JP4730257B2 - Thermal lens reciprocating optical path switching device and optical path switching method - Google Patents

Description

  The present invention relates to an optical path switching device and an optical path switching method using a thermal lens forming element, which are useful in the fields of optoelectronics 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 incorporated into the light absorption layer in the thermal lens forming element, the control light in the wavelength band that the light absorption layer absorbs, and the wavelength that the light absorption layer does not absorb When the control light is not irradiated, the signal light travels straight through the hole of the mirror. On the other hand, when the control light is irradiated, it is tilted with respect to the traveling direction of the signal light. Invented a method of changing the optical path by reflecting using a mirror with a hole provided and a device therefor (see Patent Document 1). The background art prior to the present invention is described in detail in Patent Document 1.

  The present inventors have also disclosed an optical control type optical path switching type optical signal transmission device and 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).

Japanese Patent No. 3809908 JP 2005-234356 A

  The invention described in Patent Document 1 is an optical signal light that does not use an electric circuit or a mechanical movable part, is highly durable, has no polarization dependence, and can freely set the angle and direction of optical path switching. There are provided an optical path switching device and an optical path switching method with a sufficiently practical response speed that can be used in multiple connection with little intensity attenuation. However, if the signal light whose beam cross-sectional shape has been converted into a “doughnut shape” by the thermal lens effect is to be coupled into a single-mode optical fiber with a simple lens optical system, there is a restriction that it is difficult to increase the coupling efficiency.

  On the other hand, as described in Patent Document 2, the basic unit of the optical path switching device using the thermal lens forming element is combined in two stages, and the signal light of the donut cross section is passed through the second thermal lens forming element, whereby the beam cross section It is possible to convert the energy distribution of approximately to a Gaussian distribution. However, in this case, the optical system of the apparatus becomes complicated, and it takes a lot of time for adjustment, and there remains a problem that a control light source needs to be added for forming the second thermal lens.

  According to the present invention, the signal light whose shape of the beam cross section is converted into the “doughnut shape” by the thermal lens effect is converted into an approximately Gaussian distribution of the energy of the beam cross section by an optical system as simple as possible. The purpose is to increase the coupling efficiency to the mode optical fiber.

  The optical path switching device of the present invention has the following features.

(1) a light absorbing layer disposed so that at least the control light is focused;
Means for converging and irradiating at least the light absorption layer with control light having a wavelength selected from a wavelength band absorbed by the light absorption layer and signal light having a wavelength selected from a wavelength band not absorbed by the light absorption layer When,
By using a thermal lens that includes the light absorption layer and is based on a refractive index distribution that is reversibly formed due to a temperature rise that occurs in the region where the control light has absorbed the control light and the surrounding region. When the control lens is not irradiated and a thermal lens is not formed, the converged signal light is emitted at a normal opening angle, and when the control lens is irradiated and a thermal lens is formed, the converged signal is emitted. A thermal lens forming element that realizes a state in which light is emitted at an opening angle larger than a normal opening angle in correspondence with the presence or absence of irradiation of the control light;
A mirror provided with a hole through which the signal light emitted from the thermal lens forming element at a normal opening angle is collimated by changing the normal opening angle by a light receiving lens, and has a larger opening angle than usual. A mirror with a hole that makes regular reflection after changing and collimating the signal light emitted from the thermal lens forming element while spreading from the light receiving lens with a larger opening angle than the normal.
Means for separating the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction after being regularly reflected by the holed mirror;
Equipped with a,
Signal light traveling in the direction first incident on the thermal lens forming element and signal light traveling in the reverse direction after being regularly reflected by the holed mirror are respectively coupled to the single mode optical fiber .

(2) As means for separating the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction after being regularly reflected by the holed mirror,
A hole provided between the light receiving lens and the mirror with a hole, through which the signal light emitted from the thermal lens forming element at a normal opening angle is collimated by changing the normal opening angle by the light receiving lens. A quarter wave plate provided with
In order to selectively reflect the signal light whose polarization plane is rotated 90 degrees by passing through the quarter-wave plate and then being regularly reflected by the mirror with the hole, and passing through the quarter-wave plate with the hole again. And a polarizing beam splitter provided.

  (3) The means for separating the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction after being regularly reflected by the holed mirror is an optical circulator.

