JP4007329B2 - Arrayed waveguide grating - Google Patents

Description

  The present invention relates to an arrayed waveguide diffraction grating, and more particularly to an arrayed waveguide diffraction grating in which an arrayed waveguide is arranged in a small area to reduce the overall size.

In the prior art, as shown in FIG. 10, an arrayed waveguide using bent waveguides 207 and 208 is used for a waveguide type diffraction grating (see, for example, Patent Document 1). In this case, the optical path length difference between adjacent arrayed waveguides is made constant.
JP 2002-174740 A

  However, the bending radii of the bending waveguides 207 and 208 are determined in consideration of bending loss, and the minimum bending radius Rmin depends on the refractive index difference (Δ) between the core and cladding of the waveguide. Since Δ = 0.3 to 0.75% and Rmin = 25 to 5 mm, the size of the arrayed waveguide diffraction grating becomes large. An arrayed waveguide diffraction grating having a large size limits the number of products manufactured from one substrate, which hinders cost reduction. Further, when the dimension of the arrayed waveguide portion is large, the refractive index of the waveguide is not uniform. This causes a difference in optical path length difference between the arrayed waveguides and degrades the performance of the waveguide type diffraction grating. In order to solve these problems, a method of reducing the minimum waveguide bending radius using a waveguide having a large Δ (= 1.5 to 2.0%) is used. In this case, the size of the arrayed waveguide is reduced, but the coupling loss is increased due to the difference in the spot shape with the optical fiber to be connected. Therefore, it is necessary to insert a spot size converter.

  In view of the above-described problems, an object of the present invention is to provide an arrayed waveguide diffraction grating capable of reducing the area in which the arrayed waveguide is disposed without reducing the minimum waveguide bending radius.

The arrayed waveguide grating of the present invention includes a plurality of input-side single mode waveguides into which input light is incident, an input-side slab waveguide into which light emitted from the input-side single mode waveguide is incident, and the input There are a plurality of arrayed waveguides in which the optical path length difference between the adjacent arrayed waveguides is constant by entering the light emitted from the side slab waveguide, and there are 6 in each of the arrayed waveguides , all of which are adjacent to each other. The corresponding array waveguide exists at different positions in the longitudinal direction of the arrayed waveguide diffraction grating, and is a 90-degree bent reflection structure that reciprocates the optical path twice in the longitudinal direction, and the light emitted from the arrayed waveguide is incident. An output-side slab waveguide, and a plurality of output-side single-mode waveguides that emit light output from the output-side slab waveguide.

According to the present invention, the area of the arrayed waveguide portion can be reduced and both the vertical and horizontal sizes can be reduced , and the array waveguide diffraction grating can be downsized and the influence of refractive index nonuniformity can be suppressed. Connected. As a result, it is possible to increase the number of products manufactured on one substrate, and it is possible to reduce the cost and stabilize the performance. Furthermore, since this shape can be realized by a waveguide having a small refractive index difference with a small coupling loss with an optical fiber, a spot size converter becomes unnecessary.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing a configuration of an arrayed waveguide diffraction grating according to a first embodiment related to the present invention. The arrayed waveguide diffraction grating of the present embodiment includes an input side single mode waveguide 11, an output side single mode waveguide 12, an input side slab waveguide 13, an output side slab waveguide 14, and an input side tapered waveguide 15. , Output side tapered waveguide 16, bent array waveguide (inner side) 17, bent array waveguide (outer side) 18, and reflecting structure 19. The light incident on the arrayed waveguide grating of this embodiment is reflected by the reflection structure 19 in the waveguide and propagates through the output-side waveguide.

  FIG. 2 is an enlarged view showing the configuration of the tapered waveguide in the present embodiment. The tapered waveguide 15 according to the present embodiment includes a straight waveguide 151 and a bending waveguide 152. In order to realize the incidence to the bending array waveguides 17 and 18 with low loss, the tapered linear waveguide 151 is used, and the bending waveguide 152 is used from the place where the single mode waveguide width is obtained. The waveguides 17 and 18 are made parallel.

