Echelle Grating Demux with Metal-Filled Trench Mirror
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Solution Overview
Problem
Manufacturing distributed Bragg reflector (DBR) mirrors with pitches less than 300 nanometers in silicon nitride (SiN) layers of silicon photonic integrated circuits (PICs) is difficult or impossible, which hampers the development of broadband mirrors capable of reflecting multiple wavelength channels effectively.
Innovation Solution
A metal-filled trench is formed between the SiN slab waveguide and dielectric cladding material to create a mirror at the grating teeth of the Echelle grating, allowing for broadband reflectivity and enabling the separation of wavelength channels, with tungsten used for its suitable reflectivity and broadband response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DBR mirrors with pitch less than 300 nanometers are manufactured in SiN layers, then broadband reflectivity for multiple wavelength channels is achieved, but manufacturing precision and fabrication feasibility deteriorate
Solution Approach 1:
The patent changes the pitch parameter from less than 300 nanometers to greater than 300 nanometers, making the mirror structure manufacturable with standard fabrication processes while still achieving broadband reflectivity through the metal material properties
Solution Approach 2:
The patent uses composite material structure combining metal (for broadband reflectivity) with SiN layer and dielectric cladding, where the metal layer provides the reflective function without requiring sub-300nm pitch fabrication
2Ease of manufacture
If metal-filled trench is used instead of DBR mirror, then ease of manufacture improves, but device complexity increases
Solution Approach 1:
The patent extracts the reflective function from the complex DBR mirror structure and implements it through a simpler metal-filled trench, removing the need for sub-300nm pitch fabrication while maintaining broadband reflectivity
Solution Approach 2:
The patent changes the structural parameters of the mirror from a multi-layer DBR configuration to a metal-filled trench with pitch greater than 300 nanometers, simplifying the fabrication process while achieving the same optical function
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 facilitates the effective separation and reflection of multiple wavelength channels, overcoming the fabrication challenges of DBR mirrors with small pitches, and is compatible with CMOS foundry rules, enhancing the manufacturability of Si photonic devices.
Implementation Method 1
the light diffracts in a free-space propagation region and impinges on a grating that is on a Roland circle and has blazed angles. Light reflects from the grating leading to constructive interference for each of n input wavelengths
Implementation Method 2
The metal-filled trench forms a mirror at the grating teeth to reflect incident light from the first waveguide toward the multiple second waveguides or from the multiple second waveguides toward the first waveguide
Data Source
AI summary
In an example, an Echelle grating wavelength division multiplexing (WDM) device includes a first waveguide, a slab waveguide, multiple second waveguides, an Echelle grating, and a metal-filled trench. The first waveguide includes either an input waveguide or an output waveguide. The multiple second waveguides are optically coupled to the first waveguide through the slab waveguide. The multiple second waveguides include multiple output waveguides if the first waveguide includes the input waveguide or multiple input waveguides if the first waveguide includes the output waveguide. The Echelle grating includes multiple grating teeth formed in the slab waveguide. The metal-filled trench forms a mirror at the grating teeth to reflect incident light from the first waveguide toward the multiple second waveguides or from the multiple second waveguides toward the first waveguide.