  The optical path switching method of the present invention also has the following characteristics.

(4) The light absorbing layer in the thermal lens forming element including at least the light absorbing layer is selected from the control light having a wavelength selected from the wavelength band absorbed by the light absorbing layer and the wavelength band not absorbed by the light absorbing layer. The signal light of the wavelength is converged and irradiated, and the arrangement of the light absorption layer is adjusted so that at least the control light is focused in the light absorption layer, and the light absorption layer absorbs the control light When a thermal lens is used that is not irradiated with control light and a thermal lens is formed by using a thermal lens based on a refractive index distribution that occurs reversibly due to a temperature rise that occurs in the region and its surrounding region, the converged signal light Is emitted from the thermal lens forming element at a normal opening angle, and when a control lens is irradiated to form a thermal lens, the converged signal light has a front opening angle larger than the normal opening angle. And a state of emitting the thermal lens forming device, is realized in correspondence to the presence or absence of irradiation of the control light,
When the control light is not irradiated and a thermal lens is not formed, the signal light emitted from the thermal lens forming element at a normal opening angle is collimated by changing the normal opening angle by a light receiving lens, and then the signal light is Go straight through the hole in the mirror with a hole that has a hole to pass through,
On the other hand, when a thermal lens is formed by irradiation with control light, the signal light emitted while spreading from the thermal lens forming element with a larger opening angle than usual is changed by the light receiving lens to change the opening angle of the spreading. After that, regular reflection using the reflective surface of the mirror with a hole,
Furthermore, the optical path is changed by separating the signal light that travels in the direction first incident on the thermal lens forming element and the signal light that is specularly reflected by the mirror with holes and travels in the reverse direction ,
The signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the opposite direction after being regularly reflected by the holed mirror are coupled to the single mode optical fiber, respectively, and coupled to the single mode optical fiber. To increase .

  (5) When separating the signal light that travels in the direction first incident on the thermal lens forming element and the signal light that is specularly reflected by the mirror provided with the hole and proceeds in the reverse direction, it is specularly reflected by the mirror with the hole. Then, the signal light traveling in the reverse direction is rotated by 90 degrees using the quarter wavelength plate, and the signal light having the polarization plane rotated by 90 degrees is taken out by using the polarization beam splitter.

  (6) In order to separate the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction after being regularly reflected by the mirror with holes, it is extracted using an optical circulator.

  By the apparatus and method of the present invention, the signal light whose beam cross-sectional shape has been converted to a “doughnut shape” by the thermal lens effect is converted into a substantially Gaussian distribution by the simple optical system, and The coupling efficiency to a single mode optical fiber can be increased.

(First embodiment)
FIG. 1 is a schematic configuration example according to the first embodiment of the present invention. As illustrated in FIG. 1, the first embodiment of the present invention includes an optical fiber 100 for incident signal light, a collimating lens 30 for making the signal light substantially parallel, an optical fiber 200 for incident control light, and an incident light. A polarizing beam splitter 20 that transmits signal light but reflects signal light that has been switched back and reflected, a collimating lens 31 that makes control light substantially parallel light, a mirror 41 that reflects control light, and signal light and control light. The dichroic mirror 40, the thermal lens forming element 10, the condensing lens 50 as a condensing means for condensing the signal light 1 and the control light 2 on the light absorption layer 15 of the thermal lens forming element 10, and the heat. A light receiving lens 60 that makes the light transmitted through the lens forming element 10 substantially parallel light, and a 1/4 wave with a hole that makes the signal light 6 that is irradiated with control light and spreads in a ring shape and whose optical path is switched circularly polarized. A plate 70, a mirror 80 with a hole that reflects the signal light 6 that is irradiated with the control light and spreads in a ring shape and whose optical path is switched, the optical fiber 111 of the straight signal light, and the signal light 5 that goes straight when the control light is not irradiated , And a converging lens 90 for converging to the optical fiber 111 of the straight-ahead signal light as the convergent light 101, the optical fiber 112 of the signal light whose optical path has been switched, and the hole in which the control light is irradiated and spread in a ring shape and the optical path is switched The signal light reflected by the attached mirror 80, reflected by the deflecting beam splitter 20 through the light receiving lens 60, the thermal lens forming element 10, the condensing lens 50, and the dichroic mirror 40 is condensed, and the optical path is switched as convergent light 102. And a condensing lens 91 that condenses the signal light that has been collected onto the optical fiber 112. As shown in FIG. 1, for example, as shown in FIG. 1, in order to guide the signal light reflected by the holed mirror 80 to the optical fiber 112, the mirror 42 that reflects the signal light emitted from the polarization beam splitter 20 The control light 2 may be directly incident on the dichroic mirror 40 without providing the mirror 41 described in FIG.

