JP2006139225A - Wavelength converter and wavelength conversion method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new wavelength conversion technique which employs neither electric circuit nor mechanical movable part and thereby is neither affected by electromagnetic interference, nor becomes a cause of electromagnetic interference, and which utilizes a light beam with a wide range of wavelength selection, and further has high durability. <P>SOLUTION: The wavelength converter is equipped with: a signal light beam input portion (12) to make a pulsed signal light beam (14) with a specified wavelength incident; a light source (13) for a light beam for conversion to emit a light beam (15) for conversion with a wavelength different from that of the signal light beam (14); a thermal lens forming means (11) having a light absorption layer film with a wavelength band absorbing the signal light beam (14) and transmitting the light beam (15) for conversion and exhibiting a thermal lens effect; and a conversion light beam selecting means emitting, as the light beam for conversion, only the light beam for conversion emitted with an angle larger than an usual angle of aperture out of the emitted light beams for conversion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The invention of this application relates to a wavelength conversion device and a wavelength conversion method. More specifically, the invention of this application is a novel wavelength conversion device and wavelength conversion method preferably used particularly in the fields of optical communication and optical information processing.

  A wavelength converter is an important optical element in the optical communication field and the optical information processing field. This wavelength converter converts, for example, a pulse signal having a specific wavelength into a pulse signal having another wavelength. An example of a conventional wavelength converter is schematically shown in FIG.

  The wavelength converter shown in FIG. 1 receives incident pulsed light having a wavelength of 1.55 μm, which is a wavelength band of optical communication, by a photodiode (PD) (1), and outputs a laser diode (LD) (2) with the output. Driven to emit pulsed light having a wavelength of 780 nm.

On the other hand, with the rapid spread of the Internet and the like, realization of a faster optical network is desired. Therefore, realization of various optical elements capable of high-speed response is desired.
Takao Fujiwara, Keiichiro Fuwa, Takayoshi Kobayashi, Laser-induced thermal lens effect and its application to colorimetric method, "Chemical", Kagaku Dojin, Vol. 36, No. 6, pp. 432-438 (1981) Takehiko Kitamori, Goro Sawada, Photothermal Conversion Spectroscopy, “Bunseki”, published by the Japan Society for Analytical Chemistry, March 1994, pp. 178-187 Takashi Hiraga, Norio Tanaka, Kikuko Hayami, Tetsuro Moriya, Creation of dye aggregates / aggregates, structural evaluation, photophysical properties, "Electronics Research Institute Vocabulary", Ministry of International Trade and Industry 59, No. 2, pp. 29-49 (1994)

  However, in the conventional wavelength conversion apparatus as shown in FIG. 1, it is necessary to supply power to an electronic circuit of optical pulse → electrical pulse conversion and an electronic circuit of electric pulse → optical pulse conversion. To realize high-speed optical networks and the like, there are problems such as being easily affected, the electronic circuit can cause electromagnetic interference, and the wavelength that can be used is limited because it uses a laser diode (LD) etc. Therefore, it has been desired that light having a wide wavelength selection range that is not affected by electromagnetic interference and does not cause electromagnetic interference can be used. Also, it has been desired to realize a highly durable wavelength conversion device that can perform high-speed wavelength conversion without using an electric circuit or a mechanically movable part.

  Therefore, the invention of this application was made in view of the circumstances as described above, and does not use an electric circuit or a mechanical movable part, is not affected by electromagnetic interference, and does not cause electromagnetic interference. It is an object of the present invention to provide a novel wavelength conversion device and a wavelength conversion method that enable use of light with a wide range, and that have high durability.

  In order to solve the above-mentioned problems, the invention of this application includes, firstly, a signal light input unit that receives pulsed signal light having a specific wavelength and a conversion that irradiates conversion light having a wavelength different from that of the signal light. So that the signal light and the conversion light are focused on the optical light source, the light absorption layer film having a wavelength band exhibiting the absorption property for the signal light and the transmission light for the conversion light, and the light absorption film. A refractive index distribution that reversibly occurs due to a temperature rise that occurs in the area where the light absorption layer film absorbs the signal light and the peripheral area thereof, each of which includes means for irradiating and converging and the light absorption layer film. By using a thermal lens based on the above, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle, and the control light is irradiated to form the thermal lens. The converged conversion light is less than the normal opening angle. A lens that emits light with a larger opening angle corresponding to the presence or absence of signal light irradiation, and conversion light that is emitted at an angle larger than the normal opening angle among the converted light that is emitted. A conversion light selection unit that emits only light as conversion light, and a condensing unit that condenses the conversion light from the conversion light selection unit and converts it to pulsed conversion light having a wavelength different from that of the signal light, Provided is a wavelength conversion device.

  Second, a signal light input unit that receives pulsed signal light having a specific wavelength, a conversion light source that emits conversion light having a wavelength different from that of the signal light, and absorptivity to the signal light. A light absorption layer film having a wavelength band that is transparent to the conversion light, means for irradiating the light absorption film so that the signal light and the conversion light are focused so as to be focused, and the light absorption By using a thermal lens including a layer film, and based on a refractive index distribution reversibly generated due to a temperature rise occurring in a region where the light absorption layer film absorbs the signal light and a peripheral region thereof, the signal light is When the thermal lens is not formed without irradiation, the converged conversion light is emitted at a normal opening angle, and when the control lens is irradiated and the thermal lens is formed, the converged conversion light is normal. A signal indicating that the light is emitted at an opening angle larger than the opening angle. Thermal lens forming element realized corresponding to the presence or absence of irradiation, and converted light selection means for emitting, as converted light, only the conversion light emitted from the thermal lens forming element at a normal opening angle among the converted light emitted And a condensing unit that condenses the converted light from the converted light selecting means and converts it into pulsed converted light having a wavelength different from that of the signal light.

  Thirdly, a signal light input unit that receives pulsed signal light having a specific wavelength, a conversion light source that emits conversion light having a wavelength different from that of the signal light, and absorptivity to the signal light. A light absorption layer film having a wavelength band that is transparent to the conversion light, means for irradiating the light absorption film so that the signal light and the conversion light are focused so as to be focused, and the light absorption By using a thermal lens including a layer film, and based on a refractive index distribution reversibly generated due to a temperature rise occurring in a region where the light absorption layer film absorbs the signal light and a peripheral region thereof, the signal light is When the thermal lens is not formed without irradiation, the converged conversion light is emitted at a normal opening angle, and when the control lens is irradiated and the thermal lens is formed, the converged conversion light is normal. A signal indicating that the light is emitted at an opening angle larger than the opening angle. A thermal lens forming element that is realized corresponding to the presence or absence of irradiation, and a state in which only conversion light that is emitted at an angle larger than a normal opening angle is emitted as converted light among the emitted conversion light, A conversion light selection means capable of selecting only the conversion light emitted at an opening angle as a conversion light, and a wavelength different from the signal light by condensing the conversion light from the conversion light selection means There is provided a wavelength conversion device comprising a condensing unit for converting the pulse-shaped converted light.

  Fourthly, in any one of the first to third inventions, the polarization state of the outgoing converted light is switched between the same state and the different state from the polarization state of the incident signal light. Provided is a wavelength conversion device comprising polarization state switching means.

  In addition, the fifth includes a light absorption layer film having a wavelength band that is at least absorbable for pulsed signal light having a specific wavelength and exhibits transparency for conversion light having a wavelength different from that of the signal light. The light absorption film of the thermal lens forming element is irradiated with the signal light and the conversion light so as to focus each other, and the light absorption layer film absorbs the signal light and the temperature rises in the surrounding area. By using a thermal lens based on the reversible refractive index distribution caused by this, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle. When a thermal lens is formed by irradiation with control light, the converged conversion light is emitted at an opening angle larger than the normal opening angle, corresponding to the presence or absence of signal light irradiation. Of the emitted conversion light, usually Only the conversion light emitted at an angle larger than the opening angle is selectively emitted as converted light, and the emitted converted light is condensed to form pulsed converted light having a wavelength different from that of the signal light. A wavelength conversion method is provided.

  In addition, the sixth embodiment includes a light absorption layer film having a wavelength band that is at least absorbable for pulsed signal light having a specific wavelength and has transparency for conversion light having a wavelength different from the signal light. The light absorption film of the thermal lens forming element is irradiated with the signal light and the conversion light so as to focus each other, and the light absorption layer film absorbs the signal light and the temperature rises in the surrounding area. By using a thermal lens based on the reversible refractive index distribution caused by this, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle. When a thermal lens is formed by irradiation with control light, the converged conversion light is emitted at an opening angle larger than the normal opening angle, corresponding to the presence or absence of signal light irradiation. Of the emitted conversion light, usually Only the conversion light emitted from the thermal lens forming element at the opening angle is selectively emitted as converted light, and the emitted converted light is condensed to form pulsed converted light having a wavelength different from that of the signal light. A wavelength conversion method is provided.

