JP4839691B2 - Optical device, optical branching device, and optical wavelength multiplexer / demultiplexer - Google Patents

Description

  The present invention relates to an optical element that can split input light into a plurality of branched lights of equal intensity, and an optical branching element and an optical wavelength multiplexer / demultiplexer using the optical element.

  In optical communication, an optical branching element that branches one or more input lights into a plurality of outputs is used.

  As an optical branching element employing an optical waveguide structure, three types are widely known. The following outlines each format.

  In the first type, Y branch waveguides are connected to V stages (V is an integer of 1 or more) in a binary tree shape. This type of optical branching element is applied to a connection between a station and each subscriber in an optical communication network, a so-called subscriber system.

This type of optical branching element has the advantage that there is little variation in the intensity of each branched light extracted by the V-stage Y branching waveguide (outgoing side branching waveguide) which is the final stage. However, due to the structure in which the Y branching waveguides are connected in multiple stages, this type of optical branching device has the following problems.
(1) Bad characteristics (such as loss of branch light intensity) are likely to accumulate in each Y branch waveguide.
(2) Since the number of Y branch waveguides (= 2 ^V −1) increases according to the number of branched lights to be taken out, that is, the number of branch waveguides on the output side (= 2 ^V ), a large number of branches on the output side When the waveguide is provided, the structure of the optical branching element becomes complicated.
(3) If the loss of light at the branch point is reduced by narrowing the branch angle of the Y branch waveguide, the total length of each Y branch waveguide increases, resulting in an increase in the size of the optical branch element.

In the second type, an incident-side waveguide is connected to one end face of a multimode waveguide, and a plurality of outgoing-side branching waveguides are provided on the other end face facing the one end face (for example, Patent Documents). 1).

  This type of optical branching element has the advantage that there is little variation in the intensity of each branched light extracted by the outgoing side branching waveguide. However, this type of optical branching element has a total length proportional to the square of the lateral width when the lateral width (the length in the direction perpendicular to the light propagation direction) is increased by providing a number of branching waveguides on the outgoing side. (Length in a direction parallel to the light propagation direction) becomes longer. As a result, there is a problem that the optical branching element is increased in size.

In the third type, the incident-side waveguide is connected to one end face of the planar waveguide, and light emitted from the planar waveguide is guided to a plurality of outgoing-side branch guides provided on the other end face facing the one end face. The light is received by the waveguide (see, for example, Patent Document 2 and Patent Document 3). This type of optical branching element is applied to an arrayed waveguide grating (hereinafter also referred to as AWG). The optical branching element of this type has an advantage that the structure is simple because only the incident side waveguide and the outgoing side branching waveguide are connected to the planar waveguide.
JP 2001-91768 A (FIG. 1) Japanese Patent Laid-Open No. 2001-13336 (FIG. 1) US Pat. No. 6,442,308 (FIG. 2)

  In the third type of optical branching element, the intensity distribution of the light emitted to the planar waveguide becomes almost Gaussian by spreading by diffraction. Therefore, in the branching waveguide on the exit side that exists in the vicinity of the peak of the Gaussian distribution, that is, in the vicinity of the intersection between the optical axis of the exiting light and the other end surface, it is possible to obtain a branched light having a high intensity. However, the intensity of the branched light is weak in the exit side branched waveguide that exists near the bottom of the Gaussian distribution, that is, at a position off the optical axis.

  Thus, the third type of optical branching element is derived from the intensity distribution of the light emitted from the outgoing side branching waveguide to the planar waveguide, and the intensity of the extracted light is increased for each outgoing side waveguide. There is a problem of variation.

  The present invention has been made in view of the problems of the above-described third type of optical branching element.

  Accordingly, a first object of the present invention is to provide an optical element in which an incident-side waveguide and a planar waveguide are connected, and an optical element that suppresses variation in intensity of light emitted to the planar waveguide. It is in.

  In addition, the second object of the present invention is to use the above-described optical element to equalize the intensity of light extracted by a plurality of output side branching waveguides, and to be compact and simple in structure. The object is to provide an optical branching element.

  A third object of the present invention is to provide an optical wavelength multiplexer / demultiplexer using the above-described optical branching element.

  The optical element according to claim 1 includes a plurality of incident-side branching waveguides branched from one incident-side waveguide, and a planar waveguide having one end face connected to the branching waveguide.

  Each of the branching waveguides causes branched light having the same phase and light intensity to enter the planar waveguide as a Gaussian beam from each of the branching waveguides, and has a positional relationship satisfying the following conditions. Connected with.

(1) First and second branches of branched light that is arbitrarily selected from the plurality of incident-side branching waveguides and sequentially propagates from the adjacent first and second branching waveguides to the planar waveguide. Light and
(2) Two points on the plane corresponding to the half value of the peak value of the light intensity of the branched light having a Gaussian distribution in a plane parallel to the surface of the planar waveguide are set as the first and second points, respectively. When the straight lines continuously connecting the first and second points along the propagation direction of the branched light are respectively the first and second half-value lines,
The first half-value line of the first branched light and the second half-value line of the second branched light are at the same position on the plane, and the second half-value line of the first branched light and the first half value of the second branched light A line is at a position spaced apart on a plane.

  According to the optical element of the first aspect, the branched lights emitted from the branched waveguide to the planar waveguide have the same phase. Therefore, the sum of the intensity distributions of any two or more branched lights is given by the simple sum of the intensity distributions of the respective branched lights.

  Consider the intensity distribution of the sum of the first and second branched light beams emitted from the first and second branched waveguides that are sequentially adjacent, that is, any two adjacent branched waveguides.

  At this time, the first half-value line of the first branched light and the second half-value line of the second branched light match, that is, they are at the same position. That is, the points which are half the intensity distributions of the first and second branched lights overlap each other. Thereby, the intensity distribution of the sum of the first and second branched lights has a region (plateau region) where the intensity is substantially constant between the peaks of both.

  In the optical element according to claim 2, when the beam divergence angle of each of the first and second branched lights is θ / 2, the crossing angle at one end face of the first and second branched waveguides is θ. It is characterized by that.

  According to the optical element of the second aspect, when the angle formed between the optical axes of the first and second branched lights and the half-value line, that is, the spread angle of the branched light is θ / 2, the first and second The first and second optical axes of the two branched light beams intersect with each other in a plane including one end face of the planar waveguide, and the angle formed by the optical axes of the first and second branched light beams is θ. A branching waveguide is disposed. Thus, the first half-value line of the first branched light and the second half-value line of the second branched light are always in the same position in the planar waveguide. In addition, the spread angle of the entire branched light in the planar waveguide can be increased.

  Here, the “optical axis” indicates a straight line obtained by continuously connecting the peak values of the light intensity distribution of the branched light along the propagation direction of the branched light. The “optical axis” is synonymous with “peak straight line” described later.

  The optical branching element according to claim 3 includes the above-described optical element, and the planar waveguide includes the other end face parallel to the one end face, and a plurality of incident side branch waveguides connected to the one end face. A plurality of exit-side branching waveguides are connected to the region of the other end surface within the reach of all the branched light beams that propagate from and reach the other end surface.

  According to the optical branching element of the third aspect, the intensity distribution of the sum of all the branched lights on the other end face has a plateau region having a constant intensity within the reach of all the branched lights. By providing the exit side waveguide within the range of the plateau region, the intensity of light incident on each of the exit side branch waveguides can be made substantially equal.

The optical element of the reference example includes a plurality of incident-side branching waveguides branched from one incident-side waveguide, and a planar waveguide having the one end face connected to the branching waveguide.

  Each of the branching waveguides causes branched light having the same phase and light intensity to enter the planar waveguide as a Gaussian beam from each of the branching waveguides, and has a positional relationship satisfying the following conditions. Connected with.

(1) The branched light that is incident on the planar waveguide from the first and second branched waveguides adjacent to each other and propagates is defined as the first and second branched lights,
(2) The two points on the plane corresponding to the half value of the peak value of the light intensity of the branched light having a Gaussian distribution in the plane parallel to the surface of the planar waveguide are defined as the first and second points, respectively.
(3) The straight lines that continuously connect the first and second points along the propagation direction of the branched light are respectively defined as first and second half-value lines,
(4) When a point on the plane corresponding to the peak value of the light intensity of the branched light is a peak point, and (5) When a straight line continuously connecting the peak points along the propagation direction of the branched light is a peak straight line,
The peak straight line of the first branched light and the peak straight line of the second branched light intersect on the plane, and the first half-value line of the first branched light and the second half-value line of the second branched light are on the plane. The length of the perpendicular line intersecting at a position farther from the one end face than the intersection of the peak straight lines and extending from the intersection of the first half-value line of the first branched light and the second half-value line of the second branched light to the one end face Is the same for any branching waveguide pair selected as a pair of first and second branching waveguides that are sequentially adjacent from a plurality of branching waveguides.

According to the optical element of the reference example , at the intersection of the first half-value line of the first branched light and the second half-value line of the second branched light, the first and second branched lights have peak points in the light intensity distribution. Points that are spaced apart and have half the peak value of each light intensity distribution overlap. Thereby, the intensity distribution of the sum of the first and second branched lights has a region (plateau region) where the intensity is substantially constant between the peaks of both. Further, the lengths (distances) of the perpendicular lines extending from the intersection of the first half-value line of the first branched light and the second half-value line of the second branched light to the one end face of the planar waveguide are sequentially adjacent, that is, The same is true for all of the waveguide branch pairs composed of any adjacent first and second branch waveguides. As a result, in the plane including all the intersections described above, the points having half the peak intensity are overlapped with each other, so that the sum of the intensity distributions of all the branched lights has a wide constant intensity region (plateau region). Become a thing.

In the optical element of the reference example , the peak straight lines of all the branched lights incident into the planar waveguide from the plurality of incident-side branch waveguides intersect each other at one point on the plane, and each of the incident-side branch waveguides Is connected to one end face.

According to the optical element of the reference example , the branched waveguides are arranged so that the peak straight lines (optical axes) of all the branched lights intersect at one point in the planar waveguide. Thereby, the divergence angle as the whole branched light in a planar waveguide can be enlarged.

The optical branching element of the reference example includes the above-described optical element, and the planar waveguide has the other end face parallel to the one end face, and the distance between the other end face and the one end face is the first branch light of the first branch light. The length is equal to the length of the perpendicular line extending from the intersection of the half-value line and the second half-value line of the second branched light to one end surface, and propagates from a plurality of incident-side branch waveguides connected to the one end surface. A plurality of exit-side branching waveguides are connected to the region of the other end face within the reach of all the branched lights reaching the other end face.

According to the optical branching device of the reference example , the other end surface provided with the plurality of emission-side waveguides is located on one end surface from the intersection of the first half-value line of the first branch light and the second half-value line of the second branch light. It is provided apart from the one end face by a length equal to the length of the dropped perpendicular. As a result, the other end surface includes all the intersections. Therefore, the intensity distribution of the sum of all the branched lights on the other end surface has a plateau region with a constant intensity within the reach of all the branched lights. By providing the exit side waveguide within the range of the plateau region, the intensity of light incident on each of the exit side branch waveguides can be made substantially equal.

The optical branching element according to a fourth aspect further includes a branching portion between the incident side waveguide and the plurality of branching waveguides. This branching unit has a hierarchical structure with n stages (n is an integer equal to or greater than 1), and in the mth hierarchy (m is an integer satisfying 1 ≦ m ≦ n), one input light is converted into two output lights. There are 2 ^m-1 waveguide branch points that branch into

The waveguide branch point belonging to the first layer where m = 1 uses light propagating through the incident side waveguide as input light.

