JP2006201408A - Wavelength multiplexed light coupler and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength multiplexed light coupler which has high isolation while reducing reflection loss of incident light and is small in size and inexpensive, and to provide a manufacturing method of the wavelength multiplexed light coupler. <P>SOLUTION: The wavelength multiplexed light coupler 1 is provided with a first lens 31 which turns incident light into parallel light, a first optical filter 41 which is formed on a second surface 31b of the lens 31 and transmits light of wavelength λ1 and a second optical filter 43 which is formed on a first surface 31a of the lens 31, transmits light of wavelength λ2 and reflects light of wavelength other than the same. The optical filter 43 and an antireflection film 50 are formed on the first surface 31a. The antireflection film is formed in an incident light passage region of the first surface 31a and the optical filter 43 is not formed in the region. The optical filter 43 is formed in an outgoing light passage region where reflected light from the optical filter 41 on the first surface 31a is passable and the antireflection film 50 is not formed in the said region. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wavelength division multiplexing optical coupler and a manufacturing method thereof.

Conventionally, PON (Passive Optical Network) is one of network systems for FTTx (Fiber To The x, x = Home) that introduces optical communication into an access system between a subscriber and a station. For this purpose, light of different wavelengths is used for the upstream signal from the subscriber to the station and the downstream signal from the station to the subscriber. In some cases, analog signals (image signals) having different wavelengths are multiplexed and used. For example, the 1310 nm band is used for the upstream signal (Upstream Data), and the 1490 nm band or the 1550 nm band is used for the downstream signal (Downstream Data). For this reason, an OLT (Optical Line Termination) or ONU (Optical Network Unit) provided on the station side and the subscriber side needs a wavelength multiplexing optical coupler for demultiplexing and multiplexing signals of the respective wavelengths.

  As a wavelength multiplexing optical coupler used for the above purpose, one having a configuration as shown in FIG. 10 is known (for example, see Patent Document 1). In this wavelength multiplexing optical coupler, an optical filter 206 having a predetermined transmission wavelength band is used to multiplex / demultiplex the two wavelengths λ1 and λ2. The light in which λ 1 and λ 2 are multiplexed enters from the incident light optical fiber 201, is converted into parallel light by the lens 204, and enters the optical filter 206. The light of wavelength λ 1 is reflected by the optical filter 206 and coupled to the first outgoing light fiber 202 via the lens 204. The light of wavelength λ2 passes through the optical filter 206, is collected by the lens 205, and is coupled to the second optical fiber 203 for outgoing light.

  This optical coupler is also called a three-port coupler in which the incident light optical fiber 201 is a common port, the outgoing light optical fiber 202 is a reflection port, and the outgoing light optical fiber 203 is a transmission port. The internal configuration of the 3-port coupler is a type in which a bandpass filter is inserted between a two-core collimator consisting of two optical fibers and a collimating lens and a single-core collimator consisting of one optical fiber and a collimating lens ( Patent Document 1), a type in which a bandpass filter is inserted in a branch portion of an optical waveguide that branches in a Y-shape (Patent Document 2), and the like are known.

  When a gradient index rod lens is used as a collimating lens in the former type, this lens is cylindrical, and the end surface that becomes the light incident / exit surface can be made flat, so it is assembled in combination with an optical filter or optical fiber. It is easy and can be reduced in size (for example, refer to Patent Document 3).

  As the optical filter, a band-pass filter that transmits only light in a predetermined wavelength band or an edge filter (long wavelength transmission type or short wavelength transmission type) that uses a predetermined wavelength as an end (wavelength edge) of the transmission wavelength band is used. be able to.

Further, as couplers for performing multiplexing / demultiplexing of three wavelengths or more, for example, there are technologies described in Patent Document 4 and Patent Document 5, respectively.
JP-A-1-295210 JP-A-63-33707 JP 2003-240960 A JP 54-17044 A U.S. Pat. No. 4,744,424

  By the way, in the above-described wavelength division multiplexing optical coupler, a crosstalk prevention amount (isolation) indicating how much light of a wavelength other than the predetermined wavelength band is mixed into the reflection port and the transmission port is an important characteristic. However, in a normal optical filter, there is so-called residual reflection that is not related to the filter characteristics generated on the surface or the like. For this reason, in the optical couplers described in Patent Documents 1 to 3, the isolation of the reflection port using the reflected light of each filter is usually about 12 dB, and even if the transmission ripple can be adjusted appropriately, it is about 18 dB at most. The limit is to get. For this reason, it is difficult to increase the isolation of all channels (ports) (20 dB or more).

  The present invention has been made by paying attention to such conventional problems, and its purpose is to provide a small and inexpensive wavelength division multiplexing optical coupler having high isolation while reducing reflection loss of incident light. And providing a manufacturing method thereof.

  In order to solve the above-described problem, the invention according to claim 1 is configured such that when incident light in which optical signals having a plurality of wavelengths are multiplexed is incident from a single optical fiber for incident light, the incident light is separated for each wavelength. In the wavelength division multiplexing optical coupler that separates the optical signal into a plurality of optical fibers for outgoing light, the incident light emitted from the optical fiber for incident light and incident from the first surface is converted into parallel light and second A first lens that emits from a surface, and a first filter group that is disposed on the second surface side of the lens and includes a first optical filter that reflects light having a first wavelength among the plurality of wavelengths. A first optical fiber for outgoing light arranged so that the end face is located at a position where the parallel light reflected by the first optical filter is emitted from the first surface and collected; and the optical fiber A first wavelength disposed between the end surface of the first surface and the first surface An optical filter element that constitutes a second filter group including a second optical filter that transmits light and reflects light of other wavelengths, the optical filter element in addition to the second filter group An antireflection film is provided, and the antireflection film is formed in an incident light passage region through which the incident light emitted from the end face of the incident light optical fiber passes. The second optical filter is formed in an outgoing light passage region through which reflected light from the first optical filter passes, and the reflected light is not reflected in the outgoing light passage region. The gist is that the protective film is not formed.

  According to this, by providing the second optical filter that transmits the light of the first wavelength and reflects the light of the other wavelength on the first surface of the first lens, Since the residual reflection component present in the reflected light can be removed, the amount of light other than that wavelength mixed into the transmitted light (light having the first wavelength) of the second optical filter is reduced. Thereby, the isolation of the port using the reflected light of the first optical filter is improved. That is, it is possible to increase the isolation of the transmitted light that passes through the second optical filter and is coupled to the first optical fiber for outgoing light.

