Order Sidebands Research Articles

Filterless radio-over-fiber system that generates 80 and 160 GHz millimeter waves based on two MZMs.

In this paper, we propose a radio-over-fiber system with no filters and generate 80 and 160 GHz millimeter (mm) waves via two Mach-Zehnder modulators (MZMs). The two MZMs, biased at the maximum transmission point, are used to suppress odd-order sidebands. By controlling the phase difference between the RF driving signal of the two MZMs, the $\pm({4}{n - 2})$-order is canceled. By adjusting the optical attenuator and phase shifter, the 0-order sideband is canceled, so only the $\pm 4{n}$-order sidebands are left. The simulation results show that using a 10 GHz RF signal to drive the MZMs, we obtain an 80 GHz mm wave signal with a 36.59 dB optical sideband suppression ratio (OSSR), a 30.27 dB radio frequency sideband suppression ratio (RFSSR), and a 160 GHz mm wave signal with a 30.34 dB OSSR and 24.77 dB RFSSR. The results are consistent with the theoretical analysis. Because no optical filter is employed and only two MZMs are used, the system exhibits a simple structure, good performance and is low cost.

Efficient Brillouin Optomechanical Interaction Assisted by Piezomechanics on the SOI Platform

A hybrid silicon/aluminum nitride waveguide on the silicon-on-insulator platform is proposed to achieve an efficient Brillouin optomechanical interaction. Both intra-optical-mode and inter-optical-mode Brillouin scattering can be achieved. The novel arrangement of symmetric electrodes provides out-of-plane electric fields for piezoelectric materials and the possibility of suspended waveguides and cavities. The piezomechanical interaction coupling strength and the Brillouin optomechanical interaction coupling strength are numerically calculated. The simulation results show that near-unity internal conversion efficiency from the microwave domain to the optical domain can be achieved. Relatively low microwave power can be used to produced up to 5 order sidebands acousto-optical modulation. The proposed scheme paves the way for efficient classical and quantum application in integrated silicon photonics.

All-optical pulse peak power stabilization and its impact in phase-OTDR vibration detection

We present an all-optical technique for the stabilization of laser power using the nonlinear Kerr effect and experimentally demonstrate improvement of vibration recovery in direct-detection phase-sensitive optical time domain reflectometry (Φ-OTDR). A pulsed or continuous wave optical signal impressed with a sinusoidal modulation generates sidebands while experiencing self-phase modulation in a nonlinear medium which can be utilized to stabilize the peak power of the signal. By adjusting the peak power at the entrance of the Kerr medium, the signal created at the first order sideband exhibits reduced peak power fluctuations and can be extracted using a band-pass filter. Experimental results show that the generated pulses with stabilized peak power improve vibration detection in a Φ-OTDR with a direct-detection scheme. This technique can be combined with other performance enhancement techniques to allow for the detection of weak signals, and reduces the need of an optoelectronic-based power control loop on a fiber laser.

Enhanced Kelly sidebands of mode-locking fiber lasers for efficient terahertz signal generation

Intensity enhancement of the ±1 order Kelly sidebands of soliton mode-locking fiber laser is investigated to achieve efficient terahertz (THz) signal generation. A model is presented for studying on the ±1 order Kelly sidebands. Two key factors are found and their relationships with the intensity of the ±1 order Kelly sidebands are confirmed and quantified. A technical method which is introducing a highly nonlinear fiber (HNLF) in laser cavity is proposed for enhancing the sideband intensity. Consequently, intensity difference of 10 dB between the ±1 order sidebands and the central soliton in optical spectrum has been achieved. Using the data of the optical spectrum including the strong ±1 order sidebands, frequency spectrum of generated THz signals is calculated. The intensity of the required THz signal is increased significantly at 30 times larger than that without using the HNLF-based method.

Nonlinear resolution enhancement of an FBG based temperature sensor using the Kerr effect.

