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Far-Red Spectrum of Second Emerson Effect: A Study Using Dual-Wavelength Pulse Amplitude Modulation Fluorometry
摘要： Non-additive enhancement of the photosynthesis excited by simultaneous illumination with far-red light and light of shorter wavelengths is called as “second Emerson effect”. Its action spectra are well-known as a photosynthetic yield’s dependence on light wavelength in red (630-690 nm) spectral region at a constant-wavelength far-red illumination near 700-715 nm. However, the opposite dependence of the photosynthetic yield’s of shorter constant-wavelength light (red or blue) on light wavelength in far-red (690-760 nm) spectral region was never studied. In this study the action spectrum of second Emerson effect was studied using a fast-Fourier dual-wavelength Pulse Amplitude Modulation (PAM) fluorometry. Chlorophyll fluorescence in ailanthus (Ailanthus altissima Mill.) leaves was excited with blue modulated light. Far-red induced decrease of fluorescence (fluorescence shift-FRIFS) was studied in response to illumination of leaves with a background light from 690 to 760 nm (10 nm step), calculating FRIFS = (F0-Fs)/F0, where F0-fluorescence measured without and Fs-with far-red light. Maximum FRIFS was observed at 720 nm (11.8%), but it still remained considerable at 740, 750 nm and a low FRIFS values were revealed at 690 and even at 760 nm. Measurements carried out with blue saturating flashes during and after far-red illumination showed the increase of quantum yield of Photosystem II (PSII), calculated as Fv/Fm at 720 nm background light. FRIFS had lower values under excitation with red modulating light. It is concluded that FRIFS is a result of a photochemical quenching caused by an additional selective far-red excitation of PSI in conditions when PSII is preferably excited by blue light thus leading the PSI to limit non-cyclic electron flow. The contradiction between the known absorption spectra of PSI-light harvesting complex I and the observed action spectrum of second Emerson effect (FRIFS spectrum) is discussed.
关键词： Photosystem II,Ailanthus Altissima,Photosystem I,Second Emerson Effect,Fast-Fourier PAM-Fluorometry,Far-Red Light,Thylakoid Electron Transport
更新于2025-11-14 15:30:11
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Design of PAM-DMT-based Hybrid Optical OFDM for Visible Light Communications
摘要： In this letter, a pulse-amplitude-modulated based hybrid optical orthogonal frequency division multiplexing (PHO-OFDM) scheme is proposed. We use the high order quadrature-amplitude-modulation to replace the one-dimensional pulse-amplitude-modulated on the even subcarriers for compensating the data capacity weakness of the conventional pulse amplitude modulated discrete multitone (PAM-DMT). The combined time-domain PHO-OFDM signal has a larger amplitude range than the original PAM-DMT but with a reduced peak-to-average power ratio (PAPR). Besides that, a flexible power allocation method is introduced to the proposed PHO-OFDM systems to fully exploit the whole dynamic range of LEDs. The simulation results show that, under the same average bit rate, the proposed PHO-OFDM scheme has a better bit error rate performance compared with the conventional PAM-DMT scheme, thus demonstrating its application potential in visible light communications.
关键词： visible light communications (VLC),pulse-amplitude-modulated discrete multitone (PAM-DMT),optical orthogonal frequency division multiplexing (O-OFDM)
更新于2025-09-23 15:22:29
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On the Complexity Reduction of the 2nd-order Volterra Nonlinear Equalizer for IM/DD systems
摘要： To cope with the various nonlinear signal distortions in IM/DD transmission systems, a theoretical analysis on the Volterra nonlinear equalizer (VNLE) is provided, focusing on computational complexity aspects. The analysis yields a simple reduced-complexity scheme for the 2nd-order VNLE (R2-VNLE) based on a performance-complexity trade-off. An experimental verification is performed with single-sideband 28-GBaud PAM-4 electro-absorption modulated signals, generated by a distributed-feedback laser, over transmission distances of up to 80-km of standard single-mode fiber in the C-band. A comparison of the results for different equalization schemes, including a signal-signal beat interference mitigation technique, shows superior performance for the R2-VNLE.
