High-order Sideband Research Articles

Influence of Unwanted First-Order Sideband on Optical Vector Analysis Based on Optical Single-Sideband Modulation

Optical vector analyzer (OVA) based on optical single-sideband (OSSB) modulation is attractive due to its potential sub-Hz resolution. However, the accuracy and dynamic range are limited by the unwanted sidebands of the OSSB signal, including the high-order sidebands and the unwanted first-order sideband. Previously, the influence of the high-order sidebands has been studied and several methods to suppress the errors induced by the high-order sidebands have been proposed. However, the investigation of the influence of the unwanted first-order sideband is still insufficient. In this paper, an analytical model is established and a numerical simulation is performed to comprehensively study the impact of the unwanted first-order sideband on the accuracy and dynamic range of the OSSB-based OVA. Then the simulation results are verified by experiment, which indicates that the unwanted first-order sideband has evident influence on the measurement accuracy and places a restriction on the dynamic range. Given that some prior information of the transmission responses is known, certain parameters of the device under test may still be achievable with high accuracy even when large unwanted first-order sideband is presented. This study may provide guidance in design and application of the OSSB-based OVA.

Coulomb-interaction-dependent effect of high-order sideband generation in an optomechanical system

High-order sideband generation in an optomechanical system coupled to a charged object is discussed, and the features of Coulomb-interaction-dependent effect are identified. We show that the Coulomb-interaction-dependent effect of high-order sideband generation exhibits essential difference between the case of weak control field and strong control field. In the weak control field case, the output spectra are in the perturbative regime and there is hardly any Coulomb-interaction-dependent effect in an optomechanical system coupling to an object with a small amount of charge. In the strong control field case, the output spectra are in the nonperturbative regime and robust Coulomb-interaction-dependent effect arises even if there are few charges. The amplitudes of specific sidebands are also discussed, and it is shown that Coulomb interaction plays an important role in achieving optomechanical control. Due to the extremely sensitive charge number, the Coulomb-interaction-dependent effect of high-order sideband generation is remarkable in many aspects and may be used to precision measurement of electrical charges beyond the linearized optomechanical interaction.

Generation of a frequency-quadrupled phase-coded signal using optical carrier phase shifting and balanced detection.

A novel approach for photonic generation of a frequency-quadrupled phase-coded signal using optical carrier shifting and balanced detection is proposed and demonstrated. The key component of the scheme is an integrated dual-polarization quadrature phase shift-keying (DP-QPSK) modulator. In the modulator, an RF signal is applied to the upper QPSK modulator to generate high-order optical sidebands, while an electrical coding signal is applied to the bottom QPSK modulator to perform optical carrier phase shifting. After that, a frequency-quadrupled phase-coded signal with an exact π-phase shift is generated through balanced detection. The proposed scheme has a simple, compact structure and good tunability. Besides, a phase-coded pulse can be directly obtained when a three-level rectangular coding signal is applied. A proof-of-concept experiment is carried out. The generation of a 2-Gbit/s phase-coded signal with a frequency tuning from 12.12 to 28 GHz is experimentally demonstrated, and the generation of a phase-coded microwave pulse is also verified.

Investigation of high gain dual-pump phase sensitive amplifiers

In this paper, we investigated a high gain dual-pump degenerate phase sensitive amplifiers. We achieved a 22-dB signal gain with a nonlinear phase shift of 2rad in the 3-nm pump-wavelength separation scheme. Here, we optimized the fiber dispersion to weaken the de-amplification effect of high-order sidebands based on a 27-wave numerical model. By using such a narrow-wavelength-separation dual-pump phase sensitive amplifier scheme, we achieved a 3.3-dB optical signal-noise-ratio improvement compared with that of erbium doped fiber amplifier with the same gain.

