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Ram Adapa (Fellow, IEEE) received the B.S. degree from Jawaharlal Nehru Technological University, India, the M.S. degree from IIT Kanpur, India, and the Ph.D. degree from the University of Waterloo, ON, Canada, all in electrical engineering.

Fano lineshapes and electro-magnetically induced transparency-like peaks in the transmittance of a transverse electric polarization silicon-on-insulator symmetric meandering distributed feedback photonic structure are demonstrated. The coupling constants at the five identical directional couplers are varied to obtain the desired spectral responses. The numerically simulated and experimentally measured transmittance spectra are in good agreement with each other. The numerically calculated and experimentally measured insertion loss for the symmetric meandering distributed feedback structure with directional coupler coupling length Lc = 10 μm are respectively −5 dB and −17 dB, including the grating couplers. Fano lineshapes with mode splitting is observed at directional coupler coupling constant value C of 0.24. For coupling constant value of C ∼ 0.78, electro-magnetically induced transparency-like peaks are observed, and spectrally adjusted by varying the directional coupler coupling length. Fano lineshapes show an extinction ratio of more than 26 dB and slope ratio of 368 dB/nm. Electro-magnetically induced transparency-like peaks show a quality-factor on the order of 5 × 104. The symmetric meandering distributed feedback structure shows promise for possible applications as an optical switch, and an optical filter in wavelength division multiplexing and data networks, as well as optical sensors in optical diagnostics, using silicon photonics.

We demonstrate light coupling from femtosecond laser written diamond waveguide operating at the telecommunication wavelengths to a silicon microsphere resonator. Type II waveguides are written on a diamond platform and Fabry-Perot resonances are excited in the diamond waveguides by bare fiber coupling in and out of the waveguide. The Fabry-Perot resonances have a free spectral range of 87 pm, and a maximum Q-factor of 3.9 × 104. The diamond waveguide is used to excite TM-polarized whispering gallery modes of the 1 mm silicon microsphere, since the type II waveguides support TM modes better as compared to TE modes. The whispering gallery mode spacing is measured as 0.257 nm and the highest Q-factor is 6.2 × 104. This evanescent coupling method to high Q-factor silicon microsphere resonances by femtosecond laser written diamond waveguides can be further used for filtering and sensing applications in various photonic lightwave circuits.

We demonstrate a Type Ib diamond (nitrogen impurity of >5 ppm) microsphere whispering-gallery mode resonator in the near-infrared wavelengths between 1426.10 nm and 1427.42 nm in the 90 degrees elastic-light-scattering for both transverse magnetic (TM) and transverse electric (TE) polarizations. The highest measured whispering-gallery mode quality-factor is in the order of 10(4), and the mode spacing is 0.332 nm both for TM and TE polarizations. The coupling of the continuous-wave tunable infrared excitation laser to the diamond microsphere is achieved by a single-mode silica optical-fiber half-coupler. Such a diamond resonator can further be used as stable optical-frequency-comb generating or lasing microcavities by exploiting the nitrogen-vacancy centers present within the diamond.

Distributed meandering waveguide based fiber optic components are introduced, categorized, and numerically analyzed in the near-infrared. The building block of all meandering waveguide components is the meandering loop mirror. The other components are the meandering resonator, meandering distributed feedback structure, symmetric and antisymmetric meandering resonator, symmetric and antisymmetric meandering distributed feedback structures giving rise to transmission spectra with Lorentzian, Rabi, Fano, coupled resonator induced transparency, and winged Lorentzian lineshapes. With this variety of spectral responses, distributed meandering waveguide fiber optic components are suitable as filters, and delay line elements in fiber optic communication, and as sensor elements in fiber optic diagnostics., Higher Education Commission (HEC) of Pakistan

In this article, Fano lineshape whispering gallery modes were observed in the light scattering spectrum of a silicon microsphere in near-infrared telecommunication wavelengths. A simple model is presented to explain the transition from Lorentzian lineshape to the Fano lineshape resonances with the coupled-mode theory of multiple whispering gallery modes. Polar mode spacing of 0.23 nm is observed in the spectra, which correlates well with the calculated value. The quality factor of the Lorentzian and Fano resonances are on the order of 105. By using an appropriate interface design for the microsphere coupling geometries, Fano lineshape optical resonances herald novel device applications for silicon volumetric lightwave circuits.