  In FIG. 1, a polarization-preserving optical fiber is used as the optical fiber 100 for incident signal light. A laser diode having an oscillation wavelength of 780 nm was used as the light source of the signal light 1 and was incident through the optical fiber 100 of signal light capable of transmitting the wavelength of 780 nm. Further, a laser diode having an oscillation wavelength of 660 nm was used as the light source of the control light 2 and was incident through the optical fiber 200 of incident control light capable of transmitting the wavelength of 660 nm. As the collimating lenses 30 and 31, aspherical lenses having a focal length of 8 mm were used. In the polarization beam splitter 20, the incident signal light 1 in a non-polarized state is transmitted, while the signal light 7 whose polarization plane is rotated by 90 degrees, which is reversed by switching the optical path, is reflected. The dichroic mirror 40 transmits the 780 nm signal lights 1 and 7 but reflects the 660 nm control light 2. Needless to say, the positions of the signal light and the control light may be reversed so that the signal light of 780 nm is reflected and the control light of 660 nm is transmitted.

  The control light 1 and the signal light 2 are condensed at the same place on or near the incident surface of the light absorption layer of the thermal lens forming element 10 by a condensing lens 50 having a focal length of 8 mm.

  The thermal lens forming element 10 can hold a liquid film having a thickness of 100 μm by precisely polishing a quartz glass round plate having a diameter of 10 mm and a thickness of 1 mm fused and bonded to a ring-shaped quartz glass having a diameter of 10 mm and an inner diameter of 8 mm. The dye solution described later was put into the product processed as described above, and another quartz glass having a diameter of 10 mm and a thickness of 1 mm was bonded with an ultraviolet curable resin.

  The light absorption layer 15 of the thermal lens forming element 10 includes a phthalocyanine dye, copper (II) 2,9,16,23-tetra-tert-butyl-29H, 31H-phthalocyanine (Copper (II) 2,9,16 , 23-tetra-tert-butyl-29H, 31H-phthalocyanine) dissolved in 1,2-dichlorobenzene at a pigment concentration of 0.5% by weight. The absorbance spectrum of the light absorption layer 15 is shown in FIG.

  When the control light 2 is not irradiated, the signal light 1 passes through the thermal lens forming element 10 as it is, and is coupled to the optical fiber 111 of the straight signal light by the light receiving lens 60 and the condenser lens 90. When the control light 2 is not irradiated, the signal light 5 passes through holes provided in each of the quarter-wave plate 70 with holes and the mirror 80 with holes and enters the condenser lens 90. The light receiving lens 60 was an aspherical lens having a focal length of 8 mm, and the condenser lens 90 was an aspherical lens having a focal length of 13 mm. The hole diameters of the quarter-wave plate 70 with a hole and the mirror 80 with a hole pass through the light-receiving lens 60 in a state where the control light 2 is not irradiated so that the signal light passes without being kicked when the control light is not irradiated. It was adjusted to be 10 to 20% larger than the beam diameter of the signal light.

  When the control light 2 is irradiated, the signal light 6 spreads in a ring shape, passes through the holed quarter-wave plate 70, becomes circularly polarized light, is reflected by the holed mirror 80, and is again formed with the holed quarter-wave plate 70. And the polarization plane of the light becomes linearly polarized light rotated 90 degrees. Then, the light receiving lens 60, the thermal lens forming element 10, and the condenser lens 50 are traced in reverse to the incident time, reflected as the backward signal light 7 by the polarization beam splitter 20, changed in direction by the mirror 42, and then the condenser lens. The signal light whose optical path has been switched in 91 is condensed on the optical fiber 112. The condensing lens 91 is also an aspheric lens having a focal length of 13 mm. The three-dimensional arrangement of the light receiving lens 60 and the angle of the mirror with holes 80 were precisely adjusted so that the light reflected by the mirror with holes 80 traces the place where the incident light traveled. If the position of the light receiving lens and the angle of the mirror 80 with a hole are accurately adjusted, the signal light spread in a ring shape returns to the same circular beam as the original incident again, and the optical path 112 of the signal light whose optical path has been switched is returned. Incidence efficiency increased. When the beam cross-sectional energy distribution of the signal light incident on the optical fiber 112 of the signal light whose optical path was switched was measured using a beam profiler, it was confirmed that the signal light returned to a Gaussian distribution.

