Showing papers on "Injection locking published in 2019"

Coherent injection locking of quantum cascade laser frequency combs

Abstract: Quantum cascade laser (QCL) frequency combs are a promising candidate for chemical sensing and biomedical diagnostics1–4. They are electrically pumped and compact, making them an ideal platform for on-chip integration5. Until now, optical feedback is fatal for frequency comb generation in QCLs6. This property limits the potential for integration. Here, we demonstrate coherent electrical injection locking of the repetition frequency to a stabilized radio-frequency oscillator. We prove that the injection-locked QCL spectrum can be phase-locked, resulting in the generation of a frequency comb. We show that injection locking is not only a versatile tool for all-electrical frequency stabilization, but also mitigates the fatal effect of optical feedback. A prototype self-detected dual-comb set-up consisting only of an injection-locked dual-comb chip, a lens and a mirror demonstrates the enormous potential for on-chip dual-comb spectroscopy. These results pave the way to miniaturized and all-solid-state mid-infrared spectrometers. Quantum cascade laser frequency combs are coherently locked to an external radio-frequency source even in extremely high-feedback conditions. The internal phase-locking mechanism and the possibility of all-electric stabilization are investigated.

OIM: Oscillator-Based Ising Machines for Solving Combinatorial Optimisation Problems

Abstract: We present a new way to make Ising machines, i.e., using networks of coupled self-sustaining nonlinear oscillators. Our scheme 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., adding noise, and turning subharmonic locking on and off smoothly) 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. 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 present working hardware prototypes using CMOS electronic oscillators.

A coherent nanomechanical oscillator driven by single-electron tunnelling.

Abstract: A single-electron transistor incorporated as part of a nanomechanical resonator represents an extreme limit of electron-phonon coupling. While it allows for fast and sensitive electromechanical measurements, it also introduces backaction forces from electron tunnelling which randomly perturb the mechanical state. Despite the stochastic nature of this backaction, under conditions of strong coupling it is predicted to create self-sustaining coherent mechanical oscillations. Here, we verify this prediction using time-resolved measurements of a vibrating carbon nanotube transistor. This electromechanical oscillator has intriguing similarities with a laser. The single-electron transistor, pumped by an electrical bias, acts as a gain medium while the resonator acts as a phonon cavity. Despite the unconventional operating principle, which does not involve stimulated emission, we confirm that the output is coherent, and demonstrate other laser behaviour including injection locking and frequency narrowing through feedback.

A 2.5–5.75-GHz Ring-Based Injection-Locked Clock Multiplier With Background-Calibrated Reference Frequency Doubler

Abstract: A low-jitter, low-power ring oscillator (RO)-based injection-locked clock multiplier (ILCM) is presented. It employs a background-calibrated reference frequency doubler to increase the RO noise suppression bandwidth, a digital delay-locked loop (DLL) to achieve second-order suppression of RO noise, and a digital frequency-tracking loop (FTL) to continuously tune the oscillator’s free-running frequency and ensure a robust operation across process, voltage, and temperature (PVT) variations. A least-mean-square (LMS) algorithm is used to accurately cancel the deterministic jitter (DJ) caused by input duty cycle errors. Fabricated in the 65-nm CMOS process, the prototype ILCM occupies an active area of 0.09 mm2 and generates an output clock in the range of 2.5–5.75 GHz using a 125-MHz reference clock. At 5 GHz, it achieves an integrated jitter of 335 fsrms, while consuming 5.3 mW of power. This translates to the best reported figure-of-merit (FoM) of −242.4 dB for a ring-based ILCM at this high frequency.