Meandering waveguide distributed feedback structures are introduced as novel integrated photonic lightwave circuit elements, and analyzed in the frequency domain by the transfer matrix method. The directional coupling of the electromagnetic field occurs at the meander coupling points. The meandering loop mirror is the building block of all meandering waveguide-based lightwave circuit elements. The simplest uncoupled meandering distributed feedback structure exhibits Rabi splitting in the transmittance spectrum. The symmetric and antisymmetric coupled meandering distributed feedback geometries can be utilized as bandpass, Fano, or Lorentzian filters or Rabi splitters. Meandering waveguide distributed feedback structures with a variety of spectral responses can be designed for a variety of lightwave circuit element functions.

In this study we show an optical biosensor concept, based on elastic light scattering from sapphire micro-spheres. Transmitted and elastic scattering intensity of the microspheres (radius 500 mu m, refractive index 1.77) on an optical fiber half coupler is analyzed at 1510 nm. The 0.43 nm angular mode spacing of the resonances is comparable to the angular mode spacing value estimated using the optical size of the microsphere. The spectral linewidths of the resonances are in the order of 0.01 am, which corresponds to quality factors of approximately 10(5). A polydopamine layer is used as a functionalizing agent on sapphire microspherical resonators in view of biosensor implementation. The varying layer thickness on the microsphere is determined as a function of the resonance wavelength shift. It is shown that polymer functionalization has a minor effect on the quality factor. This is a promising step toward the development of an optical biosensor. (C) 2014 Elsevier B.V. All rights reserved.

Avogadro constant determines the number of particles in one mole of a substance, thus relating the molar mass of the substance to the mass of this substance. Avogadro constant is related to Systeme Internationale base units by defining the very concept of chemical quantity. Revisions of the base units created a need to redefine the Avogadro constant, where a collaborative work called the Avogadro Project is established to employ optical interferometry to measure the diameter of high quality 100 mm silicon spheres. We propose far-infrared spectroscopy for determining the Avogadro constant by using elastic scattering from the 100 mm Avogadro Project silicon spheres. Similar spectroscopic methods are already in use in the near-infrared, relating whispering gallery modes of the 1 mm silicon spheres to the diameter of the spheres. We present numerical simulations in the far-infrared and the near-infrared, as well as spatially scaled down elastic scattering measurements in the near-infrared. These numerical and experimental results show that, the diameter measurements of 100 mm single crystal silicon spheres with elastic scattering in the far-infrared can be considered as an alternative to optical interferometry. We would like to acknowledge the partial support of this work by the Scientific and Technological Research Council of Turkey (TUBITAK) project number 114F312. M.H.H., F.A., and M.R.C. would like to acknowledge support from the Higher Education Commission (HEC) of Pakistan. We would like to thank Koc University Surface Science and Technology Center (KUYTAM) for help with scanning electron microscopy (SEM) and mass measurements of the 1 mm Si sphere. Publisher's Version

We report on the coupling of whispering gallery modes in a 500-mu m-radius silicon microsphere to a femtosecond-laser-inscribed glass optical waveguide. The shallow glass waveguide with a large mode field diameter in the near-infrared is written at a depth of 25 mu m below the glass surface, resulting in a high excitation impact parameter of 525 mu m for the microsphere. The excited whispering gallery modes of the silicon microsphere have quality factors of approximately 10(5) in the 90 degrees elastic scattering and 0 degrees transmission. Integration of such spherical silicon microresonators on femtosecond-laser-inscribed glass waveguides is promising for photonic communication, computation, and sensing applications. (C) 2018 Optical Society of America.

