JP3618193B2 - Optical circuit element and wavelength router - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical circuit element that controls an equiphase surface of guided light.
[0002]
[Prior art]
As a conventional optical circuit element of this type, for example, there is one disclosed in Document I (Electronics Letters, Vol. 24, pp. 385-386, (1988)). The optical circuit element disclosed in the document I includes curved waveguides having different curvatures and different lengths in an array on a substrate (FIG. 1 of the document I).
[0003]
These bent waveguides have a width of 3 μm (page I, page 386, third row of Document I) and are ridge-shaped bent waveguides. In the element disclosed in this document I, the phase of the guided light is controlled by utilizing the difference in optical path length for each bent waveguide. This type of optical circuit element can be used as various functional elements such as a multiplexer, a demultiplexer, and a wavelength filter.
[0004]
[Problems to be solved by the invention]
However, in the case of the conventional technology described above, when the refractive index difference between the bent waveguide and the substrate or the width of the bent waveguide varies, the equivalent refractive index of the bent waveguide changes. For example, in the case of Document I, since the width of the curved waveguide is narrow, the processing variation of the waveguide width is likely to occur, so that the equivalent refractive index is likely to vary due to this. When the equivalent refractive index of the waveguide changes, an error (hereinafter also referred to as a phase error) occurs with respect to the phase difference to be given by the waveguide. Therefore, it is difficult to perform desired phase control.
[0005]
As one of techniques for avoiding this, there has been a technique disclosed in, for example, Japanese Patent Laid-Open No. 6-194539.
[0006]
Japanese Patent Laid-Open No. 6-194539 discloses a configuration in which curved waveguides each having a straight waveguide connected to both ends are provided in an array (for example, FIG. 1 of the publication). In the case of this technique, the lengths of the arrayed waveguides are different. Therefore, a predetermined phase difference can be given to the guided light in each waveguide (Gazette page 4, column 5, lines 27-30). However, in the case of this technique, the fundamental mode propagates in the vicinity of the outer edge of the bent waveguide in the bent waveguide portion (see the fourth column, page 3, page 7 to 6 from the bottom). Therefore, the propagation constant does not depend on the width of the waveguide (see page 3, column 4, column 5 from the bottom). Therefore, it is possible to prevent a phase error due to the fluctuation of the waveguide width in the bent waveguide.
[0007]
However, even with the technique disclosed in Japanese Patent Laid-Open No. 6-194539, the phase error due to the variation in the waveguide width in the straight waveguide portion cannot be removed. Also, since each curved waveguide has a different curvature (because of different radii), the equivalent refractive index is different for each curved waveguide (details will be described later with reference to FIG. 1 in comparison with the present invention). ). Therefore, this also causes a phase error.
[0008]
Therefore, it is desired to realize an optical circuit element having a phase control unit in which a phase error is less likely to occur than in the past.
[0009]
[Means for Solving the Problems]
Therefore, according to the present invention, in an optical circuit element having a phase control unit for controlling the phase of guided light, the phase control unit is provided at least in a planar waveguide and in the planar waveguide,(I)~(C)And a plurality of arc-shaped low refractive index regions satisfying the above condition.
[0010]
(I): Each of the plurality of arc-shaped low refractive index regions has the same curvature but a different length.
[0011]
(B): Each of the plurality of arc-shaped low refractive index regions is arranged in parallel with the convex side of the arc facing the same direction, in order from the shortest length along the direction.
[0012]
(C): When a line segment corresponding to a tangent at each end point is extended from both ends of each of the plurality of arc-shaped low refractive index regions to the outside of the low refractive index region, the line segments are respectively formed on both end sides. The plurality of arc-shaped low-refractive index regions are arranged so as to generate gathering points.
[0013]
According to the optical circuit element of the present invention, the following effects can be obtained. This will be described with reference to FIGS.
[0014]
Here, FIG. 1A is a diagram for explaining a state of wave guide in the optical circuit element of the present invention. However, FIG. 1A shows a planar waveguide 11 and a plurality of arc-shaped low refractions provided in the planar waveguide 11 for simplification.rateLow refractive index region 13 of one of the regions₁The figure which paid its attention to is shown. FIG. 1B is a diagram showing a refractive index distribution along the radius R direction of the arc in the system shown in FIG. FIG. 1C is a diagram showing an equivalent refractive index distribution (details will be described later) for the system shown in FIG.
