JP2006091326A - Optical filter, optical connector, and optical adaptor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high cut-off optical filter whose cut-off percentage is not degraded even when using an optical fiber having a grating part with a cut-off rate of 30dB or more, and also to provide an optical connector and an optical adaptor. <P>SOLUTION: The optical filter comprises: an optical fiber in which the refractive index of the core 1 varies periodically in the longitudinal direction and the grating part 2 cutting off the light in undesired wavelength areas by 30 dB or more; and a ferrule 4 in which the light in the undesired wavelength areas is transmitted and the optical fiber is fixedly inserted into a penetrating micropore. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical filter, an optical connector, and an optical adapter used for optical communication.

  In recent years, FTTH (Fiber to the Home) has been proposed to promote an advanced information communication society. This FTTH will be described with reference to FIG.

  FTTH is a network that draws optical fibers to individual homes and provides integrated communication services such as telephone, computer communication, and CATV (cable / TV and optical network wiring method). As shown in the figure, an optical line terminator called OLT (Optical Line Terminal) is disposed in the telephone station 100, and an optical cable is laid from the OLT to each user. An optical drop cable 103 is laid on the user 102.

  As shown in FIG. 9B, the optical drop cable 103 includes an optical fiber 105 and an optical cord 106 that covers the optical fiber 105, and an ONU (Optical Network Unit) of the user 102 via the optical connector 107. ) Is connected to an optical network device 104.

  In the optical fiber line, signal light of wavelength 1310 nm band and 1550 nm band for data communication and monitoring light of wavelength 1650 nm band for monitoring the state of the optical fiber are superimposed. In the optical network device 104, if the monitoring light in the 1650 nm band is incident as it is, the data communication is seriously affected. Therefore, it is necessary to sufficiently attenuate the optical network device 104 immediately before entering the optical network device 104.

  For this reason, the optical connector 107 that makes light incident on the optical network device 104 incorporates an optical filter that blocks monitoring light in the wavelength 1650 nm band by reflecting it and transmits signal light in the wavelength 1310 nm band and 1550 nm band. is doing.

  An optical filter includes an optical fiber having a fiber grating built in a ferrule of an optical connector. Examples of such a fiber grating optical filter include those disclosed in Patent Documents 1 to 3. In this case, the grating length is limited by the length of the ferrule, and it is necessary to design the cutoff filter within the range of the length.

Such a fiber grating built-in connector is manufactured by first irradiating an optical fiber with ultraviolet light through a phase mask to produce a fiber grating, and inserting a fiber grating portion of the optical fiber into a fine hole provided in a ferrule. Then, the ferrule end face is polished and stored in the connector housing.
JP-A-10-142447 Japanese Patent Laid-Open No. 9-304645 JP-A-9-269435

  Conventionally, when the cutoff rate of the fiber grating optical filter is about 20 to 25 dB, no difference was found in the cutoff characteristics before and after the connectorization.

  However, when the cutoff rate of the fiber grating optical filter exceeds 30 dB, the cutoff rate after being made into a connector tended to deteriorate from the initial cutoff rate. Furthermore, when the cutoff rate of the original fiber grating optical filter exceeded 40 dB, the cutoff rate after the connectorization became 40 dB or less, and the required cutoff characteristics could not be obtained.

  In addition, the same phenomenon has been confirmed even in a shape called an adapter. The optical adapter is polished so that both ends of the ferrule can be connected to the optical connector, housed in a housing, and used by connecting the optical connector to both ends.

  Thus, when the cutoff rate of the original fiber grating optical filter is 30 dB or more, it has been difficult to realize a cutoff filter that does not deteriorate the cutoff rate with the fiber grating built-in connector.

  The reason why the blocking rate is reduced as described above will be described with reference to FIG. FIG. 9C is a schematic configuration diagram showing the optical connector 107, in which an optical fiber 105 is inserted into a fine hole penetrating in the longitudinal direction of a cylindrical ferrule 110 made of ceramic, and the optical fiber 105 is fixed with resin. . A grating portion 111 is formed on the core 108 at the tip of the optical fiber 105.

  Although the optical fiber 105 is inserted and fixed in the fine hole of the ferrule 110, since the resin applied to the outer periphery of the optical fiber 105 is not uniform at the entrance of the ferrule 110, the optical fiber 105 is distorted. To do. Due to this distortion, light is coupled from the waveguide mode propagating through the core 108 to the clad mode propagating through the clad 109.

  Since the core 108 is the only portion where the refractive index of the grating portion 111 is changed, the light propagating through the clad 109 is hardly affected and passes through the clad 109 without being blocked.

