Photodiode Photodetector Research Articles

Performance analysis of optical extra-WBAN links based on realistic user mobility modeling

We address the features channel characterization and performance evaluation for wireless body-area networks (WBANs) in medical applications during a walk scenario using optical wireless transmission. More specifically, we focus on optical extra-WBAN uplink communication between a central coordinator node (CN) placed on the patient’s body and an access point (AP) in a typical hospital room. To characterize the optical wireless channel, we use a Monte Carlo ray tracing-based method and take into account the effects of body shadowing and mobility based on realistic models, in contrast to the previous simplistic models considered in the literature. Using this approach, we derive the dynamic behavior of the channel DC gain for different configurations of the CNs and APs. Furthermore, based on the obtained results, we develop a statistical channel model based on kernel density estimation, which we use to investigate the impact of CN and AP placement on the communication link parameters. Also, based on the outage probability criterion, we discuss the link performance and further analyze the improvement in performance achieved through spatial diversity, i.e., by using multiple APs in the room, for different photodetector types, under different background noise conditions. The presented results show that CN placement and user’s local and global mobility significantly impact the performance of extra-WBAN links, which can nevertheless be reduced using spatial diversity. Finally, the presented performance analysis shows that a single AP equipped with an avalanche photodiode photodetector allows an acceptable link performance for low-to-moderate background noise conditions, whereas multiple APs equipped with PIN photodetectors should be used in the case of moderate-to-strong background noise.

The Interaction between Quantum Dots and Graphene: The Applications in Graphene‐Based Solar Cells and Photodetectors

AbstractGraphene with a series of neoteric electronic and optical properties is an intriguing building block for optoelectronic devices. Over the past decade, graphene‐based solar cells (SCs) and photodetectors (PDs) which can convert light signals to electrical signals have received burgeoning exploration. However, limited light absorption hampers the performance of these devices. Quantum dots (QDs) possess a strong confinement effect, a large exciton energy, and long exciton lifetime, enhancing the interaction between incident light and graphene. Especially, as the density of states near the Dirac point of graphene is ultralow, it is easy to modify the Fermi level of graphene by inserting quantum dots at the interface between graphene and light, thereby enhancing the performance of graphene‐based optoelectronic devices. The characteristics of QDs and crucial physical mechanisms of the interaction and energy transfer in QDs/graphene nanohybrids are systematically addressed. The factors influencing the efficiency of energy transfer are also analyzed quantitatively. Moreover, the experimental process of QD‐enhanced technologies for SCs, photoconductors, phototransistors, and photodiode PDs is reviewed. Eventually, a conclusion is given and the remaining challenges and future development for QDs/2D materials hybrid systems is discussed. Possible steps toward large‐scale commercial applications and integration into optoelectronic networks are suggested.

Studying thermal performance of the PIN-photodiode photodetectors based on MGL and GNR

The novel approach proposed in the present study is to use graphene based materials in the structure of the available infrared photo detectors in order to improve their parameters. The photo detector under study is PIN photodiode photodetector with no internal gain, but a very wide wavelength. In this paper, we have shown that the graphene-based detectors can exhibit high responsivity and detectivity at elevated temperatures in a wide radiation spectrum due to high values of the quantum efficiency and relatively low rates of thermo generation which lead them to surpass other detectors substantially.

Photocurrent enhancement of HgTe quantum dot photodiodes by plasmonic gold nanorod structures.

The near-field effects of noble metal nanoparticles can be utilized to enhance the performance of inorganic/organic photosensing devices, such as solar cells and photodetectors. In this work, we developed a well-controlled fabrication strategy to incorporate Au nanostructures into HgTe quantum dot (QD)/ZnO heterojunction photodiode photodetectors. Through an electrostatic immobilization and dry transfer protocol, a layer of Au nanorods with uniform distribution and controllable density is embedded at different depths in the ZnO layer for systematic comparison. More than 80 and 240% increments of average short-circuit current density (Jsc) are observed in the devices with Au nanorods covered by ∼7.5 and ∼4.5 nm ZnO layers, respectively. A periodic finite-difference time-domain (FDTD) simulation model is developed to analyze the depth-dependent property and confirm the mechanism of plasmon-enhanced light absorption in the QD layer. The wavelength-dependent external quantum efficiency spectra suggest that the exciton dissociation and charge extraction efficiencies are also enhanced by the Au nanorods, likely due to local electric field effects. The photodetection performance of the photodiodes is characterized, and the results show that the plasmonic structure improves the overall infrared detectivity of the HgTe QD photodetectors without affecting their temporal response. Our fabrication strategy and theoretical and experimental findings provide useful insight into the applications of metal nanostructures to enhance the performance of organic/inorganic hybrid optoelectronic devices.

