Optical Crosstalk Effects Research Articles

Mechanism causing the spatial distribution non-uniformity of the prompt optical crosstalk effect in G-APD cells of silicon photomultipliers

Mechanism causing the spatial distribution non-uniformity of the prompt optical crosstalk effect in G-APD cells of silicon photomultipliers

Manufacturing a high-transmittance quantum-dot pixel frame using magnetic field and vibration field composite stamping

A simple way to complement full-color micro-light-emitting diode (micro-LED) displays is to employ ultraviolet or blue micro-LEDs with quantum dot (QD) converters. A pixel frame is essential for precisely locating the QD converter on a micro-LED chip and to limit the optical cross-talk effect. The limitations of pixel frames prepared by the commonly-used lithography technique, such as shallow depth and high dependence on high-transmittance substrates, have not been resolved in previous studies. In this study, we propose a magnetic-vibration composite stamping (MVCS) process to prepare a high-aspect-ratio and high-transmittance QD pixel frame. Magnetic extinction particles were employed, regulated, and converged into the wall of the pixel frame under the combined function of magnetic and vibration fields. Compared with the pixel frame prepared by the traditional stamping process, the pixelated QD converter achieved a 4.5-fold increase in the maximum photoluminescence intensity. Combining the micro-LED and pixelated QD converters in the pixel frame prepared by MVCS provides an alternative and practical approach for full-color micro-LED displays.

Color gamut change by optical crosstalk in high-resolution organic light-emitting diode microdisplays.

Herein, the color gamut change by optical crosstalk between sub-pixels in high-resolution full-color organic light-emitting diode (OLED) microdisplays was numerically investigated. The color gamut of the OLED microdisplay decreased dramatically as the pixel density of the panel increased from 100 pixels per inch (PPI) to 3000 PPI. In addition, the increase in thickness of the passivation layer between the bottom electrode and the top color filter results in a decrease in the color gamut. We also calculated the color gamut change depending on the pixel structures in the practical OLED microdisplay panel, which had an aspect ratio of 32:9 and a pixel density of 2,490 PPI. The fence angle and height, refractive index of the passivation layer, black matrix width, and white OLED device structure affect the color gamut of the OLED microdisplay panel because of the optical crosstalk effect.

Fabrication of self-aligning convergent waveguides of microlens arrays to collect and guide light.

The optical properties of microlens arrays may be significantly affected by the optical crosstalk effect between adjacent lenses. Recently, this issue has triggered increasing attention in the scientific community. In this study, an integrated microlens array (MLA) consisting of self-aligning convergent waveguides of microlenses was fabricated. The optical crosstalk effect does not influence the performance of such system. Based on the self-focusing effect principle, self-writing of the waveguide array was achieved in a photosensitive polymer. The light collection and guiding performance of the MLA with and without thermal cross-linking treatment was analyzed in depth. The relation between the stray light and the filling rate of the MLA shows that a high filling rate decreases the optical crosstalk. Finally, an integrated MLA with a large area, high uniformity, and excellent optical performance was fabricated.

Monolitic Hybrid Transmitter-Receiver Lens for Rotary On-Axis Communications

High-speed rotary communication links exhibit high complexity and require challenging assembly tolerances. This article investigates the use of optical wireless communications (OWC) for on-axis rotary communication scenarios. First, OWC is compared with other state-of-the-art technologies. Different realization approaches for bidirectional, full-duplex links are discussed. For the most promising approach, a monolithic hybrid transmitter-receiver lens is designed by ray mapping methodology. Ray tracing simulations are used to study the alignment-depended receiver power level and to determine the effect of optical crosstalk. Over a distance of 12.5 m m , the lens achieves an optical power level at the receiver of − 16.2 dBm to − 8.7 dBm even for misalignments up to 3 m m .

Heterogeneous Integration of Three-Primary-Color Photoluminescent Nanoparticle Arrays with Defined Interfaces.

