Optik

In biological suspensions, the forward light scattering is done mainly by the contribution of the suspended cells. The multiple scattering is almost always unavoidable, its contribution being described by Monte Carlo simulations or by approximate analytical formula. The Monte Carlo approach we propose moves one photon at a time and checks all scattering centers to find, at each simulation step, which one will scatter the photon. The validation of the simulation results is performed by comparing the obtained angular distribution with the predictions of the effective phase function theory reported recently in the literature and with the angle resolved experimental measurements performed on human red blood cells (RBCs) in suspensions at different hematocrits. The results show a good agreement in the small concentration range.

Sol-gel routes to metal oxide nanoparticles in organic solvents under exclusion of water have become a versatile alternative to aqueous methods. We focus on the preparation of well-aligned ZnO nanorod arrays using non-aqueous sol-gel synthesis route, where ZnO nanorods arrays have been grown on glass substrates. This work provides a systematic study of controlled morphology and crystallinity of ZnO nanorod arrays. The investigation demonstrates that the synthesis process conditions of ZnO thin film have strong influences on the morphology and crystallinity of the ZnO nanorod arrays grown thereon, where non-aqueous process offers the possibility of better understanding and controlling the reaction pathways on the molecular level, enabling the synthesis of nanomaterials with high crystallinity and well-defined, uniform particle morphologies. Here the annealing temperature plays an important role on the growth of nanostructures of the ZnO grains and nanorod arrays. The scanning electron microscopy (SEM) image shows that the growth of ZnO nanorod arrays are high-quality single crystals growing along the c-axis perpendicular to the substrates. A detailed analysis of the growth characteristics of ZnO nanostructures as functions of growth time is also reported.

The transmission light intensity method is carried out on a classical platform to study the reciprocity of Faraday effect in water-based Fe 3 O 4 ferrofluid and its diluents. Setting the polarization direction of the analyzer at an angle of 45 • to that of the polarizer, the switchable DC magnetic field and the alternating magnetic field are imposed to ferrofluid. The ferrofluid film is replaced by magneto-optical glass for contrastive experiments. The results indicate that ferrofluid is different with magneto-optical glass. Even though the direction of magnetic field is reversed, the rotation direction of the polarized light does not change for ferrofluid. The theoretical model of magneto-optical rotation was used to describe the origin of the reciprocity of Faraday effect in ferrofluid and the non-reciprocity in magneto-optical glass. These findings suggest that the magnetic moments of nanoparticles in ferrofluid tend to the same orientation with the magnetic field because of the rotation of particles.

In this work, we study the performance of free space optical links with fading statistics modelled by the negative exponential distribution which describes channels under strong atmospheric turbulence conditions. We investigate the availability and the practical channel capacity's bounds, for links with fast and slow fading statistics, with line of sight architecture and intensity modulation with direct detection, through the evaluation of the outage probability and the outage and average capacity. Moreover, the average error probability, for on-off keying cases, is estimated. For these, very significant, magnitudes we extract closed form mathematical expressions for, practically valuation of link's performance.

An influence of acoustic wave diffraction on the modulation instability of the backward stimulated Brillouin scattering in fibers is numerically investigated, when a small feedback for the Stokes wave is present. The cases of acoustic waveguide and anti-waveguide fibers are considered. It is shown that a presence of acoustic diffraction may expand the region of occurrence of modulation instability and may lead to 2-5 times increasing the peak amplitude of output Stokes pulses. In this case, a stable train of short powerful Stokes pulses of nanosecond duration is produced at the output.

