This PDF file contains the front matter associated with SPIE Proceedings Volume 9744, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Pulsed Laser Deposition (PLD) is used to produce Er-doped lead-niobium germanate (PbO–Nb₂O₅–GeO₂) and fluorotellurite (TeO₂–ZnO–ZnF₂) thin film glasses. Films having high refractive index, low absorption and large transmission are obtained in a narrow processing window that depends on the actual PLD configuration (O₂ pressure ∼a few Pa, Laser energy density ∼2-3 J cm^-2 for the results presented in this work). However, Er-doped thin film glasses synthetized at room temperature using these experimental parameters show poor photoluminescence (PL) performance due to non-radiative decay channels, such as a large OH^- concentration. Thermal annealing allows improving PL intensity and lifetime (τ_PL), the latter becoming close to that of the parent Er-doped bulk glass. In addition, the use of alternate PLD from host glass and rare-earth targets allows the synthesis of nanostructured thin film glasses with a controlled rare-earth concentration and in-depth distribution, as it is illustrated for Er-doped PbO–Nb₂O₅–GeO₂ film glasses. In this case, PL intensity at 1.53 μm increases with the spacing between Er-doped layers to reach a maximum for a separation between Er-doped layers ≥ 5 nm, while τ_PL is close to the bulk value independently of the spacing. Finally, the comparison of these results with those obtained for films grown by standard PLD from Er-doped glass targets suggests that nanostructuration allows reducing rare-earth clustering and concentration quenching effects.

Direct laser writing technique is now widely used in particular in glass, to produce both passive and active photonic devices. This technique offers a real scientific opportunity to generate three-dimensional optical components and since chalcogenide glasses possess transparency properties from the visible up to mid-infrared range, they are of great interest. Moreover, they also have high optical non-linearity and high photo-sensitivity that make easy the inscription of refractive index modification. The understanding of the fundamental and physical processes induced by the laser pulses is the key to well-control the laser writing and consequently to realize integrated photonic devices. In this paper, we will focus on two different ways allowing infrared buried waveguide to be obtained. The first part will be devoted to a very original writing process based on a helical translation of the sample through the laser beam. In the second part, we will report on another original method based on both a filamentation phenomenon and a point by point technique. Finally, we will demonstrate that these two writing techniques are suitable for the design of single mode waveguide for wavelength ranging from the visible up to the infrared but also to fabricate optical components.

White light emission characteristics of Dy³⁺ -doped CaF₂, KPb₂Cl₅ and KPb₂Br₅ are investigated. Absorption, emission and lifetime measurements of these samples are performed to analyze the data. All these materials revealed bright white light under 405 nm diode laser excitation.

CaF₂ is a cubic material and Erbium enters the lattice in triply ionized state. Erbium occupies Ca sites in the material. Defects occur in the material because a trivalent dopant ion replaces a divalent host ion. Er³⁺ occupies several different sites. Absorption spectrum of Er³⁺-doped CaF₂ revealed absorption peaks at 255, 365, 379, 407, 441, 449, 487, 522, 539, 652 and 798 nm. When the sample was excited with an 800 nm near-infrared laser it revealed emissions at 390, 415, 462, 555, 665 and 790 nm. The absorption and emission peaks are identified with Er³⁺ spectral transitions. The sample color appears to be either white or green under near-infrared laser excitation. Emission color was found to be dependent on the pump laser wavelength used and laser power. Excitation spectral recordings were made by tuning the pump laser wavelength. The sample emission appears to be white under near-infrared excitation as well as violet laser excitation. Excited state lifetimes are measured to analyze the data. Our studies indicate that this sample is useful in solid state lighting applications.

Progress in fabrication and mid-IR lasing of Cr and Fe thermal-diffusion and radiation enhanced thermal diffusion doped II-VI binary and ternary polycrystals is reported. We demonstrate novel design of mid-IR Fe:ZnSe and Cr:ZnSe/S solid state lasers with significant improvement of output average power up to 35W@4.1 μm and 57W@2.5 μm and 20W@2.94 μm. We report significantly improved output characteristics of polycrystalline Cr:ZnS/Se lasers in gain-switched regime: 16 mJ at 200 Hz, pulse duration 5 ns with tunability over 2400-3000 nm as well as Kerr-Lens-Mode-Locked regime in terms of average power (up to 2 W), peak power and pulse energy (0.5 MW and 24 nJ, respectively), and pulse duration (less than 29 fs).