  In addition, the seventh embodiment includes a light absorption layer film having a wavelength band that is at least absorbable for pulsed signal light having a specific wavelength and has transparency for conversion light having a wavelength different from that of the signal light. The light absorption film of the thermal lens forming element is irradiated with the signal light and the conversion light so as to focus each other, and the light absorption layer film absorbs the signal light and the temperature rises in the surrounding area. By using a thermal lens based on the reversible refractive index distribution caused by this, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle. When a thermal lens is formed by irradiation with control light, the converged conversion light is emitted at an opening angle larger than the normal opening angle, corresponding to the presence or absence of signal light irradiation. Of the emitted conversion light, usually Only the conversion light emitted at an angle larger than the opening angle is emitted as the converted light or only the conversion light emitted at the normal opening angle is selected as the converted light to be emitted. The wavelength conversion method is characterized in that the light is condensed into pulsed converted light having a wavelength different from that of the signal light.

  Furthermore, according to the present invention, in the fifth to seventh inventions, it is possible to switch the polarization state of the outgoing converted light to the same or different state from the polarization state of the incident signal light. A characteristic wavelength conversion method is provided.

  According to the first and fifth inventions of this application, the use of light having a wide wavelength selection range that is not affected by electromagnetic interference and does not cause electromagnetic interference without using an electric circuit or a mechanical movable part. In addition, it is possible to provide a novel wavelength conversion technique with high durability.

  According to the second and sixth inventions, in addition to the above effects, there is an advantage that converted light having a phase opposite to that of the incident signal can be obtained.

  According to the third and seventh inventions, in addition to the above effects, there is an advantage that the converted light having the same phase or opposite phase as the incident signal can be selected and obtained.

  According to the fourth and eighth inventions, in addition to the above effects, there is an advantage that it is possible to select and obtain converted light having the same polarization state as the polarization state of the incident signal and a different polarization state.

  The invention of this application has the features as described above, and an embodiment thereof will be described below.

  In the wavelength conversion device and the wavelength conversion method of the invention of this application, a thermal lens forming element using a thermal lens effect is used. Here, the thermal lens effect means that molecules that absorb light in the central part of light absorption convert light into heat, and this heat is propagated to the surroundings, resulting in a temperature distribution. The refractive index of the light changes such that the refractive index changes spherically from the light absorption center to the outside, resulting in a distribution in which the refractive index at the light absorption center is low and the refractive index increases toward the outside, which functions like a concave lens. It is a phenomenon that shows.

  The thermal lens effect has been used for a long time in the field of spectroscopic analysis, and now it is possible to perform ultrasensitive spectroscopic analysis that detects light absorption by a single molecule (Non-Patent Document 1 and Non-Patent Document). 2).

  The inventors of this application are also aiming to develop a new information processing technique using an all-optical type optical element or the like, and an organic nanoparticle photothermal lens forming element in which an organic dye aggregate is dispersed in a polymer matrix (see Non-Patent Document 3). We have been researching the light control system. Currently, the control light (633 nm) is used to modulate the signal light (780 nm), the control light and the signal light are coaxially and confocally incident, and a thermal lens formed transiently by absorption of the control light Has developed a device with the principle of operation that the signal light is refracted by this, and has achieved a high-speed response of about 20 nanoseconds.

  A wavelength conversion device according to a first aspect of the present application includes a signal light input unit that inputs pulsed signal light having a specific wavelength, a conversion light source that irradiates conversion light having a wavelength different from the signal light, and a signal A light absorption layer film having a wavelength band that exhibits absorption for light and transparency for conversion light, and the light absorption film are focused and irradiated so that the signal light and the conversion light are focused. And a thermal lens based on a refractive index distribution reversibly generated due to a temperature rise occurring in a region where the light absorption layer film absorbs signal light and its peripheral region. As a result, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle, and when the control lens is irradiated and the thermal lens is formed, the light is converged. When the conversion light is larger than the normal opening angle The thermal lens forming element that realizes the radiating state corresponding to the presence or absence of signal light irradiation, and the converted light that is emitted at an angle larger than the normal opening angle among the converted light that is emitted is converted light And a condensing unit for condensing the converted light from the converted light selecting means and converting it into pulsed converted light having a wavelength different from that of the signal light.

  FIG. 2 shows a conceptual diagram of an embodiment of the wavelength conversion device of the invention of this application. The wavelength of a material (in this case, a dye) used for an example light absorption layer film used in the thermal lens forming element of FIG. FIG. 3 shows the relationship between the absorption characteristics and the transmission characteristics, and FIG. 4 shows a schematic apparatus configuration example.

  In the wavelength conversion device of this embodiment, a light control type thermal lens forming element (11) is used, an optical pulse signal having an arbitrary wavelength A is incident as signal light (14) from a signal input unit (12), and conversion light is used. From the light source (13), continuous light having an arbitrary wavelength B is made incident as conversion light (15), and an optical pulse having an arbitrary wavelength B is emitted as converted light (16). As the signal light (14) incident from the signal input unit (12), light from various light sources conventionally used including a laser light source can be used. Moreover, although a laser apparatus is used suitably for the conversion light source (13), it is not limited to this.

  The thermal lens forming element (11) is provided with a light absorption layer film having a wavelength band as shown in FIG. That is, this light absorption layer film has a large absorptance with respect to the wavelength A, a large transmissivity with respect to the wavelength B, and a refractive index effect (a large refractive index change with respect to a change in temperature). ). Since the wavelength band has various forms depending on the material of the light absorption layer film, the wavelengths A and B can be arbitrarily selected by selecting the material.

  The configuration of the wavelength conversion device of this embodiment will be described more specifically with reference to FIG. 4. The thermal lens forming element (11) exhibits high absorptivity with respect to the signal light (14), and the conversion light (15). For example, a light-absorbing layer film having a wavelength band exhibiting high transparency can be used. For example, a dye-containing solution having such a wavelength band can be accommodated in a transparent optical cell. For example, a fiber amplifier is used as the signal input unit (12), signal light (14) having an optical pulse with a wavelength of 1.55 μm in the optical communication wavelength band is incident, and a laser diode (LD) ( 13), and the conversion light (15) made of laser light (continuous light) having a wavelength of 650 nm is incident. In this case, as the thermal lens forming element (11), for example, a tetrahydrofuran (TFT) solution of a dye (trade name: CIR-960; manufactured by Nippon Carlit Co., Ltd .: exhibits a large absorption in the near infrared region (780-1500 nm)) is transparent. What was accommodated in the optical cell can be used. The form of the absorption and transmission wavelength band of this dye CIR-960 is different from that of FIG.

  The optical system of the apparatus of FIG. 4 will be described. In addition to the thermal lens forming element (11), the lens (21), the lens (22), the optical mixer (23), the lens (24), the lens (25), and the converted light. A selection member (26) and a lens (27) are provided. Reference numeral 31 denotes a signal output unit (optical fiber). The thermal lens forming element (11) sends the signal light (14) as parallel light to the optical mixer (23), and the lens (22) converts the conversion light (15) as parallel light into the optical mixer (23). To send to. The optical mixer (23) serves to converge the transmitted signal light (14) and conversion light (15) so as to focus on the light absorption layer film of the thermal lens forming element (11). For example, a polarizing beam splitter, a non-polarizing beam splitter, a dichroic mirror, or the like can be used. The lens (25) converts the conversion light (15) that has passed through the thermal lens forming element (11) into parallel light. The converted light selection member (26) blocks the normal opening angle conversion light (15a) emitted when no thermal lens is formed in the thermal lens forming element (11), and in the thermal lens forming element (11). Only the conversion light (15b) emitted when the thermal lens is formed and having an angle larger than the normal opening angle is emitted. The converted light selection member (26) preferably has a function of blocking the signal light (14) that has passed through the thermal lens forming element (11). As the conversion light selection member (26), for example, a metal plate such as aluminum coated with a carbon black paint as a material that absorbs light having wavelengths of 1.55 μm and 650 nm can be used. The lens (27) performs the role of collecting the emitted conversion light (15b) as converted light (16).

  Next, the operation of the wavelength conversion device of the embodiment of FIG. 4 will be described.

  In the apparatus having the configuration as shown in FIG. 4, a pulsed signal light (14) having a wavelength of 1.55 μm is incident from a fiber amplifier as a signal input unit (12), and is converted into parallel light by a lens (21) (23). ) On the other hand, a laser beam (continuous light) having a wavelength of 650 nm is emitted as a conversion light (15) from a laser diode which is a conversion light source (13), and is converted into parallel light by a lens (22). Sent to. Here, the phase and polarization state of the conversion light (15) are the same as those of the signal light.

  The optical mixer (23) converges the transmitted signal light (14) and conversion light (15) so as to focus on the light absorption layer film of the thermal lens forming element (11).

