JP4883306B2 - Wavelength conversion device and wavelength conversion method - Google Patents

Description

  The present invention relates to a wavelength conversion device and a wavelength conversion method. More specifically, the present invention relates to a novel wavelength conversion apparatus 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, drives a laser diode (LD) 2 with the output, and outputs a wavelength. It emits 780 nm pulsed light.

  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.

  However, in the conventional wavelength converter 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 eagerly desired that light having a wide wavelength selection range can be used without being affected by the electromagnetic interference and without causing the electromagnetic interference. 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 inventors of the present invention use a light having a wide wavelength selection range in Patent Document 1 without using an electric circuit or a mechanically movable part, not being affected by electromagnetic interference, not causing electromagnetic interference. We have proposed a new wavelength conversion technology that is possible and has high durability.

  A wavelength conversion device based on this wavelength conversion technology includes a signal light input unit that receives pulsed signal light having a specific wavelength, a conversion light source that irradiates conversion light having a wavelength different from that of signal light, and signal light. A light-absorbing layer having a wavelength band that exhibits absorptivity and transparency to conversion light, means for irradiating the light-absorbing layer so that the signal light and the conversion light are focused so as to be focused, and the light absorption Signal light is irradiated by using a thermal lens based on a refractive index distribution that reversibly occurs due to a temperature rise that occurs in a region where the light absorption layer absorbs signal light and its surrounding region. When a thermal lens is not formed, the converged conversion light is emitted at a normal opening angle, and when the control lens is irradiated to form a thermal lens, the converged conversion light is at a normal opening angle. The light is emitted with a larger opening angle than And a thermal lens forming optical element that realizes in correspondence with the presence or absence of signal light irradiation, and out of the emitted conversion light, only conversion light emitted at an angle larger than the normal opening angle is emitted as conversion light. And a conversion light selection means capable of selecting only a conversion light emitted at a normal opening angle as a conversion light, and condensing the converted light selected by the conversion light selection means. In addition, the light-emitting device includes a condensing unit that generates pulsed converted light having a wavelength different from that of the signal light.

Furthermore, Patent Document 2 proposes an optical switch that changes the refractive index of the switch material by irradiation of a control beam and changes the optical path of the signal beam without using electrical or mechanical means.
JP 2006-139225 A U.S. Pat.No. 4,585,301

  According to the wavelength conversion technique proposed in Patent Document 1, the use of light having a wide wavelength selection range without using an electric circuit or a mechanically movable part, not affected by electromagnetic interference, causing no electromagnetic interference. However, since many optical components are still required, there is room for further improvement for full-scale practical application.

  On the other hand, it is conceivable to apply the optical path switching method disclosed in Patent Document 2 to this wavelength conversion technique. In this case, however, the deflection angle cannot be increased so much and the laser beam that changes the refractive index has a large power. There was a problem that was necessary.

  The present invention has been made in view of such circumstances, and can reduce the number of optical components and reduce the cost, and can be affected by electromagnetic interference without using an electric circuit or a mechanically movable part. Therefore, it is possible to provide a wavelength conversion device and a wavelength conversion method that do not cause electromagnetic interference, can use light with a wide wavelength selection range, have high durability, and are expected to be put into practical use. Let it be an issue.

In order to solve the above-described problems, the present invention firstly includes a signal light input unit that receives pulsed signal light having a specific wavelength, and conversion light that irradiates conversion light having a wavelength different from that of the signal light. A light source, a thermal lens-forming optical element having a light absorption layer having a wavelength band that absorbs signal light and transmits light for conversion , and each of the light absorption layer includes signal light and conversion light. The condensing point is condensed so that the signal light and the conversion light are different from each other by 25 to 50 μm in the direction perpendicular to the optical axis when the incident light is incident on the incident surface of the thermal lens forming optical element as parallel light . The thermal lens forming optical element includes a first condensing unit, and the thermal lens forming optical element is based on a refractive index distribution reversibly generated due to a temperature rise occurring in a region where the light absorption layer absorbs signal light and a peripheral region thereof. By using the lens, the signal light is not irradiated and the thermal lens When not formed, the conversion light is emitted as non-deflected light that does not change the traveling direction, and when the thermal lens is formed by irradiation with signal light, the conversion light is emitted as deflected light whose traveling direction is changed. The state is realized in correspondence with the presence or absence of the signal light irradiation, and among the conversion light emitted from the thermal lens forming optical element, only the conversion light emitted as the deflection light is emitted as the conversion light. A conversion light selection unit capable of selecting a state and a state in which only conversion light emitted as non-polarized light is emitted as conversion light, and condensing the conversion light from the conversion light selection unit to obtain signal light There is provided a wavelength conversion device comprising a second light condensing unit that converts pulsed converted light having a wavelength different from the above.

