Frequency Down-conversion Research Articles

Cascaded modulator topology for frequency conversion in antenna remoting applications.

A new cascaded modulator structure that has the ability to realize high conversion efficiency microwave frequency downconversion, while at the same time able to overcome two fundamental limitations in the dual-parallel modulator approach, is presented. It is based on utilizing the polarization-dependent modulation efficiency property in LiNbO3 electro-optic modulators. The new structure allows the modulators for the RF signal and local oscillator (LO) modulation to be placed in different locations suitable for antenna remoting applications, and it has infinite isolation between the LO and RF signal ports. We present experimental results demonstrating that the proposed structure can be used to realize high conversion efficiency frequency downconversion over wide RF and intermediate frequency (IF) signal frequency ranges as the reported dual-parallel-modulator-based microwave photonic frequency downconverter. Very high isolation of more than 70dB between the LO and RF signal ports is also demonstrated.

Low Threshold, Dual-Wavelength, Mid-Infrared Optical Parametric Oscillator

In this letter, we demonstrated a dual-wavelength (DW) mid-infrared optical parametric oscillator (OPO) that was pumped by two independent fiber lasers fixed at 1018 nm and 1080 nm, and realized phase-matched signal beam coupling by tuning grating period of PPLN. Based on signal beam coupling, two interesting phenomena were observed for the first time. One is that the OPO threshold for 1018 nm and 1080 nm pump beams could be drastically lowered from 15.4 W to 266 mW and from 13.5 W to 1.38 W separately. The other is that the total idler power obtained when the OPO was simultaneously pumped by two fiber lasers was higher than sum of idler power obtained when the OPO was independently pumped by two fiber lasers, revealing obvious parametric gain enhancement. It also indicated that the two independent OPO processes became coherent when two signal beams were coupled. The results exhibit great potential in practical applications such as frequency down-conversion of some special near-infrared laser sources such as pulsed single-frequency sources, spectrum high-speed swept sources, and ultra-short pulse sources with low duty cycle.

High-Linearity Bottom-Plate Mixing Technique With Switch Sharing for $N$-path Filters/Mixers

A four-path filter/mixer for surface acoustic wave (SAW)-less frequency division duplex (FDD) radio receivers is proposed, targeting high linearity and compression requirements. A bottom-plate mixing technique improves linearity by reducing the gate-source voltage modulation of the MOSFET switches. Differential bottom-plate mixing allows for switch sharing which halves the effective switch resistance to reduce drain-source voltage modulation. The first four-path switch-RC filter stage with bottom-plate mixing and a shared switch renders 2nd-order voltage-domain RF-bandpass filtering around the LO frequency. Extra out-of-band rejection is implemented combined with V-I conversion and zero-IF frequency down-conversion in the second cross-coupled switch-RC four-path stage, which offers a low-ohmic high-linearity current path for out-of-band interferers. A prototype chip fabricated in a 28-nm CMOS technology achieves an out-of-band IIP3 of +44 dBm, IIP2 of +90 dBm and blocker 1-dB gain-compression point of +13 dBm for a blocker frequency offset of 80 MHz. At this offset frequency, the measured desensitization is only 0.6 dB for a 0-dBm blocker, and 3.5 dB for a 10-dBm blocker at 0.7-GHz LO (i.e., 6- and 9-dB blocker noise figure). The chip consumes 38-96 mW for LO-frequencies of 0.1-2 GHz and occupies an active area of 0.49 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Analysis, Calibration, and Performance Evaluation of a Generalized &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$N$ &lt;/tex-math&gt; &lt;/inline-formula&gt;-Phase Quadrature Phase Shift Frequency Selective Receiver

In this paper, a new low-power and blocker-tolerant receiver architecture, the generalized N-phase quadrature phase shift frequency selective (QPS-FS), is proposed and analyzed that is suitable for radio frequency (RF) energy harvesting networks. A complete comparative analysis of the N-phase QPS-FS receiver with conventional N-path passive mixer (P-M) receiver is also provided. The QPS-FS receiver utilizes the impedance translation concept to improve the receiver selectivity but eliminates the need of an active multiphase clock generation circuit used in the conventional N-path P-M receivers. It uses a single clock signal source at the desired signal carrier frequency and a phase shift network in the RF path of the receiver for frequency downconversion and quadrature (I/Q) demodulation. The QPS-FS receiver requires a slower clock signal source, the frequency of which is equal to the desired band RF signal carrier frequency ( $f_{c})$ as opposed to at least N/2 times $f_{c}$ for the conventional N-path P-M receivers. Consequently, the lower frequency clock source requirement extends the frequency coverage of the receiver by a factor of at least N/2 for a given clock source with a fixed maximum frequency. Reduction of the operating frequency and elimination of the active multiphase clock generation circuit would also eventually reduce the overall power consumption for the whole receiver system as confirmed through measurements. A wideband receiver calibration approach provides less than 2% of error vector magnitudes between the transmitted and received constellation points for various modulated signals having bandwidths up to 4 MHz.