  In addition, the waveguide branch point belonging to the m-th layer satisfying 2 ≦ m ≦ n−1 uses the light input from one waveguide branch point belonging to the m−1-th layer as input light, and the m + 1-th layer. Output light is output to each of the two waveguide branch points belonging to the hierarchy.

Further, the total number of 2 ⁿ⁻¹ waveguide branch points belonging to the nth layer where m = n is 2 ⁿ
The branching waveguides are connected, and output light as branching light is output to the branching waveguides.

According to the optical branching element of claim 4 , the branching portion has a waveguide branching point for branching one input light in two directions and outputting two output lights over n layers. It is provided in a hierarchy. The waveguide branching point belonging to the mth layer (2 ≦ m ≦ n−1) branches the input light input from one waveguide branching point belonging to the m−1th layer in two directions. The output light is output to each of the two waveguide branch points belonging to the (m + 1) th layer. Therefore, two branching waveguides are connected to each of 2 ⁿ⁻¹ waveguide branching points belonging to the nth layer which is the last layer. As a result, a total of 2 ⁿ branch waveguides are connected to the waveguide branch points belonging to the nth layer. That is, with this branching section, one light propagating through the incident-side waveguide can be branched into ²ⁿ branched lights having the same intensity.

In the optical branching device according to claim 5 , the Y branching waveguide is composed of an input waveguide propagating input light connected to an arbitrary waveguide branching point and two output waveguides propagating output light. The angle formed by the two output waveguides through which the output light propagates is within 4 °.

According to the optical branching element of the fifth aspect , the waveguide branch point is configured as the branch point of the Y branch waveguide. In this Y branching waveguide, the angle between the output waveguides through which the two output lights propagate is set to be within 4 °. As a result, the input light is branched into two output lights at the waveguide branch point without loss of intensity.

In the optical branching element according to the sixth aspect , the incident-side branching waveguide is formed in a curved shape.

According to the optical branching element of the sixth aspect , even if the number of branching waveguides is large, the branching waveguide between the branching part and the planar waveguide is curved, so that the incident side The optical path lengths from the waveguide to the exit can be made equal.

The optical wavelength multiplexer / demultiplexer according to claim 7 is connected to the one or more input waveguides, the fan-shaped first planar waveguide connected to the input waveguide, and the first planar waveguide, An arrayed waveguide grating composed of a plurality of channel waveguides whose length is changed by a predetermined length, a second planar waveguide connected to the channel waveguide of the arrayed waveguide grating, and a second planar waveguide And a plurality of output waveguides to be connected. Then, each of the individual channel waveguide and the element portion formed of the second planar waveguide and a plurality of output waveguides of the optical wavelength demultiplexer is an optical branching element described above, the individual channel waveguides The second planar waveguide and the plurality of output waveguides correspond to the incident-side waveguide of each optical branching element, and the planar waveguide and the plurality of outgoing-side branching waveguides of each optical branching element Also correspond in common .

According to the optical wavelength multiplexer / demultiplexer according to the seventh aspect , the above-described optical branching element is used for the element portion composed of the channel waveguide and the second planar waveguide. As a result, the wavelength distribution is separated by the arrayed waveguide grating, and the intensity distribution of the light emitted from each channel waveguide to the second planar waveguide has a region (plateau region) where the intensity is substantially constant. Become. Therefore, the intensity of light incident on the plurality of output waveguides can be made substantially equal.

According to the optical elements of the first and second aspects, variation in the intensity of the light emitted to the planar waveguide can be suppressed. That is, the intensity distribution of the sum of the branched lights emitted to the planar waveguide has a constant intensity region (plateau region) without intensity variation.

According to the optical branching element of the third aspect, it is possible to equalize the intensity of the light extracted by the plurality of exit side branching waveguides provided on the other end face of the planar waveguide. In addition, since the light propagating through the incident side waveguide is branched into a plurality of branched lights and emitted to the planar waveguide so that the optical axes of the branched lights cross each other, the spread angle of the entire branched light is increased. Can be bigger. As a result, the distance between the one end surface and the other end surface can be shortened, that is, the planar waveguide can be miniaturized.

According to the optical branching element according to any one of claims 4 to 6 , since the structure in which the waveguide branching point for branching the 1 input light to the 2 output light is hierarchized as the branching part is adopted, the structure is A simple optical branching element can be obtained.

According to the optical wavelength multiplexer / demultiplexer of the seventh aspect , the intensity of light received by the plurality of output waveguides can be made substantially equal.

Hereinafter, embodiments and reference examples of the present invention will be described with reference to the drawings. Each drawing is merely a schematic representation of the shape, size, and arrangement relationship of each component to the extent that the present invention can be understood. In the following, preferred configuration examples and reference examples of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments and reference examples .

( Reference Example 1 )
A configuration example of the optical element of Reference Example 1 will be described with reference to FIGS. FIG. 1 is a partially cutaway plan view showing the overall configuration of the optical element of Reference Example 1. FIG. FIG. 2 is an enlarged plan view of a main part in which the branching part is enlarged in FIG. FIG. 3 is an enlarged plan view of a main part in which the vicinity of the emitting part is enlarged in FIG. FIG. 4 is an enlarged plan view of a main part in which the vicinity of the emitting part is enlarged in FIG. FIG. 5 is a schematic diagram for explaining the nature of one branched light. FIG. 6 is a schematic diagram showing adjacent branching waveguides together with branching light. FIG. 7 is a schematic diagram showing the sum of intensity distributions of two branched lights. FIG. 8 is a schematic diagram showing the sum of intensity distributions of two branched lights. FIG. 9 is a schematic diagram for explaining the arrangement of the branching waveguides. FIG. 10 is a schematic diagram showing the sum of the intensity distributions of all branched lights. FIG. 11 is a schematic diagram illustrating a modification of the optical element of Reference Example 1 .

<Description of Configuration Example of Reference Example 1 >
Referring to FIG. 1, the optical element 10 is provided on a substrate 12 and includes an incident side waveguide 14, an optical branching and emitting portion 16, and a planar waveguide 18.

Here, the incident-side waveguide 14, the optical branching and emitting portion 16, and the planar waveguide 18 are arranged on the substrate 12 in this order along the propagation direction of light propagating through the incident-side waveguide 14.

  The substrate 12 is a right-sided quadrilateral having a predetermined thickness, that is, a square or rectangular plate. The substrate 12 is a quartz substrate.

The incident side waveguide 14 is a channel waveguide. The channel waveguide 14 is a quartz region whose refractive index is higher than that of the peripheral region by doping Ge or the like into the substrate 12. The end surface 14 a of the incident side waveguide 14 is connected to the end surface 12 a of the substrate 12 without a step. Light propagating through a waveguide (not shown) provided outside the substrate 12 is introduced into the incident-side waveguide 14 from the end face 14a.

  The light branching and emitting unit 16 includes a branching unit 20 and an emitting unit 22.

The branching unit 20 is interposed between the incident-side waveguide 14 and the emitting unit 22, and 2 ⁿ (n is an integer of 1 or more) branches of light propagating through the incident-side waveguide 14 having the same intensity. It has a function of branching to light B ₁ , B ₂ ,..., B _N. Details of the configuration of the branching unit 20 will be described later.

When used as a subscript, the numerical value 2 ⁿ is simply expressed as N. In addition, when it is not necessary to distinguish the individual branched lights B ₁ , B ₂ ,..., B _N , they are collectively referred to as “branched light B”. In FIGS. 1 and 2 and subsequent figures, when it is not necessary to consider the spread of light due to diffraction in the planar waveguide 18, the branched light B is transmitted in the propagation direction (optical axes: Ax ₁ , Ax ₂ , ..., Ax _N ) only.

The emission unit 22 propagates 2 ⁿ pieces of branched light B branched by the branch unit 20, and adjacent branched lights B _g−1 and B _g (g is an integer of 2 ≦ g ≦ 2 ⁿ ) and Has a function of determining the propagation direction so that the branched light beams B _g-1 and B _g intersect at one point O in the planar waveguide 18 and emitting them to the planar waveguide 18. The emission part 22 includes 2 ⁿ branch waveguides 23 ₁ , 23 ₂ ,..., 23 _N , and one end of each of the exit parts 22 is an exit port for emitting the branched light B to the planar waveguide 18. 26 ₁ , 26 ₂ ,..., 26 _N. Here, the branching waveguides 23 ₁ , 23 ₂ ,..., 23 _N are arranged in order according to the order of subscripts (1, 2,..., N (= 2 ⁿ )). . Details of the configuration of the emission unit 22 will be described later.

Here, when it is not necessary to distinguish the individual branch waveguides 23 ₁ , 23 ₂ ,..., 23 _N , they are collectively referred to as “branch waveguides 23”. Similarly, when it is not necessary to distinguish the individual exit ports 26 ₁ , 26 ₂ ,..., 26 _N , these are collectively referred to as “exit ports 26”.

Here, the optical path length from the incident side waveguide 14 to the exit port 26 is branched light _{B 1,} B 2, ..., _{B N} is which branch waveguides ₂₃ 1, ₂₃ 2, ... or 23 _N Regardless of whether or not they are propagated, they are of equal length.

  The planar waveguide 18 is a two-dimensional waveguide, and includes a first region 18a that is substantially rectangular in plan view, and a convex portion 18b that protrudes in a convex shape from the first region 18a toward the emitting portion 22. . An exit port 26 is provided on one end surface 18c of the projecting portion 18b on the exit portion 22 side.

<Description of configuration example of branching section>
Next, with reference to FIG. 2 and FIG. 3, the detail of the structure of the branch part 20 is demonstrated.

As shown in FIG. 2, the branching unit 20 includes a total of 2 ⁿ −1 waveguide branching points 24. Each waveguide branch point 24 has a function of branching one input light IN (arrow in FIG. 3) into two output lights OUT (arrow in FIG. 3).

FIG. 3 shows an enlarged plan view of the structure near one waveguide branching point 24 included in the branching section 20. The waveguide branch point 24 is a branch of the Y branch waveguide 28 composed of one input waveguide 24 _in that the input light IN propagates and two output waveguides 24 _out and 24 _out that the output light OUT propagates. Configured as a point.

The two output waveguides 24 _out and 24 _out have the same length, and are arranged symmetrically with respect to a straight line obtained by extrapolating the center line C of the input waveguide 24 _in . The angle η formed by the output waveguides 24 _out and 24 _out is about 3 °.

The input light IN propagating through the input waveguide 24 _in is branched at the waveguide branching point 24 and output as output light OUT having an intensity equal to the two output waveguides 24 _out and 24 _out .

As shown in FIG. 2, the total number of 2 ⁿ -1 waveguide branch points 24 includes n layers L ₁ , L ₂ ,.
... they are arranged in a hierarchical structure consisting of L _n. Here, a waveguide branch point belonging to the m-th layer L _m (m is an integer of 1 ≦ m ≦ n) is denoted as a waveguide branch point 24 _m . The m-th layer L _m includes 2 ^m−1 waveguide branch points 24 _m .

  Hereinafter, the structure of the branch part 20 will be described separately in the case where 1: m is 1, 2: m is 2 to n-1, and 3: m is n.

