JP4163553B2 - Arrayed waveguide diffraction grating type optical multiplexer / demultiplexer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an arrayed waveguide grating optical multiplexing / demultiplexing circuit with improved flatness in a transmission wavelength band.
[0002]
[Prior art]
Currently, an optical wavelength division multiplexing communication system using a plurality of optical wavelengths is being actively developed to expand communication capacity. In this optical wavelength division multiplexing communication system, optical wavelength multiplexing / demultiplexing that multiplexes optical signals of a plurality of wavelengths on the transmitter side or demultiplexes a plurality of optical signals in one optical fiber to different ports on the receiver side. As a wave circuit, an arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit is widely used.
[0003]
FIG. 1 shows an example of a conventional arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit (for example, see Non-Patent Document 1). On a flat substrate 100, an input waveguide 101, a first slab waveguide 102, An arrayed waveguide 103, a second slab waveguide 104, and an output waveguide 105 are formed.
[0004]
In the above configuration, the light guided to the input waveguide 101 spreads in the first slab waveguide 102 and is branched to the respective arrayed waveguides 103. Then, it is multiplexed again by the second slab waveguide 104 and guided to the output waveguide 105.
[0005]
Here, the optical field pattern projected on the array waveguide end of the first slab waveguide 102 is basically copied to the end of the second slab waveguide 104 on the array waveguide side. In the arrayed waveguide 103, adjacent optical waveguides are designed so that their optical path lengths are different by exactly ΔL, and the field has an inclination depending on the wavelength of the input light. By this inclination, the position where the optical field is focused on the output waveguide side of the second slab waveguide 104 changes for each wavelength, and as a result, wavelength demultiplexing becomes possible.
[0006]
Such an arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit is becoming an indispensable optical component in an optical wavelength multiplexing communication system in which a plurality of signals having different wavelengths are transmitted through one optical fiber.
[0007]
FIG. 2 shows another example of a conventional arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit, in this example, the transmission wavelength characteristic for each wavelength is flattened to expand the band (for example, see Non-patent Document 2 and Patent Document 1). As shown in FIG. 1B, the joint portion between the input waveguide 101 and the first slab waveguide 102 of the arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit shown in FIG. A parabolic waveguide 106 is provided.
[0008]
In this configuration, a secondary mode electric field is generated due to the discontinuity between the input waveguide 101 and the parabolic waveguide 106. As a result, a bimodal electric field distribution as shown in FIG. 3 is formed by superimposing the electric field of the 0th-order mode and the electric field of the second-order mode at the terminal portion of the parabolic waveguide 106.
[0009]
FIG. 3 shows the electric field distribution at the end portion of the parabolic waveguide. The electric field distribution 201 of the zeroth mode showing a normal Gaussian distribution and the secondary mode showing a distribution having one valley between two peaks. Is superimposed on the electric field distribution 202 to form a bimodal electric field distribution 203. In FIG. 3, the vertical axis represents the electric field amplitude, and the horizontal axis represents the position (x) in the width direction of the core, where the core center is zero.
[0010]
As described above, this bimodal electric field distribution is regenerated on the output waveguide side of the second slab waveguide 104 and coupled to the output waveguide 105, so that the bandwidth can be expanded by flattening the transmission wavelength characteristics. The
[0011]
[Non-Patent Document 1]
K. Okamoto, “Fundamentals of Optical Waveguides”, Academic Press, 2000
[Non-Patent Document 2]
K. Okamoto and A.M. Sugita, “Flat septctral response arrayed-waveguide grading multipleplexer with parabolic waveguide horns”, Electronics Letters, Vol. 32, no. 18, pp. 1661-1662, 1996
[Patent Document 1]
Japanese Patent Laid-Open No. 9-297228
[Problems to be solved by the invention]
However, the conventional arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit shown in FIG. 2 has the following problems to be solved.
[0013]
That is, since the origin of the bimodal electric field distribution shown in FIG. 3 is the second-order even mode of the waveguide, a waveguide in which a high-order mode called a second-order mode is difficult to be excited (for example, the relative refractive index difference Δ is The small low Δ waveguide) has a problem that it is difficult to obtain a broadband optical multiplexer / demultiplexer.
