RSS 1.0Photonics Laboratory
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Recent Submissions
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Submarine optical fiber communication provides an unrealized deep-sea observation network(Scientific Reports, Springer Science and Business Media LLC, 2023-09-18) [Article]Oceans are crucial to human survival, providing natural resources and most of the global oxygen supply, and are responsible for a large portion of worldwide economic development. Although it is widely considered a silent world, the sea is filled with natural sounds generated by marine life and geological processes. Man-made underwater sounds, such as active sonars, maritime traffic, and offshore oil and mineral exploration, have significantly affected underwater soundscapes and species. In this work, we report on a joint optical fiber-based communication and sensing technology aiming to reduce noise pollution in the sea while providing connectivity simultaneously with a variety of underwater applications. The designed multifunctional fiber-based system enables two-way data transfer, monitoring marine life and ship movement near the deployed fiber at the sea bottom and sensing temperature. The deployed fiber is equally harnessed to transfer energy that the internet of underwater things (IoUTs) devices can harvest. The reported approach significantly reduces the costs and effects of monitoring marine ecosystems while ensuring data transfer and ocean monitoring applications and providing continuous power for submerged IoUT devices.
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Multifunctional difluoroboron β-diketonate-based luminescent receiver for a high-speed underwater wireless optical communication system(Optics Express, Optica Publishing Group, 2023-09-14) [Article]The last decade has witnessed considerable progress in underwater wireless optical communication in complex environments, particularly in exploring the deep sea. However, it is difficult to maintain a precise point-to-point reception at all times due to severe turbulence in actual situations. To facilitate efficient data transmission, the color-conversion technique offers a paradigm shift in large-area and omnidirectional light detection, which can effectively alleviate the étendue limit by decoupling the field of view and optical gain. In this work, we investigated a series of difluoroboron β-diketonate fluorophores by measuring their photophysical properties and optical wireless communication performances. The emission colors were tuned from blue to green, and >0.5 Gb/s data transmission was achieved with individual color channel in free space by implementing an orthogonal frequency-division multiplexing (OFDM) modulation scheme. In the underwater experiment, the fluorophore with the highest transmission speed was fabricated into a 4×4 cm2 luminescent concentrator, with the concentrated emission from the edges coupled with an optical fiber array, for large-area photodetection and optical beam tracking. The net data rates of 130 Mb/s and 217 Mb/s were achieved based on nonreturn- to-zero on-off keying and OFDM modulation schemes, respectively. Further, the same device was used to demonstrate the linear light beam tracking function with high accuracy, which is beneficial for sustaining a reliable and stable connection in a dynamic, turbulent underwater environment.
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Beam wander prediction with recurrent neural networks(Optics Express, Optica Publishing Group, 2023-08-14) [Article]Among the problems that prevent free-space optical communication systems from becoming a truly mainstream technology is beam wander, which is especially important for structured light beams since beam misalignment introduces additional crosstalk at the receiver. The paper suggests a recurrent neural network-based (RNN) solution to predict beam wander in free space optics (FSO). The approach uses past beam center of mass positions to predict future movement, significantly outperforming various prediction types. The proposed approach is demonstrated using under-sampled experimental data over a 260 m link as a worst-case and over-sampled simulated data as a best-case scenario. In addition to conventional Gaussian beams, Hermite- and Laguerre-Gaussian beam wander is also investigated. With a 20 to 40% improvement in error over naive and linear predictions, while predicting multiple samples ahead in typical situations and overall matching or outperforming considered predictions across all studied scenarios, this method could help mitigate turbulence-induced fading and has potential applications in intelligent re-transmits, quality of service, optimized error correction, maximum likelihood-type algorithms, and predictive adaptive optics.
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Chaotic-cavity surface-emitting lasers for optical wireless communication and low-speckle illumination(APL Photonics, AIP Publishing, 2023-08-14) [Article]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.
