The plant genus Lagochilus (Lamiaceae) comprises 44 species that are broadly distributed over Cen... more The plant genus Lagochilus (Lamiaceae) comprises 44 species that are broadly distributed over Central Asia with 18 species occurring in the flora of Uzbekistan [1]. Tincture of the herb and roots of L. inebrians Bunge, which is indigenous in Uzbekistan [2], are used in folk medicine as a sedative, analgesic, and hemostatic agent [3]. The hemostatic activity is due to the diterpene alcohol lagochilin. Hemostatic materials based on this compound were fabricated [4]. Diterpenes (lagochilin and its acetates) [5-7] and iridoids (8-O-acetylharpagide and harpagide) [8] were observed in L. inebrians. However, the chemical composition of this plant is inadequately studied. The enzyme-inhibiting activity has not been studied. The BuOH extract of the aerial part of L. inebrians afforded 5-hydroxy-7,4′-dimethoxyflavone (1), β-sitosterol (2), stigmasterol (3), daucosterol (4), lagochilin (5) [5], and 8-O-acetylharpagide (6) [8]. Compounds 1-4 were isolated for the first time from this plant. The chemical structures were identified using IR, mass, and NMR spectra that were taken on the instruments described earlier [9, 10]. Aerial parts of L. inebrians were collected on June 26, 2017, in Ukhum Pass in the Nuratau mountains of Jizzakh Oblast. Taxonomic identification came from the Institute of Botany, Academy of Sciences of Uzbekistan. A specimen of L. inebrians is preserved in the herbarium collection under code No. 1768. The species was determined by Dr. A. R. Batoshev. Milled air-dried aerial parts of L. inebrians (2 kg, <5% moisture) were extracted with MeOH (5 × 8 L). The resulting MeOH extracts were combined and evaporated at 40°C. The condensed extract (160 g, 8% calculated for air-dried raw material) was dissolved in distilled H 2 O (1:1) and fractionated sequentially by polarity using CHCl 3 (4 × 500 mL) to remove low-molecular-mass slightly polar compounds and n-BuOH (4 × 500 mL). Then, the BuOH extract was evaporated to afford dry extract (75 g, 3.75%). The BuOH extract was mixed with silica gel and placed onto a chromatography column of silica gel (100-200 mesh, Tianjin Sinomed Pharmaceutical, China) in a 30:1 ratio to the amount being separated. Compounds were eluted by solvent systems CHCl 3 (fraction A);
Usually considered as the first step in content-based video retrieval, shot boundary detection (S... more Usually considered as the first step in content-based video retrieval, shot boundary detection (SBD) is crucial to subsequent high-level applications like video summarization. The paper proposes an accurate video shot boundary detection method based on singular value decomposition (SVD), through the use of different mathematical theorems and interpretations. In our contribution, adaptive feature extraction is performed using the Frobenius norm of low rank approximation matrices. Each frame will be mapped into ˜ k-dimensional vector in the singular space according to each segment. The classification of continuity values is then achieved via double thresholding technique for detecting the hard cuts. For gradual transitions detection, the folding-in technique, known as SVD-updating, is used for the first time in video shot boundary detection. This allows for accurate detection in reduced computational time, as it is no longer necessary to recalculate the whole SVD decomposition for segment correction. Experimental results on four different datasets, including the TRECVid 20 01, 20 02 and 2005 SBD tasks, show the effectiveness of our detector, which outperforms recent related methods in detecting both hard and gradual transitions.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2013
In the diagnosis of various brain disorders by analyzing the brain magnetic resonance images (MRI... more In the diagnosis of various brain disorders by analyzing the brain magnetic resonance images (MRI), the segmentation of corpus callosum (CC) is a crucial step. In this paper, we propose a fully automated technique for CC segmentation in the T1-weighted midsagittal brain MRIs. An adaptive mean shift clustering technique is first used to cluster homogenous regions in the image. In order to distinguish the CC from other brain tissues, area analysis, template matching, in conjunction with the shape and location analysis are proposed to identify the CC area. The boundary of detected CC area is then used as the initial contour in the Geometric Active Contour (GAC) model, and evolved to get the final segmentation result. Experimental results demonstrate that the proposed technique overcomes the problem of manual initialization in existing GAC technique, and provides a reliable segmentation performance.
