4,576 research outputs found
Statistical PT-symmetric lasing in an optical fiber network
PT-symmetry in optics is a condition whereby the real and imaginary parts of
the refractive index across a photonic structure are deliberately balanced.
This balance can lead to a host of novel optical phenomena, such as
unidirectional invisibility, loss-induced lasing, single-mode lasing from
multimode resonators, and non-reciprocal effects in conjunction with
nonlinearities. Because PT-symmetry has been thought of as fragile,
experimental realizations to date have been usually restricted to on-chip
micro-devices. Here, we demonstrate that certain features of PT-symmetry are
sufficiently robust to survive the statistical fluctuations associated with a
macroscopic optical cavity. We construct optical-fiber-based coupled-cavities
in excess of a kilometer in length (the free spectral range is less than 0.8
fm) with balanced gain and loss in two sub-cavities and examine the lasing
dynamics. In such a macroscopic system, fluctuations can lead to a
cavity-detuning exceeding the free spectral range. Nevertheless, by varying the
gain-loss contrast, we observe that both the lasing threshold and the growth of
the laser power follow the predicted behavior of a stable PT-symmetric
structure. Furthermore, a statistical symmetry-breaking point is observed upon
varying the cavity loss. These findings indicate that PT-symmetry is a more
robust optical phenomenon than previously expected, and points to potential
applications in optical fiber networks and fiber lasers.Comment: Submitted to Nature Communications, Pages 1-19: Main manuscript;
Pages 20-38: Supplementary material
Nonlinear reversal of PT symmetric phase transition in a system of coupled semiconductor micro-ring resonators
A system of two coupled semiconductor-based resonators is studied when lasing
around an exceptional point. We show that the presence of nonlinear saturation
effects can have important ramifications on the transition behavior of this
system. In sharp contrast with linear PT-symmetric configurations, nonlinear
processes are capable of reversing the order in which the symmetry breaking
occurs. Yet, even in the nonlinear regime, the resulting non-Hermitian states
still retain the structural form of the corresponding linear eigenvectors
expected above and below the phase transition point. The conclusions of our
analysis are in agreement with experimental data.Comment: 9 pages, 8 figure
Integrable nonlinear parity-time symmetric optical oscillator
The nonlinear dynamics of a balanced parity-time symmetric optical microring
arrangement are analytically investigated. By considering gain and loss
saturation effects, the pertinent conservation laws are explicitly obtained in
the Stokes domain-thus establishing integrability. Our analysis indicates the
existence of two regimes of oscillatory dynamics and frequency locking, both of
which are analogous to those expected in linear parity-time symmetric systems.
Unlike other saturable parity time symmetric systems considered before, the
model studied in this work first operates in the symmetric regime and then
enters the broken parity-time phase.Comment: 6 pages, 5 figures, accepted for publicatio
DESIGN & IMPLEMENTATION OF FRACTIONAL – N FREQUENCY SYNTHESIZER
This research involves design & implementation of fractional – N frequency synthesizer with the following specifications: Frequency range (2350– 2750) MHz,Step size (1 kHz), Switching time 8.9 μs, & phase noise @10 kHz = -115dBc & spurious -69 dBc The third order Fractional –N technique was chosen to satisfy the design requirements. In this system the modulator placed on digital phase-locked loop to control the fractional value of the
frequency division ratio thereby eliminating spurious and allowing good phase noise performance. The development in I.C. technology provides the simplicity in the design of fractional –N frequency synthesizer because it implements the phase frequency detector(PFD) , prescalar,modulator & reference divider in single chip. Therefore our system consists of a single chip contains (low phase noise PFD, charge pump, prescalar, modulator & reference divider), voltage controlled oscillator , loop filter & reference oscillator. The application of this synthesizer in frequency hopping systems, wireless transceivers ,GSM &
