Exail header advanced solutions for directed energy lasers

Directed
Energy
Laser

Demand for high power fiber lasers has increased tremendously in recent years. They are used in industrial machines, LIDAR systems, very high-energy laser facilities (inertial fusion, plasma), and recently in optical systems that can deliver very high power for defense applications. Compared with chemical lasers, free-electron lasers or solid-state lasers which are expensive and complex to implement, fiber lasers offer many advantages: compactness, lower mass allowing easier deployment, lower production and operating costs, higher reliability over time, resistance to severe environments, etc.

Today, phasing multiple fiber sources of several kilowatts by optical combination can result in laser architectures delivering powers of tens to hundreds of kilowatts. Exail offers particularly adapted optical components for the development of laser architectures delivering high power: LiNbO3 phase modulators (in 1-2 µm), doped fibers (in 2 µm) and Variable Optical Delay Lines (VODL).

Combining laser beams to gain power

Coherent Beam Combination (CBC)

Gaining power with several combined laser beams can be done by superimposing lasers of distinct wavelengths in a uniform laser output. The combination of several lasers by Coherent Beam Combination (CBC) allows a real-time control of their relative phases to permanently maintain constructive interferences and thus guarantee maximum power efficiency during the combination.

Exail developed dedicated low frequency phase modulators, and matching RF amplifiers, for high-power coherent beam combining applications. These modulators are necessary to compensate for the dispersion along the optical paths occurring within optical fibers. These phase variations are due to the laser operating environment, for example slow temperature changes. To maintain a constructive power combination of several beams, a low frequency phase modulation up to MHz is necessary. Exail has developed dedicated low frequency phase modulators: NIR-MPX-LN-0.1 and MPX2000-LN-0.1. An RF amplifier: the DR-VE-0.1-MO, is also available to be used with the modulator: it meets the specifications of the RF signal and perfectly matches the modulator both mechanically and electrically. 

In addition to the low-frequency phase modulators, Exail also offers optical delay lines (Variable Optical Delay Lines - VODL), based on micro-optic assemblies. They are necessary to align the optical paths of the different laser channels. As with phase modulators, the VODL are available in the same wavelength range where lasers are operating.

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Exail schema coherent beam combination cbc

Coherent laser seeder

First stage amplifier

Second stage amplifier

Power combiner

Delivery fiber

Low Frequency Phase Modulator

Transform mirror

Laser output

Exail schema coherent beam combination cbc
Coherent Beam Combination

Spectral Beam Combination (SBC)

The construction of a high-power fiber laser by combining different laser beams can also be done with the Spectral Beam Combination (SBC) technique. Different laser beams emitting a continuous signal, centered on distinct wavelengths, are superimposed by adaptive optics. The result of the laser system is a uniform intensity distribution and an optical signal with power proportional to the number of laser beams combined.

However, the maximum transmitted optical power in each fiber amplifier is severely constrained by the non-linear Brillouin effect. This effect, also called Stimulated Brillouin Scattering (SBS) can be mitigated by broadening the laser linewidth (to spread the spectral power density some GHz around the central wavelength) by the means of an electro-optical phase modulator. To create these side bands, three different RF sources can be combined with the electro-optical phase modulator. A sinusoidal electric signal, a “white noise” or a telecom “PRBS – Pseudo- Random-Bit-Sequence”. With this technique, optical output higher than a kilowatt continuous signal can be reached, spectrally modulated, and combined with other fiber amplifiers to obtain the final and expected laser power level.

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Spectral beam combination 1

Wide Bandwith Phase modulator

Fiber laser chassis

Fiber laser module

Laser seeder

Optical amplification

Delivery fiber

Fiber array

Transform mirror

Laser output

Diffraction grating

Spectral beam combination 1
Spectral Beam Combination

An integrated solution for Coherent Beam Combination (CBC)

The Modbox-CBC is an optimized multi-channels phase modulation solution for multibeam coherent combination. Such a turnkey laser seeder embeds multi-beams phase modulators arrays, and Variable Optical Delay Line in option. This integrated solution ensures high optical performances thanks to the selection of high grade modulators to ensure an accurate, adjustable, and reliable phase-lock modulation solution for CBC technique. The ModBox-CBC is available in the 1 µm and 2 µm range.

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Exail schema an integrated solution for coherent beam combination 3

Temperature controllers

Variable Optical Delay Lines (VODL)

Phase Modulator

Optical fiber storage

RF driver

Exail schema an integrated solution for coherent beam combination 3

Fiber solutions to develop high-power laser architectures

2 µm fiber laser sources for defense applications

High-energy lasers emitting in the sub-2 µm range find applications in the fields of Directional Infrared CounterMeasures (DIRCM) and Directed Energy Lasers (DEL). Even if still more expensive than the 1 or 1.5 µm lasers, the 2 µm lasers have as a considerable asset to be “eye-safe”, meaning that our eye is sensitive to its beam and instinctively closes itself when touched.

On top of the modulation solution and the integrated micro-optics benches (VODL), Exail leverages 20 years of experience in manufacturing specialty optical fibers. Its portfolio counts a range of thulium (Tm) & holmium (Ho) doped fibers for amplifiers and fiber lasers, as well as Fiber Bragg Gratings, addressing the 2 µm market. They are key components for the development of laser architecture in the 2 µm range that are as efficient as possible, and that can deliver high power (around 200 W).

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2 m fiber laser sources for defense applications

Thulium & Holmium Doped-Fiber

Exail portfolio counts Thulium (Tm) & holmium (Ho) doped fibers for amplifiers and fiber lasers, as well as Fiber Bragg Gratings, addressing the 2 µm market. They are key components for the development of laser architecture in the 2 µm range that are as efficient as possible, and that can deliver high power (around 200 W).

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Exail ground-breaking approach to design, develop and integrate setups with industry-grade optical building blocks, using ultra-accurate assembly.

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