Month: May 2022

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.   

Do Fiber Optic Cables Need Amplifiers?

Fiber optic cables are playing an essential role in creating highly reliable and high-performing optical communication systems and networks. When a signal propagates in a cable for a long distance, it becomes essential to install amplifiers in the network to prevent any distortion or weakening of the signal. In the same way, when light (or optical) signals travel in a fiber optic cable over a long distance, it also needs a fiber in-line amplifier to restore the strength of the light signal. Let’s learn about fiber optical amplifiers in detail.

What is a fiber optical amplifier?

A fiber optical amplifier is a special device that is specifically designed to boost (amplify) light-wave signals traveling across fiber optic cables without changing these signals into electrical form.

The use of optical amplifiers in optical fiber communication applications allows you to retain the optical integrity of the whole system.

What is the need for a fiber optical amplifier?

Wherever data is transmitted in the form of optical signals through a fiber cable, you need a fiber optical amplifier to preserve the strength of optical signals. Typically, when signals are sent from one end to another, then the quality and strength of the signal degrade due to various factors. If a fiber optical amplifier is not used and a degraded signal is sent to the other end, it becomes difficult or sometimes even impossible to regain the original information sent via that particular signal.

Since optical signals carry information in an optical communication network, the use of an electronic amplifier is not preferred; otherwise, some additional units will be needed to convert optical signals into electrical signals and then again need to convert the electrical signals into optical signals after amplification. This process is not only time-consuming but also makes the entire system more expensive and labor-intensive. Plus, data transmission will also be slower.

Therefore, fiber optical amplifiers are installed to amplify optical signals so that data signals can be transmitted at a faster rate and the integrity of data and information carried by signals remains intact.

In short, optical amplifiers allow you to transmit signals over long distances and at a faster rate without any attenuation or distortion.

Different Types of Optical Amplifiers

Optical amplifiers are usually categorized into three categories, namely:

  • Semiconductor amplifiers
  • Doped fiber amplifiers
  • Raman amplifiers

Among all these three amplifiers, doped fiber amplifiers are more commonly used in fiber communications, fiber laser, and fiber sensor applications. Abbreviated as DFA, the active medium of a doped fiber amplifier is created by doping silica core slightly with rare earth elements, usually erbium. Hence, doped fiber amplifiers are popularly known as erbium-doped fiber amplifiers (EDFA).

Sometimes, optical amplifiers are also used in long-distance optical communication networks, optical fiber distributed sensing, and fiber laser applications. These amplifiers are based on the principle of Raman scattering and don’t need the population inversion mechanism for amplification purposes. To amplify signals, these amplifiers utilize standard transmission fiber cables.

DK Photonics is a world-class optical passive component manufacturer based in China and its offerings also include high-quality and reliable fiber optical amplifiers that are widely acclaimed for achieving high gain and low noise amplification. For any queries related to fiber amplifier orders, please get in touch with us.

The Role of Optical Fibers in Fiber Optics Applications and PM Components

In this post, we will first explain what optical fiber is and its types in brief and then discuss the role of optical fibers in fiber optics applications and in PM components.

What is optical fiber?

An optical fiber is a thin, hollow, flexible, and transparent tube-like wire that is either made of glass or plastic and is designed to transmit light signals. It facilitates the transmission of optical signals over long distances and at higher bandwidth levels.

Types of Optical Fibers

  • Polarization-maintaining (PM) fibers
  • Single-mode fibers
  • Multi-mode fibers
  • Rare-earth-doped fibers
  • Highly nonlinear fibers
  • Hollow-core fibers
  • Multi-core fibers, and more

The Role of Optical Fibers and Their Importance

Fiber optics technology is based on the optical fibers that act as waveguides for light. Think of optical fibers as the fundamental part of fiber optics systems and fiber optics communication applications. Optical fibers carry light signals over long distances which enable engineers to transmit information faster, quicker, and in a more reliable way.

They are intrinsically safe as no electrical signals are involved in transferring data (data is transferred via light). When it comes to bandwidth, no current technology is better than optical fibers as they provide more bandwidth and carry more data than copper cables of the same diameter.

Their performance is not restricted by the cable itself but by the electronic components that constitute the system. The use of optical fibers also leads to a decrease in latency, makes data interception incredibly difficult, and can withstand water and temperature fluctuations. What’s more, they don’t produce any electromagnetic interference.

Thus, the use of optical fibers has literally improved the quality, performance, security, and handling capability of data transmission. That’s what makes optical fibers perfect for fiber optics communication.

If we talk particularly about PM optical fibers, they are used in special applications, such as fiber optic sensing, slab dielectric waveguides, interferometry, fiber optics communication, polarization-sensitive systems, and more where it is a requirement to maintain the polarization state of the incoming signal.

Did you know that optical fibers are also used to connect many fiber-optic elements?

While some fiber optic elements are typically made of fibers, other elements are made of different materials but are coupled to fibers. Here are a few examples of PM components:

  • PM couplers that are used to combine light coming from different sources into one fiber
  • Fiber Bragg gratings that are used as wavelength-selective reflectors in telecom and WDM applications
  • Fiber collimators that can launch a collimated beam into a fiber
  • Optical isolators, rotators, and circulators that are used for manipulations depending on beam polarization

Most PM components use PM optical fibers in one way or another; they are either made of PM optical fibers or are connected using PM fibers.

