Showing papers on "Optical Carrier transmission rates published in 2020"
TL;DR: This work proposes a scheme for implementing on-chip silicon (de)multiplexers with simultaneous wavelength-, mode-, and polarization-division ( de) multiplexing capability, constructed by using cascaded subwavelength grating-based contra-directional couplers.
Abstract: Leveraging the physical dimensions of an optical carrier (e.g., wavelength, mode, or polarization) allows significant scaling of the transmission capacity for optical communications. Here we propose a scheme for implementing on-chip silicon (de)multiplexers with simultaneous wavelength-, mode-, and polarization-division (de)multiplexing capability. The device is constructed by using cascaded subwavelength grating (SWG)-based contra-directional couplers. To verify the feasibility of the proposed structure, we perform a proof-of-concept experiment of an 8-channel (de)multiplexer with two wavelengths, two modes, and two polarizations. The insertion losses are lower than 6.6 dB and the crosstalk values are below −18.7dB at around 1540 nm and 1550 nm for all the eight channels.
26 citations
TL;DR: Experimental results show that merely two iterations of cancellation are sufficient to mitigate signal-signal beat interference (SSBI) and the requirement of receiver bandwidth for DSB based CADD scheme is relaxed by 41%.
Abstract: The recent decade has witnessed the evolution and enormous demand of the high-capacity data center interconnect (DCI), in such application scenarios spectral efficiency, optical field recovery and cost-effectiveness are highly desirable. Compared to coherent detection, direct detection does not require local oscillators, resulting in a simpler transceiver structure and thus a lower-cost solution for DCIs. To overcome chromatic dispersion induced power fading, field recovery enabled by direct detection has drawn extensive research interests. To date, various proposed direct detection schemes concentrate mainly on single sideband (SSB) modulation. Compared to double sideband (DSB) modulation, however, one sideband of SSB is unfilled and hence SSB poses higher requirement on the receiver bandwidth. Besides, the complexity and cost of implementing precisely aligned optical filtering poses burden for adopting SSB. Accordingly, we recently proposed a novel direct detection scheme called carrier assisted differential detection (CADD), which can realize the field recovery of complex-valued DSB signals with the aid of an optical carrier. In this letter, we carry out the first-time experimental demonstration of the CADD receiver. 54-Gb/s OFDM signals are transmitted over 160-km standard single-mode fiber with digital chromatic dispersion compensation at the receiver, indicating the ability to reconstruct optical field of DSB signals. For signal-signal beat interference (SSBI) which extensively exists in direct detection, experimental results show that merely two iterations of cancellation are sufficient to mitigate SSBI. More importantly, compared to various SSB based receiver schemes, the requirement of receiver bandwidth for DSB based CADD scheme is relaxed by 41%.
24 citations
TL;DR: A photonic method for multioctave and reconfigurable frequency-stepped radar waveform generation is proposed and experimentally demonstrated based on an optical frequency shifting loop (OFSL).
Abstract: A photonic method for multioctave and reconfigurable frequency-stepped radar waveform generation is proposed and experimentally demonstrated based on an optical frequency shifting loop (OFSL). When a rectangular optical pulse is applied to the OFSL, a frequency-stepped optical signal can be generated. Beating the signal with another continuous-wave optical carrier, an electrical frequency-stepped waveform can be obtained. By meticulously adjusting the relations between the time duration of the rectangular optical pulse and the loop delay of the OFSL, the frequency-hopping rate (or the frequency-hopping period) of the generated frequency-stepped signal can be reconfigured. An experiment is carried out. The generation of frequency-stepped signals with frequency intervals of 1 GHz, 3 GHz, 5 GHz, 8 GHz, and 10 GHz is realized. The reconfigurability of the frequency-hopping period is also investigated and different frequency-hopping periods of 189, 10.2, 5.1, and 2.42 ns are achieved.
19 citations
15 Aug 2020
TL;DR: In this paper, a programmable microwave photonic bandpass filter with a rectangular frequency response and a reconfigurable spectral resolution is presented. Butler et al. achieved these features through dual-sidebands processing of a phase modulated signal using a network of four optical ring resonators in a low-loss silicon nitride (Si3N4) circuit.
Abstract: We demonstrate a programmable microwave photonic bandpass filter with a rectangular frequency response and a reconfigurable spectral resolution. We achieved these features through dual-sidebands processing of a phase modulated signal using a network of four optical ring resonators in a low-loss silicon nitride (Si3N4) circuit. Furthermore, we integrate a pair of optical ring resonators in the same circuit to precisely control the amplitude and phase of the optical carrier to enhance the noise performance of the filter. We achieved filtering with a tunable bandwidth from 2 to 7 GHz with optical carrier suppression up to 6 dB, a maximum RF gain of -10 dB, and a minimum noise figure of 27 dB. These experiments are expected to provide a feasible design to approach fully integrated microwave photonic filters with improved link gain and reduced noise figure.
