This PDF file contains the front matter associated with SPIE Proceedings Volume 11276, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The traditional ways of tuning a Silicon photonic network are mainly based on the thermal-optic effect or the free carrier effect of silicon. The drawbacks of these methods are the volatile nature and the extremely small change in the complex refractive index (Δn<0.01). In order to achieve low energy consumption and smaller footprint for applications such as photonic memories or computing, it is essential that the two optical states of the system exhibit high optical contrast and remain non-volatile. Phase change materials (PCMs) such as GST provide a solution in that it exhibits drastic contrast in refractive index between the two non-volatile crystallographic states which can be switched reversibly. Here, we first show that GST can be integrated with a Si ring resonator to demonstrate a quasi-continuous optical switch with extinction ratio as high as 33dB. Secondly, we demonstrated GST-integrated 1×2 and 2×2 Si photonic switches using a three-waveguide coupler design which exhibits a low insertion loss of ~1dB and a compact coupling length of ~30μm. The crosstalk is as small as -10dB over a bandwidth of 30nm. Lastly, we explore the potential of two emerging PCMs Sb2S3 and GeSe for extreme low loss operation of reconfigurable photonic integrated circuit (PIC).

A method for creating photorefractive electroholographic gratings with sustained operational longevity is presented and demonstrated. The method circumvents the thermal decay and erasure during readout characteristic of photorefractive devices by augmenting the device with a built-in mechanism that writes and periodically and/or continuously refreshes the space-charge gratings which are the core elements of such devices. The mechanism was demonstrated in a slab waveguide constructed in a KLTN:Cu crystal. The space-charge grating was created by illuminating the slab waveguide through a binary grating mask deposited on top of the surface of the crystal by incoherent illumination from a LED. The electroholographic performance manifested by the grating was similar to that of gratings constructed by interfering beams. This makes electroholography to be the basis for a viable technology for performing wavelength selective switching and electrical wavelength tuning at the device level, and enables their assembly in integrated photonic circuits.

For further improvement of phase change material switches, relationships between optical characteristics of phase change materials(PCM) and the performance of optical switches were investigated. PCM optical switch is optimized for the both states of the insertion loss to be balanced. With optimized three-channel directional coupler switch, the refractive index difference between amorphous and crystalline state was inversely proportional to the insertion loss.

We investigated at room temperature the Franz-Keldysh effect in GeSn layers with Sn concentrations up to 13%. Several p-i-n stacks with indirect and direct band-gaps were grown by Reduced Pressure Chemical Vapor Deposition (RPCVD) with Ge2H6, Si2H6 and SnCl4 precursors. Direct band-gap energies and absorption coefficient were determined in transmission by electro-absorption measurements. The direct band-gap position was consistent with our k.p model. A maximum modulation of 1% was obtained at the direct band gap for a 0.5 V bias.

In this work, we experimentally demonstrate a FSR-free, MRR-based, coupling modulator that integrates a bent, grating-based contra-directional-coupler (contra-DC) into a microring cavity to achieve an FSR-free response at its through port. Our modulator suppresses the amplitude response at all but one resonance, operating mode (hence, has an FSR-free response). In our modulator, coupling modulation is used and is achieved by modulating a relatively short, 210 μm long, p-n junction phase-shifter in a two-point coupler (which forms the drop-port coupler of the MRR). We demonstrate open eyes at 2.5 Gbps and discuss how the effects of DUV lithography on the contra-DC limited the electro-optic bandwidth of the fabricated modulator to 2.6 GHz. In these proceedings, we also cover details of the device design and the small and large signal characterization of the device, including an analysis of the effect of lithography on the “as-fabricated" device performance. We also discuss how to significantly improve the electro-optic bandwidth in future implementations by accounting for these lithographic effects in the device design flow and layout.

We have recently developed a novel electro-optic modulator via external electrical gating of 2D MoS₂ bilayers deposited within the inner regions of a silica hollow core anti-resonant fiber. The MoS₂ film acts as the electro-optically active material, responding with increased absorption of waveguided modes when in the presence of an externally applied electric field. The bilayer is formed via a liquid phase deposition method, in which the single source precursor ammonium tetrathiomolybdate is thermally decomposed into MoS₂. The device has to date demonstrated modulation depths of >3.5dB, at an operating DC voltage of 1500 V with an optical insertion loss of 7.5dB. We have thus developed a novel, active, composite material anti-resonant fiber (CM-ARF) technology platform, which despite high voltage requirements, show excellent potential for all-fiber electro-optical design and operation.

Light carries a great deal of information in the form of amplitude, phase, and polarization, any or most powerfully all, of which may be exploited for the characterization of materials or development of novel technologies. However, extracting the full set of information carried by light becomes increasingly difficult as sample feature sizes shrink and the footprint and cost of detection schemes must decrease as well. Here, a fiber-based interferometric scheme is deployed to extract this information from optical systems which may be assessed three dimensionally down to the nanoscale and/or temporally up to the bandwidth of electronic data acquisition available. The setup utilizes a homemade fiber stretcher to achieve phase-locking of the reference arm and is compatible with heterodyning. More interestingly, a simplified and less expensive approach is demonstrated which employs the fiber stretcher for arbitrarily frequency up-converted (with respect to driving voltage frequency) phase modulation in addition to locking. This improves the detection system’s size, weight, power, and cost requirements, eliminating the need for an acousto-optic modulator and reducing the drive power required by orders of magnitude. High performance is maintained as evidenced by imaging amplitude and phase (and inherently polarization state) in micro and nano optical systems such as lensed fibers and focusing waveguide grating couplers previously imaged only for intensity distribution.