Highly efficient continuous-wave mid-infrared generation based on intracavity difference frequency mixing

We report on a new scheme for efficient continuous-wave (CW) mid-infrared generation using difference frequency generation (DFG) inside a periodically poled lithium niobate (PPLN)-based optical parametric oscillator (OPO). The pump sources were two CW fiber lasers fixed at 1018 nm and 1080 nm. One worked as the assisted laser to build parametric oscillation and generate an oscillating signal beam while the other worked at low power ( ${\leqslant}3~\text{W}$ ) to induce DFG between it and the signal beam. The PPLN temperature was appropriately adjusted to enable OPO and DFG to synchronously meet phase-matching conditions. Finally, both low-power 1018 nm and 1080 nm pump beams were successfully converted to $3.1~\unicode[STIX]{x03BC}\text{m}$ and $3.7~\unicode[STIX]{x03BC}\text{m}$ idler beams, respectively. The conversion efficiencies of the 1018 nm and 1080 nm pumped DFG reached 20% and 15%, respectively, while their slope efficiencies reached 19.6% and 15%. All these data were comparable to the OPOs pumped by themselves and never realized before in traditional CW DFG schemes. The results reveal that high-efficiency frequency down-conversion can be achieved with a low-power near-infrared pump source.

Recent progress on new infrared nonlinear optical materials with application prospect

Nonlinear optical (NLO) crystals can convert the frequencies of existing lasers to other favorable wavelength ranges, and are hence important material basis of photoelectron technology. Currently, there is an urgent need to investigate new NLO materials in the deep UV and IR range. In this review, we focus on the recent progress on new IR NLO materials with application prospect. The main challenge of discovering new practically usable IR NLO crystals is to synthesize new materials that can achieve the coexistence of various desirable properties including sufficient SHG coefficients, wide mid-far IR transparency range, high laser damage threshold, moderate birefringence, favorable single-crystal growth habit, and stable physicochemical properties. Here, we highlight that the research strategy combining “structural design” with “exploratory synthesis” can greatly increase the efficiency of identifying new practical IR NLO materials in metal chalcogenides. Several classes of IR NLO materials with excellent overall performance have been found, such as BaGa4Se7 and BaGa2GeSe6. Moreover, the research on these materials has gone beyond crystal structure and preliminary characterization. Great efforts have been carried out in the bulk crystal growth, in the thorough measurement of their physical properties using bulk crystals, in the evaluation of their IR laser output performance, and eventually in the fabrication of laser device. In the frequency down-conversion OPOs pumped by the conventional 1 µm laser, BaGa4Se7 has realized the stable output of mid-far IR laser output with the highest power and widest wavelength range so far. In this review, instead of covering all compounds with IR NLO properties, our discussion will only focus on those showing good overall IR NLO performance and application prospect, especially on those of which large size single crystals have been already obtained. This review then concludes with an outlook on what efforts could be made in the future.

Terahertz emission from laser-driven gas plasmas: a plasmonic point of view

We disclose an unanticipated link between plasmonics and nonlinear frequency down-conversion in laser-induced gas-plasmas. For two-color femtosecond pump pulses, a plasmonic resonance is shown to broaden the terahertz emission spectra significantly. We identify the resonance as a leaky mode, which contributes to the emission spectra whenever electrons are excited along a direction where the plasma size is smaller than the plasma wavelength. As a direct consequence, such resonances can be controlled by changing the polarization properties of elliptically-shaped driving laser pulses. Both, experimental results and 3D Maxwell consistent simulations confirm that a significant terahertz pulse shortening and spectral broadening can be achieved by exploiting the transverse driving laser beam shape as an additional degree of freedom.

