Multimode Interference Coupler for Slot Photonic Crystal Waveguides
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Solution Overview
Problem
Current multimode interference couplers for photonic crystal waveguides are either complex, costly, and inefficient, with coupling efficiencies below 90% and requiring lengthy tapering structures to reduce propagation loss.
Innovation Solution
A novel multimode interference (MMI) coupler integrated with a slot photonic crystal waveguide, optimized by adjusting the width to set the phase difference close to π and the termination parameter to 0, achieving a coupling efficiency exceeding 90% with a compact structure of less than 1.5 μm length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multimode interference couplers are used, then coupling efficiency is improved, but device length increases significantly
Solution Approach 1:
The patent changes the termination parameter τ from conventional values (0.5 at edge of period) to 0 (at lattice point), and adjusts the width parameter WM to 1.6√(3α). These parameter changes enable the coupler to achieve >90% coupling efficiency with a compact length of ≤1.5 μm, resolving the contradiction between coupling efficiency and device length.
2Reliability
If mirrored coupler structures are used, then coupling efficiency exceeds 80%, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the complex mirrored coupler structure (dielectric mirror or Gaussian mirror) from the design. By using a simple MMI coupler with specific parameters (WM=1.6√(3α), τ=0), the invention achieves >90% coupling efficiency without requiring complicated mirror fabrication processes, thus reducing manufacturing complexity and cost.
3Loss of energy
If tapered coupler structures are used, then propagation loss is reduced, but device length increases to several hundred microns
Solution Approach 1:
The patent changes the termination parameter from conventional τ=0.5 to τ=0, and sets the width parameter WM=1.6√(3α). These parameter changes enable the coupler to achieve adiabatic tapering effects with a compact length of ≤1.5 μm, reducing propagation loss without requiring lengthy taper structures of several hundred microns.
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
The MMI coupler provides a 20 dB efficiency enhancement over a 35 nm optical bandwidth, significantly reducing propagation loss and power consumption, making it more practical and efficient for embedded board-level interconnects and various optical communication applications.
Implementation Method 1
multimode interference coupler configured to optically couple a strip waveguide to a slot photonic crystal waveguide
Implementation Method 2
Introducing line defects into a photonic crystal lattice permits an electromagnetic wave having a frequency within the bandgap of the structure to be guided through the photonic crystal
Data Source
AI summary
The present invention provides an optical apparatus having a multimode interference coupler configured to optically couple a strip waveguide to a slot photonic crystal waveguide. The multimode interference coupler has a coupling efficiency to the slot photonic crystal waveguide greater than or equal to 90%, a width that is approximately equal to a defect width of the slot photonic crystal waveguide, a length that is equal to or less than 1.5 μm, and interfaces with the slot photonic crystal waveguide at an edge of a period that gives a termination parameter of approximately zero. The optical apparatus may also include an insulation gap disposed between the multimode interference coupler and the slot photonic crystal waveguide, wherein the length of the multimode interference coupler is reduced by approximately one half of a width of the insulation gap.