Month: June 2022

What Is a Faraday Mirror and How Does It Work?

Faraday mirrors

A Faraday Mirror is a fiber optic polarization rotator mirror that is used for making a wide range of passive fiber optics components. It is an important invention that made it possible to create passive polarization-maintaining components.

Earlier, the main issue was to maintain the state of polarization as the beam travels across the fiber. This can be easily achieved by using a polarization-maintaining (PM) fiber which is designed for the very same purpose. However, PM fibers and PM-fiber-based devices used to be extremely expensive for many applications and were also difficult to handle.

An optical beam that travels in a typical single-mode (SM) fiber undergoes random changes in birefringence due to stress, vibration, or temperature variation. The use of the Faraday rotator mirror can help resolve this issue.

What is a Faraday mirror?

A Faraday mirror is a fiber optic device that can be used for both the reference mirror and the probing mirror. It works as a phase conjugate mirror by introducing a phase delay of 90 degrees. This feature allows the mirror and the return path of the optical beam to compensate for any induced birefringence automatically.

What is a Faraday mirror made of?

A high-quality Faraday mirror is made of Terbium Gallium Garnet (TGG). TGG is a crystal that is currently the best magneto-optical material for Faraday rotators and isolators. It is considered best because of the high Verdant constant and superior Faraday Effect. It has a higher thermal conductivity and high resistance to laser damage.

How does a Faraday mirror work?

A Faraday mirror works based on the Faraday Effect. In this device, a non-reciprocal rotation of a polarization state occurs as the light beam passes through a special optical medium under the effect of the magnetic field. We will discuss its working with the help of Faraday rotator as its main application is this device.

A Faraday rotator mirror (FRM) consists of a fiber collimator, Faraday rotator, and mirror.

As the orthogonal wave light components pass the optical fiber in the forward direction, they will experience a rotation of 45 degrees in the clockwise direction. When they are reflected by the mirror, they pass the Faraday rotator again, which is a non-reciprocal device, and the polarization state of the reflected optical signal will experience a rotation of another 45 degrees in the same direction as the input signal. Hence, the resultant rotation is 90 degrees. Now, the orthogonal components pass the fiber back but in a complimentary fiber axis and you obtain a linearly polarized light on the close end of the fiber with a rotation of 90 degrees.

Do you need Faraday mirrors to manufacture your fiber optics components or for your research projects? You can easily buy it online at DK Photonics.

Features and Applications of 780nm Optical Isolators

The high-power dual-stage optical isolator 780nm is a polarization-independent fiber element that enables all polarized light to propagate in one direction while blocking it in the opposite direction.

It is not possible to adjust the polarization of input light in many applications. In such instances, a polarization-independent optical fiber isolator with a wavelength of 780nm is required. 780nm optical fiber is a critical component that protects lasers, amplifiers, and ASE sources from instabilities caused by spurious back-reflected light.

Overview of the 780nm Optical Isolators

Low-power lasers benefit from the flexibility, convenience, and performance of the I-780-LM compact designs. I-780-LM covers the wavelength range of 770 to 790nm. A Faraday rotator constructed of LPE film is included in this design.

Due to the absorption of the Faraday rotator material, this type is only advised for low-power applications. For OEM requirements, metal-bonded or hermetic construction alternatives are available. I-780-LM has a standard wavelength of optimization of 780nm.

Applications

  • Semiconductor Laser Modules
  • Tunable Laser Modules
  • Small Form Factor Laser Modules

Features

  • Low Insertion Loss
  • High Isolation
  • Micro-Miniature Size
  • Broad Bandwidth
  • Wide temperature range
  • Polarization alignment

Single Mode / Single Frequency Laser Diode, 780nm DFB, 4mW

The DFB laser is made with discrete-mode (DM) technology, which results in a low-cost laser diode with mode-hop-free tuneability, high SMSR, and a narrow linewidth.

These laser diodes come in a variety of wavelengths ranging from 776 to 784nm, making them ideal for Rb-based atomic clocks, Rubidium sensing, and interferometry applications.

The fiber-coupled butterfly package includes a TEC and a thermistor for precise temperature and wavelength control.

780nm for Rubidium-Based Atomic Clocks

These 780nm lasers operate reliably and without mode hop over a broad wavelength tuning range. These Rubidium-based atomic clocks and spectrometer lasers have a single longitudinal mode. The low linewidth output is ideal for high-performance applications in a variety of environments.

