JP2013178289A - Acousto-optical filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acousto-optical filter device capable of improving a side lobe ratio and an extinction ratio, reducing characteristic variation, and decreasing size and cost.SOLUTION: An acousto-optical filter device 1 has a first port A in which input light is inputted; a second port B outputting the input light, and to which output light is added; and a third port C outputting the output light inputted from the second port B. The second port B includes an optical path control element 4 connected to an input/output port 7 of the acousto-optical filter element 2, and a waveguide member 15 connecting the second port B of the optical control element 4 and the input/output port 7 of the acousto-optical filter element 2.

Description

  The present invention relates to an acousto-optic filter device that selectively outputs light of a predetermined wavelength in incident light, and more specifically, an acousto-optic filter device using a so-called folded waveguide that reflects light by a light reflector. About.

  In various optical communication devices and optical spectrum analyzers, acousto-optic filter devices that selectively transmit only light of a certain wavelength are used. As this acousto-optic filter device, an optical waveguide having a surface acoustic wave element portion is known. In the acousto-optic filter having such a configuration, the mode of light propagating through the waveguide is converted by a surface acoustic wave. Here, in order to improve the wavelength selectivity as the performance of the filter, the length of the region causing the mode conversion, that is, the interaction region where the surface acoustic wave interacts with the light propagating through the optical waveguide. What is necessary is just to lengthen length.

  In the following Patent Document 1, an acousto-optic filter device shown in FIG. 12 is disclosed. In the acoustooptic filter device 1001, five acoustooptic filter units 1003 to 1007 are configured on a substrate 1002. Taking the acousto-optic filter unit 1003 as an example, in the acousto-optic filter unit 1003, polarization separation units 1003a and 1003b are provided on the input side and output side of the optical waveguide, respectively. An IDT 1003c and a thin film 1005 are formed between the polarization separation units 1003a and 1003b. The surface acoustic wave excited by the IDT 1003c interacts with the light propagating through the optical waveguide, and the mode of the guided light is converted. The thin film 1003d is provided to promote this mode conversion.

  In the acousto-optic filter device 1001, reflection films 1008 to 1010 are provided on end surfaces 1002 a and 1002 b of the substrate 1002. Thereby, the three acoustooptic filter elements 1003 to 1005 and the three acoustooptic filter elements 1005 to 1007 are connected in series, respectively. Therefore, it is said that the optical path length is lengthened, whereby the sidelobe ratio can be increased and the wavelength selectivity can be increased.

Japanese Patent Laid-Open No. 11-237517

  However, in the acousto-optic filter device 1001, the reflection films 1008 to 1010 pass the acousto-optic filter unit different from the acousto-optic filter unit through which the optical signal before being reflected is reflected after the optical signal is reflected. Pass through. Therefore, there is a problem that the filter characteristics vary as a result due to variations between the acoustooptic filter units 1003 to 1005 and between the acoustooptic filter units 1005 to 1007.

  In addition, since the plurality of acoustooptic filter units 1003 to 1007 are formed on the substrate 1002, there is a problem that the acoustooptic filter device 1001 becomes large.

  In addition, since the processing accuracy of the folded portion of the optical waveguide is required, there is a problem that it is difficult to design and manufacture the optical waveguide configured on the substrate 1002.

  An object of the present invention is to provide an acousto-optic filter device that can effectively enhance wavelength selectivity, reduce variations in characteristics of the filter device, and can be further miniaturized.

  The acousto-optic filter device according to the present invention has first and second end faces facing each other, an input / output port formed on the first end face, and a Thr light output port formed on the second end face. And a drop light output port, a substrate having an optical waveguide formed on the surface thereof, and an interdigital formed on the substrate for converting a mode of light propagating through the optical waveguide Between the transducer, the first polarization separation unit provided in the optical waveguide between the input / output port and the interdigital transducer, and between the interdigital transducer and the Thr light output port and Drop light output port A second polarization separation unit provided in the optical waveguide.

