Patent Description:
For general prior art, reference is made to patent documents [<NUM>] and [<NUM>].

Patent document [<NUM>] discloses an optical connector with a built-in photodetector for detecting light in the optical connector; an adapter for detachably receiving an optical connector, comprising an electrode configured to electrically contact an electrode of the optical connector; a connection apparatus comprising an arrangement of adapters for detachably receiving a plurality of optical connectors, each adapter comprising an electrode configured to electrically contact an electrode of the respective optical connector; a system with an interface configured to make an optical connection with an optical connector and a processing unit configured to receive from the connector an indication and to generate a feedback signal indicative of said indication; and/ an optical connector responsive to light to generate an electrical signal.

Patent document [<NUM>] is directed to the creation of optical waveguiding devices from standard optical fibers by the creation of zones of permanently altered refractive index characteristics therein. A high intensity femtosecond laser beam is focused at a predetermined target region in the fiber so as to soften the glass material at the target region. After aligning the focal region with the target region in the fiber there will be relative movement between the focal region and the fiber, which has the effect of sweeping the focal region across the fiber in a predetermined path, so as to create a secondary waveguide path. A portion of the light traveling along the core is removed from the core along the secondary waveguide path such that the device can be utilized as an attenuator, an optical tap, or a polarimeter.

As an optical branching technique, a wavelength multiplexing coupler or the like using an arrayed waveguide grating is known. Also, to realize optical sensing and monitoring of a transmission path, an optical side output technique using a tap waveguide has been suggested. By the optical side output technique, an optical waveguide is formed by laser processing in a fiber, and part of the power of light is output from the core (see Non Patent Literature <NUM>, for example).

A conventional wavelength multiplexing coupler is large in size, and has reflection and loss that are larger at connecting points. Therefore, it is difficult to dispose such wavelength multiplexing couplers at multiple points in a transmission path. Further, conventional tap waveguides are easily disposed at multiple points in a transmission path, but it is difficult to increase the wavelength selectivity of these tap waveguides.

Therefore, to solve the above problem, the present invention aims to provide an optical side input/output circuit that has wavelength selectivity and is easily disposed at multiple points in a transmission path, and an optical connector.

To achieve the above object, an optical side input/output circuit according to the present invention includes a tap waveguide having wavelength selectivity.

Specifically, an optical side input/output circuit according to the present invention and defined in claim <NUM> includes:.

Further, an optical connector according to the present invention and defined in claim <NUM> includes the optical side input/output circuit.

The optical side input/output circuit has a long-period fiber grating formed to give wavelength selectivity to the tap waveguide. Having the tap waveguide, the optical side input/output circuit is easily disposed at multiple points in a transmission path. Further, the optical side input/output circuit can input/output light of a desired wavelength with the long-period fiber grating. Thus, the present invention can provide an optical side input/output circuit that has wavelength selectivity and is easily disposed at multiple points in a transmission path, and an optical connector.

The grating portion of the optical side input/output circuit according to the present invention has a normalized frequency V of <NUM> or higher at the desired wavelength, and the tap portion satisfies <MAT> <MAT> <MAT> and <MAT>.

Here, dt represents a diameter of the tap waveguide, dc represents a diameter of the core of the optical fiber, δn represents a refractive index change amount of the tap waveguide with respect to the optical fiber, ncore and nclad represent a refractive index of the core of the optical fiber and a refractive index of a cladding, respectively, and α represents an angle (°) formed by the core of the optical fiber and the tap waveguide.

The refractive index of the core of the grating portion of the optical side input/output circuit according to the present invention is higher than the refractive index of the core of the tap portion. As the higher-order mode is excited in the grating portion, light of the desired wavelength can be tapped even in a case where the higher-order mode does not propagate in the tap portion.

The optical side input/output circuit according to the present invention is characterized in that a plurality of sets of the tap portion and the grating portion is continuously arranged in the optical fiber. Further, the optical side input/output circuit according to the present invention further includes a light receiver that is disposed on the side surface of the optical fiber, and receives light output from the tap portion. Tapping can be performed at a plurality of locations in the transmission path, and thus, control on the transmission path and multistage optical power feeding can be performed.

