JP6299170B2 - Optical waveguide device - Google Patents

Description

  The present invention relates to an optical waveguide device, and in particular, an optical waveguide is formed on a substrate, and the optical waveguide includes a main waveguide that propagates signal light and a guide for unnecessary light that guides unnecessary light emitted from the main waveguide. The present invention relates to an optical waveguide device including a waveguide.

  In the optical communication field and the optical measurement field, an optical waveguide element having an optical function such as an optical modulator is frequently used. Some optical waveguide elements are provided with an optical waveguide by thermally diffusing a metal such as Ti on a substrate made of quartz, lithium niobate, or a semiconductor material, or by forming a ridge-shaped convex portion.

  In an optical waveguide device using such a substrate, when a plurality of optical waveguides are formed in the same substrate, or when a lot of branching portions and multiplexing portions are formed in the optical waveguide, a part of the optical waveguide Unnecessary light emitted from the light couples to other parts of the optical waveguide, causing deterioration of optical characteristics. Further, the Mach-Zehnder type optical modulator causes deterioration of optical characteristics such as an ON / OFF extinction ratio.

  In Patent Documents 1 to 3 and the like, as shown in FIG. 1, a waveguide for unnecessary light (31 to 33) for guiding unnecessary light is provided separately from the main waveguide 2 (21 to 23) for propagating signal light. A configuration that is provided on the substrate 1 and suppresses unnecessary light from recombining with the main waveguide is disclosed. The unnecessary light waveguide is not only directly connected to the main waveguide as in Patent Document 1, but also is disposed apart from the main waveguide as in Patent Document 2 or 3. Moreover, when crossing the main waveguide (22) as in Patent Document 1 (see the portion indicated by the dotted line A), a part of the unnecessary light waveguide (32, 41 to 42) is divided. Is also disclosed.

  Further, Patent Document 1 discloses that the light absorbing means 5 is disposed in a part of the unnecessary light waveguide in order to absorb and eliminate unnecessary light guided by the unnecessary light waveguide. In addition, the code | symbol 4 of FIG. 1 has shown the light-receiving means for light-receiving the radiation mode light from the multiplexing part 21. FIG.

  When optical waveguides are integrated, such as a Mach-Zehnder type optical waveguide or a nested optical waveguide that is a nested combination of Mach-Zehnder type optical waveguides, light that includes radiation mode light from the multiplexing part or branching part There are many places where light leaks from the waveguide and the like, and removal of unnecessary light becomes a very serious problem.

  In addition, when the thickness of the substrate is thin, for example, when it has a thickness of 30 μm or less, unnecessary light is easily trapped in the substrate, and compared with the case where the substrate has a sufficient thickness such that the substrate has a thickness of 500 μm or more. The recombination rate is extremely high. In addition, when the light receiving element is disposed on or around the substrate, unnecessary light is likely to enter the light receiving element, making it difficult to perform highly accurate monitor detection.

  Furthermore, as the optical waveguide is integrated, the place where the absorbing means 5 for absorbing unnecessary light is arranged is limited, and the material that can be used as the light absorbing material is limited in the manufacturing process of the optical waveguide element, It may be difficult to exert a sufficient light absorption effect. Even when the light receiving means 4 that receives light waves such as radiation mode light is disposed, it is necessary to process unnecessary light leaked behind the light receiving element. As shown in FIG. 1, unnecessary light (L1) leaked behind the light receiving element or unnecessary light (L2) that cannot be absorbed travels to the side edge 11 of the substrate and is reflected by the side edge (side) 11. As a result, it returns to the main waveguide 2 side again.

Japanese Patent No. 5071542 JP 2011-164388 A Japanese Patent Laid-Open No. 2004-46021

  The problem to be solved by the present invention is to provide an optical waveguide device that solves the above-described problems, suppresses reflection of unnecessary light on the side surface of the substrate, and prevents deterioration of optical characteristics.

