Coupled-cavity Structure Research Articles

Modeling optical transistor based on the pole effect of parity-time symmetric coupled cavities

In order to achieve a new kind of optical transistor model, we construct a parity-time (PT) symmetry coupled cavity structure. The gain cavity G is made of semiconductor InGaAsP doped with quantum well and the loss cavity is made of the same material as G but periodically inserted by graphene sheets. Through a parameter optimizing, the structure reaches the PT-symmetry pole state with a huge transmittance. The voltage on the graphene sheets as an input signal can modulate the pole state and results in an amplification output of transmittance. Through proper static working points, the structure can achieve the amplification in phase, out phase and of doubling frequency.

Static Hybrid Quantum Nodes: Toward Perfect State Transfer on a Photonic Chip

Hybrid integrated quantum photonic circuits have the potential to scale up the number of quantum nodes and to build a network with distributed quantum-information-processing units at affordable resources. A central need of such systems is to have near-unity success-rate state transfer between the quantum nodes. This turns out to be a grand challenge since stringent conditions of spatial mode matching and time-reversal symmetry between the sending and receiving nodes have to be simultaneously satisfied. Here we devise a type of hybrid quantum node consisting of a single solid-state quantum system and a coupled-cavity structure toward achieving perfect state transfer between two distant nodes connected via waveguides. The hybrid node possesses flexibility in tailoring the temporal profile of the emitted single-photon wave packet without any dynamic modulation. In particular, we show it could emit time-reversal symmetric single-photon wave packets and fully couple the emission to the waveguide, fulfilling the conditions for perfect quantum state transfer. We develop a complete theoretical framework and provide a clear physical picture of the protocol for transferring a superposition state. We show ideally the simple node structures with one, two, and three chain-coupled microring resonators could lead to total success rates of 90.5%, 97.5%, and 99.3%, respectively. We then further discuss the influence of imperfections and experimental realizations of our scheme with integrated quantum photonics.

Design and analysis of a quasi-TM03 mode G-band extended interaction radiation source

A disk-loaded coupled cavity structure operating in the quasi-TM03 mode has been used here to develop a high electron efficiency, high output power terahertz radiation source, demonstrating that it is possible to concentrate the axial field energy along the source’s central axis within a large cavity. Compared with traditional extended interaction devices operating at the same frequency band, the operating mode of this present device provides a sizable beam tunnel capacity that can support efficient energy conversion between the electron beam and the high frequency field. The developed electron optical system is based on a cylindrical electron beam of 0.3 mm radius and is capable of producing a beam current of 0.65 A at a bias of 16.4 kV. Particle in cell simulations show that such new design approaches can achieve kilowatt-level output power at 0.22 THz with a high electron efficiency of 11.5%.

Quantum Dot Lasers: Directly Modulated Single‐Mode Tunable Quantum Dot Lasers at 1.3 µm (Laser Photonics Rev. 14(3)/2020)

In article number 1900348, Yating Wan and co-workers demonstrate directly modulated, single-mode, tunable InAs/GaAs quantum dot (QD) lasers at 1.3 µm wavelength range, by combining the advantages of QDs with a special designed half-wave coupled cavity structure. Without involving re-growth steps or sub-wavelength grating lithography, 27-channel wavelength switching was achieved with side-mode-suppression-ratio of around 35 dB and output power of over 9 mW.

Directly Modulated Single‐Mode Tunable Quantum Dot Lasers at 1.3 µm

AbstractWavelength tunable lasers are increasingly needed as key components for wavelength resource management technologies in future dense wavelength division multiplexing (DWDM) systems. While material systems with multiple quantum wells as an active region are widely used in long‐wavelength tunable lasers, the unique advantages of InAs/GaAs quantum dots (QDs) for low‐power operation, excellent thermal stability, and wide spectral bandwidth may open a new avenue in this field. Combining the advantages of QDs with a special designed half‐wave coupled cavity structure, directly modulated, single‐mode, tunable InAs/GaAs QD lasers are demonstrated at 1.3 µm wavelength range. The half‐wave coupler provides an active–active coupled‐cavity tunable structure without involving gratings or multiple epitaxial growths, producing synchronous power transfer in the two output waveguides and high single‐mode selectivity. 27‐channel wavelength switching is achieved with side‐mode‐suppression‐ratio of around 35 dB. Under continuous‐wave electrical injection, over 9 mW output power can be measured with 716 kHz Lorentzian linewidth, 4 GHz 3‐dB bandwidth, and 8 Gbit s−1 non‐return‐to‐zero signal modulation by directly probing the chip.

