InAs quantum-dot lasers that feature distributed feedback and lateral evanescent-wave coupling have been demonstrated in operation at a wavelength of 1.3 µm. These lasers are prototypes of optical-communication oscillators that are required to be capable of stable single-frequency, single-spatial-mode operation.
A laser of this type (see figure) includes an active layer that comprises multiple stacks of InAs quantum dots embedded within InGaAs quantum wells. Distributed feedback is provided by gratings formed on both sides of a ridge by electron lithography and reactive-ion etching on the surfaces of an AlGaAs/GaAs waveguide. The lateral evanescent-wave coupling between the gratings and the wave propagating in the waveguide is strong enough to ensure operation at a single frequency, and the waveguide is thick enough to sustain a stable single spatial mode.
In tests, the lasers were found to emit continuous-wave radiation at temperatures up to about 90 °C. Side modes were found to be suppressed by more than 30 dB.
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Refer to NPO-30503, volume and number of this NASA Tech Briefs issue, and the page number.
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Laterally Coupled Quantum-Dot Distributed-Feedback Lasers
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Overview
This document presents advancements in the development of laterally coupled InAs quantum-dot distributed-feedback (DFB) lasers, specifically designed to operate at a wavelength of 1.3 μm. These lasers are significant for high-speed optical communication systems, as they provide stable single-frequency, single-spatial-mode operation, which is essential for effective data transmission.
The active medium of these lasers consists of multiple stacks of InAs quantum dots embedded within InGaAs quantum wells. The design incorporates laterally coupled gratings that are created using electron lithography and reactive-ion etching on an AlGaAs/GaAs waveguide. This configuration allows for strong lateral evanescent-wave coupling, ensuring that the laser operates at a single frequency while maintaining a stable single spatial mode.
In testing, these lasers demonstrated the ability to emit continuous-wave radiation at temperatures up to 90 °C without the need for facet coating. They achieved side mode suppression ratios exceeding 30 dB, indicating a high level of performance in minimizing unwanted modes that could interfere with the primary signal.
The document outlines the novelty of this work, emphasizing how the laterally coupled etched gratings provide sufficient coupling for single-mode light emission while allowing for a thick enough waveguide to ensure stability. This innovation differentiates it from other methods, such as those using metal gratings, which may not offer the same level of operational stability due to their thin waveguide structures.
The motivation behind this research stems from the need for reliable light sources in optical communication systems, particularly as InAs quantum dot lasers present a promising alternative to the currently used InGaAs/InP lasers. The document also discusses future plans to improve the characteristics of quantum dot DFB lasers, design novel quantum dot devices, and explore the potential for extended wavelength lasers.
Overall, this work represents a significant step forward in laser technology, with implications for the telecommunications industry and the development of more efficient and reliable optical communication systems. The research was conducted at the Jet Propulsion Laboratory under NASA's sponsorship, highlighting its relevance to advanced technological applications.
