Doubly Resonant OPO with Mobile Crystal for Fast Frequency Scanning
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Solution Overview
Problem
Existing optical parametric oscillators face limitations in frequency tuning range and scanning speed due to imperfections in piezoelectric shims and the need for costly control systems, which restrict their application and efficiency.
Innovation Solution
A doubly resonant optical parametric oscillator with a nonlinear crystal that is mobile in the xz plane at an inclined angle, allowing simultaneous adjustment of signal and complementary cavity lengths to maintain mode coincidence without external correction, enabling continuous frequency tuning over a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If piezoelectric shims are used to adjust cavity lengths for frequency tuning, then frequency tuning capability is improved, but scanning speed is limited and control system complexity increases
Solution Approach 1:
The patent transforms the static cavity length adjustment mechanism into a dynamic one by introducing a movable mirror mounted on a piezoelectric actuator. This allows real-time, continuous adjustment of the optical cavity length, enabling fast frequency scanning without the limitations of fixed piezoelectric shims. The dynamic adjustment capability directly addresses the scanning speed limitation while maintaining frequency tuning precision.
Solution Approach 2:
The patent replaces the complex mechanical adjustment system involving multiple piezoelectric shims and manual alignment mechanisms with a simplified electro-mechanical system using a single piezoelectric actuator controlling mirror position. This substitution reduces mechanical complexity while improving response speed through electrical control of the actuator.
2Measurement precision
If external correction systems are implemented to maintain mode coincidence, then spectral purity is improved, but device complexity and cost increase
Solution Approach 1:
The patent implements a self-correcting mechanism where the movable mirror automatically adjusts the cavity length to maintain mode coincidence between the signal and complementary cavities. The system uses the inherent relationship between cavity lengths and mode frequencies to self-regulate, eliminating the need for external correction systems while maintaining high spectral purity.
Solution Approach 2:
The patent introduces a feedback mechanism where the position of the movable mirror is continuously adjusted based on the mode coincidence condition. By monitoring the spectral output and adjusting the mirror position accordingly, the system maintains optimal operation without requiring complex external correction equipment.
3Adaptability or versatility
If cavity lengths are adjusted independently to tune frequency, then frequency range is improved, but mode coincidence is lost and parasitic modes appear
Solution Approach 1:
The patent changes the control parameter from independent cavity length adjustments to a coupled adjustment mechanism. By controlling the movable mirror position, the system simultaneously adjusts the effective optical path length in a way that maintains the required relationship between signal and complementary cavity modes, enabling wide frequency tuning without losing mode coincidence.
Solution Approach 2:
The patent introduces asymmetry in the cavity structure by making one cavity length adjustable via mirror position while keeping the other fixed. This asymmetric design allows independent control of the optical path difference between cavities, enabling frequency tuning while maintaining mode coincidence through the controlled asymmetry rather than requiring symmetric independent adjustments.
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
This approach enhances the frequency tuning range and scanning speed while reducing implementation costs, allowing for continuous tuning beyond the parametric gain width without parasitic mode issues, with minimal deviation in optical lengths and maintaining high spectral purity.
Implementation Method 1
Second-order nonlinear processes are used in optics to produce new radiation from a primary radiation source... One of these processes, known from the prior art as 'optical parametric conversion' makes it possible to generate two radiations, called signal and complementary, from a so-called pump radiation
Implementation Method 2
it is necessary that the wave vectors of the different radiations noted K J , with j = p, s or c, comply with a condition known from the prior art as an 'exact phase matching condition' or 'quasi phase matching condition'
Implementation Method 3
the crystal is mobile in the plane xz in a direction inclined by a non-zero angle β with respect to the direction x such as to simultaneously change the respective optical lengths ls and lc of the two resonant cavities
Implementation Method 4
a first resonant cavity for the signal radiation... with a second resonant cavity for the complementary radiation... forming a doubly resonant resonator
Data Source
Figure 1~2
Figure 3a~3b
Figure 4
AI summary
A doubly resonant optical parametric oscillator with achromatic phase-maintaining pump feedback comprising a pump radiation source (11) (fp), a nonlinear crystal (7) located within two resonant cavities for signal radiation (fs) and complementary radiation (fc), of respective optical lengths ls and lc, and forming a doubly resonant resonator for a single pair of longitudinal signal and complementary modes, the crystal is prismatic in shape with its rear face (9) inclined at a non-zero angle α with respect to the x direction orthogonal to the z direction of radiation propagation, the crystal (7) being mobile in the xz plane.The crystal (7) is mobile along a direction forming a non-zero angle β with respect to the x direction to allow the rapid frequency sweep of the oscillator, the value of β is fixed so that the displacement of the crystal (7) is accompanied by a change in the respective optical lengths ls and lc of the two resonant cavities in a ratio such that the double resonance between the longitudinal modes of each cavity is maintained, thanks to which the values of the frequencies fs and fc are continuously tunable over a wide range without having to resort to a cavity length control and correction device capable of guaranteeing the coincidence of modes between the two cavities.