  The optical waveguide connects the input / output optical waveguide section connecting the input / output port and the first polarization separation section, the first polarization separation section, and the second polarization separation section. And a drop optical waveguide section connecting the first and second optical waveguide sections through which single mode light is transmitted, the second polarization separation section, and the drop light output port, and the second optical waveguide section. A Thr optical waveguide section connecting the polarization separation section and the Thr optical output port; The first and second optical waveguide portions have interaction regions where surface acoustic waves excited by the interdigital transducer interact with light propagating through the first and second optical waveguide portions. In addition, a light reflector is provided so as to reflect the light guided to the Drop optical waveguide portion or the Thr optical waveguide portion.

  The acousto-optic filter device according to the present invention is further input from the first port to which input light is input, the second port that outputs input light and is given output light, and the second port. A third port for outputting the output light, wherein the second port is connected to the input / output port of the acoustooptic filter element, and a second port of the optical path control element A waveguide member connecting the port and the input / output port of the acousto-optic filter element.

  In a specific aspect of the acousto-optic filter device according to the present invention, the light reflector is formed on an end surface portion where the Drop light output port or the Thr light output port is formed on the second end surface of the substrate. Yes. In this case, the acousto-optic filter device can be downsized.

  In another specific aspect of the acousto-optic filter device according to the present invention, an end surface portion of the substrate on which the Drop light output port or Thr light output port of the substrate is formed is guided to the Drop light output port. It is orthogonal to the traveling direction of the incoming light. In this case, the light reflection efficiency by the light reflector can be increased, and the filter characteristics of the acousto-optic filter device can be further enhanced.

  In the present invention, the light reflector can be formed of an appropriate light reflective material. Preferably, a reflective film made of metal is used. In that case, the reflective film can be formed easily and with high accuracy simply by forming a metal film on the end face of the substrate of the acousto-optic filter device. The light reflector may be a laminated film formed by laminating a plurality of films. In the case of the laminated film, a suitable light reflector can be easily formed according to the band characteristics of the acoustooptic filter device by appropriately selecting the constituent films.

  In still another specific aspect of the acoustooptic filter device according to the present invention, the light reflector is formed in the Drop optical waveguide portion or the Thr optical waveguide portion. In this case, since the light reflector is formed in the substrate, the acousto-optic filter device can be further reduced in size.

  In still another specific aspect of the acousto-optic filter device according to the present invention, the light reflector is a light reflector provided outside the substrate, and the Drop light output port of the light reflector and the substrate or An optical fiber connecting the Thr light output port is further provided. Thus, the light reflector may be provided outside the substrate.

  In still another specific aspect of the acousto-optic filter device according to the present invention, a reflected return light suppressing means for suppressing reflected return light at the Thr light output port or at the Drop light output port is further provided. . In this case, since the reflected return light can be sufficiently suppressed, the filter characteristics of the acousto-optic filter device can be further enhanced.

  In still another specific aspect of the acoustooptic filter device according to the present invention, when the configuration having the interdigital transducer, the first and second polarization separation units, and the optical waveguide is an acoustooptic filter element unit. The at least one second acoustooptic filter element unit is provided between the input / output port formed on the first end surface of the substrate and the acoustooptic filter element unit, and the acoustooptic filter element unit of the previous stage. The Drop light output port or Thr light output port and the input / output port of the next stage are connected in series.

  In the acousto-optic filter device according to the present invention, the light guided from the input / output port is mode-converted in the interaction region of the first and second optical waveguide portions, but after being reflected by the light reflector. Light is also mode converted in the interaction region. Therefore, the filter characteristics can be improved without increasing the size of the substrate, that is, the wavelength selectivity of the acousto-optic filter device can be effectively increased.

  In addition, as described above, the Drop light or Thr light is reflected by the light reflector, and the reflected light is mode-converted again in the interaction region of the first and second optical waveguide portions, and is output from the input / output port. Guide to the optical path control element and output. Therefore, the light passes through the same interaction region before reaching the light reflector and after being reflected by the light reflector. Accordingly, variations in filter characteristics hardly occur.

