Showing papers on "Optical Carrier transmission rates published in 2019"

32 Gb/s chaotic optical communications by deep-learning-based chaos synchronization.

Abstract: Chaotic optical communications were originally proposed to provide high-level physical layer security for optical communications. Limited by the difficulty of chaos synchronization, there has been little experimental demonstration of high-speed chaotic optical communications, and point to multipoint chaotic optical networking is hard to implement. Here, we propose a method to overcome the current limitations. By using a deep-learning-based scheme to learn the complex nonlinear model of the chaotic transmitter, wideband chaos synchronization can be realized in the digital domain. Therefore, the chaotic receiver can be significantly simplified while still guaranteeing security. A successful transmission of 32 Gb/s messages hidden in a wideband chaotic optical carrier was experimentally demonstrated over a 20 km fiber link. We believe the proposed deep-learning-based chaos synchronization method will enable a new direction for further development of high-speed chaotic optical communication systems and networks.

Silicon-on-insulator-based microwave photonic filter with widely adjustable bandwidth

Abstract: We demonstrate a silicon-based microwave photonic filter (MPF) with flattop passband and adjustable bandwidth. The proposed MPF is realized by using a 10th-order microring resonator (MRR) and a photodetector, both of which are integrated on a photonic chip. The full width at half-maximum (FWHM) bandwidth of the optical filter achieved at the drop port of the 10th-order MRR is 21.6 GHz. The ripple of the passband is less than 0.3 dB, while the rejection ratio is 32 dB. By adjusting the deviation of the optical carrier wavelength from the center wavelength of the optical bandpass filter, the bandwidth of the MPF can be greatly changed. In the experiment, the FWHM bandwidth of the proposed MPF is tuned from 5.3 to 19.5 GHz, and the rejection ratio is higher than 30 dB.

Photonic-assisted wideband frequency downconverter with self-interference cancellation and image rejection

Abstract: A photonic-assisted wideband frequency downconverter with self-interference cancellation and image rejection for in-band full-duplex radio-over-fiber systems based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed. The upper dual-parallel Mach–Zehnder modulator (DP-MZM) of the DP-QPSK modulator is used to cancel the self-interference directly in the optical domain and generate two first-order optical sidebands of the desired received radio frequency (RF) signal. The lower DP-MZM generates two optical sidebands of the local oscillator signal with the optical carrier suppressed via properly biasing the modulator. The optical signals generated from the two DP-MZMs are combined, and then the upper and lower optical sidebands of the combined signal are separated by a wavelength division multiplexer (WDM). The two outputs from the WDM are detected by two photodetectors and then combined at a 90° hybrid coupler to achieve frequency downconversion and image rejection. A simulation is performed. A quadrature phase-shift keying (QPSK)-modulated RF signal is successfully downconverted to a 1-GHz intermediate frequency signal with self-interference and image frequency cancelled. The performance of the frequency downconverter is also evaluated.

Polarization-Tracking-Free PDM Supporting Hybrid Digital-Analog Transport for Fixed-Mobile Systems

Abstract: For fixed services such as hybrid fiber-coaxial and passive optical network with deployed fiber networks, it is desirable to exploit the potentials to support wireless services in fifth-generation (5G) mobile data communications on the top of the existing fixed networks. We propose a polarization-division multiplexing (PDM) scheme to achieve the co-delivery of independent signals for fixed-mobile convergence. This is achieved by removing unwanted optical carrier in each polarization, and thus the proposed system can resolve the polarization-tracking issue in conventional PDM. It has been demonstrated in this letter that the polarization-tracking-free PDM system can support the co-transmission of respective 70-Gbps digital and analog signals over 20-km single mode fiber. Experimental results have shown low crosstalk between two polarizations. The proposed PDM system is compatible with wavelength-division-multiplexing (WDM) network and is capable of enhancing the spectral efficiency of WDM channels. The inherent single-sideband feature of the proposed PDM also enhances long-range services.

Wideband microwave electro-optic image rejection mixer.

