JP2011043665A - Wavelength multiplexer/demultiplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use a wavelength multiplexer/demultiplexer independent of polarization and to easily manufacture the wavelength multiplexer/demultiplexer. <P>SOLUTION: The wavelength multiplexer/demultiplexer includes a first optical waveguide part 13 having a first input/output end 13a, a second optical waveguide part 15 and a third optical waveguide part 17 which are respectively formed as planar waveguides on one and the same plane. The first optical waveguide part, the second optical waveguide part and the third optical waveguide part are continuously connected in the described order. The first optical waveguide part, which excites 0-order and primary order mode light beams, is formed in a form that the width continuously increases from the first input/output end to the boundary 13b of the first and the second optical waveguide parts. The number m<SB>1</SB>, in the phase difference m<SB>1</SB>π between 0-order mode TE light and the primary order mode TE light which are input from the first input/output end and arrive at the boundary 15a between the second optical waveguide part and the third optical waveguide part, and the number m<SB>2</SB>, in the phase difference m<SB>2</SB>π between 0-order mode TM light and the primary order mode TM light which are input from the first input/output end and arrive at the boundary between the second optical waveguide part and the third optical waveguide part, both become even numbers or odd numbers for the light having the first wavelength. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wavelength multiplexer / demultiplexer that multiplexes / demultiplexes light of different wavelengths, and more particularly to a wavelength multiplexer / demultiplexer that can be used independently of polarization.

  As is well known in the art, in an optical subscriber system, optical transmission from a subscriber to a station, that is, upstream transmission, and optical transmission from the station to a subscriber, that is, downstream transmission, are performed by a single optical fiber. Therefore, light having different wavelengths is used for uplink transmission and downlink transmission. Therefore, in such an optical subscriber system, it is necessary to provide a wavelength multiplexer / demultiplexer for multiplexing and demultiplexing light of different wavelengths on both the station side and the subscriber side. A wavelength multiplexer / demultiplexer used on the subscriber side is called an ONU (Optical Network Unit) (see, for example, Patent Documents 1 to 5).

  In recent years, an optical waveguide type wavelength multiplexer / demultiplexer that does not require optical axis alignment has been studied as the wavelength multiplexer / demultiplexer described above. As such a wavelength multiplexer / demultiplexer, for example, one using a Mach-Zehnder interferometer, one using a directional coupler, one using a multimode interference optical waveguide, and the like are known.

  A wavelength multiplexer / demultiplexer using a Mach-Zehnder interferometer has an advantage that wavelength characteristics can be designed using circuit theory. However, the Mach-Zehnder type wavelength multiplexer / demultiplexer composed of Si used for the ONU has a drawback that it is difficult to design because the wavelength dependency of the equivalent refractive index and coupling coefficient is large.

  Further, the wavelength multiplexer / demultiplexer has a drawback that the crosstalk characteristic is easily deteriorated due to the difference in the waveguide width.

  On the other hand, in the wavelength multiplexer / demultiplexer using the multimode interference optical waveguide, in the above-described optical subscriber system, the light having a wavelength of about 1.3 μm, which is mainly used for upstream transmission, It is possible to separate light having a wavelength of about 1.5 μm used for transmission (see Non-Patent Document 1, for example).

US Pat. No. 4,860,294 U.S. Pat. No. 5,764,826 US Pat. No. 5,960,135 U.S. Pat. No. 7,072,541 JP-A-8-163028

Baojun Li et al. “1 × 2 optical waveguide filters based on multimode interference for 1.3- and 1.55-μm operation”, Optical Engineering, vol. 41, no. 3, pp 723-727 (March, 2002)

  However, the wavelength multiplexer / demultiplexer disclosed in Non-Patent Document 1 has a large polarization dependency and can be used only for one of the TE component and the TM component.

  In addition, since the wavelength multiplexer / demultiplexer disclosed in Non-Patent Document 1 is configured using SiGe as a material, it is difficult to create, for example, as compared with an element using Si as a material.

  The present invention has been made in view of such problems. Accordingly, an object of the present invention is to provide a wavelength multiplexer / demultiplexer that can be used independently of polarization and can be easily produced.

  In order to achieve the above object, a wavelength multiplexer / demultiplexer according to the present invention has the following characteristics.

  That is, the wavelength multiplexer / demultiplexer according to the present invention includes a first optical waveguide section having a first input / output end, a second optical waveguide section, and a second input / output end, each formed as a planar waveguide in the same plane. And a third optical waveguide portion including a second sub-waveguide having a third input / output end.

