JP5453656B2 - Thermal lens forming element and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical path switching device and a thermal lens forming element used in an optical path switching method and a manufacturing method thereof, which are useful in the fields of optical electronics and photonics such as optical communication and optical information processing.

  As an optical path switching method and apparatus based on a completely new principle, the inventors of the present invention have a control light absorption region in a thermal lens forming element, a control light in a wavelength band absorbed by the control light absorption region, and a control light absorption region. The signal light in the wavelength band that is not absorbed is converged and irradiated so that the optical axes coincide with each other. When the control light is not irradiated, the signal light travels straight through the hole in the mirror, while the control light is irradiated. In this case, the inventors have invented a method and an apparatus for changing the optical path by reflecting using a mirror with a hole provided to be inclined with respect to the traveling direction of the signal light (see Patent Document 1). The background art prior to the present invention is described in detail in Patent Document 1.

  The inventors have also invented an optical control type optical path switching type optical signal transmission device and an optical signal optical path switching method using a combination of a plurality of thermal lens forming elements and mirrors with holes (see Patent Document 2). When the control light is irradiated in the optical path switching methods described in Patent Document 1 and Patent Document 2, the beam cross-sectional shape of the signal light becomes a ring shape due to the thermal lens effect. Therefore, this method is hereinafter referred to as “ring beam method”.

  The inventors have also filed the invention described below. The control light in the wavelength band that is absorbed by the control light absorption region and the signal light in the wavelength band that is not absorbed by the control light absorption region are incident on the control light absorption region in the thermal lens forming optical element. The light and the signal light are irradiated so as to converge in the control light absorption region, and the control light and the signal light are irradiated such that the positions of the convergence points of the control light and the signal light are different from each other. The signal light is diffused after converging at or near the incident surface of the control light absorption region in the light traveling direction. Thereby, a thermal lens is formed reversibly due to the temperature rise occurring in the control light absorption region and the peripheral region thereof, and the refractive index is changed by the formed thermal lens, An optical change method and an optical path switching device characterized by changing the traveling direction of the signal light have been disclosed (see Patent Documents 3 to 5). In Patent Documents 3 to 5, the control light absorption region of the thermal lens forming optical element is disclosed in which a pigment is dissolved in a solvent and sealed in a glass container, and as the solvent, at least the pigment to be used is dissolved. Suitable when the temperature rises at the time of forming the thermal lens without being thermally decomposed and having a boiling temperature (boiling point) of 100 ° C. or higher, preferably 200 ° C. or higher, more preferably 300 ° C. or higher. It is described that it can be used. However, Patent Documents 3 to 5 do not describe the temperature characteristics of the refractive index and viscosity of the solvent. In the optical path switching methods described in Patent Documents 3 to 5, the beam cross-sectional shape of the signal light is kept substantially circular even when the control light is irradiated. Therefore, this method is hereinafter referred to as “round beam method”.

  Some of the present inventors irradiate an optical cell filled with a liquid photoresponsive composition with control light having a wavelength to which the photoresponsive composition is sensitive, and a signal in a wavelength band different from that of the control light. A light control method for performing intensity modulation and / or light flux density modulation of the signal light transmitted through the optical cell by reversibly changing light transmittance and / or refractive index, wherein the control light and the light Signal light is converged and irradiated to the optical cell, and regions having the highest photon density in the vicinity of the respective focal points of the control light and the signal light are mutually in the photoresponsive composition in the optical cell. The optical paths of the control light and the signal light are respectively arranged so as to overlap, and the signal light beam bundle that diverges after passing through the photoresponsive composition in the optical element is reflected by the signal light convergence means. Also small Invented a light control method characterized by separating and extracting signal light beam bundles in a region that has been strongly subjected to intensity modulation and / or light beam density modulation by receiving light with a convex lens or concave mirror having a numerical aperture (Patent Document 6). reference). Patent Document 6 also does not describe the temperature characteristics of the refractive index and viscosity of the solvent. Patent Document 6 describes a thermal lens forming element in a form in which a flat rectangular parallelepiped space composed of two glass plates and a spacer of an optical cell is filled with a dye solution. There is no description at all regarding the fluctuation of the thermal lens effect when the direction is changed.

Some of the present inventors have called an optical cell filled with a liquid photoresponsive composition as a thermal lens forming element, and used as a solvent for a dye solution that absorbs control light having a wavelength to which the photoresponsive composition is sensitive. A solvent having a viscosity at 160 ° C. or higher of 0 to 3 mPa · s and a viscosity value at 160 ° C. of the viscosity at 40 ° C. of 1 or higher and 6 or lower; As a cell form, the dye solution is filled in a first space in the shape of a cylinder having an optical axis of incident signal light as a central axis or an N prism (N is an integer of 4 or more) circumscribing the cylinder. As an absorption region, the first space is connected to the second space via a solution introduction path and a weir, and the second space is filled with the dye solution and the inert gas bubbles 14. It disclosed (refer patent document 7). In the thermal lens forming element (optical cell) of Patent Document 7, only a method of sealing a dye solution by adhering a lid to the dye solution injection hole of the optical cell with an adhesive is disclosed.

Japanese Patent No. 3809908 Japanese Patent No. 3906926 JP 2007-225825 A JP 2007-225826 A JP 2007-225827 A Japanese Patent No. 3504076 JP 2009-175164 A

  The present invention eliminates the method of adhering a lid to an injection hole after injecting a dye solution into an optical cell of a thermal lens forming element, and eliminates the possibility of solvent molecules, oxygen molecules, and water molecules permeating through the adhesive layer. For the purpose.

  Another object of the present invention is to reduce the manufacturing cost by simplifying the shape of the optical cell of the thermal lens forming element.

  Another object of the present invention is to minimize fluctuations in the thermal lens effect when the orientation of the thermal lens forming element is changed with respect to the direction of gravity.

  The present invention has the following features.

(1) A thermal lens forming element comprising an optical cell filled with a dye solution prepared by dissolving a dye that absorbs light of control light in a solvent without absorbing light of the wavelength of the signal light,
The optical cell has a control light absorption region arranged so that at least the control light is focused,
The shape of the control light absorption region is a square cross-section hollow tube having two outer planes and two inner planes parallel to each other for a total of four of the planes, the two outer planes and 2 being parallel to each other Both inner planes are perpendicular to the optical axis when the control light is not irradiated and the signal light travels straight, and the sizes of the two outer planes and the two inner planes parallel to each other are The area where the light and signal light are incident and the area where the signal light which goes straight or is switched after passing through the optical path passes are flat, and both ends of the square cross-section hollow tube are melt sealed at the melting point of the material. The control light absorption region has a control light having a wavelength selected from a wavelength band absorbed by the control light absorption region and a wavelength selected from a wavelength band not absorbed by the control light absorption region. And the control light and the signal light are irradiated so that the positions of the convergence points of the control light and the signal light are the same or different, and the control light absorption region absorbs the control light, and A thermal lens is formed based on the refractive index distribution that is reversibly formed due to the temperature rise that occurs in the surrounding area,
When the control light is not irradiated and a thermal lens is not formed, the converged signal light is emitted in a normal opening angle and a straight direction, and
When the control light is irradiated so that the positions of the convergence points of the control light and the signal light are the same to form a thermal lens, the converged signal light has an opening angle larger than a normal opening angle. When the control lens is irradiated with the control light and the thermal lens is formed so that the positions of the convergence points of the control light and the signal light are different from each other, the converged signal light has a normal opening angle. A different opening angle and a state of emitting in a direction different from the straight direction,
Realized corresponding to the presence or absence of irradiation of the control light ,
And,
The dye solution is present as one liquid column without bubbles at one end in the square cross-section hollow tube, and one bubble for maintaining the one liquid column is present at the other end as a liquid column of the dye solution. Exists in contact with
The pressure of the bubbles at room temperature is 0.4 to 0.7 atm,
When the pressure is 0.4 to 0.5 atm, the volume of the bubbles is 20% or more and 60% or less of the volume of the square cross-section hollow tube,
When the pressure is 0.6 atm, the volume of the bubbles is 25% or more and 60% or less of the square cross-section hollow tube volume,
When the pressure is 0.7 atm, the bubble volume is 40% or more and 60% or less of the square cross-section hollow tube volume .

(2) The thermal lens forming element according to the above (1), wherein the oxygen concentration in the gas constituting the one bubble is 0.5 ppm or less and 0 ppm or more .

(3) The non-reflective coating film having a thickness of 10 nm to 200 μm made of a transparent organic polymer film having a refractive index of 1.2 to 1.4 is provided on the surface of the square cross-section hollow tube (1) Or a thermal lens forming element according to (2).

