JP2010266628A - Optical control element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical control element which can efficiently remove unnecessary high-order mode light without complicating a production process thereof. <P>SOLUTION: The optical control element includes: a substrate 1 having an electro-optical effect; an optical waveguide (2-5) formed on the substrate; and a control electrode for controlling light waves to be propagated through the optical waveguide. The optical waveguide is composed of an outputting waveguide part 4 for leading out basic mode light and a sub-waveguide part 5 which is connected to the outputting waveguide part and used for leading out the high-order mode light. A removing means 6 is arranged which is formed to be contacted with the sub-waveguide part and used for removing the high-order mode light to be propagated through the sub-waveguide part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light control element, and in particular, a substrate having an electrooptic effect, such as an optical modulator or an optical switch, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating through the optical waveguide. The present invention relates to a light control element having

  In the optical communication field and the optical measurement field, an optical control element provided with a control electrode for controlling an optical waveguide and a light wave propagating through the optical waveguide on a substrate having an electro-optic effect, such as an optical modulator or an optical switch Is frequently used.

  In order to detect the operation state of the light control element, for example, as shown in Patent Document 1, the radiation mode light emitted from the light modulator is reflected by a groove provided on the substrate and monitored by the light detector. In addition, as shown in Patent Document 2 or 3, a method of deriving high-order mode light such as radiation mode light out of the substrate using a monitoring optical waveguide has been proposed.

  In the light control element, it is necessary to properly separate the fundamental mode light, which is signal light, and the higher order mode light such as the emission mode light of the optical modulator and the OFF light of the optical switch. The mode light is configured so that it does not re-enter the optical waveguide through which the fundamental mode light propagates, and the higher-order mode light is not incident as stray light on the monitoring means for monitoring the operation state of the light control element as described above. Etc. are indispensable.

  For this reason, a shielding means is provided in a region where higher order mode light such as radiation mode light propagates. However, a method of forming a recess such as a groove in the substrate and embedding the light-absorbing substance in the recess as the shielding means complicates the manufacturing process and causes a reduction in the mechanical strength of the substrate with a thin thickness. . In addition, methods such as forming a high refractive index region in the substrate and forming a light absorbing material film on the substrate surface have been disclosed, but many structures such as an optical waveguide and a control electrode are incorporated in the substrate surface. In order to eliminate unnecessary high-order mode light in advance, securing a sufficient installation area for these shielding means limits the degree of freedom in designing the light control element, and also reduces the size of the light control element. It becomes a hindrance factor.

JP-A-4-24610 JP 2006-301612 A JP 2008-46589 A

  An object of the present invention is to provide a light control element that can eliminate the above-described problems and efficiently remove unnecessary higher-order mode light without complicating the manufacturing process of the light control element.

  In order to solve the above problems, an invention according to claim 1 includes a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating through the optical waveguide. In the light control element, the optical waveguide has an output waveguide section for deriving fundamental mode light and a sub-waveguide section connected to the output waveguide section for deriving higher-order mode light, and the sub-waveguide A removing means for removing high-order mode light that is formed in contact with the portion and propagates through the sub-waveguide portion is provided.

  The invention according to claim 2 is the light control element according to claim 1, wherein the waveguide width on the incident side of the sub waveguide section is narrower than the width of the output waveguide section, and is in contact with the removing means. In the region, the width of the sub-waveguide portion is wider than the width of the output waveguide portion.

  The invention according to claim 3 is the light control element according to claim 1 or 2, wherein the removing means is a high refractive index film or a metal film having a higher refractive index than the optical waveguide.

  The invention according to claim 4 is the light control element according to claim 3, wherein the metal film is a part of the control electrode.

  The invention according to claim 5 is the optical control element according to any one of claims 1 to 4, wherein the output waveguide is an output waveguide of an optical waveguide constituting a Mach-Zehnder interferometer, or an optical switch It is any one of the output waveguides.

  According to the first aspect of the present invention, in a light control element comprising a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating through the optical waveguide, The waveguide has an output waveguide section for deriving fundamental mode light and a sub-waveguide section connected to the output waveguide section for deriving higher-order mode light, and is formed in contact with the sub-waveguide section. Since the removal means for removing the higher-order mode light propagating through the sub-waveguide section is provided, only the higher-order mode light can be selectively removed. In addition, the removing means only needs to be provided on the sub-waveguide from which the higher-order mode light is derived, and the area occupied by the removing means on the substrate of the light control element is extremely limited. Further, the sub-waveguide portion can be formed simultaneously with the formation of the normal optical waveguide including the output waveguide portion, so that the manufacturing process is not complicated.

