Order Sidebands Research Articles

Millimeter wave frequency generation based on variations in coupling coefficients of a silicon add-drop microring resonator

A microwave photonic system with silicon add-drop microring resonator as the core photonic device is analyzed for microwave/millimeter wave frequency generation. The primary concept of the proposed study relies on varying the coupling coefficients of the silicon add-drop microring resonator. Unequal coupling coefficients between the ring cavity and bus waveguides are one of the parameters which are responsible for generating second, third order sidebands in the radio frequency spectrum generated at the photodetector. Another parameter of interest is the phase difference between the two radio frequency signals which are fed to the Mach–Zehnder modulators of the proposed system. A 1 GHz sinusoidal signal with 1V peak-to-peak amplitude results in a third order sideband generation whose frequency corresponds to 3 GHz. The coupling coefficients in this case are 0.2 and 0.8, between ring cavity, top and bottom waveguides respectively. It is also observed that, phase difference of 90◦ between the input radio frequency signals results in highest power of the third order sideband generated in the output radio frequency spectrum whose frequency corresponds to the multiple of input radio frequency.

Excitation of nonlinear second order betatron sidebands for knock-out slow extraction at the third-integer resonance

Radio frequency knock out resonant slow extraction is a standard method for extracting stored particle beams from synchrotrons by transverse excitation. Classically, the beam is excited with an rf field comprising a frequency band around one of the betatron sidebands. This article demonstrates that the third-integer resonance commonly used for the slow extraction induces nonlinear motion, resulting in the appearance of additional sidebands of higher order at multiples of the betatron tune. Measured and simulated beam spectra are presented, revealing these sidebands and the beam’s response to being excited at first and second order sidebands. The feasibility of using a second order sideband for the purpose of slow extraction is demonstrated. This results in a significant improvement in the temporal structure (spill quality) of the extracted beam, but at the cost of higher excitation power requirements. This is observed both experimentally and in tracking simulations. The mechanism behind the observed improvement is explained using beam dynamics simulations. Published by the American Physical Society 2024

A novel frequency 32-tupling ROF system without bit walk-off effect based on MZM with inserting pilot

A novel scheme for a frequency 32-tupling millimeter wave (MMW) radio over fiber(ROF) system without the bit walk-off effect is proposed. The operation principle and feasibility of our proposed scheme are theoretically analyzed and verified with simulation experiments. The main part of our scheme is a ±16th order sidebands generator (SG) which is constructed by eight Mach-Zehnder modulators (MZM) connected in parallel. In the back-to-back(BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±16th order sidebands are generated by the SG. In the data transmission case, the data signal is split into two beams first, one of which modulates the RF drive signal with an electrical phase modulator (PM), and the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can be modulated only to the +16th order sideband of the output of the SG. The optical carrier from the CW laser is split into two paths, one is sent into the SG, and the other is used as a pilot. The output signal of SG is combined with the pilot signal and is transmitted to the base station(BS) via optical fiber. In BS, the pilot signal is filtered out by an FBG and used as the carrier for uplink for carrier reuse. After filtering out the pilot, the signal from the FBG which is ±16th order sidebands is injected into the photodetector, and a frequency 32-tupling MMW with downlink data is generated. The influence on the bit error rate (BER) and Q factor by the key parameters in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion, greatly increase the fiber transmission distance, but also effectively improve the performance of the downlink, it has important application prospects in ROF systems.

A Novel Frequency Doubling Radio on Fiber System Without Bit Walk-Off Effect by Inserting a Pilot Frequency Signal

A novel insertion pilot-frequency signal method for doubling frequency radio on fiber (ROF) system is proposed. At the center station (CS), the carrier emitting from the continuous wave (CW) laser is split into two branches. In one branch, a composite RF drive signal formed by combining the data modulated by a phased modulator (PM) and the data gained by an electrical gainer (EG) is loaded to the Mach-Zehnder modulator (MZM) to produce ± 1th order sideband signals. The data signal of down link is modulated only on −1th order sideband. The other branch is used as the pilot signal. At the base station (BS), the pilot signal is reflected out using a fiber Bragg grating (FBG) and used as the carrier for the uplink. The signal passing through the FBG is sent into the photodetector, and the twofold millimeter wave signal is generated. The mathematical analysis and simulated experiment are given. The innovation of this paper is to introduce the pilot optical signal method for carrier reuse in ROF, it can overcome the poor tunability and degraded downlink performance in the conventional carrier reuse in ROF. The effect of bit walk-off is eliminated due to the data of downlink and uplink being modulated on the −1th and 0th order sideband respectively.