(1: When m is 1)
In one waveguide branch point 24 ₁ belonging to the first layer L ₁ , the incident-side waveguide 14 is an input waveguide 24 _in . The two output waveguides 24 _out and 24 _out are connected to _two waveguide branch points 24 ₂ and 24 ₂ belonging to the second layer L ₂ , respectively. That is, the waveguide branch point 24 ₁ uses the light propagating through the incident-side waveguide 14 as the input light IN, branches the input light IN into two output lights OUT having the same intensity, and the waveguide branch point 24 _2. , 24 ₂ .

(2: When m is 2 to n-1)
Within a range of 2 ≦ m ≦ n−1, an arbitrary waveguide branch point 24 _m belonging to the mth layer L _m is one waveguide branch point 24 _m− belonging to the _m− 1th layer L _m−1. the light input from ₁ as the input light iN, the input light iN, (m + 1) -th hierarchy _{L m +} 2 pieces of waveguide branch point ₂₄ belonging to ₁ m + 1 branches into two output light OUT of mutually equal intensity, _{24 m + 1} To output.

Note that the distinction between the output waveguide 24 _out and the input waveguide 24 _in is relative (convenient) and changes depending on which layer is focused. In other words, consider taking one and the waveguide branching point _{24 m-1} belonging to the m-1 hierarchy _{L m-1,} a waveguide for connecting the waveguide branch point 24 _m of the m hierarchy _{L m} as an example. The waveguide is the output waveguide 24 _out when viewed from the waveguide branch point 24 _m−1 . However, when viewed from the waveguide branch point 24 _m , the input waveguide 24 _in is obtained.

(3: When m is n)
The n-th layer L _n that is the final layer is provided with a total of 2 ⁿ⁻¹ waveguide branch points 24 _n . Then, two output waveguides 24 _out are connected to each of the waveguide branch points 24 _n . In the n-th layer L _n , the output waveguide 24 _out also serves as the branching waveguide 23. As a result, a total of 2 ⁿ branch waveguides 23 ₁ , 23 ₂ ,..., 23 _N are connected to a total of 2 ⁿ⁻¹ waveguide branch points 24 _n belonging to the nth layer L _n. .

Thus, the branch unit 20, since they have mutually connected structures 2 ⁿ -1 one Y-branch waveguide 28 (see FIG. 3) over n stages congruent shapes, incident-side waveguide The optical path length from 14 to the waveguide branch point 24 _n belonging to the n-th layer L _n is equal regardless of the path taken by the branched lights B ₁ , B ₂ ,..., B _N.

<Description of configuration example of emission unit>
Next, with reference to FIG. 4, the detail of the structure of the emission part 22 is demonstrated.

  As shown in FIG. 4, the emission unit 22 is divided into two areas, a propagation area 30 and an emission angle adjustment area 32.

In propagation region 30, the branching waveguide 23, the branch portion 20, and more particularly, is connected to the n-hierarchy L _n belonging waveguide branch point 24 n as described above _(see FIG. 2). In the propagation region 30, the branching waveguide 23 extends in a substantially S-shaped curve with a smoothly changing curvature in order to avoid a loss of the intensity of the propagating branched light B. .

Here, the branch waveguide _{23 1,} 23 2, ..., 23 from the waveguide branch point 24 _n of _N, exit port _{26 1,} 26 2,..., The optical path length to 26 _N branch waveguide 23 ₁ , 23 ₂ ,..., 23 _N are equal in length regardless of _N.

  As described above, since the optical path length in the propagation region 30 is the same regardless of the branched light B, as a result, the optical path length from the incident-side waveguide 14 to the exit 26 is equal regardless of the branched light B. .

In the emission angle adjustment region 32, the branch waveguides 23 ₁ , 23 ₂ ,..., 23 _N are formed in a straight line. The branching waveguide _{23 1,} 23 2, ..., the ends of the 23 _N are emission port _{26 1,} 26 2, ..., has a 26 _N, one end surface 18c of each planar waveguide 18 It is connected to the.

<Description of example of arrangement of branching waveguide>
Referring to FIGS. 5 to 9, the emission angle adjusting branching waveguide _{23 1,} 23 2 in the region 32, ..., every arrangement of 23 _N, the branched light _B 1 emitted from the _{respective, B} 2, .., _{BN and} the properties of _N will be described in detail.

First, referring to FIG. 5, it will be described any properties of the branched light B _m of one. FIG. 5 is a diagram in which the branched light _Bm and its intensity distribution are overlapped.

The branched light B _m emitted from the emission port 26 _m becomes a Gaussian beam, and propagates along the optical waveguide Ax _m along the optical axis Ax _m while spreading due to diffraction. Here, the optical axis Ax _m indicates a straight line obtained by continuously connecting the peak values (light intensity = I _max ) of the intensity distribution described below along the propagation direction of the branched light B _m .

As shown in FIG. 5, the branched light B _m has a Gaussian distribution of intensity distribution in any plane S ₁ and plane S ₂ orthogonal to the optical axis Ax _m . In this intensity distribution, a straight line obtained by connecting the points H ₁ and H ₂ that are half the peak intensity I _max (1/2 × I _max ) along the propagation direction of the branched light B _m , and the point H _The straight lines obtained by connecting ₃ and H ₄ are respectively referred to as half-value lines HB _mL and HB _mR .

In addition, an angle formed by one of the half-value lines HB _mR and HB _mL and the optical axis Ax _m is defined as a spread angle θ / 2 of the branched light B _m .

The divergence angle θ / 2 is a plane S ₀ perpendicular to the optical axis Ax _m of the branched light B _m immediately after being emitted from the emission port 26 _m to the planar waveguide 18 with the wavelength of the branched light B _m as λ. It is known that λ / D ₀ when the half-value width of the intensity distribution is 2D ₀ .

Next, referring to FIG. 6, two branching waveguides 23 _g−1 and 23 _g arranged adjacent to each other are arbitrarily selected from 2 ⁿ branching waveguides 23, and these branching waveguides are selected. A phenomenon that occurs when the branched lights B _g-1 and B _g emitted from 23 _g-1 and 23 _g overlap each other will be described.

The branching waveguides 23 _g-1 and 23 _g are spaced apart from one end face 18c provided with the exit ports 26 _g-1 and 26 _g . The branching waveguides 23 _g-1 and 23 _g are constituent elements of the adjacent waveguide pair P.

In the adjacent pair of waveguides P, and the branching waveguide _{23 g-1,} the first referred to as branching waveguide _{23 g-1,} the branching waveguide 23 _g, referred to as a second branch waveguide 23 _g. Further, the branched light _{B g-1} emitted from the first branch waveguide _{23 g-1} referred to as a first branched light _{B g-1,} the branched light _{B g} emitted from the second branch waveguide 23 _g second branch It referred to as the light _{B g.}

The first and second branching waveguides 23 _g-1 and 23 _g are arranged such that the optical axis Ax _g-1 and the optical axis Ax _g intersect at one point O in the planar waveguide 18. Here, the first branched light _{B g-1} in the propagation direction (the optical axis _{Ax g-1),} the propagation direction (the optical axis Ax _g) direction composite optical axis which is vectorially combining the second branched light _{B g} AA. In this example, the case where the branching waveguides 23 _g-1 and 23 _g are arranged symmetrically with respect to the combined optical axis AA is shown.

  Further, “one point O in the planar waveguide 18” is a concept that does not include the case where the one point O exists in the plane including the one end surface 18c of the planar waveguide 18.

The first branch light B _g-1 emitted from the first branch waveguide 23 _g-1 propagates along the optical axis Ax _g-1 while spreading at the spread angle θ / 2 as described above. Here, of the two half-value lines of the first branched light B _g-1 , the half-value line closer to the second branch waveguide 23 _g is referred to as a second half-value line BH _{(g-1): 2} , The half-value line far from the second branch waveguide 23 _{g is referred} to as a first half-value line BH _{(g−1): 1} .

Similarly, the second branched light B _g emitted from the second branch waveguide 23 _g propagates along the optical axis Ax _g while spreading at a spread angle θ / 2. Here, one of the two half-lines of the second branched light _{B g,} side of half line closer to the first branch waveguide _{23 g-1,} the first half line _{BH (g): 1} and referred, and, The half-value line far from the first branch waveguide 23 _{g-1 is referred} to as a second half-value line BH _{(g): 2} .

As is apparent from FIG. 6, the first branched light _{B g-1} of the first and second half line _{BH (g-1): 1} , BH (g-1): and _2, the second branched light _{B g} The first and second half-value lines BH _{(g): 1} and BH _{(g): 2} intersect at four intersections C ₁ , C ₂ , C ₃ , and C ₄ .

More specifically, the intersection _{C 1} is first branched light _{B g-1} of the second half line _{BH (g-one):} and _2, the first half line _BH of the second branched light _{B g (g): 1} DOO is at the point of intersection, the shortest distance between the end surface 18c of the four intersections _C 1 -C _4. Here, it includes intersection _{C 1,} and a plane perpendicular to synthesize the optical axis AA and _{S C1.}

Intersection _{C 2,} the first branched light _{B g-1} of the first half line _{BH (g-one): 1} and, first half line _BH of the second branched light _{B g (g): point 1} and intersect It is.

Intersection _{C 3} is first branched light _{B g-1} of the second half line _{BH (g-one): 2} and the second half line _BH of the second branched light _{B g (g):} in _{that 2} and intersect is there. Here, a plane including the intersection points C ₂ and C ₃ and orthogonal to the combined optical axis AA is _{denoted as SC 23} .

Intersection _{C 4,} the first branched light _{B g-1} of the first half line _{BH (g-one): 1} and, second half line _BH of the second branched light _{B g (g): 2} and is the point of intersection Of the four intersections C _{1 to} C ₄ , the distance to the one end face 18 c is the longest. Here, it includes intersection _{C 4,} and a plane perpendicular to synthesize the optical axis AA and _{S C4.}

Next, with reference to FIG. 7 and FIG. 8, the intensity distribution of the sum of the first and second branched lights B _g−1 and B _{g on} the surfaces S _C1 , S _C23 and S _C4 will be considered. The intensity distribution shown in FIGS. 7 and 8 is viewed from the direction of the arrow X in FIG. Further, as described above, since the optical path lengths from the incident-side waveguide 14 (see FIG. 1) to the exit ports 26 _g and 26 _g−1 are equal, the first and second branched lights B _g−1 and B _g are If the divergence angle θ / 2 is sufficiently small, the phases are equal in the planar waveguide 18. Therefore, the branched light _{B g,} since there is no need to consider the interference of _{B g-1} with each other, the intensity distribution of the sum of the first and second branched light _{B g-1, B g} is a simple sum of the two.

FIG. 7A shows a sum intensity distribution obtained by superimposing the intensity distributions of the first and second branched lights B _g−1 and B _{g on} the surface S _C1 .

7A, 7B, and 8, the thick dotted lines in the figure indicate the intensity distributions of the individual branched lights B _g-1 and B _g , and the solid line indicates the branched light B _The sum intensity distribution obtained by superimposing the intensity distribution of _g and the intensity distribution of B _g-1 is shown.

In the intersection point _{C 1,} although the wavefront of both the branched light _{B g-1, B g} is not spherical wave, the spaced and both peaks _{P g-1} and _{P g} is placed, and the first branched light _{B g-1} half point of the peak intensity _I max _{(P g-1)} and _{(1/2 × I max)} , half point of the peak intensity _I max of the second branched light _{B g (P g)} and (1/2 × _{I max)} Match. As a result, the intensity distribution of the sum of both branched lights B _g-1 and B _g has a region (plateau region) PL in which the intensity is substantially constant between both peaks P _g-1 and P _g .

FIG. 7B shows the intensity distribution of the sum of the first and second branched lights B _g−1 and B _{g on} the surface _SC23 .