Note that the respective inventions described above can be combined as appropriate.

The present invention can provide an optical side input/output circuit that has wavelength selectivity and is easily disposed at multiple points in a transmission path, and an optical connector.

An embodiment of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to these embodiments. Note that components having the same reference numerals in the present description and the drawings indicate the same components.

<FIG> is a diagram for explaining an optical side input/output circuit <NUM> according to this embodiment. The optical side input/output circuit <NUM> includes:.

The optical fiber <NUM> is a step-index fiber that is defined by the diameter dc of the core <NUM>, the diameter df of the optical fiber <NUM>, the refractive index ncore (the refractive index of the portion not including the grating) of the core <NUM>, and the refractive index nclad of a cladding <NUM>. In the optical fiber <NUM>, the grating portion <NUM> and the tap portion <NUM> are formed in this order in the longitudinal direction. The direction in which light can enter the tap waveguide <NUM> is the optical waveguide direction. In <FIG>, the optical waveguide direction is the direction from left to right. Further, the direction in which the tap waveguide <NUM> faces the side surface of the optical fiber <NUM> from the core <NUM> is the tap direction. In <FIG>, the tap direction is the direction inclined in the forward direction with respect to the optical waveguide direction.

The grating portion <NUM> converts only light of the wavelength to be extracted from the light propagating in the core <NUM> of the optical fiber <NUM>, into an LP11 mode with a long-period grating. A grating structure can be formed by femtosecond laser processing, CO2 laser processing, or grating pressing, for example.

The tap portion <NUM> includes the tap waveguide <NUM> extending from the center of the core <NUM> toward the side surface of the optical fiber <NUM> (the interface with the cladding <NUM>) at an angle α. The tap portion <NUM> selectively extracts only the LP11 mode from the core <NUM> by controlling the angle α between the tap waveguide <NUM> and the core <NUM>, the diameter dt of the tap waveguide <NUM>, and the refractive index of the tap waveguide <NUM>.

Here, light to be coupled from the core <NUM> to the tap waveguide <NUM> is defined as tap light, and light directly propagating in the core <NUM> is defined as transmitted light. For example, by connecting a light receiving element to the output end (the side surface of the optical fiber <NUM>) of the tap portion <NUM>, it is possible to extract and receive only the tap light from the optical fiber <NUM>.

In the tap portion <NUM>, the efficiency of coupling from the core <NUM> to the tap waveguide <NUM> greatly depends on the propagation mode of the light propagating in the core <NUM>. This is because, the higher the mode, the smaller the confinement, and the easier the coupling to the tap waveguide <NUM>. Accordingly, only the higher-order mode can be coupled to the tap waveguide.

To couple only the higher-order mode to the tap waveguide <NUM> herein, the refractive index of the tap waveguide <NUM> and the value of the diameter dt are important. If these values are too great, the NA of the tap waveguide <NUM> becomes larger, and the LP01 mode is also easily coupled thereto. Therefore, the transmitted light loss increases. If these values are too small, on the other hand, the NA of the tap waveguide <NUM> becomes smaller, and the higher-order mode is not easily coupled thereto. Therefore, the efficiency of coupling of the tap light to the tap waveguide <NUM> becomes lower. That is, it is necessary to appropriately determine the refractive index of the tap waveguide <NUM> and the value of the diameter dt.

Further, in order to couple the light of the higher-order mode to the tap waveguide <NUM> with high efficiency, and transmit the light of the basic mode while confining the light in the core <NUM>, it is necessary to make α sufficiently smaller, and adiabatically change the mode (see Non Patent Literature <NUM>, for example). When α is large, the LP01 mode is also coupled to a radiation mode under the influence of the tap waveguide <NUM>, and a loss occurs. Therefore, the upper limit value of α is determined from the viewpoint of the loss in the LP01 mode. On the other hand, α can take any greater value than <NUM>, but the total length Ltap of the tap portion <NUM> is determined by α according to the expression shown below. Accordingly, the lower limit value of α is determined from the viewpoint of the required condition for the propagation loss of the tap waveguide <NUM> and the total length of the device. [Mathematical Expression <NUM>] <MAT>.