  FIG. 3 is a diagram showing various parameters necessary for the design of the present embodiment. If the length of the input-side slab waveguide 13 is f, the length of the straight waveguide 151 is t, and the maximum divergence angle is θ, the coordinates (xi, yi) of the end of each straight waveguide 151, bending The coordinates (xai, yai) of the end of the waveguide 152 and the bending radius Ri of the bending waveguide 152 can be expressed using these symbols. Here, it is necessary to consider separately when the number of arrayed waveguides is even (2n) and odd (2n + 1).

(1) In the case of an even number In the region where the Y coordinate is positive, there are n arrayed waveguides. The spread angle θi of each arrayed waveguide in the input side slab waveguide 13 is
θi = (i−1 / 2) Δθ
It becomes. i represents the i-th arrayed waveguide (i = 1, 2,..., n), and Δθ represents a difference in spread angle between the arrayed waveguides, and is represented by the following equation.
Δθ = 2θ / (2n−1)
From the above, (xi, yi) is
xi = (f + t) cosθi
yi = (f + t) sinθi
It becomes.

Next, let us consider making all the arrayed waveguides parallel. Bending waveguides 152 having different bending radii are used, and the bending radius Rmin of the nth array waveguide existing at the end is minimized. Using Rmin, the point (xan, yan) where the tangent of the bending waveguide extending from the point (xn, yn) is parallel to the X axis is derived. (Xan, yan) is as follows.
xan = xn + Rmin sin θn
yan = yn + Rmin (1-cosθn)
Since the spacing d of each arrayed waveguide needs to be uniform,
d = yan / (n−1 / 2)
It can be expressed. Thereby, the point yai of each arrayed waveguide can be easily obtained. On the other hand, xai is determined by the bending radius Ri of each bending waveguide 152. Since the y-coordinates of the start point and the end point of the bending waveguide 152 are obtained, Ri is Ri = (yai-yi) / (1-cosθi)
It can be expressed. Therefore, xai and yai are respectively xai = xi + Ri sinθi
yai = d (i−1 / 2)
It becomes. Each arrayed waveguide is parallel to the x-axis at a uniform interval d, but the value of xai is different. Since the relationship xa1>xa2>...> xan is established, the end faces of the other arrayed waveguides are extended to xa1. An arrayed waveguide having a negative Y coordinate is formed by inverting these arrayed waveguides. The input side tapered waveguide 15 shown in FIG. 2 is designed by the above method.

(2) In the case of odd number In the region where the Y coordinate is positive, there are n arrayed waveguides. Since there are waveguides on the X axis, i = 0, 1,..., N is assumed. The main difference from the even number is the spread angle θi of each array waveguide and the distances d and yai of each array waveguide. Each parameter is shown below.
θi = iΔθ
d = yan / n
yai = id
However, Δθ is θ / n. The definition of other parameters is the same as (1).

  Next, a design method of the reflecting structure 19 and the bent array waveguides 17 and 18 will be described. The X coordinates of the starting points of all the bent array waveguides 17 and 18 are equally xai, and the Y coordinates are separated by a distance d. Furthermore, since the reflection structures 19 in the respective arrayed waveguides are equal, it can be assumed that the incident angles to the reflection structures 19 are all equal.

FIG. 4 is a diagram for explaining a method for deriving the bending radius of the bending array waveguide in the present embodiment. First, a method for deriving the bending radius of the bending array waveguide from the starting points of the bending array waveguides 17 and 18 separated by the distance d so that the angles of incidence on the reflecting structure 19 are equal will be described. Let Rai be the bending radius of the bending waveguide connecting the point (xa1, yai) and the point (xci, yci). However, i is determined by the number of arrayed waveguides, and is 1 to 2n for an even number and 1 to (2n + 1) for an odd number.
Since Ra1 = Rmin when the dimension of the arrayed waveguide is minimized, the central angle θa is determined. Since the reflection structures are equal, the slopes of the tangent lines at the point (xci, yci) are all equal. And yci is the same for all i. From the basis of these conditions, FIG. 4, the following two equations are obtained.
Rai + 1 = d + d1 + Rai
Rai cos θa = Rai + 1 cos θa− (Rai + 1−Rai−d)
Solving these simultaneous equations, Rai + 1 is Rai + 1 = {Rai (θa−1) −d} / (cosθa−1)
It becomes. Since Ra1 = Rmin is given as an initial condition, the bending radius of each bending waveguide is obtained.