At the intersections C ₂ and C ₃ , the intensity distributions of both branched lights B _g-1 and B _g are almost the same. Thus, with the surface _{S C23,} so that the two peaks _{P g-1} and _{P g} each other match. As a result, the intensity distribution of the sum of the branched lights B _g−1 and B _g is a Gaussian distribution with a peak intensity of approximately 2I _max .

Figure 8 is the intensity distribution of the sum of the first and second branched light _{B g-1, B g} in the plane _{S C4.} Intensity distribution shown in FIG. 8, by branched light _{B g-1, B g} at a point O in the planar waveguide 18 intersects, the intensity distribution in the plane _{S C1} (FIG. 7 (A)), the branched light The left and right positions of B _g-1 and B _g are reversed.

In the intersection point _{C 4,} with the wavefront of the two branched light _{B g-1, B g} is spherical waves, the spaced and both peaks _{P g-1} and _{P g} is placed, and the first branched light _{B g-1} half point of the peak intensity _I max _{(P g-1)} and _{(1/2 × I max)} , half point of the peak intensity _I max of the second branched light _{B g (P g)} and (1/2 × _{I max)} Match. As a result, the intensity distribution of the sum of both branched lights B _g-1 and B _g has a region (plateau region) PL in which the intensity is substantially constant between both peaks P _g-1 and P _g .

The first branched light _{B g-1} of the first and second half line _{BH (g-1): 1} , BH (g-1): _2, first and second second branched light _{B g} Of the four intersections C ₁ , C ₂ , C ₃ , and C ₄ at which the half-value lines BH _{(g): 1} and BH _{(g): 2} intersect, the sum intensity distribution has a plateau region PL, and wavefront and a plateau achieved point _{C PLg C 4} points is a spherical wave manner. In other words, the plateau achievement point C _PLg includes the first and second half-value lines BH _{(g−1): 1} and BH _{(g−1): 2 of} the first branched light B _g−1 and the second branched light. The distance from one end face 18c among the _four intersections C ₁ , C ₂ , C ₃ , C ₄ intersecting with the first and second half-value lines BH _{(g): 1} and BH _{(g): 2 of} B _g Is the longest intersection.

One plateau achievement point C _PLg exists for each adjacent waveguide pair P. In addition, since there are a total of 2 ⁿ -1 adjacent waveguide pairs P including the first and second branch waveguides 23 _g-1 and 23 _g , there are also 2 ⁿ -1 plateau achievement points C _PLg. . For reasons that will be described later, these 2 ⁿ -1 plateau achievement points C _PLg are all equal in distance H to the one end face 18c. Here, it referred to as the plane containing all of the plateau achieved point C _PL plateau achieve surface S _PL.

Next, referring to FIG. 9, the arrangement of the branch waveguides 23 ₁ , 23 ₂ ,..., 23 _{N in} the emission angle adjustment region 32, that is, the branched lights B ₁ , B _{2 ,.} The emission angle will be described.

In FIG. 9, two adjacent branched waveguides 23 _g-1 and 23 _g are arbitrarily selected from the 2 ⁿ branched waveguides 23, and the branched light B _g− emitted from each is selected. ₁ and _Bg are shown.

Here, the branching waveguides 23 _g-1 and 23 _g are arranged on the one end face 18c provided with the exit ports 26 _g-1 and 26 _g so as to be separated from each other by a distance d. The branching waveguides 23 _g-1 and 23 _g are constituent elements of the adjacent waveguide pair P.

The branched light B _g-1 is emitted from the branch waveguide 23 _g-1 to the planar waveguide 18 at an emission angle α _g-1 . That is, the angle formed by the normal line of the one end face 18c and the optical axis Ax _g-1 is α _g-1 . Similarly, the branched light B _g is emitted from the branch waveguide 23 _g to the planar waveguide 18 at the emission angle α _g . In other words, the angle between the normal and the optical axis Ax _g of one end surface 18c is alpha _g. Further, the branched lights B _g-1 and B _g propagate through the planar waveguide 18 while spreading at a spread angle θ / 2.

The size of the distance H between the end face 18c and the plateau achieved point C _PLg Since plateau achieved point C _PLg is restricted by the condition that exists in the planar waveguide 18, one end face of the planar waveguide 18 The length is equal to or shorter than the length in the direction orthogonal to 18c.

At this time, in order for the plateau achievement point C _PLg to exist between the two branched lights B _g-1 and B _g , the first half-value line BH _(g-1) of the branched light B _g-1 is _{: 1} And the second half-value line BH _{(g): 2} of the branched light B _g must intersect in the planar waveguide 18.

  The condition for that is expressed by the following formula (1).

H tan (α _g−1 −θ / 2) = d + H tan (α _g + θ / 2) (1)
Furthermore, when the distance between the point O where the optical axes Ax _g-1 and Ax _{g of} the branched lights B _g-1 and B _g intersect and the one end face 18c is H 2 _O , the optical axes Ax _g-1 and Ax _g are The condition for intersecting at one point O is expressed by the following equation (2).

H _O tan (α _g−1 ) = d + H _O tan (α _g ) (2)
Therefore, the emission angles α _g−1 and α _g are determined so as to satisfy these two equations at the same time, and the branching waveguides 23 _g−1 and 23 are set so as to be the emission angles α _g−1 and α _{g. What} is necessary is _just to arrange | position _g .

  In other words, the optical branching element 10 described above has a configuration as described below.

  That is, the optical branching element 10 includes three or more branching waveguides 23 branched from one incident-side waveguide 14 and a planar waveguide 18 having the one end face 18c connected to the branching waveguide 23. Yes.

Here, the points H ₁ , H ₂ (H ₃ , H corresponding to the half value ½ × I _max of the peak intensity I _max of the branched light B emitted from the branch waveguide 23 to the planar waveguide 18 as a Gaussian beam. ₃ ) is defined as a half-value line BH by two straight lines connecting the optical axes Ax of the branched light B.

  Note that the branched lights B emitted from the respective branched waveguides 23 have the same phase and the same intensity.

At this time, the following two conditions hold simultaneously.
(1) The optical axes Ax of all the branched lights B intersect at a point O in the planar waveguide 18.
(2) Each any neighboring and the branching waveguide 23 and the first and second branch waveguides _{23 g-1,} 23 _g, first branched light _{B g} emitted from the first branch waveguide _{23 g-1 -1} of two half-value lines BH _{(g-1): 2} and BH _{(g-1): 1} , the first half-value line BH _(g-1) far from the second branch waveguide 23 _{g : 1} and, two half lines of the second branch waveguide 23 _g emitted from the branched light _{B g BH (g): 1} , BH (g): of the _two, from the first branching waveguide _{23 g-1} Distant second half-value line BH _{(g): When} the intersection with ₂ is _defined as a plateau achievement point _CPLg , the distance H between the plateau achievement point _{CPLg and} the one end face 18c is _equal to all the adjacent branched waveguides 23. _It becomes equal for _g−1 and 23 _g . The branching waveguide 23 is disposed so as to satisfy these two conditions.

In FIG. 9, the outgoing angles α _g−1 and α _g of the branched lights B _g−1 and B _g are drawn with an inclination more than the actual in consideration of easy understanding. Therefore, though the intensity distribution of the branched light _{B g-1} in the plateau achieved surface _{S PL} is, across the optical axis _{Ax g-1} is distorted asymmetrically and broad, as a result, the branched light _{B g-1} and _{B g} I get the impression that the intensity distribution of the sum of and can not have a constant intensity region (plateau region PL). However, in the actual optical element 10, since the emission angles α _g-1 and α _g are small angles close to 0 °, the intensity distribution of the branched lights B _g-1 and B _g is a Gaussian distribution without distortion. Can be approximated well. Therefore, the intensity distribution of the sum of the branched light _{B g-1, B g} in the plateau achieved surface _{S PL} will have a substantially constant intensity region (plateau region PL).

Also, if, by the output angle alpha _g-1 of the branched light B _g-1 is increased, when it becomes impossible to ignore the distortion of the intensity distribution in the plateau achieved surface S _PL is emitted branched light B _g-1 by widening the opening width of the exit port 26 _g-1 to may be optimized intensity distribution of the branched light B _g-1 in the plateau achieved plane S _PL. That is, when the opening width of the exit _26g-1 is increased, the intensity distribution of the branched light _Bg-1 becomes sharper (the peak intensity increases). Therefore, if the peak intensity of the branched light B _g-1 in the plateau achieved surface S _PL to be equal to the peak intensity of the branched light B _g, the intensity distribution of the sum of the two branched light B _g-1, B _g is It has a plateau region PL.

<Description of operation example of optical element>
Next, the operation of the optical element 10 will be described with reference mainly to FIGS.

Referring to FIG. 1, the light propagating through the incident-side waveguide 14 propagates through the branching unit 20 of the optical branching and emitting unit 16, so that 2 ⁿ branched lights B ₁ , B ₂ ,. - is split into _{B N.} The branched light _{B 1,} B 2, ..., _{B N} are branched emitting portion 22 of the light branching emitting portion 16 waveguide _{23 1,} 23 2, ..., it is propagated through the 23 _N.

In the emission angle adjusting region 32 (FIG. 6), the angle formed between the branch waveguides 23 _g-1 and 23 _g adjacent to each other is arranged so as to satisfy the above expressions (1) and (2). ing. As a result, the branched light beams B ₁ , B ₂ ,..., B _N that have propagated through the branch waveguides 23 ₁ , 23 ₂ ,..., 23 _N have the optical axes Ax ₁ , Ax ₂ ,. Ax _N is intersect at a point O in the planar waveguide 18, and, at an angle as to satisfy the equation (1) and (2), the exit port _{26 1,} 26 2, · · ·, 26 _N To the planar waveguide 18.

Planar waveguide 18 branched light _B 1 emitted _into, B 2, · · ·, _{B N,} the optical axis _{Ax 1,} Ax 2, · · ·, with Ax _N intersect at a point O, respectively divergence It propagates in the planar waveguide 18 while expanding at θ / 2.

Then, the branched light _{B g-1, B g} adjacent to each other, the first half line _BH branched light _{B g-1 (g-1} ): 1 and a second half line _BH branched light _{B g (g): The two} intersect each other at a plateau achievement point _CPLg where the distance from the one end face 18c is H.

Here, in FIG. ^{10, 2} n -1 pieces of plateau achieved point _{C PL2,} C PL3 · · _·, a plane containing the _{C PLN} (hereinafter, also referred to as a plateau achieved _surface) branched light _B 1 in the _{S PL,} B ₂ ,..., B _N indicates the sum of the intensity distributions. The dotted line in FIG. 10 shows the intensity distribution of the individual branched light B _m, and a solid line is the intensity distribution of the sum of the branched light B _m.

Branched light _{B 1,} B 2, · · ·, the intensity distribution of the _{B N} is that partially overlap, it can be seen that the broad plateau region PL is formed.

<Description of effects of Reference Example 1 >
Thus, the optical element 10 of Example 1, the branched light _{B 1,} B 2, · · ·, the optical axis _Ax 1 of _{B N,} Ax 2, · · ·, a point in the planar waveguide 18 Ax _N Branching is performed so that the half-value lines BH _{(g−1): 1} and BH _{(g): 2} intersect at plateau achievement points C _PL2 , C _PL3 ,..., C _PLN. Waveguides 23 ₁ , 23 ₂ ,..., 23 _N are arranged. Further, incident-side waveguide 14 exit port ₂₆ 1 to ₂₆ 2, ..., the optical path length to 26 _N, the branched light _{B 1,} B 2, equal regardless ..., the propagation path of _{B N} ing.