The hysteresis properties in bistable polarization switching (PS) of vertical-cavity surface-emit... more The hysteresis properties in bistable polarization switching (PS) of vertical-cavity surface-emitting lasers (VC-SELs) induced by variable-polarization optical feedback (VPOF) are investigated numerically. We mainly concentrate on the influence of sweep rate of the polarizer angle on the bistable PS for the cases with different feedback strengths and feedback delays. The output in the time domain and the representation on the Poincaré sphere plot are further presented to describe the two PS processes. The results show that the size of the hysteresis cycle of the PS follows a power-law relationship versus the sweep rate of the polarizer angle, and the feedback strength and feedback delay can modify the hysteresis properties significantly. A larger feedback strength leads to a narrower hysteresis loop, while a larger feedback delay gives rise to a wider hysteresis loop. Therefore the VPOF provides a new method for obtaining the controllable bistable PS in VCSELs, which is potentially interesting for applications that require polarization-bistable VCSELs.
The antioxidant activity and the total phenolic content, as well as the influence of petroleum et... more The antioxidant activity and the total phenolic content, as well as the influence of petroleum ether, chloroform and methanol extracts from the leaves of Gynotroches axillaris, on microorganisms were studied. The total phenolic contents were evaluated by using Folin-Ciocalteu reagent and the obtained values ranged from 70.0 to 620 mg GAE/g. The efficiency of antioxidation, which was identified through the scavenging of free radical DPPH, exhibited that the highest IC50 was in the methanolic extract (44.7 µg/mL) as compared to the standard ascorbic acid (25.83 µg/mL) and to standard BHT (17.2 µg/mL). In vitro antimicrobial activity of extracts was tested against Gram-negative bacteria, Gram-positive bacteria and fungi. Methanol extract showed activity in the range (225-900 μg/mL) with both types, while petroleum ether and chloroform extracts were only active with Bacillus subtilis. The three extracts strongly inhibited all fungi with activity 225-450 μg/mL. The toxicity test against ...
Calotropis procera plant belongs to the Asclepiadaceae family. It is prescribed to treat bronchit... more Calotropis procera plant belongs to the Asclepiadaceae family. It is prescribed to treat bronchitis, asthma, cough, infections, cancer, ascites, intestinal worms, cutaneous diseases, eczema, leprosy and also aid to stimulate the immune system. The leaves of C. procera were investigated for their phytochemical and anti-microbial activity. Chemical screening of leaves ethanolic extract exhibited to contain active compounds like alkaloids, terpenoids, flavonoids, saponins, and reducing sugar. The antibacterial activity of C. procera leaves against four different bacteria revealed that the ethanolic extracts could kill only Staphylococcus aureus and Basillus subtilis, but more resisted by Pseudomonas sp., and Escherichia coli compare to the standard antibiotic streptomycin. GC-MS analysis of the ethanolic extracts indicated that the highest percentage in 100% ethanolic leaves extract belongs to camphene 6.22%, thebaine 7.59% dodecanoic acid 19.15%, and linolenic acid ethyl ester 14.87%,...
This study presents the results of an experimental investigation of the polarization switching (P... more This study presents the results of an experimental investigation of the polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs) using the so-called polarization-rotated optical feedback mechanism. In particular, the experiments is performed by changing the laser driving current, optical feedback (OF) level, modulation signal parameters, such as frequency, modulation-depth in order to assess their influences on the PS of VCSEL. We show that a smaller polarization angle θ p is required to realize PS with increasing the level of OF. Moreover, for a fixed OF level and increased bias current a smaller θ p is required to ensure PS. However, for a fixed OF and variable modulation parameters, both the frequency and modulation-depth lead to the elimination of PS over the entire range of measurement.
