Waveguide Formation Research Articles

Modeling the nonlinear photoabsorptive behavior during self-written waveguide formation in a photopolymer

Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they can exhibit a large refractive index change and high photo-sensitivity. In free radical photo-polymerization systems, the dyes, functioning as the photosensitizer, strongly influence the material properties. During photo-illumination the spatial and temporal evolution of the dye concentration is an important factor leading to nonlinear absorption. In this paper, based on an investigation of the photochemical mechanisms, we analyze the nonlinear photo-absorptive effect during the photo-initiation processes. The time varying exposing light distribution is calculated and used to iteratively estimate the evolving cross-sectional refractive index and loss coefficient values. The model enables a more accurate and physical description of the optically induced growth of SWWs in such systems. Then SWWs formed in dry acrylamide/polyvinyl alcohol (AA/PVA) based photopolymer samples, containing different initial dye concentrations, are experimentally examined. The nonlinear absorptive behavior is quantified by comparing the model predictions and the experimental results.

Formation of luminescent optical waveguides in silicate glass matrix by the ion-exchange technique

We present spectra of the alkali-silicate glasses with copper ions in near-surface area, introduced by ion exchange of different temperature and duration. It is shown that the reduction of Cu2+ in the near-surface area causes existence of Cu+ and neutral atoms in glass after the ion-exchange in divalent salt. The ion-exchange itself involves only Cu+ and Na+ ions. The formation of subnanometer clusters Cun is due to neutral copper atoms staying in near-surface zone. We have shown that the waveguide layer in near-surface area, made by ion-exchange, has а visible luminescence with the excitation by UVradiation. At the same time, the contribution to luminescence is made by Cu+ ions, molecular clusters Cun and by dimers Cu+ - Cu+ . During the high-temperature ion-exchange at 600 °С the formation and destruction equilibrium shift of molecular clusters Cun can be seen. An hour ion-exchange leads to molecular clusters Cun destruction, while at time periods less than 30 min and around 18 hours it leads to the formation of Cun. The sample turns green after 18,5 hours ion-exchange showing formation of a considerable amount of divalent copper ions Cu2+ therein.

飞秒激光在钛蓝宝石晶体中刻写双线型波导的研究

Ti: sapphire crystal is one of the most important materials as a laser medium, due to its broad absorption band and widely tunable output band, therefore it has wide application in integrated optics. By femtosecond laser with repetition rate of 1 kHz, central wavelength of 800 nm and pulse width of 120 fs, double line waveguide in Ti:sapphire crystal is transversely written. The impacts of the processing conditions, i.e., inscribing depth, writing speed and the track distance on the waveguide formation are systematically studied, and the waveguide with better guiding mode is achieved when laser pulse energy is 2 μJ, inscribing depth is 175 μm, writing speed is 90 μm/s and the distance between two tacks is 26 μm. And the double line waveguide shows polarization dependent optical guiding. Based on the near-field mode intensity, the refractive index profile of the optical waveguide is reconstructed, and the max positive refractive index change is about 1.9×10-4. In addition, by using the scattering technique, the propagation loss of the waveguide is 1.82 dB/cm. ©, 2015, Science Press. All right reserved.

Method of Formation of Waveguides on the Basis of Any Polymeric Materials

This paper describes a new type of polymeric waveguides which has the core, cladding medium and active nodes made from the same material. Part of the polymer is removed in cladding medium by formation of nanopores. The pores can be filled with liquid crystals (LC) in order to create an active composite medium needed for electrically controlled nodes formation.

Specific features of the formation of optical waveguides in silicate glass at high energy and doze of electron irradiation

The formation of an optical waveguide in silicate glass that contains alkali-metal ions is experimentally studied under electron irradiation at an energy of 50 keV and a doze of 25–50 mC/cm2. A gradient waveguide with a maximum variation in the refractive index of 0.01–0.04 is formed in the glass due to irradiation. It is demonstrated that a variation in the refractive index results from both field migration of alkalimetal ions to the region of negative space charge and structural modifications in the glass related to the destruction of glass structure by high-energy electrons.

