Single Photodiode Research Articles

Laser Driven Miniature Diamond Implant for Wireless Retinal Prostheses.

The design and benchtop operation of a wireless miniature epiretinal stimulator implant is reported. The implant is optically powered and controlled using safe illumination at near-infrared wavelengths. An application-specific integrated circuit (ASIC) hosting a digital control unit is used to control the implant's electrodes. The ASIC is powered using an advanced photovoltaic (PV) cell and programmed using a single photodiode. Diamond packaging technology is utilized to achieve high-density integration of the implant optoelectronic circuitry, as well as individual connections between a stimulator chip and 256 electrodes, within a 4.6mm × 3.7mm × 0.9mm implant package. An ultrahigh efficiency PV cell with a monochromatic power conversion efficiency of 55% is used to power the implant. On-board photodetection circuity with a bandwidth of 3.7MHz is used for forward data telemetry of stimulation parameters. In comparison to implants which utilize inductively coupled coils, laser power delivery enables a high degree of miniaturization and lower surgical complexity. The device presented combines the benefits of implant miniaturization and a flexible stimulation strategy provided by a dedicated stimulator chip. This development provides a route to fully wireless miniaturized minimally invasive implants with sophisticated functionalities.

Automatic mode-matching of a Fabry-Pérot cavity with a single photodiode and spatial light modulation

Conventional cavity alignment sensing uses multi-element photodiodes to sense the matching of a laser beam to the mode of a cavity. We present a new approach that uses a single-element photodiode combined with deformable mirrors to modulate orthogonal codes across distinct spatial regions of the laser wavefront. By decoding the photodiode signal it is possible to map the mode mismatch and produce error signals for feedback to the mirrors to optimize the coupling of the laser to the cavity. We characterise this sensing and control system experimentally and demonstrate closed-loop enhancement of cavity alignment and mode matching.

Accurate Visible Light Positioning Using Multiple-Photodiode Receiver and Machine Learning

Visible light positioning (VLP) is a promising indoor localization method as it provides high positioning accuracy and allows for leveraging the existing lighting infrastructure. Photodiode (PD)-based receiver is a commonly used tag for VLP. However, a tag employing a single PD requires three or more luminaires to be visible. This article presents a VLP system that uses a custom-made tag utilizing multiple PDs. It applies received signal strength (RSS)-based fingerprinting using a weighted k-nearest neighbor (WkNN) algorithm for localization. Experimental results show that it is possible to localize using less than three luminaires with high accuracy. The Manhattan and Matusita distance metrics are found to provide lower localization accuracy than the Euclidean metric for the WkNN algorithm. The creation of a dense fingerprinting database through 2-D interpolation is presented as a method to reduce the cost of time and labor. The localization performance of the VLP system does not degrade noticeably with the fabricated database. The localization accuracy of the WkNN algorithm is shown to be better than that of a multilayer perceptron (MLP)-based regressor. The developed VLP system is also experimentally benchmarked against the HTC Vive showing comparable performance.

Generalized Kramers–Kronig receiver for coherent terahertz communications

High-speed communication systems rely on spectrally efficient modulation formats that encode information both on the amplitude and on the phase of an electromagnetic carrier. Coherent detection of such signals typically uses rather complex receiver schemes, requiring a continuous-wave (c.w.) local oscillator (LO) as a phase reference and a mixer circuit for spectral down-conversion. In optical communications, the so-called Kramers-Kronig (KK) scheme has been demonstrated to greatly simplify the receiver, reducing the hardware to a single photodiode. In this approach, an LO tone is transmitted along with the signal, and the amplitude and phase of the complex signal envelope are reconstructed from the photocurrent by digital signal processing. This reconstruction exploits the fact that the real and the imaginary part, or, equivalently, the amplitude and the phase of an analytic signal are connected by a KK-type relation. Here, we transfer the KK scheme to high-speed wireless communications at THz carrier frequencies. We use a Schottky-barrier diode (SBD) as a nonlinear element and generalize the theory of KK processing to account for the non-quadratic characteristics of this device. Using 16-state quadrature amplitude modulation (16QAM), we transmit a net data rate of 115 Gbit/s at a carrier frequency of 0.3 THz over a distance of 110 m.

