Single-mode dual-core fibers are characterized by geometrical, optical, transmission, and mechanical parameters, with each core supporting single-mode propagation for long-distance, low-loss applications.

Core and Fiber Geometry

A dual-core fiber contains two light-transmitting cores within a single cladding, allowing simultaneous signal transmission in each core . Key geometrical parameters include:

• Core diameter: Typically around 8–10 µm for single-mode operation at 1310–1550 nm .
• Cladding diameter: Standard 125 µm, ensuring compatibility with connectors and splicing .
• Core concentricity error: Measures the offset between the core and cladding centers, affecting coupling efficiency.
• Cladding non-circularity: Deviation from a perfect circle, influencing mode propagation uniformity.

Optical Parameters

Single-mode dual-core fibers are designed to support one propagation mode per core, minimizing modal dispersion. Important optical parameters include:

• Mode Field Diameter (MFD): Defines the effective light-carrying area of each core, typically 9–10 µm at 1310 nm .
• Cut-off wavelength: The wavelength below which higher-order modes may propagate; ensures single-mode operation.
• Chromatic dispersion: Variation of propagation speed with wavelength, critical for long-distance transmission.
• Macrobending loss: Attenuation due to fiber bending, specified to maintain low loss in practical installations.
• Refractive index profile: Determines light confinement and dispersion characteristics.

Transmission and Mechanical Parameters

• Attenuation coefficient: Loss per unit length, typically <0.35 dB/km at 1310 nm and <0.22 dB/km at 1550 nm .
• Polarization Mode Dispersion (PMD): Differential delay between polarization states, important for high-speed systems.
• Differential Group Delay (DGD): Relevant in dual-core fibers for sensing or multiplexing applications .
• Mechanical properties: Tensile strength, elongation, and environmental resistance to ensure reliability during installation and operation.

Parameter Representation in Dual-Core Applications

For dual-core fibers, parameters are often represented per core and for the combined fiber, including:

• Core-specific MFD, chromatic dispersion, and attenuation.
• Cross-talk between cores, which should be minimized for independent signal transmission.
• Link attributes: Statistical or worst-case design values for concatenated fiber segments, including total attenuation, DGD, and non-linear coefficients .

Applications

Single-mode dual-core fibers are used in:

• High-capacity long-haul communication: Doubling data channels without increasing fiber count.
• Fiber optic sensors: Dual-core fibers in Fabry–Perot or Mach–Zehnder interferometers allow simultaneous measurement of parameters like pressure and temperature with low cross-sensitivity .
• Advanced multiplexing systems: Supporting spatial division multiplexing for next-generation networks. In summary, single-mode dual-core fiber parameters are represented through a combination of geometrical, optical, transmission, and mechanical specifications, with careful attention to core-specific characteristics, cross-talk, and system-level link attributes to ensure optimal performance in communication and sensing applications .