(4) at least, angles made preforms for quartz glass square section hollow tubes used as rectangular cross-section container of the thermal lens forming device, the two outer planes and two inner planes parallel to each other physician A step of deforming into a mold-section hollow tube;
Cutting the square cross-section hollow tube into a hollow tube having both ends open;
Sealing one end of a square cross-section hollow tube having two outer planes and two inner planes parallel to each other ;
A step of preparing a dye solution in which a dye that does not absorb the light of the signal light and absorbs the light of the control light is dissolved in a solvent;
Injecting the dye solution into a square cross-section hollow tube having two parallel outer flat surfaces and two inner flat surfaces sealed at one end;
After injecting the dye solution, vacuuming the space where the dye solution of the square cross-section hollow tube is not injected, and then temporarily sealing with an adhesive; and
Heating and sealing one end of the square cross-section hollow tube at a position where the dye solution does not exist in the square cross-section hollow tube into which the dye solution has been injected;
The manufacturing method of the thermal lens formation element which has this.

  Low manufacturing cost of thermal lens forming element that exhibits thermal lens effect with low power of less than 30mW of control light, high response speed of less than 1ms for ring beam method and less than 10ms for round beam method Can be realized. Further, it is possible to provide a thermal lens forming element with little variation in the thermal lens effect even when the direction of the element is changed with respect to the direction of gravity. Furthermore, the thermal lens formation element which can be used in the temperature range of -40-85 degreeC can be provided. Furthermore, if the thermal lens forming performance is maintained for 5 years or more under actual use conditions, a thermal lens forming element capable of this can be provided.

It is a schematic block diagram of the cross section of the thermal lens formation element in Embodiment 1 of this invention. It is a schematic block diagram of the cross section of the thermal lens formation element in Embodiment 1 of this invention, and is a case where a cross section is a square. It is a schematic block diagram of the cross section of the thermal lens formation element in Embodiment 1 of this invention, and is a case where a cross section is a rectangle. It is a schematic process drawing for demonstrating the filling process of the pigment | dye solution to the square cross-section hollow tube for thermal lens formation elements in Embodiment 1 of this invention. It is a schematic block diagram of an example of the optical path switching apparatus using the thermal lens formation element of this invention. It is a schematic block diagram of an example of the optical path switching apparatus using the thermal lens formation element of this invention. It is a mass spectrometry gas chromatogram of solvent # 1 used for the thermal lens formation element of the present invention. It is a graph showing the refractive index and temperature dependence of solvent # 1 used for the thermal lens formation element of this invention. It is a graph showing the refractive index and temperature dependence of solvent # 2 used for a comparative example. It is a graph showing the viscosity and temperature characteristic of solvent # 1 and solvent # 2. The thick line indicates the characteristics of solvent # 1, and the thin line indicates the characteristics of solvent # 2. It is a figure which shows the response | compatibility of the cross-sectional shape of the signal light beam radiate | emitted from the thermal lens formation element of this invention, and control light power, Comprising: It is a signal light beam (round beam of Gaussian distribution) when not irradiating control light. It is a figure which shows the correspondence of the cross-sectional shape of the signal light beam radiate | emitted from the thermal lens formation element of this invention, and control light power, Comprising: It is a signal light beam cross section at the time of irradiating control light power 2.2mW. It is a figure which shows the response | compatibility of the cross-sectional shape of the signal light beam radiate | emitted from the thermal lens formation element of this invention, and control light power, Comprising: It is a signal light beam cross section at the time of irradiating control light power 4.3mW. It is a figure which shows the correspondence of the cross-sectional shape of the signal light beam radiate | emitted from the thermal lens formation element of this invention, and control light power, Comprising: It is a signal light beam cross section at the time of irradiating control light power 7.6mW. It is a figure showing the waveform of control light and signal light observed with an oscilloscope. It is a figure showing the waveform of control light and signal light observed with an oscilloscope. It is a figure showing the relationship between the frequency which interrupts control light, and the intensity | strength (amplitude) of the signal light by which the optical path was switched. It is a figure showing the relationship between the frequency which interrupts control light, and the intensity | strength (amplitude) of the signal light by which the optical path was switched. It is a figure showing the relationship between the change angle | corner and control light power in the round beam type optical path switching apparatus using the thermal lens formation element of this invention and a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings of FIGS. 1B is a cross-sectional view taken along the line AA ′ in FIG. 1A, and FIGS. 2A and 2B are cross-sectional views taken along the line BB ′ in FIG. is there.

(Embodiment 1)
FIG. 1A to FIG. 1B are schematic configuration diagrams of an example of a thermal lens forming element 1 according to Embodiment 1 of the present invention.

Configuration of thermal lens forming element:
[Square cross-section hollow tube]
Quartz glass is preferably used as the material of the square cross-section hollow tube used in the thermal lens forming element 1 of the present invention and having two outer planes and two inner planes parallel to each other for a total of four such planes.

  The thickness S of the quartz glass plate constituting the tube wall of the square cross-section hollow tube is preferably 100 μm to 500 μm. If the thickness S of the quartz glass plate material is thinner than 100 μm, the quartz glass plate is easily damaged due to insufficient strength. On the other hand, if the thickness of the quartz glass plate is greater than 500 μm, the degree of deterioration of the beam shape of the signal light that is incident while converging or the signal light that is emitted while diffusing and changing is affected by refraction, that is, the beam cross-sectional shape This is not preferable because the deviation from the yen increases.

  The size of the square cross-section hollow tube is determined to be the optimum size in relation to processing constraints, the length of the liquid column length of the dye solution injected into the inside, and the size of the thermal lens effect. Is done.

  First, as a processing restriction, when the end of the square cross-section hollow tube having a width of 1 mm or less on the outer plane is sealed by heating and melting at a melting point of about 170 ° C. of quartz glass, the end of the inner dye solution is melted. The distance H of the sealing portion is a minimum of 10 mm, the upper limit is not limited in processing, and is preferably as short as possible from the viewpoint of industrial use, and is preferably within 15 mm. On the other hand, it is preferable that the size of the square cross-section hollow tube is limited in processing, and the length M of the liquid column of the dye solution injected therein is about 1 mm at the minimum and about 15 mm at the maximum. If the length M of the liquid column is shorter than 1 mm, the plane portion through which the signal light and the control light pass may be affected by the shape of the melt-sealed end face of the square cross-section hollow tube. There is no particular upper limit on the length M of the liquid column, but it is preferably shorter than 15 mm at the longest in the dye solution filling operation. Accordingly, when the liquid column of the dye solution is brought to one end of the square cross-section hollow tube and filled with a length of 5 to 10 mm, the total length of the square cross-section hollow tube is 20 to 25 mm. .

  On the other hand, the distance between the two inner planes of the square cross-section hollow tube used for the thermal lens forming element 1, that is, the thickness of the dye solution (optical path length d) is optimal from the viewpoint of the response speed of thermal lens formation and extinction. The size is determined. That is, in order to form the thermal lens in the control light absorption region as effectively as possible, a certain amount of thermal energy needs to be accumulated in a specific region. For example, when a dye thin film is directly formed on a glass substrate by vacuum vapor deposition, even if the control light is convergently irradiated, the generated heat is instantaneously diffused, so that a detectable thermal lens effect does not occur. As a result of investigating the magnitude of the thermal lens effect by using the dye solution described later and changing the thickness of the dye solution in which the control light and the signal light travel, the thickness (optical path length d) of the dye solution is 200 μm to 500 μm. It was found to be suitable. When the thickness of the dye solution is less than 200 μm, even if the control light power is increased, loss due to heat diffusion becomes dominant, and a large thermal lens effect cannot be obtained. In addition, even if the thickness of the dye solution is thicker than 500 μm, the magnitude of the thermal lens effect does not change. On the other hand, the signal light beam diffuses in the dye solution obliquely or with respect to the incident surface and the exit surface. However, the degree of deterioration of the shape of the signal light beam after emission due to traveling for a long distance increases, which is not preferable. In the above experiment, “the size of the thermal lens effect” means the ring size of the cross section of the outgoing signal light in the case of the ring beam method, and the signal light emitted from the thermal lens forming element in the case of the round beam method. The optical path switching angle can be clearly detected and compared.

