JP2009258757A - Optical monitor, and optical monitor array and optical system using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical monitor for bidirectional communication including an optical fiber and having a low insertion loss and high light receiving efficiency with a reduced size, and an optical monitor array and an optical system using the same. <P>SOLUTION: The optical monitor configured to receive a first light propagating in one direction within a core of the optical fiber by a first optical detector and receive a part of a second light propagating in a direction reverse to the first light within the core has a substituted area in which a part of the clad of the optical fiber is substituted by a substituting material having a refractive index more than the refractive index of the core in a cutout shape. The center of a light receiving element of the first optical detector is located forward in the advancing direction of the first light propagating in the core from the optical fiber longitudinal center of the substituted area, and the center of a light receiving element of the second optical detector is located forward in the advancing direction of the second light propagating in the core from the optical fiber longitudinal center of the substituted area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical monitor for bidirectional communication used for monitoring an optical signal or optical power in an optical communication system or an optical power transmission system.

  In optical communication systems and optical power transmission systems, it is necessary to monitor the operating status of these systems. More specifically, the monitoring of the optical power level in an optical signal processor such as an optical amplifier (amplifier), optical attenuator (attenuator), optical gain equalizer (amplifier / attenuator), and switching path in an optical switching device It is necessary to confirm.

  A simple configuration that realizes such a requirement is that after the incident communication light is branched into the outgoing communication light and the monitor light by an optical multiplexer / demultiplexer such as an optical fiber coupler, a light receiving element is placed at the end of the optical fiber that propagates the monitor light. It is the structure which monitors communication light by arrange | positioning. However, with such a configuration, it is difficult to answer the demand for miniaturization of the optical monitor.

  In response to the demand for miniaturization, for example, Patent Document 1 discloses the following optical waveguide device. A discontinuous portion such as a notch (groove) is provided in the direction perpendicular to the optical waveguide direction on the upper portion of the optical waveguide platform on which the optical waveguide is formed, and a photodetector is mounted so as to cover the groove. A part of the signal light extracted from the light discontinuous portion of the optical waveguide is detected by the light receiving element of the photodetector. As an example of a method for extracting signal light from the optical discontinuous portion of the optical waveguide, a groove is formed in the cladding layer to expose the core layer, or a dielectric material having a high refractive index is loaded in the groove so that a part of the signal light is extracted. The method of taking out as a leaky wave is shown.

  Regarding the optical fiber device, Patent Document 2 discloses the following configuration. With a portion of the cladding protruding from one surface of the substrate, the protruding portion of the optical fiber held curved is shaved and removed to form an optical coupling plane. By disposing a high refractive index layer on the optical coupling plane, a part of the optical signal propagating through the core is leaked to the photodetector for monitoring.

JP 2001-13339 A US Pat. No. 6,744,494

  Since the optical communication network is composed of optical fibers, the optical waveguide device tends to have a large loss when connected to the optical communication network, as compared to the optical fiber device. In the above conventional example, the extracted light is not necessarily received efficiently. For example, in a configuration in which a gap layer is present in front of the light receiving element, there is a problem in that it is difficult to receive light efficiently because light extracted from the core is difficult to propagate. Further, in the configuration in which the groove is provided in the core layer itself, the loss increases.

  Further, in the configuration disclosed in Patent Document 2, an optical coupling plane is formed by scraping and removing a part of a curved optical fiber, so that the optical coupling plane that determines the amount of optical signal extraction can be freely formed. The degree is limited by how the optical fiber is bent. Therefore, there is a case where the optimum shape cannot be processed. Specifically, when processing the optical fiber deep in the depth direction to the vicinity of the core and shortening in the length direction, it is necessary to reduce the bending radius of the optical fiber, which is difficult to process. As a result, there is a concern that low insertion loss and high light receiving efficiency may become insufficient when manufacturing an optical monitor. Furthermore, since the optical fiber requires a certain curvature, it is disadvantageous for miniaturization. In addition, in the three-dimensional configuration in which the optical fiber or the substrate on which the optical fiber is fixed and the light receiving element have a certain inclination, the difficulty in controlling the inclination may deteriorate the characteristics.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a small-sized, low insertion loss and high light-receiving efficiency optical monitor configured with an optical fiber, and an optical monitor array and an optical system using the optical monitor. Objective.

