Low-Coherence Light Source Using Waveguide Cavity for Speckle Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Coherent light sources often produce speckle noise due to interference patterns when passing through scattering media, which can hinder diagnostic and therapeutic applications like optical coherence tomography and spectroscopy.
Innovation Solution
Increasing the optical cavity length of a light source using an optical waveguide to reduce the temporal coherence length of emitted light to be shorter than the scattering distance associated with the target area, thereby minimizing speckle noise, and incorporating a signal normalization system to compensate for intensity fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the optical cavity length is increased to reduce temporal coherence length, then speckle noise is reduced, but the device complexity and stability requirements increase
Solution Approach 1:
The optical cavity is segmented into multiple sections including a gain medium section and a waveguide section. The waveguide section is further divided into multiple cascaded waveguides or sections with different group velocities, allowing the total optical path length to be extended without proportionally increasing the physical cavity size. This segmentation enables achieving long temporal coherence length (low coherence) while managing device complexity.
Solution Approach 2:
The patent transitions from a simple linear cavity to a multi-dimensional optical path structure using waveguides that can be arranged in cascaded or parallel configurations. By utilizing the spatial arrangement of multiple waveguide sections with different optical path lengths, the system achieves extended effective cavity length without linearly increasing physical dimensions, thereby reducing speckle noise while controlling complexity.
2Object-affected harmful factors
If the optical cavity length is increased to reduce temporal coherence length, then speckle noise is reduced, but the cavity stability becomes more difficult to maintain
Solution Approach 1:
The optical cavity is divided into stable, modular sections including a gain medium and multiple waveguide sections. Each section can be independently optimized and stabilized, with the overall cavity stability maintained through the modular architecture. This segmentation allows long effective cavity length for low coherence while preserving stability through manageable, discrete components.
Solution Approach 2:
Waveguides serve as intermediary elements that couple the gain medium to the output while providing a stable, controlled optical path. The waveguides with different group velocities act as mediators that extend the optical path length without introducing the mechanical instabilities associated with long free-space optical paths, thereby maintaining cavity stability while achieving low temporal coherence.
3Measurement precision
If the temporal coherence length is reduced to be shorter than scattering distance, then image clarity is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The optical path is segmented into multiple waveguide sections with individually controllable lengths and group velocities. This segmentation allows the total optical path length to be precisely controlled through the cumulative effect of discrete sections, each of which can be manufactured with standard precision tolerances. The modular approach avoids the need for a single extremely precise long cavity, thereby reducing overall manufacturing precision requirements while achieving the required temporal coherence length.
Solution Approach 2:
The patent utilizes changes in group velocity as a key parameter across different waveguide sections. By varying the group velocity parameter (through different waveguide geometries, materials, or configurations) rather than relying solely on precise physical length control, the system achieves the required optical path length differences with relaxed manufacturing tolerances. This parameter-based control enables precise temporal coherence management without stringent manufacturing precision requirements.
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 approach effectively reduces speckle noise in images and spectral signals by ensuring the temporal coherence length of the light is shorter than the scattering distance, enhancing the clarity and accuracy of diagnostic and therapeutic medical imaging and spectroscopy applications.
Implementation Method 1
The apparatus includes a first optical waveguide positioned within the first optical cavity. The first optical waveguide has a length selected to cause a temporal coherence length of light emitted from the first optical cavity to be shorter than a scattering distance associated with the target area.
Implementation Method 2
Increasing the optical cavity length of a light source to cause the temporal coherence length of the emitted light to be shorter than a scattering distance associated with the target area
Implementation Method 3
Gain media can include media that provide gain through 'population inversion' such as a semiconductor gain medium of a solid-state laser
Implementation Method 4
The first gain medium is configured to cause a plurality of the longitudinal modes of the first set to oscillate over an oscillation band within the first gain band when the first gain medium is pumped at an operative level
Implementation Method 5
reflectors defining a first optical cavity. The first optical cavity defines a first set of longitudinal modes
Implementation Method 6
This 'speckle effect' can lead to noise in a detected image or spectral signal. Speckle can also be caused in other contexts including, for example, after a beam traveling through air scatters from a rough surface
Data Source
AI summary
The invention features an apparatus and an associated method for illuminating a target area. The apparatus includes reflectors defining a first optical cavity. The first optical cavity defines a first set of longitudinal modes. The apparatus includes a first gain medium defining a first gain band. The first gain medium is configured to cause a plurality of the longitudinal modes of the first set to oscillate over an oscillation band within the first gain band when the first gain medium is pumped at an operative level. The apparatus includes a first optical waveguide positioned within the first optical cavity. The first optical waveguide has a length selected to cause a temporal coherence length of light emitted from the first optical cavity to be shorter than a scattering distance associated with the target area.