  The width D of the inner plane of the rectangular cross-section hollow tube used for the thermal lens forming element 1 is such that the control beam and the signal beam are converged and incident on the plane portion, and the signal beam is emitted while spreading. , And the beam diameter and output position of the signal light emitted by changing the optical path. It is assumed that the signal light passes through the center of a circle 9 (its diameter Q = D) inscribed in the inner plane 6 or 7 of the square cross-section hollow tube. Specifically, when the larger beam diameter of the signal light and control light incident on the thermal lens forming element 1 is R, the minimum value of the width D of the inner plane of the square cross-section hollow tube is It may be about twice as large as the larger beam diameter R. When the minimum value of the width D or the minimum value of the length M is smaller than 2R, the signal light emitted while spreading may be blocked by the inner side surface orthogonal to the inner plane of the rectangular cross-section hollow tube. The beam diameter R is the largest when collimated collimated light from the multimode fiber is incident as signal light or control light, and R is around 100 μm. That is, the minimum value of 2R, that is, D is 200 μm.

  The width D of the inner flat surface of the square cross-section hollow tube is twice the thickness S of the quartz glass plate material due to restrictions on the strength of the quartz glass constituting the tube wall of the square cross-section hollow tube. If it exceeds, it becomes easy to break. When the thickness S is 100 μm, the restriction of the signal light or the control light beam, that is, D is 200 μm, the two restrictions are satisfied simultaneously. When the thickness S is 200 to 250 μm, the maximum value of D is 400 to 500 μm, which is suitable in terms of intensity and transmission of signal light or control light beam.

In summary, preferred embodiments of the dimensions of the square cross-section hollow tube used in the thermal lens forming element 1 are as follows:
(1) Tube wall thickness S of the square cross-section hollow tube: 200 to 250 μm
(2) Width D of inner plane of the square cross-section hollow tube: 400 to 500 μm
(3) Width D of outer plane of the square cross-section hollow tube: 800 to 1000 μm
(4) Distance between two inner planes of the square cross-section hollow tube d: 200 to 500 μm
(5) Length M of the liquid column of the dye solution injected into one end inside the square cross-section hollow tube:
1-15mm
(6) Distance H between the end portion of the internal dye solution and the melt-sealed portion: 10 to 15 mm.

[Manufacture of square cross-section hollow tubes]
A square cross-section hollow tube 3 used in the thermal lens forming element 1 of the present invention is manufactured by melt-drawing and cooling a preform of a square cross-section hollow tube manufactured by a known method by a known method. be able to. A preferred embodiment in terms of the dimensions of the square cross-section hollow tube is as described above.

  The following tolerances must be satisfied for the parallelism and smoothness of the four surfaces (two outer planes 4, 5 and two inner planes 6, 7) of the rectangular cross-section hollow tube through which the signal light passes. Is preferred. The X, Y, and Z axes are defined as follows.

X-axis: Longitudinal direction of the square cross-section hollow tube Y-axis: Parallel to the four faces of the square cross-section hollow tube through which signal light passes and orthogonal to the long axis of the square cross-section hollow tube Z-axis: Angle Direction of signal light passing perpendicularly through the four surfaces 4, 5, 6, and 7 of the mold section hollow tube (1) Smoothness: λ / 4 for light with a wavelength (λ) of 980 to 1600 nm
(2) Angle deviation in the X axis direction with respect to the Z axis: 1 degree or less, preferably 0.5 degrees or less (3) Angle deviation in the Y axis direction with respect to the Z axis: 1 degree or less, preferably 0.5 degrees or less

[Cutting and cleaning of square cross-section hollow tubes]
The length (H + M) in the major axis direction of the thermal lens forming element 1 is, for example, 20 to 25 mm when the length M of the liquid column of the dye solution is 10 mm. In order to manufacture the thermal lens forming element 1 having this length, a length (specifically, 2 to 3 times the length (H + M) is compensated for in advance by compensating for the length of a portion lost in a process described later. 50-80 mm), it is preferable to cut the square cross-section hollow tube. The square cross-section hollow tube can be cut by a known method. Debris generated during cutting may enter the inside of the square cross-section hollow tube. After cutting, the inside and outside of the square cross-section hollow tube are washed with a known cleaning solvent, washed, and then dried. Let

[One-end sealing and vacuum drying of square cross-section hollow tube]
One end of the square cross-section hollow tube is heated and melted with a burner and sealed. It is preferable to confirm that the pinhole does not remain by magnifying and observing the sealed portion with an optical microscope. Since moisture in the combustion gas of the burner may condense inside the melt-sealed square cross-section hollow tube, the square cross-section hollow tube sealed once is connected to a suitable vacuum container (not shown). ) And vacuum-dried while heating to 80 ° C. or higher, for example. If the pressure inside the vacuum drying chamber reaches less than 3 × 10 ⁻⁴ Pa, the drying is sufficient.

[Solution injection into hollow tube with square cross section]
In order to avoid the adverse effects of moisture and oxygen on the dye solution, the preparation of the dye solution and the following injection process are preferably performed in a glove box (not shown) that satisfies the following conditions.
(1) Oxygen concentration less than 0.5 ppm (2) Moisture concentration less than 0.5 ppm (dew point temperature -80 ° C or less)

  The sealable vacuum container (not shown) is put into the glove box through a pass box, and then the one-end-sealed rectangular cross-section hollow tube 8 after vacuum drying is taken out. The solution injection tube 20 is inserted into the inside of the one-end sealed square cross-section hollow tube 8 until the tip reaches the sealed end of the one-end sealed square-section hollow tube 8, and the dye solution is passed through the solution injection tube 20. Inject. The injection amount of the dye solution is adjusted so that the length of the liquid column of the dye solution is 1 to 15 mm after the solution injection tube 20 is pulled out.

[Temporary sealed hollow tube with one end temporarily sealed]
Adhesive that requires one hour or more for curing the one-end-sealed rectangular cross-section hollow tube 8 in which the dye solution is injected on the melt-sealed end side, and has no component that volatilizes when the pressure is reduced to the pressure described later. Place it in a container containing the agent and place it in a suitable vacuum chamber (eg, the pass box), for example, maintain the pressure at 0.4 atm and wait for the adhesive to cure. As the adhesive, for example, an epoxy adhesive having no volatile component can be suitably used. The amount of the adhesive used is preferably a minimum amount for temporarily sealing the open end of the one-end-sealed square cross-section hollow tube 8, for example, 50 to 100 mg. The size of the container for containing the adhesive is, for example, high It is 10-20 mm in length and is large enough to vertically support the one-end sealed square cross-section hollow tube 8, and the cross-section is the minimum necessary for inserting the one-end sealed square cross-section hollow tube 8 It may be a large size, for example, a circle having a diameter of 2 to 3 mm.

[Sealing the other end of the square tube]
After the adhesive is cured and the temporary sealing of the one-end sealed square cross-section hollow tube 8 is completed, the one-end sealed square cross-section hollow tube 8 is taken out from the glove box / the vacuum chamber and filled with the dye solution. The part where the dye solution does not exist is melt-sealed with a gas burner. By performing the melting and sealing within 1 second using a burner flame of the minimum necessary size, the melting and sealing of quartz glass can be completed without affecting the internal dye solution. In order to confirm the completeness of the sealed state of the thermal lens forming element 1 of the present invention completed by sealing both ends, the weight (10 to several tens of milligrams) of the thermal lens forming element 1 was precisely measured in μg units. Thereafter, for example, after heating was continued at 85 ° C. for 1000 hours, the weight was accurately measured. As a result, it was confirmed that the weight change was within ± 2 μg, and it was found that the sealing was complete.

[Non-reflective coating]
For the refractive index of air, the refractive index of quartz glass, which is the material of the square cross-section hollow tube of the thermal lens forming element 1 of the present invention, is 1.46 to 1.50 in the infrared region with a wavelength of 1.5 μm. Therefore, if the non-reflective coating is not performed, a reflection loss of 4 to 5% is generated with respect to the signal light or the control light that is perpendicularly incident on the outer plane 4 or 5, so that the signal light and the control light to be used are used. It is recommended to apply an anti-reflection (AR) coating corresponding to the wavelength of. As the AR coat, a known one can be used. For example, a dielectric multilayer film corresponding to the wavelength of signal light and control light to be used, or a transparent organic polymer film having a refractive index intermediate between the refractive indices of air and quartz glass can be used. However, the vacuum process for forming the transparent organic polymer film on the surface of the thermal lens forming element 1 is usually low in productivity by batch processing and exposed to high temperature. In order to prevent contamination of the inside of the square cross-section hollow tube of the thermal lens forming element 1, for example, both ends of the square cross-section hollow tube are temporarily melt-sealed and a dye solution is injected. It is necessary to add a process such as opening one end before. On the other hand, a method in which an AR coating layer is formed by applying a solution obtained by dissolving a transparent organic polymer in an appropriate volatile solvent to the surface of the thermal lens forming element 1 by dipping or the like, and drying it. AR coating is possible after injecting the dye solution into the inside of the square cross-section hollow tube 1 and melting and sealing both ends, and the manufacturing process can be rationalized. The refractive index of the transparent organic polymer is preferably 1.2 to 1.4 in the infrared region having a wavelength of 1.5 μm from the visible light region. A refractive index of about 1.35 is more preferable. Even if the refractive index is smaller or larger than the above range, the effect of reducing the reflection loss is small. As a specific example of the transparent organic polymer solution, a solution obtained by dissolving an organic fluororesin “CYTOP” (registered trademark) (manufactured by Asahi Glass Co., Ltd.) in a fluorine-based solvent can be preferably used. The refractive index of this polymer film is 1.34. The thickness of the AR coating film by coating is preferably 10 nm to 200 μm. If it is thinner than this, a pinhole may be formed in the coating film. Moreover, when a film thicker than this is formed by a coating method, unevenness in film thickness tends to occur. If the thickness of the AR coating film is 100 μm to 200 μm, the planar portion of the thermal lens forming element 1 of the present invention made of very thin quartz glass can be reinforced to improve impact resistance.