Meandering waveguide distributed feedback structures are novel integrated photonic lightwave and microwave circuit elements. Meandering waveguide distributed feedback structures with a variety of spectral responses can be designed for a variety of lightwave and microwave circuit element functions. Distributed meandering waveguide (DMW) structures [1] show a variety of spectral behaviors with respect to the number of meandering loop mirrors (MLMs) [2] used in their composition as well as their internal coupling constants (Cs). DMW spectral behaviors include Fano resonances, coupled resonator induced transparency (CRIT), notch, add-drop, comb, and hitless filters. What makes the DMW special is the self-coupling property intrinsic to the DMW’s nature. The basic example of DMW’s nature is motivated through the analogy between the so-called symmetric meandering resonator (SMR), which consists of two coupled MLMs, and the resonator enhanced Mach-Zehnder interferometer (REMZI) [3]. A SMR shows the same spectral characteristics of Fano resonances with its self-coupling property, similar to the single, distributed and binary self coupled optical waveguide (SCOW) resonators [4]. So far DMWs have been studied for their electric field intensity, phase [5] and phasor responses [6]. The spectral analysis is performed using the coupled electric field analysis and the generalization of single meandering loop mirrors to multiple meandering distributed feedback structures is performed with the transfer matrix method. The building block of the meandering waveguide structures, the meandering loop mirror (MLM), is the integrated analogue of the fiber optic loop mirrors. The meandering resonator (MR) is composed of two uncoupled MLM’s. The meandering distributed feedback (MDFB) structure is the DFB of the MLM. The symmetric MR (SMR) is composed of two coupled MLM’s, and has the characteristics of a Fano resonator in the general case, and tunable power divider or tunable hitless filter in special cases. The antisymmetric MR (AMR) is composed of two coupled MLM’s. The AMR has the characteristics of an add-drop filter in the general case, and coupled resonator induced transparency (CRIT) filter in a special case. The symmetric MDFB (SMDFB) is composed of multiple coupled MLM’s. The antisymmetric MDFB (AMDFB) is composed of multiple coupled MLM’s. The SMDFB and AMDFB can be utilized as band-pass, Fano, or Lorentzian filters, or Rabi splitters. Distributed meandering waveguide elements with extremely rich spectral and phase responses can be designed with creative combinations of distributed meandering waveguides structures for various novel photonic circuits. References [1 ] C. B. Dag, M. A. Anil, and A. Serpenguzel, “Meandering Waveguide Distributed Feedback Lightwave Circuits,” J. Lightwave Technol, vol. 33, no. 9, pp. 1691–1702, May 2015. [2] N. J. Doran and D. Wood, “Nonlinear-optical loop mirror,” Opt. Lett. vol. 13, no. 1, pp. 56–58, Jan. 1988. [3] L. Zhou and A. W. Poon, “Fano resonance-based electrically reconfigurable add-drop filters in silicon microring resonator-coupled Mach-Zehnder interferometers,” Opt. Lett. vol. 32, no. 7, pp. 781–783, Apr. 2007. [4] Z. Zou, L. Zhou, X. Sun, J. Xie, H. Zhu, L. Lu, X. Li, and J. Chen, “Tunable two-stage self-coupled optical waveguide resonators,” Opt. Lett. vol. 38, no. 8, pp. 1215–1217, Apr. 2013. [5] C. B. Dag, M. A. Anil, and A. Serpenguzel, “Novel distributed feedback lightwave circuit elements,” in Proc. SPIE, San Francisco, 2015, vol. 9366, p. 93660A. [6] C. B. Dag, M. A. Anil, and A. Serpenguzel, “Meandering Waveguide Distributed Feedback Lightwave Elements: Phasor Diagram Analysis,” in Proc. PIERS, Prague, 1986–1990 (2015).

Diamond's nitrogen-vacancy (NV) centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and because they can be found, manipulated, and read out optically. An important step forward for diamond photonics would be connecting multiple diamond NVs together using optical waveguides. However, the inertness of diamond is a significant hurdle for the fabrication of integrated optics similar to those that revolutionized silicon photonics. In this work, we show the fabrication of optical waveguides in diamond, enabled by focused femtosecond high repetition rate laser pulses. By optimizing the geometry of the waveguide, we obtain single mode waveguides from the visible to the infrared. Additionally, we show the laser writing of individual NV centers within the bulk of diamond. We use mu-Raman spectroscopy to gain better insight on the stress and the refractive index profile of the optical waveguides. Using optically detected magnetic resonance and confocal photoluminescence characterization, high quality NV properties are observed in waveguides formed in various grades of diamond, making them promising for applications such as magnetometry, quantum information systems, and evanescent field sensors.

We observed whispering gallery modes in the 90 degrees elastic light scattering and 0 degrees transmission spectra of a 500 mu m silicon microsphere in the near-infrared telecommunication wavelengths. The whispering gallery modes have quality factors on the order of 10(5). An autocorrelation function analysis of the 90 degrees elastic light scattering and 0 degrees transmission spectra is performed. The differential autocorrelation of the 90 degrees elastic light scattering and 0 degrees transmission spectra reveal a spectral mode spacing 0.23nm of the whispering gallery modes, which can be used for spectral calibration as well as the calibration of the microsphere size. The spectral shift of the whispering gallery modes can be measured for biosensing applications. An estimation analysis is performed for the adsorption of 30 DNA base pairs on the microsphere results in a wavelength shift of 0.57 nm, which is approximately 40 times the linewidth of the whispering gallery modes. This high sensitivity heralds silicon microspheres as possible candidates for biosensing applications.

