Optical Mm-wave Research Articles

Distinguishing the effect of frequency selective fading of a low cost 64 quadrature amplitude modulation direct-detection OFDM ROF system employing fiber Bragg grating to generate optical mm-wave

Distinguishing the effect of frequency selective fading of a low cost 64 quadrature amplitude modulation direct-detection OFDM ROF system employing fiber Bragg grating to generate optical mm-wave

Effect of Phase Noise on the Optical Millimeter-Wave Signal in the DWDM-RoF System

In this study, we examined the effect of phase noise on the optical millimeter-wave (mm-wave) signal in a dense wavelength division multiplexing radio-over-fiber (DWDM-RoF) system. A single modulator was used to generate the optical mm-wave signal in the DWDM-RoF system. This paper addresses the impact of phase noise, which results from phase imbalance, on the optical mm-wave signal. To lower the effect of phase noise on the optical mm-wave signal, the phase imbalance should be controlled. The phase imbalance can be controlled and decreased by adjusting the phase at the phase shift (PS). The system performance was analyzed using various parameters such as bit error rate (BER), signal-to-noise ratio (SNR), optical signal to noise ratio (OSNR), and error vector magnitude (EVM). From the results, we found the phase imbalance affected the optical mm-wave signal due to the imbalanced splitting of the signal intensity at the MZM. The phase imbalance impacts the phase noise, which impacts the optical mm-wave signal. The phase noise could be decreased by controlling the phase imbalance at the phase of 5π/12. The best results at the phase of 5π/12 were collected for phase noise at 0.02 degrees.

A novel bidirectional RoF link with compensated SBS and RB for 16-QAM OFDM based mm-wave downlink and uplink vector signal generation and transmission on a single fiber

A novel bidirectional RoF link with compensated SBS and RB for 60 GHz OFDM-based 16-QAM downlink and uplink vector signal generation and co-propagation over a single fiber is proposed. At the central station (CS), 60 GHz optical mm-wave is generated and modulated in the optical single-sideband modulation (OSSB) technique by the 16-QAM OFDM downlink vector signal. At the base station (BS), the 60 GHz downlink signal is detected by a high-speed photodetector (PD). The 60 GHz electrical mm-wave signal is transmitted to the user end by an antenna. The uplink carrier is extracted from the unmodulated sideband of the mm-wave downlink vector signal. This reduces the complexity of BS and makes it free from the laser source. The 16-QAM OFDM-based mm-wave uplink signal is received from the user end through an antenna and down-converted to a 10 GHz uplink vector signal. The uplink signal modulates the extracted blank carrier in the OSSB technique. The uplink and downlink vector signals are co-propagated through the standard single bidirectional fiber. Although the carrier reuse over a single fiber reduces the fiber capacity by half, it generates non-linear backscattering such as Rayleigh Backscattering (RB) and Stimulated Brillouin Scattering (SBS). A theoretical analysis is made on the backscattered power and its effect on the fiber transmission. The compensation of SBS by maintaining the SBS threshold and mitigation of RB is carried out by appropriate modulation technique. In addition, downlink and uplink signal with different data rate is transmitted through the compensated bidirectional RoF link, and the transmission performance is analyzed. Based on the analysis, the theoretical model for simultaneous downlink and uplink signal transmission over a single fiber is proposed and verified by the software simulation. The compensated bidirectional RoF link shows up a better performance up to 75 km with negligible power penalty.

Modulation Index and Phase Imbalance of Dual-Sideband Optical Carrier Suppression (DSB-OCS) in Optical Millimeter-Wave System

This paper presents a Dual-sideband Optical Carrier Suppression (DSB-OCS) technique which is used to generate an optical millimeter-wave (mm-wave) signal in radio over fiber (RoF) systems. The proposed system employs a Dual-Electrode Mach-Zehnder Modulator (DE-MZM) and a carrier of 40 GHz mm-wave for data transmission through the RoF systems. Characteristics determining the performance of the system, among which are the modulation index, phase imbalance and dispersion parameters, are included. The performance evaluations of the system show that the mm-wave signal output power follows MZM’s transfer function when the modulation index is raised. Moreover, the generated optical mm-wave signal power is affected by phase imbalance and optical splitting ratio. It is observed that the optical fiber dispersion influences the DSB-OCS system by decreasing the amplitude of the mm-wave and the signal-to-noise ratio (SNR).