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Initial demonstration of AlGaAs-GaAsP-beta-Ga2O3 n-p-n double heterojunctions(arXiv, 2023-08-12) [Preprint]Beta phase gallium oxides, an ultrawide-bandgap semiconductor, has great potential for future power and RF electronics applications but faces challenges in bipolar device applications due to the lack of p-type dopants. In this work, we demonstrate monocrystalline AlGaAs_GaAsP_beta phase gallium oxides n-p-n double-heterojunctions, synthesized using semiconductor grafting technology. By transfer printing an n-AlGaAs_p-GaAsP nanomembrane to the n-beta phase-Ga2O3 epitaxial substrate, we simultaneously achieved AlGaAs_GaAsP epitaxial n-p junction diode with an ideality factor of 1.29 and a rectification ratio of 2.57E3 at +/- 2 V, and grafted GaAsP_beta_phase_gallium oxides p-n junction diode exhibiting an ideality factor of 1.36 and a rectification ratio of 4.85E2 at +/- 2 V.
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Semiconductor Emitters in Entropy Sources for Quantum Random Number Generation(Annalen der Physik, Wiley, 2023-08-01) [Article]Random number generation (RNG) is needed for a myriad of applications ranging from secure communication encryption to numerical simulations to sports and games. However, generating truly random numbers can be elusive. Pseudorandom bit generation using computer algorithms provides a high random bit generation rate. Nevertheless, the reliance on predefined algorithms makes it deterministic and predictable once initial conditions are known. Relying on physical phenomena (such as measuring electrical noise or even rolling dice) can achieve a less predictable sequence of bits. Furthermore, if the physical phenomena originate from quantum effects, they can be truly random and completely unpredictable due to quantum indeterminacy. Traditionally, physical RNG is significantly slower than pseudorandom techniques. To meet the demand for high-speed RNG with perfect unpredictability, semiconductor light sources are adopted as parts of the sources of randomness, i.e., entropy sources, in quantum RNG (QRNG) systems. The high speed of their noise, the high efficiency, and the small scale of these devices make them ideal for chip-scale QRNG. Here, the applications and recent advances of QRNG are reviewed using semiconductor emitters. Finally, the performance of these emitters is compared and discuss their potential in future technologies.
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A high-order finite volume method for Maxwell's equations in heterogeneous and time-varying media(arXiv, 2023-07-21) [Preprint]We develop a finite volume method for Maxwell's equations in materials whose electromagnetic properties vary in space and time. We investigate both conservative and non-conservative numerical formulations. High-order methods accurately resolve fine structures that develop due to the varying material properties. Numerical examples demonstrate the effectiveness of the proposed method in handling temporal variation and its efficiency relative to traditional 2nd-order FDTD.
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Wide-field-of-view optical detectors for deep ultraviolet light communication using all-inorganic CsPbBr3 perovskite nanocrystals(Optics Express, Optica Publishing Group, 2023-07-17) [Article]Optical wireless communication (OWC) links suffer from strict requirements of pointing, acquisition, and tracking (PAT) between the transmitter and receiver. Extending the narrow field-of-view (FoV) of conventional light-focusing elements at the receiver side can relax the PAT requirements. Herein, we use all-inorganic CsPbBr3 nanocrystals (NCs) to extend various optical concentrators’ FOV to 60°, regardless of the original FOV values of the concentrators. Given the robustness of UV light against communication channel misalignment, the used CsPbBr3 NCs provide another advantage of converting transmitted UVC light into a green color that matches the peak absorption of the widely available Si-based detectors. We evaluated the feasibility of the reported wide FoV optical detectors by including them in deep UV OWC systems, deploying non-return-to-zero on-off keying (NRZ-OOK) and orthogonal-frequency division multiplexing (OFDM) modulation schemes. The NRZ-OOK and OFDM schemes exhibit stable communication over the 60° FoV, providing data transmission rates of 100 Mb/s and 71.6 Mb/s, respectively, a unique capability to the reported design.