Elastic light scattering is performed in the original band of optical fiber communication at 1300 nm for a 500 μm sapphire microsphere placed on a silica optical fiber half coupler. The morphology dependent resonances (MDRs) are observed in the transverse magnetically (TM) polarized and transverse electrically (TE) polarized 0∘ transmission and 90∘ elastic scattering obtained from the sapphire microsphere. The TE and TM MDRs can be detected selectively with the use of a Glan polarizer. The TE and TM polarization selectivity provides the ability to select relative MDR to BG levels. The TM polarization provides higher MDR signal to background ratio (SBR) and is suitable for optical monitoring, biological sensing or any other optoelectronic application that requires a high resolution optical filter. The polar angular mode spacing of 0.36 nm of the resonances correlates well with the optical size of the sapphire microsphere. The autocorrelation of the 90∘ elastic scattering spectra also shows peaks at 0.36 nm. The spectral linewidths of the resonances are on the order of 0.1 nm, which corresponds to quality factors on the order of 104. A sapphire sphere with a radius of 500 μm and relative refractive index of 1.31, resonances will red-shift by 1.01 nm (0.077%). This shift is on the order of 10 linewidths, making sapphire biophotonic sensors an interesting alternative to silica biophotonic sensors.

The effect of the discrete values of the refractive index of the surrounding medium on the spectral behavior of the whispering-gallery modes (WGMs) in the elastic scattering spectra of high-refractive-index silica microspheres submerged in fluids, such as air, water, and glycerol, is studied. The elastic scattering spectral measurements, as well as the spectral autocorrelation analysis of these elastic scattering spectra show that the spectral-mode spacing, the spectral-mode density, and the spectral-mode definition of the WGMs decrease as the refractive index of the surrounding fluid increases. We believe that this work opens up the way for optofluidic applications of high-refractive-index silica microsphere-based guided wave optics., Scientific and Technological Research Council of Turkey (TÜBİTAK); European Commission

Elastic light scattering from a germanium microsphere with a radius of 2000 µm is analyzed numerically in the terahertz region from 297 µm to 303 µm. Germanium has a high refractive index (n = 4) in the terahertz range [1], which makes it possible to trap light effectively and achieve high quality factor whispering gallery modes (WGMs) [2]. Microsphere WGMs have high quality factors [3,4] and germanium microsphere WGMs [5] can find many applications in the terahertz range, which can be exploited for astronomical [6] and security [7] applications. We studied 90° elastic scattering and 0° transmission spectra from the germanium microsphere using the generalized Lorenz-Mie theory (GLMT) [8,9]. The excitation terahertz source can be coupled to the germanium microsphere through single mode terahertz waveguides [10]. The numerical simulations are performed for both transverse electric (TE) and transverse magnetic (TM) polarization [11] of the terahertz excitation source. The WGM mode spacing, i.e., the spectral separation of the modes with the same radial mode number and consecutive polar mode orders, can be used for the analysis of the microsphere WGM spectra [12]. We observed a mode spacing of 2.4 µm, which agrees well with the theoretically estimated value of the WGM mode spacing. All in all, germanium microspheres with their high quality factor WGMs might find applications in terahertz photonics.

Because of their ultrahigh optical nonlinearities and extremely broad transparency window, germanium microsphere resonators offer the potential for optical processing devices, especially in the mid-infrared (mid-IR) wavelengths. As a semiconductor material for microphotonics applications [1], germanium is particularly attractive owing to its large nonlinearity, high optical damage threshold compared with traditional nonlinear glass materials, and above all, its broad transparency window, extending from the near-IR into the mid-IR. Germanium based optical components have found numerous applications in imaging systems operating in the mid-IR wavelengths, where the principal natural greenhouse gases do not exhibit strong absorption. These applications include rapid sensing and diagnosis [2,] [3], industrial process controls, environmental monitors to hazardous chemical detection [4]. Germanium also is a good electromagnetic shielding material, an attribute that has become increasingly important for modern military applications, where other signals (within the millimeter and centimeter wavelength range) can be strong enough to interfere with nearby IR systems. Elastic light scattering from a germanium microsphere has already been observed in the near-IR [5]. Here, elastic light scattering from a germanium microsphere in the mid-IR region is numerically analyzed using generalized Lorenz-Mie theory (GLMT) [6]. Light interaction with microspheres of various materials is of much interest because of their photonic properties [7]. Germanium has a refractive index of 4, which is even higher than the refractive index of silicon (3.5) in the mid-IR region. The higher refractive index results in higher quality factor morphology dependent resonances (MDRs). A higher value of Q indicates a longer lifetime of the photons trapped inside the cavity and a narrower MDR. Here, the MDRs are observed numerically in the transverse magnetically (TM) and transverse electrically (TE) polarized 90° elastic scattering and 0° transmission for a 40 µm radius germanium microsphere in the mid-IR wavelengths ranging from 5.4 µm to 5.6 µm [8]. The mode spacing of approximately 41 nm between the resonances with the same radial mode order and consecutive polar mode number shows good correlation with the optical size of the germanium microsphere. The germanium microsphere with its high quality factor MDRs can be suitable for optical monitoring and sensing applications in the mid-IR, which require a high spectral resolution [9].

