High Sensitivity Fiber Refractive Index Sensors Based on Asymmetric Supermodes Interference in Tapered Four Core Fiber

We demonstrate high sensitivity fiber refractive index (RI) sensor based on asymmetric supermode interferences in tapered four core fiber (TFCF). To make TFCF-based RI sensors, the whitelight was launched into any one of the cores to define the excitation orientation and is called a vertex-core excitation scheme. When the four-core fiber (FCF) was gradually tapered, the four cores gathered closer and closer. Originally, the power coupling occurred between its two neighboring cores first and these three cores are grouped to produce supermodes. Subsequently, the fourth diagonal core enters the evanescent field overlapping region to excite asymmetric supermodes interferences. The output spectral responses of the two cores next to the excitation core are mutually in phase whereas the spectral responses of the diagonal core are in phase and out of phase to that of the excitation core at the shorter and longer wavelengths, respectively. Due to the lowest limitation of the available refractive index of liquids, the best sensitivity can be achieved when the tapered diameter is 10 μm and the best RI sensitivity S is 3249 nm/RIU over the indices ranging from 1.41–1.42. This is several times higher than that at other RI ranges due to the asymmetric supermodes.

PENGARUH PERUBAHAN DIMENSI TERHADAP NILAI ISOLASI PADA BRANCH LINE COUPLER

Luasnya perairan nasional menjadi tantangan tersendiri bagi pemerintah dalam upaya pengamanan wilayah laut dari tindakan pelanggaran hukum. Indonesia perlu mengawasi betul-betul wilayah yang paling rawan agar sumber daya ikan nasional bisa dinikmati oleh masyarakat. Caranya, pangkalan bagi kapal-kapal pengawas (KKP, Bakamla, TNI AL) perlu dibangun di wilayah tersebut. Salah satu upaya yang perlu dilakukan yaitu peningkatan pengawasan secara ketat pemerintah dengan cara meningkatkan keamanan sekaligus menyusun aturan yang tepat agar bisa mencegah terjadinya pelanggaran hukum. kemampuan TNI AL dan Polri untuk menjaga seluruh wilayah laut, maka mereka harus menggunakan radar pengawas pantai. Radar pulsa ini mempunyai gelombang elektromagnetik yang diputus secara berirama, dan hanya memiliki satu antena yang digunakan untuk mengirim dan menerima sinyal. Untuk mengirim dan menerima sinyal, radar ini membutuhkan pemisah yang disebut duplekser. Duplekser berfungsi untuk mengisolasi sinyal yang ditransmisikan dan sinyal yang diterima dan komponen utama dari duplexer adalah Branch-Line Hybrid Coupler. Coupler memiliki parameter yang menunjukkan kinerja seperti: Return Loss, Power Coupling, Insertion Loss dan nilai isolasi. Dalam penelitian ini dilakukan penelitian untuk mengetahui pengaruh perubahan dimensi terhadap nilai isolasi pada Branch line coupler. Isolasi sangat penting karena mempengaruhi kinerja duplekser. Nilai yang lebih kecil semakin baik kinerja duplekser tersebut. Penelitian ini dilakukan dengan memodifikasi panjang dan lebar saluran impedansi Coupler. Branch-Line Coupler dirancang dalam bentuk mikrostrip dan difabrikasi menggunakan substrat FR-4 yang memiliki konstanta dielektrik 4,6, tebal 1,3 mm, dan frekuensi operasi 3 GHz. Untuk mendapatkan nilai optimasi karakteristik isolasi, kanal impedansi harus dimodifikasi, yaitu panjang dan lebar seri lengan (Z0 = 50 ), panjang dan lebar seri lengan (Z0 = 35,35 ), dan panjang dan lebar lengan shunt (Z0 = 50 ). Hasil optimasi isolasi didapatkan -67.786 dB.

Physical processes in a low-power inductive plasma source in the presence of a weak magnetic field

Research into the influence of a weak external magnetic field (<150 G) on the efficiency of power coupling to plasma and on the structure of axial RF fields in plasma is presented. Power coupling to the discharge plasma as well as the structure of the axial component of RF magnetic fields are shown to depend on the external magnetic field’s magnitude in a nonmonotous manner.

Recent progress in modeling ICRF-edge plasma interactions with application to ASDEX Upgrade

This paper summarizes recent progress in modeling the interaction between Ion Cyclotron Range of Frequency (ICRF) waves and edge plasma with application to ASDEX Upgrade. The basic theories, the development of ICRF and edge plasma codes, the integrated modeling methods and some key results are reviewed. In particular, the following physical aspects are discussed: 1. ICRF power coupling; 2. Slow wave propagation; 3. ICRF-rectified sheath; 4. ICRF-induced convection; 5. ICRF-edge turbulence interaction. Moreover, comprehensive integrated modeling strategies by including all necessary codes in one package and solving multiple physical issues self-consistently are discussed.