This talk will describe our group’s advances and outline future work in the measurement and manipulation of thermal emission. First, I will discuss our efforts to improve thermal-emission metrology, especially for low-temperature thermal emitters and/or those with temperature-dependent emissivity. Then, I will describe our use of phase-transition materials including vanadium dioxide and the rare-earth nickelates to demonstrate new phenomena, including negative- and zero-differential thermal emittance, radiative thermal runaway, and thermo-dichroism. The talk will include discussion of opportunities of thermal-emission engineering for infrared camouflage and thermoregulation.

Tunable mid-wave infrared (MWIR) filters are highly desirable in a wide variety of imaging and sensing applications. Here, we demonstrate a solid-state, actively tunable, narrowband MWIR transmission filter based on a plasmonic nanohole array (PNA) design integrated with the phase change material GeSbTe (GST). Through finite-difference time domain simulations and experimental results, we show narrowband (~100nm), high-efficiency (~90%) transmission filtering, tunable across the entire MWIR spectrum (1~10µm). The active tunability of the GST/PNA filter has been experimentally demonstrated by single-shot pulsed laser irradiation-induced phase transformation and the device shows consistent behavior across a number of phase change cycles.

AlAs0.56Sb0.44 is a promising avalanche material which can be grown lattice-matched to InP and therefore use InGaAs as the absorption region in a Separate Absorption and Multiplication APD (SAM-APD). The electron and hole ionisation coefficients in this material are very dissimilar and our experiments show that this leads to AlAs0.56Sb0.44 having the lowest excess noise performance of any InP based material system (F = 2.2 at M = 40) reported to date. Simulations suggest that operation at 1550 nm and 25 GB s-1 with a sensitivity of -25.7 dBm is possible in a normal incidence SAM-APD.

There is an increasing demand for highly sensitive near infrared (NIR) detectors due to many rapidly growing application areas, such as LiDAR and optical communications. Despite the limited NIR absorption, silicon is a common substrate material in NIR detectors due to low cost and maturity of the technology. To boost the NIR performance of silicon devices, one option is texturizing the front and/or back surface to reduce reflectance and extend the optical path by scattering. Here we demonstrate silicon photodiodes with nanostructured front surface (i.e. black silicon fabricated with reactive ion etching (RIE) that exhibit significantly enhanced external quantum efficiency (EQE) at NIR wavelengths compared to typical state-of-the-art silicon photodiodes. The detectors exhibit over 90% EQE with wavelengths up to 1040 nm and above 60% at 1100 nm. Identical detectors with a planar surface are also investigated revealing that the enhancement from black silicon effectively corresponds to increasing the substrate thickness up to 43% at 1100 nm depending on the thickness of the active layer and back surface structure. This confirms that in addition to reduced reflectance, scattering of transmitted light induced by black silicon plays a key role in the EQE enhancement which benefits especially devices such as backside illuminated photodetectors where very thin substrates are required. We also demonstrate that the high EQE of the black silicon detectors is maintained at incidence angles up to 60 degrees allowing excellent performance in applications where the light is not always perpendicular.

Emerging applications in sensing, LIDAR, spectroscopy, and SWIR imaging require photodetectors operating at wavelengths beyond the range of silicon technology and that can be produced cost-effectively for very high-volume consumer and commercial markets. In this paper, Array Photonics, Inc. introduces a new generation of photodetectors designed to meet these requirements. We provide an update on PIN photodetectors and detector arrays based on our dilute nitride material (GaInNAsSb) grown epitaxially on and lattice matched to gallium arsenide (GaAs) substrates. We present our latest photodetector results demonstrating broadband operation from 450 nm to 1450 nm with peak responsivity of over 0.85 A/W at 1300 nm and dark current density of 3×10^-5 A/cm² at -1V bias voltage. These dilute nitride-on-GaAs photodetectors are now commercially available as single elements, 1-D arrays and small 2-D arrays and are referred to as eGaAs™ (extended GaAs) photodetectors. We also briefly discuss ongoing work to migrate from 4” (100 mm) to 6” (150 mm) GaAs wafers and the implementation of larger size 2-D arrays for imaging applications in the automotive and industrial markets.

Optical characterization of PureGaB germanium-on-silicon (Ge-on-Si) photodiodes was performed for wavelengths between 255 nm and 1550 nm. In PureGaB technology, chemical vapor deposition is used to grow germanium islands in oxide windows to the silicon substrate and then cap them in-situ with nm-thin layers of first gallium and then boron, thus forming nm-shallow p⁺n diodes. These PureGaB Ge-on-Si photodiodes are CMOS compatible and characterized by low leakage currents. Here they are shown to have high responsivity in the whole ultraviolet (UV) to near infrared (NIR) wavelength range. Particularly, two sets of diodes were studied with respect to possible detrimental effects of the Al metallization/alloying process steps on the responsivity. Al-mediated transport of the Ge and underlying Si was observed if the PureGaB layer, which forms a barrier to metal layers, did not cover all surfaces of the Ge islands. A simulation study was performed confirming that the presence of acceptor traps at the Ge/Si interface could decrease the otherwise high theoretically attainable responsivity of PureGaB Ge-on-Si photodiodes in the whole UV to NIR range. A modification of the device structure is proposed where the PureGaB layer covers not only the top surface of the Ge-islands, but also the sidewalls. It was found that to mitigate premature breakdown, it would be necessary to add p-doped guard rings in Si around the perimeter of Ge islands, but this PureGaB-all-around structure would not compromise the optical performance.

