JP5936910B2 - Etalon filter and method for producing etalon - Google Patents

Description

  The present invention relates to an etalon used in a laser system or an optical communication system and a method for manufacturing the etalon.

  A composite type etalon having a light-transmitting part configured by bonding two or more light-transmitting bodies is known (for example, Patent Document 1). In this composite etalon, one surface of the translucent part is an incident surface, the other surface is an exit surface, and a reflective film is formed on the entrance surface and the exit surface. In Patent Document 1, an antireflection film is provided between two light-transmitting bodies to be bonded together, and the reflection between the light-transmitting bodies is suppressed, whereby the waveform of the spectrum of the intensity of light transmitted through the etalon (transmission waveform). It is supposed that the maximum value and the minimum value are aligned.

JP 2005-10734 A

  The antireflection film is composed of a multilayer film, and by design of the material (refractive index) and thickness of each film, and the number of layers of the multilayer film, the reflectivity is almost as close to 0 in design. Become. However, in practice, the reflectivity does not become zero due to variations in film thickness and refractive index during manufacture. For example, reflection of about 0.2% occurs. As a result, the transmission waveform of the etalon may be disturbed.

  An object of the present invention is to provide an etalon that can suppress the influence of reflection on an interface located between a pair of reflecting films on optical characteristics, and a method for manufacturing the etalon.

  An etalon according to one embodiment of the present invention includes a first light-transmitting body having a first outer surface that constitutes one of an incident surface and an output surface, and a first inner surface on the back surface, and the other of the incident surface and the output surface. And a second inner surface on the back surface thereof, the second inner surface is opposed to the first inner surface, and the second outer surface is parallel to the first outer surface. A second light-transmitting body, a first reflective film that covers the first outer surface, and a second reflective film that covers the second outer surface, the first inner surface and the second inner surface At least one is comprised including the surface which inclines with respect to the said 1st outer surface and the said 2nd outer surface.

  Preferably, the first inner surface and the second inner surface are bonded together.

  Preferably, the first light transmitting body has a positive change in optical path length due to a temperature change, and the second light transmitting body has a negative change in optical path length due to a temperature change.

  Preferably, it has a first intermediate surface and a second intermediate surface behind the first intermediate surface, the first intermediate surface and the second intermediate surface are parallel to each other, and the first intermediate surface is opposed to the first inner surface. The second intermediate surface further includes a third light transmitting body facing the second inner surface, and the first inner surface and the second inner surface are parallel to each other, The second light transmitting body is made of the same material.

  Preferably, the first intermediate surface and the first inner side surface are bonded together, and the second intermediate surface and the second inner side surface are bonded together.

  Preferably, the first light-transmitting body and the second light-transmitting body have a positive or negative change in optical path length due to a temperature change, and the third light-transmitting body has a change in optical path length due to a temperature change. Is the other of positive and negative.

  Preferably, the first inner surface and the second inner surface oppose each other via a gap.

  The manufacturing method of the etalon which concerns on 1 aspect of this invention WHEREIN: The 1st mother board | substrate which has the 1st outer main surface and the 1st inner main surface of the back surface, the 2nd outer main surface, and the 2nd inner main surface of the back surface. A second mother board, and a third mother board having a first intermediate main surface bonded to the first inner main surface and a second intermediate main surface bonded to the second inner main surface, The first outer main surface and the second outer main surface are parallel to each other, and the first inner main surface, the first intermediate main surface, the second intermediate main surface, and the second inner main surface are parallel to each other. A step of forming a laminated substrate; and a step of dividing the laminated substrate in plan view. In the step of forming the laminated substrate, the first inner main surface, the first intermediate main surface, the second The intermediate main surface and the second inner main surface are inclined with respect to the first outer main surface and the second outer main surface. Forming the multilayer substrate formed by a surface, the step of dividing, the inclined surface is divided.

  According to said structure or procedure, the influence which the reflection in the interface located between a pair of reflecting films has on an optical characteristic can be suppressed.

1 is a schematic side view of an etalon according to a first embodiment of the present invention. The figure which shows typically the transmission characteristic of an etalon. The typical side view of the etalon which concerns on the 2nd Embodiment of this invention. 4 (a) to 4 (c) are diagrams showing a procedure of the manufacturing method of the etalon of FIG. Fig.5 (a)-FIG.5 (c) are figures which show the continuation of FIG.4 (c). The typical side view of the etalon which concerns on the 3rd Embodiment of this invention. The block diagram which shows the application example of the etalon of FIG. The figure which shows the modification of the inner surface of an etalon.

