Broadband Light Source Assembly Using Normal Dispersion Fiber
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Solution Overview
Problem
Known broadband light source assemblies suffer from high levels of relative intensity noise (RIN) in the white light generated, making them unsuitable for certain applications such as achieving the required on-product overlay (OPO) with precision.
Innovation Solution
A broadband light source assembly comprising a femtosecond pump laser emitting pulses of radiation with an energy per pump pulse of greater than 50 nJ, and an all-normal dispersion optical fiber that receives these pulses, resulting in full conversion into broadband radiation with reduced RIN.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a broadband light source assembly uses modulation instability (MI) based whitelight generation, then broadband radiation is generated, but the relative intensity noise (RIN) becomes too high for precision applications
Solution Approach 1:
The patent changes the dispersion parameter of the optical fiber from anomalous dispersion (used in MI-based sources) to normal dispersion. This parameter change fundamentally alters the whitelight generation mechanism from modulation instability to self-phase modulation, thereby reducing RIN while maintaining broadband radiation generation capability
Solution Approach 2:
Instead of using the conventional approach of generating whitelight through modulation instability in anomalously dispersive fibers, the patent inverts the approach by using normal dispersion fibers and self-phase modulation. This inversion of the generation mechanism resolves the RIN problem while achieving the same broadband output
2Measurement precision
If higher power spectral density is achieved in broadband radiation, then application precision improves, but relative intensity noise increases
Solution Approach 1:
By changing the dispersion parameter to normal and adjusting the pump pulse energy to greater than 50 nJ, the patent achieves a favorable operating point where high power spectral density is obtained through efficient self-phase modulation while keeping RIN below 10^-5 [Hz^-1/2], satisfying precision measurement requirements
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 proposed solution achieves lower levels of relative intensity noise (RIN < 10^-5 [Hz^-1/2]) in the generated radiation, enhancing the precision of applications like on-product overlay (OPO) and allowing for higher power spectral density in the broadband radiation.
Implementation Method 1
Spectral broadening of the input radiation may be dominated by modulation instability, self-phase modulation, or soliton dynamics
Implementation Method 2
Spectral broadening of the input radiation may be dominated by modulation instability, self-phase modulation, or soliton dynamics
Implementation Method 3
an all-normal dispersion optical fiber arranged to receive the pulses of radiation
Data Source
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AI summary
A broadband light source assembly comprising: a femtosecond pump laser arranged to emit pulses of radiation, wherein the pulses of radiation have an energy per pump pulse of greater than 50 nJ; and an all-normal dispersion optical fiber arranged to receive the pulses of radiation.