We demonstrate the enhancement of the resolution of a fiber optical sensor using all-optical signal processing. By sweeping the frequency of a tunable laser across a fiber Bragg grating, a signal corresponding to the reflection spectrum of the FBG is generated. If another laser with fixed power and frequency is launched into a highly nonlinear fiber along with the FBG-shaped signal, the Kerr effect gives rise to a number of frequency sidebands, where the power in each of the sidebands is proportional an integer exponent of the signal and pump powers. By filtering out particular sidebands, this potentiation effect reduces the width of the FBG-shaped signal, making shifts in its central wavelength easier to distinguish. We report a maximum resolution enhancement factor of 3.35 obtained by extracting the n = -4 order sideband, and apply resolution enhancement to improve the resolution of an FBG based temperature sensor. The method described in this paper can be applied to existing fiber based sensors and optical systems to enhance their resolution.

Filterless Radio-Over-Fiber System to Generate 40 and 80 GHz Millimeter-Wave

A filterless radio-over-fiber system to generate 40 and 80 GHz millimeter-wave was proposed by using two Mach-Zehnder modulators (MZMs). The two MZMs are biased at the maximum transmission point to suppress odd-order sidebands. By adjusting the modulation index of the two MZMs and the radio frequency drive signals, only the two 2nd and 4th order sidebands are retained. Subsequently, by adjusting the polarization direction to generate 40 and 80GHz frequency millimeter-wave signal. Detailed theoretical analyses and simulations are provided. The simulation results show that the 40 GHz millimeter-wave signal was obtained with 30 dB optical sideband suppression ratio (OSSR) and the 80 GHz millimeter-wave signal was obtained with 25 dB OSSR. Thanks to the higher OSSR, the generated MMW signal is not greatly affected by power fluctuations during transmission or frequency tuning. Furthermore, the effects of the modulation index, bias voltage and extinction ratios deviate from the ideal value on millimeter-wave performance are also analyzed and verified, showing the proposed scheme is relatively flexible from the limitation of filter fixed bandwidth and economical.

A new method for terahertz signal generation using Kelly sidebands of mode-locking fiber laser

A new method for generation of terahertz (THz) signal by using the ±1 order Kelly sidebands of mode-locking (ML) fiber laser is proposed. A physical model is built up to characterize the sidebands. In experiment, the ±1 order Kelly sidebands with large and small spacing were obtained from two lab-made ML fiber lasers operating at 1550 nm and 1064 nm wavebands, respectively. By photomixing the ±1 order sidebands, experimental result showed that desired THz signals were generated at frequencies of 0.914THz and 0.187THz from the two lasers. It is found that the total dispersion and filtering bandwidth of the grating used in the laser cavity play significant roles in determining spacing and intensity of the ±1 order Kelly sidebands, which correspond to frequency and intensity of generated THz signals. Besides, bandwidth and stability of the ±1 order Kelly sidebands are investigated both theoretically and experimentally for their influence on the THz signal generation.

Time-Stretched Femtosecond Lidar Using Microwave Photonic Signal Processing

A real-time ranging lidar with 0.1 Mega Hertz update rate and few-micrometer resolution incorporating dispersive Fourier transformation and instantaneous microwave frequency measurement is proposed and demonstrated. As time-stretched femtosecond laser pulse passing through an all-fiber Mach-Zehnder Interferometer, where the detection light beam is inserted into the optical path of one arm, the displacement is encoded to the frequency variation of the temporal interferogram. To deal with the challenges in storage and real-time processing of the microwave pulse generated on a photodetector, we turn to all-optical signal processing. A carrier wave is modulated by the time-domain interferogram using an intensity modulator. After that, the frequency variation of the microwave pulse is uploaded to the first order sidebands. Finally, the frequency shift of the sidebands is turned into transmission change through a symmetric-locked frequency discriminator. In experiment, A real-time ranging system with adjustable dynamic range and detection sensitivity is realized by incorporating a programmable optical filter. Standard deviation of 7.64 {\mu}m, overall mean error of 19.10 {\mu}m over 15 mm detection range and standard deviation of 37.73 {\mu}m, overall mean error of 36.63 {\mu}m over 45 mm detection range are obtained respectively.

