Showing papers on "Injection locking published in 2021"

Ultrafast Ising Machines using spin torque nano-oscillators

Abstract: Combinatorial optimization problems are known for being particularly hard to solve on traditional von Neumann architectures. This has led to the development of Ising Machines (IMs) based on quantum annealers and optical and electronic oscillators, demonstrating speed-ups compared to central processing unit (CPU) and graphics processing unit (GPU) algorithms. Spin torque nano-oscillators (STNOs) have shown GHz operating frequency, nanoscale size, and nanosecond turn-on time, which would allow their use in ultrafast oscillator-based IMs. Here, we show using numerical simulations based on STNO auto-oscillator theory that STNOs exhibit fundamental characteristics needed to realize IMs, including in-phase/out-of-phase synchronization and second harmonic injection locking phase binarization. Furthermore, we demonstrate numerically that large STNO network IMs can solve Max-Cut problems on nanosecond timescales.

How Frequency Injection Locking Can Train Oscillatory Neural Networks to Compute in Phase.

Abstract: Brain-inspired computing employs devices and architectures that emulate biological functions for more adaptive and energy-efficient systems. Oscillatory neural networks (ONNs) are an alternative approach in emulating biological functions of the human brain and are suitable for solving large and complex associative problems. In this work, we investigate the dynamics of coupled oscillators to implement such ONNs. By harnessing the complex dynamics of coupled oscillatory systems, we forge a novel computation model--information is encoded in the phase of oscillations. Coupled interconnected oscillators can exhibit various behaviors due to the strength of the coupling. In this article, we present a novel method based on subharmonic injection locking (SHIL) for controlling the oscillatory states of coupled oscillators that allow them to lock in frequency with distinct phase differences. Circuit-level simulation results indicate SHIL effectiveness and its applicability to large-scale oscillatory networks for pattern recognition.

Engineering the spectral bandwidth of quantum cascade laser frequency combs.

Abstract: Quantum cascade lasers (QCLs) facilitate compact optical frequency comb sources that operate in the mid-infrared and terahertz spectral regions, where many molecules have their fundamental absorption lines. Enhancing the optical bandwidth of these chip-sized lasers is of paramount importance to address their application in broadband high-precision spectroscopy. In this work, we provide a numerical and experimental investigation of the comb spectral width and show how it can be optimized to obtain its maximum value defined by the laser gain bandwidth. The interplay of nonoptimal values of the resonant Kerr nonlinearity and cavity dispersion can lead to significant narrowing of the comb spectrum and reveals the best approach for dispersion compensation. The implementation of high mirror losses is shown to be favorable and results in proliferation of the comb sidemodes. Ultimately, injection locking of QCLs by modulating the laser bias around the round trip frequency provides a stable external knob to control the frequency-modulated comb state and recover the maximum spectral width of the unlocked laser state.

Frequency-Modulated Continuous-Wave LIDAR and 3D Imaging by Using Linear Frequency Modulation Based on Injection Locking

Abstract: We propose and demonstrate a frequency modulated continuous-wave (FMCW) light detection and ranging (LiDAR) system, which employs double-sideband modulation combining with injection-locking to generate triangular linear frequency modulation light source. A fiber laser working as master laser is modulated by a Mach-Zehnder modulator to produce two first-order sidebands with tuning range of 8–14 GHz, one of which is extracted and amplified by a slave distributed feedback laser. A large carrier suppression ratio up to 20 dB is realized. The experiment results show the spatial resolution of the proposed LiDAR is 2.5 cm, equaling to the theoretical value. The velocity measurement is also performed by extracting Doppler shift. Finally, by combining the proposed LiDAR with 2-axis mechanical galvanometer scanner, the 3D imaging with high precision is realized, and the real scene is well restored. The proposed LiDAR system realizes pure linear frequency modulation without complex linearization algorithm or clock sampling circuit, and has advantages of simple structure and high precision.

