JPH07245438A - A pair of reflecting mirrors, a resonator using these reflecting mirrors, and a wavelength tunable laser device incorporating the resonators. - Google Patents

Abstract

(57) [Abstract] [Purpose] A pair of reflecting mirrors and resonators that can resonate idler light and signal light together without setting a large number of optical thin film layers, and this resonator are incorporated. Provided is a wavelength tunable laser device. [Structure] Optical thin films 31, 32, 41, 42 are provided on both sides of the transparent substrate of the input side reflecting mirror 3 and the output side reflecting mirror 4, and an idler is formed by the optical thin films 31, 41 provided on the non-opposing side of each reflecting mirror. The film is set to resonate one of the light or the signal light, and the optical thin film 32 provided on the opposite side of each reflecting mirror,
It is characterized in that a film is set so that the other light is resonated by 42. Then, the number of layers of the optical thin film can be reduced as compared with the conventional method in which the signal light and the idler light are resonated by the optical thin film provided only on one side of the substrate, and the crack phenomenon of the optical thin film at the time of film formation can be avoided. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable laser device by optical parametric oscillation for converting incident pump light into a signal light and an idler light, and more particularly to a wavelength tunable laser device incorporated in the wavelength tunable laser device. The present invention relates to a pair of reflecting mirrors that resonate with idler light, a resonator using the reflecting mirrors, and a wavelength tunable laser device incorporating the resonators.

[0002]

2. Description of the Related Art Optical parametric oscillation (hereinafter referred to as OPO. OPO: Opti
Laser wavelength conversion by cal parametric oscillation is performed by an eye-safe laser (wavelength: 1.4 to 1.8 μm),
Enables near infrared wavelength tunable laser for spectroscopic chemical analysis.

Wavelength conversion by OPO will be briefly described below with reference to a schematic configuration diagram of an OPO wavelength tunable laser device.

First, this wavelength tunable laser device has, for example, as shown in FIG. 11, a pump light source a which outputs a pump light p having a wavelength λp, and KTiOPO ₄ or RbTiO 3.
A wavelength conversion element b composed of a non-linear optical crystal such as PO ₄ and arranged rotatably around the Y axis of the crystal (direction of arrow f in FIG. 11), and a pump around the wavelength conversion element b. It is provided with a pair of reflecting mirrors c and d which are respectively arranged on the light source side and on the opposite side to form a resonator, and the pump light p having a wavelength λp and a polarization direction of Y axis direction is transmitted from the pump light source a to the wavelength conversion element b. When incident, it oscillates idler light i having a wavelength λi and a polarization direction of Z axis, and signal light s having a wavelength λs and a polarization direction of Y axis.

FIG. 11 is a schematic configuration diagram of the OPO wavelength tunable laser device as viewed from above. Further, in FIG. 11, black double circles and arrows indicating the pump light p, the signal light s, and the idler light i mean the polarization directions of the respective lights. For signal light and idler light,
The shorter wavelength is generally called the signal light and the longer wavelength is called the idler light. Further, the relationship between the pump light, the signal light, and the idler light can be expressed by the following mathematical formula (1) from the law of conservation of energy.

[0006]

[Equation 1] In the OPO wavelength tunable laser device, when the wavelength conversion element b is rotated about the Y axis in the direction indicated by the arrow f, the incident angle of the pump light p with respect to the wavelength conversion element b changes correspondingly. Therefore, the signal light s
Therefore, the wavelength λs and the wavelength λi of the idler light i can be continuously changed. For example, N of wavelength 1.06 μm
d: YAG laser is used, and KT is used as the wavelength conversion element b.
When iOPO ₄ (hereinafter referred to as KTP) is applied,
When the wavelength conversion element b is rotated within the range in which the pump light is effectively incident on the wavelength conversion element b, the wavelengths of the idler light and the signal light change in the range of about 1.6 to 3.2 μm.

By the way, in the above OPO wavelength tunable laser device, one or both of the idler light and the signal light is obtained as the output light, so that a high reflectance is conventionally provided on the opposing surfaces of the pair of reflecting mirrors c and d which form the resonator. Optical thin film c1, d1
Is provided. For example, when both the signal light and the idler light are obtained as the output light, in the input side reflecting mirror c arranged on the pump light source a side, one surface of the optically transparent substrate has a reflectance of both the idler light and the signal light. To 98
%, The optical thin film c1 is formed by alternately laminating two kinds of substances having different refractive indexes in a film shape. Further, in the output side reflecting mirror d arranged on the side opposite to the pump light source a, An optical thin film in which two kinds of substances having different refractive indexes are alternately laminated in a film shape so that the reflectance is 60% to 90% for both idler light and signal light on one surface of an optically transparent substrate.
forming d1. Further, antireflection films b1 and b2 for idler light and signal light are provided on both surfaces of the wavelength conversion element b arranged in the resonator.
b2 also prevents the laser output from being reduced due to reflection.

The pump light source a has a wavelength of 1.06 μm.
Nd: YAG laser, KTP for the wavelength conversion element b, sapphire substrate with a refractive index of 1.73 for the optically transparent substrates of the reflecting mirrors c and d, and 1.41 for the optical thin film material. A SiO ₂ layer and a Ta ₂ O ₅ layer having a refractive index of 1.92 are used, and a phase matching angle (an angle for the pump light, idler light, and signal light to be phase-matched) of the nonlinear optical crystal that constitutes the wavelength conversion element is used. Angle from Z axis) θ =
When the idler light having a wavelength of approximately 2.5 to 3 μm and the signal light having a wavelength of approximately 1.6 to 1.9 μm are resonated in the range of 60 ° to 70 °, the following formulas (2) to (4) are used according to a conventional method. The required number of layers of each optical thin film is determined by providing the SiO ₂ layer on the sapphire substrate, providing the Ta ₂ O ₅ layer as the second layer on the SiO ₂ layer, and alternately stacking the layers alternately in the above-mentioned case. Of the optical thin film c1 of 81 layers (the specific contents of each layer are shown in Tables 1 and 2 below), and the optical thin film d1 of the output side reflecting mirror d is 29 layers (the specific contents of each layer are shown in Table 3 below). Shown).