In Expression (<NUM>), the unit of α is radian.

In a general single-mode fiber, the diameter df of the optical fiber <NUM> is <NUM>. For example, to set the tap portion Ltap to <NUM> or shorter, α needs to be set to <NUM>° or greater.

The grating portion <NUM> includes the grating <NUM> with pitch Λ. For example, the grating <NUM> is a long-period fiber grating (LPG). To convert only a desired wavelength λ from the LP01 mode to the LP11 mode in the grating portion <NUM>, the pitch Λ is set so as to satisfy the following expression.

Here, neff1 represents the effective refractive index of the basic mode (LP01) propagating in the core <NUM>, neff2 represents the effective refractive index of the higher-order mode (LP11), and λ represents the wavelength in vacuum. Note that an effective refractive index means an effective refractive index in a state in which any grating is not included.

<FIG> is a graph for explaining the relationship among the effective refractive index neff1 of the basic mode, the effective refractive index neff2 of the higher-order mode (LP11), the grating pitch Λ, and the wavelength λ. In <FIG>, the abscissa axis indicates the wavelength λ, the first ordinate axis indicates the effective refractive index, and the second ordinate axis indicates the grating pitch Λ. The optical fiber is calculated as a step-type refractive index distribution having a core radius of <NUM> and a relative refractive index difference Δcore = <NUM>% of the core, so as to be equivalent to a general single-mode fiber. Note that the relative refractive index difference Δcore of the core is defined by the expression shown below. [Mathematical Expression <NUM>] <MAT>.

The dot-and-dash line indicates the effective refractive index neff1 of the LP01 mode with respect to the wavelength λ, the dotted line indicates the effective refractive index neff2 of the LP11 mode with respect to the wavelength λ, the solid-line indicates the refractive index of the cladding (<NUM> at all wavelengths), and the dashed line indicates the grating pitch Λ at which the LP01 mode is converted into the LP11 mode with respect to the wavelength λ.

Further, the grating portion <NUM> needs to be a structure capable of transmitting the LP11 mode. For example, in the structure described with reference to <FIG>, the LP11 mode does not exist in the regions of a wavelength of <NUM> or longer, and therefore, light of a wavelength of <NUM> or longer cannot be extracted as tap light. The condition for propagation of the higher-order mode is defined as V > <NUM>, using the normalized frequency V value shown in the following expression (see Non Patent Literature <NUM>, for example). [Mathematical Expression <NUM>] <MAT>.

That is, it is necessary to set the core diameter dc (represented by dcore in Expression (<NUM>)), the refractive index ncore of the core, and the relative refractive index difference Δcore of the core so that Expression (<NUM>) becomes <NUM> or greater in the wavelength of the light to be output as the tap light.

<FIG> is a graph for explaining the relationship between the grating length Lg and the amount of coupling between modes at a wavelength of <NUM>. Here, the amount of coupling is obtained by normalizing the power of each mode output from the grating portion <NUM> with the power of the incident light when the LP01 mode enters the grating portion <NUM>. The grating pitch Λ is <NUM>, which is obtained at the wavelength of <NUM> from the dashed line in <FIG>.

As the grating length Lg is made to change, the respective amounts of coupling change. That is, it is possible to control the efficiency of conversion to the LP11 mode by adjusting the grating length Lg of the grating portion <NUM> in accordance with the power to be extracted into the tap waveguide <NUM>.

