Multimode vs. Polyimide: Fiber Selection – How 50/125 or 62.5/125 Affects Your Sensing Bandwidth

When selecting optical fibers for extreme environments, engineers usually focus on temperature resistance (such as the +350°C limit of OFSCN® 300°C Polyimide Fiber) and coating protection (Polyimide or Carbon). However, for Multimode Fiber (MM Fiber), a crucial yet often overlooked factor is the core size: the two main specifications are 50/125 µm and 62.5/125 µm.

[Beijing Dacheng Yongsheng Technology Co., Ltd. (DCYS)] is committed to providing extreme environment solutions tailored to your specific needs. This article will deeply analyze the difference between these two multimode core sizes and how they impact your sensing bandwidth and system compatibility in harsh environments.

I. The Core Difference: Numerical Aperture and Bandwidth

Multimode Fiber (MM) allows multiple light rays (modes) to transmit simultaneously within the core. Its advantage lies in easier light source coupling, but its drawback is that intermodal dispersion limits transmission distance and speed.

Specification Name	Core/Cladding Size (µm)	Numerical Aperture (NA)	Intermodal Dispersion (Bandwidth)
OM2 / OM3 / OM4	50/125	Typically 0.20	High Bandwidth (Suitable for Gigabit/10 Gigabit Ethernet)
FDDI / OM1	62.5/125	Typically 0.275	Lower Bandwidth (Suitable for shorter distances or slower applications)

1. Core Size and Coupling Efficiency

• 62.5/125 µm: Features a larger core and usually a higher Numerical Aperture (NA). This means it can collect and accept more optical power.
  • Advantage: Ideal for sensing or communication systems using low-cost, incoherent light sources like LEDs, offering high coupling efficiency and greater alignment tolerance.
  • Applicable Scenarios: Scenarios where bandwidth requirements are low but demands for optical power reception or system simplicity are high.
• 50/125 µm: Features a smaller core and lower Numerical Aperture.
  • Advantage: Lower intermodal dispersion, allowing it to support higher transmission speeds and longer distances.
  • Applicable Scenarios: Systems requiring high-speed data transmission (such as 10G or higher) or high-precision fiber optic temperature sensing that requires a narrower light source.

2. Core Size and Sensing Bandwidth

For data communication, "bandwidth" refers to the supported data rate. However, in Distributed Fiber Optic Sensing (DOFS), "bandwidth" can be understood as the comprehensive capability relating to effective sensing distance and response speed.

• Pursuing Long-Distance Sensing: If your sensing system needs to cover several kilometers, 50/125 µm is likely the better choice. Although it couples less optical power, the signal is maintained better over long distances due to less intermodal dispersion, allowing the system to achieve a longer unrepeated sensing range.
• Alignment Difficulty and Field Maintenance: Splicing and connecting fibers in downhole oil/gas or industrial sites is challenging. The larger core of 62.5/125 µm makes field alignment less difficult, simplifying maintenance and troubleshooting.

II. Selection Principles for Polyimide Fiber

The OFSCN® 300°C Polyimide Multimode Fiber is available in both 50/125 µm and 62.5/125 µm specifications to adapt to different engineering requirements.

Selection Requirement	Recommended Specification	Reason for Recommendation
High Bandwidth/Long-Distance Transmission	50/125 µm	Lower intermodal dispersion, better suited for high-precision distributed sensing or systems needing 10G communication support.
High Coupling Efficiency/Easy Alignment	62.5/125 µm	Larger core and NA, easier to couple incoherent light sources, reducing difficulty in field installation and maintenance.
System Compatibility	50/125 µm	Most modern high-speed communication (OM3/OM4) uses the 50/125 specification, offering stronger compatibility for future upgrades.

III. Summary: Your Choice Determines Your System's Future

The choice between 50/125 µm and 62.5/125 µm is not about which is inherently better, but which is more suitable for your application scenario:

• If your application involves long-distance distributed sensing or requires high-speed data transmission, choose 50/125 µm.
• If your system emphasizes ease of use, utilizes low-cost light sources, or values convenient field maintenance, choose 62.5/125 µm.

Regardless of the specification your extreme environment project requires, [Beijing Dacheng Yongsheng Technology Co., Ltd. (DCYS)] can provide you with Polyimide optical fiber products boasting excellent temperature resistance from -200°C to +350°C.

Please visit our official website to learn more product details or contact our expert team for customized fiber selection advice.

[Beijing Dacheng Yongsheng Technology Co., Ltd. (DCYS)]

Official Website: https://www.ofscn.org

Product Link: https://www.ofscn.org/optical-fibers/polyimide-coated-mm-300.html