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 | Fluctuations and Noise | General Optics | Laser Devices and Laser Physics |
Laser Material Processing | Light Detection & Characterization | Light Pulses | Lightwave Communications |
Methods | Non-laser Light Sources | Nonlinear Optics | Optical Amplifiers |
Optical Materials | Optical Metrology | Optical Resonators | Optoelectronics |
Photonic Devices | Physical Foundations | Quantum Photonics | Vision, Displays and Imaging |
| A | B | C | D | E | F | G | H | I | J | K | L | M |
| N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Numerical Experiments With Soliton Pulses in Fibers
We investigate various details of soliton pulse propagation in passive fibers, using numerical simulations.
#pulses#nonlinearities
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
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
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
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
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
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:
| 2026-05-20 | Why 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.
| 2026-05-08 | Photonics 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.
| 2026-01-07 | The Best Tools for Purchasing of Photonics Products |
The RP Photonics tools for responsible purchasing with a structured purchasing process have been improved further.
| 2025-12-04 | AI 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.
| 2025-11-03 | Lost 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.
| 2025-09-30 | Concept 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.
| 2025-08-25 | Photon 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.
| 2025-08-18 | Do 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.
| 2025-07-30 | More 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?
| 2025-04-01 | Have 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.
| 2025-02-27 | Tools 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.
| 2025-02-07 | New 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.
| 2024-09-16 | Education 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.
| 2024-05-28 | Developing 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.
| 2024-04-23 | How 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.
| 2024-04-08 | New 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.
| 2023-11-20 | Using 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.
| 2023-11-16 | Citing 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.
| 2023-09-06 | Can 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.
| 2023-05-25 | The 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.
Latest ArticlesOccasionally, new articles are added; the last ones: |
Latest Substantially Improved ArticlesRP frequently improves existing articles. (This is how the high quality level is achieved!) The last substantially improved articles: |
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