  Since the ceramic ferrule 110 is opaque and has a relatively clean surface in the micropores, the light reaching the outer periphery of the clad 109 is reflected and returns to the center of the optical fiber 105 to change the cladding mode. The power of the propagating light propagates without being attenuated so much, and coupling from the clad mode to the waveguide mode occurs at the output end of the optical connector 107 due to axial misalignment or the like.

  Therefore, even if the waveguide mode is blocked by the grating unit 111, a slight amount of light that has propagated through the cladding mode is coupled to the waveguide mode at the output end, thereby degrading the cutoff rate.

  On the other hand, in the optical adapter, the incident end is also connected to the optical connectors, and perturbation such as axial deviation occurs, so that coupling to the cladding mode occurs. After that, the same phenomenon as in the case of the optical connector occurs, causing a drop in the blocking rate.

  The rate at which the blocking rate changes is determined by the ratio of the intensity of light transmitted without being blocked by the grating portion 111 and the intensity of light coupled to the cladding mode and again coupled to the waveguide mode. When the blocking rate is about 20 to 25 dB, the intensity of the light transmitted through the grating portion 111 is sufficiently larger than the intensity of the light propagating through the cladding mode, so that the blocking rate is not substantially changed. On the other hand, when the blocking rate is larger than 30 dB, the intensity of light transmitted through the grating portion 111 and the intensity of light propagating through the cladding mode become approximately the same, so that it is observed that the blocking rate is reduced.

  FIG. 10 is a graph showing the cutoff characteristics of a conventional optical filter, and shows the cutoff rate when the fiber grating is housed in a zirconia ferrule and when it is not housed. In the wavelength 1650 nm band, the blocking rate is about 50 to 80 dB when not housed in the ferrule, whereas the blocking rate is degraded to about 40 to 50 dB when housed.

  The present invention has been made in view of the above. As an object of the present invention, a high cutoff optical filter, an optical connector, and an optical connector that do not deteriorate the cutoff rate even when an optical fiber having a grating portion with a cutoff rate of 30 dB or more is used. To provide an adapter.

  The optical filter of the present invention includes an optical fiber in which a grating portion that periodically changes the refractive index of the core in the longitudinal direction and blocks light of an unnecessary wavelength region by 30 dB or more is formed at a tip portion, and the unnecessary wavelength region. It consists of a ferrule in which light is transmitted and the optical fiber is internally fixed in a fine hole penetrating.

  In the optical filter of the present invention, the length of the ferrule in the longitudinal direction is 7 mm or more.

  In the optical filter of the present invention, the ferrule has a higher refractive index than the cladding of the optical fiber in the unnecessary wavelength region.

  An optical connector according to the present invention includes the optical filter according to any one of claims 1 to 3, wherein one end of the ferrule is fixed along the extending direction of the fine hole, and the extending direction of the fine hole is provided. It is characterized by comprising an extended protrusion protruding outward from the ferrule and a ferrule hold that fixes one end of the extended protrusion.

  The optical adapter of the present invention includes an optical fiber having a grating portion that periodically changes the refractive index of the core in the longitudinal direction and blocks light of an unnecessary wavelength region by 30 dB or more, and fixing the optical fiber internally. A ferrule that penetrates through the microscopic hole that transmits the light in the unnecessary wavelength region, and the ferrule is fixed internally, so that the first and second optical connectors or receptacles can be connected to each other, and the first and second optical connectors or And a housing for allowing the receptacles to butt and connect to both end faces of the ferrule.

  According to the optical filter of the present invention, the grating portion that cuts off 30 dB or more in the fine hole of the ferrule whose longitudinal length is 7 mm or more made of transparent glass having a higher refractive index than the clad of the optical fiber is the tip portion. Since the tip of the optical fiber formed inside is fixed internally, the intensity of the light coupled to the cladding mode is sufficiently attenuated until it reaches the output coupling part, and the coupling of the light to the waveguide mode is substantially ignored. Even when an optical fiber having a grating portion with a cutoff rate of 30 dB or more is used, deterioration of the cutoff rate can be prevented.

  In addition, according to the optical connector of the present invention, the grating portion that cuts off 30 dB or more in the fine hole of the ferrule made of transparent glass having a refractive index higher than that of the clad of the optical fiber and having a longitudinal length of 7 mm or more. Since the optical filter with the tip of the optical fiber formed at the tip is fixed internally, the intensity of the light coupled to the cladding mode is sufficiently attenuated until it reaches the output coupling, and the light to the waveguide mode is The coupling ratio can be made so small that it can be substantially ignored, and even when an optical fiber having a grating portion with a cutoff ratio of 30 dB or more is used, deterioration of the cutoff ratio can be prevented.

