Single-mode fiber can transmit TE mode and TM mode

Single-mode fibers do not support pure TE or TM modes; they support a single hybrid mode that combines both electric and magnetic field components.

Understanding TE and TM Modes

TE (transverse electric) modes have an electric field entirely perpendicular to the direction of propagation, while TM (transverse magnetic) modes have a magnetic field entirely perpendicular to the propagation direction . In waveguides with homogeneous dielectric filling, TE and TM modes can exist independently, but in optical fibers, the cylindrical geometry and refractive index profile create coupling between the longitudinal and transverse field components .

Single-Mode Fiber Characteristics

A single-mode fiber is designed to support only the fundamental mode, often denoted as HE11, which is a hybrid mode containing both transverse electric and magnetic components . The fiber's core radius and refractive index difference are chosen so that the V-number is below 2.405, ensuring that no higher-order modes propagate . Because of this, pure TE or TM modes cannot propagate in a single-mode fiber; the fiber inherently supports a hybrid mode that approximates the fundamental propagation with minimal dispersion .

Comparison with Multimode Fibers

In contrast, multimode fibers can support multiple modes, including higher-order hybrid modes, and in theory, could support modes that are closer to pure TE or TM under idealized conditions . However, in practical optical fibers, even multimode propagation involves hybrid modes due to the cylindrical symmetry and boundary conditions at the core-cladding interface .

Key Takeaway

While TE and TM modes are fundamental concepts in waveguides, single-mode optical fibers transmit only a single hybrid mode (HE11). Pure TE or TM modes are not supported because the fiber geometry and refractive index profile couple the longitudinal and transverse field components, making hybrid modes the natural solution for single-mode propagation .