These intensity distribution of the sum obtained by superposing branched light B in the plateau achieved plane S _PL are each branched light B _1, B _2, · · ·, it becomes simple sum of the intensity distribution of B _N, strength By overlapping the half-value points of the distribution, a plateau region PL having a substantially constant intensity is formed in the sum intensity distribution. In other words, it is possible in plateau achieve surface S _PL, obtain light without variation in intensity.

In addition, by connecting the Y branch waveguides 28 over the n layers in the branching section 20, 2 ⁿ branched lights B having the same intensity can be easily obtained with a simple structure.

Further, by setting the angle formed by the output waveguides 24 _out and 24 _out in one Y branch waveguide 28 within 4 °, the intensity of light at the waveguide branch point 24 that is the branch point of the Y branch waveguide 28. This loss can be made sufficiently small for practical use.

In addition, since the 2 ⁿ branch waveguides 23 are formed in an S-shape in which the curvature changes smoothly in the propagation region 30, it is possible to suppress the loss of the intensity of the propagating branch light B and to reduce the incident side. The optical path lengths from the waveguide 14 to the exit 26 can be easily made equal.

<Description of Modification of Reference Example 1 >
Here, quartz is used as the substrate 12 in this reference example , but the material constituting the substrate 12 is a design matter, and preferably, for example, a compound semiconductor, silicon, plastic, or the like can be used.

Further, in the Y branch waveguide 28 constituting the branch portion 20, the angle formed by the output waveguides 24 _out and 24 _out is preferably within 4 °, more preferably within 3 °.
However, if the loss of light at the waveguide branch point 24 can be tolerated, the angle formed by the output waveguides 24 _out and 24 _out may be larger than 4 °.

In Reference Example 1 , the light propagating through the incident-side waveguide 14 is branched into an even number ( ²ⁿ ) of branched light B in the branching unit 20, but the branched light B is an even number. There is no need, and an odd number may be used.

Further, even if some of the 2 ⁿ branched waveguides 23 are not connected to the planar waveguide within the practically allowable range of the intensity drop of the branched light B as a whole, the optical element 10 is The same effect as described above is achieved.

In Reference Example 1 , the light propagating through the incident-side waveguide 14 is branched at the branching portion 20 using 2 ⁿ Y-branching waveguides 28. However, if the branching unit 20 can branch the light propagating through the incident-side waveguide 14 into the branched light B having the same intensity, the branching unit 20 does not need to be configured by the Y-branch waveguide 28. Can be applied.

In the propagation region 30, the 2 ⁿ branch waveguides 23 are formed in an S shape if the optical path lengths of the branch waveguides 23 can be made equal and the loss of the intensity of the branch light B can be suppressed. Is not limited. For example, the refractive indexes of 2 ⁿ branch waveguides 23 may be made different so that the optical path lengths are made equal.

In Reference Example 1 , only one incident-side waveguide 14 is connected to the planar waveguide 18. For example, as shown in FIG. 11A, two or more incident-side waveguides are used. 14 'and 14' may be connected to the planar waveguide 18 through the optical branching and emitting sections 16 'and 16'.

Further, in the reference example 1, 2 ⁿ the branch waveguides 23, which had been connected only to one-of the planar waveguide 18, for example, as shown in FIG. 11 (B), of 2 ⁿ the branch The waveguide may be divided and connected to a plurality of planar waveguides 18 ′ and 18 ′.

Further, in the reference example 1, a plateau achieved surface S _PL has been a plane parallel to the end surface 18c, a plateau achieved surface S _PL, arcuate with a curvature equal to a curvature of the wavefront of the branched light B You may form in the curved surface. However, in this case, it is necessary to adjust the emission angle α of the branched light B emitted from the branched waveguide 23 so that all the plateau achievement points are included in this arcuate curved surface.

( Reference Example 2 )
A configuration example of the optical branching element of Reference Example 2 will be described with reference to FIG. FIG. 12 is a plan view showing the overall configuration of the optical branching element of Reference Example 2 .

<Description of Configuration Example of Reference Example 2 >
Referring to FIG. 12, the optical branching element 50 of Reference Example 2 is configured such that the other end surface 18 d having a plurality of emission-side waveguides 36 is provided opposite to the one end surface 18 c in the planar waveguide 18. The structure is the same as that of the optical element 10 of Reference Example 1 . Therefore, in FIG. 12, detailed description of components common to those in FIGS.

The optical branching element 50 includes the optical element 10 described in Reference Example 1 and a plurality of emission-side waveguides 36 provided on the other end face 18 d of the planar waveguide 18. The other end surface 18d is parallel to the one end surface 18c, and the distance from the one end surface 18c is set to H described above. That is, the other end surface 18d is formed on a surface that matches the plateau achieve surface S _PL described above. That is, the other end face 18d is formed so as to include all the plateau achievement points _CPLg .

  Two or more, here, i (i is an integer of 2 or more) emission-side waveguides 36 are provided on the other end face 18d. Note that the opening width (light receiving width) of the emission-side waveguide 36 is the same regardless of the emission-side waveguide 36.

Here, of the branch waveguide 23, the branch waveguides 23 ₁ and 23 _N existing at both ends on the one end face 18c are referred to as one end branch waveguide 23 ₁ and the other end branch waveguide 23 _N , respectively.

Here, the intersection of the optical axis Ax ₁ of the branched light B ₁ emitted from the one-end branch waveguide 23 ₁ to the planar waveguide 18 and the other end face 18 d is C _a, and similarly, the other-end branch waveguide 23 _N the intersection of the optical axis Ax _N and the other end surface 18d of the branched light _{B N} emitted into the planar waveguide 18 from the _{C b.}

At this time, all the branched lights B ₁ , B ₂ ,..., B _N are irradiated between the intersection points C _a and C _b on the other end face 18d. That is, the reachable range of all the branched lights B ₁ , B ₂ ,..., B _{N on} the other end face 18d is between the intersections C _a and C _b . I light receiving openings are arranged in the region of the other end face 18d within this reachable range.

  In addition, the exit-side waveguides 36 extend so that the center lines 36c of the i exit-side waveguides 36 respectively intersect one point O in the planar waveguide 18.

<Description of effects of Reference Example 2 >
Thus, according to the optical branching element 50 of Example 2 is provided with a second end face 18d so as to match the plateau achieve surface S _PL. Accordingly, the sum intensity distribution of the branched light B on the other end face 18d has a wide plateau region PL as shown in FIG. The plateau region PL is because it is formed across the width between the intersection C _a and C _b, by providing the i present on the exit side waveguide 36 between the intersection C _a and C _b, the exit side The light reception intensity of light per waveguide 36 can be made equal for all i emission-side waveguides 36.

Further, the optical branching element 50 of Reference Example 2 branches light propagating through the incident-side waveguide 14 into ²ⁿ branched lights B, and the optical axis Ax of these branched lights B is a point within the planar waveguide 18. The light is emitted so as to intersect at O. As a result, the spread angle β of the branched light B as a whole can be increased. That is, by causing the optical axis Ax to intersect at one point O, the spread angle β of the entire branched light B is changed to 2 ⁿ × θ / 2 (the spread angle θ / 2 per one branched light B is The angle obtained by multiplying the number ²ⁿ can be increased. Thereby, even if the distance H between the one end face 18c and the other end face 18d is short, the entire branched light B can be irradiated to a wide range of the other end face 18d, and the optical branching element 50 can be downsized.

This can be understood more clearly in Reference Example 2 assuming the case of n = 0 (not within the scope of the present invention). When n = 0, the light propagating through the incident-side waveguide 14 is emitted to the planar waveguide 18 as one without being branched. The light divergence angle is θ / 2, which is about ½ ⁿ of the divergence angle of the entire 2 ⁿ branched lights B. Therefore, the one end face 18c and the other end face 18d required for the light emitted to the planar waveguide 18 without branching to be irradiated on the other end face 18d in the same range as the entire branched light B are provided. Is about ²ⁿ times as long as the entire branched light B is irradiated.

Further, the optical branching element 50 of Reference Example 2 has a simple structure including a Y branching waveguide 28, a planar waveguide 18, and a channel waveguide (incident side waveguide 14, branching waveguide 23, and outgoing side waveguide 36). The structure is simple because of the combination of the elements.

<Description of Modification of Reference Example 2 >
In the optical branching element 50 of Reference Example 2 , consider the case where two or more incident-side waveguides 14 ′ are provided as shown in FIG. In this case, the optical axes Ax ₁ ′ and Ax _N ′ of the branched lights B ₁ ′ and B _N ′ existing at both ends of the branched light B ′ emitted from the light branching and emitting part 16 ′ to the planar waveguide 18 However, it is preferable to arrange the branching waveguide 23 ′ so that all the emission-side waveguides 36 are within the angle range formed by the other end face 18d. By doing in this way, the light reception intensity of the light per one output side waveguide 36 can be made equal in all i output side waveguides 36.

In addition, as described in Reference Example 1 , there are two points (C ₁ and C ₄ ) where the intensity distribution of the sum of the branched lights B _g−1 and B _g in the planar waveguide 18 has the plateau region PL. and, of which, it adopted the _{C 4} after the optical axis _{Ax g-1} and Ax _g intersect as a plateau achieved point _{C PL} (see FIG. 6). This is because the emission-side waveguide 36 can be arranged radially if the other end face 18d is provided so as to include C ₄ (C _PL ) in consideration of the propagation direction of the branched light B. In contrast, if assuming that provided at the other end surface 18d in C _1, it is necessary to place the outgoing side waveguide 36 so as to intersect with each other, the difficulty of designing the optical branch element 50 is increased.

(Embodiment 1 )
A configuration example of the optical branching element according to the first embodiment will be described with reference to FIGS. FIG. 13 is a plan view showing the overall configuration of the optical branching element of the first embodiment. FIG. 14 is an enlarged plan view of a main part in which the vicinity of the emission angle adjustment region of the optical branching element is enlarged. FIG. 15 is a schematic diagram showing adjacent branching waveguides together with branching light. FIG. 16 is a schematic diagram showing the sum of intensity distributions of two branched lights.

<Description of Configuration Example of Embodiment 1 >
Referring to FIG. 13, the optical branching device 60 of the first embodiment has the exception that the intersection (one point) O ′ of the optical axis Ax of the branched light B exists in a plane including the one end face 18 c of the planar waveguide 18. This is the same as the light branching element 50 of Reference Example 2 . Therefore, in FIG. 13, the detailed description regarding a structure is abbreviate | omitted suitably about the component in common with FIGS. Here, the “surface including the one end surface 18c” indicates a surface whose distance measured in the normal direction from the one end surface 18c is zero.

  As shown in FIG. 13, in the optical branching element 60, the output-side waveguide 36 is arranged such that the center line of the i output-side waveguides 36 intersects at one point O ′ in the plane including the one end face 18c. Is provided.

Among the branching waveguides 23, the branching waveguides 23 ₁ and 23 _N existing at both ends on the one end face 18 c are respectively referred to as one end branching waveguide 23 ₁ and the other end branching waveguide 23 _N.