[0009]

[Equation 2]

[Equation 3]

[Equation 4] Here, n _r is the refractive index of the r-th layer, d _r is its physical film thickness, n _o is the refractive index of air (medium), and n _s is the refractive index of the optically transparent substrate. The required number of layers is calculated by gradually changing the optical film thickness nd (n: refractive index, d: physical film thickness) of each layer, or by increasing or decreasing the number of film layers. The number of film layers and the film thickness of each layer to obtain the characteristics are obtained by a simplex method using a personal computer. Further, in calculating each of the optical thin films c1 and d1, it is noted that the reflectance at the wavelength of 1.06 μm is lowered so that the pump light is not reflected. Also, the above formulas (2) to (4)
Assumes that a laser beam of wavelength λ is vertically incident. In addition, FIG. 12 shows the optical thin film c1 thus obtained.
Shows the spectral reflectance characteristic calculated by the above equation, and FIG. 13 shows the spectral reflectance characteristic calculated by the optical thin film d1.

[0010]

[Table 1]

[Table 2]

[Table 3]

[0011]

By the way, when the number of layers of the laminated film provided on the substrate exceeds 40, cracks are easily generated in the laminated film due to the internal stress of the film itself. The optical thin film c1 whose number of film layers is 81 is a thin film which is practically difficult to apply.

Therefore, in the conventional OPO wavelength tunable laser device, a wavelength region of 2.5 to 5 is used instead of the structure in which the idler light and signal light resonators are constituted by one set of reflecting mirrors.
A pair of reflecting mirrors that resonate only 3 μm idler light,
Two pairs of another pair of reflecting mirrors that resonate only the signal light having a wavelength region of 1.6 to 1.9 μm are prepared.
The structure is such that a pair of reflecting mirrors can be alternately and interchangeably incorporated through appropriate exchanging members. That is, in the pair of reflecting mirrors that resonate only one of the idler light and the signal light, the number of film layers of the optical thin film can be set small.

However, in the wavelength tunable laser device having such a structure, it is necessary to reconfigure the reflecting mirror each time the light to be output is changed, and the replacement member is required as a component member of the device. There is a problem that it is not possible to cope with the strongly demanded downsizing of laser devices and reduction of manufacturing cost.

The present invention has been made by paying attention to such a problem, and an object of the present invention is to provide a resonator for a wavelength tunable laser device which can cope with downsizing of the laser device and reduction of manufacturing cost. More specifically, to provide a pair of reflecting mirrors capable of resonating idler light and signal light, a resonator using the same, and a wavelength tunable laser device incorporating the resonator. is there.

[0015]

That is, the invention according to claim 1 is composed of a nonlinear optical crystal and is rotatably provided around the Y axis of the crystal, and the incident pump light is signal light and idler light. Based on a pair of reflecting mirrors for a wavelength tunable laser device, which are respectively arranged on the pump light source side and the opposite side of the wavelength conversion element for converting into An input side reflecting mirror arranged on the light source side is an optically transparent substrate, and non-opposing side optical provided on the pump light incident surface of the substrate and having a high reflection function for one of the signal light and the idler light. A thin film and an opposing optical thin film provided on the opposite surface of the substrate and having an antireflection function for the one light and a high reflection function for the other light, and a pump. An output-side reflecting mirror arranged on the side opposite to the source is provided on the surface of the optically transparent substrate facing the input-side reflecting mirror, and has an antireflection function for the one light and Opposing optical thin film having a high reflection function for the other light, and a high reflection function for the one light provided on the opposite surface of the substrate and an antireflection function for the other light. It is characterized in that it is composed of a non-opposing side optical thin film.

In the pair of reflecting mirrors according to the first aspect of the present invention, optical thin films are provided on both surfaces of each optically transparent substrate of the input side reflecting mirror and the output side reflecting mirror, and the input side reflecting mirror is provided. By utilizing the high reflection function of the non-opposing optical thin film on the non-opposing side and the high reflection function of the non-opposing optical thin film on the output side reflecting mirror, only one of the signal light and the idler light is resonated and the opposition on the input side reflecting mirror is achieved. Since only the other light of the signal light and the idler light is resonated by the high reflection function of the side optical thin film and the high reflection function of the opposite side optical thin film in the output side reflecting mirror, one pair of reflecting mirrors It is possible to reduce the number of film layers of each optical thin film, although the resonators for both idler light are configured.

When one of the signal light and the idler light is reflected by the opposing optical thin film of the input reflecting mirror and the opposing optical thin film of the output reflecting mirror, the non-opposing side of the input reflecting mirror is reflected. Since it is difficult to resonate one of the lights with the optical thin film and the non-opposing optical thin film of the output reflecting mirror, the opposing optical thin film of the input reflecting mirror and the opposing optical thin film of the output reflecting mirror are It is necessary to provide an antireflection function for the one light. Further, when the other light resonated by the opposite optical thin film of the input side reflecting mirror and the opposite side optical thin film of the output side reflecting mirror is reflected by the non-opposing side optical thin film of the output side reflecting mirror, Since light cannot be used as output light, it is necessary for the non-opposing optical thin film of the output side reflecting mirror to have an antireflection function for the other light.