1 is a schematic plan view of an acousto-optic filter device according to a first embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a second embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a third embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a fourth embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a fifth embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a sixth embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a seventh embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to an eighth embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device according to a ninth embodiment of the present invention. It is the figure which compared the characteristic of the acousto-optic filter in this invention, and the characteristic of the acousto-optic filter apparatus in a comparative example. It is a schematic plan view of an acousto-optic filter device according to a tenth embodiment of the present invention. It is a schematic plan view of an acousto-optic filter device in a conventional example.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a schematic plan view of an acousto-optic filter device according to a first embodiment of the present invention.

  The acoustooptic filter device 1 includes an acoustooptic filter element 2. A circulator 4 as an optical path control element is connected to the acousto-optic filter element 2 via an optical fiber 3 as an optical waveguide member. The circulator 4 has first to third ports A to C. Light input from the first port A is output from the second port B, and light input from the second port B is output from the third port C. As such a circulator 4, a known circulator can be used as appropriate. An optical coupler may be used as the optical path control element.

The acousto-optic filter element 2 has a substrate 2A. The substrate 2A is made of a piezoelectric substrate, and in this embodiment is made of X-propagation Y-cut LiNbO ₃ . However, the substrate 2A may be formed of another piezoelectric body.

  An optical waveguide 6 is formed on the substrate 2A by thermally diffusing Ti.

  An input / output port 7 is provided on the first end surface 2a of the substrate 2A. Further, a port 8 is provided on the first end face 2 a at a position away from the input / output port 7. A Thr light output port 9 and a Drop light output port 10 are provided on the second end surface 2b opposite to the first end surface 2a. The optical waveguide 6 is provided so as to connect these ports.

  An IDT electrode 11 for exciting a surface acoustic wave is provided on the substrate 2A. The IDT electrode 11 is made of an appropriate metal or alloy such as Al. The IDT electrode 11 is connected to a high frequency voltage applying device 12 for exciting a surface acoustic wave.

  On the substrate 2 </ b> A, a first PBS 13 is provided between the input / output port 7 and the IDT electrode 11. PBS means a polarization separation unit. Such a polarization separation unit is configured according to the structure of a known polarization separation element. A second PBS 14 is provided on the opposite side of the first PBS with the IDT electrode 11 in between. A region surrounded by broken lines D and E between the IDT electrode 11 and the first PBS 13 is an interaction region X described later.

  The form of the optical waveguide will be described more specifically. An input / output waveguide section 15 is provided so as to connect the input / output port 7 and the first PBS 13. Further, a waveguide portion 16 is provided so as to connect the port 8 and the first PBS 13. First and second optical waveguide portions 17 and 18 are provided so as to connect the first PBS 13 and the second PBS 14. The first and second optical waveguide portions 17 and 18 are waveguides that propagate single-mode light. The interaction region X is provided in a part of the portion where the first and second optical waveguide portions 17 and 18 are provided. Here, the region between the broken lines D and E in FIG. In the interaction region X, the surface acoustic wave excited by the IDT electrode 11 interacts with the light propagating through the first and second optical waveguide portions 17 and 18, and the mode of the propagating light is converted.

  A Thr light output waveguide 19 is provided so as to connect the second PBS 14 and the Thr light output port 9. The Drop optical waveguide 20 is connected so as to connect the second PBS 14 and the Drop light output port 10. In the end surface portion where the Drop light output port 10 is provided, a light reflector 21 is provided on the second end surface 2b. The light guided from the drop optical waveguide 20 to the drop light output port 10 is reflected by the light reflector 21, propagates again through the drop optical waveguide 20, and reaches the second PBS 14. Accordingly, the drop light output port 10 is not necessarily a part that outputs light to the outside, but is a drop light output port for convenience.

