A simplified dual-output and filter-free photonic-assisted single sideband mixer is proposed, which uses a 2×2 optical coupler (OC) instead of a 2×4 optical hybrid to process optical modulation signals. Using two dual-parallel Mach–Zehnder modulators (DPMZMs) in parallel to achieve carrier-suppressed single-sideband modulation of the radio frequency (RF) signal and carrier-suppressed double-sideband (CS-DSB) modulation of the local oscillator (LO) signal at DPMZM1 and CS-DSB modulation of the LO signal only at DPMZM2, with a 2×2 OC coupling, the down- and up-converted RF signals can be obtained simultaneously and output separately. Because the −1st-order or +1st-order optical sidebands of the LO signal can be canceled out via a 2×2 OC instead of a 2×4 optical hybrid or an optical filter in previous reports, the proposed mixer has a simplified structure and a large bandwidth. Simulation results show that the proposed mixer has mixing spurs suppression of over 30 dB, frequency tunability, and spurious-free dynamic range of over 101.55 dB·Hz2/3. In addition, to evaluate the mixer performance for the broadband signal, 16-quadrature amplitude modulation RF vector signals with tunable center frequency are applied to the mixer, and the measured error vector magnitudes of the down- and up-converted vector signals are <1.53%.
We propose and demonstrate a figure-nine polarization-maintaining fiber laser with a nonlinear amplifying optical loop mirror (NALM) as a fast saturable absorber. The oscillator includes a non reciprocal phase shifter, which can achieve low mode locking threshold and excellent self starting performance. The repetition frequency of the laser reaches 101.8 MHz. The signal-to-noise ratio of a single frequency is approximately 70 dB. The pulse duration of the laser is 80 fs. By employing cut-back techniques to accurately compensate for intracavity dispersion, we are able to achieve a flat and broad spectral output with a full width at half maximum (FWHM) of better than 62.5 nm at the center wavelength of 1584.4 nm. Thisrepresentsthe broad FWHM spectrum observed in all polarization-maintaining fiber NALM lasers.
A simple scheme to generate a dual-band complementary linearly chirped microwave waveform using a Mach–Zehnder modulator (MZM) paralleled with a phase modulator (PM) is proposed. In the scheme, a five-line optical frequency comb, generated by MZM, is combined with a phase modulated optical chirp waveform by a baseband parabolic signal or a single-chirp signal as two beams with inverse relative phases via a 2 × 2 optical coupler. After balanced detection with heterodyne beating, the dual-band complementary linearly chirped microwave waveform is generated for the two driving cases, and they demonstrate different enhanced performances. The dual-band complementary linearly chirped microwave waveforms with center frequency of 20 and 40 GHz are generated simultaneously for both cases by simulation. The generated two complementary linearly chirped waveforms with a baseband parabolic driving signal have a larger bandwidth of 7.6 GHz, corresponding to larger pulse compression ratios (PCRs) of 1462.86 and 1365.33, which could effectively improve the range Doppler resolution in modern radar systems, although their peak-to-sidelobe ratios (PSRs) are only 12.98 and 12.97 dB. Although for the case with a single-chirp driving signal, the PSRs of the two waveforms with a bandwidth of 4 GHz are higher, 13.66 and 13.67 dB, respectively, but with the PCRs of only 787.69 and 758.52, which is of practical significance for radar detection in weak targets and multitargets.
A photonic method for simultaneously measuring the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signal is proposed and verified by simulation. The echo signals are applied to a dual-parallel dual-drive Mach–Zehnder modulator for modulating the lightwave with carrier-suppressed double-sideband pattern. The lightwave carrying the echo signals is coupled with the lightwave carrying the local oscillator signal, and their upper and lower sidebands are separated by an interleaver. Then, the optical signals are converted into low-frequency electrical signals by two identical photodiodes, and the parameters of DFS and AOA are obtained by processing two low-frequency photocurrents. In the simulation, the measurements of the DFSs in the range of ± 1 MHz with errors < ± 9 × 10 − 4 Hz and the AOAs from 1.82 deg to 90 deg with errors <0.9 deg are realized, and the orientation of DFS can also be distinguished by comparing the phase difference of two electrical signals.