Here, in the invention according to claim 1,
As shown in FIG. 7A, the signal light s is resonated by the opposite optical thin film 32 of the input reflecting mirror 3 and the opposite optical thin film 42 of the output reflecting mirror 4, and the non-opposing side of the input reflecting mirror 3 is made. The optical thin film 31 and the optical thin film 41 on the non-opposing side of the output side reflecting mirror 4 may resonate the idler light i.
As shown in (B), the opposite optical thin film 3 of the input side reflecting mirror 3
2 and the opposite side optical thin film 42 of the output side reflecting mirror 4 resonate idler light i, and the non-opposing side optical thin film 31 of the input side reflecting mirror 3 and the non-opposing side optical thin film 41 of the output side reflecting mirror 4 give a signal. You may take the structure which resonates the light s. However, in order to obtain the same effect as the invention according to claim 1,
As shown in (A), the opposite optical thin film 3 of the input side reflecting mirror 3
2 and the non-opposing optical thin film 41 of the output reflecting mirror 4 resonate the signal light s, and the non-opposing optical thin film 31 of the input reflecting mirror 3 and the opposing optical thin film 42 of the output reflecting mirror 4 idler. It is also possible to adopt a configuration in which the light i is resonated. As shown in FIG. 8B, an idler is formed between the facing optical thin film 32 of the input reflecting mirror 3 and the non-facing optical thin film 41 of the output reflecting mirror 4. It is also possible to employ a configuration in which the light i is resonated and the signal light s is resonated by the non-opposing optical thin film 31 of the input side reflecting mirror 3 and the opposing optical thin film 42 of the output side reflecting mirror 4.
The invention according to claim 2 is made for such a technical reason.

That is, the invention according to claim 2 is a wavelength conversion element which is made of a non-linear optical crystal and is rotatably provided around the Y-axis of the crystal and which converts incident pump light into signal light and idler light. Centered on the pump light source side and the opposite side, respectively, and is arranged on the pump light source side on the premise of a pair of reflecting mirrors for the wavelength tunable laser device that constitute the resonator of the signal light and the idler light. The input side reflecting mirror is an optically transparent substrate, a non-opposing side optical thin film provided on the pump light incident surface of the substrate and having a high reflection function for one of the signal light and the idler light, and this substrate. It is provided on the opposite surface and has an anti-reflection function for one of the above lights and a high-reflection function for the other light, and is formed on the opposite side optical thin film, The output-side reflecting mirror to be placed is provided on the surface of the optically transparent substrate facing the input-side reflecting mirror of this substrate and has an antireflection function for the other light and at the same time for the one light. An opposing optical thin film having a high reflection function, and a non-opposing optical thin film provided on the opposite surface of the substrate and having a high reflection function for the other light and an antireflection function for the one light. It is characterized by being composed of.

Also, in the pair of reflecting mirrors according to the second aspect of the present invention, optical thin films are provided on both surfaces of each optically transparent substrate of the input side reflecting mirror and the output side reflecting mirror, and the input side reflecting mirror is provided. By utilizing the high reflection function of the non-opposing optical thin film on the non-opposite side and the high reflection function of the opposing optical thin film on the output side reflecting mirror, only one of the signal light and the idler light is resonated and the opposite side of the input side reflecting mirror Since only the other light of the signal light and the idler light is resonated by the high reflection function of the optical thin film and the high reflection function of the non-opposing side optical thin film in the output side reflecting mirror, the same as the invention according to claim 1. 1
It is possible to reduce the number of film layers of each optical thin film, even though the resonators for both the signal light and the idler light are constituted by the pair of reflecting mirrors.

When one of the signal light and the idler light is reflected by the opposite optical thin film of the input reflecting mirror, the non-opposing optical thin film of the input reflecting mirror and the opposite side of the output reflecting mirror. Since it becomes difficult for the optical thin film to resonate the one light, it is necessary for the opposite optical thin film of the input side reflecting mirror to have an antireflection function for one light. Similarly, when the other light of the signal light and the idler light is reflected by the opposite side optical thin film of the output side reflecting mirror, the opposite side optical thin film of the input side reflecting mirror and the non-opposing side optical thin film of the output side reflecting mirror are used. Since it becomes difficult to resonate the other light, it is necessary for the opposing optical thin film of the output-side reflecting mirror to have an antireflection function for the other light. Further, when the one light resonated by the non-opposing optical thin film of the input side reflecting mirror and the opposite side optical thin film of the output side reflecting mirror is reflected by the non-opposing side optical thin film of the output side reflecting mirror, Since the above light cannot be used as output light, it is necessary for the non-opposing optical thin film of the output side reflecting mirror to have an antireflection function for the one light.

Here, the pair of reflecting mirrors 3 and 4 shown in FIG. 8A is a combination of the reflecting mirror 3 shown in FIG. 7A and the reflecting mirror 4 shown in FIG. 7B. Yes,
In addition, the pair of reflecting mirrors 3 and 4 shown in FIG.
Shows a combination of the reflecting mirror 3 in FIG. 7B and the reflecting mirror 4 in FIG. 7A.