  Further, according to the optical adapter of the present invention, the grating portion that cuts off 30 dB or more in the fine hole of the ferrule whose longitudinal length is 7 mm or more made of transparent glass having a higher refractive index than the clad of the optical fiber. Since the optical filter with the tip of the optical fiber formed at the tip is fixed internally, the intensity of the light coupled to the cladding mode is sufficiently attenuated until it reaches the output coupling, and the light to the waveguide mode is The coupling ratio can be made so small that it can be substantially ignored, and even when an optical fiber having a grating portion with a cutoff ratio of 30 dB or more is used, deterioration of the cutoff ratio can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example 1
First Embodiment An optical filter according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram showing an optical filter according to the present invention, in which the refractive index of the core 1 periodically changes in the longitudinal direction, and a grating portion 2 that blocks light of 1650 nm band by 30 dB or more is formed at the tip portion. And a ferrule 4 made of transparent glass through which a fine hole for fixing the tip of the optical fiber is fixed. The tip surface 4a of the ferrule 4 is polished.

  The outer diameter of the ferrule 4 is 2.5 mm, and the length d in the longitudinal direction is 7 mm or more and 25 mm or less. The reason why the thickness is set to 7 mm or more is to secure a grating length necessary for realizing desired characteristics, and the reason why the length is set to 25 mm or less is to improve productivity and reduce the size of the optical filter.

  Further, the refractive index of the ferrule 4 is assumed to be larger than the refractive index of quartz glass used for the clad 3 of the optical fiber.

  Next, the operation of the optical filter of this embodiment will be described. The waveguide mode 1650 nm band light passing through the core 1 is blocked by the grating section 2. On the other hand, the light in the cladding mode leaking from the core 1 and propagating through the cladding 3 of the optical fiber oozes out from the cladding 3 and spreads into the ferrule 4 and is scattered. This is because the refractive index of the ferrule 4 is larger than the refractive index of the cladding 3. And since the outer diameter of the clad 3 is 0.125 mm, the outer diameter of the ferrule 4 is 2.5 mm and the cross-sectional area is 400 times, the scattered light is clad in the vicinity of the front end face 4a of the emission end. The ratio of light coupled from the mode to the guided mode is so small that it can be substantially ignored, and the deterioration of the cutoff rate can be prevented.

Here, with reference to FIG. 2, the reflection of light when light is incident on the boundary surface between the material having the refractive index n _{1 and} the material having the refractive index n _{2 from} the material side having the refractive index n ₁ will be described. FIG. 2A shows a case where n ₁ > n ₂ . In this case, when the incident angle θ is smaller than the angle called the critical angle θ _C = sin ⁻¹ (n ₂ / n ₁ ), the light is totally reflected at the boundary surface, and the light is reflected on the medium side having the refractive index n _1. It is confined. FIG. 2 (b) shows the case of n ₁ <n ₂ , in which case there is no angle called the critical angle, the light is not totally reflected, and a part of the light is reflected at the boundary surface, returning to the medium side of the refractive index n _1, some light propagates in the medium side of the refractive index n _2.

  In the optical filter of this embodiment, since the refractive index of the ferrule 4 is larger than the refractive index of the cladding 3, this corresponds to the case of FIG. 2B, and the light coupled to the cladding mode is at the interface between the ferrule 4 and the cladding 3. Total reflection does not occur and the optical fiber is not confined to the cladding 3 side.

  However, even when the refractive index of the ferrule 4 is smaller than the refractive index of the cladding 3, the effect of the present embodiment is not completely lost. The light that enters the total reflection state is a part of the light that propagates in the clad mode, and a part of the light propagates to the ferrule 4 as in this embodiment, so that a certain amount of attenuation effect is obtained.

  Although it is considered that the coupling from the clad mode to the waveguide mode can be prevented even if a material that absorbs light is used as the material of the ferrule 4, the outer diameter of the optical fiber built in the ferrule 4 is 0. Since the inner diameter of the fine hole of the ferrule 4 is required to be as high as 0.126 mm with respect to 125 mm, it is difficult to select a material that absorbs light, but glass can be processed with high accuracy. .

  FIG. 3 is a graph showing the cutoff characteristics of the optical filter of the present embodiment, and shows the cutoff rate when the grating portion 2 is housed in the transparent glass ferrule 4 and when it is not housed. In the wavelength 1650 nm band, a blocking rate of about 50 to 80 dB is shown both in a state where the ferrule 4 is not stored and in a stored state, and the blocking rate is not deteriorated.