BPSK photonic millimeter-wave generation and transmission based on frequency quadrupling

A novel scheme for generating BPSK photonic millimeter-wave (MM-wave) with frequency quadrupling is designed and demonstrated, frequency quadrupling is based on dual-parallel Mach-Zehnder Modulator (DPMZM) without an optical filter. In the scheme, by adjusting the phase of local radio frequency (RF) signal, the bias point of sub-MZM and the gain of data signal appropriately, only the +2nd-order sideband carries data signal while the −2nd-order sideband bears pure RF signal. Theoretical derivation and simulation experiment are provided for the BPSK photonic MM-wave generation scheme, the effects of Extinction ratio (EXT) and RF modulation index of sub-MZM on optical sideband suppression ratio (OSSR) of the generated photonic MM-wave are evaluated. Furthermore, a 2.5 Gb/s data signal distribution performance is investigated, the generated BPSK optical mm-wave signal could be distributed 80 Km with the devised scheme at BER = 10–9, while the transmission distance is around 20 Km for the previous reported scheme.

Photonic generation of millimeter-wave signal through frequency 12-tupling using two cascaded dual-parallel polarization modulators

In this paper, filterless photonic generation of millimeter-wave (mm-wave) signal through frequency 12-tupling via two cascaded dual-parallel polarization modulators (DP-PolMs) is proposed. The principle of operation of the proposed system is theoretically analysed and verified by computer simulation. From the theoretical analysis, the frequency 12-tupling mm-wave signal is shown to be generated by properly adjusting the modulation indices of PolMs, polarization directions of the modulated optical signals, and the phases of the RF drive signals applied to the DP-PolM. The simulation results show that the generated frequency 12-tupling optical mm-wave has high purity with an optical sideband suppression ratio (OSSR) of 25.1 dB and radio frequency spurious suppression ratio (RFSSR) of 19.1 dB. Theoretically obtained results are in good agreement with the simulation results. Furthermore, taking into consideration the practical implementation, the influence of non-ideal parameters on the OSSR and RFSSR are analyzed.

Integrated Wavelength-Tuned Optical mm-Wave Beamformer With Doubled Delay Resolution

Integrated optical true time delay lines attract lots of attention for optically controlled mm-wave beam steering due to its low-loss/broadband performance and stable/compact system architecture. However, for remotely-controlled networks, the techniques that require local-site actively-tuned elements would make the network control more complicated. A passive design using wavelength-tuning is regarded as a promising candidate. In this paper, an integrated wavelength-tuned optical mm-wave beamformer with doubled delay resolution is proposed and demonstrated in a generic InP platform. A bidirectional looped-back arrayed waveguide grating (AWG) module acts as the stepwise tunable delay unit. By introducing an extra AWG router for delay mode (positive/negative) selection and a bidirectional optical interface, a pure λ-tuned, resolution-doubled optical delay network is realized without using any active component (e.g. heaters, current injection) at the local site. This photonic passive design is more beneficial to the remotely-controlled mm-wave beam steering system. Furthermore, the AWG router potentially allows multi-port wavelength switching to support the scaling-up of the network. The fabrication-caused delay error of <; 1.1 ps is experimentally verified on-chip. A further proof-of-concept 38-GHz fiber-wireless beam steering system with a 186° angular steering is experimentally demonstrated using QAM-4 modulation. Accurate mm-wave phase shifts originated from the proposed optical beamformer are obtained, which proves the effectiveness of the tunable integrated beamformer.

Improved filterless sextupling optical MM-wave generation and RoF transmission

A novel scheme is proposed and demonstrated for frequency sextupling optical millimeter-wave generation based on dual-parallel Mach-Zehnder Modulator (MZM) without optical filtering. The sextupling optical mm-wave with data only carried by one sideband is generated, theoretical analysis and simulation verification are provided for the frequency multiplication scheme. Furthermore, a 2.5 Gb/s data transmission performances are evaluated, the data signal could be transmitted 160 Km with the proposed scheme at BER = 10−9, while the distribution distance is less than 30 Km with the traditional scheme to obtain identical BER.

