Compact Faraday Rotator Using High Verdet Constant Oxide
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Solution Overview
Problem
Conventional optical isolators using terbium gallium garnet (TGG) crystals are large in size due to the requirement for a significant length to achieve a 45° Faraday rotation angle, leading to increased magnetic field leakage and difficulties in handling, while also having a limited extinction ratio, which is insufficient for high-output lasers like fiber lasers.
Innovation Solution
A Faraday rotator with a higher Verdet constant, combined with a magnet material and magnetic circuit providing a large magnetic flux density, is used to reduce the size of the optical module, allowing for a shorter sample length and improved extinction ratio, thereby enhancing spatial freedom and reducing the risk of optical damage from high-output lasers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional TGG crystal is used as the Faraday rotator, then the optical isolator can achieve the required 45° Faraday rotation angle, but the device becomes large in size and difficult to handle
Solution Approach 1:
The patent changes the material parameter (Verdet constant) from conventional TGG crystal to a new oxide material with higher Verdet constant, enabling the same 45° rotation angle to be achieved with a shorter sample length, thus reducing device size and improving handling ease
Solution Approach 2:
The patent reduces the sample length dimension of the Faraday rotator from conventional lengths (implied to be several cm) to 5mm or less, transforming the device from a large bulky component to a compact one that is easy to handle and integrate
2Reliability
If a conventional TGG crystal is used as the Faraday rotator, then the optical isolator can function, but the extinction ratio is limited and insufficient for high-output lasers
Solution Approach 1:
The patent changes the material composition parameter to use an oxide with specific rare-earth element content (40-80 atomic percent) that provides both the required Faraday rotation and significantly improved extinction ratio, making the isolator suitable for high-output laser applications
Solution Approach 2:
The patent uses a composite oxide material containing multiple rare-earth elements (such as terbium, dysprosium, holmium, erbium, thulium, ytterbium, and/or gadolinium) to achieve superior optical properties including high extinction ratio and adequate Faraday rotation angle
3Ease of operation
If the sample length of the Faraday rotator is reduced to minimize device size, then the device becomes compact, but the extinction ratio may deteriorate
Solution Approach 1:
The patent identifies a specific material composition range (40-80 atomic percent rare-earth elements) that provides sufficiently high Verdet constant and optical absorption characteristics, enabling the sample length to be reduced to 5mm or less while maintaining both compactness and high extinction ratio
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 results in a compact optical module with a high extinction ratio and low loss, suitable for high-output lasers, offering improved design flexibility and durability against high-power light, while maintaining effective isolation properties.
Implementation Method 1
a magnet that applies a magnetic field in the direction of light transmission of the Faraday rotator (optical axis direction)
Implementation Method 2
When light is incident on the Faraday rotator in this configuration, a phenomenon occurs in which the plane of polarization rotates in the Faraday rotator. This is a phenomenon called the Faraday effect
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A Faraday rotator is provided that includes a Faraday element having a Verdet constant at a wavelength of 1.06 µm of at least 0.27 min/(Oe·cm), a first hollow magnet disposed on the outer periphery of the Faraday element, and second and third hollow magnet units disposed so as to sandwich the first hollow magnet on the optical axis. The second and third hollow magnet units include 2 or more magnets equally divided in a direction of 90 degrees relative to the optical axis. A magnetic flux density B (Oe) applied to the Faraday element is in the range of 0.5 × 104 ≤ B ≤ 1.5 × 104. The Faraday element has a length L (cm) in the range of 0.70 ≤ L ≤ 1.10, and an external diameter D (cm) in the range of 0.20 ≤ D ≤ 0.60 and consists of terbium oxide (Tb2O5) and one element selected from the group of scandium, yttrium, and lanthanoid elements other than terbium.