Injection locking and pulling phenomena in an optoelectronic oscillator.

Abstract: Injection locking and pulling characteristics of a long-loop optoelectronic oscillator (OEO) that has a large number of closely-spaced longitudinal modes are theoretically analyzed and experimentally evaluated. A differential phase equation that relates the phase difference between the OEO and the injected microwave signal to its instantaneous beat angular frequency is derived in the time domain. Based on the differential phase equation, both the locking and pulling characteristics of an injection-locked OEO are studied, and the phase noise performance is analyzed. It is found that the locking and pulling performance depends upon three parameters, the initial frequency difference between the frequency of the signal generated by the free-running OEO and frequency of the injected microwave signal, the voltage ratio between the signal generated by the free-running OEO and the injected microwave signal, and the Q factor of the free-running OEO. The phase noise performance depends upon the locking range, the phase noise performance of the free-running OEO as well as that of the injected microwave signal. The analysis is validated experimentally. Excellent agreement is found between the theoretical analysis and the experimental demonstration.

Low-noise amplification of dissipative Kerr soliton microcomb lines via optical injection locking lasers

Abstract: The dissipative Kerr soliton microcomb provides a promising laser source for wavelength-division multiplexing (WDM) communication systems thanks to its compatibility with chip integration. However, the soliton microcomb commonly suffers from a low-power level due to the intrinsically limited energy conversion efficiency from the continuous-wave pump laser to ultra-short solitary pulses. Here, we exploit laser injection locking to amplify and equalize dissipative Kerr soliton comb lines, superior gain factor larger than 30 dB, and optical-signal-to-noise-ratio (OSNR) as high as 60 dB obtained experimentally, providing a potential pathway to constitute a high-power chip-integrated WDM laser source for optical communications.

Controlling Quantum Cascade Laser Optical Frequency Combs through Microwave Injection

Abstract: In this work, control over the precise state emitted by quantum cascade laser frequency combs through strong radio-frequency current modulation close to their repetition frequency is demonstrated. In particular, broadening of the spectrum from about 20 cm$^{-1}$ to 60cm$^{-1}$ can be achieved throughout most of the current dynamical range while preserving the coherence, as measured by shifted wave interference Fourier transform spectroscopy (SWIFTS). The required modulation frequency to achieve this broadening is red-shifted compared to the free-running beatnote frequency at increasing modulation powers starting from 25 dBm, whereas the range where it occurs narrows. Outside of this maximum-bandwidth range, the spectral bandwidth of the laser output is gradually reduced and the new center frequency is red- or blue-shifted, directly dependent on the detuning of the modulation frequency. By switching between two modulation frequencies detuned symmetrically with respect to the free-running beatnote, we can generate two multiplexed spectral regions with negligible overlap from the same device at rates of at least 20 kHz. In the time-domain we show with both SWIFTS and interferometric autocorrelation (IAC) measurements a transition from quasi-continuous output to pulsed ($\tau_p \approx 55$ ps) output by ramping up the injection power to 35 dBm.

A Compact 196 GHz FSK Transmitter for Point-to-Point Wireless Communication with Novel Direct Modulation Technique

Abstract: A compact, fully-integrated 196GHz FSK transmitter for point-to-point wireless communication is prototyped with a 55nm SiGe BiCMOS process, demonstrating a single-channel data rate of 10Gb/s with a chip area of 0.68mm2. The achieved single-channel data rate is around 5x higher compared with all other FSK wireless transmitters and the chip area is around 4x smaller compared with other state-of-the-art sub-THz wireless transmitters. Unlike conventional FSK transmitters which encode data with two oscillators at different frequencies or with the control voltage of varactors in the LC tank, the proposed FSK transmitter performs data modulation by varying the phase shift of tunable phase shifting couplers in a coupled oscillator loop, resolving the issues of extra power consumption and long frequency settling time. In theory, frequency shift based on this mechanism is instantaneous without overshoot/undershoot issues.

