Semiconductor Laser External Resonator Mode Stability
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Solution Overview
Problem
Conventional semiconductor laser devices with external resonators suffer from unstable lasing modes, leading to variations in lasing wavelength and output power, making them unsuitable for accurate measurement or testing applications.
Innovation Solution
A semiconductor laser device with an external resonator configuration that includes a semiconductor light-emitting element that does not oscillate light by itself, combined with a resonator mirror and a wavelength control element, such as a narrow band pass filter or anamorphic prism pair, to stabilize the lasing mode and wavelength through fast modulation drive and confocal optical systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a semiconductor laser device uses a conventional external resonator configuration with a semiconductor laser that oscillates light by itself, then the device can achieve lasing, but the lasing mode becomes unstable and the wavelength varies with drive current changes
Solution Approach 1:
The patent extracts the light oscillation function from the semiconductor laser itself and relocates it to an external resonator. The semiconductor laser is configured not to oscillate light by itself, but only to emit light that is then oscillated by the external resonator, thereby eliminating the unstable Fabry-Perot modes inherent in conventional semiconductor lasers and achieving stable single-mode lasing.
Solution Approach 2:
The patent introduces a wavelength control element (such as a diffraction grating or prism) as an intermediary in the external resonator. This wavelength control element selectively controls specific wavelengths to form standing waves, acting as a mediator that ensures stable single-mode oscillation while allowing wavelength tuning through rotation or adjustment of the element.
2Measurement precision
If the wavelength is selected using a wavelength control element in the external resonator, then wavelength selection is achieved, but the longitudinal mode becomes multi-mode when the semiconductor laser oscillates light by itself
Solution Approach 1:
The patent removes the light oscillation function from the semiconductor laser and places it exclusively in the external resonator. This extraction ensures that even when a wavelength control element is present, the system maintains single-mode oscillation because the external resonator's standing wave conditions, rather than the semiconductor laser's Fabry-Perot modes, determine the lasing characteristics.
Solution Approach 2:
The patent changes the fundamental parameter of light oscillation from occurring within the semiconductor laser cavity to occurring in the external resonator. This parameter change transforms the mode structure from multi-mode (determined by semiconductor laser cavity length) to single-mode (determined by external resonator and wavelength control element), enabling both precise wavelength selection and mode stability.
3Speed
If fast modulation drive is performed by supplying a drive current with a high-frequency wave superimposed, then fast modulation is achieved, but the lasing wavelength varies and output power changes abruptly when light returns from optical component end faces
Solution Approach 1:
The patent extracts the oscillation function to an external resonator, making the lasing characteristics independent of the semiconductor laser's internal cavity modes. This extraction stabilizes the lasing wavelength and output power even during fast modulation drive, because the external resonator maintains stable standing waves regardless of high-frequency current variations or light feedback from optical components.
Solution Approach 2:
The external resonator configuration inherently provides stable feedback through its standing wave formation. The wavelength control element and resonator geometry create a feedback mechanism that is less sensitive to drive current fluctuations and external light feedback, maintaining lasing stability during fast modulation operations.
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 achieves highly stable longitudinal-mode lasing and wavelength control, reducing variations in lasing wavelength and output power, even with changes in drive current, thereby enhancing the accuracy and reliability of the semiconductor laser device for measurement and testing applications.
Implementation Method 1
a wavelength control element which is formed by a narrow-band band pass filter, or the like, and is disposed in the optical path of the external resonator
Implementation Method 2
an external resonator configured to oscillate light emitted from the semiconductor light-emitting element
Implementation Method 3
an external resonator comprising a resonator mirror disposed outside the semiconductor light-emitting element
Data Source
AI summary
A semiconductor laser device with external resonator with stable longitudinal mode regardless of variation of drive current is disclosed. The device includes: a semiconductor light-emitting element having a pair of end faces with a light emitting section disposed therebetween, and an external resonator configured to oscillate light emitted from the semiconductor light-emitting element, the external resonator being formed by a resonator mirror disposed outside the semiconductor light-emitting element and one of the pair of end faces that is farther from the resonator mirror, wherein, as the semiconductor light-emitting element, a semiconductor light-emitting element having a structure which does not oscillate light emitted therefrom by itself is used. The device further includes a wavelength control element disposed in the optical path within the external resonator and configured to select a wavelength range of the light, and a driver circuit configured to perform fast modulation drive of the semiconductor light-emitting element.