  The first optical waveguide portion, the second optical waveguide portion, and the third optical waveguide portion are continuously connected in this order.

  In the wavelength multiplexer / demultiplexer according to the present invention, the propagation light propagates between the first input / output end and the second input / output end, and between the first input / output end and the third input / output end.

  The first optical waveguide section excites 0th-order and first-order mode light and is linear in the width direction along the boundary from the first input / output end toward the boundary with the second optical waveguide section. It is formed in a wide shape.

In the wavelength multiplexer / demultiplexer according to the present invention, the first wavelength propagating light is input from the first input / output end, sequentially propagates through the first optical waveguide portion and the second optical waveguide portion, and the second optical A coefficient m ₁ in a phase difference m ₁ π given by the following equation (1) between the TE light of the 0th-order mode and the TE light of the first-order mode that has reached the boundary between the waveguide portion and the third optical waveguide portion; The TM light in the 0th order mode that is input from the first input / output end, propagates sequentially through the first optical waveguide section and the second optical waveguide section, and reaches the boundary between the second optical waveguide section and the third optical waveguide section, and 1 The width of the first input / output end and the length of the first optical waveguide portion where the coefficient m ₂ in the phase difference m ₂ π given by the following equation (2) with the TM light in the next mode is an even number or an odd number. The width of the second optical waveguide portion and the length of the second optical waveguide portion are set.

φ _TE1 + Δβ _TE1 L = m ₁ π (1)
Here, φ _TE is the amount of phase change that occurs in the TE light in the first optical waveguide section, and Δβ _TE is the propagation constant of the zero-order mode TE light and the propagation of the TE light in the first-order mode in the second optical waveguide section. The difference from the constant, L, is the length of the second optical waveguide section perpendicular to the width direction and along the plane.

φ _TM + Δβ _TM L = m ₂ π (2)
Here, φ _TM is the amount of phase change that occurs in the TM light in the first optical waveguide section, and Δβ _TM is the propagation constant of the TM light in the 0th-order mode and the propagation of the TM light in the 1st-order mode in the second optical waveguide section. It is the difference from the constant.

  By having the structural features as described above, according to the present invention, it is possible to multiplex / demultiplex wavelengths in both TE light and TM light, that is, it can be used independently of polarization. Thus, a wavelength multiplexer / demultiplexer that can be easily produced can be obtained.

It is a figure showing roughly the principal part of the wavelength multiplexer / demultiplexer by a 1st embodiment, and a wavelength multiplexer / demultiplexer has the 1st optical waveguide part, the 2nd optical waveguide part, and the 3rd optical waveguide part. It is a top view shown along the formed plane. It is a figure which shows roughly the principal part of the wavelength multiplexer / demultiplexer by 1st Embodiment, and shows the cut end of the cross section which cut the wavelength multiplexer / demultiplexer along the II line | wire shown in FIG. It is the end view seen from. It is a characteristic view with which it uses for description of the wavelength separation characteristic of the wavelength multiplexer / demultiplexer by 1st Embodiment.

  A wavelength multiplexer / demultiplexer according to an embodiment of the present invention will be described below with reference to the drawings. Each drawing merely schematically shows the shape, size, and arrangement relationship of each component to the extent that the present invention can be understood. Therefore, the configuration of the present invention is not limited to the illustrated configuration example.

<First Embodiment>
In the first embodiment, a wavelength multiplexer / demultiplexer including a first optical waveguide portion, a second optical waveguide portion, and a third optical waveguide portion will be described.

  1 and 2 are diagrams schematically showing a main part of a wavelength multiplexer / demultiplexer according to a first embodiment of the present invention. FIG. 1 is a plan view showing a wavelength multiplexer / demultiplexer along a plane on which a first optical waveguide portion, a second optical waveguide portion, and a third optical waveguide portion are formed. FIG. 2 is an end view of the wavelength multiplexer / demultiplexer as seen from the direction of the arrow of the cross section cut along the line II shown in FIG.

  In the actual wavelength multiplexer / demultiplexer, the entire surface of the wavelength multiplexer / demultiplexer is embedded in the cladding in the structure shown in FIG. However, in FIG. 1, the clad is omitted in order to clearly show the characteristic portion according to the first embodiment.

  The wavelength multiplexer / demultiplexer 11 according to the first embodiment includes a first optical waveguide portion 13, a second optical waveguide portion 15, and a third optical waveguide portion 17.

  The first optical waveguide section 13, the second optical waveguide section 15, and the third optical waveguide section 17 are formed as multimode planar waveguides on the same plane, and are sequentially and integrally formed in this order. Connected and formed.