  As described above, according to the optical filter of this embodiment, the grating is formed in the fine hole of the ferrule 4 having a longitudinal length of 7 mm or more and 25 mm or less made of transparent glass having a higher refractive index than the cladding 3 of the optical fiber. Since the distal end portion of the optical fiber formed by the portion 2 at the distal end portion is fixed internally, the magnitude of light coupled from the cladding mode to the waveguide mode can be reduced, and deterioration of the cutoff rate can be prevented.

(Example 2)
Second Embodiment An optical connector according to a second embodiment of the present invention will be described with reference to FIGS.

  FIG. 4 is a schematic configuration diagram showing the optical connector 9 of the present invention. One end of the optical filter of the first embodiment and the ferrule 4 of the optical filter are fixed along the extending direction of the micropore, An extending protrusion 8 that protrudes outward from the ferrule 4 along the extending direction, and a ferrule hold 7 that fixes one end of the extending protrusion 8 are provided. The optical fiber 5 housed in the fine hole of the ferrule 4 is fixed with a resin 6.

  Next, the operation of the optical connector of this embodiment will be described. The waveguide mode 1650 nm band light passing through the core 1 is blocked by the grating section 2. On the other hand, the light in the cladding mode leaking from the core 1 due to the distortion generated by the resin 6 and propagating through the cladding 3 of the optical fiber 5 oozes out from the cladding 3 and spreads into the ferrule 4 as in the first embodiment. Scattered. Accordingly, since the intensity in the vicinity of the front end surface 4a of the emission end of the clad mode is sufficiently small, the light coupled from the clad mode to the waveguide mode becomes practically negligible, thereby preventing deterioration of the cutoff rate. it can.

  FIG. 5 is a schematic diagram showing the configuration of the final form of the optical connector of the present embodiment, and an optical connector 9 having a ferrule 4 on which an optical fiber is fixed internally, and an extending protrusion 8 that holds the ferrule 4; A caulking ring 11 that is caulked and fixed to the extending protrusion 8, a housing 10 that houses the optical connector 9, a stop ring 13 that is inserted into the rubber boot 14, and an outer peripheral portion of the extending protrusion 8 project in an annular shape. A spring 12 that is inserted between the ferrule hold 7 and urges the ferrule 4 forward, and a cover 15.

  According to the optical connector of the present embodiment, the grating portion 2 is formed in the fine hole of the ferrule 4 made of a transparent glass having a refractive index higher than that of the clad 3 of the optical fiber and having a length in the longitudinal direction of 7 mm or more and 25 mm or less. Since the distal end portion of the optical fiber formed at the distal end portion is internally fixed, it is possible to prevent light coupling from the clad mode to the waveguide mode and to prevent deterioration of the cutoff rate.

(Example 3)
A third embodiment of the optical adapter according to the present invention will be described with reference to FIGS.

  FIG. 6 is a schematic configuration diagram showing an optical filter used in Example 3 of the optical adapter of the present invention. The grating that periodically changes the refractive index of the core 1 in the longitudinal direction and blocks light of 1650 nm band by 30 dB or more. An optical fiber formed with the portion 2 and a ferrule 16 made of transparent glass through which a fine hole for fixing the optical fiber is passed. The both end surfaces 16a and 16b of the ferrule 16 are polished. The optical fiber that is internally fixed to the ferrule 16 has the same length as the length d of the ferrule 16.

  FIG. 7 is a schematic diagram showing the configuration of an optical adapter according to a third embodiment of the present invention. The optical filter shown in FIG. 6 is connected to the receptacle and the insertion hole 17a for fixing the optical filter and allowing the optical connector 18 to be connected. And a housing 17 having a connecting portion 17b.

  Next, the operation of the optical adapter of this embodiment will be described. When the housing 18b of the optical connector 18 is inserted into the insertion hole 17a of the housing 17 of the optical adapter, and the tip end surface 18a of the ferrule of the optical connector 18 and the end surface 16b of the ferrule 16 of the optical adapter are connected to each other, perturbation such as misalignment Therefore, coupling of guided mode light passing through the core 1 to the cladding mode occurs.

  However, as in the first and second embodiments, the clad mode light propagating through the clad 3 oozes out from the clad 3 and spreads into the ferrule 16 and scatters. Therefore, the light in the clad mode is not coupled from the clad mode to the waveguide mode in the vicinity of the end face 16a at the emission end, and the degradation of the cutoff rate can be prevented.

  According to the optical adapter of this embodiment, the grating portion 2 is formed in the fine hole of the ferrule 16 having a longitudinal length of 7 mm or more and 25 mm or less made of transparent glass having a higher refractive index than the clad 3 of the optical fiber. Since the formed optical fiber is internally fixed, it is possible to prevent light coupling from the clad mode to the waveguide mode and to prevent deterioration of the cutoff rate. Moreover, the optical adapter of a present Example enables what is called a male-female connection.