<First Embodiment>
(Composition of etalon)
FIG. 1 is a side view schematically showing an etalon 1 according to the first embodiment of the present invention.

  The etalon is provided on the translucent part 3 having the first outer surface 51A and the second outer surface 51B parallel to each other, the first reflective film 5A provided on the first outer surface 51A, and the second outer surface 51B. A second reflective film 5B.

  In the following, “first”, “A”, etc. may be omitted for the configurations given “first”, “A”, etc. For example, the first outer surface 51A and the second outer surface 51B are simply referred to as the “outer surface 51” and may not be distinguished from each other.

  One of the pair of outer surfaces 51 (first outer surface 51A in the example of FIG. 1) constitutes an incident surface of the light Lt, and the other (second outer surface 51B in the example of FIG. 1) emits the light Lt. Configure the surface. The light Lt incident on the light transmitting part 3 is repeatedly reflected between the pair of reflecting films 5, and only light having a predetermined frequency defined by the optical path length of the light transmitting part 3 is emitted. The optical path length is represented by nd when light passes through a medium having a refractive index n by a distance d. Although FIG. 1 illustrates the case where the light Lt is incident on the incident surface perpendicularly, the light Lt may be incident on the incident surface obliquely.

  The translucent part 3 includes a first translucent body 7A and a second translucent body 7B bonded to the first translucent body 7A.

  The first translucent body 7A has the first outer side surface 51A described above and the first inner side surface 55A serving as the back surface thereof. The 2nd translucent body 7B has the 2nd outer surface 51B mentioned above and the 2nd inner surface 55B used as the back surface. The first inner side surface 55A and the second inner side surface 55B are joined to face each other.

  Each translucent body 7 has, for example, a trapezoidal side surface, and in each translucent body 7, the inner side surface 55 is inclined with respect to the outer side surface 51 at an inclination angle θ. As is clear from the fact that the outer side surfaces 51 are parallel to each other and the inner side surfaces 55 are joined together, the inclination angle θ is the same in the first light transmitting body 7A and the second light transmitting body 7B. In addition, the shape (planar shape of the outer surface 51 and the inner surface 55) of each light-transmitting body 7 viewed in the transmission direction of the light Lt may be an appropriate shape such as a rectangle or a circle.

  Since the inner side surface 55 is inclined with respect to the outer side surface 51, the reflected light Lt ′ reflected on the inner side surface 55 proceeds in a direction inclined with respect to the normal of the outer side surface 51. Accordingly, the reflected light Lt ′ diverges without being resonated between the pair of reflecting films 5. For example, in the example of FIG. 1, the reflected light Lt ′ is emitted to the outside of the etalon 1 from the upper surface of the etalon 1. As a result, the influence of the reflected light Lt ′ on the characteristics of the etalon 1 is suppressed.

  For example, when the light Lt is incident on the first outer side surface 51A perpendicularly, the light transmitted through the inner side surface 55 is refracted at the inner side surface 55, so that the light emitted from the etalon 1 is second The light is emitted in a direction inclined at an angle α with respect to the normal of the outer side surface 51B. Accordingly, the etalon 1 and the optical elements before and after the etalon 1 are arranged in consideration of this angle α (refraction at the inner side surface 55).

  The inclination angle θ only needs to be somewhat larger than 0 °. If it is somewhat larger, the influence of the reflected light Lt ′ is suppressed as compared with the prior art. In addition, since the processing accuracy of the parallelism of the entrance and exit surfaces of the etalon is usually in units of seconds (for example, 10 seconds to 30 seconds), if the inclination angle θ is 1 minute or more, the inner surface 55 is intentionally removed. It can be estimated that the side surface 51 is inclined (the present invention is used).

  Further, the inclination angle θ is preferably 0.1 ° or more and 0.5 ° or less. If the angle is 0.1 ° or more, the above-described effect of diverging the light Lt ′ is sufficiently obtained. On the other hand, when the angle is 0.5 ° or less, the deterioration of the characteristics due to the change in the optical path length nd according to the position of the etalon 1 described later is sufficiently small.

  The thickness and the like of the translucent body 7 may be appropriately set according to desired optical characteristics, and are, for example, 100 μm to 2 mm. The surface roughness and parallelism of each surface may be appropriately set according to desired optical characteristics and the accuracy thereof. For example, the surface roughness is less than 1 nm and the parallelism is less than 1 minute. Such a minute surface roughness and high-precision parallelism can be obtained by optical polishing of each surface, for example.

