High-Tolerance Edge Coupler with Tapered Thickness for PICs
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Solution Overview
Problem
Coupling losses in photonic integrated circuits (PICs) occur due to thickness and misalignment between edge couplers and optical transmitters or receivers, leading to inefficient energy transfer.
Innovation Solution
The edge coupler is designed with a thickness that tapers from a narrow end to a wide end, aligned with a pedestal in the oxide layer, ensuring vertical alignment of optical transmitters or receivers, and a trench etching process is used to form the coupler and pedestal for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the edge coupler has a uniform thickness, then the manufacturing process is simple, but coupling losses increase due to misalignment with optical transmitters or receivers
Solution Approach 1:
The edge coupler employs a tapered thickness profile where the thickness varies along the length of the coupler, being thinner at one end and thicker at the other. This local variation in geometric quality enables different sections of the coupler to interface with components of different heights, thereby achieving precise alignment with both the waveguide and the optical transmitter or receiver while minimizing coupling losses.
Solution Approach 2:
The invention introduces a dimensional change by transitioning from a uniform thickness design to a tapered thickness design along the longitudinal axis of the edge coupler. This dimensional variation in the thickness parameter allows the coupler to bridge the height difference between the waveguide and the optical transmitter or receiver, enabling precise alignment in the vertical dimension while maintaining continuous optical coupling.
2Reliability
If the edge coupler thickness is increased to match optical transmitter height, then alignment improves, but the waveguide coupling efficiency decreases
Solution Approach 1:
The tapered thickness profile creates local quality variations where different sections of the edge coupler have different thicknesses optimized for their specific functions: the thinner section maintains efficient coupling with the waveguide, while the thicker section achieves proper alignment with the optical transmitter or receiver, thereby resolving the contradiction between alignment accuracy and coupling efficiency.
Solution Approach 2:
The continuous tapering of the edge coupler thickness creates a dynamic transition zone that gradually adapts the optical mode from the waveguide dimensions to the optical transmitter or receiver dimensions. This dynamic geometric transition enables smooth mode matching, preventing abrupt discontinuities that would cause reflection and coupling losses, while simultaneously achieving the required alignment height.
3Manufacturing precision
If a tapered thickness design is used, then alignment precision improves, but device complexity increases
Solution Approach 1:
The invention changes the geometric parameter of the edge coupler from a constant thickness value to a continuously varying tapered thickness profile. This parameter change enables precise alignment with components of different heights while maintaining a relatively simple monolithic structure that can be fabricated using standard semiconductor processing techniques, thus achieving high alignment precision without excessive structural complexity.
Data Source
AI summary
An edge coupler has a wide end, a narrow end, and a tapering thickness. The narrow end is coupled to a waveguide in a photonic integrated circuit (PIC). The wide end is coupled to an optical transmitter or receiver. The edge coupler thickens by tapering downward into the buried oxide layer of a BOX substrate. An upper surface of the edge coupler may be planar. A pedestal may be formed in the oxide layer so that a laser diode mounted on the pedestal will be vertically aligned to the edge coupler. Alternatively, the pedestal may be formed in a substrate under the oxide layer so that the core of an optical fiber mounted on the pedestal will be vertically aligned to the edge coupler. The pedestal may be in a cavity that facilitates horizontal alignment between the laser diode, optical fiber, or other such device and the edge coupler.