In order to solve the above problems, the optical waveguide device of the present invention has the following technical features.
(1) An optical waveguide device having an optical waveguide formed on a substrate, the optical waveguide including a main waveguide that propagates signal light, and a waveguide for unnecessary light that guides unnecessary light emitted from the main waveguide. In this case, an unnecessary light collecting unit that collects unnecessary light between the main waveguide and the side edge portion of the substrate along substantially the same direction as the signal light propagating through the main waveguide is mainly transmitted. An optical waveguide is formed, and unnecessary light emitted from the unnecessary light waveguide is introduced into the unnecessary light collecting waveguide, and the unnecessary light collecting waveguide is formed on the substrate. It is characterized by being arranged at a distance of 10 μm or more from the side end .

(2) In the optical waveguide device according to (1), the unnecessary light collecting waveguide is disposed on both sides of the main waveguide so as to sandwich the main waveguide.

(3) The optical waveguide device according to (1) or (2), wherein the unnecessary light waveguide is directly connected to the unnecessary light collecting waveguide.

(4) The optical waveguide device according to any one of (1) to (3), wherein the optical waveguide element is a boundary line defining the waveguide for collecting unnecessary light when the substrate is viewed in plan, The boundary line close to the side end is shaped so that unnecessary light emitted from the unnecessary light waveguide is totally reflected at the boundary surface of the unnecessary light collecting waveguide including the boundary line. Is set.

(5) In the optical waveguide device according to any one of (1) to (4), the unnecessary light collecting waveguide absorbs the unnecessary light provided on the downstream side in the direction in which the unnecessary light propagates. And at least one of an antireflection structure for the unnecessary light to the unnecessary light condensing waveguide provided at the end of the substrate.
(6) In the optical waveguide device according to any one of (1) to (5), the waveguide width of the unnecessary light collecting waveguide is set to be three times or more of the waveguide width of the single mode waveguide. It is characterized by being.

According to the present invention, an optical waveguide is formed on a substrate, and the optical waveguide includes a main waveguide that propagates signal light, and a waveguide for unnecessary light that guides unnecessary light emitted from the main waveguide. In the element, unnecessary light that collects unnecessary light between the main waveguide and the side edge portion of the substrate in substantially the same direction as the signal light propagating through the main waveguide is mainly propagating. A collecting waveguide is formed, and unnecessary light emitted from the unnecessary light waveguide is introduced into the unnecessary light collecting waveguide, and the unnecessary light collecting waveguide is formed on the substrate. The unnecessary light guided in the unnecessary light waveguide is collected in the unnecessary light collecting waveguide, and the unnecessary light is reflected on the side surface of the substrate. Is suppressed. Accordingly, it is possible to provide an optical waveguide element in which unnecessary light is effectively suppressed from recombining with the main waveguide, and deterioration of optical characteristics and the like are prevented.

It is a figure which shows an example of the conventional optical waveguide element. It is the schematic explaining the optical waveguide element of this invention. It is a figure which shows the 1st Example of the waveguide for unnecessary light condensing in the optical waveguide element of this invention. It is a figure which shows the 2nd Example of the waveguide for unnecessary light condensing in the optical waveguide element of this invention. It is a figure which shows the 3rd Example of the waveguide for unnecessary light condensing in the optical waveguide element of this invention. It is a figure which shows the 4th Example of the waveguide for unnecessary light condensing in the optical waveguide element of this invention. It is a figure which shows the 5th Example of the waveguide for unnecessary light condensing in the optical waveguide element of this invention.

Hereinafter, the present invention will be described in detail using preferred examples.
As shown in FIG. 2, the optical waveguide device of the present invention has an optical waveguide formed on a substrate 1, and the optical waveguide guides a main waveguide 2 that propagates signal light and unnecessary light emitted from the main waveguide. In an optical waveguide element including waveguides for unnecessary light (a, b1 to b3, c1 to c3, d1 to d2, e, and f1 to f3), the main waveguide 2 and the side end portion 11 of the substrate The unnecessary light collecting waveguide 6 for collecting unnecessary light is formed along substantially the same direction as the direction in which the signal light propagating through the main waveguide is mainly propagating. In the optical waveguide, unnecessary light emitted from the unnecessary light waveguide is introduced.