A General Theory of Injection Locking and Pulling in Electrical Oscillators—Part I: Time-Synchronous Modeling and Injection Waveform Design

Abstract: A general model of electrical oscillators under the influence of a periodic injection is presented. Stemming solely from the autonomy and periodic time variance inherent in all oscillators, the model’s underlying approach makes no assumptions about the topology of the oscillator or the shape of the injection waveform. A single first-order differential equation is shown to be capable of predicting a number of important properties, including the lock range, the relative phase of an injection-locked oscillator, and mode stability. The framework also reveals how the injection waveform can be designed to optimize the lock range. A diverse collection of simulations and measurements, performed on various types of oscillators, serve to verify the proposed theory.

Tunable low-drift spurious-free optoelectronic oscillator based on injection locking and time delay compensation

Abstract: A finely tunable low-drift spurious-free single-loop optoelectronic oscillator (OEO) incorporating injection locking and time delay compensation is proposed and experimentally demonstrated. In the proposed OEO, one mode of a single-loop OEO is injection locked by a tunable electronic oscillator resulting in single-mode oscillation. A time delay compensation system is used to compensate the OEO’s loop length change caused by environmental changes, such as temperature and strain. Tuning of the oscillation frequency is realized by controlling the injection frequency and absolute loop length of the single-loop OEO. In the experiments, when the ambient temperature varies between 22°C and 31°C within 1000 s, an output signal at the frequency of 10.664 GHz with a frequency drift better than −0.1 ppb and side-mode suppression ratio greater than 78 dB has been realized. Also, the OEO can be tuned with a precise frequency step of 10 Hz.

Frequency-modulated continuous-wave microwave generation using stabilized period-one nonlinear dynamics of semiconductor lasers

Abstract: Frequency-modulated continuous-wave (FMCW) microwave generation is studied using a semiconductor laser operating at stabilized period-one (P1) nonlinear dynamics when subject to comb-like (CL) optical injection. The phase locking established between the P1 dynamics and the CL optical injection not only improves the P1 oscillation stability considerably but also provides a mechanism to change the P1 oscillation frequency through varying the modulation frequency of the CL optical injection. As a result, a stable FMCW microwave at a central frequency of up to 40 GHz is generated with its frequency varying linearly, triangularly, or step-wisely over a range of 4 GHz during a repeated time period that can be reconfigured at least from 100 ns to 10 ms. This system is capable of operation up to at least 100 GHz.

Multiple-frequency measurement based on a Fourier domain mode-locked optoelectronic oscillator operating around oscillation threshold

Abstract: We propose and experimentally demonstrate a photonic-assisted approach to microwave frequency measurement based on frequency-to-time mapping using a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) operating around oscillation threshold. A relationship between the frequency of the unknown input microwave signals and the time difference of the output pulses is established with the help of the frequency scanning capability of the FDML OEO and, thus, can be used for microwave frequency measurement. The proposed scheme is characterized as having broad bandwidth, high resolution, multiple-frequency detection capability, and tunable measurement range. Microwave frequency measurement with a measurement range up to 16 GHz and a low measurement error of 0.07 GHz is realized.

Electro-optic THz dual-comb architecture for high-resolution, absolute spectroscopy.

Abstract: An absolute-frequency terahertz (THz) dual-frequency comb spectrometer based on electro-optic modulators for tunable, high-resolution, and real-time rapid acquisition is presented. An optical line of a master frequency comb (filtered via optical injection locking) serves as the seed to electro-optically generate a pair of new frequency combs (probe and local oscillator). Photomixing both combs with another coherent line from the same original master comb generates a narrow linewidth THz dual-comb with teeth frequencies that can be referenced to a radio-frequency standard. The system is validated with a proof-of-principle measurement of a microwave filter in the W-band.