According to a second aspect of the present invention, in the first invention, a polarization state switching unit that switches a polarization state of the outgoing converted light to a state that is the same as or different from a polarization state of the incident signal light is provided. The wavelength converter characterized by the above is provided.

In addition, the present invention thirdly includes a light absorption layer having a wavelength band that absorbs pulsed signal light having a specific wavelength and exhibits transparency for conversion light having a wavelength different from that of the signal light. When the signal light and the conversion light are incident on the light absorption layer of the thermal lens forming optical element, respectively, and the signal light and the conversion light are incident on the incident surface of the thermal lens forming optical element as parallel light. Refraction that occurs reversibly due to the temperature rise occurring in the area where the light absorption layer absorbs signal light and its surrounding area, by condensing the light so that it is 25 to 50 μm different in the direction perpendicular to the optical axis By using a thermal lens based on the rate distribution, when the signal light is not irradiated and the thermal lens is not formed, the conversion light is emitted as unpolarized light that does not change the traveling direction, and the control light is irradiated. If a thermal lens is formed, convert light A state in which the light is emitted as the deflected light whose direction is changed is realized in correspondence with the presence or absence of the irradiation of the signal light. Provide a wavelength conversion method characterized in that only one of the light is switched and 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 To do.

Further, fourthly, in the third invention described above, the wavelength of the converted light that is emitted can be switched between the polarization state of the incident signal light and the same or different state Provide a conversion method .

According to the invention of this application, the following effects can be obtained.
The number of optical parts can be reduced, cost can be reduced, no electrical circuit or mechanical moving parts are used, no influence of electromagnetic interference, no cause of electromagnetic interference, and wide wavelength selection range It is possible to provide a novel wavelength conversion technique that makes it possible to use light, has high durability, and is expected to be put into practical use.
Further, there is an advantage that converted light having a phase opposite to that of the incident signal can be obtained.
Further, there is an advantage that it is possible to select and obtain converted light having the same phase or opposite phase as the incident signal.
Further, there is an advantage that converted light having the same polarization state as the incident signal and a different polarization state can be selected and obtained.

  The conceptual diagram of the wavelength converter which concerns on one Embodiment of this invention is shown in FIG. 2, The wavelength and absorption of the material (in this case pigment | dye) used for the light absorption layer of an example used for the thermal lens formation optical element of FIG. The relationship between the characteristics and the transmission characteristics is shown in FIG.

  In the wavelength conversion device of the present embodiment, the optical control thermal lens forming optical element 11 is used, and an optical pulse signal having an arbitrary wavelength A is made incident as a signal light 14 from the signal input unit 12, and at an arbitrary wavelength from the conversion light source 13. The B continuous light is incident as the conversion light 15, and an optical pulse having an arbitrary wavelength B is emitted as the conversion light 16. As the signal light 14 incident from the signal input unit 12, light from various light sources conventionally used such as a laser light source can be used. A laser device is preferably used for the conversion light source 13, but is not limited thereto.

  The thermal lens forming optical element 11 is provided with a light absorption layer having a wavelength band as shown in FIG. That is, this light absorption layer has a large absorptance with respect to the wavelength A, a large transmittance with respect to the wavelength B, and a refractive index effect (shows a large refractive index change with respect to a change in temperature). It shall have. Since the wavelength band has various forms depending on the material of the light absorption layer, the wavelengths A and B can be arbitrarily selected by selecting the material. The above is the same as that described in Patent Document 1 by the present inventors, but differs in the points described in detail below.