Fabric defect detection has been an active area of research since a long time and still a robust system is needed which can fulfill industrial requirements. A robust automatic fabric defect detection system (FDDS) would results in quality products and more revenues. Many different approaches and method have been tried to implement FDDS. Most of them are based on two approaches, one is statistical like gray level co-occurrence (GLCM) and other is transform based like Gabor filter. This paper presents a new scheme for automated FDDS implementation using GLCM and also compare it with Gabor filter approach. GLCM texture statistics are extracted and plotted against the inter-pixel distance of GLCM as signal graph. The non-defective fabric image information is compared with the test fabric image. In Gabor filter based approach, a bank of Gabor filter with different scales and orientations is generated and fabric images are filtered with convolution mask. The generated magnitude responses are compared for defect decision. In our implementation of both approaches in same environment, the GLCM approach produces higher defect detection accuracies than Gabor filter approach and more computationally efficient.

This paper reports the effects of pre- and post-compensation using CRZ modulation format in long-haul WDM optical transmission link using wavelengths in three bandwidths viz. 1537.4; 1550; 1562.6 nm at per channel bit rates of 10 Gbit/s. It has been investigated here that optimization of dispersion map results in improved management of nonlinear effects in long-haul light wave systems operating in the quasi-linear regime. In addition, pre- and post-dispersion compensation was applied at the transmitter and receiver depending on the signal wavelength, which resulted in improvement of performance metrics viz. Q2 (dB), BER and OSNR over longer transmission distances. It is reported here that optimum values of Q2 dB of 17.1 dB, BER of 8.4933e−015 and OSNR of 30.1 dB are obtained at 1550 nm at a transmission distance of 7360 km with pre- and post-compensation using CRZ modulation format.

A brief review of the properties of transmission diffraction gratings is presented. Two types of gratings will be analyzed: thin and volume gratings explaining how the efficiency of the different orders that propagate inside the gratings can be calculated in both cases. For thin diffraction gratings the so-called amplitude transmittance method is applied in order to get the amplitude of the different orders, whereas in the case of volume gratings more complex methods are needed, such as Coupled Wave or modal theories. We will comment on the thin matrix decomposition method (TMDM), firstly proposed by Alferness, which gives a very intuitive approach and connects the properties of thin gratings to the properties of volume ones. The thin matrix decomposition method consists in dividing the volume grating in a number of thin gratings and applying the amplitude transmittance method to each thin grating. In this way the output of a grating will be considered as the input of the next and any individual grating can be treated by the amplitude transmittance method. The novelty of this work is that a comparison is made between the analytical expressions obtained by Alferness using the TMDM with the numerical results obtained using the coupled wave (CW) and rigorous coupled wave (RCW) theories for the efficiencies of the zero, first and second order when a plane wave incides onto a sinusoidal diffracion grating at the second on-Bragg replay angular condition.

This paper presents the modeling and characterization of an optical fiber grating for maximum reflectivity. Grating length and change in refractive index are the critical parameters in contributing to the performance of fiber Bragg grating. The wavelength chosen for analysis is from the third window to minimize the attenuation. The reflection spectra, bandwidth and side lobes strength were analyzed with different lengths and change in refractive index. The simulations are based on solving coupled mode equations by transfer matrix method that describes the interaction of guided modes.

Pada era globalisasi sekarang perkembangan optik semakin berkembang pesat. Kita yang hidup di zaman modern tidak dapat menghindari perkembangan tersebut, jadi kita harus mengikuti perkembangan tersebut agar tidak terlindas oleh perkembangan zaman yang terus maju kedepan. Perkembangan alat optik sangatlah bermanfaat dalam kehidupan kita seperti yang telah kita ketahui dalam bidang pendidikan, kesehatan, dan sekitar lingkungan masyarakat pun juga telah menggunakan perkembangan alat optik

bertujuan untuk mengetahui penggunaan spektrometer optik dengan benar, memahami prinsip penguraian cahaya oleh prisma, dan menentukan indeks bias dan daya dispersi prisma. Praktikum ini terdiri dari dua kegiatan, kegiatan 1 menentukan sudut pembias prisma dan  kegiatan 2 menentukan indeks bias dan daya dispersi prisma.

