Pulse Amplitude Modulation Research Articles

Effects of experimental CO2 enrichment on the PSII photochemical efficiency of Symbiodinium sp. in Acropora millepora

Enrichment of seawater with CO2 decreases the concentration of the carbonate ion while increasing that of hydrogen and bicarbonate ions. We use pulse-amplitude-modulation (PAM) fluorometry to investigate whether, in the absence of warming, and in sub-saturating light, these changes affect the PSII photochemical efficiency of _Symbiodinium_ sp. in the reef-building coral _Acropora millepora_. We assessed this experimentally with 30-min-interval saturation pulse analyses at 25 °C, a daily peak in the intensity of the photosynthetically active radiation (PAR) at ~65 µmol quanta m–2 s–1, and a seawater _p_CO2 that we gradually increased over nine days from ~496 to ~1290 μatm by injection of CO2-enriched air. Nine 14-day time series, which, except one, were recorded at the growing apices of a coral branch, revealed diel oscillations in the PSII photochemical efficiency characterized by a steep nocturnal decrease followed by a steep increase and peak in the morning, a daily minimum at midday (∆F/Fm’,midday), and a daily maximum at the onset of darkness at 19:00 h (Fv/Fm,19:00 h). An inadvertent shift in the position of one of the PAM fluorometer measuring heads revealed differences between the basal part and the growing coral apices of a coral branch in ∆F/Fm’midday and Qm. In ambient seawater (Control) _Symbiodinium_ sp. exhibited a gradual decrease, over the course of the experiment, in ∆F/Fm’,midday, Fv/Fm,19:00 h, and the slope of the linear regression between the relative electron transport rate and the intensity of PAR (rETR/PAR). Although two of three successive experiments indicated that CO2 enrichment counteracted these trends, statistical analyses failed to confirm an influence of _p_CO2 on ∆F/Fm’,midday, Fv/Fm,19:00 h, and Qm, rendering this experiment inconclusive.

Unambiguous acquisition algorithm based on sub‐correlation functions combination for semi‐integer CPM signals

AbstractDue to the nonlinear nature of continuous phase modulation (CPM), most existing unambiguous acquisition algorithms are ineffective in eliminating the ambiguity threat faced by semi‐integer CPM signals. To address this issue, this letter proposes an unambiguous acquisition algorithm based on sub‐correlation functions combination (SCFC). The main idea of this algorithm is to decompose the first pulse amplitude modulation waveform derived from the Laurent decomposition into sub‐signal waveforms that are appropriate for CPM signals. The final unambiguous function is obtained by combining the autocorrelation function of the received CPM signal with the sub‐correlation functions derived from the sub‐signal waveforms and the received CPM signal. Simulation results demonstrate that the SCFC algorithm can eliminate the ambiguity threat of semi‐integer CPM signals with relatively minor detection loss. Moreover, the proposed algorithm successfully retains a narrow main peak and exhibits superior multipath resistance.

Performance Analysis of Modulation Techniques for Indoor Free Space Optics

This paper deals with designing and analyzing the performance of indoor Free Space Optics (FSO) link for various modulation techniques in diffused channel conditions. At the present time, FSO is widely adopted because of its features; high speed, security, low power consumption and unlicensed spectrum. LEDs and LASERs are optimum choice to cater the dynamic range of requirements for optical communication system. The indoor FSO system has been simulated in Optisystem 14 software using various modulation schemes under different attenuation factors which may influence the performance of the system. In this paper, we have analyzed the performance of different modulation schemes such as Return to Zero, Non-Return to Zero, Phase Shift Keying, Pulse Amplitude Modulation, Quadrature Amplitude Modulation and Minimum Shift Keying. This work mainly focuses on the parameters; Bit Error Rate, Q-factor and power corresponding to transmission distance achieve minimum attenuation.

Photosynthetic Characteristics of Benthic Microalgae Measured by HPLC and Diving Pulse Amplitude Modulated (PAM) Fluorometry on the Nakdong River Estuary of the Korean Peninsula

Photosynthetic Characteristics of Benthic Microalgae Measured by HPLC and Diving Pulse Amplitude Modulated (PAM) Fluorometry on the Nakdong River Estuary of the Korean Peninsula

Normal-Incidence Germanium Photodetectors Integrated with Polymer Microlenses for Optical Fiber Communication Applications.