KEYWORDS: Extremely high frequency, Signal generators, Picosecond phenomena, Electronic filtering, Radio optics, Modulation, Optical engineering, Phase shifts, Modulators, Signal detection
A simple scheme is proposed for generating frequency 16-tupling millimeter-wave (MMW) signal based on cascaded Mach–Zehnder modulators (MZMs) and an optical phase shifter (PS) without optical filter. Theoretical analysis is given to generate the high-quality 16-tupling MMW signal by eliminating the undesired optical carrier and sidebands. Simulations show that the generated 16-tupling optical MMW signal has the optical sideband suppression ratio higher than 29.85 dB and radio frequency (RF) spurious sideband suppression ratio higher than 23.9 dB. The impact of non-ideal modulation index, extinction ratio, and phase difference of optical PS- and RF-driven signal applied to the cascaded MZMs are discussed and analyzed. After different lengths of fiber transmission, the generated optical MMW signal shows good performance. Furthermore, the influence of different laser linewidths on the transmission performance of the generated MMW signal is also performed and analyzed.
We have proposed an 8 phase-shift-keying (PSK) optical millimeter-wave (MMW) signal generation scheme with frequency quintupling enabled by an electro-optical phase modulator (PM) and a wavelength selective switch. In this scheme, the radio frequency (RF) carrier with 8PSK signal is modulated on the lightwave via the PM with simple precoding but constant Euclidean distance, and is recovered to the original 8PSK signal with the frequency-quintupling RF carrier based on the phase periodicity of an 8PSK signal. By optimizing the voltage amplitude of the 8PSK RF driving signal, the generated frequency-quintupled 8PSK MMW signal is maximized at a given laser launch power. A radio over fiber simulation link is built to demonstrate the theoretical analysis. The simulated constellations and bit-error-rate curves show that the frequency-quintupling 8PSK MMW signal has good transmission performance. The simulation results agree well with our theoretical prediction.
KEYWORDS: Extremely high frequency, Polarization, Signal detection, Microwave radiation, Analog electronics, Hybrid fiber radio, Radio optics, Modulation, Signal attenuation, Network architectures
Full-duplex mobile fronthaul (MFH) architecture with a colorless remote radio unit (RRU) and further RRU (F-RRU) based on radio over fiber technology (F-RRU) is proposed. Such MFH architecture can carry out low- and high-frequency hybrid networking for common seamless wide coverage and high data rate requirements in hotspot areas. Optical millimeter-wave signal is abstracted by an interleaver in the RRU and then is transmitted to multiple F-RRUs. The polarization multiplexing technology and power splitters employed make the RRU and F-RRU free from the laser sources, as the uplink optical carrier is abstracted from the downlink. Simulations are conducted to demonstrate the reliability of the proposed MFH architecture, and results show that the radio signals maintain strong performance after standard single mode fiber transmission.
A microwave photonic phase shifter that can realize a full 360-deg phase shift is presented. In the scheme, an optical polarization modulator is used to generate a single-sideband optical microwave signal with two orthogonally polarized tones, then a polarization sensitive electro-optical phase modulator is used to introduce the relative phase shifts between the two orthogonally polarized tones to realize the desired phase shift for the microwave signal in the photocurrent, and the phase shift of the microwave signal increases linearly with the DC driving voltage while it keeps a constant amplitude. The simulation results show that continuous phase shift with tuning range from −180 deg to +180 deg is realized for the microwave with the frequency from 4 to 38 GHz and the amplitude variation of the phase-shifted microwave signal is <1 dB.
This paper proposes an original scheme to generate the photonic dual-tone optical millimeter wave (MMW) carrying the 16-star quadrature-amplitude-modulation (QAM) signal via an optical phase modulator (PM) and an interleaver with adaptive photonic frequency-nonupling without phase precoding. To enable the generated optical vector MMW signal to resist the power fading effect caused by the fiber chromatic dispersion, the modulated −5th- and +4th-order sidebands are selected from the output of the PM, which is driven by the precoding 16-star QAM signal. The modulation index of the PM is optimized to gain the maximum opto-electrical conversion efficiency. A radio over fiber link is built by simulation, and the simulated constellations and the bit error rate graph demonstrate that the frequency-nonupling 16-star QAM MMW signal has good transmission performance. The simulation results agree well with our theoretical results.
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.