An AlGaAs/GaAs‐based planar Gunn diode oscillator with a fundamental frequency operation of 120 GHz

ABSTRACTThis letter reports the highest fundamental oscillator operating frequency of 120 GHz for gallium arsenide (GaAs)‐based Gunn diode. The letter describes the design, fabrication, and test of the aluminum gallium arsenide (AlGaAs)/(GaAs) planar Gunn diode with an anode to cathode separation of 1 μm and channel width of 120 μm. The planar Gunn diode was designed with an integrated series inductor in coplanar waveguide format. The experimental results showed that the planar Gunn diode oscillated at a fundamental frequency of 120.47 GHz with an RF output power −9.14 dBm. This is highest fundamental frequency and power recorded for a GaAs‐based Gunn diode. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2449–2451, 2014

Spectral broadening in femtosecond pulse written filamentary waveguides in periodically poled lithium niobate.

The authors report the filamentary waveguide formation and the significant spectral broadening based on periodically poled lithium niobate substrate. The modified morphology contributes to the combined effects of optical diffraction and self-focusing with the dependence on pulse intensity. Up to 4 times broadening of the FF wave and about 47 nm spanning of the SH wave with the pump power of 19.5 mW are achievable under 1550 nm excitation. Spectral evolution by cubic nonlinearity inside the waveguide has been obtained numerically, and provides a reasonable agreement with the experimental results.

Investigation of Carbon ion-implanted waveguides in tungsten bronze (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 single crystal

Planar optical waveguides were fabricated in (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 (CSBN25) crystal by 6.0-MeV C+ ion implantation with fluences of 2, 4 and 6×1014ions/cm2 at room temperature. The mode parameters, refractive indices profiles are measured and the refractive indices behavior in the waveguide region is discussed. The shape of nuclear energy loss distribution of the C+ implantation was similar to those of the waveguide refractive index profiles, which means an inherent relationship between the waveguide formation and the energetic energy deposition. The extraordinary refractive index has a small positive change in the surface region after the implantation.

Silicon photodetectors integrated with vertical silicon nitride waveguides as image sensor pixels: Fabrication and characterization

The current trend toward image sensors with ever-increasing pixel counts is prompting continual reductions in pixel area, leading to significant cross-talk and efficiency challenges. The realization of image sensor pixels containing waveguides presents a means for addressing these issues. The fabrication of such pixels is however not straightforward. Conventional waveguides employed in integrated optics are horizontal, but waveguides needed for the proposed sensor must be vertical and integrated with photodetectors. Here, the authors describe a fabrication process for vertical silicon nitride waveguides integrated with silicon photodetectors. The authors describe the etching, deposition, and planarization techniques that enable the formation of silicon nitride waveguides embedded in silicon dioxide. They also describe a fabrication process for silicon photodetectors, including a means for ensuring that their photosensitive areas have sizes consistent with those of photodetectors employed in conventional image sensors. In addition, the authors perform optical and electrical characterization of the fabricated devices. The results demonstrate the ability of the fabricated waveguides to guide light onto the photodetectors with high efficiency.

Oxygen-implanted optical planar waveguides in Er3+/Yb3+-codoped silicate glasses for integrated laser generation

Er 3+ /Yb 3+ -codoped silicate glasses are good candidates for the application of laser actions and signal amplification. Optical planar waveguides in Er 3+ /Yb 3+ -codoped silicate glasses are fabricated by 6.0-MeV oxygen-ion implantation with a dose of 6.0×10 14 ions/cm 2 at room temperature. The SRIM 2010 code is carried out to simulate the energy losses during the implantation process in order to obtain a better understanding of the waveguide formation. The guiding modes and near-field intensity distributions of the waveguide are characterized by the prism-coupling and end-face coupling methods. The refractive index profile and light propagation mode of the planar waveguide are numerically calculated by the reflectivity calculation method and finite difference beam propagation method. The waveguide has a “well+barrier ” refractive index distribution and its optical loss is ∼1.02 dB/cm . The microluminescence and absorption investigation reveal that fluorescent and transmission properties in the waveguide are well preserved with respect to the bulk, suggesting promising potential for waveguide amplifiers and lasers.