  [1] In the present invention, a part of the first light propagating in one direction through the core of the optical fiber is a first photodetector, and the second is propagated in the direction opposite to the first light through the core. In an optical monitor in which part of the light is received by the second photodetector, the optical fiber has a replacement region in which a part of the cladding of the optical fiber is replaced with a replacement material having a refractive index equal to or higher than the refractive index of the core. And the center of the light receiving element of the first photodetector is located on the front side in the traveling direction of the first light propagating through the core with respect to the longitudinal center of the replacement region, and the second light The center of the light receiving element of the detector is located on the front side in the traveling direction of the second light propagating through the core from the center of the replacement region in the longitudinal direction of the optical fiber. With this configuration, light leaked in the replacement region of the optical fiber cladding can be efficiently detected by the light receiving element. Therefore, the optical fiber is a compact, low insertion loss and high light receiving efficiency light for bidirectional communication. A monitor can be realized.

  [2] Further, the present invention provides the above [1], wherein a gap between any one of the photodetectors and the optical fiber is filled with a filling material having a refractive index equal to or higher than a refractive index of a clad. It is an optical monitor of description. With this configuration, light leaked from the optical fiber can be efficiently guided to the light receiving element, and the light receiving efficiency of the optical monitor can be further improved.

  [3] Further, the present invention provides the above [1] to [2], wherein the replacement region has a bottom portion having a distance of more than 0 μm and not more than 3 μm as a portion closest to the core. The optical monitor according to any one of the above. With this configuration, it is possible to further reduce the loss of the optical monitor.

[4] The present invention is, with respect to the refractive index n _c of the core and the refractive index n _o of the replacement material,
Δn = (n _o −n _c ) / n _c × 100 [%]
The refractive index difference ratio Δn defined by is 0.65% or more,
The [Delta] n, the longitudinal length L _a of the optical fiber of the bottom portion of the optical fiber longitudinal length L ₀ and the light receiving element of the one of the optical detectors,
0.024 × Δn + 0.21 ≦ L ₀ / L _a ≦ 0.081 × Δn + 0.29
The optical monitor according to [3], characterized in that: With this configuration, an optical monitor excellent in the balance between low insertion loss and high light receiving rate can be realized.

[5] Further, in the present invention, an angle θ [] formed by a straight line connecting the center of the bottom optical fiber in the longitudinal direction and the center of the light receiving element of any one of the photodetectors in the longitudinal direction of the optical fiber and the extending direction of the core. °] it is, with respect to the refractive index n _c of the core and the refractive index n _o of the replacement material,
Δn = (n _o −n _c ) / n _c × 100 [%]
For the refractive index difference ratio Δn defined by
1.13 × Δn + 5.5 ≦ θ ≦ 1.13 × Δn + 11
The optical monitor according to any one of [3] to [4], wherein With this configuration, it is possible to realize a small, low insertion loss and high light receiving efficiency optical monitor with excellent light receiving efficiency.

[6] In the present invention, it is preferable that the replacement region has an inclined surface inclined with respect to the core extending direction on the front side in the traveling direction of any light propagating through the core. An optical monitor according to any one of the above. According to this configuration, since the leaked light from the core is reflected by the inclined surface, it is efficiently received by the light receiving element. In particular, it is effective when the refractive index n _o of the replacement material replacement region is small. For example, it is preferable that n _o is providing the inclined surface is less than 0.65. With this configuration, it is possible to realize a small, low insertion loss and high light receiving efficiency optical monitor with excellent light receiving efficiency.

  [7] Further, the present invention is the optical monitor according to [6], wherein an angle formed between the inclined surface and the extending direction of the core is 3 ° or more and 8 ° or less. With such a configuration, it is possible to improve the light receiving efficiency, and an optical monitor with a small size, a low insertion loss, and a high light receiving efficiency can be realized.

  [8] The present invention is an optical monitor array using two or more optical monitors according to any one of [1] to [7]. With such a configuration, it is possible to provide a small, low insertion loss and high light receiving efficiency optical monitor array composed of optical fibers.

  [9] In the present invention, the optical monitor according to any one of [1] to [7] is connected to an optical fiber for optical transmission, and the intensity of an optical signal propagated through the optical fiber is detected. Is an optical system characterized by With this configuration, it is possible to reduce the size and loss of the entire optical system.

  According to the present invention, it is possible to realize a small-sized, low insertion loss and high light-receiving efficiency optical monitor configured for optical communication, an optical monitor array and an optical system using the optical monitor.

