Wavy water-to-air optical camera communication system using rolling shutter image sensor and long short term memory neural network.

We propose and experimentally demonstrate for the first time up to the authors' knowledge a wide field-of-view (FOV) water-to-air optical transmission using rolling-shutter (RS) based optical camera communication (OCC). Here, we evaluate the proposed OCC system without water ripple and with different percentage increases of water ripple. Long short term memory neural network (LSTM-NN) is utilized to mitigate the wavy water turbulence induced link outage and to decode 4-level pulse-amplitude-modulation (PAM4) RS pattern by meeting the pre-forward error correction bit-error-rate (pre-FEC BER = 3.8 × 10-3). We also evaluate the FOVs of the proposed water-to-air RS-based OCC system. This can be implemented by using different angular rotations of the camera. Experimental results show that the proposed OCC system can support ±70°, ± 30°, and ±30° rotations around the z-, y- and x-directions, respectively when operated at 6 kbit/s and decoded using LSTM-NN.

Metasurface-driven polarization-division multiplexing of PCSEL for optical communications.

Free-space optical communications hold promising advantages, including a large bandwidth, access to license-free spectrum, high data rates, quick and simple deployment, low power consumption, and relaxed quality requirements. Nevertheless, key technical challenges remain, such as a higher transmission efficiency, a lower transmission loss, and a smaller form factor of optical systems. Here, we demonstrate the viability of circular-polarization-multiplexed multi-channel optical communication using metasurfaces alongside a photonic-crystal surface-emitting laser (PCSEL) light source at wavelength of 940 nm. Through the light manipulation with metasurface, we split the linearly polarized incidence into left and right circular polarizations with desired diffraction angles. Such orthogonal polarization states provide a paradigm of polarization division multiplexing technique for light communication. The PCSEL light source maintains a low divergence angle of about 0.373 degrees after passing through an ultra-thin metasurface without further bulky collimator or light guide, making end-to-end (E2E) and device-to-device (D2D) communications available in a compact form. Both light source and modulated polarized light exhibit a - 3 dB bandwidth over 500 MHz, with successful 1 Gbit/s transmission demonstrated in eye diagrams. Our results affirm that metasurface effectively boosts transmission capacity without compromising the light source's inherent properties. Future metasurface designs could expand channel capacity, and its integration with PCSEL monolithically holds promise for reducing interface losses, thereby enhancing efficiency.

Bi-Directional Free-Space Visible Light Communication Supporting Multiple Moveable Clients Using Light Diffusing Optical Fiber.

In this work, we put forward and demonstrate a bi-direction free-space visible light communication (VLC) system supporting multiple moveable receivers (Rxs) using a light-diffusing optical fiber (LDOF). The downlink (DL) signal is launched from a head-end or central office (CO) far away to the LDOF at the client side via a free-space transmission. When the DL signal is launched to the LDOF, which acts as an optical antenna to re-transmit the DL signal to different moveable Rxs. The uplink (UL) signal is sent via the LDOF towards the CO. In a proof-of-concept demonstration, the LDOF is 100 cm long, and the free space VLC transmission between the CO and the LDOF is 100 cm. 210 Mbit/s DL and 850 Mbit/s UL transmissions meet the pre-forward-error-correction bit error rate (pre-FEC BER = 3.8 × 10-3) threshold.

Unmanned-aerial-vehicle based optical camera communication system using light-diffusing fiber and rolling-shutter image-sensor.

We put forward and demonstrate a light-diffusing fiber equipped unmanned-aerial-vehicle (UAV) to provide a large field-of-view (FOV) optical camera communication (OCC) system. The light-diffusing fiber can act as a bendable, lightweight, extended and large FOV light source for the UAV-assisted optical wireless communication (OWC). During UAV flying, the light-diffusing fiber light source could be tilted or bended; hence, offering large FOV as well as supporting large receiver (Rx) tilting angle are particularly important for the UAV-assisted OWC systems. To improve the transmission capacity of the OCC system, one method based on the camera shutter mechanism, which is known as rolling-shuttering is utilized. The rolling-shuttering method makes use of the feature of complementary-metal-oxide-semiconductor (CMOS) image sensor to extract signal pixel-row by pixel-row. The data rate can be significantly increased since the capture start time for each pixel-row is different. As the light-diffusing fiber is thin and occupies only a few pixels in the CMOS image frame, Long-short-term-memory neural-network (LSTM-NN) is used to enhance the rolling-shutter decoding. Experimental results show that the light-diffusing fiber can satisfactorily act as an "omnidirectional optical antenna" providing wide FOVs and 3.6 kbit/s can be achieved, accomplishing the pre-forward error correction bit-error-rate (pre-FEC BER = 3.8 × 10-3).

Optical Beam Steerable Visible Light Communication (VLC) System Supporting Multiple Users Using RGB and Orthogonal Frequency Division Multiplexed (OFDM) Non-Orthogonal Multiple Access (NOMA).

In order to achieve high-capacity visible light communication (VLC), five dimensions in physics, including frequency, time, quadrature modulation, space, and polarization can be utilized. Orthogonality should be maintained in order to reduce the crosstalk among different dimensions. In this work, we illustrate a high-capacity 21.01 Gbit/s optical beam steerable VLC system with vibration mitigation based on orthogonal frequency division multiplexed (OFDM) non-orthogonal multiple access (NOMA) signals using red, green, and blue (RGB) laser-diodes (LDs). The OFDM-NOMA can increase the spectral efficiency of VLC signal by allowing high overlapping of different data channel spectra in the power domain to maximize the bandwidth utilization. In the NOMA scheme, different data channels are digitally multiplexed using different levels of power with superposition coding at the transmitter (Tx). Successive interference cancellation (SIC) is then utilized at the receiver (Rx) to retrieve different power multiplexed data channels. The total data rates (i.e., Data 1 and Data 2) achieved by the R/G/B OFDM-NOMA channels are 8.07, 6.62, and 6.32 Gbit/s, respectively, achieving an aggregated data rate of 21.01 Gbit/s. The corresponding average signal-to-noise ratios (SNRs) of Data 1 in the R, G, and B channels are 9.05, 9.18 and 8.94 dB, respectively, while that of Data 2 in the R, G, and B channels are 14.92, 14.29, and 13.80 dB, respectively.

