Showing papers on "Optical Carrier transmission rates published in 2023"

Integrated sensing and communication in an optical fibre

Abstract: The integration of high-speed optical communication and distributed sensing could bring intelligent functionalities to ubiquitous optical fibre networks, such as urban structure imaging, ocean seismic detection, and safety monitoring of underground embedded pipelines. This work demonstrates a scheme of integrated sensing and communication in an optical fibre (ISAC-OF) using the same wavelength channel for simultaneous data transmission and distributed vibration sensing. The scheme not only extends the intelligent functionality for optical fibre communication system, but also improves its transmission performance. A periodic linear frequency modulation (LFM) light is generated to act as the optical carrier and sensing probe in PAM4 signal transmission and phase-sensitive optical time-domain reflectometry (Φ-OTDR), respectively. After a 24.5 km fibre transmission, the forward PAM4 signal and the carrier-correspondence Rayleigh backscattering signal are detected and demodulated. Experimental results show that the integrated solution achieves better transmission performance (~1.3 dB improvement) and a larger launching power (7 dB enhancement) at a 56 Gbit/s bit rate compared to a conventional PAM4 signal transmission. Meanwhile, a 4 m spatial resolution, 4.32-nε/[Formula: see text] strain resolution, and over 21 kHz frequency response for the vibration sensing are obtained. The proposed solution offers a new path to further explore the potential of existing or future fibre-optic networks by the convergence of data transmission and status sensing. In addition, such a scheme of using shared spectrum in communication and distributed optical fibre sensing may be used to measure non-linear parameters in coherent optical communications, offering possible benefits for data transmission.

A Multiband Microwave Photonic Filter Based on a Strongly Coupled Microring Resonator With Adjustable Bandwidth

Abstract: A bandwidth-tunable multiband microwave photonic filter (MPF) using a strongly coupled microring resonator (MRR) with optical phase modulation is demonstrated theoretically and experimentally. Two notches of the MRR adjacent to the optical carrier break the intrinsic balance of the phase-modulated signal and then two sub-MPFs are formed thanks to the conversion from phase modulation to intensity modulation (PM-IM). The frequency responses of the two sub-MPFs are superimposed to form a passband with a fixed center frequency. Due to the periodicity of the MRR transmission spectrum, multiple passbands separated by a certain spacing appear in the frequency domain and combine to form a multiband MPF, whose bandwidth can be adjusted by tuning the wavelength of the carrier. The tunable bandwidth and shape factors ranging from 0.73 GHz to 2.73 GHz and 5.06 to 1.38 are experimentally performed. The number of passbands can be reconfigured. The proposed multiband MPF has the potential to be employed in modern multi-standard wireless communication systems.

Photonic Generation of Background-Free Phase-Coded Microwave Pulses with Elimination of Power Fading

Abstract: We report a novel photonic scheme to generate background-free phase-coded microwave pulses with elimination of power fading by cascading a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM is driven by a radio frequency (RF) signal to generate two first-order optical sidebands with an orthogonal polarization state, while the PolM is driven by a three-level electrical coding signal. By properly adjusting the polarization state, a series of background-free frequency-doubled phase-coded microwave pulses can be generated after optical-to-electrical conversion. Benefiting from the carrier-suppressed single-sideband (CS-SSB) modulation, the proposed signal generator can suppress the chromatic-dispersion-induced power-fading effect, which has excellent potential for long-distance fiber transmission. In addition, the system can directly generate phase-coded microwave signals in pulse mode by truncating continuous wave (CW) microwave signals. Moreover, the microwave signal generator has wideband tunability since no optical filter is involved in our scheme. The proposed method was theoretically analyzed and experimentally verified. Phase-coded microwave pulses centered at 14 GHz and 19.2 GHz with a bit rate of 0.5 Gb/s were successfully generated.

