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We report detailed theoretical analysis on the influence of the fused depth, launch mode and taper ratio on the performance of side-pumping combiner. The theoretical analysis indicates that the coupling efficiency and loss mechanism of the combiner is closely related to the fused depth, tapering ratio and the launch mode. Experimentally, we fabricate combiners consisting of two pump fibers (220/242 μm, NA=0.22) and a signal fiber (20/400 μm, NA=0.46). The combined pump coupling efficiency of two pump port is 97.2% with the maximum power handling of 1.8 kW and the insertion signal loss is less than 3%.

We have developed a chip-scale optofluidic sensor for biomolecular detection, by tapering laterally aligned silica microfiber and capillary to form a modal interferometer. With the pre-immobilization of DNA probes, the sensor is capable of selectively detecting single-stranded microRNA-let7a (molecular weight: 6.5 k) by measuring the spectral shift of the interferometric spectrum. A log-linear response from 2 nM to 20 μΜ and a minimum detectable concentration of 212 pM (1.43 ng/mL) have been achieved. The sensor is promising for future diagnosis applications due to its high sensitivity, resistance to environmental perturbations, improved portability, and intrinsic connection to fiber optic measurement.

We model output characteristics of the 1645 nm 8 mJ 10 ns 100 Hz Q-switched Er:YAG DPSSL. The laser is end pumped at a wavelength of 1532 nm. Fiber-coupled diode laser module was 10 nm FWHM, 12 W CW, 200 μm, NA 0.22. Various tapering of the active rod has been considered for 1 mm diameter, 20 mm long and 0.5% Er doping. We discuss the heat deposition process, the energy storage efficiency and the average power limitations for Q-switched regime of generation and amplification, and find the system scalable for the high power operation.

In this work, we present a novel and simple optical solution for MEMS LiDARs. The idea is based on increasing the collection optics throughput by removing the MEMS mirror from the path of the collected light, while inserting a multi-segment tapered structure to collect the light from a wide angle. The tapered also converts the large size optical spot captured to a small area compatible with the requirement of low detector noise dimensions. The expected improvement in the collected power is analyzed versus the tapering angle of a single tapered structure. A multi-segment optical system, or multiple tapered structure arranged in parallel, is also introduced allowing for the optimization of the acceptance angle and the power improvement ratio. Using a 3-segment mirror, the expected improvement is about 15x with an acceptance angle of ±30 degrees. The design of a single element taper section is fabricated using aluminum-coated acrylic and tested experimentally showing an improvement of about 7x in the coupled power through an angle of ±10 degrees in good agreement with the theoretical expectations.

A tapered hybrid microfiber comprising a metal core and a glass silicate cladding is the platform proposed here for the development of plasmonic sensing devices. The existence of the glass cladding provides several advantages over pure metal tips while exhibiting high enhancement factors at the tip apex up to 104. Optimization of the fiber tapering process conditions can be achieved by using different metals having different melting points, viscosity and thermal expansion coefficients as well as composite fibers with different glass and metal core diameter in order to achieve tapered microwires with the desirable geometrical and operational characteristics.

We report a high-sensitivity refractive index sensor based on microfiber long period gratings (MLPGs) fabricated by a CO2 laser line-by-line inscription. The microfiber was fabricated by using hydrofluoric acid (HF) to etch a conventional single mode fiber (SMF). The MLPGs were fabricated by periodically tapering the microfiber with CO2-laser pulse line by line. We showed that a 45-period long period grating with about 15 dB attenuation dip can be realized in the microfiber with a diameter of ~32μm. The MLPGs were found to have a very high sensitivity to external refractive index, in which the sensitivity of the MLPGs can be 4 times than that of a normal long period grating (LPG).

We report light-driven instability and optomechanical self-oscillation of a fused silica “nanospike” at low gas pressures. The nanospike (tip diameter 400 nm), fabricated by thermally tapering and HF-etching a single mode fiber (SMF), was set pointing at the endface of a hollow-core photonic crystal fiber (HC-PCF) into the field created by the fundamental optical mode emerging from the HC-PCF. At low pressures, the nanospike became unstable and began to self-oscillate for optical powers above a certain threshold, acting like a phonon laser or "phaser". Because the nanospike is robustly connected to the base, direct measurement of the temporal dynamics of the instability is possible. The experiment sheds light on why particles escape from optical traps at low pressures.

