A BSTRACT —We solve the coupled mode equations governing the chalcogenide nonlinear fiber Bragg gratings (FBGs) numerically, and obtain the bistability characteristics. The characteristics of the chalcogenide nonlinear FBGs such as: switching threshold intensity, bistability interval and on-off switching ratio are studied. The effects of FBG length and its third order nonlinear refractive index on FBG characteristics are investigated. We obtain an interesting result that independent of the third order nonlinear refractive index; there exists an optimum FBG length of about 6 mm at which the on-off switching ratio becomes maximized. It is also found that by increasing the nonlinearity, the maximum value of on-off switching ratio decreases. The results of this paper can be mainly used for designing all- opticalswitches and memories.
High-speed optical communication networks with ter- abit transmission capabilities attract much attention, in terms of high capability and exibility in optical signal processing. Such ultrafast optical signal process- ing can be achieved using a Symmetric Mach Zehnder (SMZ) alloptical switch family, including an origi- nal SMZ switch [1,2], a Delayed Interference Signal- wavelength Converter (DISC) , and a Polarization Discrimination SMZ (PD-SMZ) . The Semiconduc- tor Optical Amplier (SOA) is a key element in many ultrafast switching schemes. The speed of switches based on SOA is limited, especially because of SOA carrier dynamics. To overcome this limitation, dierent approaches have been used. Wang et al. proposed and experimentally demonstrated a SOA based dierential
From these three equations, one can observe that TPA and FCA strongly influence the loss of cw signals through Cross Absorption Modulation (XAM) as well . For this reason, the optimal power of the control signal has to be determined as a tradeoff between a large switching efficiency and the amount of induced nonlinear loss. The silicon arm acts as a phase shifter that, in the MZI configuration, switches the power from one arm to the other. On the other hand, XAM introduces a nonlinear loss, which contributes to the formation of a “dark pulse” at both the cross and bar output of the MZI. The effects of XAM can be limited by choosing a control-signal power below the level at which the effect of TPA cannot be considered as negligible.
all-optical flip-flop based on 2 semiconductor lasers is shown in , the lasers are coupled such that when one laser is “ON” it quenches the other. A device based on coupled micro ring lasers is presented in , the device is implemented on an InP/InGaAsP photonic integrated circuit. The two output states of the flip-flop are due to clock-wise and anti-clock-wise laser modes in the coupled rings. Low power device where the two output states are clock-wise and anti-clock-wise laser modes in a single micro disk laser is implemented on a silicon chip in . A device based on Distributed Feedback (DFB) semiconductor laser and a holding beam is shown in , where the bistability is due to spacial hole burning effect. In , an alloptical flip-flop based on dispersive bistabolity in Vertical Cavity Semiconductor Optical Amplifier (VCSOA) is implemented. The device is reset by cross gain modulation (XGM) in the presence of a holding beam. These devices require holding beams or they generate output at both states, other types of devices are bistable laser diodes. The bistable laser diode does not require a holding beam. The bistable laser diodes have two states; OFF states (no optical output), or ON state. In  , a saturable absorber is implemented within the gain la- ser cavity to achieve optical bistability, in a bistable laser diode. In  , bistable la- ser diodes are investigated. The optical bistability is due to nonlinear distributed optical feedback within the laser cavity.
As shown by equation (4.5b) the nonlinear contribution to phase change is inversely proportional to its amplitude and directly related to the cosine of the relative phase between the four waves involved. As illustrated in Fig.4.1 the spectral distribution of the phase <p (co) has, in the first stages, a maximum for values of oi at which the phase change rate is moderate so that the contributions made by the cosine terms add mostly in phase or with postive signs for a given distance. In the outer parts of the spectrum this phase maximum turns into a discontinuity as illustrated in Fig. 4.2a. Once a phase difference between the center and side frequencies has been induced, equation (4.5a) reveals that power is transferred from the spectral components with lower phases < j > (< d ) to those with higher phases as illustrated in Fig. 4.2b. We remark from Fig. 4.1 that for the parameters used here, even a linear dispersion of 9 x 10 sec /cm (or 70 psec/(nm.km) ) contributes little to the phase.