Abstrak: Penelitian ini bertujuan untuk menetukan jarak fokus dan cacat bayangan pada lensa dengan sistem optik. Hasil penelitian menunjukkan bahwa jarak fokus lensa berubah sesuai dengan jarak benda ke layar. Pada jarak benda ke layar sebesar 50 cm, maka jarak fokusnya 0,1001 ± 0,0005 cm. Saat jarak benda ke layar sebesar 55 cm, maka jarak fokusnya 0,1018 ± 0,0005 cm. Saat jarak benda ke layar sebesar 60 cm, maka jarak fokusnya 0,1035 ± 0,0007 cm. Dengan persamaan Bessel saat jarak benda ke layar sebesar 50 cm, maka jarak fokusnya (1250 ± 3) x 10 −4 cm. Saat jarak benda ke layar sebesar 55 cm, maka jarak fokusnya (1300 ± 3) x 10 −4 cm. Saat jarak benda ke layar sebesar 60 cm, maka jarak fokusnya (1500 ± 2) x 10 −4 cm. Pada pengamatan tentang cacat bayangan di dapatkan hasil bahwa diafragma memiliki hubungan dengan cacat bayangan. Saat bayangan di halangi oleh diafragma maka dihasilkan bayangan yang lebih tegak dan lurus. Semakin jauh jarak benda ke layar, maka jarak fokus yang dihasilkan akan semakin besar. Penggunaan lensa positif dan negatif dengan panjang fokus lebih besar dapat digunakan bersama untuk menghasilkan sistem lensa pengumpul yang memiliki aberasi (cacat bayangan) jauh lebih sedikit dibandingkan dengan lensa tunggal dengan fokus yang sama. Kata kunci: jarak fokus, jarak benda, cacat bayangan, layar, lensa.

Pendahuluan Perkembangan dunia sains dan teknologi yang terus maju dan para ilmuwan mengembangkan suatu konsep terapan yang memanfaatkan terhadap perbesaran suatu intensitas cahaya. Hal ini disebut sebagai LASER (Light Amplification by Stimulated Emission of Radiation). Laser merupakan suatu alat yang dapat memancarkan cahaya mulai dari panjang gelombang inframerah yang paling jauh, daerah cahaya tampak, sampai pada daerah vakum ultraviolet serta daerah sinar-X. Cahaya yang dipancarkan oleh laser dihasilkan dari stimulasi emisi radiasi dari medium dalam laser. Meningkatnya minat dalam penggunaan laser untuk tujuan pengobatan, membawa dampak kemajuan dalam bidang kedokteran. Pada beberapa penyakit mata, sinar laser digunakan secara rutin untuk koagulasi darah dan memblokir pembuluh darahvena. Laser gas merupakan salah satu dari jenis laser yang sangat bermanfaat bagi kehidupan manusia. Laser gas sendiri dibagi menjadi beberapa jenis berdasarkan fungsi dan jenis gas penyusunnya. Oleh karena itu penyusun ingin menyusun makalah mengenai laser gas ini selain untuk memenuhi tugas, diharapkan makalah ini membantu mahasiswa untuk memahami tentan laser gas. Desain Laser Helium tereksitasi ke sebuah level tertentu karena tabrakan elektron. Energi ditransfer dengan cepat ke atom neon netral yang mempunyai tingkat energi sedikit dibawah atom helium. Ini adalah level laser yang lebih atas. Transisi laser yang paling penting pada panjang gelombang 633 nm. Gambar 15. Bagian-bagian laser He-Ne(Sumber: http://www.olympusfluoview.com) Laser He-Ne dipompa secara terus menerus, biasanya mnggunakan powersuplay DC. Power suplay DC ini khususnya pada rentang 0,3-15 mlwatt atau lebih pada transverse mode 00. Banyak laser He-Ne memakai cermin setengah pada tabung plasma. Keuntungan laser sangat sedikit; sudut Brewster windows esensial untuk mencegah berkurangnya pantulan. Bahkan, kaca keluaran itu mempunyai reflektansi lebih dari 99% dengan tabung plasma sepanjang 15 atau 20 cm. KarenaBrewster window,keluarannya menyebar pada bidang vektor elektrik termasuk poros laser dan garis normal Brewster window.