  FIG. 4 is a diagram more specifically showing the configuration of the main part of the wavelength conversion device of the present embodiment. This wavelength converter has a conversion light source (13 in FIG. 2) (not shown), an input port 22 for taking in conversion light 21, which is continuous (CW) light from the conversion light source, and a conversion light source. An input port 24 for taking in pulsed signal light 23 having a wavelength different from the wavelength of the light 21 is provided. A first collimating lens 25 for converting incident conversion light 21 into parallel light is disposed on the downstream side of the input port 22. In order to convert incident signal light 23 into parallel light on the downstream side of the input port 24. The second collimating lens 26 is arranged. For convenience, FIG. 4 shows parallel light as a straight line having no width. An optical mixer 27 is disposed on the downstream side of the first collimating lens 25 and the second collimating lens 26, and the optical mixer 27 transmits the conversion light 21 that is parallel light from the first collimating lens 25. Then, the signal light 23 which is parallel light from the second collimating lens 26 is reflected and its optical path is changed. A first condenser lens 28, a thermal lens forming optical element 29, a third collimator lens 30, a wavelength selective transmission filter 31, a branch mirror 32, and a second condenser lens 33 are respectively provided downstream of the optical mixer 27. Has been placed. The first condenser lens 28 condenses (converges) the conversion light 21 and the signal light 23 from the optical mixer 27 on the light absorption layer of the thermal lens forming optical element 29. Here, the conversion light 21 and the signal light 23 are incident on the first condenser lens 28 at positions shifted in a direction perpendicular to the optical axis, and the optical axis is also incident on the light absorption layer of the thermal lens forming optical element 29. The light is incident at a position shifted in a direction perpendicular to the light beam, and the condensing point is separated.

  The thermal lens forming optical element 29 emits unpolarized light that does not change the traveling direction when only the conversion light 21 is incident, and forms the thermal lens when the conversion light 21 and the signal light 23 are incident simultaneously. Then, the conversion light 21 is emitted as deflected light whose traveling direction is changed. The third collimating lens 30 converts the conversion light 21 (unpolarized light and deflected light) and the signal light 23 into parallel light. The wavelength selective transmission filter 31 transmits the conversion light 21 and cuts the signal light 23. A branch mirror 32 provided downstream of the wavelength selective transmission filter 31 branches the non-deflected light and the deflected light, and the deflected light is reflected to change its optical path. Unpolarized light travels straight. Further, a mirror 34 for further changing the optical path of the deflected light whose optical path has been changed and a third condenser lens 35 for condensing the light from the mirror 34 are disposed above the branch mirror 32 in the drawing. In addition, this wavelength converter has two output ports 36 and 37. The output port 36 outputs light of unpolarized light collected by the second condenser lens 33 when the signal light 23 is off. The output port 37 changes the optical path by the branch mirror 32 and the mirror 34 when the signal light 23 is turned on, and outputs the light of the deflected light condensed by the third condenser lens 35. In this wavelength converter, either non-deflected light output from the output port 36 or deflected light output from the output port 37 is converted light. It is possible to provide a switching selection means for selecting either non-deflected light or deflected light as converted light.

  In the present wavelength conversion device, as described above, the wavelength of the conversion light 21 is light having a wavelength that shows transparency to the light absorption layer of the thermal lens forming optical element 29. In addition, as the wavelength of the signal light 23, light having a wavelength that exhibits absorption with respect to the light absorption layer of the thermal lens forming optical element 29 is used.

  The material of the light absorption layer in the thermal lens forming optical element 29 used in the present wavelength conversion device, the wavelength band of the conversion light 21 and the wavelength band of the signal light 23 are, for example, the wavelength or wavelength of the signal light 23 first. The optimum combination of the light absorbing layer material and the wavelength of the conversion light 21 can be selected for determining the band and then controlling the band. However, the present invention is not limited to this.

  As the first collimating lens 25, the second collimating lens 26, and the third collimating lens 30, for example, an aspherical lens having a focal length of 8 mm can be used, but the focal length does not need to be 8 mm and is smaller. Needless to say, an even shorter focal length may be used in order to obtain a wavelength conversion device. Further, although it is not necessary to use an aspheric lens, an aspheric lens is preferable in order to reduce the size and weight.

  As the optical mixer 27, for example, a known optical member such as a dichroic mirror that transmits the conversion light 21 and reflects the signal light 23 can be used. Of course, it is needless to say that the positions of the input port 22 and the input port 24 may be interchanged so that the conversion light 21 is reflected and the signal light 23 is transmitted.

  As the first condenser lens 28, the second condenser lens 33, and the third condenser lens 35, for example, an aspherical lens having a focal length of 8 mm can be used, but the focal length is not necessarily 8 mm. Needless to say, a shorter focal length may be used in order to obtain a smaller wavelength converter. Further, although it is not necessary to use an aspheric lens, an aspheric lens is preferable in order to reduce the size and weight.