Abstract: We present an electro-optic downconverting mixer with image rejection capabilities. By using a dual-drive Mach-Zehnder modulator (DD-MZM) to modulate an optical carrier with both a signal and a local oscillator, and an asymmetric Mach-Zehnder interferometer (AMZI) to filter the optical spectrum into two separate ports, we generate photocurrents with a phase relationship controlled via direct current (DC) bias voltage applied to the DD-MZM. By choosing these photocurrents to be in quadrature and combining them in a 90-degree electrical hybrid we achieve over 40 dB of image rejection, with a 3 dB bandwidth of approximately 20 GHz limited mainly by the AMZI free spectral range. We demonstrate downconversion of a 1 Gbaud quadrature phase-shift keyed (QPSK) signal even in the presence of a strong interfering image tone.

A Coherent Homodyne TO-Can Transceiver as Simple as an EML

Abstract: The introduction of low-cost coherent signal reception is one of the great challenges in optical telecommunications since its opto-electronic sub-systems are associated with a high degree of complexity. In this work, we propose a disruptive approach: the re-use of widely deployed direct-detection technology for simultaneous coherent homodyne reception and transmission. We first show that an externally modulated laser (EML) is sufficient to perform both, coherent reception and transmission functionality. Second, we prove that homodyne detection applies to the EML-based scheme in virtue of an injection-locked local oscillator, which for low input power levels is pulled to the optical carrier frequency of the incident data signal. The proposed methodology for coherent reception enables a greatly simplified transceiver as optical layer hardware. As we will demonstrate, it just requires single fiber access, a single radio frequency port, and can be implemented in a transistor-outline package. Full-duplex transmission with coherent homodyne reception is experimentally validated, showing 2.5 Gb/s transmission over 27.5 km reach and a loss budget of 28 dB, and coherent Gigabit Ethernet connectivity—without the use of optical layer digital signal processing functions.

Photonic Generation of a Dual-Band Polyphase-Coded Microwave Signal With a Tunable Frequency Multiplication Factor

Abstract: A photonic approach to generate dual-band polyphase-coded microwave signal with a tunable frequency multiplication factor is proposed. The scheme contains a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator, a polarization modulator (PolM), and a balanced detector. When the bias voltages of the DP-QPSK modulator is properly adjusted, a double-sideband signal will be generated with one sideband along the X polarization of the PolM, with the optical carrier and the other sideband along the Y polarization. Then, the PolM is employed to modulate the optical signal with a phase-coded microwave signal. After the photoelectric balanced detection, polyphase-coded microwave signals with frequency multiplication factors of one, two, and four can be generated. In addition, the proposed scheme can simultaneously produce two phase-coded microwave signals with different carrier frequencies. The proposed system finds a potential application in dual-band radar. In the experiment, a binary- and a quaternary-phase-coded signal with 5.5, 11, and 22 GHz carrier frequencies are generated.

Ultrafast and ultrahigh-resolution optical vector analysis using linearly frequency-modulated waveform and dechirp processing

Abstract: We propose and experimentally demonstrate an ultrafast and ultrahigh-resolution optical vector analyzer (OVA) using linearly frequency-modulated (LFM) waveform and dechirp processing. An optical LFM signal, achieved by modulating an electrical LFM signal on an optical carrier via carrier-suppressed optical single-sideband (OSSB) modulation, is separated into two portions. One portion (denoted as the reference signal) directly goes through the reference path, and the other (denoted as the probe signal) undergoes magnitude and phase changes by an optical device under test (DUT) in the measurement path. After balanced photodetection, the reference signal and the probe signal are mixed to perform a dechirp operation. A relatively low-frequency electrical signal is generated, which can be sampled by a low-speed analog-to-digital converter. As a result, the frequency responses of the DUT can be extracted at a high speed by post digital signal processing. Thanks to the large chirp rate of the electrical LFM signal and the dechirp processing, the proposed LFM-based OVA enables ultrafast measurement speed and ultrahigh frequency resolution. We perform an experiment in which a narrowband tunable optical filter is characterized. The measurement speed reaches 1 ns/point, and the frequency resolution is 1.6 MHz.

Expansion and phase correlation of a wavelength tunable gain-switched optical frequency comb.

