Applications In Integrated Optics Research Articles

Spatiotemporal continuum generation in polariton waveguides

We demonstrate the generation of a spatiotemporal optical continuum in a highly nonlinear exciton–polariton waveguide using extremely low excitation powers (2-ps, 100-W peak power pulses) and a submillimeter device suitable for integrated optics applications. We observe contributions from several mechanisms over a range of powers and demonstrate that the strong light–matter coupling significantly modifies the physics involved in all of them. The experimental data are well understood in combination with theoretical modeling. The results are applicable to a wide range of systems with linear coupling between nonlinear oscillators and particularly to emerging polariton devices that incorporate materials, such as gallium nitride and transition metal dichalcogenide monolayers that exhibit large light–matter coupling at room temperature. These open the door to low-power experimental studies of spatiotemporal nonlinear optics in submillimeter waveguide devices.

Solid-state random microlasers fabricated via femtosecond laser writing

Here we demonstrate resonant random lasing in Rhodamine B-doped polymeric microstructures fabricated by means of femtosecond laser writing via two-photon polymerization. To the best of our knowledge, this is the first demonstration of random lasing action in on-chip microdevices. Their feedback mechanism relies on diffuse reflections at the structure sidewall surfaces, which is known as spatially localized feedback since the scattering centers lie over the edges of the gain medium. By exciting the structures with a pulsed laser at 532 nm, a multimode emission with randomly distributed narrow peaks was observed, in accordance with the random nature of the feedback mechanism. Interestingly, their lasing threshold was found to be on the order of tens of nanojoules, which is comparable to what had been achieved for usual microcavities, thereby demonstrating the potentiality of these devices as solid-state lasers for integrated optics applications.

Ge22As20Se58 glass ultrafast laser inscribed waveguides for mid-IR integrated optics

Ultrafast laser inscription has been used to produce channel waveguides in Ge22As20Se58 glass (GASIR-1, Umicore N.V). The mode field diameter and waveguide losses at 2.94 μm were measured along with the waveguide dispersion in the 1 to 4.5 μm range, which is used to estimate the zero-dispersion wavelength. Z-scan measurements of bulk samples have also been performed to determine the nonlinear refractive index. Finally, mid-IR supercontinuum generation has been shown when pumping the waveguides with femtosecond pulses centered at 4.6 μm. Supercontinuum spanning approximately 4 μm from 2.5 to 6.5 μm was measured which, to the best of the authors’ knowledge, represents the broadest and the deepest IR supercontinuum from an ultrafast laser inscribed waveguide to date. This work, combined with the long wavelength transmission of GASIR-1 up to 15 μm, paves the way for realizing further ultrafast laser inscribed waveguide devices in GASIR-1 for mid-IR integrated optics applications.

Self-Assembly of Metal Oxide Nanoparticles in Liquid Metal toward Nucleation Control for Graphene Single-Crystal Arrays

Summary We have achieved the spontaneous assembly of alumina nanoparticles on a liquid metal surface and further synthesized a very-large-scale graphene single-crystal array. The effective electrical field established as a result of the electrical charge of the alumina nanoparticles in the liquid metal ensures the ordered self-assembly of the alumina islands and lays the foundation for precise spatial control of graphene nucleation, leading to the formation of graphene single-crystal arrays. In addition, controlling the density of the alumina in the liquid metal can precisely tune the periodicity of the arrays. This simple strategy, which is unlike the usual solid/aqueous solution system, opens up new territory for nanoparticle assembly. Focusing on the origin of the nanoparticle interaction that drives the self-assembly of ordered structure in the liquid metal system is a promising avenue for triggering more interesting applications.

High sensitivity waveguide micro-displacement sensor based on intermodal interference

An optical waveguide displacement sensor according to core-cladding modes interference is theoretically proposed and experimentally demonstrated. Ultraviolet sensitive SU-8 polymer on silica is used as the guiding layer. It is covered by a 12 nm thick planar gold grating. The air gap sensing head which consists of the waveguide end and the single-mode fiber facet can realize the displacement detection by monitoring the wavelength dip shifting in transmission spectra. Cladding modes propagating in the exposed SU-8 can be effectively excited by the end-fire coupling because of the mode field mismatch between the SU-8 waveguide and lead-in fiber. A sinusoidal pattern transmission spectrum in C-band with the depth of over 14 dB can be observed due to the interference between the core and cladding modes. Peaks in the transmission spectrum vary continuously with the position offset of input fiber facet from the center of waveguide end. Both the sensitivity and the stability of sensing are enhanced by the introduction of nanometric gold gratings. The fabricated displacement sensor exhibits a high sensitivity of 2.3 nm μm−1, promising potentials for micromechanical processing and integrated optics application.