Temperature-independent strain measurement is achieved resorting to a taper fabricated on a Bragg fibre using a CO 2 laser. The characteristic bimodal interference of an untapered Bragg fibre is rendered multimode after taper fabrication and the resulting transmission spectra are analysed as temperature and strain change. The intrinsic strain sensitivity exhibited by the Bragg fibre is increased 15 fold after tapering and reaches 22.68 pm/μepsilon. The difference in wavelength shift promoted by variations in temperature and strain for the two fringes studied is examined and strain sensing with little temperature sensitivity is achieved, presenting a sensitivity of 2.86 pm/μepsilon, for strain values up to 400 μepsilon.

Herein we present the experimental implementation of a power coupling device that combines the technology of tapered, multicore microstructured optical fibres (MOFs) with ferrofluidic overlayers. Power coupling between different cores of a tapered, multicore MOF is demonstrated, utilizing magneto-refraction effects induced by magnetic field stimulus into a ferrofluidic outcladding surrounding of the multicore optical fibre taper. By tapering the multicore all-solid MOF to a specific diameter, the excitation of all the adjacent cores through the central one is achieved. Transmission spectra measurements of the individual cores proved that light coupling between fiber cores can be manipulated by magnetic field stimulus. We anticipate that such a type of magneto-tunable power-coupling photonic device can find applications in optical magnetometry, imaging and optical communications.

We present a concept of a silicon slab based 2D integrating cell where photonic crystal (PhC) reflectors are used in order to confine light in a two-dimensional area to acquire a long propagation length. The evanescent field of the guided wave can be used for sensing applications. We use FDTD simulations to investigate the dependence of the reflectivity of photonic crystal mirrors with a hexagonal lattice. The reflectivity in ΓM direction demonstrates reduced vertical losses compared to the ΓK direction and can be further improved by adiabatically tapering the hole radii of the photonic crystal. A small hexagonal 2D integrating cell was studied with PhC boundaries oriented in ΓM and ΓK direction. It is shown that average reflectivities of 99% can be obtained in a rectangular 2D cell with optimized reflector design, limited only by residual vertical scattering losses at the PhC boundary. This reflectivity is already comparable to the best metallic reflectors.

We present a linear all-fiber device exhibiting the functionality of a circulator, albeit for multimode fibers. We define a pseudo-circulator as a linear three-port component that transfers most of a multimode light signal from Port 1 to Port 2, and from Port 2 to Port 3. Unlike a traditional circulator which depends on a nonlinear phenomenon to achieve a non-reciprocal behavior, our device is a linear component that seemingly breaks the principle of reciprocity by exploiting the variations of etendue of the multimode fibers in the coupler. The pseudo-circulator is implemented as a 2x2 asymmetric multimode fiber coupler, fabricated using the fusion-tapering technique. The coupler is asymmetric in its transverse fused section. The two multimode fibers differ in area, thus favoring the transfer of light from the smaller to the bigger fiber. The desired difference of area is obtained by tapering one of the fiber before the fusion process. Using this technique, we have successfully fabricated a pseudo-circulator surpassing in efficiency a 50/50 beam-splitter. In all the visible and near-IR spectrum, the transmission ratio exceeds 77% from Port 1 to Port 2, and 80% from Port 2 to Port 3. The excess loss is less than 0.5 dB, regardless of the entry port.

By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting quantum cascade lasers (QCLs) virtually complete carrier-leakage suppression is achieved, as evidenced by high values for both the threshold-current characteristic temperature coefficient T 0 (283 K and 242 K) and the slope-efficiency characteristic temperature coefficient T 1 (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm 2 and 1.88 kA/cm 2 , respectively. In addition, due to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30- 40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both efficient carrier-leakage suppression as well as fast and efficient carrier extraction, the values for the internal differential efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting in the 7-11 μm wavelength range.

We propose an in-line modal coupler based on a multicore fiber (MCF) which can be readily fabricated by using the adiabatic tapering method. The intermodal coupling of the in-line modal coupler apparently generated the transmission oscillation of the center core and the multiple side core modes depending on the waist diameter. The reduction of the waist diameter of the adiabatically tapered MCF could dramatically change its sensitivities to strain, temperature, and ambient index. We believe that experimental results are very useful to fabricate the in-line modal coupler based on the MCF and to improve the performance of the fiber-optic sensors by controlling the waist diameter of the adiabatically tapered MCF.

Geometrical shaping of non-adiabatic single tapers is used to modify the filtering characteristics. The fiber tapers are shaped by successive tapering. The taper shaping produces deeper rejection bands. As an application of the shaped tapers, fluidic temperature sensing cells were fabricated. In a first case, the wavelength shift of a single rejection band was monitored, showing a nonlinear response and low sensitivity to temperature changes. In a second case, a shaped taper fluidic cell containing two rejection bands was used, and the wavelength shift of the half intensity points of the transmission band (between the rejection bands) was taken as a measure of the temperature change. In this case, the fluidic cell showed a linear sensitivity of 481.9 pm/°C in a temperature range of 25°C-60°C.