It is the schematic which shows the 1st structural example of the optical monitor of this invention. It is the schematic which shows the 2nd example of the cross-sectional shape of the replacement area | region of the optical monitor of this invention. Of the distance g between the bottom and the core when the parameter is a diagram showing the relationship between the bottom length L ₀ and the insertion loss IL. FIG. 5 is a diagram showing a relationship between _a ratio L ₀ / L _{a of a} bottom length L _{0 to} a length La of _a light receiving element and a refractive index difference ratio Δn. It is the example which changed the notch shape in this invention. In this invention which changed notch shape, it is a figure which shows the relationship between angle (theta) ₂ of an inclination part, and insertion loss IL. In this invention, it is a figure which shows the relationship (a) of refractive index difference ratio (DELTA) n and the angle (theta) of an optimal light receiving element position, and the relationship (b) of deviation (DELTA) (theta) from an optimal light receiving element position, and normalized light reception power. It is the schematic which shows the 2nd structural example of the optical monitor of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited by these Examples.

  FIG. 1 is a schematic diagram showing a first configuration example of an optical monitor according to the present invention. FIG. 1A corresponds to a cross-sectional view of the side surface of the optical monitor. FIG. 1B corresponds to a cross-sectional view taken along the line AA ′ in FIG. The optical monitor 100 of the present invention includes an optical fiber 101 and a photodetector 102. The optical fibers 101 are arranged in a straight line. The linear arrangement is advantageous for downsizing the optical monitor. The photodetector 102 is arranged such that the normal line of the light receiving surface of the light receiving element 109 of the detector is orthogonal to the axis of the optical fiber 101, that is, the light receiving surface of the light receiving element is parallel to the axis of the optical fiber. When the angle between the light receiving surface of the light receiving element and the axis of the optical fiber increases, the detector height increases. For example, when a light receiving element having a length of 1 mm is used, the angle between the light receiving surface and the optical fiber is preferably less than 10 ° in order to suppress an increase in height due to the inclination of the light receiving element to less than 0.2 mm. . More preferably, the light receiving surface of the light receiving element and the axis of the optical fiber are parallel. With this configuration, the optical monitor can be reduced in height and size, and the assembly can be simplified. Here, the optical fiber 101 may be a single-mode compatible optical fiber or a multi-mode compatible optical fiber. Alternatively, it may be a glass optical fiber or a plastic fiber. The photodetector 102 has an electrical signal terminal for detecting received light as an electrical signal on the back surface, that is, the surface where the light receiving element 109 is not disposed. However, this terminal is not shown. The optical fiber is preferably arranged on the substrate. However, illustration of the substrate is omitted. It is desirable that a groove for aligning optical fibers is formed in the substrate. In order to reduce the size of the optical monitor, it is desirable to sandwich the optical fiber between the substrate and the photodetector. The illustration of the package member including the illustrated optical monitor is also omitted.

  A part of the clad 105 of the optical fiber 101 is removed in a cutout shape to form a replacement region 106. The notch shape means that the optical monitor is configured to have a notch shape, and the replacement region is notched so that light leakage is concentrated on the portion, and the rest It is possible to prevent useless leakage from the portion. The replacement region 1006 is filled with a replacement material having a higher refractive index than the core 103. Here, since the refractive index of the cladding of the optical fiber is slightly lower than the refractive index of the core, an optical signal can be confined and propagated in the core. However, the optical signal is not confined only in the core, but part of the optical signal oozes out to the cladding around the core as evanescent light. Therefore, by replacing the cladding around the core where the evanescent light has oozed out with a replacement material having a refractive index equal to or higher than the refractive index of the core, the propagation light 104 propagating through the optical fiber is leaked to the outside of the optical fiber 108. Can be taken out as. The center in the optical fiber longitudinal direction at the bottom of the replacement region adjacent to the core is defined as the center in the optical fiber longitudinal direction of the replacement region.

  The cut-out replacement region 1006 interacts with the evanescent light portion of the propagating light 104 propagating through the core 103 to generate leaked light 108. The replacement material may be a curable material or a non-curable material. For example, it is possible to use glass, resin, oil, or a composite material thereof. It is desirable to use a liquid such as resin or oil as the replacement material because it facilitates filling of the replacement region 1006 and makes it difficult for air gaps that would otherwise interfere with light leakage and light propagation to other than the detection portion. In addition, the use of a resin that is curable with respect to heat, ultraviolet rays, or the like is that a desired shape can be maintained by replacing the replacement region in the cladding with the resin and then curing the resin. It is advantageous.

  Examples of the cross-sectional shape of the replacement region 106 in the axial direction of the optical fiber include a kamaboko type defined below and a suspicious kamaboko type. The kamaboko shape was defined as a shape that does not include the center axis of the circle when the cylinder is cut by a plane parallel to the center axis of the circle and not passing through the center of the circle. The replacement region 1006 shown in FIG. 1B is an example of a kamaboko type. At this time, the kamaboko-shaped planar portion is arranged close to the core 103. At this time, the center in the longitudinal direction of the optical fiber of the kamaboko-shaped flat portion is set as the center of the replacement region 106. The suspicious kamaboko type was defined as the shape that does not include the center axis of the circle when the cylinder is cut by a curved surface that is parallel to the center axis of the circle and does not pass through the center of the circle. At this time, the suspicious kamaboko-shaped mold has a shape in which the kamaboko-shaped plane is a curved surface. The replacement region 1006 shown in FIG. 2 is an example of a suspicious kamaboko type.