We present a novel photon-acid diffusion method to integrate polymer microlenses (MLs) on a four-channel, high-speed photo-receiver consisting of normal-incidence germanium (Ge) p-i-n photodiodes (PDs) fabricated on a 200 mm Si substrate. For a 29 µm diameter PD capped with a 54 µm diameter ML, its dark current, responsivity, 3 dB bandwidth (BW), and effective aperture size at -3 V bias and 850 nm wavelength are measured to be 138 nA, 0.6 A/W, 21.4 GHz, and 54 µm, respectively. The enlarged aperture size significantly decouples the tradeoff between aperture size and BW and enhances the optical fiber misalignment tolerance from ±5 µm to ±15 µm to ease the module packaging precision. The sensitivity of the photo-receiver is measured to be -9.2 dBm at 25.78 Gb/s with a bit error rate of 10-12 using non-return-to-zero (NRZ) transmission. Reliability tests are performed, and the results show that the fabricated Ge PDs integrated with polymer MLs pass the GR-468 reliability assurance standard. The demonstrated photo-receiver, a first of its kind to the best of our knowledge, features decent performance, high yield, high throughput, low cost, and compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication processes, and may be further applied to 400 Gb/s pulse-amplitude modulation four-level (PAM4) communication.

Fabrication Tolerances’ Impact on an ODAC-Based PAM-4 Transmitter

Photonic integrated circuits (PIC) devices are impacted by fabrication tolerances and therefore, prior knowledge of such variations could improve the PIC fabrication process and overall yield. This paper presents a method for predicting the fabrication impacts on a telecommunication optical digital to analog converter (oDAC)-based pulse amplitude modulator level four (PAM-4) transmitter as a case study where the certainty of this passive device is subjected to random variation. Our findings allow us to estimate the production yield in a fabrication scenario using the symbol error rate (SER) benchmark and this contributes to the study of the viability of oDAC PAM-4 transmitters to replace conventional electrical digital to analog converter (eDAC) PAM-4 transmitters.

Weight-adaptive joint mixed-precision quantization and pruning for neural network-based equalization in short-reach direct detection links.

Neural network (NN)-based equalizers have been widely applied for dealing with nonlinear impairments in intensity-modulated direct detection (IM/DD) systems due to their excellent performance. However, the computational complexity (CC) is a major concern that limits the real-time application of NN-based receivers. In this Letter, we propose, to our knowledge, a novel weight-adaptive joint mixed-precision quantization and pruning approach to reduce the CC of NN-based equalizers, where only integer arithmetic is taken into account instead of floating-point operations. The NN connections are either directly cutoff or represented by a proper number of quantization bits by weight partitioning, leading to a hybrid compressed sparse network that computes much faster and consumes less hardware resources. The proposed approach is verified in a 50-Gb/s 25-km pulse amplitude modulation (PAM)-4 IM/DD link using a directly modulated laser (DML) in the C-band. Compared with the traditional fully connected NN-based equalizer operated with standard floating-point arithmetic, about 80% memory can be saved at a minimum network size without degrading the system performance. Quantization is also shown to be more suitable to over-parameterized NN-based equalizers compared with NNs selected at a minimum size.

P‐149: The Optical Taste of MLED Display: From the Mini‐/Micro‐LED Optical Property to the Design of Pixel Circuit

Mini‐LED and Micro‐LED have ultrahigh luminance and excellent color saturation to be used in MLED display based on COG (Chip on Class). In this paper, two pitch‐0.6 mm MLED displays with pulse hybrid modulation (PHM) and pulse amplitude modulation (PAM) driving Mode separately is proposed. And we discuss the influences of the intrinsic optical characteristics of Mini‐LED and Micro‐LED on the design of MLED display pixel circuit. In particular, surface brightness distributions of different gray scale are tested to theoretically analyze the pocking phenomenon in different ways.

38‐1: Invited Paper: Micro Light‐Emitting Diode Pixel Circuit and Driving Method Considering Wavelength Shift

We proposed micro light‐emitting diode (μLED) pixel circuits and driving methods. Because the wavelength shift of μLEDs occurs as the current density is varied, we designed pixel circuits based on pulse width modulation (PWM), hybrid PWM and pulse amplitude modulation (PAM), and quaternary digital driving.

