Frequency-doubled Signal Research Articles

Tunable and Reconfigurable Fundamental, Frequency-Doubled and Dual-Frequency RF Signal Generator

Tunable and Reconfigurable Fundamental, Frequency-Doubled and Dual-Frequency RF Signal Generator

Dual vector millimeter-wave signal generation based on optical carrier suppression modulation and direct detection with one photodetector.

We propose a novel, to the best of our knowledge, scheme for dual vector millimeter-wave (mm-wave) signal generation and transmission, based on optical carrier suppression (OCS) modulation, precoding, and direct detection by a single-ended photodiode (PD). At the transmitter side, two independent vector radio frequency (RF) signals with precoding, generated via digital signal processing (DSP), are used to drive an in-phase/quadrature (I/Q) modulator operating at the optical OCS modulation mode to simultaneously generate two independent frequency-doubling optical vector mm-wave signals, which can reduce the bandwidth requirement of transmitter's components and enhance spectral efficiency. With the aid of the single-ended PD and subsequent DSP at the receiver side, two independent frequency-doubling vector mm-wave signals can be separated and demodulated without data error. Based on our proposed scheme, we experimentally demonstrate the generation, transmission, and detection of 2-Gbaud 30-GHz quadrature-phase-shift-keying (QPSK) and 2-Gbaud 46-GHz QPSK signals over 10-km single-mode fiber-28 (SMF-28) and 1-m wireless transmission. The results indicate that the bit-error ratio (BER) of the dual vector mm-wave signals can each reach the hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10-3.

A Microwave Photonic Frequency-Doubling Phase Shifter Based on Dual-Parallel Mach–Zehnder Modulators

A microwave photonic frequency-doubling phase shifter with a broad bandwidth and large tuning range is proposed in this paper. Frequency doubling and phase shifting are realized by processing the input microwave signal in the optical domain at a dual-drive dual-parallel Mach–Zehnder modulator (DD-DPMZM) and a dual-parallel Mach–Zehnder modulator (DPMZM). The input signal is split into two branches through a 90-degree hybrid splitter. One signal is sent to the DD-DPMZM to achieve a phase-shifted carrier-suppressed up-sideband by tuning the bias voltage, and the other is sent to the DPMZM to realize a carrier-suppressed down-sideband. By beating the phase-shifted up-sideband and the down-sideband at a photodetector (PD), the input signal is frequency doubled and phase shifted. The proposed frequency-doubling phase shifter is simulated. The results show that the frequency-doubled signal has a phase-tuning range from 0 to 360 degrees. In addition, the influence of the amplitude and phase unbalance of the 90-degree hybrid splitter on the magnitude variation and phase deviation of the frequency-doubling phase shifter is studied.

Durable Testing and Analysis of a Cleaning Sieve Based on Vibration and Strain Signals

Cleaning is one of the most important steps in the harvesting process, and the prolonged and high-load operation of the vibrating sieve can decrease its reliability. To uncover the structural flaws of the cleaning sieve in the crawler combine harvester and establish a foundation for quality inspection, this paper proposes a method for durability testing and analysis using vibration and strain signals. Via the modal analysis of the cleaning sieve, the most susceptible areas for fault signals are identified. Subsequently, a specialized test rig exclusively designed for the examination of the durability of the cleaning sieve is constructed. After following 96 h of uninterrupted operation, the vibration plate of the cleaning sieve sustains damage, resulting in atypical noise. A signal analysis reveals that the primary vibration signal of the cleaning sieve primarily consists of a fundamental frequency of 5 Hz, corresponding to the driving speed, as well as a frequency doubling signal of 50 Hz. After the occurrence of damage, the peak amplitude of the received vibration signal increases by over 86.3%. Furthermore, the strain gauge sensor situated on the support plate of the rear sieve detects anomalous signals with frequencies exceeding 300 Hz, which are accompanied by a considerable rise in the power spectral density. This research has significant importance for enhancing the service life of the cleaning sieve and optimizing the overall machine efficiency.

Frequency-Doubled Triangular Pulse Signal Generation with Variable Symmetry Based on a Dual-Polarization Quadrature Phase-Shift Keying Modulator

Frequency-Doubled Triangular Pulse Signal Generation with Variable Symmetry Based on a Dual-Polarization Quadrature Phase-Shift Keying Modulator

Precision improvement of patch potential measurement in a scanning probe equipped torsion pendulum

Patch effect is important for ultra-sensitive experiments involving closely spaced conducting surfaces. A scanning probe equipped torsion pendulum is an experimental apparatus for measuring spatial resolved patch potential on conductive surfaces. An effective approach to improve its measurement precision is by the optimization on the amplitude and frequency of the injected signal in the probe. In this paper, a method based on single- and double-frequency signal injection modes is proposed. The analysis results demonstrate that the potential resolution could achieve the level of 2-4 μV/Hz1/2. In the same integration time, the surface potential precision in the double-frequency mode is twice better than that in the single-frequency mode. In addition, when achieving the same measurement precision, the double-frequency mode takes less time than the single-frequency mode, which improves the measuring efficiency.