A comprehensive study of mid-wavelength infrared (MWIR) InAs/InAsSb type-II superlattice (T2SL) photodetectors was performed for full characterization of the E-O performance, reliability, and linearity as well as response speed. Teledyne Judson Technologies has recently developed high operating temperature (HOT) MWIR InAs/InAsSb T2SL large area discrete detectors of 0.25mm and 1mm for front-side illumination. The 50% cut-off wavelength of the detectors ranges from ~5.4 to ~5.7μm at room temperature. For the reliability tests, the T2SL detectors were thermally cycled and humidity tested. Initial testing data showed excellent stability to the temperature and humidity, indicating the T2SL detectors have long-term stability. Linearity, response speed and capacitance were measured at various temperatures and reverse biases. This work presents comprehensive test results, data analysis, and discussion, showing these large size, discrete T2SL detectors have the potential to replace conventional MWIR detector materials.

The theoretical model of rare earth doped optical devices based on the rate equations and the power propagation equations can be employed for recovering, via an indirect approach, the rare earth spectroscopic parameters. As an example, the model for an erbium doped silica-tin dioxide, SiO₂ - SnO₂ : Er³⁺, glass ceramic waveguide is considered. Two different pumping schemes are employed to excite the erbium ions, the direct pumping at 378 nm and the indirect pumping at 307 nm via the tin dioxide. The achievable optical gain per unit length at 1533 nm is then evaluated for both pumping cases. The ratio between the two simulated optical gains is compared with the emission intensity measurements to estimate the value of the SnO₂-Er³⁺ energy transfer coefficient. The particle swarm optimization algorithm is applied in order to find the SiO₂ - SnO₂ : Er³⁺ glass ceramic spectroscopic parameters which properly match the simulated optical gains ratio with the experimentally measured emission ratios. In the same way, the pump power coupled in the glass ceramic waveguide is also recovered. The SnO₂-Er³⁺ energy transfer coefficient is estimated to be about 6.1 × 10^-22 m³/s.

We present the fabrication by Surface Plasma Chemical Vapor Deposition (SPCVD) and All Solution Doping (ASD) of step-index Nd-doped fibers with a 30/125μm (core/cladding diameters) geometry and a low numerical aperture (NA) near 0.05. A phospho-alumino-silicate (SiO₂-Al₂O₃-P₂O₅-Nd₂O₃) core composition was used to reduce the formation of Nd³⁺ ions clusters while keeping a low refractive index through the peculiar AlPO₄ chemical complex. Operated in CW laser regime, a 0.053 NA fiber generated up to 17W of output power at 921nm, limited by the available pump power at 808nm (51W), yielding a 37% power conversion efficiency. The profile of the output beam for a bend diameter of ~12cm is gaussian and nearly diffraction limited (M² ~1.1). This is in good agreement with the large discrepancy, in terms of calculated bending losses, between the fundamental LP₀₁ and the higher order modes.

We report the production of active double waveguides in germanate glasses, GeO₂-PbO doped with Nd³⁺, by direct femtosecond laser writing. The glasses were produced using the melt-quenching technique and the active waveguides were written using 30 fs laser pulses at 800 nm with different parameters of writing speeds and pulse energies depending on the rare earth elements used for doping. The photo-induced refractive index change was 5.2x10^-3. The Nd doped sample exhibited a relative gain of 3.6 dB/cm for 1.6 mW of 805 nm pump power. The results obtained in present work demonstrate that Nd³⁺ doped GeO₂-PbO glasses are promising materials for the fabrication of integrated amplifiers, lossless components and lasers based on germanate glasses.

Random lasers are cheap and easy to fabricate, having several different applications such as early cancer detection, encryption and Speckle-free imaging. However, few fabricated random lasers present high efficiency, which limits their possible applications. In a recent work, our group achieved a record efficiency by developing random lasers that use compacted, polydispersed yttrium vanadate doped with neodymium (Nd³⁺:YVO₄) powders to create separate regions for gain and light diffusion. Large particles are responsible for the light diffusion, while the small particles that occupy the spaces between them create gain pockets, absorbing the pumped light. In this work, this strategy is refined by using passive particles (SiO₂) for light diffusion, restricting the laser active particles to the gain pockets. The first attempt with this strategy used 30% of Nd³⁺:YVO₄ small powders and 70% of large SiO₂ particles. Without any further optimization, the result achieved is already 40% of the highest obtained efficiency in the previously studied Nd³⁺:YVO₄ polydisperse sample, showing a promising result to further improve this new strategy and reach even larger efficiencies with less laser active material.