  In addition, since the antireflection film is formed on the first surface of the first lens on which the incident light in which the optical signals having a plurality of wavelengths are multiplexed is emitted from the incident light optical fiber, the incident light is Can be suppressed from returning to the optical fiber for incident light, and the reflection loss of incident light can be reduced. Since the antireflection film is formed in the incident light passage region on the first surface and is not formed in the outgoing light passage region, it does not affect the characteristics of the second optical filter. The second optical filter transmits the first wavelength and reflects other wavelength components out of the light demultiplexed by the first optical filter (reflected light from the filter). Although the isolation of the outgoing light coupled to the outgoing optical fiber is improved, the incident light is not affected.

Therefore, it is possible to realize a small and inexpensive wavelength division multiplexing optical coupler having high isolation while reducing reflection loss of incident light.
According to a second aspect of the present invention, in the wavelength division multiplexing optical coupler according to the first aspect, the first surface of the first lens is a flat surface, and the optical filter element is provided in close contact with the first surface. It is a summary. According to this, since the first lens and the optical filter element can be integrated, the position adjustment at the time of assembly becomes easy.

  According to a third aspect of the present invention, in the wavelength division multiplexing optical coupler according to the second aspect, the first lens has a first end surface corresponding to the first surface and a second end surface corresponding to the second surface. The gist of the present invention is a gradient index rod lens. According to this, the first lens, the incident light optical fiber, and the first outgoing light optical fiber can be arranged substantially on a straight line, and a small-sized and easy-to-assemble wavelength multiplexing optical coupler is realized. Can do.

  According to a fourth aspect of the present invention, in the wavelength division multiplexing optical coupler according to any one of the first to third aspects, the first filter group has a narrow transmission wavelength range in order along the traveling direction of the parallel light. A plurality of optical filters arranged in such a manner that the plurality of optical filters are arranged on the optical axis of the first lens so as to reflect optical signals of a plurality of wavelengths included in the parallel light in different directions. The first outgoing optical fibers are arranged at different angles with respect to each other, and the first outgoing light optical fiber is a position where the reflected light from each optical filter of the first filter group is coupled. It includes a plurality of optical fibers arranged so that the end face is positioned at the end. According to this, the optical signal can be separated for each wavelength from the incident light (wavelength multiplexed signal) in which the optical signals of two or more types of wavelengths are multiplexed, and can be distributed to the corresponding optical fiber of each port.

  According to a fifth aspect of the present invention, in the wavelength division multiplexing optical coupler according to any one of the first to fourth aspects, incident light that is transmitted through all the optical filters of the first filter group and is incident from the third surface A second lens that collects the light emitted from the fourth surface, and a second optical fiber for outgoing light that is arranged so that the end surface is located at the position condensed by the second lens. In addition, the gist is included. According to this, the light which permeate | transmitted all the optical filters of the 1st filter group can also be utilized.

  According to the sixth aspect of the present invention, when incident light in which optical signals of two wavelengths are multiplexed is incident from a single optical fiber for incident light, the incident light is separated into optical signals for each wavelength. In the wavelength multiplexing optical coupler that distributes the light to the outgoing optical fiber, the incident light emitted from the incident optical fiber is incident from the first surface, converted into parallel light, and emitted from the second surface. A first lens that is disposed to face the second surface of the first lens and reflects the first wavelength light included in the incident light converted to the parallel light and transmits the second wavelength light. And the first outgoing light arranged such that the end face is located at the position where the light of the first wavelength reflected by the first optical filter is condensed via the first lens. Formed directly on the first surface of the first optical lens and the first optical fiber The second optical filter, a second lens that condenses the light having the second wavelength that has passed through the first optical filter, and the light having the second wavelength that is condensed through the second lens. And a second optical fiber for outgoing light arranged so that the end face is located at a position where the second optical filter and the antireflection film are formed on the first surface of the first lens. The antireflection film is formed in an incident light passage region on the first surface through which the incident light emitted from the end face of the incident light optical fiber passes, and is formed in the incident light passage region. The second optical filter is not formed, and the second optical filter is formed in an outgoing light passage region on the first surface through which reflected light from the first optical filter passes. The antireflection film is not formed in the outgoing light passage region. The the gist.

According to this, since the residual reflection component existing in the reflected light from the first filter can be removed by providing the second optical filter, the transmitted light (of the first wavelength) of the second optical filter can be removed. The amount of light other than that wavelength mixed in the light) is reduced. Thereby, the isolation of the port using the reflected light of the first optical filter is improved.

  In addition, since the antireflection film is formed on the first end face of the first lens on which the incident light in which the optical signals of two wavelengths are multiplexed is emitted from the incident optical fiber, the incident light Can be suppressed from returning to the optical fiber for incident light, and the reflection loss of incident light can be reduced. Since the antireflection film is formed in the incident light passage region on the first end face of the first lens and is not formed in the emission light passage region, it does not affect the characteristics of the second optical filter. The second optical filter transmits the first wavelength and reflects other wavelength components out of the light demultiplexed by the first optical filter (reflected light from the filter). Although the isolation of the outgoing light coupled to the outgoing optical fiber is improved, the incident light is not affected. Therefore, it is possible to realize a small and inexpensive wavelength division multiplexing optical coupler having high isolation while reducing reflection loss of incident light.

  The invention according to claim 7 is the wavelength division multiplexing optical coupler according to claim 6, wherein the first wavelength and the second wavelength are any of wavelength ranges of 1260 to 1360 nm, 1480 to 1500 nm, and 1550 to 1560 nm. It is a summary to include.

  According to this, by selecting one of the above-mentioned three wavelength ranges for the first wavelength and the second wavelength, the upstream and downstream signals for FTTx and the analog image signal are adapted to the existing optical fiber network. It becomes possible to transmit in the wavelength range.

  According to an eighth aspect of the present invention, in the method for manufacturing a wavelength division multiplexing optical coupler according to the second or sixth aspect, the step of masking the incident light passing region on the first surface of the first lens, and the incident light A step of forming a dielectric multilayer film constituting the second optical filter on the first surface with the passage region masked, and removing the mask together with the dielectric multilayer film formed on the mask Including the step of performing.