Widely tunable frequency-doubling optoelectronic oscillator using a polarization modulator and a phase-shifted fiber Bragg grating

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

Nonlinear Suppression of a Dual-Tube Coriolis Mass Flowmeter Based on Synchronization Effect

Nonlinear interference components exist in the output signals of dual-tube Coriolis mass flowmeters (CMFs) which affect the sensitivity and accuracy of the devices. This nonlinearity still appears under zero flow, which is manifested when the output signal contains a frequency doubling signal. This study (1) investigated an additional-mass method to suppress the nonlinear frequency doubling phenomenon, (2) established a coupling system vibration model with additional mass, built a dynamic differential equation for the vibration of the double-beam coupling system from the Lagrange equation, (3) obtained amplitude frequency information using a fourth-order Runge–Kutta method, (4) determined the suppression effect of the additional mass on the nonlinear frequency doubling phenomenon, and (5) experimentally verified the CMF. The results showed that the base coupled the vibrations of two beams, and the symmetric additional mass suppressed the nonlinear frequency doubling phenomenon, thus suppressing low or high frequencies. Also, the effect of pipeline defects simulated under asymmetric additional mass was obtained through numerical analysis and experimental data. Flowmeters with a required measuring frequency range had the optimal suppression effect on nonlinear frequency doubling and provided theoretical guidance for the nondestructive testing of measuring tubes.

Second harmonic generation in thin permalloy film

Second harmonic generation versus strength and direction of the applied static magnetic field was measured for a thin permalloy (Ni80Fe20) film in a microstrip line at a driving frequency of 1 GHz and maximum input power of ∼110 mW. The measurements revealed two peaks in the double frequency signal—in the low static field (∼10 Oe) and the high one (∼45 Oe). To explain these findings, a macrospin model of a thin magnetic film with in-plane uniaxial magnetic anisotropy was considered. A perturbation expansion of the Landau–Lifshitz–Gilbert equation provided an explanation of the experimental data. The analysis of the model revealed that the low-field peak was caused by the longitudinal second-order magnetization component and the high-field peak by the transversal one. It was also shown that the uniaxial magnetic anisotropy of the film and the dependence of the magnetic damping parameter on the applied field play an important role in the process of the second harmonic generation. The results obtained give insights into some peculiarities of the nonlinear magnetization dynamics that are important in the development of magnetic film-based devices in the field of microwave signal processing and manipulation.

Development of a deep-ultraviolet pulse laser source operating at 234 nm for direct cooling of Al+ ion clocks.

We report on the development of a 250-MHz 234 nm deep-ultraviolet pulse source based on a flexible wavelength-conversion scheme. The scheme is based on a frequency-doubled optical parametric oscillator (FD-OPO) together with a cascaded frequency conversion process. We use a χ(2) nonlinear envelope equation to guide the design of an intra-cavity OPO crystal, demonstrating a flexible broadband tunable feature and providing as high as watt-level of a frequency-doubled signal output centered at 850 nm, which is served as an input wave for the cascaded frequency conversion process. As much as 3.0 mW of an average power at 234 nm is obtained, with an rms power stability of better than 1% over 20 minutes. This deep-ultraviolet pulse laser source can be used for many applications in quantum optics and for direct laser cooling of Al+ ion clocks.

Tunable frequency-multiplying optoelectronic oscillator based on a dual-parallel Mach-Zehnder modulator incorporating a phase-shifted fiber Bragg grating

A tunable frequency-multiplying optoelectronic oscillator (OEO) based on a dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. In the proposed system, the tunable fundamental microware signal is generated by a tunable optoelectronic oscillator incorporating a phase-shifted fiber Bragg grating (PS-FBG). By adjusting the DC bias of the DPMZM, the frequency-doubled microwave signal with a tunable frequency range from 11 GHz to 20 GHz and the frequency-quadrupled microwave signal with a tunable frequency range from 22.5 GHz to 26 GHz are generated. The phase noises of the fundamental, frequency-doubled and frequency-quadrupled signals at 10 kHz offset frequency are −105.9 dBc/Hz, −103.3 dBc/Hz and −86.2 dBc/Hz, respectively.