  Table 1 shows the measurement data. No. Reference numeral 1 denotes a case where the control light is not incident and the straight traveling signal light 5 is converged and incident on the optical fiber 111 of the straight traveling signal light. No. 2, as Comparative Example 1, after making the control light incident into a ring-shaped beam, the quarter-wave plate 70 with a hole and the mirror with a hole 80 in FIG. 1 were removed, and the straight signal light was made incident on the optical fiber 111. Is the case. Details will be described later. No. Reference numeral 3 denotes a case where the signal light whose optical path is switched is incident on the optical fiber 112 as in the present embodiment. The optical fiber 111 for straight signal light and the optical fiber 112 for signal light whose optical path has been switched are single mode quartz fibers having a core diameter of about 6 μm.

(Second Embodiment)
FIG. 2 is a schematic configuration example of an optical path switching apparatus according to the second embodiment of the present invention. In the second embodiment of the present invention, the same optical members as those in the first embodiment are given the same numbers.

  2 is different from FIG. 1 in that the polarizing beam splitter 20, the condensing lens 91, and the quarter-wave plate 70 are not used, and an optical circulator 300 is used instead.

  In general, as a device “optical isolator” that allows light to pass only in one direction, a device using polarized light is used. Here, when three or more optical isolators are connected in a ring shape, the light can be transmitted in one rotational direction but not transmitted in the reverse direction. This is called “optical circulator”.

  In FIG. 2, an optical fiber 100 for incident signal light is a single mode quartz fiber having a core diameter of about 9.5 μm.

  A laser diode with an oscillation wavelength of 1550 nm is used as the light source for signal light, and this is made incident from the optical fiber 100 for signal light. On the other hand, a laser diode with an oscillation wavelength of 980 nm is used as the light source for control light. 200. As the collimating lenses 30 and 31, aspherical lenses having a focal length of 8 mm were used. The dichroic mirror 40 transmits 1550 nm signal light but reflects 980 nm control light. Needless to say, the positions of the signal light and the control light may be reversed so that the signal light of 1550 nm is reflected and the control light of 980 nm is transmitted.

  The control light 1 and the signal light 2 are condensed at the same place on or near the incident surface of the light absorption layer of the thermal lens forming element 10 by a condensing lens 50 having a focal length of 8 mm. As the light absorption layer 15 of the thermal lens forming element 10, infrared absorbing cyanine dye 8- [2-Chloro-3- (2,4-diphenyl-6,7-dihydro-5H-chromone-8-ylmethylene) -cyclohex -1-enylmethylene] -2,4-diphenyl-5,6,7,8-tetorahydro-chromenylium perchlorate dissolved in 1,2-dichlorobenzene at 0.2% by weight, a quartz cell with a cell gap of 500 μm And used.

  When the control light is not irradiated, the signal light 5 passes through the thermal lens forming element 10 as it is, and is condensed by the light receiving lens 60 and the condensing lens 90 onto the optical fiber 111 of the straight signal light. When the control light is not irradiated, the signal light 5 passes through the hole of the holed mirror 80. The light receiving lens 60 was an aspherical lens having a focal length of 8 mm, and the condenser lens 90 was an aspherical lens having a focal length of 13 mm. The hole diameter of the holed mirror 80 was 4 mmφ.

  When the control light is irradiated, the signal light 6 spreads in a ring shape, is reflected by the mirror 80 with a hole, and follows the light receiving lens 60, the thermal lens forming element 10, and the condenser lens 50 in reverse to the incident time, It enters the optical circulator 300 as the retrograde signal light 7 and finally enters the optical fiber 112 of the signal light whose optical path has been switched. The position of the light receiving lens 60 and the angle of the mirror 80 with a hole were adjusted so that the light reflected by the mirror 80 with a hole traces the place where the incident light has traveled. When the position of the light receiving lens 60 and the angle of the mirror 80 with a hole are accurately adjusted, the signal light expanded in a ring shape returns to the same circular beam as the original incident again, and the signal light whose optical path has been switched by the optical circulator 300. The incident efficiency on the optical fiber 112 was as high as in the case of the first embodiment.

