WO2009098829A1

WO2009098829A1 - Optical waveguide and method for manufacturing same

Info

Publication number: WO2009098829A1
Application number: PCT/JP2008/073302
Authority: WO
Inventors: Masashige Ishizaka; Yutaka Urino
Original assignee: Nec Corporation
Priority date: 2008-02-06
Filing date: 2008-12-22
Publication date: 2009-08-13

Abstract

Disclosed is an optical waveguide in which not only the width of a rib portion of a rib optical waveguide is monotonously reduced but also the width of a slab portion thereof is reduced. In a connection portion of the rib optical waveguide and a channel optical waveguide, the width and thickness of the slab portion of the rib optical waveguide are equalized to the width and thickness of a core portion of the channel optical waveguide. In the connection portion, the cross-sectional shapes of the rib optical waveguide and the channel optical waveguide are equal, so the mode field shape of the rib optical waveguide nearly matches the mode field shape of the channel optical waveguide. Thus, the channel optical waveguide and the rib optical waveguide can be connected with low loss, and special characteristics (advantages) of the channel optical waveguide and the rib optical waveguide can complement each other.

Description

Optical waveguide and method for manufacturing the same

The present invention relates to an optical waveguide and a method for manufacturing the same.

Conventionally, planar light circuits (PLC: Planner Lightwave Circuits) play an important role as a key component supporting the recent optical communication market with AWG (Arrayed Waveguide Grating) and splitters, etc. as the development and commercialization centered on quartz systems. Has been fulfilled. Recently, the development of new functional elements such as a tunable light source in which a compound semiconductor amplifier (SOA: Semiconductor Optical Amplifier) is mounted in a hybrid on a quartz PLC is also progressing, and active elements and passive elements are mounted on a common PLC substrate. Attempts to realize a smaller and cheaper system on a single chip have become active.

However, as the functions required for PLCs become more complex and sophisticated, the element size of PLCs and the power consumption for driving PLCs are increasing, and there are limits to the functions and performance that can be realized with quartz systems. I came. Therefore, research and development of SOI (Silicon on Insulator) waveguides applying Si microfabrication technology such as silicon (Si) fine wires and photonic crystals (PC) is advancing, making them compact, low power consumption, and low cost. The possibility of a basic part characterized by this is being investigated.

Examples of the SOI optical waveguide include a channel optical waveguide and a rib optical waveguide.

A channel-type optical waveguide (Si wire waveguide) has the advantage that light can be propagated even with a bending radius of several microns to 10 microns with almost no optical loss, and the optical circuit can be miniaturized. is there. On the other hand, the disadvantage is that the influence of changes in structural parameters such as width and thickness on optical characteristics such as propagation loss and effective refractive index is large, and manufacturing tolerance is extremely small. This is an important issue particularly when a resonator, a filter, or the like is created by a PLC.

As an advantage of the rib-type optical waveguide, the light wave propagation loss, the above-mentioned structural tolerance, etc. are improved by an order of magnitude compared to the channel-type optical waveguide. This is an advantage when creating PLCs with various functions. On the other hand, as its disadvantage, the minimum bending radius is about 50 microns, and it cannot be bent more steeply than the channel type optical waveguide.

Thus, each of the channel type optical waveguide and the rib type optical waveguide has advantages and disadvantages.

Introducing technologies related to waveguides.

JP-A-8-146248 discloses an optical coupling device. The optical coupling device converts the mode size. The upper and lower waveguide guide layers are sandwiched between an upper clad layer and a lower clad layer having a refractive index lower than that of the waveguide guide layer. A low-refractive index layer having a refractive index lower than that of the lower cladding layer is disposed below, and the thickness of at least one of the waveguide guide layer and the upper cladding layer is reduced toward the output end. .