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Energy Recycling from Distributed Fiber-Optic Sensors(IEEE Photonics Technology Letters, Institute of Electrical and Electronics Engineers (IEEE), 2023-07-14) [Article]Distributed fiber-optic sensors (DFOS) have been widely deployed in a wide range of applications. The operational principle of such DFOS typically relies on monitoring light backscattered due to pumping optical pulses in an optical fiber. Once the DFOS’ optical pump pulses reach the distal end of the optical fiber, the power carried by each pulse is conventionally wasted and dissipated to the medium surrounding the fiber without a benefit. Here, we report on energy harvesting from the DFOS’ optical pulses to recycle the wasted optical power for electric-consuming devices supply. We demonstrated the feasibility of this concept by harvesting energy from a fiber-optic distributed acoustic sensor (DAS) and a distributed temperature sensor (DTS). The study further investigates the impact of changing the pulse repetition rate within the 5–25 kHz range on the harvested power. Without any disturbances in the DFOS functionalities, power values of up to 0.871 mW were harvested as a proof-of-concept demonstration.
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Engineering Metal–Organic Frameworks with Tunable Colors for High-Performance Wireless Communication(Journal of the American Chemical Society, American Chemical Society (ACS), 2023-07-08) [Article]Metal-organic frameworks (MOFs) have emerged as excellent platforms possessing tunable and controllable optical behaviors that are essential in high-speed and multichannel data transmission in optical wireless communications (OWCs). Here, we demonstrate a novel approach to achieving a tunable wide modulation bandwidth and high net data rate by engineering a combination of organic linkers and metal clusters in MOFs. More specifically, two organic linkers of different emission colors, but equal molecular length and connectivity, are successfully coordinated by zirconium and hafnium oxy-hydroxy clusters to form the desired MOF structures. The precise change in the interactions between these different organic linkers and metal clusters enables control over fluorescence efficiency and excited state lifetime, leading to a tunable modulation bandwidth from 62.1 to 150.0 MHz and a net data rate from 303 to 363 Mb/s. The fabricated color converter MOFs display outstanding performance that competes, and in some instances surpasses, those of conventional materials commonly used in light converter devices. Moreover, these MOFs show high practicality in color-pure wavelength-division multiplexing (WDM), which significantly improved the data transmission link capacity and security by the contemporary combining of two different data signals in the same path. This work highlights the potential of engineered MOFs as a game-changer in OWCs, with significant implications for future high-speed and secure data transmission.
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Compact, low-cost, and low-crosstalk orbital angular momentum sorter based on binary grating(Optics and Laser Technology, Elsevier BV, 2023-06-28) [Article]This paper demonstrates the design, fabrication, and testing of a compact, low-cost, low-crosstalk orbital angular momentum (OAM) sorter. The sorter is based on optical geometric transformation (OGT). This sorter can realize the separation of the OAM states as the traditional sorter, but uses a compact design that utilizes only two phase modulations to realize the transformation and focus. The phase modulations are introduced by distorting the binary gratings by curving the geometrical structure rather than optical path difference. The fabrication is simple and only needs single-step lithography and single-step dry etching on a fused quartz plate. The etching depth error does not affect the sorting result but only the diffraction efficiency. In the experiment, the two binary gratings are fabricated on the same substrate to lower the degrees of freedom of alignment and ensure uniform etching depth. The sorter is further improved by incorporating fan-out diffraction, resulting in a higher separation and lower cross-talk. This sorter can provide a compact, low-cost, low-crosstalk device to realize OAM demultiplexing.
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Wearable sensors for monitoring marine environments and their inhabitants(Nature Biotechnology, Springer Science and Business Media LLC, 2023-06-26) [Article]Human societies depend on marine ecosystems, but their degradation continues. Toward mitigating this decline, new and more effective ways to precisely measure the status and condition of marine environments are needed alongside existing rebuilding strategies. Here, we provide an overview of how sensors and wearable technology developed for humans could be adapted to improve marine monitoring. We describe barriers that have slowed the transition of this technology from land to sea, update on the developments in sensors to advance ocean observation and advocate for more widespread use of wearables on marine organisms in the wild and in aquaculture. We propose that large-scale use of wearables could facilitate the concept of an ‘internet of marine life’ that might contribute to a more robust and effective observation system for the oceans and commercial aquaculture operations. These observations may aid in rationalizing strategies toward conservation and restoration of marine communities and habitats.