  According to this, on the first surface of the first lens, the second optical filter is removed from the incident light passage region through which the incident light emitted from the end face of the incident light optical fiber passes, and the incident light. A second optical filter can be formed in a portion excluding the passage region.

  The invention according to claim 9 is the method of manufacturing a wavelength division multiplexing optical coupler according to claim 8, wherein the dielectric multilayer film constituting the second optical filter formed on the first surface is formed on the dielectric multilayer film. A step of masking the outgoing light passage region, a step of forming the antireflection film on the dielectric multilayer film where the outgoing light passage region is masked, and the reflection formed on the mask. And a step of removing together with the prevention film.

  According to this, on the dielectric multilayer film formed on the first surface of the first lens, the antireflection film is removed from the outgoing light passage region, and the antireflection is applied to a portion excluding the outgoing light passage region. A film can be formed.

  As described above, according to the present invention, it is possible to realize a small and inexpensive wavelength division multiplexing optical coupler having high isolation while reducing reflection loss of incident light.

(One embodiment)
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
[Configuration of wavelength multiplexing optical coupler]
FIG. 1 shows the structure of a wavelength division multiplexing optical coupler 1 according to an embodiment of the present invention.

  In this wavelength multiplexing optical coupler 1, incident light (wavelength multiplexed signal) obtained by multiplexing optical signals having a plurality of wavelengths (in this example, two wavelengths λ 1 and λ 2) is incident from one incident optical fiber 23. At this time, it is a two-wavelength wavelength multiplexing optical coupler that separates (divides) the incident light into optical signals for each wavelength and distributes them to two optical fibers 26 and 24 for outgoing light.

  In this wavelength division multiplexing optical coupler 1, the second surface 31b is a second end surface of the first optical filter 41 that reflects the light of the first wavelength λ1 included in the incident light and transmits the light of the second wavelength λ2. Are provided with a gradient index rod lens 31 as a first lens formed by direct film formation. Further, the wavelength division multiplexing optical coupler 1 condenses the light having the first wavelength λ1 reflected by the first optical filter 41 via the gradient index rod lens 31 (hereinafter referred to as “first lens”). The first optical fiber for outgoing light 24 is provided so that the end face is located at the position where it is placed. The wavelength multiplexing optical coupler 1 transmits the first optical filter 41 and the second optical filter 43 formed by direct film formation on the first surface 31 a that is the first end surface of the first lens 31. And a gradient index rod lens 32 as a second lens for condensing light of the second wavelength λ2. Further, the wavelength division multiplexing optical coupler 1 has an end face located at a position where the light of the second wavelength λ2 is condensed through a gradient index rod lens (hereinafter referred to as “second lens”) 32. A second outgoing optical fiber 26 is provided.

  In the wavelength division multiplexing optical coupler 1, incident light obtained by multiplexing optical signals of two wavelengths (two wavelengths of 1310 nm and 1550 nm) emitted from the incident light optical fiber (common port) 23 is transmitted through the first lens 31. Incident on one surface 31a. The wavelength division multiplexing optical coupler 1 separates incident light into two wavelengths, converts a 1310 nm optical signal from a first outgoing optical fiber (second port) 24, and a 1550 nm optical signal to a second outgoing light. The light is emitted from the fiber (first port) 26. In the following description, it is assumed that the first wavelength λ1 is 1310 nm and the second wavelength λ2 is 1550 nm. In the following description, the incident light optical fiber 23 and the two outgoing light optical fibers 26 and 24 are referred to as optical fibers 23, 24, and 26, respectively.

  The optical fiber 23 and the optical fiber 24 are held so that their optical axes (core central axes) are parallel to each other by a capillary 28 as a holding member provided in a cylindrical glass penetrating two pores. A so-called two-core optical fiber pigtail 21 is formed. A first lens 31 is disposed to face the end face of the two-core optical fiber pigtail 21. The opposing end surfaces of the two-core optical fiber pigtail 21 and the first lens 31 are inclined by about 4 to 8 degrees with respect to the optical axis so that the reflected light at each end surface does not return to the optical fiber 23. In addition, it is preferable for assembly that these end faces are substantially parallel.

  The first lens 31 converts incident light emitted from the optical fiber 23 and incident from the first surface 31a into parallel light, and condenses the parallel light reflected by the optical filter 41 on the second surface 31b. It serves to couple to the fiber 24. That is, the two-core optical fiber collimator 20 is configured by a combination of the two-core optical fiber pigtail 21 and the first lens 31.

  On the other hand, one optical fiber 26 is held by a capillary 29 as a holding member, like the optical fibers 23 and 24, and constitutes a single-core optical fiber pigtail 22. A second lens 32 is disposed to face the end face of the single-core optical fiber pigtail 22. The opposing end faces of the single-core optical fiber pigtail 22 and the second lens 32 are inclined by about 4 to 8 ° with respect to the optical axis so that the reflected light at each end face does not return to the optical fiber 23. In addition, it is preferable for assembly that these end faces are substantially parallel.

The second lens 32 collects parallel light incident from an end surface (third end surface) 32a opposite to the end surface (fourth end surface 32b) facing the single-core optical fiber pigtail 22 to collect the optical fiber. 26 to join. That is, the single-core optical fiber collimator 10 is configured by a combination of the single-core optical fiber pigtail 22 and the second lens 32.

  The two-core optical fiber collimator 20 and the single-core optical fiber collimator 10 are configured such that the second surface 31b of the first lens 31 and the third end surface 32a of the second lens 32 face each other so that parallel light can be coupled. Has been placed.

  In the wavelength division multiplexing optical coupler 1 of this example, two edge filters are used as optical filters that are divided into two filter groups depending on the positions to be arranged. The first optical filter 41 belonging to the first filter group is provided between the first lens 31 and the second lens 32. The second optical filter 43 belonging to the second filter group is provided between the first lens 31 and the optical fiber 24. The first optical filter 41 and the second optical filter 43 are formed directly on the second surface 31 b and the first surface 31 a of the first lens 31, respectively, and are integrated as a filter-equipped lens 33. The second optical filter 43 is formed at a position that acts only on the light coupled to the optical fiber 24 and does not act on the light incident from the optical fiber 23.

