Category: PM Isolator

Are 1064nm High Power Isolators are TGG-Based or Faraday-Based?

The 1064nm high-power isolators are small optical passive components that permit the light to travel in one direction only, operate at 1064nm wavelength, and are widely used in high-power fiber laser and amplifier applications. They help prevent any reflected light from going back to the source and hence, reduce feedback problems. These optical isolators are specifically designed to handle high power and hence, many high-power isolators can handle even a hundred Watts. On the other hand, low-power isolators can work with only 0.5 or 1 to 5 Watts.

Do high-power isolators use TGG or Faraday materials?

While some high-power isolators contain TGG crystals, others may have alternative Faraday materials. Take note that TGG crystals are also a type of Faraday material and they are the most common crystals used for optical isolators. Let’s find out what using TGG crystals and alternative Faraday materials means for high-power isolators.

What is TGG?

TGG stands for Terbium Gallium Garnet (Tb3Ga5O12). It is the most commonly used single-crystal Faraday rotator for optical isolator applications. Since TGG can melt congruently under the temperature of ~1825 degrees Celsius, large crystals of TGG can be easily made using the Czochralski technique. While one can easily grow these crystals in large sizes, bulk defects do not allow for fully utilizing these crystals. Some of these defects include color centers, dislocations, strain areas, etc.

TGG is widely used in 1064nm high-power isolators but it is very sensitive to increase absorption at this wavelength. Typical values for absorption at 1064nm for TGG range from 0.20 to 0.30%/cm.

What are Alternative Faraday Materials to TGG?

Since there are intrinsic limitations in the performance of TGG crystals, alternative Faraday materials are being explored and researched for delivering higher performance. The two great examples of alternative Faraday materials include lithium terbium fluoride (TLF) (LiTbF4) and potassium terbium fluoride (KTF) (KTb3F10).

These are small crystals that possess small non-linear refractive indices and thermo-optic coefficients, while also exhibiting Verdet constants similar to or near to those of TGG crystals. Hence, TLF and KTF are also being considered for making high-power isolators.

Contrary to TGG, these two single-crystal Faraday materials melt incongruently, which means they are difficult to grow. Besides, their growth is flux-type, precipitate inclusions and scatter-type defects are also present in these crystals unless their melt stoichiometry is done under a controlled environment. Among these two crystals, the most focus is given to KTF because of the stringent crystallographic alignment requirements.

Both of these materials exhibit improved absorption at shorter wavelengths. But, unlike TGG, color center formations and cation valence alterations are reduced in TLF and KTF. Therefore, they are considered promising for optical isolators for visible wavelength lasers.

However, nowadays, 1064nm high-power isolators that are made using TGG crystals are more common, affordable, and easily available, which makes them a a convenient choice for fiber lasers and various other applications.

At DK Photonics, we offer not only 1064nm high-power isolators but also various other high-power isolators that operate at different wavelengths. Besides, we also offer low-power PM optical isolators. So, whether you need standard optical isolators or custom optical isolators, get in touch with us.

How Does Polarization Maintaining Fiber Work?

Polarization-maintaining fiber is a fundamental component in fiber optics. It is often abbreviated as PMF or PM fiber. In simple terms, it is a single-mode optical fiber that allows the linearly polarized light to preserve its polarization state while propagating across it, given that the linearly polarized light is properly launched into the fiber. Consequently, there is negligent or no cross-coupling of optical power between two polarization modes. This type of optical fiber is essential for applications where polarization preservation is important.

Now that you know what polarization-maintaining optical fiber is, let’s dive into how it works.

How Polarization-Maintaining Optical Fiber Works

To make polarization-maintaining optical fiber work, a systematic linear birefringence is intentionally introduced. It allows two well-defined polarization modes to travel across the fiber with very different phase velocities.

PM fiber is often characterized by its beat length for a particular wavelength, represented as Lb. The beat length is the distance over which the wave in one mode experiences an additional delay of one wavelength when compared to the other polarization mode. Hence, PM optical fiber of the length Lb /2 is considered equivalent to the half-wave plate.