Here, the intersection of the optical axis Ax ₁ of the branched light B ₁ emitted from the one-end branch waveguide 23 ₁ to the planar waveguide 18 and the other end face 18 d is C _a, and similarly, the other-end branch waveguide 23 _N the intersection of the optical axis Ax _N and the other end surface 18d of the branched light _{B N} emitted into the planar waveguide 18 from the _{C b.}

At this time, all the branched lights B ₁ , B ₂ ,..., B _N are irradiated between the intersection points C _a and C _b on the other end face 18d. That is, the reachable range of all the branched lights B ₁ , B ₂ ,..., B _{N on} the other end face 18d is between the intersections C _a and C _b . I light receiving openings are arranged in the region of the other end face 18d within this reachable range.

Further, for the reason described later, in the optical branching element 60 of the first embodiment, there is no particular limitation on the distance between the one end face 18c and the other end face 18d.

  With reference to FIG. 14, the structure of the emission angle adjustment region 38 of the optical branching element 60 will be described.

In emission angle adjusting region 38, the branching waveguide 23, the branching waveguide _{23 1,} 23 2, ..., the optical axis _{Ax 1,} Ax 2 of the branched light B emitted from the 23 _N, ..., Ax _N Are arranged so as to intersect at one point O ′ in the plane including the one end face 18c. Here, the two branching waveguides 23 _g-1 and 23 _g adjacent to each other are arranged so as to form an angle θ (an angle twice the spread angle θ / 2 of one branching light B). . In other words, the branch waveguide _{23 g-1, 23 g} along the propagation direction of the branched light _{B g-1, B g,} an angle θ is arranged so as to approach each other.

Next, referring to FIG. 15, with respect to the arrangement of the two branch waveguides 23 _g-1 and 23 _{g that} are arranged adjacent to each other in the emission angle adjustment region 38, the branched lights B _g-1 and B _g emitted from each of them. _This will be described together with _g . The branching waveguides 23 _g-1 and 23 _g are arbitrarily selected from 2 ⁿ branching waveguides 23.

The exit port _{26 g-1} of the branch waveguides _{23 g-1,} and the exit port 26 _g of the branching waveguide 23 _g, coincides at one end surface 18c, forms a single common exit port 26c. Here, the branching waveguides 23 _g-1 and 23 _g are constituent elements of the adjacent waveguide pair P.

In the adjacent pair of waveguides P, and the branching waveguide _{23 g-1,} the first referred to as branching waveguide _{23 g-1,} the branching waveguide 23 _g, referred to as a second branch waveguide 23 _g. Further, the branched light _{B g-1} emitted from the first branch waveguide _{23 g-1} referred to as a first branched light _{B g-1,} the branched light _{B g} emitted from the second branch waveguide 23 _g second branch It referred to as the light _{B g.}

The first branched light B _g-1 emitted from the first branched waveguide 23 _g-1 propagates along the optical axis Ax _g-1 while spreading at a spread angle θ / 2. Here, of the two half-value lines of the first branched light B _g-1 , the half-value line closer to the second branch waveguide 23 _g is referred to as a second half-value line BH _{(g-1): 2} , The half-value line far from the second branch waveguide 23 _{g is referred} to as a first half-value line BH _{(g−1): 1} .

Similarly, the second branched light B _g emitted from the second branch waveguide 23 _g propagates along the optical axis Ax _g while spreading at a spread angle θ / 2. Here, one of the two half-lines of the second branched light _{B g,} side of half line closer to the first branch waveguide _{23 g-1,} the first half line _{BH (g): 1} and referred, first The half-value line far from the branching waveguide 23 _{g-1 is referred} to as a second half-value line BH _{(g): 2} .

In the optical branching device 60, the first branch waveguide _{23 g-1} and an angle theta of the second branch waveguide 23 _g, first and second branched light _{B g-1, B g} divergence angle theta / 2 of The size is twice as large. As a result, the first half-value line BH _{(g-1): 1 of} the first branched light B _g-1 always coincides with the second half-value line BH _{(g): 2 of} the second branched light B _g . That is, they are at the same position in the planar waveguide 18.

Referring now to FIG. 16, consider the intensity distribution of the sum of the first and second branched light _{B g-1, B g} in the plane _{S C.} The intensity distribution shown in FIG. 16 is viewed from the direction of arrow Y in FIG.

The thick dotted line in FIG. 16 indicates the intensity distribution of the first and second branched lights B _g-1 and B _g , and the solid line indicates the intensity distribution of B _g-1 of the first branched light and the second branched light B _The sum intensity distribution obtained by adding the intensity distribution of _g is shown.

According to FIG. 16, spaced and both peaks _{P g-1} and _{P g} is, and the first branched light _{B g-1} of the first half line _{BH (g-1): 1} and the second branched light _{B g} Second half-value line BH _{(g): On} the straight line that coincides with ₂ , the half-value point (1/2 × I _max ) of the peak intensity I _max (P _g-1 ) of the first branched light B _g-1 , The half-value point (1/2 × I _max ) of the peak intensity I _max (P _g ) of the second branched light B _g coincides. As a result, the intensity distribution of the sum of both branched lights B _g-1 and B _g has a region (plateau region) PL in which the intensity is substantially constant between both peaks P _g-1 and P _g .

That is, in Reference Examples 1 and 2, the optical axes Ax _g-1 and Ax _g of the first and second branched lights B _g-1 and B _g intersect at one point O in the planar waveguide 18. _Therefore , only at the plateau achievement point _CPL , the intensity distribution of the sum of the first and second branched lights B _g-1 and B _g has a plateau region PL (see FIG. 6 or FIG. 9). However, the optical branch element 60 of the first embodiment, the first branched light _{B g-1} of the first half line _{BH (g-one): 1} and a second half line _BH of the second branched light _{B g (g) : 2} always matches, so the intensity distribution of the sum of both branched lights B _g-1 and B _g always has a plateau region PL regardless of the distance from the one end face 18c.

  In other words, the optical branching element 60 described above has a configuration as described below.

  That is, the optical branching element 60 includes two or more branching waveguides 23 branched from one incident-side waveguide 14 and a planar waveguide 18 having the one end face 18c connected to the branching waveguide 23. Yes.

Here, the points H ₁ , H ₂ (H ₃ , H corresponding to the half value ½ × I _max of the peak intensity I _max of the branched light B emitted from the branch waveguide 23 to the planar waveguide 18 as a Gaussian beam. ₃ ) is defined as a half-value line BH, which is a straight line connecting the branched light B along the optical axis Ax, and an angle between the half-value line BH and the optical axis Ax of the branched light B is θ / 2.

  Note that the branched lights B emitted from the respective branched waveguides 23 have the same phase and the same intensity.

At this time, the following two conditions hold simultaneously.
(1) The optical axes Ax of all the branched lights B intersect at one point O ′ in the plane including the one end face 18c.
(2) When arbitrary adjacent branching waveguides 23 are first and second branching waveguides 23 _g-1 and 23 _g , respectively, from the first and second branching waveguides 23 _g-1 and 23 _g The angle formed by the optical axes Ax _g-1 and Ax _g of the first and second branched lights B _g-1 and B _g respectively emitted is θ.

  The branching waveguide 23 is disposed so as to satisfy these two conditions.

<Description of the effects of the first embodiment>
Thus, the optical branching device 60 of the first embodiment, the optical axis _{Ax g-1,} Ax _g, crossed at one point O 'in the plane including the end face 18c, and the optical axis _{Ax g-1} Since the angle formed by Ax _g is twice the spread angle θ / 2 of the branched light B, the first half-value line BH _{(g−1): 1 of} the first branched light B _{g− 1} and the second branched light B _g of the second half line _{BH (g): 2} and always coincide. As a result, regardless of the distance from one end surface 18c, the intensity distribution of the sum of the first branched light B _g-1 and the second branched light B _g always has a plateau region PL. As a result, as long as the exit-side waveguide 36 is provided between the intersections C _a and C _b , the light receiving intensity of the exit-side waveguide 36 is i regardless of the distance between the one end face 18c and the other end face 18d. It can be made equal for all of the output waveguides 36 of the book. In addition, the distance between the other end face 18d and the one end face 18c provided with the emission-side waveguide 36 can be arbitrarily selected. As a result, the degree of freedom in designing the optical branching element 60 increases.

Further, the optical branching device 60 of the first embodiment branches light propagating through the incident-side waveguide 14 into ²ⁿ branched lights B, and the optical axis Ax of these branched lights B is one of the planar waveguides 18. The light beams are emitted so as to intersect with each other at an angle θ at one point O ′ in the plane including the end face 18c. Thereby, the divergence angle (beta) (refer FIG. 13) as the branch light B whole can be enlarged. That is, by causing the optical axis Ax to intersect at a single point O ′, the spread angle β of the entire branched light B is changed to 2 ⁿ × θ / 2 (the branched light B to the spread angle θ / 2 per one branched light B). The angle obtained by multiplying the number ²ⁿ by ²ⁿ ) can be increased. As a result, the optical branching element 60 can be reduced in size for the same reason as described in the reference example 2 .

<Description of Modified Example of Embodiment 1 >
The optical branching device 60 of the first embodiment can be variously modified as described in the reference example 1 .

Considering the ease of manufacturing the exit angle adjustment region 38 in which 2 ⁿ branch waveguides extend toward one point O ′, the number of branch waveguides 23 is practically 2 (n = 1) or 4 (n = 2).

(Embodiment 2 )
A configuration example of the second embodiment will be described with reference to FIGS. FIG. 17 is a plan view showing the overall configuration of the optical branching element of the second embodiment. FIG. 18 is a diagram for explaining the first simulation. FIG. 19 is a diagram for explaining the second simulation.

<Description of Configuration Example of Embodiment 2 >
Referring to FIG. 17, the optical branching device 70 of the second embodiment, the optical branch element 60 of the first embodiment, n = 1, i.e., corresponding to the case of the branch waveguide 23 are two. Therefore, in FIG. 17, detailed description of components common to those in FIGS.

As shown in FIG. 17, since n = 1 in the optical branching element 70, the branching unit 20 includes only one waveguide branch point 24 ₁ and includes only one layer L ₁ (first layer). Consists of. The emission section 22 is configured by the _two branch waveguides 23 ₁ and 23 ₂ connected to the waveguide branch point 24 ₁ .

The two branch waveguides 23 ₁ and 23 ₂ are arranged symmetrically with respect to the light propagation direction Ax ₀ in the incident-side waveguide 14. Then, in the propagation region 30, they are arranged so as to be separated from each other along the propagation direction Ax ₀ at an angle of about 3 °, bent at an obtuse angle at the bent portion 42, and in the emission angle adjustment region 38. , an angle of theta, along the propagation direction Ax _0, are arranged so as to approach each other.

The exit ports 26 ₁ and 26 ₂ of the branching waveguides 23 ₁ and 23 ₂ coincide with each other at the one end face 18c to form one common exit port 26c.

Further, an intersection between the optical axis Ax ₁ and the other end surface 18d of the branched light _{B 1} emitted from the emission port 26 ₁ and _{C a,} the other with the optical axis Ax ₂ of the branched light _{B 2} emitted from the emission port 26 ₂ the intersection of the end face 18d is taken as C _b, the outgoing side waveguide 36 of eight is provided on the other end surface 18d between the two intersection C _a and C _b.

Result of light branching element 70 has such a configuration, the exit port ₂₆ 1, 26 ₂ from the branched light _{B 1} emitted into the planar waveguide 18 the optical axis Ax ₁ and the optical axis Ax ₂ of branched light _{B 2} is , Intersect at one point O ′ in the plane including the one end face 18c.