Performance analysis of hybrid SAC-OCDMA-OFDM model over free space optical communication

Recently, free space optical (FSO) communication network has gained popularity because of its unlicensed spectrum, high data rate, low power consumption and ease of installation. Spectral amplitude coded optical code division multiple access (SAC-OCDMA) technique has become significant because of enhanced network capacity, privacy, and simultaneous use of multiple asynchronous users. However, the climatic turbulence causes signal fluctuations and degrades the quality of the received signal. Therefore, to improve the quality of the received signal in this work, SAC-OCDMA technique is integrated with orthogonal frequency division multiplexing (OFDM) technique and performance of such hybrid model is investigated. Two SAC-OCDMA codes are proposed in this work referred as triangular matrix-zero cross correlation (TM-ZCC) and pulse shifting substitution-zero cross correlation (PSS-ZCC) codes. The hybrid model uses the novel one dimensional (1D) SAC-OCDMA codes with two different types of receivers such as modified AND (M-AND), and single photodiode detection (SPD) receivers over Gamma-Gamma fading channel to evaluate the bit error rate (BER) performance of the proposed hybrid model. It is observed from the simulation results that the hybrid SAC-OCDMA-OFDM model with SPD detection receiver performs better in terms of bit error rate (BER) than that of M-AND detection receiver. Furthermore, it is also observed from the simulation results that the hybrid model based on the proposed TM-ZCC code performs better than the proposed PSS-ZCC code in terms of BER and higher FSO distance coverage. The performance of the proposed model is estimated for 20 and 30 active users simultaneously at various data rates. The TM-ZCC and PSS-ZCC codes are generated using MATLAB platform and the proposed hybrid SAC-OCDMA-OFDM model is validated using optisystem version 15 over the Gamma-Gamma fading channel.

Low frequency noise in double heterostructure P-InAsSbP/n-InAs mid-IR photodiodes at cryogenic temperature: Photovoltaic mode and forward bias

Low frequency photocurrent noise, as well as the forward current noise are studied for the first time in mid-infrared InAsSbP/InAs double heterostructure photodiodes at 100 K. Two types of photodiodes are identified. For the first type, the spectral noise density, SI, depends on frequency as 1/fγ. For the second type, generation-recombination (GR) noise component dominates. Our results show that in those samples, it is one and the same local center that is responsible for the noise over the entire photocurrent range. The forward current noise in all samples is lower than that previously observed in InAsSbP/InAs single heterostructure photodiodes at 77 K. In samples demonstrating 1/fγ noise, the spectral noise density, SI, is proportional to the square of the current. In samples with GR noise, we also observe SI ~ I2 dependences in a certain current range. At higher currents, the noise decreases or tends to saturate. We show that at 100 K, the Nyquist noise is dominant and can be used for estimating the specific detectivity at photocurrents Iph ≤ 5·10−9 A for samples showing 1/fγ. noise, and at Iph ≤ 2·10−9 A for samples presenting GR noise component. At higher Iph the photocurrent noise should be also taken into account.

224-Gbps single-photodiode PAM-4 transmission with extended transmitter bandwidth based on optical time-and-polarization interleaving.

We have proposed and demonstrated the optical time-and-polarization interleaving (OTPI) technique, which can effectively extend the transmitter bandwidth for an intensity modulation and direct detection (IM/DD) optical system. The 224-Gbit/s line-rate OTPI-PAM-4 signal is successfully transmitted over a 500-m standard single-mode fiber (SSMF) in the C band, using the transmitter with a bandwidth of 25 GHz and the receiver with a single photodiode. By using a 33%-return-to-zero (RZ) pulse train, a bit-error ratio (BER) below 7% hard-decision forward error correction (HD-FEC) threshold is achieved. BER below 20% soft-decision forward error correction (SD-FEC) threshold is also realized using a carrier suppressed return-to-zero (CSRZ) pulse train. The OTPI technique can also be used for more higher-order pulse amplitude modulation (PAM) formats, making it a promising technique for next-generation high-speed optical interconnects.

Enabling Multiple Access in Visible Light Communication Using Liquid Crystal Displays: A Proof-of-Concept Study

The directionality of optical signals provides an opportunity for efficient space reuse of optical links in visible light communication (VLC). Space reuse in VLC can enable multiple-access communication from multiple light emitting transmitters. Traditional VLC system design using photo-receptors requires at least one receiving photodetector element for each light emitter, thus constraining VLC to always require a light-emitter to light-receptor element pair. In this paper, we propose, design and evaluate a novel architecture for VLC that can enable multiple-access reception using a photoreceptor receiver that uses only a single photodiode. The novel design includes a liquid-crystal-display (LCD) based shutter system that can be automated to control and enable selective reception of light beams from multiple transmitters. We evaluate the feasibility of multiple access on a single photodiode from two light emitting diode (LED) transmitters and the performance of the communication link using bit-error-rate (BER) and packet-error-rate (PER) metrics. Our experiment and trace based evaluation through proof-of-concept implementation reveals the feasibility of multiple LED reception on a single photodiode. We further evaluate the system in controlled mobile settings to verify the adaptability of the receiver when the LED transmitter changes position.