For example, various wet etching processes and dry etching processes can be used to remove the cladding in the replacement region. An example of an etchant in wet etching is ammonium fluoride (NH ₄ F), and an example of an etchant in dry etching is CF ₄ or SF ₄ . In either case, a portion that is not desired to be etched is masked with a protective material, and only a necessary portion is removed by etching. By performing etching under appropriate conditions, processing with excellent dimensional accuracy can be realized. Alternatively, the cladding in the replacement region may be removed by precision machining such as dicing.

  It is preferable for the light receiving element 109 to receive as much leakage light 108 as possible, and it is desirable to receive all of the light. Actually, by increasing the surface area of the light receiving element 109, the leaked light 108 that can be received can be increased. However, when the area of the light receiving element 109 is increased, the dark current of the light receiving element 109 increases. An increase in dark current is undesirable because it adversely affects the measurement accuracy of received light power. For this reason, the area of the light receiving element 109 should be as small as possible.

  In order to increase the light receiving power without increasing the size of the light receiving element 109, the light receiving element 109 may be disposed at the propagation position of the leakage light 108. As a result of the examination, it was found that the leaked light 108 propagates gradually away from the core 103 as shown in FIG. Although not shown, it has been found that when the propagation light 108 reaches the interface between the replacement region 1006 and the clad 105, it is transmitted through the interface and hardly propagates with almost no change in the propagation direction. Therefore, the propagation position of the propagation light 108 outside the optical fiber is located in front of the center position of the replacement region in the longitudinal direction of the optical fiber, and may be located in front of the end portion of the replacement region 1006. In accordance with this, the center of the light receiving element 109 is located in front of the center position of the replacement region in the longitudinal direction of the optical fiber, and in some cases, in front of the end of the propagation region 1006. It can receive light.

  The light receiving element 109 of the photodetector 102 is preferably installed as close to the optical fiber 101 as possible, more preferably in contact with the optical fiber 101 or the replacement region. The gap between the light receiving element 109 of the photodetector 102 and the optical fiber 101 is preferably filled with a filling material 114 having a refractive index equal to or higher than the refractive index of the clad 105. When the leakage light 108 propagates from a material having a high refractive index to a material having a low refractive index, a large amount of reflection is caused, so that the optical power received by the light receiving element is reduced. However, by filling the gap between the light receiving element 109 of the photodetector 102 and the optical fiber 101 with the filling material 114 having a refractive index higher than the refractive index of the clad 105, the propagation path of the leaked light 108 has a gap or extremely There is no material having a low refractive index, and the light receiving element 109 can obtain high light receiving efficiency.

  The filling material 114 is preferably made of the same material as the replacement material. By making the filling material 114 and the replacement material the same, the number of materials can be reduced and the process can be simplified. As another desirable form, the optical fiber 101 and the photodetector 102 are bonded and fixed using the filling material 114, which is advantageous in simplifying the process. More desirably, the filling material 114 is made of the same material as the replacement material, and the optical fiber 101 and the photodetector 102 are bonded and fixed using the filling material. As a result, unnecessary reflection and scattering can be prevented, and the number of materials can be reduced and further processes can be simplified.

  In order to improve the light receiving efficiency, it is desirable to reduce the thickness of the material 114 filled in the gap between the optical fiber 101 and the light receiving element 109 of the photodetector so that the photodetector 102 is as close to the optical fiber 101 as possible. . If the filling material 114 is made thinner, the filling material 114 can suppress the loss of the leaked light 108 due to absorption / scattering and the like, and the light receiving element 109 can receive stronger leaked light. At this time, the photodetector 102 and the optical fiber 101 may contact each other.