Frequency-octupled phase-coded signal generation based on carrier-suppressed high-order double sideband modulation

An approach for photonic generation of a frequency-octupled phase-coded signal based on carrier-suppressed high-order double sideband modulation is proposed and experimentally demonstrated. The key component of the scheme is an integrated dual-polarization quadrature phase shift keying modulator, which is used to achieve the carrier-suppressed high-order double sideband modulation. At the output of the modulator, two fourth-order optical sidebands are generated with the optical carrier suppressed. After that, a Sagnac loop incorporating a fiber Bragg grating and a phase modulator is employed to separate the two optical sidebands and phase modulate one sideband with a binary coding signal. The approach features large carrier frequency tuning range for the generated phase-coded signal from several megahertz to beyond the W-band. A proof-of-concept experiment is carried out. The 2 Gbit/s phase-coded signals with frequencies of 16.48, 21.92, and 29.76 GHz are generated.

Highly linear W-band receiver front-end based on higher-order optical sideband processing

A highly linear W-band receiver front-end based on higher-order optical sideband (OSB) processing is proposed and experimentally demonstrated. Two-tone analysis shows that by manipulating higher-order OSBs, the third-order intermodulation distortion (IMD3) introduced by optoelectronic components (mainly modulators) in the receiver front-end can be further suppressed, and a 9 dB improvement of the ratio of the fundamental and IMD3 can be attained. In the experiment, the spurious-free dynamic range of the W-band receiver front-end is up to 122.1 dB·Hz2/3, with improvement by 9 dB compared with that of only processing the five OSBs.

Photonic Generation of Frequency and Bandwidth Multiplying Dual-Chirp Microwave Waveform

A photonic approach to generate a frequency and bandwidth multiplying dual-chirp microwave waveform using a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and demonstrated. In the proposed scheme, an RF carrier is applied to one QPSK modulator and a baseband single-chirp waveform is applied to another. By setting the driving signals applied to the modulator and adjusting the dc bias phases in the modulator, high-order optical sidebands can be obtained with the optical carrier suppressed. After optical to electrical conversion, a frequency-doubling and bandwidth-quadrupling, or frequency-quadrupling and bandwidth-octupling dual-chirp microwave can be generated. The approach is verified by simulation. Dual-chirp microwave waveforms with 16-GHz central frequency, 2048-MHz bandwidth and 32-GHz central frequency, 4096-MHz bandwidth are generated through an 8-GHz RF carrier and 512-MHz bandwidth baseband signal. The generated dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution.

Single-mode instability in standing-wave lasers: The quantum cascade laser as a self-pumped parametric oscillator

We report the observation of a clear single-mode instability threshold in continuous-wave Fabry-Perot quantum cascade lasers (QCLs). The instability is characterized by the appearance of sidebands separated by tens of free spectral ranges (FSR) from the first lasing mode, at a pump current not much higher than the lasing threshold. As the current is increased, higher-order sidebands appear that preserve the initial spacing, and the spectra are suggestive of harmonically phase-locked waveforms. We present a theory of the instability that applies to all homogeneously broadened standing-wave lasers. The low instability threshold and the large sideband spacing can be explained by the combination of an unclamped, incoherent Lorentzian gain due to the population grating, and a coherent parametric gain caused by temporal population pulsations that changes the spectral gain line shape. The parametric term suppresses the gain of sidebands whose separation is much smaller than the reciprocal gain recovery time, while enhancing the gain of more distant sidebands. The large gain recovery frequency of the QCL compared to the FSR is essential to observe this parametric effect, which is responsible for the multiple-FSR sideband separation. We predict that by tuning the strength of the incoherent gain contribution, for example by engineering the modal overlap factors and the carrier diffusion, both amplitude-modulated (AM) or frequency-modulated emission can be achieved from QCLs. We provide initial evidence of an AM waveform emitted by a QCL with highly asymmetric facet reflectivities, thereby opening a promising route to ultrashort pulse generation in the mid-infrared. Together, the experiments and theory clarify a deep connection between parametric oscillation in optically pumped microresonators and the single-mode instability of lasers, tying together literature from the last 60 years.