  In the present wavelength conversion device, the conversion light 21 and the signal light 23 are condensed by the first condenser lens 28 at or near the incident surface of the light absorption layer of the thermal lens forming optical element 29 in the light traveling direction. . When the conversion light 21 and the signal light 23 are condensed at the same position near the incident surface of the light absorption layer of the thermal lens forming optical element 29, the conversion light 21 spreads in a donut shape. This situation is shown in FIG. When the signal light 23 is not present, the conversion light 21 is a round beam as shown in the photograph 1a of FIG. 5A, but when the signal light 23 is simultaneously irradiated to the same place, the conversion light 21 shown in FIG. It has a donut shape as shown in Photo 1b. It is considered that the light-absorbing layer incident surface has a clear and large donut shape. In the present wavelength conversion device, the incident surface of the light absorption layer is a surface corresponding to a position where the donut shape is clear and large when the conversion light 21 and the signal light 23 are condensed at the same place. To do. Of course, the conversion light 21 and the signal light 23 that are actually used in the present wavelength conversion device are separated by about 25 to 50 μm in the direction perpendicular to the optical axis at the position of the condensing point, so a donut shape is not formed, but at the time of adjustment The conversion light 21 and the signal light 23 are incident on the same point to form a donut shape, and then the condensing points of the conversion light 21 and the signal light 23 are separated to adjust the position. In addition, when the distance between the condensing points of the conversion light 21 and the signal light 23 is less than 25 μm, a round beam as shown in FIG. When the conversion light 21 becomes a crescent-shaped beam, if it is condensed and then incident on the optical fiber, the incident efficiency is reduced, which may impair practicality. Further, when the distance exceeds 50 μm, the deflection angle tends to decrease.

  Although the thermal lens forming optical element 29 has a schematic configuration as shown in FIG. 6, only the light absorption layer is shown in FIG. 4 for ease of explanation. In FIG. 6, the light absorbing layer 42 of the thermal lens forming optical element 41 (29) is used by sealing a dye in a solvent in a glass container 43. As the dye that is soluble in the solvent, a dye that exhibits absorbency in the wavelength region of the signal light to be used and does not absorb in the wavelength region of the conversion light to be used and exhibits transparency can be used. For example, the glass container 43 through which the laser beam 44 transmits can have a glass thickness of about 500 μm, and the light absorption layer 42 can have a thickness of about 200 to 1000 μm.

  Specific examples of the dye include, for example, xanthene dyes such as rhodamine B, rhodamine 6G, eosin and phloxine B, acridine dyes such as acridine orange and acridine red, azo dyes such as ethyl red and methyl red, porphyrin dyes, Phthalocyanine dyes, cyanine dyes such as 3,3′-diethylthiacarbocyanine iodide, 3,3′-diethyloxadicarbocyanine iodide, triarylmethane dyes such as ethyl violet and Victoria Blue R, naphthoquinone A dye, an anthraquinone dye, a naphthalene tetracarboxylic acid diimide dye, a perylene tetracarboxylic acid diimide dye, or the like can be suitably used. Moreover, these pigment | dyes can be used individually or in mixture of 2 or more types.

  As the solvent, a solvent that dissolves at least the dye to be used can be used. However, the temperature (boiling point) of boiling without being thermally decomposed when the temperature rises during the formation of the thermal lens is 100 ° C. or higher, preferably 200. Those having a temperature of at least ° C, more preferably at least 300 ° C can be suitably used. Specifically, inorganic solvents such as sulfuric acid, halogenated aromatic hydrocarbons such as o-dichlorobenzene, aromatic substituted aliphatics such as 1-phenyl-1-xylylethane or 1-phenyl-1-ethylphenylethane Organic solvents such as hydrocarbons and nitrobenzene derivatives such as nitrobenzene can be suitably used.

  As the wavelength selective transmission filter 31, a dielectric filter or the like that shields the signal light 3 slightly transmitted through the thermal lens forming optical element 41 (29) and transmits the conversion light 1 can be used. If the signal light 23 is absorbed to the extent that there is no practical problem with the thermal lens forming optical element 41 (29), the wavelength selective transmission filter 31 is not necessarily used.

  Further, the thermal lens forming optical element 41 (29) basically has the absorption and transmission wavelength characteristics as described above, and has only to have a light absorption layer capable of forming a thermal lens, thereby promoting light absorption. It can be of various structures as described in JP-A-2005-265986 related to the application of the present inventors, such as a layer to be heated, a heat transfer layer, and a heat insulating layer.

  Here, the deflection of the conversion light 21 by the thermal lens formation in the thermal lens forming optical element 41 (29) will be described.