optical flip-flop are suggested and implemented. In , an alloptical flip-flop based on a micro disk laser where the two states correspond to clock-wise and anti-clock-wise mode is implemented. An alloptical flip-flop based on coupled micro laser rings is implemented in . Flip-flop based on a single DFB laser structure is shown in . Alloptical flip-flops based on multi-mode interference bistable laser diode are described in -. All these flip-flops require a holding beam, or, some of them gererate output modes in both ON and OFF states. All opti- cal flip-flops based on bistable laser diode are discussed in  , and they do not require a holding beam. In  , the flip-flop is Fabry-Perot laser cavity that includes a saturable absorber, where the optical loss in the cavi- ty is reduced at high light intensity in the laser cavity. In , an alloptical flip-flop based on a DFB structutre with a periodic negative nonlinearity is simulated. The flip-flop does not require a holding beam, and it requires a periodic negative nonlinear coefficient that alters the grating strength which is difficult to fabricate. In , an alloptical flip-flop based on a chirped nonlinear DFB structure is simulated. In this structure, the chirped grating prevents lasing due to the lacking of an optical feedback (OFF state). The negative nonlinear coefficient in- creases in magnitude linearly along the structure. The chirp is reduced when high optical power exists in the structure (because the nrgative nonlinear coefficient reduces the revractive index along the structure gradually) and a laser mode builds up. The structure in  requires a gradual increase in the linear refractive index of the wave guiding layer which is difficult to achieve. Also, it requires a gradual increase in magnitude of the nonli- near coefficient along the wave-guiding layer. This design could be achieved by using multiple sections of dif- ferent linear and nonlinear coefficients. Each section has constant linear refractive index and constant negative nonlinear coefficient. However each section has slightly different linear and nonlinear coefficient as both of them must increase gradually along the structure. This could be difficult to fabricate, and we look for another simpler design.
One of the leader in MEMS technology today is Lucent Technologies. Lucent is poised to offer their first all-optical routing system this year called the WaveStar LambdaRouter. The Lamb- daRouter uses a 256x256 array of movable mirrors to direct light from one fiber to another. Advantages of the MEMS architecture include scalability, low power consumption, low loss, compact size, and protocol transparency. Lucent’s current system can support single channel data rates as high as 40 Gb/s. MEMS offers a simple solution to the optical switching prob- lem and avoids the electronic conversion required in standard routers but the applications area is somewhat limited. Since MEMS are inherently mechanical, they are limited in speed. The Lucent LambdaRouter can move its mirrors only on a time scale of 10 ms. While this is ap- propriate for optical circuit switching and optical layer restoration protection switching, it is not nearly fast enough to support switching on a packet-by-packet basis required by IP routing. Fur- thermore electronic hardware must still be used to obtain the routing information to control the switch. Due to the mechanical nature of MEMS, long-term reliability and packaging are still critical issues in these systems that will be proved over time. Additional advances in MEMS will most likely be able to upgrade the speed of these switches. The MEMS based switches will most likely interconnect service providers and large cities where continuous traffic streams are established for longer periods of time between fixed locations.
percontinuum spectrum could be achieved by pumping it with 610f s laser pulses at 68W peak power and a wavelength of 1550nm. This can be com- pared with 350nm achieved in a 4.7cm silicon nanowire using 100f s pulses . By comparing the 1W input power of the silicon experiment with the 68W input power of the chalcogenide experiment, it is clear that even though the chalcogenide results are promising, the silicon results are superior. This is due to the fact that the silicon fabrication technology is more mature. The pattern definition and etching for high quality photonic wires requires a higher level of precision than the fabrication of rib-waveguides. Rib waveg- uides benefit from a lower field intensity at the surfaces, hence roughness and imperfections have less impact on the propagation losses. The lower inten- sity is due to the bigger mode in rib-waveguides. This affects the nonlinear response negatively, which has to be compensated for by higher input powers. A step towards higher mode confinement in chalcogenide glasses was the first demonstration of photonic crystals in chalcogenide glasses that were fab- ricated by focused ion beam (FIB) milling  in 2005. The first photonic crystals that were fabricated using electron beam lithography and dry etch- ing were fabricated by Yinlan et.al. in 2007 , avoiding the parasitic ion implantation of FIB milling. Even though, similar fabrication techniques to
parameters such as average single bond strength, optical electronegativity, optical energy gap, refractive index, optical basicity and third order nonlinear susceptibility are discussed with respect to titanium concentration. Gamma ray transmission and the parameters which affect these processes; attenuation coefficients and half value layer, were studied using the mixture rule of the XCOM program, in the energy range (1 keV-100 GeV). The results obtained probably provide good biased for prediction of new nonlinear materials and can be used as an environmentally friendly substitute for lead for industries besides their radiation-shielding property.
In fig.5 Simulink model of a 200V/16V DC-DC converter has been proposed .In fig.6.output waveforms of the proposed converter is shown. In the proposed converter there is total six switches out of it Q1,Q3,Q5 are given with same duty cycle and Q2,Q4,Q6 are same having same duty cycle. Though the switches have same duty cycle all the switches not on for the same time In the proposed converter there are total six switches in which all are under goes soft switching for different duty cycles Fig.7 & Fig.8 shows the simulation results for D=20%.