Surface plasmon-based nanophotonic devices are advanced in high-sensitivity of wavelength, which can be used to fabricate narrow band color filters. But when SP is excited by grating-coupled structure, the evanescent wave is limited on the interface of metal and dielectric. We design a tunable transmissive filter, consisting of two same sinusoids metal gratings with corresponding substrates and a modulation layer. Herein the dielectric medium is used as the modulation layer and is sandwiched between two metallic gratings. The two metallic gratings are symmetric. If the incident TM wave satisfies the momentum matching condition, the SP excitation at the first metal-dielectric interface will arouse the SP excitation with the same frequency on the second metal-dielectric interface. Then waves with a certain spectrum bandwidth transmit to the far field. The way to tune the selected wavelength is changing the grating period and the distance between two metal gratings in the range of SP penetrating depth. We analyze the influence of the structure profile on the wavelength selectivity. Results show that this novel color filter can realize a continuous shift of transmission peak in the visible range. The transmissivity is higher than 60%. It can be applied to the high resolution display devices to improve the quality of color images.

We demonstrate a Sagnac based fiber optic current sensor using only 10cm of terbium doped fiber with a high Verdet constant of 15.5 rad/Tm at a wavelength of 1300nm. Measurements of the fiber inside a solenoid show over 40dB of open loop dynamic range as well as a minimum detectable current of 0.1mA. In order to decrease size while increasing sensitivity even further, we consider integrated magneto-optic waveguides as the sensing element. Using silicon waveguides alongside magneto-optic material such as cerium doped yttrium iron garnet (Ce:YiG), we model the Verdet constant to be as high as 10,000 rad/Tm. This improvement by three orders of magnitude shows potential for magnetooptic waveguides to be used in ultra-high sensitivity optical magnetometers and current sensors. Finally, we propose a fully integrated optical current sensor using heterogeneous integration for silicon photonics.

Rayleigh scatter in optical fiber communication systems has long been considered a nuisance as a loss mechanism, although applications have used such scatter to probe the fiber for faults and propagation loss using time domain reflectometry (OTDR). It is however only with the development of Frequency domain reflectometry (OFDR) and coherent-phase OTDR that Rayleigh scatter has been probed to its deepest and can now be used to measure strain and temperature along a fiber, leading to the first distributed sensing applications. However, Rayleigh scatter remains very weak giving rise to very small signals which limits the technique for sensing. We show here a new technique to significantly enhance the Rayleigh scatter signal by at least two orders of magnitude, in a standard optical fiber with simple UV exposure of the core. A study of various exposures with different types of fibers has been conducted and a phenomenological description developed. We demonstrate that such an increase in signal can enhance the temperature and strain sensitivity by an order of magnitude for distributed sensing with an OFDR technique. Such improved performance can lead to temperature/strain RMS noise levels of 6 mK and 50 nε for 1 cm spatial resolution in UV exposed SMF-28, compared to the typical noise level of 100 mK for the same spatial resolution in the similar unexposed fiber.

Optical wireless communications (OWC) offers the potential for high-speed and mobile operation in indoor networks. Such OWC systems often employ a fixed transmitter grid and mobile transceivers, with the mobile transceivers carrying out bi-directional communication via active downlinks (ideally with high-speed signal detection) and passive uplinks (ideally with broad angular retroreflection and high-speed modulation). It can be challenging to integrate all of these bidirectional communication capabilities within the mobile transceivers, however, as there is a simultaneous desire for compact packaging. With this in mind, the work presented here introduces a new form of transceiver for bi-directional OWC systems. The transceiver incorporates radial photoconductive switches (for high-speed signal detection) and a spherical retro-modulator (for broad angular retroreflection and high-speed all-optical modulation). All-optical retromodulation are investigated by way of theoretical models and experimental testing, for spherical retro-modulators comprised of three glasses, N-BK7, N-LASF9, and S-LAH79, having differing levels of refraction and nonlinearity. It is found that the spherical retro-modulator comprised of S-LAH79, with a refractive index of n ≈ 2 and a Kerr nonlinear index of n₂ ≈ (1.8 ± 0.1) × 10^-15 cm²/W, yields both broad angular retroreflection (over a solid angle of 2π steradians) and ultrafast modulation (over a duration of 120 fs). Such transceivers can become important elements for all-optical implementations in future bi-directional OWC systems.

