Photonic generation of high quality frequency-tunable millimeter wave and terahertz wave

A scheme for the photonic generation of frequency-tunable millimeter wave and terahertz wave signals based on a highly flat optical frequency comb is proposed and demonstrated experimentally.The frequency comb is generated using two cascaded phase modulators(PMs)and an electro-absorption modulator(EAM).The frequency comb covers a 440-GHz frequency range,with 40-GHz comb spacing and less than 2-dB amplitude variation.By filtering out two of the comb lines with 50 dB out of the band suppression ratio,high frequency-purity and low phase noise millimeter wave or terahertz wave signals are successfully generated,with frequencies ranging from 40 to 440 GHz.     

Photonic approach to the measurement of time-difference-of-arrival and angle-of-arrival of a microwave signal

We propose and experimentally demonstrate a photonic approach to the measurement of the time-difference-of-arrival (TDOA) and the angle-of-arrival (AOA) of a microwave signal. In the proposed system, the TDOA and the AOA are equivalently converted into a phase shift between two replicas of a microwave signal received at two cascaded modulators. The light wave from a CW laser is externally modulated by the microwave signal at the first modulator, which is biased to suppress the optical carrier, leading to the generation of two first-order sidebands, which are further modulated by the phase-delayed microwave signal at the second modulator. Two optical components at the carrier wavelength are generated. The total power at the carrier wavelength is a function of the phase shift due to the coherent interference between the two components. Thus, by measuring the optical power, the phase shift is estimated. The AOA is calculated from the measured phase shifts. In our experiment, the phase shift of a microwave signal at 18 GHz from -160° to 40° is measured with measurement errors of less than ±2.5°.     

20-GHz optical pulse source based on cascaded electroabsorption modulators

A high-quality low-timing-jitter 20-GHz optical pulse train is generated by using two cascaded sinusoidally driven electroabsorption modulators (EAMs) at very low bias voltage of -0.8 V in conjunction with a tunable distributed feedback (DFB) semiconductor laser. An approximate transform-limited optical pulse,with the pulse width less than 7 ps, the spectral width of 0.3 nm, and the side-mode suppression ratio (SMSR) above 20 dB, is obtained by tuning the optical delay line.     

A simple image-reject mixer based on two parallel phase modulators

A simple photonic microwave image-reject mixer (IRM) using two parallel phase modulators is proposed. First, a photonic microwave mixer with phase shift ability is achieved using two parallel phase modulators (PMs), an optical bandpass filter, three polarization controllers, three polarization beam splitters and two balanced photodetectors. At the output of the mixer, two frequency downconverted signals with tunable frequency difference can be obtained. By adjusting the phase difference as 90° and utilizing an electrical 90° hybrid, the useless components can be eliminated, and the image reject operation is realized. The key advantage of the proposed scheme is the usage of PM, which avoid the DC bias shifting problem and make the system simple and stable. A simulation is performed to verify the proposed scheme, a relative ??90° or 90° phase shift can be obtained between the two output ports of the photonic microwave mixer, at the output of the IRM, 60 dB image-reject ratio is obtained.     

High-repetitive frequency millimeter-wave signal generation using multi-cascaded external modulators based on carrier suppression technique

We have numerically and experimentally investigated how to generate high-repetitive frequency millimeter (mm)-wave using multi-cascaded intensity modulators based on optical carrier suppression (OCS) scheme. We have found the rule how to generate the high-repetitive frequency mm-wave by adjusting the repetitive frequency of the radio-frequency (RF) signals and the phase relation between the RF signals on the intensity modulators. Based on this rule, we have experimentally demonstrated to generate over 80 GHz optical mm-wave.     

