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Description

The 1950nm Faraday mirror is a fiber optic polarization rotation device designed to compensate for polarization fluctuations and improve stability in optical systems. Combining a Faraday rotator with a reflective mirror structure, the device rotates the polarization state of reflected light by 90 degrees, helping suppress polarization-induced signal degradation in fiber optic networks, interferometers, fiber lasers, sensing systems, and coherent optical communication applications. Faraday mirrors operating near 1950 nm are widely used in thulium-doped fiber laser systems, mid-infrared photonics, fiber sensing, and advanced optical instrumentation.

What is a Faraday Mirror?

A Faraday mirror (also called a Faraday rotator mirror) combines a Faraday rotator with a reflective mirror to rotate the polarization state of reflected light by 90 degrees. Because the Faraday rotation effect is non-reciprocal, polarization distortions accumulated during forward propagation through optical fiber are automatically compensated during the return path.

This property makes Faraday mirrors especially valuable in:

  • fiber interferometers,
  • coherent optical systems,
  • fiber optic gyroscopes,
  • fiber lasers,
  • optical sensing applications.

The polarization compensation behavior of Faraday mirrors is a defining characteristic of these devices.

How Faraday Mirrors Work

Light entering a Faraday mirror first passes through a Faraday rotator that rotates the polarization state by 45 degrees. After reflection from the internal mirror, the light passes through the rotator a second time, resulting in a total polarization rotation of 90 degrees.

Because Faraday rotation is non-reciprocal, polarization disturbances introduced in the optical fiber are effectively compensated on the return path, improving polarization stability and reducing signal fading.

This non-reciprocal polarization behavior is central to Faraday mirror operation.

Why Polarization Compensation is Important

Polarization fluctuations in optical fiber systems can introduce signal fading, measurement instability, and noise in interferometric and coherent optical systems. Faraday mirrors automatically compensate for polarization changes caused by birefringence and environmental disturbances in optical fibers, significantly improving system stability and signal reliability.

This is especially important in:

  • fiber sensing,
  • coherent communication,
  • fiber gyroscopes,
  • precision interferometric measurements.

1950nm Optical Systems and Thulium Fiber Lasers

The 1950 nm wavelength region is important for thulium-doped fiber lasers, mid-infrared photonics, spectroscopy, sensing, and medical laser systems. Faraday mirrors operating near 1950 nm help maintain polarization stability in these advanced optical systems.

1950nm Faraday Mirror

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Specifications

Center Wavelength: 1950 nm
Operating Bandwidth: 30 nm
Insertion Loss (max): 0.9 dB
Faraday Rotation Angle (single Pass): 45 deg deg
Operating Bandwidth: ±30 nm
Max. Insertion Loss: 0.9 dB (Typ. 0.6 dB)
Faraday Rotation Angle (Single Pass): 45°
Rotation Angle Tolerance Over Wavelength And Temperature: ±2.0°
Max. PDL: 0.10 dB
Max. Optical Power: 500 mW
Fiber Type: SMF-28e (default) or SM1950
Operation Temperature: -5 ~ +70 °C

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Features

  • Optimized for 1950 nm Wavelength – Precisely engineered for 1950 nm center wavelength (±30 nm bandwidth), ensuring stable performance in eye-safe and mid‑IR fiber laser and amplifier systems.
  • High Polarization Rotation Accuracy – True 45° single‑pass Faraday rotation with tight ±2° tolerance over wavelength and temperature, ideal for polarization compensation and interferometric setups.
  • Low Insertion Loss – Typical insertion loss of 0.6 dB (max. 0.9 dB), minimizing signal degradation and improving overall system efficiency in demanding optical links.
  • High Return Loss & Isolation – High return loss design significantly reduces back‑reflections and unwanted feedback into lasers, enhancing stability and protecting upstream components.
  • Epoxy‑Free Optical Path – Optical path is completely epoxy free, providing excellent long‑term reliability, ultra‑low outgassing, and superior high‑temperature stability compared to adhesive‑based designs.
  • Compact and Robust Package – Small form factor cylindrical housing (e.g. Ø5.5 × 35 mm typical) enables easy integration into space‑constrained fiber modules, sensor heads, and test fixtures.
  • High Power Handling – Supports up to 500 mW optical input power, suitable for many fiber laser cavities, amplifiers, and nonlinear optics setups at 2 μm.
  • Low Polarization Dependent Loss (PDL) – Maximum PDL of 0.10 dB maintains signal integrity in polarization‑sensitive systems and improves measurement repeatability in test instrumentation.
  • Standard and Specialty Fiber Options – Available with SMF‑28e (default) or SM1950 fiber to match common 2 μm component platforms and simplify splicing and system integration.
  • Versatile Pigtail & Connector Configurations – Custom fiber lengths, buffer diameters (e.g., 0.9 mm loose tube), and connector types available, allowing easy drop‑in replacement and tailored OEM solutions.
  • Wide Operating Temperature Range – Designed for operation from -5°C to +70°C, suitable for lab, industrial, and telecom environments with daily and seasonal temperature variations.
  • Polarization Insensitivity for Complex Systems – Converts arbitrary input polarization into a controlled, rotated state upon reflection, effectively canceling polarization fluctuations in interferometers and bidirectional links.
  • Ideal for Fiber Lasers and Amplifiers at 2 μm – Well suited for Tm/Ho‑doped fiber lasers, Brillouin amplifiers, and cavity designs that require polarization diversity or feedback control at 1950 nm.
  • Enhanced Performance in Measurement & Sensing – Excellent choice for fiber‑optic interferometers, OTDR setups, coherent detection schemes, and distributed sensing where polarization‑induced fading must be mitigated.
  • Telecom & Fiber Network Compatibility – Supports deployment in fiber‑optic LAN, access networks, and specialty telecom links that operate in or near the 2 μm band, improving system stability over long distances.
  • Reliable in Harsh and Long‑Term Operation – Rugged construction, epoxy‑free design, and carefully selected materials ensure long lifetimes in industrial, aerospace, and field‑deployed systems.
  • Customizable to Application Needs – Rotation angle configuration (45° design for 90° round‑trip effect), package style, fiber type, pigtail length, and connector options can be tailored to specific OEM or research requirements.
  • Designed and Manufactured by DK Photonics – Backed by an experienced photonics manufacturer with strong engineering support, fast customization, and global shipment from Shenzhen, China.