Traditional photolithography methods of fabrication of micro-opto-electro-mechanical systems (MOEMS) can be substituted with graphene to minimize cost and enhance optofluidic system integration. The use of optical disc drives allows graphite oxide to undergo (near infrared) light exposure, with a specified pattern, and transformation to graphene, also with this specified pattern. This work describes the fabrication methods, electrical conduction and hydrophobicity characteristics for graphene microsystems. The fabrication characterisation involves a comparison of graphene fabrication of microsystems with photolithography fabrication. Graphene fabrication was observed to be comparable to the photolithography fabrication, with a comparable minimum feature size. The electrical characterisation involves resistivity measurements of graphene which decrease from n = 1 (where n represents the dose of light exposure in the disc drive), and saturates at n = 12, representing the final transformation to graphene from graphite oxide. The microfluidic characterisation of the graphene surface involves contact angle measurements and favourable wetting properties are shown. By increasing the fabrication dose, the contact angle rises from 50 degrees until saturation at 116 degrees, allowing for contact angle tunability over this range. Overall, fabrication of MOEMS is found to be successfully achievable using graphene fabrication.

The rapid development of high power laser near 2 µm increases the demand of optical isolators and optical circulator that require materials with low optical absorption and high Verdet constant in that wavelength region. We have studied the magneto optical properties of three different kinds of chalcogenide glasses, Te2As3Se5, GeSe9, and Ge25As15S60, and Dysprosium doped borate glasses with different weight percentages from 60 wt.% to 75 wt.%. The Verdet constant of diamagnetic glasses is highly dependent on the dispersion of refractive index as a function wavelength and also absorption edge, while in the paramagnetic glasses the concentration of rare earth element ( Dy3+) plays the main role. The Verdet constant of both type of glasses decreases monotonically as a function of wavelength. The average resonant wavelength of Dy3+ glasses were found to be in the region of far UV while for Te2As3Se5, GeSe9, and Ge25As15S60 were 500, 330, 250 nm respectively. The Verdet constant of Dy3+ doped borate glass increases linearly as a function of Dy3+ concentration in 2 um region. The Verdet constant of chalcogenide glasses increase linearly as function of square of absorption edge wavelength. The highest Verdet constant in Dy glasses was measured to be -414 deg/T/m for 75 wt.% Dy3+ doped borate glass. The highest Verdet constant at 1940 nm was obtained to be 870 deg/T/m for Te2As3Se5 which is the highest Verdet constant reported in diamagnetic and paramagnetic glasses to the best of our knowledge. The figure of merit was found to be around 550 deg/T in 2 µm region for the telluride glass.

Materials power key technological advancements in areas such as communications, consumer electronics, aerospace, automotive and energy. Silica has become the status quo because of its abundance and affordability. Advances in areas such as quantum computing, AI and IoT will require new materials with performance envelope beyond the traditional (i.e. global internet data is rapidly growing beyond petabytes/s/km). A long-time competitor to silica, heavy metal fluoride glasses represent an attractive candidate due to their optical transmission window that extends deep into the infrared (IR) and recently also in the UV (200nm-800nm). Although ZBLAN was the early frontrunner for 2.5μm transatlantic links with no repeaters, silica won the race in the 1980’s, due to the development of repeaters at 1.5μm. Today this reliance on silica is hurting the industry by forcing retrofitting of new applications. It is becoming clear that the demands of the next generation of communications cannot be solved with additional investments in a silica-based infrastructure. Silica has now maxed out also its affordability not just its signal transmission capacity. An equivalent to Moore’s law applicable to information speed and capacity carried through optical fibers has been emerging, and silica is not up to the task. The time for ZBLAN is now. Building on advances of the past several decades, fluoride technology (i.e. ZBLAN, InF3) has the unique properties to transmit light over [0.3-5.3]μm with theoretical attenuation as low as ~6.4•10^-3 dB/km at 2.32μm – two orders of magnitude better than silica. This paper provides a solid reference to calculate the theoretical spectrum of ZBLAN attenuation and includes a thorough discussion on areas of improvement that, once implemented, will lead to the manufacturing of ZBLAN that approaches its ultimate performance. An up-to-date ZBLAN-silica comparison is provided, including values of material properties that underlie both attenuation and stimulated Brillouin scattering (SBS) power threshold estimations. Contrary to existing beliefs, current ZBLAN intrinsic fiber strength is only a factor of 2-3 lower than that of silica. The breaking radius of a standard SMF-28 fiber is <1.5mm and <4mm for ZBLAN with the latter being available in jacketed form to comply with industrial requirements. Fluoride fibers inherently provide naturally a much wider bandwidth than silica with up to 100x usable number of data channels, <2 petabytes per second of data with no amplification for 1,000km or more and no need to carry power for said amplification lines. By comparison, current undersea cables use one repeater for amplification every 100-150km, at a cost of ~$1M each. In addition, the low phonon energy characteristic of fluoride glasses and the high solubility towards a wide spectrum of rare-earth elements are conducive to a broad range of robust and reliable fluoride fiber lasers emitting more power and/or at wavelengths inaccessible before. Last but not least, the dispersive properties of fluoride fibers and other nonlinear effects lead to supercontinuum spectral broadening that can be extended from 0.8-4.1μm up to 15 μm when cascading fluoride fibers with other types of fibers. Fluoride fiber technology is a solid and competitive solution for a wide spectrum of photonic applications (spectroscopy, medical diagnosis), data transmission (ultra-long haul, submarine) and beyond.