  When the signal light 23 is absorbed by the light absorption layer of the thermal lens forming optical element 41 (29), the temperature of the light absorption layer rises and the refractive index changes. As the temperature increases, the refractive index generally changes in a decreasing direction. The intensity distribution of laser light emitted from a normal laser light source or laser light emitted from a normal laser light source and transmitted through an optical fiber is a Gaussian distribution. Further, the light obtained by condensing the laser light with a lens or the like has a Gaussian distribution. Therefore, the refractive index distribution in the light absorption layer irradiated with the signal light 23 has the lowest refractive index on the optical axis of the signal light 23 and the decrease in the refractive index around the signal light 23 is reduced. Further, since there is heat conduction, the refractive index changes even in a portion where light is not irradiated.

  FIG. 7 is a diagram illustrating a situation in which the conversion light 45 (21) is deflected. In order to simplify the description, in FIG. 7, light refraction due to the difference in refractive index between the light absorption layer and the medium around the light absorption layer is ignored. In FIG. 7, the light absorption layer 42 of the thermal lens forming optical element 41 (29) is irradiated with only the conversion light 45 (21), the conversion light 45 (21), and the signal light 46 (23). In the case where is simultaneously irradiated. In the figure, reference numeral 47 denotes conversion light transmitted through the light absorption layer 42 of the thermal lens forming optical element 41 (29) when the signal light 46 (23) is not irradiated. Reference numeral 48 denotes conversion light transmitted through the light absorption layer 42 of the thermal lens forming optical element 41 (29) when the signal light 46 (23) is irradiated. Further, the light intensity distribution 49 of the signal light in the vicinity of the incident surface of the light absorption layer 42 of the thermal lens forming optical element 41 (29), and the vicinity of the emission surface of the light absorption layer 42 of the thermal lens forming optical element 41 (29). The light intensity distribution 50 is also shown.

  FIG. 7a schematically shows the optical path of the laser light when the laser light is not condensed, and FIG. 7b schematically shows the optical path of the laser light when the laser light is condensed as in the present wavelength converter. The intensity distribution regions 49 and 50 of the laser light when the laser light is not condensed do not change between the vicinity of the entrance surface and the exit surface of the light absorption layer 42. This means that the conversion light 45 (21) passes through the region where the refractive index changes little as it travels through the light absorption layer. On the other hand, when the laser beam is condensed, the intensity distribution regions 49 and 50 of the laser beam are greatly changed near the incident surface and the exit surface of the light absorption layer 42, and the region is expanded near the exit surface. This means that the refractive index also gradually increases, and the action of receiving a larger deflection as the conversion light 45 (21) advances through the light absorption layer 42 is exerted. Since the refractive index change changes substantially in proportion to the signal light power, the refractive index change decreases as the light absorption layer 42 is advanced.

  In FIG. 7b, the conversion light 45 (21) is also condensed on the incident surface of the light absorbing layer 42 of the thermal lens forming optical element 41 (29), but it may be near the incident surface. In particular, the conversion light 45 (21) may be condensed on the light exit surface side of the light absorption layer 42 a little. The conversion light 45 (21) and the signal light 46 (23) are incident on the same surface in the light traveling direction. However, the light does not have to be exactly the same and may be slightly shifted. .

  The deflection angle changes when the following conditions change.

1. 1. Position of the light absorbing layer 42 of the thermal lens forming optical element 41 (29) with respect to the condensing (converging) point of the first condenser lens 28 for the conversion light 45 (21) and the signal light 46 (23). 2. Signal light power Signal light position (distance perpendicular to the optical axis of the conversion light 45 (21) and the signal light 46 (23) at the condensing point of the first condenser lens 28)
4). 4. Thickness of the light absorption layer 42 of the thermal lens forming optical element 41 (29) 5. Signal light wavelength and conversion light wavelength In addition to this, the dye concentration of the light absorption layer 42 also varies depending on the material of the light absorption layer 42, the light collection angle of the signal light 46 (23) and the conversion light 45 (21) to the light absorption layer 42, and the like.

  In an example of the wavelength converter, conversion light 21 having a wavelength of 1550 nm is made incident on an input port 22 by a single-mode quartz optical fiber having a core diameter of 9.5 μm, and signal light 23 having a wavelength of 980 nm is single-mode quartz having a core diameter of 9.5 μm. The input light is made incident on the input port 24 by an optical fiber, and the conversion light 21 and the signal light 23 are made almost parallel light by the first collimating lens 25 and the second collimating lens 26 having a focal length of 8 mm, and the thickness of the light absorption layer is 500 μm. The light absorbing layer was condensed and made incident on the thermal lens forming optical element 29 having a transmittance of 95% at a wavelength of 1550 nm and a transmittance of 0.2% at a wavelength of 980 nm by the first condenser lens 28 having a focal length of 8 mm.

