Integrated Optical Isolator Using Magnetooptic Grating
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Solution Overview
Problem
Current optical isolators for semiconductor laser sources face challenges in achieving satisfactory isolation ratios due to limitations in materials and integration complexity, particularly with existing magnetooptic Kerr effect-based isolators, which suffer from high insertion losses and dimensional constraints.
Innovation Solution
The solution involves an optoelectronic device with a magnetooptic diffraction grating exhibiting a non-reciprocal variation in the real part of the effective optical index, coupled with an amplifying structure, where the grating's parameters are optimized to achieve low reflection in one direction and high reflection in the opposite direction, enhancing optical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an optical isolator using the magnetooptic Kerr effect is integrated into a semiconductor laser device, then optical isolation is achieved, but insertion loss increases and device dimensions become constrained
Solution Approach 1:
The patent changes the fundamental parameter being exploited from the imaginary part of the optical index (absorption) to the real part of the optical index (phase). By using a plasma layer whose refractive index can be dynamically controlled via carrier injection, the device achieves non-reciprocal phase modulation that translates to intensity modulation after polarization conversion, thereby achieving isolation without relying on strong absorption that causes insertion loss.
Solution Approach 2:
The patent replaces the traditional magnetooptic Kerr effect mechanism with an electro-optic mechanism using plasma dispersion. Instead of using ferromagnetic materials and magnetic fields, the invention uses a plasma layer in a waveguide where electrical current controls the refractive index, substituting a magnetic field-based system with an electric field-based system that has lower loss and better integration potential.
2Reliability
If traditional magnetooptic isolators are used, then optical isolation is provided, but device complexity and integration difficulty increase
Solution Approach 1:
The patent merges the isolator function directly into the laser cavity structure by integrating the plasma layer waveguide with the laser active region. The isolator components (plasma layer, polarizers, waveguide) are combined into a single integrated structure that can be fabricated using standard semiconductor processing techniques, eliminating the need for separate discrete isolator components and reducing overall device complexity.
Solution Approach 2:
The patent changes from using magnetooptic materials requiring magnetic field application to using a plasma layer controlled by electrical current. This parameter change enables direct integration with semiconductor laser fabrication processes and eliminates the need for complex magnetic field generation and alignment systems, thereby reducing device complexity.
3Reliability
If the magnetic layer thickness is increased to improve isolation ratio, then optical confinement factor increases, but optical losses increase
Solution Approach 1:
The patent changes from exploiting absorption (imaginary part) to exploiting phase modulation (real part). The plasma layer's refractive index change with carrier concentration provides non-reciprocal phase shift without significant absorption. This parameter change allows achieving high isolation ratios through phase interference mechanisms rather than absorption, thereby avoiding the trade-off between isolation ratio and optical losses.
Solution Approach 2:
The patent substitutes the absorption-based magnetooptic Kerr effect with a phase-based plasma dispersion effect. By using electro-optic phase modulation instead of magnetic absorption, the device achieves isolation through interference of phase-modulated beams rather than differential absorption, eliminating the fundamental trade-off between isolation ratio and optical losses that plagues absorption-based approaches.
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 effectively improves optical isolation by amplifying the non-reciprocal variation of the real part of the optical index using a diffraction grating, reducing parasitic light absorption and enhancing the performance of semiconductor laser-based optical devices.
Implementation Method 1
a magnetooptic diffraction grating exhibiting a non-reciprocal variation in the real part of the effective optical index
Implementation Method 2
the grating is made of a magnetooptic material exhibiting a Kerr effect and includes a series of periodically spaced structures causing periodic optical confinement
Data Source
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AI summary
The general field of the invention is that of optical devices comprising a semiconductor laser emission source and an optical isolator, which are integrated. These devices are used mainly in the field of high-data-rate digital telecommunications. The device according to the invention comprises at least one buried optical waveguide (2) in the stripe form, in which an optical wave can propagate at a first given wavelength, said device also including a plane diffraction grating (4) coupled to said optical waveguide, said grating including a series of uniformly spaced identical structures (41) made of a magnetooptic material exhibiting a Kerr effect and having a non-reciprocal optical index, said index having a first value in a first direction of propagation of the optical wave and a second value in the opposite direction, the shape, the period, the number of structures and the optical index difference being such that, in a first direction of propagation of the optical wave, the grating has a low reflection coefficient (R) and, in the opposite direction of propagation of the optical wave, the grating has a high reflection coefficient (R), so as to achieve optical isolation with respect to the propagation wave.