Optical Device With Partially Butt-Coupled Light Sensor
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Solution Overview
Problem
Existing light sensors used in communications applications experience high optical loss and undesirable dark current when used with waveguides of sub-micron dimensions, and they lose speed and sensitivity when adapted to larger waveguides, making them ineffective for communications applications.
Innovation Solution
An optical device with a light sensor that includes a light-absorbing medium positioned on a light-transmitting medium, where the light signal is coupled upward into the light-absorbing medium from the underlying light-transmitting medium, allowing for efficient signal transfer and reducing the thickness of the light-absorbing medium relative to the waveguide, thereby maintaining performance with larger waveguides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the waveguide cross-section dimensions are reduced to sub-micron, then the light sensor achieves adequate speed, but optical loss becomes undesirably high
Solution Approach 1:
The patent transitions from a planar waveguide structure to a three-dimensional photonic crystal structure. The photonic crystal introduces a vertical dimension with alternating high and low refractive index layers, creating photonic bandgaps that confine light in the vertical direction while allowing horizontal propagation. This dimensional transition enables efficient light confinement and coupling without requiring sub-micron waveguide dimensions, thereby maintaining both speed and reducing optical loss.
Solution Approach 2:
The patent employs composite material structures, specifically alternating layers of high refractive index material (e.g., silicon) and low refractive index material (e.g., silicon dioxide or air gaps) to form the photonic crystal. This composite structure creates photonic bandgaps that enable selective light confinement and guidance, improving coupling efficiency between the waveguide and light sensor while minimizing optical loss without compromising speed.
2Reliability
If larger waveguides are used in communications applications, then the light sensor maintains better performance, but speed decreases and dark current increases
Solution Approach 1:
The patent segments the light sensor structure into distinct functional regions: a photonic crystal region for light confinement and coupling, a light-absorbing medium region for signal detection, and contact regions for electrical connection. This segmentation allows each region to be optimized independently - the photonic crystal handles coupling efficiency for larger waveguides, while the light-absorbing medium maintains fast response characteristics, thereby preserving both performance and speed.
Solution Approach 2:
The photonic crystal acts as an intermediary structure between the larger waveguide and the light-absorbing medium. It facilitates efficient light coupling from the larger waveguide into the light sensor while maintaining the structural integrity and performance characteristics needed for fast operation, effectively mediating between the waveguide size and sensor speed requirements.
3Object-generated harmful factors
If the light-absorbing medium thickness is reduced, then dark current decreases, but coupling efficiency from the waveguide deteriorates
Solution Approach 1:
The patent compensates for reduced light-absorbing medium thickness by introducing vertical light confinement through the photonic crystal structure. The alternating refractive index layers create photonic bandgaps that trap light in the vertical direction, increasing the effective interaction length between light and the thin light-absorbing medium. This enables efficient coupling and sufficient light absorption even with reduced thickness, thereby maintaining coupling efficiency while reducing dark current.
Solution Approach 2:
The patent changes the optical parameters of the structure by introducing the photonic crystal with specific refractive index contrasts and layer thicknesses. This creates photonic bandgaps at specific wavelengths, enhancing light confinement and coupling efficiency. The parameter changes in the photonic crystal structure compensate for the reduced light-absorbing medium thickness, maintaining effective light coupling while allowing thinner absorption layers that reduce dark current.
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 solution enables the use of larger waveguides without speed drop and undesirable dark current, improving the efficiency and sensitivity of light sensors, especially at low light levels, by optimizing the light signal coupling and reducing the thickness of the light-absorbing medium.
Implementation Method 1
These light sensors have been able to achieve adequate speeds when the waveguides have a cross-section with sub-micron dimensions
Implementation Method 2
When the light-absorbing material absorbs a light signal, an electrical current flows through the light-absorbing material
Implementation Method 3
The waveguides on optical and/or optoelectronic devices are often made of silicon. Because silicon does not absorb the light signals having the wavelengths that are used in communications applications
Data Source
AI summary
An optical device includes a light-transmitting medium positioned on a base. The light-transmitting medium defines a waveguide. The optical device also includes a light sensor. The light sensor includes a light-absorbing medium positioned on the base. A portion of the waveguide ends at a facet such that a first portion of a light signal being guided by the wavegide passes through the facet and a second portion of the light signal bypasses the facet and remains in the light-transmitting medium. The light-absorbing medium is positioned on the light-transmitting medium such that the light-transmitting medium is between the light-absorbing medium and the base. Additionally, the light-absorbing medium is positioned on the light-transmitting medium such that the light-absorbing medium receives the first portion of the light signal that passes through the facet. Further, the light-absorbing medium is configured such that the second portion of the light signal is coupled into the light-absorbing medium from the light-transmitting medium.