Now consider the fact that random coupling might occur between two polarization states over a significant length of PM fiber. In such a scenario, at the very initial point 0 along with the fiber, the wave in polarization mode 1 induces amplitude into mode 2 at some phase.

However, at point ½ Lb along with the fiber, the same coupling coefficient between the two polarization modes induces an amplitude into mode 2 which now becomes 180 degrees out of phase with the wave coupled at point 0 and hence results in cancellation.

Now, at point Lb along with the fiber, the coupling is again in its original phase but then, at 3/2 Lb it will get again out of phase. This phenomenon will keep occurring so on.

Hence, the chances of coherent addition of wave amplitudes through cross-coupling over distances that are larger than Lb get eliminated. Most of the power of the wave remains in its original polarization mode and therefore, exits the fiber in the same mode as well.

Thus, optical fiber connectors that are used for PM fibers are specifically used in a way so that the two polarization modes remain aligned with each other and exit in a specific orientation.

Remember that polarization-maintaining fiber doesn’t function like a polarizer as it doesn’t polarize the light. It simply maintains the linear polarization of the launched linearly polarized light that aligns with one of the fiber’s polarization modes. If a linearly polarized light is launched into the fiber at a different angle, it will excite both polarization modes and will allow the light wave to propagate at slightly different phase velocities.

DK Photonics is a top-notch China-based manufacturer of polarization-maintaining fiber in a variety of specifications. If you don’t see PM fiber with the specifications that you need, don’t worry. We also offer customized orders. So, please feel free to contact us to discuss your custom specifications for PM fibers.   

Understanding PM Optical Isolators: Some Important Applications

Optical reflection is one of the few significant causes of performance degradation in amplifiers and fiber lasers. However, this significant issue can easily be dealt with by using high-quality optical isolators. For those of you who are not familiar with these devices, an optical isolator may be defined as a small device that are designed and created to transmit optical signals in a single direction. Now, this particular device tends to come in two different versions – polarization-insensitive optical isolators and polarization-maintaining optical isolators.

Although both of these versions of optical isolators are effective enough to block any returning light, the insertion loss in a polarization-maintaining optical isolator tends to depend on the input polarization. In this blog, we will shed some light on this particular version of optical isolators.

About Polarization Maintaining (PM) Optical Isolators

Polarization maintaining optical isolators (PM optical isolators) are known to be not just simpler but also very compact when it comes to their design, making them highly suitable for polarization maintaining fiber applications. This type of optical isolator is also highly useful in certain scenarios where an input free space beam of constant polarization tends to pass across the Faraday optics. In both of these applications, the linearly polarized beam that comes from the source is aligned with the transmission axis of the optical isolator.

Even though you can find several types of optical isolators in the market such as fiber-embedded isolators, all-fiber isolators, fiber Faraday rotator isolators, and many others, the core of a commercially available optical isolator tends to consist of a Faraday rotator and a couple of birefringent crystals.

What are the applications of Polarization Maintaining Optical Isolators?

Polarization-maintaining optical isolators have been gaining more and more prominence with each passing day due to the important role they play in modern transmission systems and fiber optic systems. The following are some of the most significant applications of PM optical isolators.

  • One of the main applications of PM optical isolators is that they are useful in applications that are sensitive to unwanted optical reflections and need the presence of polarized light. Since the fact that even a low optical reflection can be enough to increase the laser phase noise, wavelength stability, and intensity noise, the use of PM optical isolators tends to become inevitable in such applications.
  • Polarization maintaining optical isolators are also used in telecommunications and other similar areas such as the likes of biotechnology and sensing such as fiber-optic gyros. Not only this, PM optical isolators can also be seen extensively used in various other applications including fiber amplifiers, fiber sensors, fiber lasers, and so on and so forth.

These were just some of the many applications of polarization-maintaining optical isolators. So, now that you have gained enough knowledge about these devices, you would be able to make the right decision for your particular requirements. However, you must ensure that you deal with a reliable and highly reputed service provider in order to reap all the benefits.

What Are the Different Uses of Polarization Maintaining Optical Isolators?