We reported a few high-sensitivity optical strain sensors based on different types of in-fiber FPIs with air bubble cavities those were fabricated by use of a commercial fusion splicer. The cavity length and the shape of air bubbles were investigated to enhance its tensile strain sensitivity. A FPI based on a spherical air bubble was demonstrated by splicing together two sections of standard single-mode fibers, and the spherical air bubble was reshaped into an elliptical air bubble by mean of repeating arc discharge, so the strain sensitivity of the FPI based on an elliptical air bubble was enhanced to 6.0 pm⁄μe owe to the decrease of the air cavity length. Moreover, a unique FPI based on a rectangular air bubble was demonstrated by use of an improved technique for splicing two sections of standard single mode fibers together and tapering the splicing joint. The sensitivity of the rectangular-bubble-based strain sensor was enhanced to be up to 43.0 pm/μe and is the highest strain sensitivity among the in-fiber FPI-based strain sensors with air bubble cavities reported so far. The reason for this is that the rectangular air bubble has a sharply taper and a thin wall with a thickness of about 1 μm. Moreover, those strain sensors above have a very low temperature sensitivity of about 2.0 pm/oC. Thus, the temperature-induced strain measurement error is less than 0.046 μe/oC.

We demonstrate a polarization-insensitive coupler interfacing multicore-fiber (MCF) to silicon waveguides. It comprises a 3D glass fanout transforming the circular MCF core-arrangement to linear and performing initial tapering, followed by a Spot-Size-Converter on the silicon chip. Glass waveguides are formed of multiple overlapped modification elements and appropriate offsetting thereof yields tapers with symmetric cross-section. The Spot-Size-Converter is an inverselytapered silicon waveguide with a tapered polymer overcladding where light is initially coupled, whereas phase-matching gradually shifts it towards the silicon core. Co-design of the glass fanout and Spot-Size-Converter obtains theoretical loss below 1dB for the overall Si-to-MCF transition in both polarizations.

Tapering will raise the signal loss in an end-pumped (N+1)×1 type combiner. In this paper, the Thermally Expanded Core (TEC) technique is used in the signal loss optimization experiment with the tapering ratio of the pump combiner is 0.6. The experimental results indicate that the coupling efficiency of the 1.55μm signal light increases from 81.1% to 86.6%, after being heated 10 minutes at the homo-waist region of the tapered signal fiber with an 8mm wide hydroxygen flame. Detail analysis shows that the TEC technique can both reduce the loss of the LP01 mode and the LP11 mode in the signal fiber.

Supercontinuum generation (SCG) was investigated in tapered tellurite microstructured optical fibers (MOFs) for various taper profiles. We emphasize on the procedure for finding the dispersion profile that achieve the best width of the SC spectra. An enhancement of the SCG is achieved by varying the taper waist diameter along its length in a carefully designed, and an optimal degree of tapering is found to exist for tapers with an axially uniform waist. We also show the XFROG spectrograms of the pulses propagating through different tapered fibers, confirming the optimized taper conditions.

We report on the first observation of the Brillouin gain spectrum in a perfluorinated graded-index plastic optical fiber (POF) tapered by a heat-and-pull technique. The Stokes power was slightly enhanced by tapering probably on account of higher optical power density in the core. In addition, the Brillouin frequency shift was decreased by ~40 MHz, which was experimentally verified to be partially caused by high temperature applied to the POF during the taper fabrication process. We anticipate that our findings will provide a basic principle of temperature sensing with “memory” function.

A highly-birefringent elliptic microfiber is fabricated by use of the CO2-laser machining and fusion tapering methods. The fiber ellipse can be well controlled with modification of the CO2 laser output power. Both positive and negative sensitivities are observed for the structure to be used in the refractive index sensing application, in contrast to the previously-reported microfiber devices. Moreover, the maximum obtained sensitivity is as high as 195348nm/RIU (refractive index unit) around refractive index of 1.35887, which is one order of magnitude higher than other microfiber counterparts. The temperature-cross sensitivity of 0.007nm/°C is quite low.