Further, the emission angle adjusting region 38, by branching waveguide ₂₃ 1, 23 ₂ are disposed at an angle theta, a half line BH ₁ split light _{B 1} and half line BH ₂ split light _{B 2} Propagate in the planar waveguide 18 with always matching. That is, a plateau region PL is formed in a region sandwiched between the optical axes Ax ₁ and Ax ₂ in a plane orthogonal to the propagation direction Ax ₀ . Since the angle formed by the optical axes Ax ₁ and Ax ₂ is θ, the plateau region PL has a spread angle of the angle θ.

<Description of Simulation of Embodiment 2 >
It will now be described two simulation performed for the optical branching device 70 of the second embodiment.

  FIG. 18 is a diagram for explaining the first simulation. In FIG. 18, the vertical axis represents the length (μm) along the light propagation direction (longitudinal direction: hereinafter referred to as Z direction) of the optical branch element 70, and the horizontal axis represents the optical branch element 70. It is the length (μm) in the direction orthogonal to the light propagation direction (short direction: hereinafter referred to as X direction). Further, the seven graphs shown in FIG. 18 indicate the X-direction intensity distribution of light at the Z-direction position corresponding to the baseline of the graph. In these graphs, the height from the baseline indicates the light intensity (arbitrary unit). For easy understanding, FIG. 18 shows the optical branching element 70 shown in FIG. 17 as a gray portion.

  The optical branching element 70 used in the first simulation has a length in the X direction of 100 μm and a length in the Z direction of 1200 μm. More specifically, the length of the incident-side waveguide 14 along the Z direction is about 50 μm, the length of the optical branching and emitting section 16 along the Z direction is about 550 μm, and the Z direction of the planar waveguide 18 The length along the line is approximately 600 μm.

The incident-side waveguide 14 and the branching waveguides 23 ₁ and 23 ₂ are single-mode waveguides having a width in the direction orthogonal to the light propagation direction of 5 μm. The branch angle of the branching waveguide ₂₃ 1, 23 _2, i.e., the angle formed between the branching waveguides 23 ₁ and 23 ₂ in the propagation region 30 was about 3 °.

The refractive index of the incident-side waveguide 14, the branching waveguides 23 ₁ and 23 ₂ and the planar waveguide 18 is 1.47, and the refractive index of the substrate 12 other than the waveguide region is 1.46. The wavelength of the propagated light was 1.55 μm.

As shown in FIG. 18, as a result of the simulation under such conditions, the intensity distribution of the sum of the branched lights B ₁ and B _{2 in} the planar waveguide 18 has a plateau region PL of about 750 μm in the Z direction. It can be seen that this plateau region PL is maintained until the other end surface 18d (Z≈1150 μm) of the planar waveguide 18 is formed.

  As a result of calculating the intensity of light incident on the eight outgoing-side waveguides 36 connected to the other end face 18d of the planar waveguide 18, the uniformity thereof was a value better than 0.5 dB.

  FIG. 19 is a diagram for explaining the second simulation. In FIG. 19, the Z axis is a length (μm) along the light propagation direction (longitudinal direction) of the light branching element 70, and the X axis is a direction (short side) perpendicular to the light propagation direction of the light branching element 70. Direction) (μm), and the I-axis indicates the light intensity (arbitrary unit). The eight graphs shown in FIG. 19 indicate the X-direction intensity distribution of light at the respective Z-direction positions.

The optical branching element 70 used in the second simulation sets the angle formed by the branching waveguides 23 ₁ and 23 ₂ in the propagation region 30 to about 25 ° in order to avoid light loss at the waveguide branching point 24 ₁ . And, the same as the first simulation, except that the length of the branching waveguides 23 ₁ and 23 ₂ in the propagation region 30 is set to about 350 μm.

  As shown in FIG. 19, also in the second simulation, it can be seen that the plateau region PL is formed in the planar waveguide 18 and the plateau region PL is maintained until reaching the other end surface 18d.

  As a result of calculating the intensity of light incident on the eight outgoing-side waveguides 36 connected to the other end face 18d of the planar waveguide 18, the uniformity thereof was a value better than 0.5 dB.

<Description of the effect of Embodiment 2 >
Thus, according to the optical branching device 70 of the second embodiment, the optical axis Ax ₁ split light _{B 1} and the optical axis Ax ₂ of branched light _{B 2} is at an angle theta, including one end face 18c since so as to intersect at a point O 'in the plane, the divergence angle of light obtained by superimposing the two branch light B ₁ and branch light B _2, enlarged to twice that of the single branched optical And the plateau region PL can be formed. As a result, the size of the light branching element 70 can be reduced, and the intensity of the light extracted by the outgoing side branching waveguide 36 can be made equal.

(Embodiment 3 )
A configuration example of the optical branching element according to the third embodiment will be described with reference to FIG. FIG. 20 is a plan view showing an emission angle adjustment region of the light branching element according to the third embodiment.

<Description of Configuration Example of Embodiment 3 >
Referring to FIG. 20, the optical branching device 80 of the third embodiment has a configuration in which the optical branching device 50 of Reference Example 2 and the optical branching device 60 of the first embodiment are combined. . In the optical branching element 80, the structures of the incident-side waveguide 14, the branching section 20, the planar waveguide 18, and the exit-side branching waveguide 36 are the same as those in the reference example 2 and the first embodiment. Detailed description of the structure is omitted.

  As shown in FIG. 20, the optical branching element 80 corresponds to a case where n = 2, that is, four branching waveguides 23 are provided.

At the exit angle adjustment region 44 of the optical branch element 80, the surface and the branching waveguide 23 ₂ and 23 _3, the optical axis _Ax 2, Ax ₃ of the branched light _B 2, _{B 3} emitted from each including one end surface 18c It is arranged so as to intersect at one point O ′. Here, the branching waveguides 23 ₂ and 23 ₃ are arranged so as to form an angle θ (an angle twice the spreading angle θ / 2 of one branching light B). The exit port 26 ₂ of the branching waveguide 23 _2, and the exit port 26 ₃ of the branching waveguide 23 _3, consistent at one end surface 18c, forms a single common exit port 26c. Here, a direction in which the propagation direction of the branched light B ₂ (optical axis Ax ₂ ) and the propagation direction of the branched light B ₃ (optical axis Ax ₃ ) are combined in a vector manner is defined as a combined optical axis AA. The synthetic optical axis AA extends in a direction that coincides with the normal line of the one end face 18c.

Further, the emission angle adjusting region 44 of the optical branch element 80, and the branching waveguide 23 ₁ and 23 ₄ are arranged symmetrically about the exit port 26c. The distance between the exit port ₂₆ 1, 26 ₄ and the exit port 26c is a d, respectively. In the branching waveguides 23 ₁ and 23 ₄ , the optical axes Ax ₁ and Ax ₄ of the branched lights B ₁ and B ₄ emitted from the respective branching waveguides 23 ₁ and 23 ₄ are crossed at a single point O on the combined optical axis AA in the planar waveguide 18. Are arranged to be.

These four branching waveguides 23 ₁ , 23 ₂ , 23 ₃ , and 23 ₄ constitute three adjacent waveguide pairs P1, P2, and P3. That is, the adjacent waveguide pair P1 includes the branched waveguides 23 ₁ and 23 ₂ . Adjacent pair of waveguides P2 consists branching waveguide 23 ₂ and 23 _3. The adjacent waveguide pair P3 is composed of branch waveguides 23 ₃ and 23 ₄ .

Next, with respect to the arrangement of the branch waveguides 23 ₁ , 23 ₂ , 23 ₃ , and 23 ₄ for each of the adjacent waveguide pairs P 1, P 2, and P ₃ , the branched lights B ₁ , B ₂ , B ₃ , and B that are emitted from each of them. ₄ and will be described.

In the adjacent waveguide pair P1 composed of the branching waveguides 23 ₁ and 23 ₂ , the optical axes Ax ₁ and Ax ₂ of the branched lights B ₁ and B ₂ intersect in the planar waveguide 18 and the branched light B _The branching waveguides 23 ₁ and 23 ₂ are arranged so that the first half-value line BH _{1-1 of} 1 and the second half-value line BH _2-2 of the branched light B ₂ intersect at the plateau achievement point _CPL2 . Yes. The plateau achievement point _CPL2 has a distance H from the one end face 18c.

In the adjacent waveguide pair P2 composed of the branched waveguides 23 ₂ and 23 ₃ , the optical axes Ax ₂ and Ax ₃ of the branched lights B ₂ and B ₃ are one point in the plane including the one end surface 18 c of the planar waveguide 18. intersect at O ', and the first half line _{BH 2-1} branched light _{B 2,} as the second half line _{BH 3-2} branched light _{B 3} matches, the branching waveguide ₂₃ 2, 23 ₃ is arranged.

In the adjacent waveguide pair P3 composed of the branched waveguides 23 ₃ and 23 ₄ , the optical axes Ax ₃ and Ax ₄ of the branched lights B ₃ and B ₄ intersect in the planar waveguide 18 and the branched light B Branch waveguides 23 ₃ and 23 ₄ are arranged so that the first half-value line BH _3-1 of the _third line and the second half-value line BH _4-2 of the branched light B ₄ intersect at the plateau achievement point C _PL4 . Yes. The plateau achievement point _CPL4 has a distance H from the one end face 18c.

In the present embodiment, the intersection of the optical axis Ax ₁ and Ax ₂ in adjacent waveguides pairs P1, and the need to intersection of the optical axis Ax ₃ and Ax ₄ in adjacent waveguides pair P3 are coincident There is no.

In summary, in the optical branching element 80, each adjacent waveguide pair P1, P2, P3 satisfies either of the following two conditions.
(1) Half-value lines match (adjacent waveguide pair P2).
(2) At the plateau achievement point in the planar waveguide where the optical axes of the branched light intersect in the planar waveguide, and the half-value lines are longer than the intersection of the optical axes by the distance from the one end face 18c. Intersect (adjacent waveguide pair P1, P3).

In the adjacent waveguide pair P1, P3 that satisfies the condition (2), the distances between the plateau achievement points C _PL2 , C _PL4 and the one end face 18c are set equal to H.

Next, the arrangement angles of the branch waveguides 23 ₁ , 23 ₂ , 23 ₃ , and _{2 4} will be described.

The branching waveguides 23 ₂ and 23 ₃ constituting the adjacent waveguide pair P2 are arranged so as to approach each other along the synthetic optical axis AA at an angle θ with respect to each other. That, alpha ₂ is θ / 2, α ₃ is (π-θ / 2).

Further, as described above, the intersection between the optical axis Ax ₁ and Ax ₂ in adjacent waveguides pairs P1, and, no need to intersection of the optical axis Ax ₃ and Ax ₄ in adjacent waveguides pair P3 are coincident Therefore, the branching waveguides 23 ₁ and 23 ₂ constituting the adjacent waveguide pair P1 may be arranged so as to satisfy only the above-described expression (1).

  That is, the following formula (3) is obtained by modifying the above formula (1).

H tan (α ₁ −θ / 2) = d + H tan θ (3)
By the way, since θ is given by 2λ / D ₀ as described above, a suitable angle range of α ₃ is given by the equation (3).

Similarly, the branch waveguide 23 ₃ and 23 ₄ constituting the adjacent pair of waveguides P3 is arranged so as to satisfy the equation (1).

  That is, the above equation (1) can be transformed into the following equation (4).

H tan (π−θ) = d + H tan (α ₄ + θ / 2) (4)
By the way, since θ is given by 2λ / D ₀ as described above, a suitable angle range of α ₄ is given by the equation (4).