<FIG> is diagrams for explaining the structure and the characteristics of the tap portion <NUM>. <FIG> is a diagram for explaining the structure of the tap portion <NUM>. The tap waveguide <NUM> is formed with the angle α in the core <NUM>. The refractive index of the core <NUM> is represented by ncore, and the refractive index of the cladding <NUM> is by nclad. The tap waveguide <NUM> can be formed in the optical fiber <NUM> by a femtosecond laser processing technique as disclosed in Non Patent Literature <NUM>. At this stage, the amounts of modulation of the refractive indexes of the core <NUM> and the cladding <NUM> by a femtosecond laser (the differences in the refractive indexes changed by the laser) are defined as δncore and δnclad, respectively. Accordingly, in the refractive index of the tap waveguide <NUM> is expressed as ncore + δncore in the portion overlapping the core <NUM>, and is expressed as nclad + δnclad in the portion overlapping the cladding <NUM>.

<FIG> are graphs for explaining an electrical field distribution when light enters the tap portion <NUM> from the direction of the arrow in <FIG> is a graph obtained when light entered in the LP01 mode, and <FIG> is a graph obtained when light entered in the LP11 mode. Note that the calculation was performed on the assumption that the wavelength is <NUM>, dc = <NUM>, Δcore = <NUM>%, α = <NUM>°, and dt = <NUM>. Further, since the Ge addition amount in a general single-mode fiber is as small as several mol%, the difference in the amount of modulation of the refractive index between the core <NUM> and the cladding <NUM> by a femtosecond laser depending on the material is considered sufficiently small. Accordingly, it can be considered that δncore and δnclad are substantially equal, and δncore = δnclad = δn = <NUM>. Hereinafter, δncore and δnclad will be written as δn.

As illustrated in <FIG>, the light of the LP01 mode is not coupled to the tap waveguide <NUM>, and continues to propagate in the core <NUM>. On the other hand, as illustrated in <FIG>, the light of the LP11 mode is coupled to the tap waveguide <NUM>, and does not propagate in the core <NUM>. As described above, by appropriately designing the tap waveguide <NUM>, it is possible to selectively couple only the light of the LP11 mode to the tap waveguide <NUM>, and extract the light.

The optical side input/output circuit <NUM> preferably has a low loss of transmitted light to be received by the tap portion <NUM>. With connection of optical side input/output circuits <NUM> in multiple stages being taken into consideration, the loss per one optical side input/output circuit <NUM> is preferably restricted to <NUM> dB or smaller. <FIG> is a graph for explaining the α dependence of the loss of transmitted light to be received by the tap portion <NUM> (the insertion loss at the tap portion <NUM>) when the light of the LP01 mode entered the tap portion <NUM>. The solid line, the dotted line, and the dot-and-dash line indicate data in cases where the ratio between the diameter dt of the tap waveguide and the diameter dc of the core was <NUM>, <NUM>, and <NUM>, respectively. Also, the other parameters were set as follows: the refractive index modulation amount δn = <NUM>, the ratio of the refractive index modulation amount to the refractive index difference between the core and the cladding δn/ (ncore - nclad) = <NUM>, the wavelength = <NUM>, dc = <NUM> gm, dt = <NUM>, and Δcore = <NUM>%.

The insertion loss at the tap portion <NUM> monotonically increases in proportion to α. For example, to restrict the insertion loss to <NUM> dB or smaller, α is only required be set to <NUM>°, <NUM>°, and <NUM>° or smaller, when dt/dc = <NUM>, <NUM>, and <NUM>, respectively.

Meanwhile, in the optical side input/output circuit <NUM>, the light of the LP11 mode is preferably coupled to the tap waveguide <NUM> as much as possible. To extract and receive the light of the LP11 mode, a coupling efficiency of <NUM>% or higher is desirable. <FIG> is a graph for explaining the α dependence of the efficiency of coupling to the tap waveguide <NUM> when the light of the LP11 mode entered the tap portion <NUM>. The meanings of the respective lines and the respective parameters are the same as those in <FIG>.

