Showing papers on "Step-index profile published in 2007"

Refractometric sensor based on whispering-gallery modes of thin capillarie.

Abstract: Whispering-gallery modes resonances of submicron wall thickness capillaries exhibit very large wavelength shifts as a function of the refractive index of the medium that fills the inside. The sensitivity to refractive index changes is larger than in other optical microcavities as microspheres, microdisks and microrings. The outer surface where total internal reflection takes place remains always in air, enabling the measure of refractive index values higher than the refractive index of the capillary material. The fabrication of capillaries with submicron wall thickness has required the development of a specific technique. A refractometer with a response higher than 390 nm per refractive index unit is demonstrated. These sensors are readily compatible with microfluidic systems.

Single-Mode Waveguides With SU-8 Polymer Core and Cladding for MOEMS Applications

Abstract: Fabrication and optical characterization of single-mode polymeric embedded waveguides are performed. A specific material combination (SU-8 2005 as core and the modified SU-8 mr-L 6050XP as cladding) is chosen in order to obtain a small refractive index difference for single-mode propagation combined with the conventional fabrication method UV lithography to facilitate the integration of different types of optical detection methods on lab-on-a-chip systems. We analyze the behavior of the refractive index and carefully observe how the value of the refractive index can be tailored during processing. We show that we can fabricate waveguides with an index difference in the order of 10-3 , where both the core material and the cladding material are based on SU-8. The refractive index measurements are performed on thin polymeric films, while further optical characterizations are performed on waveguides with a height of 4.5 mum. We study the mode profiles of these waveguides and confirm that only the fundamental mode is excited. We also study the absorption spectra of the material in the wavelength range 800-1600 nm combined with cut-back measurements. We find that the waveguides have a propagation loss of 0.2-3 dB/cm in this wavelength range

Fiber optic sensing of liquid refractive index

Abstract: An optical fiber, partially stripped of its cladding is shown to sense refractive index of a liquid in which the uncladded sensing region is immersed, to a high degree of precision and over a wide range of refractive index. The slope of sensor response is found to be non linear, can have either sign and can change sign at around refractive index of the fiber. The sensitivity of the sensor to refractive index change is dependent on cladding thickness and is a maximum at an intermediate thickness value. It is insensitive to the presence of absorption at the wavelength at which refractive index is being measured and to the chemical nature of the solute. Experiments designed to show that cladding modes are responsible for sensing are described.

Dual-peak long-period fiber gratings with enhanced refractive index sensitivity by finely tailored mode dispersion that uses the light cladding etching technique

Abstract: We have experimentally investigated the mode dispersion property and refractive index sensitivity of dual-peak long-period fiber gratings (LPGs) that were sensitized by hydrofluoric acid (HF) etching. The nature of the coupled cladding modes close to the dispersion turning point makes the dual-peak LPGs ultrasensitive to cladding property, permitting a fine tailoring of the mode dispersion and index sensitivity by the light cladding etching method using HF acid of only 1% concentration. As an implementation of an optical biosensor, the etched device was used to detect the concentration of hemoglobin protein in a sugar solution, showing a sensitivity as high as 20 nm/1%.

Photonic bandgap fiber for refractive index measurement

Abstract: The use of photonic bandgap fibers for refractive index measurement has been demonstrated. The demonstrated PBGF has a wavelength shift of 280 nm in the falling photonic bandgap edge when the ambient refractive indices change from 1.333 to 1.39, which agrees well with the analytical prediction. A sensitivity of 2 × 10 −6 RIU is possible to be achieved assuming the demodulation system can resolve 0.01 nm wavelength shift.