[0015]
Planar waveguide 11 and arc-shaped low refractive index region 13₁  Maxwell's equations can be described as follows, for example, as disclosed in Reference II (Journal of Lightwave Technology (J. Lightwave Technology Vol. 11, November 1993, p. 1737). ing.
[0016]
[∂²/ ∂u²+ {K₀ ²n_t ²(U) -r_t ²}] Ψ_t(U) = 0
However, u = R_tln (r / R_t), R_tIs an arc-shaped low refractionrateThe radius of the region, r is the radial position, k₀= 2π / λ, λ is the wavelength of light to be guided, n_t(U) = n {r (u)} · exp (u / R_t), R (u) = R_t・ Exp (u / R_t). Ψ_t(U) represents the field distribution of light.
[0017]
Where radius R_tIs sufficiently larger than the field distribution (u / R_t<< 1), as disclosed in Document II, low refractionrateIn the vicinity of the region 13 (near the wavelength), n_t(U) = n (R_t+ U) (1 + u / R_t).
[0018]
n (R_t  Since + u) is the original refractive index profile, the equivalent refractive index profile n_t  (U) is a function 1 + u / R that increases in the radial direction to the original refractive index profile n._t  It will be a thing multiplied. This is schematically shown in FIG.
[0019]
Then, the planar waveguide 11 and the arc-shaped low refractive index region 13 are formed.₁  In the system constituted by the arc-shaped low refractive index region 13₁  The inner edge (edge portion) 13a of the sapphire has a waveguide structure. Therefore, the light is arc-shaped low refractive index region 13.₁  It propagates along the inner edge 13a. This state is shown as a light field distribution 15 in FIGS.
[0020]
For this reason, in the present invention, light is not affected by the concept of the width of the waveguide. Therefore, there is no phase error due to the fluctuation of the waveguide width.
[0021]
Furthermore, the arc-shaped low refractive index region 13₁  From the dispersion curve, it can be seen that the equivalent refractive index does not change so much with respect to the change in the refractive index distribution n using the above-described fundamental mode in the waveguide structure generated at the inner edge (edge portion) 13a. Therefore, the planar waveguide 11 and the low refractive index region 13₁  Even if the refractive index changes, the equivalent refractive index does not change much. Therefore, even if a refractive index change occurs in a planar waveguide or a low refractive index region, a phase error hardly occurs.
[0022]
In addition, the above n_t  As can be understood from the equation, the radius R_t  Changes, n_t  As a result, the equivalent refractive index of the waveguide structure also changes. In the case of the prior art disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-194539, since the radius is different for each bent waveguide, the equivalent refractive index also changes for each bent waveguide. However, in the present invention, the radius R_t  Therefore, the equivalent refractive index in the above-described waveguide structure is the same for each of the plurality of arc-shaped low refractive index regions.
[0023]
In addition, since the lengths of the plurality of low refractive index regions are different from each other, a predetermined phase difference is given to the light propagating through the plurality of low refractive index regions.
[0024]
As described above, according to the present invention, an optical circuit element including a phase control unit in which a phase error is less likely to occur than in the prior art is realized.
[0025]
In implementing this invention, the plurality of arc-shaped low refractionsrateIn the vicinity of both ends of each region, it is preferable to provide a mode conversion unit that mutually converts a guided light mode propagating through the planar waveguide and a guided light mode propagating through the phase control unit.
DETAILED DESCRIPTION OF THE INVENTION
[0026]
In this way, light propagating through the planar waveguide can be converted into a propagation mode suitable for the phase control unit, while light propagating through the phase control unit can be converted into a propagation mode suitable for the planar waveguide. Therefore, light can be propagated efficiently.