  The substrate constituting the optical waveguide device of the present invention is not particularly limited as long as it is a material capable of forming an optical waveguide on the substrate, such as quartz, lithium niobate, and a semiconductor material. When the light wave propagating through the optical waveguide is modulated by an electric field formed by an electrode such as an optical modulator, it is preferable to use a substrate having an electro-optic effect such as lithium niobate or lithium tantalate. In addition, when a thin substrate of 30 μm or less is used, the present invention can be effectively applied.

  As a method for forming the optical waveguide, a method of thermally diffusing a metal such as Ti into the substrate to form a portion having a higher refractive index than the substrate material, a method of forming a ridge waveguide by forming irregularities on the substrate surface, etc. Is applicable.

  As the waveguide for unnecessary light, the waveguide means for unnecessary light disclosed in Patent Documents 1 to 3 can be adopted. For example, since the radiation mode light radiated from the multiplexing unit is guided, the unnecessary light waveguide can be disposed in contact with or separated from the multiplexing unit. As in Patent Document 1, it is also possible to use a waveguide for unnecessary light arranged in the main waveguide before the branching section in order to remove higher-order mode light before being guided to the branching section. Further, it is possible to provide a waveguide for unnecessary light that collects leaked light that leaks out of the main waveguide and propagates in the substrate.

  Further, the unnecessary light waveguide is not only formed as one continuous optical waveguide as indicated by symbols a and e in FIG. 2, but also as indicated by symbols b1 to b3, c1 to c3, and f1 to f3. It is also possible to divide and configure when straddling another optical waveguide such as a main waveguide.

  The unnecessary light waveguide can be formed by joining a plurality of waveguides (c2, d2) as indicated by the dotted line C. The combined unnecessary light can be derived by a single unnecessary light waveguide (c3).

  The feature of the optical waveguide device of the present invention is that an unnecessary light condensing waveguide 6 is disposed between the main waveguide 2 and the side end portion 11 of the substrate. Then, unnecessary light guided by the unnecessary light waveguide is collected in the unnecessary light collecting waveguide, and the unnecessary light is prevented from being reflected on the side surface of the substrate, and is performed in each unnecessary light waveguide. Unnecessary light can also be processed in a lump in the unnecessary light collecting waveguide. Thereby, the recombination of unnecessary light to the main waveguide is suppressed, and deterioration of the optical characteristics of the optical waveguide element can be prevented. In addition, the light absorbing means arranged for each unnecessary light waveguide can be omitted, and the configuration related to the optical waveguide element can be simplified. Further, unnecessary light leaking behind the light receiving element (reference numeral 4 in FIG. 1) arranged on the substrate can also be collected in the unnecessary light collecting waveguide and reliably processed.

  The unnecessary light condensing waveguide is disposed between the main waveguide 2 and the side end (side surface) 11 of the substrate, and the direction in which the signal light propagating through the main waveguide 2 is mainly propagated (see FIG. 2 in the direction from the left to the right). This is because most of the unnecessary light has a vector component directed in the same direction as the signal light, and the unnecessary light is efficiently collected.

  The unnecessary light collecting waveguide is preferably arranged at a position separated by 10 μm or more from the side end (side surface) 11 of the substrate. This is not only to secure a space for cutting the substrate during the manufacture of the optical waveguide element, but also to scatter unnecessary light propagating through the waveguide for collecting unnecessary light due to the surface roughness of the side end (side surface). This is to eliminate the influence of.

  The unnecessary light waveguide basically has a width larger than that of the single mode waveguide. The waveguide width of the unnecessary light collecting waveguide is preferably at least three times the waveguide width of the single mode waveguide, more preferably at least five times. This makes it possible to stably guide unnecessary light in various modes including single mode and higher-order mode light.