Optimum sensitivity of single-mode D-type optical fiber sensor in the intensity measurement

Abstract: To improve the sensitivity of a single-mode D-type optical fiber sensor in the refractive index range 1.33–1.40, we selected parameters such as, a D-type optical fiber sensor made of a single mode fiber with 4 mm long and 4 μm core radius, a Au-coating with a thickness range of 20–60 nm, a wavelength of 632.8 nm, and an incident angle at the range of 88–89.5° to simulate. These reflectance simulations are based on the surface plasmon resonance (SPR) theory. The results show that the optimum sensitivity for a specific refractive index measurement corresponds to a specific Au film thickness. The optimum sensitivity is close to a value of 40 (1/RIU (refractive index unit)). The best resolution is better than 2.5 × 10−5 RIU as the minimum intensity variation is 0.1%. This device is used to detect the refractive index or gas or liquid concentration in real time, and it has some merits such as, small, easy to manufacture, compact and inexpensive and could be in vivo test.

Optical thin film, semiconductor light emitting device having the same and methods of fabricating the same

Abstract: Provided are a highly transmissive optical thin film having an improved structure, in which, optical reflection (due to a difference in the refractive index between a semiconductor material and the air, when light is extracted from a semiconductor light emitting device into the air) may be suppressed, an optical output loss may be reduced and light transmittance efficiency may be maximized or increased, a semiconductor light emitting device having the same, and methods of fabricating the same. The optical thin film may include a first material layer having a first refractive index, a second material layer formed on the first material layer and having a second refractive index that is smaller than the first refractive index, and a graded-refractive index layer interposed or inserted between the first material layer and the second material layer and having a multi-layer structure in which refractive index distribution gradually decreases in the range between the first refractive index and the second refractive index as the refractive index distribution progresses from the first material layer toward the second material layer.

Optical material and method for modifying the refractive index

Abstract: A method for modifying the refractive index of an optical, polymeric material. The method comprises irradiating select regions of the optical, polymeric material with a focused, visible or near-IR laser having a pulse energy from 0.05 nJ to 1000 nJ. The irradiation results in the formation of refractive optical structures, which exhibit little or no scattering loss. The method can be used to modify the refractive index of an intraocular lens following the surgical implantation of the intraocular lens in a human eye. The invention is also directed to an optical device comprising refractive optical structures, which exhibit little or no scattering loss and are characterized by a positive change in refractive index.

Anti-resonant reflecting optical waveguide for imager light pipe

Abstract: An anti-resonant reflecting optical waveguide structure for reducing optical crosstalk in an image sensor and method of forming the same. The method includes forming a trench within a plurality of material layers and over a photo-conversion device. The trench is vertically aligned with the photo-conversion device and is filled with materials of varying refractive indices to form an anti-resonant reflecting optical waveguide structure. The anti-resonant reflecting optical waveguide structure has a core and at least two cladding structures. The cladding structure in contact with the core has a refractive index that is higher than the refractive index of the core and the refractive index of the other cladding structure. The cladding structures act as Fabry-Perot cavities for light propagating in the transverse direction, such that light entering the anti-resonant reflecting optical waveguide structure remains confined to the core. This reduces the chance of photons impinging upon neighboring photo-conversion devices.

Mechanics and refractive power optimization of tunable acoustic gradient lenses

Abstract: Tunable acoustic gradient index (TAG) lenses create tunable multiscale Bessel beams. These lenses are fluid-filled cylindrical cavities within which an acoustic radial standing wave is excited. This standing wave modulates the density, and thereby the refractive index within the lens. Spatial gradients in the refractive index can be used for lensing. A predictive model for the steady-state fluid mechanics behind TAG lenses driven with a sinusoidal voltage signal is presented here. The model covers inviscid and viscous regimes in both the resonant and off-resonant cases. The density fluctuations from the fluidic model are related to refractive index fluctuations. The entire model is then analyzed to determine the optimal values of lens design parameters for greatest lens refractive power. These design parameters include lens length, radius, static refractive index, fluid viscosity, sound speed, and driving frequency and amplitude. It is found that long lenses filled with a fluid of high refractive index an...

