Alexander Gumennik

All-in-Fiber Chemical Sensing

A new all-in-fiber trace-level chemical sensing approach is demonstrated. Photoconductive structures, embedded directly into the fiber cladding along its entire length, capture light emitted anywhere within the fibers hollow core and transform it directly into an electrical signal. Localized signal transduction circumvents problems associated with conventional fiber-optics, including limited signal collection efficiency and optical losses. This approach facilitates a new platform for remote and distributed photosensing.

Electrooptical effects in glass forming liquids of dipolar nano-clusters embedded in a paraelectric environment

Studies of the electrooptic effect in potassium tantalate niobate (KTN) and Li doped KTN in the vicinity of the ferroelectric phase transition are reported. It was observed that in KTN the standard electrooptic behavior is accompanied by electrically induced depolarization of the light traversing through the crystal. This behavior is attributed to the influence of the fluctuating dipolar clusters that are formed in KTN above the ferroelectric phase transition due to the emergence of the Nb ions out of the center of inversion of the unit cell. It was shown in addition that this behavior is inhibited in Li doped KTN, which enables exploiting the large electrooptic effect in these crystals.

Enhanced chemiluminescent detection scheme for trace vapor sensing in pneumatically-tuned hollow core photonic bandgap fibers

We demonstrate an in-fiber gas phase chemical detection architecture in which a chemiluminescent (CL) reaction is spatially and spectrally matched to the core modes of hollow photonic bandgap (PBG) fibers in order to enhance detection efficiency. A peroxide-sensitive CL material is annularly shaped and centered within the fibers hollow core, thereby increasing the overlap between the emission intensity and the intensity distribution of the low-loss fiber modes. This configuration improves the sensitivity by 0.9 dB/cm compared to coating the material directly on the inner fiber surface, where coupling to both higher loss core modes and cladding modes is enhanced. By integrating the former configuration with a custom-built optofluidic system designed for concomitant controlled vapor delivery and emission measurement, we achieve a limit-of-detection of 100 parts per billion (ppb) for hydrogen peroxide vapor. The PBG fibers are produced by a new fabrication method whereby external gas pressure is used as a control knob to actively tune the transmission bandgaps through the entire visible range during the thermal drawing process.

Construction of an optical wire imprinted in potassium lithium tantalate niobate by He+ implantation

A channel waveguide constructed in potassium lithium tantalate niobate (KLTN) substrate by the implantation of He+ ions at 1.65MeV is presented. The waveguide has a trapezoidal profile with a crystalline KLTN core surrounded by amorphized KLTN created by the implantation. The implantation was done through a 2μm thick gold stopping mask with a trapezoidal groove. During the implantation, the contour of the groove was replicated beneath the surface of the substrate forming the trapezoidal cladding of the channel waveguide. The channel waveguide is designed as the interconnecting element in electro-optical integrated circuits.

Thermal stability of a slab waveguide implemented by α particles implantation in potassium lithium tantalate niobate

A slab waveguide was fabricated in a potassium lithium tantalate niobate crystal by the implantation of He2+ ions at 2.26 MeV. The waveguide profile and loss were evaluated by measuring the dark mode TE spectrum using the prism coupling method at λ=1.3μm. The implantation generated amorphous cladding layer 5μm below the surface of the crystal with a refractive index lower by 3.9% then that of the substrate. The propagation loss of the waveguided modes was found to be 0.1–0.2dB∕cm. Thermal stability of the waveguide was obtained by isothermal annealing at 351 and 446 °C. Following the annealing the waveguide index profile remained unchanged when subjected to annealing at 150 °C for one week.

A tunable channel waveguide array fabricated by the implantations of He + ions in an electrooptical KLTN substrate.

An electrooptical channel waveguide array was constructed in potassium lithium tantalate niobate substrate by the implantation of He(+) ions at high energies. The array was fabricated by two successive implantation sessions at 1.6 MeV and 1.2 MeV through a comb-like stopping mask that limited the implanted ions to penetrate the substrate in 1 microm wide stripes periodically distributed at 3.5 microm intervals. This generated a grating of amorphized stripes with reduced refractive index. This was followed by a uniform implantation of He(+) ions at 1.8 MeV which created a bottom cladding layer below the array. Wave propagation in the array was studied by focusing a light beam at 636 nm into the central channel, and observing the wavefront it created at the output plane of the array. It was found that applying an electric field across the array strongly affects the coupling between adjacent channels and governs the width of the wavefront at the output plane.

Submerged waveguide constructed by the implantation of C12 ions in electro-optic crystals

Submerged slab waveguide was fabricated in a KLTN crystal. The waveguide was produced by the implantation of 12C ions at two energies, which created two cladding layers between which the guiding core is sandwiched.

Design methodology of refractive index engineering by implantation of high-energy particles in electro-optic materials

Slab waveguides were constructed in K(1-x)Li(x)Ta(1-y)Nb(y)O(3) crystals by the implantation of (12)C(+4) ions at 30 MeV and (16)O(+5) ions at 30 and 40 MeV. The waveguides were characterized by a prism coupler setup. A refractive index drop of 10.9% was observed in a layer formed by the implantation of (16)O(+5) ions at 30 MeV. The carbon-implanted waveguides were found to be thermally stable after annealing at 450 degrees C. A semiempirical formula for predicting the change in the refractive index given the parameters of the implantation process was developed. It is argued that the combination of the basic implantation process with the semiempirical formula can be developed to become a generic method for constructing complex electro-optic circuits with a wave-guided architecture.

Refractive index engineering by fast ion implantations: a generic method for constructing multi-components electro-optical circuits

Refractive index engineering (RI_Eng) by ion implantations is a generic methodology for constructing multi-component integrated circuits of electrooptic and nanophotonic devices with sub-wavelength features operating in the visible - near IR wavelengths. The essence of the method is to perform spatially selective implantations for sculpting complex 3D pre-designed amorphized patterns with sub-wavelength features and reduced refractive index within the volume of the substrate. A number of devices that were constructed in a substrate of potassium lithium tantalate niobate are described, including a submerged slab waveguide, an optical wire and a channel waveguide array.

Self-assembled fibre optoelectronics with discrete translational symmetry

Fibres with electronic and photonic properties are essential building blocks for functional fabrics with system level attributes. The scalability of thermal fibre drawing approach offers access to large device quantities, while constraining the devices to be translational symmetric. Lifting this symmetry to create discrete devices in fibres will increase their utility. Here, we draw, from a macroscopic preform, fibres that have three parallel internal non-contacting continuous domains; a semiconducting glass between two conductors. We then heat the fibre and generate a capillary fluid instability, resulting in the selective transformation of the cylindrical semiconducting domain into discrete spheres while keeping the conductive domains unchanged. The cylindrical-to-spherical expansion bridges the continuous conducting domains to create ∼104 self-assembled, electrically contacted and entirely packaged discrete spherical devices per metre of fibre. The photodetection and Mie resonance dependent response are measured by illuminating the fibre while connecting its ends to an electrical readout.