Doktora Tezi / Doctoral Thesis

Bu çalışma, kelam düşüncesinde yer verilen bilimsel bilgi ve kelamın bilim ile kurduğu ilişkiyi ele almaktadır. Kelamcılar, kelamın teşekkülü ile birlikte bilim tarihi açısından bilim olarak kabul edilen alanlarla ilişki kurmuş, kelam eserlerinde bu bilgi türüne benimseme ya da eleştiri bağlamında yer vermiştir. Allah’ın görülmesinin imkanının tartışıldığı rü’yetullah meselesi, görme duyumunun teorik açıklamasını içermesi bağlamında kelamcıların bilimin araştırma alanına giren görme konusundaki yaklaşımları üzerinden kelam-bilim ilişkisini incelemeye müsait bir konudur.

Çalışma iki bölümden oluşmaktadır. Birinci bölümde rü’yetullah konusu, problemin tarihsel sürecinden başlamak üzere, erken dönem Mu‘tezile Eş‘arîyye ve Mâtürîdîyye kelamındaki tartışmalar çerçevesinde ortaya konulmuştur. Bu çerçevede Allah’ın görülemeyeceği ve görülebileceği iddialarının akli ve nakli delilleri ele alınmış, zaman ve mekan açısından Allah’ın görülmesinin tartışıldığı bağlamlar ayrıca incelenmiştir. İkinci bölümde rü’yetullah tartışmaları sebebiyle kelam içerisinde yer alan bilim olarak görme duyumunun teorisi tespit edilmiştir. Bu çerçevede kelamcıların görmenin gerçekleşebilmesi için gerekli olan şartlar, görme süreci, görmenin gerçekleşme biçimi, görmeyi engelleyen problemler ve nelerin görülebileceği konularındaki yaklaşımları incelenmiştir. Kelamcıların bilimsel bilgi ile kurduğu ilişki ise, görme olgusu çerçevesinde teolojinin bilimsel açıklamayı belirlemesi ve bilimsel açıklamanın teolojiyi belirlemesinin örnekleri üzerinden açıklanmıştır. Son olarak kelamcıların görme konusundaki temel iddialarının güncel bilim açısından değerlendirmesi yapılmıştır.

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In this doctoral thesis, the scientific knowledge in Islamic theology (Kalām) and the relationship between theology and science has been studied. Islamic theologians (Mutakallimūn), with the formation of Kalām, established relations with the fields categorized as science in terms of the history of science, and included parts of this knowledge in their books. Vision of God (Ruʿyat Allāh) issue is a suitable subject for examining the Kalām-science relationship because of Mutakallimūn’s investigation of the theoretical explanation of the sense of sight within the subject.

This study consists of two chapters. In the first chapter, the subject of Ruʿyat Allāh is portrayed within the framework of the discussions in the early Muʿtazilah, Ashʿariya and and Māturīdīyah Kalām, starting with the history of the problem. The proofs of Mutakallimūn about whether Ruʿyat Allāh is possible or not are discussed and various aspects of the issue in terms of time and place are also scrutinized. In the second chapter, Mutakallimūn’s theory of vision, which is the science within Kalām due to the problem of Ruʿyat Allāh, is unveiled. In this context, assumptions of Mutakallimūn about the conditions necessary for seeing, the mechanism of seeing, the problems that prevent seeing and what can be seen are examined. The relationship between Kalām and scientific knowledge is explained through examples of theology's determination of scientific explanation and the scientific explanation's determination of theology within the framework of sight. Lastly, principal claims of the Mutakallimūn about vision are evaluated in terms of contemporary science.

