Photodiode Receiver Structure With Concave Mirror Light Focusing
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Solution Overview
Problem
In optical communications, particularly in intersatellite and space communication, semiconductor light receiving elements face challenges in maintaining high sensitivity and response speed due to the limited light receiving area and increased reflectance issues with existing concave mirror configurations, which reduce the amount of light incident on the photodiode.
Innovation Solution
A light receiving device configuration featuring a semiconductor light receiving element with a photodiode on a first semiconductor substrate and a concave mirror on a second transparent semiconductor substrate, where the concave mirror has a convex surface with a reflective film to focus light near the first surface, and an adhesive resin is used to reduce reflections and align the elements for optimal light collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the diameter of the light absorption layer is reduced to increase response speed, then the response speed improves, but the light receiving area decreases and sensitivity deteriorates
Solution Approach 1:
The patent transitions from a planar light receiving structure to a three-dimensional optical path by introducing a concave mirror that reflects and focuses light from the back surface. This allows the light absorption layer to maintain a small diameter for high response speed while the concave mirror provides a large effective light receiving area by collecting light over a broader spatial range and directing it to the photodiode.
Solution Approach 2:
The patent combines the photodiode and concave mirror into a single integrated semiconductor substrate structure. The concave mirror is formed on the back surface of the same substrate that contains the photodiode, merging the light collection function (large area mirror) with the light detection function (small photodiode) into one unified device, thereby achieving both high sensitivity and high response speed.
2Area of stationary object
If a conventional concave mirror configuration is used to increase light receiving area, then the light receiving area increases, but reflectance increases and light incident on photodiode decreases
Solution Approach 1:
The patent optimizes the focal length of the concave mirror and the distance between the mirror and photodiode to achieve optimal light focusing. By carefully controlling these geometric parameters, the design ensures that reflected light is efficiently focused onto the photodiode surface while minimizing stray reflections. The focal length is specifically designed to account for the substrate thickness and refractive index to maximize light incident on the photodiode.
Solution Approach 2:
The patent introduces an adhesive layer as an intermediary between the concave mirror and the photodiode. This adhesive layer serves as an optical medium that reduces reflection losses at the interface between the mirror and the photodiode, thereby increasing the amount of light that reaches the photodiode while maintaining the large light receiving area provided by the concave mirror.
3Area of stationary object
If the distance between concave mirror and photodiode is increased to increase light receiving area, then the light receiving area increases, but the structural thickness increases and alignment precision becomes more difficult
Solution Approach 1:
The patent achieves a large light receiving area without proportionally increasing the substrate thickness by utilizing the reflective geometry of the concave mirror. The mirror is formed on the back surface of a thin substrate, and its curved geometry provides a large effective collecting area while maintaining a compact overall structure. The focal point of the mirror is positioned close to the photodiode, allowing efficient light focusing within a short distance.
Solution Approach 2:
The patent optimizes the focal length of the concave mirror to be comparable to or smaller than the substrate thickness, allowing the light focusing function to be achieved within a compact vertical space. By adjusting the curvature radius and focal length parameters of the concave mirror, the design achieves optimal light collection efficiency while maintaining a thin overall device structure and facilitating precise alignment between the mirror and photodiode.
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 enhances light collection efficiency by reducing reflections and allowing more incident light to reach the photodiode, improving sensitivity and response speed while tolerating positional changes and low-intensity signals.
Implementation Method 1
a concave mirror that reflects incident light toward the semiconductor light receiving element
Implementation Method 2
the incident light incident from the first surface is reflected by the reflective film and focused at a condensing position near the first surface
Implementation Method 3
an adhesive resin is used to reduce reflections and align the elements for optimal light collection
Implementation Method 4
a semiconductor light receiving element that converts an incident optical signal into an electrical signal and outputs the electrical signal
Data Source
AI summary
A semiconductor light receiving element in which a photodiode is formed on the main surface side of a first semiconductor substrate, and a cone ave mirror reflecting an incident light toward the light receiving element. The concave mirror comprises a flat first surface of the second semiconductor substrate that is transparent to the incident light, a convex surface formed in a convex shape toward the side opposite to the first surface on the second surface side opposite to the first surface, and a reflective film formed on the convex surface, and the incident light entering from the first surfaceside is reflected by the reflective film to a condensing positionnear the first surface, and the light receiving element was fixed to the first surface so as to overlap the light focusing position of the concave mirror.