Solving combinatorial optimisation problems using oscillator based Ising machines

Abstract: We present OIM (Oscillator Ising Machines), a new way to make Ising machines using networks of coupled self-sustaining nonlinear oscillators. OIM is theoretically rooted in a novel result that establishes that the phase dynamics of coupled oscillator systems, under the influence of subharmonic injection locking, are governed by a Lyapunov function that is closely related to the Ising Hamiltonian of the coupling graph. As a result, the dynamics of such oscillator networks evolve naturally to local minima of the Lyapunov function. Two simple additional steps (i.e., turning subharmonic locking on and off smoothly, and adding noise) enable the network to find excellent solutions of Ising problems. We demonstrate our method on Ising versions of the MAX-CUT and graph colouring problems, showing that it improves on previously published results on several problems in the G benchmark set. Using synthetic problems with known global minima, we also present initial scaling results. Our scheme, which is amenable to realisation using many kinds of oscillators from different physical domains, is particularly well suited for CMOS IC implementation, offering significant practical advantages over previous techniques for making Ising machines. We report working hardware prototypes using CMOS electronic oscillators.

Injection locking and noise reduction of resonant tunneling diode terahertz oscillator

Abstract: We studied the injection-locking properties of a resonant-tunneling-diode terahertz oscillator in the small-signal injection regime with a frequency-stabilized continuous THz wave. The linewidth of the emission spectrum dramatically decreased to less than 120 mHz (half width at half maximum) from 4.4 MHz in the free running state as a result of the injection locking. We experimentally determined the amplitude of injection voltage at the antenna caused by the injected THz wave. The locking range was proportional to the injection amplitude and consistent with Adler’s model. While increasing the injection amplitude, we observed a decrease in the noise component of the power spectrum, which manifests the free-running state, and an alternative increase in the injection-locked component. The noise component and the injection-locked component had the same power at the threshold injection amplitude as small as 5 × 10−4 of the oscillation amplitude. This threshold behavior can be qualitatively explained by Maffezzoni’s model of noise reduction in general limit-cycle oscillators.

Highly Efficient Full-Duplex Coherent Optical System Enabled by Combined Use of Optical Injection Locking and Frequency Comb

Abstract: We propose a novel point-to-point (P2P) coherent optical link based on optical frequency comb and injection-locking optical process, featuring single wavelength and wavelength division multiplexing (WDM) full-duplex coherent transmission over a fiber link up to 100-km distance. With light sources and local oscillators that are injection locked to an optical frequency comb, simultaneous down-stream and up-stream operations at the same wavelength using full-duplex coherent optical transceivers have been experimentally demonstrated. 32-GBd dual-polarization quadrature phase shift keying (DP-QPSK) and dual-polarization 16 quadrature amplitude (DP-16QAM) modulation formats have been investigated in the setup. When using QPSK, full-duplex operation up to 100 km has been achieved, which introduces 2.2 dB penalty at the hard-decision forward-error-correction (HD-FEC) and 1.3 dB penalty at the soft-decision forward-error-correction (SD-FEC) threshold. When using 16QAM, full-duplex operation up to 80 km has been successfully achieved and as large as 2 dB penalty is observed at the HD-FEC threshold, and 1 dB penalty at the SD-FEC threshold. The penalty mainly comes from continuous and discrete reflection impairments.

Microwave photonic injection locking frequency divider based on a tunable optoelectronic oscillator

Abstract: We present a novel broadband divide-by-2 microwave photonic injection locking frequency divider (ILFD) based on a dual-loop optoelectronic oscillator (OEO). In the proposed scheme, a tunable microwave photonic filter is used to replace the traditional electrical filter, which makes sure a large tuning range of the ILFD. The microwave photonic ILFD whose center frequency tracks the tunable frequency of the free-running OEO, links up with every single locking range together. Thus the frequency range is only determined by the tunable OEO. In the experiment, a wide operating frequency range from 4.51 GHz to 34.88 GHz is realized. Furthermore, a divide-by-3 ILFD is experimentally demonstrated with the help of a frequency mixer.

