Fiber Laser Dispersion Compensation for Microscopy
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Solution Overview
Problem
Current systems lack a viable commercial solution for generating high power femtosecond pulses in the 920 and 1300 nm wavelength windows, essential for two-photon microscopy, due to the absence of appropriate fiber lasing materials and effective fiber delivery methods.
Innovation Solution
A fiber laser system is developed to generate and deliver femtosecond pulses in the 920 and 1300 nm ranges using neodymium (Nd) fiber amplifiers, thulium (Tm) fiber lasers, and optical parametric amplification, with dispersion compensation using holey, photonic crystal, and Kagome fibers to achieve high power and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fiber laser based ultrashort pulse sources are used for medical imaging and microscopy, then robustness and long term stability are improved, but the ability to generate high power femtosecond pulses in the 920 and 1300 nm wavelength windows deteriorates due to absence of appropriate fiber lasing materials
Solution Approach 1:
The patent uses optical parametric amplification (OPA) as an intermediary process to convert pump light at one wavelength into signal and idler beams at desired wavelengths (920 nm and 1300 nm). This allows fiber laser systems to generate pulses at wavelengths where direct fiber lasing materials are unavailable, resolving the contradiction between system robustness and wavelength versatility.
Solution Approach 2:
The patent employs nonlinear optical processes including difference frequency mixing and Raman shifting to change the wavelength parameter of the laser output. By using Tm fiber lasers (1.9 μm) combined with frequency doubled Er fiber lasers (780 nm) to produce 1300 nm pulses, and Nd fiber amplifiers for 920 nm pulses, the system achieves multiple wavelength outputs from fiber-based platforms.
2Object-affected harmful factors
If ultrashort pulses are delivered through optical fibers, then eye safety and compact delivery are improved, but pulse broadening due to dispersion deteriorates the ultrashort pulse quality
Solution Approach 1:
The patent applies dispersion compensation techniques in advance before pulse delivery through the fiber. By pre-compensating for the dispersion that will occur during fiber transmission, the system maintains ultrashort pulse widths at the output despite the eye-safe fiber delivery medium.
Solution Approach 2:
The patent introduces specialized dispersion compensating fibers (holey fibers, photonic crystal fibers, and Kagome fibers) as intermediary elements that counteract the dispersive effects of the delivery fiber. These compensating fibers act as mediators that restore pulse quality while allowing safe fiber-based delivery.
3Power
If Nd fiber amplifiers are used to amplify 920 nm pulses, then high power output is improved, but gain depletion due to amplified spontaneous emission near 1060 nm deteriorates the amplification efficiency
Solution Approach 1:
The patent extracts or removes the problematic 1060 nm amplified spontaneous emission from the system using optical filters. By selectively blocking this wavelength while allowing 920 nm transmission, the system maintains high amplification efficiency without energy loss to spontaneous emission at the wrong wavelength.
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
The system provides high-quality, ultrashort pulses with pulse widths in the range of 100 fs to 200 fs, enabling efficient two-photon microscopy by maximizing photon excitation and minimizing pulse broadening, thus overcoming the limitations of existing technologies.
Implementation Method 1
pulses generated with a fs seed (fs input) source are amplified in neodymium (Nd) fiber amplifier stage(s)
Implementation Method 2
a thulium (Tm) fiber laser operating at 1.9 μm
Implementation Method 3
a frequency doubled Er fiber laser emitting at 780 nm
Implementation Method 4
In some embodiments optical parametric amplification (OPA) may be utilized, which further allows for a wavelength tunable source
Implementation Method 5
a wavelength in the 1.3 μm (1300 nm) spectral range can be obtained via difference frequency mixing of a frequency doubled Er fiber laser emitting at 780 nm with a thulium (Tm) fiber laser operating at 1.9 μm
Implementation Method 6
subsequent frequency doubling can also be implemented
Implementation Method 7
Raman shifting of a Tm or holmium (Ho) fiber laser in a fluoride fiber to 2.6 μm
Implementation Method 8
with dispersion compensation using holey, photonic crystal, and Kagome fibers to achieve high power and stability
Data Source
AI summary
In one aspect, the present disclosure describes a fiber laser system for the generation and delivery of femtosecond (fs) pulses in multiple wavelength ranges. For improved versatility in multi-photon microscopy, an example of a dual wavelength fiber system based on Nd fiber source providing gain at 920 and 1060 nm is described. An example of a three-wavelength system is included providing outputs at 780 nm, 940 nm, and 1050 nm. The systems include dispersion compensation so that high quality fs pulses are provided for applications in microscopy, for example in multiphoton microscope (MPM) systems.