Design of an omnidirectional mirror using one dimensional photonic crystal with graded geometric layers thicknesses

We propose a flexible design for one-dimensional photonic crystals (1D-PCs) with a controllable omnidirectional band gap covering the optical telecommunication wavelengths which are 0.85 μm, 1.3 μm and 1.55 μm. We used for this design the chirped grating. Chirping is applied to geometric thicknesses of layers. It takes two forms, one is linear and the other is exponential. We exploit this technique to have the suitable omnidirectional band gap covering the maximum of optical telecommunication wavelengths. With a quarter wave structure, we can have an omnidirectional band gap generating only one of these wavelengths. With graded structure, we obtain, as is reported in this paper, an omnidirectional band gap which covers the wavelengths 1.3 μm and 1.55 μm at the same time with a large bandwidth. We also achieve an omnidirectional band gap containing the wavelength 0.85 μm and which is obviously larger than that of the quarter wave stack.     

Real-space observation of photonic nanojet in dielectric microspheres

The three-dimensional real-space observation of photonic nanojet in different microspheres illuminated by a laser is reported. The finite-difference time-domain technique is used to perform the three-dimensional numerical simulation for the dielectric microspheres. The key parameters of photonic nanojet are measured by using a scanning optical microscope system. We reconstruct the three-dimensional real-space photonic nanojets from the collected stack of scanning images for polystyrene microspheres of 3 μm, 5 μm, and 8 μm diameters deposited on a glass substrate. Experimental results are compared to calculations and are found in good agreement with simulation results. The full width at half-maximum of the nanojet is 331 nm for a 3 μm microsphere at an incident wavelength of 633 nm. Our investigations show that photonic nanojets can be efficiently imaged by a microsphere and straightforwardly extended to rapidly distinguish the nano-objects in the far-field optical system.     

Ultrasmall optical logic gates based on silicon periodic dielectric waveguides

An ultrasmall silicon periodic dielectric waveguides-based multimode interference all-optical logic gate has been proposed. The device consists of three 205 nm wide single-mode input waveguides, a 1.1 μm wide and 5.5 μm long multimode interference waveguide, and three 205 nm wide single-mode output waveguides. The total length and width of the device are 13.7 μm and 3.2 μm, respectively. By changing the states of the input optical signals and/or control signals launched into the device, multifunctional logic functions including OR, NAND, NOR, and NOT gates are performed, and each logic function can be realized at a specific output waveguide in accordance with the launched control signals. The ultrasmall multifunctional logic device has potential applications in high density photonic integrated circuits.     

Low-threshold all-fiber 1000 nm supercontinuum source based on highly non-linear fiber

We present an highly efficient all-fiber compact supercontinuum source that exhibits a nearly flat spectrum from 1.1 μm to 2.1 μm. This broadband infrared optical source is made-up of a highly non-linear fiber pumped by a 1.55 μm self-Q-switched Er-Brillouin nanosecond pulsed fiber laser, which in turn is pumped by a low-power 1480 nm laser diode. In this work we highlight the great potential of highly non-linear fiber for supercontinuum generation with respect to conventional dispersion-shifted fiber by demonstrating a significant 10 dB power enhancement in the short wavelength side of the supercontinuum.     

Wavelength conversion based on high nonlinear microstructured fiber

A wavelength conversion based on high nonlinear microstructured fiber is demonstrated. Core diameter and pitch of the microstructured fiber used in this wavelength conversion method are 2.05 μm and 5.0 μm, respectively. Diameter of the air-holes in the fiber cladding is 4.50 μm, the nonlinear coefficient of the microstructured fiber is 112.2 W^?1 km^?1 and it is 60 times higher than that of a conventional dispersion-shift fiber, the length of the fiber is 100 m. Four-wave-mixing effect is improved in the high nonlinear microstructure fiber and then the efficiency of the wavelength conversion is improved also. 10 Gbps Not-Return-to-Zero (NRZ) modulation format and 10 Gbps Return-to-Zero (RZ) modulation format are converted effectively by our method. This study can provide a new alternative solution for high effective all-light wavelength conversion in high speed optical communication systems with multi-wavelengths and all-light optical networks.     