Coherent photosynthetic activity between deciduous arboreal trees.

The long-term time course of photosynthetic activity in arboreal trees of aspen Populus tremula L. and birch Betula pendula Roth species native for Kola Subarctic was observed through 2014–2017 yr vegetation seasons in terms of PAM (Pulse Amplitude Modulated) foliage chlorophyll fluorescence measurements in situ. The temporal pair- wise correlation chlorophyll fluorescence pattern between any leaf blades couple for the whole any single crone as well as for proximate tree crones was found. The abrupt temperature drops and other environmental changes promote transition to blades coherence, the most synchronicity between trees was observed in 2014th fall. The global synchronization between any leaf couple was often preceded by transition of the foliar blades photosynthetic activity in common coherent quasi-cyclic rhythm. It is suggested that mutual crone’s intra and inter temporal organization and cooperative assimilation promote resistance and optimal realization of adaptive species potential.

Laser-sound reproduction by pulse amplitude modulation audio streams

Recently, the possibility to reproduce complex continuous acoustic signals via pulsed laser-plasma sound sources was demonstrated. This was achieved by optoacoustic transduction of dense laser pulse trains, modulated via single- or multi-bit Sigma–Delta, in the air or on solid targets. In this work, we extend the laser-sound concept to amplitude modulation techniques. Particularly, we demonstrate the possibility of transcoding audio streams directly into acoustic pulse streams by analog pulsed amplitude modulation. For this purpose, an electro-optic modulator is used to achieve pulse-to-pulse amplitude modulation of the laser radiation, similarly to the multi-level Sigma–Delta method. The modulator is directly driven by the analog input stream through an audio interface. The performance of the system is evaluated at a proof-of-principle level for the reproduction of test audio signals such as single tones, double tones and sine sweeps, within a limited frequency range of the audible spectrum. The results are supported by computational simulations of the reproduced acoustic signals using a linear convolution model that takes as input the audio signal and the laser-generated acoustic pulse profile. The study shows that amplitude modulation allows for significant relaxation of the laser repetition rate requirements compared to the Sigma–Delta-based implementation, albeit at the potential cost of increased distortion of the reproduced sound signal. The nature of the distortions is analyzed and a preliminary experimental and computational investigation for their suppression is presented.

Phenology and the response of photosynthesis to irradiance and temperature gradient in the herbal drug red alga, Chondria armata (Rhodomelaceae, Ceramiales) from Kagoshima, Japan

Seasonal changes in the size of the herbal drug red alga Chondria armata (Rhodomelaceae, Ceramiales) were investigated in Kagoshima, Japan, which is near the northern distributional limit in the western Pacific. Additionally, its photosynthetic response to irradiance and temperature was examined using dissolved oxygen sensors and a pulse amplitude modulation (PAM)-chlorophyll fluorometer. This alga was observed in tidepools throughout the year; its height and weight were greatest in December and the lowest in April and May. The net photosynthesis of the photosynthesis–irradiance (P–E) curve determined at 28°C quickly saturated at 113 µmol photons m-2 s-1, with minimal inhibition even at 1000 µmol photons m-2 s-1. The gross photosynthesis of the photosynthesis–temperature (P–T) curved over 8 to 40°C, measured at 500 µmol photons m-2 s-1, peaked at 30.1°C and decreased rapidly below 20°C and above 36°C, respectively. Similarly, the effective quantum yield (ΔF/Fm') after a 3-day culture during 4–40°C at 50 µmol photons m-2 s-1 remained stable between 16°C and 32°C but decreased outside of this range. The combined effect of irradiance (200 [low] and 1000 [high] µmol photons m-2 s-1) and temperature (28, 22, and 16°C) revealed that ΔF/Fm' declined during exposure to high irradiance at all temperature treatments. However, it mostly recovered after a subsequent 12-hour period of dim-light acclimation at 28°C and 22°C. In contrast, those at 16°C could not recover, indicating the occurrence of low-temperature light stress. This alga appears to be well-adapted to the irradiance and temperature environment at the study site. However, the winter temperature appears to approach its threshold level, and the occurrence of strong light during the winter might adversely affect the abundance of this alga near its northern distributional limit.

