Compact Optical Isolator Using Direction-Dependent Waveguide
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Solution Overview
Problem
Conventional optical isolators are large and difficult to integrate in guided-optics format due to the need for a Faraday rotator and polarizers, and existing waveguide isolators require high-precision interference and long waveguides, making them challenging to miniaturize and integrate on a chip.
Innovation Solution
A waveguide section with a propagation constant shift that is direction-dependent, utilizing a non-reciprocal magneto-optic medium with a nonzero off-diagonal permittivity tensor, allowing for a single-mode optical isolator with different cutoff frequencies for forward and reverse waves, enabling compact integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical isolators use Faraday rotators and polarizers, then optical isolation is achieved, but the device becomes large and difficult to integrate in guided-optics format
Solution Approach 1:
The invention extracts and eliminates the polarizers from the conventional optical isolator structure, retaining only the essential non-reciprocal phase shifting function. This simplification removes the components that make integration difficult while preserving the core optical isolation capability through the waveguide-based non-reciprocal phase shifter.
Solution Approach 2:
The invention replaces the mechanical/optical component assembly of Faraday rotators and polarizers with an integrated waveguide structure that uses magneto-optic materials. This substitution transitions from a discrete component system to an integrated photonic circuit, enabling guided-optics format integration while maintaining optical isolation function.
2Ease of manufacture
If asymmetric Mach-Zehnder waveguide interferometer is used, then polarizers are not required, but high-precision interference and long waveguides are required
Solution Approach 1:
The invention changes the operational parameters by using non-reciprocal phase shifting through magneto-optic materials instead of relying on long waveguide paths for interference. This parameter change allows for shorter waveguide lengths while achieving the same optical isolation effect, as the non-reciprocity is induced by the magnetic material properties rather than path length differences.
3Reliability
If Faraday rotator rotates linear-polarization angle by 45 degrees, then optical isolation is achieved, but the waveguide becomes relatively large
Solution Approach 1:
The invention applies local quality by concentrating the non-reciprocal phase shifting function in a localized magneto-optic material region within the waveguide. Instead of requiring a long Faraday rotator section, the magneto-optic material provides the necessary phase shift in a compact volume, reducing the overall isolator size while maintaining optical isolation performance.
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 achieves optical isolation by tailoring waveguide dimensions and magnetization direction, resulting in a compact, high-precision optical isolator that effectively blocks reverse propagating waves without the need for polarizers, suitable for integrated optics.
Implementation Method 1
At least one part of the cross-section is a non-reciprocal magneto-optic medium, which has nonzero off-diagonal permittivity tensor components. This inhomogeneity induces the propagation constant shift, which is propagation-direction-dependent.
Data Source
AI summary
Various optical isolator embodiments are disclosed. Embodiments comprise a waveguide section utilizing materials that induce a propagation constant shift that is propagation-direction-dependent. Embodiments are characterized by a cutoff frequency for forward propagating waves that is different than the cutoff frequency for reverse waves. A particular embodiment is constructed as a single-mode waveguide on a substrate. The cross-section of the waveguide is inhomogeneous in terms of materials. This inhomogeneity induces a propagation constant shift, which is propagation-direction-dependent. This device works as an optical isolator from the cut-off frequency of the lowest forward wave (lower frequency) to one for the lowest reverse wave (higher frequency). Various configurations consistent with the principles of the invention are disclosed.