Optical reflection is a significant cause of the performance degradation in fiber lasers and amplifiers. This issue can easily be resolved by the use of optical isolators. An optical isolator is a small device designed to transmit optical signals in one direction. It comes in two versions: polarization maintaining optical isolators and polarization insensitive optical isolators.

While both types of optical isolators block any returning light, the insertion loss in a polarization maintaining optical isolator depends on the input polarization.

Polarization Maintaining (PM) Optical Isolators

Polarization Maintaining (PM) optical isolators are simpler and very compact in design and highly suitable for polarization maintaining fiber applications. They are also used in scenarios where an input free space beam of constant polarization passes across the Faraday optics. In both types of applications, the linearly polarized beam from the source is aligned with the transmission axis of an optical isolator.

While most passive optical components are reciprocal, optical isolators are usually non-reciprocal. Meaning, optical isolators allow an optical beam to pass in the forward direction with minimal losses while preventing it to propagate in the backward direction.

Though different types of optical isolators can be found in the market such as all-fiber isolators, fiber-embedded isolators, fiber Faraday rotator isolators, and waveguide-based isolators, the core a typical commercially available optical isolator consists of a Faraday rotator with 45-degree rotation and a pair of birefringent crystals.

Applications of PM Optical Isolators

PM optical isolators are playing an increasingly important role, especially in modern optical transmission systems and fiber optic systems. They are mainly used in applications that are sensitive to unwanted optical reflections and require polarized light. Even a very low optical reflection can cause a significant increase in laser phase noise, intensity noise, and wavelength stability. Hence, the use of optical isolators in such applications becomes inevitable.

Another crucial application of polarization maintaining optical isolator is distributed-feedback lasers that are widely used in transmission systems. The distributed feedback laser frequency is said to be very sensitive to the reflection coupled back to the laser cavity due to the single-cavity mode. Since the laser gain profile is not flat, the frequency fluctuation also leads to power instability. Hence, it becomes quite essential to achieve isolation from the optical circuitry and its reflection.

In some cases, Fabry-Perot lasers may also require isolation from the system to enhance the power stability. When Fabry-Petro lasers have fewer cavity modes, the need for isolation in the system increases even more.

Besides, PM optical isolators are widely used in telecommunications and other areas such as biotechnology and sensing (such as fiber-optic gyros). Plus, you will also find their extensive usage in other applications such as fiber lasers, fiber amplifiers, and fiber sensors.

1064nm PM Isolator: Applications, Features, and Specifications

Are you looking for a non-reciprocal fiber optic device that allows the flow of optical power in only one direction? Well, if your answer is yes, then you should consider the 1064 polarization-maintaining fiber optic isolator because it prevents reflections in the backward direction. By using PM fibers, you can maintain the 1064 PM optical isolator state of polarization of the light. Today, you can easily find both PM and non-PM types of these 1064nm optical isolators.

Basics of 1064nm PM Isolator:

This PM isolator is based on the non-reciprocal Faraday Effect – a longitudinal magnetic field generates a rounded birefringence that rotates the alignment of the incoming polarization.

Applications of 1064nm PM isolator

The primary application of the 1064nm polarization-maintaining isolator is to protect the transmission of the laser diode from back reflections. That’s because such reflections increase the noise in the system by disrupting the diode’s operation. The 1064nm PM isolator also enhances the steadiness of fiber amplifiers by lessening the chances of reaction, which can cause undesirable oscillation.

Fiber-Coupled 1064nm PM Isolator:

A fiber-coupled 1064nm PM isolator is a device that works like an optical diode. That is, it transmits in one direction while blocking light in the other direction. You can find such isolators in fiber-coupled form – with input and output coupled to single-mode fibers.

The 1064nm PM isolator is generally positioned at the output of the optical source to avert the light reflection from returning to the source. Moreover, Doped Fiber utilizes the 1064nm PM isolators for avoiding an oscillating behavior.

