Phase-Locked Chirped Laser Spectrometer Without External Modulators
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Solution Overview
Problem
Existing chirped laser dispersion spectroscopy (CLaDS) systems require external optical modulators, which increase size, cost, power consumption, and complexity, and are limited by modulation frequency constraints due to the use of acousto-optical and electro-optical modulators.
Innovation Solution
Generate optical frequency signals using actively phase-locked coherent optical sources, such as a master and slave tunable lasers, with a common bias current supply and beam combining optics, eliminating the need for external modulators and enabling programmable phase modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external optical modulators (acousto-optic or electro-optical) are used to generate optical frequency signals in CLaDS systems, then the dispersion signal can be measured, but the system size, cost, power consumption, and complexity increase
Solution Approach 1:
The patent removes the external optical modulator component from the CLaDS system. Instead of using acousto-optic or electro-optical modulators to generate the optical frequency signals, the invention uses direct laser frequency modulation through current modulation of the laser diode, eliminating the modulator and its associated complexity
Solution Approach 2:
The patent combines the laser source and frequency modulation function into a single integrated system. The laser diode serves both as the optical source and the frequency modulator, with the modulation achieved through direct current control of the laser, merging what were previously separate components
2Ease of operation
If acousto-optic or electro-optical modulators are used for optical modulation, then frequency modulation can be achieved, but the modulation frequency is constrained by the modulator characteristics
Solution Approach 1:
The patent changes the modulation approach from external modulator-based frequency control to direct laser parameter modulation. By modulating the laser diode current, the optical frequency is directly controlled, allowing flexible modulation frequencies limited only by the laser diode's response characteristics rather than modulator constraints
Solution Approach 2:
The patent implements dynamic frequency modulation through real-time current control of the laser diode. The modulation frequency and depth can be dynamically adjusted by changing the current modulation parameters, providing adaptability across a wide frequency range
3Measurement precision
If absorption-based laser spectrometry is used for gas detection, then molecular species can be detected, but non-linear signal behavior occurs at high mole fractions causing false negatives
Solution Approach 1:
The patent exploits the phase relationship between absorption and dispersion signals. By using frequency modulation and detecting the dispersion component (which is the derivative of absorption with respect to frequency), the system achieves linear signal behavior at high concentrations while absorption-based methods suffer from non-linearity due to the Beer-Lambert law
4Measurement precision
If photodetector gain is increased to improve signal-to-noise ratio in absorption spectroscopy, then detection sensitivity improves, but signal clipping occurs and dynamic range is limited
Solution Approach 1:
The patent uses dynamic frequency modulation and detection methods to achieve signal processing that maintains linearity across a wide dynamic range. The frequency-modulated dispersion signal detection approach allows the photodetector to operate in a linear regime while still achieving high sensitivity through the derivative nature of the dispersion signal
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 provides a cost-effective, compact, and efficient CLaDS system with improved modulation frequency flexibility and reduced noise, achieving low mole fraction detection and wide dynamic range without non-linear signal behavior.
Implementation Method 1
active-phase locking means to render the phases of the first and second beams coherent with each other and to produce at least one radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal
Implementation Method 2
produce at least one radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal
Implementation Method 3
a beam combining optical element, preferably a beam splitter to produce a single beam from the first and second tunable lasers
Implementation Method 4
a photodetector; and active-phase locking means
Implementation Method 5
measure frequency variations due to the refractive index change caused by dispersion from an optical absorption line of the measurand
Implementation Method 6
chirped laser dispersion spectroscopy (CLaDS) and variants thereof
Data Source
Figure 1
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AI summary
The invention provides a chirped laser dispersion spectrometer having two tunable lasers each with a bias current supply, a chirp signal source to provide a matching chirp pattern, a beam splitter to produce a single beam from the two first and second tunable lasers and active-phase locking means to render the two beams phase coherent and to produce a radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal. The invention also provides a method for generating at least two optical frequency signals for use in a frequency modulation spectroscopy (FMS) process for the detection and/or measurement of molecular species in a gas mixture and a method for generating at least two optical frequency signals for use in a chirped laser dispersion spectroscopy (CLaDS) process for the detection and/or measurement of molecular species in a gas mixture. The invention provides an efficient and cost-effective CLaDS system which maintains optical modulation whilst enabling greater change of the modulation frequency.