Optoelectronic Module Speckle Reduction via Modulated Bragg Reflector
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Solution Overview
Problem
Semiconductor lasers used in optoelectronic modules can produce undesirable interference effects like speckles due to their coherent electromagnetic radiation, leading to uneven illumination and disturbing patterns, especially in visible wavelength ranges.
Innovation Solution
The optoelectronic module employs a semiconductor laser and a photonic chip with a modulated Bragg reflector to generate secondary electromagnetic radiation with a varying dominant wavelength, increasing spectral bandwidth and reducing coherence, thereby minimizing speckle interference. This is achieved by coupling primary radiation into a waveguide and using multiple semiconductor lasers with different dominant wavelengths, along with anti-reflection coatings and specific materials like LiNb, ITO, and SiN for waveguides and Bragg reflectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If semiconductor lasers are used to emit coherent electromagnetic radiation, then good beam quality and high luminance are achieved, but undesirable interference effects like speckles occur
Solution Approach 1:
The patent applies dynamics by modulating the dominant wavelength of the electromagnetic radiation over time. The Bragg reflector's periodic structure is dynamically adjusted through electrical modulation signals, causing the reflected wavelength to vary. This temporal variation in wavelength reduces the coherence length of the radiation, thereby minimizing speckle interference while maintaining high luminance from the semiconductor laser source.
Solution Approach 2:
The patent changes the parameter of dominant wavelength dynamically. By applying electrical modulation signals to the Bragg reflector, the reflector's periodic structure is adjusted, which directly changes the wavelength of the reflected electromagnetic radiation. This parameter change transforms the coherent radiation into less coherent radiation with varying wavelength, reducing speckle effects while preserving the high luminance advantage.
2Object-generated harmful factors
If the dominant wavelength of electromagnetic radiation is modulated to increase spectral bandwidth, then coherence length decreases and speckle interference is reduced, but device complexity increases
Solution Approach 1:
The patent introduces a Bragg reflector as an intermediary component between the semiconductor laser and the output. This intermediary device modulates the dominant wavelength of the radiation by reflecting specific wavelengths based on its periodic structure. The Bragg reflector acts as a mediator that transforms the coherent radiation into less coherent radiation with increased spectral bandwidth, thereby reducing speckle interference without requiring direct modification of the laser source itself.
Solution Approach 2:
The patent replaces mechanical wavelength tuning mechanisms with an electrical modulation system. Instead of using mechanical components to change the wavelength, the invention uses electrical modulation signals applied to the Bragg reflector to achieve wavelength modulation. This substitution of mechanical systems with electrical control reduces device complexity while achieving the desired effect of reducing speckle interference through increased spectral bandwidth.
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 effectively reduces or eliminates speckle interference, enhancing the optical characteristics and efficiency of the optoelectronic module by decreasing coherence and increasing spectral bandwidth, resulting in improved illumination patterns and miniaturization of optical systems.
Implementation Method 1
A second waveguide 220 is arranged downstream of the Bragg reflector 30. The Bragg reflector 30 has a reflectivity which is modulated by an electrical modulation signal
Implementation Method 2
The first waveguide is at least partially surrounded by a material having a lower refractive index for the primary electromagnetic radiation than the material of the first waveguide itself. Thus, the primary electromagnetic radiation is confined within the waveguide and propagates along the first waveguide.
Implementation Method 3
The optoelectronic module 1 comprises at least one semiconductor laser 10 and a photonic chip 20. A semiconductor laser is intended for the emission of a coherent electromagnetic radiation
Implementation Method 4
The first waveguide 210 extends from a side face 20A of the photonic chip 20 to the Bragg reflector 30
Data Source
AI summary
An optoelectronic module comprising at least one semiconductor laser and a photonic chip is described herein. The semiconductor laser emits a primary electromagnetic radiation which is coupled into the photonic chip. The photonic chip comprises at least one first waveguide and at least one optical Bragg reflector having a reflectivity which is modulated by an electrical modulation signal. A secondary electromagnetic radiation is coupled out of the photonic chip by means of at least one second waveguide, wherein the secondary electromagnetic radiation has a dominant wavelength which is modulated in dependence of the electrical modulation signal. Further, a method for operating an optoelectronic module and a Head-Mounted Display comprising an optoelectronic module are provided.