Unambiguous real-time terahertz frequency metrology using dual 10 GHz femtosecond frequency combs

Terahertz frequency metrology by radio frequency downconversion using femtosecond optical sampling relies on the harmonic factor retrieval between the terahertz frequency and the optical sampling rate. At typical femtosecond laser repetition rates, this imposes an ambiguity for frequency metrology. We report on a dual-comb sampling system for the unambiguous frequency measurement of terahertz quantum cascade lasers with hertz-level precision. Two Ti:sapphire oscillators with 10 GHz repetition rate are used for the electro-optic sampling of terahertz radiation at 2.5 THz emitted by actively mode-locked terahertz quantum cascade lasers with 9.7 GHz and 19.6 GHz repetition rates. By coherent downconversion, the emitted terahertz waveforms are measured in the radio frequency domain. The terahertz frequency comb is stabilized by employing a phase-locked loop on a radio frequency beat-note signal. A second infrared sampling comb is used to measure the absolute frequencies of the terahertz radiation. This method, which is based on the detuning of the sampling repetition rates, allows the direct retrieval of the quantum cascade laser’s absolute frequency in real time without using additional optical frequency references for calibration. In order to demonstrate the feasibility of the stabilization and readout technique, a high-resolution spectroscopy measurement on gaseous methanol is presented.

Flexible TWDM-RoF system with good dispersion tolerance for downlink and uplink based on additional SCS.

A high-efficiency full-duplex radio-over-fiber (RoF) system incorporating time- and wavelength-division multiplexing technology is proposed in this paper, which is more flexible for the wavelength assignment based on an additional subcentral station (SCS). The periodic power fading effect resulting from a radio frequency signal transmitted over an optical fiber is effectively eliminated for the downlink and uplink. Colorless base stations are achieved by a centralized allocation strategy of upstream light sources. At the SCS, an optical cross-connect unit is employed to enhance the utilization of light sources and the flexibility of the proposed RoF system. Simultaneously, the requirements of high-bandwidth modulators and photodetectors are significantly reduced with a centralized optical carrier suppressed modulation and an all-optical frequency downconversion at the SCS. On the basis of the additional SCS, a 26GHz full-duplex experiment system is demonstrated, and two 1.25Gbps baseband data signals for downlink and uplink are successfully transmitted over a 40km standard single-mode fiber.

24 GHz 1Tx 2Rx FMCW 송수신기 설계

This paper presents a 24-GHz frequency-modulated continuous wave(FMCW) radar transceiver with two Rx and one Tx channels in 65-nm complementary metal-oxide-semiconductor(CMOS) process and implemented it on a radar system using the developed transceiver chip. The transceiver chip includes a 14× frequency multiplier, low-noise amplifier, down-conversion mixer, and power amplifier(PA). The transmitter achieves &gt;10 dBm output power from 23.8 to 24.36 GHz and the phase noise is −97.3 GHz/Hz at a 1-MHz offset. The receiver achieves 25.2 dB conversion gain and output P1dB of −31.7 dBm. The transceiver consumes 295 mW of power and occupies an area of 1.63×1.6 mm2. The radar system is fabricated on a low-loss Duroid printed circuit board(PCB) stacked on the low-cost FR4 PCBs. The chip and antenna are placed on the Duroid PCB with interconnects and bias, gain blocks and FMCW signal-generating circuitry are mounted on the FR4 PCB. The transmit antenna is a 4×4 patch array with 14.76 dBi gain and receiving antennas are two 4×2 patch antennas with a gain of 11.77 dBi. The operation of the radar is evaluated and confirmed by detecting the range and azimuthal angle of the corner reflectors.

Optically Tunable Microwave Frequency Downconversion Based on an Optoelectronic Oscillator Employing a Phase-Shifted Fiber Bragg Grating

We demonstrate an approach to achieve optically tunable microwave frequency downconversion based on an optoelectronic oscillator (OEO) incorporating a tunable microwave photonic filter. The wideband tunable local oscillation (LO) is generated in the OEO through simply tuning the frequency difference between the optical carrier and the reflection notch of a phase-shifted fiber Bragg grating (PS-FBG). The LO and the input radio-frequency (RF) signal are combined and added to the OEO loop by a single-phase modulator. Through transmitting one modulation sideband of the LO via the reflection notch of the PS-FBG and combining it with the optical carrier split from the laser source, the oscillation of the LO in the OEO is maintained. The reflected modulation sidebands of the LO and the RF signal from the PS-FBG are exported out of the OEO loop and enter a narrow-band photodetector to achieve optically tunable microwave frequency downconversion. Our method is experimentally evaluated, in which optically tunable LOs in the frequency range 6-15 GHz are generated, and RF signals in the frequency range 7-16 GHz are successfully downconverted to intermediate frequency band around 1 GHz.