Characterization of a multifunctional active demultiplexer for optical frequency combs

Abstract: We report on a multifunctional active demultiplexer for optical frequency combs. The proposed technique, based on injection locking, combines the functionality of a tunable demultiplexer, gain equalizer and an optical amplifier, all in one device. Validation of the concept is experimentally demonstrated through simultaneous demultiplexing and amplification of combs with various free spectral ranges (2.5 to 15 GHz), achieving an adjacent channel suppression ratio > 35 dB and an output power of 7.5 dBm. The functionality of the demultiplexer is extended to that of a gain equalizer, by filtering comb tones with powers 10 dB below the spectral peak, whilst maintaining a suppression ratio > 30 dB and a constant output power. This feature increases the number of comb lines suited for data modulation (i.e. usable lines), by a factor of ~1.7. Finally, we test the stability of such a demultiplexer, by measuring the frequency drift, beat tone power variations and phase correlation between demultiplexed tones.

Ising Machine Based on Electrically Coupled Spin Hall Nano-Oscillators

Abstract: The Ising machine is an unconventional computing architecture that can be used to solve NP-hard combinatorial optimization problems more efficiently than traditional von Neumann architectures. Fast, compact oscillator networks which provide programmable connectivities among arbitrary pairs of nodes are highly desirable for the development of practical oscillator-based Ising machines. Here we propose using an electrically coupled array of GHz spin Hall nano-oscillators to realize such a network. By developing a general analytical framework that describes injection locking of spin Hall oscillators with large precession angles, we explicitly show the mapping between the coupled oscillators' properties and the Ising model. We integrate our analytical model into a versatile Verilog-A device that can emulate the coupled dynamics of spin Hall oscillators in circuit simulators. With this abstract model, we analyze the performance of the spin Hall oscillator network at the circuit level using conventional electronic components and considering phase noise and scalability. Our results provide design insights and analysis tools toward the realization of a CMOS-integrated spin Hall oscillator Ising machine operating with a high degree of time, space, and energy efficiency.

Spin Laser Local Oscillators for Homodyne Detection in Coherent Optical Communications.

Abstract: We numerically investigate spin-controlled vertical-cavity surface-emitting lasers (spin-VCSELs) for local oscillators, which are based on an injection locking technique used in coherent optical communications. Under the spin polarization modulation of an injection-locked spin-VCSEL, frequency-shifted and phase-correlated optical sidebands are generated with an orthogonal polarization against the injection light, and one of the sidebands is resonantly enhanced due to the linear birefringence in the spin-VCSEL. We determine that the peak strength and peak frequency in the spin polarization modulation sensitivity of the injection-locked spin-VCSEL depend on detuning frequency and injection ratio conditions. As a proof of concept, 25-Gbaud and 16-ary quadrature amplitude modulation optical data signals and a pilot tone are generated, and the pilot tone is used for the injection locking of a spin-VCSEL. An orthogonally-polarized modulation sideband generated from the injection-locked spin-VCSEL is used as a frequency-shifted local oscillator (LO). We verify that the frequency-shifted LO can be used for the homodyne detection of optical data signals with no degradation. Our findings suggest a novel application of spin-VCSELs for coherent optical communications.

Coherently-averaged dual comb spectrometer at 7.7 µm with master and follower quantum cascade lasers.