Radio-over-fibre for generation and transmission32-tupling frequency optical millimeter wave with polarization modulators

Radio-over-fibre for generation and transmission32-tupling frequency optical millimeter wave with polarization modulators

Generation of frequency 16‐tupling millimeter wave without filtering based on cascaded Mach–Zehnder modulator

AbstractA scheme of generating millimeter‐wave signals with 16 times frequency using a cascaded Mach–Zehnder modulator (MZM) is proposed. Optical delay lines (ODLs) are used to place between cascaded MZMs, two MZMs work at the maximum transmission point. By controlling the modulation index of the MZM and the delay of the ODL, 0‐order, ‐order, and ‐order sidebands can be generated. The optical phase shifter and attenuator are adjusted to eliminate the 0‐order sideband, and the photodetector output generates a frequency 16‐tupling millimeter wave (MMW). In the simulation platform, a 160‐GHz MMW signal can be obtained by taking a 10‐GHz radio frequency signal as the driving signal of two MZMs. The optical sideband suppression ratio is 29.92 dB, and the radio frequency sideband suppression ratio is 24.89 dB. Further, the effect of system performance on optical devices under nonideal conditions is also discussed.

A Novel Radio on Fiber System for Frequency 32-Tupling Millimeter-Wave Generation and Transmission Using Polarization Modulators

A new radio on fiber (ROF) scheme for generation and transmission frequency 32-tupling millimeter-wave (MMW) is proposed. At the central station (CS), six PoIMs are used to construct the ±16 order sidebands generator which can generate ±16 order sidebands. The sideband of +16th order is separate out by an optical interleaver from the output of ±16 order sidebands generator first, then the data of down-link signal is modulated on it. At the base station (BS), a portion sideband of −16th order from the down-link optical signal is separted out with a fiber Bragg grating (FBG) first, then the up-link data is modulated on it for carrier reuse. The remaining ±16th order sidebands from the FBG are beat in a photodetector (PD), then the frequency 32-tupling MMW signal with the down-link data is generated. The key part of this system is the ±16th order sideband generator, in which the ±16th order sidebands with the carrier component can be generated by adjusting the amplitudes and initial phases of the radio frequency (RF) signals loaded on the PoIMs, and the carrier can be cancelled by two 1×2 optical coupler with adjustable splitting ratio and 180° optical phase shifter (OPS). The principle of operation to generate frequency 32-tupling is theoretically analyzed and verified by simulation experiments. The optic sideband suppression ratio (OSSR) of the generated sidebands of ±16th order from the theoretical derivation and experiments are 29.974 dB and 29.793 dB, respectively, the RF spurious suppression ratio (RFSSR) of the obtained frequency 32-tupling MMW from theoretical derivation and experiment are 23.960 dB and 23.814 dB, respectively, which verifies the feasibility of our method. The transmission experiments are carried out. For 30 km fiber with 2.5 Gbps data rate, the Q value and power penalty for up-link and down-link are greater than 6 and less than 0.4 dB, respectively.

