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Measuring effective electro-optic coefficient at 1040?nm by spectral intensity modulation with THz time-domain spectroscopy
摘要： We report a single method for measuring the e?ective electro-optics (EO) coe?cient only by spectral intensity modulation with a terahertz time-domain spectroscopy (THz-TDS) device. Compared with conventional methods, the measuring device based on THz-TDS by probing the spectral intensity modulation is simple, rapid, and highly sensitive. It does not require special preparation process, electrode contact or applying high voltage on the sensor samples. The EO coe?cients of four kinds of materials, namely, ZnTe and GaP crystals, DAST wafer and GaSe ?lm, are measured at 1040 nm. The results showed good agreement with literature data by the conventional methods.
关键词： E?ective electro-optic coe?cient,EO materials,Spectral intensity modulation,THz-TDS
更新于2025-11-28 14:24:03
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Intensity modulation-based spectral polarization measurement method of coded aperture
摘要： This paper presents a spectral polarization measurement method for single-frame imaging. The method is based on intensity-modulated, coded aperture measurement, comprising a spectral polarization intensity modulation and a compressive sensing spectral imaging system. The incident light is modulated by two multistage phase retarders and a polarizer, and the spectrum's Stokes parameters are shifted to different frequency channels. The spectrum of the modulated light is obtained by a spectral imaging system composed of a coded aperture and a dispersive prism. The modulated spectral information is reconstructed using the TwIST algorithm, and the Stokes elements can be demodulated from it. Taking a pixel as an example, numerical simulations of the modulation of incident light intensity modulation, spectral reconstruction, and demodulation of Stokes parameters show that the method can acquire spectral polarization information of sparse images. This process needs only one measurement of the object and is therefore capable of high-speed acquisition.
关键词： Intensity modulation,Stokes parameters,Coded aperture
更新于2025-09-23 15:23:52
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Error performance of optical wireless communication systems exercising BPSK subcarrier intensity modulation in non-Kolmogorov turbulent atmosphere
摘要： Subcarrier intensity modulation (SIM) scheme is preferred due to efficient bandwidth usage superiority over other modulation techniques such as on–off keying (OOK), pulse position modulation (PPM). In this paper, we investigate the bit error rate (BER) performance of optical wireless communication (OWC) system using binary phase shift keying (BPSK) SIM in non-Kolmogorov turbulent atmosphere. We pay attention to the weak turbulence conditions by using Rytov approximation and considering that the receiver is a PIN photodetector. Propagating beam type is Gaussian. It is seen that BER performance of the BPSK SIM OWC is significantly affected from non-Kolmogorov power law exponent, load resistor, responsivity of the PIN photodetector, bandwidth, beam source size, turbulence strength and noise factor.
关键词： Subcarrier intensity modulation,Optical wireless communication,Bit error rate,Atmospheric turbulence
更新于2025-09-23 15:23:52
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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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Millimeter-wave home area network prospect with cost-effective RoF links
摘要： The growth towards the millimeter-wave band in the home area networks (HAN) leads to high data rate transmission to satisfy the new user services. Unfortunately, the transmission coverage in this band is limited to short distances because of the strong air absorption and obstacles such as walls. The effort is then focused on the extension of the network coverage of the wireless link in this band. Solutions based on multiple connected access points to optical fibers are useful methods to ensure wireless connectivity to the entire home. For HAN applications, radio-over-fiber (RoF) using intensity modulation and direct detection technique is the mostly favorite technology for the transmission of a broadband wireless signal because dealing with a cost-effective solution. We investigate in this paper the performance of such RoF-wireless architecture with low-cost optoelectronic modules through the error vector magnitude (EVM) metric. The RoF links investigated are a directly modulated VCSEL with integrated photoreceiver module, an electroabsorption-modulated laser with PIN photodiode and a Mach–Zehnder Modulator with PIN photodiode. A simulation approach based on equivalent electrical circuit models of photonic components is developed in ADS (Advanced Design System) by using a co-simulation technique that combines both analog and digital signals. The downlink channel of the complete transmission system including wireless channel and frequency conversion circuits to millimeter-wave (mm-wave) band is studied by simulation. The obtained results of EVM show good performances of cost-effective links with QPSK and 16-QAM modulation over a dynamic range of 15 dB.
关键词： Radio over fiber,Intensity modulation–direct detection,Home area network,Wireless channel
更新于2025-09-23 15:22:29
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Precise Performance Analysis of Dual-Hop Mixed RF/Unified-FSO DF Relaying with Heterodyne Detection and Two IM-DD Channel Models
摘要： This paper provides precise performance analysis of the dual-hop mixed radio frequency (RF)/unified free space optical (FSO) decode-and-forward (DF) relaying system, in which the heterodyne detection (HD) and the intensity modulation-direct detection (IM-DD) are taken into account for FSO detection. To this end, we derive closed-form expressions for the outage probability, average bit error rate (BER), and the ergodic channel capacity of this system. In this analysis, we utilize, for the first time as per our knowledge, a precise channel capacity result for the IM-DD channel. Moreover, this is the first time that not only the (IM-DD input-independent) but also the (IM-DD cost-dependent) AWGN channel is considered in such system analyses. Additionally in this study, we assume that the first hop (RF link) follows Nakagami-m fading, and the second hop (FSO link) follows Málaga (M) turbulence with pointing errors. These fading and turbulence models contain other models (such as Rayleigh and Gamma-Gamma) as special cases, thus our analyses can be seen as a generalized one from the RF and FSO fading models point of view. Also, in BER derivation, we assume that the modulation schemes in the two hops can be different, since not all modulation schemes are suitable for IM-DD FSO links. In addition, the system performance is investigated asymptotically at high signal to noise ratios (SNRs). This investigation leads to new non-reported coding gain and diversity order analyses of such system. Interestingly, we find that in the FSO hop, at high transmitted powers, all the considered FSO detectors result in the same diversity order. Furthermore, we provide simulation results that verify the accuracy of the obtained analytical and asymptotic expressions.