  The PBSs 13 and 14 can be formed by forming Ti films having a thickness of 90 nm and then heating them at a temperature of 1040 ° C. for about 8 hours to diffuse Ti.

  In the present embodiment, the light reflector 21 is formed of a metal film made of A1. But the metal film which comprises the light reflector 21 is not specifically limited, Al, Ag, Au, Mo, Cr, Ti, Ta, Cu, or Ni or these alloys can be used suitably. The light reflector 21 may be formed of a laminated film. The reflectance of light by the light reflector 21 has wavelength dependency. Therefore, when the light reflector 21 is formed of a metal film or a laminated film, an appropriate material may be selected according to the wavelength of light to be reflected. Thereby, loss can be reduced.

  Preferably, on the second end surface 2b, the end surface portion on which the metal film constituting the light reflector 21 is formed is in a direction perpendicular to the direction of light propagating through the drop optical waveguide 20. desirable. Thereby, the reflection efficiency can be increased and the loss can be reduced.

  An optical fiber holding member 22 is provided at a portion where the optical fiber 3 is connected to the input / output port 7. The optical fiber holding member 22 is made of, for example, synthetic resin or glass, and is provided to ensure the coupling of the optical fiber 3 to the input / output port 7. The optical fiber holding member 22 is not necessarily provided.

  Next, the operation of the acousto-optic filter device 1 will be described. First, when input light is given to the port A of the circulator 4 as indicated by an arrow G, the input light is guided to the optical fiber 3 from the port of the circulator 4. The input light is given to the input / output port 7 of the acoustooptic filter element 2 through the optical fiber 3.

  Input light having a TE mode and a TM mode is guided from the input / output port 7 to the input / output waveguide section 15. The TE mode light is guided to the second optical waveguide unit 18 to travel straight through the first PBS 13. On the other hand, the TM mode extends from the first PBS 13 to the first optical waveguide portion 17.

  In the first optical waveguide portion 17, TM mode light propagates along the direction of the arrow shown in the figure, but in the interaction region X, it interacts with the surface acoustic wave and is converted to the TE mode.

  Similarly, in the second optical waveguide section 18, the propagating TE mode interacts with the surface acoustic wave in the interaction region X and is converted to the TM mode. Accordingly, TE mode light is given from the first optical waveguide portion 17 to the second PBS 14, and the TE mode light travels straight and is guided to the Drop optical waveguide 20. The TM mode light propagating through the second optical waveguide section 18 is guided from the second PBS 14 to the Drop optical waveguide 20. Accordingly, in the Drop optical waveguide 20, the TE mode + TM mode light travels toward the Drop light output port 10. Then, the TE mode + TM mode light is reflected by the light reflector 21 and propagates again through the drop optical waveguide 20 toward the input / output port 7 side.

  When the reflected TE mode + TM mode light reaches the second PBS 14, since the TE mode goes straight, the TE mode light is guided to the first optical waveguide unit 17. In the first optical waveguide portion 17, the reflected TE mode light is mode-converted again in the interaction region X to become the TM mode. The light converted to the TM mode again is guided to the input / output waveguide section 15 through the first PBS 13.

  On the other hand, of the reflected TE mode + TM mode light, the TM mode is guided to the second optical waveguide section 18 via the second PBS 14. Therefore, the TM mode that has been reflected is mode-converted again in the interaction region X to become the TE mode. The TE mode light is applied to the first PBS 13, but the TE mode light travels straight and is guided to the input / output waveguide unit 15. In this way, the modulated TE mode + TM mode light is given to the optical fiber 3 through the input / output port 7 through two mode conversions. When this light is applied to the port B of the circulator 4 through the optical fiber 3, it is output from the port C of the circulator 4.

