There is great difficulty in implementing lateral gratings in GaSb-based lasers. Commercially, single-frequency GaSb lasers have been fabricated using metal gratings deposited laterally to the ridge-waveguide (RWG) stripe. The disadvantage of this is that the laser performance is compromised by additional optical loss due to radiation absorption by the metal. Fabricating lasers in this way limits the potential for high-power performance. A better method is to etch gratings into the semiconductor, but generally, patterning these grating structures is difficult because of nonuniformity of the grating pattern and etching difficulty due to sub-micrometer dimensions.
Laterally coupled distributed feedback (LC-DFB) Type-I GaSb-based diode lasers were demonstrated that exhibit low internal loss comparable to laser devices without grating structures, approximately 5 cm–1. The successful performance of these lasers is attributed to the optimized fabrication of uniformly etched lateral gratings along the laser ridge waveguide.
Using a unique E-beam resist spinning technique, a method was developed that results in uniform application of the resist such that the pattern is directly adjacent to the ridge sidewall. This is done by bonding the wafer to a 4-in. (≈10-cm) silicon platform such that the length of the ridges is parallel to the vector of resist spreading, in contrast to standard methods of spinning where the ridge orientation is not fixed to this vector, resulting in a non-uniform thickness of the resist on either side of the ridge.
The lasers have been fabricated with etched lateral gratings and have been shown to be superior in performance to devices with metal gratings. As a result, the lasers have been considered for high-power applications such as lidar and spectrometers that require lasers with greater than 10 mW.
Lidar currently uses solid-state lasers. The new technology is 100 times smaller and has fewer components with possibly the same performance. By bonding the wafers on a stable platform such that the length of the RWG structures is parallel to the radial flow of the resist spread, a uniform resist film thickness along both RWG sidewalls is achieved.
This work was done by Clifford F. Frez and Siamak Forouhar of Caltech for NASA’s Jet Propulsion Laboratory. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. For more information, contact
This Brief includes a Technical Support Package (TSP).
Uniformly Etched Lateral Gratings Applied to Pre-existing Ridge Waveguides
(reference NPO-48933) is currently available for download from the TSP library.
Don't have an account?
Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing research on "Uniformly Etched Lateral Gratings Applied to Pre-existing Ridge Waveguides." Conducted under a contract with NASA and associated with the California Institute of Technology, this research aims to enhance the performance of optical devices, particularly in the context of aerospace applications.
The primary focus of the study is on the fabrication techniques used to create lateral gratings on ridge waveguides, which are essential components in photonic devices. The document includes illustrations that demonstrate different resist application techniques and their impact on coating uniformity. Specifically, it compares the results of using a non-uniform electron beam resist mask versus a uniformly coated resist layer, highlighting the importance of uniformity in achieving optimal etching results.
The research underscores the significance of precise fabrication methods in the development of advanced optical components. Uniformly etched gratings are crucial for improving the efficiency and performance of devices such as lasers and sensors, which are vital for various aerospace missions. The findings presented in this document are part of NASA's broader initiative to promote technological advancements with potential commercial applications.
Additionally, the document serves as a resource for those interested in the technological transfer of aerospace-related developments. It provides contact information for further inquiries and emphasizes compliance with U.S. export regulations, indicating the proprietary nature of the information contained within.
Overall, this Technical Support Package encapsulates key advancements in the field of photonics, particularly regarding the integration of lateral gratings with ridge waveguides, and highlights the collaborative efforts between NASA and Caltech in pushing the boundaries of technology for future aerospace endeavors.