Applications

  • 1950 nm fiber laser systems – polarization-insensitive cavity designs, linear–to–circular polarization conversion, and return-path stabilization in high-power 2 µm laser setups.
  • Fiber amplifiers at 2 µm (Thulium- and Holmium-doped) – mitigation of polarization-dependent gain, improved stability in high‑power EDF/TDFA/HDFA pre‑amp and booster stages.
  • Coherent optical communication links – reduction of polarization-induced fading, enhanced signal integrity in 2 µm coherent transmit/receive chains.
  • Fiber optic LAN and access networks – improvement of link stability and BER by eliminating polarization sensitivity in short- and medium-reach fiber links.
  • Optical fiber sensing systems – Faraday Mirror in reflectometric configurations (OFDR, OTDR-based sensors) and distributed temperature/strain sensing around 2 µm.
  • Fiber interferometers – suppression of polarization-induced fluctuations in Michelson, Mach–Zehnder, Sagnac, and asymmetric interferometers used for precision metrology.
  • Brillouin/Stimulated Raman scattering systems – stabilization of Brillouin amplifiers and distributed Brillouin sensing by depolarizing the round-trip path.
  • Polarization-diverse measurement setups – calibration and reference reflection in polarization analyzers, PMD/PDL test benches, and optical spectrum analyzers with external interferometers.
  • Fiber optic component testing – return-path mirror for insertion loss, return loss, and polarization sensitivity measurements of in-line components at 1950 nm.
  • Coherent LiDAR and 3D imaging at 2 µm – stable reference reflection and mitigation of polarization fading in coherent detection and FMCW LiDAR architectures.
  • Free-space to fiber coupling modules – polarization-rotation mirror termination in collimator assemblies and compact optical heads for 2 µm sources.
  • Optical antenna remoting and phased-array feeds – polarization‑insensitive reflection in analog RF‑over‑fiber and phased-array timing distribution networks.
  • Quantum optics and quantum communication experiments – controlled polarization rotation and stable reflective termination in 2 µm quantum channels and testbeds.
  • Optical coherence tomography and biomedical imaging (2 µm band) – enhancement of fringe visibility and robustness to sample-induced polarization changes.
  • Gas sensing and environmental monitoring – stable reflective end for 1950 nm interrogation of gas absorption lines in fiber-coupled sensor heads.
  • Industrial and medical laser delivery systems – feedback control, cavity monitoring, and stable reflective references in 2 µm surgical and materials-processing systems.
  • Research and development in 2 µm photonics – general-purpose polarization-rotation mirror for lab setups exploring new 2 µm components, fibers, and devices.

