Photonic Integrated Circuit Laser Isolator Integration
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Solution Overview
Problem
Integration of optical isolators with photonic integrated circuits (PICs) faces challenges due to limited accuracy in mounting and high complexity, leading to increased costs and optical losses, particularly when using lenses for alignment and magneto-optical films with incompatible CMOS foundry processing.
Innovation Solution
The integration of a bulk Faraday rotator optical isolator within a recessed substrate, utilizing tapered waveguides to align and direct the laser beam without lenses, allowing precise alignment and reducing optical losses by using silicon nitride or silicon oxynitride waveguides, which are compatible with CMOS processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lenses are used for alignment between laser and optical isolator, then alignment accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent removes lenses from the optical path between the laser and optical isolator. Instead of using lenses for alignment, the invention employs direct waveguide-to-isolator coupling with precision mounting of the isolator in a recess, thereby simplifying the device structure while maintaining alignment accuracy.
Solution Approach 2:
The patent introduces a recess structure in the substrate as an intermediary element. The optical isolator is mounted in this recess, which provides mechanical support and precise positioning, enabling accurate alignment without requiring lenses. The recess acts as a mediator between the laser waveguide and the isolator.
2Reliability
If magneto-optical films are used in optical isolator, then isolation function is achieved, but CMOS foundry processing compatibility is lost
Solution Approach 1:
The patent changes the material parameter of the optical isolator from magneto-optical films to bulk optical materials (such as fused silica or other dielectric materials). This parameter change allows the isolator to be fabricated using standard CMOS-compatible processes while still achieving the required optical isolation function through alternative mechanisms such as Faraday rotation in bulk materials or polarizing beam splitting.
3Reliability
If bulk Faraday rotator is used in optical isolator, then strong isolation is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent performs preliminary action by pre-mounting the bulk Faraday rotator isolator in a recess that is precisely fabricated during the CMOS processing sequence. This preliminary mounting, done before final device assembly, establishes accurate alignment between the laser waveguide and isolator, reducing the precision requirements for subsequent assembly steps.
Solution Approach 2:
The patent employs a nested structure where the optical isolator is placed within a recess in the substrate, and the laser waveguide is integrated within the same substrate. This nesting arrangement provides mechanical stability and maintains precise relative positioning between components, reducing mounting accuracy requirements.
4Loss of energy
If tapered waveguides are used to direct beam, then optical losses are reduced, but waveguide fabrication complexity increases
Solution Approach 1:
The patent applies local quality by creating tapered waveguides only in specific regions where beam coupling is required (at the interfaces between laser and isolator, and between isolator and output waveguide). The majority of the waveguide structure maintains a simple rectangular cross-section, thereby reducing overall fabrication complexity while still achieving low optical loss through localized tapering.
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 accurate alignment and reduced optical losses, enhancing the yield and reducing product costs by eliminating the need for lenses and active alignment, while maintaining low insertion loss and strong isolation.
Implementation Method 1
The most common type of optical isolator is based on a Faraday rotator, which uses the magneto-optic effect to rotate the polarization of incident light. Optical isolators of this sort are generally referred to as Faraday isolators. Typically, the operating parameters of the Faraday rotator (choice of magneto-optic material, length, and magnetic field strength) are chosen to rotate the polarization by ±45° depending upon the direction of travel.
Implementation Method 2
The most common type of optical isolator is based on a Faraday rotator, which uses the magneto-optic effect to rotate the polarization of incident light.
Implementation Method 3
A waveguide is configured to direct the beam emitted by the laser into the optical isolator.
Data Source
AI summary
An optoelectronic device includes a substrate, having a recess formed therein. An optical isolator is mounted in the recess. A laser includes a stack of epitaxial layers on the substrate and emits a beam of radiation toward the recess along a direction parallel to a surface of the substrate. A waveguide directs the beam emitted by the laser into the optical isolator.