Fiber Optics and Optical Communications|60 Article(s)
Theoretical investigation of core mode cut-off condition for tapered multicore fiber
Xuanfeng Zhou, Zilun Chen, Hang Zhou, and Jing Hou
Core mode cutoff is a useful concept not only for a tapered single-core fiber (SCF) but also for a tapered multicore fiber (MCF) to realize cladding mode transmission. In this paper, cut-off conditions of either core mode for tapered SCFs or supermodes for MCFs are theoretically investigated. Rigorous analytical formulas are derived for the modes of SCF by a three-layer waveguide model, and an approximation formula of the cut-off condition is given for the LP01 mode. The supermodes of MCFs are analyzed by the coupling mode theory, and the cut-off condition is calculated by a numerical method. Simulation results show that the in-phase supermode of MCFs has a similar cut-off condition with that of SCF. Based on this property, a convenient approximate formula is given to estimate the cut-off condition of the in-phase supermode for tapered MCFs.
Photonics Research
  • Publication Date: Aug. 14, 2015
  • Vol. 3, Issue 5, 05000224 (2015)
20.231  Gbit/s tricolor red/green/blue laser diode based bidirectional signal remodulation visible-light communication system
Liang-Yu Wei, Chin-Wei Hsu, Chi-Wai Chow, and Chien-Hung Yeh
Photonics Research
  • Publication Date: Apr. 19, 2018
  • Vol. 6, Issue 5, 05000422 (2018)
Investigation on performance of special-shaped 8-quadrature amplitude modulation constellations applied in visible light communication
Jiaqi Zhao, Chaoyi Qin, Mengjie Zhang, and Nan Chi
Light-emitting diode (LED)-based visible light communication (VLC) has become a potential candidate for nextgeneration ultra-high-speed indoor wireless communication. In this paper, four special-shaped 8-quadrature amplitude modulation (QAM) constellations are investigated in a single-carrier VLC system. It is numerically verified and experimentally demonstrated that circular (7,1) shows obvious superiority in the performance of the dynamic range of signal voltage peak-to-peak (vpp) value and bit error rate (BER). Next best is rectangular, followed by triangular; circular (4,4) has the worst performance. A data rate of 1.515 Gbit/s is successfully achieved by circular (7,1) employing a red chip LED over 0.5 m indoor free space transmission below a BER threshold of 3.8 × 10?3. Compared with circular (4,4), the traditional 8-QAM constellation, circular (7,1) provides a wider dynamic range of signal vpp, a higher data rate, and a longer transmission distance. To the best of our knowledge, this is the first investigation into the performance differences of special-shaped 8-QAM constellations in a highspeed, single-carrier VLC system, and the results comprehensively demonstrate that circular (7,1) is the optimal option.
Photonics Research
  • Publication Date: Nov. 15, 2016
  • Vol. 4, Issue 6, 06000249 (2016)
Spectrally efficient multi-band visible light communication system based on Nyquist PAM-8 modulation
Nan Chi, Mengjie Zhang, Jianyang Shi, and Yiheng Zhao
High-speed multi-user access with high spectral efficiency is one of the key challenges for band-limited visible light communication (VLC) systems. In this paper, we propose a novel scheme for effective multiple-access VLC systems based on multi-band, Nyquist-filtered pulse amplitude modulation (PAM)-8 modulation. Within this scenario, the spectral efficiency can be improved from 1.5 to 2.73 b/s/Hz by implementing an appropriate Nyquist filter to suppress spectral bandwidth. We experimentally demonstrate a multi-band VLC system at 1.2 Gb/s after 1 m indoor free space transmission. The system performances have also been thoroughly investigated for different sub-band numbers, utilizing a rectangular filter in the frequency domain and a Nyquist filter based on square root raised cosine. The results show that the Nyquist-filtered PAM-8 signal can outperform a rectangular filtered signal. The maximum improvement of system capacity is up to 1.67 times for the Nyquist-filtered multi-band system. The results clearly show the advantage and feasibility of multi-band Nyquist PAM for high-speed multiple-access VLC systems.
Photonics Research
  • Publication Date: Sep. 18, 2017
  • Vol. 5, Issue 6, 06000588 (2017)
Polarization-maintaining few mode fiber composed of a central circular-hole and an elliptical-ring core
Jiajia Zhao, Ming Tang, Kyunghwan Oh, Zhenhua Feng, Can Zhao, Ruolin Liao, Songnian Fu, Perry Ping Shum, and Deming Liu
We propose a novel waveguide design of a polarization-maintaining few mode fiber (PM-FMF) supporting ≥10 non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core, a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δneff between the adjacent guided modes could be kept larger than 1.32×10 4 over the whole C+L band. The proposed fiber structure can be flexibly tailored to support an even larger number of modes in PM-FMF (14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.