Next, for the non-opposing optical thin film and the opposing optical thin film provided on both surfaces of each optically transparent substrate, an optical transparent body having a low refractive index and an optical transparent body having a high refractive index are usually used. It is formed by alternately stacking films. At that time, the required number of stacked layers and film thickness are calculated by a computer using the mathematical formulas (2) to (4). Then, according to the obtained result, a film is formed by an appropriate film forming means such as an electron beam vacuum evaporation method or a sputtering method. When forming a film, the film-forming speed such as vapor deposition, the heating temperature of the optically transparent substrate, the partial pressure of oxygen introduced, etc. change the film stress value inside the laminated film. The internal stress should be weakened or adjusted appropriately so that the stress is canceled out comprehensively. When SiO ₂ and Ta ₂ O ₅ are applied as the low refractive index optical transparent material and the high refractive index optical transparent material, after forming the film, oxygen or atmospheric air is used in accordance with a conventional method. Annealing treatment is performed at 200 to 300 ° C. for 10 to 20 hours. This annealing treatment is a treatment for making the brown coloring of the optical thin film immediately after vapor deposition colorless. The brown coloring of the optical thin film is caused by lack of oxygen in the Ta ₂ O ₅ layer during film formation.

Here, as shown in FIG. 9A, when the optical thin films 11 and 12 are formed on the front and back surfaces of the optically transparent substrate 10, after vapor deposition on one surface, a vacuum is returned to the atmosphere and a film material is set. If vacuuming is performed again after heating again after heating, cracks may occur in the optical thin film that is initially deposited depending on the film material, vapor deposition conditions, and substrate heating temperature.
In such a case, the method of forming the reflecting mirror with one optically transparent substrate is changed to two transparent substrates 51, 52 bonded together with an optical adhesive 50 as shown in FIG. 9B. This can be avoided by configuring this. The invention according to claim 3 is made for such a technical reason.

That is, the invention according to claim 3 is premised on the pair of reflecting mirrors according to the invention according to claim 1 or 2, and the input side reflecting mirror and the output side reflecting mirror are provided with the non-opposing side optical thin film on one surface. An optical first transparent substrate provided, an optical second transparent substrate provided with an optical thin film on the opposite side on one side, and an optical device having the same refractive index as these transparent substrates and the opposite surfaces of the respective transparent substrates An adhesive is provided.

According to the pair of reflecting mirrors of the present invention, the non-opposing side optical thin film and the opposing side optical thin film are optical substrates which are separate substrates and an optical first transparent substrate. It has a structure formed separately on a second transparent substrate, and an optical first transparent substrate and an optical second transparent substrate, which are formed by separately forming respective optical thin films, are pasted together via an optical adhesive. Since the input side reflection mirror and the output side reflection mirror can be manufactured by combining them, it is possible to avoid the crack phenomenon of the optical thin film, which is likely to occur when the optical thin films are formed on both surfaces of one optically transparent substrate. Becomes

In the invention according to claim 3, it is premised that the refractive index of the optical adhesive for bonding the optical first transparent substrate and the optical second transparent substrate is equal to the refractive index of each transparent substrate. . This is because if the refractive indexes are different, idler light and signal light are reflected at the interface between each transparent substrate and the optical adhesive. In such a case, as shown in FIG. 9C, by providing antireflection films 61 and 62 for the refractive index of the optical adhesives at the interfaces between the transparent substrates 51 and 52 and the optical adhesives 50, respectively. It is possible to avoid it. The invention according to claim 4 is made for such a technical reason.

That is, the invention according to claim 4 is premised on the pair of reflecting mirrors according to the invention according to claim 1 or 2, wherein the input side reflecting mirror and the output side reflecting mirror are provided with the non-opposing side optical thin film on one side. An optical first transparent substrate provided, an optical second transparent substrate provided with an optical thin film on the opposite side on one side, and an optical system in which these transparent substrates have different refractive indices and the opposite surfaces of the respective transparent substrates are bonded together. An adhesive is provided, and an antireflection film for the refractive index of the optical adhesive is provided on each bonding surface of the respective transparent substrates.

Here, in the invention according to claims 1 to 4, when the transparent substrate is not a flat surface, the resonator length is different between the outer (ie, non-opposing side) surface and the inner (ie, opposing side) surface of each reflecting mirror. The radius of curvature of the outer surface and the inner surface of the reflecting mirror may be changed in consideration of the difference in the above.

Next, the invention according to claim 5 and claim 6
The present invention relates to a resonator including a pair of reflecting mirrors and a wavelength tunable laser device incorporating the resonator according to the first to fourth aspects of the present invention.

That is, the invention according to claim 5 is a wavelength conversion element which is made of a non-linear optical crystal and is rotatably provided around the Y-axis of the crystal and converts incident pump light into signal light and idler light. A resonator for a wavelength tunable laser device, which is composed of a pair of reflecting mirrors arranged on the pump light source side and on the opposite side of the pump light source side, respectively. The invention according to claim 6 is characterized in that a pair of reflecting mirrors according to claim 4 is incorporated.
A wavelength conversion element which is made of a non-linear optical crystal and is rotatably provided around the Y axis of the crystal, and converts the incident pump light into a signal light and an idler light, and a pump light source with the wavelength conversion element as the center. It is premised on a wavelength tunable laser device comprising a cavity and a cavity constituted by a pair of reflecting mirrors arranged on the opposite side, respectively, and the cavity according to claim 5 is incorporated as the cavity. It is what

In the sixth aspect of the invention, KTiOPO ₄ , RbTiOPO ₄ or the like is applied as the non-linear optical crystal constituting the wavelength conversion element as in the conventional case.