Here are a few features of 1064nm PM Isolators:

  • Polarization maintaining
  • Low insertion loss
  • High isolation and return loss
  • High reliability and stability

Here are a few Specifications of 1064nm PM Isolator

  • Center Wavelength (nm)   1064
  • Operating Wavelength Range (nm)  ±5-10
  • Top Isolation at 23 ℃ (dB)  30-35
  • Min. Isolation at 23 ℃ (dB)   25-28
  • Max. Insertion Loss at 23 ℃ (dB)  1.2
  • Lowest Extinction Ratio at 23 ℃ (dB)   >20
  • Min. Return Loss (Input /Output) (dB)  50
  • Max. Average Optical Power (W)     0.3~200
  • Max. Peak Power for ns Pulse (kW)   1~50
  • Max. Tensile Load (N)    5
  • Operating Temperature (°C)  -5 to +50
  • Storage Temperature (°C)  -10 to +60

Important Things to Note:

  1. The 1064nm PM isolator can be customized, and the above specifications are subject to change.
  2. Unless specified, the slow axis of the fiber is aligned with the key of the PM fiber connector.
  3. Bare fiber doesn’t support the connector’s weight.

You should consider the 1064nm PM isolator if you’re looking for a high-quality passive device that can transmit the optical signals in one direction and block all the undesirable optical reflections.

A Brief Introduction to Polarization Maintaining Isolators and what’s Inside Them

Polarization maintaining isolator which ‘at times’ is also called fiber optic isolator and polarization maintaining optical isolator. It allows and keeps light to travel in one direction only. Its prime job is to prevent back reflection and backscattering in the reverse direction, for all states of polarization. In technical terms, the device is a two-port micro-optic isolator built with PM panda fiber. The isolator is commonly used in lasers, fiber optic systems, and amplifier systems. It actually prevents feedback which is not at all required in an optical oscillator.

Some devices in which this isolator is used

PM isolator is utilized all over the world majorly in communication systems, instrumentation applications, and polarization maintaining fiber-optic amplifiers. The isolator is also used in fiberoptic system testing and fiber-optic LAN system and CATV fiberoptic links.

Some of the many great features of these isolators

  • High isolation capacity
  • High Extinction Ratio
  • High Return Loss
  • Low Insertion Loss

Every fiber optic isolator has an optical fiber inside of it which is the most important component. Let’s now discuss how it works.

Optical fiber inside such isolators is a thin strand made of pure glass. It acts as a guide for the light wave over long distances by following the principle of ‘total internal reflection’. These are very effective when the light waves try to pass between two varying media.

The fiber inside these devices including polarization maintaining optical isolator is composed of two layers of glass – the core and the cladding. The core typically carries the actual signal of light and the glass layer surrounding the core is called cladding. In comparison to the core, the cladding has a lower refractive index. All of this causes total internal reflection successfully within the core.

What is transmitted over fiber?

Most fibers work in pairs where digital signals are encoded in light’s analog pulses preferably via the NRZ modulation – Non-Return to Zero. Since they operate in pairs, one is used to transmit while the other to receive, however, both signals can also be sent over a single stand.

Basic yet most used fiber types

  • SMF – Single Mode Fiber
  • MMF – Multi-Mode Fiber

The actual difference basically lies in the size of the core. SMF has an in-depth narrow core not more than 9µm which allows the propagation to just a single mode of light, whereas, MMF has a greatly wider core somewhere around 50µm and 62.5µm is also available on the market. MMF allows multiple modes of light to propagate. They both have their different characteristics along with their own pros & cons.

Types of Optical Isolator and their Working

An optical isolator, especially a Faraday isolator, is a device which transmits light in a certain direction while eliminating the back reflection and backscattering at any polarized state. It is generally categorized into two categories – Polarization Sensitive Optical Isolators and Polarization-Insensitive Optical Isolators. As I have already mentioned them as Faraday Isolators, it is obvious that they use the Faraday Effect of the Magneto-optical crystal. To know more about these isolators, let’s discuss the two types of optical isolators and how they work.

Polarization Sensitive Optical Isolators

These are the simplest Faraday Isolators which work only when the input beam has a guided linear polarization.