Linearization and dispersion tolerable technique for remote access unit in uplink RoF system based on gain-saturated RSOA cascaded EAM

A novel scheme of a remote access unit which is based on an electroabsorption modulator cascaded by a gain-saturated reflective semiconductor optical amplifier is proposed to improve a transmission performance of uplink signal. The cascaded gain-saturated reflective semiconductor optical amplifier plays a role in enhancing linearity of the electroabsorption modulator as well as suppressing dispersion-induced carrier suppression in the uplink transmission using its nonlinear gain property. In the proposed scheme, carrier-to-interference ratio of transmitted 10-GHz band uplink signal was improved by 10.7 dB and the dispersion-induced carrier suppression of 5.65-GHz RF carrier was greatly mitigated by 33.4 dB through the 75.6-km optical link.     

Dispersion Robustness of Millimeter Waves Generated by Up-Conversion Strategies

Abstract

The performance degradation caused by transmission along dispersive single-mode fibers of optically generated millimeter-wave signals using up-conversion is theoretically assessed and validated by numerical simulation. Up-conversion techniques based on optical double sideband, optical single sideband, and optical carrier suppression are considered. The generation of 60 GHz by frequency tripling using the optical single sideband is shown to be particularly tolerant to the fiber dispersion. The practical imbalance of Mach-Zehnder modulators is taken into account for optical carrier suppression modulation, where the finite extinction ratio is found to increase tolerance to fiber dispersion.     

Photon Generation Scheme of 32-Fold Millimeter-Wave Signal Based on Mach-Zehnder Modulator

This paper proposes a 32-tupling frequency millimeter-wave (MMW) filter-free system based on four Mach-Zehnder Modulators (MZM) connected in parallel and cascaded with a simple radio-fiber (RoF) link structure. The four MZMs are all at the maximum transmission point (MATP), and the radio frequency (RF) driving voltage phase difference between MZMs is π /2. The center carrier is suppressed by using an optical attenuator (OATT) and an optical phase shifter (OPS). Two parallel MZMs can generate ±8th order and ±12th order optical sidebands, and the ±4th order optical sidebands can be suppressed by adjusting the modulation index m of the MZM, using cascaded two dual-parallel MZMS(DPMZM) and the phase difference of the RF signal source is π/4 to generate ±16th order optical sidebands. The theoretical analysis and simulation experiments are performed for the scheme proposed in this paper. The results show that the simulated and theoretical values of the optical sideband suppression ratio (OSSR) for ±16th order optical sideband signals are 60.02 and 59.96 dB, respectively, and the simulated and theoretical values of the RF sideband suppression ratio (RFSSR) for the 32-tupling MMW signal are 56.34 and 53.94 dB, respectively.     

无光滤波六倍频微波信号产生的系统设计

基于两个级联偏振调制器,提出了一种高频谱纯度、稳定的六倍频微波信号产生方法。该方法通过适当调整偏振片的偏振方向、射频驱动信号电压和相位,实现无光滤波器条件下、任何波段六倍频微波信号的产生。利用Optisystem平台搭建的仿真系统,以S波段4 GHz信号为例,验证了该设计系统产生的六倍频信号质量,并分析了非理想射频驱动电压和相位对六倍频信号质量的影响,结果表明:该设计系统能产生最大光边带抑制比、射频无杂散抑制比分别为21.3,15.2 dB的六倍频微波信号;且非理想驱动电压和相位差的偏离应控制在理想值5%的范围之内。     

Design of millimeter-wave fiber-wireless downlink with remote local-oscillator delivery by using dual-electrode Mach-Zehnder modulators configured for optical single-sideband modulations

An optical fiber-wireless system operating in millimeter-wave (MMW) bands may include numerous optical remote access points (RAPs) of which the cost is critical to implement such systems in real market. In this paper, we design an optical fiber communication system for MMW optical fiber downlink transmission with remote MMW local-oscillator (LO) delivery for intermediate frequency (IF) fiber uplink transmission. The new design is based on two dual-electrode Mach-Zehnder modulators in parallel both configured for optical single-sideband modulations. By using the proposed design, a conventional RAP can be simplified in structure to reduce the cost. Our numerical results show that, with the proposed design, 1-Gbit/s binary-phase-shift-keying (BPSK) data at a 42-GHz sub-carrier frequency can be transmitted over a 20-km standard single-mode optical fiber followed by a wireless transmission of several kilometers. Moreover, a MMW LO at 37-GHz frequency can be remotely delivered over tens of kilometers of a standard single-mode fiber with acceptable deterioration in the LO phase noise for IF uplink fiber transmission.     