Phytochemicals and anti-inflammatory activity were investigated in the leaves of Pellacalyx sacca... more Phytochemicals and anti-inflammatory activity were investigated in the leaves of Pellacalyx saccardianus from the Rhizophoraceae family. The powdered leaves were extracted using methanol in a soxhlet extractor. Purification of the methanol extract yielded two new compounds, (3S)(6R)-3-(4 0hydroxybenzyl)-6-(6 00-hydroxyphenethyl)-2,2-dimethyl-piperidin-4-one and 1,2-O-(1-methylethylidene)fucoside, together with six known compounds, b-amyrin palmitate, squalene, 24-ethylcholesta-5,22,25-trien-3b-ol, 5R-hydroxy-1,7-bis(5-hydroxyphenyl)heptan-3-one, 1,7-bis(4-hydroxyphenyl) hept-4-en-3-one and methyl-L-fucoside. An anti-inflammatory assay using COX-2 revealed that b-amyrin palmitate possessed the highest inhibitory effect (96.8%) at the lowest concentration (0.01 mM), which was higher than that of the positive controls, resveratrol (90.2%, 0.01 mM) and indomethacin (79.20%, 100 mM). This is the first report on the isolation of phytochemicals from the leaves of P. saccardianus and their anti-inflammatory activity. 2015 Published by Elsevier B.V. on behalf of Phytochemical Society of Europe.
Gynotroches axillaris is the only species of Gynotroches from Rhizophoraceae family. Sequential e... more Gynotroches axillaris is the only species of Gynotroches from Rhizophoraceae family. Sequential extraction of powdered leaves of Gynotroches axillaris using petroleum ether, chloroform and methanol afforded three extracts with percentage yield 4.6%, 1.6% and 15% respectively. Fractionation and purification of petroleum ether extract yielded triterpene ester, β-amyrin palmitate as the major compound, and two fatty acids, palmitic acid and myristic acid. The methanol extract yielded two flavonoids assigned as quercetin-3-O-L-rhamnoside and catechin. The structures were determined by MS, IR and NMR (1D and 2D). The tyrosinase inhibition assay of petroleum ether, chloroform, methanol extracts and the pure compounds were screened against tyrosinase enzyme. The inhibition percentage (I%) of methanol extract against tyrosinase enzyme was stronger than the other extracts with I% values 68.4%. Quercetin-3-O-L-rhamnoside (59%) was found to be the highest in the tyrosinase inhibition activity compared to standard Kojic acid (83%), whereas catechin and β-amyrin palmitate were inactive.
Journal of King Abdulaziz University-Islamic Economics, 1993
... Uzair, Mohammad (1982) Central Banking in an Interest-Free Banking System, in Mohammad Ariff ... more ... Uzair, Mohammad (1982) Central Banking in an Interest-Free Banking System, in Mohammad Ariff (ed.), Monetary and Fiscal Economics of Islam, pp. 211-235. ... Zangeneh, Hamid (1989) Islamic Banking: Theory and Practice in Iran, Comparative Economic Studies, pp. 67-84. ...
In this paper we experimentally show how the rotating polarisation optical feedback (RPOF) influe... more In this paper we experimentally show how the rotating polarisation optical feedback (RPOF) influences the optical chaotic regime and the correlation between the two orthogonally polarization modes of VCSEL. Our results show that high-quality anti-phase polarization chaos synchronization is achieved between the two polarization modes when subjected to RPOF. The quality of the chaotic synchronization is depending on polarization angle of the optical feedback
In vast majority of the semiconductor laser applications such as communication systems employing ... more In vast majority of the semiconductor laser applications such as communication systems employing a high pump source and optical fibre, the edge emitting lasers are the dominant source and are widely used. However, edge emitting lasers are too costly requiring optical fibre coupling. Therefore attention has been focused on vertical-cavity surface-emitting lasers (VCSELs) with potentially low manufacturing cost for optical communication systems. In this paper the influence of current modulation on the polarization properties of VCSEL is subjected to different modulation schemes, which has been investigated experimentally. The results for three modulation techniques are compared in terms of reduction of the threshold current Ithof 850 nm single-mode VCSEL device. We demonstrated that both the modulation frequency and modulation amplitude of the input signal play an important role in reducing the current threshold of VCSEL.
