JP2010256552A - Optical circuit element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress light absorption and optical loss, while making heat conduction between a heating element or a cooling element and a core more efficient. <P>SOLUTION: An optical circuit element which changes the phase of a light propagating through an optical waveguide by thermooptical effect; has a light phase shift optical waveguide 11 that is configured with a clad 11a and the core 11b covered with the clad 11a, a heater 12, and a carbon nanotube 13 that is buried in the clad 11a; and functions as a heat transfer member that thermally connects the heater 12 with the core 11b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical circuit element, and more particularly to an optical circuit element used for adjusting light intensity, optical phase, and the like.

  Among optical circuit elements, for example, a Mach-Zehnder Interferometer type optical switch (hereinafter, referred to as “MZI type optical switch”) is widely used for spatial switching of optical circuits. A general MZI type optical switch performs switching of light propagating through a waveguide using a thermo-optic effect (change in refractive index due to heat). The basic structure of such an MZI type optical switch is schematically shown in FIG. In a general MZI type optical switch, an optical phase shift waveguide 104 composed of a clad 102 and a core 103 is formed on a substrate 101. Further, a heater 105 is provided on the clad 102 of the optical phase shift waveguide 104. In the MZI type optical switch having the structure as illustrated, the phase of light propagating through the waveguide 104 is shifted by changing the refractive index of the optical phase shift waveguide 104 by heating the heater 105. Thereby, light is switched by the cooperative action of the heated optical phase shift waveguide and the other optical phase shift waveguide (not shown).

  However, the heat generated from the heater 105 shown in FIG. 4 is conducted while being dissipated inside the clad 102. Further, it is also conducted to the substrate 101 below the clad 102. For this reason, the core 103 cannot be efficiently heated, and there is a problem that power consumption necessary for switching is large and switching response speed is low.

  A structure shown in FIG. 5 is known as a structure for solving the above problem. In the structure shown in FIG. 5, a gap (heat insulating portion 106) is provided around the optical phase shift waveguide 104. However, the structure shown in FIG. 5 has a problem that the device processing process for forming the heat insulating portion 106 becomes complicated. In addition, there is a problem that the mechanical strength and reliability of the device are low.

  Therefore, Patent Document 1 describes an MZI type optical switch having the structure shown in FIG. In the MZI type optical switch shown in FIG. 6, a fiber reinforced composite material 107 and a buffer layer 108 are disposed between the heater 105 and the core 103. The fiber reinforced composite material 107 has anisotropy and a high thermal conductivity only in one direction. The buffer layer 108 is disposed to prevent light absorption by the fiber reinforced composite material 107.

Japanese Patent Laid-Open No. 2004-198754

  In the structure disclosed in Patent Document 1, a buffer layer is provided to prevent light absorption by the fiber-reinforced composite material. However, the buffer layer generally has a low thermal conductivity. Therefore, the two purposes of improving the heat conduction efficiency between the heater and the core and suppressing light absorption are not sufficiently achieved.

  The present invention has been made in view of the above-mentioned problems, and its purpose has been sufficiently achieved by the two purposes of improving the heat conduction efficiency between the heating element or the cooling element and the core and suppressing light absorption. An optical circuit element is provided.

  An optical circuit element of the present invention is an optical circuit element that changes the phase of light propagating through an optical waveguide by a thermooptic effect, and includes an optical waveguide composed of a clad and a core covered by the clad, and a heating element or a cooling element. It has an element and the carbon nanotube as a heat-transfer member embedded in the said clad and thermally connecting the said heating element or the said cooling element, and the said core.

  According to the present invention, an optical circuit element is realized in which two purposes such as improvement of heat conduction efficiency between a heating element or cooling element and a core and suppression of light absorption and light loss are sufficiently achieved.

It is a schematic diagram which shows an example of embodiment of the optical circuit element of this invention. It is a schematic diagram which shows the other example of embodiment of the optical circuit element of this invention. It is a schematic diagram which shows the further another example of embodiment of the optical circuit element of this invention. It is a schematic diagram showing a basic structure of a general MZI type optical switch. It is a schematic diagram showing the structure of an MZI type optical switch in which a gap (heat insulating part) is provided around the optical phase shift waveguide. It is a schematic diagram showing the structure of the MZI type optical switch described in Patent Document 1.

(Embodiment 1)
Hereinafter, an exemplary embodiment of the optical circuit element of the present invention will be described in detail with reference to FIG.

The optical circuit element according to the present embodiment is an MZI type optical switch that performs switching by changing the refractive index of a waveguide by a thermo-optic effect and changing the phase of light propagating to the waveguide. As shown in FIG. 1, an optical phase shift waveguide 11 is provided on the substrate 10, and a heater 12 is provided on the optical phase shift waveguide 11. The optical phase shift waveguide 11 includes a clad 11a made of SiO ₂ and a core 11b made of Si. Furthermore, a plurality of carbon nanotubes 13 as heat transfer members are disposed inside the clad 11a and between the heater 12 and the core 11b. Furthermore, the carbon nanotubes 13 are arranged such that the axial direction (longitudinal direction) is orthogonal to the outer wall of the core 11b. In addition, a polymer material with little light absorption may be disposed around the carbon nanotubes 13 instead of the cladding 11a (SiO ₂ ).