  As shown by dotted lines B1 to B5 in FIG. 2, the unnecessary light waveguide and the unnecessary light condensing waveguide can be disposed not only directly but also spaced apart from each other. is there. In that case, the shape of the exit end face of the unnecessary light waveguide and the boundary surface are prevented so that unnecessary light emitted from the unnecessary light waveguide is not reflected by the boundary surface of the unnecessary light collecting waveguide. It is necessary to adjust the shape.

  The unnecessary light condensing waveguide 6 can achieve the above-described various effects even if it is disposed at least one in the vicinity of the side end portion 11 of the substrate. However, as shown in FIG. It is possible to more effectively suppress the reflection of unnecessary light and the like by arranging two with the two interposed therebetween.

  The end of the unnecessary light condensing waveguide 6 can be arranged at the end of the substrate or in the vicinity thereof so as to emit the condensed unnecessary light from the substrate. Further, as shown in FIG. 2, one or more light absorbing means (51, 52) as an unnecessary light absorbing structure is provided in the middle of the unnecessary light collecting waveguide 6 (downstream in the direction in which unnecessary light propagates). It is possible to arrange and absorb the unnecessary light collected and disappear. As a material constituting the light absorbing means, various materials such as metal can be used as in Patent Document 1. Further, by disposing antireflection means 53 such as an antireflection film at the substrate end as the antireflection structure, it is possible to suppress a problem that unnecessary light is reflected by the substrate end surface and reversely moves. It goes without saying that the absorption structure and the antireflection structure can be provided together with respect to the same unnecessary light collecting waveguide.

  Next, the shape of the unnecessary light collecting waveguide in the vicinity of the connection portion between the unnecessary light waveguide and the unnecessary light collecting waveguide will be described. Specifically, by simply connecting the unnecessary light waveguide to the unnecessary light condensing waveguide, unnecessary light can be collected due to the angular relationship between the unnecessary light waveguide and the unnecessary light condensing waveguide. May penetrate through the waveguide for use. In the present invention, in order to solve this problem, as shown in FIGS. 3 to 7, a boundary line (outer boundary line LO and inner boundary line) that defines the waveguide for collecting unnecessary light when the substrate is viewed in plan view. LI) and the boundary line (outer boundary line LO) close to the side edge of the substrate is the unnecessary light collecting waveguide in which unnecessary light emitted from the unnecessary light waveguide includes the boundary line. At least the shape of the boundary line (LO) is set so as to be totally reflected at the boundary surface.

FIG. 3 is a diagram showing the first embodiment, and shows an enlarged view of a connection portion between the unnecessary light waveguide and the unnecessary light collecting waveguide. When the angle between the unnecessary light waveguide and the unnecessary light condensing waveguide is θ and the spread angle of the light emitted from the unnecessary light waveguide is α, the unnecessary light from the unnecessary light waveguide is not leaked. In order to couple to the unnecessary light collecting waveguide, it is necessary to satisfy the following formula (1).
θ + α <p / 2−Φ ・ ・ ・ Formula (1)
Here, Φ represents the total reflection angle at the waveguide interface.
For example, when the refractive index in the optical waveguide is n ₁ and the refractive index n _{0 of the} substrate is defined as Φ = sin ⁻¹ (n ₀ / n ₁ ).

FIG. 4 is a diagram showing a second embodiment. There is a waveguide for unnecessary light having a width w1 and a waveguide for collecting unnecessary light having a width w2, which are related to an angle θ, and the light incident on the waveguide for collecting unnecessary light from the waveguide for unnecessary light is a beam divergence angle. Has α. At this time, the maximum angle of incident light from the unnecessary light guide waveguide with respect to the unnecessary light condensing waveguide is θ + α. Here, when a part of the boundary line LO in FIG. 4 is bent to form the boundary line LO1, if the angle β formed by the boundary line LO1 is θ, if θ + α−β satisfies the total reflection condition, the waveguide Can be guided in a state where unnecessary light is confined. This is expressed by equation (2).
θ + α−β <p / 2−Φ ・ ・ ・ ・ ・ Expression (2)