The measurement of spectral emittance is a key topic in the study of new compositions, depositions and mechanical machining of materials for solar absorption and for renewable energies. In this work we report on the realization and testing of a new experimental facility for the measurement of directional spectral emittance which provides emittance spectral information in a controlled environment at medium-high temperatures up to 1300 K. The device is composed by a vacuum chamber with electrical heater optically connected with a visible and an FT-IR spectrometer. A split mirror permits to calibrate the system as it directs toward the detector the signal deriving from a calibrated blackbody. A ZnSe window allows to measure normal radiance in 0.6-17 μm spectral range. In this device the first test were carried out comparing the results obtained for HfC and TaB2 ultra-refractory ceramic samples to previous monochromatic measurements performed in a research solar furnace, obtaining a good agreement. Then, in order to confirm the reliability of the acquired spectral emittance curve, we compared it to that calculated from the room temperature spectrum in 2.5-17 μm spectral range, showing a similar spectral trend.

Photo-thermo-refractive (PTR) glass is a multicomponent silicate glass doped with Ce³⁺ and Ag⁺ which is extensively used for holographic recording of volume Bragg gratings (VBGs). Possibility of recording of advanced, complex holograms in the PTR glass is of current interest as it offers great opportunities in imaging and laser systems control. However, the glass does not have capabilities for recording of complex holograms with using light from the visible / IR spectral region due to its UV photosensitivity. Extension of the PTR-glass sensitivity range into the visible / IR spectral region was carried out by doping the original glass with trivalent terbium ions. Photosensitivity mechanism was implemented by means of excited state absorption using a UV photon and a visible photon for excitation of the Tb³⁺ 5d¹4f⁷ band. For the first time refractive index modulation on the order of 2x10^-4 was obtained in PTR glass after exposure to the visible / IR light. Resulting magnitude of induced refractive index allows for high efficiency complex hologram fabrication in Tb³⁺ doped PTR glass for use which in the visible / IR region. Holographic capabilities of Tb³⁺ doped PTR glass were demonstrated by recording a complex hologram in the glass using green and blue light.

For high-speed optical beam scanning, we developed a novel planar optical deflector using KTa1-xNbxO3 (KTN) crystals. When a KTN deflector is operated at high frequencies, heat generated by KTN causes a decrease in its relative dielectric constant, which limits the deflection angle at frequencies above 200 kHz. To overcome this problem, we decreased the thickness of KTN to reduce its capacitance because the heat it generates is proportional to its capacitance. We arranged the two electrodes on the same surface, whereas previously reported structures have each electrode on opposite surfaces. We successfully reduced KTN’s capacitance to 1/30 of that previously reported. The deflection angle of this novel structure at 700 kHz is 16.89 mrad, which is more than half of that at 100 kHz, while the deflection angle of previously reported thick KTN rapidly decreases at more than 200 kHz. The experimental results indicate that our proposed planar optical deflector is effective for suppressing heat generation in KTN and improving the scanning speed of deflectors.

The refractive index distribution in the core-cladding region of an optical fiber plays an important role in determining the transmission and dispersion properties of the waveguide. The refracted near-field technique (RNF) is among the most widespread techniques used for measuring the refractive index profile of optical fibers and is based on illuminating the end-facet of a fiber with a focused beam whose vertex angle greatly exceeds the acceptance angle of the fiber, which is immersed in an index matching liquid. What one observes are then the refracted unguided rays rather than the guided rays. Nevertheless, the standard refracted near-field technique cannot be applied to a wide range of optical fibers e.g. if their shapes are not axially symmetric. In this work we demonstrate a modified method which allows 2-D imaging of the refractive index profile and thereby overcoming the axial symmetric limitation of the standard RNF. The new system is operating at 630 nm and based on the same principle of the RNF, but the optical path is reversed so that the light at the fiber end-facet is collected by an objective lens and detected by a CCD camera. The method does not require scanning over the fiber end-facet. Thus the system is faster and less sensitive to vibrations and external conditions compared to the standard RNF, furthermore it allows averaging to improve the signal to noise ratio. The spatial resolution of the system is determined by the numerical aperture of the objective and by the resolution of the CCD camera. To calibrate the setup, a reference multi-step index fiber provided by National Physical Laboratory was used.