Photonics Research
  • Publication Date: May. 30, 2017
  • Vol. 5, Issue 3, 03000261 (2017)
High-speed optical secure communication with external noise source and internal time-delayed feedback loop
Yudi Fu, Mengfan Cheng, Xingxing Jiang, Quan Yu, Linbojie Huang, Lei Deng, and Deming Liu
We propose and experimentally demonstrate a novel physical layer encryption scheme for high-speed optical communication. A 10 Gb/s on-off keying signal is secretly transmitted over 100 km standard single-mode fiber. The intensity-modulated message is secured by the encryption mechanism, which is composed of an external noise source and an internal time-delayed feedback loop. The external noise serves as an entropy source with sufficient randomness. The feedback loop structure in the transmitter introduces a time-domain encryption key space, and a corresponding open-loop configuration at the receiver side is used for synchronization and decryption. Experiment results show the effectiveness of the proposed scheme. For a legitimate terminal, bit error rate below 10 8 can be obtained. Decryption degradations with the mismatch of different hardware parameters are researched. The time delay in the feedback loop provides a sensitive encryption key. For other hardware parameters, the system is robust enough for synchronization. Meanwhile, the time-delay signature of the loop is able to be well concealed by the external noise. Moreover, the proposed scheme can support density wavelength division multiplexing transmission with a relatively simple structure. This work also provides a new concept to establish optical secure communication by combining a time-delayed feedback chaotic system and random noise.
Photonics Research
  • Publication Date: Oct. 31, 2019
  • Vol. 7, Issue 11, 11001306 (2019)
Stimulated Brillouin scattering induced all-optical modulation in graphene microfiber
Jiwen Zhu, Xuemei Cheng, Yali Liu, Ruiduo Wang, Man Jiang, Diao Li, Baole Lu, and Zhaoyu Ren
Graphene microfibers are burgeoning modulators with great potential in all-optical communication. One of the critical issues that remains to be understood is the dynamic mechanism of light–graphene interaction. Here, we propose a power dependent modulation by using 980 nm pump light and 1064 nm signal light via graphene microfiber, and the results show a strong transmission reduction and frequency blue shift with the increase of pump power. The experimental observation is attributed to a stimulated Brillouin scattering process induced by the pump light. Power and frequency variations are a result of energy transition of the scattered phonon in the fiber. This work reveals the nonlinear effect process in the light–graphene interaction and provides a new method for power and frequency control with graphene all-optical modulation.
Photonics Research
  • Publication Date: Jan. 01, 2019
  • Vol. 7, Issue 1, 01000008 (2019)
Mode- and wavelength-multiplexed transmission with crosstalk mitigation using a single amplified spontaneous emission source
Yetian Huang, Haoshuo Chen, Hanzi Huang, Zhengxuan Li, Nicolas K. Fontaine, Roland Ryf, Juan Carlos Alvarado, Rodrigo Amezcua-Correa, John van Weerdenburg, Chigo Okonkwo, A. M. J. Koonen, Yingxiong Song, and Min Wang
We propose to use the low-coherence property of amplified spontaneous emission (ASE) noise to mitigate optical crosstalk, such as spatial, polarization, and modal crosstalk, which currently limits the density of photonic integration and fibers for dense space-division multiplexing. High optical crosstalk tolerance can be achieved by ASE-based low-coherence matched detection, which avoids dedicated optical lasers and uses spectrally filtered ASE noise as the signal carrier and as a matched local oscillator. We experimentally demonstrate spatial and modal crosstalk reduction in multimode fiber (MMF) and realize mode- and wavelength-multiplexed transmission over 1.5-km MMF supporting three spatial modes using a single ASE source. Performance degradation due to model dispersion over MMF is experimentally investigated.
Photonics Research
  • Publication Date: Nov. 01, 2019
  • Vol. 7, Issue 11, 11001363 (2019)
4 × 4 MIMO fiber-wireless transmission based on an integrated four-channel directly modulated optical transceiver
Di Zhang, Yao Ye, Lei Deng, Di Li, Haiping Song, Yucheng Zhang, Minming Zhang, Shu Wang, and Deming Liu
In this paper, an integrated compact four-channel directly modulated analog optical transceiver is proposed and fabricated. The 3 dB bandwidth of this optical transceiver exceeds 20 GHz, and the measured spurious-free dynamic range is up to 91.2 dB·Hz2/3. The optical coupling efficiency (CE) is improved by using a precise submicron alignment technique for lens coupling in a transmitter optical subassembly, and the highest CE is achieved when the oblique angle of the arrayed waveguide grating using a silica-based planar lightwave circuit (AWG-PLC) in receiver optical sub assembly is set to 42°. Based on the proposed optical transceiver, we have experimentally demonstrated a 6.624 Gbit/s 4×4 multi-input multioutput (MIMO) 16-quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) radio signal over 15.5 km standard single mode fiber, together with 1.2 m wireless transmission in both an uplink and a downlink. To cope with the channel interference and noise of the fiber-wireless transmission system, a low-complexity MIMO demodulation algorithm based on lattice reduction zero-forcing (LR-ZF) is designed. In our experiment, 1.6 dB power penalty is achieved by using the proposed LR-ZF algorithm, compared to the commonly used zero-forcing algorithm. Moreover, this LR-ZF algorithm has much less complexity than the optimal maximum-likelihood sequence estimation (MLSE) at a given transmission performance. These results not only demonstrate the feasibility of the integrated optical transceiver for MIMO fiber-wireless application but also validate that the proposed LR-ZF algorithm is effective to eliminate the interference for hybrid fiber-wireless transmission.
Photonics Research
  • Publication Date: Nov. 27, 2019
  • Vol. 7, Issue 12, 12001461 (2019)