[0033]

According to the pair of reflecting mirrors of the present invention, the input side reflecting mirror arranged on the pump light source side is provided on the optically transparent substrate and the pump light incident surface of the substrate, and The non-opposing side optical thin film having a high reflection function for one of light and idler light, and an antireflection function for the one light provided on the opposite surface of the substrate and for the other light. An output-side reflecting mirror, which is composed of an opposite-side optical thin film having a high reflection function and is arranged on the opposite side of the pump light source, is an optically transparent substrate and a surface of the substrate facing the input-side reflecting mirror. Is provided on the opposite side optical thin film having an anti-reflection function for the one light and a high reflection function for the other light, and a high optical performance for the one light provided on the opposite surface of the substrate. It has a reflection function and the other light And a non-opposing optical thin film having an anti-reflection function, and a high reflection function of the non-opposing optical thin film in the input reflecting mirror and a high reflecting function of the non-opposing optical thin film in the output reflecting mirror. Utilizing only one of the signal light and the idler light to resonate, the signal light is reflected by the high reflection function of the opposite side optical thin film in the input side reflecting mirror and the high reflection function of the opposite side optical thin film in the output side reflecting mirror. Since only the other light of the idler light and the idler light is resonated, the number of film layers of each optical thin film can be reduced even though the resonator for both the signal light and the idler light is configured by one set of reflecting mirrors. Is possible.

According to the pair of reflecting mirrors of the second aspect of the present invention, the input side reflecting mirror arranged on the pump light source side is provided on the optically transparent substrate and the pump light incident surface of this substrate. A non-opposing optical thin film having a high reflection function for one of the signal light and the idler light, and an antireflection function for the one light provided on the opposite surface of the substrate and the other light. On the other hand, an output side reflection mirror, which is composed of an opposite side optical thin film having a high reflection function and is arranged on the side opposite to the pump light source, is an optical transparent substrate and the input side reflection mirror of this substrate. An opposite side optical thin film provided on the opposite surface and having an antireflection function for the other light and a high reflection function for the one light, and an opposite optical film provided on the opposite surface of the substrate for the other light And has a high reflection function And a non-opposing optical thin film having an anti-reflection function for the other light, and the high reflecting function of the non-opposing optical thin film in the input reflecting mirror and the high optical thickness of the opposite optical thin film in the output reflecting mirror. Utilizing the reflection function to resonate only one of the signal light and idler light, and the high reflection function of the opposite side optical thin film in the input side reflecting mirror and the high reflection function of the non-opposing side optical thin film in the output side reflecting mirror. Since only the other one of the signal light and the idler light is resonated in, the pair of reflecting mirrors constitutes a resonator for both the signal light and the idler light as in the invention according to claim 1. Nevertheless, the number of film layers of each optical thin film can be reduced.

Next, according to the pair of reflecting mirrors of the third aspect of the present invention, the first reflecting mirror of the input side and the reflecting mirror of the output side are provided with the non-opposing side optical thin film on one surface. And a second optical transparent substrate provided with an optical thin film on the opposite side on one surface, and an optical adhesive having these transparent substrates and the opposite surfaces of the respective transparent substrates having the same refractive index attached to each other. The input side reflecting mirror and the output side reflecting mirror are formed by bonding the optical first transparent substrate and the optical second transparent substrate on which the respective optical thin films are formed separately, through an optical adhesive. Since it can be manufactured, it is possible to avoid the crack phenomenon of the optical thin film, which is likely to occur when the optical thin films are formed on both surfaces of one optically transparent substrate.

According to the pair of reflecting mirrors according to the invention described in claim 4, the input side reflecting mirror and the output side reflecting mirror are the optical first transparent substrate provided with the non-opposing side optical thin film on one surface. , An optical second transparent substrate provided with an optical thin film on the opposite side on one side, and an optical adhesive having a refractive index different from those of the transparent substrates and bonding the opposite sides of the respective transparent substrates, and each transparent Since each of the transparent substrates is provided with an antireflection film for the refractive index of the optical adhesive on the bonding surface of the substrate, the transparent substrate is applied despite the optical adhesive having a different refractive index. It is possible to prevent the phenomenon of reflection of idler light and signal light at the interface between the resin and the optical adhesive.

On the other hand, according to the resonator of the invention described in claim 5, a pair of reflecting mirrors arranged on the pump light source side and on the opposite side of the wavelength conversion element are provided.
Since it is composed of the pair of reflecting mirrors according to the invention described in 3 or 4, it is possible to resonate both the idler light and the signal light with this one resonator.

According to the wavelength tunable laser device of the invention described in claim 6, the set of reflecting mirrors resonates the idler light and the signal light with a pair of reflecting mirrors. Since the resonator is incorporated, the laser device can be downsized and the manufacturing cost can be reduced.

[0039]

EXAMPLES The present invention will be described with reference to a reflecting mirror, which is manufactured by forming an optical thin film on the opposite side and an optical thin film on the non-opposing side on different optically transparent substrates and then adhering the thin film on each other through an optical adhesive. An example will be described in detail.

First, an Nd: YAG laser with a wavelength of 1.06 μm is used as the pump light source 1, and a KT is used as the wavelength conversion element 2.
When P is used, the relationship between the phase matching angle θ and the wavelength λi of the generated idler light i and the wavelength λs of the signal light s is shown in FIG. 10 (IEEE JOURNAL OF QUANTUM ELECTRONIC
S, VOL.27, NO.5, P.1137, MAY 1991). According to FIG. 10, when the phase matching angle θ is changed in the range of 60 to 70 degrees, the idler light i having a wavelength of about 2.5 to 3 μm,
It shows that the signal light s having a wavelength of about 1.6 to 1.9 μm oscillates. In this embodiment, a pair of reflecting mirrors that resonate both the idler light and the signal light in one resonator are manufactured.