For next-generation long-haul communication systems, space-division multiplexing (SDM) is suggested as a promising technique for providing orders of magnitude increase in transmission capacity. Optical amplifiers for multimode fibers are the crucial components to realize SDM systems, while few-mode fiber (FMF) has the advantage of strong intensity overlap between different modes that allows sharing of single pump across multiple signal modes. FMF-based erbiumdoped fiber amplifiers (FM-EDFA) have been intensively studied. Since SDM is exceedingly reliant on DSP technique and thus has more stringent requirement on noise performance, FMF-based distributed Raman amplifier (FM-DRA) benefits from relatively lower noise figure (NF) compared with FM-EDFA. Yet much less work has been done in this area. To implement FM-DRAs in SDM systems, their performance should be carefully optimized. In this paper, modal gain and saturation characteristics of intermodal Raman amplification in FMFs have been fully investigated by tailoring the refractive-index profiles and doping levels of different FMF designs. For 50-km-long FMF with -3 dBm signal at 1550 nm and a 20-25 dBm pump at 1455 nm, the optimized modal-equalization of Raman gain and NF are provided depending on various fiber cross-section and pumping configuration with respect to modes/wavelengths. The pumpsignal modal-overlap integrals for each of the four mode-groups with normalized frequency V=5 have been exploited, resulting in a mean gain of 10 dB within 1 dB of equalization for 16 gain coefficients. Our results show it should be possible to design FMF with larger intermodal nonlinearity and better dispersion characteristics to achieve desirable Raman gain.

We report here the potential of fiber optical parametric amplification (FOPA) by using highly nonlinear chalcogenide double-cladding fibers. The fibers are designed with an AsSe₂-based core layer surrounded by two cladding layers. The size and the refractive index differences (dn) between the core and cladding are investigated to obtain flattened chromatic dispersion spectra over a wide wavelength range up to the mid-infrared window. The inner cladding with dn₂ is added to suppress the variation of the chromatic dispersion caused by the fluctuation of the core diameter. Our numerical calculations shows that very broad anomalous dispersion ranges from 5.0 μm up to 11.0 μm where the chromatic dispersion is less than 10 ps/km-nm can be obtained when the core diameter varies from 2.0 to 9.0 μm and the inner cladding diameter is kept at 9.0 μm. The dn₁ and dn₂ are 0.30 and 0.02, respectively. The FOPA calculation is carried out using a 3-cm-long fiber whose core diameter is 3 μm. When the pump power is 3 W at 5320 nm, a very broad gain bandwidth is obtained from 3.3 up to 11 μm. Moreover, the gain spectrum is flattened (about 32 ± 1 dB) in the ranges from 3.3 to 4.1 μm and from 7.5 up to 11.0 μm. When the core diameter fluctuates from 2.0 to 5.0 μm, the FOPA gain spectra can be maintained.

We successfully synthesized Er³⁺/Yb³⁺ co-doped KY₃F₁₀ nanocrystals by a facile hydrothermal method. The average size of the as-prepared nanocrystals was about 60 nm based on the observation of scanning electron microscope. Under the excitation of a 976 nm laser, the Er³⁺/Yb³⁺ doped KY₃F₁₀ nanocrystals showed intense near-infrared emission band centered at 1539 nm. The optimal concentrations of Er³⁺ were carefully selected according to the quantum yield measurement for a stronger emission in the C-band. The as-prepared nanocrystals were dispersed into a monomer, bisphenol A ethoxylate diacrylates, in which self-written waveguides can be fabricated under the irradiation of an induced laser at 450 nm. The KY₃F₁₀: Er³⁺/Yb³⁺ nanocrystals embedded polymer waveguide were fabricated by laser-induced self-written technique. Two pieces of single mode fiber were well connected with the waveguide in the fabrication procedure. Under a 976 nm laser pumping, amplified spontaneous emission at 1539 nm was observed in the KY₃F₁₀: Er³⁺/Yb³⁺ nanocrystals doped waveguide.