In this first paper we experimentally show how the rotating polarisation-preserved optical feedba... more In this first paper we experimentally show how the rotating polarisation-preserved optical feedback (RPPOF) in VCSELs influences the chaotic regime and the correlation between two polarization modes (XP and YP). Our results could be the base of a novel chaotic optical communication system where the RPPOF is modulated with input data, thus changing the chaotic dynamics of the emitting VCSEL and influencing the synchronisation with 2nd VCSEL at the receiver.
2014 9th International Symposium on Communication Systems, Networks & Digital Sign (CSNDSP), 2014
ABSTRACT The influence of variable-polarization optical feedback (VPOF) on the polarization mode ... more ABSTRACT The influence of variable-polarization optical feedback (VPOF) on the polarization mode switching (PMS) properties of a vertical-cavity surface-emitting laser (VCSEL) has been investigated experimentally. Rotated-polarization optical feedback is considered. At high levels of optical feedback VCSEL exhibits an abrupt PMS when the polarization angle is swept from 00 to 900 and vice versa. We observe a hysteresis loop (HL) beyond the polarization angle of 450, which is barely affected by the level of feedback. The experimental results demonstrate that the size of HL strongly depends on the feedback level, where a narrower and wider width HL are observed at higher and lower levels of feedback, respectively. An external optical feedback with the VPOF can significantly alter the bistability properties of PMS in VCSELs. VPOF can provide a new method to obtain the controllable bistable PMS in VCSELs, which is extremely useful for applications that use the optical bistability (OB).
The plant genus Lagochilus (Lamiaceae) comprises 44 species that are broadly distributed over Cen... more The plant genus Lagochilus (Lamiaceae) comprises 44 species that are broadly distributed over Central Asia with 18 species occurring in the flora of Uzbekistan [1]. Tincture of the herb and roots of L. inebrians Bunge, which is indigenous in Uzbekistan [2], are used in folk medicine as a sedative, analgesic, and hemostatic agent [3]. The hemostatic activity is due to the diterpene alcohol lagochilin. Hemostatic materials based on this compound were fabricated [4]. Diterpenes (lagochilin and its acetates) [5-7] and iridoids (8-O-acetylharpagide and harpagide) [8] were observed in L. inebrians. However, the chemical composition of this plant is inadequately studied. The enzyme-inhibiting activity has not been studied. The BuOH extract of the aerial part of L. inebrians afforded 5-hydroxy-7,4′-dimethoxyflavone (1), β-sitosterol (2), stigmasterol (3), daucosterol (4), lagochilin (5) [5], and 8-O-acetylharpagide (6) [8]. Compounds 1-4 were isolated for the first time from this plant. The chemical structures were identified using IR, mass, and NMR spectra that were taken on the instruments described earlier [9, 10]. Aerial parts of L. inebrians were collected on June 26, 2017, in Ukhum Pass in the Nuratau mountains of Jizzakh Oblast. Taxonomic identification came from the Institute of Botany, Academy of Sciences of Uzbekistan. A specimen of L. inebrians is preserved in the herbarium collection under code No. 1768. The species was determined by Dr. A. R. Batoshev. Milled air-dried aerial parts of L. inebrians (2 kg, <5% moisture) were extracted with MeOH (5 × 8 L). The resulting MeOH extracts were combined and evaporated at 40°C. The condensed extract (160 g, 8% calculated for air-dried raw material) was dissolved in distilled H 2 O (1:1) and fractionated sequentially by polarity using CHCl 3 (4 × 500 mL) to remove low-molecular-mass slightly polar compounds and n-BuOH (4 × 500 mL). Then, the BuOH extract was evaporated to afford dry extract (75 g, 3.75%). The BuOH extract was mixed with silica gel and placed onto a chromatography column of silica gel (100-200 mesh, Tianjin Sinomed Pharmaceutical, China) in a 30:1 ratio to the amount being separated. Compounds were eluted by solvent systems CHCl 3 (fraction A);
