1.5 µm Fiber Laser for Atmospheric Turbulence Correction
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Solution Overview
Problem
Current active imaging systems lack a reliable illumination source capable of emitting high energy pulses at 1.5 µm wavelength with a high repetition rate, suitable for correcting atmospheric turbulence effects in optical directed energy weapons, while maintaining eye safety and efficient beam quality.
Innovation Solution
The system employs a chain of erbium-doped and ytterbium-co-doped fiber lasers, distributing energy across multiple fibers to achieve high energy pulses of up to 250 mJ at 1 kHz, combined with an optical system that adjusts the field of observation and beam quality through a matrix arrangement of lenses and prisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a single high-energy fiber amplifier is used, then the extractable energy is limited by saturation effects, but increasing the fiber diameter degrades beam quality
Solution Approach 1:
The invention divides a single high-energy amplifier into multiple parallel fiber amplifiers (e.g., 7 fibers for 70 mJ, 25 fibers for 250 mJ). Each fiber maintains small core diameter for good beam quality while the parallel arrangement provides cumulative energy. The amplifiers are driven in parallel by a common pump source, achieving high total energy extraction without sacrificing individual fiber beam quality.
2Power
If the pump repetition rate is increased to achieve high average power, then the energy per pulse decreases due to crystal absorption and thermo-mechanical limitations
Solution Approach 1:
The invention changes the pump wavelength parameter from conventional 808 nm to 940 nm, which better matches the absorption band of erbium-doped fiber. This parameter change enables efficient pumping at high repetition rates (up to 1 kHz) while maintaining high energy per pulse (250 mJ at 1 kHz demonstrated). The fiber medium's flexible thermal properties allow high repetition rate operation without the thermo-mechanical limitations of solid-state crystals.
3Use of energy by moving object
If a conventional solid laser is used for high energy output, then the system can achieve high energy per pulse, but the repetition rate is limited to low values
Solution Approach 1:
The invention replaces conventional solid-state laser crystals with erbium-doped fiber as the active medium. This substitution enables operation at high repetition rates (kHz range) while maintaining high energy per pulse (250 mJ). The fiber's superior thermal conductivity and flexible geometry allow efficient heat dissipation at high pump rates, overcoming the fundamental limitations of crystal-based solid lasers.
4Adaptability or versatility
If the field of observation is adjusted using optical zoom, then the illumination must cover variable angles, but a fixed illumination source cannot adapt to different target distances
Solution Approach 1:
The invention couples the high-energy fiber laser source with an optical zoom system that dynamically adjusts the field of observation. The illumination system adapts to different target distances and observation angles by modifying the optical path through zoom lenses, allowing the same high-energy source to effectively illuminate targets at varying ranges while maintaining beam quality and energy density.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration delivers a high-energy, short-pulse optical beam with adjustable field of observation, effectively overcoming atmospheric turbulence and eye safety constraints, enabling precise target tracking and imaging.
Implementation Method 1
a chain of amplifiers (N) in parallel, each amplifier comprising a laser medium in the form of an erbium-doped fiber or an erbium-doped and ytterbium-co-doped fiber
Implementation Method 2
Each of these N amplifiers makes it possible to generate a beam of quality 20 mm.mrad and to deliver pulses of a few hundred nanoseconds wide at a repetition frequency of the order of 1 kHz with an energy level of 10 mJ per pulse
Implementation Method 3
combined with an optical system that adjusts the field of observation and beam quality through a matrix arrangement of lenses and prisms
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention relates to a pulsed-laser imaging source emitting at a wavelength of about 1.5 microns over a spectral band (??) of a few nanometers and delivering a power of between at least a few tens of millijoules and several hundred millijoules, characterized in that it comprises: a source (Ds) emitting a wave having pulses of duration longer than about a few tens of nanoseconds; a set of amplifiers (Ampli1, Ampli2, Ampli3) delivering an amplified wave from the wave output by the pulsed source; and a set of N fibres (Fi) connected in parallel, supplied with the amplified wave, each of the fibres connected in parallel being coupled to an output amplifier.