A General Theory of Injection Locking and Pulling in Electrical Oscillators—Part II: Amplitude Modulation in $LC$ Oscillators, Transient Behavior, and Frequency Division

Abstract: A number of specialized topics within the theory of injection locking and pulling are addressed. The material builds on our impulse sensitivity function (ISF)-based, time-synchronous model of electrical oscillators under the influence of a periodic injection. First, we show how the accuracy of this model for $LC$ oscillators under large injection is greatly enhanced by accounting for the injection’s effect on the oscillation amplitude. In doing so, we capture the asymmetry of the lock range as well as the distinct behaviors exhibited by different $LC$ oscillator topologies. Existing $LC$ oscillator injection locking and pulling theories in the literature are subsumed as special cases. Next, a transient analysis of the dynamics of injection pulling is carried out, both within and outside of the lock range. Finally, we show how our existing framework naturally accommodates locking onto superharmonic and subharmonic injections, leading to several design considerations for injection-locked frequency dividers (ILFDs) and the implementation of a low-power dual-modulus prescaler from an injection-locked ring oscillator. Our theoretical conclusions are supported by simulations and experimental data from a variety of $LC$ , ring, and relaxation oscillators.

A Phasor-Based Analysis of Sinusoidal Injection Locking in LC and Ring Oscillators

Abstract: A new perspective into the locking behavior of LC and ring oscillators is presented. By decomposing a sinusoidal injection current into in-phase and quadrature-phase components, exact expressions for the amplitude and phase of an injection-locked LC oscillator which hold for any injection strength and frequency are derived and confirmed by simulation. The analysis, which can be naturally extended to an arbitrary LC resonator topology, leads to a rigorous understanding of the fundamental physics underlying the locking phenomenon. Furthermore, an investigation of the different necessary and sufficient conditions for injection locking to occur is carried out, leading to a more precise notion of the lock range. The ring oscillator is also analyzed in an analogous fashion, resulting in simple yet accurate closed-form expressions for the fractional lock range in the small-injection and long-ring regimes; the expressions are validated by simulations of single-ended inverter-based ring oscillators in 65-nm CMOS. The mathematics behind how the injection modifies the phase delay contributed by each stage in the ring is discussed. A corollary that generalizes the small-injection lock range to any feedback-based oscillator topology is established. Conceptual and analytical connections to the existing literature are reviewed.

On-Chip Dual-Comb Source Based on Terahertz Quantum Cascade Lasers Under Microwave Double Injection

Abstract: High-power broadband terahertz dual-comb sources are of great importance for fast high-resolution spectroscopy, but are rare because of the lack of high-performance terahertz radiation sources. Here the authors demonstrate a broadband terahertz dual-comb source on a chip, based on electrically pumped quantum cascade lasers and microwave double injection. By injection locking the two lasers at slightly different round-trip frequencies, even weak microwave power can significantly broaden the dual-comb bandwidth. Furthermore, the double-injection technique allows direct evaluation of the carrier offset noise of the terahertz laser combs.

Analysis of Injection Locking and Pulling in Single-Loop Optoelectronic Oscillator

Abstract: Injection-locking characteristics of a single-loop optoelectronic oscillator (OEO) under an independent sinusoidal RF signal injection are investigated. The mathematical model of the unlocked-driven system is developed to represent phase perturbation of the generated output RF signal caused by the RF injection signal. The closed-form expressions of the output RF spectra distorted due to RF signal injection are derived to formulate the behavior of the injection-pulled OEO. Using the phase dynamics equation, a phase noise model is developed to quantify the influence of RF injection signal on the phase noise performance of the oscillator. It is shown that our analytical model is capable of predicting the injection locking and estimating the injection pulling behavior of the single-loop OEO under RF signal injection. The theoretical results are validated by the experimental results.

Design of Crystal-Oscillator Frequency Quadrupler for Low-Jitter Clock Multipliers

Abstract: Implementation of low-noise power-efficient clock multipliers requires low-noise high-frequency reference clocks. This paper presents ways to generate such reference clocks at four times the frequency of a standard crystal oscillator (XO) output frequency. Using extensive digital correction techniques, a 216-MHz reference clock with an integrated jitter of 77 $\text {fs}_{\mathrm{ rms}}$ is generated from a 54-MHz Pierce XO. A ring oscillator-based injection locking clock multiplier driven by the proposed quadrupler is used to demonstrate the efficacy of the quadrupler. Fabricated in a 65-nm CMOS process, the proposed clock multiplier occupies an active area of 0.16 mm2 and achieves 366 $\text {fs}_{\mathrm{ rms}}$ integrated jitter at 4.752-GHz output frequency while consuming 6.5-mW power from a 1.0-V supply of which 1.5 mW is consumed in the quadrupler.