Single Longitudinal Mode Optofluidic Microring Laser Based on a Hollow-Core Microstructured Optical Fiber

A single longitudinal mode microring dye laser based on a simplified hollow-core microstructured optical fiber (SHMOF) is proposed and demonstrated. The dye laser uses a submicron thickness silica microring embedded in the SHMOF as resonator and has the characteristic of a low threshold of 664 nJ/mm2. The factors that influence the single longitudinal mode excitation are discussed and the possible operation principle is analyzed. Meanwhile, the single longitudinal mode emissions at several different wavelengths are realized by using different dyes as gain medium, which indicates that the lasing wavelength of the laser is scalable. Time domain characteristics of the lasing are also measured and they are synchronous with the lateral pumping laser. The attractive possibility of developing microfluidic single longitudinal mode dye laser within the SHMOF presents opportunities for integrated optics applications and biomedical analysis with high sensitivity.

High Verdet constants and diamagnetic responses of GeS2-In2S3-PbI2 chalcogenide glasses for integrated optics applications.

Chalcogenide glasses as kind of diamagnetic magneto-optical materials have promising applications in the field of integrated optics and optical communication systems due to their excellent properties, such as easy to be processed into waveguide and temperature independence of the Verdet constants. For clarifying the influence factors following the compositional variation on Faraday effect and finding a glass with a large Verdet constant, novel pseudo-ternary chalcogenide glass system, GeS2 - In2S3 - PbI2, was prepared and investigated. The composition, wavelength and temperature dependences on the Verdet constants were systematically investigated at the wavelengths of 635, 808, 980 and 1319 nm. PbI2 was confirmed to have positive contribution to the Verdet constant and the Becquerel rule was proved to be an effective guidance for predicting the Verdet constant in chalcogenide glasses. The 60GeS2·15In2S3·25PbI2 glass was found to possess the largest Verdet constant (V = 0.215 min·G-1·cm-1, @808nm), which is great larger than that of commercial diamagnetic glasses. These glasses also possess good glass-forming ability and VIS-IR transmittance, therefore be a good candidate for next-generation integrated optical isolator and other magneto-optical devices.

Monolithic CMOS-compatible zero-index metamaterials.

Zero-index materials exhibit exotic optical properties that can be utilized for integrated-optics applications. However, practical implementation requires compatibility with complementary metallic-oxide-semiconductor (CMOS) technologies. We demonstrate a CMOS-compatible zero-index metamaterial consisting of a square array of air holes in a 220-nm-thick silicon-on-insulator (SOI) wafer. This design supports zero-index modes with Dirac-cone dispersion. The metamaterial is entirely composed of silicon and offers compatibility through low-aspect-ratio structures that can be simply fabricated in a standard device layer. This platform enables mass adoption and exploration of zero-index-based photonic devices at low cost and high fidelity.

Second harmonic generation and waveguide properties in perovskite Na0.5Bi0.5TiO3 nanowires.

Nanowires with nonlinear optical properties such as second harmonic generation (SHG) are essential elements for an all-optical integrated photonic circuit. However, the existing materials face challenges for applications in a wide wavelength range. To cope with the challenges, ferroelectric nanowires are considered promising candidates, especially for SHG applications. In this Letter, we study SHG and waveguide properties in perovskite Na0.5Bi0.5TiO3 (NBT) nanowires. Strong SHG is observed in NBT nanowires illuminated by a 1064 nm laser radiation. For the waveguide studies, these NBT nanowires show a waveguide propagation loss as low as 0.01 dB/μm at 532 nm. This work suggests potential applications in future integrated optics with NBT nanowires.