[0027]
As the mode converter, a low refractive index region (second low refractive index region, see FIG. 4) having a planar shape in which the width of the planar waveguide portion is narrowed toward the arc-shaped low refractive index region is used. Is preferred. In this way, light from the planar waveguide can be collected and condensed to the same width as the field distribution 15 described with reference to FIG. 1, so that the light from the planar waveguide can be efficiently transmitted to the phase control unit. You can enter. On the other hand, when the light propagated through the phase control unit is output to the planar waveguide, it can be returned to a spherical wave.
[0028]
In addition, each of the arc-shaped low refractive index region and the second low refractive index region is preferably configured by a region from which the corresponding portion of the planar waveguide is removed. Thus, the arc-shaped low refractive index region and the second low refractive index region can be easily manufactured.
[0029]
In carrying out the present invention, an input / output waveguide having an end located at a portion corresponding to the point where the line segments gather in the planar waveguide, and one or more input / output waveguides arranged in line with the input / output waveguide are arranged. When the output waveguide group is provided in the planar waveguide, various functional elements such as a wavelength router and a demultiplexer can be realized.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the optical circuit element of the present invention will be described below with reference to the drawings. However, each drawing schematically shows the size, shape, and arrangement relationship of each component so that the present invention can be understood. Moreover, in each figure, the same component is shown with the same number.
[0031]
1. First embodiment
FIG. 2 is a plan view showing a basic configuration (first embodiment) of the optical circuit element of the present invention.
[0032]
In the optical circuit element of the present invention, the planar waveguide 11 and the following are provided in the planar waveguide 11.(I)~(C)A plurality of arc-shaped low refractive index regions 13 satisfying the following condition:₁~ 13_FiveThus, the phase control unit 20 is configured. Of course, the number of arc-shaped low refractive index regions is not limited to the illustrated example.
[0033]
Here, the planar waveguide 11 is composed of a medium made of a material capable of guiding light, for example, a film formed on a substrate or a base. Examples of such a medium include a substrate and a film made of any suitable material such as glass, a compound semiconductor, and a polymer.
[0034]
Further, the low refractive index region 13₁~ 13_FiveEach is a region showing a lower refractive index than the planar waveguide 11. For example, it is easy to configure this region by removing each predetermined portion of the planar waveguide 11. Low refraction of the air layer of the removal tracerateBecome an area.
[0035]
However,(I): A plurality of arc-shaped low refractive index regions 13₁~ 13_FiveEach has the same curvature but different lengths. However,(B): A plurality of arc-shaped low refractive index regions 13₁~ 13_FiveIn each case, the convex side of the arc is directed in the same direction (from the bottom to the top in the drawing in FIG. 2), and in order from the shortest length along the direction, that is, in the example of FIG.₁~ 13_FiveAre arranged in parallel in this order. However,(C): A plurality of arc-shaped low refractive index regions 13₁~ 13_FiveA line segment Lr corresponding to a tangent line at each end point from both ends₁~ Lr_FiveAre extended to the outside of the region, and a plurality of arc-shaped low refractive index regions 13 are formed so that the points P where the line segments are gathered are formed on both ends.₁~ 13_FiveAre arranged in the planar waveguide 11 (details of this arrangement method will be described later).
[0036]
Line segment Lr₁  ~ Lr₅  Are a plurality of arc-shaped low refractive index regions 13 from the point P.₁  ~ 13₅  It corresponds to the optical path to each.
[0037]
In the phase control unit 20 shown in FIG. 2, as already described with reference to FIG.₁~ 13_FiveA waveguide structure results along each inner edge. Further, the arc-shaped low refractive index region 13 from the point P₁~ 13_FiveThe optical path length is different for each optical path passing through each. As a result, low refractionrateRegion 13₁~ 13_FiveThe light propagating through each exhibits a phase difference. Therefore, a phase control unit is configured.
[0038]
Then, an example of the formation method of the phase control part 20 of this invention is demonstrated below. In the following description, the above-described line segment Lr₁  ~ Lr₅  Is the line segment Lr_S  And an arc-shaped low refractive index region 13₁  ~ 13₅  Is an arc-shaped low refractive index region 13_S  And may also be represented as representatives. However, S is a value ranging from 1 to the number of low refractive index regions (the same applies to S below).