Combined frequency and time domain measurements on injection-locked, constriction-based spin Hall nano-oscillators

Abstract: We demonstrate a combined frequency and time domain investigation of injection-locked, constriction-based spin Hall nano-oscillators by Brillouin light scattering (BLS) and the time-resolved magneto-optical Kerr effect (TR-MOKE). This was achieved by applying an ac current in the GHz regime in addition to the dc current which drives auto-oscillations in the constriction. In the frequency domain, we analyze the width of the locking range, the increase in intensity, and the reduction in the linewidth as a function of the applied direct current. Then, we show that the injection locking of the auto-oscillation allows for its investigation by TR-MOKE measurements, a stroboscopic technique that relies on a phase stable excitation, in this case given by the synchronisation to the microwave current. Field sweeps at different dc currents clearly demonstrate the impact of the spin current on the Kerr amplitude. Two-dimensional TR-MOKE and BLS maps show a strong localization of the auto-oscillation within the constriction, independent of the external locking.

Suppression of Systematic Errors in Brillouin Optical Correlation Domain Analysis Based on Injection-Locking

Abstract: Brillouin optical correlation domain analysis (BOCDA) is an established method for the measurement of Brillouin frequency distribution, where direct modulation of a distributed feedback laser diode (DFB-LD) is usually adopted to implement a frequency-modulated light source. Recently, we reported that a phase delay occurring between the amplitude and frequency variations, called AM-FM phase delay, in the output of the modulated DFB-LD can cause considerable errors in the Brillouin frequency measured by a BOCDA system. The error induced by the AM-FM phase delay is systematic since it cannot be suppressed by averaging process while constantly distorts the distribution map of Brillouin frequency. In this paper, we demonstrate the suppression of the adverse effects of the AM-FM phase delay using an injection-locked DFB-LD as a light source of BOCDA system. Theoretical explanation on the origin of the systematic error in the BOCDA measurement is provided by simulations. The investigation on the modulation characteristics of the master and slave LD's in the injection-locking is performed, the result of which shows that the injection locking not only reduces the depth of amplitude modulation, but also keeps the phase delay of near 180° in a wide range of modulation frequency. In test measurements, the systematic errors are reduced by more than 70% on average using the slave LD as a common light source of the BOCDA system.

Stochastic polarization switching induced by optical injection in bimodal quantum-dot micropillar lasers.

Abstract: Mutual coupling and injection locking of semiconductor lasers is of great interest in non-linear dynamics and its applications for instance in secure data communication and photonic reservoir computing. Despite its importance, it has hardly been studied in microlasers operating at μW light levels. In this context, vertically emitting quantum dot micropillar lasers are of high interest. Usually, their light emission is bimodal, and the gain competition of the associated linearly polarized fundamental emission modes results in complex switching dynamics. We report on selective optical injection into either one of the two fundamental mode components of a bimodal micropillar laser. Both modes can lock to the master laser and influence the non-injected mode by reducing the available gain. We demonstrate that the switching dynamics can be tailored externally via optical injection in very good agreement with our theory based on semi-classical rate equations.