Waveguide radio-wave propagation in the equatorial ionosphere according to the Interkosmos-19 data

Additional strongly remote (up to 2000 km) radio-signal reflection traces on Intercosmos-19 ionograms obtained in the equatorial ionosphere have been considered. These traces, as a rule, begin at frequencies slightly lower than the main trace cutoff frequencies, which indicates that an irregularity with a decreased plasma density exists here. The waveguide stretched along the magnetic-field line is such an inhomogeneity in the equatorial ionosphere. The ray tracing confirm that radio waves propagate in a waveguide and make it possible to determine the typical waveguide parameters: −δNe ≥ 10%, with a diameter of 15–20 km. Since the waveguide walls are smooth, an additional trace is always recorded distinctly even in the case in which main traces were completely eroded by strong diffusivity. Only one additional trace (of the radio signal X mode) is usually observed one more multiple trace is rarely recorded. Waveguides can be observed at all altitudes of the equatorial ionosphere at geomagnetic latitudes of ±40°. The formation of waveguides is usually related to the formation of different-scale irregularities in the nighttime equatorial ionosphere, which result in the appearance of other additional traces and spread F.

Femtosecond laser‐written waveguides in thulium‐doped fluoroindate glass for S‐band amplification

Channel waveguides were written in a fluoroindate bulk glass containing thulium, with a femtosecond laser operating at 800 nm, 100 fs pulses and a repetition rate of 1 kHz. Formation of waveguides occurred for average powers from 1 to 8 mW (corresponding to energies of 1–8 μJ) and scan velocities in the range of 0.1–4 mm/s. Passive optical characterisation included visual inspection by an optical microscope, insertion loss and mode profile. Active characterisation was performed by co-propagating pumping in a dual-pump scheme that included an 808 nm and a 1054 nm laser diode for an efficient inversion of the 3H4 level, which is responsible for stimulated emission in the 1460–1530 nm spectral range. Preliminary tests show a net gain of 2.5 dB at 1487 nm, for straight waveguides 1 cm long. Applications include the fabrication of lossless components working in the S-band region of the optical communication spectrum.

Formation of self-trapping waveguides in bulk PMMA media doped with Phenanthrenequinone

Experimental and theoretical investigations of light self-trapping waveguides in a bulk polymeric medium based on polymethylmethacrylate (PMMA) with photosensitive phenanthrenequinone (PQ)-molecules are examined. Self-channeling was generated for the first time in this nonlinear bulk PQ-PMMA media with a thickness up to several millimeters and 0.1 mol. % PQ-concentration. The experimental formation of volume waveguide structures with a length of 2 - 3 cm at different laser wavelengths (405 nm, 488 nm, and 514.5 nm) was demonstrated. The calculations based on a model for the laser beam propagation in the bulk PQ-PMMA medium with competitive nonlinearities are in a good agreement with the experiments.

Fluorescence-active Waveguides by the Sol-Gel Method. Theory and Application

Active waveguides can be applied in environmental sensors, telecommunication, medicine, computers and electronic convertors. The sol-gel technology allows formation of planar and fiber waveguides incorporating fluorescent organic and inorganic dopands. Several sol-gel matrices which enable the incorporation of lanthanides and their complexes and fluorescent organic molecules are presented. A short description of the theory of luminescence of lanthanides is outlined and examples of active waveguides known today are given. The mechanisms for infrared to visible light conversion are explained. Suggestions for practical approach to novel active waveguides are given. Increase of fluorescence as a result of an interaction of fluorescent species with metal nanoparticles is presented.

Use of quasi-local photorefractive response to generated superficial self-written waveguides in lithium niobate

We report the formation of surface self-written waveguides by means of surface pyrolitons in lithium niobate. By a specific orientation of the crystal axis the quasi-local slow photorefractive response of lithium niobate was used to induce a self-confined beam exactly at the crystal-air interface. The mode profile of the photo-induced waveguide is strongly asymmetric due to the interface presence.

