Wavelength-Stabilized Light-Emitting Device With External Cavity
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Solution Overview
Problem
Existing semiconductor diode lasers and surface-emitting lasers face challenges such as temperature-dependent wavelength variation, broad beam divergence, limited output power, and inflexibility in wavelength selection due to their design, which affects their performance and efficiency.
Innovation Solution
A light-emitting device with a multilayer interference reflector and an external cavity that provides wavelength stabilization by selecting specific angles and reflectivity spectra to achieve constructive interference, allowing for high output power and tunable wavelength operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional semiconductor diode laser or surface-emitting laser is used, then the device structure is simple, but the wavelength varies with temperature and the beam divergence is broad
Solution Approach 1:
The device is segmented into distinct functional layers: a substrate, a multilayer interference reflector with specific thicknesses of high and low refractive index layers, an active region, and cladding layers. Each layer serves a specific purpose in controlling the optical properties and wavelength stability.
Solution Approach 2:
The patent changes the optical parameters by using a multilayer interference reflector with specific thicknesses of layers having different refractive indices. The reflector is designed with alternating layers of high refractive index (e.g., GaAs) and low refractive index (e.g., GaAlAs) materials, where the thickness of each layer is precisely controlled to achieve constructive interference at the desired wavelength, thereby stabilizing the emission wavelength against temperature variations.
2Power
If a conventional laser design is used, then the output power is limited, but the device structure remains simple
Solution Approach 1:
The laser structure employs composite materials consisting of alternating layers of GaAs (high refractive index) and GaAlAs with different aluminum compositions (low refractive index). This composite multilayer structure creates a distributed Bragg reflector that enhances optical confinement and enables higher output power density while maintaining wavelength stability.
Solution Approach 2:
The patent transitions from a simple planar structure to a vertically stacked multilayer structure, adding the dimension of layer thickness control. By precisely controlling the thickness of each layer in the vertical dimension, the device achieves both high output power and wavelength stability without significantly increasing lateral complexity.
3Adaptability or versatility
If a conventional surface-emitting laser is used, then the wavelength selection is inflexible, but the device is easier to manufacture
Solution Approach 1:
The patent enables wavelength selection flexibility by changing the thickness parameters of the multilayer interference reflector layers. By adjusting the thickness of the high and low refractive index layers during epitaxial growth, different wavelengths can be selected and stabilized. The aluminum composition in the GaAlAs layers can also be varied to tune the refractive index and achieve different wavelength selections.
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 enables wavelength-stabilized light emission across a broad spectral range and angle, enhancing the performance and flexibility of semiconductor diode lasers by minimizing thermal wavelength shifts and increasing output power density.
Implementation Method 1
A light-emitting device with a multilayer interference reflector and an external cavity that provides wavelength stabilization by selecting specific angles and reflectivity spectra to achieve constructive interference
Data Source
AI summary
A light emitting device is disclosed that emits light from the surface in a broad spectral range and in a broad range of angles tilted with respect to the direction normal to the exit surface. An apparatus for generating wavelength-stabilized light is formed of a light-emitting device, an external cavity and at least one external mirror. Light emitted by the light-emitting device at a certain preselected angle, propagates through the external cavity, impinges on the external mirror and is reflected back. Light emitted at other angles does not impinge on the external mirror. Thus, a feedback occurs only for the light emitted at a preselected angle. Light impinged on the external mirror and reflected back undergoes interference with the emitted light. The interference can be constructive or destructive. Constructive interference results in a positive feedback. The positive feedback occurs, if light emitted by the light-emitting device is reflected back and reaches the active region in phase, i.e. if the phase matching between emitted and reflected light waves occurs. The positive feedback conditions are met at one or a few selected wavelengths within the luminescence spectrum of the active region. Then the apparatus generates wavelength-stabilized light. In different embodiments, an apparatus may operate as a wavelength-stabilized light-emitting diode, a wavelength-stabilized superluminescent light-emitting diode, or a wavelength-stabilized laser.Various embodiments are possible which are distinguished in a way of optical coupling between a light-emitting device and an external mirror. The coupling can be realized via the far-field zone of the light emitted by the light-emitting device, via the near-field zone, or via a single epitaxial structure.An apparatus for the frequency conversion is disclosed further comprising a non-linear crystal located within the external cavity.