18 citations
TL;DR: In this paper, a filter-free photonic approach for measuring microwave Doppler frequency shift (DFS) based on two cascaded electro-optic modulators and a fixed low-frequency reference signal is proposed.
Abstract: A filter-free photonic approach for measuring microwave Doppler frequency shift (DFS) based on two cascaded electro-optic modulators (EOMs) and a fixed low-frequency reference signal is proposed. An optical carrier is carrier-suppressed single-sideband modulated by the transmitted signal and the reference signal at EOM-I. The output from EOM-I is then single-sideband modulated by the echo signal at EOM-II. Subsequently, the output from EOM-II is injected into a photodetector to implement optical-to-electrical conversion. Both the value and direction of the DFS can be obtained by analyzing the frequency of the generated low-frequency electrical signal. The proposed approach has a compact structure and no optical filtering is needed. An experiment is performed to verify the proposed approach. For different microwave frequencies from 7 to 16 GHz, DFS from −100 to 100 kHz is measured, with a measurement error of less than ±0.05 Hz. The stability of the system is also verified. Within 30 minutes, the change of measurement error is less than ±0.05 Hz.
18 citations
TL;DR: In this paper, a microwave frequency measurement system utilizing the optical injection technology in a semiconductor laser is proposed, where a single-wavelength optical carrier is generated and divided into two parts.
Abstract: A microwave frequency measurement system utilizing the optical injection technology in a semiconductor laser is proposed. A single-wavelength optical carrier is generated and divided into two parts. One part is intensity-modulated by a control signal with a triangular shape and then injected into a semiconductor laser to generate a frequency scanning optical sideband. The other part is modulated by the microwave signal under test, which is then coupled with the frequency scanning optical sideband and detected by a photodetector (PD). The output of the PD is filtered by an electrical passband filter and detected by an envelope detector. Electrical pulses will be obtained with the time interval proportional to the microwave frequency. Thus the microwave frequency can be retrieved from the time interval of the generated pulses. A proof of concept experiment is taken. The microwave frequency measurement from 3 to 40 GHz is achieved, and the frequency measurement errors are within ±30 MHz.
17 citations
TL;DR: In this article, the authors proposed and experimentally demonstrated a technique for simultaneous dissemination of optical and radio frequencies over an optical-fiber link with a single optical actuator and dual-optical phase stabilization.
Abstract: In this paper, we propose and experimentally demonstrate a technique for simultaneous dissemination of optical and radio frequencies (RF) over an optical-fiber link with a single optical actuator and dual-optical phase stabilization. The optical actuator, namely electro-optic modulator (EOM), can simultaneously be served with a coupler and a dual optical frequency shifter to couple an RF frequency and an optical frequency and to efficiently suppress the phase noise of the two optical frequencies introduced by the fiber link with dual-optical phase stabilization, respectively. We experimentally demonstrate 193 THz optical carrier dissemination with a stability of $1.2\times 10^{-15}$ at the integration time of 1 s and $3.5\times 10^{-17}$ at 10,000 s, and 0.9 GHz RF frequency dissemination with a stability of $5.7\times 10^{-13}$ at 1 s and $5.2\times 10^{-16}$ at 10,000 s over a 30 km optical fiber link in a single telecommunication channel. This proof-of-principle experiment is particularly useful for users who need both RF and optical frequencies simultaneously, but do not have cumbersome and expensive optical combs, and also provides a promising solution towards a robust and flexible ultrastable optical frequency network for multi-user dissemination based on a frequency division multiplexing technique.
17 citations
TL;DR: In this paper, a photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity is proposed, where a dual-drive Mach-Zehnder modulator (DD-MZM) in a dualpolarization binary phase-shift keying (DP-BPSK) modulator is used as an optical interference canceller.
Abstract: A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity is proposed. A dual-drive Mach–Zehnder modulator (DD-MZM) in a dual-polarization binary phase-shift keying (DP-BPSK) modulator is used as an optical interference canceller, which cancels the self-interference from the received signal and generates two optical sidebands of the signal of interest (SOI) in the received signal. Another DD-MZM in the DP-BPSK modulator is used to provide a pure optical carrier. By combing the optical signals from the two DD-MZMs and beating them at a photodetector, the SOI can be recovered. In addition, if the SOI needs to be transmitted in optical fiber, the power fading effect caused by fiber dispersion can be overcome by simply introducing a proper phase shift to the pure optical carrier. An experiment is performed. RF self-interference cancellation (SIC) with a bandwidth up to 2 GHz is experimentally demonstrated and a cancellation depth of more than 20 dB is achieved even if the bandwidth of the self-interference is about 2 GHz. The SIC with 25-km fiber transmission and the RF power of the SOI after 25-km fiber transmission are also demonstrated, which proves that the SIC has very good immunity to fiber dispersion and the SOI can be transmitted without power fading.