One of the pair of translucent bodies 7 (referred to as the first translucent body 7A in the present embodiment) is formed of a material whose change in optical path length with respect to a temperature change is positive (characteristic index is positive), and the other ( In the present embodiment, the second light-transmitting body 7B is formed of a material whose change in optical path length with respect to temperature change is negative (characteristic index is negative). In FIG. 1, a material having a positive characteristic index is located on the incident side and a material having a negative characteristic index is located on the outgoing side. However, the relationship between the incident and outgoing and the positive / negative of the characteristic index is opposite to that in FIG. May be. An example of the material having a positive characteristic index is quartz (SiO ₂ ). An example of a material having a negative characteristic index is strontium titanate (SrTiO ₃ ).

  The first inner surface 55A and the second inner surface 55B are preferably joined by a method that does not use an organic adhesive such as optical contact or atomic diffusion bonding. This is because the variation in the thickness of several microns of the organic adhesive causes a specific decrease or variation in the etalon such as FSR, extinction ratio, wavelength temperature characteristics, and the like.

  An antireflection film (not shown) may be interposed between the first inner side surface 55A and the second inner side surface 55B. The antireflection film may have the same configuration as a known one. That is, the antireflection film is formed so that the optical path length is close to or coincides with a quarter wavelength of the light transmitted through the etalon 1, and more preferably, the refractive index of the antireflection film is on both sides of the antireflection film. It is formed so as to be close to or coincident with the geometric mean of the refractive index of the positioned medium (in this embodiment, the first light transmitting body 7A and the second light transmitting body 7B). Further, the antireflection film may be composed of, for example, a multilayer film made of the same material as that of the reflective film 5 described in detail later. In addition, the optical path length and refractive index of each medium may be those appropriately set within the range of the assumed operating temperature of the etalon 1.

The reflective film 5 is configured, for example, by laminating a plurality of thin films 6 having different refractive indexes. The plurality of thin films 6 are made of, for example, a dielectric. The dielectric is, for example, silicon dioxide (SiO ₂ ), titanium dioxide (TiO ₂ ), or tantalum pentoxide (Ta ₂ O ₅ ). The materials, the number of layers, and the thickness of the plurality of thin films 6 are designed so that desired optical characteristics (for example, reflectance) can be obtained. The thickness of each thin film 6 is, for example, about submicron, and the number of stacked thin films 6 is, for example, 10 or less. The plurality of thin films 6 are fixed in close contact with each other, and the reflective film 5 is fixed in close contact with the light transmitting body 7.

FIG. 2 is a diagram schematically showing the transmission characteristics of the etalon 1. In FIG. 2, the horizontal axis indicates the wavelength λ, and the vertical axis indicates the transmission coefficient T. The transmission coefficient T is a ratio I _out / I _in between the intensity I _in of the light Lt before being incident on the etalon and the intensity I _out after being emitted from the etalon.

As already described, the light Lt incident on the etalon 1 is repeatedly reflected between the pair of reflective films 5 and emitted from the etalon 1. Therefore, in the etalon 1, the transmission coefficient T periodically increases at the m-th order peak wavelength λ _m (peak frequency ν _m ). In general, the FSR is expressed by the interval (ν _m −ν _{m + 1} ) of the peak frequency ν _m , but in FIG. 2, the FSR is shown between the peak wavelengths for the purpose of helping understanding.

The FSR is schematically represented by the following equation (1) using the optical path length nd of a medium sandwiched between a pair of reflective films.
FSR = c / (2nd cos θ) (1)
Where c is the speed of light, n is the refractive index of the medium, d is the thickness of the medium, and θ is the refraction angle of the light in the medium.

When the medium sandwiched between the pair of reflective films is composed of a plurality of media i, the optical path length nd is expressed by the following equation (2).
nd = Σn _i d _i (2)
Here, n _i and d _i are the refractive index and thickness of the medium i.

In the etalon 1, since the medium sandwiched between the pair of reflective films 5 is the first light transmitting body 7A and the second light transmitting body 7B, the optical path length of each light transmitting body 7 is defined as n ₁ d ₁ , n Assuming ₂ d ₂ , the optical path length nd is expressed by the following equation (3).
nd = n ₁ d ₁ + n ₂ d ₂ (3)
In the case where an antireflection film is interposed between the pair of light transmitting bodies 7, the optical path length of the antireflection film may be taken into consideration.

  Here, one of the first light-transmitting body 7A and the second light-transmitting body 7B has a positive change in the optical path length with respect to the temperature change, and the other has a negative change in the optical path length with respect to the temperature change. The change in length is canceled out at least partially between the pair of light transmitting bodies 7, and the change in the optical path length nd is suppressed in the entire light transmitting part 3. As a result, the temperature change of the FSR due to the temperature change is suppressed.