[0039]
In the structure shown in FIG._SAnd the line segment Lr_SArc-shaped low refractive index region 13 connected to_SL is the sum of half length_SIt expresses. That is, line segment Lr from point P_SThrough the arc-shaped low refractive index region 13_SThe length of the waveguide up to half the position (position intersecting the center line Y in FIG. 2)_SIt expresses. The length issmallArc-shaped low refractive index region 13₁In the line segment PQ (also referred to as a reference line PQ) connecting the locality center Q and the point P, the length L of the waveguide_SLp is the length when projected_SIt expresses.
[0040]
Here, the arc-shaped low refractive index region 13_S  Half of the length is 2πR_S  ・ Φ_S  / 2π = R_S  ・ Φ_S  L_S  L_S  = Lr_S  + R_S  φ_S  Can be rewritten.
[0041]
Where φ_S  Can be any value depending on the design, but here φ_S  = Θ_S  And Where θ_S  Is the reference line PQ and line segment Lr_S  Is the angle between
[0042]
φ_S  = Θ_S  If compared with the case where it does not do so, for example, the region 13 from the point P₁  ~ 13₅  Loss when distributing light to This is the line segment Lr_S  And region 13_S  This is because the vicinity of the starting point is parallel.
[0043]
Further, the arc-shaped low refractive index region 13_S  Each radius R_S  Are the same value R. Therefore, L_S  L_S  = Lr_S  + Rθ_S  Can be rewritten.
[0044]
Then, adjacent L_S  The difference between them is ΔL_S  This ΔL_S  Is
ΔL_S  = (Lr_{S + 1}  + Rθ_{S + 1}  )-(Lr_S  + Rθ_S  ) = Lr_{S + 1}  -Lr_S  + Rθ_{S + 1}  -Rθ_S  = ΔLr_S  + RΔθ_S        ... (a) However, ΔLr in the equation (a)_S  = Lr_{S + 1}  -Lr_S  And Δθ_S  = Θ_{S + 1}  −θ_S  It is.
[0045]
ΔL_S  Is replaced with ΔLef, the equation (a) can be rewritten into the following equation (b). Here, ΔLef is each L_S  The optical path length difference for obtaining a desired phase difference.
[0046]
ΔLef = ΔLr_S  + RΔθ_S      ... (b)
On the other hand, the above Lp_S  Is Lp_S  = Lr_S  cosθ_S  + Rsinφ_S  (See FIG. 2). However, as mentioned above, φ_S  = Θ_S  Lp_S  Is Lp_S  = Lr_S  cosθ_S  + Rsinθ_S  It can be expressed.
[0047]
Adjacent Lp_S  ΔLp is the difference between them_S  This ΔLp_S  Is
ΔLp_S  = ΔLr_S  ・ Cos θ_S  + Lr_S  (-Sinθ_S  ) Δθ_S  + Rcosθ_S  ・ Δθ_S        ... (c)
It becomes.
[0048]
In this equation (c), ΔLr_S  ・ Cos θ_S  And Lr_S  (-Sinθ_S  ) ・ Δθ_S  And R · cos θ_S  ・ Δθ_S  Each is a value of each part as shown in FIG.
[0049]
By the way, Lp_S  As already explained, L_S  Is projected on the reference line PQ, so ΔLp_S  = 0. Therefore, the equation (c) can be rewritten as the following equation (d).
[0050]
ΔLr_S  ・ Cos θ_S  + (R cos θ_S  -Lr_S  sinθ_S  ) Δθ_S  = 0 (d)
Next, ΔLr is modified by modifying the above equation (b)._S  = ΔLef−RΔθ_S  And substitute this into the above equation (d). Then
(ΔLef−RΔθ_S  ) ・ Cosθ_S  + (R cos θ−Lr_S  sinθ_S  ) Δθ_S  = 0 (e)
Is obtained. If you rewrite this,
ΔLef · cos θ_S  -RΔθ_S  ・ Cos θ_S  + RΔθ_S  ・ Cos θ_S  -Lr_S  sinθ_S  ) Δθ_S  = 0
It becomes. Further organizing this formula,
ΔLef · cos θ_S  -Lr_S  sinθ_S  Δθ_S  = 0 (f)
Is obtained.