Frequency Down-Conversion of Dual-Wavelength Raman Fiber Laser in PPLN-Based Optical Parametric Oscillator

We report on frequency down-conversion of dual-wavelength (DW) Raman fiber laser in a periodically poled lithium niobate-based optical parametric oscillator. The DW pump source was fixed at 1060 and 1111 nm that was obtained based on stimulated Raman scattering effect by combining a home-made linearly polarized 1060-nm fiber laser and 137-m-long polarization-maintaining passive fiber. The total pump power went through three stages, in the latter two of which the 1111-nm wave appeared. In the entire experiment, the 1060-nm pump beam achieved parametric oscillation and generated 1626-nm signal beam and 3056-nm idler beam. The 1111-nm pump beam generated 3503-nm idler beam based on difference frequency generation (DFG) between itself and 1626-nm signal beam in the second stage. With power enhancement, it built independent parametric oscillation in the third stage and generated 1621-nm signal beam as well as 3530-nm idler beam. The DW idler power ranged from 3.94 to 7.78 W in the latter two stages. The power and efficiency characteristics in frequency conversion processes of 1060- and 1111-nm pump beams were also analyzed separately.

Ultrahigh-Resolution Optical Vector Analysis for Arbitrary Responses Using Low-Frequency Detection

We propose and experimentally demonstrate an ultrahigh-resolution optical vector analyzer (OVA) for arbitrary responses measurement by using microwave photonic frequency down-conversion and fixed low-frequency detection. It avoids high-speed photodetection and ultrawideband electrical phase-magnitude detection, which are the key challenges to the previous OVAs based on microwave photonics (MWPs). Additionally, the proposed OVA has the capability of measuring arbitrary spectral responses. A high-resolution optical frequency-swept signal generated by using MWP-based techniques is separated into two parts. One portion propagates through an optical device under test (DUT) and then directs to a photodetector (PD), which carries out the spectral responses. In the other branch, the optical signal is accurately shifted by a small frequency and then sent to the PD. By square-law detection, the spectral responses of the optical DUT are thus transferred to a low-frequency photocurrent with a frequency equaling to the shifted frequency. Thus, the spectral responses can be obtained by detecting the photocurrent using a low-frequency electrical phase-magnitude detector working at a fixed frequency. In the experiment, a measurement system is established, by which the magnitude and phase responses of optical devices, such as an optical Hilbert transformer and an optical bandpass filter, are successfully measured. The measurement results are verified by the previous MWP-based OVAs and a commercial instrument.

High performance photonic microwave frequency down-conversion using a dual-drive dual-parallel Mach-Zehnder modulator

ABSTRACTPhotonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed. The MZM on the up path of the DP-MZM is used to generate SSB modulation signal, while the MZM on the bottom path of the DP-MZM is unmodulated. By adjusting the amplitude and phase of the unmodulated optical carrier, two optical carriers are cancelled out, which improves the performance of the system with reduced local oscillator (LO) power and large suppression of mixing spurious sidebands. The frequency down-conversion approach is theoretically analyzed and verified by simulation. Simulation results show that the power of frequency down-conversion signal is at least 39 dB higher than that of the mixing spurious sidebands. Besides, 9.5 dB gain, 2.8 dB noise figure (NF) and 1.9 dB spurious-free dynamic range (SFDR) improvements can be obtained compared with the previous OCS modulation frequency down-conversion scheme while the required LO power is 10 dB, 5 dB and 5 dB lower than that of the OCS modulation scheme, respectively.

Tunable mid-infrared generation via wide-band four-wave mixing in silicon nitride waveguides

We demonstrate wide-band frequency down-conversion to the mid-infrared (MIR) using four-wave mixing (FWM) of near-infrared (NIR) femtosecond-duration pulses from an Er:fiber laser, corresponding to 100THz spectral translation. Photonic-chip-based silicon nitride waveguides provide the FWM medium. Engineered dispersion in the nanophotonic geometry and the wide transparency range of silicon nitride enable large-detuning FWM phase-matching and results in tunable MIR from 2.6 to 3.6μm on a single chip with 100-pJ-scale pump-pulse energies. Additionally, we observe up to 25dB broadband parametric gain for NIR pulses when the FWM process is operated in a frequency up-conversion configuration. Our results demonstrate how integrated photonic circuits pumped with fiber lasers could realize multiple nonlinear optical phenomena on the same chip and lead to engineered synthesis of broadband, tunable, and coherent light across the NIR and MIR wavelength bands.