Preferably, the pair of light-transmitting bodies 7 is made of a material (refractive index) selected so that changes in the optical path length due to temperature changes are substantially canceled out (so that the absolute values of the changes are approximately equal). And the thickness is set. That is, when it is assumed that the length of the optical path length resulting from the temperature change is expressed by a linear function, the pair of light-transmitting bodies 7 is made of a material (refracted so that the following expression (4) is generally satisfied. Rate) and thickness are set.
Σγ _i n _i d _i = 0 (4)
Where n _i and d _i are the refractive index and thickness of the medium i (translucent member 7) located between the pair of reflective films at a predetermined reference temperature, and γ _i n _i d _i is when the temperature changes by 1 ° C. the amount of change in optical path length _{n i d} i, _γ i is the temperature coefficient of the optical path length _n i _{d i.}

Specifically, in the etalon 1, since the medium sandwiched between the pair of reflective films 5 is the first light transmitting body 7A and the second light transmitting body 7B, the expression (4) is expressed by the following expression (5 ).
γ ₁ n ₁ d ₁ + γ ₂ n ₂ d ₂ = 0 (5)
_One of γ ₁ and γ ₂ is positive and the other is negative.

  As described above, the material (refractive index) is selected and the thickness of each light-transmitting body 7 is set so that the expression (1) is satisfied for the desired FSR and the expression (4) is satisfied. The

In the etalon 1, since the inner side surface 55 is inclined with respect to the outer side surface 51, the thicknesses d ₁ and d ₂ of the translucent body 7 are in the direction along the outer side surface 51 (up and down direction in FIG. 1). It depends on the position. In designing, an appropriate representative value may be used, for example, using d ₁ and d ₂ at the center of the optical path.

If the inclination angle θ is too large, the change in d ₁ and d ₂ depending on the position becomes large, and as a result, the characteristics of the etalon 1 deteriorate. However, as described above, when the inclination angle θ is 0.5 ° or less, the deterioration of the characteristics of the etalon 1 is sufficiently small.

  The manufacturing method of the etalon 1 may be substantially the same as the manufacturing method of a known composite type etalon. For example, the inner surface 55 (or the outer surface 51) is inclined with respect to the outer surface 51 so that the inner surface 55 is inclined with respect to the outer surface 51 when each light-transmitting body 7 is formed. It may be realized by polishing, or may be realized by polishing the outer surface 51 so that the inner surface 55 is inclined with respect to the outer surface 51 in the light-transmitting portion 3 after being bonded.

(Example)
The etalon according to the example was manufactured under the following conditions, and the influence of the reflected light was investigated.
First translucent body 7A:
Material: Crystal Z plate (refractive index 1.52)
Thickness: 1.5mm
Second translucent body 7B
Material: Strontium titanate (refractive index 2.28)
Thickness: 0.3mm
Inclination angle θ: 0.1 °
Reflectivity of the reflective film 5: 50%
Bonding method of inner side surface 55: optical contact (before bonding, excimer light was applied to inner side surface 55 in order to improve the bonding strength).
Incident light: Incident perpendicular to the incident surface FSR: 50 GHz

  The reflectance at the inner side surface 55 is about 4% due to the difference in refractive index between the first light transmitting body 7A and the second light transmitting body 7B. Therefore, when the inclination angle θ is 0 °, about 4% of the reflected light affects the characteristics of the etalon, and as a result, the transmission waveform is disturbed. However, when the tilt angle θ is 0.1 °, the reflected light affecting the characteristics of the etalon is reduced to 0.04%. That is, an effect equivalent to the reflectance of 0.04% was obtained. As in the example shown in FIG. 2, a periodic transmission waveform was obtained. The angle α of the emitted light was 0.08 °.

<Second Embodiment>
FIG. 3 is a side view schematically showing the etalon 201 according to the second embodiment.

  The etalon 201 is different from the translucent part 3 of the etalon 1 of the first embodiment in the configuration of the translucent part 203. The other configuration of the etalon 201 is the same as that of the etalon 1 of the first embodiment. However, the specific material, film thickness, and the like of the reflective film 5 may be appropriately set according to the difference in the configuration of the light transmitting portion 203.

  In the translucent part 3 of the first embodiment, the first translucent body 7A and the second translucent body 7B are joined, whereas in the translucent part 203 of the present embodiment, the first translucent part 7A is joined. A third light transmitting body 207C is interposed between the body 207A and the second light transmitting body 207B.