Two-Way 5G NR Fiber-Wireless Systems Using Single-Carrier Optical Modulation for Downstream and Phase Modulation Scheme for Upstream

Abstract: Fifth-generation (5G) millimeter-wave (MMW)/sub-THz signals over a two-way fiber-wireless system using single-carrier optical modulation for downstream and phase modulation (PM) scheme for upstream are proposed and implemented for the first time. Compared to multi-carrier optical modulation, using single-carrier optical modulation in downlink is attractive because it can suppress RF power fading due to fiber dispersion and interference caused by optical beating from multiple carriers. Furthermore, compared to intensity modulation scheme, using PM scheme with remotely injection-locked distributed feedback laser diode in uplink is attractive because it enables high robustness to noise and distortion. Through 40-km single-mode fiber, 500-m free-space optical, and 2-m/1-m/0.5-m (downstream)/4-m (upstream) RF wireless cascaded-medium, 5G new radio (NR) MMW/sub-THz signals are transported with low bit error rates and clear constellations in downlink/uplink performance. Such a newly-built two-way 5G NR fiber-wireless system shows promise to perform 5G NR evolution in MMW and sub-THz frequencies, which has significant impacts on fiber-wireless integration.

Analysis of a photonic integrated circuit for passive optical network for 5G NR.

Abstract: This work presents the performance analysis of a passive optical network (PON) proposal with photonic integrated circuits (PIC). The PON architecture was simulated on MATLAB, focusing on the main functionalities of the optical line terminal, distribution network, and network unity regarded its effects on the physical layer. We show a simulated PIC, implemented on MATLAB through its analytic transfer function equation, used to implement orthogonal frequency division multiplexing in the optical domain to enhance the current optical networks for the 5G New-Radio (NR) scenario. We analyzed the OOK and optical PAM4 compared with phase modulation formats such as the DPSK and DQPSK. All modulation formats can be directly detected for the case in the study, simplifying the reception. Consequently, this work achieved a maximum symmetric transmission capacity of 1.2 Tbps over 90 km of standard single-mode fiber with 128 carriers, 64 carriers for downstream and 64 for upstream, obtained from an optical frequency comb with 0.3 dB flatness. We concluded that phase modulation formats associated with PIC could increase PON capability and push further our current scenario to the 5G new era.

Linearization of a Dual-Parallel Mach-Zehnder Modulator Using Optical Carrier Band Processing

Abstract: The linearization of a microwave photonic link based on a dual-parallel Mach-Zehnder modulator is theoretically described and experimentally demonstrated. Up to four different radio frequency tones are considered in the study, which allow us to provide a complete mathematical description of all third-order distortion terms that arise at the photodetector. Simulations show that a complete linearization is obtained by properly tuning the DC bias voltages and processing the optical carrier and. As a result, a suppression of 17 dBm is experimentally obtained for the third-order distortion terms, as well as a SDFR improvement of 3 dB. The proposed linearization method enables the simultaneous modulation of four different signals without the need of additional radio frequency components, which is desirable to its implementation in integrated optics and makes it suitable for several applications in microwave photonics.

A microwave photonic mixer with complete suppression of LO spurious

Abstract: Microwave photonic mixer owns the advantages of wide frequency coverage range and large processing bandwidth. However, the LO spurious of the mixer is still high, which severely limits its application where the LO spurious locate at the band of interest. In this paper, a novel microwave photonic mixer with complete suppression of LO spurious is proposed. A dual-drive mach-zehnder modulator (DD-MZM) is adopted. The LO signal and RF signal are applied to the DD-MZM through the two driven ports. The optical signal is controlled to make the LO signal to be the phase modulation and the IF signal to be the intensity modulated. Finally, after the intensity detection completed by the photodetector, only the IF signal will be preserved and the LO spurious can be all suppressed. A proof-of-concept experiment is performed. Experimental result shows that 50-dB suppression of LO spurious can be realized.