Wedge-cell technique as a simple and effective method for chromatic dispersion determination of liquid crystals

In this letter we present a wedge-cell method and then compare it with other techniques that can be used to determinate refractive indices of liquid crystalline materials. This simple goniometric technique is of particular significance when used for liquid crystalline materials characterized by high refractive indices, for which refractometric methods are approaching their upper limits. Importantly, a measurement technique proposed here requires relatively small amount of a liquid crystalline material and gives appropriate results for different light sources from the wide spectral range, allowing thus for chromatic dispersion curves (in different temperatures) to be obtained. Full Text: PDF References M.O. Ko, S. Kim, J. Kim, B.W. Lee, M.Y. Jeon, "Measurement of Effective Refractive Index of Nematic Liquid Crystal in Fabry-Perot Etalon", J. Opt. Soc. Korea 19, 346 (2015). CrossRef K. Thingujama, S. Sarkara, B. Choudhurya, A. Bhattacharjeea, "Effect of Temperature on the Refractive Indices of Liquid Crystals and Validation of a Modified Four-Parameter Model", Acta Phys. Polonica A 122(4), 754 (2012). CrossRef T.A. El-Dessouki, M. Roushdy, N.I. Hendawy, M.M. Naoum, A.A. Zaki, "Optical Measurements of Thermotropic Liquid Crystals", J. Modern Physics 4, 39 (2013). CrossRef J. Li, S. Wu, S. Brugioni, R. Meucci, S. Faetti, "An Experimental Method for Determination of the Refractive Index of Liquid Samples Using Michelson Interferometer" J. Appl. Phys. 97, 073501 (2005). CrossRef B. Abbas, M.A. Khalil, "An Experimental Method for Determination of the Refractive Index of Liquid Samples Using Michelson Interferometer", Acta Phys. Polonica A 129, 59 (2016). CrossRef S.R. Kachiraju, D. A. Gregory, "Determining the refractive index of liquids using a modified Michelson interferometer", Opt. Laser Techn. 44, 2361 (2012). CrossRef J. Yan, M. Jiao, L. Rao, S. Wu, "Direct measurement of electric-field-induced birefringence in a polymer-stabilized blue-phase liquid crystal composite", Opt. Expr. 18, 11450 (2010). CrossRef K.A. Rutkowska, U.A. Laudyn, R.T. Rutkowski, M.A. Karpierz, T.R. Wolinski, J. Wójcik, "Nonlinear light propagation in photonic crystal fibers filled with nematic liquid crystals", Proc. SPIE 6582, 658215 (2007). CrossRef J. Li, C. Wen, S. Gauza, R. Lu, S. Wu, "Refractive indices of liquid crystals for display applications", J. Display Techn. 1, 51 (2005). CrossRef K. Rutkowska, A. Kozak, K. Orzechowski, "Chromatic dispersion measurements of selected liquid crystalline materials for integrated optics applications," Proc. SPIE (in press) (2016). E. Nowinowski-Kruszelnicki, J. Kędzierski, Z. Raszewski, L. Jaroszewicz, R. Dąbrowski, M. Kojdecki, W. Piecek, P. Perkowski, K. Garbat, M. Olifierczuk, "High birefringence liquid crystal mixtures for electro-optical devices", Optica Applicata 42, 167 (2012). DirectLink

Advantages of UV210 polymer for integrated optics applications: comparison of ridge and photoinscripted strip waveguide performances

We report on the propagation performance comparison of two waveguide structures obtained from the same UV210 photoresist. Ridge waveguide structures were fabricated by deep ultraviolet photolithography, and photoinscripted strip waveguides were realized by the same process, excluding the last development step. Structural and optical studies were carried out for both waveguide families, highlighting a well-controlled photolithography process. Predictions of the propagating modes were also led using the beam propagation method, showing a good agreement with experiments in single-mode propagation. Propagation losses were evaluated at 635 nm by cut-back measurement, showing mean loss values that are slightly lower for photoinscripted waveguides than for ridge waveguides. UV210 photoinscripted waveguides thus combine a fast and low-cost process, reduced optical losses, and a planar surface with as many advantages for more complex integrated components.