Minimized photoluminescent devices require both high-density fluorescent arrays and minimal cross-talk between neighboring pixels on the limited area. However, the challenges to achieve the overall integration of nanomaterial-based devices hinder the development of microscale full-color displays, including micro/nanoarray density, orientation control, multimaterial interface morphology, and uniform colors. Here, we report a heterogeneous integration approach to control the orientation, combination, and density of fluorescent micro/nanoarrays on flexible substrates. By controlling the defined interface and critical shrinkage width of liquid bridges, the width of three-primary-color micro/nanolines reached 100 nm. The interval between two parallel luminous lines is down to 40 μm, and the optical cross-talk effect is remarkably reduced. This work provides a facile approach to prepare high-performance micro-photoluminescent and imaging arrays for next-generation flexible display and lighting technology.

Monolithic 300 Gb/s Parallel Transmitter in InP-Based Generic Photonic Integration Technology

In order to meet the constantly rising traffic demands in optical transport systems for data and telecommunications, compact, power efficient, and low-cost optical transmitters are needed that offer easy scalability toward higher transmission capacities. Photonic integrated circuit technology based on the InP material has long enabled the monolithic integration of tunable sources with modulators and opened the way toward large-scale wavelength-division multiplexed parallel transmitters. In this paper, we present the design and performance of a monolithic tunable 8 × 40 Gb/s parallel transmitter chip with more than 220 components and state-of-the-art capacity density metric. A generic photonic integration approach was followed, in which the transmitter is constituted from well-developed subcircuits and building blocks, facilitating its design and manufacturing. With the trend toward large-scale integration with increasing component densities and smaller chip sizes, proximity effects in form of crosstalk are limiting further miniaturization efforts. We analyze electrical, thermal, and optical crosstalk effects that are relevant to the transmitter design, discuss appropriate mitigation techniques, and indicate the limitations of the current technology.

Optical cross-talk reduction in a quantum-dot-based full-color micro-light-emitting-diode display by a lithographic-fabricated photoresist mold

In this study, a full-color emission red–green–blue (RGB) quantum-dot (QD)-based micro-light-emitting-diode (micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect, a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs’ jetted mold to further increase the reuse of UV light. The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively.

Electro-Optical Characterization of SiPMs With Green Bandpass Dichroic Filters

There is an increasing interest to use silicon photomultipliers (SiPMs) in medical applications like Photoplethysmography or Functional Near Infrared Spectroscopy, allowing the monitoring of physiological signs through non-invasive equipment. The use of large area SiPMs with embedded color filters for environmental light rejection could bring relevant advantages in these applications in terms of higher signal-to-noise ratio of the measurements. Here, we report on the first electro-optical characterization results obtained on n-on-p SiPMs with green interference bandpass filters glued on the top side of the detector SMD package. We will show how the use of the filter considerably increases, especially for large overvoltage values, the SiPM dark noise rate, due to the significant amplification of optical cross-talk effects (up to 150% of dark current increase at 50%-OV). This makes necessary a careful evaluation of the SiPMs performances in order to define the best operating conditions and layout characteristics of the detectors that will be used in the final applications.

Noise Reduction in Silicon Photomultipliers for Use in Functional Near-Infrared Spectroscopy

Silicon photomultipliers (SiPMs) have been recently proposed for different applications in medical imaging area, inclunding functional near-infrared spectroscopy (fNIRS), due to their single photon sensitivity, fast timing response, low operation bias, compactness, and low cost. Here, we report on the electro-optical performances of an SiPM technology suitably optimized for continuous wave (CW)-fNIRS application through the integration of a near-infrared (NIR) long-pass filter on the detector’s package. The use of the filter considerably decreases, especially for large overvoltage (OV) values, the SiPM’s dark noise rate, due to the significant reduction of optical cross talk effects (up to 90% of dark current reduction at 50%-OV). Moreover, the filter reduces also the absorption of environmental light of more than 85% in the SiPMs linear operation range above the breakdown, allowing at the same time a good photon detection efficiency in all the NIR range above 700 nm cut-on wavelength. These results open new perspectives for the employment of large area SiPMs operating with improved signal-to-noise ratio in advanced CW-fNIRS systems.