Pulsewidth-tunable CSRZ-DQPSK signal generation using DPMZMs

This letter proposes and experimentally demonstrates a simple scheme for generating 40-GBaud carriersuppressed return-to-zero differential quadrature phase shift keying(CSRZ-DQPSK) modulation signals with tunable pulsewidths using two dual-parallel Mach-Zehnder modulators(DPMZMs).The duty cycle of the generated 40-GHz CSRZ-DQPSK pulse train is continuously tuned from 31% to 62%,with the full-width at half-maximum tuned from 7.8 to 15.5 ps,by electrically tuning the delay between the two sine-clock signals in one of the DPMZMs.Error-free performance is achieved after 320-km transmission.     

Optical frequency comb generation based on three parallel Mach–Zehnder modulators with recirculating frequency shifting loop

We theoretically and numerically study an approach for optical frequency comb (OFC) generation, by utilizing recirculating frequency shifting (RFS) loop based on three parallel Mach–Zehnder modulators (MZMs). Our results show that three parallel MZMs can generate a single-side-band (SSB) signal with 36 dB optical carrier suppression (OCS) ratio. Furthermore, the 60-tone OFC signal with 30 dB side-mode suppression ratio (SMSR) and 4 dB maximum power fluctuation is achieved, and 20 of the OFC signal possess the power fluctuation of less than 1 dB. Our approach provides a novel way of generating OFC with excellent SMSR and good power fluctuation.     

Wideband optical phase modulator half-wave voltage measurement technique based on phase modulation optical link

We measured the half-wave voltage V_π of LiNbO₃ phase modulators in the broadband frequency range by analyzing the gain of phase modulation interference demodulation optical link. This is a new high practical value measurement method for half-wave voltage of LiNbO₃ phase modulators in wideband frequency range, and can accurately predict the nonlinear frequency characteristics of phase modulation optical link.     

Femtosecond-laser-based synthesis of ultrastable microwave signals from optical frequency references

We use femtosecond laser frequency combs to convert optical frequency references to the microwave domain, where we demonstrate the synthesis of 10-GHz signals having a fractional frequency instability of < or =3.5 x 10(-15) at a 1-s averaging time, limited by the optical reference. The residual instability and phase noise of the femtosecond-laser-based frequency synthesizers are 6.5 x 10(-16) at 1 s and -98 dBc/Hz at a 1-Hz offset from the 10-GHz carrier, respectively. The timing jitter of the microwave signals is 3.3 fs.     

Microwave Photonic Up- and Down-Converter with Tunable Phase Shift Based on an Integrated Dual-Polarization Dual-Parallel Mach–Zehnder Modulator without Optically Filtering

ABSTRACT

In this paper, we propose and numerically simulate a microwave photonic phase-tunable frequency converter (MPPTFC) without optically filtering to realize both frequency up- and down-conversion and a full 360° phase-shift for the microwave signal based on an integrated dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In the proposed scheme, both microwave RF signal and frequency-tunable local oscillator (LO) are modulated on the lightwave by single-sideband carrier suppression (SSB-CS) modulation to generate optical orthogonally polarized optical tones carrying RF signal with up- or down-converted frequency. A PolM that can support lightwave modulation with opposite modulation indices in transverse electric (TE) and transverse magnetic (TM) modes is used to introduce a phase difference between the two modes. Then the orthogonally polarized optical tones are aligned into a single polarized state by a polarizer (Pol) and detected by a photodiode (PD), a frequency-converted and phase-shifted microwave signal can be obtained. Simulation results demonstrate that the proposed MPPTFC can up-/down-convert the microwave signal with a tunable frequency shift of LO frequency and realize a 360° continuously tunable phase shift via the DC bias voltage of the PolM simultaneously.     