High-Power Microwave Generation Through Distributed Optical Amplification Into a Photodiode Array on an Open Indium Phosphide Platform

High power handling is crucial to the performance of microwave photonic systems. Taking a fabless research approach, the high-power performance of the photodiodes on an open indium phosphide photonic integration platform is characterized experimentally. For improved power handling two travelling wave structures are presented. Open-ended operation at reduced bandwidth penalty, but with a potential gain in output microwave power of 6 dB is considered, analysing the effect of aperiodic loading and stub reflections. The single photo diode is found to have 1-dB compression of 5 dBm with 20 mA and −8 dBm with 10 mA at 1 GHz and 30 GHz respectively. For a 4-branch distributed photodiode array these numbers are improved to 16 dBm with 58 mA and −1 dBm with 45 mA, again at 1 GHz and 30 GHz respectively. Further the power conversion efficiency of the photodiodes is improved almost by a factor of four from 2.8% to 10.6% at 1 GHz, and the effect of included amplification on the efficiency is analysed. The limitations of the design is analysed through comparison of simulations with measurements and a discussion of the possible improvements and scaling of the method is given.

MDW and EDW/DDW codes with AND subtraction/single photodiode detection for high performance hybrid SAC-OCDMA/OFDM system

In this paper, a hybrid system is introduced using orthogonal frequency division multiplexing (OFDM) technique with spectral amplitude coding optical code division multiple access (SAC-OCDMA). In this system, the AND subtraction detection is used with the modified double weight (MDW) and enhanced double weight (EDW) codes, in addition to the single photodiode detection with the diagonal double weight (DDW) code. The proposed system achieves performance enhancement in the performance enhancement concerning the maximum allowable number of users, signal to noise ratio and (minimum) bit error rate (BER) $${\Re}$$. The proposed codes that used with AND subtraction detection techniques are: MDW and EDW, while the DDW codes are used with single photodiode detection (SPD). Detection techniques are investigated to reduce the effect of both the multiple access interference and phase induced intensity noise. A comparison is performed between the conventional SAC-OCDMA systems and OFDM with SAC-OCDMA. The obtained results reveal that OFDM with SAC-OCDMA gives better performance than conventional SAC-OCDMA. OFDM with SAC-OCDMA using DDW code with SPD detection can support a high bit rate up to 10 Gbps for 70 users with a BER of 10–9.

SSB Single Carrier and Multicarrier in C-Band FSO Transmission With KK Receiver

With the increasing demand of bandwidth, a higher capacity communication system is required for optical short link and access network. Intensity modulation/direct detection (IM-DD) is considered as a reasonable method in access network, due to its low cost and power consumption. However, it reduces the spectral efficiency compared with IQ modulation. In addition, single-sideband (SSB) signal occupies less bandwidth than double-sideband signal (DSB). However, SSB systems suffer from signal-signal beat interference (SSBI) from photodiodes (PDs). Recently, Kramers–Kronig (KK) receiver is proposed to mitigate SSBI. Meanwhile, single-sideband (SSB) signal is the prerequisite for KK scheme, and this kind of signal is also tolerant to fiber chromatic dispersion and multipath-fading. On the other hand, free-space optical (FSO) communication is becoming a promising candidate for next generation optical access network. Thus we experimentally demonstrate the KK scheme in 20 km SSMF and 20 m FSO links with both single carrier signal and multicarrier signal. We compare the performance between them with and without pre-equalization (pre-EQ). With the help of probabilistically shaped (PS) mapping to gives an increase in the sensitivity over an additive white Gaussian noise (AWGN). We reach a 117bit/s transmission with a spectral efficiency of 5.85 bit/s/Hz of 20 Ghz bandwidth with single modulator and single photodiode (PD) in fiber-FSO system.