  Thus, in order to arrange the first optical waveguide section 13, the second optical waveguide section 15, and the third optical waveguide section 17, the first optical waveguide section 13, the second optical waveguide section 15, and the third optical waveguide are disposed. The waveguide portion 17 is formed on a common substrate 19.

That is, the substrate 19 is made of single crystal Si. A clad 21 made of SiO ₂ is laminated on the substrate 19. The wavelength multiplexer / demultiplexer 11 including the first optical waveguide portion 13, the second optical waveguide portion 15, and the third optical waveguide portion 17 is along the substrate surface 19a of the substrate 19, that is, along the same plane. Si is embedded in the clad 21 as a material.

Here, in this embodiment, when the wavelength multiplexer / demultiplexer 11 is used in the above-described optical subscriber system, that is, for example, light having a wavelength of 1.31 μm as an upstream optical signal, For example, when light having a wavelength of 1.49 μm is used as a signal, the wavelength multiplexer / demultiplexer 11 including the first optical waveguide portion 13, the second optical waveguide portion 15, and the third optical waveguide portion 17 is made of Si. The refractive index is preferably set to 3.5, for example, and the refractive index of SiO ₂ constituting the clad 21 is preferably set to 1.46, for example.

In the first embodiment, the wavelength multiplexer / demultiplexer 11 is configured as a single-mode optical waveguide in the vertical direction, that is, in the thickness direction of the substrate 19. Therefore, these first optical waveguide portion 13 are integrally formed, the thickness D ₁ of the second optical waveguide portion 15, and a third optical waveguide 17 is preferably 0.5μm or less, more preferably, It is set to 0.3 μm.

  Here, such a wavelength multiplexer / demultiplexer 11 can be easily manufactured, for example, by preparing a known SOI substrate.

That is, first, an SOI substrate in which a single crystal Si layer, a SiO ₂ film, and a Si film are stacked in this order is prepared. Then, by partially removing the Si film using a known etching technique, the first optical waveguide portion 13, the second optical waveguide portion 15, and the third optical waveguide portion described above are formed from the remaining portion of the Si film. 17 is formed. Thereafter, the first optical waveguide portion 13, the second optical waveguide portion 15, and the third optical waveguide portion 17 thus formed are buried on the entire surface of the SOI substrate to deposit a SiO ₂ film. As a result, the wavelength multiplexer / demultiplexer 11 is formed on the single crystal Si substrate, that is, the substrate 19 as described above, embedded in the clad 21 made of SiO ₂ .

  The first optical waveguide portion 13 has a first input / output end 13 a as a side surface 13 a facing the boundary 13 b with the second optical waveguide portion 15. The first optical waveguide section 13 is connected to the station side device (see FIG. 5) at the first input / output end 13a via the first input / output optical waveguide 23 which is a single mode optical waveguide. (Not shown) and optically connected.

  The connection position between the first input / output optical waveguide 23 and the first input / output end 13a is designed based on the following conditions. That is, the connection position of the first input / output optical waveguide 23 is input from the first input / output optical waveguide 23 to the first input / output end 13a and sequentially propagates through the first input / output optical waveguide 23 and the second optical waveguide section 15. When the light to reach the boundary 15a between the second optical waveguide section 15 and the third optical waveguide section 17, an interference pattern corresponding to the wavelength is generated from the second optical waveguide section 15 and the first sub-guide described later. It is designed to be maximized at the connection position with the waveguide 25 or the second sub-waveguide 27.

  In addition, when light having a wavelength of, for example, 1.31 μm is used as the upstream optical signal and light having a wavelength of, for example, 1.49 μm is used as the downstream optical signal, the first input / output optical waveguide 23 is a wavelength multiplexer / demultiplexer. 11 is preferably formed to have a thickness of 0.3 μm and, for example, a width of 0.3 μm, that is, a width along the first input / output end 13a.

In addition, the wavelength multiplexer / demultiplexer 11 according to the first embodiment is configured as a wavelength multiplexer / demultiplexer corresponding to the excitation light in the 0th order and the first order mode. For this purpose, the first optical waveguide section 13 is formed as an optical waveguide that excites 0th-order and first-order mode light. That is, the first output terminal 13a, the width W ₁ along the boundary 13b is set so as to excite the light of 0-order and first-order mode. A specific preferred example of the width W ₁ of the first output terminal 13a will be described later. In this embodiment, hereinafter, a direction along the boundary 13b is referred to as a width direction, and a dimension along the width direction is referred to as a width. Further, a direction perpendicular to the width direction and along the plane on which the first optical waveguide portion 13, the second optical waveguide portion 15, and the third optical waveguide portion 17 are formed, that is, along the substrate surface 19a. A length direction and a dimension along the length direction are referred to as a length.

