Frequency-doubled Signal Research Articles

Frequency-Doubled Microwave Signal Generation and Phase Shifting With Arbitrary Signal Amplitude

A photonic-assisted frequency-doubled microwave signal generation and phase shifting approach with arbitrary signal amplitude is proposed. The key device in the proposed technique is a dual-polarization quadrature phase-shift keying modulator, whose two sub-dual-parallel Mach-Zehnder modulators are both biased as a carrier-suppressed single-sideband modulator but generating two opposite first-order optical sidebands. The phase difference between the orthogonally polarized two first-order optical sidebands and the polarization state of the optical signal are tuned independently by a polarization controller. After the optical signal from the polarization controller is combined via a polarizer and detected at a photodetector, a frequency-doubled microwave signal is generated, whose phase and amplitude can be independently controlled by tuning the polarization controller. An experiment is performed. Frequency-doubled microwave signals with carrier frequencies from 10 to 40 GHz are generated and phase shifted over 360° phase range with arbitrary signal amplitude. The proposed technique can not only be operated as a phase and amplitude tunable frequency-doubled microwave source, but also find applications in phased array radar systems as a wideband frequency-doubled multichannel phase shifter.

Spin current and second harmonic generation in non-collinear magnetic systems: the hydrodynamic model

We report a theoretical study of the second harmonic generation in a noncollinearly magnetized conductive medium with equilibrium spin current. The hydrodynamic model is used to unravel the mechanism of a novel effect of the double frequency signal generation that is attributed to the spin current. According to our calculations, this second harmonic response appears due to the ‘non-adiabatic’ spin polarization of the conduction electrons induced by the oscillations in the non-uniform magnetization forced by the electric field of the electromagnetic wave. Together with the linear velocity response this leads to the generation of the double frequency spin current. This spin current is converted to the electric current via the inverse spin Hall effect, and the double-frequency electric current emits the second harmonic radiation. Possible experiment for detection of the new second harmonic effect is proposed.

Microwave frequency doubling by synchronising and polarisation multiplexing the optical signals from a dual‐output Mach–Zehnder modulator

A technique is experimentally demonstrated to double the frequency of a microwave signal by synchronising and polarisation multiplexing the optical signals from a dual-output Mach–Zehnder modulator. The frequency-doubled tone at 4 GHz is 41.2 dB stronger than the residual fundamental-frequency tone. The strongest side tone is found at 12 GHz (sixth order) and is suppressed by 32.7 dB. The phase noise of the frequency-doubled signal is −104.1 dBc/Hz at an offset of 10 kHz, an increase of 6.7 dB over that of the initial signal. This technique does not rely on electronic or optical filters or amplifiers and is demonstrated using commercial off-the-shelf components.

Multi-format signal generation using a frequency-tunable optoelectronic oscillator.

A novel photonic approach for multi-format signal generation based on a frequency-tunable optoelectronic oscillator (OEO) is proposed using a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) integrated in the DP-QPSK modulator is properly biased to serve as an equivalent phase modulator, which functions in conjunction with a phase-shifted fiber Bragg grating (PS-FBG) in the OEO loop as a high-Q microwave photonic band-pass filter. The lower DP-MZM in the DP-QPSK modulator injected by the oscillation signal functions as a frequency multiplier, a phase-coded microwave signal generator or an optical frequency comb generator, respectively, with different signal injection methods. An experiment is performed. When the lower DP-MZM serves as a frequency multiplier, tunable frequency-doubled and quadrupled microwave signals up to 40 GHz are generated without using an optical notch filter; and if it functions as a phase-coded microwave signal generator, fundamental and frequency-doubled binary phase-coded microwave signals are generated with a tunable frequency. Furthermore, tunable five-line optical frequency combs are also generated using the compact system without an external RF source. The performance of the generated signals is also investigated.

