Day: March 6, 2019

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.

All about In-line Polarizer, Types, and Other Supportive Component

The in-line polarizer is a micro-optic device typically used to convert unpolarized light into polarized one including high extinction ration in the case. It is effectively used to enhance the signal’s extinction ration. A good quality in-line polarizer offers a high extinction ratio, high return loss, low insertion loss, and absolute environmental reliability and stability. It is ideally used in high-speed communication systems and applications like test instrumentation.

There’re two most common types of the in-line polarizer – Pigtail and No-tail.

Pigtail vs. No-tail:

In the pigtail version of the in-line polarizer, input/output fibers are attached to the package, whereas no-tail version often comes with two fiber connectors mounted straight on the package. No-tail version is best for applications where there’s no need for extra fiber length and a number of fiber jumpers/connections are already in the system.

The pigtailed polarizers are best used for fiber systems requiring optical components spliced to the networks or extra fiber is required to fill the gap between the lengths. This version of polarizer provides a great level of flexibility in device mounting and installation. The typical pigtail length is 1 to 2 meters on each side. The diameter of fiber buffer or jacket can be specified by an individual while discussing the requirements with an in-line polarizer manufacturer.

Pigtail fiber type

The pigtailed in-line polarizers have input/output fiber in three types of combinations:

  • SM/SM – Single mode to single mode
  • SM/PM – Single mode to polarization maintaining fiber
  • PM/PM – Polarization maintaining to polarization maintaining fiber

SM/SM fiber pigtailed polarizer works bi-directionally. The input and output ports are exchangeable except if the client determines a special combination of connectors.

SM/PM fiber pigtailed polarizer has the transmission hub of the polarizer adjusted to the slow axes of the polarization maintaining fiber. The output PM fiber is additionally keyed to the slow axes at the connector. Both the fibers are typically marked as ‘SM’ and ‘PM’ before shipment.

PM/PM fiber pigtailed in-line polarizer has (similar to SM/PM) polarizer transmission hub adjusted to the slow axes of both PM fibers. In spite of the fact that the PM/PM in-line polarizer is also bi-directional, it is often advised that client connects the device as indicated by the predetermined input and out directions in order to achieve the best extinction ration. They are also marked before shipment.

Fiber connectors

As per a client’s specification’s fiber connectors can either be SC/PC, FC/PC or FC/APC. Fiber connectors should always be cleaned with the help of fiber connector cleaning techniques followed as per the industry standard.

Following are some in-line polarizer applications

  • Fiber Amplifiers
  • Fiber lasers
  • Fiber Sensor
  • Test and Measurement
  • Communications System

Some of the top features which are common with every polarizer

  • Low Insertion Loss
  • High Power Handling
  • High Extinction Ratio
  • Low Cost
  • High Reliability

You can also add one or more features according to your requirements. In addition, it is advised to choose a trusted supplier who has been providing quality polarizers and other fiber optic products for a long time in your country.

Know about major uses and benefits of optical isolators!!

An optical isolator is mainly a passive magneto-optic device that makes the traveling of light unidirectional. The operation of the isolator is usually based on the Faraday Effect.

Optical Isolators can generally be categorized into two main polarizations including polarization-independent isolators as well as polarization-dependent isolators. While Polarization-dependent isolators utilize output and input polarizers along with a Faraday rotator, the Polarization-independent isolators use output and input birefringent wedges including a Faraday rotator.

Uses of Polarization Insensitive Optical Isolator   

Optical isolators are used in many applications, including laser applications where they are mainly utilized to prevent unwanted feedback into the laser source. This feature helps in not affecting the coherence of the laser while affecting any potential damage to the diode as the feedback is capable of frequency noise, shift, amplitude fluctuation or mode hopping.

Thus, it is one of the key devices in order to gain a stable laser diode operation. In situations where there are high-speed optical fiber transmittance amplifiers as well as routes, optical isolators are also considered indispensable devices due to their major capability of removing the adverse impact of return beams of light. They can also be called as photocouplers, optoisolators, and optocouplers.

Apart from these, there are many more uses of Polarization Isensitive Optical Isolators that makes them an important element for traveling the light from one direction to another.

Some of the major uses are provided below:

  1. They are used as a part of wavelength division multiplex systems (WDM), optical time area reflect meters, fiber intensification frameworks, and also as an important instrument for a test.
  2. Optical circulators are also largely utilized for converting or transforming the current unidirectional fiber optic communication link. They certainly change the communication link to a duplex link by installing the circulators at each finish of the polarization optical circulator.

Besides these important uses, the optical circulators also have several amazing benefits that make its utilization more important and necessary for traveling of light. The major benefits stated below are the ones that make the use of the optical circulators even more beneficial.

  1. Though the polarization Isensitive Optical Isolators are costly, they are more durable and reliable as compared to other circulators which are available in the market.
  2. Optical isolators are a good sensitive receiver and also they have better performance than the other ones.
  3. They are a better amplifier and are stronger than other isolators.
  4. When it comes to the final performance of optical circulators, polarization Isensitive optical isolators are far better and are more powerful in their workings.
  5. All the elements included in the optical isolators are aligned to a single platform that eliminates the use of several connectors and external ports.

Last but not least, you must also note that these isolators are the ones which are largely being accepted and used in various industries and streams.