin plates 10 and 20, respectively, the reflectance at the bonding interface is 0 due to the close refractive index values of LiCAF and S-FSL5. It is as small as 0.09%. For this reason, even when the AR film 40 is not formed, it is possible to ensure the periodicity of the optical characteristics and the uniformity of the maximum value. Therefore, the AR film 40 is not necessarily required if the transparent thin plates 10 and 20 having close refractive index values are selected so that the degree of reflection at the bonding interface is reduced. In this way, the step of forming the SR film 40 can be omitted, and the manufacturing cost of the composite etalon element 1 can be reduced.

When the AR film 40 is not formed, it is practically desirable to suppress the reflectance at the bonding interface to 0.3% or less. For this purpose, the difference in refractive index may be 0.160 or less. That is, when LiCAF is selected as the transparent thin plate 10, the material selected as the transparent thin plate 20 may be selected from those having a refractive index in the range of 1.226 to 1.546. For example, quartz, S-FPL51, S-FPL52, S-FPL53, quartz, or the like can be selected. In this embodiment, the case where LiCAF is selected as the transparent thin plate 10 has been described. However, the present invention is not limited to this, and SrTiO ₃ or TiO ₂ is selected as the transparent thin plate 10 and the difference in refractive index is 0.160. You may select the transparent thin plate 20 which becomes the following according to these.

  As described above, as shown in Examples 1 to 4, the composite etalon element 1 of the present invention has a configuration in which the transparent thin plates 10 and 20 are bonded together via the AR film 40. The reflection of light incident on the inside of the type etalon element 1 at the bonding interface is reduced. Thus, by suppressing the reflection at the bonding interface to be low, the change in the spectral transmittance of the composite etalon element 1 can be made periodic. Thereby, the maximum value and the minimum value of the change in the spectral transmittance can be made to be substantially constant, and the wavelength interval at which the maximum value is taken can also be made substantially constant. Therefore, the composite etalon element 1 of the present invention can have stable optical characteristics regardless of the wavelength (frequency).

Next, it will be described that the composite etalon element 1 of the present invention has stable optical characteristics (spectral transmittance characteristics) regardless of temperature. When the thickness of the optical material is D and the refractive index of the material is n, the optical distance D ₀ is represented by nD. The change in the optical distance D ₀ when the temperature change occurs is expressed by the following derivative.

となる。 Here, if the linear expansion coefficient α is 1 / D · dD / dt, the equation (1) is

It becomes.

In formula (2), (α + 1 / n · dn / dt) is defined as the characteristic index of the optical material. When this characteristic index is a positive coefficient, the optical distance D ₀ of the optical material increases as the temperature rises. Conversely, when the characteristic index is a negative coefficient, the optical distance D ₀ of the optical material decreases as the temperature rises.

Since the composite type etalon element 1 of the present embodiment has two kinds of optical materials bonded together, the composite type etalon element 1 can be obtained by setting these thicknesses as D ₁ and D ₂ and the refractive indexes as n ₁ and n _2. The optical distance D ₀ is given by the sum of n ₁ D ₁ and n ₂ D ₂ . The temperature change of the optical distance D ₀ of the composite etalon element 1 is expressed by the following equation.

Therefore, in order for the composite etalon element 1 to maintain a constant optical distance regardless of temperature, dD ₀ / dt only needs to be approximated to zero. Therefore, for this purpose, D ₂ should be in the following relationship with D ₁ from Equation (3).

The coefficients corresponding to (α ₁ + 1 / n ₁ · dn ₁ / dt) and (α ₂ + 1 / n ₂ · dn ₂ / dt) are characteristic indexes of the respective materials. As can be seen from equation (4), if the sign of the characteristic index of one optical material is different from the sign of the value of the characteristic index of the other optical material, the thicknesses D ₁ and D ₂ are set to an appropriate thickness ratio. In the composite type etalon element 1, the optical distance D ₀ does not depend on the temperature and is maintained at a constant value.