17 citations
TL;DR: This proposed polarisation-tracking free PDM-based fibre-FSO convergent system is notable because it not only incorporates the fibre backbone and optical wireless feeder, but it also simplifies the framework since complicated polarised-tracking mechanism and DSP approach are not involved.
Abstract: A polarisation-division-multiplexing (PDM)-based four-level pulse amplitude modulation (PAM4) fibre-free-space optical (FSO) convergent system with optical band-pass filters (OBPFs) for polarisation de-multiplexing is feasibly demonstrated for the first time. In a PDM scenario with PAM4 modulation, the transmission capacity of fibre-FSO convergent systems is enhanced four times with an aggregate channel capacity of 128 Gb/s (64 Gb/s PAM4/polarisation × 2 polarisations). With an OBPF, polarisation-tracking free de-multiplexing is attained by eliminating other optical carrier with orthogonal polarisation. An OBPF is a simple polarisation de-multiplexing scheme in which the polarisation-orthogonal carrier can be effectively de-multiplexed and the cross-polarisation interference can be nearly eliminated. Compared with traditional PDM-based fibre-FSO convergent systems with sophisticated polarisation-tracking mechanism and elaborate digital signal processing (DSP) approach, it reveals a noteworthy one with the advantage of simplicity. Through 25 km single-mode fibre transport and 500 m FSO link, sufficiently low bit error rate and qualified PAM4 eye diagrams are attained. This proposed polarisation-tracking free PDM-based fibre-FSO convergent system is notable because it not only incorporates the fibre backbone and optical wireless feeder, but it also simplifies the framework since complicated polarisation-tracking mechanism and DSP approach are not involved.
16 citations
TL;DR: The proposed silicon nanocavity is competent to process microwave signals, which has many useful applications in on-chip energy-efficient microwave photonic systems.
Abstract: We propose and experimentally demonstrate a continuously tunable all-optical microwave filter based on a photonic crystal (PC) L3 cavity. Due to the small cavity mode volume and prominent optical properties, the required power to arouse the cavity nonlinear effects is low as microwatt level. Moreover, the cavity resonance could be continuously shifted by finely adjusting the input powers. Therefore, under optical single sideband modulation, the frequency interval between the optical carrier and cavity resonance could be controllable. In this case, the central frequency of the microwave photonic filter (MPF) could be continuously tuned with low power consumption. To the best of our knowledge, the experimental tuning efficiency of 101.45 GHz/mW is a record for on-chip tunable all-optical microwave filters. With dominant features of all-optical control, ultra-high tuning efficiency (101.45 GHz/mW), large rejection ratios (48 dB) and compact footprint (100 µm2), the proposed silicon nanocavity is competent to process microwave signals, which has many useful applications in on-chip energy-efficient microwave photonic systems.
16 citations
TL;DR: The integration of PDM-QPSK with coherent detection and DSP provides a viable platform to develop spectral-efficient IsOWC links and illustrates a better performance in terms of spectral efficiency and figure of merit.
Abstract: Inter-satellite optical wireless communication (IsOWC) links have been exploited by many researchers as a viable technology to transmit information amongst two or more satellites using optical carrier signals and outer space as the medium of propagation medium. IsOWC links can securely transmit information all over the globe. The present study discusses a spectral-efficient large-speed single-channel IsOWC system using polarization division multiplexed-quadrature phase shift keying (PDM-QPSK) scheme. Coherent detection has been used at the receiver terminal for receiver sensitivity improvement. A digital signal processing (DSP) module to mitigate losses due to nonlinearity effects and for estimating carrier phase has been used at the receiver. We have analyzed the proposed link performance by investigating the required optical signal to noise ratio (OSNR) to achieve a target bit error rate (BER). The reported results show a faithful 160 Gbit/s transmission at 40,000 km with good BER. Also, we numerically investigate the OSNR performance of link for increasing pointing errors. Further, a comparative analysis of the proposed link with previous literature illustrates a better performance in terms of spectral efficiency and figure of merit (maximum transmission range $${\times} $$
information transmission rate). The integration of PDM-QPSK with coherent detection and DSP provides a viable platform to develop spectral-efficient IsOWC links.
TL;DR: In this article, the authors proposed and experimentally demonstrated microwave photonic filters with high rejection ratios and large tuning ranges of the central frequency and bandwidth leveraging four cascaded opto-mechanical microring resonators (MRRs).
