Nonlinear Chirp Element for Fiber Amplifier SPM Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current UV-DUV laser inspection systems face challenges in generating narrow bandwidth UV laser light due to Self Phase Modulation (SPM) effects in fiber amplifiers, which increase spectral bandwidth beyond acceptable limits, making it difficult to achieve high resolution imaging with low frequency UV-DUV laser light.
Innovation Solution
A fiber-based fundamental light source is developed that incorporates a nonlinear chirp element, such as Bragg gratings or electro-optic modulators, to compensate for SPM characteristics, allowing for high peak power and narrow bandwidth fundamental light generation, which is then converted to desired UV-DUV frequencies using a frequency conversion module.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If fiber amplifiers are used to generate high peak power fundamental light, then the peak power is improved, but the spectral bandwidth increases beyond acceptable limits due to SPM effects
Solution Approach 1:
A nonlinear chirp element is introduced before the fiber amplifier to pre-compensate for the SPM effect. The nonlinear chirp has an opposite sign to the SPM-induced chirp, so that when the light passes through the amplifier, the two chirps cancel each other out, maintaining narrow spectral bandwidth while achieving high peak power
Solution Approach 2:
The nonlinear chirp element acts as an intermediary component between the seed laser and the fiber amplifier. It modifies the phase of the input light to counteract the SPM effect that will occur in the amplifier, enabling the amplifier to deliver high power without excessive bandwidth broadening
2Power
If conventional fiber amplifiers are used, then high peak power is achieved, but the FWHM bandwidth increases ten-times beyond seed light bandwidth
Solution Approach 1:
The nonlinear chirp element pre-applies a phase modulation with opposite sign to the expected SPM chirp. This preliminary anti-action ensures that when the light undergoes SPM in the fiber amplifier, the net chirp is minimized, keeping the FWHM bandwidth close to the seed light bandwidth even at high peak powers
3Power
If conventional fiber amplifiers are used, then high peak power is achieved, but the E95 bandwidth increases seven-times beyond seed light bandwidth
Solution Approach 1:
The nonlinear chirp element compensates for SPM effects across the entire pulse duration, not just at the peak. This ensures that the energy-containing portion of the spectrum (E95 bandwidth) remains narrow, achieving seven-times improvement over conventional amplifiers while maintaining high peak power
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 solution effectively reduces the spectral bandwidth of the fundamental light, achieving a ten-times reduction in FWHM and seven-times improvement in E95 bandwidth, enabling the cost-effective manufacture of high resolution laser inspection systems with improved imaging capabilities.
Implementation Method 1
Current UV-DUV laser inspection systems face challenges in generating narrow bandwidth UV laser light due to Self Phase Modulation (SPM) effects in fiber amplifiers
Implementation Method 2
A fiber-based fundamental light source is developed that incorporates a nonlinear chirp element, such as Bragg gratings or electro-optic modulators, to compensate for SPM characteristics
Implementation Method 3
which is then converted to desired UV-DUV frequencies using a frequency conversion module
Data Source
AI summary
A laser system for semiconductor inspection includes a fiber-based fundamental light source for generating fundamental light that is then converted/mixed by a frequency conversion module to generate UV-DUV laser light. The fundamental light source includes a nonlinear chirp element (e.g., a Bragg grating or an electro-optic modulator) that adds a nonlinear chirp to the seed light laser system prior to amplification by the fiber amplifier(s) (e.g., doped fiber or Raman amplifiers). The nonlinear chirp includes an x2 or higher nonlinearity and is configured to compensates for the Self Phase Modulation (SPM) characteristics of the fiber-based amplifiers such that fundamental light is generated that has a spectral E95 bandwidth within five times that of the seed light. When multiple series-connected amplifiers are used, either a single nonlinear chirp element is provided before the amplifier string, or a chirp elements are included before each amplifier.