An Optical Frequency Shifter Based on High-Order Optical Single-Sideband Modulation and Polarization Multiplexing

We propose and experimentally demonstrate a novel electro-optic frequency shifter with frequency multiplication operation based on high-order optical single-sideband (SSB) modulation and polarization multiplexing using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. By changing the dc bias phases of the modulator and the phase difference between the input RF signals, two-high-order SSB modulation signals are generated from the two QPSK modulators. After that, the two optical signals are polarization multiplexed and then projected to one direction to remove the low-order sidebands while only the high-order sideband is reserved. The scheme is numerically analyzed with the modulation indices of the modulator for optimal operation. A distinct advantage of this approach is the capability to generate a frequency shifting with a continuous and ultrawide tunable range (more than ±100 GHz), and the tuning operation is accurate, simple, and flexible. An experiment is carried out to achieve a frequency-doubled optical frequency shifter. A continuous frequency shifting ranged from −36 to 36 GHz is experimentally verified.

Enhanced high-order sideband generation and clear carrier-envelope phase-dependent effects in three-mode cavity optomechanics

Besides the standard optomechanics with an optical mode coupled to a mechanical mode through the radiation pressure force, three-mode optomechanical systems including two cavity modes interacting with a mechanical mode have recently drawn much attention. In this paper, we propose a scheme for enhanced high-order sideband generation (HSG) and clear carrier-envelope phase-dependent (CEP) effects in a three-mode cavity optomechanical system, where two optical cavity modes are coupled to a common mechanical resonator. In the present scheme, the left cavity mode is coherently pumped by a continuous-wave (CW) control field and an intense nanosecond signal pulse, and the cavity output via the loss channel is monitored. The right cavity mode is only pumped by a CW driving field. Via numerical simulations, we show that when the right pump is turned off, the effect of HSG can be observed in the output spectrum of the left cavity mode in the non-perturbative regime. However, when the right cavity mode is pumped at its blue sideband, enhanced HSG can be achieved and a clear CEP effect can be observed in the generated high-order sideband spectra. This study may provide the further insight of the HSG and CEP effects in cavity optomechanics in the nonlinear and non-perturbative regime, and may find potential applications in the areas of optical communications and quantum information processing.

Nonlinear optomechanics with gain and loss: amplifying higher-order sideband and group delay

We study the nonlinear optomechanically induced transparency (OMIT) with gain and loss. We find that (i) for a single active cavity, significant enhancement can be achieved for the higher-order sidebands, including the transmission rate and the group delay; (ii) for active–passive-coupled cavities, hundreds of microsecond of optical delay or advance are attainable for the nonlinear sideband pulses in the parity-time-symmetric regime. The active higher-order OMIT effects, as firstly revealed here, open up the way to make a low-power optomechaical amplifier, which can amplify both the strength and group delay of not only the probe light but also its higher-order sidebands.

Optical vector analysis based on double-sideband modulation and stimulated Brillouin scattering.

A high-resolution and high-accuracy optical vector analysis based on optical double-sideband modulation and stimulated Brillouin scattering is proposed and experimentally demonstrated. Different from the conventional OVA based on optical single-sideband modulation, in which the measurement range is limited by the bandwidth of the microwave and optoelectronic components, and the measurement accuracy is restricted by the high-order sidebands, the proposed technique measures the magnitude and phase responses by making use of both ±1st-order sidebands without spectrum response aliasing. As a result, the measurement range is doubled, and the high-order, sideband-induced errors only appear at specific frequencies that are predictable and removable. A proof-of-concept experiment is carried out. The transmission response of a fiber Bragg grating, in a range of 80GHz, is measured with a resolution of less than 667kHz by using 40GHz microwave components.