关键词： PAM-4,Volterra filter,direct detection,Nonlinear equalization,optical interconnects,intensity modulation
更新于2025-09-23 15:22:29
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In Vivo 3D Imaging of Retinal Neovascularization Using Multimodal Photoacoustic Microscopy and Optical Coherence Tomography Imaging
摘要： The pathological process of neovascularization of the retina plays a critical role in causing vision loss in several diseases, including diabetes, retinal vein occlusion, and sickle cell disease. Retinal neovascularization can lead to vitreous hemorrhage and retinal detachment, yet the pathological process of neovascularization is a complex phenomenon under active investigation. Understanding and monitoring retinal neovascularization is critically important in clinical ophthalmology. This study describes a novel multimodal ocular imaging system which combines photoacoustic microscopy (PAM) and a spectral domain optical coherence tomography (SD-OCT) to improve the visualization of retinal neovascularization (RNV), their depth, and the surrounding anatomy in living rabbits. RNV was induced in New Zealand rabbits by intravitreal injection of vascular endothelial growth factor (VEGF). The retinal vasculature before and after injection at various times was monitored and evaluated using multimodal imaging including color fundus photography, fluorescein angiography (FA), OCT, and PAM. In vivo experiments demonstrate that PAM imaging distinctly characterized the location as well as the morphology of individual RNV with high contrast at a safe laser energy of 80 nJ. SD-OCT was used to identify a cross-sectional structure of RNV. In addition, dynamic changes in the retinal morphology and retinal neovascularization were observed at day 4, 5, 6, 7, 9, 11, 14, 28, and day 35 after VEGF injection. PAM demonstrated high-resolution optical absorption of hemoglobin and vascular imaging of the retina and choroid with increased depth of penetration. With the current multimodal imaging system, RNV can be easily visualized in both 2D and 3D angiography. This multimodal ocular imaging system provides improved characterization of the microvasculature in a safe manner in larger rabbit eyes.
关键词： PAM,VEGF,multimodal imaging,optical coherence tomography,photoacoustic microscopy,retinal neovascularization,vascular endothelial growth factor,OCT
更新于2025-09-23 15:22:29
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Measurement of Photosynthesis Using PAM Technology in a Purple Sulfur Bacterium <i>Thermochromatium tepidum</i> (Chromatiaceae)
摘要： We demonstrate that Blue-diode-based pulse amplitude modulation (PAM) technology can be used to measure the photosynthetic electron transport rate (ETR) of purple sulfur bacteria (Thermochromatium tepidum, Chromatiaceae). Previous studies showed that PAM technology could be used to estimate photosynthesis in purple nonsulfur bacteria and so PAM technology can be used to estimate photosynthesis of both kinds of purple photosynthetic bacteria. The absorptance of Thermochromatium films on glass fiber disks was measured and used to calculate actual ETR. ETR vs Irradiance curves fitted the waiting-in-line model (ETR = (ETRmax * E/Eopt) * exp (1-E/Eopt)). Yield (Y) was only 0.3–0.4. Thermochromatium saturates at 325 ± 13.8 μmol photons m?2 s?1 or ~15% sunlight and shows photoinhibition at high irradiances. A pond of Thermochromatium would exhibit classic surface inhibition. Photosynthesis is extremely low in the absence of an electron source: ETR increases in the presence of acetate (5 mol m?3) provided as an organic carbon source and also increases in the presence of sulfite (3 mol m?3) but not sulfide and is only marginally increased by the presence of Fe2?. Nonphotochemical quenching does occur in Thermochromatium but at very low levels compared to oxygenic photo-organisms or Rhodopseudomonads.
关键词： photosynthesis,PAM technology,photoinhibition,absorptance,Thermochromatium tepidum,purple sulfur bacteria,electron transport rate
更新于2025-09-23 15:22:29
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Interplay of Bit Rate, Linewidth, Bandwidth, and Reach on Optical DMT and PAM with IMDD
摘要： We theoretically compare the performance of optical discrete multi-tone (DMT) and pulse amplitude modulation (PAM) using intensity modulated, direct detection (IMDD). PAM is a lower cost, lower complexity solution than DMT, however it is more vulnerable to chromatic dispersion on the C band. We compare DMT and PAM taking into consideration the interplay of laser linewidth, fiber length, transmission rate, and channel bandwidth. We use a semi-analytical model to examine bit error rates. We study how system parameters shift the performance advantages between DMT and PAM. Our model can also be used to find the best hardware solution and frequency band for a target modulation format and bit error rate.
关键词： PAM,O-band,C-band,chromatic dispersion,DMT,bandwidth,laser linewidth
更新于2025-09-23 15:22:29
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Decoding of 10-G Optics-Based 50-Gb/s PAM-4 Signal Using Simplified MLSE
摘要： A simpli?ed maximum likelihood sequence estimation (MLSE) based on Viterbi algorithm has been proposed. Experimental results show that compared with the conventional MLSE, the proposed algorithm saves the multiplication by 25% with no sensitivity penalty when the memory length of MLSE is 2 both in the 25 Gb/s nonreturn to zero and 50 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission systems. In order to further reduce the number of multiplications in the 50 Gb/s PAM-4 transmission system, we use 75 taps of feed-forward equalization to equalize the received PAM-4 signal into duo-binary PAM-4 (DB-PAM-4) signal and then use MLSE with the memory length of 1 to decode, which improves the sensitivity performance by 1.8 dB and reduces the computing complexity by ～98% compared with conventional MLSE (L = 4) method. As a result, a 10-km C-band transmission of 50 Gb/s PAM-4 signal is achieved using optical transceivers with a combined 3-dB bandwidth of ～8 GHz, and only 107 multiplications are required by using our proposed simpli?ed algorithm for equalization.