  FIG. 5 is a diagram for explaining a method of adjusting the optical path length in the present embodiment. An optical path length difference ΔL is provided between the arrayed waveguides in order to obtain the characteristics of the arrayed waveguide diffraction grating. In an arrayed waveguide having a reflective structure, the shape between the incident-side waveguide and the reflecting-side waveguide is the same, so that an optical path length difference of (ΔL / 2) is given on one side. Since the optical path length difference in the bending waveguide of each arrayed waveguide portion is usually ΔL / 2 or less, a linear waveguide 181 is added to match the optical path length difference. At this time, the length of the straight waveguide 181 is determined in consideration of the optical path length difference from the end of the straight waveguide 151 to the start of the bent array waveguide 18. The final structure is shown in FIG.

  FIG. 6 is a diagram showing the configuration of the reflecting structure in the present embodiment. The reflection structure 19 includes an input / output single mode waveguide 21 (configured by a bent waveguide and a straight waveguide), a slab waveguide 22, and an elliptical metal reflection surface 23. The elliptical focal point 24 of the elliptical metal reflecting surface 23 is positioned in the input / output single mode waveguide 21. This is the configuration of the smallest reflective structure 19. In a system in which the focal length f where the spot diameter can be ignored is several mm or more, spots are imaged on the spot at a symmetrical position 2 f away from the lens or mirror on the optical axis. The spot position to be performed is shorter than 2f. At a certain focal length fmin, the image forming position is equal to f, and when the focal length is further shortened, there is no point at which images are formed. In this configuration, the distance from the end of the single mode waveguide 21 to the mirror reflection point is fmin. In this configuration, the minimum reflection structure 19 is used. However, it is possible to use a mirror having a focal length such that f> fmin.

FIG. 7 (a) is a diagram showing a configuration of an arrayed waveguide grating according to the second embodiment related to the present invention. The arrayed waveguide diffraction grating of the present embodiment includes an input-side single mode waveguide 31, an output-side single mode waveguide 32, an input-side slab waveguide 33, an output-side slab waveguide 34, and an input-side tapered waveguide 35. , Output side tapered waveguide 36, input side array waveguide 37, output side array waveguide 38, first reflection structure 39, second reflection structure 40, and linear waveguide 41. The straight waveguide 41 connects the first and second reflection structures 39 and 40.

  The first reflecting structure 39 and the second reflecting structure 40 have a structure in which the left and right are reversed, and FIG. 7B shows an enlarged configuration of the second reflecting structure 40. The second reflection structure 40 includes an input / output single mode waveguide 51, a slab waveguide 52, and an elliptical metal reflection surface 53, and the input / output single mode waveguide 51 is in a position perpendicular to each other. . The elliptical focal point 54 of the elliptical metal reflecting surface 53 is positioned in the input / output single mode waveguide 51.

The feature of this embodiment is that an arrayed waveguide diffraction grating that is smaller than that of the first embodiment can be realized by using two reflecting structures bent at 90 degrees. The design up to the input side and output side tapered waveguides 35 and 36 is the same as in the first embodiment. Since the first and second reflection structures 39 and 40 bent 90 degrees are the same in each array waveguide, the length difference between the straight input side, the output side array waveguides 37 and 38, and the straight waveguide 41 is different. Provides a constant optical path length difference ΔL. Since the distance between the arrayed waveguides at the ends of the input-side and output-side tapered waveguides 35 and 36 is d, the length of the straight waveguide 41 connecting the bent structures is expressed as Mi + 1 = Mi + 2d. Here, i = 1, 2,..., N. Since the array waveguide interval d is about several tens of μm, the optical path difference between the array waveguides is mainly given by the input side and output side array waveguides 37 and 38. If the lengths of the input-side and output-side arrayed waveguides 37 and 38 are set equal to Li, the following equation is obtained.
Li + 1 = Li + (ΔL-2d) / 2
In this case, however, it is necessary to finely adjust Li by finally considering the optical path difference between the arrayed waveguides generated when the input side and output side tapered waveguides 35 and 36 are designed.