  According to the invention of claim 2, the incident-side waveguide width of the sub-waveguide portion is narrower than the width of the output waveguide portion, and in the region in contact with the removing means, the width of the sub-waveguide portion is Since the output waveguide section has a portion wider than the width of the output waveguide section, higher-order mode light can be selectively introduced into the sub-waveguide section, and is propagated in multimode in the region where the removal means is disposed, and the removal means It is possible to further enhance the removal effect by.

  According to the invention of claim 3, since the removing means is a high refractive index film or a metal film having a higher refractive index than that of the optical waveguide, in the case of the high refractive index film, the high-order mode light is emitted outside the light control element. In the case of a metal film, high-order mode light can be absorbed efficiently, so that the removal efficiency can be increased. In addition, unlike the conventional example, no concave portion such as a groove is formed, so that the mechanical strength is not lowered even for a light control element using a thin substrate.

  According to the invention of claim 4, since the metal film is a part of the control electrode, it is possible to form a removing means at the same time when forming the control electrode, and to avoid complication of the manufacturing process. . In particular, by using a part of the ground electrode constituting the control electrode as the removal means, it is possible to select the installation place of the removal means relatively freely.

  According to the invention of claim 5, since the output waveguide is one of the output waveguide of the optical waveguide constituting the Mach-Zehnder interferometer or the output waveguide of the optical switch, the higher-order mode light is By using the present invention even for an optical modulator or an optical switch that is likely to be generated, unnecessary high-order mode light can be efficiently removed.

It is a top view which shows the 1st Example which concerns on the light control element of this invention. It is sectional drawing in the arrow A-A 'of FIG. It is a figure explaining the relationship between the output waveguide part and sub-waveguide part in the light control element of this invention. It is a top view which shows the 2nd Example which concerns on the light control element of this invention. It is a top view which shows the 3rd Example which concerns on the light control element of this invention. It is a top view which shows the 4th Example which concerns on the light control element of this invention. It is a top view which shows the 5th Example based on the light control element of this invention.

The light control element of the present invention will be described in detail below.
As shown in the first embodiment of FIG. 1, the light control device of the present invention propagates through the optical waveguide (1), the optical waveguide (2-5) formed on the substrate, and the optical waveguide. In the light control element having a control electrode (not shown) for controlling the light wave to be transmitted, the optical waveguide is connected to the output waveguide section 4 for deriving the fundamental mode light and the output waveguide section 4 and is high. A sub-waveguide section 5 for deriving the next-mode light, and a removing means 6 for removing higher-order mode light that is formed in contact with the sub-waveguide section 5 and propagates through the sub-waveguide section 5; It is provided.

  According to the light control element of the present invention, only the higher-order mode light can be selectively removed by the sub-waveguide section 5. FIG. 2 is a cross-sectional view taken along arrow A-A ′ in FIG. As shown in FIG. 2, the removal means 6 only needs to be provided on the sub-waveguide 5 from which the higher-order mode light is derived, and the area occupied by the removal means on the substrate of the light control element may be extremely limited. There is no need to provide light shielding means at many locations on the substrate as in the prior art.

As the substrate 1 having an electro-optic effect, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), a quartz-based material, or the like can be used. In order to form the optical waveguide (2-5), a method of forming an optical waveguide on the surface of the substrate by Ti or the like using a thermal diffusion method or a proton exchange method, or a method of forming an optical waveguide with a ridge shape corresponding to the waveguide and so on. The control electrode (not shown) is composed of a signal electrode and a ground electrode, and can be formed by forming a Ti / Au electrode pattern on the substrate surface and using a gold plating method or the like. Further, if necessary, a buffer layer such as dielectric SiO ₂ can be provided on the surface of the substrate after the formation of the optical waveguide, but the surface of the optical waveguide 5 in contact with the removing means 6 has a low buffer layer or the like. When a refractive index layer is provided, the light removal effect is reduced, so it is preferable not to form these film bodies in the region.

  Since both the output waveguide section 4 and the sub-waveguide section 5 are part of the optical waveguide, they can be formed by a thermal diffusion method such as Ti as in the optical waveguide constituting the light control element as described above. In addition, since the optical waveguides can be formed at the same time as the normal optical waveguide, the manufacturing process is not complicated. In the first embodiment of FIG. 1, the optical waveguide 2 constitutes a Mach-Zehnder interferometer, and the sub-waveguide portion 5 according to the present invention constitutes the Mach-Zehnder interferometer constituting the output waveguide portion 4. Are connected to the output waveguide.

  The fundamental mode light, which is the ON mode light emitted from the multiplexing unit 3 of the interferometer, propagates to the output waveguide unit 4, and is emitted from the multiplexing unit 3 to the sub-waveguide unit 5. Higher order mode light such as radiation mode light that becomes OFF mode light is propagated.