[Dye solution]
The dye solution in the present invention is a solution in which a dye that does not absorb signal light wavelength but absorbs control light is dissolved in a solvent.

[Dye]
The dye used in the thermal lens forming element of the present invention must satisfy the following severe requirements.

(A) Withstand the irradiation of the convergent laser in the absorption wavelength band of the control light for 2,000 hours or more, preferably tens of thousands of hours or more.
(B) Withstand a temperature increase exceeding 200 ° C. at the convergence position of the converging laser in the absorption wavelength band of the control light for 2,000 hours or more, and tens of thousands of hours if possible.
(C) Do not form solid particles such as decomposition products, reaction products, or aggregates by irradiation with a converging laser in the controlled light absorption wavelength band and temperature rise.
(D) Do not cause light absorption or light scattering in the wavelength band of signal light.

As specific examples of the dye, in the case of a signal light wavelength of 980 to 2000 nm, the following solvent-soluble phthalocyanine derivatives can be suitably used according to the band of the control light wavelength.
650-670 nm: 1,5,9,13-tetra-tert-butyl copper phthalocyanine,
685-715 nm: 1,5,9,13-tetra-tert-butyloxyvanadium phthalocyanine,
730-830 nm: 2,11,20,29-tetra-tert-butyloxyvanadium naphthalocyanine,
840-890 nm: 5, 9, 14, 18, 23, 27, 32, 36-octa-n-butoxy-2,3-copper naphthalocyanine.

[solvent]
The solvent used in the thermal lens forming element of the present invention must satisfy a plurality of requirements as follows.

[1] The dye used for the thermal lens forming element of the present invention is stably dissolved at an appropriate concentration.
[2] Endure 2,000 hours or more, preferably tens of thousands of hours if possible, with signal light and control light laser irradiation.
[3] Withstand a temperature rise exceeding 200 ° C. at the convergence position of the signal light and the control light laser for 2,000 hours or more, preferably tens of thousands of hours or more.
[4] Do not form solid particles such as decomposition products, reaction products, or aggregates by irradiation with signal light and control light laser and temperature rise.
[5] Do not cause light absorption or light scattering in the wavelength band of signal light.
[6] Respond sensitively to heat generation and temperature rise accompanying light absorption at the converging position of the control light laser, and indicate a refractive index change per change of 1 ° C. of 0.0004 or more.

[Melting point and boiling point of solvent]
In order to widen the application field as a thermal lens forming element, it is preferable that the usable temperature range is wide. For example, in order to utilize in the field of optical communication, it is required to operate without any trouble in a temperature range of -40 ° C to 85 ° C. If the melting point of the solvent is less than −40 ° C., it is possible to meet such a requirement in a low temperature range. In addition, when the temperature has already reached 85 ° C. in the state where the control light is not irradiated, the temperature of the control light irradiation portion can be 200 ° C. or higher in order to fully function as a thermal lens forming element. If so, the dye solution needs to be in a liquid state even when the temperature reaches about 300 ° C. That is, the boiling point of the solvent used in the thermal lens forming element of the present invention is preferably 200 ° C. or higher, and preferably over 300 ° C. if possible. The chemical structure of the solvent component need not be a single structure, but may be a mixture.

As a solvent suitably used for the thermal lens forming element of the present invention, a mixed solvent of the following four structural isomers (with the same molecular weight) is recommended. This solvent is hereinafter referred to as “Solvent # 1”.
First component: 1-phenyl-1- (2,5-xylyl) ethane Second component: 1-phenyl-1- (2,4-xylyl) ethane Third component: 1-phenyl-1- ( 3,4-Xylyl) ethane / fourth component: 1-phenyl-1- (4-ethylphenyl) ethane

  A mass spectrometric gas chromatogram of solvent # 1 is shown in FIG. All four main peaks have a molecular ion peak mass of 210. The correspondence between the individual peaks and the chemical structure is unsolved, but it is clear that the mixture is a structural isomer mixture having the same molecular weight.

Various physical properties of the solvent # 1 are as follows.
・ Appearance: Colorless transparent liquid ・ Odor: Weak aromatic odor ・ Boiling point: 290-305 ℃
Melting point: -47.5 ° C
・ Vapor pressure: 0.067Pa (25 ℃)
・ Vapor density: 7.2 (Air = 1)
Specific gravity (water = 1): 0.987
-Water solubility (20 ° C): Insoluble in water.
Volume thermal expansion coefficient (25 ° C to 85 ° C): about 5%

  On the other hand, examples of the solvent having a boiling point of 300 ° C. or higher and that dissolves the phthalocyanine derivative well include alkylnaphthalene oil for oil diffusion pump “Lion S” (Lion Corporation). This solvent is hereinafter referred to as “Solvent # 2”. The volume coefficient of thermal expansion (25 ° C. to 85 ° C.) of solvent # 2 is about 4%.

  Although the thermal lens forming element using solvent # 2 instead of solvent # 1 shows the thermal lens effect, the ring beam method has a ring size larger than that of solvent # 1 when compared with the same control light power. It was small and the response speed was slow. In the case of the round beam method, the change angle is smaller than that of the solvent # 1, and the response speed is slow.

  In order to elucidate the cause of the quality of the thermal lens effect due to the kind of the solvent, the following examination was performed.

[Measurement of temperature change of refractive index]
The refractive index from 20 ° C. to 90 ° C. was measured using a sample part warm water circulation refractometer NAR-2T type (manufactured by Atago Co., Ltd.). Changes in refractive index and temperature of solvent # 1 and solvent # 2 are shown in FIGS. 7 and 8, respectively.

The observed temperature change of the refractive index can be approximated by a straight line, and it is determined that there is no particular problem even if extrapolating to 200 ° C. or higher. The temperature change coefficient of the refractive index was measured as follows.
Solvent # 1: -0.00048866
Solvent # 2: -0.00042963
That is, it was found that although there was a difference in refractive index and temperature change coefficient between solvent # 1 and solvent # 2, it was not so remarkable.

[Measurement of temperature change of viscosity]
When the viscosity and temperature changes of solvent # 1 and solvent # 2 were measured and compared, it was found that there was a significant difference, leading to the present invention.

  Viscosity and temperature change can be measured by placing the sample liquid in a measuring device such as a capillary viscometer or Heppler type falling ball viscometer and heating the whole to a specified temperature, and then measuring the temperature of the sample liquid. There is a method in which only the temperature is increased and a viscosity sensor is measured together with the temperature by inserting a rotary sensor or tuning fork sensor into the liquid. When the measurement temperature is set to a high temperature of 150 ° C. or higher, it is not easy to perform the measurement operation while uniformly heating the temperature of the entire viscometer. Therefore, a measurement method in which only the sample liquid is heated is adopted. In the method of inserting a rotary sensor into a sample liquid, it is difficult to accurately control the depth at which the sensor is submerged, and it is difficult to accurately measure the temperature of the sensor when the temperature is raised. Then, a tuning fork type sensor having a small heat capacity was inserted into the sample liquid at a certain depth, and the viscosity was measured from the change in the resonance frequency. Use a tuning fork vibration type viscometer SV-10 (manufactured by A & D Co., Ltd.) as a measuring device, calibrate it at a temperature of about 25 ° C. using a standard solution of JIS standard “viscosity 10”, The temperature change was measured. Note that the upper limit of the measurement temperature was set to 160 ° C. due to the specifications of the apparatus. The amount of the sample liquid was 100 ml, and it was heated on a hot plate with a magnetic stirrer at a heating rate of 5 ° C./min with gentle stirring. As the temperature rises, the volume of the sample liquid expands and the liquid level rises. Therefore, a sample container and a hot plate with a magnetic stirrer were placed on a lab jack, the height of the sample container was adjusted, and the positional relationship between the tuning fork sensor of the viscometer and the sample liquid level was kept constant.