  The shapes (excluding dimensions) in the side view of the first light transmitting body 207A and the second light transmitting body 207B are the same as those of the first light transmitting body 7A and the second light transmitting body 7B in the first embodiment. That is, each of the first light transmitting body 207 </ b> A and the second light transmitting body 207 </ b> B is formed in a trapezoidal shape, and has an outer surface 51 and an inner surface 55 that is inclined with respect to the outer surface 51.

  The third light transmitting body 207C has a first intermediate surface 57A and a second intermediate surface 57B that are parallel to each other, for example, in a side view. The first intermediate surface 57A is joined to the first inner surface 55A, and the second intermediate surface 57B is joined to the second inner surface 55B. It is preferable that the bonding be performed by a method that does not use an organic adhesive such as an optical contact, or that an antireflection film may be interposed between the bonding surfaces in order to improve the transmittance. This is the same as the embodiment.

  As is clear from the pair of intermediate surfaces 57 being parallel to each other, the pair of inner surfaces 55 are also parallel to each other. Similarly to the first embodiment, the pair of outer side surfaces 51 are parallel to each other, and the inclination angle θ is the same for the first light transmitting body 207A and the second light transmitting body 207B.

  In the present embodiment, the first light transmitting body 207A and the second light transmitting body 207B are formed of the same material. The first light transmitting body 207A and the second light transmitting body 207B are formed of a material whose optical path length change due to temperature change is one of positive and negative (in this embodiment, positive), and the third light transmitting body The body 207C is made of a material whose optical path length change due to temperature change is the other of positive and negative (in this embodiment, negative).

  In the same way as in the first embodiment, the three translucent bodies 207 are selected for their materials (refractive index) and set in thickness so that the expressions (1) and (4) are satisfied.

However, since the first light transmitting body 207A and the second light transmitting body 207B are formed of the same material, they correspond to the first light transmitting body 207A, the second light transmitting body 207B, and the third light transmitting body 207C. Assuming that the subscripts are 1, 2 and 3, respectively, the optical path length nd (Equation (2)) of the entire translucent portion 203 is expressed by the following Equation (6).
nd = n ₁ (d ₁ + d ₂ ) + n ₃ d ₃ (6)
Moreover, (4) Formula becomes like the following (7) Formula.
γ ₁ n ₁ (d ₁ + d ₂ ) + γ ₃ n ₃ d ₃ = 0 (7)

  According to the second embodiment described above, first, since the inner surface 55 (intermediate surface 57) is inclined with respect to the outer surface 51, the same effects as those of the first embodiment are exhibited. That is, since the reflected light Lt ′ travels in a direction inclined with respect to the normal of the outer surface 51, the reflected light Lt ′ diverges without being resonated between the pair of reflective films 5, and the influence of the reflected light Lt ′ on the characteristics of the etalon 201 Is reduced. In FIG. 3, the reflected light Lt ′ generated by reflecting the light transmitted through the first light transmitting body 207A at the interface between the first light transmitting body 207A and the third light transmitting body 207C, and the third light transmitting body. The two reflected lights Lt ′ of the reflected light Lt ′ generated by reflecting the light transmitted through the body 207C at the interface between the third transparent body 207C and the second transparent body 207B are shown.

Further, since the third light transmitting body 207C having the parallel intermediate surface 57 is interposed between the first light transmitting body 207A and the second light transmitting body 207B, unlike the first embodiment. Further, there is no characteristic deterioration caused by the change of d ₁ and d ₂ depending on the position along the outer side surface 51 (up and down direction in FIG. 3). That is, since d ₁ + d ₂ and d ₃ are constant regardless of the position, nd in the equation (6) is constant, and hence the FSR in the equation (1) is also constant. Also, equation (7) is satisfied regardless of the position.

  For the above reason, the upper limit of the preferable range of the inclination angle θ is also larger than that in the first embodiment. Although the inclination angle θ is not limited to an upper limit in terms of optical characteristics, it is practically 3 ° or less from the viewpoint of mounting defects caused by an inclined polishing process and a large light shift amount t. Is preferred.

Further, if d ₁ + d ₂ is constant, the ratio of d ₁ and d ₂ does not affect the expressions (1) and (7), and therefore will be described later with reference to FIG. As described above, it is possible to employ an efficient method of manufacturing the etalon 201 by cutting the etalon 201 from the mother substrate (wafer).