  FIG. 5 is a diagram showing a third embodiment. For straight light coupled from the unnecessary light waveguide to the unnecessary light collecting waveguide, the angle of the boundary line is reduced from the middle of the boundary line LO1 to form the boundary line LO2. As a result, as shown by the arrow D in FIG. 5, the width of the waveguide for collecting unnecessary light after the straight light is coupled can be reduced compared with the case where the boundary line LO1 is extended, and occupies the substrate. The use area of the waveguide for collecting unnecessary light can be reduced.

  FIG. 6 is a diagram showing a fourth embodiment. The unnecessary light waveguide guides unnecessary light directly from the source of unnecessary light by using a single mode waveguide (width W1). When a single mode waveguide is used in this way, light confinement is strong, and the bending radius of the waveguide can be made smaller than that of a slab waveguide. Further, since the optical waveguide is thin, it is advantageous in that the area occupied on the substrate can be saved.

  FIG. 7 is a diagram showing a fifth embodiment. When unnecessary light propagates from the left to the right of the figure in the unnecessary light collecting waveguide, the unnecessary light is near the root of the unnecessary light waveguide. ). In order to suppress the spread of the unnecessary light in the upward direction, a part of the boundary line LI is projected to the main waveguide side as the boundary line LI1, so that the unnecessary light is also guided to collect unnecessary light. It is possible to suppress leakage from the waveguide.

  As described above, according to the optical waveguide device of the present invention, it is possible to provide an optical waveguide device that suppresses the reflection of unnecessary light on the side surface of the substrate and prevents the deterioration of optical characteristics and the like.

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Main waveguide 4 Light-receiving means 5,51,52 Light absorption means 53 Antireflection means 6 Waveguide for unnecessary light condensing a, b1-b3, c1-c3, d1-d2, e, f1-f3 For unnecessary light Waveguide LO, LO1, LO2 Outer boundary line LI, LI1 Inner boundary line

Claims (6)

An optical waveguide is formed on a substrate, and the optical waveguide includes a main waveguide that propagates signal light and an unnecessary light waveguide that guides unnecessary light emitted from the main waveguide.
For collecting unnecessary light between the main waveguide and the side edge portion of the substrate, in which the unnecessary light is collected in substantially the same direction as the signal light propagating through the main waveguide is mainly propagating. A waveguide is formed,
The unnecessary light collecting waveguide is introduced with unnecessary light emitted from the unnecessary light waveguide, and the unnecessary light collecting waveguide is separated from the side edge of the substrate by 10 μm or more. An optical waveguide device characterized by being arranged . The optical waveguide device according to claim 1,
The waveguide for collecting unnecessary light is disposed on both sides of the main waveguide so as to sandwich the main waveguide. In the optical waveguide device according to claim 1 or 2,
The optical waveguide device, wherein the unnecessary light waveguide is directly connected to the unnecessary light collecting waveguide. The optical waveguide device according to any one of claims 1 to 3,
The boundary line that demarcates the unnecessary light condensing waveguide when the substrate is viewed in plan, and the boundary line close to the side edge of the substrate is the unnecessary light emitted from the unnecessary light waveguide. The shape of the boundary line is set so as to be totally reflected at the boundary surface of the unnecessary light collecting waveguide including the boundary line. The optical waveguide device according to any one of claims 1 to 4,
The unnecessary light condensing waveguide is directed to an absorption structure for absorbing the unnecessary light provided downstream in the direction in which the unnecessary light propagates, or to the unnecessary light condensing waveguide for the unnecessary light provided at the substrate end. An optical waveguide device having at least one of the antireflection structures.   The optical waveguide device according to any one of claims 1 to 5,
  An optical waveguide element characterized in that the waveguide width of the unnecessary light collecting waveguide is set to be three times or more the waveguide width of the single mode waveguide.

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