Generation of a Fundamental/Doubled Frequency Phase-Coded Microwave Signal Based on Polarization Multiplexed Technology

Abstract: Microwave photonic phase-shifting technology can be used to generate high-frequency, broadband, and tunable phase-coded microwave signals, which are helpful in solving the contradiction between the detection range and the range resolution in radar systems. A method for generating a reconfigurable carrier phase-coded signal of a fundamental or doubled carrier frequency, based on polarization multiplexed technology, is proposed and verified by the experiments in this paper. A dual-parallel dual-polarization Mach–Zehnder modulator (DP-DPMZM) and a polarization-dependent phase modulator (PD-PM) were used to load the carrier and the phase-shifting signal, respectively. By reasonably configuring the state of the RF switch and the bias voltages of the sub-DPMZM, the fundamental or doubled carrier frequency can be obtained through photoelectric conversion. The reconfigurable carrier frequency gives the system a wider work bandwidth range and can effectively reduce the frequency requirement for local oscillator (LO) signals. By adjusting the driving voltage, the broadband microwave signal can be phase-shifted within the range of 360°, and when the phase-shifted control signal is a multilevel amplitude signal, it can generate binary, quaternary, or other high-order phase-coded signals, which have high reconfigurable performance and potential application value in multifunctional radar systems. In addition, the scheme has wideband tunability, since no optical filter is involved. The proposed scheme was theoretically analyzed and experimentally verified. Binary, quaternary, and octal phase-coded signals, with fundamental and doubled frequencies centered at 8 GHz and 16 GHz, were successfully generated.

A Photonics-Assisted Binary/Quaternary Phase-Coded Microwave Signal Generator Applicable to Digital I/O Interfaces

Abstract: A photonics-assisted binary/quaternary phase-coded microwave signal generator with fundamental/doubling reconfigurable carrier frequency applicable to digital I/O interfaces is proposed and has been verified by experiments. This scheme is based on a cascade modulation scheme, which is used to reconfigure fundamental/doubling carrier frequency and load the phase-coded signal, respectively. By controlling the radio frequency (RF) switch and the bias voltages of the modulator, the switching of the fundamental or doubling carrier frequency can be realized. When the amplitudes and sequence pattern of the two independent coding signals are set reasonably, binary or quaternary phase-coded signals can be realized. The sequence pattern of coding signals is applicable to digital I/O interfaces and can be directly generated through the IO interfaces of FPGA instead of an expensive high-speed arbitrary waveform generator (AWG) or other digital-to-analog conversion (DAC) systems. A proof-of-concept experiment is carried out, and the performance of the proposed system is evaluated from the aspects of phase recovery accuracy and pulse compression capability. In addition, the influence of residual carrier suppression and polarization crosstalk in non-ideal states on phase shifting based on polarization adjustment has also been analyzed.

Reconfigurable and Tunable Multi-output Optoelectronic Oscillator Based on Stimulated Brillouin Scattering Effect

Abstract: In this paper, a reconfigurable and tunable optoelectronic oscillator (OEO) based on the stimulated Brillouin scattering (SBS) effect is proposed and theoretically demonstrated. Based on the same structure, the OEO can generate one tunable microwave signal, two output microwave signals, or multi-frequency tunable signals. In order to obtain the carrier-suppressed double sideband (CS-DSB) signal, the single drive MZM is considered at the minimum transmission point (MITP). After passing through the tunable optical bandpass filter (TBPF), we can obtain the carrier-suppressed single sideband (SC-SSB) signal. By using the controllable SC-SSB signals, the corresponding signals are constructed. In the proposed structure, multi-pump lights are generated using carrier suppression single-sideband modulation and an optical tunable filter. As a consequence, a reconfigurable and tunable OEO can be achieved. By using one laser and an arbitrary waveform generator (AWG), multiple-frequency tunable microwave signals can be generated. The design concept and simulated results show that the proposed OEO is flexible, which can be used to offer the possibility to process multi-type microwave signals simultaneously.