To this end, the opposing surfaces of the reflecting mirrors 3 and 4 have an antireflection function for idler light i having a wavelength of about 2.5 to 3 μm and a signal having a wavelength of 1.6 to 1.9 μm. Opposing optical thin film 32 having a high reflection function for light s,
42 on the non-opposing side optical thin film 3 having a high reflection function for the idler light i on the non-opposing side surface of the input side reflecting mirror 3.
1 and a non-opposing optical thin film 41 having an antireflection function for the signal light s and a high reflecting function for the idler light i on the non-opposing surface of the output side reflecting mirror 4.
May be formed (see FIGS. 1 and 7A). In this embodiment, the optical thin films 31 and 32 provided on the input side reflecting mirror 3 have a reflectance of 98% or more with respect to idler light and signal light, and the optical thin film 4 provided on the output side reflecting mirror 4.
The reflectance for the idler light of 1 and 42 and the reflectance for the signal light is about 90 ± 2%.

[Design of Optical Thin Film] Therefore, SiO ₂ and Ta ₂ O ₅ are applied as thin film materials, a parallel plate made of sapphire is used as an optically transparent substrate, and each of the optical thin films 31 to 42 has the following conditions. So that the optical film thickness nd (n: n) of each layer is obtained by the simplex method using a personal computer based on the above equations (2) to (4).
The number of film layers and the film thickness of each layer were obtained by gradually changing the refractive index, d: physical film thickness) or increasing or decreasing the number of film layers. In the calculation, it was assumed that the laser light was vertically incident on each optical thin film.

A. Opposing optical thin film 32 of input side reflecting mirror 3 Reflectivity for wavelengths of about 1.6 to 1.9 μm 98% or more Reflectivity for wavelengths of about 2.5 to 3 μm 2% or less b. Non-opposing side optical thin film 31 of input side reflecting mirror 3 Reflectivity for wavelength of about 2.5 to 3 μm 98% or more c. Opposing optical thin film 42 of output side reflecting mirror 4 Reflectivity for wavelength of about 1.6 to 1.9 μm 90 ± 2% Reflectivity for wavelength of about 2.5 to 3 μm 2% or less d. Non-opposing side optical thin film 41 of output side reflecting mirror 4 Reflectivity for wavelength of about 2.5 to 3 μm 90 ± 2% Reflectivity for wavelength of about 1.6 to 1.9 μm 2% or less And these four types of optical thin films Examples of the film design of Table 4 (opposing optical thin film 32 of the input side reflecting mirror 3), Table 5 (non-opposing optical thin film 31 of the input side reflecting mirror 3), Table 6 (opposing the output side reflecting mirror 4) Side optical thin film 42) and Table 7 (non-opposing side optical thin film 41 of output side reflecting mirror 4). Further, a graph of the calculated spectral reflectance of the optical thin film in the film configuration shown in Tables 4 to 7 is shown in FIG.
Opposing optical thin film 32), FIG. 3 (non-opposing optical thin film 31 of input reflecting mirror 3), FIG. 4 (opposing optical thin film 42 of output reflecting mirror 4), and FIG. 5 (output reflecting mirror). No. 4 non-opposing side optical thin film 41).

[0044]

[Table 4]

[Table 5]

[Table 6]

[Table 7] [Formation of Optical Thin Film] Next, each optical thin film was formed based on the above calculation results. An electron beam vacuum vapor deposition apparatus was used for film formation. First, an optically transparent substrate made of sapphire was heated to 300 ° C. and evacuated to 5.0 × 10 ⁻⁶ Torr. When the SiO _{2 is} vapor-deposited, the vapor deposition rate is 0.7 n
m / min. Controlled to be. On the other hand, during Ta ₂ O ₅ vapor deposition, oxygen was introduced so as to be maintained at 1.0 × 10 ⁻⁴ Torr, and the vapor deposition rate was 0.2 nm / min. Controlled to be. An optical interference type film thickness monitor was used to control the film thickness during vapor deposition, and a crystal vibration monitor was used to control the vapor deposition rate. The vapor deposition conditions were determined so that cracks would not occur in the formed optical thin film.

These vapor deposition conditions differ depending on the distance from the vapor deposition source of the vacuum vapor deposition apparatus to the optically transparent substrate, the position where oxygen is introduced, the position where the oxygen partial pressure is measured, the exhaust speed, and the like. Sometimes it's not absolute.

In this way, the opposing optical thin film 32 having the optical characteristics shown in a is formed on one surface of the optical second transparent substrate 52 which constitutes a part of the input side reflecting mirror 3 (FIG. 1B). Then, the optical second transparent substrate 5 is broken by vacuum breaking.
I took out 2. Next, a non-opposing side optical thin film 31 having the optical characteristics shown in b is formed on one surface of the optical first transparent substrate 51 which constitutes a part of the input side reflecting mirror 3 (see FIG. 1B), Hereinafter, the same operation is repeated to form an opposite side optical thin film 42 having the optical characteristic indicated by c on one surface of the optical second transparent substrate forming a part of the output side reflecting mirror 4, and The non-opposing side optical thin film 41 having the optical characteristic indicated by d is formed on one surface of the first transparent substrate.

[Lamination with Optical Adhesive] Next, an optical transparent substrate made of sapphire having a refractive index of 1.73 with respect to a laser beam having a wavelength of about 2.5 to 3 μm is laminated with a refractive index of 1 at the same wavelength. .52 and an optical adhesive having a refractive index different from that of the optically transparent substrate are used, and therefore antireflection films 61 and 62 are provided on the bonding surfaces of the optically first transparent substrate 51 and the optically second transparent substrate 52. It was In addition, the output side reflecting mirror 4
A similar antireflection film was formed on the bonding surfaces of the first optical transparent substrate and the second optical transparent substrate constituting the above. An example of such an antireflection film has a refractive index of 1.58 and an optical film thickness of 0.343λo (λo is a designed center wavelength,
A single layer of Al ₂ O _{3 (} o = 2.0 μm) has been applied. Further, FIG. 6 shows a graph of the calculated spectral reflectance of this antireflection film.