(Comparative Example 1)
FIG. 3 shows a schematic configuration diagram of an optical path switching device using the mirror 400 with a hole described in Patent Document 1. In addition, the same code | symbol is attached | subjected to the structure demonstrated in the said 1st, 2nd embodiment, and the description is abbreviate | omitted.

  As schematically illustrated in FIG. 3, an optical fiber 100 for incident signal light, a collimating lens 30 for making the signal light substantially parallel, an optical fiber 200 for incident control light, and a collimating lens 31 for making the control light substantially parallel. A mirror 41 for reflecting the control light, a dichroic mirror 40 for combining the signal light and the control light, and a condensing means for condensing the signal light 1 and the control light 2 on the light absorption layer 15 of the thermal lens forming element 10. A condensing lens 50, a thermal lens forming element 10, a light receiving lens 60 that makes light transmitted through the thermal lens forming element 10 substantially parallel light, and a signal light that is irradiated with control light and spreads in a ring shape and whose optical path is switched. 6, a mirror 400 with a hole for reflecting 6, an optical fiber 111 for straight signal light, and the signal light 5 that travels straight when the control light is not irradiated are collected, and the straight signal light is used as convergent light 101. The condensing lens 90 coupled to the optical fiber 111, the optical fiber 112 of the signal light whose optical path has been switched, and the control light is irradiated and spread in a ring shape, and the signal light reflected by the mirror 400 with the hole whose optical path has been switched is condensed. A condensing lens 91 to be collected, and an optical fiber 112 for signal light that is collected by the condensing lens 91 and into which the convergent light 102 enters.

  In FIG. 3, a laser diode having an oscillation wavelength of 780 nm is used as the light source of the signal light 1 and is incident through the optical fiber 100 of signal light capable of transmitting the wavelength of 780 nm. In addition, a laser diode having an oscillation wavelength of 660 nm was used as the light source of the control light 2 and was incident through the optical fiber 200 of incident control light capable of transmitting the wavelength of 660 nm. As the collimating lenses 30 and 31, aspherical lenses having a focal length of 8 mm were used. The dichroic mirror 40 transmits the 780 nm signal lights 1 and 7 but reflects the 660 nm control light 2.

  The control light 1 and the signal light 2 are condensed at the same place on or near the incident surface of the light absorption layer of the thermal lens forming element 10 by a condensing lens 50 having a focal length of 8 mm.

  As the thermal lens forming element 10 and the light absorption layer 15, the same ones as described in the first embodiment were used.

  When the control light 2 is not irradiated, the signal light 1 passes through the thermal lens forming element 10 as it is, and is coupled to the optical fiber 111 of the straight signal light by the light receiving lens 60 and the condenser lens 90. When the control light 2 is not irradiated, the signal light 5 passes through the hole 401 provided in the mirror 400 with a hole, and further passes through the dichroic mirror 48 that reflects the leakage light of the control light and enters the condenser lens 90. To do. The light receiving lens 60 was an aspherical lens having a focal length of 8 mm, and the condenser lens 90 was an aspherical lens having a focal length of 13 mm. The diameter of the hole 401 of the mirror with hole 400 is the beam diameter of the signal light that passes through the light receiving lens 60 in a state where the control light 2 is not irradiated so that the signal light passes when the control light is not irradiated is hardly kicked. On the other hand, it was adjusted to be 10 to 20% larger.

  When the control light 2 is irradiated, the signal light 6 spreads in a ring shape, collimated by the light receiving lens 60, and then changed in direction by a mirror 46 that is provided for the arrangement of the optical system, and then applied to the condenser lens 91. Then, the light is condensed and coupled to the optical fiber 112 of the signal light whose optical path has been switched. The condensing lens 91 is also an aspheric lens having a focal length of 13 mm.

  The experimental results of the optical fiber coupling efficiency in this comparative example are shown in Table 1. No. As shown in FIG. 2, it was significantly inferior to the first and second embodiments.