Influence of the antireflection,window, and active layers on optical properties of exponential-doping transmission-mode GaAs photocathode modules

In order to well study the influence of the thickness and doping concentration on optical properties of transmission-mode GaAs photocathode, three exponential-doping and one uniform-doping photocathode modules were prepared by molecular beam epitaxy with a structure of glass/Si₃N₄/Ga_1 ? xAl_xAs/GaAs. By use of the spectrophotometer, the optical properties were separately measured including the reflectivity and transmissivity curves. Based on thin film optical principles, the optical properties and their integral values are calculated by matrix formula for the four-layer photocathode module. The result shows that the antireflection and window layers affect the peak and valley of the optical property curves and the active layer influences the absorptivity values of the transmission-mode cathode modules. The photocathode module has high absorptivity within the response waveband when the optimal module has the Si₃N₄ antireflection layer of 0.1 μm, the Ga_1 ? xAl_xAs window layer of more than 0.4 μm, and the GaAs active layer of 1.5 μm–2 μm and low average doping concentration.     

Spectral characteristics of polymer micro-fiber MZI near 1550 nm

The authors have produced the polymer micro-fiber with a highly optical conductive efficiency of 83% and 89% for the pump light of 532 nm and 1550 nm, respectively. The authors constructed a Mach–Zehnder Interferometer (MZI) by a micro-manipulation method and measured the different interference spectra by micro-adjusting the path difference of the dual interference arms of MZI under a microscope. Due to the path difference, the coherent length of the corresponding spectrum continuously and slightly decreases from 20 μm, 13.5 μm, 10.6 μm to 8 μm. The relationships between this particular MZI structure and the surrounding temperature, as well as the refractive index changes can be determined via the evanescent field and the thermally induced expansion or contraction effect, which will be reflected in the interference spectrum.     

Compact WDM demultiplexer for seven channels in photonic crystal

We demonstrate a new device concept for wavelength division demultiplexing based on planar photonic crystal waveguides. The filtering of wavelength channels is realized by shifting the cutoff frequency of the fundamental photonic bandgap mode in consecutive sections of the waveguide. The shift is realized by modifying the size of the border holes.The proposed demultiplexer has an area equal to (16.5 μm × 6.5 μm) and thus it is verified that this structure is very small and can be integrated easily into optical integrated circuits with nanophotonic technologies. The output wavelengths of designed structure can be tuned for communication applications, around 1550 nm. The wavelengths of demultiplexer channels are λ₁ = 1.590 μm, λ₂ = 1.566 μm, λ₃ = 1.525 μm, λ₄ = 1.510 μm, λ₅ = 1.484 μm, λ₆ = 1.450 μm, λ₇ = 1.400 μm respectively. Designs offering improvement of number of the separate wavelengths (seven), miniaturization of the structure (107.25 μm²) is our aim in this work.In our structure, we consider that the 2D triangular lattice photonic crystal is composed of air holes surrounded by dielectric. Its parameters are: radius of holes (r = 0.130 μm), lattice constant (a = 0.380 μm), and index of membrane (n = 3.181:InP). The numerical model used to simulate the structure of the demultiplexer is based on the finite difference time domain (FDTD).     

High energy femtosecond OPA pumped by 1030 nm Yb:KGW laser.

We present a traveling-wave-type optical parametric amplifier (OPA) pumped at 1.03 μm by a Yb:KGW laser that produces tunable high-energy pulses of 6.5–4 μJ in the mid-infrared (mid-IR) region from 3.6 to 7 μm. Pumping with negatively chirped pulses generates nearly transform-limited (TL) mid-IR pulses of 300–330 fs length. Pumping with TL pulses of 200 fs not only decreases the output energy by a factor of 1.5, but also decreases the mid-IR pulse-length to 160 fs after additional compression. The compact and simple OPA setup is ideal for femtosecond infrared experiments in the fingerprint region.     

10.6 μm Infrared light photoinduced insulator-to-metal transition in vanadium dioxide

Vanadium dioxide has excellent phase transition characteristic. Before or after phase transition, its optical, electrical, magnetic characteristic hangs hugely. It has a wide application prospect in many areas. Now, the light which can make vanadium dioxide come to pass photoinduced phase transition range from soft X-ray to medium infrared light (6.9 μm, 180 meV). However, whether 10.6 μm (117 meV) long wave infrared light can make vanadium dioxide generate photoinduced phase transition has been not studied. In this paper, we researched the response characteristic of vanadium dioxide excited by 10.6 μm infrared light. We prepared the vanadium dioxide and test the changes of vanadium dioxide thin film’s transmittance to 632.8 nm infrared light when the thin film is irradiate by CO₂ laser. We also test the resistivity of vanadium dioxide. Excluding the effect of thermal induced phase transition, we find that the transmittance of vanadium dioxide thin film to 632.8 nm light and resistivity both changes when irradiating by 10.6 μm laser. This indicates that 10.6 μm infrared light can make the vanadium dioxide come to pass photoinduced phase transition. The finding makes vanadium has a potential application in recording the long-wave infrared hologram and making infrared detector with high resolution.     