A full-duplex fiber-wireless link with a uniform single sideband differential quaternary phase-shift keying optical millimeter-wave signal is proposed to provide wired or 40-GHz band wireless access alternatively. The uniform optical millimeter-wave signal that supports services for wired or wireless users is produced via an LiNbO3 Mach-Zehnder modulator. After being transmitted to the hybrid optical network unit (HONU), it can be demodulated in different patterns on the demand of the user terminals for wired or wireless access. Simultaneously, part of the blank optical carrier abstracted from it is reused as the uplink optical carrier, so the HONU is free from the laser source, and thus, the complexity and cost of the system are reduced. Moreover, since the two tones of the dual-tone optical millimeter wave come from the same source, they maintain high coherency even after being transmitted over fiber. Additionally, the downlink data are carried by one tone of the dual-tone optical millimeter wave, so the downlink optical millimeter-wave signal suffers little from the fiber chromatic dispersion and laser phase noise. The theoretical analysis and simulation results show that our proposed full-duplex link for alternative wired and wireless access maintains good performance even when the transmission link with standard single mode fiber is extended to 30 km.
KEYWORDS: Quadrature amplitude modulation, Radio over Fiber, Modulation, Eye, Modulators, Radio optics, Signal attenuation, Signal detection, Oscillators, Telecommunications
This paper has proposed a radio-over-fiber (RoF) link carrying two 10Gb/s 16-QAM mm- wave signal streams. Since
the dual-tone 40GHz optical mm-wave are generated by frequency quadrupling via a LiNbO3 modulator and the two
QAM signal streams are modulated on each tone by single sideband (SSB) modulation, the frequency requirements of
the RF local oscillators and the optical modulators are reduced to 10GHz, which means a cost-effective RoF implement.
Since the mm-wave signals in the photocurrent are generated by beating in a SSB pattern, the optical mm-wave signal
has great tolerance to the fiber dispersion. Moreover, one optical mm-wave carrier carries two16-QAM 10Gb/s data
streams, our link scheme has a higher bandwidth efficiency. The simulation results show that both the constellation
diagrams and the eye diagrams of the two different QAM streams are well accepted even after 60 km fiber transmission.
A new optical heterodyning method based on the Fiber Bragg Grating Filters is proposed. Because the two optical waves
for heterodyning are filtered from a single laser, this technique can eliminate the phase noise of the usual optical
heterodyning technology and the system performance is improved. With the simulation results, the system's transmission
performance of the optical millimeter wave by the new method is verified.
KEYWORDS: Phase modulation, Radio optics, Dispersion, Modulators, Radio over Fiber, Modulation, Microwave radiation, Signal detection, Eye, Telecommunications
We have theoretically investigated the transmission performance of the optical microwave up-conversion link by using a
phase modulator and a dispersive fiber (standard single mode fiber). A theoretical approach has lead to the evaluation of
the influence of dispersion on the 60 GHz radio-over-fiber (ROF) links. According to our theoretically analysis, the data
signals carried by optical millimeter (mm)-wave after transmission along fiber suffer not only from fading but also from
the time shift of the code edges due to the fiber dispersive, which limits the transmission distance of the optical mm-wave
signals. The simulation results agree well with our theoretical analysis.
KEYWORDS: Radio over Fiber, Signal attenuation, Eye, Networks, Optical amplifiers, Telecommunications, Computer simulations, Picosecond phenomena, Radio optics, Hybrid fiber radio
In this paper, a Radio Over Fiber (ROF) system with bus network topology using optical carrier suppression (OCS)
technique is investigated. The loss along the optic fiber bus link is analyzed theoretically. The transmission distance of
the ROF signal is investigated and simulated. The capacity N of the ROF system, that is, the largest number of BSs the
system can accommodate,is also calculated and simulated. And the simulated results certify our theoretical analysis. Also,
as the result N is not ideal, a method to compensate the loss along the bus link is introduced and again, the capacity and
transmission distance after the compensation is calculated and simulated. The result show that after the use of optical
amplifier, the signal was improved and the capacity was enlarged and the transmission distance was extended.
We theoretically investigate the generation, transmission and detection of the label signal in the optical SCM label switching system and clarify that the degradation of the label signal results from the fiber chromatic dispersion and the incomplete filtering out of the payload carrier. Our theoretical results show that the signal degradation is mainly caused by the fading effect and the expansion of the code edges. We also quantitatively analyze these theoretical results. The deep suppression of the optical carriers at receiver can greatly reduce the fading effect, and the electrical filtering and heterodyne detection techniques can improve the performance of the label signal. The time shift of the code edges leads to the closure of the label codes, which greatly limits the transmission distance as well as the radio frequency to generate the label subcarriers especially for the label with a high bit rate. SSB SCM can not only eliminate the closure of the label codes, but also reduce the fading effect. To our knowledge, this is the first time to develop a detail theoretical model to well explain the experimental results for SCM label switching systems.
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