Hereinafter, suitable dimensions of the optical monitor will be described. The optical monitor is required to monitor the signal light with high accuracy without affecting the signal light propagating through the core as much as possible. This requirement can be expressed by the insertion loss IL and the light receiving efficiency R. The insertion loss IL is a parameter representing the loss of the propagation light 104. In general, the larger the leakage light 108, the larger the insertion loss IL. The light receiving efficiency R is a parameter indicating how efficiently the leaked light can be received by the light receiving element 109. The closer to 1, the higher the efficiency. Assuming that the input optical power to the device is P _in , the output optical power from the device is P _out , the leakage light power is P _leak , and the received light power is _Prec , both are expressed by the following equations.
IL = −10 log (P _out / P _in ) = − 10 log ((P _in −P _leak ) / P _in )
R = P _rec / P _leak
If the insertion loss IL is large, the loss of the propagation light 104 propagating through the core 103 is large, which is not desirable. On the other hand, if the insertion loss IL is too small, the leakage light 108 is also reduced, and the light receiving power at the light receiving element 109 is lowered, which is not desirable because the monitoring accuracy is lowered. It is desirable to increase the light receiving efficiency R as much as possible. When expressed quantitatively, 0.3 ≦ IL ≦ 1.0 dB and 0.8 ≦ R
Is desirable.

The partial substitution region is closest to the core and the bottom, and a bottom length L ₀ of the optical fiber length in the longitudinal direction of the bottom. First, the gap g between the bottom and the core will be described. 3 to the distance g between the bottom and the core 103 when a parameter, indicating a bottom length L ₀ of the relationship between insertion loss IL. Here, if the bottom length L ₀ is less than 50 μm, it is difficult to ensure the processing accuracy, and if it exceeds 400 μm, there may be a problem in securing the strength during processing. Therefore, the bottom length L ₀ is preferably 50 to 400 μm. With respect to the bottom length L ₀ in this range, the distance g between the bottom and the core is set to be more than 0 μm and not more than 3 μm, and 0.3 ≦ IL ≦ 1 which is a condition for ensuring the light receiving ability and realizing the low insertion loss. 0.0 [dB] is obtained. More preferably, the gap g between the bottom and the core is 1 μm or more and 2 μm or less.

Then the ratio L ₀ / L _a bottom length L ₀ with respect to the optical fiber longitudinal length L _a of the light receiving element 109, the refractive index difference ratio Δn of the replacement material and the core is described. Here the refractive index difference ratio Δn is defined by the following equation refractive index of the replacement region n _o, a refractive index of the core as n _c.
Δn = (n _o −n _c ) / n _c × 100 [%]
4 shows the length of the light receiving element 109 that realizes 0.3 ≦ IL ≦ 1.0 dB and 0.8 ≦ R with respect to the insertion loss IL and the light receiving efficiency R when the gap g between the bottom and the core is 1 μm and 2 μm. It is showing the relationship between the specific L ₀ / La and the refractive index difference ratio Δn of the bottom length L _o for L _a. In the points indicated by ◯ in the figure, both low insertion loss and high light receiving efficiency are achieved in both cases where the gap g between the bottom and the core is 1 μm and 2 μm. In the region indicated by x in the figure, low insertion loss and high light receiving efficiency are not compatible in at least one of cases where the gap g between the bottom and the core is 1 μm and 2 μm. Detailed values of each point are shown in Table 1.

A region in which 0.3 ≦ IL ≦ 1.0 dB and 0.8 ≦ R, which is a desirable relationship between the insertion loss IL and the light receiving efficiency R, can be expressed by the following equations (1) and (2).
0.024 × Δn + 0.21 ≦ L ₀ / L _a ≦ 0.081 × Δn + 0.29 (1)
0.65 ≦ Δn ―――――――――――――――――――――――――― (2)
Therefore, by selecting Δn and L ₀ / La within a range satisfying the relationship of the expressions (1) and (2), an optical monitor with low insertion loss and high light receiving efficiency can be realized. Although there is no particular limitation on the upper limit of Δn, Δn is 17% or less when a realistic material is selected.

  By the way, when Δn takes a positive value close to 0%, the angle when the leaked light 108 moves away from the core 103 becomes small. For this reason, the deviation angle between the propagation direction of the leaked light 108 and the normal direction of the light receiving surface of the light receiving element 109 increases. This corresponds to the spread of the leaked light 108 for the light receiving element 109. Therefore, when Δn takes a positive value close to 0%, specifically, when Δn is less than 0.65% as shown in FIG. 4, it is difficult to achieve high light receiving efficiency. At this time, if the light receiving element 109 is enlarged in order to sufficiently receive the leaked light 108, the dark current increases and adversely affects the measurement accuracy of the received light power. Further, another factor that makes it difficult to achieve high light receiving efficiency is that if the angle at which the leaked light 108 moves away from the core 103 is small, the leaked light propagates through the substitution region 106 and then passes through the cladding 105 in front of the substitution region 106. Propagated, and then passes through the filling material 114 toward the light receiving element 109. At this time, since the incident angle when the leaked light 108 propagates from the clad 105 to the filling material 114 is also reduced, the leaked light 108 is partially reflected at the interface between the clad 105 and the filling material 114.