Large dynamic range optical vector analyzer based on optical single-sideband modulation and Hilbert transform

A large dynamic range optical vector analyzer (OVA) based on optical single-sideband modulation is proposed and demonstrated. By dividing the optical signal after optical device under test into two paths, reversing the phase of one swept sideband using a Hilbert transformer in one path, and detecting the two signals from the two paths with a balanced photodetector, the measurement errors induced by the residual −1st-order sideband and the high-order sidebands can be eliminated and the dynamic range of the measurement is increased. In a proof-of-concept experiment, the stimulated Brillouin scattering and a fiber Bragg grating are measured by OVAs with and without the Hilbert transform and balanced photodetection. Results show that about 40-dB improvement in the measurement dynamic range is realized by the proposed OVA.

Giant enhancement of optical high-order sideband generation and their control in a dimer of two cavities with gain and loss

Parity-time ($\mathcal{PT}$) symmetric systems, which rely on the balanced gain-loss condition and render the Hamiltonian non-Hermitian, have provided a new platform to engineer effective light-matter interactions in recent years. Here we explore the high-order sideband features of the output fields obtained from a $\mathcal{PT}$-symmetric optical system consisting of a passive nonlinear cavity coupled to an active linear cavity. By employing a perturbation technique, we derive analytic formulas used to determine the nonlinear transmission coefficient of optical second-order sideband in this structure. Using experimentally achievable parameters, it is clearly shown that the efficiency of the second-order sideband generation can be greatly enhanced in the $\mathcal{PT}$-symmetric dimer, extremely in the vicinity of the transition point from unbroken- to broken-$\mathcal{PT}$ regimes. Moreover, we further analyzed the influences of the system parameters, including the photon-tunneling rate between two cavities, Kerr nonlinearity strength, and optical detuning, on the second-order sideband generation. Subsequently we investigate the higher-order sideband output spectrum by numerical simulations, where the sideband amplitude also is largely enhanced in the $\mathcal{PT}$-symmetric arrangement, compared with the passive-passive double-cavity system. Our obtained results provide a new avenue for acquiring optical high-order sidebands and operating light, which may inspire further applications in chip-scale optical communications and optical frequency combs.

Optical High-Order Sideband Comb Generation in a Photonic Molecule Optomechanical System

An optical high-order sideband comb generation scheme is theoretically and numerically studied in a photonic molecule optomechanical system. The photonic molecule optomechanical system consists of two directly coupled optical microcavities with one cavity of the molecule supports a mechanical mode. The system is coherently driven by an input two-tone laser, which consists of a continuous-wave coupling field and an intense continuous-wave pump field. Based on the nonlinear effect of high-order sideband generation in the nonperturbative regime, the optical high-order sideband combs consisting of equally spaced spectral lines in frequency space can be generated in both cavities of the molecule. This paper reveals that the comb generation is associated with the cavity-cavity coupling strength, and the comb generation and manipulation in a controlled way might be achieved using the proposed setup.

Lightwave-driven quasiparticle collisions on a subcycle timescale

Ever since Ernest Rutherford first scattered α-particles from gold foils1, collision experiments have revealed unique insights into atoms, nuclei, and elementary particles2. In solids, many-body correlations also lead to characteristic resonances3, called quasiparticles, such as excitons, dropletons4, polarons, or Cooper pairs. Their structure and dynamics define spectacular macroscopic phenomena, ranging from Mott insulating states via spontaneous spin and charge order to high-temperature superconductivity5. Fundamental research would immensely benefit from quasiparticle colliders, but the notoriously short lifetimes of quasiparticles6 have challenged practical solutions. Here we exploit lightwave-driven charge transport7–24, the backbone of attosecond science9–13, to explore ultrafast quasiparticle collisions directly in the time domain: A femtosecond optical pulse creates excitonic electron–hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying wave packet dynamics, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands17–19 of the optical excitation. A full quantum theory explains our observations microscopically. This approach opens the door to collision experiments with a broad variety of complex quasiparticles and suggests a promising new way of sub-femtosecond pulse generation.