  In FIG. 8, a light detector having a slit opening is provided in the in-plane direction perpendicular to the optical axis immediately before the branching mirror 32 in FIG. 4, and the conversion light 21 measured by moving the light detector is measured. The light intensity distribution is shown. In FIG. 8, a line 51 (solid line connecting round dots) is unpolarized light when no signal light is irradiated, and a line 52 (solid line connecting square points) is deflection when a signal light power of 7.8 mW is irradiated. The light line 53 (solid line connecting the dots) represents the light intensity distribution of the deflected light when the signal light power of 12.9 mW is applied. In the case of the deflected light 51 when the signal light power is 7.8 mW, the light 51 is overlapped with the non-deflected light 52 at the bottom of the intensity distribution and is insufficiently separated from each other. The deflected light 53 when 9 mW is irradiated is sufficiently separated from the unpolarized light 52. Therefore, it can be seen that the non-deflected light and the deflected light when the signal light power of 12.9 mW is irradiated by the branch mirror 52 can be separated. In FIG. 8, the signal light position (distance perpendicular to the optical axis of the conversion light 21 and the signal light 23 at the condensing point of the first condenser lens 28) is 35 μm and is converted from the signal light 23. The working light 21 was collected at a location approximately 30 μm from the light incident surface of the light absorbing layer, and the thickness of the light absorbing layer was 500 μm.

  FIG. 9 shows the relationship between the signal light power and the deflection angle. It can be seen that the deflection angle increases as the signal light power increases. In FIG. 9, the signal light position (distance perpendicular to the optical axis of the conversion light 21 and the signal light 23 at the condensing point of the first condenser lens 28) is 35 μm, the signal light 23 and the conversion light. No. 21 was condensed at a position advanced by about 60 μm from the light incident surface of the light absorption layer.

  In the present wavelength converter, the third collimating lens 30, the second condensing lens 33, and the third condensing lens 35 shown in FIG. 4 have the same focal length of 8 mm. This is the angle between the optical axis of the deflected light and the optical axis of the non-deflected light when the mirror 32 does not branch. In the case of this example, the signal light power is 6.7 mW, about 6.7 degrees, the signal light power 12.9 mW is about 10.1 degrees, and the signal light power 18 mW is about 13.2 degrees. .

  In FIG. 10, the incident positions of the condensing points of the conversion light 21 and the signal light 23 on the light absorption layer 42 of the thermal lens forming optical element 41 (29) shown in FIG. 6 (denoted as “light absorption layer position”). And the deflection angle. In FIG. 10, the position of the light absorption layer on the horizontal axis is the position of the light incident surface on the light absorption layer 42 of the thermal lens forming optical element 41 (29) (position with respect to the condensing point of the signal light 23 and the conversion light 21). It is. Point 0 is the position of the condensing point of the signal light 23 and the conversion light 21, which is the state of FIG. 7b. The minus direction is the light traveling direction. At the plus position, the conversion light 21 and the signal light 23 are collected in the light absorption layer 42 of the thermal lens forming optical element 41 (29). The vertical axis represents the deflection angle. In FIG. 10, the signal light power is about 12.9 mW, and the signal light position (with respect to the optical axes of the conversion light 21 and the signal light 23 at the condensing point of the first condenser lens 28 in FIG. 4). The distance in the perpendicular direction) was 35 μm, and the thickness of the light absorption layer 42 was 500 μm.

  Further, FIG. 11 shows an incident position (that is, a light absorption layer) of a convergence (condensation) point of the conversion light 21 and the signal light 23 to the light absorption layer 42 of the thermal lens forming optical element 41 (29) shown in FIG. An example of measurement data of a separation distance between (position), unpolarized light and deflected light is shown. When the incident position on the light absorption layer 42 is about 60 μm, the separation distance is close to 0, but when the position is shifted from this, the separation distance becomes large. In FIG. 11, the positive and negative signs of the separation distance are set such that the incident point of the conversion light 21 is the origin (that is, 0 point) and the deflection direction is positive. In FIG. 11, the signal light power is 15.4 mW, the thickness of the light absorption layer 42 is 1000 μm, and the signal light position (the light of the conversion light 21 and the signal light 23 at the condensing point of the first condenser lens 28). The distance perpendicular to the axis) was 25 μm.

