Master Oscillator Fiber Amplifier
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Acronym: MOFA or MOPFA
Definition: a laser system containing a fiber amplifier for boosting the output power
More general term: master oscillator power amplifier
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DOI: 10.61835/5ac Cite the article: BibTex plain textHTML Link to this page LinkedIn
The term master oscillator fiber amplifier (MOFA, MOPFA, or fiber MOPA) is a variation of the term master oscillator power amplifier (MOPA), meaning a system containing a laser oscillator and a power amplifier, where the latter is a fiber amplifier. The latter is usually a cladding-pumped high-power amplifier, often based on an ytterbium-doped fiber. The main attractions of such fiber-based power amplifiers are:
- A high output power can be achieved with a high power efficiency.
- The cooling system can be relatively simple.
- The beam quality can be high; it is often close to diffraction-limited.
- The gain can easily be as high as tens of decibels. For comparison, most bulk amplifiers, particularly those with high average output power, have a much lower gain, often only of the order of 3 dB.

For higher power levels, a second amplifier stage with double-clad fiber may be added. The seed laser diode may be operated in a pulsed regime.
However, the use of fibers also has disadvantages:
- Various kinds of optical fiber nonlinearities can make it difficult to reach very high peak powers and pulse energies in pulsed systems. For example, a few millijoules of pulse energy in a nanosecond pulse system are already considered high for a fiber device, whereas bulk lasers can provide much higher energies. In single-frequency systems, stimulated Brillouin scattering (SBS) can severely limit the output power.
- Due to the high gain, fiber amplifiers are relatively sensitive to back-reflections e.g. from a workpiece. At high power levels, it is not easy to use a Faraday isolator for solving this problem, particularly when a high suppression of reflected light is required.
- The polarization state is often undefined and unstable, unless polarization-maintaining fibers are used.
It can be attractive to use a gain-switched laser diode (→ picosecond diode lasers) as seed laser for a fiber MOPA. Such devices compete with Q-switched lasers, e.g. for application in laser marking. Their advantages partly lie in their flexibility concerning output formats: it is easy to modify not only the pulse repetition rate but also the pulse duration and shape, and of the course the pulse energy.
A special aspect of MOFAs is that the saturation power even of a large mode area double-clad fiber is low compared with the typical output power. Therefore, the power extraction can be as efficient as in a fiber laser, even for relatively low seed powers.
More to Learn
Encyclopedia articles:
- master oscillator power amplifier
- optical amplifiers
- fiber amplifiers
- high-power fiber lasers and amplifiers
Blog articles:
- The Photonics Spotlight 2008-09-24: “Decoupling Pulse Duration and Pulse Energy”
- The Photonics Spotlight 2008-12-16: “Why Fiber Amplifiers, not Fiber Lasers?”
Suppliers
The RP Photonics Buyer's Guide contains 40 suppliers for high-power fiber lasers and amplifiers. Among them:
Thorlabs

Thorlabs manufactures ytterbium (Yb) doped high-power femtosecond fiber lasers, the FSL1030X1 and FSL1030X2, with tunable repetition rates from 1 – 11 MHz; they produce pulse energies up to 12 µJ or pulse widths down to 130 fs, respectively. These systems compliment our full line of ultrafast lasers and amplifiers and specialized optics, including nonlinear crystals, chirped mirrors, low GDD mirrors/beamsplitters, highly nonlinear fiber, and dispersion compensating fiber.
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.
AdValue Photonics

AdValue Photonics produces various kinds of fiber lasers emitting in the wavelength regions around 1 μm, 1.5 μm and 2 μm. Some offer quite high output powers. For example, we have compact and yet powerful large mode area fiber amplifier modules, which can deliver more than 120 W.
RPMC Lasers

Serving North America, RPMC Lasers offers a variety pulsed and CW fiber lasers and fiber amplifiers with wavelengths between ≈1 and ≈1.5 microns (harmonics and OPA wavelengths available). These fiber lasers can be configured in an OEM or turnkey system, with pulsed versions available from 100 fs up to 125 ns with rep rates from 5 kHz up to 20 MHz. Applications include material processing, LIDAR, micromachining, intra-satellite free-space communications, telecom, and more. Standard and custom options available. Let RPMC help you find the right laser today!
TOPTICA Photonics

This product line enables the power boost of lower power solution without compromise on signal quality up to 130 W. No added phase noise and very little addition of intensity noise is the key for a number of application (AMO physics, high end instrumentation).
IR fiber lasers & amplifiers: Single frequency CW output for your power hungry application: high power up to 130 W. Advanced quantum technology applications demand high performance and high power light sources. Be it gravitational wave detection or quantum computing.
VIS fiber lasers & amplifiers: Single frequency CW output for your power hungry application: High power up to 10 W and ultra-low intensity noise. Industrial applications like high performance metrology in the semicon industry or quantum computing require extremely stable, reliable and powerful laser sources.
Menlo Systems

Menlo Systems' high-power fiber lasers based on erbium or ytterbium doped fiber use polarization maintaining (PM) components only. Our patented figure 9® laser technology ensures excellent stability and low-noise operation. We offer solutions for scientific research as well as laser models engineered for OEM integration.
MPB Communications

MPBC specializes in high-power fiber lasers and amplifiers, offering solutions tailored for single-frequency and high-power applications across their telecommunications, space and laser product lines. In their telecommunications lineup, MPBC's 2RU Boosters deliver up to 30 dBm of output power, ideal for demanding telecom and utility network applications in the terrestrial or submarine fields.
With TRL-9 optical amplification technology and 30 years of experience in providing optical amplifiers for submarine and terrestrial communications, MPBC is now a leading supplier of optical amplifiers for space applications. Some product offerings include:
- Space amplifiers with up to +37 dBm of output power
- Ground station amplifiers with up to 50 W of output power
In the fiber laser product line, MPBC's continuous wave near-IR lasers provide exceptional high-power performance, with air-cooled packages reaching up to 50 W and water-cooled options ranging from 50 W to over 100 W. Their single-frequency Raman fiber amplifiers and lasers are designed for precision and stability, delivering low phase and intensity noise, narrow spectral linewidths, and long coherence lengths. These systems amplify single-frequency seed sources from milliwatts to several watts in the NIR, enabling frequency doubling for stable, narrow-linewidth, low-noise visible output.
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.
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