Novel Oxide-Confined Vertical-Cavity Surface-Emitting Laser Array with Graphene-Based Transparent Conductive Layer/Mode Filter and Its Applications in Fiber Optic Communications

With the explosion of information traffic due to the Internet, electronic commerce, computer networks, and multimedia, the need for a transmission medium with the bandwidth capabilities for handling such vast amounts of information is paramount. Fiber optics communications, with its comparatively infinite bandwidth, low loss, and electromagnetic interference immunity, has proven to be the solution. In fiber optic system, the use of a high performance optical transceiver module is very important because the digital signals must be first converted into light signals and then propagated through an optical fiber. At the terminal end of the fiber, the received signals will be re-converted to the original information by the same modules. In the future, further improvement to optical transceiver module efficiency is crucial for applications of high-speed, long-distance data communications. Compared with other semiconductor lasers, vertical-cavity surface-emitting lasers (VCSELs) featured improved device performance and low production cost are considerably suitable for the use in a cost-effective optical communication system, such as local area network. Therefore, in this project, a high-power (＞ 10 mW) single-transverse-mode (SMSR ＞ 25 dB) oxide-confined VCSEL array (VCSEL array) will be performed for the realization of a high-speed (＞ 10 Gbps), long-distance (~km) data communication system. For VCSELs with a large oxide aperture, a metal grid (functions as a spatial mode filter) will be coated onto the light exiting surface to achieve spatial modulation of the reflectivity of top distributed Bragg reflector (DBR). As a result of increased mirror loss, the presence of high-order transverse modes (located at the periphery of each pixel) can be easily filtered out from the emission spectrum. Experimentally, we shall optimize the designs of the spatial mode filter, e.g., the dimension of the light-emitting pixels can be further shrunk to less than 4 × 4 μm2 to support single mode operation. In addition, the transparent phase-matching layers can also be used to achieve coherent emissions for all pixels provided there exists a phase difference of π between the neighboring pixels. On the other hand, it is important to achieve uniform current injection to each pixel as a larger array was used. Graphene-based transparent conductive layer (transmittance ＞ 90%) grown by chemical vapor deposition could be done for that. In addition, the Au doping process will be developed to reduce the sheet resistance (＜ 50 Ω/…) of graphene films, which helps to improve the output performance of the VCSEL arrays. Instead of using metal grid as a spatial mode filter, the light emitted from the VCSELs can be absorbed to a certain range by using an external resonant cavity. This cavity is consisted of a single/few layer graphene absorber with a broad absorption range and sandwiched between two reflective mirrors, i.e., a highly reflective mesh film and the top DBR of the VCSELs. Such novel approach has not yet been found in VCSEL array, further studies are necessary!

Project ID:PB10308-3334
External Project ID:MOST103-2221-E182-021