  As described above, according to the acousto-optic filter device 1 of the present embodiment, the light guided from the input / output port 7 is modulated twice in the interaction region X. In other words, the acoustooptic filter device 1 corresponds to a structure in which two stages of acoustooptic filters having the interaction region X are connected in series. Therefore, the side lobe ratio and extinction ratio in the filter characteristics of the acousto-optic filter device 1 can be increased. Further, since one interaction region X is used twice, the interaction length is doubled. Therefore, the pass band can be narrowed and the wavelength selectivity can be effectively enhanced.

  In addition, in the acoustooptic filter device 1001 described in Patent Document 1, the acoustooptic filter unit before reflection and the acoustooptic filter unit through which the light after reflection passes are different. For this reason, instability of characteristics due to variations between acousto-optic filter sections has been a problem.

  On the other hand, in the acousto-optic filter device 1 of the present embodiment, the reflected light also passes through the optical waveguide before being reflected by the light reflector 21, and therefore due to such variation between the acousto-optic filter units. Instability of characteristics does not occur.

  Furthermore, since it is only necessary to provide an acousto-optic filter portion having one interaction region X on the substrate 2A, the cost can be reduced and further miniaturization can be achieved.

  FIG. 2 is a schematic plan view showing an acousto-optic filter device 31 according to the second embodiment of the present invention. The acousto-optic filter device 31 of the second embodiment is different from the acousto-optic filter device 1 of the first embodiment except that a grating reflector 32 is provided in the substrate 2A instead of the light reflector 21. This is the same as in the first embodiment. Therefore, about the same part, suppose that the description of 1st Embodiment is used by attaching | subjecting the same reference number.

  In the acousto-optic filter device 31 of the second embodiment, in the Drop optical waveguide 20 connecting the second PBS 14 and the Drop light output port 10 in the substrate 2A, the grating whose refractive index changes along the optical path length. A reflector 32 is provided. Therefore, as in the first embodiment, the TE mode + TM mode light propagating through the drop optical waveguide 20 is reflected by the grating reflector 32 and reaches the second PBS 14 again.

  Therefore, also in the second embodiment, similarly to the first embodiment, both the light before reflection and the light after reflection pass through the interaction region X and are modulated. Therefore, the same effect as the first embodiment can be obtained. Further, since the grating reflector 32 may be provided in the substrate 2A, the acoustooptic filter element 2 can be reduced in size.

  FIG. 3 is a schematic plan view showing an acousto-optic filter device 41 according to the third embodiment of the present invention.

  In the acousto-optic filter device 41 of the third embodiment, the light reflector 21 in the first embodiment is provided outside the substrate 2A. The Drop light output port 10 and the light reflector 21 are connected by an optical fiber 42 as a waveguide member. Thus, the light reflector 21 may be provided outside the substrate 2A. Even in that case, similarly to the first embodiment, the propagated TE mode + TM mode light can be reflected by the light reflector 21 and guided to the drop optical waveguide 20 again. Therefore, also in the acousto-optic filter device 41 of the third embodiment, the same effect as that of the acousto-optic filter device 1 of the first embodiment can be obtained.

  In addition, in this embodiment, since the optical reflector 42 is used to connect the light reflector 21, the light reflector 21 can be easily provided at an arbitrary position with respect to the substrate 2A.

  FIG. 4 is a schematic plan view of an acousto-optic filter device 43 according to the fourth embodiment of the present invention. In the present embodiment, the second end surface 2b of the substrate 2A has an inclined surface portion 2c and a vertical direction end surface portion 2d. The inclined surface portion 2c is inclined with respect to a direction orthogonal to the direction in which the Thr light output waveguide 19 extends. That is, although the inclined surface portion 2c is a flat surface portion, the angle α formed between the normal line and the Thr light output waveguide 19 reaching the inclined surface portion 2c is set to a value larger than zero. This α is preferably set to an angle such that the reflected light when the light reaching the inclined surface portion 2c from the Thr light output waveguide 19 is reflected does not return to the Thr light output waveguide 19 again. Therefore, α is desirably about 8 degrees or more.