Japanese Patent Application Laid-Open No. 5-249331 discloses a waveguide beam spot conversion element. The waveguide-type beam spot conversion element is an optical waveguide that emits light, and has an output optical waveguide portion that emits substantially single-mode light, and a core that is continuous with the core of the output optical waveguide portion. A spot size conversion optical waveguide section for converting the spot size and a light propagation section for propagating the converted spot light are disposed on the substrate. In this waveguide type beam spot conversion element, the core of the optical waveguide part for spot size conversion is changed to a taper shape in the width direction toward the tip of the element, the taper is made thin in the thickness direction, and the core is spot size At least one second core having a refractive index higher than that of the substrate is disposed on at least one of the upper and lower cores of the output optical waveguide unit and the spot size converting optical waveguide unit. It is characterized by that.

Japanese Patent Laid-Open No. 2002-374035 discloses a semiconductor laser element. The semiconductor laser element includes a stacked structure in which a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer different from the first conductivity type are sequentially stacked. In the vicinity thereof, a waveguide region is formed that restricts the spread of light in the width direction and guides light in a direction orthogonal to the width direction. The waveguide region has a first waveguide region and a second waveguide region. The first waveguide region is a region in which light is confined in the restricted active layer by a difference in refractive index between the active layer and the regions on both sides thereof by limiting the width of the active layer. . The second waveguide region is characterized in that light is confined by effectively providing a refractive index difference in the active layer.

JP 2006-517673 A discloses an optical device. The optical device includes a single mode waveguide supporting a first optical mode in a first region and a second optical mode in a second region, the waveguide including at least one wing extending outward from the guide layer. It is out.

Each of the above-described channel type optical waveguide and rib type optical waveguide has advantages and disadvantages. Therefore, an object of the present invention is to connect a channel type optical waveguide and a rib type optical waveguide with low loss, and to complement the characteristics (advantages) of the channel type optical waveguide and the rib type optical waveguide. An object of the present invention is to provide a waveguide and a manufacturing method thereof.

The optical waveguide of the present invention includes a first cladding layer formed on a substrate, a core layer formed on the first cladding layer, and a second cladding layer covering the first cladding layer and the core layer. And. The core layer includes a rib-type optical waveguide and a channel-type optical waveguide. The rib-type optical waveguide includes a slab portion formed on the first clad layer and a rib portion formed on the slab portion. The length of the slab portion extends from one end portion to the other end portion in the optical waveguide direction, and the width thereof is reduced in the optical waveguide direction. The length of the rib portion extends from one end portion to the other end portion in the optical waveguide direction, the width thereof decreases in the optical waveguide direction, and is narrower than the width of the slab portion. The channel-type optical waveguide includes a core portion formed on the first cladding layer. The length of the core portion extends from one end to the other end in the optical waveguide direction, and one end is connected to the other end of the slab portion. The thickness and width of the core part are equal to the thickness and width of the other end part of the slab part, respectively. Thus, according to the optical waveguide of the present invention, the channel-type optical waveguide and the rib-type optical waveguide can be connected with low loss, and the characteristics (advantages) of the channel-type optical waveguide and the rib-type optical waveguide are complemented. be able to.

The objects, effects, and features of the above invention will become more apparent from the description of the embodiments in conjunction with the accompanying drawings.

FIG. 1 is a perspective view showing a configuration of an optical waveguide according to an embodiment of the present invention. FIG. 2A shows the mode-feel shape of the fundamental mode in the waveguide cross section 111. FIG. 2B shows the mode-feel shape of the fundamental mode in the waveguide cross section 112. FIG. 2C shows a mode-feel shape of the fundamental mode in the waveguide cross section 113. FIG. 3A shows the calculation result of the lightwave electric field amplitude in the horizontal direction (direction X) in the rib-type optical waveguide and the channel-type optical waveguide. FIG. 3B shows the calculation result of the light wave electric field amplitude in the vertical direction (direction Z) superimposed on the rib type optical waveguide and the channel type optical waveguide. FIG. 4A illustrates a process for manufacturing an optical waveguide according to an embodiment of the present invention. FIG. 4B illustrates a process for manufacturing an optical waveguide according to an embodiment of the present invention. FIG. 4C illustrates a process for manufacturing an optical waveguide according to an embodiment of the present invention. FIG. 4D shows a process for manufacturing an optical waveguide according to an embodiment of the present invention. FIG. 4E illustrates a process for manufacturing an optical waveguide according to an embodiment of the present invention. FIG. 5 shows a 1 × 8 optical switch to which an optical waveguide according to an embodiment of the present invention is applied.