  FIG. 9 shows the viscosity / temperature characteristics of solvent # 1 and solvent # 2 measured as described above. In any solvent, when the temperature rises from room temperature, the viscosity rapidly decreases, and then the degree of decrease gradually decreases from around 100 ° C. At 150 ° C or higher, the viscosity change gradually changes. It turns out that it becomes. Moreover, in FIG. 9, it turns out that the viscosity change with respect to the temperature of solvent # 2 (thin curve) is very large compared with solvent # 1 (thick curve). In order to quantitatively represent such a difference in viscosity and temperature characteristics, a numerical value (η1 / η2) obtained by dividing a viscosity value (η1) at 40 ° C. slightly higher than room temperature by a viscosity value (η2) at 160 ° C. It was decided to use. In the field of lubricating oil, a numerical value obtained by dividing the viscosity value at 40 ° C. by the viscosity value at 100 ° C. is used as a numerical expression of the viscosity / temperature characteristics. When the temperature was raised from room temperature and measured, 40 ° C. was selected as the representative temperature on the low temperature side because it was a region where the rate of temperature rise began to stabilize. Due to the limitations of the specifications of the viscometer used, we decided to use a viscosity of 160 ° C as the value on the high temperature side. However, since the viscosity change with respect to the temperature change becomes slow above 150 ° C, the high temperature side related to the thermal lens effect It is judged that it is meaningful as a representative value of. Table 1 shows the results of three measurements taking measurement errors into account.

  When η1 / η2 is compared for solvent # 1 and solvent # 2, the viscosity change η1 / η2 at 40 ° C./160° C. of solvent # 1 is 5.00 on average, while that of solvent # 2 is 13.7 And big. Considering this difference in viscosity and temperature characteristics in the process of “thermal lens formation”, the temperature of the dye solution rises due to the heat generated at the focused control light beam convergence point (size is on the order of several μm). However, when thermal expansion and a decrease in refractive index occur and the region propagates to the periphery, the viscosity around room temperature is relatively low as in solvent # 1, and the viscosity change with temperature rise is small. That is, it is presumed that the shear stress between the solvent molecules is small, and “propagation of thermal expansion” (a phenomenon involving movement of molecules unlike simple heat conduction) proceeds smoothly. On the other hand, when the viscosity near room temperature is relatively high like solvent # 2 and the viscosity change with increasing temperature is large, “propagation of thermal expansion” is hindered by large shear stress with the adjacent “cold solvent molecules”. In addition, it is considered that “propagation of thermal expansion” occurs only when the temperature of neighboring molecules increases (that is, the vibration of molecules increases) due to normal “thermal conduction” and the viscosity decreases. The decrease in the refractive index due to the temperature rise is largely due to “volume expansion = decrease in density”. As a result, “the solvent # 1 in which the volume expansion region propagates faster is faster than the slower solvent # 2, “Refractive index lowering region = thermal lens effect region is widened”.

  From the above viewpoints, as a result of measuring and comparing the viscosity and temperature characteristics of various solvents and comparing them with the magnitude and response speed of the thermal lens effect, the temperature of the solvent in the dye solution of the particularly excellent thermal lens forming element -As viscosity characteristics, the viscosity at 160 ° C or higher is 0 to 3 mPa · s, and the viscosity value η2 of the solvent at 160 ° C divided by the viscosity value η1 of the solvent at 40 ° C η1 / η2 Was found to be 1 or more and 6 or less. The viscosity of a preferable solvent at 160 ° C. or higher is 3 mPa · s or less, and the lower limit is not particularly limited as long as it is a value larger than 0 mPa · s. When the viscosity at 160 ° C. or higher exceeds 3 mPa · s, the thermal lens forming characteristics are further deteriorated and the response speed is lowered as compared with the case of the solvent # 2, and the practicality as a thermal lens forming element is lost. The upper limit 6 of the value η1 / η2 obtained by dividing the viscosity value η1 of the solvent at 160 ° C. by the viscosity value η1 of the solvent at 40 ° C. is a solvent that gives a high thermal lens effect / response speed almost equal to that of the solvent # 1 When the control light power is the same and compared with solvent # 1, the optical path switching angle due to the thermal lens effect becomes smaller or the response speed becomes slower. The lower limit of η1 / η2 is not particularly limited as long as it is a value larger than 1.

  Using the above-mentioned viscosity / temperature characteristics as essential requirements, and further adding the restrictions [1] to [6] of the above-listed solvent requirements and “boiling point 200 ° C. or higher, melting point −40 ° C. or lower” The types of solvents that can be produced are very limited. Specifically, the mixed solvent “solvent # 1” (having the composition shown in FIG. 6) described in detail above and those having a changed composition can be used particularly preferably.

[Inert gas bubbles]
As shown in FIGS. 1A and 1B, the thermal lens forming element 1 of the present invention has a single dye solution 10 at one end of a partially flattened square cross-section hollow tube 3. The column is present without bubbles, and one bubble 11 made of an inert gas described later is in contact with the liquid column of the dye solution 10 at the other end. Since the dye solution exists as a single liquid, even if the thermal lens forming element 1 is impacted from the outside by the frictional force between the wall of the square cross-section hollow tube and the solution, the liquid is not easily divided. It has become.

  A suitable length H of the square cross-section hollow tube 3 of one bubble 11 made of an inert gas is 10 to 15 mm as described above.

  On the other hand, the bubble ratio (K / T) in which the volume K of one bubble 11 made of an inert gas occupies the total internal volume T of the thermal lens forming element 1 is small in order to avoid the adverse effects of the liquid column splitting. Is preferred. Further, when the temperature of the thermal lens forming element 1 rises, the pressure of the bubble 11 rises due to the compression of the bubble 11 due to the temperature rise of the dye solution 10 and the pressure rise based on the gas state equation due to the temperature rise of the bubble 11 itself. To do. Here, since the thickness of the quartz glass which comprises the thermal lens formation element 1 is 100-500 micrometers, there exists a possibility of bursting by the internal pressure rise. In order to reduce the pressure increase of the bubbles 11 accompanying the temperature increase of the thermal lens forming element 1, it is preferable that the bubble ratio K / T is large. Here, as described above, since the distance between the end of the dye solution 10 in the thermal lens forming element 1 and the melt-sealed portion is a minimum of 10 mm, the bubble ratio K / T is a square shape of the thermal lens forming element 1. It is calculated by the formula [1] from the length (H + M) in the long axis direction of the cross-section hollow tube.

[Equation 1]
K / T = 10 / (H + M) [1]

  Assuming that the room temperature is 25 ° C. and the temperature at the time of temperature increase is 85 ° C. (this temperature is widely used in reliability testing of electronic components in the telecommunications field), the volumetric thermal expansion of the dye solution 10 accompanying this temperature change. The rate is estimated to be about 4 to 5%, and about 10% when the temperature is raised above 100 ° C. Since the change in the volume of the liquid due to the pressure is so small that it cannot be observed unless it is an ultrahigh pressure of several megapascals, when the gas and the liquid coexist in the sealed container, the volume of the gas is compressed by the amount of thermal expansion. The When the volume of the bubble 11 at room temperature is V1, the volume of the liquid is V3, the volume of the bubble 11 at the time of temperature rise is V2, the volume of the liquid is V4, and the volume expansion coefficient of the liquid is ΔV, the following relationship is established.

[Equation 2]
V3 = 100-V1 [2]
[Equation 3]
V4 = V3 × ΔV (3)
[Equation 4]
V2 = 100-V4 [4]

  If n is the number of gas molecules, R is the gas constant, the pressure of the bubble 11 of the volume V1 at room temperature T1 is P1, and the pressure of the bubble 11 of the volume V2 at the temperature T2 is P2, the gas equation of state is It is as follows.

[Equation 5]
P1 * V1 = n * R * T1 [5]
[Equation 6]
P2 * V2 = n * R * T2 [6]

Therefore, the pressure increase factor F of the bubble 11 calculated from the gas equation of state is calculated by the following formula:
[Equation 7]
F = P2 / P1 = (T2 / T1) × (V1 / V2) (7)

  From the above, when the pressure of the bubble 11 at room temperature is assumed to be 0.5 atm, the pressure of the bubble 11 when the temperature rises is calculated as shown in Tables 2 and 3.