  The vertical end surface portion 2d is set to a direction perpendicular to the extending direction of the portion where the Drop optical waveguide 20 reaches the second end surface 2b. Therefore, also in this embodiment, the same effect as the acousto-optic filter device 1 of the first embodiment can be obtained. Moreover, even if the Thr light is reflected by the inclined surface portion 2c, the Thr light does not enter the Thr light output waveguide 19 again, so that noise due to the Thr light can be reduced.

  In the present embodiment, the inclined surface portion 2c is provided to reduce the noise due to the Thr light. However, other structures may be used. That is, as the reflected return light suppressing means for suppressing the reflected return light, for example, a structure in which light is diffracted, scattered or absorbed in the Thr light output waveguide 19 may be provided. Further, an optical attenuator may be provided in the Thr light output port 9 or in the Thr light output waveguide 19.

  Further, an optical attenuator may be connected to the Thr light output port 9 via an optical fiber. In this case, it is desirable to provide the inclined surface portion 2c so that the reflected light does not return at the boundary between the substrate 2A and the optical fiber.

  FIG. 5 is a schematic plan view showing an acousto-optic filter device according to a fifth embodiment of the present invention.

  In the first to fourth embodiments, the acousto-optic filter device using Drop light has been described. However, in the acousto-optic filter device of the present invention, Thr light may be used. 5 to 8 are schematic plan views of the acousto-optic filter devices according to the fifth to eighth embodiments using Thr light.

  As shown in FIG. 5, in the fifth acoustooptic filter device 51, the light reflector 21 is provided on the second end surface 2 b in the portion where the Thr light output port 9 is exposed. On the other hand, the light reflector 21 is not provided in the portion where the Drop optical waveguide 20 reaches the second end face 2b. In other respects, the fifth embodiment is the same as the first embodiment.

  Accordingly, in the fifth embodiment, the light input from the input / output port 7 reaches the second PBS 14 as in the first embodiment. From the second PBS 14, the Thr light reaches the Thr light output waveguide 19, is reflected by the light reflector 21, and reaches the second PBS 14 again. On the other hand, the TE mode + TM mode light from the second PBS 14 to the Drop optical waveguide is output as it is from the Drop light output port 10 and is hardly reflected at the second end face 2b. Accordingly, the reflected light, that is, Thr light is again applied from the second PBS 14 to the first and second optical waveguide portions 17 and 18, passes through the interaction region X, undergoes modulation, and then the first To PBS13.

  Then, this Thr light is given to the optical fiber 3 through the input / output waveguide section 15 and given to the port B of the circulator 4. Therefore, the light modulated twice is output from the output port C of the circulator 4. Thus, in the present invention, the acousto-optic filter may be configured so that the Thr light is reflected by the light reflector 21 and output from the circulator 4.

  Also in the present embodiment, the side lobe ratio and the extinction ratio can be increased because the two-stage connection filter configuration is used as in the first embodiment, except that the light used is different. Further, since the interaction length can be doubled, the bandwidth can be reduced. Further, instability of characteristics due to variations between the acousto-optic filter portions is unlikely to occur. In addition, the substrate can be reduced in size and the manufacturing cost can be reduced.

  The sixth to eighth embodiments shown in FIGS. 6 to 8 are the same as the second to fourth embodiments except that Thr light is used. Therefore, about the same part, the description will be used suitably by attaching | subjecting the same reference number.

  In the acoustooptic filter device 61 of the sixth embodiment shown in FIG. 6, the grating reflector 32 used in the second embodiment is provided in the Thr light output waveguide 19. In the acousto-optic filter device 71 of the seventh embodiment shown in FIG. 7, the optical fiber 42 and the light reflector 21 are connected to the Thr light output waveguide 19.

  In the acoustooptic filter device 81 of the eighth embodiment shown in FIG. 8, the light reflector 21 is provided with the inclined surface portion 2c at the end surface portion where the drop light output port 10 is open. The vertical end surface portion 2d is provided at an end surface portion where the Drop light output port 10 is open.