A magnetic-field-tuned photonics device based on magnetic fluid (MF) and a square tapered no-core fiber (NCF) sandwiched between two single-mode fibers (SMFs) has been proposed. The enhanced evanescent field effect in the NCF is achieved by tapering the square NCF utilizing a fusion splicer. The spectral dependence of the proposed device on the applied magnetic-field intensity has been investigated. The results indicate that a maximal sensitivity of -18.7pm/Oe is obtained for a magnetic field strength ranging from 25Oe to 450Oe. The proposed tunable device has several advantages, including low cost, ease of fabrication, compact structure, and high sensitivity.

A focused CO 2 laser beam has been previously used to successfully fabricate both symmetric and asymmetric long period fiber gratings which have been used for a variety of sensing applications. However fabrication by a CO 2 laser beam demands a time consuming laser scanning process which increases the difficulty and cost of fabrication. In this paper a fibre sensor based on a fibre heterostructure with a simple configuration consisting of a series of periodical tapers in a photonic crystal fibre (PCF) sandwiched between two singlemode fibres is proposed and investigated experimentally. The tapers are periodically fabricated along the PCF section using a CO 2 laser beam. The proposed fibre heterostructure can be used for strain sensing by measuring the wavelength blueshift of the multimode interference dip of the transmission spectrum as a function of strain. An average stain sensitivity of -68.4 pm/μ e has been experimentally achieved over a microstrain range from 0 to 100 μ e. Assuming in practice that the sensor is interrrogated with a ratiometric power measurement system, then the strain resolution is estimated to be better than 1.18×10 -2 microstrain. The mechanisms for refractive index modulation periodically tapered PCF under tensile strain measurements are complex but may be regarded as a combination of stress-relaxation and refractive index perturbations over the length of the tapered PCF induced by strain and by tapering. The proposed fibre strain sensor has the advantage of low temperature sensitivity (average 8.4 pm/°C) and an experimental demonstration of this reduced sensitivity is also presented. The proposed strain sensor benefits from simplicity of fabrication and achieves a competitive sensitivity compared with other existing fibre-optic sensors.

The use of cantilevered piezoelectric bimorphs under transversal excitations is an area of research well reported in literature. These devices may be tapered into triangular geometries in order to enhance axial strain over the surfaces of the device for more reliable operation. This study reports the comparison of rectangular and triangular cantilevered bimorphs of equal volume and matching resonance frequency, where it is seen that tapering geometry enhances the electromechanical coupling coefficient, which may not necessarily be the only parameter involved in enhancing power output. This is indicated in the case of a triangular cantilevered device without a proof mass, which with increased coupling is unable to outperform a rectangular device. The addition of a nominal proof mass on a rectangular and triangular device increases not only the electromechanical coupling coefficient, but also increases the damping ratio in the devices. This effect is more pronounced in the case of triangular bimorphs, and a 40% improvement in power output is seen. Therefore, these studies provides insights into the changing parameters with changing shapes, which may provide better optimization parameters for improving piezoelectric energy harvesting from cantilevered devices.

A method of providing consistent uniform and controlled zone heat at a fiber’s surface is presented using a CO2 laser with axicon reflective elements. This optical configuration converts a laser beam into a light structure resembling a disc or cone that can band a fiber’s perimeter. The characteristic of this structure is its inherent ability to deliver increasing power density through uniform convergence toward the structure’s center thus applying the appropriate melting heat to varying sizes of fiber. By offsetting the light structure, precise localized zone heating and annealing of specific areas at a fiber’s surface can be achieved as well. This is essentially a passive devise into which active feedback elements can be incorporated to allow precise control of processes such as splicing, tapering, ball and axicon lensing, end capping, and combiner fabrication.

We made two types of three-mode multiplexers with three single-mode input cores and one enlarged output core. Light in each input core evolved adiabatically into just one of the LP01, even-LP11 and odd-LP11 modes of the output core. In the first type, the transition between inputs and output was formed by the controlled collapse of selected holes in a photonic crystal fibre with three cores in an equilateral triangular array. In the second type, three standard single-mode fibres were made dissimilar and tapered together within a fluorine-doped silica capillary. In both cases the output light patterns matched the LP01 and LP11 distributions as expected, with broadband operation across at least 100 nm in the near-IR, low insertion losses and mode purities exceeding 10 dB.

A fiber refractive index (RI) sensor based on a Mach–Zehnder interferometer (MZI) formed by sandwiching a thinned taper between two abrupt tapers. The abrupt tapers and the thinned taper are easily fabricated by a commercial fiber fusion splicer and a homemade tapering machine, respectively. The sensor has been experimentally demonstrated for RI sensing by monitoring its spectral shifts. The experimental results show that the sensor with a thinner taper has higher sensitivity due to the strong evanescent field interaction. A sensitivity of 3808.4 nm/RIU (refractive index unit) is obtained, which is about 100 times higher than that of the conventional taper-based MZI sensors.

