External Cavity Tunable Laser Wedge Etalon Mode Hopping
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Solution Overview
Problem
Tunable lasers face issues with mode hopping, which introduces unwanted intensity noise due to the inability to simultaneously tune wavelength and cavity length without causing frequency shifts, leading to unreliable emission tuning.
Innovation Solution
A laser system with a wavelength discriminating structure, such as an etalon, where the angle of incidence of the laser input is selectively changed to simultaneously adjust the cavity length and frequency, using a shear plate configuration with rotating etalon mirrors on matched wedges to prevent mode hopping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the wavelength of laser emission is tuned by changing the optical space between etalon mirrors, then the wavelength can be adjusted, but mode hopping occurs causing unwanted intensity noise
Solution Approach 1:
The patent changes multiple parameters simultaneously - specifically, it changes both the optical space between etalon mirrors and the angle of incidence of the laser beam on the etalon. This coordinated parameter change allows wavelength tuning while maintaining the laser output on a single longitudinal mode, preventing mode hopping and the associated intensity noise that would occur with single-parameter tuning.
2Adaptability or versatility
If wavelength-selective optical elements are placed in the laser cavity to select a particular longitudinal mode, then laser tuning is achieved, but the laser can only support certain discrete modes causing mode hopping
Solution Approach 1:
The patent introduces dynamic control of two parameters simultaneously - the optical space between etalon mirrors and the angle of incidence. This dynamic coordination allows the laser to continuously track a single longitudinal mode across a tuning range, rather than jumping between discrete modes. The etalon is rotated about an axis transverse to the optical path to change the angle of incidence, creating a dynamic solution that maintains mode stability.
3Measurement precision
If the etalon FSR is made substantially larger than the desired tuning range to ensure single peak transmission, then wavelength selection is improved, but the bandwidth of transmission peaks limits the tuning range
Solution Approach 1:
The patent adds another dimension to the tuning mechanism by introducing angle of incidence as a second independent parameter. Instead of relying solely on changing the optical space between mirrors (one dimension), the system now varies both the optical space and the angle at which the laser beam strikes the etalon. This two-dimensional approach allows the system to achieve both precise wavelength selection and extended tuning range simultaneously.
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 reliable tuning of laser emission across a significant wavelength range without mode hopping, achieving a narrow linewidth and precise frequency control with reduced intensity noise.
Implementation Method 1
Transmission through an etalon is generally low except for a series of peaks, which are approximately equally spaced at an interval known as the free spectral range (FSR) of the etalon
Implementation Method 2
the first and second substrates and said respective first and second mirrors are configured to act as an effective, substantially shear plate
Data Source
AI summary
A tunable narrow linewidth laser is provided, wherein an adjustable etalon structure is employed to simultaneously tune the wavelength of the laser transmission and the length of the laser cavity. The etalon structure is an effective, relatively thick shear plate comprised of transparent matched wedge-shaped substrates and a pair of parallel, partially transmissive mirrors with a space therebetween. Rotation of the etalon structure relative to the laser input changes the angle of incidence to the first substrate and the etalon angle, thereby changing the wavelength of the laser light and also changing the length of the external laser cavity. Thus, reliable frequency tuning is achieved, without mode hopping.