  The deflection angle varies depending on the signal light wavelength and the conversion light wavelength. The shorter the wavelength, the greater the deflection angle.

  As mentioned above, although an example of the wavelength converter of this embodiment has been described, the present invention is not limited to the above, and various modifications and changes are possible.

For example, according to the present invention, in place of the signal input unit including the input ports 22 and 24, the first collimating lens 25, the second collimating lens 26, and the optical mixer 27 shown in FIG. It is good also as a signal input part using the 2-core optical fiber ferrule 65 as shown. The two-core optical fiber ferrule 65 includes a conversion light emitting fiber 66 and a signal light emitting fiber 67 arranged in parallel. As these optical fibers 66 and 67, for example, a clad layer of a single-mode quartz optical fiber having a core of 9.5 μm is etched to a desired thickness with hydrofluoric acid. The portion to be etched is only a few mm of the tip of the optical fiber. The thickness “ω” of the optical fiber after etching can be determined by the following relationship with the distance “χ” perpendicular to the optical axis of the converging point of the conversion light and the signal light collected on the light absorption layer. .
(Formula 1)
ω = χ / m
Here, m is the imaging magnification of the first condenser lens 28.

  Even with such a configuration, the same effects as those of the above embodiment can be obtained, and the configuration of the light incident portion can be further simplified.

  Next, examples of the present invention will be described.

  In the wavelength converter shown in FIG. 4, the thermal lens forming optical element 29 is a dye-containing solution having a wavelength band that exhibits high absorption with respect to the signal light 23 and high transmittance with respect to the conversion light 21. What was accommodated in the transparent optical cell was used. Specifically, as a light absorption layer of the thermal lens forming optical element 29, a tetrahydrofuran (TFT) solution of a dye (trade name: CIR-960; manufactured by Nippon Carlit Co., Ltd .: shows a large absorption in the near infrared region (780-1500 nm)). What was accommodated in the transparent optical cell was used. The form of the absorption and transmission wavelength band of the dye CIR-960 is different from that of FIG. 3 and has the wavelength band as described above.

  In the wavelength converter of FIG. 4, pulsed signal light 23 having a wavelength of 1.55 μm is incident from a fiber amplifier serving as an input port 24, and is sent to the optical mixer 27 as parallel light by the second collimating lens 26. On the other hand, laser light having a wavelength of 650 nm (continuous light) is taken into the input port 22 as conversion light 21 from a laser diode that is a conversion light source, and is converted into parallel light by the first collimator lens 25 and sent to the optical mixer 27. . The phase and polarization state of the conversion light 22 are the same as those of the signal light.

  The optical mixer 27 condenses the transmitted signal light 23 and conversion light 21 on the light absorption layer of the thermal lens forming optical element 29 with their respective condensing points different in the direction perpendicular to the optical axis. I let you.

  In the thermal lens forming optical element 29, when the pulsed signal light 23 is on (or high), the thermal absorption layer is highly absorbable for light having a wavelength of 1.55 μm, so a thermal lens is formed. At this time, since the conversion light 21 was formed as a thermal lens, the conversion light 21 was emitted as the conversion light 21 of the deflected light whose traveling direction was changed due to the characteristics of the refractive index. The conversion light 21 is converted into parallel light by the third collimating lens 30, and the signal light 23 is cut by the wavelength selective transmission filter 31, reflected by the branch mirror 32, changed in direction, and further reflected by the mirror 34, The converted light was emitted from the output port 37 to the optical fiber by the third condenser lens 35.

  On the other hand, in the thermal lens forming optical element 29, when the pulsed signal light 23 is on (or low), the signal light 23 is not irradiated on the light absorption layer, and thus no thermal lens is formed. Therefore, the conversion light 21 is output from the output port 36 as unpolarized light, and is cut by a blocking means (not shown).

  Therefore, the presence or absence of the thermal lens is repeated by turning on / off the pulse of the signal light 23 (or high / low), and the wavelength data of the signal light 23 is converted into the wavelength data of the converted light of the same phase. The The response speed of the thermal lens forming optical element is very fast at several tens of nanoseconds, so the response speed is very fast and light of various wavelengths can be used without using an electric circuit or mechanical moving parts. 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. Furthermore, since optical components can be reduced, cost reduction can be achieved.