Optical resonators made of dielectric and semiconductor microsphere cavities are of interest due to their whispering gallery modes (WGMs) [1,2]. Initially the WGMs of the microspheres have been excited with plane waves [3]. Later on, single mode optical fiber excitation has been used to couple to the WGM's of the microspheres [4]. Optical waveguides can also be used for the excitation of microresonator WGMs [5]. WGM's have already been observed in the near-infrared (near-IR) transmission of semiconductor resonators such as silicon microspheres [6] and germanium microspheres [7]; since germanium in particular, has certain advantages in photonic applications due to its large nonlinearity, high optical damage threshold and most importantly, its wide transparency range (2 – 15 µm). Moreover, germanium has a refractive index (4), which is more than twice of the refractive index of silica (1.5) giving rise to higher quality factor modes [8,9]. Here, we performed numerical simulation of the 90° elastic scattering in addition to the 0° transmission from a germanium microsphere in the near-IR. We simulated the elastic scattering spectrum from 1.9 µm to 2.1 µm of the germanium microsphere with a 10 µm radius using the generalized Lorenz-Mie theory (GLMT) [10] for both transverse electric (TE) and transverse magnetic (TM) polarization excitation. The numerical simulations resulted in a spectral mode spacing of 12 nm, which is in accordance with the theoretical estimations. The WGMs excited in germanium microspheres can be used in optical applications such as mechanical or thermal sensing [11–13].

Far-infrared (far-IR) elastic light scattering from a germanium microsphere excited by a Gaussian beam is numerically simulated using generalized Lorenz-Mie theory (GLMT) [1]. Microspheres possess optical resonances [2,3], known as morphology dependent resonances (MDRs) [4] or whispering gallery modes (WGMs) [5]. WGMs can also exist in optical resonators of various other shapes such as microdisks, and microtoroids [6]. WGMs of microspheres of different materials result in interesting elastic scattering spectra [7]. The semiconductor material, germanium has a refractive index of 4 in the far-IR [8], which is higher than the refractive index of the more common semiconductor materials, such as silicon. The high refractive index of germanium results in high quality factor WGMs [9]. The germanium microsphere simulated in this study has a radius of 120 µm. The far-IR spectral simulation region ranges from 19.8 µm to 20.2 µm. The light can be coupled to the germanium microsphere by using a tapered fiber coupler, an optical fiber half coupler (OFHC), [10] or an optical waveguide [11]. The 0° transmission and 90° elastic scattering from the germanium microsphere is studied for both the transverse electric (TE) and transverse magnetic (TM) polarizations. A spectral mode spacing of approximately 180 nm is observed in the numerical results, which correlates well with the theoretically calculated mode spacing [12]. Among the possible applications of the WGM excitation in germanium microspheres are optical modulators [13], mechanical, and thermal sensing [14].

The microspheres, with their high quality factor morphology dependent resonances (MDRs), are ideal optical resonators for three dimensional volumetric lightwave circuits. The microsphere leads itself to various lightwave circuit element applications such as channel dropping filters [1], tunable filters [2], optical modulators [3], and dynamic tuners [4]. So far we have realized these applications using silicon spheres coupled with optical fiber half couplers manufactured from single mode optical fibers. Biosensing might also be realized with these silicon microsphere resonators [5]. On the integrated optics side, we recently introduced distributed feedback (DFB) meandering waveguides as novel integrated optical elements [6]. We analyzed silicon DFB meandering waveguides, which can exhibit a variety of spectral responses such as coupled resonator induced transparency (CRIT) filter, Fano resonator, hitless filter, Lorentzian filter, Rabi splitter, self-coupled optical waveguide (SCOW), and tunable power divider. In this talk, we will focus on the properties of silicon spherical resonators and distributed feedback (DFB) meandering waveguides and their potential as lightwave components.

