Search Results (15)

An all-optical single-longitudinal-mode (SLM) forward Brillouin microwave oscillator (FB-MO) with an unbalanced Fiber Mach–Zehnder interferometer (UF-MZI) for microwave photonics (MWP) generation is proposed and experimentally investigated. UF-MZI consists of an optical coupler (OC), a polarization controller (PC), and two asymmetric length arms with 5 km and 500 m single-mode fibers (SMFs), which implements two unbalanced length feedback rings that are connected to one another. One long-length ring with a forward Brillouin gain cooperates with the other short-length ring to maintain a spectral Vernier effect and improve the effective free spectral range (FSR). By contrast with traditional optoelectronic oscillators (OEOs), this design does not require any photoelectric conversion devices and additional modulation, avoids external electromagnetic interference, and side-mode suppression and linewidth are favorable. Experimental results reveal that the 3-dB linewidth of the all-optical SLM FB-MO with UF-MZI is about 140 Hz. The acoustic-mode and side-mode suppression ratios are 26 dB and 31 dB. Within 60 min of the stability experiment, the power and frequency stability fluctuation were ±1 dB and ±100 Hz. Thanks to its long main ring cavity length, our all-optical SLM FB-MO with UF-MZI maintains good phase-noise performance. The measurement shows that a phase noise as low as −120 dBc/Hz at an offset frequency of 100 kHz is achieved. This SLM MWP generation technology holds great potential for applications in radar monitoring and wireless communication systems. Full article

In this study, a model of a double-quantum-dot system driven by two-mode microwave photons is presented. The quantum master equation is derived from the system’s Hamiltonians, and the expression for the steady-state current is obtained. Electronic tunneling properties are then analyzed. The results revealed that different two-mode quantum microwave photons have varying effects on the tunneling current within the double-quantum-dot system, with a steplike current trend emerging. The tunneling current showed pronounced negative differential conductance for both coherent and squeezed microwave photons. Furthermore, the tunneling current was significantly influenced by changing the squeezing coefficient and phase. The asymmetric evolution of the tunneling current under varying bias voltages also depends on the asymmetry in system parameters. These findings are crucial for manipulating the transport properties of double-quantum-dot systems in nanostructured devices. Full article

We present a 520 μJ microsecond burst-mode pulse fiber amplifier with a GHz-tunable intra-burst repetition rate and a nearly flat-top pulse envelope. The amplifier architecture comprises a microsecond pulse seed, a high-bandwidth electro-optic modulator (EOM), two pre-amplifier stages, a waveform-compensated acoustic-optic modulator (AOM), and two main amplifier stages. To address amplified spontaneous emission (ASE) and nonlinear effects, a multistage synchronous pumping scheme that achieved a maximum energy output of 520 μJ and has a peak power of 160 W was used. To produce a flat-topped burst pulse envelope, the AOM generates an editable waveform with a leading edge and a high trailing edge to compensate for waveform distortion, resulting in a 5 μs nearly flat-top pulse envelope at maximum energy. The laser provides an adjustable intra-burst pulse repetition rate range of 1–5 GHz through the high-bandwidth EOM modulation. The intra-burst pulse jitter time of the laser remains below 4.31 ps at different frequencies. Moreover, the beam quality of the amplifier is M²x = 1.04 and M²y = 1.1. This amplifier exhibits promising potential and can be further amplified as an optical drive source for high-power, large-bandwidth microwave photon (MWP) radar applications. Meanwhile, it is also potentially applicable as a pulse source for high-speed optical communications, the high-precision processing of special materials, and LIDAR ranging. Full article

Microwave photonics (MWP) applications often require a high optical input power (>100 mW) to achieve an optimal signal-to-noise ratio (SNR). However, conventional silicon spot-size converters (SSCs) are susceptible to high optical power due to the two-photon absorption (TPA) effect. To overcome this, we introduce a silicon nitride (SiN) SSC fabricated on a silicon-on-insulator (SOI) substrate. When coupled to a tapered fiber with a 4.5 μm mode field diameter (MFD), the device exhibits low coupling losses of <0.9 dB for TE modes and <1.4 dB for TM modes at relatively low optical input power. Even at a 1W input power, the additional loss is minimal, at approximately 0.1 dB. The versatility of the SSC is further demonstrated by its ability to efficiently couple to fibers with MFDs of 2.5 μm and 6.5 μm, maintaining coupling losses below 1.5 dB for both polarizations over the entire C-band. This adaptability to different mode diameters makes the SiN SSC a promising candidate for future electro-optic chiplets that integrate heterogeneous materials such as III-V for gain and lithium niobate for modulation with the SiN-on-SOI for all other functions using advanced packaging techniques. Full article