  Here, the first optical filter 41 belonging to the first filter group reflects light having the first wavelength λ1 and transmits light having the second wavelength λ2. The optical filter 41 is designed so that the transmitted light having the wavelength λ2 can be isolated from the reflected light by 40 dB or more. In practice, however, the light reflected by the optical filter 41 has a residual reflection in the transmitted wavelength range. Since there are components, the isolation of the light of wavelength λ1 and the light of wavelength λ2 at the reflection port is about 12 dB. Here, “isolation of reflected light” indicates how much light having a wavelength other than the wavelength λ 1 is mixed with the light having the first wavelength λ 1 reflected by the first optical filter 41. The amount of crosstalk prevention. In the following description, “isolation of reflected light” is referred to as “reflection isolation”.

  On the other hand, the second optical filter 43 belonging to the second filter group transmits light having the first wavelength λ1 and reflects light having the second wavelength λ2. As shown in FIGS. 2A and 2B, the optical filter 43 is an outgoing light passage region on the first surface 31 a of the first lens 31 through which the reflected light from the first optical filter 41 passes. 52, and is not formed in the incident light passage region 51 through which the light emitted from the optical fiber 23 passes. Since the second optical filter 43 is provided so as to overlap the first optical filter 41 (that is, the reflected light from the optical filter 41 is incident on the second optical filter 43), the optical filter 41 is provided. It may be inferior in properties. In order to obtain an isolation of 40 dB or more as a whole, the reflection isolation is about 12 dB. Therefore, the isolation of transmitted light may be 30 dB or less, and an inexpensive optical filter can be used. Here, “isolation of transmitted light” means crosstalk that indicates how much light having a wavelength other than the wavelength λ1 is mixed with the light having the first wavelength λ1 transmitted through the second optical filter 43. Refers to the amount of inhibition. In the following description, “transmission isolation” is referred to as “transmission isolation”.

  On the other hand, an antireflection film 50 for reducing loss due to reflection is provided on the first surface 31a of the lens 31 on which light emitted from the optical fiber 23 is incident (see FIGS. 2A and 2B). ). The antireflection film 50 has a characteristic that the reflectance is 0.5% or less over the entire wavelength region from 1250 nm to 1650 nm. Further, as shown in FIGS. 2A and 2B, the antireflection film 50 is formed in the incident light passage region 51 on the first surface 31a of the first lens 31, and the outgoing light passage region. 52 is not formed.

Since the second optical filter 43 and the antireflection film 50 formed on the first surface 31a of the first lens 31 have different film configurations, it is usually necessary to perform film formation by shielding the other separately. However, the incident light passage region 5 through which the outgoing light from the optical fiber 23 passes on the first surface 31a.
1 and the outgoing light passage region 52 through which the reflected light from the optical filter 41 passes is only about 100 μm apart. Therefore, shielding (masking) with a jig or the like is difficult because there is a problem of positional accuracy, such as deformation due to thermal expansion in the shielding part when it is naturally heated during film formation.

  Therefore, in this example, a so-called lift-off method in which the shielding is performed by applying a shielding film is used. That is, a resin or the like is applied to a portion where the second optical filter 43 that is a dielectric multilayer film is not formed to be shielded (masked), and a dielectric multilayer film is formed thereon. Next, the underlying resin (shielding portion) is dissolved and removed together with the dielectric multilayer film, and the dielectric multilayer film is attached only to a portion of the first surface 31a. The same procedure is repeated when the antireflection film 50 is formed on the dielectric multilayer film.

  In the wavelength multiplexing optical coupler 1 having the above configuration, the periphery of the two-core optical fiber pigtail 21 and the filter lens 33 is fixed with an epoxy resin 60 while leaving a minute gap (see FIG. 1). Further, after aligning the single-core optical fiber pigtail 22 so that the light of the second wavelength λ2 that has passed through the first optical filter 41 is coupled to the optical fiber 26 with the minimum loss, The periphery of the core optical fiber pigtail 22 is fixed with an epoxy resin 60 while leaving a minute gap (see FIG. 1).

  In addition, the wavelength division multiplexing optical coupler 1 has a final form by covering a protective case (housing) after completing the work of aligning all components and fixing them with the epoxy resin 60 as shown in FIG. desirable. The outer shape of the case can be a small tube, in which case the diameter is several mm and the length is several tens of mm.

(Manufacturing method of wavelength multiplexing optical coupler)
Next, a manufacturing method of the wavelength multiplexing optical coupler for manufacturing the wavelength multiplexing optical coupler 1 will be described with reference to FIGS.

  This method of manufacturing a wavelength multiplexing optical coupler is characterized by the following points. That is, the second optical filter 43 is formed in the outgoing light passage region 52 on the first surface 31 a of the first lens 31 and is not formed in the incident light passage region 51. The antireflection film 50 is formed in the incident light passage region 51 on the first surface 31 a and is not formed in the outgoing light passage region 52.

The manufacturing method of the wavelength multiplexing optical coupler includes the following steps.
(Step 1) A step of masking the incident light passage region 51 on the first surface 31a of the first lens 31 (see FIG. 3A). In this step, as shown in FIG. 3A and FIG. 4A, a shielding material 53 is applied so as to cover only the incident light passage region 51.

(Step 2) A step of forming a dielectric multilayer film 54 on the first surface 31a where the incident light passage region 51 is masked by the shielding material 53 (see FIG. 3B).
(Step 3) A step of removing the shielding material 53 as a mask together with the dielectric multilayer film 54 formed on the shielding material 53 (see FIG. 3C).

  (Step 4) A step of masking the outgoing light passage region 52 on the dielectric multilayer film 54 formed on the first surface 31a (see FIG. 3D). In this step, as shown in FIG. 3D and FIG. 4B, a shielding material 55 is applied so as to cover only the outgoing light passage region 52.

(Step 5) A step of forming an antireflection film 50 on the dielectric multilayer film 54 with the outgoing light passage region 52 masked (see FIG. 3E).
(Step 6) A step of removing the shielding material 55 as a mask together with the antireflection film 50 formed thereon (see FIG. 3F).

  Through the above steps, the second optical filter 43 is formed in the outgoing light passage region 52 on the first surface 31 a of the first lens 31 and is not formed in the incident light passage region 51. Further, the antireflection film 50 is formed in the incident light passage region 51 on the first surface 31 a and is not formed in the outgoing light passage region 52.

(Example)
Next, an example of the above embodiment will be described.
In the wavelength division multiplexing optical coupler 1 of this embodiment, the diameter of the tubular protective case (not shown) is 5.5 mm and the length is about 40 mm. In this wavelength division multiplexing optical coupler 1, the following characteristics based on the optical communication standard B-PON were set as target specifications.