Centralized Fiber-Distributed Data Communication and Sensing Convergence System Based on Microwave Photonics

A unified data communication and radar sensing system towards millimeter-wave (mm-wave) applications with extended coverage is proposed and experimentally demonstrated. In the unified system, the transmission and reception of mm-wave signals are implemented by microwave photonics technologies, and the orthogonal frequency division multiplexing (OFDM) signal is employed for communications and radar sensing simultaneously. The superheterodyne optical carrier suppression (HeteroOCS) is used to up-convert the intermediate frequency (IF) OFDM signal to the mm-wave band in the central office (CO). The optical mm-wave signal is transmitted to the remote antenna units (RAUs) via optical fibers. The echo signal is received by the RAU which is remotely connected to the CO by an analog photonic link based on a polarization modulator (PolM). In the transmitter and receiver links, the chromatic dispersion of optical fibers is overcome by the HeteroOCS and the PolM, respectively. The baseband units (BBU) centralized in the CO is used to process the radar sensing signal. A pre-delayed trigger signal is proposed to overcome the fiber length limitation. A proof-of-concept experiment is performed. Two targets with distances of 1.64 m and 3.40 m are successfully detected separately. The communication function of the system is also verified. 1 m wireless transmission of 1.56 Gb/s data rate is achieved below the forward error correction limit.

Photonics-Assisted Technologies for Extreme Broadband 5G Wireless Communications

We summarize the enabling technologies for photonics-assisted broadband millimeter-wave (mm-wave) communication, which is a promising candidate for the enhanced mobile broadband (eMBB) communications, one of the three main typical application scenarios of 5G wireless networks. These enabling technologies, mainly focusing on the improvement of the system structure, include broadband mm-wave signal generation with simple and cost-effective schemes, multiple-input multiple-output architecture with polarization-multiplexing optical mm-wave signal, advanced multilevel modulation, optical or electrical multicarrier modulation, antenna polarization multiplexing and the employment of the high-gain mm-wave antenna, multi-band multiplexing, and broadband mm-wave signal detection. We also review the advanced digital signal processing (DSP) for heterodyne coherent detection, which can be applied into the photonics-assisted mm-wave communication systems, to further enhance the system performance for a given system structure and certain available devices. Based on these enabling technologies and advanced DSP, we have realized over 1 Tb/s wireless signal transmission at D-band and over 2.5 km wireless transmission with a bit rate up to 54 Gb/s at W-band. Our work verifies the photonics-assisted broadband mm-wave communication can meet the high-data-rate demand of eMBB.

Photonic generation of high-purity 60 GHz millimeter-wave signal requiring only 10 GHz radio frequency local oscillator

A novel approach to generate 60 GHz millimeter-wave from a 10 GHz radio frequency signal using an integrated nested DD-MZM without optical filter is proposed and demonstrated. The simulation results show that the generated frequency sextupling optical mm-wave has high purity with an OSSR exceeding 29 dB and a RFSSR of 25 dB, which is consistent with the theoretical analysis. Besides, a RoF link model is established to investigate the transmission performance. The eye diagram keeps clear even when the optical mm-wave is transmitted over 60 km and the power penalty is about 0.4 dB after fiber transmission of 50 km.

A Novel Radio-Over-Fiber System Based on Carrier Suppressed Frequency Eightfold Millimeter Wave Generation

We propose a novel and simple scheme for photonic frequency eightfold millimeter wave (mm-wave) generation with optical carrier suppression based on only one single-drive Mach–Zehnder modulator (MZM). According to our theoretical analysis and experimental demonstration, by adopting designed direct current bias voltage of MZM and the amplitude voltage of the radio frequency (RF) drive signal, two fourth-order optical subcarriers are generated via a single-drive MZM. Furthermore, the corresponding optical central carrier and undesired sidebands are suppressed simultaneously. Based on our proposed scheme, the generation of 72-GHz optical mm-wave by an RF signal of 9 GHz without any optical filtering is experimentally demonstrated. The radio-over-fiber system with 3.5-Gb/s OOK downstream link based on this generated 72-GHz mm-wave is also experimentally demonstrated. As we know, it is the first time to realize frequency eightfold mm-wave signal generation with simultaneous carrier suppression by using only one single-drive MZM in experiment.