[0014]
In addition, when the primary mode as shown in FIG. 4 is excited due to misalignment of the core or the like, a symmetric even mode and an asymmetric odd mode are superimposed, so the bimodal electric field distribution is As shown in FIG. 5, there is a problem that the left and right are asymmetric, and as a result, the shape of the transmission spectrum is inclined to narrow the passband.
[0015]
4 shows the electric field distribution 301 of the primary mode, and FIG. 5 shows the electric field distribution at the end of the parabolic waveguide when the primary mode is excited. The vertical and horizontal axes are the same as those in FIG. Are the same. In FIG. 5, 401 is an electric field distribution when the primary mode shown in FIG. 4 is generated, 402 is an electric field distribution when a primary mode in which peaks and valleys are opposite to those in FIG. 4 is generated, and 403 is a primary mode. The electric field distribution in the case where there is no is shown.
[0016]
An object of the present invention is to solve the above-described problems and provide an arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit having a transmission wavelength band characteristic having a wide band and good flatness.
[0017]
[Means for Solving the Problems]
In order to solve the above-described problem, in the present invention, instead of the parabolic waveguide in the conventional arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit, light is propagated at the junction between the input waveguide and the first slab waveguide. Z = (1 / A) {(w / 2) ^ γ-a ^ γ} with respect to the axis z
γ> 2
(However, A and γ are shape parameters, and a is ½ of the core width of the input waveguide.) By providing a tapered waveguide having a core width w defined by an expression (power function), the bandwidth can be increased. Realize.
[0018]
FIG. 6 shows a main part of the arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit of the present invention, that is, a tapered waveguide. FIG. 6A shows a schematic shape of the tapered waveguide 107, and FIG. ) Shows the detailed shape of the tapered waveguide 107 when γ is changed (γ = 2, 2.5, 3.0, 3.5) (however, not the entire waveguide but the shape of only one side from the core center) ).
[0019]
Here, γ = 2 indicates the case of the conventional parabolic waveguide, and it can be seen that the change in the vicinity of the input end is larger in the case of the tapered waveguide of the present invention in which γ is larger than 2.
[0020]
In order to examine more quantitatively, the change rate dx / dz of the core width is shown in FIG. The higher the rate of change, the easier the higher order modes are excited. It can be seen that the taper waveguide of the present invention in which γ is larger than 2 has a large change rate dx / dz at the input end of z = 0 μm, as compared with the conventional parabolic waveguide of γ = 2.
[0021]
In addition, if a large change rate is given to the input end in the conventional parabolic waveguide, only the value of the shape parameter A is changed. Therefore, the change rate of the portion excluding the input end is inevitably a large numerical value. , Radiation loss increases.
[0022]
However, according to the tapered waveguide of the present invention, since a large discontinuity can be given only to the input end, radiation loss can be suppressed.
[0023]
Further, in order to clarify the effectiveness of the present invention, the relationship between the transmission wavelength band characteristics including the conventional example and the shape parameter γ is shown in FIG. Here, the channel spacing is designed to be 100 GHz and Δ = 0.45%. It can be seen that the band is expanded as the value of γ increases.
[0024]
Conventionally, only the factor A, which is a shape parameter, is examined, and the γ dependency, which is a requirement of the present invention, has not been studied at all.
[0025]
FIG. 9 shows the flatness of the transmission wavelength band characteristic and the γ dependency of the loss in the present invention. Here, a ratio of 3 dB bandwidth to 1 dB bandwidth was used as an index indicating flatness. That is, the smaller the index value, the better the flatness. From the figure, it can be seen that the configuration of the present invention is superior to the conventional case (γ = 2). Further, since the flatness is constant in the region of γ> 3.5, the configuration of the present invention is effective when 2 <γ ≦ 3.5.
[0026]
From the above results, according to the present invention, since there is a large discontinuity at the input end of the tapered waveguide, the secondary mode can be easily excited even in the low Δ waveguide. That is, it is expected to realize an arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit having a transmission wavelength band characteristic having a wide bandwidth and good flatness.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0028]
(First embodiment)
FIG. 10 shows the manufacturing process of the first embodiment of the arrayed waveguide diffraction grating type optical multiplexer / demultiplexer according to the present invention, and the shape of the waveguide itself is as described in FIG.