  Since the light Lt incident on the etalon 201 is refracted in the opposite directions on the first inner side surface 55A and the second inner side surface 55B, the light (light beam) emitted from the second outer side surface 51B is not With respect to the light incident on the side surface 51A, the light is emitted in parallel with a predetermined shift amount t. For example, the thickness of the third light transmitting body 207C is 0.3 mm, the refractive index of the third light transmitting body 207C is 2.28, the refractive index of the light transmitting body 207 on both sides thereof is 1.52, and the tilt angle θ is 0.1. Assuming 1 °, the shift amount t is 0.0003 mm. The amount of deviation is so small that it does not cause a problem when the etalon 201 is used.

  4 (a) to 4 (c) and FIGS. 5 (a) to 5 (c) are diagrams showing an example of a method for manufacturing the etalon 201. FIG.

  First, as shown in FIG. 4A, a first mother board 271A, a second mother board 271B, and a third mother board 271C are prepared. The first mother substrate 271A is divided to become the first light transmitting body 207A, and the second mother substrate 271B is divided to become the second light transmitting body 207B. The mother substrate 271C becomes the third light transmitting body 207C by being divided.

  The first outer main surface 273A and the first inner main surface 275A of the first mother board 271A are surfaces that become the first outer surface 51A and the first inner surface 55A, and the first inner main surface 275A is the first outer main surface 275A. It is inclined with respect to the surface 273A at an inclination angle θ (FIG. 3). Similarly, the second outer main surface 273B and the second inner main surface 275B of the second mother board 271B are surfaces to be the second outer surface 51B and the second inner surface 55B, and the second inner main surface 275B is the first inner surface 275B. 2 Inclined at an inclination angle θ with respect to the outer main surface 273B. On the other hand, the first intermediate main surface 277A and the second intermediate main surface 277B of the third mother substrate 271C are surfaces that become the first intermediate surface 57A and the second intermediate surface 57B, and are parallel to each other. The inclination of the inner main surface 275 with respect to the outer main surface 273 may be realized by polishing or may be realized by slicing.

  4A illustrates the case where the planar shape of the mother substrate 271 is rectangular, the planar shape of the mother substrate 271 may be other shapes such as a circle. Further, the side surface of the mother substrate 271 may not be perpendicular to the outer main surface 273.

  Each inner main surface 275 is optically polished. Further, each intermediate main surface 277 is optically polished so that the thickness of the third mother substrate 271C becomes the designed thickness of the third light transmitting body 207C (for example, within a design value ± 0.1 μm). ing. In the etalon 201, when an antireflection film is interposed between the inner side surface 55 and the intermediate surface 57, a thin film serving as an antireflection film is formed on the inner main surface 275 or the intermediate main surface 277. .

  Next, as illustrated in FIG. 4B, the inner main surface 275 and the intermediate main surface 277 are joined to form a stacked body 279. As already mentioned, the joining is preferably performed without using an organic adhesive. As an example, in the case of an optical contact, dirt on the inner main surface 275 and the intermediate main surface 277 is cleaned by irradiation with excimer light or the like, and annealing is performed at 200 to 300 ° C. after bonding.

  Next, as shown in FIG. 4C, the outer main surface 273 is optically polished so that the thickness of the stacked body 279 becomes the designed thickness of the light transmitting portion 203 of the etalon 201. From the viewpoint of increasing the parallelism of the pair of outer main surfaces 273, the optical polishing is preferably double-side polishing.

  Next, as shown in FIG. 5A, a reflective film 281 to be the reflective film 5 is formed on the outer main surface 273 (only the reflective film 281 on the first outer main surface 273A side is shown). The method for forming the reflective film may be the same as a known method.

  Then, as shown in FIGS. 5B and 5C, the stacked body 279 on which the reflective film 281 is formed is cut vertically and horizontally to obtain a plurality of etalons 201. The cutting may be performed by a known dicer or slicer.

A plurality of etalons 201 fabricated by such manufacturing method, each other in a direction in which the thickness _{d 1} of the first transparent body 207A and the thickness _{d 2} of the second transparent body 207B third transparent body 207C is inclined Is different. However, since d ₁ + d ₂ and d ₃ are constant, the FSR represented by the equation (1) is the same among the plurality of etalons 201, and in any of the plurality of etalons 201, Equation (7) is satisfied. Therefore, the etalon 201 having uniform characteristics is manufactured in a lump.

  Of the two kinds of materials constituting the mother board 271, the third mother board 271C, which is a parallel plate, is first formed of a material having a high refractive index, and the first mother board 271A and the first mother board 271A are formed of a material having a low refractive index. It is preferable to form the two mother substrates 271B. By doing so, the thickness variation of the entire translucent portion 203 is reduced, and consequently the variation of FSR and temperature characteristics is also reduced.