Hereinafter, an optical waveguide according to an embodiment of the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

[Constitution]
FIG. 1 is a perspective view showing a configuration of an optical waveguide according to an embodiment of the present invention. The optical waveguide includes a first clad layer 102 formed on the substrate 101, a core layer formed on the first clad layer 102, and a second clad that covers the first clad layer 102 and the core layer. A cladding layer 104.

Therefore, when a silicon layer is applied to the core layer, a silicon oxide film is applied to the first cladding layer 102 and the second cladding layer 104. In this case, the substrate 101, the first cladding layer 102, and the core layer constitute an SOI (Silicon on Insulator) substrate.

The core layer has a higher refractive index than the first cladding layer 102 and the second cladding layer 104. The core layer includes a rib type optical waveguide and a channel type optical waveguide.

The rib-type optical waveguide includes a slab part 107 formed on the first clad layer 102 and a rib part 105 formed on the slab part 107. The length of the slab part 107 and the rib part 105 extends from one end part to the other end part in the first direction Z (hereinafter referred to as the direction Z), and the width decreases monotonously in the direction Z. . The slab part 107 and the rib part 105 are what is called a taper shape. A direction Z represents an optical waveguide direction (light waveguide direction).

Here, the length of the rib part 105 and the slab part 107 represents the length in the direction Z parallel to the substrate 101. The widths of the rib portion 105 and the slab portion 107 are parallel to the substrate 101 and represent the length in the second direction X (hereinafter, direction X) perpendicular to the direction Z. The thickness (height) of the rib part 105 and the slab part 107 represents the length of a third direction Y (hereinafter, direction Y) that is parallel to the substrate 101 and perpendicular to the directions Z and X Yes. The widths of the one end and the other end of the rib portion 105 are 1.0 microns and 0.1 microns, respectively, and the thickness of the rib portion 105 is 1.2 microns. The width of the one end part and the other end part of the rib part 105 is narrower than the width of the one end part and the other end part of the slab part 107, respectively. The thickness and width of the other end of the slab 107 are 0.3 and 0.5 microns, respectively.

The channel type optical waveguide includes a core portion 103 formed on the first cladding layer 102. The length of the core portion 103 extends from one end portion to the other end portion in the direction Z, and one end portion is connected to the other end portion of the slab portion 107.

Here, the length, width, and thickness of the core portion 103 represent the lengths in the directions Z, X, and Y, respectively. The thickness and width of the core portion 103 are 0.3 and 0.5 microns, respectively. That is, the thickness and width of the core portion 103 are equal to the thickness and width of the other end portion of the slab portion 107, respectively.

The operation mechanism of this embodiment will be described.

The light wave incident on the rib-type optical waveguide (rib portion 105, slab portion 107) propagates from one end of the rib portion 105 and slab portion 107 to the other end, and the connection between the rib-type optical waveguide and the channel-type optical waveguide. Propagate to unit 108. The light wave incident on the channel type optical waveguide (core portion 103) propagates from one end portion of the core portion 103 to the other end portion.

With the configuration and operation described above, the optical waveguide according to the embodiment of the present invention achieves the following effects.

When the optical waveguide according to the embodiment of the present invention is cut along the direction X, one end of the rib-type optical waveguide, the connecting portion 108 between the rib-type optical waveguide and the channel-type optical waveguide, and the other end of the channel-type optical waveguide are The cross sections to be represented are waveguide

cross sections

111, 112, and 113, respectively. FIGS. 2A to 2C show the mode feel shapes of the fundamental modes in the

waveguide cross sections

111, 112, and 113 (only half in the lateral direction (direction X) in consideration of symmetry), respectively. FIG. 3A shows the calculation result of the light wave electric field amplitude in the horizontal direction (direction X) in the rib type optical waveguide and the channel type optical waveguide, and FIG. 3B shows the rib type optical waveguide and the channel type optical waveguide. Fig. 5 shows the calculation result of the light wave electric field amplitude in the vertical direction (direction Z) in an overlapping manner.

