Edge-Coupled Photodetector Eliminates Bulky Sub-Mounts
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Solution Overview
Problem
Conventional optical communication systems using laser diodes require bulky and expensive 'wrap-around' sub-mounts for photodiode feedback, which complicates monitoring and stabilization of optical power output.
Innovation Solution
A photodiode device is mounted on a single flat surface with the laser diode, featuring a substrate with a first facet for light entry and a second facet for internal reflection towards a photoactive region, allowing for non-normal angle light reception and avoiding reflection back to the laser diode, thus eliminating the need for bulky sub-mounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a top-side coupled photodiode is used in an L-shaped configuration to detect laser backlight, then the photodetector can monitor optical power output, but it requires a bulky and expensive wrap-around sub-mount
Solution Approach 1:
The patent inverts the conventional top-side coupled configuration by using edge-coupled photodiodes that detect light from the laser diode edge rather than from the top. This inversion eliminates the need for the complex wrap-around sub-mount structure while maintaining optical power monitoring capability. The photodiodes are positioned to receive light through the substrate edge, fundamentally changing the geometric relationship between components.
Solution Approach 2:
The patent transitions from a three-dimensional wrap-around sub-mount structure to a planar configuration where photodiodes are mounted on the same flat substrate as the laser diode. By changing the spatial arrangement from vertical/L-shaped to planar/coplanar, the design eliminates the need for complex mechanical support structures while maintaining functional performance.
2Measurement precision
If light is received at a normal angle through the substrate, then the photodiode can efficiently detect light, but reflected light is reflected back toward the laser diode causing interference
Solution Approach 1:
The patent introduces asymmetric angular relationships between the incident light path and the reflected light path. By orienting the photodiode active region at a specific angle relative to the substrate surface, the design ensures that reflected light does not return to the laser diode. This asymmetric geometric configuration eliminates feedback interference while maintaining efficient light detection through the substrate edge.
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 enables efficient monitoring and stabilization of optical power output, reducing costs and complexity while maintaining accurate feedback for maintaining predictable optical output in optical communication systems.
Implementation Method 1
The photodiode device receives light through a first facet of the substrate and internally reflects the received light off a second facet toward a photoactive region of the photodiode
Implementation Method 2
a photodiode fabricated on a top surface of the substrate for measuring an intensity of the light that enters the first facet of the substrate
Data Source
AI summary
A device is disclosed for monitoring power from a laser diode. The device includes a substrate having a top surface and a first facet perpendicular to the top surface through which light enters the substrate. The device further includes a second facet onto which light that has entered the substrate through the first facet along an optical axis that is non-normal to the first facet is incident. The device further includes a photodiode fabricated on the top surface of the substrate for measuring an intensity of the light that enters the first facet of the substrate along the optical axis that is non-normal to the first facet. The light that has entered the substrate through the first facet along the optical axis that is non-normal to the first facet is reflected by the second facet toward a photoactive region of the photodiode.