Transferable Integrated Optical SU8 Devices: From Micronic Waveguides to 1D-Nanostructures

We report on optical components for integrated optics applications at the micro- and nanoscale. Versatile shapes and dimensions are achievable due to the liquid phase processability of SU8 resist. On the one hand, by adjusting the UV-lithography process, waveguiding structures are patterned and released from their original substrate. They can be replaced on any other substrate and also immerged in liquid wherein they still show off efficient light confinement. On the other hand, filled and hollow 1D-nanostructures are achievable by the wetting template method. By exploiting the large range of available SU8 viscosities, nanowires of diameter ranging between 50 nm and 240 nm, as well as nanotubes of controllable wall thickness are presented. Optical injection, propagation, and coupling in such nanostructures are relevant for highly integrated devices.

Modelling evanescent field components in metal-oxide core waveguides for nonlinear applications

In a thin film planar geometry, the guiding effect due to the linear index results in light confinement in the thin film layer, at the same time causing evanescent waves to decay into the outer substrate or cladding layers. The magnitude of the field in the cladding is dependent on the characteristics of the waveguide and the wavelength of the wave. In this paper, we have modelled four metal-oxide core waveguides with prime focus on the evanescent field as light propagates through these optical structures. ZnO waveguide structure is taken as the benchmark. The evanescent path resembles a soliton consistent with the input soliton solution. A comparison is also carried out with a lower metal oxide core, MgO and a higher index TiO2. The variation in refractive index with input wavelength induces second order nonlinearity in these waveguide structures. For the simulated structures, mode field distributions are plotted against the refractive index. The magnitude of evanescent field also reduces with an increase in the input wavelength for the structures. The nature of the soliton path is insightful for the development of evanescent field based sensors. Optical waveguides with metal-oxide cores can act as a cheaper substitution to nanophotonic devices and integrated optics applications. With the study of evanescent phenomena in such structures, a minimally invasive manufacturing method without disturbance to the core may be made beneficial.

Waveguide fabrication in KDP crystals with femtosecond laser pulses

Optical waveguides fabricated in potassium dihydrogen phosphate (KDP) by ultrafast laser pulses are demonstrated. Dependent on the incident pulse energy, two different types of refractive index modification have been induced. For moderate laser powers, type I homogeneous waveguides are created. At higher pulse energies, type II waveguides are formed in the stressed area surrounding regions of laser-induced damage. Double-line and four-line structures are applied to the type II guides to increase mode confinement. Polarization sensitivity and transmission properties of the written waveguides are characterized and discussed. The results indicate that high-quality waveguides can be fabricated in KDP, which has potential for further applications in nonlinear integrated-optics.

Prism-Coupler Revisited: Analysis and Performance Characteristics Using the Finite-Difference Frequency-Domain Method

The performance of the two-dimensional input prism-coupler configuration for integrated optics applications is analyzed as a function of its critical parameters using the finite-difference frequency-domain (FDFD) method for both TE and TM polarizations. The rigorous FDFD results are compared to the traditional approximate plane-wave-based model developed by Ulrich [R. Ulrich, J. Opt. Soc. Amer., 60, 1337–1350 (1970)] and a modification of it which seems to perform better especially with varying angle of incidence of the exciting Gaussian beam. The FDFD method is formulated for both TE and TM polarizations in conjunction with the uniaxial-perfect-matching-layer absorbing boundary condition as well as with the total-field/scattered-field technique for the incident field implementation. Effective permittivity regularization methods are applied for computational efficiency. The approximate Ulrich’s model generally follows the rigorous results but usually either underestimates or overestimates the prism-coupler’s efficiency and performs worst for the TM polarization.

Sub-wavelength grating components for integrated optics applications on SOI chips.

In this paper we demonstrate silicon on insulator (SOI) sub-wavelength grating (SWG) optical components for integrated optics and sensing. Light propagation in SWG devices is studied and realized with no cladding on top of the waveguide. In particular, we focused on SWG bends, tapers and directional couplers, all realized with compatible geometries in order to be used as building blocks for more complex integrated optics devices (interferometers, switches, resonators, etc.). Fabricated SWG tapers for TE and TM polarizations are described; they allow for connecting SWG devices to regular strip waveguides with loss lower than 1 dB per taper. Our SWG directional coupler presents a very compact design and a negligible wavelength dependence of its crossover length (and as a consequence of its coupling coefficient, κ), over a 40 nm bandwidth. This wavelength flatten response represents a bandwidth enhancement with respect to standard directional couplers (made using strip or rib waveguides), in particular for the TE mode. SWG bends are demonstrated, their loss dependence on radius is analyzed, and fabricated bends have a loss in the range 0.8-1.6 dB per 90 degrees bend. Simulated and measured results show promise for large-scale fabrication of complex optical devices and high sensitivity sensors based on SWG waveguides with engineered optical properties, tailored to specific applications.