As an optical material, it is generally known that there are many practical materials having a positive characteristic index, but no practical material having a negative characteristic index is generally known. However, the present inventors have found that there are SrTiO ₃ and TiO ₂ (rutile type) of optical crystals as practical materials having a negative characteristic index. SrTiO ₃ is isotropic and has a refractive index of 2.279 and a characteristic index of -10.516 × 10 ⁻⁶ . TiO ₂ is tetragonal and has a refractive index of 2.453 in the c-axis direction and a characteristic index of −15.807 × 10 ⁻⁶ .

Table 1 shows examples of combinations of optical materials constituting the composite etalon element 1 and the thickness ratios of these optical materials determined based on the refractive index, characteristic index, and equation (4) of these materials. The material having the negative characteristic index shown in Table 1 (material 1 in Table 1, the material having a negative coefficient of the present invention) is the above-mentioned SrTiO ₃ , TiO ₂ (rutile type), LiCAF. On the other hand, the example which combined the material (material 2 of Table 1, the material which has a positive coefficient of this invention) which has a positive characteristic index is shown.

In Table 1, S-TIH53, S-LAH58, S-NSL3, S-FSL5, S-FTM16, S-FPL51, S-FPL52, S-FPL53, S-BAH11, S-BAH12, S-BAH32 are stocks. It is an optical glass made by the company OHARA. Note that TiO ₂ and quartz are set so that light rays are incident in the c-axis direction.

  For example, S-TIH 53 and S-LAH 58 are high refractive materials and are examples in which the overall thickness of the composite etalon element 1 can be reduced. Quartz is an example of a common optical material.

Moreover, it is desirable that the two types of optical materials have values having similar linear expansion coefficients. That is, if the linear expansion coefficient has a close value, it is possible to reduce the possibility that the optical adhesion at the bonding interface is shifted due to the temperature change. For example, the linear expansion coefficient of SrTiO ₃ is 9.0 × 10 ⁻⁶ , whereas S-NSL3, S-FSL5, and S-FTM16 all have a linear expansion coefficient of 9.0 × 10 ^−6. . The linear expansion coefficient of TiO ₂ is about 8.97 × 10 ⁻⁶ .

Moreover, S-FPL51, S-FPL52, and S-FPL53 are low photoelastic materials and are examples that are optically stable materials against external force. The combination of SrTiO ₃ and quartz and the combination of TiO ₂ and quartz are examples of combinations of optical crystals.

Specific examples of the thicknesses of two kinds of bonding materials are shown. In the combination of SrTiO ₃ and S-TIH 53 shown in Example 1, when the FSR is 100 GHz, they can be 238.85 μm and 512.55 μm, respectively (about 0.75 mm as a whole). Further, when the FSR is 50 GHz, they can be 477.69 μm and 1025.09 μm, respectively (about 1.50 mm as a whole). When the FSR is 25 GHz, they can be 955.38 μm and 2050.18 μm, respectively (about 3.01 mm as a whole).

In the combination of SrTiO ₃ and quartz shown in Example 2, when the FSR is 100 GHz, they can be 237.53 μm and 643.36 μm, respectively. When the FSR is 50 GHz, they can be 475.06 μm and 1286.72 μm, respectively. When the FSR is 25 GHz, they can be 950.11 μm and 2573.44 μm (approximately 3.52 mm as a whole), respectively.

Further, in the combination of TiO ₂ and S-BAH11, when the FSR is 100 GHz, respectively, 217.22 μm, 574.66 μm, when the FSR is 50 GHz, respectively, 434.44 μm, 1149.31 μm, and when the FSR is 25 GHz, respectively. 868.88 μm and 2298.62 μm (about 3.17 mm as a whole). In the combination of LiCAF and S-BAH32 shown in Example 3, when the FSR is 100 GHz, 918.42 μm and 131.77 μm, respectively, when the FSR is 50 GHz, 183.83 μm and 263.53 μm, respectively, and the FSR is 25 GHz. In each case, it can be set to 3673.67 μm and 527.07 μm (totally about 4.20 mm).
Thus, when the composite type etalon element 1 in which the FSR of the present invention is set to 25 GHz is compared with the optical element (thickness of about 4.3 mm) using the LiCaAlF ₆ of the conventional example, both are the composite type etalon element of the present invention. It can be seen that the etalon element 1 is further downsized.