  In the thermal lens forming element (11), when the pulsed signal light (14) is on (or high), the light absorption layer film has high absorptivity with respect to light having a wavelength of 1.55 μm, so a thermal lens is formed. To do. At this time, the conversion light (15) is emitted as conversion light (15b) at an angle larger than the normal opening angle due to the characteristics of the refractive index because of the formed thermal lens. The conversion light (15a) is converted into parallel light by the lens (25) and is condensed by the lens (27).

  On the other hand, in the thermal lens forming element (11), when the pulsed signal light (14) is on (or low), the light absorbing layer film is not irradiated with the signal light (14), and thus no thermal lens is formed. . Therefore, the conversion light (15) is emitted as the conversion light (15a) at a normal opening angle. This conversion light (15a) is blocked by the converted light selector (26).

  Therefore, the presence or absence of the thermal lens is repeated by turning on / off (or high / low) the pulse of the signal light (14), and the wavelength data of the signal light (14) becomes the wavelength of the converted light (16). Converted to data. Since the response speed of the thermal lens forming element is very high, tens of nanoseconds, the response speed is very high without using an electric circuit or a mechanical movable part, and light of various wavelengths can be used. Moreover, wavelength conversion with high durability becomes possible. Further, since wavelength conversion is performed only with light, it is not affected by electromagnetic interference and does not cause electromagnetic interference.

  Next, a wavelength conversion device according to another embodiment of the present invention will be described.

  FIG. 5 is a view similar to FIG. 4 showing the configuration of the wavelength conversion device of this embodiment. In FIG. 5, the same reference numerals are given to the same functions as those in FIG. The wavelength converter shown in FIG. 5 is configured such that the input light and the converted light have opposite phases, while the wavelength converter shown in FIG. 4 has the same phase as the input light. In terms of configuration, the converted light selection unit (26) of the wavelength conversion device of FIG. 4 is not provided, and the thermal lens is formed in the thermal lens forming element (11) instead of the lens (25). The lens (28) for allowing only the conversion light (15a) having the normal opening angle when the thermal lens is formed is provided without entering the conversion light (15b) having an angle larger than the normal opening angle. Is. Accordingly, a lens (29) having a smaller diameter than the lens (27) is provided. With such a configuration, the phase of the obtained converted light (16) is opposite to that of FIG.

  Note that the conversion light (15b) having an angle larger than the normal opening angle when the thermal lens is formed may be separated into another optical path by using a perforated mirror or the like so as to be blocked. Also good.

  Next, a wavelength conversion device according to still another embodiment of this application will be described.

  In the wavelength conversion device of this embodiment, the polarization state of outgoing converted light is different from the polarization state of incident signal light. In this case, in the configuration of the wavelength conversion device of FIG. 4 or FIG. 5, a member that changes the polarization state is provided in the middle of the conversion light (15), for example, in the middle of the lens (22) and the optical mixer (23). That's fine. As a member that changes the polarization state, a glass plate (so-called polaroid plate) provided with an oriented polyvinyl alcohol film containing iodine can be used.

  Moreover, in the wavelength converter of this embodiment, in order to obtain the converted light (16) in a state in which the polarization state is not changed and a state in which the polarization state is changed, any of the mechanisms may be selected.

  Next, the thermal lens forming element used in the invention of this application will be described in detail.

[Thermal lens forming element]
In the invention of this application, as the thermal lens forming element, for example, one having a laminated film type structure can be suitably used, and examples of the laminated film structure include the following combinations.
(1) The light absorbing layer film alone. However, the light absorption layer film is literally a single layer film of “light absorption film” alone, or a two-layer structure of “light absorption film / thermal lens formation layer”, or “light absorption film / thermal lens formation layer / light”. Any of the three-layer laminated thin film called “absorbing film” may be used. The following “light absorption layer film” from (2) to (10) includes the same structure as described above.
(2) Light absorption layer film / heat insulation layer film (3) Heat insulation layer film / light absorption layer film / heat insulation layer film (4) Light absorption layer film / heat transfer layer film (5) Heat transfer layer film / light absorption layer film / Heat transfer layer film (6) Light absorption layer film / Heat insulation layer film / Heat transfer layer film (7) Heat transfer layer film / Light absorption layer film / Heat insulation layer film (8) Heat transfer layer film / Light absorption layer film / Thermal insulation layer film / Heat transfer layer film (9) Heat transfer layer film / Heat insulation layer film / Light absorption layer film / Heat insulation layer film (10) Heat transfer layer film / Heat insulation layer film / Light absorption layer film / Heat insulation layer film / Transmission Thermal layer film (11) Refractive index distribution type lens / (Light transmission layer /) Thermal lens forming element of (1) to (10) above (12) Refractive index distribution type lens / (Light transmission layer /) Above (1) (10) Thermal lens forming element / (light transmissive layer /) gradient index lens The above “(light transmissive layer /)” means that a light transmissive layer is provided if necessary. Furthermore, an antireflection film (AR coating film) may be provided on the light incident surface and the light emitting surface as necessary.

  FIG. 6 is a cross-sectional view illustrating an example of the configuration of the thermal lens forming element. As illustrated in FIG. 6, the thermal lens forming element (500) includes, for example, a gradient index lens (507) / light transmission layer (506) from the incident side of the signal light (509) and the conversion light (508). ) / Heat transfer layer film (501) / light absorption layer film (503) / thermal lens forming layer (505) / light absorption layer film (504) / heat transfer layer film (502). Note that the light rays of the signal light (509) shown in FIG. 6 are schematic, and refraction between the respective layer films is omitted.

  FIG. 7 is a cross-sectional view illustrating another example of the configuration of the thermal lens forming element. As illustrated in FIG. 7, the thermal lens forming element (600) has, for example, a heat transfer layer film (601) / light absorption layer film (603) from the incident side of the signal light (609) and the conversion light (608). ) / Thermal lens formation layer (605) / light absorption layer film (604) / heat transfer layer film (602). In this case, the signal light (609) and the conversion light (608) are incident on the thermal lens forming element (600) while being condensed by the condenser lens (610) provided outside. Note that the light rays of the signal light (609) shown in FIG. 7 are schematic, and refraction between the respective layer films is omitted.

  Furthermore, a schematic view illustrating a dye solution-filled thermal lens forming element is shown in FIG. As illustrated in FIG. 8, the dye solution-filled thermal lens forming element (800) includes incident and exit surface glasses (801) and (802), side glasses (803) and (804) acting as a heat transfer layer film. A dye solution that acts as a light absorption layer film and a thermal lens forming layer from the introduction port (807) of the introduction tube (806) to the dye filling portion (808) of the optical cell (809) surrounded by the bottom glass (805) And the inlet (807) is sealed. That is, it has a simple element structure of heat transfer layer film / light absorption layer film / heat lens forming layer / heat transfer layer film.

  The materials of the light absorption layer film, the thermal lens formation layer, the heat retaining layer film, the heat transfer layer film, the light transmission layer, and the gradient index lens, the manufacturing method thereof, the thickness of each, and the like will be described below in order. .

  The materials of the light absorption layer film, the thermal lens forming layer, the heat retaining layer film, the heat transfer layer film, the light transmission layer, and the gradient index lens used in the invention of this application are within the range that does not hinder the function. In order to improve processability and improve the stability and durability as an optical element, it contains known antioxidants, ultraviolet absorbers, singlet oxygen quenchers, dispersion aids, etc. as additives. Also good.

[Material of light absorption layer film]
Various known materials can be used as the light-absorbing material used for the light-absorbing layer film in the thermal lens forming element used in the invention of this application.

If the example of the light absorptive material used for the light absorption layer film | membrane in the thermal lens formation element used by invention of this application is specifically mentioned, for example, GaAs, GaAsP, GaAlAs, InP, InSb, InAs, PbTe, Single crystals of compound semiconductors such as InGaAsP and ZnSe, fine particles of the compound semiconductor dispersed in a matrix material, single crystals of metal halides doped with different metal ions (for example, potassium bromide, sodium chloride, etc.), Single particles of cadmium chalcogenides such as CdS, CdSe, CdSeS, CdSeTe, etc., in which fine particles of metal halide (for example, copper bromide, copper chloride, cobalt chloride, etc.) are dispersed in a matrix material, or doped with different metal ions such as copper Crystals, fine particles of the cadmium chalcogenide Dispersed in trix material, semiconductor single crystal thin film such as silicon, germanium, selenium, tellurium, polycrystalline thin film or porous thin film, dispersed semiconductor fine particles such as silicon, germanium, selenium, tellurium in matrix material, Ruby, alexandrite, garnet, Nd: YAG, sapphire, Ti: sapphire, Nd: YLF, etc. Single crystal (so-called laser crystal) corresponding to gems doped with metal ions, Niobium doped with metal ions (for example, iron ions) Ferroelectric crystals such as lithium oxide (LiNbO ₃ ), LiB ₃ O ₅ , LiTaO ₃ , KTiOPO ₄ , KH ₂ PO ₄ , KNbO ₃ , BaB ₂ O ₂ , metal ions (for example, neodymium ions, erbium ions, etc.) Doped quartz glass, soda glass, ho In addition to silicate glass and other glasses, those obtained by dissolving or dispersing a dye in a matrix material and amorphous dye aggregates can be preferably used.