关键词： feed-forward equalization (FFE),four-level pulse-amplitude modulation (PAM-4),Viterbi algorithm,Maximum likelihood sequence estimation (MLSE)
更新于2025-09-23 15:21:01
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Evaluation of the Impact of MZM Frequency Response on BER Performance of PAM-4 Modulated WDM-PON
摘要： Continuous growth of data tra?c in optical access networks is driving the increase of utilized data rates even up to 25 Gbit/s per wavelength. While due to utilization of signals with large electrical bandwidth, requirements on the bandwidth of electrical and electro-optical components increase signi?cantly. Addressing that, the feasibility of application of the minimal transmitter and receiver bandwidth has received considerable attention. In this research, via numerical simulation in VPI Photonics Design Suite software we evaluate the impact of the shape of MZM frequency response based on amplitude frequency response (S21) from commercial MZM speci?cation. Moreover, addressing the requirements on numerical simulation models that ensure simulation of MZM frequency response curve for prediction of the overall system performance, we have also evaluated several analytical frequency responses (corresponding to the responses of 1 and 4-pole, Bessel and Gaussian ?lters) with di?erent 3-dB bandwidth values. Based on the obtained results, we propose the approach for the simulation of MZM frequency response that is the most relevant for our utilized PAM-4 modulated WDM-PON system with 25 Gbit/s bitrate per channel.
关键词： MZM frequency response,PAM-4 modulated WDM-PON,numerical simulation,VPI Photonics Design Suite,BER performance
更新于2025-09-23 15:19:57
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Optical properties of corals distort variable chlorophyll fluorescence measurements
摘要： Pulse amplitude modulated (PAM) fluorimetry is widely used in photobiological studies of corals, as it rapidly provides numerous photosynthetic parameters to assess coral ecophysiology. Coral optics studies have revealed the presence of light gradients in corals, which are strongly affected by light scattering in coral tissue and skeleton. We investigated whether coral optics affects variable chlorophyll fluorescence measurements and derived photosynthetic parameters by developing planar hydrogel slabs with immobilized microalgae and with bulk optical properties similar to those of different types of corals. Our results show that PAM-based measurements of photosynthetic parameters differed substantially between hydrogels with different degrees of light scattering but identical microalgal density, yielding deviations in apparent maximal electron transport rates by a factor of 2. Furthermore, system settings such as the measuring light intensity affected F0, Fm and Fv/Fm in hydrogels with identical light absorption but different degrees of light scattering. Likewise, differences in microalgal density affected variable chlorophyll fluorescence parameters, where higher algal densities led to greater Fv/Fm values and relative electron transport rates. These results have important implications for the use of variable chlorophyll fluorimetry in ecophysiological studies of coral stress and photosynthesis, as well as other optically dense systems such as plant tissue and biofilms.
关键词： light scattering,PAM fluorimetry,photosynthesis,hydrogels,variable chlorophyll fluorescence,coral optics
更新于2025-09-19 17:15:36
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Low complexity soft-decision Viterbi algorithm (SOVA) for IM/DD 56 Gbps PAM-4 system
摘要： In this paper, a soft-decision Viterbi algorithm (SOVA) combined with low-density parity check (LDPC) is investigated to achieve high chromatic dispersion tolerance and alleviate the high OSNR requirement in pulse amplitude modulation 4-level (PAM-4) systems. To reduce complexity increase over a maximum likelihood sequence equalizer (MLSE), we propose a non-binary SOVA algorithm combining the conventional SOVA and the hard decision Viterbi algorithm (VA). To achieve low complexity, only one competing path in a state and time index is used to update reliability. After the updating process, reliabilities that remain to be un-updated are set to a fixed value according to the hard decided VA output. Also, the proposed algorithm generates reliability scalars instead of a reliability vector. The proposed algorithm was verified experimentally in a 56 Gbps PAM-4 system with the transmission distance of 20 km. The results demonstrates that the proposed algorithm has OSNR gain of 0.3 dB over conventional SOVA with lower complexity at the BER of 10-6.
关键词： IM/DD,MLSE,optical fiber communication,LDPC,PAM-4
更新于2025-09-19 17:15:36