A novel approach to calibrate a phase-shift formed in a long-period fiber grating (LPG) is proposed and successfully demonstrated, which is based on the use of either a power- or a wavelength-interrogation technique to the loss-peak existed in the transmission spectrum of the phase-shifted LPG. Moreover, in this study, by tapering a LPG with CO 2 laser, phase-shift is successfully created at central part of the LPG. Finally, base on the use of this kind of phase-shifted LPG, a simultaneous measurement for the temperature and the surrounding refractive index has been proposed and experimentally demonstrated.

The concept of cascading Photonic Crystal Fiber (PCF) tapers is proposed, and the numerical model of supercontinuum (SC) generation in cascaded PCF tapers is clarified. Using self-compiled program, the SC generation in cascaded PCF tapers with identical and different structural parameters are numerically simulated. Hence the function of cascading is illustrated. Via cascading PCF tapers with same structural parameter, we can overcome the limitation of the tapering rig to enhance the nonlinear interaction length. Via cascading PCF tapers with different structural parameter, we can not only enhance the interaction length, but also obtain higher nonlinearity and more manageable dispersion to increase the qualities of SC, such as spectral range and flatness.

In this paper, the effect of tapered asymmetrical gammadion on the optical rotational properties and sensitivity detection of biomolecular structures is presented. The asymmetrical structure is made up of gold material on a glass structure and immersed in water. The chirality of the un-rotated array is first determined by measuring the circular dichroism (CD) spectrum. Three modes, arising from Bloch periodic theory and surface resonance mode are observed. Then each asymmetrical gammadion structure is tapered at the arms. Tapering fraction, which define the ratio of tapered end to the untapered end is used for defining the new design. The designs are then fabricated using e-beam lithography and tested using the polarimeter for CD spectra. The spectra show that the three CD modes changes in degree amplitude and wavelength, especially for smaller tapering fractions.

This work reports the fabrication of asymmetric fiber tapers using a pulsed CO 2 laser as a heat source. The laser has its beam focused on the side of the fiber by using a moveable mirror and a convergent lens while the softened fiber is stretched by a translation stage. The tapering process uses a superposition of step tapers that are produced after sweeping the laser spot over a previously calculated length of the fiber. Constant speeds in all the translation stages are used in the process. A pulsed laser source with a low cost power control is also used to fabricate asymmetric tapers having a relatively low loss.

The semiconductor micropillar is attractive for cavity QED experiments. For strong coupling, the figure of merit is proportional to Q/√V , and a design combining a high Q and a low mode volume V is thus desired. However, for the standard submicron diameter design, poor mode matching between the cavity and the DBR Bloch mode limits the Q . We present a novel adiabatic design where Bloch-wave engineering is employed to improve the mode matching, allowing the demonstration of a record-high vacuum Rabi splitting of 85 μe V and a Q of 13600 for a 850 nm diameter micropillar.

Photonic wires have recently demonstrated very attractive assets in the field of high-efficiency single photon sources. After presenting the basics of spontaneous emission control in photonic wires, we compare the two possible tapering strategies that can be applied to their output end so as to tailor their radiation diagram in the far-field. We highlight the novel “photonic trumpet” geometry, which provides a clean Gaussian beam, and is much less sensitive to fabrication imperfections than the more common needle-like taper geometry. S4Ps based on a single QD in a PW with integrated bottom mirror and tapered tip display jointly a record-high efficiency (0.75±0.1 photon per pulse) and excellent single photon purity. Beyond single photon sources, photonic wires and trumpets appear as a very attractive resource for solid-state quantum optics experiments.

Recently, the high power fiber laser has attracted much attention and the laser power combiner is one of the key components for power scaling in the high power laser system. Up to now, several methods have been exploited to develop the combiner and among them the tapered fusion bundling method becomes one of the most popular and reliable technology. In the conventional tapered fusion bundling method, the input fibers were bundled with the honeycomb configuration then fused tapered and spliced to the output fiber. In the method, however, the fiber ports configuration was constrained to certain values such as 3×1, 7×1, 19×1, and 35×1 to satisfy the compactness and reliability in the bundling procedure. In this study, we suggest a novel double bundling method to make combiners with the large flexibility in the fiber port configuration. In making the (14-18)×1 combiners, seven input fibers in the honeycomb stacking configuration was fused bundled and a single layer of secondary 7-11 fibers were stacked outside of the bundle and subsequently tapered and spliced to a output fiber. As a result, (14-18)×1 laser power combiners were made using 105/125 μm input fibers (0.15 NA) and a 200/220 μm output fiber (0.46 NA). In the bundling procedures a LPG torch was used and process parameters such as the gas flow and the tapering length/speed/frequency were optimized. The power transmission efficiency of the combiner was larger than 93% in all ports at the handling power of 100 W.