Rare-earth (RE) doped optical fibers are extensively used in lasers and optical amplifier devices. These key applications rely on the qualities of silica glass: mechanical and chemical stability, high optical damage threshold, low cost, etc. However, silica glass has certain characteristics which may make it less efficient compared to other types of glass, particularly in some potential applications using RE ions: high phonon energy, low solubility of RE ions, etc. To overcome these limitations, one recent strategy consists of developing a fabrication method which triggers RE encapsulation in phase-separated nanoparticles. The development of this family of optical fibers was driven by this requirement: the particles must be as small as possible to avoid light scattering. However, recent studies discussed in this article tend to disapprove this doxa. First, we present the fabrication process of such fibers, emphasizing the drawing step as a process to control the shape and size of the nanoparticles. Then, we discuss on the characterization of the composition of these nanoparticles at the nm-scale. To reach this goal, we took advantage of a recent technology: Atom Probe Tomography. These results will be compared with molecular dynamics simulations. We demonstrate that the phase-separated nanoparticle composition and therefore the chemical environment of the encapsulated RE ions is nanoparticles size dependent. As a consequence, the smallest nanoparticles, promoted by the doxa, would offer limited alteration of the luminescent properties. Finally, light scattering is not only an issue but is also an opportunity to develop new temperature, strain, refractive index multiplexed optical fiber sensors.

We investigate the mechanisms underlying a mode suppression effect observed in polymer microcavities containing graphene oxide (GO) aiming at the development of on-chip integrable photonic devices. The GO-doped microcavities (cavity loaded Q-factor of 20000 at 1550 nm) are fabricated by means of two-photon polymerization via direct laser writing. The saturable absorption and optically induced thermal lens effects prompted by GO are investigated through nonlinear measurements using both the ultrafast and continuous-wave Z-scan technique and our preliminary results suggest that optically induced thermal lens may be playing a major role in the mode suppression observed in the GO-doped polymer microcavities.

Temporal coherence control is a vital tool to achieve power scaling by overcoming stimulated Brillouin scattering (SBS). Conventional methods through phase modulation, with a sinusoidal drive or white noise source are limited in the achievable linewidth tunability due to the bandwidth of the RF drive and/or power handling of the phase modulator. Linewidth tuning range can be further increased by phase modulation amplification through cascaded four-wave mixing between multiple input lasers. When the input lasers are correlated, linewidth does not change with mixing order. However, in the case of uncorrelated input lasers, the linewidth increases progressively with increase in cascaded order. In this work, continuous linewidth tuning is achieved in two parts. From single frequency to ~7GHz, a single input laser at the required wavelength is line-broadened with phase modulation driven by a filtered white-noise source. Beyond this, two uncorrelated pumps are chosen, similarly broadened, amplified and sent through highly nonlinear fiber which performs cascaded four-wave mixing based phase modulation amplification. A demultiplexer extracts the required cascaded order and the two input lasers are tuned in wavelength appropriately to ensure the output center wavelength is constant. With the two effects together, continuous linewidth tuning at a single C-band wavelength from single frequency to more than 30GHz is achieved. The upper limit can be enhanced with power scaling. These principles can be translated to 1064nm wavelength, relevant to power combining and SBS limited power scaling of Ytterbium lasers using a combination of 1064nm phase modulators and nonlinear PCFs for cascaded four-wave mixing.

Hybrid optical fibers, i.e. optical fibers that combine, in the same structure, glass with crystal, metal, polymer or a second type of glass, open access to a wide range of optical properties or optical functions not accessible to common single-glass-made optical fibers. Silicon-core fibers are one type of hybrid fibers that have been intensively studied since 2006 with the aim to take benefit of the mid-infrared transparency of silicon or to implement opto-electrical functions in the optical fiber itself. Some of the unique optical properties of these semiconductor-core fibers have been demonstrated but it is admitted that optical losses are still today a drag on the rise of performances and hence devote specific attention. Post-processing based on laser or thermal annealing can be applied on the as-drawn fibers to improve core crystallinity and then reduce optical losses. However, such processing techniques have been demonstrated on centimeter-long fibers only. In the present paper, we demonstrate as-drawn silicon-core fiber with loss level below 0.2 dB/cm on the 1250-1650nm wavelength range, this fiber being continuously manufactured over length exceeding one hundred of meters. Several fibers have been fabricated from a rod-in-stack approach and different core dimensions ranging from about 0.8 to 3.4 μm have been successively realized and extensive characterizations (XRD, micro-Raman spectroscopy, TEM and ToF-SIMS analysis) have been conducted on the 3.4 μm core fiber. The crystalline state of the core, the absence of oxygen contamination and the optical transmission from 1.1 to 4 μm will be presented.