Usually considered as the first step in content-based video retrieval, shot boundary detection (S... more Usually considered as the first step in content-based video retrieval, shot boundary detection (SBD) is crucial to subsequent high-level applications like video summarization. The paper proposes an accurate video shot boundary detection method based on singular value decomposition (SVD), through the use of different mathematical theorems and interpretations. In our contribution, adaptive feature extraction is performed using the Frobenius norm of low rank approximation matrices. Each frame will be mapped into ˜ k-dimensional vector in the singular space according to each segment. The classification of continuity values is then achieved via double thresholding technique for detecting the hard cuts. For gradual transitions detection, the folding-in technique, known as SVD-updating, is used for the first time in video shot boundary detection. This allows for accurate detection in reduced computational time, as it is no longer necessary to recalculate the whole SVD decomposition for segment correction. Experimental results on four different datasets, including the TRECVid 20 01, 20 02 and 2005 SBD tasks, show the effectiveness of our detector, which outperforms recent related methods in detecting both hard and gradual transitions.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2013
In the diagnosis of various brain disorders by analyzing the brain magnetic resonance images (MRI... more In the diagnosis of various brain disorders by analyzing the brain magnetic resonance images (MRI), the segmentation of corpus callosum (CC) is a crucial step. In this paper, we propose a fully automated technique for CC segmentation in the T1-weighted midsagittal brain MRIs. An adaptive mean shift clustering technique is first used to cluster homogenous regions in the image. In order to distinguish the CC from other brain tissues, area analysis, template matching, in conjunction with the shape and location analysis are proposed to identify the CC area. The boundary of detected CC area is then used as the initial contour in the Geometric Active Contour (GAC) model, and evolved to get the final segmentation result. Experimental results demonstrate that the proposed technique overcomes the problem of manual initialization in existing GAC technique, and provides a reliable segmentation performance.
The hysteresis properties in bistable polarization switching (PS) of vertical-cavity surface-emit... more The hysteresis properties in bistable polarization switching (PS) of vertical-cavity surface-emitting lasers (VC-SELs) induced by variable-polarization optical feedback (VPOF) are investigated numerically. We mainly concentrate on the influence of sweep rate of the polarizer angle on the bistable PS for the cases with different feedback strengths and feedback delays. The output in the time domain and the representation on the Poincaré sphere plot are further presented to describe the two PS processes. The results show that the size of the hysteresis cycle of the PS follows a power-law relationship versus the sweep rate of the polarizer angle, and the feedback strength and feedback delay can modify the hysteresis properties significantly. A larger feedback strength leads to a narrower hysteresis loop, while a larger feedback delay gives rise to a wider hysteresis loop. Therefore the VPOF provides a new method for obtaining the controllable bistable PS in VCSELs, which is potentially interesting for applications that require polarization-bistable VCSELs.
The antioxidant activity and the total phenolic content, as well as the influence of petroleum et... more The antioxidant activity and the total phenolic content, as well as the influence of petroleum ether, chloroform and methanol extracts from the leaves of Gynotroches axillaris, on microorganisms were studied. The total phenolic contents were evaluated by using Folin-Ciocalteu reagent and the obtained values ranged from 70.0 to 620 mg GAE/g. The efficiency of antioxidation, which was identified through the scavenging of free radical DPPH, exhibited that the highest IC50 was in the methanolic extract (44.7 µg/mL) as compared to the standard ascorbic acid (25.83 µg/mL) and to standard BHT (17.2 µg/mL). In vitro antimicrobial activity of extracts was tested against Gram-negative bacteria, Gram-positive bacteria and fungi. Methanol extract showed activity in the range (225-900 μg/mL) with both types, while petroleum ether and chloroform extracts were only active with Bacillus subtilis. The three extracts strongly inhibited all fungi with activity 225-450 μg/mL. The toxicity test against ...