Working:

Their working is simple in which a polarized beam is passed through the first polarizer with minimum loss, then pass through 45 degree Faraday rotator and finally passed through the second polarizer with its transmitting axis being rotated by 45 degree in order to ensure that transmission losses are as low as possible.

When this light is reflected back to the output port with unmodified polarization state, it will fully pass through the output polarizer, but due to 45 degree rotated direction of polarization, the light will be blocked at the input polarizer or can be sent to separate output port. In case if the rotator’s rotation angle deviates from 45 degree due to any reason such as fabrication errors, the degree of isolation would be reduced. The problem is that we always need an isolator with high isolation which may be reduced in these kinds of isolators due to several reasons.

Polarization Insensitive Optical Isolators

A Polarization Insensitive Optical Isolator is the device which functions for arbitrary polarization of the input beam. As many fibers don’t maintain the polarization, such devices are often suitable and required in the context of fiber optics. Moreover, optical fiber communication systems are operated with arbitrary polarization state; so you need to use the Faraday Isolators and other components which can cope with undefined polarization state.

Principle:

The basic principle of PI optical isolator is to spatially separate the orthogonal polarization components of i/p beam with the help of a polarizer. Then, send them through Faraday rotator and combine the components again in the second polarizer.

The thing to note here is that polarization insensitive optical isolator doesn’t preserve the polarization state as there is an undefined relative phase change between the two components of polarization. This phase change is dependent on temperature and wavelength.

These isolators are widely used in telecommunication industry and various other applications in laser technology. They are characterized by high isolation, low insertion loss and excellent temperature stability. In the market, these isolators are available in various wavelengths and bandwidths. So, before making a purchase, clarify which specific isolator would be suitable for your use.

All You Need to Know About Fiber Optic System

There several types of passive optic components that are used in a modern day optical transmission system to help perform a number of functions. These components are divided into four categories-  branching devices such as couplers and splitters; connecting devices such as connectors and splices; performance-improving devices such as attenuators, polarizers, dispersion compensators, and isolators and; filtering devices such as fiber Bragg gratings, add/drop filters, and wavelength-division multiplexers (WDMs)/demultiplexers.

Polarization Maintaining Isolator
Polarization Maintaining Isolator

In a fiber optic system isolators have been playing a very important role. And on the other hand where all the passive components that reciprocal, isolators are opposite, they normally are nonreciprocal. They let the passage come through of the optical beam in the forward direction with negative losses and at the same time blocking the transmission in the backward direction with 40- to 70-dB losses.

Types of fiber optic isolators:

  • Polarization effect: a p-dependent isolator should be used if the extinction ratio is important for one. And it can be used with anything, either polarization-maintaining fiber or a regular single-mode fiber. But if the system lacks the polarization dependence, the obvious choice has to be the p-independent isolator.
  • Single-stage or dual-stage: there are two isolator modules in a single package of a dual stage fiber optic isolator allowing >55 dB of isolation. And in most of the applications, a single stage fiber optic provides the required amount of isolation. Dual-stage isolators only add to the cost of the process and bring in losses. A lot of manufacturers out there offer more than two in a single category. If you have a system that would require a lesser grade, it should be taken into consideration for saving yourself from the losses.
  • Wavelength: if you want to go for something that is lesser expensive and highly available then the obvious choice to go for would be standard telecommunications wavelengths of 1310 and 1550 nm. The more commonly available fiber-optic isolators for the visible and near-infrared portions of the spectrum are the ones that are bulky and far more expensive in comparison to the standard telecommunications type.
  • Reliability: until and unless your vendor is ready to provide you with a test report on reliability, make sure you always perform a few quality tests after getting the isolators. The easiest and the most important test that you can conduct is the temperature cycling test. You can use a freezer and a laboratory oven or a hot plate to let go the isolators through a few temperature cycles, in case the environmental chamber is not available. Once you are done with the temperature cycling test, also go for a quick check of measuring the important parameters at room temperature.
  • Termination: maybe it is necessary to use a frequent connection, but chances are it’s not, in these cases always use a fusion splice in place of connectors because the differences in performance in insertion loss and return loss are significant.
  • Price: you can do two important things and significantly save a lot of costs. Firstly, you should always stick to standard products. And secondly, if you want to combine two or three functions into one component, go ahead with hybrid components

Each and every optical system has its own set of requirements and buying a fiber optic isolator can be a very confusing task. So follow these thumb rules to buy yourself one and make your task a cake walk.

