Преобразование мод в гибридных волноводных структурах на основе ниобата лития для согласования со стандартным одномодовым оптическим волокном

Topology of a hybrid waveguide device, which performs an effective transformation of a standard gradient titanium in-diffused waveguide mode to a hybrid waveguide mode, is considered. With its help a rather large optical mode with size optimal for coupling with standard single-mode fibers can be converted to a mode with a smaller size. Two the most perspective materials for hybrid waveguide fabrication were considered: silicon and titanium dioxide. The theoretical analysis has shown that transformation efficiency of more than 99% is achievable for waveguide devices based on titanium dioxide with contact lithography resolution.

Frequency and mode measurement techniques for megawatt-class gyrotrons

State-of-the-art vacuum electron tubes such as gyrotrons, deliver RF output powers up to more than 2 MW at frequencies up to 170 GHz. In terms of the very high power levels, a proper verification of the gyrotron components itself and measurements during gyrotron operation are vital to prevent possible fatal errors. Several basic RF measurement setups, which are used at IHM/KIT, are discussed. Currently, their upper frequency limit is 175 GHz. In terms of future gyrotron operation above 200 GHz, upgrades of the measurement setups for operation up to 260–330 GHz are prepared. The experimental devices discussed herein are a quasi-optical mode generator for the verification of the quasi-optical gyrotron output system, the window measurement test stand to verify the ceramic gyrotron output window and the frequency diagnostic system to measure the operating frequency and thereby the excited mode.

Nonlocal nonreciprocal optomechanical circulator

A nonlocal circulator protocol is proposed in hybrid optomechanical system. By analogy with quantum communication, using the input-output relationship, we establish the quantum channel between two optical modes with long-range. The three body nonlocal interaction between the cavity and the two oscillators is obtained by eliminating the optomechanical cavity mode and verifying the Bell-CHSH inequality of continuous variables. By introducing the phase accumulation between cyclic interactions, the unidirectional transmission of quantum state between optical mode and two mechanical modes are achieved. The results show that nonreciprocal transmissions are achieved as long as the accumulated phase reaches a certain value. In addition, the effective interaction parameters in our system are amplified, which reduces the difficulty of the implementation of our protocol. Our research can provide potential applications for nonlocal manipulation and transmission control of quantum platforms.

Anti-$\mathcal{PT}$-symmetric Kerr gyroscope

Non-Hermitian systems can exhibit unconventional spectral singularities called exceptional points (EPs). Various EP sensors have been fabricated in recent years, showing strong spectral responses to external signals. Here we propose how to achieve a nonlinear anti-parity-time ($\mathcal{APT}$) gyroscope by spinning an optical resonator. We show that, in the absence of any nonlinearity, the sensitivity or optical mode splitting of the linear device can be magnified up to 3 orders than that of the conventional device without EPs. Remarkably, the $\mathcal{APT}$ symmetry can be broken when including the Kerr nonlinearity of the materials and, as the result, the detection threshold can be significantly lowered, i.e., much weaker rotations which are well beyond the ability of a linear gyroscope can now be detected with the nonlinear device. Our work shows the powerful ability of $\mathcal{APT}$ gyroscopes in practice to achieve ultrasensitive rotation measurement.

Design of electrically driven single-photon source based on intra-cavity contacted microcavity with oxide-confined optical apertures emitting at 1.3 μm

We propose a hybrid microcavity design of a 1.3 μm range electrically driven single-photon source (SPS) consisting of two high-contrast dielectric distributed Bragg reflectors which surround a 3λ-thick semiconductor cavity with two intra-cavity contact layers and four 40-nm-thick oxide-confined apertures. According to 3D finite-difference time-domain modelling, the overall photon-extraction efficiency of ~74% and the Purcell factor of ~13 can be obtained by properly adjusting the position of oxide-confined apertures relative to the electric field of the fundamental optical mode. The studied SPS design also demonstrates a coupling efficiency of up to 13% within numerical aperture 0.12 in contrast to ~5% reached for a conventional semiconductor micropillar.