On the other hand, it has been found that the light receiving efficiency can be improved by changing the shape of the replacement region. That is, an inclined surface inclined with respect to the core extending direction is provided on the front side in the traveling direction of the core propagation light in the replacement region, and the leaked light is converged by reflecting the leaked light on the inclined surface, so that the light receiving efficiency Can be improved. FIG. 5 shows an example of a structure in which an inclined surface is provided in front of the kamaboko type replacement region. The interval between the inclined surface 216 and the core 103 gradually increases as it goes to the front side in the traveling direction of the core propagation light. At this time, a part of the leakage light 108 is reflected by the inclined surface 216 and then received by the light receiving element 109. FIG. 6 shows the relationship between the angle θ2 formed by the inclined surface 216 and the core 103, the insertion loss IL, and the light receiving efficiency R. This is an example when Δn = 0.27%, L ₀ / L _a = 1/3, and g = 1 μm. By appropriately selecting the angle θ2 formed by the inclined surface and the core 103, it is possible to improve the light receiving efficiency without greatly reducing the insertion loss. When the angle θ2 formed by the inclined surface and the core 103 is in the range of 3 ° or more and 8 ° or less, the light receiving efficiency 1.6 times or more can be obtained as compared with the case where the inclined portion is not provided.

As described above, the leakage light 108 can be efficiently received by setting the center of the light receiving element 109 forward of the center position of the replacement region in the longitudinal direction of the optical fiber. More desirably, the light receiving element 109 is disposed at a position where the light receiving efficiency R is maximized. The position of the light receiving element at this time is defined as the optimum position. FIG. 7A shows the refractive index difference ratio Δn and the angle formed by the core 103 and the straight line connecting the center of the optical fiber in the longitudinal direction of the bottom and the center 112 of the light receiving element when the light receiving element 109 is disposed at the optimum position. It shows the relationship with θ (θ is an angle from the light propagation direction in the core extending direction). From the figure, between the refractive index difference ratio Δn and the angle θ [°] of the optimum light receiving element position, θ = 1.13 × Δn + 6.5.
It was found that there is a relationship.

FIG. 7B shows the light receiving power with respect to the shift Δθ [°] from the angle θ of the optimum light receiving element position, normalized by the light receiving power at the angle of the optimum light receiving element position. In order to maintain high light receiving efficiency, it is desirable that the normalized light receiving power shown in FIG. More desirably, it is 0.95 or more. By setting Δθ to a value in the range of −1 ° or more and + 4.5 ° or less, the normalized light receiving power of 0.9 or more can be realized. More desirably, by setting Δθ to a value in the range of −1 ° or more and + 3 ° or less, the normalized light receiving power of 0.95 or more can be realized. That is, from FIGS. 7A and 7B, the angle θ [°] formed by the core 103 and the straight line connecting the center in the longitudinal direction of the optical fiber and the center 112 of the light receiving element with respect to the refractive index difference ratio Δn. 1.13 × Δn + 5.5 ≦ θ ≦ 1.13 × Δn + 11
Is desirable. By installing the light receiving element at a position where θ is within this range, 0.9 or more can be realized for the standardized light receiving power. More preferably, the angle θ [°] is set to 1.13 × Δn + 5.5 ≦ θ ≦ 1.13 × Δn + 9.5 with respect to the refractive index difference ratio Δn.
By setting the value in the range, 0.95 or more can be realized for the standardized light receiving power.

  FIG. 8 is a schematic diagram showing a second configuration example of the optical monitor of the present invention. FIG. 8 corresponds to a cross-sectional view of the side of the optical monitor. The optical monitor of the present invention is characterized in that a second light receiving element 109B is provided for the optical monitor of the first configuration example shown in FIG. Therefore, the optical monitor of the configuration example shown in FIG. 8 generates the leaked lights 108A and 108B independently from the propagation lights 104A and 104B propagating in one optical fiber 101 in both directions, and independently receives the light receiving elements 109A. , 109B. Other symbols in FIG. 8 indicate the same contents as in FIG. Further, in FIG. 8, as in FIG. 1, an electrical signal terminal for detecting received light as an electrical signal on the back surface of the photodetector 102, that is, the surface where the light receiving element 109 is not arranged, is illustrated. Not shown. Also, the illustration of the package member that includes the illustrated optical monitor is omitted.