FIGS. 51 to 54 are composite etalon elements in the case where SrTiO ₃ and S-TIH 53, SrTiO ₃ and quartz, TiO ₂ and S-BAH 11, LiCAF and S-BAH 32 are selected as combinations of two kinds of materials, respectively. 1 shows a change in center wavelength with respect to a temperature change (hereinafter referred to as temperature stability). It should be noted that the thicknesses of the two materials constituting the composite etalon element 1 are formed so as to satisfy the formula (4).

A line a in FIG. 51 represents the temperature stability of the composite etalon element 1. The line b, c represents the temperature stability of the S-TIH53, SrTiO _3, respectively. From FIG. 51, it can be seen that S-TIH 53 and SrTiO ₃ have the effect of shifting the center wavelength in the positive and negative directions with respect to the temperature change, respectively. And by using these materials and configuring them at an appropriate thickness ratio, the composite etalon element 1 has almost zero change in the center wavelength regardless of the temperature. That is, the change amount with respect to the temperature at the center wavelength (1550 nm) of the composite etalon element 1 can achieve about 0 pm / K.

A line a in FIG. 52 represents the temperature stability of the composite etalon element 1. Lines b and c represent the temperature stability of quartz and SrTiO ₃ , respectively. From FIG. 52, quartz and SrTiO ₃ have the effect of shifting the center wavelength in the positive and negative directions with respect to the temperature change, respectively. By using these materials and configuring them with an appropriate thickness ratio, In the composite type etalon element 1, the amount of change in the center wavelength is almost zero regardless of the temperature.

A line a in FIG. 53 represents the temperature stability of the composite etalon element 1. The line b, c represents the temperature stability of the S-BAH11, TiO _2, respectively. From FIG. 53, S-BAH11 and TiO ₂ have the effect of changing the center wavelength in the positive and negative directions with respect to the temperature change, respectively, and should be configured with an appropriate thickness ratio using these materials. Thus, in the composite type etalon element 1, the change amount of the center wavelength becomes almost zero regardless of the temperature.

Note that the composite type etalon element 1 of this example includes TiO ₂ and crystal that are not isotropic as an optical crystal, but these crystal axes (c-axis) are parallel to the incident direction of the light beam. Has been placed. Even with this arrangement, the composite etalon element 1 can have the change amount of the center wavelength almost zero regardless of the temperature. As described above, since the crystal axis (c-axis) is not inclined with respect to the light beam, the polarization dependence of the composite etalon element 1 can be eliminated.

The composite etalon element 1 may be formed in a state where the crystal axis (c-axis) of TiO ₂ is inclined with respect to the incident direction of the light beam. For example, as shown in Table 1, TiO ₂ has a refractive index of 2.7093 in the a-axis direction and a characteristic index of −22.300 × 10 ⁻⁶ . That is, even when tilted by 90 degrees with respect to the c-axis, TiO ₂ has a negative coefficient of characteristic index. Therefore, by combining the composite etalon element 1 with the thickness ratio shown in Table 1 in combination with the S-LAH58 having a positive characteristic index, the composite etalon element 1 having excellent temperature stability is obtained. Can do.

In addition, the refractive index of TiO _{2 in} an angle direction of 45 degrees with respect to the a axis and the c axis is 2.5686, and the characteristic index is −19.400 × 10 ⁻⁶ . Also in this case, by combining the composite etalon element 1 with the thickness ratio shown in Table 1 in combination with the S-LAH 58 having a positive characteristic index, the composite etalon element 1 having excellent temperature stability is obtained. Obtainable. The composite etalon element 1 configured by tilting the c-axis at a predetermined angle with respect to the incident direction of the light beam is when the incident light is linearly polarized and the direction of vibration of the electric field is in a plane perpendicular to the b-axis of the crystal. It is said. When the TiO ₂ crystal axis direction is inclined, the temperature stability is maintained even when an optical crystal material (for example, quartz) is selected as the other material to be bonded in addition to the S-LAH58 (optical glass). An optical material 1 having excellent properties can be configured.