Example 4
Embodiment 4 of the optical adapter of the present invention will be described with reference to FIG.

  FIG. 8 is a schematic diagram showing the configuration of an optical adapter according to a fourth embodiment of the present invention. The optical filter of FIG. 6 can be connected to the first and second optical connectors 20 and 21 by fixing the optical filter internally. And a housing 19 having first and second insertion holes 19a and 19b.

  Next, the operation of the optical adapter of this embodiment will be described. The housings 21a and 21b of the first and second optical connectors 20 and 21 are inserted into the first and second insertion holes 19a and 19b of the housing 19 of the optical adapter, and the first and second optical connectors 20 and 21 are inserted. When the front end surfaces 20a and 21a of the ferrule 16 and the both end surfaces 16a and 16b of the ferrule 16 of the optical adapter are connected to each other, perturbation such as axial misalignment occurs. Coupling to the mode occurs.

  However, as in the first to third embodiments, the clad mode light propagating through the clad 3 oozes out from the clad 3 and spreads into the ferrule 16 and scatters. Therefore, the light in the clad mode is not coupled from the clad mode to the waveguide mode in the vicinity of the end face 16a (or 16b) at the emission end, and deterioration of the cutoff rate can be prevented.

According to the optical adapter of this embodiment, the grating portion 2 is formed in the fine hole of the ferrule 16 having a longitudinal length of 7 mm or more and 25 mm or less made of transparent glass having a higher refractive index than the clad 3 of the optical fiber. Since the formed optical fiber is internally fixed, it is possible to prevent light coupling from the clad mode to the waveguide mode and to prevent deterioration of the cutoff rate. In addition, the optical adapter of this embodiment enables so-called female-female connection.

It is a schematic block diagram which shows the optical filter of Example 1 of this invention. It is a figure explaining the relationship between a refractive index and reflection of light. It is a graph which shows the interruption | blocking characteristic of the optical filter of FIG. It is a schematic block diagram which shows the optical connector of this invention. It is the schematic which shows the structure of the last form of the optical connector of this invention. It is a schematic block diagram which shows the optical filter used for Example 3 of the optical adapter of this invention. It is a schematic block diagram which shows Example 3 of the optical adapter of this invention. It is a schematic block diagram which shows Example 4 of the optical adapter of this invention. It is a figure explaining FTTH and the conventional optical connector. It is a graph which shows the interruption | blocking characteristic of the conventional optical filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core 2 Grating part 3 Cladding 4,16 Ferrule 4a End surface 5 Optical fiber 6 Resin 7 Ferrule hold 8 Extension protrusion 9 Optical connector 10, 17, 19 Housing 11 Caulking ring 12 Spring 13 Stop ring 14 Rubber boot 15 Cover 16a, 16b End face 17a, 19a, 19b Insertion hole 17b Connection part 18, 20, 21 Optical connector 18a, 20a, 21a End face 18b, 20b, 21b Housing 100 Telephone station 101 Closure 102 User 103 Optical drop cable 104 Optical network device 105 Optical fiber 106 Optical cord 107 Optical connector 108 Core 109 Clad 110 Ferrule 111 Grating part

Claims (5)

An optical fiber in which a grating portion that periodically changes the refractive index of the core in the longitudinal direction and blocks light of an unnecessary wavelength region by 30 dB or more is formed at a tip portion;
An optical filter comprising a ferrule that transmits light in the unnecessary wavelength region and in which the optical fiber is fixed internally in a through hole.   The optical filter according to claim 1, wherein a length of the ferrule in a longitudinal direction is 7 mm or more.   The optical filter according to claim 1, wherein the ferrule has a higher refractive index than the cladding of the optical fiber in the unnecessary wavelength region. Having the optical filter according to claim 1,
One end is fixed along the extending direction of the fine hole, and the extending protrusion that protrudes the ferrule outward along the extending direction of the fine hole,
An optical connector comprising: a ferrule hold for fixing one end of the extending protrusion. An optical fiber formed with a grating portion that periodically changes the refractive index of the core in the longitudinal direction and blocks light of an unnecessary wavelength region by 30 dB or more;
A ferrule that penetrates through the fine holes for fixing the optical fiber internally and transmits light in the unnecessary wavelength region;
A housing for fixing the ferrule to the interior, enabling connection of the first and second optical connectors or receptacles, respectively, and allowing the first and second optical connectors or receptacles to butt and connect to both end faces of the ferrule, respectively; An optical adapter comprising:

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