Between the elements constituting the optical monitor of the configuration, or spacing g between the bottom and the core 103, the ratio of the bottom length L ₀ to the length L _a of the light receiving element, the refractive index difference ratio Δn of replacement material and the core 103 The angle θ [°] formed by the core 103 and the line connecting the center of the light receiving element and the center 112 of the bottom is preferably the same as the relationship described in the first configuration example. That is, the angle between the core and the straight line connecting the center in the longitudinal direction of the optical fiber at the bottom and the center of the second light receiving element 109B is the angle from the core extending direction opposite to the case of the first light receiving element. is there. Further, a material example and a manufacturing method example may be the same as those of the first structure example. In the second configuration example, a bidirectional light monitor having a small size, a low insertion loss, and a high light receiving efficiency can be realized by providing the second light receiving element to the first configuration example. The optical monitor of this configuration can also be configured with an optical monitor having an inclined surface 216. In this case, inclined surfaces are respectively formed in front and rear of the replacement region 106.

  The optical monitor array of the present invention is configured by using two or more optical monitors of the present invention. Since the optical monitor used in the present invention has a low loss, even when a large number of optical monitors are used, the loss due to the detection of the light intensity is small, so that a low-loss monitor array can be provided. Further, since the optical monitor to be configured can be downsized without requiring the bending of the optical fiber, a plurality of the optical monitors can be used to form an array, thereby forming a small array as a whole. For example, when wavelength multiplexed signals are demultiplexed by a demultiplexer and an optical monitor is provided for each wavelength signal, a plurality of optical monitors are arranged in parallel so that their longitudinal directions are substantially parallel to each other in the package. It is good also as an optical monitor which has two or more sets of input / output by accommodating. Further, the parallel arrangement may be arranged so that adjacent optical monitors have the same direction, or can be arranged in parallel so that they are alternately reversed.

  An optical system using the optical monitor of the present invention is configured by connecting the optical monitor of the present invention to an optical fiber for light propagation, and monitors the intensity of an optical signal propagated through the optical fiber. According to the present invention, an optical system having a small size, a low insertion loss, and a high light receiving efficiency can be provided by using the optical monitor. For example, in an optical signal processor such as an optical amplifier (amplifier), an optical attenuator (attenuator), an optical gain equalizer (amplifier / attenuator), the output side of the optical signal processor, and in some cases, the input side Then, an optical monitor is installed, and the operation of the optical signal processor, for example, the amplification factor and attenuation amount is confirmed, and the optical system is configured to feed back to the signal processor.

  As another example of an optical system, for example, in an optical switching device, an optical monitor is installed in the output side path of the optical switching device, and in some cases also in the input side path, and the operation of the optical switching device, for example, switching is performed. It is configured as an optical system that confirms the maintenance of a route and an appropriate route switching state and feeds back to the optical switching device.

  By combining the optical monitor of the present invention with these or other optical signal processors and optical switching devices, the optical monitor portion of the optical system can be reduced in size, so that the overall optical system can be reduced in size. At the same time, the system can be provided with an optical monitoring function with low insertion loss and high light receiving efficiency.

(Example 1)
A specific configuration example of the present invention is shown below. The basic configuration is the same as that shown in FIG. 1 and will be described with reference to FIG. The optical fiber 101 is a single-mode optical fiber having a clad 105 diameter of 125 μm and a core 103 diameter of 9 μm. The photodetector 102 uses a photodiode having a light receiving element 109 of 300 μm in diameter and a light receiving sensitivity of 1000 mA / W. Replacement area 106 formed by removing the cladding by wet etching using an etchant of ammonium fluoride (NH 4 _F), and its bottom length L ₀ is 150 [mu] m, i.e. 0.5 times the light receiving element length L _a, The gap g between the core and the bottom is 2 μm. In the replacement region 1006, an ultraviolet curable resin having a refractive index difference ratio Δn with respect to the core of 5.08% is replaced as a replacement material. The refractive index difference ratio Δn of the resin is a refractive index difference ratio after the resin is cured. After the application of the resin, the photodetector 102 is arranged so that the light receiving element center 110 is positioned 233 μm ahead of the center of the bottom. At this time, an angle θ between the straight line connecting the center of the bottom and the center 110 of the light receiving element and the core is 13.5 °. The light receiving element 109 and the optical fiber 101 are brought into contact with each other through the resin. At this time, although the light receiving element 109 and the optical fiber 101 are in line contact geometrically, as shown in FIG. 1B and FIG. 2, the resin is applied so that the resin spreads to the portion not in line contact. Then, the resin is cured. In the optical monitor 100 of this configuration example, the insertion loss is 0.4 dB for light having a wavelength of 1550 nm, the light receiving efficiency is R = 0.85, and the output of the photodetector is 69 mA / W.