Trilateration‐based indoor localization engineering technique for visible light communication system

SummaryThis article is aimed at designing positioning system using visible light communication technology by incorporating three different diversity schemes, namely, transmit diversity (TD), receive diversity (RD), and angle diversity. For the TD, multiple transmitters with single receiver (MISO) is used to obtain the target location using frequency division multiplexing (FDM) and variable phase approach. To deploy RD, the proposed system comprises multiple receivers and single transmitter (SIMO). Only one transmitter's absolute coordinates are required to obtain the location coordinates of optical receivers. FDM and time division multiplexing access schemes have been utilized to transmit the unique signals by light‐emitting diodes (LEDs). To implement angle diversity, orientation of transmitter and receiver is considered for positioning purposes. Under this environment, there is no constraint for the LEDs to be installed on ceiling; they can be at any point within the room or at different heights. The information regarding spherical coordinates (representing the orientation) of LEDs (single or multiple) is used to determine the coordinates or the orientation of receiver having multiple or single photodiodes, respectively. Under multiple orientations, this system is analyzed with both scenarios, that is, MISO and SIMO.

Diffuse correlation spectroscopy towards dynamic topography of blood flow index in deep tissues: A multi-channel system and experiment validation

Near-infrared (NIR) diffusion correlation spectroscopy (DCS) provides a novel tool for clinical monitoring of blood flow in deep tissues. While DCS has the advantages of non-invasiveness, high sensitivity and large penetration depth, accelerating its data acquisition process to realize real-time imaging is still an on-going task. We have proposed herein a 10-detection-channel DCS system for dynamic topography of the blood flow index. In the design, an imaging speed up to 1 frame/s can be achieved by taking the advantage of the concurrency of a multi-channel multi-delay designed hardware correlator, the improved NIR-sensitivity of a single photon avalanche photodiode detector and the high efficiency of the prior-guided fitting procedure for the blood flow index extraction. We firstly evaluated the flow-rate resolution, measurement fidelity and imaging depth of the system using phantom experiments, and then performed in-vivo experiments on human arm to demonstrate the ability of the proposed methodology to capture blood flow changes in terms of their shapes and positions.

End-to-end Learned, Optically Coded Super-resolution SPAD Camera

Single Photon Avalanche Photodiodes (SPADs) have recently received a lot of attention in imaging and vision applications due to their excellent performance in low-light conditions, as well as their ultra-high temporal resolution. Unfortunately, like many evolving sensor technologies, image sensors built around SPAD technology currently suffer from a low pixel count. In this work, we investigate a simple, low-cost, and compact optical coding camera design that supports high-resolution image reconstructions from raw measurements with low pixel counts. We demonstrate this approach for regular intensity imaging, depth imaging, as well transient imaging. Our method uses an end-to-end framework to simultaneously optimize the optical design and a reconstruction network for obtaining super-resolved images from raw measurements. The optical design space is that of an engineered point spread function (implemented with diffractive optics), which can be considered an optimized anti-aliasing filter to preserve as much high-resolution information as possible despite imaging with a low pixel count, low fill-factor SPAD array. We further investigate a deep network for reconstruction. The effectiveness of this joint design and reconstruction approach is demonstrated for a range of different applications, including high-speed imaging, and time of flight depth imaging, as well as transient imaging. While our work specifically focuses on low-resolution SPAD sensors, similar approaches should prove effective for other emerging image sensor technologies with low pixel counts and low fill-factors.

Channel-Aware Adaptive Physical-Layer Network Coding Over Relay-Assisted OFDM-VLC Networks

In this article, we propose and experimentally demonstrate the full-duplex channel-aware adaptive physical-layer network (APNC) coding over orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) to boost the capacity of relay-assisted VLC networks. The network encoding is realized by detecting signals coming from different terminal nodes simultaneously with a single photodiode at the relay node, which then achieves the amplify-and-forward function. At the receiver of each terminal node, the desired signal can be reconstructed by applying the corresponding APNC decoding to the detected interfered signal from the relay node. The use of adaptively loaded OFDM not only addresses the inherent frequency fading issue in VLC systems but also relaxes the synchronization issue at the relay node. The detailed principles of the proposed full-duplex channel-aware APNC scheme are presented, and its performance is experimentally investigated in a two-way-relay (TWR) VLC network. Experimental results show that the proposed scheme exhibits superior BER performance to other existing network scheduling schemes. For a TWR-VLC network with a fixed 600-Mb/s throughput, we achieve around two orders of magnitude reductions in the bit-error-rate (BER) by using the proposed channel-aware APNC scheme compared to other schemes, and BERs of 3.96 × 10−4 and 5.32 × 10−4 are attained for the two transmission links in the TWR network, respectively.