  That is, even when the volumetric thermal expansion coefficient of the dye solution 10 due to the temperature change is 10%, if the bubble ratio is 20 to 60%, the temperature rises when the pressure of the bubble 11 at room temperature is 0.5 atm. It is possible to maintain the pressure of the bubble 11 at the time of the temperature substantially below atmospheric pressure. When the bubble ratio is smaller than the above range, the length of the dye solution-filled portion is unpreferably practically unfavorable, and when the bubble ratio is larger than the above range, the length of the bubble portion is unnecessarily long.

  Further, Table 4 shows the results of trial calculation of the pressure of the bubbles 11 at the time of temperature rise when the pressure of the bubbles 11 at room temperature is 0.4 to 0.8 atm.

When the pressure of the bubbles 11 at room temperature is 0.4 atm or less, there is an increased risk that the liquid column of the dye solution is divided when subjected to an impact. Further, it can be seen that when the pressure of the bubble 11 at room temperature exceeds 0.7 atm and approaches 0.8 atm, when the temperature rises to 85 ° C., the risk of the thermal lens forming element 1 bursting increases. Furthermore, the optimum range of the bubble ratio changes as follows according to the pressure of the bubble 11 at room temperature.
20 to 60% at 0.4 to 0.5 atm,
25 to 60% at 0.6 bar,
40 to 60% at 0.7 atm.

  As the kind of inert gas, helium, nitrogen, argon, xenon, or the like can be preferably used.

  Using the dye solution filling apparatus filled with these inert gases, the residual oxygen concentration is measured with an oxygen concentration meter, and the dye solution is injected into the thermal lens forming element 1 and sealed, so that the residual oxygen concentrations are different. A plurality of thermal lens forming elements 1 having bubbles 11 made of an inert gas were produced. As the dye solution 10, 1,5,9,13-tetra-tert-butylcopper phthalocyanine is added to the solvent # 1 as a dye that easily undergoes oxidative decomposition due to singlet oxygen when irradiated with light in the presence of oxygen molecules. Used by dissolving at weight%. This dye solution undergoes rapid photooxidative degradation of the dye within a few days under room light irradiation in the atmosphere. When the residual oxygen in the bubbles 11 made of inert gas is several ppm, the absorption spectrum of the 1,5,9,13-tetra-tert-butyl copper phthalocyanine solution hardly changes at room temperature. However, when a heat acceleration test at 85 ° C. is performed, if the residual oxygen concentration is 0.5 ppm or less, the absorption spectrum of the dye does not change for 10,000 hours or more, but about a sample having a residual oxygen concentration exceeding 0.5 ppm. The decrease in absorbance due to dye decomposition was confirmed at 85 ° C. for several thousand hours. Needless to say, the preferable lower limit of the residual oxygen concentration is 0 ppm. Actually, 0.5 ppm or less is sufficient. The residual oxygen concentration of 0.5 ppm or less can be realized, for example, by using a commercially available high purity argon gas or by using a circulating gas regenerator.

[Application to ring beam optical path switching]
FIG. 4 is a schematic configuration diagram of an example of a ring beam type optical path switching device using the thermal lens forming element 1 of the present invention. Details of the ring beam type optical path switching device are described in Patent Document 1. As an outline, the input signal light / incident signal light emitted from the optical fiber 400 is converted into a substantially parallel beam 401 by the collimator lens 40, transmitted through the dichroic mirror 42, and further converged by the condenser lens 43. The light is incident on the thermal lens forming element 1 as light. On the other hand, the control light emitted from the control light / optical fiber 410 is reflected by the dichroic mirror 42 as a substantially parallel beam 411 by the collimator lens 41, and the optical axis of the signal light beam 401 is made coincident. And converged to enter the thermal lens forming element 1 as convergent light. In the ring beam type optical path switching device and method, the control light and the signal light are converged and incident on the control light absorption area of the thermal lens forming element with the same optical axis, and the convergence areas of both the control light and the signal light overlap, The optical system is finely adjusted so as to be positioned near the signal light incident side of the control light absorption region. Then, the control light converged and incident on the vicinity of the signal light incident side of the thermal lens forming element / control light absorption region proceeds while being absorbed in the control light absorption region, and the absorbed light energy is changed to heat, and the dye A density decrease and a refractive index decrease due to the thermal expansion of the solution cause a thermal lens having a specific shape in the light traveling direction. Thus, when the signal light converged and incident inside the thermal lens formed in the control light absorption region travels while spreading, the energy distribution of the beam cross section of the signal light that was Gaussian at the time of incidence is converted into a ring shape. The light is emitted from the thermal lens forming element 1 at an opening angle larger than the angle when the control light is not irradiated. The outgoing signal light is received by a light receiving lens 44 having a numerical aperture larger than that of the condenser lens 43, converted into a substantially parallel beam, and then is sent to a signal light / optical path 45 when traveling straight without being irradiated with control light. When the light is incident on the mirror 45 with a hole provided with a hole of a size large enough to allow the signal light beam to travel straight without being irradiated with the control light, the control light is irradiated. If not, the signal light (straight-ahead signal light) 421 goes straight, enters the coupling lens 46, converges, and enters the straight-ahead output side signal light / optical fiber 420. On the other hand, when the control light is irradiated, the signal light converted into the ring beam by the thermal lens effect is reflected around the hole of the holed mirror 45, converged by the coupling lens 47, and the optical path switching signal light 431. Then, it enters the optical path switching output side signal light / optical fiber 430.

  10a to 10d, a laser having a wavelength of 1550 nm is used as a signal light source, a laser having a wavelength of 660 nm is used as a control light source, and 1,5,9,13-tetra-tert-butylcopper phthalocyanine is used as a pigment in a solvent # 1 in 0.2. The correspondence between the cross-sectional shape of the outgoing signal light beam and the control light power when the thermal lens forming element 1 (optical path length d = 500 μm) of the present invention is filled with a solution dissolved at a concentration of weight% is shown. When the control light is not irradiated, the beam cross-section of the signal light is a round beam having a Gaussian distribution as shown in FIG. 10a. When the control light power is increased to 2.2 mW, 4.3 mW, and 7.6 mW, the beam cross section of the signal light changes as shown in FIGS. 10b, 10c, and 10d, respectively. In this case, when the control light power is 4.3 mW, the shape and size of the ring are optimum. When the power is 2.2 mW, the power is insufficient and the “openness of the ring” is insufficient, and when the power is 7.6 mW, The control light is too strong, the shape of the thermal lens is disturbed, and multiple rings are formed.

  The ring beam type optical path switching device using the thermal lens forming element of the present invention has a control light power as small as 4 to 5 mW, and a Gaussian distribution / round beam when the control light is not irradiated and a control light when the control light is irradiated. Ring beam conversion can be performed.

  In order to investigate the response speed of the ring beam type optical path switching device using the thermal lens forming element of the present invention, the control light power is set at a duty ratio of 1: 1 (that is, the ratio of the control light source lighting time to the turn-off time is 1: 1). The waveform was changed intermittently, and the intensity change waveform of the straight control light was observed with an oscilloscope. In FIG. 4, a part of the control light (incident control light) 411 incident on the thermal lens forming element 1 is guided to the photodetector and the optical path corresponding to the control light waveform 4110 measured on the oscilloscope and the blinking of the control light 411. The switched signal light (optical path switching signal light) 431 is guided to a photodetector and a signal light waveform 4310 measured on an oscilloscope is shown in FIGS. In addition, the vertical axis | shaft of FIG. 12 is expanded 3 times compared with the case of FIG. The result of measuring the amplitude L of the waveform 4310 of the optical path switching signal light 431 corresponding to the interruption of the control light 411 at that time is set to the frequency of the rectangular wave that interrupts the control light 411 from 0.1 kHz to 100 kHz. It is shown in FIG.

  In FIG. 11, the frequency of a rectangular wave that interrupts the control light 411 (FIG. 4) is 500 Hz. If the amplitude L of the waveform 4310 of the signal light corresponding to the intermittent signal light at this time is 1, the control light 411 is In the frequency range of intermittent rectangular waves of 0.2 to 2 kHz, the amplitude L was approximately 1. That is, it was confirmed that complete optical path switching was possible at a response speed of 250 microseconds.

  As an example when the frequency is further increased, a waveform 4310 of signal light at a frequency of 20 kHz is shown in FIG. As can be seen from FIG. 12, when the control light is turned off before the switching of the optical path due to the thermal lens effect is completed, the waveform of the signal light becomes a saw blade and the amplitude L decreases.