A new detector concept for silicon photomultipliers

A new design and principle of operation of silicon photomultipliers are presented. The new design comprises a semiconductor substrate and an array of independent micro-phototransistors formed on the substrate. Each micro-phototransistor comprises a photosensitive base operating in Geiger mode and an individual micro-emitter covering a small part of the base layer, thereby creating, together with this latter, a micro-transistor. Both micro-emitters and photosensitive base layers are connected with two respective independent metal grids via their individual micro-resistors. The total value of signal gain in the proposed silicon photomultiplier is a result of both the avalanche gain in the base layer and the corresponding gain in the micro-transistor. The main goals of the new design are: significantly lower both optical crosstalk and after-pulse effects at high signal amplification, improve speed of single photoelectron pulse formation, and significantly reduce the device capacitance.

利用多像素光子计数器的光学串话效应提高光子探测效率

利用多像素光子计数器的光学串话效应提高光子探测效率

A 32-channel photon counting module with embedded auto/cross-correlators for real-time parallel fluorescence correlation spectroscopy.

Fluorescence correlation spectroscopy (FCS) is a well-established technique to study binding interactions or the diffusion of fluorescently labeled biomolecules in vitro and in vivo. Fast FCS experiments require parallel data acquisition and analysis which can be achieved by exploiting a multi-channel Single Photon Avalanche Diode (SPAD) array and a corresponding multi-input correlator. This paper reports a 32-channel FPGA based correlator able to perform 32 auto/cross-correlations simultaneously over a lag-time ranging from 10 ns up to 150 ms. The correlator is included in a 32 × 1 SPAD array module, providing a compact and flexible instrument for high throughput FCS experiments. However, some inherent features of SPAD arrays, namely afterpulsing and optical crosstalk effects, may introduce distortions in the measurement of auto- and cross-correlation functions. We investigated these limitations to assess their impact on the module and evaluate possible workarounds.

End-to-End Multicore Multimode Fiber Optic Link Operating up to 120 Gb/s

A full multicore fiber optic link is demonstrated, transmitting greater than 100 Gb/s through a single strand of multimode fiber for the first time. The fiber, which consists of seven graded-index multimode cores, is used to transmit up to 120 Gb/s over 100 m using a custom multicore-fiber interfacing transmitter and receiver. 2-D arrays of vertical-cavity surface-emitting lasers (VCSELs) and vertically illuminated photodiodes (PDs) are fabricated with a geometry corresponding to the outer six cores of the seven-core fiber, which is arranged in a hexagonal pattern. Both flip-chip and wire-bonding technologies are used to package the VCSEL and PD chips with multichannel transmitter and receiver integrated circuits. Amplitude and timing margins of the end-to-end signals are analyzed through bit-error-rate (BER) measurements. The effects of electrical and optical crosstalk are shown to result in negligible degradation to the BER performance.

SPAD array module for multi-dimensional photon timing applications

Multi-dimensional time correlated single-photon counting has reached a prominent position among analytical techniques employed in the medical and biological fields. The development of instruments able to perform temporal and spectral fluorescence analysis (sFLIM) at the same time is limited by the performance of single-photon detectors, since currently available arrays cannot simultaneously satisfy all the requirements. To face this rising quest, a fully-parallel eight-channel module, based on a monolithic single-photon avalanche diode (SPAD) array with great temporal resolution, high photon detection efficiency and low dark count rate, has been designed and fabricated. The system relies on a novel architecture of the single pixel, based on the integration of the timing pick-up circuit next to the photodetector, making the negative effects of electrical and optical crosstalk on photon timing performance negligible. To this end, the custom technological process used to fabricate the SPAD has been modified, allowing the integration of MOS transistors without impairing the structure and the performance of the detector. The single channel is complemented by an external active quenching circuit, fabricated in a standard CMOS technology, that ensures high maximum counting rate (>5 MHz) and low after-pulsing (<2%). Finally, the output timing signals are read and conditioned by proper CMOS electronics. The complete system shows a very good temporal resolution of about 45 ps (FWHM).