  In the configuration example shown in FIG. 1, the first optical waveguide portion 13 has a tapered planar shape, that is, continuously from the first input / output end 13 a toward the boundary 13 b with the second optical waveguide portion 15. And it is formed in the trapezoid shape which becomes wide in the width direction linearly, Preferably it is an isosceles trapezoid shape. The trapezoid has, for example, an upper side 13a that is parallel to each other, a lower side 13b that is longer than the upper side, and two sides that are equal in length and connect between the ends of the upper side and the lower side. In addition, the first optical waveguide section 13 has a first input / output end 13a and a first input / output end 13a between the first input / output end 13a corresponding to the upper side and the first input / output optical waveguide 23 for the purpose of improving the degree of freedom in design. It is good also as a structure which additionally contains the rectangular-shaped optical waveguide which has equal width (not shown).

In the configuration example shown in FIG. 1, the second optical waveguide portion 15 is an optical waveguide having a rectangular planar shape, and the length of the first side at the boundary 13 b with the first optical waveguide portion 13. The width W ₂ corresponding to the height and the width corresponding to the length of the lower side 13 b of the first optical waveguide portion 13 are aligned.

  In addition, the third optical waveguide portion 17 has a second side 15a of the second optical waveguide portion 15 that faces the boundary 13b between the first optical waveguide portion 13 and the second optical waveguide portion 15, that is, the boundary 15a. Two optical waveguide portions 15 are connected.

  Further, the third optical waveguide portion 17 is composed of a first sub-waveguide 25 and a second sub-waveguide 27 each having a trapezoidal shape, more preferably an isosceles trapezoidal shape, and the upper side is longer than the upper side. It has a lower side and two sides having the same length connecting the ends of the upper side and the lower side.

  The first sub-waveguide 25 and the second sub-waveguide 27 are separated from each other, and the lower sides of the second optical waveguide portion 15 and the boundaries 15aa and 15ab corresponding to a part of the second side 15a are connected to each other. Yes.

  In addition, the first sub-waveguide 25 has the second input / output end 25a as one end (corresponding to the above-described upper side) facing the boundary 15aa, and the second sub-waveguide 27 is one end (described above) facing the boundary 15ab. The third input / output terminal 27a has a third input / output terminal 27a.

  The first sub-waveguide 25 is connected at the second input / output end 25a via the second input / output optical waveguide 29, which is a single mode optical waveguide, in the above-described optical subscriber system (see FIG. (Not shown) and optically connected. In addition, the second sub-waveguide 27 is connected to the subscriber side device and the optical device in the optical subscriber system described above via the third input / output optical waveguide 31 which is a single mode optical waveguide at the third input / output end 27a. Connected. One of the second input / output optical waveguide 29 and the third input / output optical waveguide 31 is an optical waveguide for upstream which propagates an upstream optical signal from the subscriber side device to the wavelength multiplexer / demultiplexer 11 depending on the design. The other is used as a downstream optical waveguide for propagating a downstream optical signal from the wavelength multiplexer / demultiplexer 11 to the subscriber side device.

  Further, the first sub-waveguide 25 and the second sub-waveguide 27 are formed in a shape that continuously narrows from the boundaries 15aa and 15ab toward the second input / output end 25a and the third input / output end 27a, respectively. Has been.

Here, in order to suppress light from propagating from the second optical waveguide unit 15 to the third optical waveguide unit 17, the first sub-waveguide 25, the second sub-waveguide 27, and the second optical waveguide unit are used. It is preferable to set the widths W _3a and W _3b of the boundaries 15aa and 15ab to 15 as large as possible according to the width W ₂ of the second optical waveguide section 15. For the same reason, a separation distance W ₄ between the connection position of the first sub-waveguide 25 and the second optical waveguide portion 15 and the connection position of the second sub-waveguide 27 and the second optical waveguide portion 15 is possible. It is preferable to set as small as possible. Specific preferred examples of W _3a , W _3b , and W ₄ will be described later.

  The second input / output end 25a is formed to have the same width as the second input / output optical waveguide 29. The third input / output end 27a is formed to have the same width as the third input / output optical waveguide 31. When light having a wavelength of, for example, 1.31 μm is used as the upstream optical signal and light having a wavelength of, for example, 1.49 μm is used as the downstream optical signal, the second input / output optical waveguide 29 and the third input / output optical waveguide are used. 31 is formed integrally with the wavelength multiplexer / demultiplexer 11 with a thickness of 0.3 μm and, for example, a width of 0.3 μm, that is, a width along the second input / output end 25a and the third input / output end 27a. It is preferable.

