ASIC Substrate Light Coupling for Offset Laser Back-Facet Monitoring
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Solution Overview
Problem
Existing methods for monitoring the output of laser diodes, such as using a back-facet monitor, are impractical for ASIC designs where the laser must be located close to the ASIC, leaving no room for a back-facet monitor.
Innovation Solution
An integrated circuit configuration where the laser's back-facet is optically coupled to a substrate that acts as a light guide, allowing for back-facet illumination to be reflected to a photon-detecting monitor positioned near the laser, which is offset from the laser, enabling effective monitoring without interfering with the output beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the laser is located close to the ASIC, then the integration is improved, but no room is left for a back-facet monitor
Solution Approach 1:
The monitor is positioned at a lateral offset from the laser rather than directly behind it, utilizing the lateral dimension of the substrate. This dimensional shift allows both the laser-ASIC proximity and monitor placement to coexist within the available space.
Solution Approach 2:
The substrate serves as an optical intermediary, guiding light from the laser back-facet to the offset monitor position. This mediator enables the light path to reach the monitor without requiring direct line-of-sight alignment, resolving the spatial conflict.
2Measurement precision
If a back-facet monitor is used, then laser output monitoring is achieved, but additional space is required
Solution Approach 1:
The monitor is merged into the same substrate plane as the laser, combining their spatial locations rather than separating them into different planes or locations. This integration reduces the total area required while maintaining monitoring functionality.
Solution Approach 2:
The solution transitions from a linear arrangement (laser behind monitor) to a two-dimensional arrangement (laser and monitor offset on the same plane), efficiently utilizing available space.
3Measurement precision
If the monitor is offset from the laser, then detection efficiency is enhanced, but optical coupling complexity increases
Solution Approach 1:
The substrate itself provides the optical coupling function through its transparent and reflective properties, eliminating the need for separate optical coupling components. The substrate's inherent optical characteristics enable the offset monitor to receive sufficient light for efficient detection.
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 allows for reliable monitoring of laser output without the need for additional space, optimizing the placement of the monitor to enhance detection efficiency and reduce losses, making it suitable for compact ASIC designs.
Implementation Method 1
the substrate is transparent to a wavelength of light from the laser and the far end is reflective of at least a portion of the back-facet illumination
Implementation Method 2
a monitor capable of detecting photons, the monitor being optically coupled to the near end and offset from the laser
Data Source
AI summary
Methods and systems for an ASIC with a laser with the laser's back-facet illumination being monitored by a photodetector situated such that the substrate of the ASIC acts as a waveguide for the back-facet illumination between the laser and the photodetector (monitor). In an embodiment, the laser and monitor are situated on the same side of the ASIC and the back-facet illumination is reflected off the far end of the ASIC substrate before reaching the monitor.