Photonic Microwave Waveforms Generation Based on Frequency and Time-Domain Synthesis

In this paper, a novel photonic microwave waveform generation method with both frequency-domain synthesis (FDS) and time-domain synthesis (TDS) is proposed, for the first time to the best of our knowledge, by using cascaded modulation and an optoelectronic oscillator. By controlling the spectral lines in a polarization-modulated optoelectronic oscillator (P-M-OEO), a triangular waveform is generated according to the FDS, where a parallel part of the optimum modulation axis of the Mach–Zehnder modulator (MZM) executes carrier suppression in the P-M-OEO, while its orthogonal part is left unmodulated. A quasi-rectangular waveform is then generated by directly modulating another MZM at the quadrature point. Additionally, a sawtooth or reversed-sawtooth waveform with 50% duty cycle and 100% duty cycle can be generated in TDS. In the experiment, a 3-GHz triangular waveform, a 3-GHz high-quality microwave signal, a 6-GHz frequency doubling signal, a 3-GHz quasi-rectangular waveform, a 3-GHz 50% duty cycle sawtooth or reversed-sawtooth waveform, and a 100% duty cycle sawtooth or reversed-sawtooth with frequency doubling are obtained simultaneously. The results verify the feasibility of the proposed scheme, and it holds a potential candidate for applications in photonic microwave signals.

A Frequency-Tunable Binary Phase-Coded Microwave Signal Generator With a Tunable Frequency Multiplication Factor

A novel frequency-tunable binary phase-coded microwave signal generator with a tunable frequency multiplication factor is proposed. The key component of the proposed system is a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator, which is driven by the microwave reference signal and the coding signal. By properly controlling the bias points of the DP-QPSK modulator and the amplitudes of the microwave reference signal and the coding signal, a fundamental, frequency-doubled, frequency-tripled or frequency-quadrupled binary phase-coded microwave signal can be generated when two orthogonally polarized optical signals at the output of the DP-QPSK modulator are combined and then detected in a photodetector. The proposed system is experimentally evaluated. A binary phase-coded microwave signal is generated at the fundamental, doubled, tripled, or quadrupled frequency. The frequency tunability and the pulse compression performance of the generated phase-coded microwave signals are also experimentally studied.

A frequency multiplier for reference frequency in frequency synthesizer systems

A low jitter frequency multiplier, which requires less power, area, and design complexity than reference multiplying PLL or DLL circuits can be used to generate the reference frequency for a low phase noise frequency synthesizer. This paper proposes a mixed signal solution based on the fact that the average DC value of a signal is proportional to its duty cycle. The solution uses a feedback loop with coarse and fine delay resolution to generate a $$90^{\circ }$$ phase shifted clock that is used to produce a doubled frequency signal with 50% duty cycle. This method can be used to multiply the input frequency of 40 MHz by multiples of 2, up to 16. The design is implemented in 65 nm UMC CMOS process. Operating from 1.2-V supply, it dissipates 0.46 to 1.2 mA at output frequencies 80–640 MHz, achieving − 162.3 and − 139 dBc/Hz phase noise at 1 MHz offset, respectively.

Technique developments and performance analysis of chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering combustion thermometry.

This work characterizes the state of the art in the analysis of high-repetition-rate, ultrafast combustion thermometry using chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering (CPP fs-CARS). Several key aspects of the CARS spectroscopy system are described, including: (1)the ultrafast laser source, (2)use of the frequency-doubled idler versus signal from the optical parametric amplifier, (3)the geometry constraints for phase matching, and (4)spectral fitting for single-shot temperature measurements. A frequency-dependent instrument response function (IRF) for the detection system was modeled as a variable-width Gaussian and implemented through a frequency convolution of synthetic spectra. Proper accounting of the IRF increased spectral fitting performance in the high-frequency region where signal oscillations are weaker and narrower. Aggregated data from 25 system performance assessments taken over four months yielded accuracy and precision of 2.7% and ±3.5% for flame temperatures, and 9.9% and ±6.1% at room temperature, using the commonly reported method. A new processing technique, based on the statistical method of maximum likelihood, was implemented for turbulent flames where strong fluctuations in expected temperatures necessitate use of multiple temperature calibrations. Results from multiple sets of laser parameters are combined to generate an error-weighted temperature from the top-performing calibrations. A testing procedure was designed to characterize system performance when the range of expected temperatures is unknown, simulating the random temperature field of a highly turbulent flame. Accuracy error of the CPP fs-CARS system increased in this more-stressing test at all temperatures, but precision was significantly affected only at room temperature. System stability is characterized, and the contribution from shot-to-shot laser fluctuations on measurement precision is quantified. Finally, the near-adiabatic and steady assumptions for the Hencken burner calibration flame are examined in an axial scan; significant deviations from ideal behavior were observed only at heights of more than four diameters above the burner surface.

