Author: Fiber-MART.COM

Since several years, Polarization Maintaining Optical Circulator has become an important element in the optical communication system. But these days, its applications have expanded not only in the telecommunication field but also in imaging and medical field.

To begin with, let’s discuss what exactly is an optical circulator?

An optical circulator is mainly a multiple port non-reciprocal passive component. Its function is just similar to that of a microwave circulator, i.e. to transmit the light wave from one port to other with maximum intensity. But, at the same time, it also blocks any light transmission from one port to its previous port. Besides, the entire optical circulator process is based on the non-reciprocal polarization of the Faraday Effect.

What are the features of Polarization Maintaining Optical Circulator?

There are various features of polarization maintaining optical circulator. Mentioned below are a few major ones:

–    It has a high stability

–    It has a low insertion loss

–    It has high reliability

–    It has high optical return loss and so on.

How can optical circulators be categorized?

Optical circulators typically can be categorized into two main streams namely:

–    Polarization-dependent optical circulator, and

–    Polarization independent optical circulator

Polarization-dependent optical circulator is functional only for a light wave with a specific polarization state. This type of optical circulator is used only in some of the applications that mainly include free space communication between crystal sensing and satellites. Whereas the polarization independent optical circulator is independent of the polarization state of light. In the ordinary circulators, the polarization is certainly not maintained, however, there are polarization maintaining optical circulators available, so they can be used on behalf of it.

Besides, they can also be utilized in a wide variety of applications, but depending on its functionality, optical circulators may be divided into two groups:

–    Quasi circulator: In this circulator, the light passes through all the multiple ports, but the light from the last port is lost.

–    Full circulator: In this circulator, the light passes through all the multiple ports in a full circle.

When it comes to circulator’s design, there are many variations, but, all the non-reciprocal rotation designs certainly share the same structure with at least three functional elements namely- non-reciprocal polarization rotation elements, polarization recombining, and splitting elements, as well as polarization dependent beam steering elements.

Finally, we can say that with the large development of advanced optical networks and elements, the application of optical circulators are rapidly growing and new and advanced applications and functionalities are emerging quickly.

Since 1990, polarization maintaining optical circulator has become one of the essential components in advanced optical communication systems. Nowadays, its applications have expanded widely not only in telecommunication industry but also in medical and imaging fields. Here, we will discuss this indispensable component in detail. So, let’s start with the basics.

What is a PM Optical Circulator?

PM optical circulator is a three or four port non reciprocal passive component which functions similar to an isolator. It transmits the light wave from one port to next port with maximum intensity while maintaining polarization and blocking any light transmission from one port to the previous port. Thus, it is also featured as a unidirectional circulator.

Technology Used in PM Optical Circulators

Polarization Maintaining Optical Circulators are designed on the basis of nonreciprocal polarization rotation of the Faraday effect. As the working of optical circulators is based on several components such as Faraday rotator, birefringent crystal, waveplate and beam displacer, let’s take a quick look at each of them.

Faraday Effect:

It is a magneto-optical effect which explains the phenomenon in which polarization plane of electromagnetic wave (or light wave) is rotated inside a material under magnetic field applied in parallel to the direction of wave propagation. The unique aspect of this effect is that the direction of rotation is independent of the propagation direction of light wave, which implies that rotation is non-reciprocal.

Light Propagation in Birefringent Crystal:

Birefringent crystal is a common material used in the designing of optical circulators. The crystals used in optical circulators are typically anisotropic uniaxial which means they have two refractive indices with one optical axis. The function of this birefringent crystal depends on the propagation direction of light and its optic axis orientation (crystal cutting). The crystals which are generally used include quartz, rutile, YVO4, etc.

Waveplate:

Also called retardation plate, a waveplate is one of the applications of birefringent crystal. It is made by cutting a crystal into a particular orientation. Due to small birefringence, crystal quartz is broadly used for making waveplates.

Beam Displacer:

A birefringent crystal based beam displacer is used to split an incoming light beam into two beams with orthogonal polarization states.

Categorization of Optical Circulators

Optical circulators are mainly divided into two categories:

Polarization-dependent optical circulator

Polarization-independent optical circulator

The former type is only functional for a light wave with a particular polarization state and is only used in a few applications such as free space communications between satellites and crystal sensing.

On the other hand, the latter type is functionally independent of the polarization state of light. While in ordinary circulators, the polarization is not maintained but there are polarization maintaining optical circulators available in the market also. They are used in a large variety of applications.