  In the above manufacturing method, the outer main surface 273 and the inner main surface 275 are inclined on the first mother substrate 271A and the second mother substrate 271B before the mother substrate 271 is stacked. However, when the first mother substrate 271A to the third mother substrate 271C in the state of parallel plates are laminated to form a laminated body, and both surfaces (outer principal surface 273) of the laminated body are polished, the outer principal surface 273 and The inner main surface 275 may be inclined with respect to each other. However, in this case, since the double-side polishing of the laminate cannot be performed, it is difficult to maintain the parallelism of the outer main surface 273 as compared with the manufacturing method described above.

<Third Embodiment>
FIG. 6 is a side view schematically showing an etalon 301 according to the third embodiment.

  The etalon 301 is different from the translucent part 3 of the etalon 1 of the first embodiment in the configuration of the translucent part 303. Other configurations of the etalon 301 are the same as those of the etalon 1 of the first embodiment. However, the specific material, film thickness, and the like of the reflective film 5 may be appropriately set according to the difference in the configuration of the light transmitting portion 203.

  In the translucent part 3 of the first embodiment, the inner side surfaces 55 of the first translucent body 7A and the second translucent body 7B are bonded to each other, whereas in the translucent part 303 of the present embodiment, A gap 53 is interposed between the inner side surfaces 55. Further, the first inner side surface 55A is covered with the first antireflection film 9A, and the second inner side surface 55B is covered with the second antireflection film 9B. The first light transmitting body 7A and the second light transmitting body 7B are fixed to each other by the spacer 11.

  The shapes and materials of the first light transmissive body 7A and the second light transmissive body 7B are the same as those in the first embodiment. However, in the formula (1) and the like, since the gap 53 and the like are considered as a medium, the specific dimensions are different from those of the first embodiment.

  The gap 53 may be sealed or may not be sealed. In the case of being sealed, the gap 53 may be filled with air or a specific gas, or may be in a vacuum or a state close to a vacuum. Further, when a gas such as air is filled, the pressure in the gap 53 may be higher or lower than the atmospheric pressure.

  The spacer 11 includes, for example, a first metal layer 13A formed on the first inner side surface 55A and a second metal layer 13B formed on the second inner side surface 55B. Each metal layer 13 is configured by, for example, laminating Cr or Ta and Au sequentially from the inner side surface 55 (antireflection film 9), although not particularly illustrated. The pair of metal layers 13 are joined to each other by joining Au to each other by metal diffusion.

  Also in such an etalon 301, since the inner surface 55 is inclined, the reflected light Lt ′ is diverged and the influence of the reflected light Lt ′ on the etalon 301 is reduced as in the first embodiment. be able to. In FIG. 3, the reflected light Lt ′ generated by reflecting the light transmitted through the first light transmitting body 7A at the interface between the first light transmitting body 7A and the gap 53, and the light transmitted through the gap 53 are the gap. The two reflected light Lt 'of the reflected light Lt' produced | generated by reflecting in the interface of 53 and the 2nd translucent body 7B is shown in figure. Moreover, the preferable range of the inclination angle θ is the same as that in the first embodiment.

(Application example of etalon filter)
FIG. 7 is a block diagram showing an application example of etalon 1 (may be etalons 201 and 301).

  The etalon 1 is incorporated in a wavelength locker 103 for keeping the wavelength of light of the laser system 101 constant. The wavelength locker 103 includes, for example, a beam splitter 105 on which light dropped from the laser system 101 enters, an etalon 1 on which light transmitted through the beam splitter 105 enters, and a first light detection on which light transmitted through the etalon 1 enters. 107A and a second photodetector 107B on which the light reflected by the beam splitter 105 enters. Then, the control device 109 detects the wavelength of the light by comparing the intensity of the light detected by the first photodetector 107A and the intensity of the light detected by the second photodetector 107B, and the detected wavelength is constant. Control of the laser system 101 is executed so that

  By reducing the influence of the reflected light, the etalon 1 in which the FSR is set with high accuracy is used for such a wavelength locker 103, so that the wavelength of light can be monitored with high accuracy.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The present invention is intended to incline an interface when there is an interface between parallel reflective films. Accordingly, changes may be made as appropriate within the scope of the gist. For example, the translucent body (and the gap) positioned between the reflective films is not limited to 2 or 3, and may be 4 or more. In addition, the first inner side surface and the second inner side surface may not be parallel to each other when another light transmitting body and / or a gap is interposed therebetween.

  However, when the number of translucent members is 4 or more, the number of interfaces increases, and the characteristics deteriorate. Therefore, any of the three modes exemplified in the embodiment is preferable.

