Choosing an active fiber means balancing gain, noise, beam quality, thermal load and reliability within a specific laser architecture. Exail combines expertise in glass chemistry, rare-earth doping and fiber design to address these trade-offs. Fibers characterized under realistic operating conditions, tailored geometries and controlled manufacturing help translate our customers requirements into consistent performance, with strong batch-to-batch repeatability.

Here is an overview of the different amplification challenges we can address across the optical spectrum:

1.5 µm: From low-noise reception to power scaling

At 1.5 µm, low-noise telecommunications amplifiers and high-power LiDAR systems require different fiber designs. For telecommunications, erbium-doped fiber amplifiers boost weak signals from nanowatt levels to hundreds of milliwatts, making low noise, high gain and uniform amplification across the C or L bands essential. Exail brings 20 years of established manufacturing experience to its range of single-clad erbium (Er)-doped fibers.

For optical ground stations, coherent wind LiDAR and quantum sources, integrators are expecting doped fibers with higher output power, with good beam quality and spectral purity. Stimulated Brillouin scattering can limit amplification of narrow-linewidth signals but fibers with larger mode areas help reduce this effect. In Er/Yb co-doped fibers, ytterbium absorbs pump light at 915–980 nm and transfers the energy to erbium. It means that incomplete transfer can produce spurious emission near 1 µm, while heat and photodarkening can compromise long-term stability. Exail worked on glass composition and fiber design to set a new benchmark for power scalability and long-term reliability at 1.5 µm. Our new single-mode Er/Yb-doped fiber, featuring a 10 µm core, delivers 30 W with near-ideal beam quality and no detectable photodarkening over 700 hours. Larger-core fibers are engineered for laser systems exceeding 200 W.

2 µm: Reach laser performance across the full window

Around 2 µm, the application determines wavelength and operating regime: continuous-wave amplification at 1762 nm for barium-ion quantum systems, quasi-continuous output near 1940 nm for medical lasers, or pulsed operation beyond 2 µm for atmospheric LiDAR. Exail addresses these requirements with thulium (Tm), holmium (Ho) and Tm/Ho co-doped fibers. Single-, double- and triple-clad designs, core diameters from 4 to 60 µm, and different doping levels and numerical apertures provide options for matching pump delivery, signal guidance and gain to architecture.

Around 2.1 µm, engineers can choose Tm/Ho co-doped fibers, or Ho-doped fibers pumped close to their operating wavelength. The first approach uses cladding pumping with multimode diodes at 793 nm, while Ho-doped amplifiers can be core-pumped using a thulium laser source at 1.9 µm.

Exail tailors dopant concentrations and glass composition to each fiber design to improve energy conversion and reduce optical losses. In published tests1, a new polarization-maintaining Ho-doped fiber delivered about 25 W at 2095 nm, converting 60% of the optical pump power into output power. This nearly doubles the 34% efficiency achieved in the initial setup using a different fiber.

920 nm: Pioneering fiber design for two-photon microscopy

Two-photon microscopy commonly uses ultrashort pulses near 920 nm. In neodymium (Nd)-doped fibers, amplification competes with stronger gain near 1060 nm.

Through longstanding research collaboration and sustained industrial R&D, Exail developed an innovative W-profile Nd-doped fiber. Controlled bending suppresses competing emission above 1 µm while supporting amplification across the 890–930 nm range.

Ytterbium: From compact amplifiers to multi-kW lasers

Ytterbium (Yb) fiber selection is also influenced by the amplified spontaneous emission (ASE). At 1060 nm, ASE around 1030 nm can drain the energy available to the signal. Exail’s single-clad Yb-doped fibers offer different doping levels. Higher doping can deliver the required gain over a shorter fiber length, helping reduce ASE under suitable pumping conditions.

As power increases, nonlinear optical effects can limit performance. Narrow-linewidth continuous-wave quantum sources are sensitive to stimulated Brillouin scattering, while high-peak-power LiDAR pulses face the self-phase modulation, which broadens the pulse spectrum and stimulated Raman scattering, which transfers energy to longer wavelengths. Exail’s double-clad fibers provide different guided beam sizes and pump-light absorption levels to suit each amplifier stage.

At kilowatt power levels, stronger pump absorption is not always an advantage: concentrating heat over a shorter length can trigger transverse mode instability, heat-driven fluctuations that degrade beam quality at lower powers. Exail’s Yb-fiber with larger effective beam diameter balances pump absorption, fiber length and heat load, enabling multi-kW operation.

Raman: Reach the pump wavelength in fewer steps

Exail’s phosphorus-doped fibers offer an efficient way to generate new wavelengths through Raman conversion. With a Raman shift of approximately 40 THz, nearly three times that of germanium-doped silica, these fibers enable larger wavelength shifts in fewer conversion steps, helping simplify laser architectures. For example, starting from a 1064 nm fiber laser, a first Raman conversion near 1240 nm can provide a pump source for O-band bismuth amplifiers, while a second conversion near 1480 nm offers an attractive solution for efficient core pumping of Er-doped fibers for C-band amplification.

Space: where radiation resistance matters

In space, radiation exposure creates losses at pump and signal wavelengths, reducing the end-of-life link margin. For 20 years, Exail has pioneered radiation-hardened active fibers through extensive research and development efforts and collaboration with space agencies. We are proud to see our fibers flying aboard both prestigious scientific missions and numerous satellites within constellations.

Fiber requirements vary across an optical communication link. Coherent receivers may handle input powers as low as 10 nW. They require stable amplification with minimal added noise. Exail’s “RAD-AMP” Er-doped fibers address these needs. Transmitters require higher output power while suppressing parasitic emission near 1 µm. Radiation-hardened Er/Yb double-clad fibers support amplifier stages delivering up to 50 W. For 1 µm, NASA has worked with Exail on the qualification of its radiation-hardened Yb-doped fibers for the design of the 2W power amplifier of the LISA laser hardware.

Exail combines proven industrial experience, controlled manufacturing, and radiation testing to support reliable optical performance for space mission.

Discuss your fiber laser or amplifier requirements with Exail! 

¹ P. Baer et al., 25W-class continuous-wave holmium-doped fiber amplifier with narrow-linewidth and linear polarization (Conference proceedings of SPIE - 2026)