According to their functionality, optical circulators can also be divided into two groups.

Full Circulator – light passes through all ports in a full circle

Quasi Circulator – light passes through all ports but the light from last port is lost

Fortunately, due to the advancement in technology, you can avail highly reliable and efficient Polarization Maintaining Optical circulators not only in standard specifications but in customized specifications too.

Optical fiber is used for an electric device in which light polarization is required. And each fiber is designed to do a certain job and so is suitable for some certain applications. So you should have the knowledge of an optical fiber that you want to buy and make sure the fiber you want to buy would be perfect for your need. So we have gathered some crucial information about optical circulator used for maintaining light polarization, and that will help you choose the right fiber.

If you are looking for a circulator for devices like fiber amplifiers, fiber sensors, test and measurement appliances, coherent detecting appliances, the 1310nm&1550nm 3-port Polarization Maintaining Optical Circulator with both axis working would be the best choice. The circulator is compact and very efficient to route the incoming signals from Port 1 to Port 2, and incoming Port 2 signals to Port 3. The circulator works as a single that can be used to transmit light from an input fiber to an output fiber. It directs the light returning from the output fiber to the third port. The 3 port circulator with both axis working is like an isolator that protects the input fiber from return power but the light that is rejected can be used.

Another fiber can be also used for those applications is 3 port optic circulator with fast axis blocked. This type of circulator is also lightweight, compact and performs well. This circulator also works as the circulator (with both axis working) does. Both circulators used for maintaining polarization can handle the power ranging from 300mW to 20 W, and have center operating wavelengths ranging from 850nm to 1650nm.

Both optical circulators (with both axis working and with fast axis blocked) provide a host of benefits such as low insertion loss, high isolations, etc. Here are some key benefits that the circulator provides:

Low Insertion Loss

High Isolation

High Extinction Ratio

Low Cost

High Stability & Reliability

Apart from those two circulators that are widely used for a wide range of applications, there are other optical fibers that are used for electric devices. Whatever fiber you buy make sure it works perfectly with your device.

So before you start looking for optical fibers, get to know about your device in details. Learn everything that can help you in a way or so to decide on which type of optic fiber you should look for.

Once you are done with the type of fiber you need, find a Polarization Maintaining Optical Circulator supplier. There are many Polarization Maintaining Optical Circulator suppliers in China, you should trust only those that are reputed and have long been into the business.

The polarization maintaining (PM) tap coupler basically provides optical signal splitting with tap ratio while also preserving the exact state of polarization. By combining the PM collimators and thin-film filter technology, the polarization maintaining coupler features high return loss, low insertion loss, environmental stability, and high extinction ratio.

The PM tap coupler splits the light coming from the input PM fiber into two outputs PM fibers. The polarization state further can be aligned with the fast axis or the slow axis of the polarization maintaining fibers. The stainless steel and rugged tap coupler are mainly designed for stability as well as high optical performance. The device with split ratios from 1 to 50% is now available so you can utilize it accordingly to your needs.

Some major applications of polarization maintaining tap coupler:

There are various applications of PM tap coupler, among which the major ones include:

Monitoring signal in polarization maintaining fiber systems

Fiber sensors

Helps in power-sharing of polarization-sensitive devices and systems

Polarization maintaining interferometers

Fiber optic devices and instruments

Coherent detection

Polarization maintaining tap couplers are made of separate crystals of lights and the output port of lights emitted is different from the polarization filter coupler. The coupling ratio is more accurate, while it can also handle high power as compared to the PM filter couplers.

On the other hand, the PM couplers can also be used to split high power linearly polarized light into different paths and that too without disturbing the state of polarization (SOP). Furthermore, it can even be used as a power tap for monitoring the signal power in the PM fiber system that functions without perturbing the linear state of polarization (SOP) of light in the polarization maintaining fiber.

Features of polarization maintaining tap coupler:

Some of the major features of PM tap couplers include:

Low insertion loss

Compact inline package device

High stability power

Can handle high energy and power

The optimum optical performance in a different environment

Excellent credibility

High extinction ratio

Accurate tap ratio

Accurate coupling ratio

So, these are a few primary features and applications of polarization maintaining tap couplers that you must be aware of. Besides, if you have the requirement of this device or any other type of PM coupler with tailored specifications then you may simply talk to PM coupler manufacturers and get the best assistance for the same. Just be sure to consult the right manufacturer so you can be confident that you are investing your money and time on the right device and at the right place.