[0051]
This equation (f) is expressed as Δθ_S  Solving for
Δθ_S  = ΔLef · cos θ_S  / Lr_S  sinθ_S      ... (g)
Is obtained.
[0052]
Where Δθ_S  In order to obtain the calculation accuracy in determining_S  (Lr_{S + 1}  + Lr_S  ) / 2 = Lr_S  + ΔLr_S  / 2 and θ_S  As (θ_{S + 1}  + Θ_S  ) / 2 = θ_S  + Δθ_S  It is preferable to use / 2. This is because, as shown in FIG. 3, when the point B is obtained from the point A, the value at the point C, which is an intermediate point between the points A and B, is used instead of the value at the point A._S  This is because the calculation accuracy is improved by obtaining.
[0053]
However, ΔLr_S  And Δθ_S  Are values to be obtained from now. Therefore, ΔLr_S  ΔLr instead of_S-1  Δθ_S  Instead of Δθ_S-1  Is used.
[0054]
Then, the above equation (g) can be rewritten as the following equation (1).
[0055]
Δθ_S  = ΔLef · cos θ (θ_S  + Δθ_S-1  / 2) / (Lr_S  + ΔLr_S-1  / 2) sin (θ_S  + Δθ_S-1  / 2) (1)
ΔLr_S  With respect to, the following equation (2) is obtained from the above equation (b).
[0056]
ΔLr_S  = -R · Δθ_S  + ΔLef (2)
Then, Lr_{S + 1}  And θ_{S + 1}  Can be obtained by the following equations (3) and (4), respectively.
[0057]
Lr_{S + 1}  = Lr_S  + ΔLr_S      ... (3)
θ_{S + 1}  = Θ_S  + Δθ_S            ... (4)
According to these equations (1) to (4), Lr in FIG.₁  ~ Lr₅  And θ₁  ~ Θ₅  Is obtained as follows, for example.
[0058]
First, as an initial value, θ₁, Δθ₀, Lr₁, ΔLr₀To decide. Where ΔLr₀Is ΔLr from the equation (2).₀= -R · Δθ₀+ ΔLef. Δθ₀For example, the diffraction angle of the input waveguide when the input / output waveguide is placed at the point P (FIG. 2) and the low refractionrateRegion 13_SFrom the number of₀= (Diffraction angle of input waveguide) / (Low refractionrateRegion 13_SThe number given by Lr₁(I) Waveguide spacing in an input / output waveguide group (for example, see FIG. 4) composed of an input / output waveguide placed at point P and one or more input / output waveguides parallel to the input / output waveguide , (Ii) number of waveguides and (iii) low refractionrateRegion 13_SFrom the diffraction angle of the array consisting of₁= (Waveguide spacing) x (number of waveguides) / (low refractionrateRegion 13_SThe value given by the diffraction angle of the array of
[0059]
Each initial value θ determined as above₁  , Δθ₀  , Lr₁  And ΔLr₀  Substituting each into the above equation (1), Δθ₁  Ask for. This calculated Δθ₁  Is substituted into the above equation (2), and ΔLr₁  Ask for. Next, from the above equation (3), Lr₂  And θ from the above equation (4)₂  Ask for.
[0060]
Obtained these, θ₂  , Lr₂  , Δθ₁  , ΔL₁  Are respectively substituted into the above equation (1),..., And the above processing is repeated until S reaches the number of low refractive index regions. As a result, Lr₁  ~ Lr₅  And θ₁  ~ Θ₅  Can be requested.
[0061]
Next, θ₁The initial value is changed, and the same processing as described above is repeated. And Lp_S(See Figure 2)smallΘ₁In other words, the optical circuit element lengthsmallΘ₁Find out. And Lp_SThe mostsmallCan be θ₁Lr obtained by the above processing sequentially based on_SAnd θ_SBased on the above, an optical circuit element is configured.
[0062]
2. Second embodiment
Next, an embodiment in which the optical circuit element of the present invention is applied to a wavelength router will be described. FIG. 4A is a plan view for explaining the wavelength router 30.