  Among these, those in which a dye is dissolved or dispersed in a matrix material can be used particularly suitably because the selection range of the matrix material and the dye is wide and processing into a thermal lens forming element is easy.

  Specific examples of the dye that can be used in the invention of this application include xanthene dyes such as rhodamine B, rhodamine 6G, eosin and phloxine B, acridine dyes such as acridine orange and acridine red, ethyl red, and methyl red. Azo dyes, porphyrin dyes, phthalocyanine dyes, cyanine dyes such as 3,3′-diethylthiacarbocyanine iodide, 3,3′-diethyloxadicarbocyanine iodide, ethyl violet, Victoria Blue R Triarylmethane dyes such as naphthoquinone dyes, anthraquinone dyes, naphthalenetetracarboxylic acid diimide dyes, and perylenetetracarboxylic acid diimide dyes can be preferably used.

  In the invention of this application, these dyes can be used alone or in admixture of two or more.

The matrix material that can be used in the invention of this application is:
(1) High transmittance in the wavelength region of light used in the invention of this application;
(2) The dye or various fine particles used in the invention of this application can be dissolved or dispersed with good stability.
Any material can be used as long as the above condition is satisfied.

  Examples of inorganic solid matrix materials include metal halide single crystals, metal oxide single crystals, metal chalcogenide single crystals, quartz glass, soda glass, borosilicate glass, and so-called sol-gel methods. Other low melting glass materials can be used.

  Water, water glass (concentrated aqueous solution of alkali silicate), hydrochloric acid, sulfuric acid, nitric acid, aqua regia, chlorosulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, etc. are used as the inorganic liquid matrix material. be able to.

  In addition, as the organic liquid matrix material, for example, various organic solvents can be used. Specific examples of the organic solvent include alcohols such as methanol, ethanol, isopropyl alcohol, n-butanol, amyl alcohol, cyclohexanol, and benzyl alcohol, polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin, ethyl acetate, Esters such as n-butyl acetate, amyl acetate, isopropyl acetate, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethers such as diethyl ether, dibutyl ether, methoxyethanol, ethoxyethanol, butoxyethanol, carbitol , Tetrahydrofuran, 1,4-dioxane, cyclic ethers such as 1,3-dioxane, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloro Halogenated hydrocarbons such as loethane, 1,1,2-trichloroethane, trichlene, bromoform, dibromomethane, diiodomethane, aroma such as benzene, toluene, xylene, chlorobenzene, o-dichlorobenzene, nitrobenzene, anisole, α-chloronaphthalene Hydrocarbons, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and cyclohexane, amides such as N, N-dimethylformamide, N, N-dimethylacetamide and hexamethylphosphoric triamide Cyclic amides such as N-methylpyrrolidone, urea derivatives such as tetramethylurea and 1,3-dimethyl-2-imidazolidinone, sulfoxides such as dimethylsulfoxide, carbonates such as ethylene carbonate and propylene carbonate, Ace Nitriles such as tonitrile, propionitrile and benzonitrile, nitrogen-containing heterocyclic compounds such as pyridine and quinoline, amines such as triethylamine, triethanolamine, diethylaminoalcohol and aniline, chloroacetic acid, trichloroacetic acid, trifluoroacetic acid, In addition to organic acids such as acetic acid, solvents such as nitromethane, carbon disulfide, and sulfolane can be used. These solvents may be used as a mixture of a plurality of types.

  Furthermore, as the organic matrix material, a liquid, solid or rubber-like organic polymer material can be used. Specific examples thereof include polystyrene, poly (α-methylstyrene), polyindene, poly (4-methyl-1-pentene), polyvinylpyridine, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl acetate, polyvinyl alcohol, polychlorinated. Vinyl, polyvinylidene chloride, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl benzyl ether, polyvinyl methyl ketone, poly (N-vinyl carbazole), poly (N-vinyl pyrrolidone), methyl polyacrylate, polyethyl acrylate, polyacryl Acid, polyacrylonitrile, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polybenzyl methacrylate, polycyclohexyl methacrylate, polymethacrylic acid, Rimethacrylamide, polymethacrylonitrile, polyacetaldehyde, polychloral, polyethylene oxide, polypropylene oxide, polyethylene terephthalate, polybutylene terephthalate, polycarbonates (bisphenols + carbonic acid), poly (diethylene glycol bisallyl carbonate), 6- Nylon, 6,6-nylon, 12-nylon, 6,12-nylon, polyethyl aspartate, ethyl polyglutamate, polylysine, polyproline, poly (γ-benzyl-L-glutamate), methylcellulose, ethylcellulose, benzylcellulose, Hydroxyethyl cellulose, hydroxypropyl cellulose, acetyl cellulose, cellulose triacetate, cellulose tributyrate, alkyd Fat (phthalic anhydride + glycerin), fatty acid-modified alkyd resin (fatty acid + phthalic anhydride + glycerin), unsaturated polyester resin (maleic anhydride + phthalic anhydride + propylene glycol), epoxy resin (bisphenols + epichlorohydrin), polyurethane Resins, phenol resins, urea resins, melamine resins, xylene resins, toluene resins, guanamine resins and other resins, organic polysilanes such as poly (phenylmethylsilane), organic polygermanes, and copolymers / copolycondensates thereof. . In addition, a polymer compound obtained by plasma polymerization of a compound that is not normally polymerizable, such as carbon disulfide, carbon tetrafluoride, ethylbenzene, perfluorobenzene, perfluorocyclohexane, or trimethylchlorosilane, can be used. Furthermore, those obtained by bonding the residue of the dye to these organic polymer compounds as a side chain of the monomer unit, as a crosslinking group, as a copolymerization monomer unit, or as a polymerization initiation terminal can also be used as a matrix material. . Further, the dye residue and the matrix material may form a chemical bond.

  A known method can be used to dissolve or disperse the dye in these matrix materials. For example, the dye and matrix material are dissolved and mixed in a common solvent, then the solvent is evaporated and removed, or the dye is dissolved or dispersed in the raw material solution of the inorganic matrix material produced by the sol-gel method, and then the matrix A method of forming a material, a method of forming a matrix material by dissolving or dispersing a dye in a monomer of an organic polymer matrix material, if necessary, and then polymerizing or polycondensing the monomer; A solution prepared by dissolving a dye and an organic polymer matrix material in a common solvent is dropped into a solvent in which both the dye and the thermoplastic organic polymer matrix material are insoluble, and the resulting precipitate is filtered and dried. For example, a method of heating / melting can be preferably used. It is known that by combining the dye and the matrix material and processing methods, the dye molecules can be aggregated to form a special aggregate called “H aggregate” or “J aggregate”. The dye molecules in the matrix material may be used under conditions that form such an aggregated state or an associated state.

  A known method can be used to disperse the various fine particles in these matrix materials. For example, after the fine particles are dispersed in a matrix material solution or a matrix material precursor solution, a method of removing the solvent, into the monomer of the organic polymer matrix material, if necessary, using a solvent, A method for forming a matrix material by polymerizing or polycondensing the monomer after dispersing the fine particles, and as a precursor of the fine particles, for example, a metal salt such as cadmium perchlorate or gold chloride into an organic polymer matrix material. After dissolution or dispersion, a method of depositing fine particles of cadmium sulfide by treatment with hydrogen sulfide gas or gold fine particles by heat treatment, respectively, a chemical vapor deposition method, a sputtering method, etc. It can be used suitably.

  In the case where the dye can be present alone as an amorphous thin film with little light scattering, an amorphous dye film can also be used as the light absorption layer film without using a matrix material.

  In addition, when the dye can be present alone as a microcrystal aggregate that does not cause light scattering, the microcrystal aggregate of the dye can be used as the light absorption layer film without using the matrix material. As in the thermal lens forming element used in the invention of this application, the dye microcrystal aggregates as the light absorption layer film are composed of a thermal lens forming layer (resin etc.), a heat transfer layer film (glass etc.) and a heat insulating layer film ( In the case where the particle diameter of the dye microcrystal is not larger than 1/5 of the shorter wavelength of the wavelength of the signal light and the wavelength of the conversion light. In this case, substantially no light scattering occurs.

[Combination of light absorption layer material, wavelength band of signal light, and wavelength band of conversion light]
The material of the light absorption layer film, the wavelength band of the signal light, and the wavelength band of the conversion light used in the invention of this application can be selected and used as an appropriate combination according to the purpose of use. .

  As a specific setting procedure, for example, first, the combination of the wavelength or wavelength band of the signal light and the conversion light is determined according to the purpose of use, and the most suitable material for the light absorption layer film is selected. Good. A combination of light wavelengths may be selected.