  That is, when the response speed of the thermal lens effect is exceeded, the switching of the optical path becomes incomplete, and a part of the signal light goes straight without being switched. As shown in FIG. 13, the amplitude L of the signal light when the frequency of the rectangular wave that interrupts the control light 411 is increased from 2 kHz gradually decreases.

  In order to measure the durability of the optical path switching device of the present embodiment (shown in FIG. 4), the signal light is continuous light, while the control light is irradiated as a rectangular wave intermittent light beam having a frequency of 1 kHz and a duty ratio of 1: 1. Then, the time of the intensity amplitude of the signal light whose optical path was switched was compared. As a result, the intensity amplitude of the signal light was not attenuated even after 10,000 hours had elapsed.

[Comparative Embodiment 1]
The thermal lens forming element of the present invention shown in FIG. 4 is used in the same manner as in the case of using the solvent # 1, except that the solvent # 2 having a large viscosity change when the temperature is changed is used instead of the solvent # 1. In the ring beam type optical path switching device, the frequency of the rectangular wave that interrupts the control light 411 is set to 0.1 kHz to 20 kHz, and the amplitude of the waveform 4310 of the optical path switching signal light 431 corresponding to the intermittentness of the control light 411 at that time The result of measuring L is shown in FIG. When the frequency of the rectangular wave that interrupts the control light 411 is 20 Hz (response speed 25 milliseconds) (not shown), the amplitude L of the signal light is 1, but 200 to 500 Hz (2.5 to 1 millimeter). Second), the signal light amplitude L gradually decreases as shown in FIG. In summary, it has been found that when solvent # 2 is used, the response speed of the thermal lens forming element is reduced to less than one-fourth that of solvent # 1. As described above in detail, since the viscosity of the solvent # 2 is not easily lowered when the temperature rises, the expansion of the low density / low refractive index region accompanying the temperature rise of the signal light convergence / absorption portion is caused. It is estimated that it takes time to form the thermal lens.

[Application to round beam optical path switching]
FIG. 5 is a schematic configuration diagram of an example of a round beam type optical path switching device using the thermal lens forming element 1 of the present invention. Details of the round beam type optical path switching device are described in Patent Documents 3 to 5. As an outline, input signal light / incident signal light emitted from the optical fiber 500 is converted into a substantially parallel beam 501 by the collimator lens 50, transmitted through the dichroic mirror 52, further converged by the condenser lens 53, and converged. The light is incident on the thermal lens forming element 1 as light. On the other hand, the control light emitted from the control light / optical fiber 510 is reflected by the dichroic mirror 52 as a substantially parallel beam 511 by the collimator lens 51, further converged by the condenser lens 53, and the thermal lens forming element as convergent light. 1 is incident. In the round beam type optical path switching device and method, the control light and the signal light are converged and incident on the control light absorption area of the thermal lens forming element, and the center points of the convergence areas of both the control light and the signal light overlap each other by about 30 μm. The optical system is finely adjusted so as to be positioned near the signal light incident side of the control light absorption region. In this way, the control light that has converged and entered slightly away from the thermal lens forming element / control light absorption region in the vicinity of the signal light incident side proceeds while being absorbed in the control light absorption region, and the absorbed light energy is Instead of heat, it causes a decrease in density and a decrease in refractive index due to thermal expansion of the dye solution, and a thermal lens having a specific shape is formed in the light traveling direction. Thus, if the signal light converged and incident at different convergence positions travels inside the thermal lens formed in the control light absorption region, the traveling direction is maintained while maintaining the energy distribution of the cross section of the Gaussian round beam at the time of incidence. Is changed, the optical path is changed several degrees from the straight traveling direction when the control light is not irradiated, and the light is emitted from the thermal lens forming element 1. When this outgoing signal light is received by the light receiving lens 54 and converted into a substantially parallel beam, and the control light is not irradiated, the signal light (straight forward signal light) 521 goes straight and enters the coupling lens 56, The light is converged and enters the straight output signal light / optical fiber 520. On the other hand, when the control light is irradiated, the signal light (optical path switching signal light) 531 whose optical path has been changed as a round beam due to the thermal lens effect passes through the mirror 58, and the signal light (optical path switching signal light) 532. Is incident on the coupling lens 57, converged, and incident on the optical path switching output side signal light / optical fiber 530.

  Here, a laser beam having a wavelength of 1550 nm is used as the signal light source, a laser beam having a wavelength of 660 nm is used as the control light source, and 1,5,9,13-tetra-tert-butylcopper phthalocyanine is used as the dye. The solution dissolved in (1) was filled in the thermal lens forming element 1 (optical path length: 500 μm) of the present invention and attached to the round beam type optical path switching device shown in FIG. 5 to adjust the optical system. When the control light power is 10.0 mW, 12.2 mW, 15.3 mW, 18.7 mW, the change angle of the signal light 531 changed as a round beam by the thermal lens effect is not irradiated with the control light FIG. 15 shows the measurement results when the signal light exit direction is “0 degree” when the control light is not irradiated with the point where the signal light exits the thermal lens forming element 1 as the origin. As the control light power was increased, the change angles increased to 9.3 degrees, 11.4 degrees, 12.8, and 13.7 degrees.

  As a result of optimizing the optical path switching characteristics by adjusting the optical system by setting the control light power to 15.5 mW, the extinction ratio and insertion loss of each of the straight signal light 521 and the optical path switching signal light 532 corresponding to the turning on and off of the control light Was as shown in Table 5 and exhibited excellent optical path switching characteristics. In this measurement, the long axis of the square cross-section hollow tube of the thermal lens forming element 1 and the optical axis of the signal light are arranged perpendicular to the direction of gravity (in FIG. The major axis of the rectangular cross-section hollow tube and the optical axis of the signal light are parallel to the paper surface, and the direction of gravity is the Z-axis minus direction from the top to the bottom of the paper).

[Comparative Embodiment 2]
Using a laser having a wavelength of 1550 nm as the signal light source and a wavelength of 660 nm as the control light source, 1,5,9,13-tetra-tert-butylcopper phthalocyanine as a dye was dissolved in solvent # 2 at a concentration of 0.1% by weight. In the same manner as in this embodiment except that the solution is used, when the control light power is 10.0 mW, 12.2 mW, 15.3 mW, and 18.7 mW, the signal light is changed as a round beam by the thermal lens effect. The change angles of 531 were 6.8 degrees, 7.8 degrees, 9.4 degrees, and 10.3 degrees, respectively, which were clearly smaller than when using solvent # 1, as shown in FIG. . It is presumed that the size of the thermal lens effect induced when the same control light power is continuously applied, that is, the size of the thermal lens, can be estimated due to the difference in the solvent.

[Direction of thermal lens element and optical path switching characteristics]
As shown in FIG. 5, two outer planes and two inner planes parallel to each other for a total of four planes of the thermal lens forming element 1 in the first embodiment mounted on the round beam type optical path switching device are shown. Placed parallel to the paper surface, the long axis passing through the hollow cross-sectional center of the square hollow tube is the “Y axis” parallel to the paper surface, and the traveling direction of the signal light that is perpendicularly incident on the outer plane of the thermal lens forming element 1 Is defined as “X axis”, and the direction of moving upward from the page perpendicular to the page is defined as “Z axis”. Therefore, the case where the round beam type optical path switching device is installed with the positive direction of the Z-axis directed in the same direction as gravity is “Z−”, the case where it is installed in the opposite direction of gravity is “Z +”, and similarly, “X-” when the round beam type optical path switching device is installed with the positive direction of the X-axis directed in the same direction as gravity, “X +” when the circular beam type optical path switching device is installed, and the positive direction of the Y-axis. When the round beam type optical path switching device is installed in the same direction as gravity, “Y−” is displayed, and when it is installed in the opposite direction to gravity, “Y +” is displayed. Table 6 shows the results of measuring the extinction ratio and insertion loss of the optical path switching signal light when is turned off.

  The azimuth dependence of the extinction ratio of the optical path switching signal light is within 0.6 dB, the azimuth dependence of the insertion loss is within 0.05 dB, and no significant azimuth dependence was observed.

