Silicon Photonic Back-Reflection Circulator Using Polarization Conversion
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Solution Overview
Problem
Existing silicon photonic chips for LIDAR and optical interconnects face challenges in preventing back-reflected light from degrading laser performance, particularly in applications like computer-assisted or autonomous driving vehicles, where back-reflected light increases amplitude and phase-noise, reducing accuracy and coherence length.
Innovation Solution
The implementation of a silicon photonic chip with a quarter-wave plate and TE/TM converter to convert and isolate back-reflected light, routing it to a separate path without using magnetooptic components or electrical power, thereby preserving laser linewidth and spectral purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional optical isolators or circulators using magnetooptic components are integrated, then back-reflected light can be separated from the laser source, but the device complexity and manufacturing difficulty increase due to incompatibility with standard CMOS processing
Solution Approach 1:
The patent replaces magnetooptic components with an all-optical solution using polarization control. A quarter-wave plate converts linearly polarized light from the laser into circularly polarized light, which reflects off the target and returns with reversed handedness. The quarter-wave plate again converts this back to linear polarization but orthogonal to the original, allowing a polarizer to separate the reflected signal from the outgoing beam without any magnetic materials or complex mechanical isolators.
Solution Approach 2:
The invention changes the polarization state of light as it passes through the quarter-wave plate. The quarter-wave plate introduces a phase shift between orthogonal polarization components, transforming linear polarization to circular polarization and vice versa. This parameter change in polarization state enables the circulator function without requiring magnetooptic materials or complex device structures.
2Reliability
If nonlinear gain elements are used to create an optical circulator, then back-reflected light can be routed separately, but power consumption and cost increase due to electrical power injection requirements
Solution Approach 1:
The patent substitutes active nonlinear gain elements with passive optical components. Instead of using materials that require electrical pumping to achieve optical gain, the invention uses a quarter-wave plate and polarizer that passively manipulate light polarization. The circulator effect arises entirely from polarization transformation and optical filtering, eliminating the need for electrical power injection and associated energy consumption.
Solution Approach 2:
The quarter-wave plate and polarizer system is self-regulating and requires no external energy input. The device automatically routes outgoing and returning light based on their polarization states, which are determined by the optical path itself. The outgoing linearly polarized light is converted to circular polarization, reflects, returns with reversed handedness, and is converted back to orthogonal linear polarization, naturally directing it to the correct port without any active control or power consumption.
3Ease of operation
If thermooptic resonant structures are used to induce power-dependent index changes, then output port selection can be achieved, but significant optical absorption and heating are required which increases power consumption
Solution Approach 1:
The patent replaces thermooptic resonant structures with a polarization-based optical system. Instead of heating materials to change their refractive index and achieve port selection, the invention uses a quarter-wave plate to transform polarization states. The port selection is achieved through polarization filtering with a polarizer, which directs different polarization states to different ports without any thermal effects or optical absorption.
Solution Approach 2:
The invention converts what would normally be a loss mechanism (polarization filtering) into the useful function of port selection. The polarizer, which would normally be considered a lossy component that blocks half the light, becomes the key element that enables non-reciprocal routing and port selection without any energy input. The 'lost' light in one polarization state is actually the mechanism that creates the directional routing function.
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 solution effectively isolates back-reflected light, maintaining high laser spectral purity and accuracy in LIDAR systems, especially in safety-critical applications like autonomous driving, without increasing power consumption or optical absorption.
Implementation Method 1
a quarter wave plate (QWP) disposed on the silicon photonic chip to convert a first linearly polarized mode optical beam from a laser disposed on the silicon photonic chip, into a combination of quarter-wave phase-delayed orthogonal polarization modes optical beam
Implementation Method 2
a polarization transverse electric/transverse magnetic (TE/TM) converter disposed on the silicon photonic chip to receive from the laser, the first linearly polarized optical mode optical beam, and convert part of the optical power of the first linearly polarized optical mode optical beam to an orthogonally linearly polarized mode
Implementation Method 3
a TE polarizer or a polarizing beam splitter (PBS), disposed between the laser and the polarization TE/TM converter on the silicon photonic chip; to isolate the second linearly polarized mode optical beam from the first linearly polarized mode optical beam
Implementation Method 4
The silicon photonic chip back reflection protection/circulator technology provides a means to block back-reflections from reaching the on-chip source laser in a LIDAR or optical transceiver chip
Data Source
AI summary
Apparatuses and methods associated with silicon photonic chips, are disclosed herein. In some embodiments, a quarter wave plate (QWP) is provided to a silicon photonic chip to convert a first linearly polarized mode (e.g., TE mode) optical beam from a laser disposed on the silicon photonic chip, into a combination of orthogonal polarization modes optical beam, and to convert or contribute in converting a reflection of the combined polarized modes optical beam into a second linearly polarized mode (e.g., TM) optical beam with polarization orthogonal to the first. The optical beam is rotated relative to an axis of the QWP, or the QWP and its axis are rotated relative to a polarization axis of the optical beam. Other embodiments are also described and claimed.