[Composition of material of light absorption layer film, film thickness of light absorption layer film in light absorption layer film, and film thickness of thermal lens forming layer]
In the thermal lens forming element used in the invention of this application, the light absorption layer film is a single layer film of “light absorption film” alone, or a two-layer structure of “light absorption film / thermal lens formation layer”, or “ Any of the three-layered laminated thin films of “light absorption film / thermal lens forming layer / light absorption film” may be used, and the total thickness of the light absorption layer film is determined by the confocal distance of the converged conversion light. It is preferable not to exceed 2 times. Furthermore, when aiming at a higher response speed, it is preferable that the thickness of the light absorption layer film composed of the laminated thin film does not exceed one time the confocal distance of the converged conversion light.

  Under such conditions, the composition of the material of the light absorption layer film used in the invention of this application and the film thickness of the light absorption film (1 or 2 sheets) in the light absorption layer film, It can be set on the basis of the transmissivity of the conversion light and the signal light transmitted through the light absorption layer film. For example, first, the concentration of the component that absorbs at least the conversion light or the signal light in the composition of the material of the light absorption layer film is determined, and then the transmittance of the conversion light and the signal light transmitted through the thermal lens forming element. The film thickness of the light absorption film (1 or 2) in the light absorption layer film can be set so that becomes a specific value. Or, first, for example, according to the design requirements of the device, the film thickness of the light absorbing film (one or two) in the light absorbing layer film is set to a specific value, and then converted through the thermal lens forming element. The composition of the material of the light absorption layer film can be adjusted so that the light and signal light transmittances have specific values.

  Conversion light and signal light that pass through the light-absorbing layer film, which is optimal for extracting a sufficient size and high-speed thermal lens effect with the lowest possible optical power from the thermal lens forming element used in the invention of this application The transmittance values are as follows.

  In the thermal lens forming element used in the invention of this application, the light absorption in the light absorbing layer film is such that the transmittance of the conversion light propagating through the light absorbing layer film in the thermal lens forming element is 90% to 0%. It is recommended to control the concentration and presence state of the components and set the film thickness of the light absorption film (1 or 2) in the light absorption layer film.

  On the other hand, in the state where no signal light is irradiated, the light absorption is such that the transmittance of the conversion light propagating through the light absorbing layer film in the thermal lens forming element approaches 10% or more as the lower limit and 100% as the upper limit. It is recommended to control the concentration and existence state of the light absorption component in the layer film and to set the film thickness of the light absorption film (1 or 2 sheets) in the light absorption layer film.

  The lower limit of the thermal lens forming layer thickness in the light absorbing layer film is selected according to the material of the thermal lens forming layer as described below.

[Material of Thermal Lens Formation Layer in Light Absorption Layer Film and Film Thickness of Thermal Lens Formation Layer]
The single-layer light absorption film itself may act as a thermal lens forming layer, but the functions of light absorption and thermal lens formation are shared by different materials, and each selected optimal material is used in layers. It is preferable to do.

  As the material of the thermal lens forming layer in the light absorption layer film, liquid, liquid crystal, and solid material can be used. In particular, the thermal lens forming layer is preferably made of an organic compound selected from the group consisting of an amorphous organic compound, an organic compound liquid, and a liquid crystal. When the material of the thermal lens forming layer is liquid crystal or liquid, for example, at least one of the light absorption film and the heat transfer layer film is made of a self-form-retaining material, and the depletion corresponding to the thickness of the thermal lens forming layer is made. And a thermal lens forming layer material in a fluid state is injected into the thermal lens forming layer. On the other hand, when the material of the thermal lens forming layer is solid, the thermal lens forming layer may be formed by laminating a light absorption film on one or both sides.

  The thermal lens forming layer may not be made of a single material, and may be a laminated film of a plurality of types of solids, or may be a laminate of a solid and a liquid.

  Although the thickness of the thermal lens forming layer depends on the type of material used, the thickness may be in the range of several nanometers to 1 mm, and particularly preferably in the range of several tens of nanometers to several hundreds of micrometers. .

  As described above, the total thickness of the light absorbing layer film formed by laminating the thermal lens forming layer and one or two light absorbing films should not exceed twice the confocal distance of the converged signal. Is preferred.

  As the material for the thermal lens forming layer in the light absorption layer film, liquid, liquid crystal, and solid material can be used. In any case, a material having a large temperature dependence of the refractive index is preferable.

Typical organic compound liquid and water refractive index temperature-dependent physical property values are described in the literature [D. Solini: J.M. Appl. Phys. , Vol. 37, 3314 (1966)]. The temperature change [unit: 1 / K] of the refractive index with respect to light having a wavelength of 633 nm is larger in alcohol such as methanol (3.9 × 10 ⁻⁴ ) than in water (0.8 × 10 ⁻⁴ ). Pentane (5.7 × 10 ⁻⁴ ), benzene (6.4 × 10 ⁻⁴ ), chloroform (5.8 × 10 ⁻⁴ ), benzene (6.4 × 10 ⁻⁴ ), carbon disulfide (7. Non-hydrogen bonding organic solvents such as 7 × 10 ⁻⁴ ) are large.

  When liquid crystal is used as the material of the thermal lens forming layer in the light absorption layer film, any known liquid crystal can be used. Specifically, various cholesterol derivatives, 4′-n-butoxybenzylidene-4-cyanoaniline, 4′-alkoxybenzylidene-4-cyanoanilines such as 4′-n-hexylbenzylidene-4-cyanoaniline, 4 4'-alkoxybenzylidene such as' -ethoxybenzylidene-4-n-butylaniline, 4'-methoxybenzylideneaminoazobenzene, 4- (4'-methoxybenzylidene) aminobiphenyl, 4- (4'-methoxybenzylidene) aminostilbene Anilines, 4′-cyanobenzylidene-4-n-butoxyaniline, 4′-cyanobenzylidene-4-alkoxyanilines such as 4′-cyanobenzylidene-4-n-hexyloxyaniline, 4′-n-butoxy Carbonyloxybenzylidene-4-methoxyaniline Carbonates such as p-carboxyphenyl, n-amyl carbonate, n-heptyl, 4- (4′-ethoxyphenoxycarbonyl) phenyl carbonate, 4-n-butylbenzoic acid, 4′-ethoxyphenyl, 4-n- 4-alkylbenzoic acid, 4′-alkoxyphenyl esters such as butylbenzoic acid, 4′-octyloxyphenyl, 4-n-pentylbenzoic acid, 4′-hexyloxyphenyl, 4,4′-di-n- Azoxybenzene derivatives such as amyloxyazoxybenzene, 4,4′-di-n-nonyloxyazoxybenzene, 4-cyano-4′-n-octylbiphenyl, 4-cyano-4′-n-dodecylbiphenyl Liquid crystals such as 4-cyano-4′-alkylbiphenyls, and (2S, 3S) -3-methyl-2-chloropentano 4 ', 4 "-octyloxybiphenyl, 4'-(2-methylbutyl) biphenyl-4-carboxylic acid, 4-hexyloxyphenyl, 4'-octylbiphenyl-4-carboxylic acid, 4- (2 Ferroelectric liquid crystals such as -methylbutyl) phenyl can be used.

When a solid material is used as the material of the thermal lens forming layer in the light absorption layer film, an amorphous organic compound having a small light scattering and a large temperature dependency of the refractive index is particularly suitable. Specifically, similar to the matrix material, a known optical resin can be selected from various organic polymer materials and used. Document [Technical Information Association, “Development of Latest Optical Resins, Design of Properties and High Precision Parts, Molding Technology”, Technical Information Association (1993), P.A. 35], the refractive index change in temperature of the optical resin [unit: 1 / K] is, for example, poly (methyl methacrylate) 1.2 × 10 ⁻⁴ , polycarbonate 1.4 × 10 ⁻⁴ , Polystyrene 1.5 × 10 ⁻⁴ . These resins can be suitably used as a material for the thermal lens forming layer in the light absorption layer film.

  While the refractive index temperature dependency of the organic solvent has a merit that it is greater than that of the optical resin, there is a problem that the organic solvent boils when the temperature rise due to signal light irradiation reaches the boiling point of the organic solvent (high boiling point). No problem when using other solvents). On the other hand, the optical resin from which volatile impurities have been thoroughly removed can be used even under severe conditions in which the temperature rise due to signal light irradiation exceeds 250 ° C., for example, in the case of polycarbonate.

[Heat insulation layer film]
When a gas is used as the heat insulating layer film, an inert gas such as nitrogen, helium, neon, or argon can be suitably used in addition to air.

  When a liquid is used as the heat insulation layer film, the material has a thermal conductivity equal to or smaller than that of the light absorption layer film, and transmits the conversion light and the signal light. Any liquid can be used as long as it does not dissolve or corrode the material. For example, when the light absorbing layer film is made of polymethyl methacrylate containing a cyanine dye, fluid paraffin can be used.