  FIG. 8A is a diagram showing a configuration of an arrayed waveguide grating according to the third embodiment of the present invention. The arrayed waveguide diffraction grating of this embodiment includes an input-side single mode waveguide 61, an output-side single-mode waveguide 62, an input-side slab waveguide 63, an output-side slab waveguide 64, and an input-side tapered waveguide 65. , Output side tapered waveguide 66, input side array waveguide 67, output side array waveguide 68, third reflection structure 69, fourth reflection structure 70, and slab waveguide 71. The difference between the present embodiment and the second embodiment resides in the third and fourth reflection structures 69 and 70 and the slab waveguide 71 connecting the third and fourth reflection structures 69 and 70 in the waveguide. The third reflection structure 69 and the fourth reflection structure 70 have a structure in which the left and right are reversed, and FIG. 8B shows an enlarged configuration of the fourth reflection structure 70. The fourth reflecting structure 70 is configured by one single mode waveguide 81, a slab waveguide 82, and a parabolic metal reflecting surface 83 configured in the slab waveguide 82. The principle is that light emitted from the parabolic focal point 84 is always parallel to the axis (line connecting the parabolic focal point and the apex) after being reflected by the parabolic surface. Therefore, in FIG. 8A, the light collimated by the third reflection structure 69 is propagated into the slab waveguide 71, and the light is output by the fourth reflection structure 70 having the same shape as the third reflection structure 69. The light is condensed on the waveguide 68 and the bending of 180 degrees is realized. Since this embodiment has two reflecting structures as in the second embodiment, it can be expected to be smaller than the first embodiment.

Figure 9 is a diagram showing the structure of the arrayed waveguide grating according to a fourth embodiment of the present invention. The arrayed waveguide diffraction grating of the present embodiment includes an input-side single mode waveguide 91, an output-side single-mode waveguide 92, an input-side slab waveguide 93, an output-side slab waveguide 94, and an input-side tapered waveguide 95. , An output side tapered waveguide 96, an input side arrayed waveguide 97, an output side arrayed waveguide 98, and a 180-degree bending structure 99. The arrayed waveguide diffraction grating of this embodiment includes three sets of 180-degree bending structures shown in the second and third embodiments. In the second and third embodiments, the lateral width is reduced as compared with the conventional arrayed waveguide diffraction grating, so that the shape is elongated. In the present embodiment, by using three sets of 180-degree bending structures 99, the vertical and horizontal sizes of the arrayed waveguide diffraction grating can be reduced. The small arrayed waveguide diffraction grating shown in FIG. 9 uses the 180-degree bending structure 99 using the 90-degree bending twice, three times. That is, six reflective structures bent 90 degrees are used. The design up to the place where the directions of the respective arrayed waveguides are made parallel is the same as in the first to third embodiments. The optical path length difference ΔL between the arrayed waveguides is mainly given by the linear input side and output side arrayed waveguides 97 and 98. As described above, by adopting a structure in which the optical path is reciprocated twice in the longitudinal direction of the arrayed waveguide diffraction grating, both the longitudinal and lateral lengths of the arrayed waveguide portion can be reduced.

FIG. 8A is a diagram showing a configuration of an arrayed waveguide grating according to a third embodiment related to the present invention. The arrayed waveguide diffraction grating of this embodiment includes an input side single mode waveguide 61, an output side single mode waveguide 62, an input side slab waveguide 63, an output side slab waveguide 64, and an input side taper waveguide 65. , Output side tapered waveguide 66, input side array waveguide 67, output side array waveguide 68, third reflection structure 69, fourth reflection structure 70, and slab waveguide 71. The difference between the present embodiment and the second embodiment resides in the third and fourth reflection structures 69 and 70 and the slab waveguide 71 connecting the third and fourth reflection structures 69 and 70 in the waveguide. The third reflection structure 69 and the fourth reflection structure 70 have a structure in which the left and right are reversed, and FIG. 8B shows an enlarged configuration of the fourth reflection structure 70. The fourth reflecting structure 70 is configured by one single mode waveguide 81, a slab waveguide 82, and a parabolic metal reflecting surface 83 configured in the slab waveguide 82. The principle is that light emitted from the parabolic focal point 84 is always parallel to the axis (line connecting the parabolic focal point and the apex) after being reflected by the parabolic surface. Therefore, in FIG. 8A, the light collimated by the third reflection structure 69 is propagated into the slab waveguide 71, and the light is output by the fourth reflection structure 70 having the same shape as the third reflection structure 69. The light is condensed on the waveguide 68 and the bending of 180 degrees is realized. Since this embodiment has two reflecting structures as in the second embodiment, it can be expected to be smaller than the first embodiment.