Transmission isolation 40dB or more (wavelength range: 1260-1360, 1480-1500nm)
Reflection isolation 40dB or more (wavelength range: 1550-1565nm)
Transmission insertion loss 0.7dB or less (wavelength range: 1260-1360, 1480-1500nm)
Reflection insertion loss 0.7dB or less (wavelength range: 1550-1565nm)
In the wavelength division multiplexing optical coupler 1 of this embodiment, as the first optical filter 41, as shown in FIGS. 2A and 2B, the second surface 31b of the first lens 31 having a diameter of 1.8 mm is provided on the second surface 31b. Edge filters having wavelength characteristics that reflect light in the 1310 nm band and 1490 nm band and transmit light in the 1530 nm band were formed. This edge filter is a dielectric multilayer film in which 74 layers of SiO ₂ and TiO ₂ are alternately laminated. The film configuration of the edge filter (first optical filter 41) is shown in Table 1 below, and its theoretical characteristics are indicated by a curve 61 in FIG.

次いで、図２（ａ），（ｂ）に示すように、第２の光学フィルタ４３として、第１のレンズ３１の第１面３１ａ上の出射光通過領域５２のみに、１３１０ｎｍ帯，１４９０ｎｍ帯の光を透過し、かつ１５３０ｎｍ帯の光を反射する波長特性のエッジフィルタを形成した。このエッジフィルタは、ＳｉＯ₂とＴｉＯ₂を交互に７６層積層した誘電体多層膜である。このエッジフィルタ（第２の光学フィルタ４３）の膜構成を下記の表２に示し、その理論特性を図６の曲線６２で示す。

Next, as shown in FIGS. 2A and 2B, as the second optical filter 43, only the outgoing light passage region 52 on the first surface 31a of the first lens 31 has a 1310 nm band and a 1490 nm band. An edge filter having a wavelength characteristic that transmits light and reflects light in the 1530 nm band was formed. This edge filter is a dielectric multilayer film in which 76 layers of SiO ₂ and TiO ₂ are alternately laminated. The film configuration of this edge filter (second optical filter 43) is shown in Table 2 below, and its theoretical characteristics are shown by a curve 62 in FIG.

次いで、図２（ａ），（ｂ）に示すように、反射防止膜５０を第１面３１ａ上の入射光通過領域５１に形成した。この反射防止膜５０の膜構成を下記の表３に示し、その理論特性を図７の曲線６３で示す。

Next, as shown in FIGS. 2A and 2B, an antireflection film 50 was formed in the incident light passage region 51 on the first surface 31a. The film configuration of the antireflection film 50 is shown in Table 3 below, and its theoretical characteristics are shown by a curve 63 in FIG.

本実施例では、第１のレンズ３１の第１面３１ａに第２の光学フィルタ４３と反射防止膜５０を形成するために、入射光通過領域５１のみを覆うように図２（ａ）に示す上記遮蔽材料５３として遮蔽用のマスキング塗料を塗布する。その上に、光学フィルタ４３用の誘電体多層膜を成膜する。成膜終了後、マスキング塗料を有機溶剤を用いて除去する。これにより、入射光通過領域５１から誘電体多層膜も除去される。次に、第１面３１ａ上の出射光通過領域５２のみを覆うように、図２（ｂ）に示す上記遮蔽材料５５として遮蔽用のマスキング塗料を塗布する。その上に反射防止膜５０を成膜する。この成膜終了後、マスキング塗料を有機溶剤を用いて除去する。これによって、出射光通過領域５２から反射防止膜５０が除去される。

In this embodiment, in order to form the second optical filter 43 and the antireflection film 50 on the first surface 31a of the first lens 31, only the incident light passage region 51 is covered as shown in FIG. A masking paint for shielding is applied as the shielding material 53. A dielectric multilayer film for the optical filter 43 is formed thereon. After film formation, the masking paint is removed using an organic solvent. Thereby, the dielectric multilayer film is also removed from the incident light passage region 51. Next, a masking paint for shielding is applied as the shielding material 55 shown in FIG. 2B so as to cover only the outgoing light passage region 52 on the first surface 31a. An antireflection film 50 is formed thereon. After the film formation, the masking paint is removed using an organic solvent. As a result, the antireflection film 50 is removed from the outgoing light passage region 52.

  In this way, the filter-equipped lens 33 in which the first optical filter 41 and the second optical filter 43 are respectively formed on the second surface 31b and the first surface 31a of the first lens 31 is manufactured. The characteristics of the filter lens 33 were evaluated using an optical system as shown in FIG.

  In this optical system for characteristic evaluation, the first surface 31a of the filter-equipped lens 33 is transmitted from the incident port 71 of the two-core optical fiber pigtail 70 through the second optical filter 43 provided on the first surface 31a (FIG. 1). Wavelength-multiplexed light is incident on (see). A wavelength component (light having a wavelength λ2) transmitted through the first optical filter 41 formed on the second surface 31b (see FIG. 1) of the lens with filter 33 is converged by the collimator lens 72, and the single-core optical fiber pigtail 73 is The light intensity is measured through the transmitted light exit port 74 via the route. The light intensity measured here is the intensity of light of wavelength λ2 in the above embodiment.

  On the other hand, light having a wavelength component (light having a wavelength λ1) reflected by the first optical filter 41 of the lens with filter 33 passes through the second optical filter 43 provided on the first surface 31a and is a two-core optical fiber. The light intensity is measured by reaching the reflected light exit port 75 of the pigtail 70. The light intensity measured here is the intensity of light of wavelength λ1 in the above embodiment.

  The measurement results by such an optical system are shown in FIGS. FIG. 9B is an enlarged view of the portion with a small loss in FIG. Curves 80 in FIGS. 9A and 9B show the insertion loss of light of wavelength λ2 emitted from the transmitted light emission port 74 (the optical fiber 26 of the above embodiment), and the curve 81 shows the reflected light emission. The insertion loss of the light of wavelength λ1 emitted from the port 75 (the optical fiber 24 of the same embodiment) is shown. 9 (a) and 9 (b), it can be seen that the target specification is achieved at both ports 74 and 75. FIG.