When a solid is used as the heat insulating layer film, the heat conductivity is the same as or smaller than that of the light absorption layer film (light absorption film and thermal lens forming layer), and the polarization light and signal Any solid can be used as long as it transmits light and does not react with the material of the light absorption layer film or the heat transfer layer film. For example, when the light absorption film is made of polymethyl methacrylate containing a cyanine dye, polymethyl methacrylate [pigment-free polymethyl methacrylate [thermal conductivity at 300 K: 0.15 Wm ⁻¹ K ⁻¹ ]] is used as the heat insulating layer film. it can.

[Material of heat transfer layer film]
As the heat transfer layer film, a material having a thermal conductivity larger than that of the light absorption layer film is preferable, as long as it transmits the conversion light and the signal light and does not react with the material of the light absorption layer film or the heat insulation layer film. Any thing can be used. Examples of materials having high thermal conductivity and low light absorption in the visible light wavelength band include diamond [thermal conductivity 900 Wm ⁻¹ K ^{−1 at} 300 K], sapphire [46 Wm ⁻¹ K ⁻¹ ], quartz. Single crystal [same as 10.4 Wm ⁻¹ K ⁻¹ in the direction parallel to the c-axis], quartz glass [1.38 Wm ⁻¹ K ⁻¹ ], hard glass [1.10 Wm ⁻¹ K ⁻¹ ], etc. It can be suitably used as a thermal layer film.

[Material of light transmission layer]
The thermal lens forming element used in the invention of this application may be provided with a gradient index lens as signal light converging means laminated on the incident side of the conversion light via a light transmission layer. As the material for the light transmission layer, the same materials as those for the solid heat insulating layer film and / or the heat transfer layer film can be used. The light transmission layer literally serves not only to efficiently transmit the signal light and the conversion light but also to adhere the gradient index lens as a thermal lens forming element component. Among so-called ultraviolet curable resins and electron beam curable resins, those having a high light transmittance in the wavelength band of signal light and conversion light can be particularly preferably used.

[Method for creating thermal lens forming element]
The method for producing the thermal lens forming element used in the invention of this application is arbitrarily selected according to the configuration of the thermal lens forming element and the type of material used, and a known method can be used.

  For example, when the light absorbing material used for the light absorbing film in the thermal lens forming element is a single crystal as described above, the light absorbing film can be formed by cutting and polishing the single crystal.

  For example, a “heat transfer layer film / light absorption film / thermal lens formation using a light absorption film made of a matrix material containing a dye, a thermal lens formation layer made of an optical resin, and optical glass as a heat transfer layer film” When a thermal lens forming element having a configuration of “layer / light absorption film / heat transfer layer film” is formed, a light absorption film can be first formed on the heat transfer layer film by the following method.

  Whether a solution in which a dye and a matrix material are dissolved is applied to a glass plate used as a heat transfer layer film by a coating method such as a coating method, a blade coating method, a roll coating method, a spin coating method, a dipping method, or a spray method. Alternatively, a method of forming a light-absorbing film by printing using a printing method such as a planographic plate, a relief plate, an intaglio plate, a stencil plate, a screen, or a transfer method may be used. In this case, an inorganic matrix material preparation method by a sol-gel method can be used for forming the light absorption film.

  Electrochemical film formation methods such as electrodeposition, electropolymerization, and micelle electrolysis (Japanese Patent Laid-Open No. 63-243298) can be used.

  Furthermore, a Langmere-Blodgett method that transfers a monomolecular film formed on water can be used.

  Examples of the method utilizing polymerization or polycondensation reaction of raw material monomers include casting method, reaction injection molding method, plasma polymerization method, and photopolymerization method when the monomer is liquid.

  Sublimation transfer methods, vapor deposition methods, vacuum vapor deposition methods, ion beam methods, sputtering methods, plasma polymerization methods, CVD methods, organic molecular beam vapor deposition methods, and the like can also be used.

  A composite optical thin film characterized in that an organic optical material of two or more components is sprayed into a high vacuum container from a spray nozzle provided for each component in a solution or dispersion state, deposited on a substrate, and heat-treated The manufacturing method (Patent Publication No. 2599569) can also be used.

  The method for producing a solid light-absorbing film as described above can be suitably used when, for example, a heat insulating layer film made of a solid organic polymer material is produced.

  Next, when forming a thermal lens forming layer using a thermoplastic optical resin, a vacuum hot pressing method (Japanese Patent Laid-Open No. 4-99609) is used. A thermal lens forming element having a configuration of “/ light absorption film / heat transfer layer film” can be produced. That is, the thermoplastic optical resin powder or sheet is sandwiched between two heat transfer layer films (glass plates) having a light absorption film formed on the surface by the above method, and heated and pressed under high vacuum, A laminated thin film element having the above-described configuration can be produced.

[Material and manufacturing method of gradient index lens]
The thermal lens forming element used in the invention of this application may be provided with a gradient index lens as a signal light converging means laminated on the signal light incident side through a light transmission layer, As the material and manufacturing method of the gradient index lens, known ones can be used.

  For example, a refractive index distribution type refractive index distribution type lens can be made of an organic polymer material by utilizing a monomer penetration / diffusion phenomenon [M. Oikawa, K .; Iga, T .; Sanada: Jpn. J. et al. Appl. Phys, 20 (1), L51-L54 (1981)]. In other words, the refractive index distribution lens can be made monolithically on a flat substrate by the monomer exchange technique. For example, methyl methacrylate (n = 1.494) as a low refractive index plastic is used as a circular disk of 3.6 mmφ. Is diffused into a flat plastic substrate of polyisophthalic diacrylate (n = 1.570) having a high refractive index.

  Further, a refractive index distribution type refractive index distribution type lens can be made of an inorganic glass material by utilizing the diffusion phenomenon of inorganic ions [M. Oikawa, K .; Iga: Appl. Opt. , 21 (6), 1052-1056 (1982)]. That is, after applying a mask to a glass substrate, a circular window with a diameter of about 100 μm is provided by a photolithography method, and an electric field is applied for several hours to form a refractive index distribution by ion exchange by immersing in molten salt. By promoting ion exchange, a lens having a diameter of 0.9 mm, a focal length of 2 mm, and a numerical aperture NA = 0.23 can be formed, for example.

[Optical cell]
The optical cell used in the dye solution-filled thermal lens forming element has a function of holding the dye solution and a function of effectively giving the dye solution a shape and acting as a light absorption layer film and a thermal lens forming layer. In addition, the signal light and the control light that are converged and irradiated are received and the signal light and the conversion light are propagated to the photoresponsive plastic material, and after passing through the photoresponsive composition, it diverges. It has a function of propagating and emitting conversion light.

  The form of the optical cell used in the dye solution-filled thermal lens forming element is roughly classified into an external form and an internal form.

  As the external form of the optical cell, a plate shape, a rectangular parallelepiped shape, a quadrangular prism shape or the like is used according to the configuration of the wavelength conversion device of the invention of this application.

  The internal form of the optical cell is a form of a dye solution filling portion, and effectively imparts a form to the dye solution. Depending on the configuration of the wavelength conversion device of the invention of this application, the internal form of the optical cell can be specifically selected from among, for example, a thin film, a thick film, a plate, a rectangular parallelepiped, a quadrangular prism, a convex lens, and a concave lens. It can be selected appropriately.

Any configuration and material of the optical cell can be used as long as the following requirements are satisfied.
(1) The external form and the internal form as described above can be accurately maintained under use conditions.
(2) Be inert to the dye solution
(3) It is possible to prevent composition changes due to diffusion, permeation, and penetration of various components constituting the dye solution.
(4) The dye solution can be prevented from deteriorating due to contact with a gas or liquid existing in the use environment such as oxygen or water.

  Specifically, as the material of the optical cell, various optical glasses such as soda glass and borosilicate glass, quartz glass, sapphire, and the like can be preferably used regardless of the type of the dye solution. In addition, when the solvent of the dye solution is water or alcohol, plastics such as poly (methyl methacrylate), polystyrene, and polycarbonate can be used.

  Of the above requirements, the function of preventing the composition change and deterioration of the dye solution only needs to be exhibited within the design life of the thermal lens forming element.

  Other optical elements used in the invention of this application, that is, an optical cell having an integrated structure in which a condensing lens, a light receiving lens, a wavelength selective transmission filter, and the like are incorporated in the optical cell can be used.

[Calculation of beam waist diameter]
In order to effectively use the thermal lens effect in the invention of this application, the beam cross-sectional area of the conversion light in the region with the highest photon density near the focal point (condensing point), that is, the “beam waist” is It is preferable to set the shapes and sizes of the beam cross sections of the conversion light and the signal light so as not to exceed the beam cross sectional area of the signal light.

  Hereinafter, the case of a Gaussian beam in which the amplitude distribution of the electric field in the cross section of the traveling direction beam, that is, the energy distribution of the luminous flux is a Gaussian distribution will be described. In the following description, a case where a condensing lens (refractive index distribution type lens) is used as the beam converging unit will be described. However, the same applies when the converging unit is a concave mirror or a refractive index dispersion type lens.

