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The RP Photonics Encyclopedia

is a comprehensive, scientifically robust open access reference source in the fields of optics and photonics, from science to engineering. The 1127 educational articles are all authored by the expert Dr. Rüdiger Paschotta at RP Photonics and provide highly useful introductions to many concepts as well as practical insight for engineers.

The Encyclopedia project is supported by various sponsors and strongly connected with the RP Photonics Buyer's Guide. Together with that, it forms the leading photonics information platform.

Topical Categories Articles A–Z Tutorials
Case Studies Photonics Spotlight Latest Articles
Fiber Optics and Waveguides
Fiber Optics
and Waveguides
Fluctuations and Noise
Fluctuations
and Noise
General Optics
General Optics
Laser Devices and Laser Physics
Laser Devices and
Laser Physics
Laser Material Processing
Laser Material
Processing
Light Detection and Characterization
Light Detection & Characterization
Light Pulses
Light Pulses
Lightwave Communications
Lightwave
Communications
Methods
Methods
Non-laser Light Sources
Non-laser
Light Sources
Nonlinear Optics
Nonlinear Optics
Optical Amplifiers
Optical Amplifiers
Optical Materials
Optical Materials
Optical Metrology
Optical Metrology
Optical Resonators
Optical Resonators
Optoelectronics
Optoelectronics
Photonic Devices
Photonic Devices
Physical Foundations
Physical Foundations
Quantum Photonics
Quantum Photonics
Vision, Displays and Imaging
Vision, Displays
and Imaging
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Tutorials

Tutorial on Passive Fiber Optics

Passive Fiber Optics

This is a comprehensive introduction to fiber optics, focusing on passive (non-amplifying) fibers. It explains basic principles as well as practical aspects.

#fibers#pulses

Tutorials

Tutorial on Fiber Amplifiers

Fiber Amplifiers

You can learn about rare earth ions, how to calculate optical powers and ionic excitations in amplifiers, and on many other topics: ASE, forward vs. backward pumping, double-clad fibers, amplification of light pulses, amplifier noise, and multi-stage amplifiers.

#fibers#amplifiers#pulses

Tutorials

Tutorial on Modeling and Simulation of Fiber Amplifiers and Lasers

Modeling and Simulation of Fiber Amplifiers and Lasers

This is an physics-based introduction into the modeling of fiber amplifiers and fiber lasers, as required for efficient research and development. Many aspects of amplifier and laser operation can be simulated, leading to a solid quantitative understanding.

#fibers#amplifiers#pulses

Tutorials

Tutorial on Modeling of Pulse Amplification

Modeling of Pulse Amplification

This tutorial explains the amplification of light pulses, with particular focus on fiber amplifiers, but also some content on bulk laser amplifiers.

#fibers#amplifiers#pulses

Case Studies

Case study: Mode Structure of a Multimode Fiber

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 in the index profile, e.g. to smoothing of the index step.

#modes

Case Studies

Case study: Number of Modes of a Highly Multimode Fiber

Number of Modes of a Highly Multimode Fiber

We seek a simple equation for estimating for the number of modes of a highly multimode fiber, which can be applied to fiber designs with arbitrary shapes of the refractive index profile. Instead of applying complicated mathematics, we build a hypothesis and subject that to multiple numerical tests.

#modes

Case Studies

Case study: The Numerical Aperture of a Fiber: a Strict Limit for the Acceptance Angle?

The Numerical Aperture of a Fiber: a Strict Limit for the Acceptance Angle?

The requirement of total internal reflection would seem to set a strict limit for the angular distributions of fiber modes. However, some modes are found to exceed that limit significantly. We investigate that in detail for single-mode, few-mode and multimode fibers.

#modes#video

Case Studies

Case study: Dispersion Engineering for Telecom Fibers

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.

#modes#dispersion#telecom#video

Case Studies

Case study: Telecom Fiber With Parabolic Index Profile

Telecom Fiber With Parabolic Index Profile

We investigate how intermodal dispersion of a multimode fiber can be minimized with a parabolic doping profile.

#modes#telecom

Case Studies

Case study: Erbium-doped Fiber Amplifier for a Long-wavelength Signal

Erbium-doped Fiber Amplifier for a Long-wavelength Signal

Amplified spontaneous emission (ASE) turns out to be a limiting factor, requiring a dual-stage amplifier design.