Injection-Locked Millimeter Wave Frequency Divider Utilizing Optoelectronic Oscillator Based Optical Frequency Comb

Abstract: We propose and experimentally demonstrate a photonic millimeter-wave frequency divider based on a super-harmonic injection-locked optoelectronic oscillator (OEO) and an optical frequency comb. The optical frequency comb generator is incorporated into an OEO loop to create broadband comb lines with low noise. By injecting a millimeter-wave with frequency around N times of the fundamental oscillating frequency f0 of the OEO, the injection signal can be down-converted to an intermediate frequency (IF) signal close to the oscillating frequency of the OEO. The free running OEO is synchronized with the IF signal via an injection locking mechanism. Consequently, it forms an injection-locked frequency divider as the frequency ratio between the injection signal and OEO's output signal is precisely equal to N. We carry out an experiment to divide the 45 GHz signal into 7.5 GHz and the experimental results agree well with the theoretical analysis. By changing the frequency of the injection signal, division ratio from 2 to 5 is also demonstrated on one setup. Due to the broadband spectra of the optical comb and low phase noise characteristics of the OEO, it is potential to realize very large division ratio and low phase noise for multiple input frequencies mf 0 .

Comb-rooted multi-channel synthesis of ultra-narrow optical frequencies of few Hz linewidth.

Abstract: We report a multi-channel optical frequency synthesizer developed to generate extremely stable continuous-wave lasers directly out of the optical comb of an Er-doped fiber oscillator. Being stabilized to a high-finesse cavity with a fractional frequency stability of 3.8 × 10−15 at 0.1 s, the comb-rooted synthesizer produces multiple optical frequencies of ultra-narrow linewidth of 1.0 Hz at 1 s concurrently with an output power of tens of mW per each channel. Diode-based stimulated emission by injection locking is a key mechanism that allows comb frequency modes to sprout up with sufficient power amplification but no loss of original comb frequency stability. Channel frequencies are individually selectable with a 0.1 GHz increment over the entire comb bandwidth spanning 4.25 THz around a 1550 nm center wavelength. A series of out-of-loop test results is discussed to demonstrate that the synthesizer is able to provide stable optical frequencies with the potential for advancing diverse ultra-precision applications such as optical clocks comparison, atomic line spectroscopy, photonic microwaves generation, and coherent optical telecommunications.

Wavelength locking of Er-doped random fiber laser

Abstract: This paper demonstrates the wavelength locking of a coherent random lasing system, i.e. an Erbium-doped random fiber laser with a disordered array of fiber Bragg gratings. To lock lasing modes of the disordered system, an external seed light from a tunable laser was introduced into the cavity. It was found that different emission wavelengths/modes can be selected to emit separately through injection locking. The wavelength fluctuation of the output is less than 0.01%, and the power fluctuation is less than 4%. The proposed method is also applicable to general disordered systems, providing an efficient way to control or select light emission in these systems.

Simple laser transmitter pair as polarization-independent coherent homodyne detector.

Abstract: Coherent optical reception promises performance gains for a wide range of telecom applications and photonic sensing. However, the practical implementation and the particular realization of homodyne detection is by no means straight-forward. Local oscillator requirements and polarization management need to be cost-effectively supported for accurate signal detection at high sensitivity, preferably without relying on digital processing resources. Towards this direction we propose a conceptually simple, laser-based homodyne receiver. We exploit the injection locking of a pair of externally modulated lasers that simultaneously serve as optically synchronized local oscillators and photodetectors in a polarization-diversity analogue coherent receiver arrangement. We demonstrate signal detection at 2.5 Gb/s over an optical budget of 35 dB and a dynamic range of >20 dB. Long-term measurements over field-installed fiber confirm the correct operation independent of the polarization state of light. Stability considerations for the injection locking process are drawn in view of even higher loss budgets.

Mode Suppression in Injection Locked Multi-Mode and Single-Mode Lasers for Optical Demultiplexing

Abstract: Optical injection locking has been demonstrated as an effective filter for optical communications. These optical filters have advantages over conventional passive filters, as they can be used on active material, allowing them to be monolithically integrated onto an optical circuit. We present an experimental and theoretical study of the optical suppression in injection locked Fabry–Perot and slotted Fabry–Perot lasers. We consider both single frequency and optical comb injection. Our model is then used to demonstrate that improving the Q factor of devices increases the suppression obtained when injecting optical combs. We show that increasing the Q factor while fixing the device pump rate relative to threshold causes the locking range of these demultiplexers to asymptotically approach a constant value.