This study presents a high-temperature distributed acoustic sensor (HT-DAS) optical fiber that utilizes a single layer of unique specialty coating with elevated thermal stability applied atop a 125 μm single-mode transmission fiber, where the fiber features enhanced Rayleigh backscattering sensitivity combined with long-term robustness and survivability up to 150 °. The developed HT-DAS fiber possesses a similar level of mechanical strength and transmission loss as most industrial specialty and telecommunication optical fibers, but also exhibits remarkable distributed sensing characteristics: enhanced elastic backscattering signal intensity about 12 dB above the base Rayleigh scattering level of non-enhanced fiber. Most importantly, this fiber extends service feasibility to a relatively high temperature regime for 1 year at about 150°C, according to life-time estimation based on thermogravimetric analysis, failure mode analysis, and accelerated aging reliability test.

In this work, we present the design of a refractive Axicon lens to be used in refractive index optical sensing. The lens is designed to generate a Bessel – Gauss beam at the wavelength of 3.3 microns. At that wavelength, the absorption of the CH4 is maximum and thus a maximum change in the refractive index due to the CH4 gas is also expected. The intensity profile of the generated beam is quite sensitive to the index of refraction of the surrounding medium. Placing the optical detector at the point of maximum change in the intensity with refractive index allows the measurement of the refractive index change and hence the gas percentage with very high sensitivity. Our design shows sensitivity greater than 970 % per RIU. We also develop an analytical formulation for the intensity variation with the refractive index. The results obtained analytically are confirmed by the finite difference time domain FDTD calculation. From the analysis and the derived expressions, we demonstrate the effect of the Axicon base angle on the sensitivity and hence allow for the lens optimization to achieve maximum sensitivity for a target application.

Fully suspended InGaAs waveguide devices with holey photonic crystal waveguides (HPCWs) and Sub-wavelength waveguides (SWWs) are designed and fabricated for mid-infrared sensing at λ=6.15µm in the low index contrast InGaAs-InP platform. We experimentally detect 5 ppm ammonia in 1 mm long suspended HPCW and 3 mm long suspended SWW with propagation loss of 39.1 dB/cm and 4.1 dB/cm, respectively. This result emphasizes the advantage of SWWs which can utilize the longer devices by virtue of its low propagation loss to increase the gas sensing sensitivity compare to HPCWs.

We report a novel method to enhance the modal interference pattern in an anti-resonant negative curvature hollow-core fiber (NCHCF), enabling in-fiber multimodal interferometer in a short (few mm) length. The enhanced interference provides well defined fringes suitable for sensing; and their application for mechanical sensing is demonstrated. An 8 mm length of NCHCF was exposed to periodic arcs from a conventional splicer, leading to periodic modulation of fiber parameters along the length of the fiber. This periodic modulation alters the interaction between interfering modal fields, causing enhanced modal overlap and a four-fold increase in the intensity variation of the interference pattern. The enhanced interference dips are observed to be sensitive, with a linear response, to external mechanical forces like curvature, while being insensitive to thermal crosstalk by virtue of the hollow core design.

Traditionally the extreme hardness of diamond materials has made the machining of diamond optical components exceptionally difficult and limited applications to mostly flat components. Recent advances in diamond processing technology have made it possible to fabricate curved optical components or lenses in single crystal and polycrystalline diamond. This paper analyses a multi-spectral infrared imaging system incorporating a diamond lens and compares performance to equivalent systems that use other common infrared optical materials. Due to the broad transmission spectrum of diamond, which ranges all the way from the UV to microwave, these curved optics could find use in many different imaging applications throughout the electro-magnetic spectrum. Consideration is given to other advantages that diamond brings to the multi-spectral imaging application including small variations in refractive index as a function of both wavelength and temperature, a large Abbe number and material resilience under harsh conditions. As the development of large-area single crystal (SC) chemical vapour deposition (CVD) diamond advances, SC diamond lenses for multispectral imaging become a real possibility, with a number of advantages that we present in this paper.

Miniaturized optics are main components in many different areas ranging from smart devices over medical products to the area of automotive and mobility. Thus several million if not billions of small lenses are merged into objectives. The optical function of these objectives can only be guaranteed, if all optical surfaces not only meet the form tolerances of the optical design but also have the right position with respect to another. To ensure this, a measurement method has been developed, that is able to measure the surface form and the centration of both functional surfaces of single micro optical polymer lenses. The method bases on Optical Coherence Tomography (OCT) so that due to the tomographic measurement principle both functional surfaces can be captured in one measurement. Key challenge is the reconstruction of the geometric form of the functional surface facing away from the measurement head since it is distorted due to the refraction of light on the functional surface that faces towards the measurement head. The distortion needs to be corrected by means of backwards ray tracing. The OCT-based characterization of the single optical elements allows an adaptive assembly of micro optical imaging objectives by feeding back the individual shape of every single optical component to the assembly process. This information can be used for either selective assembly or the compensation of individual component tolerances by matching components whose form and centration errors cancel each other out in the overall system.

SnO₂-based glass-ceramics activated by rare earth ions have been extensively investigated because of the need to develop reliable fabrication protocols and clarify some interesting optical, structural, and spectroscopic features of the system. There is one important weakness in glass photonics when the rare earth ions are employed as luminescent sources. This is the low absorption cross section of the electronic states of the rare earth ions. A sensitizer is therefore requested. In the last years, we demonstrated that SiO₂-SnO₂ glass ceramics, presenting a strong absorption cross section in the UV range due to the SnO₂ nanocrystal, are effective rare earth ions sensitizers. Another interesting property of the SiO₂-SnO₂ system is its photorefractivity. The high photorefractivity of sol-gel-derived SnO₂-SiO₂ glass-ceramic waveguides has been demonstrated in several papers published by our consortium. It has been shown that the UV irradiation induces refractive index change allowing the direct writing of both channel waveguides and Bragg gratings.