Plasmon excitation by the gaussian-like core mode of a photonic crystal waveguide

Abstract: A sensor and method for surface plasmon resonance sensing, wherein a small variation of the refractive index of an ambient medium results in a large variation of loss of a sensing mode. The surface plasmon resonance sensor comprises an antiguiding waveguide including a core characterized by a refractive index and a reflector surrounding the core. The reflector has an external surface and is characterized by a band gap and a refractive index higher than the refractive index of the core. A coating is deposited on the external surface of the core, the coating defining with the ambient medium a coating/ambient medium interface. In operation, the coating is in contact with the ambient medium, and the antiguiding waveguide is supplied with an electromagnetic radiation to (a) propagate a mode for sensing having an effective refractive index lower than the refractive index of the core and higher than a refractive index of an ambient medium and (b) produce surface plasmons at the coating/ambient medium interface. The mode for sensing is phase-matched with the surface plasmons at a wavelength within the band gap and a variation of the refractive index of the ambient medium results in a variation of loss of the sensing mode to detect a characteristic of the ambient medium.

A Highly Sensitive Fiber-Optic Refractive Index Sensor Based on an Edge-Written Long-Period Fiber Grating

Abstract: A novel long-period fiber grating (LPFG) is edge-written without any destructive damage on the fiber based on the thermal shock and rapid cooling effects of the high-frequency CO2 laser pulses exposure method in this letter. The refractive index disturbance induced by high-frequency CO2 laser pulses mainly occurs in the edge region of the fiber cladding rather than in the fiber core. An edge-written LPFG with a resonant peak of ~18 dB is obtained using a standard telecommunication fiber. The experimental results show that such a novel LPFG structure has much higher refractive index sensitivity over conventional LPFGs side-written, which can be used as a refractive index sensor, or a tunable filter and modulator by controlling the refractive index sensitive film which is coated on the cladding of such an LPFG.

Optical near-field generator and near-field optical recording and reproduction apparatus

Abstract: Decrease in optical near-field intensity is prevented when an light propagating medium made of a high refractive index material, such as a waveguide or a lens, is combined with a scatterer for producing optical near-field. Near the optical near-field generating element, a second light propagating medium is disposed in contact with a first light propagating medium of a high refractive index material, such as a waveguide or a lens. The refractive index of the second light propagating medium is made smaller than the refractive index of the first light propagating medium.

Illumination device and display device incorporating the same

Abstract: An illumination device has a plurality of sealing structures each including a light-emitting diode, sealed by a high refractive index transparent material member which is further sealed by a low refractive index transparent material member. To increase a divergence angle of light radiation, the portion of the high refractive index transparent material member which covers an upper surface of the light-emitting diode is structured so as to satisfy a relation H>(L/2)/tan {sin −1 (n 1 /n 2 )}, where H represents a thickness of the high refractive index transparent material member measured at the central portion of the upper surface of the light-emitting diode, L represents the length of one side of the upper surface of the light-emitting diode, n 1 represents the refractive index of the high refractive index transparent material member and n 2 represents the refractive index of the low refractive index transparent material member.

Near-field intensity pattern at the output of silica-based graded-index multimode fibers under selective excitation with a single-mode fiber.

Abstract: Selective excitation of graded-index multimode fibers (GI-MMFs) with a single-mode fiber (SMF) has gained increased interest for telecommunication applications. It has been proposed as a way to enhance the transmission bandwidth of GI-MMF links and/or create parallel communication channels over the same GI-MMF. Although the effect of SMF excitation on the transmission bandwidth has been investigated, its impact on the near-field intensity pattern at the output face of the GI-MMF has not been systematically addressed. We have carried out an analysis of the near-field intensity pattern at the output face of silica-based GI-MMFs excited by a radially offset SMF. Simulation results exhibit all of the features displayed by experimental ones. It turns out that differential mode attenuation and delay, full intra-group mode mixing, and small deviations in the refractive index profile of the GI-MMF do not affect the overall shape of the near-field intensity, which is determined by the radial offset of the input SMF. This can be exploited in mode group diversity multiplexing links. The effect of defects in the refractive index profile, such as a central dip or peak, is also examined.