Investigation of a passively Q-switched Raman laser at 1176 nm with Nd3+:YAG/Cr4+:YAG/YAG composite crystal and a coupled cavity

To reduce the thermal lens effect and increase the efficiency, a composite crystal of Nd3+:YAG/Cr4+:YAG/YAG and a coupled cavity structure were employed in our passively Q-switched YVO4-based Raman laser system. Both the simulation and the experiment results showed that the undoped YAG crystal bonded in the end-face of Cr4+:YAG crystal can speed up the heat transfer of Cr4+:YAG crystal and reduce the temperature difference between its side surfaces and the center significantly, and the coupled cavity structure can improve the laser performance, especially at high pump power. The maximum output power of Raman laser of 0.92 W at 1176 nm was obtained with an optical-to-optical efficiency of 11.51%. The corresponding repetition rate and the pulse width is 53.5 kHz and 3.22 ns, respectively.

Passive synthesis rules of coupled-cavity quantum cascade lasers

A new approach to passive electromagnetic modelling of coupled–cavity quantum cascade lasers is presented in this paper. One of challenges in the rigorous analysis of such eigenvalue problem is its large size as compared to wavelength and a high quality factor, which prompts for substantial computational efforts. For those reasons, it is proposed in this paper to consider such a coupled-cavity Fabry-Perot resonant structure with partially transparent mirrors as a two-port network, which can be considered as a deterministic problem. Thanks to such a novel approach, passive analysis of an electrically long laser can be split into a cascade of relatively short sections having low quality factor, thus, substantially speeding up rigorous electromagnetic analysis of the whole quantum cascade laser. The proposed method allows to determine unequivocally resonant frequencies of the structure and the corresponding spectrum of a threshold gain. Eventually, the proposed method is used to elaborate basic synthesis rules of coupled–cavity quantum cascade lasers.

含矩形腔的MIM波导耦合T型腔结构Fano共振传感特性研究

含矩形腔的MIM波导耦合T型腔结构Fano共振传感特性研究

Improvement of the Beam-Wave Interaction Efficiency Based on the Coupling-Slot Configuration in an Extended Interaction Oscillator

A method aimed at improving the beam-wave interaction efficiency by changing the coupling slot configuration has been proposed in the study of extended interaction oscillators (EIOs). The dispersion characteristics, coupling coefficient and interaction impedance of the high-frequency structure based on different types of coupling slots have been investigated. Four types of coupled cavity structures with different layouts of the coupling slots have been compared to improve the beamwave interaction efficiency, so as to analyze the beam-wave interaction and practical applications. In order to determine the improvement of the coupling slot to a coupled cavity circuit in an EIO, we designed four nine-gap EIOs based on the coupled cavity structure with different coupling slot configurations. With different operating frequencies and voltages takes into consideration, beam voltages from 27 to 33 kV have been simulated to achieve the best beam-wave interaction efficiency so that the EIOs are able to work in the 2π mode. The influence of the Rb and the ds on the output power is also taken into consideration. The Rb is the radius of the electron beam, and the ds is the width of the coupling slot. The simulation results indicate that a single-slot-type EIO has the best beam-wave interaction efficiency. Its maximum output power is 2.8 kW and the efficiency is 18% when the operating voltage is 31 kV and electric current is 0.5 A. The output powers of these four EIOs that were designed for comparison are not less than 1.7 kW. The improved coupling-slot configurations enables the extended interaction oscillator to meet the different engineering requirements better.

Study on Ka-band sheet-beam, three-slot-staggered-ladder coupled-cavity traveling-wave tube in a small tunable periodic cusped magnet

A Ka-band sheet electron beam (SEB) traveling-wave tube (TWT) based on three-slot staggered-ladder (TSTL) coupled-cavity slow-wave structure (CC-SWS) is proposed. The high-frequency characteristics of TSTL SWS were analyzed in detail. A well-matched input/output coupling system that solves the problem of energy coupling between the SWS and the external circuit was designed. A new method of loading the distributed attenuator for TSTL SWS was investigated for suppressing backward wave oscillation effectively. In addition, a SEB gun which can produce the SEB conveniently was optimized. A small tunable periodic cusped magnet (STPCM) system was designed to focus the low voltage, high-current SEB, which decreases the whole dimension of the TWT sufficiently. Moreover, the special STPCM system is predicted to exhibit 100% beam transmission efficiency. Finally, the beam-wave interaction was studied. The results obtained by CST simulation show that the SEB TWT can produce output power over 5 kW within the bandwidth ranging from 31.5 to 35.5 GHz, and the maximum output power is 10.15 kW at 33 GHz, corresponding electron efficiency of 10.36%. The fabrication of the device is under way.