Measurements of the dependence of the photon-number distribution on the number of modes in parametric down-conversion

Optical parametric down-conversion (PDC) is a central tool in quantum optics experiments. The number of collected down-converted modes greatly affects the quality of the produced photon state. We use Silicon Photomultiplier (SiPM) number-resolving detectors in order to observe the photon-number distribution of a PDC source, and show its dependence on the number of collected modes. Additionally, we show how the stimulated emission of photons and the partition of photons into several modes determine the overall photon number. We present a novel analytical model for the optical crosstalk effect in SiPM detectors, and use it to analyze the results.

Comparative studies of silicon photomultipliers and traditional vacuum photomultiplier tubes

Silicon photomultipliers (SiPMs) are a new generation of semiconductor-based photon counting devices with the merits of low weight, low power consumption and low voltage operation, promising to meet the needs of space particle physics experiments. In this paper, comparative studies of SiPMs and traditional vacuum photomultiplier tubes (PMTs) have been performed regarding the basic properties of dark currents, dark counts and excess noise factors. The intrinsic optical crosstalk effect of SiPMs was evaluated.

On the efficiency of photon emission during electrical breakdown in silicon

This paper presents a study of photons that are emitted during electrical breakdown in p–n silicon diodes. The method that was developed for this study uses the optical-crosstalk effect that is observed in Geigermode-APD (G-APD) photon detectors. The outcome of this study is twofold: firstly, mainly photons with energies between 1.15 and 1.4 eV contribute to the optical crosstalk in G-APDs used in this study. This observation is explained by the strong energy dependence of the absorption length of photons in silicon. Secondly, the intensity with which photons with energies between 1.15 and 1.4 eV are emitted during a breakdown is 3 × 10 - 5 photons per charge carrier in the breakdown region. The uncertainty of the intensity is estimated to be a factor of two. For this study a simulation package Siliconphotomultiplier Simulator ( SiSi) was developed, which can be used to address various other questions that arise in the application of G-APDs.

Simultaneous multiplexing and demultiplexing of wavelength-interleaved channels in DWDM millimeter-wave fiber-radio networks

A simultaneous multiplexing and demultiplexing (MUX/DEMUX) scheme for wavelength-interleaved millimeter-wave 37.5-GHz-band fiber-radio channels spaced at 25 GHz has been proposed. The proposed MUX/DEMUX technique potentially realizes simple, compact, and low-cost central office and remote nodes by avoiding the use of wavelength-selective pre- and postprocessing hardware. The novel scheme incorporates an arrayed-waveguide grating with multiple loop-backs between the input and the output ports, in addition to multiple optical circulators and optical isolators. The multiplexing functionality of the proposed technology enables a carrier subtraction technique and consequently reduces the carrier-to-sideband ratios of the multiplexed channels. Multiplexing of the uplink channels generated via several methods is demonstrated experimentally. These techniques include generation of the channels by using the optical carriers that correspond to wavelengths spaced at the free spectral range (FSR) or multiples of the FSR from the downlink (DL) optical carriers and reuse of the DL optical carriers that are recovered by applying a wavelength reuse technique (lambdaUL =lambdaDLplusmnntimesFSR, where n=0,1,2,3,...). The demultiplexing functionality of the proposed scheme that separates the 37.5-GHz-band wavelength-interleaved DL channels spaced at 25 GHz is also demonstrated. In addition, the effect of optical crosstalk on the transmission performance of the demultiplexed channels is also characterized experimentally

Real-time location of multiple time-varying strain disturbances, acting over a 40-km fiber section, using a novel dual-Sagnac interferometer

Updated results using a novel sensing architecture based on a Sagnac interferometer are presented and, for the first time, real-time separation and positioning of multiple disturbances has been realized. A 40-km long dual-Sagnac sensor was formed by spectral slicing of light from a single, broad-band erbium-doped-fiber super-luminescent source and wavelength division multiplexed (WDM) routing around the loop to form an inherently low loss system. Independent active phase biasing of each Sagnac was employed, allowing the use of a single optical detector. The effects of residual optical cross talk between the two Sagnacs has been accurately modeled, allowing resulting errors to be corrected. The new system has capability for narrow-band fast Fourier transform (FFT) analysis of detected disturbance signals, and hence their separation in the frequency domain. For audio-frequency excitation, an average positional resolution of 100 m over a 40-km length was achieved with a postdetection signal processing bandwidth of 8 Hz.