A novel method to generate and transmit 40-tupling frequency millimeter wave over fiber based on remodulation of MZMs

An novel method to generate 40-tupling frequency millimeter (MMW) based on the remodulation of MZMs and a novel radio over fiber (ROF) system to transmit the generated MMW are proposed. At the central station (CS), the ±4th order sidebands generated by two Mach-Zehnder modulators (MZMs) in parallel are used as the optical carriers for the remodulation. The radio frequency (RF) signal for the remodulation can be generated by injecting the ±4th order sidebands in the photodetector (PD). The main components in the signal after remodulation are ±4th, ±12th and ±20th order sidebands, among them, the +20th sideband is filtered out by a fiber Bragg grating (FBG). After the +20th order sideband is modulated with the downlink data, the ±20th order sidebands are combined again and transmitted to the base station (BS) by optical fiber. At the BS, a part of −20th order sideband is filtered out with a FBG, and with which the uplink data is modulated on it and sent back to the CS for carrier wave reuse. The 40-tupling frequency MMW signal with downlink data is generated by beating the output signal from FBG in the PD. In the case of data rate is 2.5G/bps and the bit error rate is less than 10−9, the transmission distance can exceed 90 km, the power penalty of the uplink and downlink is less than 1 dB and 0.29 dB, respectively. Our scheme has simple structure, high frequency multiplier factor, it has important application prospects in MMW technology.

Experimental and theoretical investigations on the modulation capabilities of a sample of vertical cavity surface emitting laser diodes for atomic vapour applications

This paper discusses various frequency modulation and intensity modulation capabilities within a sample of direct laser current modulated identical vertical cavity surface emitting laser diodes. The presented analysis is based on measurements of the spectral amplitudes as a function of the applied modulation power at a constant modulation frequency of 3.517 GHz. Their evaluation by Bessel function fits produces the three modulation parameters: frequency modulation index, intensity modulation index (via the alpha parameter) and the side band asymmetry of the first order side bands. The variation of the laser diode’s modulation capability is discussed. It is found that the individual laser diodes show a significant variations in their modulation capabilities. Thus an experimental preselection of the laser diode is required to find laser diodes which are suitable as a light source for atomic vapour applications, with special emphasis on a coherent population trapping-based scalar magnetometers.

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

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> order and lower 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> 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/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> or 3/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> times the input RF signal frequency where <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> can be between 3 and 6. Hence the 2/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> frequency divider can realise 2/3, 1/2, 2/5 and 1/3 frequency division operation, and the 3/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> frequency divider can realise 3/4, 3/5 and 1/2 frequency division operation. The proposed 2/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> and 3/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> 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.

Photonics-Based Instantaneous Microwave Frequency Measurement System With Improved Resolution and Robust Performance

This paper presents a photonics-based instantaneous microwave frequency measurement system. The system operates based on the frequency-to-power mapping technique. The trade-off between frequency measurement range and resolution, which is present in the reported frequency-to-power-mapping based frequency measurement systems, is addressed by designing the system to produce two amplitude comparison functions (ACFs). Using two ACFs enables an RF signal frequency in a specified range to be determined while having an improved resolution and smaller errors compared to using only one ACF for frequency measurement. The proposed frequency measurement system is designed to have a simple structure and robust performance suitable for use in real world applications. The effect of the higher order sidebands and harmonics on the system performance are investigated. Proof-of-concept experiments are carried out with results showing frequency measurement errors can be reduced by using the proposed system that generates two ACFs for frequency measurement.

All-optical polarimeter for laser Stokes vector measurement using self-induced nonlinear phase modulation.

This paper utilizes an analytical model of polarization dependent frequency sideband generation via the Kerr effect in a highly nonlinear fiber to determine the state of polarization (SOP) of a laser by all-optical means. Theoretical analysis shows that the power of the nth order sideband generated by the propagation of two lasers with distinct frequencies in the nonlinear medium is proportional to cos 2n(α/2), where α is the angle between the normalized Stokes vectors representing the SOPs of the lasers on the Poincaré sphere. By tailoring the SOP of one laser acting as a reference and experimentally measuring the power of the first order sideband, the SOP of the laser under test is recovered with an error smaller than 10.22° on the Poincaré sphere corresponding to 0.8% the sphere's total area. Comparing the SOPs of two lasers without referencing them to fixed polarizers enables potential applications in remote environmental sensing, novel polarization division multiplexing schemes for enhanced telecommunication data rates, and scientific instrumentation.