Full-duplex WDM-RoF system based on OFC with dual frequency microwave signal generation and wavelength reuse

Abstract A novel full-duplex wavelength division multiplexing radio-over-fiber (WDM-RoF) system based on optical frequency comb (OFC), which can generate dual frequency microwave signal simultaneously and realize wavelength reuse for uplink transmission, is proposed. In this proposal, OFC, which serves as the optical carriers of the WDM-RoF network, is performed by cascading two electro-absorption modulators (EAMs) and a frequency modulator (FM). The optical carriers are modulated by the radio frequency (RF) signal in LiNbO3 Mach-Zehnder modulator (LN-MZM) to produce multiple optical single sidebands (OSSB). The multiple OSSB signals are divided into multiple individual channels by AWG, and each channel contains two optical carriers and two corresponding +1 order sidebands. The first optical carrier of each channel is reflected by fiber bragg grating (FBG) and reused to provide the optical source for the uplink transmission in the base station (BS), which simplify the configuration of base station. Dual-frequency microwave signals are generated in the downlink by beating the remaining second optical carrier and two +1 order sidebands. In the simulation, 6 WDM channels each carrying 2.5 Gb/s downlink data have been up-converted to 15 GHz and 25 GHz microwave signals simultaneously, and 6 WDM channels each carrying 2.5 Gb/s uplink baseband data are sent to the central station. Both downlink and uplink transmission with less than 1 dB power penalty on average after 20 km SMF transmission. This full-duplex WDM-RoF system shows high spectral-efficiency, large communication capacity, simple cost-efficient configuration and good performance over long distance transmission.

Multicolor concentric annular ultrafast vector beams.

Novel multicolor concentric annular ultrafast vector beams (MUCAU-VB) are firstly generated simply by using cascaded four-wave mixing (CFWM) in a glass plate pumped by two intense vector femtosecond pulses. A proof-of-principle experiment shows that up to 10 frequency up-conversion concentric annular radially polarized sidebands are obtained simultaneously based on CFWM process, where the spectra range of the first 7 order sidebands extending from 545 nm to 725 nm. The results prove the polarization transfer property from the pump beam to the signal beams even in the CFWM, a third-order optical parametric process. The pulse duration of the first order sideband is measured to be 74 fs which is according with those of two input beams. These novel MUCAU-VB, which are manipulated in temporal, spectral, spatial domain and polarization state simultaneously, are expected to apply in wide fields, such as manipulating particles and multicolor pump-probe experiments.

High-Fidelity Manipulation of the Quantized Motion of a Single Atom via Stern–Gerlach Splitting**Supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0304501, 2016YFA0302800 and 2016YFA0302002), the Key Research Program of Frontier Science of the Chinese Academy of Sciences (CAS) (Grant No. ZDBSLY- SLH012), the National Natural Science Foundation of China (Grant No. 11774389), the Strategic Priority

We demonstrate high-fidelity manipulation of the quantized motion of a single 87Rb atom in an optical tweezer via microwave couplings induced by Stern–Gerlach splitting. The Stern–Gerlach splitting is mediated by polarization gradient of a strongly focused tweezer beam that functions as fictitious magnetic field gradient. The spatial splitting removes the orthogonality of the atomic spatial wavefunctions, thus enables the microwave couplings between the motional states. We obtain coherent Rabi oscillations for up to third-order sideband transitions, in which a high fidelity of larger than 0.99 is obtained for the spin-flip transition on the first order sideband after subtraction of the state preparation and detection error. The Stern–Gerlach splitting is measured at a precision of better than 0.05 nm. This work paves the way for quantum engineering of motional states of single atoms, and may have wide applications in few body physics and ultracold chemistry.

Truly Distributed and Ultra-Fast Microwave Photonic Fiber-Optic Sensor

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.

3-D Analytical Model of Armature Reaction Field of IPMSM With Multi-Segmented Skewed Poles and Multi-Layered Flat Wire Winding Considering Current Harmonics

A 3-D analytical model of armature reaction field (ARF) of interior permanent magnet synchronous motor (IPMSM) with multi-segmented skewed poles (MSP) and multi-layered flat wire winding (MFWW) considering current harmonics is proposed in this paper. Firstly, based on the MFWW distribution analysis and the coil magnetic field vector superposition method, the ideal ARF functions of the MFWW considering low-order current harmonics and high-order sideband current harmonics are derived. Secondly, 3-D relative permeance functions caused by the stator slotting effect and the multi-segmented rotor magnetic barriers are presented. Thirdly, 3-D analytical expressions of ARF are obtained by multiplying the ideal ARF functions and the 3-D relative permeance functions. Additionally, the effects of low-order current harmonics, high order sideband current harmonics, MSP, and stator slotting on the spatial orders and frequencies of ARF are analyzed. Finally, the proposed model is verified by finite element method (FEM) and experiment.