Abstract: We propose and experimentally demonstrate microwave photonic filters (MPFs) with high rejection ratios and large tuning ranges of the central frequency and bandwidth leveraging four cascaded opto-mechanical microring resonators (MRRs). As half waveguides of each MRR are free-hanging in the air, the nonlinear effects in the opto-mechanical MRRs could be efficiently excited. Consequently, the transmission characteristics of the cascaded MRRs could be flexibly manipulated by adjusting the input pump powers. When the resonant wavelengths of every two MRRs are tuned to be aligned, the transmission spectrum of the silicon device is a notch bimodal distribution with high extinction ratios. The optical carrier is fixed at the flat region of the bimodal distribution. Under optical double sideband (ODSB) modulation, MPFs with high rejection ratios could be achieved due to the high extinction ratio of the cascaded rings. Moreover, the central frequency and bandwidth of the MPFs could be tuned by properly adjusting the pump powers. In the experiment, with a low power of 2.56 mW, the MPF central frequency and bandwidth could be tuned from 7.12 GHz to 39.16 GHz and from 11.3 GHz to 17.6 GHz, respectively. More importantly, the MPF rejection ratios are beyond 60 dB. Furthermore, during the bandwidth tuning process, an MPF response with approximately equiripple stopband could be realized. Owing to the dominant advantages of high rejection ratios, large tuning ranges, low power consumption and compact size, the silicon device has many significant applications in on-chip microwave systems.
TL;DR: A bidirectional in-band full-duplex radio-over-fiber system for the WDM-PON architecture is proposed and experimentally demonstrated, where the error-vector magnitude performance of the uplink transmission thereby is improved from over 45.8% to below 9.9%.
TL;DR: In this paper, a photonic approach for wideband Doppler frequency Shift (DFS) measurement and direction discrimination based on phase modulators (PMs) and optical frequency shift module is proposed and experimentally demonstrated.
TL;DR: In this paper, a hybrid microwave photonic link based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed for co-transmission of millimeter-wave (mmW) and sub-6 GHz wireless signals over a seamless singlemode fiber (SMF) and free-space optics (FSO) channels.
Abstract: A new hybrid microwave photonic link based on a polarization division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed. The link enables co-transmission of millimeter-wave (mmW) and sub-6 GHz wireless signals over a seamless single-mode fiber (SMF) and free-space optics (FSO) channels. Optimization of the chromatic dispersion (CD)-induced power fading regardless of the power fading due to the non-deterministic atmospheric turbulence (AT) is simultaneously demonstrated. Extensive simulation analysis is first presented to examine (i) the impact of CD on mmW (25 GHz) and sub-6 GHz (2.6 GHz) signals, envisioned for the 5th generation networks, and (ii) optimization of CD-induced power fading by changing the phase relations between the optical carrier and optical sidebands in each polarization channel using single tunable polarization controller. A proof-of-concept experiment is finally performed to simultaneously deliver 25 GHz and 2.6 GHz signals with 4/16/64-quadrature amplitude modulation over (i) 20 km SMF and 2 m radio wireless link and (ii) 20 km SMF, 4.2 m FSO (with AT) and 2 m radio wireless links. The optimization of the CD-induced power fading is experimentally verified and link performance shows high tolerance to CD with no power penalties and the measured error vector magnitudes well below the required limits. The predicted bit error rates are also below the forward error correction threshold of $2 \times {10^{ - 4}}$ .
TL;DR: In this article, a remotely injection-locked distributed feedback laser diode (DFB LD) was used to detect a phase-modulated 25-Gb/s/25-GHz four-level pulse amplitude modulation (PAM4) passband signal.
Abstract: A bidirectional free-space optical (FSO) communication through a 600-m free-space transmission is built, employing a phase modulation (PM) scheme and a remotely injection-locked distributed feedback laser diode (DFB LD) for presentation. With optimum injection locking, a DFB LD is excellent for duplex transceiver operations. An injection-locked DFB LD not only operates as a PM-to-intensity modulation converter with an optical detector, but also functions as an upstream optical carrier. To be the first one of employing a remotely injection-locked DFB LD to detect a phase-modulated 25-Gb/s/25-GHz four-level pulse amplitude modulation (PAM4) passband signal, the DFB LD with remote injection locking is successfully intensity-modulated with an upstream 25-Gb/s non-return-to-zero (NRZ) signal. Good bit error rate performance and clear PAM4/NRZ eye diagrams show that this FSO communication can use a remotely injection-locked DFB LD to detect the downstream phase-modulated PAM4 signal and concurrently deliver an upstream intensity-modulated NRZ signal. This bidirectional 25-Gb/s/25-GHz (downstream)/25-Gb/s (upstream) FSO communication is prominent due to its enhancement in two-way high-speed optical wireless communications.