Generation of phononic high-order sidebands via intra- and inter-mode couplings in interconnected electromechanical resonators

To efficiently manipulate parametric mode mixing is an intriguing physical issue for phonon-cavity electromechanics, which is also crucial for various technological applications ranging from frequency synthesis to nonlinear spectroscopy. Here, we theoretically investigate the dependence of phononic high-order sidebands on intra- and inter-mode couplings in two interconnected electromechanical resonators. When the system operates in a strong inter-mode coupling regime, we report that two inter-mode phonon-scattering pathways allow us to selectively obtain either odd- or even-order sidebands at different output ports. The signal intensities of the separated sidebands can be independently modulated by introducing harmonic actuation forces acting on the interconnected resonators. Once the intra-mode coupling becomes totally dominant, the direct transition between intra-mode phonons only triggers the emergence of full-order sidebands in the nonlinear responses. In this case, increasing the quality factor of the resonators is beneficial for amplifying a few low order sidebands nearby the principal modes of the resonators but sacrificing the order of the sidebands.

Ultra-high resolution mass sensing based on an optomechanical nonlinearity

Ultra-high resolution mass sensing used to be realized by measuring the changed mechanical oscillation frequency by a small mass that should be detected. In this work we present a different approach of mass sensing without directly measuring such mechanical frequency change but relying on the modified light field due to a previously less explored nonlinear mechanism of optomechanical interaction. The concerned optomechanical setup used for the mass sensing is driven by a sufficiently strong two-tone field satisfying a condition that the difference of these two drive frequencies matches the frequency of the mechanical oscillation, so that a nonlinear effect will come into being and lock the mechanical motion under the radiation pressure into a series of fixed orbits. A small mass attached to the mechanical resonator slightly changes the mechanical frequency, thus violating the exact frequency match condition. Such small change can be detected by the amplitude modification on the higher order sidebands of the cavity field. Even given a moderate mechanical quality factor for the setup, the added mass can still be detected to the levels corresponding to a mechanical frequency shift from 5 to 7 order less than the mechanical damping rate. Because the output cavity field difference for very close values of mechanical frequency is not blurred by thermal noise, such mass sensing can be well performed at room temperature. The previous tough requirements for ultra-high resolution mass sensing can be significantly relaxed by the method.

Sensitivity enhancement of fiber optical polarimetric sensors using self-induced nonlinear phase modulation via the Kerr effect.

This work presents an analytical model accounting for the impact of optical polarization on the generation of frequency sidebands by the Kerr effect in a highly nonlinear fiber. Theoretical analysis shows that for a relative polarization angle, α, between two input lasers expressed on the Poincaré sphere, the optical power of the nth order sideband is proportional to cos 2n(α/2). This theoretical result enables a novel all-optical technique for interrogating changes in polarization with higher sensitivity than conventional measurement schemes using linear polarizers. The predicted theoretical relationship between the sideband power and the relative polarization angle is verified experimentally and sensitivity enhancement by a factor of 1.45 compared to a conventional polarimetric sensor is demonstrated for the 3rd order sideband. This novel nonlinear approach, which allows dynamic range to be traded for an enhanced ability to detect small polarization variations, has potential applications in fusion reactor monitoring, instrumentation and material characterization.

Photonic Techniques for Generating a Single RF Sideband With No Second Order Sidebands

Two structures that can realise optical single sideband modulation without generating both second order upper and lower sidebands are presented. They are based on a dual-parallel Mach Zehnder modulator (DP-MZM) with an optical filter and a dual-polarisation dual-parallel Mach Zehnder modulator (DPol-DPMZM) with a 90° hybrid coupler. The former is an all-optical structure and hence it has a very wide bandwidth. The latter uses one DP-MZM to realise single sideband suppressed carrier modulation while the other DP-MZM simply passes the optical carrier. It also suppresses the third order sideband on the same side as the wanted fundamental RF modulation sideband. Hence, in an ideal situation, there is no second order harmonic component generated after photodetection. Experimental results are presented for the novel structures, which demonstrate the realisation of optical single sideband modulation without second order sidebands. The results also show large fundamental to second order harmonic power ratio over a wide input RF signal frequency range even after inserting a long single mode fibre into the system for signal transmission. The new optical single sideband modulators find applications in improving the multioctave spurious free dynamic range in a long-haul fibre optic link and reducing measurement errors in an optical vector analyser.

