UPC vs. APC Connectors: Differences, Signal Loss, and Applications

On this page:

• 1. Differences Between UPC and APC Connectors
  • APC (Angled Physical Contact) Polishing
  • UPC (Ultra Physical Contact) Polishing
• 2. Does APC or UPC Have Lower Loss?
• 3. Connector Compatibility: Can UPC and APC Be Mixed?

When transmitting a signal through fiber optics, attenuation and reflections occur. Attenuation is caused by signal losses in the fiber optic cable itself, at fusion splices, connectors, splitters, and other passive components.

Lower attenuation allows the use of less powerful and, consequently, more cost-effective optical transmission and reception equipment. Additionally, under equal conditions, attenuation directly impacts the transmission distance without errors. For connectors, attenuation and signal reflection primarily occur due to small gaps between the ferrules.

Reflections also negatively affect signal quality, especially return loss, where the signal is reflected back to the transmitter. This phenomenon leads to bit errors, reduced data transmission speed, and overheating of SFP modules. To minimize losses and reflections, different types of polishing are used in fiber optic networks, with UPC and APC being the most common.

Differences Between UPC and APC Connectors

To understand the UPC vs. APC differences, let's examine their appearance, loss reduction mechanisms, and areas of application.

APC (Angled Physical Contact) Polishing

APC connectors feature an 8-9 degree angled ferrule end-face. This design ensures that reflected signals do not return directly to the transmitter or return with significantly reduced power, minimizing the negative impact of reflections.

Key Characteristics of APC Connectors:

• Return loss: -60 dB
• Higher cost compared to other connector types
• Green connector housing for easy identification
• Angled ferrule, visibly slanted under close inspection
• Factory-assembled patch cords required – DIY assembly is nearly impossible

Where APC Polishing is Used:

APC connectors are ideal for networks that demand high signal quality and involve high-power transmissions, such as:

• PON (Passive Optical Networks)
• Cable TV (CATV) systems
• Video transmission over fiber optics

UPC (Ultra Physical Contact) Polishing

UPC connectors are polished using precise machine-based technology, ensuring a controlled spherical ferrule shape without an angle. While the reflected signal returns to the transmitter, it has significantly reduced power compared to standard PC or SPC polishing.

Key Characteristics of UPC Connectors:

• Return loss: -50 dB
• More affordable than APC connectors
• Blue connector housing for identification
• Visually smooth ferrule surface, no visible angular cut
• Commonly found in pre-terminated pigtails and patch cords

Where UPC Polishing is Used:

UPC connectors are commonly used in high-speed optical networks where minimizing loss is critical, such as:

• FTTH (Fiber to the Home)
• Data centers
• Enterprise and backbone networks

Does APC or UPC Have Lower Loss?

In terms of insertion loss, there is no significant difference between APC and UPC. Both provide:

• Nominal loss: ~0.2 dB
• Maximum allowable loss: ~0.4 dB

However, the key distinction lies in return loss (reflectance). APC performs better in applications sensitive to reflections, such as video transmission and PON networks.

Connector Compatibility: Can UPC and APC Be Mixed?

• UPC connectors are compatible with PC and SPC connectors.
• APC and UPC connectors are NOT compatible with each other.
• Attempting to connect an APC and UPC connector may damage the ferrules and lead to increased signal loss and reflections.

For best performance, always match connector types according to your network’s requirements. If low reflections and high transmission quality are priorities, APC is the preferred choice. For general high-speed data networks, UPC is often sufficient.