  A line a in FIG. 54 represents the temperature stability of the composite etalon element 1. Lines b and c represent the temperature stability of S-BAH32 and LiCAF, respectively. From FIG. 54, S-BAH32 and LiCAF have the effect of changing the center wavelength in the positive and negative directions with respect to the temperature change, respectively. In the composite type etalon element 1, the change amount of the center wavelength becomes almost zero regardless of the temperature.

As described above, the inventors have found SrTiO ₃ , TiO ₂ , and LiCAF as practical optical materials having a negative characteristic index. Then, the composite etalon element 1 of the present invention is formed by bonding optical materials having positive and negative characteristic indexes including these materials, and by appropriately setting the thickness ratio thereof, the composite etalon element It became possible to make the optical distance of the light beam passing through 1 constant regardless of the temperature. Thus, the composite type etalon element 1 of the present invention can be extremely excellent in temperature stability.

  Even when an optical crystal that is not isotropic is used as the optical material for the transparent thin plate, the composite etalon element 1 can be formed without tilting the crystal axis. Therefore, even when an optical crystal that is not isotropic is used, the amount of change in the center wavelength can be set to approximately 0 pm / K regardless of the temperature. Therefore, the composite type etalon element 1 having very little polarization dependence can be obtained. Obtainable.

  Further, in the above embodiment, the composite etalon element 1 is configured by bonding two types of optical materials of the transparent thin plates 10 and 20, but not limited to this, bonding of three or more types of optical materials is performed. You may comprise by. In this case, an AR film 40 is formed between adjacent transparent thin plates, and the ratio of the thicknesses is set so that the sum of the product of the thickness and the refractive index of each transparent thin plate is constant regardless of the temperature. Should be set.

Next, a laser module 50 for high-density wavelength division multiplexing (DWDM) communication as a laser apparatus using the composite etalon element 1 will be described. FIG. 55 shows a schematic configuration diagram of the laser module 50. In the laser module 50, the laser light emitted from the rear end face of the LD 54 serving as the laser light emitting part is incident on the half mirror 53 serving as the branching part and branched in two directions, one of which is directly applied to the PD 51 serving as the intensity detecting part. The other is used as an optical output monitor, and the other is transmitted through the composite etalon element 1 and then combined with a PD 52 as a wavelength detection unit to be used as a wavelength monitor. The PD 51 detects the intensity of the received laser beam. Further, the PD 52 detects the intensity of laser light having a predetermined wavelength that is selectively transmitted through the composite etalon element 1.
Further, the laser light emitted from the front end surface is transmitted through the lens 56 and output to the outside. Output signals from the PDs 51 and 52 are output to a control device (not shown), and the control device controls the power to the Peltier element 55 based on the output signals, thereby holding the LD 54 at a predetermined temperature. A prism may be used instead of the half mirror 53.

  Since the composite etalon element 1 of the present invention is excellent in temperature stability as described above, it is not necessary to provide a dedicated Peltier element for the composite etalon element 1, and power consumption for driving the Peltier element The amount is reduced. Accordingly, the configuration of the laser module 50 is simplified, and the manufacturing cost can be reduced. Even if an air gap type etalon element is used, there is a case where it is not necessary to dispose a Peltier element. However, since the air gap type etalon element is large in size, the size of the laser module 50 itself is increased. There was an inconvenience. Further, since the composite etalon element 1 of the present invention has a feature that the size is smaller than the conventional composite etalon element, the laser module 50 can be further downsized.

  In the above embodiment, the example in which the composite type etalon element 1 of the present invention is used in the laser module 50 for DWDM communication is shown. However, the present invention is not limited to this and can be used in a laser device such as a wavelength locker.