Broadband photonic-assisted microwave receiver with high cross-channel interference suppression and image rejection.

Abstract: A broadband photonic-assisted microwave receiver with high cross-channel interference suppression and image rejection is proposed and experimentally demonstrated. At the input of the microwave receiver, a microwave signal is injected into an optoelectronic oscillator (OEO), which functions as a local oscillator (LO) to generate a low-phase noise LO signal as well as a photonic-assisted mixer to down-convert the input microwave signal to the intermediate frequency (IF). A microwave photonic filter (MPF), realized by the joint operation of a phase modulator (PM) in the OEO and a Fabry-Perot laser diode (FPLD), is used as a narrowband filter to select the IF signal. Thanks to the wide bandwidth of the photonic-assisted mixer and the wide frequency tunable range of the OEO, the microwave receiver can support broadband operation. The high cross-channel interference suppression and image rejection are enabled by the narrowband MPF. The system is evaluated experimentally. A broadband operation from 11.27 to 20.85 GHz is demonstrated. For a multi-channel microwave signal with a channel spacing of 2 GHz, a cross-channel interference suppression ratio of 21.95 dB and an image rejection ratio of 21.51 dB are realized. The spurious-free dynamic range (SFDR) of the receiver is also measured to be 98.25 dB·Hz2/3. The performance of the microwave receiver for multi-channel communications is also experimentally evaluated.

Microwave Frequency Dividers With Reconfigurable Fractional 2/N and 3/N Division Ratios

Abstract: Two microwave photonic signal processing structures, which are capable to realise microwave frequency division with a tunable integer or non-integer division ratio, are presented. They are based on applying an input RF signal to a Mach Zehnder modulator, which is biased to generate a carrier-suppressed double sideband (DSB) or single sideband (SSB) optical signal. The carrier-suppressed DSB optical signal consists of the upper and lower 1 ^st order sidebands with a separation of two times the input RF signal frequency. The carrier of the SSB optical signal is suppressed by a fibre Bragg grating (FBG) connected to the modulator output. Hence the FBG output consists of the upper 1 ^st order and lower 2 ^nd order sidebands with a separation of three times the input RF signal frequency. The carrier-suppressed DSB or SSB optical signal is injected into a semiconductor laser. The semiconductor laser is oscillated in the period-one state that generates a number of equally spaced frequency components, which are frequency locked by the injection light wave. Beating of these optical frequency components at the photodetector produces an RF signal with a frequency of 2/ N or 3/ N times the input RF signal frequency where N can be between 3 and 6. Hence the 2/ N frequency divider can realise 2/3, 1/2, 2/5 and 1/3 frequency division operation, and the 3/ N frequency divider can realise 3/4, 3/5 and 1/2 frequency division operation. The proposed 2/ N and 3/ N frequency dividers have a very simple structure compared to the reported photonics-based microwave frequency divider that can realise both integer and non-integer frequency divisions. The frequency division ratio can be tuned by simply adjusting the forward bias current of the semiconductor laser subject to optical injection. Experimental results demonstrate the two proposed structures can realise microwave frequency division with a tunable integer and non-integer division ratio for different input RF signal frequencies of 10 to 18 GHz, and over 60 dB output signal-to-noise ratio performance. More than 27 dB suppression in the unwanted frequency components around the frequency divided signal is also demonstrated.

30 m 64-QAM multicarrier photonic-wireless communication link in the 300 GHz band