The results presented in this communication not only demonstrate the viability and outstanding properties of the SiO₂- SnO₂ glass-ceramics for photonic applications but also put the basis for the fabrication of solid state and integrated lasers. The next steps of the research are the fabrication of the channels and mirrors exploiting the photorefractivity as well as to draw glass ceramic fiber, checking the lasing action and corresponding functional characteristics. Finally, it is worth noting that the dynamic of the energy transfer from the nanocrystals to the rare earth ions is still an exciting open question.

The elaboration of chalcogenide microstructured optical fibers (MOFs) permits to combine the mid infrared transmission of chalcogenide glasses up to 18 µm to the unique optical properties of MOFs thanks to the high degree of freedom in the design of their geometrical structure. In this context, we have shown that chalcogenide preforms can be obtained by an original additive manufacturing process We have also shown that these preforms can be drawn into chalcogenide optical fibers. Those early-stage results open a new way for the elaboration of chalcogenide MOFs with more elaborate designs.

Random anti-reflection sub-wavelength structures (rARSS) on optical component surfaces have been shown to enhance transmission by reducing Fresnel reflection. These structures have a broadband anti-reflection effect, and insensitivity to high angle of incidence and polarization. We have fabricated random anti-reflection surface structures on commercially available linear gratings, using reactive ion etching. An overall enhancement was measured in the specular transmission direction, with suppression of the specular reflection to less than 1%, from initial values between 3 to 8% under 1st Bragg angle of incidence, without effecting the diffractive performance of the grating. We studied the effect of these structures on a 1.595 μm period and 1.166 μm period gratings, with and without rARSS, using scattering measurements for polarized light, at normal, 1st Bragg and 2nd Bragg incidence. The directional transmission distribution function (BTDF) was measured over 180 degrees (full field), to analyze the directionality of the scattered light and the impact of the rARSS on the optical performance of the gratings. Correlations of the surface roughness with the individual diffraction order scattering profile and overall BTDF were investigated.

Transparent Barium Phosphate glasses embedded with rare-earth ions and silver were made by the melt quenching technique. Glasses were characterized by measuring absorption, emission spectra and lifetime measurements. From the emission measurements chromaticity diagrams were generated. Color coordinates and color temperature were estimated. The glass sample with silver was subjected to heat treatment to induce nanoparticles. Effect of heat treatment on luminescence measurements was analyzed.

Nanocolloidal lasers have a potential as inexpensive high-power light sources using non-toxic and non-degradable liquid gain media. However, due to their large core and, as a result, multimode operation they have an issue of strong noise produced by mode competition. An advanced solution would be the selection of active modes down to a single-mode using the parity-time (PT) symmetry approach that originates from the analogy between the Schrödinger wave function equation in quantum mechanics and the wave propagation equation in optics. The PT symmetry lasing will be implemented when spatially inhomogeneous pumping of the nanocolloid generates gain in pumped regions equal in magnitude to the loss in the regions without pumping. When pump energy increases, PT symmetry break occurs and the laser modes split in the active modes amplified in the cavity and those that decay. The goal is to achieve a single-mode nanocolloid laser. On the way to the goal a nanocolloidal capillary optical amplifier was built using highly efficient phosphor NaYF₄: Yb³⁺ , Er³⁺ emitting at 1550-nm wavelength being pumped with a 980-nm laser diode. The amplifier was configured as a 4-cm long capillary tube made of silica filled with a colloid of 160-nm phosphor nanoparticles in a high- index fluid. Uneven pumping from the side modulated the gain of the amplifier. When the amplifier was to converted into a laser with linear resonator, uneven side pumping produced a variation of the spontaneous emission that could be interpreted as a PT symmetry related mode competition. This potentially could lead to the reduction of active modes and eventually to a single mode operation.

We report on the materials development and infrared (IR) optical spectroscopy of Dy³⁺-doped into the ternary lead halides compounds TlPb₂Br₅ and CsPbCl₃ for photonic applications. The investigated Dy-doped ternary lead halides were synthesized from purified starting materials followed by melt-growth using vertical Bridgman technique. Under optical pumping at 1.35 μm (⁶H_15/2→⁶H _9/2+⁶F_11/2), broad mid-IR emissions in the ~2.9 μm (⁶H_13/2→⁶H_15/2), ~4.3 μm (⁶H_11/2→⁶H _13/2), and ~5.4 μm (⁶H_9/2 +⁶F_11/2 →⁶H_15/2) regions were observed at room-temperature. Compared to Dy: TlPb₂Br₅, the mid-IR emission from Dy: CsPbCl₃ was significantly weaker suggesting the existence of non-radiative losses. Temperature dependent lifetime studies and a Judd-Ofelt analysis were performed for Dy: TlPb₂Br₅.