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Harnessing the Potential of Optical Communications for the Metaverse(arXiv, 2023-06-22) [Preprint]The Metaverse is a digital world that offers an immersive virtual experience. However, the Metaverse applications are bandwidth-hungry and delay-sensitive that require ultrahigh data rates, ultra-low latency, and hyper-intensive computation. To cater for these requirements, optical communication arises as a key pillar in bringing this paradigm into reality. We highlight in this paper the potential of optical communications in the Metaverse. First, we set forth Metaverse requirements in terms of capacity and latency; then, we introduce ultra-high data rates requirements for various Metaverse experiences. Then, we put forward the potential of optical communications to achieve these data rate requirements in backbone, backhaul, fronthaul, and access segments. Both optical fiber and optical wireless communication (OWC) technologies, as well as their current and future expected data rates, are detailed. In addition, we propose a comprehensive set of configurations, connectivity, and equipment necessary for an immersive Metaverse experience. Finally, we identify a set of key enablers and research directions such as analog neuromorphic optical computing, optical intelligent reflective surfaces (IRS), hollow core fiber (HCF), and terahertz (THz).
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Harnessing the Potential of Optical Communications for the Metaverse(arXiv, 2023-06-22) [Preprint]The Metaverse is a digital world that offers an immersive virtual experience. However, the Metaverse applications are bandwidth-hungry and delay-sensitive that require ultrahigh data rates, ultra-low latency, and hyper-intensive computation. To cater for these requirements, optical communication arises as a key pillar in bringing this paradigm into reality. We highlight in this paper the potential of optical communications in the Metaverse. First, we set forth Metaverse requirements in terms of capacity and latency; then, we introduce ultra-high data rates requirements for various Metaverse experiences. Then, we put forward the potential of optical communications to achieve these data rate requirements in backbone, backhaul, fronthaul, and access segments. Both optical fiber and optical wireless communication (OWC) technologies, as well as their current and future expected data rates, are detailed. In addition, we propose a comprehensive set of configurations, connectivity, and equipment necessary for an immersive Metaverse experience. Finally, we identify a set of key enablers and research directions such as analog neuromorphic optical computing, optical intelligent reflective surfaces (IRS), hollow core fiber (HCF), and terahertz (THz).
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Acousto-optic Cooperative Pointing, Acquisition and Tracking Method for Undersea Laser Communication(IEEE, 2023-06-05) [Conference Paper]Underwater laser communication has shown good performance in terms of rate, bandwidth and delay, and is a promising communication method for establishing internet of underwater things. In the past, all-optical pointing, acquisition and tracking (PAT) methods were used to establish laser links between underwater platforms. We propose a combined acousto-optical PAT method for link establishment in underwater laser communication to reduce the time consumed in the acquisition process and thus improve efficiency. The proposed method was tested and analyzed in the designed environment.
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Monocrystalline Si/β-Ga2O3 p-n heterojunction diodes fabricated via grafting(arXiv, 2023-05-30) [Preprint]The β-Ga2O3 has exceptional electronic properties with vast potential in power and RF electronics. Despite the excellent demonstrations of high-performance unipolar devices, the lack of p-type doping in β-Ga2O3 has hindered the development of Ga2O3-based bipolar devices. The approach of p-n diodes formed by polycrystalline p-type oxides with n-type β-Ga2O3 can face severe challenges in further advancing the β-Ga2O3 bipolar devices due to their unfavorable band alignment and the poor p-type oxide crystal quality. In this work, we applied the semiconductor grafting approach to fabricate monocrystalline Si/β-Ga2O3 p-n diodes for the first time. With enhanced concentration of oxygen atoms at the interface of Si/β-Ga2O3, double side surface passivation was achieved for both Si and β-Ga2O3 with an interface Dit value of 1-3 x 1012 /cm2 eV. A Si/β-Ga2O3 p-n diode array with high fabrication yield was demonstrated along with a diode rectification of 1.3 x 107 at +/- 2 V, a diode ideality factor of 1.13 and avalanche reverse breakdown characteristics. The diodes C-V shows frequency dispersion-free characteristics from 10 kHz to 2 MHz. Our work has set the foundation toward future development of β-Ga2O3-based transistors.