Long‐term stable 60 GHz optical two‐tone signal by destructive optical interference obtained from RF phase adjustment

An optical two-tone signal with 60 GHz frequency spacing is experimentally demonstrated, by sinusoidally modulating two lightwaves with different modulation indices and RF phases. By superposing two modulation lightwaves with orthogonal polarisation, polarisation orthogonality is achieved between undesired low-order optical sidebands and the desired high-order optical sidebands together with the incident light-wave. This enables us to suppress the undesired sidebands using polarisers instead of optical filter. Such operation has been implemented using optical modulator possessing RF ports for external termination, which is nested in one mode of polarisation-maintaining Sagnac interferometer (PMSI). This implementation is equivalent to optical single-sideband modulator, but required nested Mach–Zehnder structure is just one. Owing to this reduction together with use of one mode in PMSI, long-term stable operation more than 6 h has been successfully obtained, with 29 dB suppression ratio of undesired first-order sidebands against desired third-order optical sidebands.

Electronically Tuned Local Oscillators for the NOEMA Interferometer

We present an overview of the electronically tuned local oscillator (LO) system developed at the Institut de RadioAstronomie millimetrique (IRAM) for the superconductor–insulator–superconductor (SIS) receivers of the NOrthern Extended Millimeter Array interferometer (NOEMA). We modified the frequency bands and extended the bandwidths of the LO designs developed by the National Radio Astronomy Observatory (NRAO) for the Atacama Large Millimeter Array (ALMA) project to cover the four NOEMA LO frequency ranges 82–108.3 GHz (Band 1), 138.6–171.3 GHz (Band 2), 207.7–264.4 GHz (Band 3), and 283–365 GHz (Band 4). The NOEMA LO system employs commercially available MMICs and GaAs millimeter MMICs from NRAO which are micro-assembled into active multiplied chain (AMC) and power amplifier (PA) modules. We discuss the problem of the LO spurious harmonics and of the LO signal directly multiplied by the SIS mixers that add extra noise and lead to detections of unwanted spectral lines from higher order sidebands. A waveguide filter in the LO path is used to reduce the higher order harmonics level of the LO at the output of the final frequency multiplier, thus mitigating the undesired effects and improving the system noise temperature.

Tunable high-order sideband spectra generation using a photonic molecule optomechanical system.

A tunable high-order sideband spectra generation scheme is presented by using a photonic molecule optomechanical system coupled to a waveguide beyond the perturbation regime. The system is coherently driven by a two-tone laser consisting of a continuous-wave control field and a pulsed driving field which propagates through the waveguide. The frequency spectral feature of the output field is analyzed via numerical simulations, and we confirm that under the condition of intense and nanosecond pulse driving, the output spectrum exhibits the properties of high-order sideband frequency spectra. In the experimentally available parameter range, the output spectrum can be efficiently tuned by the system parameters, including the power of the driving pulse and the coupling rate between the cavities. In addition, analysis of the carrier-envelop phase-dependent effect of high-order sideband generation indicates that the system may present dependence upon the phase of the pulse. This may provide a further insight of the properties of cavity optomechanics in the nonlinear and non-perturbative regime, and may have potential applications in optical frequency comb and communication based on the optomechanical platform.

Photonic gauge potential in a system with a synthetic frequency dimension.

We generalize the concept of photonic gauge potential in real space by introducing an additional "synthetic" frequency dimension in addition to the real space dimensions. As an illustration, we consider a one-dimensional array of ring resonators, each supporting a set of resonant modes having a frequency comb with spacing Ω, and undergoing a refractive index modulation at the modulation frequency equal to Ω. We show that the modulation phase provides a gauge potential in the synthetic two-dimensional space with the dimensions being the frequency and the spatial axes. Such a gauge potential can create a topologically protected one-way edge state in the synthetic space that is useful for high-efficiency generation of higher-order side bands.