Embedded optical waveguides fabricated in SF10 glass by low-repetition-rate ultrafast laser

Symmetric embedded waveguides were fabricated in heavy metal oxide SF10 glass using slit-shaped infrared femtosecond laser writing in the low-repetition frequency regime. The impact of the writing parameters on the waveguide formation in the transverse writing scheme was systemically studied. Results indicate that efficient waveguides can be inscribed in a wide parameter space ranging from 500 fs to 1.5 ps pulse duration, 0.7-4.2 μJ pulse energy, and 5 μm/s to 640 μm/s scan speed and pointing out the robustness of the photoinscription process. The refractive index profile reconstructed from the measured near field pattern goes up to 10(-3). In addition, propagation losses of the waveguides are tolerable, with the lowest propagation loss estimated at 0.7 dB/cm. With a 5 μm/s scan speed and 3.5 μJ pulse energy in a high-dose regime, few-mode guiding was achieved in the waveguide at 800 nm signal injection wavelength. This is due to a combination of increased refractive index in the core of the trace and the appearance of a depressed cladding.

Escherichia coli-Based Biophotonic Waveguides

The rapid progresses in biological and biomedical applications with optical interfaces have motivated an ever-increasing demand for biocompatible and disposable photonic components. Generally, these biophotonic components are first integrated with biocompatible materials and then interfaced with biological samples, such as living cells, for biological use. Therefore, direct formation of biophotonic components using living cells is greatly desired because the cells would serve simultaneously as samples and optical elements for signal sensing and detection. Here, we report an optical strategy for direct formation of biophotonic waveguides (bio-WGs) with Escherichia coli. The experiments demonstrate that this facile optical strategy enables forming bio-WGs with different lengths and good light propagation performances while the propagating signal can be detected in real-time. This strategy offers a seamless interface between optical and biological worlds with natural materials and provides a new opportunity for direct sensing and detection of biological signal and information in biocompatible microenvironments.

Influence of oxygen in architecting large scale nonpolar GaN nanowires

Manipulation of the surface architecture of semiconducting nanowires with a control in surface polarity is one of the important objectives for nanowire based electronic and optoelectronic devices for commercialization. We report the growth of exceptionally high structural and optical quality nonpolar GaN nanowires with controlled and uniform surface morphology and size distribution, for large scale production. The role of O contamination (∼1 to 105 ppm) in the surface architecture of these nanowires is investigated with the possible mechanism involved. Nonpolar GaN nanowires grown under O rich conditions show inhomogeneous surface morphologies and sizes (50–150 nm) while nanowires have precise sizes of 40(±5) nm and uniform surface morphology, for the samples grown under O reduced conditions. Relative O contents are estimated using electron energy loss spectroscopy studies. Size-selective growth of uniform nanowires is also demonstrated, under the O reduced condition, using different catalyst sizes. Photoluminescence studies along with the observation of single-mode waveguide formation, as far field bright violet multiple emission spots, reveal the high optical quality of the nonpolar GaN nanowires grown under the O reduced condition.

Buried waveguide in neodymium-doped phosphate glass obtained by femtosecond laser writing using a double line approach

We fabricate a buried channel waveguide in neodymium-doped phosphate glass using a double line approach by femtosecond laser writing. Raman spectra reveal an expansion of the glass network in the laser irradiated region. Given the stress-induced positive refractive index change, waveguiding between two separated tracks is demonstrated. The refractive index difference profile of the waveguide is reconstructed from the measured near-field mode. Propagation loss is measured by scattering technique. Microluminescence spectra reveal that the Nd3+ fluorescence property is not significantly affected by waveguide formation process, which indicates that the inscribed waveguide is a good candidate for active device.

M-line spectroscopic, spectroscopic ellipsometric and microscopic measurements of optical waveguides fabricated by MeV-energy N+ ion irradiation for telecom applications

Irradiation with N+ ions of the 1.5–3.5MeV energy range was applied to optical waveguide formation. Planar and channel waveguides have been fabricated in an Er-doped tungsten–tellurite glass, and in both types of bismuth germanate (BGO) crystals: Bi4Ge3O12 (eulytine) and Bi12GeO20 (sillenite). Multi-wavelength m-line spectroscopy and spectroscopic ellipsometry were used for the characterisation of the ion beam irradiated waveguides. Planar waveguides fabricated in the Er-doped tungsten–tellurite glass using irradiation with N+ ions at 3.5MeV worked even at the 1550nm telecommunication wavelength. 3.5MeVN+ ion irradiated planar waveguides in eulytine-type BGO worked up to 1550nm and those in sillenite-type BGO worked up to 1330nm.