(Comparative Example 2)
A schematic configuration of the optical path switching device of Comparative Example 2 is shown in FIG. In addition, the same code | symbol is attached | subjected to the structure demonstrated in the said 1st, 2nd embodiment and the comparative example 1, and the description is abbreviate | omitted.

  In Comparative Example 1, the control light obtained by collimating the laser light having a wavelength of 660 nm emitted from the optical fiber of the second control light with the collimating lens 32 is superimposed on the signal light spread in a ring shape by using the dichroic mirror 45. Condensed by the second condenser lens 51 and made incident as convergent incident light 8 and 9 on the signal light emitting surface of the light absorption layer 16 of the second thermal lens forming element 11 or its vicinity. In addition, as the 2nd thermal lens formation element 11 and the light absorption layer 16, the same thing as the thermal lens formation element 10 and the light absorption layer 15 which were demonstrated in 1st Embodiment was used.

  The signal light beam is converted into a Gaussian distribution by the thermal lens formed inside the light absorption layer 16 by the second control light, and the signal light 102 is switched in the optical path via the light receiving lens 61 and the condenser lens 91. The optical fiber coupling efficiency when the signal light whose optical path has been switched is converged and incident on the optical fiber 112 was substantially the same as that of the first embodiment of the present invention.

Compared to Comparative Example 2 that shows equivalent performance, the first embodiment of the present invention has the following merits. That is,
(I) A set of optical components (light source, optical fiber 220, collimating lens 32, mirror 47) related to the second control light is not necessary.
(Ii) A set of optical components (the condensing lens 51, the thermal lens forming element 11, and the light receiving lens 61) related to the second thermal lens is not necessary.
(Iii) It is not necessary to precisely adjust the above optical components.

  The optical path switching device and the optical path switching method of the present invention can be used to transfer large-capacity digital information such as high-definition image data and high-definition video data from a server to a plurality of clients in a corporate office, factory, hospital, general home, and the like. It is suitably used in a system that selects a specific location and switches the optical path to deliver at high speed.

It is a conceptual diagram of the optical path switching apparatus of the 1st Embodiment of this invention. It is a conceptual diagram of the optical path switching apparatus of the 2nd Embodiment of this invention. It is a conceptual diagram of the optical path switching apparatus of the comparative example 1. It is a conceptual diagram of the optical path switching apparatus of the comparative example 2. It is a figure showing the transmittance | permeability spectrum of the thermal lens formation element (light absorption layer) used in Embodiment 1. FIG.

Explanation of symbols

  1 signal light, 2, 3 control light, 4 convergent incident control light and signal light, 5 rectilinear outgoing signal light, 6 outgoing signal light that spreads in a ring shape, 7 reverse signal light whose optical path has been switched, and 8 in a convergent incident ring shape Output signal light, 9 Convergent incident second control light, 10, 11 Thermal lens forming element, 15, 16 Light absorption layer, 20 Polarizing beam splitter, 30, 31, 32 Collimator lens, 40 Dichroic mirror, 41, 42, 43 mirror, 45 dichroic mirror, 46, 47 mirror, 48 dichroic mirror, 50, 51 condenser lens, 60, 61 light receiving lens, 70 quarter-wave plate with hole, 80 mirror with hole, 90, 91 condenser lens, 100 optical fiber for incident signal light, 101 straight signal light, 102 signal light whose optical path has been switched, 107 straight and reverse signal Optical fiber, 112 Straight signal optical fiber, 111 Optical path switched optical fiber, 200 Incident control optical fiber, 220 Second control optical fiber, 300 Optical circulator, 400 Tilt with respect to signal light traveling direction Mirror with hole provided, 401 Hole of mirror 400 with hole provided inclined with respect to the signal light traveling direction.