A simplified hollow-core microstructured optical fibre laser with microring resonators and strong radial emission

A simplified hollow-core microstructured optical fibre (SHMOF) laser with microring resonators and strong radial emission is demonstrated. We propose that a submicron thickness silica ring embedded in the SHMOF can act as a microring resonator, with the advantages of being both compact and solid. Furthermore, the microfluidics can be easily controlled with a side pumping scheme. We also obtained a highly stable and tunable laser. The attractive possibility of developing microfluidic dye lasers within single SHMOFs presents opportunities for integrated optics applications and biomedical analysis.

Wide-range transmitting chalcogenide films and development of micro-components for infrared integrated optics applications

Development of micro-components for IR integrated optic devices requires the elaboration of IR waveguides. It is shown that amorphous chalcogenide films from the Ge-Se-Te system are well suited to such development. Thermal and optical characteristics of films elaborated by thermal co-evaporation are first measured. The Se-rich (> 60 at. %) region with a Ge content of about 25 at. % comprises films with a vitreous transition temperature, Tg, larger than 400K, a high thermal stability (ΔT > 100K) and a well-controlled refractive index, n, owing to a weak dependence of n with composition in this region. Films in this composition region are then profitably used to develop optical structures, such as straight or S-bend waveguides, spirals, Y-junction or Mach-Zehnder interferometer, by stacking and further etching of the films. The transmission region accessible to these structures lies from telecommunication wavelength up to 16-17 µm. When a higher transmission region is required, the use of pure Ge-Te films is mandatory. A modal filter allowing a light rejection efficiency of 6.10−5 to be a part of a spatial interferometer is then elaborated.

Spectroscopic study of high Er and Er/Yb concentration doped photosensitive silicate glasses for integrated optics application

Er and Er/Yb doped photosensitive multicomponent silicate glasses with composition of 60SiO2–10GeO2–10B2O3–20Na2O (in wt.%) were prepared and characterized in terms of absorption cross-section (σa), fluorescence lifetime (τm) and concentration quenching effect. The solubility of rare earth ions in this glass is much higher (to 2wt.%) than that of conventional silicate glasses, with corresponding lifetime and quantum efficiency of τm=7.5ms and η=50%, respectively. Glasses with different Er/Yb ratios were also made to investigate the effects of Er/Yb ratios on energy transfer efficiency. A ratio of Er/Yb=0.4 showed higher absorption cross-section compared to 0.2 and 0.6. The lifetime for all samples decreased with the addition of Yb2O3. We also report on the 1.5μm emission line broadening of Er3+ ion emission in these glasses. The emission of full width at half maximum shifted from 25.7nm to 48.2nm and the increased line width was found to correlate to an increase in Er3+ concentration in such a multicomponent glass. The studied glass with multifunctional properties is proved to be a very good candidate for application in integrated optics.

Fabrication and optical properties of sol–gel derived organic–inorganic photosensitive ridge waveguide structure doped with disperse red 13

Disperse red 13 (DR13) azoaromatic chromophores were embedded into the sol–gel derived organic–inorganic hybrid waveguide films with photosensitive properties. Third-order nonlinear properties of the hybrid waveguide films were investigated by using a z-scan technique under a femtosecond laser pulse at the wavelength of 800nm. Planar waveguide properties and changes of absorbance of the hybrid films under an irradiation of the non-polarized UV light at 365nm were also characterized by a prism coupling technique and UV–visible spectroscopy, respectively. Advantages for fabrication of the functional ridge waveguide structure were demonstrated by a UV-cured imprint technique, and the results indicate that the fabrication process is simple and cost-effective. Morphological and surface profile properties of the ridge waveguide structure were observed by scanning electron microscopy and the propagation loss of the ridge waveguide structure was also measured by a cut-back method. All these results indicate that the as-fabricated waveguides are promising candidate for integrated optics applications.