Abstract: We demonstrate coherent averaging of the multi-heterodyne beat signal between two quantum cascade laser frequency combs in a master-follower configuration. The two combs are mutually locked by acting on the drive current to control their relative offset frequency and by radio-frequency extraction and injection locking of their intermode beat signal to stabilize their mode spacing difference. By implementing an analog common-noise subtraction scheme, a reduction of the linewidth of all heterodyne beat notes by five orders of magnitude is achieved compared to the free-running lasers. We compare stabilization and post-processing corrections in terms of amplitude noise. While they give similar performances in terms of signal-to-noise ratio, real-time processing of the stabilized signal is less demanding in terms of computational power. Lastly, a proof-of-principle spectroscopic measurement was performed, showing the possibility to reduce the amount of data to be processed by three orders of magnitude, compared to the free-running system.

Wideband and high-resolution spectroscopy based on an ultra-fine electro-optic frequency comb with seed lightwave selection via injection locking

Abstract: The digital ultra-fine electro-optic frequency comb (UFEOFC) enables high-resolution spectroscopy in various applications with a limited bandwidth. In this Letter, we propose a novel, to the best of our knowledge, UFEOFC-based dual-comb spectroscopy to realize megahertz resolution and broadened bandwidth. An UFEOFC with 1 MHz line-spacing and 18 GHz bandwidth is generated and resolved in a dual-comb interferometer working in quasi-integer-ratio mode. One line selected from a master EOFC with 18 GHz line-spacing via optical injection locking serves as the seed lightwave. Successive selection of 20 lines realizes wideband measurement covering 360 GHz, and a reflectance spectrum of a phase-shift fiber Bragg grating is obtained in the demonstration. A spectrum with 360,000 lines is demodulated in 26 ms due to the low injection lock dead time set to be 300µs between adjacent lines, by which the figure of merit reaches 3.39×107. The system promotes more prospects in practical spectroscopic and sensing applications.

A 213-233 GHz ×9 Frequency Multiplier Chain with 4.1 dBm Output Power in 40nm Bulk CMOS

Abstract: A ×9 frequency multiplier chain with 3-dB bandwidth of 213-233 GHz was implemented in 40nm bulk CMOS. It realized 4.1 dBm peak output power without using power combining. Two frequency triplers are cascaded to realize ninth time multiplication of the input frequency. A center-taped transformer and a notched filter are used to suppress the 1st and 2nd harmonics of tripler, respectively. A J-band power amplification block, which is similar with injection locked oscillator, was design to enhance the output power and realized harmonics suppression. Comparing with the expected 9th harmonic, the 4th and 6th harmonics are lower than 67 dB and 35 dB respectively. The other harmonics are not observed in experiment.

Injection locking and synchronization in Josephson photonics devices

Abstract: Injection locking can stabilize a source of radiation, leading to an efficient suppression of noise-induced spectral broadening and therefore, to a narrow spectrum. The technique is well established in laser physics, where a phenomenological description due to Adler is usually sufficient. Recently, locking experiments were performed in Josephson photonics devices, where microwave radiation is created by inelastic Cooper pair tunneling across a dc-biased Josephson junction connected in-series with a microwave resonator. An in-depth theory of locking for such devices, accounting for the Josephson nonlinearity and the specific engineered environments, is lacking. Here, we study injection locking in a typical Josephson photonics device where the environment consists of a single mode cavity, operated in the classical regime. We show that an in-series resistance, however small, is an important ingredient in describing self-sustained Josephson oscillations and enables the locking region. We derive a dynamical equation describing locking, similar to an Adler equation, from the specific circuit equations. The effect of noise on the locked Josephson phase is described in terms of phase slips in a modified washboard potential. For weak noise, the spectral broadening is reduced exponentially with the injection signal. When this signal is provided from a second Josephson device, the two devices synchronize. In the linearized limit, we recover the Kuramoto model of synchronized oscillators. The picture of classical phase slips established here suggests a natural extension towards a theory of locking in the quantum regime.