Residual Phase Noise Measurement of Optical Second Harmonic Generation in PPLN Waveguides

We report on the characterization, including residual phase noise and fractional frequency instability, of fiber-coupled PPLN non-linear crystals. These components are devoted to frequency doubling 871 nm light from an extended-cavity diode laser to produce a 435.5 nm beam, corresponding to the ytterbium ion electric quadrupole clock transition. We measure doubling efficiencies of up to 117.5 %/W. Using a Mach-Zehnder interferometer and an original noise rejection technique, the residual phase noise of the doublers is estimated to be lower than ${\rm -35\, dBrad^2/Hz}$ at 1 Hz, making these modules compatible with up-to-date optical clocks and ultra-stable cavities. The influence of external parameters such as pump laser frequency and intensity is investigated, showing that they do not limit the stability of the frequency-doubled signal. Our results demonstrate that such compact, fiber-coupled modules are suitable for use in ultra-low phase noise metrological experiments, including transportable optical atomic clocks.

Pattern Matching Performance Analysis Based on Linear Models with Information Backscattered from RFID Tags

Pattern matching localization algorithms are commonly proposed in complex indoor environments. Received signal strength indicator (RSSI) of radio signals backscattered from passive ultra high frequency radio frequency identification (RFID) tags is commonly used as the pattern in matching process. Considering RSSI is severely affected by multipath propagation and noise, etc., more types of patterns will be a better choice for further study. In recent years, phase information is becoming more and more important for RFID-based systems. As for the period ambiguity problem of wrapped phase information, phase difference of arrival (PDOA) of double-frequency signals can be utilized as a type of pattern instead of phase of arrival corresponding to the propagation distance. In this paper, we combine RSSI and PDOA as a brand new type of pattern named RP. In previous study, only localization accuracy is considered to prove effective. It is hard to show the matching performance of the type of pattern with the following process of localization algorithms. Here we take advantage of the linear relationship between pattern Euclidean distance and geographic locations Euclidean distance of tags fixed in reference points to evaluate the distinctiveness performance of RP in matching. The linear correlation of the model is tested at each reference point with experimental data captured from indoor scenario. By evaluating these models statistically, we think RP is better than RSSI and PDOA as a pattern.

Tunable frequency-doubled optoelectronic oscillator based on a phase modulator in a Sagnac loop

A tunable frequency-doubled optoelectronic oscillator (FD-OEO) scheme based on a phase modulator (PM) located in a Sagnac loop is proposed and experimentally demonstrated. A light wave is halved and sent to the Sagnac loop along the clockwise (CK) and counter-clockwise (CCK) directions. The light wave along the CK direction is effectively modulated in the PM, while the one along the CCK direction is not modulated due to velocity mismatch. The optical output from the Sagnac loop is separated into two parts. One part is fed back to the radio-frequency (RF) port of the PM to form an OEO loop and obtain a fundamental signal. The other part is used to obtain a frequency-doubled signal by suppressing the optical carrier. The fundamental frequency of the OEO is continuously adjustable within the range from 3 to 20GHz using a tunable electric filter, so a frequency-doubled signal with a frequency ranging from 6 to 40GHz can be obtained. The phase noise performance of the generated fundamental and frequency-doubled signal is also studied.