We report on the performance of an eye-safe laser based on a Er:YVO₄ single crystal, diode-pumped at 976 nm (⁴I_15/2→⁴I_11/2 transition) and operating at 1603 nm (⁴I_13/2→⁴I_15/2 transition) with good beam quality. A 10 mm long Er^3+:YVO₄ slab, cut with its c-axis perpendicular to the laser cavity axis, was pumped in σ-polarization and lased in π-polarization. The laser operated in a quasi-continuous wave (Q-CW) regime with nearly 9 W output power, and with a slope efficiency of about 39% with respect to absorbed power. This is believed to be the highest efficiency and highest power achieved from an Er³⁺:YVO₄ laser pumped in the 970-980 nm absorption band.

A key challenge for silicon photonic systems is the development of compact on-chip light sources. Thulium-doped fiber and waveguide lasers have recently generated interest for their highly efficient emission around 1.8 μm, a wavelength range also of growing interest to silicon-chip based systems. Here, we report on highly compact and low-threshold thulium-doped microcavity lasers integrated with silicon-compatible silicon nitride bus waveguides. The 200-μmdiameter thulium microlasers are enabled by a novel high quality-factor (Q-factor) design, which includes two silicon nitride layers and a silicon dioxide trench filled with thulium-doped aluminum oxide. Similar, passive (undoped) microcavity structures exhibit Q-factors as high as 5.7 × 10⁵ at 1550 nm. We show lasing around 1.8–1.9 μm in aluminum oxide microcavities doped with 2.5 × 1020 cm⁻³ thulium concentration and under resonant pumping around 1.6 μm. At optimized microcavity-waveguide gap, we observe laser thresholds as low as 773 μW and slope efficiencies as high as 23.5%. The entire fabrication process, including back-end deposition of the gain medium, is silicon-compatible and allows for co-integration with other silicon-based photonic devices for applications such as communications and sensing.

In this paper we present results of photoluminescence (PL), photoluminescence excitation (PLE), and time resolved PL spectroscopy of the ⁴I_13/2 → ⁴I_15/2 transition in Er optical centers in GaN epilayers grown by metal-organic chemical vapor deposition. Under resonance excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, the PL and PLE spectra reveal an existence of two types of Er optical centers from isolated and the defect-related Er centers in GaN epilayers. These centers have different PL spectra, local defect environments, decay dynamics, and excitation cross-sections. The isolated Er optical center, which can be excited by either excitation mechanism, has the same decay dynamics, but possesses a much higher cross-section under band-to-band excitation. In contrast, the defect-related Er center can only be observed through band-to-band excitation but has the largest crosssection. Our results indicate pathways for efficient optical excitation of Er-doped GaN semiconductors.

Generation of near-infrared light within the first biological optical window via frequency upconversion in Tm³⁺-doped PbGeO₃-PbF₂-CdF₂ glass excited within the second biological window at 1.319 μm is reported. The upconversion emission at 800 nm is the sole light signal observed in the entire UV-VIS-NIR spectral region making possible obtaining high contrast imaging. The dependence of the 800 nm signal upon the sample temperature was investigated and results showed an increase by a factor of x2.5 in the 30°C - 280°C range. Generation of detectable 690 nm for temperatures above 100°C in addition to the intense 800 nm main signal was also observed. The proposed excitation mechanism for the 800 nm thulium emitting level is assigned to a multiphonon-assisted excitation from the ground-state ³H₆ to the ³H₅ excited-state level, a rapid relaxation to the ³F₄ level and followed by an excited-state absorption of the pump photons mediated by multiphonons connecting the ³F₄ level to the ³H₄ emitting level.

We present the theoretical analysis and design of a novel slotted photonic crystal geometry to demonstrate an on-chip Fano resonance. The device employs three parallel-coupled slotted photonic crystal cavities on an SOI wafer. We present a systematic analysis of the evolution of the Fano line-shape, while the geometric parameters of the structure and the inter-cavity distances vary. To achieve the dynamic tunability of the Fano resonance, we have considered an active electro-optic chromophore as the cover material of our slot-based geometry. This paves a novel way towards the demonstration of a fully-integrated, electrically-controllable Fano resonant geometry on a silicon-polymer platform.

