External Cavity Laser Using Spatial Light Modulator
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Solution Overview
Problem
Existing external cavity tunable lasers face challenges in achieving high tuning speed while maintaining a wide tuning range and stability, with traditional mechanical rotation methods being unsuitable for fast tuning.
Innovation Solution
The use of multiple gain elements within a single external cavity, combined with a spatial light modulator (SLM) for digital control of wavelength selection, allows for fast, random access to any wavelength, enhancing tuning speed and stability, and the construction of the cavity from transparent solid state optical material for increased robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mechanical rotation of grating is used for laser tuning, then wavelength selection is achieved, but tuning speed is slow and direction of output beam changes
Solution Approach 1:
The patent replaces the mechanical grating rotation system with a spatial light modulator (SLM) that uses electronic control to achieve wavelength tuning. The SLM modulates the phase or amplitude of light waves directly, eliminating mechanical moving parts and enabling fast, precise wavelength selection without changing the output beam direction.
Solution Approach 2:
The patent introduces a dynamically controllable SLM that can rapidly change its modulation pattern in response to electronic signals. This dynamic control allows the laser wavelength to be tuned quickly and precisely without the inertia and mechanical constraints of rotating gratings, while maintaining stable beam output through electronic feedback control.
2Adaptability or versatility
If external cavity design is used for wide tuning range, then wavelength stability is improved, but tuning speed is limited
Solution Approach 1:
The patent replaces mechanical tuning mechanisms within the external cavity with an electronically controlled SLM. This substitution maintains the wide tuning range capability of the external cavity design while enabling rapid wavelength changes through electronic modulation, removing the speed limitation imposed by mechanical components.
Solution Approach 2:
The patent changes the control parameter from mechanical position (grating angle) to electronic modulation parameters (phase or amplitude patterns on SLM). This parameter change enables continuous, rapid wavelength tuning across the full cavity range without mechanical constraints, achieving both wide adaptability and high speed.
3Power
If single gain element is used in external cavity, then device simplicity is maintained, but output power and tuning range are limited
Solution Approach 1:
The patent merges multiple gain elements within a single external cavity structure, allowing them to operate simultaneously or in sequence. The SLM enables independent control of each gain element's contribution to the output, achieving higher total power and extended tuning range while maintaining relatively simple cavity architecture through unified electronic control.
Solution Approach 2:
The patent makes the external cavity structure universal by designing it to accommodate multiple types of gain elements (e.g., different laser media or wavelengths). The SLM provides multi-functional control capability, allowing the same cavity to support various gain elements and achieve diverse output characteristics without requiring separate cavity structures for each.
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 results in a laser source with a wider tuning range, higher output power, and enhanced spectroscopic detection sensitivity, enabling faster chemical analysis and material identification with improved resistance to external disturbances.
Implementation Method 1
The first-order diffracted beam is captured by a lens (not shown) and directed towards the SLM 28
Implementation Method 2
The light emerging from the AR coated facet is collimated with a high numerical aperture (NA) lens 24 and directed to a diffraction grating or other dispersive element 26
Implementation Method 3
A common way to force a tunable laser gain medium to produce output at a specific wavelength is to couple the gain medium to an external laser cavity. The external cavity disperses the intracavity radiation into its spectral components
Implementation Method 4
A common way to force a tunable laser gain medium to produce output at a specific wavelength is to couple the gain medium to an external laser cavity
Data Source
AI summary
A tunable laser source that includes multiple gain elements and uses a spatial light modulator in an external cavity to produce spectrally tunable output is claimed. Several designs of the external cavity are described, targeting different performance characteristics and different manufacturing costs for the device. Compared to existing devices, the tunable laser source produces high output power, wide tuning range, fast tuning rate, and high spectral resolution.