Multiband optical fiber

Abstract: An optical waveguide fiber having a core surrounded by a cladding. The core may have only a central segment, or a central segment and an annular segment surrounding the central segment. The central segment has a positive relative refractive index profile. The annular segment has a negative relative refractive index profile. The relative refractive index of the optical fiber provides an LP02 cable cutoff less than 850 nm and an LP21 cable cutoff less than 850 nm.

Refractive Index Measurement within a Photonic Crystal Fibre Based on Short Wavelength Diffraction

Abstract: A new class of refractive index sensors using solid core photonic crystal fibres isdemonstrated. Coherent scattering at the cladding lattice is used to optically characterizematerials inserted into the fibre holes. The liquid to solid phase transition of water uponfreezing to ice 1h is characterized by determining the refractive index.

Application of Fresnel diffraction to nondestructive measurement of the refractive index of optical fibers

Abstract: A nondestructive technique, based on Fresnel diffraction from phase objects, is proposed for specifying the refractive indices of optical fibers without requiring index matching liquid The method involves measurement of normalized intensity distribution on the Fresnel diffraction pattern of a monochromatic plane wave diffracted from a fiber, and evaluation of the fiber core refractive index from the intensity distribution by the least-square method It is also shown that for the case of an unknown fiber core radius, by fitting a suitable theoretical intensity distribution on the corresponding experimental intensity distribution, the core radius and refractive index can be obtained with reasonable accuracy Simulation and experimental studies show that the technique is reliable and quite sensitive to refractive index change

High refractive index material

Abstract: Disclosed is a high refractive index material having a high refractive index, which enables the formation of a waveguide by a simpler method. Also disclosed are a high refractive index member made from the high refractive index material, and an image sensor. The high refractive index material contains a resin (A) having a structural unit represented by the following general formula (a-1). [In the formula, R 1 is a hydrocarbon group, R 2 is a hydrogen atom or a hydrocarbon group, and m is an integer of 0 or 1.]

Design Optimization of Trench Index Profile for the same dispersion characteristics with SMF

Abstract: An optimized design on a trench index profile for bend-insensitive SMF is presented. The same dispersion characteristic with standard SMF with ultra low bending loss has been realized by optimization of trench index profile.

Fiber optic connector with double-clad stub fiber

Abstract: A fiber optic connector having a double-clad specialty optical stub fiber with a deep index core-to-inner-cladding profile and a raised index outer-cladding profile. The double-clad optical stub fiber abuts against a single-clad field optical fiber of the single-mode type to form an interface across which the primary mode traverses without significantly interfering with higher-order modes. The ratio of the radius of the inner cladding to the radius of the core of the stub fiber is less than 6.5:1. The index profile of the refractive index of the inner cladding is deep relative to the refractive index of the core to confine the primary mode within the core. The raised refractive index of the outer-cladding pulls the higher-order modes deeper into that region, reducing interference with the primary mode. The respective core diameters of the field and stub fibers are matched to avoid mode-field diameter mismatch.

Refractive index dependence of L3 photonic crystal nano-cavities.

Abstract: We model the optical properties of L3 photonic crystal nano-cavities as a function of the photonic crystal membrane refractive index n using a guided mode expansion method. Band structure calculations revealed that a TE-like full band-gap exists for materials of refractive index as low as 1.6. The Q-factor of such cavities showed a super-linear increase with refractive index. By adjusting the relative position of the cavity side holes, the Q-factor was optimised as a function of the photonic crystal membrane refractive index n over the range 1.6 to 3.4. Q-factors in the range 3000-8000 were predicted from absorption free materials in the visible range with refractive index between 2.45 and 2.8.

Large mode area fiber for low-loss transmission and amplification of single mode lasers

Abstract: A large mode area optical fiber includes a large diameter core (d1 up to 60μm), and a first cladding (diameter d2) wherein the difference between refractive index (n1 ) in the core and the first cladding (n2) is very small (Δn 0.4) (n3 is preferably less than 1.3). The small change in refractive index between the core and inner cladding combined with a large change in refractive index between the first cladding and second cladding provides a significantly improved single mode holding waveguide.