The coupling efficiency at the tap portion <NUM> monotonically decreases in proportion to α. For example, to achieve a coupling efficiency of <NUM>% or higher, α is only required to be set to <NUM>°, <NUM>°, and <NUM>° or smaller, when dt/dc = <NUM>, <NUM>, and <NUM>, respectively.

<FIG> is graphs for explaining the relationship between insertion loss and coupling efficiency in a core structure. Here, ncore, dc, and the wavelength are changed so that the V value becomes constant in a case where α = <NUM>. In this example, α = <NUM>°, δn = <NUM>, δn/(ncore - nclad) = <NUM>, and dt = <NUM>.

<FIG> are graphs for explaining the insertion loss of the LP01 mode and the efficiency of coupling of the LP11 mode to the tap waveguide <NUM> when Δcore was changed while dc = <NUM>. <FIG> are graphs for explaining the insertion loss of the LP01 mode and the efficiency of coupling of the LP11 mode to the tap waveguide <NUM> when dc was changed while Δcore = <NUM>%. The wavelength is adjusted so that each V value is fixed at V = <NUM>. It can be confirmed that the Δcore dependence of the loss of the LP01 mode is large when dt/dc = <NUM> (see the solid line in <FIG>), but the dependence on the core structure is small in the other structures.

<FIG> is a graph for explaining the dt/dc dependence of the efficiency of coupling of the LP11 mode, when V = <NUM>, α = <NUM>°, δn = <NUM>, δn/ (ncore - nclad) = <NUM>, the wavelength = <NUM>, dc = <NUM>, and Δcore = <NUM>%. As can be seen from <FIG>, the coupling efficiency is <NUM>% or higher in the region where <NUM> ≤ dt/dc ≤ <NUM>.

From <FIG> and <FIG>, it is considered that the coupling efficiency is <NUM>% or higher in the region where <NUM> ≤ dt/dc ≤ <NUM>, and that the dependence on the core structure is small under the condition the V value is constant. Therefore, in the description below, calculation is performed in the region where <NUM> ≤ dt/dc ≤ <NUM>, using the V value. Hereinafter, in the core structure, dc = <NUM>, Δcore = <NUM>%, and the wavelength is changed so that the V value becomes constant. However, within the region where <NUM> ≤ dt/dc ≤ <NUM>, even if the core structure changes, the characteristics can be obtained as long as the V value remains the same.

<FIG> is graphs for explaining the range of α where the insertion loss of the LP01 mode is <NUM> dB or smaller. In <FIG>, δn/ (ncore - nclad) , V, and dt/dc are changed, to obtain the maximum value of α that can restrict the insertion loss of the LP01 mode to <NUM> dB or smaller as illustrated in <FIG>. <FIG> illustrate the maximum values of α in cases where V = <NUM>, <NUM>, and <NUM>, respectively. In <FIG>, the denser the black, the smaller α needs to be. As described above, the tap portion <NUM> needs to be a structure in which the LP11 mode propagates, and therefore, the region in which the minimum V value for transmitting the LP11 mode is V = <NUM> or greater is the design region. Further, in the present invention, the coupling efficiency of extracted tap light is preferably high as described above.

<FIG> is graphs for explaining the range of the maximum value of the coupling efficiency (the efficiency of coupling of the LP11 mode to the tap waveguide when the insertion loss of the LP01 mode is <NUM> dB or smaller) obtained in the region of α (equal to or smaller than the maximum value of α) calculated in <FIG>. Note that the minimum value of α is set to <NUM>. <FIG> are data when V = <NUM>, V = <NUM>, and V = <NUM>, respectively. For example, as can be seen from <FIG>, when V = <NUM>,
there are no regions in which the coupling efficiency is <NUM> or higher, and sufficient tap light is not obtained in the region expressed as follows: <MAT> <MAT> and <MAT>.

Likewise, as can be seen from <FIG>, when V = <NUM>,
there are no regions in which the coupling efficiency is <NUM> or higher, and sufficient tap light is not obtained in the region expressed as follows: <MAT> <MAT> and <MAT>.