Wavelength synchronization technology for UDWDM-PON transmitter based on injection locking

Abstract: We propose a concept of wavelength synchronization to ensure the stability of ultra-dense channels in an ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) transmitter. A mode-locked laser is used to provide wavelength references for users. By injection locking the semiconductor laser, the separation of the wavelength reference is realized in an optical line terminal. The downlink and uplink wavelength references are interlaced and distributed to facilitate the synchronization of uplink carriers. In the optical network unit, the uplink optical carriers are filtered by injection locking semiconductor lasers, which achieve wavelength synchronization for the uplink users. In this Letter, an adaptive wavelength synchronization transmitter for UDWDM-PON is realized with a channel spacing of 5 GHz.

Cascaded SSB comb generation using injection-locked seed lasers.

Abstract: We investigate a novel concept of cascaded single side band (SSB) comb generation for improving the carrier-to-noise ratio (CNR), which degrades when the bandwidth of the SSB comb becomes wider. Wavelength-multiplexed seed lasers are simultaneously modulated in a recirculating frequency shifter loop with an SSB modulator, an Er-doped fiber amplifier, and a fiber Bragg grating whose reflective notch filter nature enables seed lasers to be synchronized through the injection locking (IL). A maximum CNR improvement of 11.3 dB is experimentally demonstrated under the IL condition. The proposed technique effectively improves the CNR of wide-bandwidth SSB combs.

Engineering the spectral bandwidth of quantum cascade laser frequency combs.

Abstract: Quantum cascade lasers (QCLs) facilitate compact optical frequency comb sources that operate in the mid-infrared and terahertz spectral regions, where many molecules have their fundamental absorption lines. Enhancing the optical bandwidth of these chip-sized lasers is of paramount importance to address their application in broadband high-precision spectroscopy. In this work, we provide a numerical and experimental investigation of the comb spectral width and show how it can be optimized to obtain its maximum value defined by the laser gain bandwidth. The interplay of nonoptimal values of the resonant Kerr nonlinearity and the cavity dispersion can lead to significant narrowing of the comb spectrum and reveals the best approach for dispersion compensation. The implementation of high mirror losses is shown to be favourable and results in proliferation of the comb sidemodes. Ultimately, injection locking of QCLs by modulating the laser bias around the roundtrip frequency provides a stable external knob to control the FM comb state and recover the maximum spectral width of the unlocked laser state.

Creating Electronic Oscillator-based Ising Machines without External Injection Locking

Abstract: Coupled electronic oscillators have recently been explored as a compact, integrated circuit- and room temperature operation- compatible hardware platform to design Ising machines. However, such implementations presently require the injection of an externally generated second-harmonic signal to impose the phase bipartition among the oscillators. In this work, we experimentally demonstrate a new electronic autaptic oscillator (EAO) that uses engineered feedback to eliminate the need for the generation and injection of the external second harmonic signal to minimize the Ising Hamiltonian. The feedback in the EAO is engineered to effectively generate the second harmonic signal internally. Using this oscillator design, we show experimentally, that a system of capacitively coupled EAOs exhibits the desired bipartition in the oscillator phases, and subsequently, demonstrate its application in solving the computationally hard Maximum Cut (MaxCut) problem. Our work not only establishes a new oscillator design aligned to the needs of the oscillator Ising machine but also advances the efforts to creating application specific analog computing platforms.

Coherently Combined DFB Laser Array Chip With Reduced Relative Intensity Noise

Abstract: The relative intensity noise (RIN) behavior of coherently combined DFB laser array by injection locking is experimentally investigated. A monolithically integrated four-element DFB laser array with a splitter and an output coupler is fabricated, and the frequency stabilities of the DFB lasers are improved to ensure a stable injection locking of DFB laser array by a master laser. It is demonstrated that the RIN of the coherently combined laser array is reduced by almost 20 dB at low frequencies compared with the free-running state. The results indicate that monolithic integration of DFB laser array under injection locking can help improve the RIN performance by eliminating variation in coupling delays and phase jitters.

