Fiber Amplifiers
Posted on 2017-08-01 as part of the Photonics Spotlight (available as e-mail newsletter!)
Permanent link: https://www.rp-photonics.com/spotlight_2017_08_01.html
Author: Dr. Rüdiger Paschotta, RP Photonics AG, RP Photonics AG
Abstract: A new algorithm has been developed for simulating the amplification of femtosecond pulses in fiber amplifiers, for example. It allows one to properly describe both the time dependence due to gain saturation and the frequency dependencies of optical fields and gain. The details have been published in the open-access journal Optics Express.
Ref.: R. Paschotta, "Modeling of ultrashort pulse amplification with gain saturation", Opt. Express 25 (16), 19112 (2017); https://doi.org/10.1364/OE.25.019112
Numerical models for the laser amplification of ultrashort pulses have been developed over many years. Surprisingly, it seems that for one relatively fundamental issue in this context there has not been a good solution until now. The point is how to simultaneously treat gain saturation and the wavelength dependencies of gain and the optical fields.
The fundamental difficulty is that gain saturation is essentially a time-dependent effect and should thus be described in the time domain, whereas frequency dependencies of course suggest to work in the frequency domain. But how to formulate (not just solve) a differential equation which correctly addresses the time and frequency domain at the same time?
I encountered that problem in the context of the development of our software RP Fiber Power, which since version V4 can simulate the amplification of ultrashort pulses e.g. in fiber amplifiers. In most cases, the problem is not severe because the pulse energies are too low for causing substantial gain saturation. In some chirped-pulse amplifier systems, however, we do see substantial gain saturation (as is necessary for efficient power conversion) in conjunction with a large gain and optical bandwidth. Note that without strongly chirped pulses in the fiber, one cannot have strong gain saturation of femtosecond pulses, since the applicable peak intensities are limited by fiber nonlinearities (in particular by nonlinear self-focusing) so that only relatively long (temporally stretched) pulses can cause substantial gain saturation.
When reviewing the literature, I found that a number of different approaches has been used to address that challenge, but all of them appears to have serious limitations:
- In some cases, one can correctly include both the time dependence through gain saturation and the frequency dependence of the gain, but not the frequency dependence of the gain saturation, since the saturation is described by a purely time-domain equation.
- Others have used a two-dimensional numerical description of pulses based on time–frequency distributions, effectively adapting matters from radiation transfer theory, which however cannot take into account coherent effects. Unfortunately, however, coherent effects can often not be ignored in the context of ultrashort pulses.
- A relatively simple and still accurate approach is possible in the context of chirped-pulse amplifiers, but here one requires quite specific assumptions on the pulses, so that such an algorithm is not well usable for an all-purpose simulation software, for example.
- It is also not practical to use Maxwell–Bloch equations, where one would have to include a lot of microscopic details of the gain medium.
I finally developed a new algorithm which has the following advantages:
- It can fully take into account both the time dependence from gain saturation and the relevant frequency dependencies.
- It is fully compatible with the typically used numerical representation of ultrashort pulses in the time or frequency domain.
- It does not require specific assumptions on the pulses – for example, a quasi-monochromatic nature of small temporal slices of a pulse.
Essentially, the new method requires some “soft” temporal slicing of pulses, where for each slice separately one applies a Fourier transform to get into the frequency domain and apply the frequency-dependent gain there; another Fourier transform leads back to the time domain. In the end, all the slices are properly combined to obtain the amplified pulse in the time domain. Some technical details of the implementation are not straightforward; various technical issues had to be solved in order to obtain an accurate and robust algorithm. That is now used in the RP Fiber Power software.
I decided to publish the details in a scientific paper, which has just appeared in an open-access journal – see the reference given at the beginning of the article. (See also the references therein if you want to learn more about the previously described algorithms.) Although that publication will allow competitors to implement the algorithm themselves, I think it is good that everyone can verify how solid scientific expertise is the basis of our simulation software.
Suppliers
The RP Photonics Buyer's Guide contains 65 suppliers for fiber amplifiers. Among them:
Cycle
Based on Cycle's own femtosecond fiber lasers, the company also offers fiber-based amplifiers (EDFA) with a center wavelength of 1550 nm to 1700 nm. This variant of the SOPRANO-15 is a very attractive solution to amplify the output of beam arrival monitors in synchrotron or FEL facilities, for example. Other custom-made fiber amplifiers are available upon request.
Active Fiber Systems
AFS’s customized kW average power and multi-mJ pulse energy ultrafast laser systems are based on AFS leading-edge fiber technology. They unite multiple main-amplifier channels using coherent combination, a technology which AFS has matured to an industrial grade. All essential parameters are software-controlled and can be tuned over a wide range, making them an extremely valuable tool for numerous application.