How effective is Polarization Maintaining (PM) Isolator?

Polarization Maintaining Isolator is also known as Fiber Optic Isolator which allows light to travel only in one direction. For any state of polarization, it minimizes the back reflection and back scattering in the reverse direction. It is a two port micro-optic device built with PM panda fiber. Polarization Maintaining Isolator is used widely in amplifier systems, fiber optic systems, and lasers. It prevents unwanted feedback into an optical oscillator and the device operations are dependent on the Faraday’s effect turn.

Polarization Maintaining Isolator
Polarization Maintaining Isolator

Faraday rotator is the main component of the optical isolator. The polarization dependent isolator mainly consists of 3 parts like an input polarizer, a Faraday rotator, and an output polarizer. The output polarizer is known as the analyser. Input polarizer vertically polarizes the light traveling in the forward direction. Using the analyser, the light traveling in the backward direction becomes polarized by 45°. The polarization dependent isolators are mainly used in free space optical systems as the polarization of source is maintained well by the system.

What are the devices in which the isolator is used?

PM isolator is used in communication systems, polarization maintaining fiber-optic amplifier and instrumentation applications. Also, the insulating system is used in CATV Fiberoptic Links, Fiberoptic System Testing and Fiberoptic LAN System.

Here are the best features of polarization maintaining optical isolator –

  • High Extinction Ratio
  • High Return Loss
  • High Isolator
  • Epoxy Free Optical Ratio
  • Low Insertion Loss

The light traveling in the forward direction is split by the input birefringent wedge into a vertical component which is called ordinary ray and a horizontal component is known as extraordinary ray. The rotator rotates both the o-ray and e-ray by 45°. Again the output birefringent wedge combines the two components. On either sides of the isolator, collimators are used and the beam is split & diverged in the isolated direction.

There are now companies who specialize in the manufacturing of the isolators for various applications. Based on the requirement of applications, isolators are manufactured precisely. Also, one can get the isolators online and the common PM Isolators available online are Polarization Maintaining Isolator 1310 & 1480 & 1550nm and Polarization Maintaining Tap Isolator 1310 & 1550nm.

Two Types Of Polarization Beam Combiners & Splitters

Polarizing Beam combiners / splitters are the devices used to combine two polarized light signals or split single non-polarized light into two polarized parts. These combiners and splitters are designed and developed to split light beams by deploying the polarization state and not by wavelength or intensity.

The polarizing beam splitters / combiners typically have 0° or 45° angle of incidence and a 90° division between the beams; this generally depends on the configuration. There are two types of Polarization beam combiners / splitters; these are described below:

  1. Incoherent Polarization Combining / Splitting

The Incoherent combining or splitting is the simpler variant and the basic technique. In this method, the resulted beams of two broad area laser diodes are sent onto a thin-film polarizer so as to reflect one of the beams while transmit the other; both of these beams then propagate in the same direction. As a result, one attains an unpolarized beam (with the combined optical power of the input beams) and the same beam quality. Consequently, the brightness gets nearly doubled.

This technique is often used for any-a-applications, for instance, end-pumping of a solid state laser with an increased power. However, the technique is not suitable for power scaling.

  1. Coherent Polarization Combining / Splitting

With coherent beam combining or splitting it is viable to attain a linear polarized state in the output, if two mutually coherent beams are combined. If two ports have the equal input powers, the output polarization would be typically rotated by 45° -depending on the polarization direction of any of the input beams.

Also, the coherent polarization combining can be repeated several times because of the linear output polarization. Thereby, this technique is suitable for power scaling.

A polarization beam combiner and splitter is often used in photonics instrumentation, optics and semiconductors to transmit p-polarized light while reflecting s-polarized light. These hold a world of worth when it comes to optics, telecommunication and fiber applications, and make the working effective as well as effortless.