Adnan Oktar (Harun Yahya)

Bu cümleyi siz okuyup bitirinceye kadar gözünüzde yaklaşık yüz milyar (100.000.000.000) işlem yapıldı. İşte bu muhteşem işlem hızı, sizi dünyanın en muhteşem aygıtlarından bir çiftine sahip yapıyor. Üstelik bu aygıtın bir benzerini insanoğlu halen üretemedi. Yaşamınızda sahip olduğunuz herşey gözleriniz ile bir anlam kazandı. Ailenizi, dostlarınızı, evinizi, işinizi, kısaca yaşamınız boyunca karşılaştığınız herşeyi gerçek anlamıyla gözleriniz sayesinde tanıdınız. Onlarsız dış dünyayı hiçbir zaman tam olarak bilemezdiniz. Gözleriniz olmasaydı bir rengin, bir şeklin, bir manzaranın, bir insan yüzünün, güzellik denen kavramın nasıl bir şey olduğunu muhtemelen hayalinizde canlandıramazdınız. Fakat, gözleriniz var, bu sayede etrafınızı görüyor, şu anda da önünüzdeki yazıyı okuyorsunuz.

The emerging field of optical wireless communication (OWC) systems is seen as potential complementary technology to the radio frequency wireless communications in certain applications. It is deemed as a possible technology in the future 5th Generation communication networks to address the spectrum congestion and improve the system's capacity. More research and developments in OWC is still needed in order for it to be adopted in current and future communication systems. This special issue brings together research papers on OWC covering free space optic, visible communications and ultraviolet communications.

For realization of future high performance integrated networks, broadband distribution and access networks and to meet the increasing demand of multimedia services with a guaranteed quality of service, RoF technology comes out as the most promising technology that combines the capacity of optical networks with the flexibility and mobility of wireless networks. Reduction in complexity at the antenna site, reduction in installation cost of access networks, possibility of dynamically allocation of radio carriers to different antenna sites, transparency and scalability are the few advantages of radio-over-fiber (RoF) technology. In this paper, we review the different challenges that limit the probable capabilities of RoF communication networks and different mitigation techniques to combat with these challenges to realize high-performance RoF links.

We present a two part study of melted microlens arrays. This first part concentrates on the production and measurement of microlens arrays while the second part examines attempts to model the microlens profiles. In this paper we first review some of the fabrication techniques used over the past twenty years to produce lens arrays. Some applications of microlens arrays are then discussed. Particular emphasis is placed on the photoresist reflow method of microlens production that was suggested by Popovic et al., as this was the method used to produce the microlens examined in this study. Lenses produced using this method can have large deviations from the spherical case, i.e. the profile that would be expected from a simple minimisation of the surface energy. These deviations have not been explained to date in the literature, however a number of possible causes for this deviation are given in this paper.

This paper presents PCFDT, which is an accurate and friendly photonic crystal fiber design tool based on fullvectorial finite element method. Photonic crystal fibers based on circular and non-circular microstructured holes, and on different propagation mechanisms have been analyzed. Comparisons with other numerical methods and experimental results have shown excellent agreement. The design tool validation includes experimental results of hybrid photonic crystal fibers, proposed by us, which made possible for the first time light be simultaneously confined and manipulated by two propagation mechanism, total internal reflection and photonic bandgap effect.

The Mueller-Jones (MJ) or pure Mueller matrix formulation has been reported by using two different matrix transformations in a condensed representation. The possibility to find other transformation matrices is explored. A complete set of unitary operators (R) is found to be closely related with the MJ matrices and with the evolution of pure states on the Poincare´sphere surface. We propose an alternative deduction for the condensed representation of the MJ matrices, obtained by using the Kronecker product operation and use of R unitary matrices as a tool to combine different Mueller matrices and changes of polarized states on the Poincare`sphere surface. Finally, it is shown explicitly that the columns of the transformation matrices are the eigenvectors of the MJ matrix associated to a non-depolarizing optical system and a corollary is established as a criterion to differentiate a Mueller matrix from an MJ matrix.

Methyl orange is an excellent nonlinear optical material. Both ordinary intense modulation holograph and the polarization holograph can be recorded in the methyl orange-polyvinyl alcohol (MO-PVA) film. The polarization state relationship among two writing beams, reading beam, and diffraction beam can be used for construction all-optical Boolean logic gate.