Influence of the surrounding refractive index on the thermal and strain sensitivities of a cascaded long period grating

Abstract: This work shows the refractive index sensitivity of a cascaded long period grating and the influence of surrounding media with a different refractive index on the device's thermal and strain sensitivities. The refractive index sensitivity of the double-grating device experiences a maximum increase of about 2.6 times when compared with the sensitivity of a single-grating device, mainly attributed to the cavity between the gratings. The maximum obtained sensitivity of −1554.1 nm per refractive index unit for the cascaded long period grating relates to a sensor resolution of about 6 × 10−6 for refractive index measurements, if an optical spectrum analyser of ±5 pm of wavelength stability is used in the experiments, whereas this resolution for the long period grating alone is 1.6 × 10−5. The strain and thermal sensitivities show an increase when the surrounding refractive index increases. These dependences rely on the influence of the surrounding refractive index on the effective index of the cladding mode. A noticeable nonlinear behaviour of the thermal response is found when the surrounding refractive index increases towards the fibre cladding index. This behaviour is attributed to the combined effects of the device's response to the temperature and refractive index.

Influence of surrounding media refractive index on the thermal and strain sensitivities of long-period gratings

Abstract: A detailed study of the thermal and strain sensitivities of a long-period grating when the device is immersed in different external media is presented. The range of refractive indices analyzed are within 1.000 to 1.447, corresponding to samples of air, water, ethanol, naphtha, thinner, turpentine, and kerosene. Within the same range of refractive indices, the strain sensitivity is between (-0.24 +/- 0.03) and (-0.94 +/- 0.11) pm/microepsilon. For the grating immersed in these fluids, the refractive index sensitivity ranges from -3 to -1035.6 nm per refractive index units. The coupling thermo-optic coefficients and the strain-optic coefficients are also measured, resulting in the range from (2.45 +/- 0.04)x10(-5) to (15.89 +/- 0.82)x10(-5) deg C(-1) and (-1.15 +/- 0.04) to (-1.61 +/- 0.04) microepsilon(-1), respectively. A noticeable nonlinear behavior of the thermal sensitivity is found for external media with refractive indices higher than 1.430.

Two-dimensional refractive index profiling by using differential near-field scanning optical microscopy

Abstract: The authors present two-dimensional reconstruction of the refractive index profile of an optical waveguide by using differential near-field optical microscopy. Using an inverse algorithm, the refractive index distribution is obtained directly from the measured optical near-field and its derivatives without any assumption of the index profile. The proposed method also takes advantage of subwavelength resolution and low noises in the waveguide region. Two-dimensional index profile reconstruction of a single mode fiber is measured for the demonstration. The measured optical field distribution and refractive index profile agree quite well with the calculated mode and the known index profile.

Radiation resistant single-mode optical fiber and method of manufacturing thereof

Abstract: A radiation resistant single-mode optical fiber has a core and a cladding, each made of fluorine-doped silica glass, in which a chlorine concentration of the core is at least 0.01 ppm, a relative refractive index difference of the core based on the refractive index for silica is between -0.30% and -0.10%, a relative refractive index difference of the core based on the refractive index for the cladding is between 0.3% and 0.5%, a cutoff wavelength is 1.27 µm or below, and a bending loss at a wavelength of 1.3 µm and a bending diameter of 20 mm is 0.5 dB/m or less.

Antireflection laminated body

Abstract: One embodiment of the present invention is an antireflection laminated body having a transparent substrate, a lower layer of low refractive index layer including a low refractive index particle, and an upper layer of low refractive index layer without a particle. In addition, in another embodiment of the present invention, the refractive index of the lower layer of low refractive index layer is 1.28-1.42, and the refractive index of the upper layer of low refractive index layer is 1.38-1.46.