A filter-free, image-reject, sub-harmonic downconverted RoF link is proposed based on a dual-polarization quadrature phase-shift keying (DP–QPSK) modulator. At the remote antenna unit, the receiving radio frequency signal is applied to the upper QPSK modulator to achieve carrier-suppressed single-sideband (CS–SSB) modulation. The local oscillator (LO) is applied to the lower QPSK modulator, achieving sub-harmonic single-sideband (SH–SSB) modulation. The I/Q mixing is realized by exploiting a two-channel photonic microwave phase shifter, which mainly consists of a modulator, two polarization controllers, and two polarizers. The image interference signal can be rejected when combing the I and Q IF signals through a 90° electrical hybrid. Because the scheme is simple and filter-free, it has a good image-reject capability over a large frequency tunable range. Moreover, due to the special SH-SSB modulation, the modulated signals are immune to the chromatic dispersion-introduced power fading effect. Last, the sub-harmonic downconverter can decrease the frequency requirement of the LO signal. Experimental results show that an image rejection ratio (IRR) greater than 50 dB can be achieved when transmitted through a 25 km single-mode fiber (SMF). Simultaneously, under different RF signals and IF signals, the IRR has no periodic power fading, only small fluctuations. Image rejection capability of the scheme for the 50-MBaud 16-QAM wideband vector signal is also verified and the demodulation of the desired IF signal with a good EVM of less than 5% is realized. Full article

We propose and demonstrate a microwave photonic system to generate multiband and multi-format microwave waveforms based on an actively mode-locked optoelectronic oscillator (AML-OEO) using a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM). In the proposed system, the upper DDMZM is injected by two baseband single-chirped signals, and the lower DDMZM is biased to realize single-sideband (SSB) modulation using a 90° hybrid coupler. The lower DDMZM is also used to construct an AML-OEO loop, which outputs microwave frequency comb signals. By setting the phase difference in the applied two single-chirped signals, multiband up-, down-, and dual-chirped microwave signals are successfully generated. Furthermore, the tunability of the system can be realized by adjusting the frequency and power of the injection signal in the AML-OEO loop, the passband of the electrical filter, and the chirp rate of the single-chirped signal. The proposed scheme is theoretically analyzed and experimentally verified. Full article

We propose extended one-way waveguide states of large-area propagation in a photonic crystal waveguide consisting of two honeycomb gyromagnetic photonic crystals with opposite external magnetic fields. When the width of the waveguide is small enough, the edge states along both boundaries of the waveguide couple with each other strongly and thus create the so-called extended one-way waveguide states. Of note, this structure supports both even and odd extended states, which can be excited under different excitation conditions. For the odd mode, electromagnetic waves have opposite phase distributions along the centerline of the waveguide on both sides, while for the even mode, they have in-phase distributions on both sides. In addition, the odd and the even modes both have the large-area propagating property. Moreover, we have carried out a microwave experiment to verify the simulation results. The measured transmission spectrum shows that the structure has strong non-reciprocity, and the measured electric field distributions of the even and odd modes prove that it supports excellent large-area transmission behaviors. These results provide feasible ideas for achieving topological high-throughput transmission. Full article

We propose and demonstrate a photonic-assisted approach for generating arbitrary microwave waveforms based on a dual-polarization dual-parallel Mach–Zehnder modulator, offering significant advantages in terms of tunability of repetition rates and anti-dispersion capability. In order to generate diverse microwave waveforms, two sinusoidal radio frequency signals with distinct frequency relationships are applied to the dual-polarization dual-parallel Mach–Zehnder modulator. By adjusting the power of the applied sinusoidal radio frequency signal, the power ratio between these orthogonal polarized optical sidebands can be changed, and thereby desired radio frequency waveforms can be obtained after photoelectric conversion. In our proof-of-concept experiment, we systematically varied the repetition rate of triangular, rectangular and sawtooth waveforms. Meanwhile, we calculated the Root Mean Square Error (RMSE) to assess the approximation error in each waveform. The RMSEs are 0.1089, 0.2182 and 0.1185 for the triangular, rectangular and sawtooth microwave waveforms with repetition rate of 8 GHz, respectively. Furthermore, after passing through 25 km single mode fiber, the optical power decreased by approximately 5.6 dB, which verifies the anti-dispersion transmission capability of our signal generator. Full article

We propose a frequency-tunable source to emit entangled microwave photons on the platform of a superconducting circuit, in which two superconducting transmission-line resonators are coupled via a capacitor and one resonator is inserted with a superconducting quantum interference device (SQUID) in the center. By pumping the circuit appropriately with an external coherent microwave signal through the SQUID, microwave photons are emitted in pairs out of the circuit. The entanglement between the two modes is demonstrated by numerically calculating the second-order coherence function and the logarithmic negativity of the output microwave signals. Due to the tunability of SQUID’s equivalent inductance, the frequencies of the entangled microwave photons can be tuned by an external flux bias in situ. Our proposal paves a new way for obtaining entangled frequency-tunable two-mode microwave photons. Full article