3 is a cross-sectional explanatory view of a composite etalon element having a single-layer antireflection film of Example 1. FIG. 3 is a graph showing spectral reflectance characteristics of a single-layer antireflection film of Example 1. FIG. FIG. 3 is an enlarged view of FIG. 2. 3 is a graph showing spectral reflectance characteristics of a single-layer antireflection film of Example 1. FIG. FIG. 3 is a cross-sectional explanatory view of a composite etalon element having two antireflection films of Example 1. 6 is a graph showing the spectral reflectance characteristics of the two-layer antireflection film of Example 1. 3 is a cross-sectional explanatory view of a composite etalon element having a three-layer antireflection film of Example 1. FIG. 3 is a graph showing spectral reflectance characteristics of the three-layer antireflection film of Example 1. FIG. 6 is a graph showing spectral transmittance characteristics of the composite etalon element of Example 1 (HR film reflectance 5%). FIG. 10 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 9. 6 is a graph showing spectral transmittance characteristics of the composite etalon element of Example 1 (HR film reflectance 18%). FIG. 12 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 11. 6 is a graph showing the spectral transmittance characteristics of the composite etalon element of Example 1 (HR film reflectance 36%). It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. 6 is a graph showing the spectral transmittance characteristics of the composite etalon element of Example 1 (HR film reflectance 79%). 16 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 6 is a graph showing spectral transmittance characteristics of the composite etalon element (no HR film) of Example 1. It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. It is a graph showing the spectral transmittance characteristic at the time of making the reflectance of the antireflection film of Example 1 different. FIG. 20 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 19. 4 is a graph showing spectral transmittance characteristics when an antireflection film is formed and when an antireflection film is not formed in the composite etalon element of Example 1 (reflectance of HR film 79%). 6 is a graph showing spectral reflectance characteristics of a single-layer antireflection film of Example 2. 6 is a graph showing the spectral reflectance characteristics of the two-layer antireflection film of Example 2. 6 is a graph showing spectral reflectance characteristics of a three-layer antireflection film of Example 2. 6 is a graph showing the spectral transmittance characteristics of the composite etalon element of Example 2 (HR film reflectance 5%). FIG. 26 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 25. 6 is a graph showing spectral transmittance characteristics of a composite type etalon element of Example 2 (HR film reflectance 18%). It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. 6 is a graph showing spectral transmittance characteristics of a composite type etalon element of Example 2 (HR film reflectance 36%). It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. 6 is a graph showing spectral transmittance characteristics of a composite type etalon element of Example 2 (HR film reflectance 79%). FIG. 32 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 31. 6 is a graph showing spectral reflectance characteristics of a single-layer antireflection film of Example 3. 10 is a graph showing the spectral reflectance characteristics of the two-layer antireflection film of Example 3. 6 is a graph showing the spectral reflectance characteristics of the three-layer antireflection film of Example 3. 10 is a graph showing the spectral transmittance characteristics of the composite etalon element of Example 3 (HR film reflectance 5%). FIG. 37 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 36. 6 is a graph showing spectral transmittance characteristics of a composite etalon element of Example 3 (HR film reflectance 80%). It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. 6 is a graph showing spectral transmittance characteristics when an antireflection film is formed and when an antireflection film is not formed in the composite type etalon element of Example 3 (HR film reflectance 80%). 6 is a graph showing spectral transmittance characteristics of a composite etalon element (no HR film) of Example 3. It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. It is a graph showing the spectral transmittance characteristic at the time of making the reflectance of the antireflection film of Example 3 different. 44 is a graph showing spectral transmittance characteristics when an antireflection film is not formed in FIG. 6 is a graph showing spectral reflectance characteristics of a single-layer antireflection film of Example 4. 6 is a graph showing spectral transmittance characteristics of a composite etalon element of Example 4 (HR film reflectance 5%). It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. 10 is a graph showing the spectral transmittance characteristics of the composite etalon element of Example 4 (HR film reflectance 80%). It is a graph showing the spectral transmittance characteristic when not forming an antireflection film in FIG. 6 is a graph showing spectral transmittance characteristics when an antireflection film is formed and when an antireflection film is not formed in the composite etalon element of Example 4 (HR film reflectance 80%). It is a graph showing the temperature characteristic of the composite type etalon element of an Example. It is a graph showing the temperature characteristic of the composite type etalon element of an Example. It is a graph showing the temperature characteristic of the composite type etalon element of an Example. It is a graph showing the temperature characteristic of the composite type etalon element of an Example. It is a block diagram of the laser module of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Composite type etalon element, 2 transparent body, 10,20 transparent body thin plate, 31, 32 HR film, 40 AR film, 40a, 40b, 40c film, 50 laser module, 51, 52 PD, 53 half mirror, 54 LD, 55 Peltier element, 56 a _{lens, d a, d b, d} c _{thickness, W a4} to _{W a4, W b3} to _{W b4} interval