After forming the above antireflection film, each optically transparent substrate was annealed at 250 ° C. for 20 hours in the atmosphere. Since this annealing condition may also vary depending on the optical thin film produced, it is desirable to select the optimum condition as appropriate.

Finally, the optical first transparent substrate 51 and the optical second transparent substrate 52 constituting the input side reflecting mirror are bonded together via the above-mentioned optical adhesive to manufacture the input side reflecting mirror 3, and at the same time. The output-side reflecting mirror 4 was also manufactured by the method described above. still,
If the refractive index of this optical adhesive is equal to the refractive index of the optically transparent substrate, it is not necessary to provide the antireflection film on the bonding surface of each transparent substrate.

[Evaluation of Wavelength Tunable Laser Device Incorporating the Reflecting Mirror] Next, the input side reflecting mirror 3 and the output side reflecting mirror 4 thus obtained are used as a wavelength conversion element 2 in a KTP.
1 was applied to the tunable laser device of FIG. 1 (A), and the performance of this device was evaluated.

As the pump light source 1, N having a wavelength of 1.06 μm is used.
Using the d: YAG laser, the wavelength conversion element 2 is rotated in the range where the phase matching angle θ of the wavelength conversion element 2 made of KTP is 60 to 70 degrees, and the idler light i having a wavelength of about 2.5 to 3 μm and the wavelength The laser light emitted from the output-side reflecting mirror 4 by resonating with the signal light s of about 1.6 to 1.9 μm was detected by the spectroscope.

As a result, the wavelength of the laser light emitted from this laser device has changed in the same manner as that of the laser light emitted from the laser device having a structure in which a plurality of sets of reflecting mirrors are alternately exchanged. confirmed. In addition, the intensity of emitted light was comparable to that of the conventional one.

In this embodiment, SiO ₂ and Ta ₂ O ₅ are applied as the thin film materials forming the facing optical thin film and the non-opposing optical thin film of the input side reflecting mirror 3 and the output side reflecting mirror 4. However, as a low refractive index substance, MgF ₂ , Ca
F ₂ , AlF ₂ , Al ₂ O ₃ or the like is used, HfF ₂ , Y ₂ O ₃ , ZrO ₂ , HfO ₂ , TiO ₂ or the like is used as the high refractive index material, and these are appropriately combined and applied. May be.

[0054]

According to the invention of claim 1, the signal light is utilized by utilizing the high reflection function of the non-opposing optical thin film in the input side reflecting mirror and the high reflection function of the non-opposing side optical thin film in the output side reflecting mirror. While resonating only one of the idler light and the idler light, the other of the signal light and the idler light by the high reflection function of the opposite side optical thin film in the input side reflecting mirror and the high reflection function of the opposite side optical thin film in the output side reflecting mirror Since only the above light is resonated, the number of film layers of each optical thin film can be reduced despite the fact that one set of reflecting mirrors constitutes both the signal light and idler light resonators. .

According to the second aspect of the invention, the signal light is generated by utilizing the high reflection function of the non-opposing optical thin film in the input side reflecting mirror and the high reflecting function of the opposite side optical thin film in the output side reflecting mirror. While resonating only one of the idler light, the other of the signal light and the idler light is provided by the high reflection function of the opposite side optical thin film in the input side reflecting mirror and the high reflection function of the non-opposing side optical thin film in the output side reflecting mirror. Since only the light of 1 is resonated, as in the invention according to claim 1,
Despite the fact that the pair of reflecting mirrors configure both the signal light and idler light resonators, the number of film layers of each optical thin film can be reduced.

Next, according to the third aspect of the present invention, the optical first transparent substrate and the second optical transparent substrate, on which the respective optical thin films are formed separately, are attached via an optical adhesive. As a result, the input side reflecting mirror and the output side reflecting mirror can be manufactured, so that it has an effect of avoiding the crack phenomenon of the optical thin film as compared with the case where the optical thin films are formed on both surfaces of one optically transparent substrate. .

According to the invention of claim 4, an antireflection film for the refractive index of the optical adhesive is provided on each of the bonding surfaces of the first optical transparent substrate and the second optical transparent substrate. Therefore, it has the effect of preventing the reflection phenomenon of idler light and signal light at the interface between each transparent substrate and the optical adhesive, even though each transparent substrate and the optical adhesive having a different refractive index are applied. There is.

On the other hand, according to the fifth aspect of the present invention, there is provided a pair of reflecting mirrors, which are arranged on the pump light source side and on the opposite side of the wavelength conversion element as a center to form a resonator.
Since it comprises a pair of reflecting mirrors described in item 2, 3 or 4, it has an effect that both the idler light and the signal light can be resonated by the pair of reflecting mirrors.

According to the sixth aspect of the invention, since a resonator for resonating the idler light and the signal light with a pair of reflecting mirrors is incorporated, the size of the laser device can be reduced. In addition, the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1A is a schematic top view of a wavelength tunable laser device according to an embodiment, and FIG. 1B is an enlarged cross-sectional view of an input side reflecting mirror thereof.

FIG. 2 is a graph showing spectral reflectance calculation values in the facing-side optical thin film of the input-side reflecting mirror according to the example.

FIG. 3 is a graph chart of spectral reflectance calculation values in the non-opposing side optical thin film of the input side reflecting mirror according to the example.