Polarization-Independent Dual-Stage Optical Isolator Fundamentals

The polarization dependence of dual-stage optical isolators using polarizers and a Faraday rotator is a severe problem. The insertion loss will rise as a result of this problem. As a result, optical isolators that are not polarization-dependent are particularly appealing for transmission systems.

By replacing the polarizers with polarizing splitters combiners, it is possible to achieve a polarization-independent design: they divide the input light into two orthogonal states of polarization that run through the Faraday cell separately to experience isolation and are recombined at the output.

Many applications in fiber optic systems necessitate high-power polarization-independent dual-stage optical isolators, which allow inputs with any polarization direction to flow through without PDLs while isolating back reflections (return lights).

The high-power dual-stage optical isolator is a vital component in optical systems. High-power dual-stage optical fiber isolators are used to ensure that laser transmitters and amplifiers are stabilized, and that transmission performance is maintained.

Can an Optical Splitter be Used as a Combiner?

It can be challenging to tell the difference between a Combiner and a Splitter because they have similar appearances. Furthermore, some splitters and combiners might be passive or active, powered or unpowered, adding to the confusion.

Let’s look at the combiner and splitter to see what they’re for.

A Combiner

A combiner is a device that combines multiple input signals of varying frequencies into a single output signal for feeding a single antenna. A combiner basically takes all of the signals and combines them, which is useful when the signals are meant to be combined.

A Splitter

On one end, splitters have a single connection and numerous connections on the other. A splitter receives one signal and splits it into two.

While signal splitting may appear to be the most convenient approach to adding more outlets, keep in mind that each time a signal is split, its power is halved. When you split the transmission, you’re sending half as much signal through each line.

You may think you have a good signal now, but if you divide it too many times, it won’t accomplish the job. Before deciding to split the signal, you need carefully assess whether you have a strong enough signal.

It is frequently recommended that two antennas be used instead of a splitter in places where the signal is extremely weak. The signal will always be divided, whether or not two devices are connected to the splitter.

Polarization Beam Combiner/Splitter

This device can function as a polarization beam combiner, combining light beams from two PM input fibers into a single output fiber, or as a polarization beam splitter, splitting the light from one input fiber into two orthogonal polarization states output fibers.

Polarization Beam Splitter/Combiner

Polarization division multiplexing or demultiplexing in optical systems to boost transmission capacity is an important application of this device. Furthermore, as a pump combiner in optical amplifiers, the device efficiently combines the output from two pump lasers into a single fiber, increasing the optical amplifier’s saturation power and reducing its polarization sensitivity.

The device’s wide operation bandwidth and strong power-handling capacity make it ideal for next-generation amplifier systems. Finally, this compact device has a durable stainless steel package built for strong optical performance and stability, and it has low excess insertion loss, low back reflection, and a high extinction ratio that are comparable to or better than others on the market.

Features:

  • Compact size
  • Low insertion loss
  • High-capacity handling
  • Rugged design

Applications:

  • Mux/DeMux polarisation division
  • Raman amplifiers and EDFA
  • Laser Fiber Systems
  • Fiber Sensor Systems
  • Instruments
  • R&D Laboratories

Polarization Beam Splitter/Combiner is available from DK Photonics, a reputable optical passive component manufacturer based in China. Contact us if you are interested in purchasing Polarization Beam Splitter/Combiner.

How is Polarization Maintained?

Light is a form of electromagnetic wave. It is made of electrical and magnetic fields that oscillate. While you can define light and its effects in terms of the magnetic field, it is easy to characterize its qualities by examining its electrical field.

Polarization Maintained

Light waves can vibrate in different directions. Polarized light is a light that vibrates in just one direction — in a single plane, such as up and down. Unpolarized light is a light that vibrates in more than one direction — in more than one plane, such as up/down and left or right.

How to Obtain Single Polarization?

A polarization filter is the most common way to achieve single polarization. These filters are built of unique materials that can block one of an electromagnetic wave’s two vibrational planes.

A polarization filter is a device that filters out half of the vibrations transmitted through a filter as light passes through it. When unpolarized light passes through a polarization filter, it becomes polarized light, which has half the intensity and vibrates in a single plane.

What is Polarization Maintaining Fiber?

A polarization-maintaining fiber (PM Fiber) is a form of single-mode fiber that maintains polarization. Single-mode fibers can convey polarized light that is randomly polarized. However, PM fiber is designed to transmit one polarization of input light.