radar because it has high switching speed ,low phase noise & low spurious level
PHYSICO-CHEMICAL ASSESSMENT OF WATER SAMPLES COLLECTED FROM SOME SELECTED STREAMS AND RIVERS IN DISTRICT GILGIT, PAKISTAN
This study aims to provide information about the drinking water quality of two streams in Chakarkote Sai and Demote Sai and two rivers in Gilgit and Hunza. Parameters were tested including physical, and chemical. The physical parameters were temperature, pH, electric conductivity (EC), total dissolved solids (TDS), turbidity, dissolved oxygen (DO), ammonia (NH4),total nitrogen (TN), total phosphorus (TP) and reactive orthophosphate (PO4). The ranges of these parameters set by WHO and NEQs, as most of the Asian countries also follow the WHO standards. All the samples were tested in the EPA certified laboratory of biological sciences department Karakorum international university Gilgit Baltistan. The minimum and maximum values of temperature 15.2-18.4, PH 6.78-6.09, EC 109.3-297 µS, TDS 53.8-149 ppm, Turbidity 0.29-88.4 NTU, DO 7.1-8.9 mg/l, TN 5.63-7.13 mg/l, NH4 0.0106-0.0151 mg/l, TP 0.042-0.143mg/l, and PO4 0.0059-0.016 mg/l. Independent T test was applied separately for both streams and rivers to determine significant difference of water properties with respect to location wise. Water parameters like DO and TP were significantly, while temperature, PH, EC, TDS, turbidity, TN, NH4, PO4 were non-significant in streams and TDS, turbidity, DO and TN were significant, while temperature, PH, EC, NH4, TP, PO4 were non-significant in rivers according to area wise
Quality of raw milk available at different markets of Mymensingh region of Bangladesh
The experiment was performed to evaluate the quality of raw milk available at different markets of Mymensingh region of Bangladesh. For this purpose the raw milk samples were collected from different markets of Mymensingh (T1), Jamalpur (T2), Netrokona (T3) and Serpur (T4) districts and immediately transferred to the Dairy Technology and Microbiology Laboratory, Bangladesh Agricultural University, Mymensingh for analysis. Parameters studied to monitor the quality of milk samples were physical (colour, flavour, taste, texture and specific gravity), chemical (acidity, fat, ash, protein, lactose, TS and SNF) and microbiological (total viable count and coliform count). Organoleptic test revealed that the raw milk samples of Mymensingh (T1) district were yellowish white 66.66%, Whitish 33.33%; Jamalpur (T2) were yellowish white 66.66%, light yellowish white 33.33%; Netrokona (T3) were yellowish white 100% and Serpur (T4) were yellowish white 33.33%, light yellowish white 33.33% and Whitish 33.33%. Samples of T₁, T2 and T3 had normal flavor (pleasant aromatic flavour) but only T4 had 33.33% abnormal flavour. All the raw milk samples were slightly sweet in taste. Milk samples collected from Netrokona (T3) showed normal texture (free flowing liquid) but Mymensingh (T₁), Jamalpur (T₂) and Serpur (T4) had free flowing liquid 66.66% and thin texture 33.33%.The specific gravity of all raw milk samples were more or less same (1.026±0.00). There were significant (P< 0.01) differences in chemical parameters (fat and protein) between the raw milk samples.Highest fat (34.30 ±1.00 g/kg) was found in Mymensingh (T₁) and highest protein (31.90±0.20 g/kg) was found in Serpur (T4). The overall percentage of acidity was 0.16 ±0.01. The average total viable count (cfu/ml) and coliform count (cfu/ml) were 19.26x10³ and 559.164, respectively and it was observed that total viable count (cfu/ml) and coliform count (cfu/ml) of milk samples were high.Itis concluded thatthe raw milk quality of different markets of Mymensingh region of Bangladesh was more or less similar butdid not fulfill the legal standard of milk composition. Poor hygienic milking, improper cleaning of dairy utensils, unhygienic handling during marketing of raw milk and use of adulterated with addition of water mayresponsible for unhealthy and inferiority of the milk
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