Tunable Frequency Comb Generation Using Quantum Cascade Lasers Subject to Optical Injection

Abstract: We dissect the enabling capabilities of the tunable period-one (P1) limit cycles of optically injected quantum cascade laser (QCL) oscillators for the generation of optical frequency combs. As such, we theoretically investigate the P1 dynamics of a QCL using a single-mode rate equation model. We find that such a P1 limit cycle occupies a rather large and wide region of the optical frequency detuning and injection level ratio map. We have not recorded evidence of chaos in this injected laser system, in marked contrast with quantum well and quantum dot cases. Contrary to interband semiconductor lasers, the QCL's oscillation frequency is generally smaller than the detuning frequency, and is reduced with increasing injection strength, due to the strong injection pulling effect. When the optical injection is operated in the vicinity of the Hopf bifurcation , the P1 oscillation produces dense optical frequency combs, owing to both the frequency pulling effect and the four-wave mixing effect. The comb spacing is continuously tunable from subgigahertz up to a few gigahertz, via fine control of either the detuning frequency and/or the injection ratio. This novel approach of the frequency comb generation is of prime importance for high-resolution detection of narrow absorption lines of gas molecules.

Injection-Locked, Single Frequency, Multi-core Yb-doped Phosphate Fiber Laser

Abstract: For the first time, we demonstrate injection locking and single frequency operation of a multi-core Yb-doped phosphate fiber laser (MCF). The 19 MCF laser cores operated in CW mode at 1030 nm. Each laser core was locked to the frequency and polarization of the single-frequency master laser, and produced milliwatts of power with similar lasing thresholds. The pump beam was homogenized with a simple technique to increase uniform lasing behavior of the cores. This behavior was verified using a MCF laser model developed in-house. This unique MCF laser can be useful for applications of coherent, coupled oscillator networks, for example in an all-optical coherent Ising machine configuration.

OIM: Oscillator-based Ising Machines for Solving Combinatorial Optimisation Problems

Abstract: We present a new way to make Ising machines, i.e., using networks of coupled self-sustaining nonlinear oscillators. Our scheme is theoretically rooted in a novel result that establishes that the phase dynamics of coupled oscillator systems, under the influence of sub-harmonic 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., adding noise, and turning sub-harmonic locking on and off smoothly) 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. 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 present working hardware prototypes using CMOS electronic oscillators.

A low phase noise quadrature VCO using superharmonic injection, current reuse, and negative resistance techniques in CMOS technology

Abstract: In this article, a low phase noise quadrature VCO (QVCO) is proposed, which uses superharmonic injection and current reuse techniques to reduce phase-noise and power consumption. The LC tank circuit quality factor is improved, using a negative resistance. PMOS transistors have also been used instead of NMOS transistors. As a result of these modifications, further phase noise reduction is achieved. The QVCO consists of a VCO operating at 2ω0 (twice the operating frequency) injecting its output signal into the common source nodes of two other oscillators operating at ω0. Using this superharmonic injection technique, in addition to phase noise reduction, the chance of injection pulling caused by powerful PA signals is reduced. Also, the current reuse technique automatically adapts its voltage to the requirement of the supplied stages, therefore, it is not limiting the VCO output swing. Designed for the 900 MHz band and simulated in a 0.18 µm CMOS technology with 1.8 V power supply, the circuit achieves a phase noise of − 141.5 dBc/Hz at 1 MHz offset frequency, while consuming 12.8 mW power. The proposed circuit is compared with several re-simulated previously published work. The comparison shows 17.5 dB reduction in phase noise compared to conventional P-QVCO, while consuming the same amount of power.

