Dark state lasers

We propose a new type of laser resonator based on imaginary "energy-level splitting" (imaginary coupling, or quality factor Q splitting) in a pair of coupled microcavities. A particularly advantageous arrangement involves two microring cavities with different free-spectral ranges (FSRs) in a configuration wherein they are coupled by "far-field" interference in a shared radiation channel. A novel Vernier-like effect for laser resonators is designed where only one longitudinal resonant mode has a lower loss than the small signal gain and can achieve lasing while all other modes are suppressed. This configuration enables ultra-widely tunable single-frequency lasers based on either homogeneously or inhomogeneously broadened gain media. The concept is an alternative to the common external cavity configurations for achieving tunable single-mode operation in a laser. The proposed laser concept builds on a high-Q "dark state" that is established by radiative interference coupling and bears a direct analogy to parity-time (PT) symmetric Hamiltonians in optical systems. Variants of this concept should be extendable to parametric-gain based oscillators, enabling use of ultrabroadband parametric gain for widely tunable single-frequency light sources

STATE AND PERSPECTIVES IN COMPETITIVENESS OF ONE FARM TYPE IN SERBIA

In the paper is analyzed competitiveness of Serbian family dairy farms in lowland region in 2007, with some aspects of possible perspectives. Globalization process, expected EU integrations and set of free trade agreements will expose Serbian farms in close future to higher level of competition. Identified structural changes, refers on dairy farms concentration and specialization in lowland region in recent years. Estimated model of cost function revealed that family farms with bigger herd size have lower average costs of milk production. Economic efficiency, measured in terms of cost efficiency, shows that larger dairy farms are more efficient. But, not all smaller farms are inefficient. Due to good management some smaller farms are competitive on national market. Milk price volatility in period 2007 to 2009 hurts all farms, but the most farms with higher average costs, which are usually inefficient dairy farms.Competitiveness, Dairy enterprise, Dairy farm, Milk production, Serbia, Agribusiness, Livestock Production/Industries,

Tunable coupled-mode dispersion compensation and its application to on-chip resonant four-wave mixing

We propose and demonstrate localized mode coupling as a viable dispersion engineering technique for phase-matched resonant four-wave mixing (FWM). We demonstrate a dual-cavity resonant structure that employs coupling-induced frequency splitting at one of three resonances to compensate for cavity dispersion, enabling phase-matching. Coupling strength is controlled by thermal tuning of one cavity enabling active control of the resonant frequency-matching. In a fabricated silicon microresonator, we show an 8 dB enhancement of seeded FWM efficiency over the non-compensated state. The measured four-wave mixing has a peak wavelength conversion efficiency of -37.9 dB across a free spectral range (FSR) of 3.334 THz ($\sim$27 nm). Enabled by strong counteraction of dispersion, this FSR is, to our knowledge, the largest in silicon to demonstrate FWM to date. This form of mode-coupling-based, active dispersion compensation can be beneficial for many FWM-based devices including wavelength converters, parametric amplifiers, and widely detuned correlated photon-pair sources. Apart from compensating intrinsic dispersion, the proposed mechanism can alternatively be utilized in an otherwise dispersionless resonator to counteract the detuning effect of self- and cross-phase modulation on the pump resonance during FWM, thereby addressing a fundamental issue in the performance of light sources such as broadband optical frequency combs

The structure of connotative dimensions judo and karate

The research was conducted in order to determine the specificity of conative dimensions of judo and karate athletes as well as their differences. To determine the specificity of the structure of the tested anthropological dimensions, the researchers tested 200 judo and karate athletes, members of judo and karate clubs in Serbia (about 100 judokas and about 100 karatekas), aged 18 to 27. For the assessment of conative characteristics, the researchers chose the measuring instrument CON6 to assess the following conative regulators: activity regulator, regulator of organic functions, regulator of defense reactions, regulator of attack reactions, system for coordination of regulatory functions, and the system for integration of regulatory functions. All the data in this study were processed at the Multidisciplinary Research Center, Faculty of Sport and Physical Education, University of Pristina through the system of data processing software programs DRSOFT developed by [ 19, 28, 17 ]. The algorithms and programs realized in this study are fully presented, and the results of the programs are analyzed

Ultra-low-loss CMOS-Compatible Waveguide Crossing Arrays Based on Multimode Bloch Waves and Imaginary Coupling

We experimentally demonstrate broadband waveguide crossing arrays showing ultra low loss down to $0.04\,$dB/crossing ($0.9\%$), matching theory, and crosstalk suppression over $35\,$dB, in a CMOS-compatible geometry. The principle of operation is the tailored excitation of a low-loss spatial Bloch wave formed by matching the periodicity of the crossing array to the difference in propagation constants of the 1$^\text{st}$- and 3$^\text{rd}$-order TE-like modes of a multimode silicon waveguide. Radiative scattering at the crossing points acts like a periodic imaginary-permittivity perturbation that couples two supermodes, which results in imaginary (radiative) propagation-constant splitting and gives rise to a low-loss, unidirectional breathing Bloch wave. This type of crossing array provides a robust implementation of a key component enabling dense photonic integration

Laser module for optical data communication system

A laser module includes a laser source and an optical marshalling module. The laser source is configured to generate and output a plurality of laser beams. The plurality of laser beams have different wavelengths relative to each other. The different wavelengths are distinguishable to an optical data communication system. The optical marshalling module is configured to receive the plurality of laser beams from the laser source and distribute a portion of each of the plurality of laser beams to each of a plurality of optical output ports of the optical marshalling module, such that all of the different wavelengths of the plurality of laser beams are provided to each of the plurality of optical output ports of the optical marshalling module. An optical amplifying module can be included to amplify laser light output from the optical marshalling module and provide the amplified laser light as output from the laser module.https://patents.google.com/patent/US11424830B2/e

Photonics design tool for advanced CMOS nodes

Recently, the authors have demonstrated large-scale integrated systems with several million transistors and hundreds of photonic elements. Yielding such large-scale integrated systems requires a design-for-manufacture rigour that is embodied in the 10 000 to 50 000 design rules that these designs must comply within advanced complementary metal-oxide semiconductor manufacturing. Here, the authors present a photonic design automation tool which allows automatic generation of layouts without design-rule violations. This tool is written in SKILL, the native language of the mainstream electric design automation software, Cadence. This allows seamless integration of photonic and electronic design in a single environment. The tool leverages intuitive photonic layer definitions, allowing the designer to focus on the physical properties rather than on technology-dependent details. For the first time the authors present an algorithm for removal of design-rule violations from photonic layouts based on Manhattan discretisation, Boolean and sizing operations. This algorithm is not limited to the implementation in SKILL, and can in principle be implemented in any scripting language. Connectivity is achieved with software-defined waveguide ports and low-level procedures that enable auto-routing of waveguide connections.Comment: 5 pages, 10 figure