Ultrashort Pulse Phase Spectrum Measurement via Spatial Light Modulator
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Solution Overview
Problem
Existing methods for measuring the phase spectrum of ultrashort pulsed light are inefficient, often requiring iterative optimization calculations and can converge to local solutions, making it difficult to accurately measure the phase spectrum in a short time.
Innovation Solution
A waveform measurement device that uses a spatial light modulator with a phase modulation hologram to modulate the phase of input light, allowing for the acquisition and comparison of intensity spectra to determine the phase spectrum, and calculates the time waveform using a frequency-time transform, with the phase spectrum determination unit setting a virtual phase spectrum to optimize the measurement process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If iterative optimization calculation methods (FROG, CESDR) are used to measure phase spectrum, then measurement accuracy can be achieved, but measurement time becomes excessively long and convergence to local solutions occurs
Solution Approach 1:
The patent applies preliminary action by using the control phase spectrum (obtained from desired time waveform) as an initial guess for the iterative optimization process. This preliminary value is much closer to the actual phase spectrum than random initialization, significantly reducing the number of iterations needed to converge while avoiding local minima. The measurement process starts from a physically meaningful initial state rather than arbitrary values.
Solution Approach 2:
The patent implements feedback by using the measured intensity spectrum and the currently estimated phase spectrum to calculate a synthesized intensity spectrum, comparing it with the measured one, and using the difference (error) to update the phase spectrum estimate. This iterative feedback loop continues until convergence, ensuring both accuracy and efficiency by guiding the optimization toward the correct solution.
2Measurement precision
If conventional iterative methods are used for phase spectrum measurement, then accurate results can be obtained, but calculation complexity and time consumption increase significantly
Solution Approach 1:
By providing the control phase spectrum as an initial guess, the patent reduces the search space for optimization algorithms. This preliminary information guides the iterative process more efficiently, reducing the number of calculation steps required and simplifying the overall computational burden while maintaining measurement accuracy.
3Measurement precision
If FROG or CESDR methods are employed to measure phase spectrum, then measurement can be performed, but convergence to local solutions rather than optimal solutions occurs
Solution Approach 1:
The control phase spectrum derived from the desired time waveform serves as a physically meaningful initial guess that is already close to the optimal solution. This preliminary action dramatically reduces the risk of convergence to local minima, as the optimization starts from a point within the basin of attraction of the global optimum rather than from arbitrary initial conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the measured intensity spectrum continuously guides the phase spectrum estimation through iterative optimization. The error between measured and synthesized intensity spectra provides directional information that reliably guides convergence toward the optimal solution, ensuring both accuracy and reliability of the measurement.
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 accurate and rapid measurement of the phase spectrum of ultrashort pulsed light, reducing calculation time and improving measurement precision by deforming the control phase spectrum to match the actual phase spectrum.
Implementation Method 1
modulating a phase of input light including two or more wavelength components for each wavelength in a spatial light modulator to which a phase modulation hologram based on a control phase spectrum
Implementation Method 2
an optical element inputting the pulsed light and outputting light having an intensity spectrum corresponding to the phase spectrum of the pulsed light
Implementation Method 3
a waveform calculation unit for calculating a time waveform of the pulsed light, using a frequency-time transform, on the basis of the phase spectrum determined in the phase spectrum determination unit and the input intensity spectrum
Data Source
AI summary
A waveform measurement device includes an input spectrum acquisition unit for acquiring an input intensity spectrum being an intensity spectrum of pulsed light, an optical element inputting the pulsed light and outputting light having an intensity spectrum corresponding to a phase spectrum of the pulsed light, an output spectrum acquisition unit for acquiring an output intensity spectrum being an intensity spectrum of the light output from the optical element, and a phase spectrum determination unit for determining the phase spectrum of the pulsed light by comparing an output intensity spectrum calculated when the pulsed light having an input intensity spectrum and a virtual phase spectrum is assumed to be input to the optical element with the output intensity spectrum acquired in the output spectrum acquisition unit. The phase spectrum determination unit sets the virtual phase spectrum by deforming the control phase spectrum.