Vertical Cavity Semiconductor Laser for Low-Noise SMI Sensing
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Solution Overview
Problem
Existing optoelectronic semiconductor devices used in self-mixing interferometry applications face high noise levels due to fluctuations in forward voltage, leading to poor Signal-to-Noise-Ratio (SNR), which complicates the measurement of optical power output and requires additional photodiodes for monitoring.
Innovation Solution
The design includes a semiconductor device with a vertically oriented emission direction, high reflectivity mirrors, and an aperture region with a diameter between 6 μm and 8 μm to maintain low electrical resistivity and single-mode optical emission, along with a tunnel junction to reduce electrical resistance and thermal noise, allowing the forward voltage to be used as a self-mixing interferometry signal without the need for a monitor diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optoelectronic semiconductor device is used, then optical power output can be measured, but high noise levels due to forward voltage fluctuations occur leading to poor Signal-to-Noise-Ratio
Solution Approach 1:
The patent changes the aperture diameter parameter to 6 μm or 8 μm, which optimizes the balance between electrical resistance and optical mode confinement. This specific parameter range reduces electrical resistance and thermal noise while maintaining single-mode operation, thereby improving Signal-to-Noise-Ratio without requiring additional photodiodes
Solution Approach 2:
The patent uses the forward voltage signal itself as the measurement signal for self-mixing interferometry, eliminating the need for a separate monitor photodiode. By treating the forward voltage as a copy or alternative representation of the optical power output, the system achieves the same measurement function with lower noise and simpler architecture
2Stability of the object's composition
If the aperture region diameter is reduced to maintain single-mode emission, then optical mode confinement is achieved, but electrical resistance increases leading to higher thermal noise
Solution Approach 1:
The patent identifies and applies the optimal aperture diameter parameter range of 6 μm or 8 μm, which represents a careful balance point. At this specific size, the aperture is large enough to maintain low electrical resistance and reduce thermal noise, yet small enough to confine the optical field to single-mode emission. This precise parameter selection resolves the contradiction between optical stability and electrical reliability
3Measurement precision
If additional photodiodes are added to monitor optical power output, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent eliminates the need for additional monitor photodiodes by using the forward voltage signal as a direct substitute for optical power monitoring. The forward voltage serves as an electrical copy or proxy for the optical signal, allowing self-mixing interferometry measurements to be performed using only the laser diode's electrical characteristics, thereby simplifying the device structure while maintaining measurement precision
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 configuration significantly reduces noise levels, enabling the use of forward voltage as a reliable SMI signal and eliminating the need for a monitor diode, while maintaining single-mode optical emission and low electrical resistivity, thus enhancing the accuracy and simplicity of self-mixing interferometry measurements.
Implementation Method 1
an active region (103) configured to emit or detect electromagnetic radiation in an emission direction (S)
Implementation Method 2
a first reflector (21) arranged on a first side of the semiconductor body (10) and a second reflector (22) arranged on a second side of the semiconductor body (10), opposite the first side. The first and second reflector preferably comprise a high reflectivity for electromagnetic radiation
Implementation Method 3
an aperture region (104). The aperture region (104) can confine an electric current in the semiconductor body (10) in a lateral direction
Implementation Method 4
an optical element (40) arranged downstream of the active region (103) in the emission direction (S). The optical element is for example a refractive or a diffractive element
Implementation Method 5
an optical element (40) arranged downstream of the active region (103) in the emission direction (S). The optical element is for example a refractive or a diffractive element
Data Source
AI summary
An optoelectronic semiconductor device (1) comprising a semiconductor body (10) having a first region (101), a second region (102) and an active region (103) configured to emit or detect electromagnetic radiation in an emission direction (S) is described herein. The optoelectronic semiconductor device (1) further comprises a first reflector (21) arranged on a first side of the semiconductor body (10) and a second reflector (22) arranged on a second side of the semiconductor body (10), opposite the first side, a first electrode (31) and a second electrode (32), an aperture region (104) and an optical element (40) arranged downstream of the active region (103) in the emission direction (S). The emission direction (S) is oriented parallel to a stacking direction of the semiconductor body (10). The first electrode (31) is arranged on the first region (101) and the second electrode (32) is arranged between the second reflector (22) and the active region (103). Further, a method for operating an optoelectronic semiconductor device (1) is provided.