Calotropis procera plant belongs to the Asclepiadaceae family. It is prescribed to treat bronchit... more Calotropis procera plant belongs to the Asclepiadaceae family. It is prescribed to treat bronchitis, asthma, cough, infections, cancer, ascites, intestinal worms, cutaneous diseases, eczema, leprosy and also aid to stimulate the immune system. The leaves of C. procera were investigated for their phytochemical and anti-microbial activity. Chemical screening of leaves ethanolic extract exhibited to contain active compounds like alkaloids, terpenoids, flavonoids, saponins, and reducing sugar. The antibacterial activity of C. procera leaves against four different bacteria revealed that the ethanolic extracts could kill only Staphylococcus aureus and Basillus subtilis, but more resisted by Pseudomonas sp., and Escherichia coli compare to the standard antibiotic streptomycin. GC-MS analysis of the ethanolic extracts indicated that the highest percentage in 100% ethanolic leaves extract belongs to camphene 6.22%, thebaine 7.59% dodecanoic acid 19.15%, and linolenic acid ethyl ester 14.87%,...
This study presents the results of an experimental investigation of the polarization switching (P... more This study presents the results of an experimental investigation of the polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs) using the so-called polarization-rotated optical feedback mechanism. In particular, the experiments is performed by changing the laser driving current, optical feedback (OF) level, modulation signal parameters, such as frequency, modulation-depth in order to assess their influences on the PS of VCSEL. We show that a smaller polarization angle θ p is required to realize PS with increasing the level of OF. Moreover, for a fixed OF level and increased bias current a smaller θ p is required to ensure PS. However, for a fixed OF and variable modulation parameters, both the frequency and modulation-depth lead to the elimination of PS over the entire range of measurement.
Phytochemicals and anti-inflammatory activity were investigated in the leaves of Pellacalyx sacca... more Phytochemicals and anti-inflammatory activity were investigated in the leaves of Pellacalyx saccardianus from the Rhizophoraceae family. The powdered leaves were extracted using methanol in a soxhlet extractor. Purification of the methanol extract yielded two new compounds, (3S)(6R)-3-(4 0hydroxybenzyl)-6-(6 00-hydroxyphenethyl)-2,2-dimethyl-piperidin-4-one and 1,2-O-(1-methylethylidene)fucoside, together with six known compounds, b-amyrin palmitate, squalene, 24-ethylcholesta-5,22,25-trien-3b-ol, 5R-hydroxy-1,7-bis(5-hydroxyphenyl)heptan-3-one, 1,7-bis(4-hydroxyphenyl) hept-4-en-3-one and methyl-L-fucoside. An anti-inflammatory assay using COX-2 revealed that b-amyrin palmitate possessed the highest inhibitory effect (96.8%) at the lowest concentration (0.01 mM), which was higher than that of the positive controls, resveratrol (90.2%, 0.01 mM) and indomethacin (79.20%, 100 mM). This is the first report on the isolation of phytochemicals from the leaves of P. saccardianus and their anti-inflammatory activity. 2015 Published by Elsevier B.V. on behalf of Phytochemical Society of Europe.