The polarization of linearly polarized light waves sent into the fiber is maintained throughout propagation in polarization-maintaining fiber, with little or no cross-coupling of optical power between the polarization modes.

This polarization-maintaining characteristic is critical for some fiber optic components that demand polarized light input, such as external modulators. This property is acquired by creating stresses in the material during the production process. Linear polarization-maintaining fiber (LPMF) and circular polarization maintaining fiber (CPMF) are the two types of polarization-maintaining fiber available.

Applications of Polarization Maintaining Fibers

  1. Fiber optic sensing, interferometry, and slab dielectric waveguides are just a few of the applications for PM optical fibers.
  • PM fibers can be used in coherent and long-distance bidirectional optical transmission systems.
  • They can also be employed in transmission applications where the polarization plane of the optical signal is critical, such as optical sensor transmission lines and optical-electrical integrated circuit coupling.
  • PM fibers are used in lithium niobate modulators, Raman amplifiers, and other polarization-sensitive devices to keep the incoming light polarized and minimize cross-coupling between polarization modes.

What Limits the Performance of PM Fibers?

PM fiber guides light in a linearly polarized form from one location to another in the most typical optical fiber telecommunications applications. It is crucial to meet several requirements to attain this result. In order to avoid launching both slow and fast axis modes, the input light must be highly polarized, resulting in an unpredictable output polarization state.

For the same reason, the electric field of the input light must be precisely aligned with a principal axis (the slow axis by industry convention) of the fiber. The rotational alignment of the joining fibers is crucial if the PM fiber line comprises segments of fiber linked by optical connectors or splices.

Lastly, connectors on PM fibers must be positioned in such a way that internal tensions do not allow the electric field to be projected onto the fiber’s undesired axis.

What is a band-pass filter used for?

Fiber bandpass filters are the optical filters that allow optical signals of certain frequencies to pass through while blocking the optical signals of other frequencies. To block the light of unwanted frequencies, they either absorb the light or reflect it or do both. You can use a band-pass filter to transmit signals in a specific range of frequencies, varying from a narrow band to a wide range.

An Overview of a Band-Pass Filter

Optical bandpass filters are micro-optics devices that transmit (or pass) a specific range (or band) of frequencies and block others. This specific range can include visible light, as well as non-visible wavelengths that fall at the infrared and ultraviolet ends of the spectrum.

Since the filter passes only a certain band of frequencies, the result is an output that comprises only light signals with desired frequencies and wavelengths.

You can define them through various characteristics, including:

  • Blocking level – how effectively and efficiently the bandpass filter is able to eliminate the unwanted wavelengths
  • Peak Transmission – how effectively the incident light is propagated and transmitted
  • Central Wavelength – the wavelength of the light at the center of the transmission band profile
  • Full Width at Half Maximum – the limits of bandwidth between which 50 percent or more light is transmitted

For instance, a very high transmission across the FWHM range with a very low transmission outside of that range is an indication that a bandpass filter is highly effective and has very little noise in the output.

What is a band-pass filter used for?

A fiber bandpass filter is used for blocking unwanted noise signals in a wide range of systems and applications, such as:

  • Fiber amplifiers
  • Fiber lasers systems
  • EDFA systems
  • DWDM systems
  • High-speed communication system
  • Instrumentation applications

Apart from this, optical bandpass filters are also used for anti-reflection and anti-glare coatings, chemical analysis, dielectric mirrors, high reflectors, IR applications, fluorescence filters, long-wave pass, shortwave pass, UV applications, and more.

Generally, bandpass filters are made in two ways. Thin-film filters and coated filters are designed through the deposition of multilayer dielectric coatings onto a substrate. On the other hand, spectral and absorption filters are made by a combination of lamination, cemented layers, and thin film coating.

Fiber bandpass filters are designed based on environmentally stable thin-film filter technology. They work by absorbing or reflecting unwanted wavelengths and transmitting only desirable parts of the light spectrum.

By combing filters and different methods, it is possible to design single laminated bandpass filters with very specific and complex properties to meet the needs of all kinds of electro-optical applications.

DK Photonics is an esteemed optical passive component manufacturer based in China, offering a wide range of fiber optics passive components, including fiber bandpass filters characterized by high isolation, low insertion loss, high extinction ratio, and excellent stability. To buy fiber bandpass filters with standard or customized specifications, please get in touch with us.