  Here, the carbon nanotube is a substance in which a hexagonal mesh sheet-like structure (graphene sheet) made of carbon is formed into a single-layer or multilayer coaxial tube. However, the graphene sheet may have a pentagonal mesh or a heptagonal mesh. A single-walled one is sometimes called a “single-wall nanotube (SWNT)”, and a multi-layered one is called a “multi-wall nanotube (MWNT)”. In particular, the double-walled one is sometimes referred to as “double wall nanotube (DWNT). The carbon nanotube in the present invention includes both single-wall nanotubes and multi-wall nanotubes.

The thermal conductivity of the carbon nanotube 13 is 3000 to 5500 [W / (m ⁻¹ K ⁻¹ )], and the thermal conductivity of SiO _{2 as} the cladding 11a is 1 [W / (m ⁻¹ K ^−1). ] And the thermal conductivity of Si as the core 11b is 168 [W / (m ⁻¹ K ⁻¹ )]. As a result, the heat generated from the heater 12 is conducted to the core 11b via the carbon nanotubes 13 that have an overwhelmingly higher thermal conductivity than the clad 11a, and the entire core 11b is efficiently heated. Further, a thermal separation part is equivalently formed around the core 11b by the clad 11a having a lower thermal conductivity than the core 11b. Therefore, the heat generated from the heater is conducted in the clad 11 a along the main surface direction of the substrate 10 and is hardly conducted to the substrate 10. In addition, heat hardly radiates from the side surface or bottom surface of the clad 11a. That is, heat is confined in the core 11b, and the core 11b is heated more efficiently.

Further, in the present embodiment, the carbon nanotubes 13 are arranged such that the longitudinal direction thereof is orthogonal to the outer wall of the core 11b. In other words, the contact area between the carbon nanotube 13 and the core 11b is very small. Therefore, even if the carbon nanotube 13 and the core 11b are in direct contact, light absorption by the carbon nanotube 13 is very small.
(Embodiment 2)
Hereinafter, another example of the embodiment of the optical circuit element of the present invention will be described in detail with reference to FIG. The optical circuit element according to the present embodiment is an MZI optical switch having the same basic structure as that of the MZI optical switch according to the first embodiment.

The MZI type optical switch according to the present embodiment is different from the MZI type optical switch according to the first embodiment in the following points. That is, in the MZI type optical switch according to the present embodiment, the carbon nanotubes 13 are arranged so as to contact only the region where the optical mode does not exist in the core 11b. Thereby, in the MZI type optical switch according to the present embodiment, light absorption by the carbon nanotubes 13 is reduced as compared with the MZI type optical switch according to the first embodiment.
(Embodiment 3)
Hereinafter, another example of the embodiment of the optical circuit element of the present invention will be described in detail with reference to FIG. The optical circuit element according to the present embodiment is an MZI optical switch having the same basic structure as that of the MZI optical switch according to the first embodiment.

  The MZI type optical switch according to the present embodiment is different from the MZI type optical switch according to the first embodiment in the following points. That is, in the MZI type optical switch according to the present embodiment, the carbon nanotubes 13 are arranged in a direction in which the longitudinal direction is perpendicular to the outer wall of the core 11b and the direction of the electric field of light propagating through the core 11b. Yes. In the present embodiment, the direction of the electric field of light propagating through the core 11 b is a direction perpendicular to the main surface of the substrate 10.

  According to the academic paper “Polarization Dependence of the Optical Absorption of Single-Walled Carbon Nanotubes” (PHYSICAL REVIEW LETTERS vol.94 (2005) pp. 087402), The light absorptance for light having an electric field parallel to the longitudinal direction is 1/100 or less. That is, the carbon nanotube has optical anisotropy with respect to light absorption. Therefore, in the MZI optical switch according to this embodiment in which the carbon nanotubes 13 are arranged in a direction in which the longitudinal direction is orthogonal to the outer wall of the core 11b and orthogonal to the electric field of light propagating through the core 11b, Light absorption by the nanotube 13 is reduced as compared with the MZI type optical switch according to the first embodiment.

  In any of the above embodiments, the light absorption by the carbon nanotubes can be further reduced by reducing the number of carbon nanotubes within a range in which a necessary and sufficient heat transfer effect can be obtained. The heater in any of the above embodiments can be changed to a cooling element.

  INDUSTRIAL APPLICABILITY The present invention can be used for an optical variable attenuator and an optical switch that are used for adjusting light intensity, optical phase, and the like in optical communication, optical exchange, optical information processing, and optical interconnection.

DESCRIPTION OF SYMBOLS 10 Substrate 11 Optical phase shift waveguide 11a Clad 11b Core 12 Heater 13 Carbon nanotube

Claims (4)

An optical circuit element that changes the phase of light propagating through an optical waveguide by a thermo-optic effect,
An optical waveguide comprising a cladding and a core covered by the cladding;
A heating or cooling element;
An optical circuit element comprising carbon nanotubes embedded in the clad and serving as a heat transfer member for thermally connecting the heating element or the cooling element and the core.   2. The optical circuit element according to claim 1, wherein the carbon nanotube is embedded in the clad so that an axial direction thereof is perpendicular to an outer wall of the core. 3.   3. The optical circuit element according to claim 1, wherein the carbon nanotube is disposed so as to be in contact with only a region where the optical mode of the core does not exist. 4.   The said carbon nanotube is embed | buried in the said cladding in the direction orthogonal to the direction of the electric field of the light which propagates the said core in the said core, The Claim 1 thru | or 3 characterized by the above-mentioned. Optical circuit element.

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