  With the configuration described above, in the wavelength multiplexer / demultiplexer 11 according to the first embodiment, the propagation light, that is, the upstream optical signal and the downstream optical signal are transmitted to the first input / output terminal 13a and the second input / output terminal 25a. And between the first input / output end 13a and the third input / output end 27a.

In order to use such a wavelength multiplexer / demultiplexer 11 without depending on polarization, the width W ₁ of the first input / output end, the length S of the first optical waveguide section 13, and the second optical waveguide section 15 The width W ₂ and the length L of the second optical waveguide section 15 need to be appropriately set according to the wavelength of the propagation light to be used and the materials constituting the wavelength multiplexer / demultiplexer 11 and the clad 21. Hereinafter, conditions for determining these dimensions will be described.

  In an optical waveguide that excites 0th-order and 1st-order mode light, the phase difference between the 0th-order mode light and the 1st-order mode light that propagates through this optical waveguide is the length of this optical waveguide section, And the product of the propagation constant difference between the 0th-order mode light and the 1st-order mode light. In an optical element configured by combining a plurality of optical waveguide portions having different widths and lengths, the phase difference between the 0th-order mode light and the 1st-order mode light propagating through this optical waveguide is , Given by the sum of the products of the length and propagation constant differences described above.

Accordingly, in the wavelength multiplexer / demultiplexer 11, the light is input from the first input / output end 13 a and sequentially propagates through the first optical waveguide portion 13 and the second optical waveguide portion 15, and the second optical waveguide portion 15 and the third optical waveguide portion are transmitted. A phase difference m ₁ π between the zero-order mode TE light and the first-order mode TE light having a certain wavelength, that is, the first wavelength, that has reached the boundary 15a with respect to 17 is given by the following equation (1). In the wavelength multiplexer / demultiplexer 11, the width of the first optical waveguide portion 13 is not constant because it is formed in a tapered shape as described above. Therefore, the phase difference between the zero-order mode light and the first-order mode light in the first optical waveguide section 13 is represented by φ _TE1 + Δβ expressed not by the product of the length and the propagation constant difference but by the phase change amount φ. _TE1 L = m ₁ π (1)
Here, φ _TE1 is the amount of phase change generated in the TE light of the first wavelength in the first optical waveguide section 13, and Δβ _TE1 is the TE wavelength of the zeroth-order mode of the first wavelength in the second optical waveguide section 15. The difference between the propagation constant and the propagation constant of the first-order mode TE light, L, is the length of the second optical waveguide section 15.

When the coefficient m ₁ is an integer in the phase difference m ₁ π thus given, light is input from the first input / output end 13a due to the interference of the TE light, and the first optical waveguide unit 13 and the second optical waveguide unit 13 The light propagates while meandering m ₁ times in the optical waveguide section 15 and is input to either the first sub-waveguide 25 or the second sub-waveguide 27.

Similarly, in the wavelength multiplexer / demultiplexer 11, the light is input from the first input / output end 13 a and sequentially propagates through the first optical waveguide portion 13 and the second optical waveguide portion 15, and the second optical waveguide portion 15 and the third optical waveguide portion 15 The phase difference m ₂ π between the first-order mode TM light and the first-order mode TM light having reached the boundary 15a with the optical waveguide portion 17 is given by the following equation (2).

φ _TM + Δβ _TM L = m ₂ π (2)
Here, φ _TM is the amount of phase change that occurs in the TM light of the first wavelength in the first optical waveguide section 13, and Δβ _TM is the zero-order mode TM light of the first wavelength in the second optical waveguide section 15. It is the difference between the propagation constant and the propagation constant of the TM light in the first-order mode.

When the coefficient m ₂ is an integer at m ₂ π given in this way, light is input from the first input / output end 13a due to the interference of the TE light, and the first optical waveguide section 13 and the second optical waveguide The signal propagates while meandering m ₂ times m ₂ and is input to either the first sub-waveguide 25 or the second sub-waveguide 27.

Therefore, the _{m 1} in _{m 1} [pi, and _{m 2} in _{m 2} [pi is, when both of an even or odd number, light input from the first input terminal 13a, namely downstream optical signal, TE light and Both the TM light is input to one of the first sub-waveguide 25 and the second sub-waveguide 27. That is, the downstream optical signal is input to the same one of the first sub-waveguide 25 and the second sub-waveguide 27 without depending on the polarization.