Optical vector analyzers based on asymmetric two-band modulation

This article presents the principle of operation and the results of experimental prototyping of optical vector analyzers based on asymmetric double sideband modulation, created at the R&D Institute of Applied Electrodynamics, Photonics and Living Systems within the framework of the state task for KNRTU-KAI. Asymmetric double sideband modulation is used to solve the problems of modern optical vector analyzers. The advantages of its use are the ability to obtain a doubled measurement frequency range (80 GHz), and, in some cases, the absence of measurement errors caused by the presence of higher order side bands in the probe radiation. The latter removes restrictions on the magnitude of the modulation index of the optical carrier, and, therefore, on the dynamic range of measurements. Two variants of optical vector analyzers with asymmetric double sideband modulation are considered - with asymmetry in frequency and amplitude. A key element of the first option is a phase-shift fiber Bragg grating, which is used to form a biased carrier asymmetric double sideband modulation signal. To implement asymmetric double sideband modulation with amplitude asymmetry, the disadvantages of the scheme implementing single sideband modulation are used to form two components of different amplitudes. To verify the developed theoretical principles, a universal set-up, described in the article, was made.

A filterless scheme of generating frequency 16-tupling millimeter-wave based on only two MZMs

In this work, we propose a new scheme to generate high-quality frequency 16-tupling millimeter-wave only by two Mach-Zehnder modulators (MZM) and without filter. The two MZMs, biased at maximum transmission point, are used for odd order sidebands suppression. By controlling the modulation index of the MZM, ±4th-order sidebands amplitude return zero. By adjusting phase shifter and the attenuator to cancel 0th-order sideband; By adjusting the phase difference between RF driving signals of two subsystems to cancel ±(4n-2)th-order optical sidebands. The feasibility of the proposed were demonstrated and discussed. Simulation results show that using 10 GHz RF signal to drive the MZMs, 160 GHz mm-wave signal with 31.35 dB optical sideband suppression ratio (OSSR) and 24.11 dB radio frequency sideband suppression ratio (RFSSR) was obtained. The results are coincide with the theoretical analysis. Furthermore, the non-ideal cases are also analyzed. Even if the modulation index, the MZM bias voltage or extinction ratios deviate from the ideal values to a certain degree, the mm-wave signals’ performance are still acceptable.

Comparative Study of Sideband Electromagnetic Force in Internal and External Rotor PMSMs With SVPWM Technique

The permanent magnet synchronous motors (PMSMs) with space vector pulsewidth modulation (SVPWM) technique will inevitably introduce sideband current harmonic components around the carrier frequency. The armature reaction field caused by the sideband current interacts with the permanent magnet field, generating sideband electromagnetic force and resulting in high-frequency noise. This paper provides a comparative study of the sideband electromagnetic force in internal and external rotor PMSMs with SVPWM technique. First, the analytical model of the electromagnetic force in internal and external rotor PMSMs is established based on the Maxwell tensor method. The source, spatial order, and frequency of the electromagnetic force is obtained. Then, the spatial and temporal characteristics of the sideband force in internal and external rotor PMSMs with different pole and slot combinations are derived and investigated. The results show that the frequency characteristics of the zeroth order sideband force in internal and external rotor PMSMs introduced by SVPWM are identical. However, the frequency characteristics demonstrate significant differences for the nonzeroth order sideband force. Finally, the theoretical analysis is validated through the finite element and experimental results, respectively. This study is benefit for the source identification and reduction of high-frequency acoustic noise for PMSMs.