Detecting WDM visible light signals by a single multi-color photodiode with MIMO processing

For the first time, to the best of our knowledge, we experimentally demonstrate that multiple-input-multiple-output (MIMO) processing allows using a single photodiode to detect simultaneously a wavelength-division multiplexing (WDM) visible light communications (VLC) signal. The photodiode has a triple junction, and when it is illuminated by a WDM signal, the junctions produce inherently three photocurrents that are unusable for detecting any of the WDM signals. However, by means of linear MIMO processing, we are able to recover the transmitted signals exactly. Bit error rate measurements confirm the effectiveness of the proposed solution. This opens a new scenario for practical WDM-VLC systems.

Color Determination from a Single Broadband Organic Photodiode

AbstractEstablishing the color of incident light is essential for many applications, such as machine vision, but generally requires either a dispersive component or multiple spectrally selective photodetectors. In contrast, here an incident spectrum is parametrized using a single broadband organic photodiode (OPD). This is achieved by exploiting the incident wavelength dependence of charge extraction caused by optically induced trap states in a metal oxide electron extraction layer, which results in an atypical spectral dependence of the reverse bias photocurrent density vs voltage (J–V) characteristics. Such dependence is augmented by confining the active layer within an optical microcavity to influence the light absorption profile and thus metal oxide trap state density. The average wavelength of an (approximately normally distributed) incident spectrum is then calculated to within ≈5 nm by algorithmically minimizing the difference between a measured J–V curve and one determined from the overlap integral of a trial spectrum with previously acquired voltage bias dependent external quantum efficiency (EQE) spectra.

A spatially resolved transmittance spectroscopy system for detecting internal rots in onions

Abstract This study presents the development of a spatially resolved transmittance system for detecting internal rots in onions, particularly small and localised rots. A two-wavelength classifier was chosen by considering sensitivities to rots and path-length variations. Near-infrared spectroscopy transmittance measurements were carried out on rot-affected onions, to determine wavelength sensitivities to the presence and severity of rots. Finite Element simulations of light transport in onions were run to determine wavelength sensitivities to source-detector separation. A spatially resolved transmittance system was then developed, using two laser diodes as sources (728 and 805 nm wavelengths) and a single photodiode as detector. The system was experimentally verified, with the measured spatial profiles of the transmittance ratios of the two source wavelengths being sensitive to variation in position and size of internal rots in onions.

Aerosol layers sensing by an eye-safe lidar near the Elbrus summit

A new generation lidar (LIght Detection And Ranging) based on a diode laser with eye-safe energy density (~10 nJ cm−2) and a single photon avalanche photodiode was used for the first time, to our knowledge, to detect clouds along the Garabashi glacier near the Elbrus mountain summit. We have observed single- and multilayered clouds near the Elbrus volcano summit from the Garbashi camp located at a 4 km distance. A high signal-to-noise ratio demonstrated the potential of the remote sensing of aerosols from distances of up to 10 km.

Interference Mitigation for Visible Light Communications in Underground Mines Using Angle Diversity Receivers.

This paper proposes two solutions based on angle diversity receivers (ADRs) to mitigate inter-cell interference (ICI) in underground mining visible light communication (VLC) systems, one of them is a novel approach. A realistic VLC system based on two underground mining scenarios, termed as mining roadway and mine working face, is developed and modeled. A channel model based on the direct component in line-of-sight (LoS) and reflections of non-line-of-sight (NLoS) links is considered, as well as thermal and shot noises. The design and mathematical models of a pyramid distribution and a new hemi-dodecahedral distribution are addressed in detail. The performances of these approaches, accompanied by signal combining schemes, are evaluated with the baseline of a single photo-diode in reception. Results show that the minimum lighting standards established in both scenarios are met. As expected, the root-mean-square delay spread decreases as the distance between the transmitters and receivers increases. Furthermore, the hemi-dodecahedron ADR in conjunction with the maximum ratio combining (MRC) scheme, presents the best performance in the evaluated VLC system, with a maximum user data rate of 250 Mbps in mining roadway and 120 Mbps in mine working face, received energy per bit/noise power of 32 dB and 23 dB, respectively, when the bit error rate corresponds to , and finally, values of 120 dB in mining roadway and 118 dB in mine working face for signal-to-interference-plus-noise ratio are observed in a cumulative distribution function.