MPB Communications
In 1995, MPB Communications provided its first generation of high-power boosters and quantum-limited noise-figure EDFAs for long-haul, unrepeatered telecom systems. MPBC amplification solutions have been adopted by system integrators in the terrestrial, submarine and utilities markets and continue to offer exceptional reliability which power communication backbones worldwide.
Today, our fiber amplifier technology can be found in our line of network-ready telecom solutions, as well as in our extensive portfolio of gain modules, and in our single-frequency Raman fiber amplifiers.
RPMC Lasers
Serving North America, RPMC offers a wide range of Telcordia grade erbium and ytterbium fiber lasers and amplifiers that are deployed in a wide range of applications, including LIDAR, mapping, 3D scanning and telecommunications. The BKtel suite of lasers and amplifiers are available in a range of wavelengths from 1030 nm to 2054 nm, with average powers up to 40 W, pulsed and CW capabilities, and numerous features, including low noise, compact package size, and a digital control system. Standard and custom solutions available. Let RPMC help you find the right laser today!
AdValue Photonics
AdValue Photonics offers fiber amplifiers for wavelength around 1 μm, 1.5 μm or 2 μm. They are suitable for pulsed or continuous-operation, narrow linewidth or broadband light.
For the 1-μm region, we have compact and yet powerful large mode area fiber amplifier modules, which can deliver more than 120 W average output power.
Thorlabs
Thorlabs manufactures erbium (Er)-, ytterbium (Yb)-, and praseodymium (Pr)-doped fiber amplifiers for applications from ultrafast pulse amplification to datacom. Along with these stand-alone benchtop amplifiers, Thorlabs has developed a family of femtosecond lasers utilizing oscillator-amplifier architectures.
TOPTICA Photonics
Our new highly reliable Raman fiber amplifiers (RFA) are based on patented technology. With their high power of up to 30 W, the amplifiers cover the wavelength range from 1120 to 1370 nm that is not accessible by Yb or Er fiber amplifiers. For wavelengths outside this range, please enquire for a custom system.
The RFA is designed using TOPTICA’s high quality engineering excellence and utilizing a stable European & North American supply chain. The all fiber design requires no re-alignment and provides a high degree of stability. The RFA offers a wide tuning range of up to 10 nm, a relative intensity noise <1% r.m.s. (10 Hz – 10 MHz) and excellent long term RMS power stability of less than 0.5% over 100 hours (with a TA pro seed laser).
DK Photonics
DK Photonics offers various erbium-doped fiber amplifiers for telecom applications, including compact amplifier modules as well as bench-top instruments with controls and displays.
Ytterbium-doped amplifiers for the 1-μm wavelength region are also available.
Le Verre Fluore
Thanks to their high rare-earth solubility (up to 100,000 ppm) and low phonon energy, LVF fluoride fibers offer dozens of active transitions, enabling a broad range of applications from visible to the mid-infrared, one of which is amplification. For example, LVF praseodymium and thulium doped fibers are used for amplification at 1.3 µm and 1.47 µm respectively. LVF doped fibers for amplification are available as single-mode fiber or double cladding fiber.
Le Verre Fluoré will soon offer laser and amplifier fiber modules. The required fiber will be integrated in a robust housing and connectorized with FC/PC, FC/APC, SMA or custom connectors depending on customer need: this is a plug-and-play module.
Depending on specific needs, modules might include single-mode or multimode splices between fluoride fibers or between silica and fluoride fibers.
AMS Technologies
For both C- and L-band operation, AMS Technologies provides a selection of CW and pulsed erbium-(Er-)doped fiber amplifiers (EDFAs) as well as Yb/Er co-doped fiber amplifiers (YEDFAs) in a wide range of configurations and gains:
- 20 and 15 dB miniature size EDFA modules
- high-power, ?27 dBm EDFA modules
- high-speed, pulsed EDFA modules, SM and PM
- single- or multi-port high-power YEDFA modules
- PM YEDFA modules
- 19”, 1U EDFA racks, also PM
- 19”, 1U YEDFA racks, also PM
- 19”, 2U multiport high-power EDFA racks
- Raman fiber amplifier module
Lumibird
Lumibird manufactures an extensive range of mature and custom-designed optical fiber amplifiers and fiber lasers. High output powers are achieved through the use of double cladding fibers pumped by broad stripe diodes. Several varieties of pumping techniques are used each optimized for specific applications. Lumibird also develops key components for producing unique and innovative light sources.
This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page and cite it, because its location is permanent. See also the RP Photonics Encyclopedia.
Note that you can also receive the articles in the form of a newsletter or with an RSS feed.
Questions and Comments from Users
Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.
Please do not enter personal data here; we would otherwise delete it soon. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.
By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.
Share this with your friends and colleagues, e.g. via social media:
These sharing buttons are implemented in a privacy-friendly way!