The minimum bend radius of optical microfiber allows very compact flexural disc accelerometers to be manufactured without significant degradation of the optical signal in terms of attenuation and depolarization. Such compact sensors have potentially very high responsivity in small packages. We demonstrate a responsivity of 4 rad/g between 100-1000 Hz for a disc wound with microfiber of 60-millimeter length and 10-micron diameter microfiber. We report the successful fabrication of a 0.4-meter length and 10-micron diameter microfiber using a new tapering setup and an automated technique is proposed for efficiently winding long lengths of microfiber onto the flexural disc.

This paper demonstrates temperature-induced tuning of the optical spectrum of a microfiber coupler covered with a low-refractive index liquid crystal (LC) layer. The microfiber coupler with a minimum waist diameter of ~6 μm is fabricated by fusing together and tapering of two standard telecom fibers using a microheater brushing technique and by placing a thin heated LC layer over the uniform taper waist region. Repeatable and reversible tuning of the optical spectrum (~4 nm) of the microfiber coupler is demonstrated for the temperature range of 50-78 °C.

In this paper, we demonstrated two methods to enhance refractive index (RI) and temperature sensitivity of a photonic crystal fiber (PCF) in-line modal interferometer built via fusion splicing, respectively. First we fabricated a tapered PCF interferometer by an etching method with acid microdroplets. The RI sensitivity greatly increases (5 times) and the size decreases after tapering the PCF, while the temperature sensitivity does not change a lot. Then we obtained another PCF interferometer by inserting a short isopropanol-filled PCF between two single mode fibers (SMFs). The temperature sensitivity increases over an order of magnitude compared with the previous non-polarimetric sensors based on air-filled PCF interferometers.

We report and demonstrate a new type of fiber wavelength division multiplexer based on central-circular cocentric core fiber. Using splicing technique to connect the central-circular cocentric core fiber and single mode fiber, then, tapering at the fusion point of two fibers. The light source whose wavelengths are 980nm and 1480nm input from the single mode fiber, then two wavelengths transferred separate well at the tapering area of the cocentric fiber. The simulation results are agreement with the theoretical analysis of the theoretical model.

We design tellurite tapered photonic crystal fibers (PCFs) for broadband mid-infrared supercontinuum (SC) generation in the few-optical-cycle regime. We show that we can move the zero dispersion wavelength (ZDW) beyond 2 μm toward mid-IR wavelength region by tapering tellurite PCFs. We demonstrate the generation of sub-two-cycle soliton selfcompressed pulses from 200 fs to 19.1 fs and show more than one octave-spanning coherent SC, extending from 1675 to 3950 nm, generated in 8 mm-long tapered tellurite PCF with low input pulse energy of 1 nJ at 2.9 μm.

We propose a simple and accurate technique for the design optimization of coupled resonator optical waveguides (CROWs). The technique is based on tapering the coupling coefficients at the CROWs stages to achieve arbitrary realizable filter response. A perturbation theory is developed for the linearization of the design problem. The coupling coefficients are expanded around a known mean coupling value. By dumping the higher order perturbation terms, we ignore the effect of multiple reflections among the rings introduced by the small adjustment of the coupling coefficients. This is a first order accurate approach as it takes into account only multiple reflections introduced by the zero order terms. The design problem is then formulated as an optimization problem. The optimal filter design is achieved by solving a constrained linear least square problem. This optimization problem can be solved efficiently to get the global optimal design. Our technique is accurate and efficient compared to other nonlinear approaches. Our technique has been verified using different proposed targeted filter responses utilizing third, fifth, and tenth order coupled ring resonators. Highly selective tenth order filter with flat response is proposed. We compared our results to the existing techniques to prove its accuracy.