Using lighting design tool to simplify the visible light positioning plan and reduce the deep learning loading.

We put forward and transform the commercially available lighting design software into an indoor visible light positioning (VLP) design tool. The proposed scheme can work well with different deep learning methods for reducing the loading of training data set collection. The indoor VLP models under evaluation include second order regression, fully-connected neural-network (FC-NN), and convolutional neural-network (CNN). Experimental results show that the similar positioning accuracy can be obtained when the indoor VLP models are trained with experimentally acquired data set or trained with software obtained data set. Hence, the proposed method can reduce the training loading for the indoor VLP.

Optical camera communication (OCC) using a laser-diode coupled optical-diffusing fiber (ODF) and rolling shutter image sensor.

We demonstrate an optical-camera-communication (OCC) system utilizing a laser-diode (LD) coupled optical-diffusing-fiber (ODF) transmitter (Tx) and rolling-shutter based image sensor receiver (Rx). The ODF is a glass optical fiber produced for decorative lighting or embedded into small areas where bulky optical sources cannot fit. Besides, decoding the high data rate rolling-shutter pattern from the thin ODF Tx is very challenging. Here, we propose and experimentally demonstrate the pixel-row-per-bit based neural-network (PPB-NN) to decode the rolling-shutter-pattern emitted by the thin ODF Tx. The proposed PPB-NN algorithm is discussed. The proposed PPB-NN method can satisfy the pre-forward error correction (FEC) BER at data rate of 3,300 bit/s at a transmission distance of 35 cm. Theoretical analysis of the maximum ODF Tx angle is also discussed; and our experimental values agree with our theoretical results.

2.805 Gbit/s high-bandwidth phosphor white light visible light communication utilizing an InGaN/GaN semipolar blue micro-LED.

We propose and implement a high-bandwidth white-light visible light communication (VLC) system accomplishing data rate of 2.805 Gbit/s utilizing a semipolar blue micro-LED. The system uses an InGaN/GaN semipolar (20-21) blue micro-LED to excite yellow phosphor film for high-speed VLC. The packaged 30 µm 2 × 4 blue micro-LED array has an electrical-to-optical (EO) bandwidth of 1042.5 MHz and a peak wavelength of 447 nm. The EO bandwidth of the white-light VLC system is 849 MHz. Bit error rate (BER) of 2.709 × 10-3 meeting the pre-forward error correction (FEC) threshold is accomplished by employing a bit and power loaded orthogonal frequency division multiplexing (OFDM) signal. The proposed white-light VLC system employs simple and inexpensive yellow phosphor film for white-light conversion, complex color conversion material is not needed. Besides, no optical blue filter is employed in the white-light VLC system. The fabrication of the InGaN/GaN semipolar (20-21) blue micro-LED is discussed, and its characteristics are also evaluated.

High-bandwidth InGaN/GaN semipolar micro-LED acting as a fast photodetector for visible light communications.

We propose and demonstrate a green semipolar (20-21) micro-light emitting diode (LED) acting as a high speed visible light communication (VLC) photodiode (PD). The micro-LED PD has the optical-to-electrical (OE) response of 228 MHz. A record data rate of 540 Mbit/s in on-off-keying (OOK) format with free-space transmission distance of 1.1 m was achieved, fulfilling the pre-forward error correction (FEC) limit. Many transmitters (Txs) and receivers (Rxs) is required to support the high density pico/femto-cells in future wireless networks, as well as the Internet-of-Things (IOT) networks. The proposed work could allow the realization of a low-cost, small-footprint and a high level of integration of VLC Txs and Rxs on the same platform.

PAM4 rolling-shutter demodulation using a pixel-per-symbol labeling neural network for optical camera communications.

The typical optical camera communication (OCC) modulation scheme is based on binary intensity modulation. To increase the transmission data rate, multi-level modulation format is highly desirable. In this work, we bring forward and demonstrate a rolling shutter 4-level pulse amplitude modulation (PAM4) demodulation scheme for OCC systems using pixel-per-symbol labeling neural network (PPSL-NN) for the first time up to the authors' knowledge. A bit-rate distance product of 28.8 kbit/s • m per color is achieved. The proposed scheme is to calculate and re-sample the pixel-per-symbol (PPS) to make sure the same number of pixels in each PAM4 symbol is corresponding to a label for the neural network. Experiment results reveal that the proposed scheme can efficiently demodulate high speed PAM4 signal in the rolling shutter OCC pattern.

Employing DIALux to relieve machine-learning training data collection when designing indoor positioning systems.

We propose and demonstrate using the DIALux software with our proposed linear-regression machine-learning (LRML) algorithm for designing a practical indoor visible light positioning (VLP) system. Experimental results reveal that the average position errors and error distributions of the model trained via the DIALux simulation and trained via the experimental data match with each other. This implies that the training data can be generated in DIALux if the room dimensions and LED luminary parameters are available. The proposed scheme could relieve the burden of training data collection in VLP systems.