Atmospheric optical CDMA communication systems via optical orthogonal codes

We propose and consider using a class of multiple-access sequences, namely, optical orthogonal codes (OOCs) in atmospheric optical code-division multiple-access systems. We obtain analytical solutions to the error probability for various channel models using positive-intrinsic-negative diode and avalanche photodiode photodetectors. In our analysis, the effects of atmospheric turbulence, ambient light, thermal noise, and multiuser interference are considered, in the context of a semiclassical photon-counting approach. The performance of the systems taking advantage of space diversity and error-correcting codes are also evaluated. Two common and widely used optical modulations, on-off keying and pulse-position modulation, are considered. Receiver structures based on correlator and chip level are used for OOC detection. Unlike the traditional chip-level receiver, here a generalized form of chip-level structure with two threshold levels is considered. Upper and lower bounds on the error probability for the above-chip-level receiver structure is obtained. From our analytical results, we can deduce that the chip-level receiver outperforms a simple correlator in the absence or weak atmospheric fading; however, in a strong fading environment, the simple correlator outperforms the chip-level receiver

Vertically integrated optics for ballistic electron emission luminescence: Device and microscopy characterizations

By integrating a p-i-n photodiode photodetector directly into a ballistic electron emission luminescence (BEEL) heterostructure with GaAs quantum-well active region, we have obtained a photon detection efficiency of more than 10%. This is many orders of magnitude higher than conventional far-field detection scheme with the most sensitive single-photon counters, enabling BEEL microscopy in systems with no optical components. Detailed analysis shows found a parasitic bipolar injection in parallel with the desired optical coupling between the BEEL heterostructure and the integrated photodiode beyond a characteristic collector bias, which may be solved by improved device design or limiting the operating window of the collector bias. Preliminary BEEL microscopy images of a homogeneous GaAs quantum-well luminescent layer show lateral variations of photon emission correlated with the collector current injection level modulated by surface features or interface defects.

Receiver characteristics of laser altimeters with avalanche photodiodes

The receiver characteristics of a laser altimeter system containing an avalanche photodiode photodetector are analyzed using the Gaussian approximation, the saddlepoint approximation, and a nearly exact analysis. The last two methods are shown to yield very similar results except when the background noise is extremely low and the probability of false alarm is high. However, the Gaussian approximation method is shown to cause significant errors even under relatively high levels of background noise and received signal energy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Word timing recovery in direct detection optical PPM communication systems with avalanche photodiodes using a phase lock loop

A technique for word timing recovery in a direct detection optical pulse position modulation (PPM) communication system is described. It tracks on back-to-back pulse pairs in the received random PPM data sequences with the use of a phase locked loop. The experimental system consisted of an AlGaAs laser diode transmitter ( lambda =833 nm) and a silicon avalanche photodiode photodetector, and its used Q=4 PPM signaling at a source data rate of 25 Mb/s. The mathematical model developed to characterize system performance is shown to be in good agreement with the experimental measurements. Use of this recovered PPM word clock, along with a slot clock recovery system described previously, caused no measurable penalty in receiver sensitivity when compared to a receiver which used common transmitter/receiver clocks. The completely self-synchronized receiver was capable of acquiring and maintaining both slot and word synchronizations for input optical signal levels as low as 20 average detected photons per information bit. The receiver achieved a bit error probability of 10/sup -6/ at less than 60 average detected photons per information bit. >

Slot clock recovery in optical PPM communication systems with avalanche photodiode photodetectors

Slot timing recovery in a direct-detection optical PPM communication system can be achieved by processing the photodetector output waveform with a nonlinear device whose output forms the input to a phase-locked loop. The choice of a simple transition detector as the nonlinearity is shown to give satisfactory synchronization performance. The RMS phase error of the recovered slot clock and the effect of slot timing jitter on the bit error probability were directly measured. The experimental system consisted of an AlGaAs laser diode ( lambda =834 nm) and a silicon avalanche photodiode photodetector. The system used Q=4 PPM signaling and operated at a source data rate of 25 Mb/s. The mathematical model developed to compute the RMS phase error of the recovered clock is shown to be in good agreement with results of actual measurements of phase errors. The use of the recovered slot clock in the receiver resulted in no significant degradation in receiver sensitivity compared to a system with perfect slot timing. The system achieved a bit error probability of 10/sup -6/ at a received optical signal energy of 55 detected photons per information bit. >

Theoretical performance of direct detection optical communication with AlGaAs laser transmitters, avalanche photodiode detectors, and color-coded PPM signaling

Theoretical performance characteristics are presented for a direct detection optical communication system that has peak power limited laser diode transmitters and avalanche photodiode photodetectors. The singal format consists of the transmission of a group of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> binary source digits as a single light pulse at one of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> nonoverlapping optical center frequencies (colors) in one of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> possible time slots. The system achieves a given received symbol error probability at lower peak signal intensities with a less complicated receiver structure than can be obtained with an ordinary pulse position modulation system of the same alphabet size and source data rate.

High gain optical detection with GaAs field effect transistors

The photoresponse of GaAs field effect transistor (FET) optical detectors to optical intensity modulation signals of moderate frequency is investigated. High ac responsivity is available at frequencies of interest in optical communications: more than 6 A/W can be obtained up to 100 MHz, with a noise equivalent power of <10(-12) W/ radicalHz. The slope of the frequency response is dependent on the otpical bias power, an effect that can be attributed to traps. The GaAs FET optical detector complements the performance of available P-I-N and avalanche photodiode photodetectors for communications by providing high photoresponse at low bias voltages.