Yes, step-index single-mode fibers exist and are widely used in optical communication systems.

Step-index single-mode fibers have a very small core diameter, typically between 2 to 15 micrometers, which allows only a single mode of light to propagate through the fiber, minimizing distortion caused by modal dispersion . The term "step-index" refers to the abrupt change in refractive index between the core and the cladding, where the core has a uniform refractive index and the cladding has a slightly lower constant refractive index .

Characteristics

• Single-Mode Operation: These fibers propagate only the fundamental mode. Single-mode operation occurs when the fiber's normalized frequency (V-number) is below approximately 2.405 .
• Core and Cladding: The core is surrounded by cladding, which can be either matched-clad (single homogeneous layer) or depressed-clad (two regions with different refractive indices) to optimize performance and reduce bending losses .
• Low Distortion: Because only one mode propagates, step-index single-mode fibers exhibit minimal modal dispersion, making them ideal for long-distance and high-bandwidth communication .
• Polarization: While the fiber supports a single spatial mode, it can guide two orthogonal polarization states, which are often treated as separate modes in practical applications .

Applications

Step-index single-mode fibers are commonly used in telecommunications, data networks, and high-speed optical systems where low signal distortion and long-distance transmission are critical. They are the standard choice for most modern fiber optic communication systems due to their high bandwidth and low attenuation. In summary, step-index single-mode fibers are a well-established type of optical fiber, characterized by a small core, abrupt refractive index change, and single-mode propagation, making them essential for high-performance optical communication .