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Passive Fibers

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Passive fibers are optical fibers without laser-active dopants in the fiber core. That usually implies that they can only passively transmit light, with some propagation losses are without amplification of the optical power. In some cases, however, nonlinear amplification mechanisms based on stimulated Raman scattering or the Kerr nonlinearity occur.

Passive fibers can be separated into many specific categories:

• by fiber materials: glass fibers, single-crystal fibers, polycrystalline fibers (→ mid-infrared fibers), silica fibers, fluoride fibers, plastic optical fibers
• by fiber designs and physical principles of light guiding: step-index fibers, graded-index fibers, photonic crystal fibers, photonic bandgap fibers, hollow-core fibers, large-core fibers, tapered fibers, nanofibers
• by their guiding properties: single-mode fibers, polarization-maintaining fibers, single-polarization fibers, few-mode fibers, multimode fibers, large mode area fibers, dispersion-shifted fibers, dispersion-decreasing fibers
• by the spectral region: near-infrared fibers, mid-infrared fibers, UV fibers
• by their application areas: delivery fibers, telecom fibers, imaging fibers (e.g. as fiber bundles), sensor fibers (→ fiber-optic sensors)

Compared with active fibers, passive fibers generally exhibit lower propagation losses and are available at lower cost.

Fibers may be equipped with fiber connectors and protective materials to form fiber cables.

Case Studies

Mode Structure of a Multimode Fiber

We explore various properties of guided modes of multimode fibers. We also test how the mode structure of such a fiber reacts to certain changes inthe index profile, e.g. to smoothening of the index step.

Case Studies

Dispersion Engineering for Telecom Fibers

We explore different ways of optimizing refractive index profile for specific chromatic dispersion properties of telecom fibers, resulting in dispersion-shifted or dispersion-flattened fibers. This also involves automatic optimizations.

Case Studies

Nonlinear Pulse Compression in a Fiber

We explore how we can spectrally broaden light pulses by self-phase modulation in a fiber and subsequently compress the pulses using a dispersive element. A substantial reduction in pulse duration by more than an order of magnitude is easily achieved, while the pulse quality is often not ideal.

Case Studies

Numerical Experiments With Soliton Pulses in Fibers

We investigate various details of soliton pulse propagation in passive fibers, using numerical simulations.

Case Studies

Collision of Soliton Pulses in a Fiber

We let two soliton pulses collide in a fiber. Surprisingly, they survive such collisions, even if we involve solitons of higher order.

Case Studies

Soliton Self-frequency Shift in Glass Fibers

We numerically simulate the soliton self-frequency shift, which is caused by stimulated Raman scattering. Influences like higher-order dispersion are found to be quite relevant.

Case Studies

Soliton Pulses in a Fiber Amplifier

We investigate to which extent soliton pulses could be amplified in a fiber amplifier, preserving the soliton shape and compressing the pulses temporally.

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