We present a linear all-fiber device exhibiting the functionality of a circulator, albeit for multimode fibers. We define a pseudo-circulator as a linear three-port component that transfers most of a multimode light signal from Port 1 to Port 2, and from Port 2 to Port 3. Unlike a traditional circulator which depends on a nonlinear phenomenon to achieve a non-reciprocal behavior, our device is a linear component that seemingly breaks the principle of reciprocity by exploiting the variations of etendue of the multimode fibers in the coupler. The pseudo-circulator is implemented as a 2x2 asymmetric multimode fiber coupler, fabricated using the fusion-tapering technique. The coupler is asymmetric in its transverse fused section. The two multimode fibers differ in area, thus favoring the transfer of light from the smaller to the bigger fiber. The desired difference of area is obtained by tapering one of the fiber before the fusion process. Using this technique, we have successfully fabricated a pseudo-circulator surpassing in efficiency a 50/50 beam-splitter. In all the visible and near-IR spectrum, the transmission ratio exceeds 77% from Port 1 to Port 2, and 80% from Port 2 to Port 3. The excess loss is less than 0.5 dB, regardless of the entry port.

In this work we successfully fabricated and measured PhCs patterned on a LiNbO₃ APE waveguide. SIMS data indicate that after 5 hours exchange time a PE layer of 3μm can be obtained. The depth of holes was 2μm by applying a large milling current. We presented experimental characterization of the PhC waveguide and a well-defined PBG was observed from the transmission spectra. An extinction ratio was estimated to be approximately 15dB. Optical transmission results indicate that deep air holes can lead to a sharp band edge. This PhC waveguide is a good candidate for further development of an ultra-compact, low-voltage LiNbO₃ modulator.

We report the coherent mid-infrared supercontinuum generation in an all-solid chalcogenide microstructured fiber with all-normal dispersion. The chalcogenide microstructured fiber is four-hole structure with core material of AsSe₂ and air holes are replaced by As₂S₅ glass rods. Coherent mid-infrared supercontinuum light is generated in a 2-cm-long chalcogenide microstructured fiber pumped by a 2.7 μm laser. The simulated and experimental results have a good match and the coherence property of supercontinuum light in the chalcogenide microstructured fiber has been studied by using the complex degree of coherence theory. Coherent mid-infrared supercontinuum generation is extended to 3.3 μm in this work.

Based on a suspended core birefringent tellurite microstructured optical fiber (BTMOF), the supercontinuum (SC) spectra are generated by pumping near the zero dispersion wavelengths (ZDWs) in the telecommunication band with a tunable picosecond fiber laser. The ZDWs of the suspended core BTMOF are calculated to be 1560 nm and 1532 nm for the X-axis and Y-axis, respectively. When the pump is polarized along the X-axis, the SC broadening is governed by the nonlinear effects of four-wave mixing (FWM), cross-phase modulation (XPM) and stimulated Raman scattering (SRS). When the pump is polarized along the Y-axis, the SC generation is governed by the nonlinear effects of SRS.

We demonstrated the waveguide photodetector (WG PD) integrated with spot-size converter (SSC) for coherent receiver of 100Gb/s operation. The WG PD integrated with SSC was designed as diluted WG, dual lateral taper structure, and PIN-photodiode. The epitaxial layers of In_xGa_1-xAs_yP_1-y/InP, In_xGa_1-xAs_yP_1-y, and InGaAs were adopted as the diluted WG, dual tapers, and absorber of PD, respectively. The shape and thickness of each structure were determined through the simulation of 3D finite-difference beam propagation method. Although the evanescent coupling was highly sensitive, we optimized the structures with simulated responsivity and polarization dependent loss (PDL) as 0.70 A/W and 0.1 dB, respectively. We successfully obtained the SSC-integrated WG PD through numerous fabrication process including photolithography. The electrical and optical properties were characterized with laser launching. Fabricated PDs had almost similar responsivity and PDL with the simulation results. The responsivity and PDL were measured as 0.7 A/W and less than 0.3 dB respectively. The 3 dB-bandwidth was measured as 34 GHz. We successfully realized low PDL and high responsivity by adopting the lateral taper structure for SSC-integrated WG PD.

This paper presents the performance analysis of a freeform lens that can be used as a first or secondary optic when combined with a point or an extended light source. The light source can be an LED. The purpose of the optic is to increase uniformity of illumination within the footprint. The analysis is performed on the freeform lens when combined with: (i) an isotopic or a Lambertian point light source (ii) an isotropic or a Lambertian extended light source. This paper shows that through a design based on energy mapping between a light source and a target plane it is possible to achieve uniform illumination. The ZEMAX ray tracing simulation shows that the uniformity reduces gradually when the size of the light source increases. The results indicate that a freeform lens combined with a point source can generate over 95% uniformity.