Abstract: In recent years, terahertz communication has attracted extensive attentions due to its large bandwidth for supporting terabit-per-second capacity. Along with the rapid evolution of terahertz optoelectronic devices, remarkable achievements have been witnessed in developing photonic terahertz communication systems with large capacities. In fact, photonics-assisted terahertz communication systems have exhibited some advantages, for instance, bridging a seamless connection between the existing optical fiber network and wireless network, offering flexible carrier switching over a wide radio frequency range, as well as supporting easy implementation of high-order complex modulation formats and multicarrier multiplexing terahertz channels. However, due to high atmospheric propagation loss, limited terahertz component bandwidth and low terahertz emission power, achieving simultaneous transmission of single-lane data rates beyond 200 Gbps is still challenging based on a single pair of terahertz transceivers. In this work, by employing subcarrier (SC) multiplexing, high-order 64-ary quadrature amplitude modulation (64-QAM) format, well-defined digital signal processing (DSP) and wideband terahertz transceivers, a multicarrier terahertz photonic-wireless communication link operating in the 300 GHz band is proposed and experimentally demonstrated. At the transmitter side, a baseband pseudo-random binary sequence (PRBS-15) signal with a baud rate of 12 Gbaud is generated from an arbitrary waveform generator (AWG), and then modulated onto an optical carrier centered at 193.414 THz. The modulated optical signal is combined with three optical carriers centered at 193.7035 THz, 193.7165 THz, and 193.7295 THz, for multi-carrier THz generation at a uni-traveling carrier photodiode (UTC-PD) featuring large bandwidth (100 GHz), which consists of three SCs centered at 286.5 GHz, 299.5 GHz and 312.5 GHz, respectively. At the receiver side, we employ a Schottky diode mixer with high sensitivity to down-convert the three terahertz SCs into the intermediate frequency (IF) domain, with three IF signals cantered at 6.5 GHz, 19.5 GHz, and 32.5 GHz, respectively, which are then processed using home-made advanced DSP routine, including a linear adaptive equalizer, compensation algorithms of frequency offset and phase noise. In the experiment, a total line data rate of 216 Gbps (72 Gbps/SC × 3 SC) over a wireless distance of 30 m is successfully transmitted, and the performance of all three SCs can reach below the hard decision forward-error-correction (HD-FEC) with 6.25 % overhead, reaching an aggregated net transmission capacity of up to 202.5 Gbps. This achievement of single-lane simultaneous transmission of beyond 200 Gbps using a single pair of 300 GHz transceivers is considered a significant step towards next-generation wireless communications.

Reconfigurable Flexible PON Downlink by using Wavelength Selective Switch and Single Intensity Modulator

Abstract: A reconfigurable passive optical network (PON) downlink has been experimentally demonstrated. A multi-carrier signal is generated in the digital domain and converted to an optical signal by a Mach-Zehnder intensity modulator. A wavelength selective switch (WSS) demultiplexes the sub-carriers for a distribution network. Each sub-carrier signal is a duo-binary filtered binary phase shift keying and directly detected at the receiver side. By changing the sub-carrier allocation and WSS port setting, the PON network can be easily reconfigured without changing the hardware configuration. The maximum capacity of 75-Gb/s with 10-km transmission and 128-way split has been achieved.

High-performance transient SBS-based microwave measurement using high-chirp-rate modulation and advanced algorithms.

Abstract: The transient stimulated Brillouin scattering (SBS) effect, enabled by optical chirp chain (OCC) technology, has already been proposed and demonstrated for microwave frequency identification with high temporal resolution. Through increasing the OCC chirp rate, the instantaneous bandwidth can be effectively extended without loss of the temporal resolution. However, the higher chirp rate results in more asymmetric transient Brillouin spectra, which worsens the demodulation accuracy when using the traditional fitting method. In this Letter, advanced algorithms, including image processing and artificial neural network, are employed to improve the measurement accuracy and demodulation efficiency. A microwave frequency measurement scheme is implemented with 4 GHz instantaneous bandwidth and 100 ns temporal resolution. Through the proposed algorithms, the demodulation accuracy of transient Brillouin spectra under 50 MHz/ns high chirp rate is improved from 9.85 MHz to 1.17 MHz. Moreover, owing to the matrix computations of the proposed algorithm, the time consumption is reduced by two orders of magnitude compared with the fitting method. The proposed method allows a high-performance OCC transient SBS-based microwave measurement, which provides new possibilities to realize real-time microwave tracking for diverse application fields.