According to the embodiment configured as described above, the following operational effects can be obtained.
The first optical filter 41 is provided with a second optical filter 43 that transmits light of the first wavelength λ1 and reflects light of other wavelengths on the first surface 31a of the first lens 31. The residual reflection component existing in the reflected light can be removed. As a result, the amount of light other than that wavelength mixed into the transmitted light (light having the first wavelength λ1) of the second optical filter 43 is reduced, and the port isolating the reflected light of the first optical filter 41 is isolated. Is improved. That is, it is possible to increase the isolation of the transmitted light that passes through the second optical filter 43 and is coupled to the first outgoing light optical fiber 24. Moreover, since the antireflection film 50 is formed on the first surface 31a on which the incident light in which the optical signals of the wavelengths λ1 and λ2 are multiplexed is emitted from the incident light optical fiber 23, the incident light is While returning to the optical fiber 23 for incident light can be suppressed, the reflection loss of incident light can be reduced. The antireflection film 50 is formed in the incident light passage region 51 on the first surface 31 a and is not formed in the outgoing light passage region 52, and thus does not affect the characteristics of the second optical filter 43. The second optical filter 43 transmits light having the first wavelength λ1 and reflects other wavelength components among the light demultiplexed by the first optical filter 41 (reflected light from the filter). This improves the isolation of the outgoing light coupled to the first outgoing optical fiber 24, but does not affect the incident light. Therefore, it is possible to realize a small and inexpensive wavelength division multiplexing optical coupler having high isolation while reducing reflection loss of incident light.

  The first lens 31 is a gradient index rod lens having a first surface 31a and a second surface 31b, and the incident light optical fiber 23 and the first output light optical fiber 24 are cores of the respective optical fibers. It is hold | maintained at the capillary 28 so that a central axis may become mutually parallel. As a result, the first lens 31, the incident light optical fiber 23, and the first outgoing light optical fiber 24 can be arranged on a substantially straight line, and the wavelength division multiplexing optical coupler 1 that is small and easy to assemble is realized. can do.

  The first optical filter 41 is in close contact with the second surface 31 b of the first lens 31. According to this, since the gradient index rod lens constituting the first lens 31 can have a flat end surface to which light is incident and an end surface to which light is emitted, a flat plate is formed on the second surface 31b of the rod lens. It is easy to bring the optical filter 41 into close contact. Further, the gradient index rod lens can be easily processed so that its end surface is inclined with respect to the optical axis, and the optical filter 41 is brought into close contact with the second surface 31b. Can be adjusted easily. Further, by using the filter lens 33 in which the optical filter 41 is in close contact with the second surface 31b of the gradient index rod lens, the number of components is reduced, and therefore the wavelength division multiplexing optical coupler 1 that can be easily assembled can be realized. .

The second optical filter 43 belonging to the second filter group is a dielectric multilayer film, and the dielectric multilayer film is formed directly on the first surface 31a of the first lens 31. This greatly facilitates the assembly of the wavelength division multiplexing optical coupler 1.

  By configuring the two-core optical fiber pigtail 21 in which the incident-light optical fiber 23 and the first outgoing-light optical fiber 24 are held by a capillary 28 as a holding member, the handling of these optical fibers 23 and 24 and Alignment is easy.

  The incident light that has passed through the first optical filter 41 and is incident from the third end face 32a is emitted from the fourth end face 32b to be condensed, and is collected by the lens 32. Since the second outgoing light optical fiber 26 is disposed so that the end face is located at the position, the light transmitted through the first optical filter 41 can also be used.

  ○ The first wavelength λ1 is in the wavelength range of 1260 to 1360 nm, and the second wavelength λ2 is in the wavelength range of 1550 to 1560 nm, so that the upstream and downstream signals and analog image signals for FTTx and the like can be converted into It becomes possible to transmit in a wavelength range suitable for.

  ○ According to the method for manufacturing a wavelength division multiplexing optical coupler, the second optical filter 43 is removed from the incident light passage region 51 on the first surface 31a of the first lens 31, and the incident light passage region 51 is The second optical filter 43 can be formed in the removed portion.

  ○ According to the above-described method for manufacturing a wavelength multiplexing optical coupler, on the second optical filter (dielectric multilayer film) 43 formed on the first surface 31a of the first lens 31, the outgoing light passage region 52 The antireflection film 50 is removed, and the antireflection film 50 can be formed in a portion excluding the outgoing light passage region 52.

In addition, this invention can also be changed and embodied as follows.
In the above embodiment, the first optical filter 41 is formed directly on the second surface 31b of the first lens 31, but the first filter group including the first optical filter is formed on both side end surfaces of the glass substrate. The optical filter chip may be fixed between the lenses 31 and 32. When combining / demultiplexing light having four or more wavelengths (four or more wavelengths), the specifications of such an optical filter chip are essential.

  In each of the above-described embodiments, the configuration example in which the second optical filter 43 and the antireflection film 50 are formed on the first surface 31a of the first lens and directly attached has been described. It is not limited to the configuration. For example, the “optical filter element” constituting the second filter group including the second optical filter 43 has an incident surface between the end surface of the first outgoing light optical fiber 24 and the first surface 31a, and the incident surface is incident light. Are inclined with respect to the optical axis. The optical filter element includes an antireflection film 50 in addition to the second filter group. The present invention can also be applied to a wavelength division multiplexing optical coupler having such a configuration.

  In the above embodiment, a 1550 nm optical signal is output from the first outgoing optical fiber (second port) 24, and a 1310 nm or 1490 nm optical signal is output from the second outgoing optical fiber (first port) 26. You may comprise so that it may radiate | emit.

  The optical filters 41 and 43 can be configured using band pass filters. Of course, the wavelength used is not limited to the two wavelengths (λ1, λ2) in the above embodiment, and may be three or more wavelengths. For example, each wavelength can be selected from a wavelength range of 1260 to 1360 nm, 1480 to 1500 nm, and 1550 to 1560 nm.

The optical filter 43 may have any shape as long as it acts only on the light coupled to the optical fiber 24 and does not act on the light incident from the optical fiber 23.
In the above embodiment, the wavelength multiplexing optical coupler 1 has been described with respect to the configuration of the optical demultiplexer that demultiplexes the wavelength multiplexed light. However, the wavelength multiplexing optical coupler having the exact same configuration multiplexes two-wavelength optical signals to 1 It can also be used as a multiplexer coupled to a single optical fiber. In this case, the incident light optical fiber 23 becomes an outgoing light optical fiber, and each outgoing light optical fiber becomes an incident light optical fiber.