Analysis of Optical Single Sideband Modulators for Radio Over Fiber Link with and without Second Order Sidebands

The analysis of Optical Single Sideband (OSSB) generation with and without second-order sidebands for Radio over Fiber (RoF) is presented. The performance of systems based on hybrid coupler with distinct phase angle and Dual-Parallel Dual-Drive Mach-Zehnder Modulator (DP-DDMZM) is compared using simulation. Impact of parameters like Single-Mode Fiber (SMF) length, Radiofrequency (RF) amplitude, and laser linewidth on Signal-to-Noise Ratio (SNR) has been investigated. It has been observed that eliminating one of the second-order sidebands with 120° hybrid coupler improves peak SNR in comparison to 90° hybrid coupler with both second-order sidebands and DP-DDMZM-based system without second-order sidebands irrespective of Continuous Wave (CW) laser linewidth.

Composite optical phase locking technology of chirp synthetic aperture lidar

An accurate chirp synthetic aperture lidar is proven, and the chirp laser signal is generated by an optical filter selecting specific sidebands from infinite sidebands, which are generated by laser signals passing through an electro-optic phase modulator driven by a chirp signal. And the bandwidth and chirp rate of the N-th order sideband is N times as large as the chirp signal by the signal generator. Then, a chirp signal with a modulation bandwidth of 1.2 GHz and a tuning rate of 12 THz/s is obtained by selecting the positive second-order sideband by an optical filter. Next, by adopting composite optical phase-locking processing, the random phase caused by the lidar system will be well offset, and the phase is stable within 0.1rad. Finally, Laboratory imaging results show that the azimuth resolution of synthetic aperture lidar is better than 0.04 m. In the future, by applying the higher-order sideband, higher tuning rates and bandwidths can be expected.

Linear and nonlinear ultrasound time reversal using a condensing raster operation

One of the weaknesses of nonlinear methods is the excitation power required to generate nonlinear effects such as higher order harmonics (single frequency) and sidebands (dual excitation). In conjunction with the high-power prerequisite, is the required sensitivity of sensors to capture nonlinear effects which can be multiple orders of magnitude lower than the fundamental/linear response of the system. In this work a semi-air coupled nonlinear ultrasound modulation method combining phase symmetry analysis and time reversal is developed, in the aim of alleviating some of these issues. Phase symmetry analysis is used to characterise the second order and modulated nonlinear responses of a dual frequency excitation signal containing a single frequency (f1) and a sweep burst (f2). Time reversal allows for optimal focusing, in this case at locations on composites panels with barely visible impact damage. Time reversed signals typically focus at single locations at a time, in this work, a raster time reversal methodology is proposed which focuses on multiple locations simultaneously. The raster methodology reduces distortions which may affect air-coupled techniques, reduces inspection time, and shows clear enhancement of damage imaging when compared against the raw fundamental response and standard time reversal.

Reconfigurable microwave photonic system with cascaded double ring resonator for generating millimeter wave signals suitable for 5G applications

A cascaded double ring resonator based microwave photonic system for generating millimeter wave signals is designed and analyzed. Variations in coupling coefficients between ring cavity and bus waveguides of the microring resonator is one of the significant aspect of this analysis. In the proposed system, sixth order sidebands (corresponding to millimeter wave frequencies) are generated upon precise selection of coupling coefficients. The optimal values of coupling coefficients which result in highest power of 60 GHz frequency component are found to be t3 = 0.7, t4 = 0.2. The millimeter wave frequency components with highest power are generated in the RF spectra of the photodetector at the drop port of MRR 2. Variations in input RF frequencies (between 1 GHz and 20 GHz) results in generation of millimeter wave signals lying in the range of 30–60 GHz. The generated millimeter wave signals are suitable for 5G small cell applications.