Frequency16-tupled optical millimeter wave generation using dual cascaded MZMs and 2.5 Gbps RoF transmission

Optical Millimeter Wave (MM-Wave) generation with the highest frequency multiplication factor is one of the most promising techniques which can eliminate the need of high frequency local oscillator at the central station. In this paper, a filterless frequency16-tupled optical MM-Wave is generated using dual stage cascaded Lithium Niobate Mach-Zehnder modulators (LN-MZM). By properly adjusting the MZM biasing parameters and phase of the RF signal, eighth order optical sidebands only are generated which can result in 16-tupled millimeter wave at the photo detector. Optical sideband suppression ratio (OSSR) of 61dB and radio frequency spurious sideband suppression ratio (RFSSR) of 48dB are achieved in this method. As no filtering is involved in the generation, tunability over entire MM-Wave frequency band can easily be achieved. Impact of various non-ideal parameters such as RF phase, Extinction Ratio(ER), optical input power imbalance between the arms on the optical and RF sidebands is analyzed. The transmission performance of this scheme is evaluated by modulating 2.5 Gbps data and transmitting the same over10km, 20km and 25km Radio over Fiber (RoF) links. Further, the impact of the laser linewidth on the transmission performances is also analysed and presented.

Four-amplitude shift keying-single sideband millimeter-wave signal generation with frequency sextupling based on optical phase modulation

We have proposed and demonstrated a scheme to generate a frequency-sextupling amplitude shift keying (ASK)-single sideband optical millimeter (mm)-wave signal with high dispersion tolerance based on an optical phase modulator (PM) by ably using the−4th-order and +2nd-order sidebands of the optical modulation. The ASK radio frequency signal, superposed by a local oscillator with the same frequency, modulates the lightwave via an optical PM with proper voltage amplitudes, the +2nd-order sideband carries the ASK signal with a constant slope while the −4th-order sideband maintains constant amplitude. These two sidebands can be abstracted by a wavelength selective switch to form a dual-tone optical mm-wave with only one tone carrying the ASK signal. As only one tone bears the ASK signal while the other tone is unmodulated, the generated dual-tone optical mm-wave signal has high dispersion tolerance.

Optical generation of millimeter waves through frequency decupling using DP-MZM with RoF transmission

In this paper, an optical generation of millimeter waves (MM-Wave) through frequency decupling using dual parallel Mach–Zehnder Modulator (DP-MZM) with Radio over Fiber transmission is demonstrated. The phases of the RF local oscillator (LO) and the modulation indices of the MZMs are carefully adjusted in order to generate 60 GHz optical MM-Wave signal from a 6 GHz RF LO. The impact of the non-ideal parameters such as modulation index, extinction ratio and the RF LO phases over the optical MM-Wave is analyzed and presented. Further, data transmission performance of the generated millimeter wave over fiber using dual tone and single tone data modulation schemes are also analyzed. The power penalty of 2.5 dB for 20 km with the dual tone modulation and 0.4 dB for 75 km with single tone modulation is achieved.

Distribution of a phase-stabilized 100.02 GHz millimeter-wave signal over a 160 km optical fiber with 4.1 × 10-17 instability.

We report a long-distance phase-stabilized millimeter-wave distribution over optical fibers, where the optical-link-induced phase noise is compensated with a high-precision photonic-generated millimeter-wave (mm-wave) voltage-controlled oscillator (VCO). The mm-wave VCO is realized based on pre-filtering and re-modulating optical spectral lines of an optical frequency comb (OFC). By adjusting the frequency spacing of the optical spectral lines extracted from the OFC, the phase error of the transmitted optical mm-wave signal can be compensated precisely. Using the mm-wave VCO, we demonstrate a distribution of a 100.02 GHz signal over spooled optical fibers and the fractional frequency instability of the system at different transmission distances is exhibited. The residual phase noise of the remote mm-wave signal after being transferred through a 160-km fiber link is measured to be -59 dBc/Hz at 1 Hz frequency offset from the carrier, and the RMS timing jitter in the frequency range from 0.01 Hz to 1 MHz reaches 62 fs. The long-term fractional frequency instability of 4.1 × 10-17 at 10000 s averaging time is achieved, and the maximum timing drift is within 0.93 ps (peak to peak) during 4 hours.

