Self-Aligned Lens Photodetector for Optical Receivers
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Solution Overview
Problem
In optical receivers, particularly those using multi-mode fibers with large cores, focusing light onto a photodetector is challenging due to the need for high precision and alignment accuracy, which is difficult to achieve with monolithically formed lenses on opaque substrates.
Innovation Solution
A flip-chip photodetector with a non-transparent substrate is mounted onto a transparent, high-refraction-index material to create an integrated detector-lens unit, allowing for precise alignment and focusing using a lens-chip with a high refractive index, such as Gallium Phosphide, and self-alignment through solder reflow, overcoming the limitations of monolithic techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a lens is monolithically formed in the substrate of a photodetector, then alignment accuracy is improved, but this approach is not suitable for photodetectors with opaque substrates at the operating wavelength
Solution Approach 1:
The patent divides the photodetector structure into separate components: the opaque substrate photodetector and the transparent lens are fabricated independently and then assembled together through flip-chip bonding, allowing each component to be optimized for its specific function without the constraints of monolithic fabrication
Solution Approach 2:
The patent introduces an intermediary transparent substrate that carries the lens and is bonded to the opaque photodetector substrate, enabling the lens to be formed in a transparent material while the photodetector remains on its optimized opaque substrate
2Productivity
If the active area of the photodetector is reduced to increase data rate, then data rate is improved, but focusing light to a very small spot with high precision becomes challenging
Solution Approach 1:
The patent changes the refractive index parameter by selecting a transparent substrate material (such as GaP or glass) with a higher refractive index than the photodetector substrate, enhancing the lens's focusing capability and enabling precise focusing onto the small active area
Solution Approach 2:
The patent employs a curved lens surface (spherical or aspherical geometry) to focus the light from the optical fiber onto the small active area of the photodetector, achieving the necessary focusing precision for high data rate operation
3Power
If a transparent lens material with high refractive index is used, then focusing capability is improved, but the lens must be precisely aligned to the photodetector active area
Solution Approach 1:
The patent employs self-aligned flip-chip bonding techniques where the lens and photodetector are automatically aligned during the bonding process, eliminating the need for separate manual alignment steps and ensuring precise positioning
Solution Approach 2:
The patent performs preliminary alignment markings and positioning features during the fabrication of both the lens substrate and photodetector, so that when they are assembled together, the alignment is already partially established, reducing the precision requirements of the final bonding step
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 enables high alignment accuracy and effective focusing of light onto a small active area, suitable for high data rate communication systems, improving the performance of optical receivers by allowing the use of better materials and configurations that were not possible with monolithic fabrication.
Implementation Method 1
Focusing the light exiting the fiber, particularly multi-mode fiber with a large core, to the photodetector becomes challenging
Implementation Method 2
mounted onto a transparent, high-refraction-index material to create an integrated detector-lens unit
Data Source
AI summary
A constructed photodetector, an optical receiver, and a receiver unit in an optical communication system are disclosed. One example of the disclosed constructed photodetector includes an optoelectronic element having an active area that converts light having a wavelength of interest into electrical signals and a substrate on a face that opposes the active area, where the substrate is non-transparent to light having the wavelength of interest. The constructed photodetector further includes a lens-chip that is at least partially transparent to light having the wavelength of interest, where the lens-chip includes a first side and an opposing second side, where the first side of the lens-chip includes an integrated lens, and where the second side of the lens-chip includes one or more electrical traces. The constructed photodetector further includes at least one connector that provides a physical and electrical connection between the optoelectronic element and the lens-chip.