Therefore, in the wavelength multiplexer / demultiplexer 11 according to the first embodiment, the width W ₁ of the first input / output end and the length of the first optical waveguide section in which both m ₁ and m ₂ are even or odd. S, the width W ₂ of the second optical waveguide portion, and the length L of the second optical waveguide portion are set.

  Further, the wavelength multiplexer / demultiplexer 11 multiplexes and demultiplexes the downstream optical signal and upstream optical signal, so that the second wavelength light different from the first wavelength is different from the first wavelength light. Designed to propagate the path. That is, in the wavelength multiplexer / demultiplexer 11, when the first wavelength light input from the first input / output end 13a is input to the first sub-waveguide 25, the light is input from the first input / output end 13a. When light having the second wavelength is input to the second sub-waveguide 27 and light having the first wavelength input from the first input / output terminal 13a is input to the second sub-waveguide 27, The second wavelength light input from the first input / output terminal 13 a is input to the first sub-waveguide 25. Since the light propagation path is reversible, the light of the second wavelength can be used as the upstream optical signal when any of these paths is established.

  Therefore, the wavelength multiplexer / demultiplexer 11 is formed based on the following conditions in addition to the above-described conditions in order to multiplex / demultiplex light of the first wavelength and the second wavelength.

The second input that is input from the first input / output end 13a, propagates sequentially through the first optical waveguide section 13 and the second optical waveguide section 15, and reaches the boundary 15a between the second optical waveguide section 15 and the third optical waveguide section 17. The phase difference m ₃ π between the 0th-order mode TE light and the first-order mode TE light of the wavelength is given by the following equation (3).

φ _TE2 + Δβ _TE2 L = m ₃ π (3)
Here, φ _TE2 is the amount of phase change that occurs in the TE light of the second wavelength in the first optical waveguide section 13, and Δβ _TE2 is the second wavelength of the TE light of the 0th mode in the second optical waveguide section 15. The difference between the propagation constant and the propagation constant of the first-order mode TE light, L, is the length of the second optical waveguide section 15.

In the case of m ₃ π given in this way, when the coefficient m ₃ is an integer, light is input from the first input / output terminal 13a due to the interference of the TE light in the same manner as the coefficient m ₁ and the coefficient m ₂ described above. Then, it propagates through the first optical waveguide section 13 and the second optical waveguide section 15 while meandering m ₃ times, and is input to either the first sub-waveguide 25 or the second sub-waveguide 27.

Therefore, when the coefficient _{m 2} odd in the coefficient _{m 1} and _{m 2} [pi in _{m 1} [pi described above, the coefficient _{m 3} and even-numbered coefficients _{m 2} in the coefficient _{m 1} and _{m 2} [pi in _{m 1} [pi is even In this case, by setting the coefficient m ₃ to be an odd number, the second wavelength light is one of the first sub-waveguide 25 and the second sub-waveguide 27 that is different from the first wavelength light. Input to the waveguide.

Therefore, in the wavelength multiplexer / demultiplexer 11 according to the first embodiment, when the coefficient m ₁ and the coefficient m ₂ are both odd, the coefficient m ₃ is an even number, and the coefficient m ₁ and the coefficient m ₂ are There is the coefficient m ₃ an odd when both the even and the width W ₁ of the first input and output _ends, the length of the first optical waveguide portion S, the width W ₂ of the second optical waveguide _portion, and a second optical waveguide The length L of the part is set.

When the wavelength multiplexer / demultiplexer 11 is used as an ONU in an optical subscriber system, the upstream optical signal input from the subscriber side device to the wavelength multiplexer / demultiplexer 11 is wavelength-multiplexed / demultiplexed with the polarization being constant. It is input to the correlator 11. Therefore, when the wavelength multiplexer / demultiplexer 11 can be used without depending on the polarization, for the light of the second wavelength used as the upstream optical signal, the coefficient m _{3 of} the condition described above for the TE light may be set.

Then, when the wavelength multiplexer / demultiplexer 11 is used as an ONU, each of the above-described ones corresponding to propagation light having a wavelength of 1.31 as an upstream optical signal and propagation light having a wavelength of 1.49 μm as a downstream optical signal. Set the dimensions. In the case of using the upstream and downstream optical signals of respective wavelengths, for example preferably, the width _{W 1} of the first output terminal 13a 0.75 .mu.m, 15 [mu] m length S of the first optical waveguide portion 13, the second 2.2μm width _{W 2} of the optical waveguide section 15, and the length L of the second optical waveguide section 15 and 62 .mu.m. As a result, the coefficient m ₁ and the coefficient m ₂ are 7.0, both of which are odd numbers. Therefore, the downstream optical signal having a wavelength of 1.49 μm includes both the first sub-waveguide 25 and the second sub-wavelength for both TE light and TM light. Of the waveguides 27, the same one sub-waveguide is input. At this time, the coefficient m ₃ is 6.0, which is an even number unlike the coefficients m ₁ and m _2. For example, the TE light having a wavelength of 1.31 μm used as the upstream optical signal is Of the waveguide 25 and the second sub-waveguide 27, the light is input to one sub-waveguide different from the wavelength of 1.49 μm.