Synchronous time multiplexing for non-line-of-sight multiple-input multiple-output optical camera communications.

In typical multiple-input multiple-output (MIMO) optical camera communication (OCC) systems, the spatial correlation of MIMO channels is large. Optical signals between light sources can easily interfere with each other, negatively impacting the overall transmission performance. In this work, we propose a time-multiplexing integral modulation scheme for a non-line-of-sight MIMO OCC system, where each LED transmits different signals to improve both the data rate and security of the system. A genetic algorithm (GA)-based adaptive multi-threshold scheme is designed to demodulate the blurred fringes in multi-level pulse amplitude modulation. The experimental results show that at a distance of 2.5 m, a data rate of 16.4 kb/s can reach with the BER performance of 3.01 × 10-3, which validates the superiority and reliability of our proposed schemes.

Dual wavelength signal generation with four wave mixing based on directly modulated laser

Dual wavelength (DW) lasers are crucial for producing petahertz (PHz) signals, which are higher value terahertz (THz) signals. The infrared and visible light sub-bands are valuable frequency range for a number of applications, including networking, multiple access techniques, next-generation mobile networks (6G), future wireless networks, and new PHz communication systems. The importune need to the high frequency signal such as THz and PHz signal for 5 and 6 next generation wireless cellular mobile networks motivate us to design an optical system to provide these signals rather than an electronic circuits. They are also beneficial for a variety of medical testing. The wavelength spacing ranging from 14 nm to 7 nm is proposed and demonstrated a dual-wavelength generation with FWM based on DML is realized at 1554 and 1548 nm. It is essential to make use of the fiber's non-linearity characteristics to ensure synchronization for continuous wave (CW) laser and directly modulated laser (DML) signals and the creation of the four wave mixing (FWM) components. With the help of OptiSystem version 14.0, the system is designed and investigated then, the desired THz signal is created as pulse amplitude modulation. The position of the FWM components within the frequency range between the spectrums of the two lasers affects the synthesis of the required signal. At the DML frequency equal to or below the CW Laser (1520 nm), neither FWM frequency components nor dual wavelength pulses exist. On the other hand, the FWM frequency components and dual wavelength pulses can only be seen when the DML frequency is greater than 1520 nm. The CW laser frequency is the main controlling factor in the generation THz signal. If the CW laser frequency is set at or below 1520 nm, the dual wavelength and THz signal are accessible. Because these frequencies are so far from the reference fiber frequency, it is impossible to produce dual wavelength pulses at frequencies higher than those mentioned above.

High-speed mid-infrared silicon-based electro-optic modulator at 2 μm

We demonstrate the Mach-Zehnder interferometer (MZI) silicon-based electro-optic modulators in the short-wave mid-infrared 2 μm band. The waveguide structure and doping position of the devices are optimized by simulation. The devices are manufactured on a 220 nm silicon-on-insulator (SOI) platform, and are measured through self-built short-wave mid-infrared measurement platform. The device with the length of 3.5 mm has a measured modulation efficiency of 1.853 V cm at 3 V reverse bias. The highspeed characterization is also performed, and the device with the length of 3.5 mm has a data rate of over 20 Gb/s at the voltage swing of 2.8 Vpp with on-off keying (OOK) modulation formats. The modulation speed of the 2 mm device can reach over 40 Gb/s with 4-level pulse amplitude modulation (PAM-4) formats at a voltage swing of 2.5 Vpp.

A driving method for gray scale multiplication of electrowetting display based on hybrid modulation

In order to solve the problem of low gray level due to the few driving chips developed based on the photoelectric characteristics of electrowetting display, a driving method based on modulation is proposed to double the gray level of electrowetting display. In this method, the driving waveform based on pulse amplitude modulation and pulse width modulation hybrid modulation is designed, and the gray level–luminance curve of the electrowetting display is measured and analyzed. On this basis, the luminance nonlinear correction is carried out, and the improvement of 64 Gy levels to 127 Gy levels is realized by the principle of human visual persistence phenomenon. The experimental results show that the proposed driving scheme can break through the limitation of the driving chip and realize the multiplication of gray levels, in which 96% gray levels increase steadily with an average luminance difference of 0.07, and at the same time enhance the contrast and improve the display effect.