Dual-Tone QPSK Optical Millimeter-Wave Signal Generation by Frequency Nonupling the RF Signal Without Phase Precoding

A novel dual-tone quadrature phase-shift keying (QPSK) optical millimeter (mm)-wave signal generation by frequency nonupling the radio-frequency QPSK signal via an optical phase modulator (PM) without phase precoding is proposed. To enable the generated optical mm-wave signal to resist the fiber chromatic dispersion degradation, the unmodulated −fourth-order and the QPSK-modulated +fifth-order sidebands are abstracted from the generated sidebands, considering the phase periodicity of a QPSK signal. The opto-electrical conversion efficiency is maximized by optimizing the modulation index of PM. An optical mm-wave generator along with a radio-over-fiber link is built, and the eye diagrams, constellations, and BER curves demonstrate that the frequency nonupling dual-tone QPSK optical mm-wave signal performs well. The simulated results agree well with the theoretical prediction.

Full-duplex radio over fiber link with colorless source-free base station based on single sideband optical mm-wave signal with polarization rotated optical carrier

Abstract A full-duplex radio-over fiber (RoF) link scheme based on single sideband (SSB) optical millimeter (mm)-wave signal with polarization-rotated optical carrier is proposed to realize the source-free colorless base station (BS), in which a polarization beam splitter (PBS) is used to abstract part of the optical carrier for conveying the uplink data. Since the optical carrier for the uplink does not bear the downlink signal, no cross-talk from the downlink contaminates the uplink signal. The simulation results demonstrate that both down- and up-links maintain good performance. The mm-wave signal distribution network based on the proposed full duplex fiber link scheme can use the uniform source-free colorless BSs, which makes the access system very simpler.

BPSK optical mm-wave signal generation by septupling frequency via a single optical phase modulator

In this paper, we have proposed a novel and simple scheme to generate the BPSK optical millimeter wave (MMW) signal with frequency septupling by using an optical phase modulator (PM) and a wavelength selective switch (WSS). In this scheme, the PM is driven by a radio frequency (RF) BPSK signal at the optimized modulation index of 4.89 to assure the 4th and 3rd-order sidebands have equal amplitudes. An wavelength selective switch (WSS) is used to abstract the −4th and +3rd-order sidebands from the spectrum generated by RF BPSK signal modulating the lightwave to form the BPSK optical MMW signal with frequency septupling the driving RF signal. In these two tones, only the +3rd-order sideband bears the BPSK signal while the −4th-order sideband is unmodulated since the phase information is canceled by the even times multiplication of the phase of BPSK signal. The MMW signal can avoid the pulse walk-off effect and the amplitude fading effect caused by the fiber chromatic dispersion. By adjusting the modulation index to assure the two tones have equal amplitude, the generated optical MMW signal has the maximal opto-electrical conversion efficiency and good transmission performance.

Optical Generation of 12-Tupling Millimeter-Wave Signal without Optical Filtering

AbstractA novel scheme is proposed for frequency 12-tupling millimeter-wave generation based on two cascaded dual-parallel Mach–Zehnder modulators (DP-MZM) without optical filtering. The impact of imperfect extinction ratio (EXT) of each sub-MZM on optical sideband suppression ratio (OSSR) and RF spurious suppression ratio (RSSR) is investigated. Theoretical and simulation results show that the proposed scheme is feasible and system performance is insensitive to EXT when EXT is not less than 29 dB. Optical mm-wave with 26.4 dB OSSR and 20.3 dB RSSR can be obtained when the DPMZM is consisted of two sub-MZMs with 30 dB EXT. Furthermore, the system performance improvement through sub-MZM modulation index enhancement is analyzed.