TL;DR: In this paper, the authors demonstrate the amplifier-less transmission of beyond 100Gbit/s signal with advanced modulation formats including discrete multi-tone (DMT) and pulse amplitude modulation (PAM) in an intensity modulation direct detection (IM-DD) system for 40-km datacenter interconnects edge (DCI-Edge) utilizing a low cost commercial 10G-class O-band directly modulated laser (DML).
Abstract: In this article, we experimentally demonstrate the amplifier-less transmission of beyond 100-Gbit/s signal with advanced modulation formats including discrete multi-tone (DMT) and pulse amplitude modulation (PAM) in an intensity modulation direct detection (IM-DD) system for 40-km datacenter interconnects edge (DCI-Edge) utilizing a low cost commercial 10G-class O-band directly modulated laser (DML) During the transmission of DMT signal, Chow Cioffi Bingham algorithm-based bit-loading (CCB-BL) and discrete-Fourier-transform spread (DFT-spread) techniques are both discussed in the bandwidth-limited communication system For the PAM single carrier communication system, look-up table (LUT) pre-distortion and time-domain pre-equalization schemes are jointly employed at the transmitter side to mitigate nonlinear distortions and insufficient bandwidth induced impairments, respectively The results show that 105-Gbit/s DFT-spread DMT, 115-Gbit/s CCB-BL DMT, and 120-Gbit/s PAM-8 signals are successfully transmitted over 40-km single mode fiber (SMF) with the bit-error-rate (BER) below hard decision forward error correction (HD-FEC) threshold of 38 × 10–3 120-Gbit/s DFT-spread DMT and CCB-BL DMT signals allocated within 20-GHz bandwidth can be successfully transmitted over 20-km SMF, and the receiver sensitivity of DFT-spread DMT outperforms CCB-BL DMT by 15-dB at the BER of 38 × 10–3 Due to the flexibility of bit-loading technique, when the allocated bandwidth of 120-Gbit/s CCB-BL DMT signal extends from 20-GHz to 25-GHz, the required received optical power (ROP) of CCB-BL DMT can be lower than DFT-spread DMT by 1-dB at the BER of 38 × 10–3 over 20-km SMF transmission In 120-Gbit/s PAM-8 system, LUT pre-distortion technique improves the system receiver sensitivity by more than 1-dB over 40-km SMF transmission This is the first time to discuss and implement different advanced modulation formats to achieve 100-Gbit/s/λ transmission in a 40-km amplifier-less IM-DD system with a low-cost O-band 10G class DML Both CCB-BL DMT and LUT pre-distortion assisted PAM-8 can achieve a BER lower than HD-FEC threshold of 38 × 10–3 when the net rate per optical carrier is higher than 100-Gbit/s, which are promising solutions for 40-km four-lane 400-GbE DCI-Edge applications
TL;DR: An experimental design of a low-cost coherent ultra-dense WDM passive optical network (UDWDM-PON) with 6.25 GHz channel spacing is reported, demonstrating the practical viability of the PON scaling from 32 up to 256 wavelength channels.
Abstract: Coherent wavelength division multiplexing (WDM) technologies have leveraged the optical communication systems in core networks, increasing the fiber capacity by transmission with advanced modulation formats and mitigation of impairments with digital signal processing. However, these solutions are too expensive for access networks, where cost, power budget, and footprint are limited. Hence, the key technology will be developing low-cost coherent transceivers providing an excellent selectivity and giving high sensitivity, which allows high splitting ratios. This paper reports an experimental design of a low-cost coherent ultra-dense WDM passive optical network (UDWDM-PON) with 6.25 GHz channel spacing. The users’ optical network unit (ONU) is built employing coherent transceivers with two paired low-cost distributed feedback (DFB) lasers, one as the local oscillator and another as the transmitter, offering simplicity and low-cost hardware; likewise, the optical line terminal (OLT) at the central office can profit from the same design. The ONU DFB lasers have wavelengths with limited thermal tunability, controlled by a thermo-electric cooler, which is used to allocate the wavelengths. A medium access control (MAC) at the OLT manages the spectrum channel allocation for ONUs, demanding connection when activation is requested: the OLT furnishes an optical carrier wavelength for the ONU to obtain connection by a control algorithm, assigning a down-channel and another paired up-channel assigned to the ONU DFB transmitter. The MAC can reassign the channels because of interference or collision in a dynamic wavelength allocation. Measures in an activation process and in channel reassignment have been performed in environmental conditions, including control signals and the physical parameters of DFB lasers, demonstrating the practical viability of the PON scaling from 32 up to 256 wavelength channels.
TL;DR: In this paper, a spectral-efficient coherent radio-over-fiber (RoF) link with linear digital phase demodulation is proposed and experimentally demonstrated, which preserves the linearity of the phase-modulated optical link from the transmitter end to the receiver end.