Dynamic aerosol and dynamic air-water interface curvature effects on a 2-Gbit/s free-space optical link using orbital-angular-momentum multiplexing

When an orbital-angular-momentum (OAM) beam propagates through the dynamic air–water interface, the aerosol above the water and the water surface curvature could induce various degradations (e.g., wavefront distortion, beam wandering, scattering, and absorption). Such time-varying degradations could affect the received intensity and phase profiles of the OAM beams, resulting in dynamic modal power loss and modal power coupling. We experimentally investigate the degradation for a single OAM beam under dynamic aerosol, dynamic curvature, and their comprehensive effects. Our results show the following: (i) with the increase of the aerosol strength (characterized by the attenuation coefficient) from ∼0 to ∼0.7–1.3 dB/cm over ∼7 cm, the power coupling ratio from OAM −1 to +2 increases by 4 dB, which might be due to the amplitude and phase distortion caused by spatially dependent scattering and absorption. (ii) With the increase of the curvature strength (characterized by the variance of curvature slope over time) from ∼0 to ∼2 × 10−5 rad2, the power coupling ratio from OAM −1 to +2 increases by 11 dB. This could be caused by both the wavefront distortion and the beam wandering. (iii) Under the comprehensive effect of aerosol (∼0.1–0.6 dB/cm) and curvature (∼6 × 10−7 rad2), there is an up to 2 dB higher modal power loss as compared with the single-effect cases. (iv) The received power on OAM −1 fluctuates in a range of ∼6 dB within a 220 ms measurement time under aerosol (∼0.1–0.6 dB/cm) and curvature (∼6 × 10−7 rad2) effects due to the dynamic degradations. We also demonstrate an OAM −1 and +2 multiplexed 2-Gbit/s on–off-keying link under dynamic aerosol and curvature effects. The results show a power penalty of ∼3 dB for the bit-error-rate at the 7% forward-error-correction limit under the comprehensive effect of aerosol (∼0.1–0.6 dB/cm) and curvature (∼6 × 10−7 rad2), compared with the no-effect case.

The Influence of Photovoltaic Cell Coverage Rate on the Thermal and Electric Performance of Semi-Transparent Crystalline Silicon Photovoltaic Windows Based on the Dynamic Power Coupling Model

Based on the energy conversion equation and dynamic power model of the semi-transparent crystalline silicon photovoltaic (PV) window (ST-PVW), through an iterative coupling solution to the operating temperature of the cell, a thermal-electric coupling calculation method for the ST-PVW is provided, and, combined with experiments, the method model was verified. Based on this model, the influence of PV cell coverage rate (PVR) on the thermal performance of the ST-PVW was studied. According to the simulation results, in summer, the heat gain of the ST-PVW decreases with the increase of PVR, and in winter, the amount of heat loss increases with the increase of PVR. For the four cities of Guangzhou, Nanjing, Beijing and Harbin, when the PVR is 1, 0.60 to 0.64, 0.28 to 0.32 and 0.26 to 0.30, respectively, the annual power consumption of the air conditioner can reach the minimum, and when the PVR is 0.16 to 0.17, 0.24 to 0.25, 0.22 to 0.23 and 0.19 to 0.20, respectively, the amount of electricity generated can just offset the power consumption of the air conditioner during the day.

Turbulence-resilient pilot-assisted self-coherent free-space optical communications using automatic optoelectronic mixing of many modes

In free-space optical communications that use both amplitude and phase data modulation (for example, in quadrature amplitude modulation (QAM)), the data are typically recovered by mixing a Gaussian local oscillator with a received Gaussian data beam. However, atmospheric turbulence can induce power coupling from the transmitted Gaussian mode to higher-order modes, resulting in a significantly degraded mixing efficiency and system performance. Here, we use a pilot-assisted self-coherent detection approach to overcome this problem. Specifically, we transmit both a Gaussian data beam and a frequency-offset Gaussian pilot tone beam such that both beams experience similar turbulence and modal coupling. Subsequently, a photodetector mixes all corresponding pairs of the beams’ modes. During mixing, a conjugate of the turbulence-induced modal coupling is generated and compensates the modal coupling experienced by the data, and thus the corresponding modes of the pilot and data mix efficiently. We demonstrate a 12 Gbit s−1 16-QAM polarization-multiplexed free-space optical link that is resistant to turbulence.