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Optical wireless communication-based 2K real-time video surveillance system for future underwater visual monitoring(SPIE, 2023-05-24) [Conference Paper]We develop an optical wireless communication-based 2K real-time video surveillance system prototype with field-programmable gate arrays. Using a 3-W blue light-emitting diode and an avalanche photo-diode, 20-m and 1.5-m real-time picture/video transmission with a high resolution of 1920 × 1080 pixels is implemented in free space and pure water channel, respectively. It indicates the good performance of the prototype, which is the first step to realize underwater visual monitoring in future human-robot interaction applications.
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Chaotic-Cavity Surface-Emitting Lasers for Optical Wireless Communication(IEEE, 2023-05-19) [Conference Paper]We demonstrated using chaotic cavities to lower the spatial coherence of vertical-cavity surface-emitting lasers. Our design achieved a 10-Gb/s data rate with a 60% increase in the optical power and double the number of modes.
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Visible-light communication using thermally evaporated CsPbBr3 perovskite thin films(AIP Advances, AIP Publishing, 2023-05-08) [Article]Lead halide perovskites are widely used in optoelectronic applications owing to their promising photophysical properties, but developing components of the order of nanoscale remains challenging. In this work, the authors fabricated cesium lead bromide (CsPbBr3) thin films of varying thicknesses and investigated their visible-light communication (VLC) performance. The thickness of the CsPbBr3 thin films was precisely controlled by using a single-beam thermal evaporation technique, and their morphology was analyzed through scanning electron microscopy and x-ray diffraction. Thicker films were found to have a homogeneous surface, with gain boundaries of increasing size and fewer surface trap states than the thinner films. Furthermore, we identified the thickness-dependent photoluminescence (PL) property of the CsPbBr3 thin films based on steady-state PL measurements and verified it by using time-correlated single-photon counting as well as femtosecond upconversion measurements. Films with thicknesses of 5, 10, and 20 nm, with enhanced surface homogeneity and purity, were used in a VLC link as color-converting fluorescent components. The 20-nm-thick CsPbBr3 film delivered the best performance because it had the highest PL intensity and the most suitable morphology, with a –3-dB bandwidth of 30.7 MHz and a net data rate of 330 Mb/s. These results reflect a facile and well-controlled approach to fabricating such films that can be used for high-power, high-speed, and large-area transmission and detection of visible-light signals.
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Interfacial band parameters of ultrathin ALD-ZrO2 on Ga-polar GaN through XPS measurements(AIP Advances, AIP Publishing, 2023-05-05) [Article]Recent demonstrations of grafted p-n junctions combining n-type GaN with p-type semiconductors have shown great potential in achieving lattice-mismatch epitaxy-like heterostructures. Ultrathin dielectrics deposited by atomic layer deposition (ALD) serve both as a double-sided surface passivation layer and a quantum tunneling layer. On the other hand, with excellent thermal, mechanical, and electrical properties, ZrO2 serves as a high-k gate dielectric material in multiple applications, which is also of potential interest to applications in grafted GaN-based heterostructures. In this sense, understanding the interfacial band parameters of ultrathin ALD-ZrO2 is of great importance. In this work, the band-bending of Ga-polar GaN with ultrathin ALD-ZrO2 was studied by x-ray photoelectron spectroscopy (XPS). This study demonstrated that ZrO2 can effectively suppress upward band-bending from 0.88 to 0.48 eV at five deposition cycles. The bandgap values of ALD-ZrO2 at different thicknesses were also carefully studied.
