Rectangular Cavity Photonic Device Optical Isolation
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Solution Overview
Problem
Current integration of photonic and electronic devices on silicon-on-insulator (SOI) substrates faces challenges with evanescent coupling, heat dissipation, and substrate cost due to thick buried oxide cladding, and non-SOI substrates require additional fabrication materials and larger substrate real estate for effective optical isolation.
Innovation Solution
A non-SOI substrate with a generally rectangular shaped lower cladding formed in a cavity beneath the photonic device, using a semiconductor substrate material for the waveguide core and oxide-filled cavity as cladding, eliminating the need for additional fabrication materials and reducing substrate real estate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick BOX cladding (greater than 1.0 µm, preferably 2.0-3.0 µm) is used to prevent evanescent coupling in SOI substrates, then optical signal loss is reduced, but heat dissipation capability deteriorates
Solution Approach 1:
The patent divides the substrate structure into distinct functional regions: a thin BOX layer (100-200 nm) for heat dissipation and a separate lower cladding structure (trench filled with low-index material) for optical isolation. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
The patent introduces a lower cladding material (such as silicon dioxide or other low-index materials) as an intermediary between the waveguide core and the substrate. This intermediary provides the necessary optical isolation while allowing the thin BOX layer to maintain thermal contact with the substrate for heat dissipation.
2Temperature
If a thin BOX cladding (100-200 nm) is used to improve heat dissipation in SOI substrates, then heat dissipation capability is enhanced, but evanescent coupling increases causing optical signal loss
Solution Approach 1:
The patent separates the heat dissipation function (handled by the thin BOX layer) from the optical isolation function (handled by the lower cladding structure), allowing each to be optimized independently.
Solution Approach 2:
The lower cladding material acts as an intermediary that provides optical isolation between the waveguide and substrate, enabling the use of a thin BOX layer for heat dissipation without suffering from evanescent coupling losses.
3Reliability
If a curved trench is etched to provide optical isolation in non-SOI substrates, then evanescent coupling is prevented, but substrate real estate requirement increases
Solution Approach 1:
The patent transitions from the symmetric curved trench design to an asymmetric rectangular trench design. The rectangular shape with straight sides and right angles allows for more compact layout and better space utilization while maintaining the necessary optical isolation through the trench depth and filled material.
Solution Approach 2:
The patent changes the geometric parameters of the trench from curved to rectangular shape, and optimizes the depth and lateral dimensions to achieve effective optical isolation with minimal substrate area. The trench depth and the refractive index contrast of the filled material are adjusted to provide sufficient isolation in a compact footprint.
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 approach effectively reduces evanescent coupling and heat dissipation issues while simplifying the fabrication process, enabling efficient integration of CMOS and photonic devices on a common substrate without the need for additional optical device fabrication materials.
Implementation Method 1
the cladding material below the waveguide core can be the buried oxide (BOX) insulator of the SOI substrate... The BOX cladding functions to prevent optical signal leakage by evanescent coupling from the silicon waveguide core to a supporting silicon substrate
Implementation Method 2
an associated lower cladding material provided in a cavity of the substrate material... a processing sequence involving etching and oxide filling
Implementation Method 3
When the Box cladding material is thick it inhibits heat flow to the underlying silicon, thus diminishing its effectiveness as a heat dissipater
Data Source
Figure 1
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Figure 3A~3D
AI summary
Disclosed method and apparatus embodiments provide a photonic device with optical isolation from a supporting substrate. A generally rectangular cavity (125) in cross section is provided below an element of the photonic device (129) and the element may be formed from a ledge of the supporting substrate which is over the cavity.