[0063]
The wavelength router includes the phase control unit 20 described in the first embodiment in the planar waveguide 11. Furthermore, the planar waveguide 11 has an input / output waveguide 31a whose end is located at a portion corresponding to the point P described in the first embodiment, and one or more input / output waveguides 31b arranged in parallel therewith, The planar waveguide 11 includes an input / output waveguide group 31 including 31c (two in the illustrated example). The input / output waveguide group 31 is provided on both sides of the phase control unit 20.
[0064]
Each input / output waveguide group 31 is an input / output waveguide group in which other input / output waveguides 31b and 31c are positioned on the left and right sides of the input / output waveguide 31a. Of course, the number of input / output waveguides constituting the input / output waveguide group 31 is not limited to three.
[0065]
Each of the input / output waveguides 31a to 31c can be constituted by, for example, a portion in which the planar waveguide 11 is left in a strip shape. That is, as shown in FIG. 4 (A), the planar waveguide portions on both sides of the portion to be striped are removed to a certain depth so that the planar waveguide 11 remains in the strip shape, and the recess 33 is formed into the planar waveguide. 11 is formed. A planar waveguide portion sandwiched between these recesses is used as an input / output waveguide.
[0066]
Further, the optical circuit element (wavelength router) 30 has an arc-shaped low refraction.rateRegion 13₁~ 13_FiveNear both ends, there is provided a mode conversion unit 35 for mutually converting the mode of guided light propagating through the planar waveguide 11 and the guided light mode propagating through the phase control unit 30.
[0067]
Details of the mode conversion unit 35 will be described with reference to FIG. Here, FIG. 4B shows an arc-shaped low refractive index region 13 in FIG.₄  , 13₅  It is the enlarged view which paid its attention to the edge part vicinity.
[0068]
In this case, the mode conversion unit 35 has an arc-shaped low refractive index region 13.₄  , 13₅  It is composed of a low refractive index region in which the width of the planar waveguide portion is narrowed toward the surface, specifically, a low refractive index region (second low refractive index region) in which the width of the planar waveguide is tapered. It is. The second low refractive index region 35a can be constituted by, for example, a removal trace obtained by removing a corresponding portion of the planar waveguide 11.
[0069]
As seen from point P, δθ_S= [(Θ_S−θ_S-1) + (Θ_{S + 1}−θ_S)] / 2, the distance W between the tips of the adjacent second low refractive index regions 35a, that is,ChiThe width W of the planar waveguide portion at the tip is W = 0.7 × δθ_S× Lr_SIt is preferable to provide the second low refractive index region 35a so as to be a value given by This is because mode conversion can be performed efficiently. In addition, the width W of the adjacent second low refractive index region 35a._EAlthough not limited to this, it is, for example, 10 μm.
[0070]
Further, the length x (see FIG. 4B) of the second low refractive index region 35a along the waveguide direction may be short, for example, about several hundred μm. With such a length, the phase error in the mode converter does not become a problem. The second low refractive index region 35a is an arcuate low refractive index region 13._S  And can be formed integrally.
[0071]
This wavelength router 30 can be used as follows, for example. For example, light input from the input port to the input / output waveguide 31a is radiated to the planar waveguide 11 after passing through the input / output waveguide 31a. This emitted light is a spherical wave. This spherical wave is converted by the mode converter 35 into a mode that propagates along the inner edge of the low refractive index region described in FIG. That is, the spherical wave isPaAre collected by the second low-refractive index region 35a and narrowed to a width equivalent to the field distribution 15 described with reference to FIG.
[0072]
The light entering the phase control unit 20 is controlled in equiphase plane by the phase control unit 20. Next, this light is returned to a spherical wave in the mode conversion unit 35 on the exit side of the phase control unit 20, and then interferes on the other input / output waveguide group 31, and the input / output waveguide group A portion having a high power density is generated on 31. This light with high power density is output from any of the input / output waveguides 31a to 31c.