(Example 2)
Another specific configuration example of the present invention is shown below. The basic configuration is the same as that shown in FIG. 8 and will be described with reference to FIG. The optical fiber and the light receiving element are the same as those in the first embodiment. Replacement area 106 formed by removing the cladding by dry etching using an etchant of CF _4, and its bottom length L ₀ is 170 [mu] m, i.e. 0.57 times the light receiving element length L _a, the interval between the core and the bottom g is 1.5 μm. The replacement region 106 is replaced with an ultraviolet curable resin having a refractive index difference ratio Δn with the core of 4.40% as a replacement material. After the application of the resin, the photodetectors 102 are arranged so that the centers 110A and 110B of the two light receiving elements are located 231 μm forward and backward from the center of the bottom, respectively. At this time, the angle θ formed between each straight line connecting the center of the bottom and the centers 110A and 110B of the light receiving element and the core is 13.7 °. The light receiving element 109 and the optical fiber 101 are brought into contact with each other through the resin. At this time, although the light receiving element 109 and the optical fiber 101 are in line contact geometrically, as in the first embodiment, the resin is applied so that the resin spreads over the portion that is not in line contact, and then the resin is cured. . In the optical monitor of this configuration example, the insertion loss was 0.6 dB with respect to light having a wavelength of 1550 nm, the light receiving efficiency was R = 0.85, and the output of the photodetector was 110 mA / W. For light with a wavelength of 1300 nm propagating in the reverse direction, the insertion loss was 0.4 dB, the light receiving efficiency was R = 0.9, and the output of the photodetector was 74 mA / W.

100, 200: optical monitor,
101: Optical fiber,
102: photodetector
103: Core,
104, 104A, 104B: propagating light,
105: cladding,
106: replacement region,
g: Space between core and bottom 108, 108A, 108B: Leakage light,
109, 109A, 109B: light receiving elements,
110, 110A, 110B: the center of the light receiving element,
L ₀ : bottom length,
112: the center of the bottom,
L _a , L _a A, L _a B: length of light receiving element,
114: Filling material,
216: Inclined surface

Claims (9)

Part of the first light propagating in one direction through the core of the optical fiber is the first photodetector, and part of the second light propagating through the core in the opposite direction to the first light is the second. In the optical monitor for receiving light by the photodetector, the first light has a replacement region in which a part of the cladding of the optical fiber is replaced with a replacement material having a refractive index equal to or higher than the refractive index of the core. The center of the light receiving element of the detector is located on the front side in the traveling direction of the first light propagating through the core from the center of the replacement region in the longitudinal direction of the optical fiber, and the center of the light receiving element of the second light detector Is located on the front side in the traveling direction of the second light propagating through the core from the center of the replacement region in the longitudinal direction of the optical fiber. 2. The optical monitor according to claim 1, wherein a gap between any one of the photodetectors and the optical fiber is filled with a filling material having a refractive index equal to or higher than a refractive index of a clad. 3. The optical monitor according to claim 1, wherein the replacement region has a bottom portion having a distance of more than 0 μm and not more than 3 μm as a portion closest to the core. 4. Relative refractive index n _c of the core and the refractive index n _o of the replacement material,
Δn = (n _o −n _c ) / n _c × 100 [%]
The refractive index difference ratio Δn defined by is 0.65% or more, the Δn, the length L _{0 of the} bottom optical fiber in the longitudinal direction, and the longitudinal direction of the optical fiber of the light receiving element of any one of the photodetectors of a length _{L a} is,
0.024 × Δn + 0.21 ≦ L ₀ / L _a ≦ 0.081 × Δn + 0.29
The optical monitor according to claim 3, wherein: An angle θ [°] formed by a straight line connecting the center of the bottom optical fiber in the longitudinal direction and the center of the optical fiber longitudinal direction of the light receiving element of any one of the photodetectors and the extending direction of the core is determined by the replacement material. relative refractive index _{n c} of the core and the refractive index _{n o,}
Δn = (n _o −n _c ) / n _c × 100 [%]
For the refractive index difference ratio Δn defined by
1.13 × Δn + 5.5 ≦ θ ≦ 1.13 × Δn + 11
The optical monitor according to claim 3, wherein the optical monitor is an optical monitor. The optical monitor according to claim 1, wherein the replacement region has an inclined surface that is inclined with respect to a core extending direction on a front side in a traveling direction of any light propagating through the core. The optical monitor according to claim 6, wherein an angle formed by the inclined surface and the extending direction of the core is 3 ° or more and 8 ° or less. An optical monitor array comprising two or more optical monitors according to claim 1. An optical system comprising: connecting the optical monitor according to claim 1 to an optical fiber for optical transmission; and detecting an intensity of an optical signal propagated through the optical fiber.

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