Claims (12)

In a composite type etalon element having a reflection film on the incident surface and the emission surface of the transparent body and utilizing multiple reflection of light inside the transparent body,
The transparent body is formed by laminating a plurality of transparent thin plates from the incident surface to the output surface,
The composite etalon element, wherein the transparent thin plate is joined to an adjacent transparent thin plate through an antireflection film.   2. The composite etalon device according to claim 1, wherein the antireflection film has a reflectance set to 0.3% or less with respect to light having a wavelength to be used.   The composite etalon device according to claim 1, wherein the antireflection film includes a single layer or a plurality of layers.   2. The composite mold according to claim 1, wherein the antireflection film is formed by being laminated on one of adjacent transparent thin plates, and is bonded to the other of the adjacent transparent thin plates by optical adhesion. Etalon element. In a composite type etalon element having a reflection film on the incident surface and the emission surface of the transparent body and utilizing multiple reflection of light inside the transparent body,
The transparent body is formed by laminating a plurality of transparent thin plates from the incident surface to the output surface,
The composite thin etalon element, wherein the transparent thin plate has a refractive index difference between adjacent transparent thin plates of 0.160 or less.   6. The composite type etalon element according to claim 1, wherein the transparent body is such that the sum of the product of the thickness of each transparent body thin plate and the refractive index is approximately invariant with respect to temperature change. The transparent body includes a transparent thin plate having a positive coefficient in which the product of the thickness and the refractive index increases with temperature change, and a transparent body having a negative coefficient in which the product of the thickness and the refractive index decreases with temperature change. Made of thin plate,
The ratio of the thickness of the transparent thin plate having the positive and negative coefficients was set so that the sum of the product of the thickness and the refractive index of each transparent thin plate was kept approximately unchanged with respect to the temperature change. 6. The composite etalon element according to claim 1, wherein the composite etalon element is characterized. The composite etalon device according to claim 7, wherein the transparent thin plate having a negative coefficient is made of any one of SrTiO ₃ , TiO ₂ , and LiCaAlF ₆ .   The composite etalon element according to claim 1, wherein the transparent body includes a transparent thin plate made of optical glass and a transparent thin plate made of optical crystal.   The composite etalon element according to claim 1, wherein the transparent body is a transparent thin plate made of an optical crystal.   The direction of the optical crystal axis of the transparent thin plate made of the optical crystal is such that the total of the product of the thickness and refractive index of the transparent thin plate is kept approximately unchanged with respect to temperature change. 11. The composite etalon device according to claim 9, wherein the composite etalon device is set to form a predetermined angle with respect to a direction from the incident surface toward the reflection surface.   A branching unit that branches the incident laser beam in two directions, an intensity detection unit that receives the laser beam branched in one direction at the branching unit and detects the intensity of the laser beam, and another direction in the spectroscopic unit 12. The composite etalon device according to claim 1, which selectively transmits laser light having a predetermined wavelength among the laser light branched into the laser beam, and a laser having a predetermined wavelength transmitted through the composite etalon device. A laser device comprising: a wavelength detector that receives light and detects the intensity of the laser beam having the predetermined wavelength.

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