Serial Quantum Cascade Laser Gain Chips for Tuning Range
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Solution Overview
Problem
The existing range of wavelength tuning for quantum cascade lasers (QCLs) in mid- and long-wave infrared is limited, which restricts their application in imaging and spectrographic analysis, as the available range is insufficient for many applications and leads to multimode operation and instability due to the electrical connection of sub-stacks.
Innovation Solution
The use of two gain chips with independent electrical biases and a tunable wavelength selective filter, where one gain chip is transparent to the wavelengths of the other, allowing for increased tuning range and stability by decoupling the electrical biasing and using a controller to specify the desired wavelength, and optionally using collimating lenses for light coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple sub-stacks are electrically connected in series within a single gain chip to expand wavelength range, then the wavelength tuning range is increased, but the system becomes unstable due to multimode operation and electrical coupling constraints
Solution Approach 1:
The patent divides the gain medium into multiple separate gain chips (first gain chip, second gain chip, etc.) that are optically coupled but electrically independent. Each gain chip contains its own sub-stacks and can be independently biased, eliminating the electrical coupling constraints that cause instability while maintaining the expanded wavelength range through optical serial connection of the chips.
2Device complexity
If a single gain chip with multiple sub-stacks is used to cover multiple wavelength bands, then the device complexity is reduced, but the ease of operation decreases due to inability to independently control each wavelength band
Solution Approach 1:
The patent segments the gain medium into multiple independently controllable gain chips, where each chip can be electrically biased separately to control its lasing wavelength band. This segmentation enables independent operation of each wavelength band while keeping the overall device configuration relatively simple through optical coupling of the chips.
Solution Approach 2:
The patent implements dynamic control by allowing independent electrical biasing of each gain chip, enabling real-time adjustment of which wavelength bands are active. The controller can selectively bias different gain chips or adjust their bias levels to dynamically control the lasing wavelength and prevent multimode operation across different bands.
3Adaptability or versatility
If the wavelength tuning range is expanded beyond the natural gain bandwidth of a single sub-stack, then more applications become accessible, but the loss of information increases due to multimode operation
Solution Approach 1:
The patent uses multiple gain chips, each optimized for specific wavelength bands, to expand the overall tuning range while maintaining spectral purity within each band. By separating the gain medium into distinct chips that can be independently controlled, the system avoids the multimode operation that occurs when a single chip attempts to cover too broad a range, thus preventing information loss.
Solution Approach 2:
The patent implements dynamic wavelength selection by selectively biasing specific gain chips based on the desired output wavelength. The controller activates only the gain chip(s) corresponding to the target wavelength band, ensuring that lasing occurs in a single mode within the selected band and preventing spectral broadening or multimode operation that would cause information loss.
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 significantly expands the wavelength tuning range and maintains stability by allowing incompatible sub-stacks to be placed in separate gain chips, reducing the number of sub-stacks needed and preventing multimode operation, thus enhancing the versatility of QCLs for various applications.
Implementation Method 1
Quantum cascade lasers (QCLs) can be used as light sources for such measurements. QCLs can be tuned in wavelengths over a significant range of wavelengths in the infrared.
Implementation Method 2
The gain chip assembly includes first and second gain chips that are coupled optically such that light travels serially between the first gain chip and the second gain chip, each gain chip is electrically biased
Implementation Method 3
The EC has a tunable wavelength selective filter that is changed in response to a control signal, light in the EC passes through the gain chip assembly
Implementation Method 4
The EC has a tunable wavelength selective filter that is changed in response to a control signal, light in the EC passes through the gain chip assembly
Data Source
AI summary
An apparatus that includes a gain chip assembly, an external cavity, and a controller is disclosed. The gain chip assembly includes first and second gain chips that are coupled optically such that light travels serially between the first gain chip and the second gain chip, each gain chip is electrically biased. The electrical bias of the first gain chip is independent of the electrical bias of the second gain chip. The external cavity has a tunable wavelength selective filter that is changed in response to a control signal. Light in the external cavity passes through the gain chip assembly. The controller determines the tunable wavelength selective filter, and the electrical bias of each of the gain chips so as to cause the apparatus to lase at a wavelength specified by a control signal to the controller.