  The wavelength multiplexing optical coupler described in the above embodiment can be incorporated not only in the OLT and ONU but also widely applicable to other optoelectronic devices such as (O / E) converters and (E / O) converters. is there.

In addition, in order to perform multiplexing / demultiplexing of three wavelengths or more, a means is known in which a plurality of three-port couplers having different wavelength bands as transmission wavelength bands are connected in cascade (for example, Patent Document 4). reference). However, in order to cascade two or more optical couplers, it is necessary to route the optical fiber. In this case, in order to prevent optical loss, the winding radius of the optical fiber is reduced to a certain level or less. It is not possible. Since a housing for housing this optical fiber is required, it cannot be made into a small tube shape like a normal three-port coupler, and is increased in size. In order to solve this problem, an optical coupler is known in which a plurality of edge filters having different edge wavelengths are stacked to form the first filter group (see, for example, Patent Document 5). In this optical coupler, the angle of each optical filter is changed, and the direction of the reflected light from each filter is changed to couple light of different wavelengths to different optical fibers. This makes it possible to separate three wavelengths or more with a single optical coupler without cascading three-port couplers, and solve the problems such as an increase in size and an increase in the number of parts as described above. However, this optical coupler cannot solve the problem of low isolation (usually about 12 dB) at the port using the reflected light of each optical filter. This is because, when using reflected light of a specific wavelength band reflected by the wavelength characteristics of each optical filter, the reflected light from the filter is related to the wavelength characteristics in addition to the reflected component of the specific wavelength band. This is because there is always a residual reflection component that is a reflection component that is not reflected, that is, a component reflected by the incident surface of the optical filter.

  The present invention can also be applied to an optical coupler that performs multiplexing / demultiplexing of three or more wavelengths constituting the first filter group by stacking edge filters having a plurality of different edge wavelengths in this manner, thereby reducing reflection loss. On the other hand, the isolation of the port using the reflected light of each optical filter can be increased, and a small and inexpensive wavelength division multiplexing optical coupler can be realized.

  That is, in the above-described embodiment, the configuration in which only the first optical filter 41 is used as the optical filter belonging to the first filter group has been described. However, the first filter group transmits along the traveling direction of parallel light. The present invention is also applicable to a configuration including a plurality of optical filters arranged so that the wavelength range becomes narrower in order. In this case, the plurality of optical filters in the first filter group reflect the optical signals having a plurality of wavelengths included in the parallel light emitted from the first lens 31 in different directions, respectively. It arrange | positions at the 2nd surface 31b side so that a different angle may be made with respect to each optical axis. In this case, instead of the first outgoing light optical fiber 24, a plurality of optical fibers are arranged so that the end faces are located at the positions where the reflected light from the respective optical filters of the first filter group is coupled. The According to this, it is possible to separate an optical signal for each wavelength from incident light (wavelength multiplexed signal) in which optical signals of three or more types of wavelengths are multiplexed and distribute them to the corresponding optical fiber of each port.

In addition, among the plurality of optical filters in the first filter group, an optical filter disposed at a position closest to the second surface 31b, for example, the optical filter 41 is brought into close contact with the second surface 31b. According to this, since the gradient index rod lens constituting the first lens 31 can have a flat end surface to which light is incident and an end surface to which light is emitted, a flat plate is formed on the second end surface of the rod lens. It is easy to adhere the optical filter. Further, it is easy to process the end surface of the rod lens so as to be inclined with respect to the optical axis, and the angle of the optical filter can be easily adjusted by closely contacting the optical filter with the second end surface. In addition, since the number of components is reduced by using a filter-attached rod lens in which the optical filter is in close contact with the end surface of the rod lens, a wavelength-multiplexed optical coupler that can be easily assembled can be realized.

  In the above-described embodiment, the configuration using the two-core optical fiber pigtail 21 in which the incident light optical fiber 23 and the first outgoing light optical fiber 24 are held by the capillary 28 as a holding member has been described as an example. The present invention can also be applied to a configuration using a multi-core optical fiber pigtail in which three or more optical fibers are held in the capillary 28. Further, the present invention can be applied to a configuration using a multi-core optical fiber pigtail in which two or more optical fibers are held in the capillary 29 instead of the single-core optical fiber pigtail 22.

  In the above embodiment, the second lens 32 is a second gradient index rod lens having a third end surface (third surface) 32a and a fourth end surface (fourth surface) 32b. Of the plurality of optical filters in the filter group, an optical filter disposed at a position closest to the third end surface 32a is brought into close contact with the third end surface 32a. The present invention can also be applied to a wavelength division multiplexing optical coupler having such a configuration. According to this, it is easy to adhere the flat optical filter to the third end face of the second lens 32. Moreover, the angle of the optical filter can be easily adjusted by bringing the optical filter into close contact with the third end face of the lens. In addition, by using a rod lens with a filter in which the optical filter is in close contact with the third end face, the number of components is reduced, so that a wavelength division multiplexing optical coupler that is easier to assemble can be realized.

  The optical filter in close contact with the third end face 32a of the second gradient index rod lens as the second lens 32 is used as a dielectric multilayer film, and the dielectric multilayer film is directly formed on the third end face. You may make it form. According to this, a large number of rod lenses with a filter can be produced by directly forming an optical filter that is a dielectric multilayer film on the third end face of the second gradient index rod lens. It becomes easy.

  In the above embodiment, the lenses 31 and 32 are not limited to gradient index rod lenses as long as they are converging lenses. However, when the lens surface is spherical or aspherical, it is necessary to use an optical filter element in which the second filter 43 (second filter group) and the antireflection film 50 are formed on separate substrates.

  In the above embodiment, a plano-convex lens may be used as the first lens 31 instead of the gradient index rod lens. In this case, the optical filter element in which the second filter 43 (second filter group) and the antireflection film 50 are integrated can be formed in close contact with the first surface 31a or by direct film formation.