Abstract: Optical signal is the best suitable one for data processing and digital signal communication for its inherent parallelism and tremendous operational speed. Conventional electronic or optoelectronic devices are unable to fulfill this due to less speed and time delay. In the case of perfect electronic flip-flop, at the time of switching turned ON, there is noticeable propagation delay on the order of nanoseconds. In the case of an opto-electronic flip-flop, although the propagation delays time is much less than those of a pure electronic flip-flop about 10 to 100 times less, there are many disadvantages still have. Some of these disadvantages are delay of response time due to the use of spatial light modulators, an O/E converter that does not operate at all frequencies or wavelengths, and the unavailability of such materials. An optical input encoding methodology may be the alternative for the performance of two inputs all-optical flip-flop operations. These operations may be conducted in all-optical mode and will be parallel in nature. All the operations may be conducted with proper exploitation of some nonlinear materials. In this communication author reported an optical encoding technique for the construction of clocked J-K flip-flop with two inputs. All the operations are conducted by the proper exploitation of nonlinear materials.
Most commercial fiber optic networks today deploy electronic switching or electro-optical switching. In order to obtain very high speeds it is essential for the signal to remain photonic throughout its path (i.e. alloptical). AllOptical Networks consist of Optical Fiber links between nodes with alloptical switching and routing of signals at the nodes without electronic regeneration AllOptical WDM Networks are very much a reality in the not too distant future with the advent of Erbium Doped Fiber Amplifiers (EDFA’s), Raman amplifiers, optical crossconnects, Non Zero Dispersion compensating fibers and other state of the art optical devices. The advantages offered by these systems in the telecommunication industry are compelling. AllOptical WDM networks offer transparency to bit rates, protocol formats and they also eliminate the need for costly electronic 3R regeneration at the intermediate nodes. Alloptical networks may form the national backbone in the not too distant future and even in the access network we may see alloptical solutions for metropoliton area networks. Fig 1 below depicts a block diagram for a typical 4 channel AllOptical WDM transmission system.
The investigation of the nonlinear dynamics of a semiconductor laser based on nonlinearoptical loop mirror (NOLM) feedback using Ge doped optical fiber was carried out experimentally. Animations of compilations of the output power as a function of time series and phase plane with effects of optical feedback level, carrier current and modulation signal strength are demonstrated as a tool to give insight into the laser dynamics. Different dynamic states, including 2×, 4× multiplication and quasi-periodic and periodic frequency-locked pulsing states extended to chaotic behaviour were ob- served by varying the parameters of modulated frequency and optical feedback strength. The frequency-locked pulsing states were observed to exhibit a harmonic frequency-locking phenomenon and the pulsing frequency is locked to a harmonic nonlinearity in loop instead of the modulated frequency.
The fifth generation systems attempt to extend the wavelength range of WDM systems and to increase the bit rate of each channel within the WDM signal (Nusinsky, 2004; Rosolem, 2006; Potenza, 1996). This led to utilization of dense wavelength-division multiplexing (DWDM) techniques. In 2000, up to 27 WDM channels each operating at 20 Gb/s were transmitted over 9000 km using hybrid amplification scheme (Agrawal, 2002; Ramaswami,. 1998). The Raman amplification technique can be exploited for signals in all three wavelength bands (i.e. C, L and S bands). The Raman amplifiers are being deployed in almost every new long-haul and ultralong-haul fiber-optic transmission systems (Islam, 2002; Namiki et al., 2002). The Raman amplifier is one of the first widely commercialized nonlinearoptical devices in telecommunication systems (Rottwitt, 2002; Bromage, 2004; Rkhelenko, 2013). The dry fibers have been developed with very small fiber losses over entire wavelength range (1300- 1675 nm). This may lead to lightwave systems with thousands WDM channels. By careful management of fiber dispersion, optical systems with bit rate higher than 100 Gb/s over several thousand kilometers can be achieved. Such systems utilize optical solitons and Raman amplification technique to overcome fiber losses (Mollenauer, 1998; Haus, 1993; Gangwar, 2007). Solitons are pulses that can preserve their shape by counteracting the negative effects of dispersion. The impressive results of fiber optics led to prediction of next- generation telecommunication infrastructure scenario based on all-optical networks including optical frequency division multiplexing (OFDM), information superhighways, coherent receivers, all-photonics switching, fiber-to-the-home (FTTH) with ATM-based digital broadband access offering interactive multimedia services and an ultimate number of interactive high definition TV (HDTV) channels. The cost of involved optoelectronics is major limitation in fulfilling these promises. FTTH represents the best technical solution for higher quality interactive multimedia communication and all of us will have fiber in our home and at our desktop one day.