Linewidth Sharpening in Optical Frequency Combs via a Gain Switched Semiconductor Laser With External Optical Feedback

Abstract: In this article, we propose a novel scheme for an optical frequency comb (OFC) generator which implements a gain switched (GS) semiconductor laser (SL) in the presence of external optical feedback (EOF). Numerical results demonstrate that with appropriate choices of the basic system parameters (i.e., the feedback coupling fraction, the laser bias current and the external cavity length), the linewidths in the OFCs generated by the GS SL with EOF can be significantly reduced below that of the free running continuous wave (CW) SL. Such a significant linewidth reduction can be described by a simple analytic expression presented in this article which is found to be in good agreement with the numerical results.

Frequency domain analysis of optoelectronic oscillators utilizing optical and RF resonators with arbitrary transfer functions

Abstract: Optoelectronic oscillators (OEOs) have attracted much attention for producing ultra-low phase-noise microwave/millimeter-wave oscillations. Traditional delay-based OEOs usually suffer from strong spurious peaks in their phase noise power spectral densities and possible mode-hopping phenomena. Some methods have been proposed in the literature such as using multi-loop architectures or injection locking to other OEOs or radio frequency (RF) oscillators to reduce these spurious peaks. In other approaches, optical filters/resonators other than optical fibers have been proposed to reduce or suppress these peaks and prevent the mode-hopping phenomenon, such as whispering gallery mode resonators (WGMRs), fiber Bragg gratings, and other forms of microwave photonic filters. Usually, approximate single-purpose approaches have been presented to analyze OEOs utilizing such resonators. Here a general framework for analyzing the performance of OEOs implementing RF and optical filters/resonators with arbitrary linear transfer functions is presented. Consequently, it can consider, for example, the most general dispersion models of the fibers as well as any OEO architecture using a combination of different optical resonators. It can also consider the noise transfer between any sidebands of the RF or optical signals and any kind of amplitude noise to phase noise transfers and vice versa. The non-idealities of the electro-optic modulators such as the chirping and finite extinction ratios can also be taken into account. The validity of the new approach is verified by comparing its results with those previously published in the literature. In particular, the case of a WGMR plus delay line OEO is considered for comparisons.

System Performance of a Scalable 79 GHz Imaging MIMO Radar With Injection-Locked LO Feedthrough

Abstract: The estimation of the direction-of-arrival in a coherent multi-channel radar system requires the distribution of the high-frequency local oscillator signal to all hardware channels. Various system concepts with distribution network or feedthrough topologies are established. While distribution networks are bulky and costly, the time delays in systems with a feedthrough topology cause systematic errors in the range evaluation. In this work, a system concept based on an injection-locked feedthrough and the related radar system analysis is presented. The disadvantage of time delays in common feedthrough architectures can be eliminated by a hardware correction using the phase shifting capabilities of the injection-locked oscillator. In addition, two software correction algorithms are presented and analyzed. The performance of the realized system is shown by radar measurements and direction-of-arrival estimations. It is proven that the phase noise of different injection-locked oscillators is fully correlated within the radar system which results in the same detection performance as in state-of-the-art radar systems using a signal distribution network. Thus, the injection-locked feedthrough imaging radar topology is a suitable concept of realizing flexible radar frontends without bulky distribution networks.

Modulation, Injection Locking, and Pulling in an Antiferromagnetic Spin-Orbit Torque Oscillator

Abstract: Antiferromagnets (AFMs) can extend the working frequency of spintronics to terahertz range while using similar geometries and concepts of gigahertz ferromagnet-based spintronic devices. Here, we investigate micromagnetically the dynamics of spin-Hall oscillators driven by the simultaneous action of a dc and an ac current. Our findings include the clear occurrence of three types of dynamics, depending on the frequency of the ac with respect to the self-oscillation frequency excited by the dc: 1) frequency modulation; 2) frequency pulling; and 3) injection locking. These results confirm the suitability of AFMs for the development of a terahertz technology which can impact the field of telecommunications.