Abstract: In this paper, a novel spectral-efficient coherent radio-over-fiber (RoF) link with linear digital phase demodulation is proposed and experimentally demonstrated. At the transmitter, to make an efficient use of the optical power and spectra, an intensity-modulated optical signal serving as the optical reference signal and a phase-modulated optical signal are polarization-multiplexed on a single optical carrier. At the receiver, the two optical signals are coherently detected with an optical local oscillator (OLO) and demodulated free of laser phase fluctuation through digital signal processing. Owing to simple and linear digital phase demodulation, an RF input signal is linearly demodulated from the optical phase without approximations and preconditions, which preserves the linearity of the phase-modulated RoF optical link from the transmitter end to the receiver end. The proposed scheme is experimentally verified by 25-km single-mode-fiber (SMF) transmission of two 16-QAM microwave vector signals at 2 GHz and 2.4 GHz, both with a symbol rate of 50 Msymbol/s. The transmission performance in term of error vector magnitude (EVM) is evaluated. Additionally, 25-km SMF transmission of the phase-modulated input signal with a spurious-free dynamic range (SFDR) of 112.8 dB·Hz2/3 is obtained.
TL;DR: The proposed high-speed FSO transmission system offers a promising solution for high-bandwidth hungry systems used for the internet of things, 5G, and smart cities and can also be used in developing fronthaul/backhaul links for future wireless networks and optical access networks.
Abstract: A high-capacity spectral-efficient dual-polarization quadrature phase-shift keying (DP-QPSK)-polarization shift-keying (PolSK) hybrid modulation scheme for terrestrial free-space optics (FSO) transmission link is proposed and investigated. A DP-QPSK signal modulated at 300 Gbps and a PolSK signal modulated at 40 Gbps are simultaneously transmitted using a single optical carrier over the FSO link. The proposed link performance is investigated under different weather conditions, where the bit error rate metric is used to evaluate the performance of the PolSK modulated signal and the error vector magnitude parameter is used for the DP-QPSK signal. The FSO link range and the required received power are carefully explored. The conducted numerical simulations of the proposed system showed reliable 340-Gbps data transmission over link ranges varying from 1.6125 to 50 km depending on the weather conditions. The impact of the channel scintillation due to atmospheric turbulence is also investigated. The proposed high-speed FSO transmission system offers a promising solution for high-bandwidth hungry systems used for the internet of things, 5G, and smart cities. It can also be used in developing fronthaul/backhaul links for future wireless networks and optical access networks. The performance of the proposed transmission system is compared with recently published work in the literature.
TL;DR: 1.48-dB superior receiver power sensitivity and 1.7-dB launch fiber power optimization are gained respectively by using LDPC-coded PS-PAM8 signals in WDM-PON, which can bring higher spectral efficiency and power loss budget for the optical distribution networks.
Abstract: A $5\times60$ Gb/s low-density parity-check (LDPC) coded WDM-PON using 8-level pulse amplitude modulation (PAM8) signals with probabilistic shaping (PS) over 20-km standard single-mode fiber (SSMF) with direct detection is proposed and experimentally demonstrated. Each optical carrier at the optical line terminal (OLT) carries a 20-Gbaud probabilistically-shaped LDPC-coded PS-PAM8 signal from a conventional uniform PAM16 signal following a designed approximate Gaussian distribution (AGD). A LDPC-based bit-interleaved coded modulation scheme with iterative decoding (BICM-ID) is utilized to recover the inherently overlapped symbols due to the proposed PS mapping. Combining decision-directed least-mean-squares (DD-LMS) and constant modulus algorithm (CMA), a blind feedback pre-equalizer is adopted to reduce the frequency loss of the signal owing to imperfect electro-optical components in experiment. As for experimental verification and application, 1.48-dB superior receiver power sensitivity and 1.7-dB launch fiber power optimization are gained respectively by using LDPC-coded PS-PAM8 signals in WDM-PON, which can bring higher spectral efficiency and power loss budget for the optical distribution networks.
TL;DR: Radio-frequency interferometry is used to enhance the Brillouin-induced delay applied to the optical sidebands that carry RF signals, while controlling the phase of the optical carrier with integrated silicon nitride microring resonators to report a delay tunability over 600 ps exploiting an enhancement factor of 30.
Abstract: True-time delays are important building blocks in modern radio frequency systems that can be implemented using integrated microwave photonics, enabling higher carrier frequencies, improved bandwidths, and a reduction in size, weight, and power. Stimulated Brillouin scattering (SBS) offers optically-induced continuously tunable delays and is thus ideal for applications that require programmable reconfiguration but previous approaches have been limited by large SBS gain requirements. Here, we overcome this limitation by using radio-frequency interferometry to enhance the Brillouin-induced delay applied to the optical sidebands that carry RF signals, while controlling the phase of the optical carrier with integrated silicon nitride microring resonators. We report a delay tunability over 600 ps exploiting an enhancement factor of 30, over a bandwidth of 1 GHz using less than 1 dB of Brillouin gain utilizing a photonic chip architecture based on Brillouin scattering and microring resonators.