Claims (6)

A light absorption layer arranged so that at least the control light is focused; and
Means for converging and irradiating at least the light absorption layer with control light having a wavelength selected from a wavelength band absorbed by the light absorption layer and signal light having a wavelength selected from a wavelength band not absorbed by the light absorption layer When,
By using a thermal lens that includes the light absorption layer and is based on a refractive index distribution that is reversibly formed due to a temperature rise that occurs in the region where the control light has absorbed the control light and the surrounding region. When the control lens is not irradiated and a thermal lens is not formed, the converged signal light is emitted at a normal opening angle, and when the control lens is irradiated and a thermal lens is formed, the converged signal is emitted. A thermal lens forming element that realizes a state in which light is emitted at an opening angle larger than a normal opening angle in correspondence with the presence or absence of irradiation of the control light;
A mirror provided with a hole through which the signal light emitted from the thermal lens forming element at a normal opening angle is collimated by changing the normal opening angle by a light receiving lens, and has a larger opening angle than usual. A mirror with a hole that makes regular reflection after changing and collimating the signal light emitted from the thermal lens forming element while spreading from the light receiving lens with a larger opening angle than the normal.
Means for separating the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction after being regularly reflected by the holed mirror;
Equipped with a,
An optical path switching device that couples a signal light traveling in the direction first incident on the thermal lens forming element and a signal light traveling in the reverse direction by being regularly reflected by the holed mirror to a single mode optical fiber, respectively. . As a means for separating the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction by being regularly reflected by the holed mirror,
A hole that is provided between the light receiving lens and the mirror with a hole, passes through the signal light emitted from the thermal lens forming element at a normal opening angle after the normal opening angle is changed and collimated by the light receiving lens. A quarter wave plate provided,
In order to selectively reflect the signal light whose polarization plane is rotated 90 degrees by passing through the quarter-wave plate and then being regularly reflected by the mirror with the hole, and passing through the quarter-wave plate with the hole again. A provided polarizing beam splitter;
The optical path switching device according to claim 1, comprising:   The optical circulator is characterized in that the means for separating the signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the reverse direction after being regularly reflected by the holed mirror is an optical circulator. 2. The optical path switching device according to 1. Control light having a wavelength selected from a wavelength band absorbed by the light absorption layer and a signal having a wavelength selected from a wavelength band not absorbed by the light absorption layer in the light absorption layer in the thermal lens forming element including at least the light absorption layer The light is converged and irradiated, and the arrangement of the light absorption layer is adjusted so that at least the control light is focused in the light absorption layer, and the light absorption layer absorbs the control light and the region thereof By using a thermal lens based on a refractive index distribution that occurs reversibly due to a temperature rise that occurs in the peripheral region, when the control light is not irradiated and a thermal lens is not formed, the converged signal light is normal. When the thermal lens is emitted from the thermal lens forming element at an opening angle and when a thermal lens is formed by irradiation with control light, the converged signal light is heated at an opening angle larger than a normal opening angle. And a state emitted from's forming element, to realize in correspondence to the presence or absence of irradiation of the control light,
When the control light is not irradiated and a thermal lens is not formed, the signal light emitted from the thermal lens forming element at a normal opening angle is collimated by changing the normal opening angle by a light receiving lens, and then the signal light is Go straight through the hole in the mirror with a hole that has a hole to pass through,
On the other hand, when a thermal lens is formed by irradiation with control light, the signal light emitted while spreading from the thermal lens forming element with a larger opening angle than usual is changed by the light receiving lens to change the opening angle of the spreading. After that, regular reflection using the reflective surface of the mirror with a hole,
Furthermore, the optical path is changed by separating the signal light that travels in the direction first incident on the thermal lens forming element and the signal light that is specularly reflected by the mirror with holes and travels in the reverse direction ,
The signal light traveling in the direction first incident on the thermal lens forming element and the signal light traveling in the opposite direction after being regularly reflected by the holed mirror are coupled to the single mode optical fiber, respectively, and coupled to the single mode optical fiber. optical path switching method characterized by enhanced.   In separating the signal light that travels in the direction first incident on the thermal lens forming element and the signal light that is regularly reflected by the holed mirror and travels in the reverse direction, it is regularly reflected by the holed mirror and reversed in the reverse direction. 5. The optical path switching according to claim 4, wherein the traveling signal light has its polarization plane rotated by 90 degrees using a quarter-wave plate, and the signal light whose polarization plane has been rotated by 90 degrees is extracted using a polarization beam splitter. Method.   A signal circulator is used to separate signal light that travels in the direction first incident on the thermal lens forming element and signal light that is specularly reflected by the mirror with holes and travels in the reverse direction. Item 5. The optical path switching method according to Item 4.

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