Cross-polarization in fiber optic cable

Could Cross-Polarization Be the Reason For Your Slow Internet? Decoding the Future of Optical Communication

Jordan Keane in Tech & Innovation August 2025 • 5 min read.

"Explore how Cross-Polarization hinders advanced optical systems and how innovative CPDM-QPSK technology can pave the way for faster, reliable internet."

In our increasingly connected world, the demand for faster and more reliable internet speeds is ever-growing. From streaming high-definition videos to participating in real-time video conferences, our daily lives depend on robust data transmission. Coherent optical communication has emerged as a promising solution, offering gigabit fiber optic transmission suitable for multimedia internet and data services.

One particularly interesting approach is homodyne coherent detection using circular polarization division multiplexing (CPDM), coupled with advanced digital signal processing (DSP). This method has shown the potential to deliver faster data rates and higher spectral efficiency, effectively mitigating fiber-related dispersive effects. With spectral efficiency reaching up to 3.2 bits/Hz, CPDM promises a significant leap forward in optical communication technology.

However, like all technologies, CPDM faces its own set of challenges. One significant hurdle is its sensitivity to phase and State of Polarization (SOP) of the incoming signal. This sensitivity makes coherent systems more complex than Intensity Modulation Direct Detection (IMDD) systems, primarily due to the intricate circuitry required for tunable narrow linewidth local oscillators, which are essential for optimal performance. In long-haul, multi-gigabit optical transmission systems based on traditional single-mode fiber optic (SMF), factors such as polarization mode dispersion (PMD), self-phase modulation, cross-phase modulation, and four-wave mixing can limit performance. These factors arise from slight birefringence caused by internal manufacturing defects and atmospheric turbulence, impacting signal quality over distance.

What is Cross-Polarization and Why Does It Matter for Your Internet Speed?

In optical fibers, light doesn't travel in a perfectly straight line. Imperfections in the fiber and external factors can cause the polarization of light to rotate randomly. When this rotation occurs, a phenomenon known as cross-polarization (XPol) arises, leading to signal interference or crosstalk between different channels. This crosstalk can significantly degrade the quality of the signal, leading to higher bit error rates (BER) and reduced system performance.

Imagine you're trying to listen to your favorite song, but someone nearby is playing a different song at the same time. The two songs interfere with each other, making it difficult to hear either one clearly. Cross-polarization in optical fibers is similar, causing interference between data channels and resulting in a less clear, less reliable signal.

Reduced Signal Quality: Cross-polarization introduces noise and interference, making it harder to distinguish the original signal.
Increased Bit Error Rate (BER): Higher BER means more errors in the data being transmitted, leading to slower speeds and potential data loss.
Power Penalties: To overcome the effects of cross-polarization, systems may require more power, reducing energy efficiency and increasing operational costs.
System Complexity: Mitigating cross-polarization requires sophisticated techniques and equipment, adding to the complexity and cost of optical communication systems.

Researchers have been working diligently to find ways to mitigate the effects of cross-polarization and improve the performance of coherent optical communication systems. One promising approach involves the use of Circular Polarization Division Multiplexing Quadrature Phase Shift Keying (CPDM-QPSK) with homodyne coherent detection. This technique aims to minimize the impact of XPol-induced crosstalk, ensuring higher data rates and more reliable transmission.

The Future of Faster, More Reliable Internet

While challenges remain, the development and refinement of technologies like CPDM-QPSK hold great promise for the future of optical communication. By addressing the issues caused by cross-polarization and other limiting factors, we can pave the way for faster, more reliable internet connections that support our ever-increasing demand for bandwidth. As research continues and new innovations emerge, the potential for optical communication to transform our digital lives remains vast and exciting.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1109/ic4me2.2018.8465664, Alternate LINK

Title: Performance Of A Cpdm-Qpsk Coherent Homodyne Optical Transmission System Due To Cross Polarization Effects

Journal: 2018 International Conference on Computer, Communication, Chemical, Material and Electronic Engineering (IC4ME2)

Publisher: IEEE

Authors: A. K. M. Sharoar Jahan Choyon, S M Raiyan Chowdhury, Satya Prasad Majumder

Published: 2018-02-01

Everything You Need To Know

What is Cross-Polarization (XPol), and why does it negatively impact internet speed?

Cross-polarization (XPol) arises when the polarization of light rotates randomly within optical fibers due to imperfections and external factors. This leads to signal interference, also known as crosstalk, between different channels. This crosstalk degrades the quality of the signal, increasing bit error rates (BER) and reducing overall system performance. Addressing Cross-polarization is important because it reduces signal quality, increases bit error rates and requires higher power which in turn increases operational costs.

What is Circular Polarization Division Multiplexing Quadrature Phase Shift Keying (CPDM-QPSK), and how does it improve data transmission?

CPDM-QPSK, or Circular Polarization Division Multiplexing Quadrature Phase Shift Keying, is a technique used with homodyne coherent detection to minimize the impact of cross-polarization-induced crosstalk in optical communication systems. It aims to ensure higher data rates and more reliable data transmission. While effective, CPDM-QPSK systems are sensitive to phase and State of Polarization (SOP) of the incoming signal, making them more complex than Intensity Modulation Direct Detection (IMDD) systems.

What benefits does homodyne coherent detection offer in the realm of optical communication?

Homodyne coherent detection using circular polarization division multiplexing (CPDM), coupled with advanced digital signal processing (DSP) offers potential to deliver faster data rates and higher spectral efficiency, effectively mitigating fiber-related dispersive effects. With spectral efficiency reaching up to 3.2 bits/Hz, CPDM promises a significant leap forward in optical communication technology.

What factors, aside from cross-polarization, can limit the performance of optical transmission systems?

Several factors limit the performance of long-haul, multi-gigabit optical transmission systems based on traditional single-mode fiber optic (SMF). These include polarization mode dispersion (PMD), self-phase modulation, cross-phase modulation, and four-wave mixing. These impairments arise from slight birefringence caused by internal manufacturing defects and atmospheric turbulence, affecting signal quality over distance. These issues must be addressed to enhance the reliability of optical communication.

How can Cross-polarization be mitigated and what are the drawbacks of this approach?

Cross-polarization can be mitigated through advanced technologies like Circular Polarization Division Multiplexing Quadrature Phase Shift Keying (CPDM-QPSK). This method minimizes XPol-induced crosstalk, thus ensuring higher data rates and more reliable transmission. However, mitigating cross-polarization often requires sophisticated techniques and equipment, which can add to the complexity and cost of optical communication systems.