  In the second embodiment (FIG. 3), the first inner surface 55A and the first intermediate surface 57A are bonded together, and the second inner surface 55B and the second intermediate surface 57B are bonded together. However, a gap may be interposed between the inner side surface 55 and the intermediate surface 57B in at least one of the first inner side surface 55A and the first intermediate surface 57A and the second inner side surface 55B and the second intermediate surface 57B. . In addition, in the case where a gap is interposed between the inner surface 55 and the intermediate surface 57 (the third light transmitting body that is a parallel plate) may not be parallel. If the pair of outer surfaces 51 are parallel to each other, the pair of inner surfaces 55 are parallel to each other, and the pair of intermediate surfaces 57 are parallel to each other, the optical path length is kept constant regardless of the position. The effect that is played. The gap may be a vacuum, or may be filled with air or a specific gas.

  The inner side surfaces of the first light transmitting body and the second light transmitting body facing each other are not limited to those configured by one plane inclined with respect to the outer surface. For example, as shown in FIG. 8, the inner side surface 455 may be configured by an arcuate curved surface (or spherical surface) in a side view. In this case, the inner side surface 455 can be regarded as including a curved inclined surface that is inclined with respect to the outer surface 51 in a part of the region 456. In other words, the inner side surface 455 is configured by combining a plurality of inclined surfaces.

  The plurality of translucent members are not limited to materials different from each other for the purpose of suppressing a change in optical path length due to a temperature change. A plurality of light-transmitting bodies may be combined according to various purposes.

  The materials of the light transmitting body, the reflection film, and the antireflection film may be changed as appropriate. For example, the translucent body may be made of quartz glass instead of quartz, or rutile may be used instead of strontium titanate.

  In the present application, the term “bonded” includes both those directly facing each other and those indirectly bonded through a thin film such as an antireflection film or an organic adhesive. (Refer to the first embodiment and FIG. 8), and other light-transmitting bodies (except for the thin film) or those having a gap between the surfaces (see the second and third embodiments) are not included. To do.

  DESCRIPTION OF SYMBOLS 1 ... Etalon, 7A ... 1st transparent body, 7B ... 2nd transparent body, 5A ... 1st reflective film, 5B ... 2nd reflective film, 51A ... 1st outer surface, 51B ... 2nd outer surface, 55A ... 1st inner surface, 55B ... 2nd inner surface.

Claims (5)

A first light-transmitting body having a first outer surface that constitutes one of an incident surface and an output surface, and a first inner surface on the back surface;
A second outer surface that constitutes the other of the incident surface and the outgoing surface; and a second inner surface on the back surface of the second outer surface, the second inner surface facing the first inner surface, and the second outer surface A second translucent body parallel to the first outer surface;
A first reflective film covering the first outer surface;
A second reflective film covering the second outer surface;
A first antireflection film covering the first inner surface;
A second antireflection film covering the second inner surface;
Have
The first antireflection film and the second antireflection film are opposed to each other while defining a gap in which a vacuum or a gas exists,
An etalon filter in which at least one of the first inner surface and the second inner surface includes a surface inclined with respect to the first outer surface and the second outer surface. The first light transmitting body has a positive change in optical path length due to a temperature change,
The etalon filter according to claim 1 , wherein the second light transmitting body has a negative change in optical path length due to a temperature change. An inclination angle of the one inner surface and the second inner surface with respect to the first outer surface and the second outer surface is 0.5 degrees or less.
The etalon filter according to claim 1 or 2. A first mother substrate translucent having a first inner surface of the first outer major surface and a back surface, and have a second outer major surface and a second inner major surface of the back, of the first mother substrate a second mother substrate formed of the same material as the material, permeability having a first intermediate main surface and a second intermediate main surface which is bonded to the second inner main surface that is bonded to the first inner main surface An optical third mother substrate, and the first outer main surface and the second outer main surface are parallel to each other, the first inner main surface, the first intermediate main surface, and the second intermediate main surface. Forming a laminated substrate whose surface and the second inner main surface are parallel to each other;
Dividing the laminated substrate vertically and horizontally in plan view;
Have
In the step of forming the laminated substrate, the first inner main surface, the first intermediate main surface, the second intermediate main surface, and the second inner main surface are the first outer main surface and the second outer main surface. Forming the laminated substrate composed of inclined surfaces with respect to
In the dividing step, the inclined surface is divided. The first mother substrate and the second mother substrate have a positive or negative change in optical path length due to a temperature change,
The third mother substrate has a positive or negative change in optical path length due to a temperature change.
The method for producing an etalon according to claim 4.

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