By now, we hope you understand the need for optical fibers in the industry and their importance.

PM Isolator, Coupler, and Circulator- The 3 Important Polarization Maintaining Components

With time, the need for Polarization Maintaining Components is increasing in telecommunications and other related industries. And it’s because Polarization Maintaining Components make the process easy for these industries and deliver quality results. 

Years ago, only a few components were available. Manufacturers were not so aware and even the industry owners were not so keen. Things were going in the right direction with the limited Polarization Maintaining Components. But, today, things have changed and there are many Polarization Maintaining Components in the market, making the functioning and process easier for the industry owners. 

Products are many but some are commonly needed by the industry owners. A few names in this list are PM isolator, PM Coupler, and PM Circulator. In this post, we will discuss these Polarization Maintaining Components. 

PM isolator

In every PM isolator, you will find an optical fiber inside. The fiber inside is a thin strand made of pure glass. The isolator or the optical fiber inside it works on the “total internal reflection” principle. It acts as a guide for the light wave over long distances. The working of a PM isolator is very effective when the light waves try to pass between varying media. 

A PM isolator is used in different applications but majorly, it is used in communication systems, instrumentation applications, and polarization-maintaining fiber-optic amplifiers. Other than this, the PM isolator is used in fiberoptic system testing and fiber-optic LAN system, and CATV fiberoptic links. 

PM coupler

It’s a device used for combining or coupling light from two or more input fibers into one output fiber. The PM coupler consists of an input section at one end and an output section at another end. Simple to understand, a PM coupler converts input light from different fibers to a single output fiber. The process becomes simple. 

The biggest advantage of the PM coupler is that its output section comprises an optical fiber, which can be made in appropriate lengths and easily tapered. Due to this, this component can be used in two separate functional units. Other than this, a PM coupler has higher longevity and is affordable to all users. 

PM circulator

The role of a PM circulator is to separate optical power traveling in opposite directions in one optical fiber. Also, it is used to achieve bi-directional transmission over a single fiber. The PM circulator is highly suitable for use in advanced communication systems and fiber-optical sensor systems because of the high isolation between the input and reflected optical power and low insertion loss. 

Other than this, a PM circulator provides high reliability and excellent optical performance. This is why it is a Polarization Maintaining Component in telecommunications, fiber optic sensing, bio-medical, and photonics research. 

Contact DK Photonics to buy Polarization Maintaining Component

We are one of the leading manufacturers of Polarization Maintaining Components globally. We follow a strict manufacturing princess with advanced production equipment in an excellent production environment. This is why you will get good quality products with quick delivery. The best part is we customize the components on demand. 

What are the differences between Circular, Isolator, & Rotator?

Today, we will discuss three different optical passive components, namely circulator & isolator & rotator. We will first talk about what these components exactly are and then share what makes them different from each other. So, if you are curious to know about these little yet important optical passive components, read the blog till the end.

Circulator & Isolator & Rotator

As we are discussing specifically optical passive components, you will learn here about optical circulators, optical isolators, and optical rotators rather than their electronic counterparts.

What is an optical circulator?

An optical circulator is a high-performance light-wave component that is designed to route the incoming light signals from Port 1 to Port 2 and the incoming light signals from Port 2 to Port 3. In short, it is designed such that the light coming from one port exits from the next port. While some circulators are three-port devices, there are also four-port circulators.

What is an optical isolator?

Also known as an optical diode, an optical isolator is an optical passive component that allows the light to travel in only one direction. Its main component is the Faraday rotator which ensures non-reciprocal rotation while maintaining linear polarization.

The polarization rotation caused by the Faraday rotator always remains in the same relative direction. It means that the rotation is positive 45 degrees in the forward direction and negative 45 degrees in the reverse direction. It happens because of the change in the relative magnetic field direction, positive one way, and negative the other way. Hence, it adds to the total of 90 degrees when light travels in the forward direction and then the same in the backward direction. This is what makes it possible to achieve higher isolation. 

What is an optical rotator?

An optical rotator is typically an in-line Faraday rotator that is designed to rotate the polarization of the input light by 45 degrees. This rotator is used for amplitude modulation of light and is an integral part of optical isolators and optical circulators.

Circulators vs. Isolators vs. Rotators

Difference between an Optical Circulator & Isolator & Rotator

An optical circulator is used to route the incoming light signals from port 1 to port 2 in a way that if some of the emitted light is reflected back to the circulator, it doesn’t exit from port 1 but from port 3. Thus, it wouldn’t be wrong to say that its function is analogous to electronic circulators.

In other words, fiber optic circulators are highly desirable where there is a need to separate optical signals that travel in opposite directions in an optical fiber.

On the contrary, an optical isolator is widely used in all those fiber optic applications where there is a need to prevent unwanted feedback into an optical oscillator, such as a laser cavity.

On the other hand,the main purpose of using an optical rotator is to achieve higher isolation, low insertion loss, high extinction ratio, and high return loss in optical devices such as optical circulators and isolators. As mentioned, they also help ensure non-reciprocal rotation while maintaining linear polarization.

DK Photonics is the leading China-based manufacturer of optical passive components, including regular and high-power optical circulators, isolators, & rotators. If you need optical passive components for your projects and want some guidance, please feel free to connect with us.