Deoxyribonucleic acid (DNA) and protein recognition are now standard tools in biology. In addition, the special optical properties of microsphere resonators expressed by the high quality factor (Q-factor) of whispering gallery modes (WGMs) or morphology dependent resonances (MDRs) have attracted the attention of the biophotonic community. Microsphere-based biosensors are considered as powerful candidates to achieve label-free recognition of single molecules due to the high sensitivity of their WGMs. When the microsphere surface is modified with biomolecules, the effective refractive index and the effective size of the microsphere change resulting in a resonant wavelength shift. The transverse electric (TE) and the transverse magnetic (TM) elastic light scattering intensity of electromagnetic waves at 600 and 1400 nm are numerically calculated for DNA and unspecific binding of proteins to the microsphere surface. The effect of changing the optical properties was studied for diamond (refractive index 2.34), glass (refractive index 1.50), and sapphire (refractive index 1.75) microspheres with a 50 µm radius. The mode spacing, the linewidth of WGMs, and the shift of resonant wavelength due to the change in radius and refractive index, were analyzed by numerical simulations. Preliminary results of unspecific binding of biomolecules are presented. The calculated shift in WGMs can be used for biomolecules detection.

Silicon microspheres are transparent in the near-infrared telecommunication bands and can be used for electrophotonic integration. We have experimentally observed blue shifts in resonance wavelengths of an electrically driven silicon microsphere of 500 mu m in radius, in the near-infrared. We have used a distributed feed back (DFB) laser operating at 1475 nm, and applied electrical potential differences up to 9 V to the silicon microsphere. We have observed blue shifts in the resonance wavelengths up to 0.05 nm, which corresponds to a change in the refractive index of 10(-4). (C) 2008 Elsevier B.V. All rights reserved.

The validation of a previously developed finite difference temperature prediction model is carried out for orthogonal machining process with a high precision infrared camera set-up, considering the temperature distribution in the tool. The thermal experiments are conducted with two different materials; Al 7075, AISI 1050, with two different tool geometries; inserts having a rake angle of 6° and 18°, for different cutting velocities and feedrates. An infrared camera set-up is utilized for the thermal experiments. The results of the high precision infrared thermal measurements are compared with the outputs of the finite difference temperature model, considering the maximum and the mean temperatures in the tool–chip interface zone and the temperature distributions on the tool take face. The maximum tool–chip interface temperature increases with increasing cutting velocity and feedrate. The relationship between the maximum tool–chip interface temperature and the rake angle of the tool is not distinctive. The experimental results show good agreement with the simulations.

Optical waveguides were fabricated with femtosecond pulsed lasers on glass and characterized by transmission measurements. Glass waveguides were later used for excitation of the whispering gallery modes in a silicon microsphere. The coupling between the silicon microsphere and the femtosecond laser inscribed optical waveguide was simulated in both 90 degrees elastic scattering and 0 degrees transmission spectra. The silicon microsphere whispering gallery modes are available for both in the transverse electric and transverse magnetic polarizations with a spectral mode spacing of 0.25 nm. Optical resonances on silicon microsphere integrated with femtosecond laser written optical waveguides may lead to future quantum optical communication devices., NA

This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 105 are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 105 are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.

The devices that are variations of inter-and intracoupled meandering optical waveguides are proposed as the lightwave circuit elements that exhibit distributed feedback. A preliminary transfer matrix method analysis is applied in frequency domain, taking the coupling purely directional and with constant coefficient on geometrically symmetric and anti-symmetric devices. The meandering loop mirror is the building block of all meandering waveguide based lightwave circuit elements. The simplest uncoupled meandering distributed feedback structure exhibits Rabi splitting in the transmittance spectrum. The symmetric and antisymmetric coupled meandering distributed feedback geometries can be utilized as band-pass, Fano, or Lorentzian filters or Rabi splitters. Meandering waveguide distributed feedback structures with a variety of spectral responses can be designed for a variety of lightwave circuit element functions and can be implemented with generality due to the analytic approach taken., NA

The operation of the hot electron light emitting and lasing in semiconductor heterostructure – vertical cavity surface emitting laser (HELLISH–VCSEL) devices is based on hot carrier transport parallel to the layers of Ga1-x Alx As p–n junction. It is therefore a field-effect device and the light emission from the device is independent of the polarity of the applied voltage. The authors present a study of the temperature dependence of the operational characteristics of the device. Experimental studies comprise the measurements of the I–V characteristics, electroluminescence, reflectivity, and temperature-dependent light-applied electric field (L–F) characteristics. To obtain the optimum operation temperature, the gain calculations, reflectivity spectra, and band gap calculations were carried out at different temperatures. The temperature dependence of the threshold electric field is compared with the model calculations, where radiative transitions without momentum (k) selection are considered.