By using polystyrene microspheres with index n=1.59 as a model system we study light focusing and transport properties of chains formed by spheres with diameters varying from 2 to 30 μm. We used techniques of imaging based on light scattering perpendicular to the axis of the chain to visualize and study periodically focused beams in such structures. The results demonstrate good agreement with geometrical optics modeling for sufficiently large spheres, D>>10λ, where D is the sphere diameter and λ is the wavelength of light. For mesoscale structures with 4 >

A numerical study of the effects of tapering a hollow-core photonic bandgap fiber (HC-PBGF) on the spatial parameters: effective area, nonlinear parameter and dispersion parameter is presented. The taper on the fiber is modeled by scaling the cross section of the original fiber geometry. Both the air and the silica contribution to the effective area and the nonlinear parameter are shown. The obtained results show a blueshift of the transmission band and of the zero-dispersion wavelength. By tapering the fiber 30%, the transmission band and the zerodispersion wavelength blueshift around 300 nm and 320 nm, respectively. HC-PBGFs have made possible the study of nonlinear optical effects and by tapering the fiber, such nonlinear phenomena can be made stronger.

Whispering-Gallery-Mode (WGM) optical microresonators have attracted growing attention because of their big potential for chemical and biological sensing. Recently, optical bottle microresonators have been fabricated from short sections of optical fibers. These double-neck bottle-shaped microresonators have some features distinguishing them from spherical microresonators. They support non-degenerate whispering-gallery modes that exhibit two well-separated spatial regions with enhanced field strength. The free spectral range (FSR) of such microresonators is about one order of magnitude smaller than that of microsphere resonators of equal diameters. It means that these microresonators have much longer optical path-lengths and can be employed for highly sensitive detection. The paper deals with the preparation and characterization of bottle optical microresonators fabricated from silica optical fibers. A simple 2D numerical modelling has been used to investigate basic spectral characteristics of microresonators with hexagonal cross-sections. Cylindrical bottle microresonators are prepared from optical fiber Corning SMF-28, while microresonators with hexagonal cross-section are prepared from an experimental hexagonal silica fiber. This novel type of bottle microresonators is expected to have much simpler mode structure than cylindrical bottle microresonators. There are compared two methods for the preparation of bottle microresonators in this paper. The first method is based on a combination of controlled local heating and tapering the fiber by the use of carbon dioxide laser Coherent GEM SELECT 50. The second method is based on weak tapering of the silica optical fiber with glass processing unit Vytran GPX-3400.

We demonstrate a technique for tapering periodically an all-solid soft glass fiber consisting of two types of lead silicate glasses by the use of a CO2 laser and investigate the bend sensing applications of the periodically-tapered soft glass fiber. Such a soft glass fiber with periodic microtapers could be used to develop a promising bend sensor with a sensitivity of -27.75 µW/m-1 by means of measuring the bend-induced change of light intensity. The proposed bend sensor exhibits a very low measurement error of down to ± 1%.

Due to start-up from shot noise, typical SASE XFEL pulses exhibit poor longitudinal coherence. Self-seeding schemes can be use to improve it. Recently, a novel single-bunch self-seeding scheme was proposed, based on a particular kind of monochromator, which relies on the use of a single crystal in Bragg-transmission geometry. In its simplest configuration, the self-seeded XFEL consists of an input undulator and an output undulator separated by such monochromator. However, in some experimental situations this simplest two-undulator configuration is not optimal. The obvious and technically possible extension is to use a setup with three or more undulators separated by monochromators. This amplification-monochromatization cascade scheme is distinguished, in performance, by a small heat-loading of crystals and a high spectral purity of the output radiation, and is particularly advantageous for the European XFEL. The power of the output signal can be further increased by tapering the magnetic field of the undulator. Once the cascade self-seeding scheme is combined with tapering in a tunable-gap baseline undulator at the European XFEL, a source of coherent radiation with unprecedented characteristics can be obtained at hard X-ray wavelengths, promising complete longitudinal and transverse coherence, and a peak brightness three orders of magnitude higher than what is presently available at LCLS. Additionally, the new source will generate hard X-ray beams at extraordinary peak (TW) and average (kW) power level. The proposed source can thus revolutionize fields like single biomolecule imaging, inelastic scattering and nuclear resonant scattering. Our self-seeding scheme is extremely compact, and takes almost no cost and time to be implemented. The upgrade proposed in this work could take place during the commissioning stage of the European XFEL, opening a vast new range of applications from the very beginning of operations. We present feasibility study and exemplifications for the SASE2 line of the European XFEL.

We propose a new electrically-pumped single-photon source design based on a quantum dot in a photonic nanowire. For realistic parameters, the design features an efficiency of 89 % predicted by numerical simulations. Unlike cavity-based designs, our approach allows for broadband spontaneous emission control and has high tolerance towards surface roughness. In the nanowire, a geometrical effect ensures good coupling between the quantum dot and the optical mode, and an inverted tapering section is introduced to adiabatically expand the mode waist and control the far field emission profile while minimizing the relative modal overlap with the metal contacts.