  In the above description, when the unpolarized light emitted from the output port 36 is converted light, the wavelength data of the signal light 23 is converted into the wavelength data of the anti-phase converted light.

  Further, in the above, an optical switching selection means for switching use of deflected light and non-deflected light may be provided.

  Further, in the above, a member that changes the polarization state is provided in the middle of the conversion light 21, for example, between the first collimating lens 22 and the optical mixer 27, and the polarization state is not changed and the polarization state is changed. The converted light may be obtained.

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 of an example used for a thermal lens formation optical element, an absorption characteristic, and a permeation | transmission characteristic. It is a figure which shows typically the principal part structure of the wavelength converter which concerns on embodiment of this invention. The figure which shows the condition of emission of conversion light when there is no signal light and when there is signal light when condensing conversion light and signal light on the same place to the light absorption layer of the thermal lens forming optical element It is. It is sectional drawing which shows schematic structure of a thermal lens formation optical element. It is explanatory drawing of the condition where the conversion light in the case of not condensing deflects. It is explanatory drawing of the condition where the conversion light at the time of condensing deflects. It is a figure which shows light intensity distribution when not irradiating signal light, and when irradiating by changing the power of signal light. It is a graph which shows the relationship between signal light power and a deflection angle. It is a graph which shows the relationship between the position of a light absorption layer, and a deflection angle. It is a graph which shows the relationship between the separation distance of non-deflected light and deflected light. It is a conceptual diagram of the two-core optical fiber ferrule of the optical switch used with the wavelength converter of another example of this invention.

11 thermal lens forming optical element 12 signal input unit (fiber amplifier)
13 Light source for conversion (laser diode)
14 Signal light 15 Conversion light 16 Conversion light 21 Conversion light 22, 24 Input port 23 Signal light 25, 26, 30 Collimator lens 27 Separator 34 Mirror 28, 33, 35 Condensing lens 29 Thermal lens forming optical element 31 Wavelength Selective transmission filter 32 Branch mirror 36, 37 Output port

Claims (4)

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 thermal lens-forming optical element having a light absorption layer having a wavelength band that absorbs signal light and transmits light for conversion;
The signal light and the conversion light are incident on the light absorption layer, and the light condensing points are perpendicular to the optical axis when the signal light and the conversion light are incident on the incident surface of the thermal lens forming optical element as parallel light. A first condensing unit that condenses light so that the position is different from 25 to 50 μm in the direction ;
The thermal lens forming optical element uses 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 absorbs signal light and a peripheral region thereof. When the thermal lens is not irradiated and the thermal lens is not formed, the conversion light is emitted as unpolarized light that does not change the traveling direction, and when the thermal lens is formed by irradiation with the signal light, the traveling direction of the conversion light is changed. The state of exiting as a deflected light is realized corresponding to the presence or absence of signal light irradiation,
Furthermore, out of the conversion light emitted from the thermal lens forming optical element, only the conversion light emitted as the deflection light is emitted as the conversion light, and only the conversion light emitted as the non-deflection light is used as the conversion light. A converted light selection unit capable of selecting the state of emission ; and
A wavelength conversion device comprising: a second condensing unit that condenses the converted light from the converted light selecting unit to form pulsed converted light having a wavelength different from that of the signal light. The wavelength conversion device according to claim 1, further comprising polarization state switching means for switching a polarization state of the outgoing converted light to a state that is the same as or different from a polarization state of the incident signal light. . In the light absorbing layer of the thermal lens forming optical element including a light absorbing layer having a wavelength band that absorbs pulsed signal light having a specific wavelength and transmits light for conversion light having a wavelength different from the signal light. In the direction perpendicular to the optical axis when the signal light and the conversion light are respectively converged at the condensing point, and the signal light and the conversion light are incident on the incident surface of the thermal lens forming optical element as parallel light. Use a thermal lens based on the refractive index distribution reversibly caused by the temperature rise that occurs in the region where the light absorption layer absorbs signal light and its surrounding region, and condenses the light so that it is at a position different by -50 μm. Thus, when the signal light is not irradiated and the thermal lens is not formed, the conversion light is emitted as unpolarized light that does not change the traveling direction, and when the control lens is irradiated and the thermal lens is formed, the conversion light is emitted. Is a polarized light with a different direction And a state of emitting, to realize in correspondence to the presence or absence of irradiation of the signal light,
Of the emitted conversion light, only one of the conversion light that is deflected light and the conversion light that is non-deflection light is switched and 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. 4. The wavelength conversion method according to claim 3, 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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