Compensation of dispersion-induced power fading in radio-over-fiber system based on stimulated Brillouin scattering

Abstract: A method to compensate for the dispersion-induced power fading in a radio-over-fiber (RoF) link is proposed and experimentally demonstrated based on stimulated Brillouin scattering (SBS). In the central office, a part of the optical carrier is used to generate frequency-definable two-tone pump light via carrier-suppressed double-sideband modulation. The two-tone pump light generates both Brillouin loss and gain spectra at the vicinity of the optical carrier when it counter-propagates with the signal light in a spool of single-mode fiber (SMF) located in the central office. Hence, the relative phase difference between the optical carrier and the ±1st -order modulation sidebands of the signal light can be freely varied by using the SBS-induced carrier phase shift, which can compensate for the power fading induced by the group-velocity dispersion in the transmission fiber between the central office and the base station. In the experiment, a flat gain in the frequency range of 10 MHz to 10 GHz is achieved for the signal transmission over 45-km SMF. The error vector magnitudes (EVMs) of the transmitted 64 QAM signals centered at 4.8 GHz and 5.0 GHz are greatly improved after dispersion-induced power fading compensation.

Design of a RoF fronthaul link based on optical generation of mm-waves for 5G C-RANs

Abstract: In this paper, a cloud-radio access networks based (C-RANs) radio-over-fiber (RoF) system have been reported with the optical generation of 28 GHz and 57 GHz millimeter-wave using phase modulation and stimulated Brillouin scattering effect in optical fibers. As a result, a cost-effective system with improved performance is achieved by the proposed method. Based on the proposed scheme, a 28 GHz (licensed band) and 57 GHz (Un-licensed band) optical millimeter-waves are generated by simulation only using 14 GHz and 16 GHz radio frequency (RF) respectively. Because the performance of any optical transmission system is limited by the Q factor and the bit error rate (BER) and any input power of the laser into the fiber needs to be less than the Brillouin threshold in order to avoid the sharp degradation of the Q factor. Also, the Brillouin threshold for this study setup is determined which is around 6 dBm in the case of licensed band and 2 dBm in the case of unlicensed band. The simulation results show that the proposed scheme can provide 100 km single-mode fiber for 28 GHz and 25 km for 57 GHz with transmission rates of 10 Gbps for both of them. In addition, a stable millimeter-wave RoF link, high quality carriers, and a reduction in nonlinearity effects are achieved with the proposed scheme.

Advanced Optical Modulators for Sub-THz-to-Optical Signal Conversion

Abstract: The use of sub-terahertz (sub-THz) and/or THz bands is a method of achieving some attractive applications such as future large-capacity radio over fiber (RoF) networks. However, in the current scenario, the performance of devices operating in the THz band is considerably worse than that of devices operating in the microwave band. An optical modulator is a device that converts electrical signals such as microwave, sub-THz, and THz signals to optical signals, and their conversion efficiency decreases when they are operated at higher frequencies. In this paper, we investigate two types of optical modulators. One is a long effective-length modulator to maximize its responsivity in the > 100 GHz range. It has an advantage for band-limited applications such as RoF. The other is a broadband modulator integrated with an electro-optic (EO) frequency-domain equalizer. The fabricated modulator achieved an over 110-GHz 3-dB bandwidth by customizing the optical circuit diagram in a traveling-wave modulator, and in a numerical estimation, the 3-dB bandwidth reached sub-THz. We also investigated the modulation distortions of the modulator with the equalizer. Using the measurement results, the optical crosstalk in the EO equalizer of the fabricated modulator was estimated to be less than −30 dB, and the distortion attributable to the EO equalizer in the modulator was sufficiently small to be negligible. We also measured a third-order intermodulation distortion, and the results showed that integration of the equalizer does not cause a degradation of modulation linearity. The obtained spurious-free dynamic range was as high as 83.3 dB.