The implementation and performance of a unidirectional all-single mode fiber hybrid passive variable optical coupler/attenuator based on a Sagnac loop mirror with a continuous variable coupling ratio using off-the-shelf optical sub-components are discussed. Parameters of two output ports of the unidirectional hybrid passive variable optical coupler/attenuator, such as maximum coupling ratio, insertion loss, excess loss, and wavelength- dependent return loss over the C-band at room temperature are reported. The reflectivity of the Sagnac loop mirror continuously varies from 0.1% to 99.9% by adjusting retarders of a polarization controller. The 3-dB coupling ratio (i.e., 50:50) between the two output ports of the hybrid passive variable optical coupler/attenuator is achieved when the reflectivity of the Sagnac loop mirror is set at 73%. The attenuation and coupling ratio range of 1.7 - 45.5 dB and 0.13 - 99.87% is achieved, respectively, from the implemented unidirectional hybrid passive variable optical coupler/attenuator. The availability of the off-the-shelf optical sub-components and achieved easy control of continuous variable coupling ratio makes the proposed unidirectional hybrid passive variable optical coupler/attenuator a cost-effective optical device for several applications including optical system testing, and general laboratory experiments.

Due to the air-guiding characteristics of the air-core, hollow-core optical fibers (HCOFs) can give rise to many potential applications including optical data transmission, terahertz propagation, power beam delivery for industrial applications such as cutting, welding, and engraving, medical applications and chemical sensing. In this work, tellurite HCOFs which have 6 air holes in the cladding and a large hollow core in the center are studied. By numerical analysis, it was realized that the confinement loss in the core will be high when the gap between two nearby cladding air -holes is large or when they connect to each other. The light propagation and transmission properties were demonstrated experimentally from 0.4 to 4.0 μm. By carefully controlling the coupling conditions, lights were coupled successfully into the air core by the fundamental mode. The transmission spectrum included high transmission bands and low transmission bands alternately due to the effect of resonant reflection and anti-resonant reflection. Due to the current operating range of the laser source, the transmission spectrum was measured up to 3.9 μm. But, it is expected to extend to the mid-IR range around 6 μm as shown in the calculation. When the input light at 2.1 μm was linearly polarized, the polarization was maintained in the fiber because the fundamental mode was dominant and the coupling efficiency of the 1^st order mode was very weak.

This analytical modeling-and-simulation paper presents a compact passive photonic filter using Mach-Zehnder Interferometer (MZI) on silicon-on-insulator (SOI) platform. MZI based wavelength filters have been demonstrated for broadband wavelength-division-multiplexing (WDM). The imbalance in MZI provides means to control the free spectral range (FSR) hence enabling designing of a photonic filter that can pass the required band and block the rest of the signal. Low loss Y-splitter/combiner are used with very small footprint to make compact size MZI. A 3D Finite-Difference Time-Domain (FDTD) simulation is performed on our design. FSR value of 50 nm was observed in the span of 100 nm wavelength range centered on 1.55 μm. The footprint of the designed filter is 15 μm x 20 μm.

We design a practical guided-mode resonance filter excited in the visible light region. We show that high background transmission over 90% at resonance wavelengths of 623 nm and 641 nm for TE and TM polarizations, respectively. Also, we investigate the sensitivity of the filter to incident angles, polarization and the refractive index of the surrounding environment. Our filter provides the resonant transmission spectral response with high sensitivities of 90 nm/RIU and 103 nm/RIU, and with a figure of merits of 1.93 and 2.13 for TM and TE polarizations, respectively. A GMR with such characteristics is expected to hold great promise a practical label-free refractive index biosensor.

Novel and commercially-relevant applications for soft X-Ray (SXR) methods - protein structural characterization, tomography, and chemical detection - are driving a demand for fast and sensitive detectors in the 20 eV to 10 keV range, often with unusual geometries to accommodate placement in beam lines and vacuum chambers. Here we present several novel CCD SXR detector solutions with high quantum efficiency and readout speed, and where the design can be modified to tilt, tile or extend the sensor from the camera body. Each of these implementations have provided quantum efficiencies peaked at 95% in the soft X-Ray regime. These CCDs while providing very high sensitivity are however generally limited to slow readout rates of ~ 1 Hz for the full frame. Scientific CMOS sensor technology can provide much faster frame rates, large field-of-view and lower readnoise floors. Here we also discuss our sCMOS based solutions for indirect hard X-Ray Detection.

Rare earth doped aluminates, such as SrAl₂O⁴:Eu²⁺,Dy³⁺ and CaAl₂O₄:Eu²⁺,Nd³⁺ , are among the best known materials for persistent luminescence or afterglow emission. Their Eu²⁺ counterparts, which were beforehand finely studied, also exhibit long lasting luminescence properties. It recently appeared that the hexagonal polymorph of SrAl₂O₄, which is not stable at room temperature, could have promising luminescent properties. A recently efficient way to elaborate the hexagonal Sr_1-x/2Al_1-xSi_xO₄:Eu²⁺, with interesting photoluminescence properties, has been developed by full glass crystallization. Still, the persistent luminescence properties of this strontium aluminosilicate compound have never been reported. Here, advanced optical properties such as persistent luminescence emission, persistent luminescence decay and thermoluminescence have been performed in order to report about the persistent luminescence potential of the strontium aluminosilicate hexagonal polymorph.