High carrier suppression double sideband modulation using polarization state rotation filter and optical external modulator

We propose a high carrier suppression double sideband modulation technique using a Mach-Zehnder modulator (MZM) and an integrated polarization state rotation filter (PSRF), which is designed to improve the carrier suppression ratio. With the functions of MZM and PSRF, about 30 dB carrier suppression ratio relative to first-order sidebands is demonstrated. Moreover, we demonstrate the optical generation of microwave/millimeter-wave signals by beating the carrier suppressed double sideband (DSB-SC) lightwave signals. The experimental results show that the improvement of carrier suppression ratio with PSRF can effectively cancel the modulating RF frequency component. A tunable and high purity microwave signal, which is limited by the bandwidth of MZM and photodetector (PD), is obtained, and it does not suffer from obvious phase noise degradation with 25 km transmission.     

Across-critical-band processing of amplitude-modulated tones

Two experiments using two-tone sinusoidally amplitude-modulated stimuli were conducted to assess cross-channel effects in processing low-frequency amplitude modulation. In experiment I, listeners were asked to discriminate between two sets of two-tone amplitude-modulated complexes. In one set, the modulation phase of the lower frequency carrier tone was different from that of the upper frequency carrier tone. In the other stimulus set, both amplitude-modulated carriers had the same modulator phase. The amount of phase shift required to discriminate between the two stimulus sets was determined as a function of the separation between the two carriers, modulation depth, and modulation frequency. Listeners could discriminate a 50 degrees-60 degrees phase shift between the modulated envelopes for tones separated by more than a critical band. In experiment II, the modulation depth required to detect modulation of a probe carrier was measured in the presence of an amplitude-modulated masker. The threshold for detecting probe modulation was determined as a function of the separation between the masker and probe carriers, the phase difference between the masker and probe modulators, and masker modulation depth (in all conditions, the rate of probe and masker modulation was 10 Hz). The threshold for detecting probe modulation was raised substantially when the masker tone was also modulated. The results are consistent with theories suggesting that amplitude modulation helps form auditory objects from complex sound fields.     

Gigabit-converged wired and wireless networks for simultaneous multi-services transmission

A novel architecture of converged radio-over-fiber(RoF) and wavelength division multiplexed passive optical network(WDM-PON) system,namely RoF-WDM-PON,is demonstrated.20-GHz 1-Gb/s radio frequency(RF) signals and 1-Gb/s baseband(BB) signals are simultaneously generated and transmitted using optical carrier suppression(OCS) modulation techniques.The proposed scheme is compatible with the conventional RoF and PON system.25-km single-mode fiber(SMF) transmission is successfully achieved.     

Hybrid silicon modulators Invited Paper

A number of active elements have been demonstrated using the hybrid silicon evanescent platform, includ- ing lasers, amplifiers, and detectors. In this letter, two types of hybrid silicon modulators, fulfilling the building blocks in optical communication on this platform, are presented. A hybrid silicon electroabsorp-tion modulator, suitable for high speed interconnects, with 10-dB extinction ratio at -5 V and 16-GHz modulation bandwidth is demonstrated. In addition, a hybrid silicon Mach-Zehnder modulator utilizing carrier depletion in multiple quantum wells is proved with 2 V.mm voltage-length product, 150-nm optical bandwidth, and a large signal modulation up to 10 Gb/s.     

Synchronized clock multiplication through optical subharmonic injection locking of an optoelectronic oscillator

We propose a remote synchronization scheme based on optoelectronic oscillators (OEO) and external modulators. Synchronized clock multiplication is demonstrated by using optical subharmonic injection locking technique. A 10-GHz slave OEO was successfully synchronized by 2.5-GHz/Gbps injecting optical clock pulse train, return-to-zero (RZ) signal and non-return-to-zero (NRZ) signal, respectively. The synchronization scheme is advantageous since it does not require strong nonlinearity presented in the master signal, and is capable of generating electrical and optical clock with small add-on phase noise.