Hybrid gigabit-passive optical network (GPON) is a hybrid passive optical network, where wavelength division multiplexing (WDM) GPON and time division multiplexing (TDM)-GPON are integrated into a single passive optical network, reducing cost and increasing the data rate. In this paper, 2.5 Gb/s GPON downstream link is presented, using the radio over fiber (RoF) technique in GPON network architecture. It has been done by means of commercial OptiSystem simulation software, where, differential phase shift keying (DPSK) modulation is proposed by using 2.4 GHz radio frequency. The propagation of radio signals along a 25 km standard single mode fiber (SMF) investigated. The simulated model can support 32 and 64 users. The analysis was made based on the performance of eye diagram, optical signal to noise ratio (OSNR), constellation diagram, error vector magnitude (EVM) and received power.

The deduction of Zernike coefficients is usually influenced by the finite number of sampling dots on interferogram and their inherited measurement errors. In this paper, a simplified Gram-Schmidt method for solving the Zernike polynomial with the higher fitting precision is presented and used to analyze the wave front aberrations for the circle interference fringe of the fine polished aluminum disk surface captured by a Twyman-Green interferometer system. We find the stability of the Zernike coefficients changes with changing the Zernike term, which has lead to the wrong expression for the wave front aberration. By analyzing the condition number of the coefficients matrix and the fitting precision of the method, it is indicated that the instability can be avoided when the Zernike term is lower than 14. Such an analysis will be valuable in solving the Zernike polynomial for the wave front aberration analysis in optical testing.

Experimental evidence is shown that confirms the Etendue invariance in speckle fields. Because of this condition, the coherence patch of the speckle field can be significantly greater than the mean size of the speckles, as is shown by double exposure speckle interferometry. es from the diffuser are optically conjugated of areas S of the order of the speckle size at the plane IP.

The refraction holodiagram RHD is analyzed here with respect to the law of refraction. Particularly, we study the surface that exactly conjugates by refraction a virtual point source with a real image or conversely. By using the total optical path as a parameter we build a diagram that consists in a family of Descartes ovals of the apple type that contains the Pascal's limaçon as a particular extreme case and the spherical surface with the Weierstrass points as another. These representations permit the straightforward application of Fermat's principle in the case of arbitrary refracting surfaces and show the shape of generalized Fresnel's zones in the intersections with any surface. Snell's law is applied to rays incident on the apple type surfaces to find out the conditions for exact conjugation. Sensitivity to optical path variations is also discussed. The RHD curves family can be represented in a Cartesian way where the ovals appear as equally spaced straight lines.

In this paper, the possibilities of generating squeezed states of light via multimode interaction in a multi-channel nonlinear directional coupler, that operates with the second-order nonlinearity, was discussed. Employing the quasiprobability positive P of phase space representation, a complete numerical solution to the time evolution equation for the Hamiltonian was obtained. Finally, demonstrations were made of the enhancement of squeezed states achieved via mixed-mode correlation.

This paper reports on a systematic investigation of the optical properties of BeZnO thin films fabricated by radio frequency reactive magnetron sputtering technique using vacuum ultraviolet spectroscopic ellipsometry (VUV-SE). The thicknesses and optical constants of the thin films were determined in the wavelength range 138-1650 nm, using VUV-SE through the Tauc-Lorentz and Gaussian models. Refractive indices and extinction coefficients of the thin films were determined to be in the range n = 1.58-1.99 and Ä = 1.0 × 10 −27 -0.37, respectively. The absorption coefficient and the optical bandgap energy were then calculated. Measurement of the polarized optical properties reveals a high transmissivity (>90%) and very low absorptivity (<4%) for BeZnO films in the visible and near infrared regions at different angles of incidence. From the angle dependence of the p-polarized reflectivity we deduced a Brewster angle of about 58.5 • .