All-optical image-reject frequency down-conversion based on cascaded electro-optical modulators

Abstract An all-optical image-reject frequency down-converter based on cascaded modulators and a wavelength demultiplexer is presented. The radio-frequency (RF) and the local-oscillator (LO) signal are fed to a phase modulator and a dual-parallel Mach–Zehnder modulator, respectively. Using a wavelength demultiplexer, two down-conversion channels can be obtained. Quadrature phase difference between the two down-converted signals is achieved by properly setting the modulator bias. Image rejection can thus be realized based on Hartley architecture. Experimental results show that image rejection ratios of 32.5 dB in a 10-MHz instantaneous bandwidth and over 50 dB for a single frequency can be obtained. The scheme can be applied to antenna remoting applications, and a 25-km fiber transmission is demonstrated.

Quantum frequency down-conversion of single photons at 1552 nm from single InAs quantum dot**Project supported by the National Key Technologies R&D Program of China (Grant No. 2018YFA0306101), the Scientific Instrument Developing Project of Chinese Academy of Sciences (Grant No. YJKYYQ20170032), and the National Natural Science Foundation of China (Grant No. 61505196).

Near-infrared single photon sources in telecommunication bands, especially at 1550 nm, are required for long-distance quantum communication. Here a down-conversion quantum interface is implemented, where the single photons emitted from single InAs quantum dot at 864 nm is down converted to 1552 nm by using a fiber-coupled periodically poled lithium niobate (PPLN) waveguide and a 1.95 μmm pump laser, and the frequency conversion efficiency is ∼40%. The single-photon purity of quantum dot emission is preserved during the down-conversion process, i.e., g(2)(0), only 0.22 at 1552 nm. This present technique advances the III–V semiconductor quantum dots as a promising platform for long-distance quantum communication.

Saturation of the low-threshold parametric decay of the O-mode pump in the fundamental harmonic ECRH experiment

The saturation regime of the low-power-threshold ordinary (O) wave parametric decay instability leading to the excitation of a localized upper hybrid (UH) wave and a low-hybrid wave is analysed. The cascade of secondary decays of a daughter UH wave to a localized UH wave and ion Bernstein wave is considered as presumably the most important nonlinear mechanism responsible for the transition to a saturation regime. A set of equations describing this nonlinear frequency down-conversion is derived and then solved both analytically and numerically under the conditions typical of the on-axis fundamental harmonic ordinary mode (O1-mode) electron cyclotron resonance heating experiments at the FTU tokamak.

Terahertz necklace beams generated from two-color vortex-laser-induced air plasma

A method for generating terahertz (THz) necklace beams from two-color vortex-laser-induced air plasma is proposed and theoretically investigated based on the frequency down-conversion process. The numerical demonstrations based on both the four-wave mixing and the photocurrent schemes confirm that the generated THz pulse is a shear necklace beam without orbital angular momentum (OAM), whose phase is manifested as the stepwise jump versus azimuthal angle. The origin of OAM vanishing is attributed to the fact that the phase difference between two-color field components does not contribute to the phase but only to the amplitude of the THz pulse.

Tunable, synchronized frequency down-conversion in magnetic lattices with defects.

We study frequency conversion in nonlinear mechanical lattices, focusing on a chain of magnets as a model system. We show that, by inserting mass defects at suitable locations, we can introduce localized vibrational modes that nonlinearly couple to extended lattice modes. The nonlinear interaction introduces an energy transfer from the high-frequency localized modes to a low-frequency extended mode. This system is capable of autonomously converting energy between highly tunable input and output frequencies, which need not be related by integer harmonic or subharmonic ratios. It is also capable of obtaining energy from multiple sources at different frequencies with a tunable output phase, due to the defect synchronization provided by the extended mode. Our lattice is a purely mechanical analogue of an opto-mechanical system, where the localized modes play the role of the electromagnetic field and the extended mode plays the role of the mechanical degree of freedom.This article is part of the theme issue 'Nonlinear energy transfer in dynamical and acoustical systems'.