Gynotroches axillaris is the only species of Gynotroches from Rhizophoraceae family. Sequential e... more Gynotroches axillaris is the only species of Gynotroches from Rhizophoraceae family. Sequential extraction of powdered leaves of Gynotroches axillaris using petroleum ether, chloroform and methanol afforded three extracts with percentage yield 4.6%, 1.6% and 15% respectively. Fractionation and purification of petroleum ether extract yielded triterpene ester, β-amyrin palmitate as the major compound, and two fatty acids, palmitic acid and myristic acid. The methanol extract yielded two flavonoids assigned as quercetin-3-O-L-rhamnoside and catechin. The structures were determined by MS, IR and NMR (1D and 2D). The tyrosinase inhibition assay of petroleum ether, chloroform, methanol extracts and the pure compounds were screened against tyrosinase enzyme. The inhibition percentage (I%) of methanol extract against tyrosinase enzyme was stronger than the other extracts with I% values 68.4%. Quercetin-3-O-L-rhamnoside (59%) was found to be the highest in the tyrosinase inhibition activity compared to standard Kojic acid (83%), whereas catechin and β-amyrin palmitate were inactive.
Journal of King Abdulaziz University-Islamic Economics, 1993
... Uzair, Mohammad (1982) Central Banking in an Interest-Free Banking System, in Mohammad Ariff ... more ... Uzair, Mohammad (1982) Central Banking in an Interest-Free Banking System, in Mohammad Ariff (ed.), Monetary and Fiscal Economics of Islam, pp. 211-235. ... Zangeneh, Hamid (1989) Islamic Banking: Theory and Practice in Iran, Comparative Economic Studies, pp. 67-84. ...
In this paper we experimentally show how the rotating polarisation optical feedback (RPOF) influe... more In this paper we experimentally show how the rotating polarisation optical feedback (RPOF) influences the optical chaotic regime and the correlation between the two orthogonally polarization modes of VCSEL. Our results show that high-quality anti-phase polarization chaos synchronization is achieved between the two polarization modes when subjected to RPOF. The quality of the chaotic synchronization is depending on polarization angle of the optical feedback
In vast majority of the semiconductor laser applications such as communication systems employing ... more In vast majority of the semiconductor laser applications such as communication systems employing a high pump source and optical fibre, the edge emitting lasers are the dominant source and are widely used. However, edge emitting lasers are too costly requiring optical fibre coupling. Therefore attention has been focused on vertical-cavity surface-emitting lasers (VCSELs) with potentially low manufacturing cost for optical communication systems. In this paper the influence of current modulation on the polarization properties of VCSEL is subjected to different modulation schemes, which has been investigated experimentally. The results for three modulation techniques are compared in terms of reduction of the threshold current Ithof 850 nm single-mode VCSEL device. We demonstrated that both the modulation frequency and modulation amplitude of the input signal play an important role in reducing the current threshold of VCSEL.
In this first paper we experimentally show how the rotating polarisation-preserved optical feedba... more In this first paper we experimentally show how the rotating polarisation-preserved optical feedback (RPPOF) in VCSELs influences the chaotic regime and the correlation between two polarization modes (XP and YP). Our results could be the base of a novel chaotic optical communication system where the RPPOF is modulated with input data, thus changing the chaotic dynamics of the emitting VCSEL and influencing the synchronisation with 2nd VCSEL at the receiver.
2014 9th International Symposium on Communication Systems, Networks & Digital Sign (CSNDSP), 2014
ABSTRACT The influence of variable-polarization optical feedback (VPOF) on the polarization mode ... more ABSTRACT The influence of variable-polarization optical feedback (VPOF) on the polarization mode switching (PMS) properties of a vertical-cavity surface-emitting laser (VCSEL) has been investigated experimentally. Rotated-polarization optical feedback is considered. At high levels of optical feedback VCSEL exhibits an abrupt PMS when the polarization angle is swept from 00 to 900 and vice versa. We observe a hysteresis loop (HL) beyond the polarization angle of 450, which is barely affected by the level of feedback. The experimental results demonstrate that the size of HL strongly depends on the feedback level, where a narrower and wider width HL are observed at higher and lower levels of feedback, respectively. An external optical feedback with the VPOF can significantly alter the bistability properties of PMS in VCSELs. VPOF can provide a new method to obtain the controllable bistable PMS in VCSELs, which is extremely useful for applications that use the optical bistability (OB).
Uploads
Papers by Salam Ahmed