A Wirelessly Powered Injection-Locked Oscillator With On-Chip Antennas in 180-nm SOI CMOS for Spectroscopy Application

Abstract: We present a wirelessly powered millimeter-sized injection-locked oscillator with on-chip antennas for material spectroscopy application. The main challenge is to design an efficient and sensitive wireless energy-harvesting front-end with integration of an on-chip antenna and a wide locking range oscillator. The on-chip antenna receives electromagnetic energy from a continuous-wave source in the X-band frequency. A superharmonic injection-locking oscillator locks to the frequency of the input and produces a synchronized signal at half the frequency of the input. This new signal is then radiated back using an on-chip dipole antenna, which resolves the conventional self-interference issue in radio-frequency identification (RFID) sensors. In addition, the locking mechanism improves the phase noise of the on-chip oscillator to -93 dBc/Hz at 100 Hz offset. The large locking range of the transmitting signal shows promising results for spectroscopy applications, which can be used for material detection and analysis.

Centralized-Light-Source Two-Way PAM8/PAM4 FSO Communications With Parallel Optical Injection Locking Operation

Abstract: For the first time up to our knowledge, a centralized-light-source two-way eight-level pulse amplitude modulation (PAM8)/four-level pulse amplitude modulation (PAM4) free-space optical (FSO) communication with parallel optical injection-locked vertical-cavity surface-emitting laser (VCSEL) transmitter is practically demonstrated. With the assistance of parallel optical injection locking, injection locking in the polarization sideband causes a simultaneous generation of the free-running orthogonal polarization sideband to form a centralized-light-source scheme. With the centralized light source, additional light source or wavelength reuse component, such as Fabry-Perot laser diode or reflective semiconductor optical amplifier, is not needed at the receiver side. It is very attractive because it enables the receiver side to share the light source remotely located at the transmitter side. Based on the centralized-light-source scheme and parallel optical injection-locking operation, the injection-locked parallel polarization sideband is used for downlink transmission, and the induced free-running orthogonal polarization sideband is transmitted and used as the optical carrier for uplink transmission. Over a 200-m free-space link, good bit-error-rate (BER) performance, the qualified PAM8, and PAM4 eye diagrams are obtained for two-way FSO communications. This proposed centralized-light-source two-way FSO communication provides a practical choice for two-way high transmission capacities and considerably develops the scenario characterized by parallel optical injection locking.

A coherent nanomechanical oscillator driven by single-electron tunneling

Abstract: A single-electron transistor embedded in a nanomechanical oscillator realises an extreme limit of electron-phonon coupling. It performs fast and sensitive electromechanical measurements but also introduces backaction forces, due to the tunnelling of individual electrons, which randomly perturb the mechanical state. Despite the stochastic nature of this backaction, under conditions of strong coupling it is predicted to create a self-sustained state of coherent mechanical oscillations. I will show how we verify this prediction using time-resolved measurements of a vibrating carbon nanotube transistor. This electromechanical oscillator has intriguing similarities with a laser, with the population inversion provided by the electrical bias and the resonator acting as a phonon cavity. I will show that the resulting emission has the same coherence as a laser, and demonstrate other laser behaviour including injection locking and feedback narrowing of the emitted signal.

Sweep Frequency Heating based on Injection Locked Magnetron

Abstract: Conventional microwave heating has serious problems such as non-uniform heating and low efficiency. A novel magnetron microwave sweep frequency heating method is proposed to improve microwave heating uniformity. In this method, the frequency-sweeping signal is injected into the magnetron by the injection frequency-locking technique, and the microwave sweep frequency heating of the magnetron is realized. In this paper, a complicated injection frequency locking system is given and analyzed and a multiphysics calculation model based on the finite element method for electromagnetic waves and heat transfer is established. The calculation of microwave sweep frequency heating is realized by the combination of COMSOL and MATLAB. The results show that the sweep frequency heating has an obvious superiority. An experiment is carried out to verify the simulation results. The simulation results are in agreement with the experimental data. Moreover, the effect of sweep bandwidth and sweep interval on heating uniformity is discussed.