Structural health monitoring (SHM) is an emerging plot of researches, yet due to this new technologies specially optical fibers sensors, we are able to monitor many variations in the civil structures. Measuring the shift wave, we can prove the influence of temperature in sensing fiber. In this paper, both Brillouin scattering and Raman scattering are used to monitor temperature along the fiber. By modeling Brillouin and Raman Spectrum will be able to deduce temperature variation with Matlab codes.

Gamma bis glycinium oxalate (GBGOx) crystal was synthesized and grown by slow evaporation solution technique. The structure of pure GBGOx crystal has been examined by single crystal X-ray diffraction analysis. The confirmation with single crystal XRD reveals that the crystal belongs to monoclinic system with space group C 2 . The FTIR spectrum was recorded to identify the expected functional groups. UV-vis-spectrum shows the lower cut off wavelength and 80% of transmittance in the UV-vis region. The photoluminescence measurement shows that the material is suitable for photonic devices. Preliminary measurement of green light emission using Kurtz powder technique indicates that their second harmonic generation (SHG) efficiency. The microhardness analysis revealed that the grown crystal belongs to soft material category. The encouraging results show that the GBGOx crystals have great potential applications in optical devices.

In recent days amino acid single crystals are gaining importance due to good optical behavior. The title compound consists of l-alanine; an amino acid and maleic acid; an aromatic organic compound. It has been successfully synthesized and the single crystal has been grown by slow evaporation solution growth. The grown single crystal has been characterized by powder X-ray diffraction (PXRD) analysis and FTIR measurements. The crystalline perfection was examined by high-resolution X-ray diffraction (HRXRD) technique and found that the specimen quality is quite good. Optical behavior has been assessed by UV-Vis analysis and found that there is no absorption in the entire visible region. The relative second harmonic generation (SHG) efficiency measurement reveals that the incorporation of maleic acid to lalanine leads to increase its value of SHG. The mechanical behavior and the thermal analysis have been carried out using Vickers microhardness and TG/DTA measurements respectively. Its hyperpolarizability was estimated by density functional theory (DFT).

For realization of future high performance integrated networks, broadband distribution and access networks and to meet the increasing demand of multimedia services with a guaranteed quality of service, RoF technology comes out as the most promising technology that combines the capacity of optical networks with the flexibility and mobility of wireless networks. Reduction in complexity at the antenna site, reduction in installation cost of access networks, possibility of dynamically allocation of radio carriers to different antenna sites, transparency and scalability are the few advantages of radio-over-fiber (RoF) technology. In this paper, we review the different challenges that limit the probable capabilities of RoF communication networks and different mitigation techniques to combat with these challenges to realize high-performance RoF links.

An influence of acoustic wave diffraction on the modulation instability of the backward stimulated Brillouin scattering in fibers is numerically investigated, when a small feedback for the Stokes wave is present. The cases of acoustic waveguide and anti-waveguide fibers are considered. It is shown that a presence of acoustic diffraction may expand the region of occurrence of modulation instability and may lead to 2-5 times increasing the peak amplitude of output Stokes pulses. In this case, a stable train of short powerful Stokes pulses of nanosecond duration is produced at the output.

By impinging a step phase-shifted white light beam on a grating-based interferometer, one of diffraction orders is modulated and interference bands so-called "Talbot bands" are formed. Here, classical Talbot bands set up is generalized to the symmetry configuration, in which two glass plates of the same thickness instead of one plate, are inserted halfway into the grating interferometer aperture. Formation of Talbot bands were studied theoretically and experimentally. Frequency impulse response of the new Talbot bands setup was, also presented. It was demonstrated that symmetric set-up causes modulation of both of two opposite orders, according to the theory. In this manner, their visibility is the same. As a result, this similarity of the visibility is reduced while the symmetric arrangement of the glass plates with respect to the optical axis, is broken.