Abstract: A novel scheme for the expansion and phase correlation of a wavelength tunable gain-switched optical frequency comb (OFC) is presented. This method entails firstly combining two gain-switched OFCs and expanding them using a phase modulator. Subsequently, the phase correlation between all the comb lines is induced through four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). In this article, the generation of 42 highly correlated comb lines separated by 6.25 GHz, with an optical carrier to noise ratio (OCNR) of more than 50 dB, is experimentally demonstrated. In addition, the wavelength tunability of the scheme, over 30 nm within the C band, is shown. Finally, the degree of phase correlation between comb lines is verified through RF beat tone linewidth measurements. The results show a five orders of magnitude reduction in the beat tone linewidth, due to FWM in an SOA.

28-GHz Wireless Carrier Heterodyned From Orthogonally Polarized Tri-Color Laser Diode for Fading-Free Long-Reach MMWoF

Abstract: A 28-GHz millimeter-wave (MMW) carrier optically heterodyned from an orthogonally polarized tri-color (3λ-⊥-SCM) transmitter, which exhibits single-carrier modulation (SCM) to suppress the dispersion induced fading distortion after long-reach transmission, is demonstrated for building up the long-reach MMW-over-fiber with a distance of 75 km. The SCM-based encoding is obtained by seeding the tri-color master into slave colorless laser diode, which only supports TE-mode feedback with a polarized suppression ratio over 40 dB. After resuming back to the SCM tri-color optical carrier with orthogonal polarization (3λ-⊥-SCM), its delivered data can suppress the intensity noise induced by beating between adjacent modes such that the single-to-noise (SNR) can be improved by 2 dB. Comparing with the traditional parallel polarized multi-carrier modulation (MCM) based tri-color optical carrier (3λ-//-MCM), the orthogonally polarized tri-color optical carrier with SCM (3λ-⊥-SCM) can deliver 64 quadrature amplitude modulation orthogonal frequency-division multiplexing (QAM OFDM) data with its maximal encoding a bandwidth of 8.3 GHz (50 Gbit/s), which provides the error vector magnitude (EVM) of 8.8%, the SNR of 21.2 dB and the bit error rate of 3.5 × 10–3 after passing through a 75-km-long single-mode fiber. To perform the MMW wireless access network (WAN) link after 75-km fiber wired transmission, the heterodyned 28-GHz MMW carrier is obtained from the orthogonally polarized SCM tri-color optical carrier (3λ-⊥-SCM) with its peak power improved by 29 dB (from –50 to –31 dBm) and CNR enhanced by 17 dB (from 32 to 49 dB), as compared to those of the parallel polarized MCM tri-color case (3λ-//-MCM). After wireless transmission for 10-m with horn-antenna pair in free space, the maximal encoding bandwidth of the 16-QAM OFDM delivered by the orthogonally polarized SCM tri-color optical carrier (3λ-⊥-SCM) is 4.5 GHz (with 18 Gbit/s capacity).

Microwave Photonic Link With Improved Dynamic Range Through π Phase Shift of the Optical Carrier Band

Abstract: A microwave photonic link (MPL) with an improved spurious-free dynamic range (SFDR) by introducing a π phase shift to the spectral complements in the optical carrier band (OCB) is proposed and experimentally demonstrated. The fundamental concept to improve the SFDR is to suppress the third-order intermodulation distortion (IMD3) terms while retaining a high gain for the fundamental terms, which is achieved by introducing a π phase shift to the OCB with the joint use of an electrical 90° hybrid coupler and a dual-parallel Mach–Zehnder modulator (DP-MZM). When detecting the optical signal from the DP-MZM at a photodetector, the IMD3 components originated from the beating between different optical sidebands can be fully cancelled, while the gain for the fundamental terms remains reasonably high. Therefore, the SFDR of the MPL is significantly increased. The proposed MPL is experimentally demonstrated. An SFDR of 108.1 dB·Hz2/3 or 120.4 dB·Hz2/3 for a noise floor of −146.9 or −163.9 dBm/Hz is achieved, which is 14 dB or 15 dB higher than that of a conventional intensity-modulation direct-detection MPL.