Further, by setting the width _{W 1} of the first output terminal 13a, as in this design example, that by a 0.75μm width _{W 1} of the first input-output terminal 13a, the first optical waveguide portion 13 Excites the 0th and 1st order mode modes. In this design example, when designing the wavelength multiplexer / demultiplexer 11, the first sub-waveguide 25 and the second sub-waveguide 27 are connected in the width direction of the second side 15 a of the second optical waveguide 15. The widths W _3a and W _3b of the boundaries 15aa and 15ab between the first sub-waveguide 25 and the second sub-waveguide 27 and the second optical waveguide section 15 are both 0.6 μm, separated by an equal distance from the midpoint. 1 and connection position of the sub-waveguide 25 and second optical waveguide portion 15, preferably in the 0.3μm the distance W ₄ between the connection position of the second sub-waveguide 27 and the second optical waveguide portion 15. The first input / output optical waveguide 23 is preferably connected to the first optical waveguide portion 13 at a position spaced by 0.15 μm from the center in the width direction of the first input / output end 13a.

  Next, wavelength separation characteristics of the wavelength multiplexer / demultiplexer 11 designed according to the above-described dimensions will be described with reference to FIG.

  FIG. 3 is a characteristic diagram for explaining the wavelength separation characteristic of the wavelength multiplexer / demultiplexer 11 according to the first embodiment. In FIG. 3, the vertical axis indicates the light intensity of propagating light input from the first input / output end 13a and output from the first sub-waveguide 25 and the second sub-waveguide 27 in an arbitrary unit. The axis is graduated in wavelength in μm.

  Further, FIG. 3 shows the input of light including TE light and TM light as polarization components from the first input / output end 13a, and the light detected in each of the first sub-waveguide 25 and the second sub-waveguide 27. The intensity is calculated while changing the wavelength. In the calculation, a three-dimensional FDTD (Finite Difference Time Domain) method was used.

  In FIG. 3, a curve 33 indicates the light intensity of the TE light output from the first sub waveguide 25. A curve 35 indicates the light intensity of the TM light output from the first sub waveguide 25. A curve 37 indicates the light intensity of the TE light output from the second sub waveguide 27. A curve 39 indicates the light intensity of the TM light output from the second sub waveguide 27.

  Referring to curve 33 and curve 35 in FIG. 3, the light intensity of the TE light and TM light output in the first sub-waveguide 25 has a peak at a wavelength near 1.49 μm, and is about 1.31 μm. With a bottom at a wavelength of. Therefore, it can be seen that the light in the vicinity of 1.49 μm input from the first input / output terminal 13a is output to the first sub-waveguide 25 for both TE light and TM light, that is, polarization independent.

  Referring to curve 37 and curve 39 in FIG. 3, the light intensity of the TE light and TM light output from the second sub-waveguide 27 has a bottom at a wavelength of about 1.49 μm. It has a peak at a wavelength of around 31 μm. Therefore, it can be seen that the light in the vicinity of 1.31 μm input from the first input / output end 13a is output to the second sub-waveguide 27, both of the TE light and the TM light, that is, polarization independent.

  In the wavelength multiplexer / demultiplexer 11 that has performed this simulation, as described above, TM light having a wavelength of 1.31 μm is not considered in the conditions for determining each dimension described above. Therefore, the curve 39 indicating the intensity of the TM light output from the second sub-waveguide 27 is near the wavelength of 1.31 μm as compared with the curve 37 indicating the intensity of the TE light output from the second sub-waveguide 27. Is slightly lower, and the bottom near the wavelength of 1.49 μm is slightly higher. However, as described above, when the wavelength multiplexer / demultiplexer 11 is used as an ONU, the upstream optical signal input from the subscriber side device to the wavelength multiplexer / demultiplexer 11 is wavelength-multiplexed / demultiplexed in a state where the polarization is constant. Is input to the device 11. Therefore, as apparent from the curve 37 in FIG. 3, the wavelength multiplexer / demultiplexer 11 reliably obtains the wavelength separation characteristic for the TE light having the wavelength of 1.31 μm used as the upstream optical signal. The multiplexer / demultiplexer 11 can be used as an ONU without any problem.