[0073]
For example, when light that is wavelength-multiplexed is input to the input / output waveguide 31 a of one input / output waveguide group 31, light having a predetermined wavelength or wavelength from one waveguide in the other input / output waveguide group 31 is input. Is output, and one or a plurality of lights having other predetermined wavelengths are output from another waveguide. A specific example of such a wavelength router will be described below.
[0074]
4 is a wavelength router described with reference to FIG. 4A, wherein the number of arc-shaped low refractive index regions is 16, and the number of input / output waveguides constituting the input / output waveguide group is increased. Configure the router. However, in designing this wavelength router, when using the above equations (1) and (2), θ₁  = 1 rad, Δθ₀  = 0.01 rad, Lr₁  = 1500 μm, R = 250 μm, and ΔLef = 20 μm.
[0075]
Then, from the waveguide located at the center of one of the input / output waveguide groups 31 of this wavelength router (the waveguide corresponding to the point P described above, the same applies hereinafter), the wavelength of 1.53 to 1.56 μm. When wavelength light of a range is input, what wavelength light is output from the waveguide located at the center of the other input / output waveguide group 31 is simulated (this is referred to as Experiment I). Separately from this, a wavelength in the range of 1.53 to 1.56 μm from the waveguide shifted from the waveguide located at the center in one input / output waveguide group 31 by one downward in FIG. Simulation of what wavelength light is output from a waveguide shifted in the upper direction of FIG. 4A from the waveguide located at the center of the other input / output waveguide group 31 when light is input. (This is called Experiment II).
[0076]
Note that the above simulation is performed on the output waveguide of the monitoring target for all the paths from the waveguide to which the light is input to the output waveguide of the monitoring target through the planar waveguide 11 and the phase control unit 20. This was done by calculating the sum in consideration of the intensity and phase of the.
[0077]
The wavelength transmittance characteristics obtained by the simulations of Experiment I and Experiment II are shown in FIG. However, in FIG. 5, the horizontal axis represents wavelength and the vertical axis represents transmittance. The result of Experiment I is indicated by a solid line, and the result of Experiment II is indicated by a broken line.
[0078]
From FIG. 5, the wavelength router in this case selectively routes two types of wavelength light to one output waveguide. In the case of Experiment I, the first light near the wavelength 1.538 and the second light near the wavelength 1.555 are selectively routed. In the case of Experiment II, the first light near the wavelength 1.535 and the second light near the wavelength 1.552 are selectively routed.
[0079]
【The invention's effect】
As apparent from the above description, according to the optical circuit element of the present invention, in the optical circuit element having the phase control unit for controlling the phase of the guided light, the phase control unit is at least a planar waveguide, Provided in the planar waveguide and(I)~(C)And a plurality of arc-shaped low refractive index regions satisfying the above condition.
[0080]
Therefore, light propagates along the inner edge (edge portion) of the arc-shaped low refractive index region. Therefore, there is no phase error due to the fluctuation of the waveguide width.
[0081]
Furthermore, since the fundamental mode in the waveguide structure generated at the inner edge (edge portion) of the arc-shaped low refractive index region can be used, the variation in the equivalent refractive index is small. Therefore, even if a refractive index change occurs in a planar waveguide or a low refractive index region, a phase error hardly occurs.
[0082]
Furthermore, since each of the plurality of arc-shaped low refractive index regions has the same radius R, the equivalent refractive index variation due to the variation in radius does not occur.
[0083]
On the other hand, since each of the plurality of low refractive index regions has a different length, a predetermined phase difference can be given to the light propagating through each of the plurality of low refractive index regions.
[0084]
Therefore, an optical circuit element having a phase control unit in which a phase error is less likely to occur than in the prior art is realized.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram for explaining the operation and effect of the present invention.
FIG. 2 is a diagram for explaining an optical circuit element according to a first embodiment of the present invention, and in particular, for explaining a basic configuration.
FIG. 3 is a diagram for explaining an optical circuit element according to the first embodiment of the present invention, and more particularly for explaining details of a formation method (design method);
FIG. 4 is a diagram for explaining an optical circuit element according to a second embodiment of the present invention, and particularly a diagram for explaining an example of a wavelength router as an application example;
FIG. 5 is an explanatory diagram of the result of simulating the characteristics of a wavelength router.