Approaching Terabits Per Carrier Metro-Regional Transmission Using Beyond-100GBd Coherent Optics With Probabilistically Shaped DP-64QAM Modulation

Abstract: This research work proposed and experimentally demonstrated beyond-100GBd probabilistically shaped coherent optics that support the transmission of a ~1.2 Tbps coded line rate and a ~0.9 Tbps net bit rate per optical carrier over metro-regional distances. Pursuing next-generation transmission systems having both high capacity approaching terabits per wavelength and high spectral efficiency require engineering efforts from different aspects, which may include the enhancement of analog-to-digital or digital-to-analog interfaces, the improvement of channel characteristics, and also the realization of better receiver sensitivities, preferably through DSP techniques such as probabilistic shaping (PS). By doing so, this work achieved a single-channel and a 112.5-GHz WDM transmission of 900G wavelengths over 800 and 400 km, respectively, which employed a PS DP-64QAM modulation format at 105 GBd, yielding a net spectral efficiency of 8.05 bits/s/Hz. Such a high symbol rate was demonstrated using a commercially available DAC unit without band-interleaving. The enhanced optical channel consists of ITU-T G.654 compliant Terawave SLA+ fiber spans with the backward-pumped Raman amplifiers. In addition, with the same PS DP-64QAM modulation format and the same enhanced channel, this research work also demonstrated that 400G wavelengths can be delivered over 2800 km supporting long-haul applications.

Simultaneous Measurement of Doppler-Frequency-Shift and Angle-of-Arrival of Microwave Signals for Automotive Radars

Abstract: A photonics-based scheme to simultaneously measure the Doppler-frequency-shift (DFS) and angle-of-arrival (AOA) of microwave signals for automotive radars is proposed in this paper. In the proposed system, an optical carrier is split into two branches. In one branch, a Mach-Zehnder modulator (MZM) is used to carry a transmitted signal, and in the other branch, a polarization-division-multiplexed MZM (PDM-MZM) is employed to imprint two echo signals. An optical filter is inserted in each branch to select one of the 1st-order sidebands, and the chosen sidebands are then sent to a dual-polarization 90-degree optical hybrid. By processing the low-frequency signals from the two orthogonal outputs of the optical hybrid, DFS (with direction identification) and AOA can be simultaneously obtained. An experiment is carried out. The DFS measurement within ±100 kHz with a measurement error of ± 2.5 Hz and the AOA measurement from 27.25° to 90° with less than ±2.3° error are realized.

Broadband Spurious-Free Dynamic Range Expander for Microwave Photonic Links Based on Optical Distortion Control

Abstract: A wideband spurious-free dynamic range (SFDR) expander that uses optical distortion control technique is proposed in this study for microwave photonic links. A third-order intermodulation distortion (IMD3), which is sensed by extracting the modulated optical carrier, will be monitored and attenuated adaptively by controlling the optical power injected into the photodetector. Therefore, the IMD3 can be suppressed below the noise floor (NF), and the SFDR can be expanded further. In addition, the sensing signal stems from the modulated optical carrier, which is independent of radio frequency. Thus, our system is essentially a broadband system whereby the dynamic range expander is applied to classical intensity modulation and direct detection microwave photonic link. Experimental results demonstrate that the SFDR is improved from 46.84 to 67.98 dB/Hz 2/3 with a -70 dBm noise power. The SFDR can even reach 150 dB/Hz 2/3 with a bandwidth of 36 GHz with a 1 Hz NF.

A RoF system based on polarization multiplexing and carrier suppression to generate frequency eightfold millimeter-wave

Abstract: In this paper, we propose and demonstrate a RoF system based on polarization multiplexing and carrier suppression to generate frequency eightfold millimeter-wave. The proposed scheme is based on one single drive Mach-Zehnder modulator and a polarization control system. By adjusting the modulation index, two-forth sidebands can be obtained. By controlling the polarization direction, our system can generate 80 GHz frequency eightfold millimeter-wave or recover optical carrier at the base station (BS). Finally, we verified the bit error rate (BER) of received optical power in the uplink and downlink. The received power penalty of uplink and downlink via 15 km single mode fiber (SMF) are 0.13 dBm and 0.34 dBm at the BER of 1 × 10 - 9 respectively. This technology opens a new path for developments in microwave photonics.