  Therefore, in the acoustooptic filter device of the sixth to eighth embodiments shown in FIGS. 6 to 8, the fifth acoustooptic filter device shown in FIG. The same effects as those of the acousto-optic filter device of the embodiment can be obtained, and the same effects as those of the second to fourth embodiments can be obtained.

  FIG. 9 is a schematic plan view of an acousto-optic filter device according to the ninth embodiment of the present invention. In the acoustooptic filter device 91 of the ninth embodiment, the second end face 2b is configured in the same manner as the acoustooptic filter device 41 of the fourth embodiment.

On the other hand, the first end face 2a is an inclined plane that is inclined with respect to the direction extending toward the input / output port 7 of the input / output optical waveguide. The angle formed by the normal of the inclined plane with respect to the direction extending toward the input / output port 7 of the input / output waveguide section 15 is α1. The extending direction of the portion 3a extending toward the substrate 2A side end of the optical fiber 3 by the optical fiber holding member 22 is α2 with respect to the direction extending toward the input / output port 7 of the input / output waveguide section 15. The optical fiber 3 is held so as to make an angle of. The angles α1 and α2 are combinations of angles that satisfy Snell's law. When the substrate 2A is LiNbO ₃ and the optical fiber 3 is made of glass, when α2 = 8 °, α1 is about 5.4 °.

  As described above, if the inclination angle α1 of the end face 2a and the inclination angle α2 of the light incident direction from the tip 3a of the optical fiber 3 are selected so that the angles α1 and α2 satisfy Snell's law, the input / output port 7 It is possible to almost eliminate the reflected return light at. Therefore, noise can be reduced and the extinction ratio can be increased.

  The solid line in FIG. 10 shows the filter characteristics of the acousto-optic filter device of the ninth embodiment shown in FIG. The broken line indicates the filter waveform extracted from the drop light output port 10 in the same manner as in the first embodiment except that the light reflector 21 prepared as a comparative example is not provided. As is apparent from FIG. 10, according to the acousto-optic filter device of the ninth embodiment, compared to the comparative example, since the filter has a two-stage connection structure, the sidelobe ratio can be effectively increased. It can also be seen that the noise level can be suppressed, and that the passband can be narrowed.

  FIG. 11 is a schematic plan view showing an acousto-optic filter device according to the tenth embodiment of the present invention. In the acoustooptic filter device 101 of this embodiment, the acoustic of the ninth embodiment is provided except that a plurality of acoustooptic filter element portions 102 and 103 are provided in series in the substrate 2A. This is the same as the optical filter device 91. That is, in the substrate 2A, the input / output port 9a of the second-stage acousto-optic filter element unit 103 is connected to the drop light output port 10a of the first-stage acousto-optic filter element unit 102. Each acousto-optic filter unit is configured similarly to the acousto-optic filter unit of the ninth embodiment. Accordingly, the same parts are denoted by the same reference numerals, and the description thereof is omitted.

  In the acoustooptic filter device 101, the acoustooptic filter element units 102 and 103 are connected in series, and light is converted by the light reflector 21, so that the acoustooptic filter device 101 has a structure in which four stages of acoustooptic filter units are connected. It becomes. Therefore, the side lobe ratio and the extinction ratio can be further increased.

  In FIG. 11, two acoustooptic filter sections are connected in series in the substrate 2A, but three or more acoustooptic filter sections may be connected in series. Moreover, although the form which outputs Drop light was demonstrated, it is applicable also to the structure which outputs Thr light like 5th-8th embodiment.

  In the present invention, a thin film for promoting the interaction and a thin film ridge for matching the phase may be provided so as to cover the interaction region X.