Z-Scan technique was originally introduced by Sheik Bahae et al. [17 ].This technique is used to measure the magnitude of both real and imaginary part of third order nonlinear susceptibility. There are two Z-scan methods namely open and closed aperture used for the measurement of nonlinear absorption coefficient and nonlinearoptical refraction for optical materials. A He–Ne laser (λ = 632.8 nm) was used as the light source and focused by a lens of 22.5 cm focal length. The light intensities, transmitted across the sample, are measured as a function of sample position in the Z-direction with respect to the focal plane either through a closed aperture (CA) or open aperture (OA) in order to resolve the nonlinear refraction and absorption coefficients. The beam was focused using a convex lens and the focal point has been taken as Z=0. By placing the sample in different positions with respect to the focus of the beam, the corresponding normalized transmission to the grown GPS crystal was measured. The diagrams for open aperture and closed aperture Z-scan curves are presented in the figures 5(a) and 5 (b). The Z-scan curves are characterized by a prefocal transmittance maximum (peak) followed by a postfocal transmittance minimum (valley) intensity. The transmission difference between peak and valley, linear transmittance aperture, the third-order nonlinear refractive index (n 2 ) of the crystal, the nonlinear absorption coefficient (β) and the third order nonlinear
frequency of electric charge carriers can not follow the alternation of the ac electric field applied beyond a certain critical frequency . In accordance with Miller rule , the lower value of dielectric constant at higher frequencies is a suitable parameter for the enhancement of SHG coefficient. It is also observed that both dielectric constant and dielectric loss depend on the temperature and increase with increase of temperature at a constant frequency . Materials with high dielectric constant at low frequency find applications in heating devices . The low dielectric loss at higher frequency region indicates that the grown crystals contain minimum optical defects .
Though the particular details of specific experimental conditions are discussed in each chapter, an overview is provided here for the sake of providing a unified orientation. All nanowires discussed in this dissertation were synthesized via the VLS mechanism with chemical vapor deposition (CVD) used to provide the vapor. In this process, a Si wafer is cleaned and covered by a 5 nm thick metal layer using plasma sputter deposition, placed in the center of a tube furnace and annealed, during which time surface forces cause the layer to separate into droplets with a diameter distribution roughly centered around 150 nm. Early attempts at colloidal gold seeds generally did not produce satisfactory results, though this speaks more towards the nuances in our particular furnace than anything else. After cooling, solid, elemental precursors were introduced upstream of the substrate, the tube evacuated, and argon carrier gas introduced to encourage transfer. † The tube was then rapidly heated and held at an elevated temperature during growth, during which time precursors begin to collect in the metallic catalyst droplets. As discussed in Chapter 1, once the liquid droplets saturate, solid nanowires nucleate at the droplet/substrate interface and continue to grow as long as precursor is provided. At the end of the growth period, the furnace is cooled via forced airflow.
In optical transmission systems a great part of the research is focused on increasing the system reach and robustness . All-optical signal regeneration is auspicious techniques to achieve this extension, which can be performing with fiber nonlinearity. Opticalnonlinear material is specially used for ultra-high speed performance. Power launched inside the optical fiber interacts with fiber material and due to refractive index several transmission impairments for example linear, nonlinear, scattering and etc. are produced . These interactions depend on the noise evolution of signals transmitted inside the fiber[3-4]. Practically nonlinear phase noise is much more dominant than amplitude noise. During system design nonlinear phase noise is dealt separately [5, 6]. Regeneration signals are based on (electronic or all-optical signal) processing both are significantly in use depends upon application. Electronic-based regeneration requires conversion of data by mean of optical-to-electrical- ]optical [7, 8]. Alloptical regeneration do not require any conversion O-E-O . An ideal regenerator would suppress noise in both the signal’s amplitude and phase [9, 10]. However, use of the complex optical-field gives rise to a new dominant limitation to system performance, namely nonlinear phase noise [13-14].
A new all-optical flip-flop based on a nonlinear Distributed feedback (DFB) structure is proposed. The device does not require a holding beam. A nonlinear part of the grating is detuned from the remaining part of the grating and has negative nonlinear coefficient. Optical gain is provided by an injected electrical current into an active layer. In the OFF state, due to the detuned section, no la- ser light is generated in the device. An injected optical pulse reduces the detuning of the nonlinear section, and the optical feedback provided by the DFB structure generates a laser light in the structure that sustains the change in the detuned section. The device is switched “OFF” by detun- ing another section of the grating by a Reset pulse. The Reset pulse reduces the refractive index of that section by the generation of electron-hole pairs. The Reset pulse wavelength is adjusted such that the optical gain provided by the active layer at that wavelength is zero. The Reset pulse is prevented from reaching the nonlinear detuned section by introducing an optical absorber in the laser cavity to attenuate the pulse. The device is simulated in time domain using General Purpose Graphics Processing Unit (GPGPU) computing. Set-Reset operations are in nanosecond time scale.