[0029]
On the silicon substrate 501, a lower clad glass soot 502 in which the SiO ₂ mainly, the core glass soot 503 with the addition of GeO ₂ in SiO ₂ are successively deposited by flame hydrolysis deposition (FIG. 10 (A)). Thereafter, the glass is made transparent at a high temperature of 1000 ° C. or higher. At this time, the glass is deposited so that the lower cladding glass layer 504 has a thickness of 30 μm and the core glass layer 505 has a thickness of 7 μm (see FIG. 10 (B)).
[0030]
Subsequently, an etching mask 506 is formed on the core glass layer 505 by using a photolithography technique (FIG. 10C), and the core glass layer 505 is patterned by reactive ion etching. After removing the etching mask 506 (FIG. 10D), an upper cladding glass 507 is formed by a flame deposition method (FIG. 10E).
[0031]
A dopant such as B ₂ O ₃ or P ₂ O ₅ is added to the upper cladding glass 507 to lower the glass transition temperature so that the upper cladding glass 507 enters a narrow gap between the patterned core glasses 505a. Yes.
[0032]
FIG. 11 shows the transmission wavelength band characteristics in the present embodiment with a channel spacing of 100 GHz designed with the shape parameter γ = 2.8, and the characteristic values in the present embodiment and the conventional arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit. The comparison is shown in FIG.
[0033]
In this embodiment, the insertion loss is about 4 dB and the 1 dB bandwidth is 0.49 nm or more, which indicates that the 1 dB bandwidth can be increased by 20% or more compared to the conventional arrayed waveguide grating optical multiplexing / demultiplexing circuit.
[0034]
(Second Embodiment)
FIG. 13 shows a second embodiment of the present invention, in which a tapered waveguide approximating the shape represented by the above formula with a plurality of straight lines is provided at the junction between the input waveguide and the first slab waveguide. FIG. 4A shows a schematic shape of the linear approximate tapered waveguide 108, and FIG. 3B shows a detailed shape of the linear approximate tapered waveguide 108 (but not the entire waveguide). , The shape of only one side from the core center).
[0035]
According to the present embodiment, since a continuous curve is approximated by dividing it into a plurality of, here, four straight lines, the design is simple.
[0036]
FIG. 14 shows the transmission wavelength band characteristics in this embodiment. The insertion loss is about 4 dB, and the 1 dB bandwidth is 0.49 nm or more, and the effectiveness of this embodiment can be confirmed.
[0037]
(Third embodiment)
FIG. 15 shows a third embodiment of the present invention, in which an example in which a mode stabilization region 109 having a core width narrower than that of the input waveguide 101 is provided at the junction between the input waveguide 101 and the tapered waveguide 107. Show.
[0038]
According to the present embodiment, since the waveguide having a narrow core width is provided as the mode stabilization region 109, suppression of an odd mode excited by disturbance or misalignment, particularly a primary mode can be expected.
[0039]
FIG. 16 shows the transmission wavelength band characteristics in the present embodiment together with the characteristics of the conventional example, and the effectiveness of the present embodiment was confirmed without the transmission spectrum being inclined as compared with the conventional example.
[0040]
(Other embodiments)
In the embodiment of the present invention described above, an arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit using a silica-based glass optical waveguide on a silicon substrate is shown. The waveguide material is polyimide, silicone, semiconductor, LiNbO. The above principle of the present invention can be applied even if the number is ₃ or the like. Further, the substrate is not limited to silicon.
[0041]
Further, the case where there is one input waveguide including the conventional example has been described so far, but it goes without saying that the present invention can be similarly applied even when there are two or more input waveguides. Needless to say, when there are two or more input waveguides, one output waveguide is included.
[0042]
The essence of the present invention is that an array waveguide diffraction grating type optical multiplexing / demultiplexing circuit having a wide bandwidth and good flatness is realized by providing a design guideline that has not been clarified in the prior art.
[0043]
In this specification, “α ^ β” represents “α to the power of β”.