At least, δn/ (ncore - nclad) and dt/dc need to be set so as to be in the region (the region in which the coupling efficiency can be <NUM> or higher, but the coupling efficiency is not necessarily <NUM> or higher in this region) excluding the region in which the coupling efficiency is neither equal to nor higher than <NUM> (the region in which the coupling efficiency is lower than <NUM>). <FIG> is graphs for explaining the region in which the coupling efficiency obtained by changing the V value is <NUM> or higher. The expression (the solid line) in <FIG> indicates the dependence of dt/dc on the V value, and the region above the solid line is the region in which the coupling efficiency can be <NUM> or higher. The two expressions (the dashed line and the solid line) in <FIG> indicate the V value dependence of δn/ (ncore - nclad) , and the region between the two straight lines is the region in which the coupling efficiency can be <NUM> or higher. Note that, as described in the explanation of the core structure dependence with reference to <FIG>, the core structure dependence is shown within the range of <NUM> ≤ dt/dc ≤ <NUM>.

As described above, to reduce the insertion loss of the LP01 mode and obtain a coupling efficiency of the LP11 mode of <NUM>% or higher, it is necessary to set δn/ (ncore - nclad) and dt/dc so as to satisfy at least the following expression.

Further, the maximum value of α in the above region is obtained by comparing <FIG> with <FIG>. In <FIG> and <FIG>, the maximum value of α in the region in which the coupling efficiency is <NUM> or higher is <NUM>, and <NUM> or more of tap light cannot be extracted at least in the region in which α is <NUM> or greater. <FIG> is a graph for explaining the V value dependence of the maximum value of α that can be tolerated. As can be seen from <FIG>, it is necessary to set α so as to satisfy the following expression.

<FIG> is a graph for explaining the insertion loss at the tap portion <NUM>. <FIG> is a graph for explaining the wavelength dependence of the efficiency of coupling of the P11 mode to the tap waveguide <NUM>. The parameters of the tap portion <NUM> are dc = <NUM>, Δcore = <NUM>%, α = <NUM>, dt = <NUM>, and δn/(ncore - nclad) = <NUM>. In the band of the wavelength of <NUM> described with reference to <FIG>, the wavelength dependence of the insertion loss is <NUM> dB or lower, and the wavelength dependence of the coupling efficiency is <NUM>% or lower, which are sufficiently small. Accordingly, within the region of about a <NUM> band, the same insertion loss and coupling efficiency can be achieved, even if the wavelengths of tap light and transmitted light are changed.

The grating portion <NUM> described in the first embodiment has a structure and a wavelength in which two modes propagate. On the other hand, in the wavelength range in which the LP11 mode does not propagate, the refractive index of the core of the entire grating portion <NUM> can be changed (raised) by femtosecond laser processing, for example, so that the LP11 mode can propagate in the grating portion <NUM>.

In the case described herein, the refractive index of the core of the entire grating portion <NUM> is made higher than the refractive index of the core <NUM> at other portions, and light including the LP11 mode excited by the grating portion <NUM> enters the tap portion <NUM>. <FIG> is a graph for explaining the α dependence of the efficiency of coupling of light of the LP11 mode (of a wavelength of <NUM>) to the tap waveguide <NUM> in this case. The dot-and-dash line, the dashed line, the dotted line, and the solid line in <FIG> indicate the data obtained when dt/dc = <NUM>, <NUM>, <NUM>, and <NUM>, respectively. Further, the respective parameters are dc = <NUM>, Δcore = <NUM>%, α = <NUM>, dt = <NUM>, and δn/(ncore - nclad) = <NUM>.

As can be seen from <FIG>, when the refractive index of the core is increased in the optical fiber portion at the stage before the tap portion <NUM>, and the LP11 mode is excited in the portion, the LP11 mode light can be selectively coupled to the tap waveguide <NUM>, even if the tap portion <NUM> is a structure that does not transmit the LP11 mode light.