  FIG. 3 is an example showing the relationship between the output waveguide section 4 and the sub-waveguide section 5 of FIG. 1, and illustrates the connection status of each waveguide section and the width of each waveguide. The output waveguide section 4 in the present invention is used when the fundamental mode light is derived, and the sub-waveguide section 5 is connected to the output waveguide section 4 with reference to the width W1 of the output waveguide section 4. The width W2 of the connected portion is the condition “W2 <W1”, and the width W3 of the portion in contact with the removing unit 6 is set to satisfy the condition “W3> W1”.

  Only the higher-order mode light can be selectively introduced into the sub-waveguide portion by setting the condition regarding the width W2. Further, by setting the condition relating to the width W3, it is possible to propagate in the multimode in the region where the removing unit is arranged, and to further enhance the removing effect by the removing unit. That is, as the width of the optical waveguide becomes wider, the center of gravity of the propagating mode light becomes more on the surface side, and the mode light is unevenly distributed on the surface side. For this reason, the light wave propagating through the sub-waveguide portion 5 can be easily removed by the removing means 6.

  As the removing means 6, a high refractive index film or metal film having a higher refractive index than that of the optical waveguide 5 can be selected. When a high refractive index film is used, high-order mode light can be efficiently derived outside the light control element. In the case of a metal film, high-order mode light can be absorbed efficiently, so that the removal efficiency can be increased. In addition, since the concave portions such as the grooves are not formed unlike the conventional shielding means, the mechanical strength is not lowered even for the light control element using a thin substrate.

  In addition, when the removal means 6 is formed of a metal film, a part of a control electrode (not shown) constituting the light control element, for example, a part of the ground electrode constituting the control electrode is used as the removal means. Thus, when the control electrode is formed, the removing means 6 can be formed at the same time, and the manufacturing process can be avoided. In addition, since the ground electrode is installed in a relatively wide area on the surface of the substrate, the degree of freedom of the installation position of the removing means 6 can be increased.

4 to 7 describe another embodiment relating to the light control element of the present invention.
FIG. 4 shows that one of the sub-waveguide portions 5 in FIG. 1 is derived as radiated light (monitor light) 10 from the light control element, monitored by a photodetector or the like, and used for drive control of the light control element. Is possible. Further, a removing means 6 is provided in the sub-waveguide portion 5 from which the monitor light is not derived.

  In FIG. 5, in order to monitor the light wave propagating through the sub-waveguide unit 5, a photodetector 20 that detects a part of the light wave propagating through the sub-waveguide unit 5 is formed on the substrate 1. And the afterglow which was not guide | induced to the photodetector 20 is comprised by the removal means 6.

  In FIG. 6, the optical coupler 7 is disposed on the light exit side of the optical waveguide, and the signal light 30 is led out of the element through the output waveguide portion 8. Higher-order mode light other than signal light is configured to be guided to the removing means 6 through the sub-waveguide portion 9.

  In FIG. 7, the optical waveguide 40 is composed of a plurality of branch portions, and an optical switch or the like can be appropriately formed in the light branch portion. In FIG. 7, a waveguide section 41 for guiding a light wave derived by an optical branching section or an optical switch, in particular, a light wave that is not used, is provided and removed using the removing means 6. In FIG. 7, the removal unit is only one port, but it can be provided in a plurality of units.

  Also in the various embodiments (second to fifth embodiments) according to FIGS. 4 to 7 described above, the configuration of the output waveguide portion and the sub-waveguide portion shown in the first embodiment, and the configuration of the removing means Needless to say, the same can be applied.

  As described above, according to the present invention, it is possible to provide a light control element capable of efficiently removing unnecessary light without complicating the manufacturing process of the light control element.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide according to Mach-Zehnder interferometer 3 Multiplexing unit 4 Output waveguide unit 5 Sub-waveguide unit 6 Removal means

Claims (5)

In a light control element having a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating through the optical waveguide,
The optical waveguide has an output waveguide section that derives fundamental mode light and a sub-waveguide section that is connected to the output waveguide section and derives higher-order mode light,
A light control element comprising a removing means for removing high-order mode light that is formed in contact with the sub-waveguide portion and propagates through the sub-waveguide portion.   2. The light control element according to claim 1, wherein the width of the waveguide on the incident side of the sub-waveguide portion is narrower than the width of the output waveguide portion, and the sub-guide is in a region in contact with the removing means. A light control element characterized in that the width of the waveguide portion has a portion wider than the width of the output waveguide portion.   3. The light control element according to claim 1, wherein the removing means is a high refractive index film or a metal film having a higher refractive index than the optical waveguide.   4. The light control element according to claim 3, wherein the metal film is a part of the control electrode.   5. The light control element according to claim 1, wherein the output waveguide is either an output waveguide of an optical waveguide constituting a Mach-Zehnder interferometer or an output waveguide of an optical switch. A light control element characterized by the above.

Images