We report a novel photonic scheme to generate background-free phase-coded microwave pulses with elimination of power fading by cascading a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM is driven by a radio frequency (RF) signal to generate two first-order optical sidebands with an orthogonal polarization state, while the PolM is driven by a three-level electrical coding signal. By properly adjusting the polarization state, a series of background-free frequency-doubled phase-coded microwave pulses can be generated after optical-to-electrical conversion. Benefiting from the carrier-suppressed single-sideband (CS-SSB) modulation, the proposed signal generator can suppress the chromatic-dispersion-induced power-fading effect, which has excellent potential for long-distance fiber transmission. In addition, the system can directly generate phase-coded microwave signals in pulse mode by truncating continuous wave (CW) microwave signals. Moreover, the microwave signal generator has wideband tunability since no optical filter is involved in our scheme. The proposed method was theoretically analyzed and experimentally verified. Phase-coded microwave pulses centered at 14 GHz and 19.2 GHz with a bit rate of 0.5 Gb/s were successfully generated. Full article

Photonics-based microwave generation brings the advantages of photonic oscillators, such as high stability, wide bandwidth, and low loss, to the microwave domain. In this paper, the generation of tunable microwave signals was investigated both theoretically and experimentally based on an all-polarization-maintaining 1-GHz mode-locked fiber laser. Based on beating between two highly chirped optical pulse trains with a relative time delay at the photodetector, tunable microwave signals could be obtained. The numerical simulations show that 40 GHz or higher microwave signals could be obtained by tuning the time delay and dispersion. To experimentally validate the theoretical model, the generation of tunable microwave signals from 2–4 GHz was demonstrated. Due to the utilization of polarization-maintaining devices, the optical output has a high degree of linear polarization of more than 99%, which verifies the enhanced system stability. These demonstrations are imperative for solidifying the advancements of recent years and could promote the utilization of photonics-based microwave generation in microwave photonics. Full article

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium is developed to calculate the transmittance spectra of the sensors. It is found that the peak transmittance of both the defective resonance within the microwave band gap (MBG) and transmitting modes outside the MBG monotonously decrease with the increase of salinity, while the resonant and transmitting mode frequencies remain unchanged. By comparing the four MPC sensor structures, the first transmitting mode in the upper frequency band outside the MBG of the 15-layer MPC sensor has the largest salinity sensing range from 0 to 40‰ with relative stable detecting sensitivity. The sensing principle is based on the fact that the dielectric loss factor of saline solution is much more sensitive to salinity than the dielectric constant in the microwave frequency band. The sensitivity, quality factor, and salinity detection range of the MPC sensors are calculated and compared. The reported defective MPC sensors are suitable to be used for non-contact salinity detection. Full article

A broadband polarization-insensitive graphene modulator has been proposed. The dual built-in orthogonal slots waveguide allows polarization independence for the transverse electric (TE) mode and the transverse magnetic (TM) mode. Due to the introduction of metal slots in both the vertical and horizontal directions, the optical field as well as the electro-absorption of graphene are enhanced by the plasmonic effect. The proposed electro-optic modulator shows a modulation depth of 0.474 and 0.462 dB/μm for two supported modes, respectively. An ultra-low effective index difference of 0.001 can be achieved within the wavelength range from 1100 to 1900 nm. The 3 dB-bandwidth is estimated to be 101 GHz. The power consumption is 271 fJ/bit at a modulation length of 20 μm. The proposed modulator provides high speed broadband solutions in microwave photonic systems. Full article

THz communications systems at carrier frequencies above 200 GHz are the key to enable next-generation mobile communication networks with 100 Gbit/s wireless data rates. One of the key questions is, which carrier frequency generation technique will be the most suitable. This is currently addressed by two separate approaches, electronics-based and photonics-based. We present in this paper a truly microwave photonic approach that benefits from the main key features of each, bandwidth, tunability, stability and fiber compatibility from photonics and power handling capability from the electronics. It is based on a Photonic Local Oscillator (PLO), generating a 100 GHz frequency, fed into an electronic frequency multiplier. A high speed uni-travelling carrier photodiode (UTC-PD) provides the 100 GHz PLO for Schottky tripler diodes, generating 300 GHz signal. To feed the UTC-PD, we present a photonic integrated mode locked laser source. According to the simulations and measurements, the developed transmitter can produce a maximum of 12 μW of THz power at 280 GHz. Full article

We propose a method to generate nonclassical states of light in multimode microwave cavities. Our approach considers two-photon processes that take place in a system composed of N extended cavities and an ultrastrongly coupled light–matter system. Under specific resonance conditions, our method generates, in a deterministic manner, product states of uncorrelated photon pairs, Bell states, and W states in different modes on the extended cavities. Furthermore, the numerical simulations show that the generation scheme exhibits a collective effect which decreases the generation time in the same proportion as the number of extended cavity increases. Moreover, the entanglement encoded in the photonic states can be transferred towards ancillary two-level systems to generate genuine multipartite entanglement. Finally, we discuss the feasibility of our proposal in circuit quantum electrodynamics. This proposal could be of interest in the context of quantum random number generator, due to the quadratic scaling of the output state. Full article