Revisiting the Fresnel-phase-matched nonlinear frequency conversion

A flexible phase-matching method is introduced to manipulate the energy flow in nonlinear frequency conversion processes. With the use of photonic crystal as the reflective medium, the phase mismatching could be adjusted by the interface and the nonlinear crystal. We call this method the reflective phase matching. Here we present an experiment to demonstrate this idea in a single-domain MgO:CLN wafer with photonic crystal on the surface. A frequency-doubling signal enhanced 52 times is achieved. The result suggests the potential of the function to one more dimension phase matching without additional artificial structure inside the crystal. In addition, the proposed reflective phase-matching method could find broad application in the nonlinear optics and laser device miniaturization and integration.

Photonic full-range phase shifter with simultaneous tunable frequency multiplying capability based on a DMZM

In this paper, a novel microwave photonic full-range phase shifter with simultaneous frequency-multiplying capability is proposed. The main device is a dual-drive Mach–Zehnder modulator (DMZM) embedded in a Sagnac loop. Under the assistance of two electrical phase shifters (EPS) and a following polarizer (Pol), the optical carrier is eliminated with desired phase tunable carrier-suppressed double-sideband (CS-DSB) signal reserved. So after photoelectric conversion, the frequency-multiplied phase tunable signals are generated. The frequency multiplication factor (FMF) switching and phase tuning operation of multiplied signals can be achieved easily by adjusting the corresponding EPS. The simulation results show that the proposed structure driven by a 10 GHz RF signal can generate a frequency-doubled signal (20 GHz) or frequency-quadrupled signal (40 GHz) that features full-phase tunable range and flat power response. What is more, the proposed phase shifter has a relatively good robustness to the non-ideal factors, large frequency operation range and good frequency tunable capability.

Wideband and Dispersion Immune Microwave Photonic Phase Shifter With Tunable Optical Carrier to Sideband Ratio

A wideband microwave photonic phase shifter (MPPS) based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is proposed and experimentally demonstrated. The proposed system has the features of chromatic dispersion (CD) immunity and tunable optical carrier to sideband ratio (OCSR), which can realize long fiber transmission distance with improved power efficiency. It is realized by carrier suppress double sideband (CS-DSB) plus optical carrier (OC) modulation at two orthogonal polarization states. The phases of output RF signals can be tuned continuously and independently by controlling the phases of the OCs. The experiment results show that the continuous 360° phase shifts of output RF signal over 5–25 GHz are both realized in the cases of back-to-back and fiber transmission. No CD-induced power fading and phase severe shaking of the RF signals appear after the dispersion compensating fiber (DCF) of −331 ps/nm at 1545 nm transmission. By optimizing the OCSR of the system, the output RF power efficiency of the proposed scheme realizes significantly improvement when input RF powers and output optical powers are both fixed. The possibility of generating frequency doubling signal is also verified.

Tunable microwave generation utilizing monolithic integrated two-section DFB laser

Tunable microwave generation and frequency up-conversion are demonstrated utilizing a monolithically integrated two-section DFB laser. The frequency of the microwave signal is tuned from 13 GHz to 40 GHz, which can be further improved by adjusting the wavelengths of the DFB lasers. Utilizing the sideband optical injection locking technique, frequency-doubled microwave signals with low phase noise of −100.9 dBc/Hz at 10 kHz and narrow linewidth of 102 Hz are obtained. In addition, the tunable range of frequency-doubled and frequency-quadrupled microwave signals are also investigated respectively.

Comparison of Acoustic and Nonlinear Optic Properties of Strontium Barium Niobate Crystals of Different Compositions

abstractBrillouin spectra and generation of the second optical harmonic in a series of SBN-x crystals with different chemical compositions are investigated in the 115–850 K temperature range. The integral intensity of the second harmonic signal follows the Arrhenius law with activation energies of ΔU = 0.09–0.3 eV. The second harmonic generation (SHG) is observed in paraelectric phase of the SBN-x crystals, revealing the presence of polar regions in the paraelectric phase. The spectral width of the SHG spectrum does not exceed 0.3 cm−1 and is temperature independent. Upper limit of the spectral width of the SHG spectrum provides lower limit of the lifetimes of polar regions, which are longer than 15 ps. It suggests that the doubled frequency signal in the paraelectric phase of the SBN-x crystals is generated in areas with lifetimes longer than 15 ps. It is shown that local polar regions cannot explain the anomalies of the elastic module near the ferroelectric phase transition in SBN-x.

