Blue-Violet Optical Isolator Using a High-Verdet Faraday Rotator
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Solution Overview
Problem
Conventional optical isolators are difficult to miniaturize for violet and blue wavelength bands due to limitations in Verdet constant and magnetic flux density, making them unsuitable for compact optical isolators required in semiconductor lasers for medical and optical measurement applications.
Innovation Solution
An optical isolator design utilizing a Faraday rotator with a Verdet constant of 750 Rad/T·m or greater and a magnetic flux density of 0.40 T or less, combined with an optical path length between 0.26 cm and 0.50 cm, using a Faraday rotator with 95% or more of an oxide represented by (TbxR1-x)2O3, and polarizers with low insertion loss and high extinction ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a Faraday rotator with a large Verdet constant is used to achieve compact size, then the isolator size is reduced, but the magnetic flux density requirement increases
Solution Approach 1:
The patent changes the material parameter (Verdet constant) by selecting specific fluoride crystals (CeF3, PrF3, NdF3) that have large Verdet constants at violet and blue wavelengths. This allows achieving the required Faraday rotation with a shorter rotator length and lower magnetic flux density, thus resolving the contradiction between compact size and magnetic field requirement
Solution Approach 2:
The patent uses composite material structures by combining fluoride crystals (CeF3, PrF3, or NdF3) with appropriate host materials to create Faraday rotators that exhibit large Verdet constants at 400-470 nm wavelength. This composite approach enables simultaneous achievement of high Verdet constant and low absorption coefficient
2Length of moving object
If the optical path length is shortened to reduce isolator size, then the isolator becomes more compact, but the Verdet constant requirement increases
Solution Approach 1:
The patent selects fluoride crystal materials (CeF3, PrF3, NdF3) that inherently possess large Verdet constants at violet and blue wavelengths. This material parameter change allows achieving the required 45° Faraday rotation with a shortened optical path length of 0.26-0.50 cm, thus resolving the contradiction between compact length and high Verdet constant requirement
3Use of energy by moving object
If conventional materials like TGG are used, then the Verdet constant is adequate, but the absorption coefficient is too high for compact design
Solution Approach 1:
The patent employs composite material structures by combining fluoride crystals (CeF3, PrF3, or NdF3) with suitable host materials to create Faraday rotators that simultaneously exhibit large Verdet constants and low absorption coefficients at 400-470 nm. This composite approach overcomes the limitation of conventional single materials like TGG
Solution Approach 2:
The patent changes the material composition parameter by using specific fluoride crystal ratios and host material combinations to achieve the optimal balance between high Verdet constant and low absorption coefficient, enabling both adequate Faraday rotation and minimal optical loss
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 design achieves a miniaturized optical isolator transparent at 400 to 470 nm with lower loss and higher isolation, enabling compact integration in semiconductor laser modules.
Implementation Method 1
When light enters the Faraday rotator in this configuration, a phenomenon occurs in which the plane of polarization rotates in the Faraday rotator. This phenomenon is called the Faraday effect, and the angle of rotation of the plane of polarization is called the Faraday rotation angle.
Implementation Method 2
a magnet that applies a magnetic field in the direction of light transmission (direction of optical axis) of the Faraday rotator
Data Source
AI summary
An optical isolator for a wavelength band of 400 to 470 nm includes: a Faraday rotator having a Verdet constant equal to or greater than 750 Rad/T·m at a wavelength of 400 nm to 470 nm; and a hollow magnet provided on an outer periphery of the Faraday rotator, wherein a magnetic flux density B(T) applied to the Faraday rotator is within the range of the following formula (1), and an optical path length L(cm) over which the Faraday rotator is provided is within the range of the following formula (2): B≤0.40 (1); 0.26≤L≤0.50 (2). Thus, a miniaturized optical isolator which is transparent at violet and blue wavelengths of 400 to 470 nm is provided.