This work is novel in that it explains the modeling and simulation of a thulium-doped fiber amplifier (TDFA) in a reconfigurable wavelength division multiplexing (WDM) system operating at 2 μm. We use the optical gain-clamping technique in order to control gain amplification and eliminate deleterious channel power fluctuations resulting from input power variation at the TDFA. The investigated system consists of 12 channels with -4 dBm total input power. Simulation results indicate that approximately1.5dB power excursion is produced after dropping 11 channels in unclamped-gain amplifier, and only 0.005 dB in a clamped-gain amplifier. Additionally, a clamped configuration brings the power excursion from 4.2 dB to under 0.08 dB, after adding 11 channels to the investigated system. Hence, optical gainclamping is a simple and robust technique for controlling the power transient in amplifiers at 2 μm.

The novel property of the mid-infrared (MIR) higher-order soliton fission in a tapered tellurite microstructured optical fiber (TMOF) is experimentally investigated. The TMOF is tapered to offer an ideal environment for the formation of optical solitons. From ∼30 to 80 mW, the redshift of the first fundamental soliton (SSFS) is obvious. From ∼80 to 120 mW, two fundamental solitons are obtained by the fission of the higher-order solitons. The redshift of the first fundamental soliton almost stops because the increased pump power is preferentially distributed to the second fundamental soliton. From ∼120 to 180 mW, obvious redshift of the first fundamental soliton is observed again, and a third fundamental soliton is obtained at ∼180 mW. With the average pump power increasing to ∼220 mW, five fundamental solitons are observed.

Multispectral and hyperspectral imaging in the long wave infrared (LWIR) spectral region has numerous applications in agriculture, astronomy^20-22, medicine, and the sensing of dangerous chemical/biological agents^23-25. One of the challenges of developing a spectral imaging system in the LWIR is the availability of spectral filters. We will report on three different design methods for realizing spectral filters in the LWIR. The first is an all-dielectric reflection filter based on the guidedmode resonance response. The second is a spatially-varying plasmonic structure that can be used to synthesize complicated spectral reflectance. The third is a Fabry-Perot design for tunable transmission. Numerical and experimental results will be presented.

CMOS logic circuits have entered the sub-100nm regime, and research is on-going to investigate the quantum effects that are apparent at this dimension. To avoid some of the constraints imposed by fabrication, entropy, energy, and interference considerations for nano-scale devices, many have begun designing hybrid and/or photonic integrated circuits. These circuits consist of transistors, light emitters, photodetectors, and electrical and optical waveguides. As attenuation is a limiting factor in any communications system, it is advantageous to integrate a signal amplifier. There are numerous examples of electrical amplifiers, but in order to take advantage of the benefits provided by optically integrated systems, optical amplifiers are necessary. The erbium doped fiber amplifier is an example of an optical amplifier which is commercially available now, but the distance between the amplifier and the device benefitting from amplification can be decreased and provide greater functionality by providing local, on-chip amplification. Zinc oxide is an attractive material due to its electrical and optical properties. Its wide bandgap (≈3.4 eV) and high refractive index (≈2) make it an excellent choice for integrated optics systems. Moreover, erbium doped zinc oxide (Er:ZnO) is a suitable candidate for optical waveguide amplifiers because of its compatibility with semiconductor processing technology, 1.54 μm luminescence, transparency, low resistivity, and amplification characteristics. This research presents the characterization of radio frequency magnetron sputtered Er:ZnO, the design and fabrication of integrated waveguide amplifiers, and device analysis.

Recently, double-clad crystalline fiber waveguides (CFWs), consisting of single crystalline or ceramic RE³⁺:YAG cores of square cross section and inner claddings of either undoped or laser-inactive-ion-doped YAG and outer claddings of sapphire, have been successfully demonstrated. These waveguides, manufactured by an Adhesive-Free Bonding (AFB®) technique, can be precisely engineered and fabricated with predictable beam propagation behavior. In this work, with high power laser designs in mind, minimum thicknesses for inner cladding are derived for different core cross sections and refractive index differences between the core and inner cladding and sapphire as outer cladding material for common laser core dopants such as Nd³⁺, Yb³⁺, Er³⁺, Tm³⁺ and Ho³⁺. All designs are intended to use high NA high power laser diode pumping to obtain high power intrinsically single transverse mode laser output. The obtained data are applicable to any crystalline fiber waveguide design, regardless of fabrication technique. As an example, a CFW with 40 μm × 40 μm 4% Tm:YAG core, 5% Yb:YAG inner cladding, and sapphire outer cladding was calculated to be intrinsically single transverse mode, with the minimum inner cladding width of 21.7 μm determined by the effective index technique [1].