Optical single sideband polarization modulator with tunable optical carrier-to-sideband ratio and its applications in microwave photonic phase shifter and optical frequency shifter.

Abstract: In this paper, a novel scheme to implement an optical single sideband (OSSB) polarization modulator (PolM) is proposed and theoretically investigated. The proposed structure contains two dual-drive Mach–Zehnder modulators inside a Mach–Zehnder interferometer whose input/output optical Y-couplers are replaced by two optical polarization beam splitters/polarization beam combiners. It is shown that by applying four equal power radio-frequency signals with appropriate phases, an OSSB polarization-modulated signal is generated. In addition, (4n+3)th-order sidebands, where n is an integer, are suppressed without the need for an optical filter. The proposed OSSB PolM can find many applications in microwave photonic (MWP) systems. For instance, by using the proposed OSSB PolM, an OSSB modulator with tunable optical carrier-to-sideband ratio (OCSR), an OSSB-suppressed carrier modulator/optical frequency shifter with ultralow spurious sidebands, and an MWP phase shifter with 360° tunable phase shifts, are proposed and theoretically investigated. Simulation results using commercial software are also presented, which are in good agreement with analytical results.

Method for suppressing the frequency drift of integrated microwave photonic filters

Abstract: The significant frequency drift of integrated microwave photonic filters (IMPFs) is caused by relatively independent frequency fluctuations of the optical carrier and the photonic integrated filter, which imposes a rigid limitation on the practical application. In this paper, a novel method is proposed for suppressing the frequency drift of IMPFs. The scheme is implemented by utilizing an on-chip high-Q microring resonator as a frequency monitoring unit to track the instantaneous frequency drifts caused by the optical carrier drift and the temperature fluctuations of the photonic integrated chip. And the same frequency tuning is simultaneously applied on the photonic integrated filter to suppress the frequency drift of IMPFs based on the differential scheme. As a proof of concept, the proposed IMPF scheme is demonstrated on the Si3N4 platform, and the frequency drift is measured to be tens of MHz in one hour. Compared with conventional IMPF schemes, the frequency drift is significantly suppressed by 86.3% without using complex laser frequency stabilization and temperature control systems.

Centralized-Light-Source Two-Way PAM8/PAM4 FSO Communications With Parallel Optical Injection Locking Operation

Abstract: For the first time up to our knowledge, a centralized-light-source two-way eight-level pulse amplitude modulation (PAM8)/four-level pulse amplitude modulation (PAM4) free-space optical (FSO) communication with parallel optical injection-locked vertical-cavity surface-emitting laser (VCSEL) transmitter is practically demonstrated. With the assistance of parallel optical injection locking, injection locking in the polarization sideband causes a simultaneous generation of the free-running orthogonal polarization sideband to form a centralized-light-source scheme. With the centralized light source, additional light source or wavelength reuse component, such as Fabry-Perot laser diode or reflective semiconductor optical amplifier, is not needed at the receiver side. It is very attractive because it enables the receiver side to share the light source remotely located at the transmitter side. Based on the centralized-light-source scheme and parallel optical injection-locking operation, the injection-locked parallel polarization sideband is used for downlink transmission, and the induced free-running orthogonal polarization sideband is transmitted and used as the optical carrier for uplink transmission. Over a 200-m free-space link, good bit-error-rate (BER) performance, the qualified PAM8, and PAM4 eye diagrams are obtained for two-way FSO communications. This proposed centralized-light-source two-way FSO communication provides a practical choice for two-way high transmission capacities and considerably develops the scenario characterized by parallel optical injection locking.

Key building blocks of a silicon photonic integrated transmitter for future detector instrumentation

Abstract: The data throughput of future detector readout systems is ever increasing. We propose a high-performance optical link, based on silicon photonics and wavelength-division multiplexing (WDM) technology, to cope with ultra-broad bandwidth requirements. The key components of the proposed optical link are monolithically integrated transmitter units, each one integrating multi-channel on-chip Echelle grating (de-)multiplexers and Mach-Zehnder modulators (MZMs). In our current design, each transmitter unit consists of four MZMs, which corresponds to four transmission channels with distinct optical carrier wavelengths, a common optical demultiplexer and a common optical multiplexer. In this paper, we present the design and experimental results of all these building blocks as well as a first transmission experiment. Additionally, experimental results of a thermal modulator to be used in a future design for working point control are presented.

