Variable vs. Passive Delay Lines: Comparing the Many Different Radio over Fiber Network Solutions

In a world filled with digital data, it’s no wonder that companies are looking for ways to transport this information wirelessly. Radio over fiber (ROF) networks provide a solution for transmitting radio signals over an optical fiber link. There are two main types of ROF systems: variable delay lines and passive delay lines. This blog post will compare and contrast these two types of systems to see which is best suited for your needs.

What are Variable Delay Lines?

A variable delay line is a device that can introduce a tunable delay into a signal. Variable delay lines are used in many different applications, including telecommunications, audio processing, and radar.

There are several different types of variable delay lines, each with its own advantages and disadvantages. The most common type of variable delay line is the electro-optic delay line, which uses an electro-optic material to introduce a tunable delay into a light signal. Electro-optic materials have a very high speed of light propagation, making them ideal for use in high-speed telecommunications applications. However, electro-optic materials are also very expensive, making them less suitable for use in commercial applications.

Another type of variable delay line is the acousto-optic delay line, which uses sound waves to introduce a tunable delay into a light signal. Acousto-optic materials have a lower speed of light propagation than electro-optic materials, but they are much less expensive. Acousto-optic materials are, therefore, more suitable for use in commercial applications.

The choice of variable delay line depends on the specific application requirements. For high-speed telecommunications applications, electro-optic delay lines are typically used. For commercial applications, acousto-optic delay lines are usually used.

variable delay line

What are Passive Delay Lines?

Passive delay lines are used to create a time delay in an electrical signal. The delay is created by the length of the transmission line, and the amount of delay can be controlled by changing the length of the line. Passive delay lines are often used in radio over fiber networks, where they can create a variable delay between the different signals in the network. This allows the network to be tuned to specific frequencies and to create custom waveforms.

Passive delay lines have several advantages over active delay lines. They are much simpler in design and do not require any power to operate. This makes them much cheaper to manufacture and more reliable. In addition, passive delay lines can be used to create very long delays, making them ideal for applications such as radio over fiber networks. 

There are a few disadvantages to passive delay lines. The main disadvantage is that they are limited in the amount of delay they can create. This means that they may only be suitable for some applications. In addition, passive delay lines are more susceptible to noise and interference than active delay lines.

The Pros and Cons of each kind of delay line

Several types of delay lines are used in radio over fiber (RoF) networks, each with its own advantages and disadvantages. Here, let’s compare the most common types of delay lines used in RoF networks: variable vs. passive.

Variable Delay Lines:


– Can be easily adjusted to change the overall length of the delay line

– Do not introduce excess noise or distortion into the signal


– More expensive than passive delay lines

– Require more power

Passive Delay Lines:


– Cheaper than variable delay lines

– Do not require power to operate

– Introduce minimal noise and distortion into the signal compared to other types of delay lines (e.g., active). 


– Cannot be easily adjusted once installed

– Length of the delay line is fixed

Which type of delay line is best for your Radio over Fiber network?

Many types of delay lines are available for Radio over Fiber networks. Each type of delay line has its own advantages and disadvantages. Your network’s best type of delay line will depend on your specific needs and requirements.

Passive delay lines are typically the most affordable option. However, they can be more challenging to install and configure. Additionally, passive delay lines can introduce additional noise into the system.

Variable delay lines offer a more flexible solution but can be more expensive. Variable delay lines also require more power than passive delay lines.

Consider a passive delay line if you’re looking for a reliable and efficient solution for your network. After reading this, you should understand the differences between variable and passive delay lines. While both have their advantages, passive delay lines tend to be more versatile and offer more benefits for radio over fiber networks.