TL;DR: This Letter investigates the requirement of digital upsampling and receiver bandwidth of the PR receiver based on alternative projection employing a dispersive element and proposes and experimentally demonstrates an iteration scheme averaging the interleaved upsampled symbols to maintain two samples per symbol for the estimated complex-valued signal.
Abstract: Phase retrieval (PR) receivers can reconstruct the full electrical field of the signal using only intensity measurements without any optical carrier. In this Letter, we investigate the requirement of digital upsampling and receiver bandwidth of the PR receiver based on alternative projection employing a dispersive element. An iteration scheme averaging the interleaved upsampled symbols to maintain two samples per symbol for the estimated complex-valued signal is proposed and experimentally demonstrated with fast algorithm convergence. The PR uses a modified Gerchberg-Saxton algorithm. Experimentally, we measure Nyquist-shaped 30-GBaud quadrature phase shift keying signals after 55-km single-mode fiber transmission using only 110 and 250 iterations to reach, respectively, the 20% and 7% forward-error correction threshold levels.
TL;DR: A novel, to the best of the authors' knowledge, interrogation scheme based on an optoelectronic oscillator (OEO) with high sensitivity and high speed response for a fiber optical current sensor utilizing a reflective interferometer is proposed and experimentally demonstrated.
Abstract: A novel, to the best of our knowledge, interrogation scheme based on an optoelectronic oscillator (OEO) with high sensitivity and high speed response for a fiber optical current sensor utilizing a reflective interferometer is proposed and experimentally demonstrated. Due to the Faraday effect, a magneto-optic phase shift induced by current variation is generated between two orthogonal light waves. The polarization-dependent properties of the Mach-Zehnder modulator are used to convert the magneto-optic phase shift into the phase difference between the optical carrier and sideband, which is then mapped to the oscillating frequency shift by closing an OEO loop. A high current sensitivity of 152.5 kHz/A with a range of 0-2.5 A is obtained in the experiment.
TL;DR: In this paper, a photonics-assisted RF channelized receiver aiming for instantaneous broadband RF signal reception is proposed and experimentally demonstrated, where an optical frequency comb (OFC) is generated through a phase modulator (PM), while in the other the optical carrier is frequency-shifted via a polarization modulator and then modulated by the captured unknown RF signal.
Abstract: For civil and military applications, the ability to instantaneously capture and process wideband RF (radio-frequency) signal is of great importance. In this paper, a novel photonics-assisted RF channelized receiver aiming for instantaneous broadband RF signal reception is proposed and experimentally demonstrated. The channelizer is composed of two branches. In one branch, an optical frequency comb (OFC) is generated through a phase modulator (PM), while in the other the optical carrier is frequency-shifted via a polarization modulator (PolM) and then modulated by the captured unknown RF signal. Next, the frequency information of the unknown signal is derived from the frequency sum and the power difference of two specific beating tones, while the incorporation of the comb spacing and the amplitude profile of the OFC enable resolving the ambiguity cases. In the experiments, four receiving channels are constructed using five selected comb lines. The reception and analysis of several RF signals including single-tone, multi-tone and linear frequency modulation (LFM) ones within 1-40 GHz are experimentally validated, which can be extended up to 72 GHz in theory. The proposed channelizer is characterized with ambiguous-free capability, low measurement errors less than 2 MHz, and an SFDR of ∼92 dB·Hz2/3.
TL;DR: The fundamental limitations of optical frequency transfer stability related to cost-effective implementation of signal transmission in duplex, unidirectional optical paths offered by a standard dense wavelength division multiplexing (DWDM) network are investigated.
Abstract: This article investigates the fundamental limitations of optical frequency transfer stability related to cost-effective implementation of signal transmission in duplex, unidirectional optical paths offered by a standard dense wavelength division multiplexing (DWDM) network. We pointed out the effect of a significant mismatch of phase fluctuations observed in pairs of fibers even when located in a common cable. We also measured the thermal sensitivities of individual DWDM optical modules in the context of the effectiveness of the signal stabilization system. Finally, we present the real implementation of the coherent optical carrier transfer in the operational DWDM network, showing the overall impact of all individual effects. We demonstrated that it is possible to obtain the long-term stability (one day averaging) within the range from ${2} \times {10}^{-{16}}$ to ${4} \times {10}^{-{16}}$ and typical frequency offset at the level of few times 10−16 in a 1500-km-long line by using the soil-deployed cables.