In the optical waveguide according to the embodiment of the present invention, not only the width of the rib portion 105 of the rib-type optical waveguide is monotonously reduced but also the width of the slab portion 107 is reduced. Therefore, in the connecting portion 108, the width and thickness of the slab portion 107 of the rib type optical waveguide are made equal to the width and thickness of the core portion 103 of the channel type optical waveguide. For this reason, since the cross-sectional shapes of the rib-type optical waveguide and the channel-type optical waveguide are equal at the connecting portion 108, the mode-field shape of the rib-type optical waveguide almost matches the mode-field shape of the channel-type optical waveguide.

Specifically, in the connecting portion 108, in addition to making the width and thickness of the slab portion 107 of the rib-type optical waveguide equal to the width and thickness of the core portion 103 of the channel-type optical waveguide, The width of the rib portion 105 is preferably sufficiently smaller than the width of the core portion 103 of the channel type optical waveguide. As a result, as shown in FIGS. 2A to 2C, the mode field shape of the rib-type optical waveguide at the connection portion 108 almost matches the mode field shape of the channel-type optical waveguide. In addition, as shown in FIGS. 3A and 3B, in the rib-type optical waveguide and the channel-type optical waveguide, even if the calculation results of the lightwave electric field amplitudes in the horizontal direction and the vertical direction are overlapped, it can be seen that both are almost the same. . That is, according to the optical waveguide according to the embodiment of the present invention, since the mode mismatch at the connection portion 108 is very small, the coupling loss is sufficiently suppressed.

Further, in the optical waveguide according to the embodiment of the present invention, the core layer (rib type optical waveguide, channel type optical waveguide), the first cladding layer 102 and the second cladding layer 104 contain the same (silicon). ing. For this reason, when the mode feel shapes of the rib-type optical waveguide and the channel-type optical waveguide match at the connection portion 108, the effective refractive indexes also match, and the Fresnel reflection at the connection portion 108 is sufficiently suppressed. Can do. That is, according to the optical waveguide according to the embodiment of the present invention, it is possible to suppress two loss factors due to the difference between the mode feel and the effective refractive index, and to reduce the waveguide connection loss as a whole.

Thus, according to the optical waveguide according to the embodiment of the present invention, the channel-type optical waveguide and the rib-type optical waveguide can be connected with low loss, and the characteristics (advantages) of the channel-type optical waveguide and the rib-type optical waveguide ) Can be complemented.

In addition, according to the optical waveguide according to the embodiment of the present invention, a small optical functional circuit with low optical loss can be realized. That is, a channel type optical circuit is used for a portion having a waveguide bend, a rib type optical circuit is used for a straight portion, and the present embodiment is used for coupling a rib type optical waveguide and a channel type optical waveguide. By applying the structure of the form, an optical functional circuit in which both bending loss and propagation loss are minimized can be realized.

[Production method]
4A-4E illustrate a process in which an optical waveguide according to an embodiment of the present invention is manufactured.

As shown in FIG. 4A, a first clad layer 102, which is a silicon oxide film, is formed on a substrate 101 (silicon substrate). Next, a core layer 121 which is a silicon layer having a thickness of 1.5 microns is formed on the first cladding layer 102. Next, a first insulating layer, which is a silicon oxide film, is laminated (formed) on the core layer 121 by a CVD (Chemical Vapor Deposition) method. Thereafter, the second insulating layer 122 (silicon oxide film) is formed on the core layer 121 by patterning so as to partially leave the first insulating layer by a photolithography process. Here, the second insulating layer 122 has a first shape 123 having a tapered shape and a second shape 124 having a linear shape. The length of the first shape 123 extends from one end to the other end in the direction Z, and the width is monotonously reduced in the direction Z. The length of the second shape 124 extends from one end to the other end in the direction Z, and one end is connected to the other end of the first shape 123. The width of the second shape 124 is equal to the width of the other end portion of the first shape 123. Here, the length, width, and thickness of the first shape 123 and the second shape 124 indicate the lengths in the directions Z, X, and Y, respectively.