A Radio over Fiber System with Simultaneous Wireless Multi-Mode Operation Based on a Multi-Wavelength Optical Comb and Pulse-Shaped 4QAM-OFDM

Abstract: In this paper, we propose a radio over fiber transmission system with simultaneous wireless multi-mode operation based on multi-wavelength optical comb and pulse shaping. This study is an initial attempt to accomplish simultaneous wireless multi-mode operation on a single optical carrier. A multi-wavelength optical comb with 13 flat optical wavelengths and space of 10 GHz is achieved by utilizing radio frequency (RF)-optics modulation and parameter configuration. The central station contains four adjacent optical wavelengths separated from the multi-wavelength optical comb by a wavelength division multiplexer, that one is modulated by 4QAM-OFDM signals with an up-converted carrier frequency of 5 GHz. The signals modulated with a single-sideband can be obtained by employing pulse shaping. The single-sideband optical signals are combined with the other three optical wavelengths and then transmitted over a standard single-mode fiber with a length of 50 km. In this arrangement, we can obtain several wireless carriers with frequencies of 5 GHz, 25 GHz, 45 GHz, and 65 GHz by direct detection. These wireless carriers are used for wireless transmission between the RF remote units and the mobile terminals. Additionally, in the radio frequency (RF) remote unit, we have three pure optical sources that can be utilized for the uplink transmission. With single channel and direct optoelectronic modulation, the optical and wireless communication with 10 Gbps can be accomplished in the whole process of system network transmission.

Performance improvements of a tunable bandpass microwave photonic filter based on a notch ring resonator using phase modulation with dual optical carriers

Abstract: A tunable bandpass microwave photonic filter can be achieved by using a notch ring resonator with optical phase modulation. However, the filter’s out of band rejection ratio and shape factor are limited due to the ring resonator’s residual phase, which can seriously degrade the filter’s performance. By using dual optical carriers and setting their wavelengths oppositely detuned from two resonant frequencies of a notch ring resonator, the residual phase induced by the ring resonator at radio frequencies falling outside the region of the notch stopband is reduced, thus the out-of-band rejection ratio and shape factor of the microwave photonic filter are greatly improved. The proposed microwave photonic filter was both verified theoretically and experimentally. Compared with single optical carrier method, the out-of-band rejection ratio of the filter can be enhanced from 17.7dB to 31.5dB, and the filter’s shape factor is improved from 3.05 to 1.78. Besides, the filter’s frequency and bandwidth can be tuned by varying the wavelengths of the two optical carriers and the ring resonator’s coupling coefficients. Finally, a tunable bandpass microwave photonic filter with frequency tuning range of 2~14GHz, 3dB bandwidth tuning range of 0.673~2.798GHz is demonstrated.

Accuracy-Enhanced Wideband Optical Vector Network Analyzer Based on Double-Sideband Modulation

Abstract: We report a method to significantly improve the accuracy of an optical vector network analyzer (OVNA) with double-sideband (DSB) modulation. The measurement errors of the DSB-OVNA mainly derive from optical carrier uncertainty and the beating between higher order optical sidebands. We propose a three-step measurement method and an accuracy-enhanced algorithm to eliminate these measurement errors perfectly. A theoretical model is built to analyze the potential measurement errors as well as to find a way to remove them. Excellent accuracy improvement of the OVNA is confirmed by a proof-of-concept experiment. The OVNA shows an ultrahigh resolution of 667 kHz over a wideband measurement range of 80 GHz.