In this work, electrical square pulses at various duty cycles are applied to a silicon microsphere resonator in order to continuously tune the refractive index of a silicon microsphere and to map the optical resonance in the time domain. A continuous-wave semiconductor diode laser operating in the L-band is used for the excitation of the silicon microsphere optical resonances. The 90 degrees transverse magnetically polarized elastic scattering signal is used to monitor the silicon microsphere resonances. We show that at a constant input laser wavelength, up to five high-quality-factor optical resonances can be scanned by dynamical electrical tuning of the silicon microsphere cavity. (C) 2014 Optical Society of America

A microcavity-based deoxyribonucleic acid (DNA) optical biosensor is demonstrated for the first time using synthetic sapphire for the optical cavity. Transmitted and elastic scattering intensity at 1510 nm are analyzed from a sapphire microsphere (radius 500 µm, refractive index 1.77) on an optical fiber half coupler. The 0.43 nm angular mode spacing of the resonances correlates well with the optical size of the sapphire sphere. Probe DNA consisting of a 36-mer fragment was covalently immobilized on a sapphire microsphere and hybridized with a 29-mer target DNA. Whispering gallery modes (WGMs) were monitored before the sapphire was functionalized with DNA and after it was functionalized with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The shift in WGMs from the surface modification with DNA was measured and correlated well with the estimated thickness of the add-on DNA layer. It is shown that ssDNA is more uniformly oriented on the sapphire surface than dsDNA. In addition, it is shown that functionalization of the sapphire spherical surface with DNA does not affect the quality factor (Q . ≈ 04) of the sapphire microspheres. The use of sapphire is especially interesting because this material is chemically resilient, biocompatible, and widely used for medical implants. ispartof: Journal of Biomedical Optics vol:19 issue:9 ispartof: location:United States status: published

Coupled cavity effects has been observed in the electroluminescence spectra of monolithic GaAs/GaAlAs double quantum well graded index separate confinement heterostructure semiconductor diode lasers. A time domain analysis has been performed in order to simulate the experimentally observed results. The theoretically calculated spectra are in good agreement with the experimentally observed spectra.

Photoluminescence (PL) spectra of AgIn5S8 single crystals were investigated in the 1.44-1.91 eV energy region and in the 10-170 K temperature range. The PL band was observed to be centered at 1.65 eV at 10 K and an excitation intensity of 0.97 W cm(-2). The redshift of this band with increasing temperature and with decreasing excitation intensity was observed. To explain the observed PL behavior, we propose that the emission is due to radiative recombination of a donor-acceptor pair, with an electron occupying a donor level located at 0.06 eV below the conduction band, and a hole occupying an acceptor level located at 0.32 eV above the valence band. (C) 1999 American Institute of Physics.

The Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure (HELLISH-1) device is a novel surface emitter which utilises hot carrier transport parallel to the layers of a Ga1−xAlxAs p-n junction incorporating a single GaAs quantum well on the n-side of the junction plane. Non-equilibrium electrons are injected into the quantum well via tunnelling from the n-layer. In order to preserve the charge neutrality in the depletion region, the junction undergoes a self-induced internal biasing. As a result the built-in potential on the p-side is reduced and hence the injection of non- equilibrium holes into the quantum well in the active region is enhanced. The work presented here shows that a distributed Bragg reflector grown below the active region of the HELLISH device increases the emitted light intensity by two orders of magnitude and reduces the emission line-width by about a factor of 3 in comparison with the original HELLISH-1 structure. Therefore, the device can be operated as an ultrabright emitter with higher spectral purity.

Photoluminescence (PL) spectra of TlInS2 layered single crystals were investigated in the 500-860 nm wavelength region and in the 11.5-100 K temperature range. We observed two PL bands centred at 515 nm (2.41 eV, A band) and 816 nm (1.52 eV, B band) at T = 11.5 K and an excitation intensity of 7.24 W cm-2. A detailed study of the A band was carried out as a function of temperature and excitation laser intensity. A red shift of the A band position was observed for both increasing temperature and decreasing excitation laser intensity in the range from 0.12 to 7.24 W cm-2. Analysis of the data indicates that the A band is due to radiative transitions from the moderately deep donor level located at 0.25 eV below the bottom of the conduction band to the shallow acceptor level located at 0.02 eV above the top of the valence band. An energy-level diagram for radiative donor-acceptor pair transitions in TlInS2 layered single crystals is proposed.