Regeneration of 200 Gbit/s PAM4 Signal Produced by Silicon Microring Modulator (SiMRM) Using Mach–Zehnder Interferometer (MZI)-Based Optical Neural Network (ONN)

We propose and demonstrate a Mach–Zehnder Interferometer (MZI)-based optical neural network (ONN) to classify and regenerate a four-level pulse-amplitude modulation (PAM4) signal with high inter-symbol interference (ISI) generated experimentally by a silicon microing modulator (SiMRM). The proposed ONN has a multiple MZI configuration achieving a transmission matrix that resembles a fully connected (FC) layer in a neural network. The PAM4 signals at data rates from 160 Gbit/s to 240 Gbit/s (i.e., 80 GBaud to 120 GBaud) were experimentally generated by a SiMRM. As the SiMRM has a limited 3-dB modulation bandwidth of ~67 GHz, the generated PAM4 optical signal suffers from severe ISI. The results show that soft-decision (SD) forward-error-correction (FEC) requirement (i.e., bit error rate, BER < 2.4 × 10−2) can be achieved at 200 Gbit/s transmission, and the proposed ONN has nearly the same performance as an artificial neural network (ANN) implemented using traditional computer simulation.

Application of Artificial Intelligence in Stimulating Plant Growth Using Electric Lighting

This paper highlights the role of artificial intelligence (AI) in electric lighting for enhancing smart agriculture. The use of electric lighting in greenhouses is widely practiced in the present time, as sunlight is poorly available in some parts of the world. Different plants have different growth in different spectrum of light. The spectrum of light in which the plant grows maximum is coined as optimum growth spectrum (OGS). Hence, this study aims to choose artificial intelligence in assessing the optimum spectrum of light for a given plant. RGB based LEDs are used and its luminous efficacy is interpreted, considering different blend of mechanisms and the yield current and temperature. Rapid light fluctuations offered by pulse amplitude modulation causes a loss in the output of the LEDs. Hence, there lies a finite gap in the light provided and the light reaching the plant. Since, LEDs are the source of light here, hence, light sources complying with higher CRI should be deployed, as used in this experiment. The overall system was so designed such that when a plant is cultivated, using image processing, AI identifies the specific plant and implements all the available data, like the optimum growth spectrum, temperature, humidity, etc. The experiment clearly emphasizes on the results which were impressive. The OGS of the given plant has been figured out and trained the system through AI to execute the growth functions for the given plant.

A 56‐GBaud lumped linear push–pull driver for Mach–Zehnder modulator in 130‐nm SiGe technology

AbstractA fully differential lumped linear driver for Mach–Zehnder modulator has been presented and assessed in 130‐nm SiGe BiCMOS technology. Multitopology peaking techniques, especially T‐coil peaking method, have been employed to flatten the frequency response and increase the bandwidth. Degeneration resistors have been used to enhance circuit linearity. Simultaneously, improvements have been made to the output stage of the conventional single emitter follower push–pull) circuit to enhance the output eye diagram quality at higher transmission rates. The fabricated driver achieved a differential gain of 16.2 dB with a bandwidth of over 50 GHz, corresponding to a fixed output swing of over 3.2 Vppd within the automatic gain control loop. Time domain measurements, limited in speed by the measurement setup, reported a data rate up to 56 Gb/s none return to zero and 40‐GBaud 4‐levels pulse amplitude modulation with a bit error rate less than 10−12.

Demonstration of IM/DD 3-Tbit/s PS-PAM8 transmission with wavelength and mode multiplexing based on neural network equalizer

We experimentally demonstrate 8-channel wavelength division multiplexing (WDM) signal transmission in 4 modes over 20-m multimode fiber (MMF) in an intensity modulation and direct-detection (IM/DD) system. By combining the probabilistic shaping (PS) technique with high order pulse amplitude modulation (PAM) format, 40-GBaud PS-PAM8 signal transmission in the WDM + MDM IM/DD system achieves a total net bit rate of 3-Tbit/s. With the aid of a multiple input single output (MISO) neural network (NN) equalizer, we obtain a 1.6-dB receiver sensitivity gain compared with traditional digital signal processing (DSP), including multiple input multiple outputs (MIMO) time domain equalizer (TDE).