#amplifiers#ASE#telecom#video

Case Studies

Case study: Erbium-doped Fiber Amplifier for Rectangular Nanosecond Pulses

Erbium-doped Fiber Amplifier for Rectangular Nanosecond Pulses

We deal with deformations of the pulse shape due to gain saturation. These can be minimized by pre-distorting the input pulses.

#amplifiers#pulses#video

Case Studies

Case study: Erbium-doped Fiber Amplifier for Multiple Signals

Erbium-doped Fiber Amplifier for Multiple Signals

We optimize an amplifier for equal output powers of signals spanning a substantial wavelength range. There is a trade-off between power efficiency and noise performance.

#amplifiers#telecom

Case Studies

Case study: ASE in Ytterbium-doped Fibers

ASE in Ytterbium-doped Fibers

We study various aspects of amplified spontaneous emission (ASE) in ytterbium-doped fibers — for example, why it is different in forward and backward directions, how the fiber length can have a crucial impact, and how the fiber core diameter matters.

#amplifiers#ASE

Case Studies

Case study: Designing a Double-clad Fiber Amplifier

Designing a Double-clad Fiber Amplifier

We develop a double-clad fiber amplifier with high gain, where we have to care about limiting losses by ASE.

#amplifiers#ASE

Case Studies

Case study: Ytterbium-doped 975-nm Fiber Lasers

Ytterbium-doped 975-nm Fiber Lasers

We explore how to realize Yb-doped fiber lasers emitting at the tricky wavelength of 975 nm. This turns out to be challenging for devices with double-clad fibers due to ASE at longer wavelengths.

#lasers#ASE#video

Case Studies

Case study: Nonlinear Pulse Compression in a Fiber

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.

#pulses#nonlinearities

Case Studies

Case study: Parabolic Pulses in a Fiber Amplifier

Parabolic Pulses in a Fiber Amplifier

We explore the regime of parabolic pulse amplification in an Yb-doped single-mode fiber. We find suitable system parameters and investigate limiting effects.

#amplifiers#pulses#nonlinearities

Case Studies

Case study: Numerical Experiments With Soliton Pulses in Fibers

Numerical Experiments With Soliton Pulses in Fibers

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

#pulses#nonlinearities

Case Studies

Case study: Collision of Soliton Pulses in a Fiber

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.

#pulses#nonlinearities

Case Studies

Case study: Soliton Self-frequency Shift in Glass Fibers

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.

#pulses#nonlinearities

Case Studies

Case study: Soliton Pulses in a Fiber Amplifier

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.

#amplifiers#pulses#nonlinearities

Case Studies

Case study: Raman Scattering in a Fiber Amplifier

Raman Scattering in a Fiber Amplifier

We investigate the effects of stimulated Raman scattering in an ytterbium-doped fiber amplifier for ultrashort pulses, considering three very different input pulse duration regimes. Surprisingly, the effect of Raman scattering always gets substantial only on the last meter, although the input peak powers vary by two orders of magnitude.

#amplifiers#pulses#nonlinearities

Case Studies

Case study: Chirped-pulse Ytterbium-doped Fiber Amplifier System

Chirped-pulse Ytterbium-doped Fiber Amplifier System

We design an ytterbium-doped chirped-pulse fiber amplifier system. We investigate how the remaining nonlinear effects limit the possible performance parameters.

#amplifiers#pulses#video

Case Studies

Case study: Supercontinuum Generation in a Germanosilicate Single-mode Telecom Fiber

Supercontinuum Generation in a Germanosilicate Single-mode Telecom Fiber

We explore supercontinuum generation in telecom fibers. This works well for wavelengths beyond the zero dispersion wavelength. For operation with shorter-wavelength pulses, other fibers are required.

#pulses#video

The Photonics Spotlight

The Photonics Spotlight is a “blog” which highlights interesting news and useful information in the area of photonics, particularly laser technology and applications.

Here are the last 20 postings:

2026-05-20Why Are Lasers Still So Expensive? The Volume–Cost Trap and Other Challenges in Photonics and Automation

Many laser systems remain expensive because they are produced in limited volumes with tight tolerances, delicate assembly and insufficient automation. This article explains the resulting volume–cost trap: cheap lasers require large markets, while many large markets can emerge only once lasers become cheaper. It discusses promising application areas, different cost-reduction paths for various laser technologies, and the broader challenges of standardization, reliability, system cost and manufacturing scale-up.