Koc University SPIE student chapter have been organizing the solar powered model vehicle race and reaching out to K-12 students. The solar powered model vehicle race for car, boat, blimp, all solar panel boat, submarine, underwater rower, amphibian, and glider have been successfully organized., NA

The polarization behavior of elastic scattering at 1473 nm is analyzed from a silicon microsphere on an optical fiber half-coupler. The 0.27 nm angular mode spacing of the resonances correlates well with the optical size of the silicon sphere. The spectral linewidths of the resonances are on the order of 10(-3) nm, which corresponds to quality factors on the order of 10(6). The transverse magnetically polarized elastic scattering signal has higher resonance to modulation depth and background ratio than the transverse electrically polarized elastic scattering signal and is suitable for high-resolution optical filtering applications such as optical monitoring and sensing. (C) 2014 Chinese Laser Press

We report the observation of morphology-dependent resonances from silicon microspheres. The dropped channels are observed both in the transmission and elastic scattering spectra in the O-band. The filter drops approximately 23% of the power at the resonance wavelength. The highest observed quality factor for the morphology-dependent resonances was on the order of 10/sup 5/. These resonances have a linewidth of 0.007 nm and a mode spacing of 0.19 nm.

We observed high quality elastic light scattering from a silicon microsphere in the standard telecommunication band. A tunable diode laser was used as the excitation source and a single mode silica optical fiber setup delivered the input laser light to the microsphere. The silicon microsphere was manipulated on the silica optical fiber half coupler (OFHC) to effectively couple the evanescent laser field to the microsphere thus exciting the whispering gallery modes (WGM's). We observed high quality factor WGM's which can lead to novel geometries and applications for silicon microsphere based optoelectronic devices, such as filters, modulators, and detectors., NA

Morphology-dependent resonances of dielectric microspheres are used for polarization-insensitive optical channel dropping from an optical fiber half coupler to a silicon photodetector in the M-band. The dropped channels are observed both in the elastic scattering and the transmission spectra. The highest quality factor morphology-dependent resonances have repetitive channel separations of 0.14 nm and linewidths of 0.06 nm. The filter drops approximately 10% (0.5 dB) of the power at the resonance wavelength. The power detected by the photodiode is estimated to be 3.5% of the power in the fiber.

Optical whispering gallery modes (WGMs) were observed in elastic scattering spectra recorded from oil-in-water emulsion droplets in a microfluidic channel. Droplets with diameters ranging between 15 and 50 mu m were trapped by optical tweezers near the tip of a single mode fiber that enabled the excitation of the WGMs using a tunable laser. Quality factors of the WGMs were observed to increase with droplet size. WGMs with quality factors of more than 10(4) were observed for droplets with diameters around 45 mu m. In some cases, recorded WGMs drifted monotonically to the blue end of the spectrum due to droplet dissolution in the host liquid. Fluctuating spectral shifts to both blue and red ends of the spectrum were also observed. These were attributed to the presence of randomly diffusing particulate contaminants in the droplet liquid, indicating the potential of optically trapped droplet resonators for optical sensing applications. (C) 2016 Optical Society of America

We analyzed silicon microspheres as the building blocks for VLSI silicon CMOS microphotonics. The silicon microsphere has twelve communication ports in three independent dimensions and can easily be integrated in longitudinal, transverse and vertical directions.

K/sub u/ band Fabry-Perot type resonances have been observed in the stop band of a metallodielectric photonic crystal by transmission measurements at microwave frequencies. The metallodielectric photonic crystal has a face centered cubic Bravais lattice structure with a lattice constant of 15 mm. Metallic spheres with 6.35 mm diameter are placed at the lattice sites. The metallodielectric photonic crystal displayed a directional bandgap with a lower band edge of 13.0 GHz, an upper band edge of 21.5 GHz and a center frequency of 17.25 GHz, corresponding to a stop bandwidth center frequency ratio of 50%. The maximum rejection at the band center is 35 dB, corresponding to a 7 dB per unit cell rejection ratio. The Fabry-Perot type resonance in the K/sub u/ band has a quality factor of 200, with a maximum transmission peak of -5 dB.