The quality factor (Q) of resonators defined in photonic crystal (PhC) membranes is known to be sensitive to the tapering of the air-holes. A small deviation from an ideal structure with perfectly vertical holes can result in orders of magnitude decrease in the Q, hence greatly jeopardizing applications of such devices in the field of cavity quantum electrodynamics (cQED). Tapering breaks the vertical reflection symmetry of the structure, allowing confined TE-like cavity modes to couple to the resonant continuum of lossy TM-like modes. We show, using a combination of finite-difference time-domain (FDTD) modeling and plane wave expansion method (PWE), that the membrane thickness plays a critical role in the mode coupling. By choosing the thickness about a third of the wavelength of the mode, the high Q of a PhC cavity can be restored despite 10 degrees taper. These findings show that high Q resonators relatively insensitive to the tapering are achievable.

The power handling capabilities of fiber lasers are limited by the technologies available to fabricate and assemble the key optical system components. Previous tools for the assembly, tapering, and fusion of fiber laser elements have had drawbacks with regard to temperature range, alignment capability, assembly flexibility and surface contamination. To provide expanded capabilities for fiber laser assembly, a wide-area electrical plasma heat source was used in conjunction with an optimized image analysis method and a flexible alignment system, integrated according to mechatronic principles. High-resolution imaging and vision-based measurement provided feedback to adjust assembly, fusion, and tapering process parameters. The system was used to perform assembly steps including dissimilar-fiber splicing, tapering, bundling, capillary bundling, and fusion of fibers to bulk optic devices up to several mm in diameter. A wide range of fiber types and diameters were tested, including extremely large diameters and photonic crystal fibers. The assemblies were evaluated for conformation to optical and mechanical design criteria, such as taper geometry and splice loss. The completed assemblies met the performance targets and exhibited reduced surface contamination compared to assemblies prepared on previously existing equipment. The imaging system and image analysis algorithms provided in situ fiber geometry measurement data that agreed well with external measurement. The ability to adjust operating parameters dynamically based on imaging was shown to provide substantial performance benefits, particularly in the tapering of fibers and bundles. The integrated design approach was shown to provide sufficient flexibility to perform all required operations with a minimum of reconfiguration.

A custom fabrication procedure for pump combiners matched to a wide variety of double-clad fibers used in high power fiber lasers has been developed. Both combiners with and without feedthrough can be fabricated with an improved repeatability thanks to a specific mechanical setup that simplifies placing the fibers in their proper location within the input bundle before the tapering and fusion processes. Extensive characterization results on 7-to-1 and on (6+1)-to-1 combiners are confirming the validity of the proposed approach.

We present a high sensitive temperature sensor based on a side-polished fiber (SPF) coupled to a tapered multimode overlay waveguide (MMOW). We have theoretically shown that the longitudinal tapering of the MMOW can be used to tune the desired wavelength range in the spectrum without any loss in the sensitivity.

It has been shown that the parabolic pulses can be generated under certain conditions within normally dispersive optical amplifiers by exploiting the interplay between gain, nonlinearity and dispersion. Passive means to generate parabolic pulses have also been exploited and in previous experiments it has been investigated e.g. in a comb-like profiled dispersion decreasing fibre or using single conventional dispersion decreasing optical fibres. Tapered microstructured optical fibres represent an alternative way to produce the required dispersion decreasing fibre. This method is ideal for producing metre-length tapers needed to efficiently generate parabolic pulses starting from femtosecond pulses. In this paper we experimentally and numerically demonstrate the possibility of parabolic pulse generation in a normally dispersive microstructured optical fibre taper. The microstructured optical fibre that was initially in the anomalous dispersion regime was tapered to achieve normal dispersion values. The fibre parameters were measured and the taper's parameters determined to obtain a desirable linear taper profile. Using novel tapering facility we fabricated 1.8m long taper. The experimental study of parabolic pulse generation has been compared with the numerical simulations. The pulse propagating through the taper was characterized using linear FROG method. A qualitative agreement between the results of experiment and simulation was demonstrated. The consistent convergence towards the parabolic pulse at the taper's output is observed with increasing in the input pulse power levels. The quality of the parabolic pulses was quantified using a misfit parameter, which reached value of 0.0032, when maximum power level has been applied. It has been shown that the initial pulse FWHM of 0.59ps has been shaped into a pulse of 1.22ps FWHM (which has a root mean square error against the parabolic fit of 0.0032). These results suggest the possibility of achieving better parabolic pulses if the optimum launching conditions can be achieved or longer taper fabricated.