Frequency conversion with nonlinear graphene photodetectors

Frequency conversion with nonlinear electronic components, a common approach for signal processing required in various communication applications, has found its operation bandwidth bottleneck due to the limited carrier mobility of the traditional materials. Meanwhile, fiber-optics communications are playing a significant role in communication services due to their excellent signal transmission properties. However, the transmitted optical signals had to be converted to electrical signals with photodetectors before frequency conversion was performed through conventional electronic devices, which make this conversion system very complex and costly. Hence, to develop a compact device that can achieve the photodetection and frequency conversion functions simultaneously is critical and significative. Here, we have proposed a novel concept for frequency conversion and demonstrated a nonlinear graphene photodetector based frequency converter that performs frequency conversion from optical signals directly. With this new concept, a frequency doubling signal at 4 GHz was obtained from a 2 GHz intensity-modulated optical signal. Moreover, using a 10 MHz intensity-modulated optical signal and another 3 GHz intensity-modulated optical signal, we show the frequency up-conversion to 3 ± 0.01 GHz. In particular, the frequency down-conversion to 100 MHz was achieved successfully by using a 2 GHz intensity-modulated optical signal and another 2.1 GHz intensity-modulated optical signal. Considering the broadband optical absorption, strong saturable absorption, high carrier mobility, and short photogenerated carrier lifetime of the graphene material, graphene photodetectors have the potential to achieve the frequency conversion of millimeter-wave band, which will open promising prospects in the domain of microwave photonics for next-gen communication systems.

Photonic Frequency Down-Converter based on a Frequency-Doubling OEO using Two Cascaded EAMs

A photonic frequency down-converter based on a frequency-doubling optoelectronic oscillator (OEO) using two cascaded electro-absorption modulators (EAMs) is proposed and experimentally demonstrated. The use of the two cascaded EAMs allows the OEO feedback loop used to generate the local oscillator (LO) signal and the down-conversion section to be structurally isolated, so that the proposed photonic frequency down-converter has high RF to LO isolation. The phase noise of the frequency-doubled 20-GHz LO signal and that of the down-converted 3-GHz IF signal were measured to be −97.80 and −95.32 dBc/Hz at an offset frequency of 10 kHz, respectively. The spurious free dynamic range measured using a two-tone test was 87.02 dB $\cdot $ Hz2/3. The bit error rate performance was also investigated with a 20-GHz RF signal modulated by 1.25 Gb/s data.

Photonic generation of frequency-decupled microwave signal based on cascaded Mach-Zehnder modulators

In order to effectively solve the generation problem of high frequency microwave signal, a frequency-decupled signal generation system based on two cascade Mach-Zehnder modulators (MZMs) is proposed. The RF drive signal is modulated by the first MZM, by adjusting the bias voltage, it is biased at the minimum transmission point (MITP). The generated signal is partly sent to the photoelectric detector (PD1) to heterodyne the first-order sidebands. With an optical coupler, the generated first-order sidebands are also used as the optical source for the second modulation. The generated frequency-doubled signal is modulated by the second MZM which is biased at the maximum transmission point (MATP), then the fifth-order sidebands signal are separated by a fiber Bragg grating from the generated sidebands. With the EDFA and PD2, the generation of a frequency-decupled microwave signal is realized. The structure is also verified by experiments, a frequency-decupled signal from 15 to 27GHz is generated by the drive source signal which is tuned from 1.5 to 2.7GHz.

Photonic low phase-noise frequency-doubling signal generation based on optoelectronic oscillator

A kind of photonic low phase-noise frequency-doubling signal generation based on an optoelectronic oscillator (OEO) is demonstrated in this paper. A microwave source drive signal is modulated on the optical signal with the first Mach-Zehnder modulator (MZM) which is biased at the minimum transmission point (MITP) to eliminate the first-order sidebands and suppress even-order sidebands. The modulated optical signal is sent to the second MZM and the multimode OEO loop which is contributed by the single mode fiber (SMF), photo-detector (PD) and RF amplifier. The frequency-doubling signal is generated by the beating of the two sidebands at a PD. Using the high Q optical comb frequency response to select the oscillation mode of the multimode OEO loop, the system can effectively improve the phase noise performance of the generated frequency-doubling signal. In the experiment, C-band and X-band signal can implement frequency doubling, compared with the microwave drive signal, above 20dB phase-noise reduction at 10kHz frequency offset from the center frequency is realized. With low cost and simple system, frequency-doubling signal with low phase-noise is realized.

Frequency-multiplying microwave photonic phase shifter for independent multichannel phase shifting.