Frequently Asked Questions

What is a 1950nm Faraday Mirror and how does it work?
A 1950nm Faraday Mirror is a passive fiber‐optic component that reflects incoming light while rotating its state of polarization by a fixed angle (typically 45° per pass, resulting in 90° round trip). It uses the Faraday effect in a magneto‐optic crystal placed in a magnetic field. When light enters the device through the fiber, it passes through the Faraday rotator, reflects off an internal mirror, and passes through the rotator again on the way back, doubling the rotation. Because the Faraday rotation is non-reciprocal, the polarization state of the reflected light is orthogonal to the input, which allows polarization effects in the fiber path to be passively compensated. This makes the device ideal for polarization-insensitive interferometers, amplifiers, and measurement setups at 1950 nm.
What are the main applications of a 1950nm Faraday Mirror?
A 1950nm Faraday Mirror is primarily used in fiber-optic systems operating around 2 µm. Typical applications include: (1) Fiber amplifiers and fiber laser cavities at 1950 nm, where the mirror helps stabilize output against polarization fluctuations; (2) Fiber interferometers and sensor systems, where it passively compensates for polarization changes in the connecting fiber; (3) Brillouin and Raman amplifier setups using 2 µm fibers; (4) Fiber-optic LAN and telecom links that utilize 1950 nm bands; and (5) Test and measurement setups, including polarization-insensitive OTDR or reflectometry arrangements in the 2 µm window. In these systems the Faraday Mirror reduces polarization-dependent loss and polarization-induced fading, improving measurement repeatability and system reliability.
What are the key performance specifications of the DK Photonics 1950nm Faraday Mirror?
The DK Photonics 1950nm Faraday Mirror is optimized for operation at 1950 nm with ±30 nm bandwidth. Key typical specifications are: maximum insertion loss ≤0.9 dB (typically ~0.6 dB without connectors), Faraday rotation angle of 45° per pass (90° round-trip) with ±2° tolerance over wavelength and operating temperature, polarization dependent loss (PDL) ≤0.10 dB, and maximum optical power handling of 500 mW. It offers high isolation, high return loss, and an epoxy-free optical path for low loss and good temperature stability. The standard fiber type is SMF‑28e or optional SM1950, and the standard operating temperature range is –5 °C to +70 °C. When connectors are added, the insertion loss typically increases by about 0.3 dB and the return loss decreases by about 5 dB, which is consistent with similar Faraday mirrors available on the market.
What fiber types, pigtail options, and connectors are available for the 1950nm Faraday Mirror?
By default the DK Photonics 1950nm Faraday Mirror is supplied with SMF‑28e fiber, but it can also be configured with SM1950 fiber for optimized performance around 2 µm. The datasheet example describes a Ø5.5 × L35 mm package with 1.0 m fiber pigtails in a 0.9 mm loose tube. Custom pigtail lengths and jacket diameters can be requested. The manufacturer notes that if connectors are required, it is not recommended to choose a 250 µm bare fiber pigtail; instead, buffered or jacketed fibers are preferred for connectorization. Standard telecom connectors such as FC/PC, FC/APC, SC/PC, SC/APC, and others can usually be provided on request, with the understanding that they slightly increase insertion loss and reduce return loss, similar to other commercial Faraday mirrors.
How does a Faraday Mirror help eliminate polarization sensitivity in fiber systems?
A Faraday Mirror converts any arbitrary polarization state at its input into the orthogonal polarization at its output after a round trip. When used at the end of a fiber link or interferometer arm, the light passes through the fiber, is rotated and reflected by the Faraday Mirror, and then travels back through the same fiber. Any birefringence or polarization rotation that the forward-going light experiences in the fiber is effectively reversed on the return path because the polarization has been rotated by 90° at the mirror. This self-compensation cancels out polarization distortions induced by the fiber, making the overall response largely polarization-insensitive. This principle is widely used in commercial polarization-diverse interferometers, Faraday rotator mirrors in fiber sensors, and polarization-insensitive amplifiers at communication and specialty wavelengths like 1950 nm.
What should I consider when specifying or ordering a custom 1950nm Faraday Mirror?
When ordering a DK Photonics 1950nm Faraday Mirror, you should specify parameters similar to those used by other Faraday mirror manufacturers: center wavelength (1950 nm), rotation angle (45° per pass is standard), package size, fiber type (SMF‑28e or SM1950), pigtail diameter and length, connector type (or bare fiber), and any special operating temperature or power handling requirements. DK Photonics uses a part number format such as FM-1950-45-1-S28-90-10-00, where each field encodes wavelength, rotation angle, package, fiber, pigtail diameter, length, and connector options. If you require non-standard bandwidth, higher power handling, special coating, or integration into a particular module footprint, you should provide a detailed written description with your RFQ so the design team can confirm feasibility and final package dimensions.
What are the environmental and reliability characteristics of this 1950nm Faraday Mirror?
The DK Photonics 1950nm Faraday Mirror is designed with an epoxy-free optical path, which improves long-term reliability, minimizes outgassing, and enhances high-temperature performance, in line with best practices used by other high-end Faraday mirror suppliers. The standard operating temperature range is –5 °C to +70 °C, suitable for most laboratory, telecom, and industrial environments, and the storage temperature range is similar (typically extending slightly lower than the operating limit according to the datasheet). The compact metallic package (e.g., Ø5.5 × L35 mm in the example) is robust and well suited for integration into fiber laser and amplifier packages. For applications requiring extended temperature ranges, hermetic sealing, or higher mechanical shock/vibration resistance, customers should discuss their requirements with DK Photonics so that package and assembly options can be tailored accordingly.

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