Silica PLC Optical Switch Trench Structure Heat Diffusion
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Solution Overview
Problem
Existing methods for reducing power consumption in Silica-based PLC optical switches, such as heat insulation grooves, thick underclad layers, and wet etching, face limitations in effectively suppressing thermal diffusion and are costly or difficult to implement, especially for mass production and maintaining optical characteristics.
Innovation Solution
A planar waveguide optical switch with a Mach-Zehnder interferometer and trench structure portions at the interface between the underclad layer and Si substrate, which suppresses heat diffusion from heaters to the Si substrate, using a trench structure formed by grooves and thermal oxidation treatment to reduce thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If heat insulation grooves are formed on both sides near the arms of the Mach-Zehnder interferometer, then heat diffusion in horizontal direction is prevented, but heat diffusion to the Si substrate in vertical direction cannot be prevented and power consumption reduction is insufficient
Solution Approach 1:
The heat insulation structure is segmented into multiple components: heat insulation grooves formed on both sides of the waveguide arms, and a heat insulation film deposited on the Si substrate surface. This segmentation allows each component to address different directions of heat diffusion (horizontal vs vertical), achieving comprehensive heat isolation and enabling sufficient power consumption reduction.
Solution Approach 2:
A heat insulation film is introduced as an intermediary layer between the Si substrate and the external environment. This film acts as a thermal barrier that prevents heat from diffusing into the Si substrate, thereby reducing the power needed to maintain the thermal state of the waveguide while not interfering with the optical function.
2Loss of energy
If the thickness of the underclad layer is increased to secure distance with Si substrate, then heat diffusion is suppressed, but deposition time and cost are exponentially increased
Solution Approach 1:
Instead of increasing the thickness parameter of the underclad layer, the invention changes the thermal insulation parameter by depositing a heat insulation film on the Si substrate surface. This parameter substitution achieves the same heat suppression effect without the exponentially increasing deposition time and cost associated with thickening the underclad layer.
Solution Approach 2:
The heat insulation approach is shifted from the vertical dimension (increasing underclad layer thickness) to the horizontal dimension (depositing heat insulation film on substrate surface). This dimensional shift achieves heat suppression while avoiding the cost and time penalties of thick film deposition.
3Loss of energy
If wet etching is used to reduce volume of Si substrate, then heat diffusion is suppressed, but process error increases and dimensional control becomes difficult
Solution Approach 1:
Instead of directly modifying the Si substrate through wet etching, the invention creates a copy of the heat insulation function using a deposited heat insulation film. This film replicates the thermal isolation effect without the dimensional control issues and process errors associated with wet etching, maintaining manufacturing precision while achieving heat suppression.
4Ease of operation
If heat is applied to optical waveguides by heaters, then ON/OFF switching is realized, but heat is transferred to Si substrate and continuous heater driving is required increasing power consumption
Solution Approach 1:
The high thermal conductivity of the Si substrate, which was previously a harmful factor causing heat loss, is converted into a benefit by covering it with a heat insulation film. This film transforms the Si substrate from a heat sink into an isolated platform, allowing the heaters to efficiently switch waveguides without continuous power supply, thereby reducing overall power consumption while maintaining switching functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces power consumption while maintaining high-quality optical performance and manufacturing stability, making it suitable for low-cost, high-volume production of optical switches.
Implementation Method 1
thermal oxidation treatment is performed on the bonded Si substrate
Implementation Method 2
a Mach-Zehnder interferometer (MZI) driven by a thermo-optical effect as described below. When heat is applied to at least one of two arm waveguides of the MZI, a refractive index of the arm waveguide is changed, and an interference state of light is changed
Implementation Method 3
it is necessary to heat the arm waveguides of the MZI by using heaters disposed near the arm waveguides
Data Source
AI summary
An optical switch is configured by providing a planar lightwave circuit layer on a top surface of a Si substrate. The circuit layer forms, on the top surface of the substrate, an optical waveguide including an underclad layer, an optical waveguide core, and an overclad layer. The optical waveguide is provided to have a structure configuring a Mach-Zehnder interferometer. A heater is provided at a position just above an arm of the core on the top surface of the clad layer, and power supply electric wires are electrically connected to both ends of the heater. In a local portion including an interface between the clad layer and the top surface of the substrate, trench structure portions as concave grooves are provided.