1 is a schematic configuration diagram illustrating a wavelength division multiplexing optical coupler according to an embodiment. (A) is an enlarged view which shows the 1st lens of the coupler, (b) is an enlarged view of the B section of FIG. 2 (a). (A)-(f) is process drawing which shows the procedure which forms the 2nd optical filter and anti-reflective film in the 1st surface of a 1st lens. (A) is explanatory drawing which shows the same 1st surface and shows the masking process of Fig.3 (a), (b) is explanatory drawing which shows the masking process of FIG.3 (d). The graph which shows the theoretical characteristic of the edge filter as a 1st optical filter. The graph which shows the theoretical characteristic of the edge filter as a 2nd optical filter. The graph which shows the theoretical characteristic of an antireflection film. The schematic block diagram which shows the optical system for the characteristic evaluation of a lens with a filter. (A) is the graph which shows the measurement result by the same optical system, (b) is the graph which expanded the part with a small loss of Fig.9 (a). The schematic block diagram which shows a prior art example.

Explanation of symbols

  λ1 ... first wavelength, λ2 ... second wavelength, 1 ... wavelength multiplexed optical coupler, 23 ... incident light optical fiber, 24 ... first outgoing light optical fiber, 26 ... second outgoing light optical fiber , 31 ... gradient index rod lens (first lens), 31a ... first surface as a first end surface, 31b ... second surface as a second end surface, 32 ... gradient index rod lens (first lens) 2 lens), 32a ... third end face, 32b ... fourth end face, 41 ... first optical filter, 43 ... second optical filter, 50 ... antireflection film, 51 ... incident light passing region, 52 ... Emission light passage region, 54... Dielectric multilayer film.

Claims (9)

When incident light in which optical signals of a plurality of wavelengths are multiplexed is incident from a single incident light optical fiber, the incident light is separated into optical signals for each wavelength, and a plurality of outgoing light optical fibers are separated. In the wavelength division multiplexing optical coupler to distribute,
A first lens that is emitted from the incident optical fiber and is incident on the first surface and is converted into parallel light and emitted from the second surface; and is disposed on the second surface side of the lens, A first filter group including a first optical filter that reflects light having a first wavelength among a plurality of wavelengths, and parallel light reflected by the first optical filter is emitted from the first surface and collected. A first optical fiber for outgoing light arranged so that an end face is located at a position to be illuminated; and an optical fiber arranged between the end face of the optical fiber and the first face for transmitting light of a first wavelength; An optical filter element that constitutes a second filter group including a second optical filter that reflects light of a wavelength other than
The optical filter element includes an antireflection film in addition to the second filter group, and the antireflection film is formed in an incident light passage region through which the incident light emitted from the end face of the incident light optical fiber passes. The second optical filter is not formed in the incident light passage region,
The second optical filter is formed in an outgoing light passage region through which reflected light from the first optical filter passes, and the antireflection film is not formed in the outgoing light passage region. A wavelength division multiplexing optical coupler. The wavelength division multiplexing optical coupler according to claim 1,
The wavelength division multiplexing optical coupler according to claim 1, wherein the first surface of the first lens is a flat surface, and the optical filter element is provided in close contact with the first surface. The wavelength division multiplexing optical coupler according to claim 2,
The wavelength division multiplexing optical coupler, wherein the first lens is a gradient index rod lens having a first end surface corresponding to the first surface and a second end surface corresponding to the second surface. . In the wavelength division multiplexing optical coupler according to any one of claims 1 to 3,
The first filter group includes a plurality of optical filters arranged so that a transmission wavelength range is sequentially narrowed along a traveling direction of the parallel light, and the plurality of optical filters are included in the parallel light. Are arranged on the second surface side so as to have different angles with respect to the optical axis of the first lens so as to reflect the optical signals of different wavelengths in different directions, and for the first outgoing light 2. The wavelength division multiplexing optical coupler according to claim 1, wherein the optical fiber includes a plurality of optical fibers arranged such that end faces thereof are located at positions where reflected light from the optical filters of the first filter group is coupled. In the wavelength division multiplexing optical coupler according to any one of claims 1 to 4,
Incident light that passes through all the optical filters of the first filter group and enters from the third surface is collected by the second lens that is emitted from the fourth surface and collected, and the second lens. And a second optical fiber for outgoing light arranged so that the end face is located at the end position. When incident light in which optical signals of two wavelengths are multiplexed is incident from one incident optical fiber, the incident light is separated into optical signals for each wavelength, and the two outgoing optical fibers are separated. In the wavelength division multiplexing optical coupler to distribute,
Incident light emitted from the incident light optical fiber is incident from the first surface, converted into parallel light, and emitted from the second surface, and opposed to the second surface of the first lens. The first optical filter that reflects the light having the first wavelength and transmits the light having the second wavelength that is included in the incident light that is arranged and converted into the parallel light, and is reflected by the first optical filter. A first optical fiber for outgoing light disposed such that an end face is located at a position where light of a first wavelength is condensed via the first lens; and the first surface of the first lens. A second optical filter formed by direct film formation on the first optical filter, a second lens for condensing the second wavelength light transmitted through the first optical filter, and the second wavelength light in the first optical filter. The second light beam for outgoing light is arranged so that the end face is located at a position where the light is condensed through the second lens. Comprising: a driver, a,
The second optical filter and an antireflection film are formed on the first surface of the first lens,
The antireflection film is formed on an incident light passage region on the first surface through which the incident light emitted from the end surface of the optical fiber for incident light passes. 2 optical filter is not formed,
The second optical filter is formed in an outgoing light passage region on the first surface through which reflected light from the first optical filter passes, and the antireflection film is formed in the outgoing light passage region. A wavelength division multiplexing optical coupler characterized by not being formed. The wavelength division multiplexing optical coupler according to claim 6,
The wavelength division multiplexing optical coupler, wherein the first wavelength and the second wavelength include any of wavelength ranges of 1260 to 1360 nm, 1480 to 1500 nm, and 1550 to 1560 nm. In the manufacturing method of the wavelength division multiplexing optical coupler according to claim 2 or 6,
Masking the incident light passage region on the first surface of the first lens;
Depositing a dielectric multilayer film constituting the second optical filter on the first surface where the incident light passage region is masked;
And a step of removing the mask together with the dielectric multilayer film formed on the mask. In the manufacturing method of the wavelength division multiplexing optical coupler according to claim 8,
Masking the outgoing light passage region on the dielectric multilayer film constituting the second optical filter formed on the first surface;
Forming the antireflection film on the dielectric multilayer film in which the outgoing light passage region is masked;
Removing the mask together with the antireflection film formed thereon, and a method for producing a wavelength division multiplexing optical coupler.

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