Power scaling analysis based on the model by Dawson et al. [1,2] for circular core fibers has been applied to estimating power scaling of crystalline fiber waveguides (CFWs) with RE³⁺ doped single crystalline or ceramic YAG (RE=rare earth: Yb, Er, Tm and Ho). Power scaling limits include stimulated Brillouin scattering, thermal lensing effect, and limits to coupling of pump light into CFWs. The CFW designs we have considered consist, in general, of a square doped RE³⁺:YAG core, an inner cladding of either undoped or laser-inactive-ion-doped YAG and an outer cladding of sapphire. The presented data have been developed for the structures fabricated using the Adhesive-Free Bonding (AFB®) technique, but the results should be essentially independent of fabrication technique, assuming perfect core/inner cladding/outer cladding interfaces. Hard power scaling limits exist for a specific CFW design and are strongly based on the physical constants of the material and its spectroscopic specifics. For example, power scaling limit was determined as ~16 kW for 2.5% ceramic Yb:YAG/YAG (core material/inner cladding material) at fiber length of 1.7 m and core diameter of 69 μm. Considering the present manufacturing limit for CFW length to be, e.g., 0.5 m, the actual maximum output power will be limited to ~4.4 kW for a Yb:YAG/YAG CFW. Power limit estimates have also been computed for Er³⁺, Tm³⁺ and Ho³⁺doped core based CFWs.

In this work, we present an electro-optical modulator based on electromagnetically induced transparency (EIT). Our modulator employs a conductor-gap-silicon (CGS) microring resonator on each side of the input waveguide in a pushpull configuration utilizing an embedded electro-optical polymer (EOP). CGS waveguides support hybrid plasmonic modes offering a sound trade-off between mode confinement and propagation loss. The modulator is designed and analyzed using 3D finite difference time domain (FDTD) simulations. To have a high quality resonator, the rings are designed to have moderate waveguide propagation losses and a sub-micron radius of R = 805 nm. With an exact capacitance of just 1.06 fF per single microring resonator and applied voltage of 2 V, the exact energy consumption is estimated to be 4.24 fJ/bit. To the best of our knowledge, this figure represents 40% less power consumption in comparison with different modulators structures. The ultra-small capacitance of the proposed modulator and the instantaneous response of the used polymer make our design suitable for high bit rate applications. At the wavelength of -1550 nm-, the insertion loss is 0.34 dB and the extinction ratio is 10.23 dB.

Our work is devoted to the collinear acousto-optical filter governed by the acoustic waves of finite amplitude. It represents a novel bulk-optical component, namely, the dispersive element for optical spectroscopy. This filter is based on specifically doped lithium niobate single crystal that unexpectedly works in the near ultraviolet range as well as this material usually works in the visible range. We examine the phenomena affecting the filter transmission efficiency and its resolution, i.e. the light-induced absorption and photorefraction. A new nonlinear approach is used to characterize performances of this collinear LiNbO3 acousto-optical filter exploiting our revealed specific acousto-optical nonlinearity. We have carried out the experiments with the collinear filter based on the congruent LiNbO₃ crystal of 6.3 cm length at λ = 405 and 440 nm to verify our analysis and estimations. We also explore an opportunity to trade an amount of the efficiency to improve the spectral resolution. The transmission efficiency steeply increases with increasing light wavelength and with decreasing length of the filter, nevertheless the efficiency still remains higher than 30% in the near ultraviolet, if the spectral resolution is limited by δλ = 0.28–0.29 Å. Moreover, we demonstrate the possibility to reach a resolution as high as δλ = 0.12–0.15 Å (R > 24600), preserving at the same time an efficiency higher than 10% over the spectral interval that we considered. It looks like our filter holds the best to our knowledge experimentally confirmed spectral resolution for any collinear acousto-optical spectrometers dedicated to space/airborne operations.