Tunable Multilayer Interference Reflector for High-Speed Optoelectronic Modulation
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Solution Overview
Problem
Current ultrahigh-speed optoelectronic devices face challenges with direct modulation due to overheating, saturation of differential gain, and high differential capacitance, leading to instability and inefficiency in continuous wave regimes, while indirect modulation methods are more complex and sensitive to operational conditions.
Innovation Solution
A device with a wavelength-tunable multilayer interference reflector controlled by voltage, using the quantum confined Stark effect to modulate transmittance, allowing for intensity modulation of light-emitting diodes or lasers, and reducing capacitance through proton bombardment and ion implantation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct modulation by injection of current into the gain region is used, then low cost is achieved, but overheating of the active region occurs and differential gain saturates with current
Solution Approach 1:
The device is segmented into two functionally independent regions: a gain region for light generation and a modulator region for intensity modulation. The gain region operates under forward bias for efficient light emission, while the modulator region operates under reverse bias for electrooptic modulation, preventing thermal overload in either region.
Solution Approach 2:
An electrooptic modulator region acts as an intermediary between the electrical control signal and the optical output. This modulator region, containing quantum wells or quantum dots, modulates the intensity of light generated in the gain region through the quantum confined Stark effect, rather than directly modulating the gain region current.
2Speed
If pump current density is increased to increase photon population, then bandwidth increases, but differential gain saturates and degradation rate increases
Solution Approach 1:
The device separates the high-current gain generation function from the modulation function. The gain region can operate at optimal current densities for high photon population without suffering from modulation-induced degradation, while the modulator region handles signal modulation at low current densities, improving overall device reliability.
Solution Approach 2:
The patent replaces direct electrical modulation of the gain region with electrooptic modulation in a separate region. This substitution allows bandwidth control through electric field effects rather than current modulation, reducing stress on the gain region and improving device longevity.
3Illumination intensity
If forward bias is applied for direct modulation, then light emission is achieved, but differential capacitance increases due to reduced effective thickness of undoped layer
Solution Approach 1:
The device structure separates the forward-biased gain region (for light emission) from the reverse-biased modulator region. This segmentation allows the undoped layer in the modulator region to maintain its full thickness and low capacitance characteristics, while the gain region handles current injection for light generation.
Solution Approach 2:
Instead of applying forward bias for modulation (which increases capacitance), the patent applies reverse bias to the modulator region. This inversion of the bias polarity enables electrooptic modulation while maintaining low differential capacitance, as the reverse-biased junction does not exhibit the same capacitance increase.
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
Enables robust, ultrafast intensity modulation with improved stability and efficiency, reducing parasitic capacitance and enhancing output power by shifting the stopband edge wavelength, thus overcoming the limitations of direct modulation and maintaining high performance across a wide range of conditions.
Implementation Method 1
The stopband edge wavelength of the wavelength-tunable multilayer interference reflector is preferably electrooptically tuned using the quantum confined Stark effect in the vicinity of the cavity mode
Implementation Method 2
reducing capacitance through proton bombardment and ion implantation
Data Source
AI summary
A device contains at least one wavelength-tunable multilayer interference reflector controlled by an applied voltage and at least one cavity. The stopband edge wavelength of the wavelength-tunable multilayer interference reflector is preferably electrooptically tuned using the quantum confined Stark effect in the vicinity of the cavity mode (or a composite cavity mode), resulting in a modulated transmittance of the multilayer interference reflector. A light-emitting medium is preferably introduced in the cavity or in one of the cavities permitting the optoelectronic device to work as an intensity-modulated light-emitting diode or diode laser by applying an injection current. The device preferably contains at least three electric contacts to apply forward or reverse bias and may operate as a vertical cavity surface emitting light-emitter or modulator or as an edge-emitting light emitter or modulator. Using a multilayer interference reflector containing tunable section allows also obtaining a wavelength-tunable laser or a wavelength-tunable resonant cavity photodetector in the case where the optical field profile in the active cavity or cavities is affected by the stopband wavelength shift. Adding additional modulator sections enables applications in semiconductor optical amplifiers, frequency converters or lock-in optical amplifiers.