Measurement of femtosecond pulses based on transient grating frequency-resolved optical gating

Femtosecond pulse measurement of ultrafast spectrum is one of the important research directions in the ultrafast laser field. The conventional femtosecond pulse autocorrelation method is implemented by measuring the autocorrelated frequency-doubling signal, and the frequency-doubling signal has wavelength selectivity, so the femtosecond pulse measurement for the case of different central wavelengths needs to replace different frequency-doubling crystals, which is very inconvenient. This paper reports a kind of modified transient grating frequency resolution optical gating for measuring the femtosecond pulses. The method combines frequency-resolved optical gating (FROG) method with four-wave mixing. Its basic process is to divide the pulse to be measured into three beams. Two of the pulses can reach spatiotemporal coincidence on optical medium through precise delay control and focus. The other pulse interacts with the transient grating, and serves as the detection light to produce signal light. The spectrum and delay time of the signal light are measured by a spectrometer, and the spectrum and electric field information of the femtosecond pulse to be measured are obtained through the inversion iterative algorithm. Because this method only needs the power density of the measured light to reach the third-order nonlinear effect, it can be applied to the femtosecond pulse measurement of any central wavelength. We use this method to measure the femtosecond pulses with the central wavelengths of 800 nm and 400 nm respectively, and the ultra-wide spectrum femtosecond pulses with the period magnitude of sub-10 fs, and compare the measurement results with the results obtained with the conventional interferometric autocorrelation instrument. They are basically consistent. The experimental results show that our frequency-resolved optical switching method based on transient grating is very effective for measuring the femtosecond pulses with different central wavelengths and pulse widths.

Photonic Vector Signal Generation Based on OEO and Optical Coherent QPSK Modulation

A novel scheme for photonic vector signal generation based on a self-starting optoelectronic oscillator (OEO) and optical coherent quadrature phase-shift keying (QPSK) modulation is proposed and experimentally demonstrated. The optical output sidebands of the OEO are employed for optical heterodyne mixing, where one first-order sideband is modulated by QPSK baseband data using a dual-parallel Mach–Zehnder modulator, followed by coherent detection so as to directly generate frequency-doubled K-band vector signals. In the experiment, a 19.9 GHz QPSK modulated vector signal with a bit rate of 100 Mb/s is generated when the OEO operates at 9.95 GHz. The generated signal is back demodulated with error vector magnitude (EVM) less than 7%.

Harmonic generation and frequency mixing at nonlinear imperfect interfaces

Imperfect interfaces can be found in a variety of natural and artificial systems. Some examples of such interfaces that are objects of ultrasonic evaluation and diagnostics include contacting mechanical components as well as closed defects in structural components. A remarkable feature of these interfaces is that they exhibit highly nonlinear responses to ultrasonic waves. Harmonic generation (generation of, e.g., double frequency signals at the incidence of a wave with a certain frequency) and frequency mixing (generation of sum/difference frequency signals at the incidence of waves of two different frequencies) are typical phenomena at these interfaces. In this presentation, a theoretical analysis of these phenomena is presented based on modeling the interface as a nonlinear spring-type interface between two similar linearly elastic media. Unlike the corresponding nonlinear acoustic effects due to material nonlinearity, the interfacial nonlinear effects considered here do not require the spatial accumulation of nonlinearly generated harmonic or sum/difference frequency components. The propagation directions and amplitudes of these nonlinearly generated components are derived for plane mono- or dichromatic incident waves. Some relevant experimental results for a contacting interface of metallic blocks subjected to different applied pressures are also presented.

A Solution for Real-Time Ionospheric Delay Using an Adaptive Kalman Filter Based on Estimating the Variance Component

Real-time solution of Global Navigation Satellite System (GNSS) epoch-differenced ionospheric delay (DID) is of great significance for real-time cycle slip detection and repair of multi-GNSS dual-frequency or trifrequency undifferenced measurements under high ionospheric activity. We construct a dynamic model of DID and perform a real-time estimate of the noise level of DID based on estimating the variance component. The estimated and predicted values of DID are obtained by designing a new adaptive Kalman filter algorithm with colored noise. Combining the predicted value and the detection method for cycle slips for Melbourne-Wübbena (MW) and Geometry-Free (GF) combination and taking into account the correlation between the predicted value and the carrier signal, we estimate the cycle slip, N2, on the second frequency of the carrier signal. The prediction and estimate of DID and detection and repair of dual-frequency cycle slip of multisystem undifferenced phase observations are measured with the GNSS multisystem observational data at different sampling rates (30 s, 15 s, 10 s, and 1 s). The results show that the DID model constructed in this paper is correct. The predicted value of DID has a high accuracy, which can effectively assist in dual-frequency cycle slip detection and repair. (1) The obtained predicted values, the estimated value, and the difference value between the two values of DID are less than 1.2 cm (STD), 1.2 cm (STD), and 0.6 cm (STD), respectively; (2) the precisions of the detection of cycle slip for MW, GF, and N2 are less than 0.083 cycles (STD), 0.4 cm (STD), and 0.071 cycles (STD), respectively; (3) with the obtained predicted value of DID to aid the detection and repair of cycle slip in GNSS double-frequency signals, a success rate of 100% can be reached.