It is a figure which shows the structure of the arrayed-waveguide diffraction grating by 1st Embodiment relevant to this invention. It is a figure which expands and shows the structure of the taper waveguide in this Embodiment. It is a figure which shows the various parameters required for the design of this Embodiment. It is a figure explaining the derivation method of the bending radius of the bending array waveguide in this Embodiment. It is a figure explaining the adjustment method of the optical path length in this Embodiment. It is a figure which shows the structure of the reflective structure in this Embodiment. It is a figure which shows the structure of the arrayed waveguide diffraction grating by 2nd Embodiment relevant to this invention. It is a figure which shows the structure of the arrayed-waveguide diffraction grating by 3rd Embodiment relevant to this invention. It is a figure which shows the structure of the arrayed-waveguide diffraction grating by 4th Embodiment based on this invention. It is a figure which shows the structure of the conventional array waveguide diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Input side single mode waveguide 12 Output side single mode waveguide 13 Input side slab waveguide 14 Output side slab waveguide 15 Input side taper waveguide 16 Output side taper waveguide 17, 18 Bending array waveguide 19 Reflection structure DESCRIPTION OF SYMBOLS 21 Input / output single mode waveguide 22 Slab waveguide 23 Ellipsoidal metal reflecting surface 24 Focus 31 Input side single mode waveguide 32 Output side single mode waveguide 33 Input side slab waveguide 34 Output side slab waveguide 35 Input Side tapered waveguide 36 Output side tapered waveguide 37 Input side arrayed waveguide 38 Output side arrayed waveguide 39 First reflective structure 40 Second reflective structure 41 Linear waveguide 51 Input / output single mode waveguide 52 Slab waveguide 53 Ellipse Type metal reflecting surface 54 focus 61 input side single mode waveguide 62 output side single mode waveguide 63 input side slab guide Path 64 output side slab waveguide 65 input side taper waveguide 66 output side taper waveguide 67 input side array waveguide 68 output side array waveguide 69 third reflection structure 70 fourth reflection structure 71 slab waveguide 81 single mode guide Waveguide 82 Slab waveguide 83 Parabolic metal reflective surface 84 Focus 91 Input side single mode waveguide 92 Output side single mode waveguide 93 Input side slab waveguide 94 Output side slab waveguide 95 Input side taper waveguide 96 Output side Tapered waveguide 97 Input-side array waveguide 98 Output-side array waveguide 99 180-degree bending structure 151 Linear waveguide 152 Bending waveguide 181 Linear waveguide 201 Input-side single-mode waveguide 202 Output-side single-mode waveguide 203 Input Side slab waveguide 204 Output side slab waveguide 205 Input side tapered waveguide 206 Output Side taper waveguide 207, 208 Bending waveguide d Array waveguide spacing

Claims (1)

A plurality of input-side single-mode waveguides on which input light is incident;
An input-side slab waveguide that receives light emitted from the input-side single-mode waveguide;
A plurality of arrayed waveguides in which the light path length difference between the adjacent arrayed waveguides is constant by entering the light emitted from the input side slab waveguide;
There are six in each of the arrayed waveguides , all of which are present at different positions in the longitudinal direction of the arrayed waveguide diffraction grating from the corresponding one of the adjacent arrayed waveguides, and the optical path is reciprocated twice in the longitudinal direction. A bending reflection structure,
An output-side slab waveguide that receives light emitted from the arrayed waveguide; and
An arrayed-waveguide diffraction grating comprising: a plurality of output-side single-mode waveguides that emit light output from the output-side slab waveguide.

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