[0044]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain effects such as an increase in the bandwidth and flatness of the arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit as compared with the prior art.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a conventional arrayed waveguide grating type optical multiplexing / demultiplexing circuit. FIG. 2 is a block diagram showing another example of a conventional arrayed waveguide grating optical multiplexing / demultiplexing circuit. FIG. 4 is a diagram showing the electric field distribution at the end of the parabolic waveguide in FIG. 2. FIG. 4 is a diagram showing the electric field distribution in the primary mode. FIG. 5 is an electric field distribution at the end of the parabolic waveguide when the primary mode is excited. FIG. 6 is a block diagram showing the main part of an arrayed waveguide grating optical multiplexing / demultiplexing circuit of the present invention. FIG. 7 is a core width of a tapered waveguide in the arrayed waveguide grating optical multiplexing / demultiplexing circuit of the present invention. FIG. 8 is a diagram showing the relationship between the transmission wavelength band characteristic and the shape parameter γ. FIG. 9 is a graph showing the flatness of the transmission wavelength band characteristic in the arrayed waveguide grating optical multiplexing / demultiplexing circuit of the present invention. FIG. 10 is a diagram showing the γ dependence of loss. Explanatory drawing of the manufacturing process of 1st Embodiment of a folding-grating type | mold optical multiplexing / demultiplexing circuit. FIG. 11 is a figure which shows the transmission wavelength band characteristic in 1st Embodiment of this invention. FIG. 13 is a diagram showing a comparison of characteristic values between the embodiment of the present invention and the conventional configuration. FIG. 13 is a configuration diagram showing the main part of the second embodiment of the arrayed waveguide grating optical multiplexing / demultiplexing circuit of the present invention. 14 is a diagram showing transmission wavelength band characteristics in the second embodiment of the present invention. FIG. 15 is a block diagram showing the main part of the third embodiment of the arrayed waveguide grating optical multiplexing / demultiplexing circuit of the present invention. FIG. 16 is a diagram showing transmission wavelength band characteristics according to the third embodiment of the present invention.
100: planar substrate, 101: input waveguide, 102: first slab waveguide, 103: array waveguide, 104: second slab waveguide, 105: output waveguide, 107: taper waveguide, 108: straight line Approximate tapered waveguide, 109: mode stabilization region, 501: silicon substrate, 502: lower clad glass soot, 503: core glass soot, 504: lower clad glass layer, 505: core glass layer, 505a: patterned core Glass, 506: Etching mask, 507: Upper clad glass.

Claims (4)

A first slab connecting an input waveguide, an output waveguide, an arrayed waveguide, and an input waveguide and an arrayed waveguide, the optical waveguide comprising a core formed on a planar substrate and a cladding around the core The waveguide includes a second slab waveguide connecting the arrayed waveguide and the output waveguide, and the arrayed waveguide includes a plurality of waveguides that are sequentially lengthened by a predetermined waveguide length difference, and includes an input waveguide or an output waveguide. In the arrayed waveguide grating optical multiplexing / demultiplexing circuit in which at least one of the waveguides includes a plurality of waveguides,
At the junction between the input waveguide and the first slab waveguide, z = (1 / A) {(w / 2) ^ γ-a ^ γ} with respect to the light propagation axis z,
3.5 ≧ γ> 2
(However, A and γ are shape parameters, and a is 1/2 of the core width of the input waveguide.)
A tapered waveguide having a core width w defined by the following equation is provided. An arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit. In the arrayed waveguide grating type optical demultiplexing circuit according to claim 1 Symbol placement,
An arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit characterized in that the shape represented by the above equation is approximated by a plurality of straight lines. The arrayed waveguide grating optical multiplexer / demultiplexer according to claim 1 or 2 ,
An arrayed waveguide diffraction grating type optical multiplexing / demultiplexing circuit characterized in that a mode stabilization region having a narrower core width than the input waveguide is provided at the junction between the input waveguide and the tapered waveguide. The arrayed waveguide grating optical multiplexing / demultiplexing circuit according to any one of claims 1 to 3 ,
An array waveguide diffraction grating type optical multiplexing / demultiplexing circuit, wherein each waveguide is composed of a silica-based glass optical waveguide on a silicon substrate.

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