Beam Multiplexer Pulse Splitting for Faster Refractive Index Writing
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Solution Overview
Problem
The speed and efficiency with which refractive index changes can be written into optical materials, such as ocular tissues, are limited by the need to deliver concentrated pulse energies without exceeding damage thresholds, which restricts the size and complexity of refractive index structures that can be achieved.
Innovation Solution
A beam multiplexer system that divides a pulsed laser beam into multiple beams with controlled temporal and spatial relationships, allowing for increased repetition rates, larger refractive index changes, and extended depth writing while maintaining below damage thresholds, by adjusting pulse energy, duration, and focusing volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If concentrated pulse energies are delivered to achieve desired refractive index changes, then the refractive index modification efficiency is improved, but the damage threshold of the optical material is exceeded causing light scattering and absorption degradation
Solution Approach 1:
The patent divides a single high-energy pulse into multiple lower-energy sub-pulses by using a beam multiplexer system with acousto-optic modulators. This segmentation allows the total energy to be delivered in distributed temporal packets that collectively achieve the desired refractive index change without exceeding the damage threshold at any single moment, thus resolving the contradiction between writing speed and material damage.
Solution Approach 2:
The patent employs periodic modulation of the laser beam through acousto-optic modulators to create a series of equally spaced sub-pulses within the original pulse duration. This periodic action distributes the energy delivery over time, maintaining average power below damage thresholds while accumulating sufficient energy deposition to achieve effective refractive index modification, thereby improving productivity without causing harmful material damage.
2Productivity
If the pulse repetition rate is increased to improve writing speed, then the productivity is improved, but the heat accumulation causes material damage
Solution Approach 1:
The patent segments each high-repetition-rate pulse into multiple lower-energy sub-pulses using acousto-optic modulators. This segmentation allows the system to operate at high repetition rates for improved writing speed while the sub-pulse structure prevents excessive heat accumulation by distributing energy delivery, thus resolving the contradiction between productivity and temperature control.
3Manufacturing precision
If the pulse energy is increased to achieve larger refractive index changes, then the manufacturing precision is improved, but the damage threshold is exceeded
Solution Approach 1:
The patent uses periodic sub-pulse modulation to deliver cumulative energy that achieves large refractive index changes equivalent to high single-pulse energy, but distributed over multiple lower-energy pulses. This periodic action maintains precision by ensuring each sub-pulse remains below the damage threshold while the cumulative effect achieves the desired manufacturing precision, thus resolving the contradiction between refractive index change magnitude and light scattering prevention.
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
Enables faster, more accurate, and efficient writing of refractive index structures, supporting 2π phase changes over extended depths, thereby enhancing optical performance and reducing the number of layers required.
Implementation Method 1
The energy regimes, while above the nonlinear absorption threshold, are typically just below the breakdown thresholds of the optical materials
Implementation Method 2
A beam multiplexer system that divides a pulsed laser beam into multiple beams with controlled temporal and spatial relationships
Implementation Method 3
directing said pulses at the tissue of the living eye and focusing said pulses to form the focus spot
Data Source
Figure 1A~1B
Figure 2~3
Figure 4~5
AI summary
A refractive index writing system includes a pulsed laser source, an objective lens for focusing an output of the pulsed laser source to a focal spot in an optical material, and a scanner for relatively moving the focal spot with respect to the optical material along a scan region. A beam multiplexer divides the output of the laser source into at least two working beams that are focused to variously shaped focal spots within the optical material. A controller controls at least one of a temporal and a spatial offset between the focal spots of the working beams together with the relative speed and direction of the scanner for maintaining an energy profile within the optical material along the scan region above a nonlinear absorption threshold of the optical material and below a breakdown threshold of the optical materials.