2026-05-08Photonics is Gaining Traction — Pushed by AI Infrastructure and Other Factors

Photonics is experiencing a renewed surge of interest, driven largely by the rapid expansion of AI infrastructure and its growing demands on data transmission and energy efficiency. This article examines the technological, economic and geopolitical factors behind this trend, while also discussing emerging applications and associated systemic risks.

2026-01-07The Best Tools for Purchasing of Photonics Products

The RP Photonics tools for responsible purchasing with a structured purchasing process have been improved further.

2025-12-04AI Versus Expert-curated Supplier Directories: How to Reliably Find Photonics Suppliers?

While general-purpose AI tools are useful for language processing and general explanations, they are unreliable for the critical task of finding specialized photonics suppliers. This is because general-purpose AI lacks systematic coverage, uses outdated data, and does not follow well-established systematic procedures. Therefore, expert-curated directories remain the premier, reliable source for complete and accurate supplier discovery in specialized technical fields.

2025-11-03Lost factors of 2 around Gaussian beams, peak intensities, damage thresholds, and effective mode areas

Formulas for peak intensities, fluence values and areas of Gaussian beam are often wrong by a factor of 2.

2025-09-30Concept Trees for the RP Photonics Encyclopedia

The RP Photonics Encyclopedia now displays concept trees for many articles, graphically indicating both more general and more specific terms covered.

2025-08-25Photon Counting Terminology: Are We Really Counting?

Photon counting is an interesting concept, but the term is often inappropriately used. Better terminology would avoid some confusion in science and even more so in technology.

2025-08-18Do Photons Have an Optical Phase?

It is interesting to ask whether photons have an optical phase – but a more precise rephrasing is required to get sensible answers. We also discuss curious two-photon quantum interference.

2025-07-30More on the question: Can monochromatic light be unpolarized?

The question whether monochromatic light can be unpolarized is addressed with an interesting gedanken experiment. Different definitions of monochromacity can be used, but which one makes most sense?

2025-04-01Have AI bots like ChatGPT Got Better on Photonics Questions?

Although AI bots have improved a lot, tests prove that they still cannot provide reliable answers on photonics questions. While semantic search works well, a photonics chatbot is currently not feasible.

2025-02-27Tools from RP Photonics for Responsible Purchasing

For avoiding trouble with purchases, a structured purchasing process is essential. RP Photonics offers well thought-through web tools for that.

2025-02-07New AI-based Features on the RP Photonics Website

RP Photonics has introduced several AI-based features on its website for the benefits of users and advertisers. The technical background is explained.

2024-09-16Education with Simulations for Active Engagement of Students: Example with Pump Absorption in an Yb-doped Fiber

For effective teaching of physics, active engagement of students is essential. It is shown in an example case on light absorption in a rare-earth-doped fiber how this can be done.

2024-05-28Developing skills for laser research and development, and how to make continuing education work for consistent success

Successful work in photonics requires a set of skills. Here, the required skills are discussed, also ways of actively improving them.

2024-04-23How Responsible Purchase Decisions for Expensive Goods Like Lasers Are Made

Purchasing sophisticated and expensive equipment like a laser system requires detailed considerations concerning the requirements, technical specifications and various qualities of potential suppliers. Applying good practices can be vital.

2024-04-08New Case Studies Complement the RP Photonics Encyclopedia

RP Photonics started to publish interesting case studies, mostly based on physical simulation models. These nicely complement the encyclopedia articles.

2023-11-20Using the Cited By Feature of Crossref

Being a member of Crossref, RP Photonics used the opportunity to implement the feature to search for publications citing a specific paper. This can be useful in various ways.

2023-11-16Citing Encyclopedia Articles

Online encyclopedia articles of high quality are suitable for citations, and in fact it may even be required to do that. The article discusses various criteria for such decisions and also provides interesting news on the RP Photonics Encyclopedia.

2023-09-06Can AI bots like ChatGPT and Bard Answer Photonics Questions?

AI chatbots, which got rather popular, are often used for researching facts. But how reliable is that in the field of photonics? Some tests lead to disappointing results.

2023-05-25The RP Photonics Website Got a New Technical Basis

In May 2023, the RP Photonics website got a new technical basis. The article explains how the new system was developed, and what are its manifold advantages for the readers and for RP Photonics itself.

Find more postings on the Photonics Spotlight page.

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The Encyclopedia and Buyer's Guide are highly popular among photonics professionals as a trusted source of high-quality information:

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