Generation of an ultraflat and power efficient optical frequency comb by cascading of electroabsorption and single-drive Mach–Zehnder modulator

We have investigated the theoretical and principal analysis of cascaded electroabsorption modulators (EAMs) and Mach–Zehnder modulator (MZM). We have proposed a technique to generate an ultraflat and power efficient optical frequency comb (OFC) by the serial cascading of two EAMs and one single-drive MZM. Continuous wave (CW) light source is modulated and spectrum broadened by two EAMs and MZM, respectively. Here, EAMs in cascaded mode produce ultrashort pulses followed by MZM, which is introduced to perform intensity modulation and tuned the power variation of even and odd order sidebands at the same level for obtaining a flat optical spectrum at the output. The first EAM acts as a subcarrier generator and the latter one acts as a subcarrier enhancer, which is followed by the MZM acting as subcarrier flatter. By this proposed technique, we have generated 63 subcarriers with 10-GHz spacing and within 2-dB power fluctuation. The generated OFC has a bandwidth of 630 GHz. This technique generates OFC with an appreciable power level and flattened optical spectrum, which is very much essential in dense wavelength division multiplexing and elastic optical networks.

Adaptive Phase-Shifted PWM based on Particle Swarm Optimization for Cascaded H-Bridge Inverter with Unequal Dc-link Voltages

The cascaded H-Bridge Multilevel Inverter has been found a promising technology in industrial applications because of its higher voltage with less distortion production. Various PWMs techniques have been proposed to push the harmonics frequencies higher than the switching frequency and thus reduces the THD as compared to non-carrier control technique based upon grid frequency. The Phase-Shifted PWM technique has an advantage over others PWM techniques because its harmonics orders are multiples of switching frequency and also depend on the number of levels of the inverter. The phase shifting angle is uniform when the equal voltage sources are adopted. However, in applications where sets of different voltage source levels feed the H-Bridge cells, the Phase Shifted PWM suffers its high order harmonics elimination capability. As a solution to alleviate this problem, an adaptive variable angle approach is proposed in this paper using Particle Swarm Optimization (PSO) algorithm to eliminate desired higher order harmonics. The algorithm is used to minimize the cost function based on high order sideband harmonics elimination equations. The results through MATLAB/Simulink environment shown in this paper confirm the reduction of sideband harmonics of higher orders, and the overall THD.

A Radio over Fiber (RoF) Based Single Sideband Modulated Passive Optical Network (PON) Using Mach Zender Modulator Based on Different Electrical Phase Shifts

Abstract This research work provides an insight on a radio over fiber (RoF) based passive optical network (RoF-PON) utilizing two diverse electrical phase shifts with optical single sideband modulation (OSSB) by exploiting Mach Zender modulator. The influence of chromatic dispersion (CD) in PONs employing single mode fiber (SMF) is a noteworthy issue and should be limited. The two techniques of OSSB modulation, in view of the two distinct angles of the hybrid coupler are employed for the design and implementation of RoF-PON. The RF signal is partitioned into two ways equally before applying it to the dual drive Mach Zender modulator input, utilizing an electrical hybrid coupler that imparts two discrete phase shifts of 90° and 120° to generate two OSSB signals individually. By utilizing traditional OSSB technique having 90° phase shift, either of the first-order sideband (lower or upper first order) suppression occurs yet second-order harmonics are still existent in the system. As opposed to this, the OSSB technique using 120° phase shift causes the suppression of either lower first order and higher second order sideband or vice versa. When contrasted to the PON based on traditional technique (90° phase shift technique), the suppression of second order sideband in PON using 120° technique lessens the system CD. Hence the PON based on 120° phase shift technique has enhanced functionality in terms of system BER, received power and power losses as compared to that with traditional OSSB technique.

Magnon-induced high-order sideband generation.

Magnon Kerr nonlinearity plays a crucial role in the study of an optomagnonical system and may bring many interesting physical phenomena and important applications. In this Letter, we report the investigation of high-order sideband generation induced by magnon Kerr nonlinearity in an optomagnonical system, which is still unexplored in this emerging research field. We uncover that the microwave driving field plays a significant role in manipulating the generation and amplification of the higher-order sidebands and, more importantly, the sideband spacing can be regulated by controlling the beat frequency between the pump laser and the probe laser, which is extremely eventful for the spacing modulation of the sideband frequency comb. Based on the recent experimental progress, our results will deepen our cognition into optomagnonical nonlinearity and may find fundamental applications in optical frequency metrology and optical communications.