As shown in FIG. 4B, using the second insulating layer 122 as a mask, the upper surface portion of the core layer 121 is etched so that the first shape 123 and the second shape 124 have the same thickness. In this case, the core layer 121 is removed by a thickness of 0.3 microns by dry etching.

As shown in FIG. 4C, the second insulating layer 122 is patterned so as to partially leave the third insulating layer 125 (silicon oxide layer) on the first shape 123 of the second insulating layer 122. Film) is formed. Here, the third insulating layer 125 has a third shape that is narrower than the first shape 123 and has a tapered shape.

4D, using the third insulating layer (125) as a mask, a rib-type optical waveguide provided with a slab portion 107 and a rib portion 105 corresponding to the first shape 123 and the second shape 124, respectively. The core layer 121 is etched so that a channel-type optical waveguide including the core portion 103 corresponding to the third shape 125 is formed. In this case, the core layer 121 is removed by a thickness of 1.3 microns by dry etching.

As shown in FIG. 4E, a second cladding layer 104, which is a silicon oxide film, is laminated (formed) by a CVD method on the first cladding layer 102, the rib-type optical waveguide, and the channel-type optical waveguide.

According to the method of manufacturing an optical waveguide according to the embodiment of the present invention, in addition to the above-described effects, the manufacturing cost of the above-described high-performance optical circuit can be reduced. That is, in two dry etching processes for creating a channel type optical waveguide and a rib type optical waveguide, a spot size converter for connecting the two waveguides is formed at the same time, so that the manufacturing process is prevented from becoming complicated. Thus, it is possible to improve the yield and reduce the manufacturing cost.

[Application example]
FIG. 5 shows a 1 × 8 optical switch to which an optical waveguide according to an embodiment of the present invention is applied.

The optical switch includes a plurality of (2 × 2)

optical switch portions

202, 203, 205, 210, 208, 212, and 213 formed on the SOI substrate 201, and a channel type optical waveguide 204. The

optical switch sections

202, 203, 205, 210, 208, 212, and 213 include directional couplers and rib-type optical waveguides, and are connected in a tree shape by the channel-type optical waveguide 204. The optical waveguide 214 (rib type optical waveguide and channel type optical waveguide) has the same configuration as the optical waveguide described above.

The 2 × 2 optical switch unit has a Mach-Zehnder interference type configuration with a rib-type optical waveguide having a waveguide width of 1.0 μm, a rib height of 1.2 μm, and a slab height of 0.3 μm. It is formed of a directional coupler and two optical waveguides arranged between them. One of the two optical waveguides includes a heater 209 for providing a phase modulation function. The channel type optical waveguide 204 connecting the optical switch portions has a crank shape having two bends having a curvature radius of 5 microns in order to reduce the element size.

The operation mechanism of this embodiment will be described below.

The signal light input from one end of the optical switch unit 202 is distributed to the

optical switch unit

203 or 205 through the channel type optical waveguide by phase adjustment by the heater, and further, the optical switch is transmitted from each optical switch through the channel type optical waveguide. The signals are distributed from the units 210 to 213, and finally distributed in two directions from each optical switch unit in the same manner. Accordingly, eight output ends can be selected as output destinations of optical signals input from one end by appropriately adjusting the heaters of the respective optical switch sections. In the 1 × 8 optical switch according to the present embodiment, a channel type optical waveguide is used in a portion that requires a sharp bend to reduce propagation loss and stability of optical characteristics (suppression of characteristic variations due to structural variations). A rib-type optical waveguide is adopted in the portion where the optical fiber is required, and a small, low loss and highly reliable optical switch element can be realized.

According to the optical switch to which the optical waveguide according to the embodiment of the present invention is applied, in addition to the above-described effects, it is possible to achieve both performance variation and miniaturization of the optical functional circuit. To reduce the size of optical functional circuits, a channel-type optical waveguide with a small bending radius is required. However, the channel-type optical waveguide has a small tolerance to the structure such as width and thickness, and it is optical with a slight change in the waveguide size. It has the characteristic that the characteristics vary greatly. In the present invention, a channel-type optical waveguide can be used only in a portion requiring waveguide bending. Therefore, it is possible to realize an optical element that is small and has little variation in optical characteristics as an entire optical functional circuit. It is.