<FIG> is diagrams for explaining methods for forming the grating portion <NUM>. <FIG> is a diagram for explaining a pressing method (Non Patent Literature <NUM>) by which a jig <NUM> is pressed against the optical fiber <NUM> from outside the optical fiber <NUM>. <FIG> is a diagram for explaining an ultrasonic method (Non Patent Literature <NUM>) by which ultrasonic waves <NUM> are emitted from outside the optical fiber <NUM>, and an acousto-optical effect is used.

The grating pitch of the grating portion <NUM> can be adjusted with the amount of pressing or the pitch of the jig <NUM> in the case of the pressing method, and with the intensity or the frequency of the ultrasonic waves <NUM> in the case of the ultrasonic method. Accordingly, by the methods as illustrated in <FIG>, the coupling amount and the extraction wavelength can be controlled from outside. Further, by the pressing method, it is not necessary to remove the coating of the optical fiber <NUM>, and thus, the influence on the core wire can be minimized.

<FIG> is a diagram for explaining an optical side input/output circuit <NUM> according to this embodiment. The optical side input/output circuit <NUM> differs from the optical side input/output circuit <NUM> described in the first embodiment, in that a plurality of sets of the tap portion <NUM> and the grating portion <NUM> is continuously arranged in the optical fiber <NUM>. In the optical side input/output circuit <NUM>, a plurality of the sets is arranged in the light propagation direction, so that path control or multistage optical power feeding can be performed at any desired location in the transmission path.

<FIG> is a diagram for explaining an optical side input/output circuit <NUM> according to this embodiment. The optical side input/output circuit <NUM> is the same as the optical side input/output circuit <NUM> described in the fourth embodiment, except for further including light receivers <NUM> that are disposed on the side surface of the optical fiber <NUM> and receive light that is output from the tap portions <NUM>. As illustrated in <FIG>, the light receivers <NUM> are attached to the side surface of the optical fiber <NUM>, so that tap light can be received. The optical side input/output circuit <NUM> can be an optical feed system that can convert tap light into electricity, and supply the electricity to each terminal of a large number of sensor terminals, for example.

<FIG> and <FIG> are diagrams for explaining an optical connector <NUM> of this embodiment. The optical connector <NUM> includes an optical side input/output circuit <NUM>. The optical side input/output circuit <NUM> is the same as the optical side input/output circuit <NUM> described in the first embodiment, except for further including a light receiver <NUM> that is disposed on the side surface of the optical fiber <NUM> and receives light that is output from the tap portions <NUM>. Although the plurality of light receivers <NUM> is provided in the fifth embodiment, this embodiment is an example in which one light receiver <NUM> is provided. Reference numeral <NUM> indicates the coating of the optical fiber <NUM>.

The optical connector <NUM> includes a ferrule <NUM> that houses the optical side input/output circuit <NUM>, and a connector plug <NUM> that serves to connect to another optical connector. The shape of the connector plug <NUM> is of SC type, FC type, LC type, MPO type, or the like, which is widely used. By inserting the optical side input/output circuit <NUM> into the optical connector <NUM>, it is possible to easily connect to another optical fiber 50a, and realize optical side inputs/outputs from the optical fiber <NUM>.

The optical side input/output circuits and the optical connector described in the first to sixth embodiments can output only a desired wavelength from a side surface of a fiber by selectively coupling only a higher-order mode to the tap portion, using a difference in the amount of coupling to the tap portion between modes in the tap portion.

Claim 1:
An optical side input/output circuit comprising:
a tap portion (<NUM>) in which a tap waveguide (<NUM>) that outputs light of a higher-order mode from a side surface of an optical fiber (<NUM>, 50a) is formed, the light of the higher-order mode being of light propagating in a core (<NUM>) of the optical fiber (<NUM>, 50a); and
a grating portion (<NUM>) that is located in a stage before the tap portion (<NUM>) in a propagation direction of the light, and has a grating that converts light of a desired wavelength from a basic mode to the higher-order mode, the grating being formed in the core (<NUM>) of the optical fiber (<NUM>, 50a).