  As is apparent from these, the wavelength multiplexer / demultiplexer 11 can multiplex / demultiplex wavelengths in both TE light and TM light, and can be used as a polarization-independent ONU. .

11: wavelength multiplexer / demultiplexer 13: first optical waveguide portion 13a: first input / output end 15: second optical waveguide portion 17: third optical waveguide portion 19: substrate 21: clad 23: first input / output optical waveguide 25 : First sub waveguide 25a: second input / output end 27: second sub waveguide 27a: third input / output end 29: second input / output optical waveguide 31: third input / output optical waveguide

Claims (5)

A first optical waveguide section having a first input / output end, a second optical waveguide section, and a first sub-waveguide having a second input / output end and a third input / output, each formed as a planar waveguide in the same plane A third optical waveguide portion comprising a second sub-waveguide having an end;
The first optical waveguide portion, the second optical waveguide portion, and the third optical waveguide portion are continuously connected in this order,
Propagating light propagates between the first input / output end and the second input / output end, and between the first input / output end and the third input / output end,
The first optical waveguide section excites 0th-order and first-order mode light and linearly extends in the width direction along the boundary from the first input / output end toward the boundary with the second optical waveguide section. Is formed in a wide shape,
For propagating light of the first wavelength,
The phase change amount generated in the TE light in the first optical waveguide portion is φ _TE , and the difference between the propagation constant of the TE light in the 0th-order mode and the propagation constant of the TE light in the first-order mode is Δβ in the second optical waveguide portion. _When the length of _TE and the second optical waveguide portion perpendicular to the width direction and along the plane is L, the input from the first input / output end, and the first optical waveguide portion and the second optical waveguide portion Propagating sequentially through the two optical waveguide portions and giving the following equation (1) of the 0th-order mode TE light and the 1st-order mode TE light reaching the boundary between the second optical waveguide portion and the third optical waveguide portion Phase difference m ₁ π
φ _TE1 + Δβ _TE1 L = m ₁ π (1)
The coefficient m ₁ in
The phase change amount generated in the TM light in the first optical waveguide part is φ _TM , and the difference between the propagation constant of the TM light in the 0th-order mode and the propagation constant of the TM light in the 1st-order mode in the second optical waveguide part is When Δβ _TM is set, it is input from the first input / output end, and sequentially propagates through the first optical waveguide unit and the second optical waveguide unit, and at the boundary between the second optical waveguide unit and the third optical waveguide unit. Phase difference m ₂ π given by the following expression (2) between the TM light in the 0th-order mode and the TM light in the 1st-order mode that has reached
φ _TM + Δβ _TM L = m ₂ π (2)
And the coefficient m ₂ in both even or odd become the first input and output ends of a width, said first optical waveguide portion of the length, the second optical waveguide portion in the width and length of the second waveguide section The wavelength multiplexer / demultiplexer characterized by the above-mentioned. The wavelength multiplexer / demultiplexer according to claim 1,
Furthermore, for propagating light having a second wavelength different from the first wavelength,
The phase change amount generated in the TE light in the first optical waveguide portion is φ _TE , and the difference between the propagation constant of the TE light in the 0th-order mode and the propagation constant of the TE light in the first-order mode is Δβ in the second optical waveguide portion. _{When TE} is input, the signal is input from the first input / output end, sequentially propagates through the first optical waveguide unit and the second optical waveguide unit, and reaches the boundary between the second optical waveguide unit and the third optical waveguide unit. The phase difference m ₃ π given by the following equation (3) between the reached zero-order mode TE light and the first-order mode TE light:
φ _TE2 + Δβ _TE2 L = m ₃ π (3)
The coefficient m ₃ at
When m ₁ and m ₂ are odd numbers, the number is even, and when m ₁ and m ₂ are even numbers, the width of the first input / output end is odd. A wavelength multiplexer / demultiplexer, wherein a length, a width of the second optical waveguide portion, and a length of the second optical waveguide portion are set. The wavelength multiplexer / demultiplexer according to claim 1 or 2,
The wavelength multiplexer / demultiplexer, wherein the first wavelength is a wavelength of 1.49 μm. In the wavelength multiplexer / demultiplexer according to any one of claims 1 to 3,
The wavelength multiplexer / demultiplexer, wherein the second wavelength is a wavelength of 1.31 μm. In the wavelength multiplexer / demultiplexer according to any one of claims 1 to 4,
A wavelength multiplexer / demultiplexer characterized by being made of Si.

Images