The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

This application is based on Japanese Patent Application No. 2008-025957 filed on Feb. 6, 2008 and claims the benefit of the priority of the application, the disclosure of that application should be cited Is incorporated here as it is.

Claims

A first cladding layer formed on the substrate;
A core layer formed on the first cladding layer;
A second cladding layer covering the first cladding layer and the core layer;
Comprising
The core layer is
A rib-type optical waveguide;
A channel-type optical waveguide;
Comprising
The rib-type optical waveguide is
A slab part formed on the first cladding layer, the length of which extends from one end to the other end in the optical waveguide direction, and the width of which is reduced toward the optical waveguide direction;
It is formed on the slab part, its length extends from one end part to the other end part in the optical waveguide direction, its width is reduced in the optical waveguide direction, and is smaller than the width of the slab part Narrow ribs,
Comprising
The channel-type optical waveguide is
A core portion formed on the first cladding layer, the length of which extends from one end to the other end in the optical waveguide direction, and one end connected to the other end of the slab portion;
Comprising
The thickness and width of the core part are equal to the thickness and width of the other end of the slab part, respectively.
Optical waveguide.
The length of the rib part, the slab part, and the core part represents a length in a first direction that is the optical waveguide direction parallel to the substrate,
The width of the rib part, the slab part, and the core part represents a length in a second direction that is parallel to the substrate and perpendicular to the first direction,
The thickness of the rib part, the slab part, and the core part represents a length in a third direction that is parallel to the substrate and perpendicular to the first and second directions.
The optical waveguide according to claim 1.
The core layer has a higher refractive index than the first and second cladding layers.
The optical waveguide according to claim 1 or 2.
The core layer is a silicon layer;
The first and second cladding layers are silicon oxide films.
The optical waveguide according to any one of claims 1 to 3.
Forming a first cladding layer on the substrate;
Forming a core layer on the first cladding layer;
Forming a first insulating layer on the core layer;
Forming a second insulating layer on the core layer by patterning to leave the first insulating layer partially, wherein the length of the second insulating layer is an optical waveguide; A first shape extending from one end to the other end in the direction and having a width reduced toward the optical waveguide direction, and a length from the one end to the other end in the optical waveguide direction And a second shape having one end connected to the other end of the first shape, and the width of the second shape is equal to the width of the other end of the first shape equally,
Etching the upper surface of the core layer using the second insulating layer as a mask so that the first and second shapes have the same thickness;
Forming a third insulating layer on the first shape of the second insulating layer by patterning so as to partially leave the second insulating layer, wherein the third insulating layer The layer has a third shape that is narrower than the first shape,
A channel-type optical waveguide comprising a rib-type optical waveguide provided with a slab portion and a rib portion corresponding to the first and second shapes, respectively, and a core portion corresponding to the third shape using the third insulating layer as a mask Etching the core layer such that a waveguide is formed;
Laminating a second cladding layer on the first cladding layer, the rib-type optical waveguide and the channel-type optical waveguide;
An optical waveguide manufacturing method comprising:
The lengths of the first to third shapes represent the length in the first direction that is the optical waveguide direction parallel to the substrate,
The widths of the first to third shapes represent a length in a second direction parallel to the substrate and perpendicular to the first direction,
The thicknesses of the first to third shapes represent a length in a third direction parallel to the substrate and perpendicular to the first and second directions.
The method for manufacturing an optical waveguide according to claim 5.
The core layer has a higher refractive index than the first and second cladding layers.
The method for producing an optical waveguide according to claim 5 or 6.
The core layer is a silicon layer;
The first and second cladding layers are silicon oxide films.
The method for producing an optical waveguide according to any one of claims 5 to 7.
The first to third insulating layers are silicon oxide films.
The method for producing an optical waveguide according to any one of claims 5 to 8.
A plurality of optical switch portions including the rib-type optical waveguide of the optical waveguide according to any one of claims 1 to 4,
The plurality of optical switch portions are connected in a tree shape by the channel-type optical waveguide of the optical waveguide according to any one of claims 1 to 4.
Light switch.