Current-injection two-color lasing in a wafer-bonded coupled multilayer cavity with InGaAs multiple quantum wells

Current-injection two-color lasing has been demonstrated using a GaAs/AlGaAs coupled multilayer cavity that is a good candidate for novel terahertz-emitting devices based on difference-frequency generation (DFG) inside the structure. The coupled cavity structure was fabricated by the direct wafer bonding of (001)- and (113)B-oriented epitaxial wafers for the efficient DFG of two modes in the (113)B side cavity, and two types of InGaAs multiple quantum wells (MQWs) were introduced only in the (001) side cavity as optical gain materials. The threshold behavior was clearly observed in the current–light output curve even at room temperature. Two-color lasing was successfully observed when the gain peaks of MQWs were considerably tuned to the cavity modes by the operating temperature.

Estimation of RF-wall loss in slow-wave structures for traveling-wave tubes

Return-loss resonance method is used to estimate the loss per unit length of two different slow-wave structures namely a tapered ferruled coupled-cavity structure operating at centimeter-wave band and a ferrule-less folded-waveguide structure operating at millimeter-wave band. The loss estimated by this method was found to be within 2.5% and 5% compared against those obtained using conventional transmission loss method (S21 value) and numerical simulation carried out using CST-Studio. This approach was found to be very simple yet reasonable accurate to estimate the loss of the periodic structures operating in cm- and mm-wave bands.

Preliminary Design and Experiment of a Ridge-Loaded Staggered Single-Slot Rectangular Coupled-Cavity Structure for -Band Traveling-Wave Tube

A novel ridge-loaded staggered single-slot rectangular coupled-cavity traveling-wave tube (CC-TWT) operating at $X$ -band is presented. It features large interaction impedance and good thermal dissipation with a moderate bandwidth. Compared with the existing staggered single-slot rectangular CC-TWT and Hughes-type TWT, this structure has the advantage of large coupled impedance and high electron efficiency, which makes it potentially useful for miniaturization in CC-TWT. The electromagnetic characteristics and the beam–wave interaction based on this slow-wave structure are investigated. The calculation results predict that it potentially could provide saturated output power over 20 kW from 8.5 to 9.8 GHz when the cathode voltage is set from 25.4 to 26.4 kV and the beam current is 5 A, respectively. The corresponding saturated gain and the electron efficiency can reach over 34.4 dB and 15.2%. From 8.6 to 9.5 GHz, the gain is even over 38.6 dB, and the electron efficiency is more than 16.9%. The cold test results show that the voltage standing wave ratio of the high-frequency structure is below 2 at the range of 8.5–10 GHz.

Fabrication of two-color surface emitting device of a coupled vertical cavity structure with InAs quantum dots formed by wafer bonding

We fabricated a two-color surface emitting device of a coupled cavity structure, which is applicable to terahertz light source. GaAs/AlGaAs vertical multilayer cavity structures were grown on (001) and (113)B GaAs substrates and the coupled multilayer cavity structure was fabricated by wafer bonding them. The top cavity contains self-assembled InAs quantum dots (QDs) as optical gain materials for two-color emission of cavity-mode lights. The bonding position was optimized for the equivalent intensity of two-color emission. We formed a current injection structure, and two-color emission was observed by current injection, although no lasing was observed.

Control of the electromagnetic environment of a quantum emitter by shaping the vacuum field in a coupled-cavity system

We propose a scheme for the ultrafast control of the emitter-field coupling rate in cavity quantum electrodynamics. This is achieved by the control of the vacuum field seen by the emitter through a modulation of the optical modes in a coupled-cavity structure. The scheme allows the on-off switching of the coupling rate without perturbing the emitter and without introducing frequency chirps on the emitted photons. It can be used to control the shape of single-photon pulses for high-fidelity quantum state transfer, to control Rabi oscillations, and as a gain-modulation method in lasers. We discuss two possible experimental implementations based on photonic crystal cavities and on microwave circuits.