DESCRIPTION OF SYMBOLS 1 ... Acousto-optic filter apparatus 2 ... Acousto-optic filter element 2A ... Board | substrate 2a ... 1st end surface 2b ... 2nd end surface 2c ... Inclined surface part 2d ... Vertical direction end surface part 3 ... Optical fiber 4 ... Circulator 6 ... Optical waveguide 7 ... On Output port 8 ... Port 9 ... Thr optical output port 9a ... Input / output port 10, 10a ... Drop optical output port 11 ... IDT electrode 12 ... High frequency voltage application device 13 ... First PBS
14 ... Second PBS
DESCRIPTION OF SYMBOLS 15 ... Input / output waveguide part 16 ... Waveguide part 17 ... 1st optical waveguide part 18 ... 2nd optical waveguide part 19 ... Thr light output waveguide 20 ... Drop optical waveguide 21 ... Optical reflector 22, 22A ... Optical fiber Holding member 31 ... Acousto-optic filter device 32 ... Grating reflector 41 ... Acousto-optic filter device 42 ... Optical fiber 43 ... Acousto-optic filter device 51, 61, 71, 81, 91, 101 ... Acousto-optic filter device 102 ... Acousto-optic filter element 103: Acousto-optic filter element

Claims (9)

An input / output port formed on the first end surface, and a Thr light output port and a Drop light output port formed on the second end surface; A substrate having an optical waveguide formed on the surface;
An interdigital transducer formed on the substrate and provided to convert a mode of light propagating through the optical waveguide;
A first polarization separation unit provided in an optical waveguide between the input / output port and the interdigital transducer;
A second polarization separation unit provided in the optical waveguide between the interdigital transducer and the Thr light output port and Drop light output port;
An input / output optical waveguide portion connecting the input / output port and the first polarization separation portion;
The first and second optical waveguide sections that connect the first polarization separation section and the second polarization separation section and transmit single mode light;
A Drop optical waveguide portion connecting the second polarization separation portion and the Drop light output port; and a Thr optical waveguide portion connecting the second polarization separation portion and the Thr light output port;
The first and second optical waveguide portions have an interaction region where surface acoustic waves excited by the interdigital transducer interact with light propagating through the first and second optical waveguide portions,
An acoustooptic filter element further comprising a light reflector provided to reflect the light guided to the Drop optical waveguide portion or the Thr optical waveguide portion;
A first port for receiving input light; a second port for outputting input light and receiving output light; and a third port for outputting output light input from the second port. An optical path control element connected to the input / output port of the acousto-optic filter element;
An acoustooptic filter device comprising: a waveguide member that connects the second port of the optical path control element and an input / output port of the acoustooptic filter element.   2. The acousto-optic filter device according to claim 1, wherein the light reflector is formed on an end surface portion where the Drop light output port or Thr light output port is formed on the second end surface of the substrate.   In the second end surface of the substrate, the substrate end surface portion on which the light reflector is formed is orthogonal to the traveling direction of the light guided to the Drop light output port or the Thr light output port. The acousto-optic filter device according to claim 2.   The light reflector is disposed separately from the second end surface of the substrate, and the light reflector and the Thr light output port or the Drop light output port located on the second end surface The acousto-optic filter device according to claim 1, wherein the light reflector is connected via an optical fiber.   The acousto-optic filter device according to claim 1, wherein the light reflector is a reflective film made of metal.   The acousto-optic filter device according to any one of claims 1 to 4, wherein the light reflector is a laminated film formed by laminating a plurality of films.   The acousto-optic filter device according to claim 1, wherein the light reflector is formed in the Drop optical waveguide portion or the Thr optical waveguide portion.   The acoustic according to any one of claims 1 to 7, wherein the acoustooptic filter element further includes reflected return light suppression means for suppressing reflected return light at the Thr light output port or the Drop light output port. Optical filter device. An input / output port formed on the first end surface of the substrate when the structure having the interdigital transducer, the first and second polarization separation units, and the optical waveguide is an acousto-optic filter element unit; Between the acousto-optic filter element unit, at least one second acousto-optic filter element unit includes a Drop light output port or a Thr light output port of the preceding acousto-optic filter element unit and an input / output port of the next stage The acousto-optic filter device is connected in series so as to be connected to each other.

Images