[Comparative Embodiment 3]
The thermal lens forming element (not shown) of Comparative Embodiment 3 is a so-called “coin-type cell”, and is composed of two members (on one sheet) obtained by processing a quartz glass plate having a thickness of 500 μm into a disk shape having a diameter of 8 mm. 1 mm diameter dye solution injection hole is provided apart from the center of the disk) and a quartz glass pipe having an outer diameter of 8 mm and an inner diameter of 6.5 mm cut and polished so as to have a height of 500 μm is stacked and fused in order. Manufactured by processing. A dye solution and an inert gas bubble (diameter of about 1 mm) are sealed in a flat cylindrical space inside the coin-type optical cell, and the dye solution injection hole is covered with an epoxy adhesive (diameter 3 mm, thickness). Sealed with a disk of quartz glass plate of 500 μm).

  The optical axis of the signal light (and control light) is the same as that of the first embodiment except that the coin-type thermal lens forming element of the third comparative embodiment is used, the dye, the solvent, and the adjustment / measurement procedure. That is, the orientation of the apparatus is set so that the beam 501 is orthogonal to the direction of gravity, and the control light wavelength 660 nm, the intensity 15.5 mW, the signal light wavelength 1550 nm, and the intensity 2 mW are incident on the round beam type optical path deflecting apparatus. The intensities of the straight signal light 521 and the optical path switching signal light 532 emitted in response to the turning-off / lighting of the control light with respect to the intensity of the signal light / signal light incident from the optical fiber were measured and compared. The results are shown in Table 7.

  As can be seen by comparing Table 7 with Table 5, when the orientation of the apparatus is set so that the optical axis of the signal light, that is, the beam 501 is orthogonal to the direction of gravity, the coin-type thermal lens of Comparative Embodiment 3 The forming element exhibits optical switch characteristics comparable to those of the partially planarized cylindrical thermal lens forming element 1 according to the first embodiment of the present invention.

  However, the round beam method is used so that the azimuth of the coin-type thermal lens forming element rotates around the central axis of the disk forming the coin shape, with the optical axis of the signal light (and control light), that is, the beam 501 as the rotation axis. The above-mentioned extinction ratio was measured by changing the direction of the optical path deflector by 45 degrees. The fluctuation of the extinction ratio was large, and a change of 1 to 2 dB was recognized.

  Further, the direction of the round beam type optical path deflecting device is changed by 45 degrees in parallel with the disk-shaped plane constituting the coin-shaped thermal lens forming element, and the direction orthogonal to the optical axis 501 of the signal light is set as the rotation axis. The intensity ratio was measured. The intensity ratio variation was even greater and the value variation reached a maximum of ± 5 dB.

  In the measurement of changing the above azimuth, a phenomenon in which the fluctuation of the intensity ratio was particularly large in a specific azimuth of the apparatus was observed several times, and the fluctuation of the signal light intensity ratio temporarily reached ± 10 dB. This is presumed that the inert gas bubbles sealed in the coin-type optical cell can move freely inside, so that the control light and signal light paths were crossed during the operation to change the orientation of the device. Is done.

  As mentioned above, as this Comparative Embodiment 3 suggests, if the inside of the optical cell of the thermal lens forming element is not partitioned properly, the “thermal convection” caused in the portion where the temperature rises inside the dye solution and in the vicinity thereof. It happens violently and undesirably affects the formation of the thermal lens as the orientation of the element changes. On the other hand, as described in detail in the first embodiment, the internal space of the partially planarized cylindrical thermal lens forming element 1 of the present invention is partitioned into a highly symmetric and moderately sized space (elongated cylindrical shape). Therefore, even if the orientation of the element changes, the influence on the optical switch characteristics can be reduced.

  As described above, the thermal lens forming element of the present invention can extremely reduce fluctuations in the thermal lens effect when the orientation of the thermal lens forming element is changed with respect to the direction of gravity.

  The present invention can be effectively used in the fields of optical communication and optical information processing.

  DESCRIPTION OF SYMBOLS 1 Thermal lens formation element, 3 square cross-section hollow tube, 4,5 outer plane, 6,7 inner plane, 8 end sealed square cross-section hollow tube, 9 circle, 10 dye solution, 11 bubble, 15, 16 , 17 Square section hollow tube sealing part, 20 solution injection tube, 40, 41, 50, 51 collimating lens, 42, 52 dichroic mirror, 43, 53 condenser lens, 44, 54 light receiving lens, 45 holes Mirror, 46, 47, 56, 57 Coupled lens, 58 Mirror, 400 Input side signal light / optical fiber, 401 Incident signal light (beam), 410 Control light / optical fiber, 411 Incident control light (beam), 420 Straight output side signal Light / Optical fiber, 421 Straight signal light, 430 Optical path switching output signal light / optical fiber, 431 Optical path switching signal light, 500 Input signal light / optical fiber, 5 01 Incident signal light (beam), 510 Control light / optical fiber, 511 Incident control light (beam), 520 Linear output signal light / optical fiber, 521 Linear signal light, 530 Optical path switching output signal light / optical fiber, 531 532 optical path Switching signal light, 4110 Control light waveform, 4310 Signal light waveform.

Claims (4)

A thermal lens forming element comprising an optical cell filled with a dye solution prepared by dissolving a dye that absorbs light of control light in a solvent without absorbing light of the wavelength of the signal light,
The optical cell has a control light absorption region arranged so that at least the control light is focused,
The shape of the control light absorption region is a square cross-section hollow tube having two outer planes and two inner planes parallel to each other for a total of four of the planes, the two outer planes and 2 being parallel to each other Both inner planes are perpendicular to the optical axis when the control light is not irradiated and the signal light travels straight, and the sizes of the two outer planes and the two inner planes parallel to each other are The area where the light and signal light are incident and the area where the signal light which goes straight or is switched after passing through the optical path passes are flat, and both ends of the square cross-section hollow tube are melt sealed at the melting point of the material. The control light absorption region has a control light having a wavelength selected from a wavelength band absorbed by the control light absorption region and a wavelength selected from a wavelength band not absorbed by the control light absorption region. And the control light and the signal light are irradiated so that the positions of the convergence points of the control light and the signal light are the same or different, and the control light absorption region absorbs the control light, and A thermal lens is formed based on the refractive index distribution that is reversibly formed due to the temperature rise that occurs in the surrounding area,
When the control light is not irradiated and a thermal lens is not formed, the converged signal light is emitted in a normal opening angle and a straight direction, and
When the control light is irradiated so that the positions of the convergence points of the control light and the signal light are the same to form a thermal lens, the converged signal light has an opening angle larger than a normal opening angle. When the control lens is irradiated with the control light and the thermal lens is formed so that the positions of the convergence points of the control light and the signal light are different from each other, the converged signal light has a normal opening angle. A different opening angle and a state of emitting in a direction different from the straight direction,
Realized corresponding to the presence or absence of irradiation of the control light ,
And,
The dye solution is present as one liquid column without bubbles at one end in the square cross-section hollow tube, and one bubble for maintaining the one liquid column is present at the other end as a liquid column of the dye solution. Exists in contact with
The pressure of the bubbles at room temperature is 0.4 to 0.7 atm,
When the pressure is 0.4 to 0.5 atm, the volume of the bubbles is 20% or more and 60% or less of the volume of the square cross-section hollow tube,
When the pressure is 0.6 atm, the volume of the bubbles is 25% or more and 60% or less of the square cross-section hollow tube volume,
A thermal lens forming element characterized in that, when the pressure is 0.7 atm, the volume of the bubbles is 40% or more and 60% or less of the volume of the square cross-section hollow tube . 2. The thermal lens forming element according to claim 1, wherein an oxygen concentration in a gas constituting the one bubble is 0.5 ppm or less and 0 ppm or more . The non-reflective coating film having a thickness of 10 nm to 200 μm made of a transparent organic polymer film having a refractive index of 1.2 to 1.4 is provided on the surface of the square cross-section hollow tube. 3. The thermal lens forming element according to 2. At least a preform for a square cross-section hollow tube made of quartz glass used as a square cross-section container of a thermal lens forming element, a square cross-section hollow tube comprising two outer planes and two inner planes parallel to each other A step of transforming into
Cutting the square cross-section hollow tube into a hollow tube having both ends open;
Sealing one end of a square cross-section hollow tube having two outer planes and two inner planes parallel to each other;
A step of preparing a dye solution in which a dye that does not absorb the light of the signal light and absorbs the light of the control light is dissolved in a solvent;
Injecting the dye solution into a square cross-section hollow tube having two parallel outer flat surfaces and two inner flat surfaces sealed at one end;
After injecting the dye solution, vacuuming the space where the dye solution of the square cross-section hollow tube is not injected, and then temporarily sealing with an adhesive; and
Heating and sealing one end of the square cross-section hollow tube at a position where the dye solution does not exist in the square cross-section hollow tube into which the dye solution has been injected;
The manufacturing method of the thermal lens formation element which has this .