Integration of millimeter-wave and optical link for duplex transmission of hierarchically modulated signal over a single carrier and fiber for future 5G communication systems

Abstract: Integration of optical and millimeter-wave systems provide a promising solution for future giga-bits per second wireless communication systems. We have proposed and simulated full-duplex transmission of a hierarchically modulated signal carrying data for two different users at a combined rate of 1.5 Gbps. Analogue modulation of the optical carrier is used for the transmission of downlink data while the same carrier is re-used by digitally modulating it with the uplink data. The use of optical analogue and digital modulation schemes allow the transmission of duplex data over a single optical fiber. A millimeter-wave channel $$\hbox {NYUSIM}\_{\mathrm{v1}}\_4$$ is integrated with the optical link. The performance of the downlink and uplink signals are evaluated in terms of error vector magnitude and bit-error rate measurements, respectively. The effect of fiber length, received optical power and data rates on the performance has also been evaluated. It is shown that for a fiber length of 10 km, the lowest error vector magnitude obtained for the hierarchically modulated signal after transmission through a 14 m millimeter-wave link is 9.5%.

Increasing the Spectral Efficiency of DDO-CE-OFDM Systems by Multi-Objective Optimization

Abstract: A multi-objective optimization was implemented to increase the spectral efficiency of direct-detection optical orthogonal frequency division multiplexing (OFDM) systems with constant-envelope (CE) signals. Based on a genetic algorithm, the optimization procedure evaluates the impact of fiber injection power in the reduction of the guard band between the optical carrier and the CE-OFDM signals, optimizing important parameters such as electrical phase modulation and optical modulation indices of the denominated DDO-CE-OFDM system. Simulation results show that a guard-band reduction around $40\%$ was achieved in a 4 Gbps optimized DDO-CE-OFDM system with 16-QAM subcarrier mapping and $-7$ dBm fiber input power. Results obtained in an experimental proof-of-concept conducted to validate the optimization procedure show that this reduction can reach $66\%$ according to a power penalty of $\approx 2$ dB demanded by the inherent spectral broadening of CE-OFDM signals, after propagation over 40 km of standard single-mode fiber.

Kerr Combs for Stimulated Brillouin Scattering Mitigation in Long-Haul Analog Optical Links

Abstract: By limiting the optical input launch power, stimulated Brillouin scattering imposes detrimental effects on long haul analog optical links. Utilizing Kerr combs generated from an integrated Silicon Nitride microring resonator, we mitigate Brillouin scattering in a 25 Km sampled analog optical link. Such combs offer reduced footprint, high repetition rates and low power consumption, rendering them attractive for next generation integrated analog photonic links. The distribution of the optical carrier power over multiple spectral lines allows launching higher total average powers, significantly improving the link performance. Operating the link in an externally intensity-modulated direct-detection architecture, we compare link metrics using a soliton or a dark pulse as the sampling frequency comb source. An advantageous aspect of the dark pulse is its high pump conversion efficiency. We find that the Kerr comb pump conversion efficiency has a direct effect on the relative intensity noise and the link noise figure. We show that the spurious free dynamic range using Kerr combs can match that of the well-established electro-optic combs.

Two-Way Transmission of Time and Frequency Signals Over Optical Fiber Communication Lines with the Help of SATRE Modems

Abstract: We study the possibility of application of SATRE modems for the transmission of reference time signals with optical carrier over fiber lines with lengths of up to 200 km. We experimentally estimated the uncertainties of comparison of time scales for the fiber communication lines with the help of SATRE modems.

300-GHz-band wireless communication using a low phase noise photonic source

Abstract: The implementation of advanced multi-level modulation schemes such as quadrature phase-shift keying (QPSK) in contrast to the conventional on-off keying (OOK) is crucial to further boost the terahertz (THz) communications speed. Thereby, the phase noise reduction in the THz range is one of the key goals that need to be urgently achieved. In this paper, a low phase-noise photonic source based on the stimulated Brillouin scattering (SBS) phenomenon is first introduced in a 300-GHz-band QPSK wireless communication link. The highest data rate at forward-error-correction limited condition was 15 Gbaud with the SBS source, and transmission characteristics are evaluated and compared with conventional optical frequency comb (OFCG)-based sources at 5 Gbaud. Our Brillouin-based photonic source has been proven to offer better performances than the OFCG-based one with respect to the phase noise, the optical carrier to noise ratio, and the bit error rate in communications.