FIG. 4 is a graph showing spectral reflectance calculation values in the facing-side optical thin film of the output-side reflecting mirror according to the example.

FIG. 5 is a graph showing the spectral reflectance calculation value of the non-opposing side optical thin film of the output side reflecting mirror in the example.

FIG. 6 is a graph showing spectral reflectance calculation values of an antireflection film provided on a bonding surface of an optical first transparent substrate and an optical second transparent substrate.

7 (A) and 7 (B) are operation explanatory views of a pair of reflecting mirrors according to claim 1. FIG.

8 (A) and 8 (B) are operation explanatory views of a pair of reflecting mirrors according to claim 2;

9 (A) to 9 (C) are sectional views showing the configuration of a reflecting mirror according to the present invention.

FIG. 10 is a graph showing the relationship between the phase matching angle θ of KTP forming the wavelength conversion element and the wavelengths of idler light and signal light.

FIG. 11 is a schematic top view of a conventional wavelength tunable laser device.

FIG. 12 is a graph showing calculated spectral reflectance values of an optical thin film of an input-side reflecting mirror according to a conventional example.

FIG. 13 is a graph showing the calculated spectral reflectance of the optical thin film of the output-side reflecting mirror according to the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pump light source 2 Wavelength conversion element 3 Input-side reflecting mirror 4 Output-side reflecting mirror 31 Non-opposing optical thin film 32 Opposing optical thin film 41 Non-opposing optical thin film 42 Opposing optical thin film 50 Optical adhesive 51 Optical first transparent substrate 52 Optical Second Transparent Substrate 61 Antireflection Film 62 Antireflection Film

Claims (6)

[Claims] 1. A pump light source side centering on a wavelength conversion element which is made of a non-linear optical crystal and is rotatably provided around the Y axis of the crystal and which converts incident pump light into signal light and idler light. In the pair of reflecting mirrors for the wavelength tunable laser device, which are respectively arranged on the opposite side and constitute the resonator of the signal light and the idler light, the input side reflecting mirror arranged on the pump light source side is an optically transparent substrate. And a non-opposing optical thin film provided on the pump light incident surface of this substrate and having a high reflection function for one of the signal light and idler light, and one of the above-mentioned light provided on the opposite surface of this substrate. On the other hand, the output-side reflecting mirror, which is composed of the opposite-side optical thin film that has an antireflection function and a high-reflecting function for the other light, and is arranged on the opposite side of the pump light source, is A bright substrate, and an opposite side optical thin film having an antireflection function with respect to the one light and having a high reflection function with respect to the other light, which is provided on a surface facing the input side reflecting mirror of the substrate. A pair of non-opposing optical thin films provided on the opposite surface of the substrate and having a high reflection function for the one light and an antireflection function for the other light. Reflector. 2. A pump light source side centering on a wavelength conversion element which is made of a non-linear optical crystal and is rotatably provided around the Y axis of the crystal and which converts incident pump light into signal light and idler light. In the pair of reflecting mirrors for the wavelength tunable laser device, which are respectively arranged on the opposite side and constitute the resonator of the signal light and the idler light, the input side reflecting mirror arranged on the pump light source side is an optically transparent substrate. And a non-opposing optical thin film provided on the pump light incident surface of this substrate and having a high reflection function for one of the signal light and idler light, and one of the above-mentioned light provided on the opposite surface of this substrate. On the other hand, the output-side reflecting mirror, which is composed of the opposite-side optical thin film that has an antireflection function and a high-reflecting function for the other light, and is arranged on the opposite side of the pump light source, is A bright substrate, and an opposing optical thin film provided on the surface of the substrate facing the input side reflecting mirror and having an antireflection function for the other light and a high reflection function for the one light, A pair of non-opposing optical thin films provided on the opposite surface of the substrate and having a high reflection function for the other light and an antireflection function for the one light. Reflector. 3. The input-side reflecting mirror and the output-side reflecting mirror each have an optical first transparent substrate having a non-opposing optical thin film on one surface, and an optical second transparent substrate having an opposing optical thin film on one surface. The pair of reflecting mirrors according to claim 1 or 2, further comprising: a transparent substrate; and an optical adhesive having the same refractive index as that of the transparent substrate and bonding the opposite surfaces of the transparent substrates to each other. 4. The input-side reflecting mirror and the output-side reflecting mirror each have an optical first transparent substrate having a non-opposing optical thin film on one surface, and an optical second transparent substrate having an opposing optical thin film on one surface. A transparent substrate and an optical adhesive having a refractive index different from those of the transparent substrates and bonding the opposite surfaces of the transparent substrates to each other are provided, and the bonding surface of each transparent substrate reflects the refractive index of the optical adhesive. The pair of reflecting mirrors according to claim 1 or 2, wherein an anti-reflection film is provided respectively. 5. A pump light source side centering on a wavelength conversion element which is made of a non-linear optical crystal and is rotatably provided around the Y axis of the crystal and which converts incident pump light into signal light and idler light. And a pair of reflecting mirrors arranged on the opposite side of the resonator for a wavelength tunable laser device, wherein the pair of reflecting mirrors according to claim 1, 2, 3 or 4 is incorporated. A resonator characterized by being provided. 6. A pump light source, a wavelength conversion element comprising a non-linear optical crystal, rotatably provided around the Y axis of the crystal, and converting incident pump light into signal light and idler light, and this wavelength. 6. A wavelength tunable laser device comprising a pump light source side and a resonator constituted by a pair of reflecting mirrors arranged on the opposite side of the conversion element as a center, wherein the resonator according to claim 5 is used as the resonator. A tunable laser device characterized by being incorporated.