Orthogonal frequency division multiplexing (OFDM) Radio over fiber (RoF) Quadrature amplitude modulation (QAM) Optical single side band (OSSB) a b s t r a c t This work is focused to carry out an investigation to estimate the performance of an OFDM-OSSB-RoF transmission system using different order of QAM sequence generator at high transmission rate. Further, the results are reported by compensating the degradations introduced by fiber dispersion using fiber Bragg grating (FBG) for the proposed Hybrid OFDM-RoF system and a comparison is presented for the performance of OFDM-RoF system with and without FBG. The results are reported by incorporating OSSB modulation scheme as it performs better ODSB modulation scheme as the later one is suffered, severely, with fading problems due to fiber dispersion. In case of hybrid RoF system with FBG, an improvement in SNR ratio and total power received is achieved in comparison to hybrid RoF system without FBG.

Photographic emulsions are still widely used in the recording of phase holograms. Several techniques have been optimized in order to produce phase holograms on photographic emulsions showing high diffraction efficiencies and low levels of noise. Among these techniques, bleached processes are one of the most interesting as they involve a relatively small number of steps and produce holograms of high quality. Of particular interest is the method of fixationfree rehalogenating bleaching because the shrinkage of the emulsion is minimum. In this paper we will study the influence of the development step in the fixation-free bleaching process applied to BB-640 emulsion. We will show that the development influences the optimum concentration of potassium bromide in the bleach solution. We will also show that good results can be obtained by using BB-640 plates for a wide variety of developers and that the values of the diffraction efficiency reached are rather high, as high as 87% for holograms developed in CW-C2.

An experimental study has been presented of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) operating in the 850 nm region of the electromagnetic spectrum. In this regard, various relevant VCSEL samples with numerous oxide aperture sizes have been fabricated and characterized. Thorough investigations of the electrical as well as optical characteristics of the fabricated samples have been performed, which include the overall device performance as a function of the oxidize aperture sizes. It is reported that the VCSELs with oxide aperture size o10 mm require low threshold currents (o1 mA). Further, the differential quantum efficiencies up to 28% corresponding to wall-plug efficiencies of up to 15% were measured for a number of these devices.

In terms of the coupled mode theory (CMT) and the transfer matrix method, we present a technique and relative formulas including the bent coupling coefficient, amplitude coupling ratio, amplitude transmission ratio and propagation power for analyzing the vertical bent coupling between a curved rectangular waveguide and a straight one. Investigations show that the bent coupling appears in an effective coupling region by both sides of the central coupling point. Beyond this effective coupling region, however, the bent coupling is very weak, and the propagation power in the waveguide is closer to a constant. As the bent radius increases, or the thickness of the coupling layer between these two waveguides decreases, this effective coupling region becomes wider, in which the coupling behavior becomes stronger.

A space-variant optical correlator is experimentally implemented based on the fractional Fourier transform. The proposed arrangement employs a fake zoom lens that enables to vary the degree of the fractional Fourier transform continuously between -1 to +1. The optical device uses as a recording medium for the holographic filter a photorefractive BTO crystal. The experimental results confirm the shift-variance properties.

This work describes the performance of a compact ''in-house built'' radio-frequency (RF)-excited CO 2 slab waveguide laser which has the innovation of having a plugged-in RF generator-amplifier module directly connected into the positive electrode of the laser head. The design circuit parameters include a matching circuit and a feedthrough element as a whole. The overall laser performance takes into account the waveguide dimension (y-axis) as approximately one-tenth of the free space transverse dimension (x-axis). The optical resonator is calculated to be in the regime of the negative branch for unstable confocal resonators, having focal lengths of f 1 ¼ 21:49 cm and f 2 ¼ 19:39 cm with geometrical amplification of 1.108. Optical output coupling mirror was set to $9.7%. The calculated waveguide length is 37.73 cm whilst the total resonator length was adjusted to 42 cm to allow coupling losses less than 1%. The laser operational efficiency was about 12% and the output beam quality of 1.13 which is close to the ideal Gaussian beam. The optical output power was accomplished by playing with different gas compositions to have a final optimized gas proportion of 1:1:2.7:0.3 correspondingly to CO 2 , N 2 , He and Xe as admixture.