介质膜集成衬底垂直外腔面发射激光器

Vertical cavity surface emitting laser( VCSEL) with external cavity which is filled by dielectric materials or air can achieve good beam quality and high power. Aiming at the problem of complex production process and loose structure of the external cavity,a kind of surface emitting laser with the dielectric film integrated on external cavity bottom substrate was designed. Multilayer dielectric insulation films grown on the surface of substrate,N-DBR,and P-DBR composed the coupled cavity structure,and the substrate was served as external cavity of VECSEL. This structure can suppress high order mode,so it can optimize the output spectrum and far-field divergence angle of beam characteristics. Based on the previous theory,we manufactured a VECSEL with active area of 200μm in diameter and external cavity length of 250 μm. The device is carried out with continuous DCcurrent of 3. 4 A at room temperature,and the power is 260 m W,the divergence angle of far field is3. 8°,the full width at half maximum of spectrum is 0. 046 nm. Obviously,compared with conventional structure of bottom emitting VCSEL,the beam quality of VECSEL devices is improved.

Advances and new functions of VCSEL photonics

A vertical cavity surface emitting laser (VCSEL) was born in Japan. The 37 years’ research and developments opened up various applications including datacom, sensors, optical interconnects, spectroscopy, optical storages, printers, laser displays, laser radar, atomic clock and high power sources. A lot of unique features have been already proven, such as low power consumption, a wafer level testing and so on. The market of VCSELs has been growing up rapidly and they are now key devices in local area networks based on multi-mode optical fibers. Optical interconnections in data centers and supercomputers are attracting much interest. In this paper, the advances on VCSEL photonics will be reviewed. We present the high-speed modulation of VCSELs based on a coupled cavity structure. For further increase in transmission capacity per fiber, the wavelength engineering of VCSEL arrays is discussed, which includes the wavelength stabilization and wavelength tuning based on a micro-machined cantilever structure. We also address a lateral integration platform and new functions, including high-resolution beam scanner, vortex beam creation and large-port free space wavelength selective switch with a Bragg reflector waveguide.

A 2.5-D frequency-domain nonlinear computer model of coupled-cavity traveling wave tubes

Purpose – The purpose of this paper is to present a 2.5-dimensional (2.5-D) frequency-domain nonlinear computer model for the beam-wave interaction of coupled-cavity traveling wave tubes (CC-TWTs). Design/methodology/approach – MKK (proposed by Malykhin, Konnov, and Komarov) equivalent circuit model is used to describe the coupled-cavity slow-wave structure. And the losses are taken into account in the MKK equivalent circuit. Instead of one-dimensional (1-D) disk model, the electron beam is divided into a set of discrete rays and the electron dynamics are treated using the three-dimensional (3-D) Lorentz force equations. Findings – The simulated result obtained show that the computer model can give a good predict for CC-TWTs in V-band. Practical implications – The computer model is capable of treating nonlinear problems. Compared with particle-in-cell simulation, the 2.5-D frequency-domain computer model spends less time. Besides, the 3-D electron trajectory can be used to design high-efficiency collectors for CC-TWTs. Originality/value – The computer model is able to simulate nonlinear problems of coupled-cavity TWT faster.

Terahertz emission from a GaAs/AlAs coupled multilayer cavity with nonlinear optical susceptibility inversion

Terahertz wave generation was demonstrated by the difference frequency generation of two cavity modes in a polarization-controlled GaAs/AlAs coupled multilayer cavity. Inversion of the second-order nonlinear optical susceptibility was achieved by face-to-face bonding of the two halves of a coupled cavity structure grown on a (113)B-oriented GaAs substrate. Signal enhancement due to this inversion was observed through the comparison of inverted and normal coupled cavity samples in both simulated and experimentally observed terahertz waveforms produced by simultaneous excitation of two cavity modes using femtosecond laser pulses.

Improvement of slow light performance for vertical-cavity surface-emitting laser using coupled cavity structure

We propose a vertical cavity semiconductor emitting laser (VCSEL) using a coupled-cavity (CC) design to broaden the bandwidths of gain and delay spectra. The structure is formed by constructing a passive cavity coupled with the active cavity. By rendering the strength of the two resonant cavities, the increased gain bandwidth by 340% and the increased delay bandwidth by 800% are achieved as compared with the signal-cavity (SC) VCSEL. The wideband spectra present more square-like passband which is expected for slow light system. By using it, a 20 Gbit/s super Gaussian signal is delayed by about 13 ps with high quality.