FIG. 9 shows the state of the light beam and the wavefront (300) in the vicinity of the focal point (301) when the Gaussian beam is converged with an opening angle 2θ using a condenser lens or the like. Here, the position where the diameter 2ω of the Gaussian beam having the wavelength λ is minimum is referred to as “beam waist”. Hereinafter, the beam waist diameter is represented by 2ω ₀ . Due to the diffraction effect of light, 2ω ₀ does not become zero but has a finite value. The definitions of the beam radii ω and ω ₀ are the distances when the position where the energy becomes 1 / e ² (e is the base of the natural logarithm) is measured from the beam center with reference to the energy of the beam center portion of the Gaussian beam. And the beam diameter is expressed as 2ω or 2ω ₀ . Needless to say, the photon density is highest in the center of the beam waist.

In the case of a Gaussian beam, the beam divergence angle θ sufficiently far from the beam waist is related to the wavelength λ and the beam waist diameter ω ₀ by the following equation [1].
(Equation 1)
π ・ θ ・ ω ₀ ≒ λ… [1]
Here, π is the circumference ratio.

Using this formula only when the condition of “far enough from the beam waist” is satisfied, the beam is collected by the condenser lens from the beam radius ω incident on the condenser lens, the numerical aperture of the condenser lens, and the focal length. The beam waist diameter ω ₀ can be calculated.

More generally, a beam waist diameter 2ω ₀ when a parallel Gaussian beam (wavelength λ) having a beam radius ω is converged by a condensing lens having an effective aperture radius a and a numerical aperture NA is expressed by the following equation [2]. Can be represented.
(Equation 2)
2ω ₀ ≒ k · λ / NA [2]
Here, since the coefficient k cannot be solved algebraically, it can be determined by performing a numerical analysis calculation on the light intensity distribution on the lens imaging plane.

When numerical analysis calculation is performed by changing the ratio of the beam radius ω incident on the condenser lens and the effective aperture radius a of the condenser lens, the value of the coefficient k in the equation [2] is obtained as follows.
(Equation 3)
When a / ω = 1, k≈0.92
When a / ω = 2, k≈1.3
When a / ω = 3, k≈1.9
When a / ω = 4, k≈3
That is, the smaller the beam radius ω is than the effective aperture radius a of the condenser lens, the larger the beam waist diameter ω ₀ .

For example, if a lens having a numerical aperture of 0.25 and an effective aperture radius of about 5 mm is used as the condenser lens and the light for polarization having a wavelength of 780 nm is converged, if the beam radius ω incident on the condenser lens is 5 mm, a / ω Is about 1, the beam waist radius ω ₀ is 1.4 μm, and ω is 1.25 mm, a / ω is about 4 and ω ₀ is calculated to be 4.7 μm. Similarly, when the signal light having a wavelength of 633 nm is converged, if the beam radius ω is 5 mm, a / ω is about 1, the beam waist radius ω ₀ is 1.2 μm, and if ω is 1.25 mm, a / ω is about 4 and ω ₀ is calculated to be 3.8 μm.

  As can be seen from this calculation example, in order to minimize the cross-sectional area of the light beam in the region where the photon density near the focal point of the condenser lens is the highest, that is, the beam waist, the intensity distribution of the light beam incident on the condenser lens The beam diameter may be expanded (beam expanding) until becomes close to a plane wave. It can also be seen that when the beam diameter incident on the condenser lens is the same, the shorter the wavelength of the light, the smaller the beam waist diameter.

  As described above, in order to effectively use the thermal lens effect in the invention of this application, the beam cross-sectional area of the conversion light in the region where the photon density in the vicinity of the beam waist is the highest is the beam break of the signal light in the beam waist. It is preferable to set the shape and size of the beam cross sections of the conversion light and the signal light so as not to exceed the area. If a Gaussian beam is used for both the conversion light and the signal light, according to the above explanation and the calculation formula, in the state of the parallel beam before being converged by the converging means such as a condensing lens, for conversion according to the wavelength The beam cross-sectional area of the conversion light in the region where the photon density in the vicinity of the beam waist is the highest is adjusted by adjusting the beam diameter of the light and the signal light, for example, by expanding the beam as necessary. The beam cross-sectional area can be not exceeded. As a means for beam expansion, a publicly known one, for example, a Kepler type optical system composed of two convex lenses can be used.

[Calculation of confocal distance Zc]
In general, in the case of a Gaussian beam, the convergent beam can be regarded as almost parallel light in the vicinity of the beam waist of the light beam converged by a converging means such as a convex lens, that is, in the section of the confocal distance Zc across the focal point. The focal length Zc can be expressed by the equation [3] using the circumference ratio π, the beam waist radius ω _0, and the wavelength λ.
(Equation 4)
Zc = πω ₀ ² / λ (3)
Substituting equation [2] into ω ₀ in equation [3] yields equation (4).
(Equation 5)
Zc≈π (k / NA) ² λ / 4 (4)
For example, when a lens having a numerical aperture of 0.25 and an effective aperture radius of about 5 mm is used as the condenser lens and the conversion light having a wavelength of 780 nm is converged, if the beam radius ω incident on the condenser lens is 5 mm, a / ω Is about 1, the beam waist radius ω ₀ is 1.4 μm, the confocal distance Zc is 8.3 μm, and ω is 1.25 mm, a / ω is about 4 and ω ₀ is 4.7 μm, the confocal distance Zc is calculated to be 88 μm. Similarly, when the change light having a wavelength of 633 nm is converged, if the beam radius ω is 5 mm, a / ω is about 1, the beam waist radius ω ₀ is 1.2 μm, the confocal distance Zc is 6.7 μm, If ω is 1.25 mm, a / ω is about 4, ω ₀ is calculated to be 3.8 μm, and the confocal distance Zc is calculated to be 71 μm.

[Numerical aperture of condensing lens and light receiving lens]
In the invention of this application, the changing light and the signal light are coaxially converged by the condensing lens and irradiated so as to focus on the thermal lens forming element. When light emitted at an angle is received by a light receiving lens and collimated into parallel light, it is recommended that the numerical aperture (hereinafter referred to as NA) of the light receiving lens is set to be larger than the NA of the condenser lens. Is done. Furthermore, the NA of the light receiving lens is preferably at least twice that of the condenser lens. However, when the effective aperture radius a of the condenser lens is larger than the beam radius ω incident on the condenser lens (that is, a / ω> 1), the substantial numerical aperture of the condenser lens is the numerical aperture of the condenser lens. Smaller than. Therefore, it is preferable that the numerical aperture of the light receiving lens is larger than the substantial numerical aperture of the condensing lens, not the condensing lens numerical aperture, and is set to be twice or more. By making the NA of the light receiving lens more than twice the NA of the condenser lens, even if the beam diameter of the signal light is expanded to more than twice that when entering the thermal lens forming element, light is received without loss. Is possible.

[Optimal film thickness of light absorption layer]
Samples are made by changing the thickness of the thermal lens forming layer without changing the thickness of one or two light absorbing films constituting the light absorbing layer film, and a plurality of thermal lenses having different optical thicknesses with a constant optical density are formed. As a result of experiments on the element, it was found that the light response speed of the thermal lens effect is sufficiently high when the double of the confocal distance Zc calculated as described above is set as the upper limit of the thickness of the light absorption layer film. It was.

  About the minimum of the film thickness of a light absorption layer film, as long as the thermal lens effect can be exhibited, it is so preferable that it is thin.

[Thickness of heat insulation layer film]
There is an optimum value (lower limit value and upper limit value) that maximizes at least one of the magnitude and speed of the optical response in the film thickness of the heat insulating layer film. The value can be experimentally determined according to the configuration of the thermal lens forming element, the material and thickness of the light absorption layer film, the material of the heat retaining layer film, the material and thickness of the heat transfer layer film, and the like. For example, ordinary borosilicate glass is used as the heat transfer layer film, polycarbonate is used as the material of the heat insulation layer film and the thermal lens forming layer, and a platinum phthalocyanine vapor deposition film is used as the light absorption film, and glass (heat transfer layer film, film thickness 150 μm) / Polycarbonate resin layer (thermal insulation layer) / Platinum phthalocyanine vapor deposition film (light absorption film, film thickness 0.2 μm) / Polycarbonate resin layer (thermal lens formation layer, film thickness 20 μm) / Platinum phthalocyanine vapor deposition film (light absorption film, film thickness) 0.2 μm) / polycarbonate resin layer (heat-retaining layer) / glass (heat transfer layer film, film thickness 150 μm) When a thermal lens forming element is prepared, the film thickness of the heat-retaining layer film is preferably 5 nm to 5 μm. More preferably, it is 50 nm to 500 nm.