[Explanation of symbols]
11: Planar waveguide
13₁  ~ 13₅  (13_S  , 13_{S + 1}  ): Arc-shaped low refractive index region
15: Light field distribution
20: Phase control unit
Lr₁  ~ Lr₅  :line segment
P: Point where line segments gather
PQ: Reference line
φ₁  ~ Φ₅  : Half the central angle of the arc-shaped low refractive index region
R: radius of arc-shaped low refractive index region
Y: Center line
30: Wavelength router
31: Input / output waveguide group
31a to 31c: input / output waveguides
33: Concave portion (part from which planar waveguide is removed)
35: Mode converter
35a: second low refractive index region

Claims (9)

In an optical circuit element having a phase control unit for controlling the phase of guided light,
The phase control unit includes at least a planar waveguide and a plurality of arc-shaped low refractive index regions provided in the planar waveguide and satisfying the following conditions (a) to (c) : An optical circuit element.
(A) : Each of the plurality of arc-shaped low refractive index regions has the same curvature but a different length.
(B) Each of the plurality of arc-shaped low-refractive index regions is arranged in parallel with the convex side of the arc facing the same direction in order from the shortest length along the direction.
(C) : When a line segment corresponding to a tangent at each end point is extended from both ends of each of the plurality of arc-shaped low refractive index regions to the outside of the low refractive index region, The plurality of arc-shaped low refractive index regions are arranged so that points where line segments are gathered are formed. The optical circuit element according to claim 1,
The propagation mode of guided light is mutually converted between the propagation mode suitable for the planar waveguide and the propagation mode suitable for the phase control unit in the vicinity of both ends of each of the plurality of arc-shaped low refractive index regions. An optical circuit element comprising a mode conversion unit. The optical circuit element according to claim 2,
Low refractive index regions each having a planar shape that is provided in the vicinity of the ends of the plurality of arc-shaped low refractive index regions and narrows the width of the planar waveguide portion toward the arc-shaped low refractive index regions ( An optical circuit element comprising a second low refractive index region) as the mode conversion unit. The optical circuit element according to claim 1,
An input / output waveguide group consisting of an input / output waveguide whose end is located at a portion corresponding to the point where the line segments gather in the planar waveguide, and one or more input / output waveguides arranged in parallel with the input / output waveguide group, An optical circuit element provided in a waveguide. The optical circuit element according to claim 1,
Each of the plurality of arc-shaped low refractive index regions is a region obtained by removing a corresponding portion of the planar waveguide. The optical circuit element according to claim 3,
Each of the second low refractive index regions is a region obtained by removing a corresponding portion of the planar waveguide, respectively. The optical circuit element according to claim 1,
Wherein a plurality of arc-shaped low refractive index connecting the points of the line segment and the center of curvature of the arc-shaped low refractive index region of minimum gather length line in the region (reference line), the plurality An angle formed with each line segment extended from each of the arc-shaped low refractive index regions is θ _S (where S is 1 to the number of the arc-shaped low refractive index regions, the same applies hereinafter),
_Let Δθ _S be the angle between adjacent line segments,
_Let Lr _{S be} the length of each line segment,
When the difference between adjacent line segments is ΔLr _S ,
The Δθ _S is defined by the following formula (1), and the ΔLr _S is defined by the following formula (2) (wherein the formula (1) and the formula (2) ΔLef is an optical path length difference for obtaining a desired phase difference, and R in equation (2) is a radius of the plurality of arc-shaped low refractive index regions.
Δθ _S = ΔLef · cos θ (θ _S + Δθ _S-1 / 2) / (Lr _S + ΔLr _S-1 / 2) sin (θ _S + Δθ _S-1 / 2) (1)
ΔLr _S = −R · Δθ _S + ΔLef (2) The optical circuit element according to claim 7,
An optical circuit element, wherein an angle θ _S formed by the reference line and each line segment is an angle φ _S that is half the center angle of an arc-shaped low refractive index region corresponding to each line segment. A wavelength router comprising the optical circuit element according to claim 4.

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