TL;DR: In this article, the authors proposed an approach to achieve truly distributed and ultra-fast fiber-optic sensing based on an active and distributed bandpass microwave photonic filter (MPF) through stimulated Brillouin scattering (SBS).
Abstract: Brillouin-based optical fiber sensing has gained considerable attention for the past few years thanks to its ability to offer distributed sensing. The major limitation of a Brillouin-based optical fiber sensor is its complexity because a time-consuming frequency-sweeping process is needed to obtain a local Brillouin gain spectrum (BGS) and to calculate the local Brillouin frequency shift (BFS). Thus, it is only suitable for static or slow-varying measurements. In this article, we propose an approach to achieve truly distributed and ultra-fast fiber-optic sensing based on an active and distributed bandpass microwave photonic filter (MPF) through stimulated Brillouin scattering (SBS). To obtain a truly distributed BFS, a counter-propagating single-shot pump pulse is launched into the fiber link and a microwave multi-tone (MMT) signal with a random initial phase distribution which is phase modulated on an optical carrier is launched into the fiber link from the other end. Due to the SBS effect, the −1st order sideband of the phase-modulated signal will experience Brillouin amplification while the +1st order sideband will experience Brillouin attenuation, and the phase-modulated signal is converted to an intensity-modulated signal. The entire operation is equivalent to a bandpass MPF. By detecting the optical signal at a photodetector (PD), a regenerated MMT signal with its magnitude and phase that are shaped by the MPF is obtained. By evaluating the regenerated MMT signal, the Brillouin information corresponding to the temperature or strain change at a specific location is revealed. The major advantage of the approach is that time-consuming frequency-sweeping process is avoided. Truly distributed strain, temperature, and vibration sensing with a 2 m spatial resolution over 49.5 m distance at a speed up to 83.3 kHz is experimentally demonstrated.
TL;DR: In this article, a simple scheme for the generation of high-quality V-band (50-75 GHz) OFDM vector millimeter-wave (mm-wave) is presented, which is only enabled by a dual-parallel Mach-Zehnder modulator (DP-MZM).
TL;DR: A cascaded distributed antenna system (DAS) for efficiently extending the coverage of the mmWave-based 5G indoor network and introduces the cascaded IFoF link structure that can support up to 13.5 dB optical power budget with following error-vector-magnitude (EVM) performance characterizations.
Abstract: We propose and demonstrate a cascaded distributed antenna system (DAS) for efficiently extending the coverage of the mmWave-based 5G indoor network. For this, we exploit the radio-over-fiber (RoF) system based on the intermediate-frequency-over-fiber (IFoF) transmission technique that is enabled to add/drop the specific wavelength to the designated remote antenna unit (RAU) with using optical splitters and coarse wavelength division multiplexing (CWDM) filters. Moreover, the IFoF transceivers (TRx) perform the subcarrier multiplexing (SCM) in order to transmit $2\times 8$ frequency allocation (FA) 5G signals per a single optical carrier, where each FA has 100 MHz bandwidth, leading each RAU to support $2\times 2$ MIMO operation. Consequently, the cascaded structure allows for the adaptive and flexible configuration of the order of MIMO in accordance of the required data throughput at the specific indoor area. We introduce the cascaded IFoF link structure that can support up-to 13.5 dB optical power budget with following error-vector-magnitude (EVM) performance characterizations. And then we experimentally demonstrate the RoF-based cascaded DAS network, showing that more than 1 Gb/s total throughput can be achieved per a single antenna. Furthermore, we examine the use of avalanche photodiode (APD) to further increase the optical power budget (i.e., the coverage) based on experiment as well as simulation.
TL;DR: The feasibility of the coherent channelized receiver is verified, the reconfigurability is demonstrated, and the error-vector magnitude curves of the directly received and the channelized quadrature amplitude modulation (QAM) signal at different amounts of beat noise are compared.
Abstract: In this Letter, based on two advanced tunable ultra-flat optical frequency comb generators (T-FOCGs), a coherent channelized receiver with high channelized efficiency and reconfigurability is proposed. In the T-FOCG, the number of 1 dB comb lines increases with the gain, but the optical power of these 1 dB comb lines has almost the constant variance. In the proposed scheme, one optical carrier can support four sub-channels. Meanwhile, the number and bandwidth of sub-channels, as well as the bandwidth and center frequency of an original broadband signal, are all tunable. In this Letter, we verify the feasibility of the coherent channelized receiver by channelizing a 4 GHz signal with a 20 GHz center frequency into four 1 GHz sub-channels, and the reconfigurability is demonstrated by channelizing a 10 GHz signal with frequencies from 18 to 28 GHz into five 2 GHz sub-channels. Moreover, the error-vector magnitude curves of the directly received and the channelized quadrature amplitude modulation (QAM) signal at different amounts of beat noise are compared.