关键词： Nakagami-m fading,Málaga (M) fading,HD,DF,heterodyne detection,Mixed RF/FSO relay network,IM-DD,decode-and-forward,intensity modulation-direct detection
更新于2025-09-23 15:22:29
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Significant improvement on electrical properties of BaSi <sub/>2</sub> due to atomic H passivation by radio-frequency plasma
摘要： We demonstrate for the ?rst time an intensity-modulated direct-detection link using four states of polarization. The four data-independent tributaries are each assigned distinct states of polarization to enable the receiver to separate the signals. Polarization rotation due to propagation over optical ?ber is tracked and compensated with simple digital signal processing in Stokes space. Transmission below the forward error correction limit is shown for maximum net bitrates of 100 Gb/s (4 × 27 GBd) and 120 Gb/s (4 × 32 GBd) over 2-km standard single-mode ?ber at a center wavelength of 1550 nm.
关键词： direct detection (DD),intensity modulation (IM),digital signal processing,Stokes space,100G,polarization
更新于2025-09-23 15:21:01
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Ultra-Wide and Flattened Optical Frequency Comb Generation Based on Cascaded Phase Modulator and LiNbO3-MZM Offering Terahertz Bandwidth
摘要： In this paper, a new technique for generation of ultra-wide and flattened optical frequency comb (OFC) based on serial cascading of a phase modulator and dual-driven Lithium-Niobate Mach Zehnder modulator (DD-LiNbO3-MZM) is proposed. Over 60 carriers were generated by carefully adjusting the RF switching voltage (RFSV) of the DD-LiNbO3-MZM and the signal frequency of the sinusoidal wave (RF) source. A low power amplified RF source with a signal driving power of ~16.9dBm is applied, and the power of CW laser is kept at 3dBm. The frequency spacing (FS) is kept at 20GHz for generating the maximum number of carriers. Nonetheless, the scheme is also tested for the FSs of 64GHz, and 32GHz. Each scenario is examined in simulation environment and the main outcomes are highlighted. The proposed scheme is comparatively simple and the FS varies with the applied RF source on the modulators. The achieved OFC lines have a tone-to-noise ratio (TNR) of over ~45dB with an undesired side mode suppression ratio of approximately 20dB. The comb lines are almost flat with a varying power deviation of around 0dB-6dB which is optimized to nearly ~0.12dB. Furthermore, the impact of the RFSV on the generated number of carriers is studied in detail. The scheme is analyzed in terms of cost efficiency, power deviations, TNR, optical signal to noise ratio, and number of achieved comb lines.
关键词： Optical Frequency Comb,Mach-Zehnder modulator,Phase modulator,Intensity modulation
更新于2025-09-23 15:19:57
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Analytic and simulative comparison of turbulent FSO system with different modulation techniques
摘要： In this paper, we characterize the performance of Intensity Modulation/Direct Detection (IM/DD) and coherent detection modulation techniques in free-space optical (FSO) communication system in terms of bit error rate (BER). The system of interest includes M-ary Pulse Position Modulation (M-PPM) in correspondence to IM/DD and M-ary Phase Shift Keying (M-PSK) and M-ary Quadrature Amplitude Modulation (M-QAM) with respect to coherent detection. The system is subjected to weak turbulence regime of log-normal channel with scintillation index less than 0.75. Coherent techniques involve the amount of signal pulses transmitted in a particular time as the major component of their generation, except IM/DD which is a result of photon intensity, i.e. the number of photons forming a pulse. It is worth mentioning that in previous studies, the performance of IM/DD techniques had been evaluated in terms of photon-count fluctuation statistics and thus the impact of fading strength of channel on signal intensity was not discussed anywhere. In this work, an objective equivalence has been achieved between these two kinds of detection by deriving the BER expression of M-PPM in terms of probability density function of signal intensity, while considering fading strength, scintillation index, thermal noise and outage probability as system parameters for numerical analysis.
关键词： M-ary Pulse Position Modulation (MPPM),M-ary Phase Shift Keying (MPSK),M-ary Quadrature Amplitude Modulation (M-QAM),Intensity Modulation/Direct Detection (IM/DD),Scintillation index,Coherent detection
更新于2025-09-19 17:15:36
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Envelope Detection of 16QAM Single Carrier Signal for IM/DD RoF System at Q-band
摘要： In this paper, an envelope detection scheme of single carrier 16-ary Intensity-Modulation/Direct-Detection (IM/DD) radio-over-fiber (RoF) system is theoretically and experimentally investigated. Based on the proposed scheme, the mm-wave 16QAM signal is down-converted to the intermediate frequency (IF) 16QAM one by an envelope detector (ED) and there is no use of a mixer at the user side. We theoretically and experimentally study the performance of the signal under various conditions. In the system, 2GBaud 16QAM signal is delivered over 25km standard single mode fiber (SSMF) link and 2.9m wireless link under bit error rate (BER) of 3.8×10-3.
关键词： Radio-over-fiber (RoF),Intensity-Modulation/Direct-Detection (IM/DD),Envelope detection
更新于2025-09-19 17:15:36