A frequency-multiplying microwave photonic phase shifter with independent multichannel phase shifting capability is proposed and demonstrated using an integrated polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) and a polarizer. By building a proper power distribution network to drive the PDM-DPMZM, two sidebands along two orthogonal polarization directions are generated with a spacing of two or four times the frequency of the driving signal. Leading the signal to a polarizer and a photodetector, a frequency-doubled or frequency-quadrupled signal with its phase adjusted by the polarization direction of the polarizer is achieved. The magnitude of the signal remains almost unchanged when the phase is adjusted. The proposed approach features compact configuration, scalable independent phase-shift channels and wide bandwidth, which can find applications in beam forming and analog signal processing for millimeter-wave or terahertz applications.

A compact frequency‐doubling opto‐electronic oscillator using cascaded electroabsorption modulators

ABSTRACTA compact frequency‐doubling optoelectronic oscillator (FD‐OEO) using two cascaded electro‐absorption modulators (EAMs) is proposed and experimentally demonstrated. The FD‐OEO is configured with two cascaded EAMs driven by signals having a 180° phase difference, so that the second EAM produces an output signal with a suppressed first‐order side band, thus generating a frequency doubled signal. The phase noise characteristics of the fundamental (10 GHz) and frequency‐doubled (20 GHz) signals are measured to be −94.25 dBc/Hz and −87.71 dBc/Hz, respectively, at a frequency offset of 10 kHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:526–529, 2016

Frequency-Doubling OEO Using the Polarization Property of LiNbO<sub>3</sub> Modulator

A frequency-doubling optoelectronic oscillator (OEO) has been proposed. In the proposed device, several passive components are introduced into the traditional OEO to handle the polarization state of the laser in the feedback loop. Making use of the polarization dependence of the LiNbO3 intensity modulator, a special double sidebands modulation is implemented where the polarization direction of the optical carrier is orthogonal with that of the first-order sidebands. Two polarizers are used to choose the specific optical components from the modulated light, which ensures that a microwave signal at the second-harmonic frequency outputs from the OEO when the fundamental frequency signal is self-oscillating in the loop. In the experiment, a 20-GHz frequency-doubled signal was generated, whose phase noise performance and immunity to the polarization drift were measured and evaluated.

A New Cascaded Stochastic Resonance System and its Application to Weak Double-Frequency Signal Separation

Weak signal detection has attracted many researchers attention all over the world. Most of the methods focus on the single frequency signal. This paper introduces a new method to separate the weak double-frequency signal overwhelmed in heavy background noise. The cascaded stochastic resonance (SR) system (CSRS) is composed of a bistable SR model in the first stage and a tristable one in the second. Based on the characteristic of the SR system, we can amplify the useful signal of high frequency using twice sampling technic to make its parameters matching the requirements of the system. In our proposed cascade stochastic resonance system, we highlight the appointed frequency from high to low successfully with adjusting the twice sampling multiple and the high pass filter band. The signal composition of different frequency can be obtained from the systems two stage output. Simulated experiment validates the CSRSs availability in weak double-frequency signal separation and also its promising application in a more complex mixed signal.

红外气体检测中谐波信号正交锁相放大器设计与实现

In order to efficiently extract the first and second harmonic signals from the differential signal in infrared gas detection based on tunable laser absorption spectroscopy,an orthogonal phase lock-in amplifier was developed.According to the principle of orthogonal lock-in amplifier and harmonic detection,the simulative experiment system based on Simulink platform was set up,and its functions were simulated and verified.The hardware system is designed and developed by adopting a digital signal processor as its core controller,which is mainly composed of a 90°phase shifter,two analog multiplier,two low pass filter,a differential signal amplifier and an AD converter.In experiment,firstly,by using standard sine-wave signals with tunable amplitudes as the signals to be measured,the amplitudes of the output signals from the fabricated lock-in amplifier and the standard amplitudes are both tested and compared.Good linear relationship is found between them,the linear fitting degree is as high as 0.99994,and the maximum error is less than 4%.Secondly,using the simulated differential signal with gas absorption as the signal to be measured,and by using fundamental square wave signal and frequencydoubled square wave signals as reference signals,both first and second harmonic signal are extracted.Because the second harmonic signal is too weak and easy to be polluted by noises,its detection error is less than 5%,and that of the first harmonic signal is less than 3.5%.The proposed system has good applicative prospects in infrared gas detection due to good stability and high price ratio.