Although not shown, in the optical branching element 80, the other end surface 18d provided with the light receiving opening of the output side waveguide 36 is a surface including the above-described plateau achievement points _CPL2 and _CPL4. The distance from the end face 18c is H.

The light receiving opening of the outgoing side waveguide 36, the intersection C of the intersection _{C a} between the optical axis Ax ₁ and the other end surface 18d of the branched light _{B 1,} the optical axis Ax ₄ and the other end surface 18d of the branched light _{B 4 b} .

<Description of the effect of Embodiment 3 >
Thus, the optical branching device 80 of the third embodiment, since the branching waveguide _{23 1,} 23 _2, 23 3, 23 ₄ are arranged as described above, including the plateau achieved point _{C PL2, C PL4} In the other end surface 18d, the intensity distribution of the sum of the branched lights B ₁ , B ₂ , B ₃ , and B ₄ has a plateau region PL. As a result, the light receiving intensity of light per output side waveguide 36 can be made equal for all of the output side waveguides 36.

<Description of Modification of Embodiment 3 >
In addition, in the optical branching element 80 of Embodiment 3 , the case where the number of the branching waveguides 23 is four was illustrated, However, The number of the branching waveguides 23 is not limited to four. That is, as exemplified in the branching waveguide ₂₃ 2, 23 _3, (wherein, t is an integer of 2 or more) neighboring branch light _{B t-1, B t} optical axis _{Ax t-1, Ax t} of intersect at a point O 'in the plane including the end face 18c of the planar waveguide 18, and the branched light _{B t-1} of the first half line _{BH (t-1): 1} and, second branch light _{B t} A plurality of branching waveguides may be provided such that the half-value line BH _{(t): 2} matches.

Similarly, the optical axes Ax _{u−1 of the} branched lights B _u−1 and B _u (where u is an integer equal to or greater than 2) as exemplified by the branch waveguides 23 ₁ , 23 ₂ and 23 ₃ , 23 _4. , Ax _u is crossed in the planar waveguide 18, and the branched light _{B u-1} of the first half line _{BH (u-1): 1,} a second half line _BH branched light _{B u (u) : May} be provided with a plurality of branching waveguides such that 2 intersects at the plateau achievement point _CPLu .

Further, the optical branching device 80 of the third embodiment can be modified in the same manner as the optical branching device 50 of the reference example 2 and the optical branching device 60 of the first embodiment.

(Embodiment 4 )
A configuration example of the optical wavelength multiplexer / demultiplexer according to the fourth embodiment will be described with reference to FIG. FIG. 21 is a plan view showing the overall configuration of the optical wavelength multiplexer / demultiplexer 90.

  Referring to FIG. 21, the optical wavelength multiplexer / demultiplexer 90 includes one input waveguide 46, a fan-shaped first planar waveguide 48 connected to the input waveguide 46, and a first planar waveguide 48. And an arrayed waveguide diffraction grating 54 composed of a plurality of channel waveguides 52 whose optical path length is changed by a predetermined length, and a second planar waveguide connected to the channel waveguide 52 of the arrayed waveguide diffraction grating 54. A waveguide 56 and a plurality of output waveguides 58 connected to the second planar waveguide 56 are provided.

In the optical wavelength demultiplexer 90, the light of the wavelength lambda ₀ of the input waveguide 46 is incident on the first planar waveguide 48 propagates the channel waveguide 52 of the optical path lengths are different. The light propagating through each channel waveguide 52 generates a phase difference, and this phase difference is converted into a change in the diffraction angle in the second planar waveguide 56 and separated for each of the wavelengths λ ₁ , λ ₂ ,. And output to the output waveguide 58.

In this optical wavelength multiplexer / demultiplexer 90, the optical branching elements 50, 60, 70, and 80 described in the reference example 2 and the first to third embodiments are added to the element portion composed of the channel waveguide 52 and the second planar waveguide 56. One or more of these are used. More specifically, the channel waveguide 52 and the second planar waveguide 56 are connected via the optical branching and emitting section 16 described in Reference Examples 1 and 2 and Embodiments 1 to 3 . In FIG. 21, the light branching and emitting part 16 is shown in a simplified manner in order to avoid complexity.

Each channel waveguide 52 corresponds to the incident-side waveguide 14 described in Reference Example 2 and Embodiments 1 to 3 , and the second planar waveguide 56 is described in Reference Example 2 and Embodiments 1 to 3 . The output waveguide 58 corresponds to the planar waveguide 18 and corresponds to the output-side branching waveguide 36 described in Reference Example 2 and Embodiments 1 to 3 .

In this way an optical wavelength division multiplexer 90 of the fourth embodiment, the device portion consisting of the channel waveguide 52 and the second planar waveguide 56, the light branching element described in Reference Example 2 and Embodiment 1-3 Since one or more of 50, 60, 70, and 80 are used, the uniformity of the intensity of the branched light B separated for each wavelength can be improved in each outgoing side branch waveguide 36.

5 is a partially cutaway plan view showing the overall configuration of the optical element of Reference Example 1. FIG. In FIG. 1, it is the principal part enlarged plan view which expanded the branch part. In FIG. 1, it is the principal part enlarged plan view which expanded the output part vicinity. In FIG. 1, it is the principal part enlarged plan view which expanded the output part vicinity. In the reference example 1 , it is a schematic diagram with which it uses for description of the property of one branch light. In the reference example 1 , it is a schematic diagram which shows an adjacent branched waveguide with branched light. It is a schematic diagram which shows the sum of the intensity distribution of two branched light. FIG. 8 is a schematic diagram showing the sum of intensity distributions of two branched lights. It is a schematic diagram with which it uses for description of arrangement | positioning of a branching waveguide. It is a schematic diagram which shows the sum of the intensity distribution of all the branched lights. 10 is a schematic diagram showing a modification of the optical element of Reference Example 1. FIG. FIG. 6 is a plan view showing an overall configuration of a light branching element of Reference Example 2 . FIG. 3 is a plan view showing an overall configuration of the optical branching element of the first embodiment. In Embodiment 1 , it is the principal part enlarged plan view which expanded the emission angle adjustment area | region vicinity of the light branching element. In Embodiment 1 , it is a schematic diagram which shows an adjacent branched waveguide with a branched light. In Embodiment 1 , it is a schematic diagram which shows the sum of the intensity distribution of two branched light. FIG. 6 is a plan view showing an overall configuration of an optical branching element according to a second embodiment. In Embodiment 2 , it is a figure with which it uses for description of 1st simulation. In Embodiment 2 , it is a figure with which it uses for description of 2nd simulation. FIG. 10 is a plan view illustrating an extraction angle adjustment region of the light branching element according to the third embodiment. FIG. 10 is a plan view showing an overall configuration of an optical wavelength multiplexer / demultiplexer according to a fourth embodiment.

DESCRIPTION OF SYMBOLS 10 Optical element 12 Board | substrate 14, 14 ' Incident side waveguide 14a End surface 16, 16' Optical branch output part 18, 18 'Planar waveguide 18c One end surface 18d Other end surface 20 Branch part 22 Output part 23 Branch waveguide 24 Waveguide branch Point 24 _in input waveguide 24 _out output waveguide 26 exit port 28 Y-branch waveguide 30 propagation region 32, 38, 44 exit angle adjustment region 36 exit side waveguide 42 bent portion 46 input waveguide 48 first plane guide Waveguide 50, 60, 70, 80 Optical branching element 52 Channel waveguide 54 Array waveguide diffraction grating 56 Second planar waveguide 58 Output waveguide 90 Optical wavelength multiplexer / demultiplexer L Layer B Branched light BH Half-value line Ax Optical axis AA synthesis optical axis O, O 'a point PL plateau region _{C PL} plateau achieved point _{S PL} plateau achieve surface S plane C intersection α outgoing angle β divergence angle θ branched light of the entire branched light Spread angle × 2

Claims (7)

An optical element comprising a plurality of incident-side branching waveguides branched from one incident-side waveguide, and a planar waveguide having one end face connected to the branching waveguide,
Wherein each of the branching waveguides are those branch guide and the phase and light intensity are equal from waveguide branch optical branch waveguide to be incident respectively to the planar waveguide as a Gaussian beam,
Each of the branched waveguides is connected to the planar waveguide in an arrangement relationship that satisfies the following conditions.
(1) First and second branched lights that are arbitrarily selected from the plurality of incident-side branching waveguides and sequentially incident on the planar waveguide from the first and second branching waveguides adjacent to each other and propagate therethrough Branch light,
(2) The two points on the plane corresponding to the half value of the peak value of the light intensity of the branched light having a Gaussian distribution in a plane parallel to the surface of the planar waveguide are set as the first and second points, respectively, and (3) When the straight lines that continuously connect the first and second points along the propagation direction of the branched light are respectively the first and second half-value lines,
The first half-value line of the first branched light and the second half-value line of the second branched light are in the same position on the plane, and the second half-value line of the first branched light and the second branch line The first half-value line of light is at a position separated on the plane. When the beam divergence angle of each of the first and second branched lights is θ / 2,
2. The optical element according to claim 1, wherein an intersection angle at the one end face of each of the first and second branch waveguides is θ. An optical branching device comprising the optical device according to claim 2,
The planar waveguide includes the other end surface parallel to the one end surface,
A plurality of exit side branch waveguides in the region of the other end face within the reach of all the branched lights that propagate from the plurality of entrance side branch waveguides connected to the one end face and reach the other end face An optical branching element characterized by comprising: A branch part is further provided between the incident side waveguide and the plurality of incident side branch waveguides,
The branching unit has a hierarchical structure with n stages (n is an integer equal to or greater than 1), and in the m-th hierarchy (m is an integer satisfying 1 ≦ m ≦ n), one input light is converted into two output lights. 2 ^m-1 waveguide branch points are provided to branch into
The waveguide branching point belonging to the first layer where m = 1 is the light propagating through the incident side waveguide as input light,
The waveguide branching point belonging to the mth layer satisfying 2 ≦ m ≦ n−1 uses the light input from one waveguide branching point belonging to the m−1th layer as input light, and enters the m + 1th layer. Output light to each of the two waveguide branch points to which it belongs,
A total of 2 ⁿ branching waveguides are connected to a total of 2 ⁿ⁻¹ waveguide branching points belonging to the nth layer where m = n, and output as branching light is connected to the branching waveguides. The light branching element according to claim 3, wherein light is output. A Y-branch waveguide is configured by an input waveguide that propagates the input light connected to an arbitrary waveguide branch point and two output waveguides through which the output light propagates,
The optical branching element according to claim 4 , wherein an angle formed by the two output waveguides through which the output light propagates is within 4 °. It said branching waveguide on the incident side, the light branching element according to claim 4 or 5, characterized in that it is formed in a curved shape. One or more input waveguides, a fan-shaped first planar waveguide connected to the input waveguide, and a plurality of optical waveguides connected to the first planar waveguide and having an optical path length changed by a predetermined length An arrayed waveguide diffraction grating composed of a channel waveguide, a second planar waveguide connected to the channel waveguide of the arrayed waveguide grating, and a plurality of output waveguides connected to the second planar waveguide In an optical wavelength multiplexer / demultiplexer with
Each element portion of individual said channel waveguide and the second planar waveguide and a plurality of the output waveguide, an optical branching element according to any one of claims 3-6,
Each said channel waveguide respond | corresponds to the incident side waveguide which each said optical branching element has,
The light characterized in that the second planar waveguide and the plurality of output waveguides correspond to both the planar waveguide and the plurality of output-side branching waveguides of each of the optical branching elements. Wavelength multiplexer / demultiplexer.