Chaotic-cavity surface-emitting lasers for optical wireless communication and low-speckle illumination

Abstract

Though necessary and advantageous in many fields, the high coherence of lasers is detrimental to their performance in certain applications, including illumination, imaging, and projection. This is due to the formation of coherence artifacts, commonly known as speckles, resulting from the interference of randomly scattering spatially coherent photons. It is possible to resolve this issue by increasing the number of mutually incoherent modes emitted from the laser. In vertical-cavity surface-emitting lasers (VCSELs), this can be performed by designing them to have chaotic cavities. This paves the way toward their use in simultaneous illumination and communication scenarios. Herein, we show that chaotic-cavity broad-area VCSELs can achieve significantly broader modulation bandwidths (up to 5 GHz) and higher data rates (up to 12.6 GB/s) compared to other low-coherence light sources, with a lower speckle contrast. We further report a novel technique for lowering the speckle contrast by carefully designing the AC signal used for communication. We show that the apparent spatial coherence is dramatically decreased by inserting a short chirp signal between symbols. Using this method with a chaotic-cavity VCSEL, the number of apparent modes can be up to 450, compared to 88 modes measured from a conventional broad-area VCSEL (a fivefold increase). In light of the recent advances in visible-light VCSELs, this work shows the potential of low-coherence surface-emitting lasers (LCSELs) in simultaneous illumination and optical wireless communication systems since they combine the high speed of lasers with the excellent illumination properties of light-emitting diodes.

Low-coherence semiconductor light sources: devices and applications

“…More recently, we showed that chaotic-cavity VCSELs with a D-shaped transverse profile can support a larger number of modes as compared to conventional circular VCSELs 99,100 . Moreover, we showed that these devices allow for high-speed communication with low-speckle illumination, especially when driven by a strong alternating current (AC) signal that is inserted between the communication symbols 33,37 . This opens the door for many applications that would benefit from the surface emission configuration and the emission direction of VCSELs.…”

“…The optical field can also be observed over most of the cavity, unlike in circular cavities that feature high-Q-factor whispering gallery modes (WGMs), which are concentrated around the edges of the cavity. This has been shown to increase the power and efficiency of VCSELs with asymmetric cavities 33,101 . Moreover, the FFPs show a mostly circularly symmetrical beam, which is useful in coupling the light into fibers.…”

“…For instance, the development of superluminescent diodes (SLDs) [22][23][24] , random lasers (RLs) [25][26][27] , broad-area lasers [28][29][30] and inhomogeneous quantum dot (QD) and quantum dash (Q-dash) broadband lasers 31,32 has drawn increasing interest in the last twenty years. Their applications have also expanded in many scenarios; for example, chaotic-cavity lasers serve as a special type of broad-area lasers, have shown their promise in reducing coherence artifacts 33,34 , which benefits the display industries. Other potential applications in diverse fields are being explored, including instability suppression 35 , illumination 36 , communication 37 , and random number generation 38 .…”

“…Their applications have also expanded in many scenarios; for example, chaotic-cavity lasers serve as a special type of broad-area lasers, have shown their promise in reducing coherence artifacts 33,34 , which benefits the display industries. Other potential applications in diverse fields are being explored, including instability suppression 35 , illumination 36 , communication 37 , and random number generation 38 . Collectively, these innovations play a pivotal role in driving breakthroughs across diverse scientific and technological fields.…”