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

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