[Film thickness of heat transfer layer film]
The film thickness of the heat transfer layer film also has an optimum value (in this case, a lower limit value) that maximizes at least one of the magnitude and speed of the optical response. The value can be experimentally determined according to the configuration of the thermal lens forming element, the material and thickness of the light absorption layer film, the material and thickness of the heat retaining layer, the material of the heat transfer layer film, and the like. For example, ordinary borosilicate glass is used as the heat transfer layer film, polycarbonate is used as the material of the heat insulation layer film and the thermal lens forming layer, and a platinum phthalocyanine vapor deposition film is used as the light absorption film, and glass (heat transfer layer film, film thickness 150 μm) / Polycarbonate resin layer (thermal insulation layer) / Platinum phthalocyanine vapor deposition film (light absorption film, film thickness 0.2 μm) / Polycarbonate resin layer (thermal lens formation layer, film thickness 20 μm) / Platinum phthalocyanine vapor deposition film (light absorption film, film thickness) 0.2 μm) / polycarbonate resin layer (thermal insulation layer) / glass (heat transfer layer film, film thickness 150 μm) When a thermal lens forming element is prepared, the lower limit of the thickness of the heat transfer layer film is preferably 10 μm. More preferably, it is 100 μm. The upper limit of the film thickness of the heat transfer layer film is not limited by the magnitude and / or speed of the optical response, but the type of condensing lens and light receiving lens used, the focal length, and the working distance (working distance) It is necessary to design in conformity.

It is a figure which shows typically an example of the conventional wavelength converter. It is a conceptual diagram of one Embodiment of the wavelength converter of invention of this application. It is a figure which shows the relationship between the wavelength of the material used for the light absorption layer film | membrane of an example used for a thermal lens formation element, an absorption characteristic, and a transmission characteristic. It is a figure which shows the schematic apparatus structural example of the said embodiment. It is a figure similar to FIG. 4 of another one Embodiment of the wavelength converter of invention of this application. It is sectional drawing which illustrated an example of the structure of a thermal lens formation element. It is sectional drawing which illustrated another example of the structure of a thermal lens formation element. It is the schematic diagram which illustrated the dye solution filling type | mold thermal lens formation element. It is the figure which showed the mode in the focus vicinity of the Gaussian beam converged with the condensing lens.

Explanation of symbols

11 Thermal lens forming element 12 Signal input section (fiber amplifier)
13 Light source for conversion (laser diode)
14 Signal Light 15 Conversion Light 15a Normal Opening Angle Conversion Light (Conversion Light)
15b Conversion light having an angle larger than the normal opening angle (converted light)
16 Conversion light 21, 22, 24, 25, 26, 27, 28, 29 Lens 23 Optical mixer 31 Signal output unit (optical fiber)

Claims (8)

A signal light input unit for inputting pulsed signal light of a specific wavelength; and
A conversion light source that emits conversion light having a wavelength different from that of the signal light;
A light-absorbing layer film having a wavelength band that exhibits absorptivity to signal light and is transmissive to conversion light;
Means for converging and irradiating the light absorption film so that the signal light and the conversion light each have a focus;
By using a thermal lens based on a refractive index distribution that reversibly occurs due to a temperature rise occurring in a region where the light absorption layer film absorbs signal light and its peripheral region, including the light absorption layer film, When signal light is not irradiated and a thermal lens is not formed, converged conversion light is emitted at a normal opening angle, and when control light is irradiated and a thermal lens is formed, converged conversion light A thermal lens forming element that realizes a state of emitting at an opening angle larger than a normal opening angle in correspondence with the presence or absence of signal light irradiation,
Of the emitted conversion light, converted light selection means for emitting only the conversion light emitted at an angle larger than the normal opening angle as converted light,
A wavelength conversion device comprising: a condensing unit that condenses the converted light from the converted light selecting means and converts it into pulsed converted light having a wavelength different from that of the signal light. A signal light input unit for inputting pulsed signal light of a specific wavelength; and
A conversion light source that emits conversion light having a wavelength different from that of the signal light;
A light-absorbing layer film having a wavelength band that exhibits absorptivity to signal light and is transmissive to conversion light;
Means for converging and irradiating the light absorption film so that the signal light and the conversion light each have a focus;
By using a thermal lens based on a refractive index distribution that reversibly occurs due to a temperature rise occurring in a region where the light absorption layer film absorbs signal light and its peripheral region, including the light absorption layer film, When signal light is not irradiated and a thermal lens is not formed, converged conversion light is emitted at a normal opening angle, and when control light is irradiated and a thermal lens is formed, converged conversion light A thermal lens forming element that realizes a state of emitting at an opening angle larger than a normal opening angle in correspondence with the presence or absence of signal light irradiation,
Of the emitted conversion light, converted light selection means for emitting only the conversion light emitted from the thermal lens forming element at a normal opening angle as converted light, and
A wavelength conversion device comprising: a condensing unit that condenses the converted light from the converted light selecting means and converts it into pulsed converted light having a wavelength different from that of the signal light. A signal light input unit for inputting pulsed signal light of a specific wavelength; and
A conversion light source that emits conversion light having a wavelength different from that of the signal light;
A light-absorbing layer film having a wavelength band that exhibits absorptivity to signal light and is transmissive to conversion light;
Means for converging and irradiating the light absorption film so that the signal light and the conversion light each have a focus;
By using a thermal lens based on a refractive index distribution that reversibly occurs due to a temperature rise occurring in a region where the light absorption layer film absorbs signal light and its peripheral region, including the light absorption layer film, When signal light is not irradiated and a thermal lens is not formed, converged conversion light is emitted at a normal opening angle, and when control light is irradiated and a thermal lens is formed, converged conversion light A thermal lens forming element that realizes a state of emitting at an opening angle larger than a normal opening angle in correspondence with the presence or absence of signal light irradiation,
Of the emitted conversion light, only the conversion light emitted at an angle larger than the normal opening angle is emitted as converted light, and only the conversion light emitted at the normal opening angle is emitted as converted light Conversion light selection means capable of performing selection with
A wavelength conversion device comprising: a condensing unit that condenses the converted light from the converted light selecting means and converts it into pulsed converted light having a wavelength different from that of the signal light.   The polarization state switching means for switching whether the polarization state of the converted light to be emitted is the same as or different from the polarization state of the incident signal light is provided. Wavelength converter. Light absorption of a thermal lens forming element including a light absorption layer film having a wavelength band that exhibits at least absorption for pulsed signal light having a specific wavelength and transparency for conversion light having a wavelength different from that of signal light The film is irradiated with the signal light and the conversion light so as to be focused so that they are focused, and the light absorption layer film is generated reversibly due to the temperature rise occurring in the area where the signal light is absorbed and the surrounding area. By using a thermal lens based on the refractive index distribution, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle, and the control light is irradiated. When the thermal lens is formed, the converged conversion light is emitted at an opening angle larger than the normal opening angle, corresponding to the presence or absence of signal light irradiation,
Of the emitted conversion light, only the conversion light emitted at an angle larger than the normal opening angle is selectively emitted as converted light,
A wavelength conversion method characterized by condensing the emitted converted light into pulsed converted light having a wavelength different from that of the signal light. Light absorption of a thermal lens forming element including a light absorption layer film having a wavelength band that exhibits at least absorption for pulsed signal light having a specific wavelength and transparency for conversion light having a wavelength different from that of signal light The film is irradiated with the signal light and the conversion light so as to be focused so that they are focused, and the light absorption layer film is generated reversibly due to the temperature rise occurring in the area where the signal light is absorbed and the surrounding area. By using a thermal lens based on the refractive index distribution, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle, and the control light is irradiated. When the thermal lens is formed, the converged conversion light is emitted at an opening angle larger than the normal opening angle, corresponding to the presence or absence of signal light irradiation,
Of the emitted conversion light, only the conversion light emitted from the thermal lens forming element at a normal opening angle is selectively emitted as converted light,
A wavelength conversion method characterized by condensing the emitted converted light into pulsed converted light having a wavelength different from that of the signal light. Light absorption of a thermal lens forming element including a light absorption layer film having a wavelength band that exhibits at least absorption for pulsed signal light having a specific wavelength and transparency for conversion light having a wavelength different from that of signal light The film is irradiated with the signal light and the conversion light so as to be focused so that they are focused, and the light absorption layer film is generated reversibly due to the temperature rise occurring in the area where the signal light is absorbed and the surrounding area. By using a thermal lens based on the refractive index distribution, when the signal light is not irradiated and the thermal lens is not formed, the converged conversion light is emitted at a normal opening angle, and the control light is irradiated. When the thermal lens is formed, the converged conversion light is emitted at an opening angle larger than the normal opening angle, corresponding to the presence or absence of signal light irradiation,
Whether the conversion light that is emitted at an angle larger than the normal opening angle is output as the conversion light, or only the conversion light that is output at the normal opening angle is output as the conversion light. Select and emit,
A wavelength conversion method characterized by condensing the emitted converted light into pulsed converted light having a wavelength different from that of the signal light.   8. The wavelength conversion method according to claim 5, wherein the polarization state of the outgoing converted light can be switched between the polarization state of the incident signal light and the same or different state.

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