Quadratic detection with two-photon quantum well infrared photodetectors

Two-photon quantum well infrared photodetectors (QWIPs) involving three equidistant subbands take advantage of a resonantly enhanced optical nonlinearity, which is six orders of magnitude stronger than in a bulk semiconductor. This approach results in a sensitive device to measure quadratic autocorrelation of mid-infrared optical pulses from modelocked quantum cascade lasers, nonlinear optical conversion, and free-electron lasers (FEL). We report on autocorrelation measurements at wavelengths in the mid-infrared and Terahertz regimes using ps optical pulses from the FEL at the Forschungszentrum Dresden Rossendorf. In particular, quadratic detection at wavelengths around 5.5 μm is still possible at room-temperature, which is crucial for applications in practical systems. We also report on a two-photon detector which works below the Reststrahlen band at 42 μm (7.1 THz).     

Mid-wave QWIPs for the [3–4.2 μm] atmospheric window

We report two approaches using Quantum Well Infrared Photodetectors for detection in the [3–4.2 μm] atmospheric window. Taking advantage of the large band gap discontinuity we demonstrated a strained AlInAs/InGaAs heterostructure on InP. The optical coupling in this structure has been experimentally and numerically investigated. The results show that the coupling is mainly due to guided modes. The second approach is based on double barrier strained AlGaAs/AlAs/GaAs/InGaAs active layers on GaAs. The segregation of the elements III in these structures has been investigated using a transmission electron microscope. The results show a strong modification of the conduction band profile. We demonstrate peak wavelengths at 3.9 μm for the InP based detector and 4.0 μm for the GaAs based detector. We report a background limited peak detectivity (2π field of view, 300 K background) at 4.0 μm of about 2 × 10¹¹ cm Hz^1/2 W^?1 at 77 K, and 1.5 × 10¹¹ cm Hz^1/2 W^?1 at 100 K.     

Single-mode fiber design proposal using evolutionary technique with ultra low bending-loss appropriate in FTTH application

A proposal for the new single mode optical fiber containing four cladding layer with ultra low bending loss is presented. The suggested design method is based on the Genetic Algorithm optimization technique. Compared to the work reported in [1], our designed structure exhibits very small bending loss over the wide communication band (1.3–1.65 μm). Simulation results show bending loss of 6.78e?14 dB/turn at 1.55 μm for single turn of 5 mm radius. The best value reported in [1] was 2e?3 dB/turn for the same wavelength and radius of curvature.     

High power Nd:YAG lasers operating at 1.3 μm wave band

The laser properties of 1.3 μm spectral region in Nd:YAG crystal and their simultaneous dual wavelength threshold condition are investigated. Three types of high power 1.3-μm Nd:YAG quasi continuous wave (QCW) lasers, which operate at 1.319 μm or 1.338 μm single wavelength, 1.319 μm and 1.338 μm simultaneous dual wavelength, are achieved with a maximum average output power of 138 W, 132 W and 120 W, respectively.     

Crystallographic orientation-dependent optical properties of GaInSb mid-infrared quantum well laser

The optical properties of compressively strained GaInSb/GaInAlSb quantum well (QW) laser are numerically studied in different crystal orientations solving envelope function equation using finite difference method. The simulation results demonstrate that there is a strong correlation between the optical gain and its emission wavelength with crystal orientation of the QW. The maximum and minimum optical gains are evaluated in the (1 1 3) and (1 1 1) crystal orientations, respectively, due to band mixing effects. The peak emission wavelength can be tuned from 2.4 μm to 2.25 μm by changing the crystal orientation from (1 1 0) to (1 1 1). Typical optical gains are evaluated 3115, 3080, 2790, 3415, and 2940 cm^?1 in (0 0 1), (1 1 0), (1 1 1), (1 1 3), and (1 3 1) crystal orientations, respectively, when the injection carrier density is 3.5 × 10¹⁸ cm^?3. The highest optical power and lower threshold current are obtained in (1 1 3) orientation for the number of quantum wells three.     

Cleaving of TOPAS and PMMA microstructured polymer optical fibers: Core-shift and statistical quality optimization

We fabricated an electronically controlled polymer optical fiber cleaver, which uses a razor-blade guillotine and provides independent control of fiber temperature, blade temperature, and cleaving speed. To determine the optimum cleaving conditions of microstructured polymer optical fibers (mPOFs) with hexagonal hole structures we developed a program for cleaving quality optimization, which reads in a microscope image of the fiber end-facet and determines the core-shift and the statistics of the hole diameter, hole-to-hole pitch, hole ellipticity, and direction of major ellipse axis. For 125 μm in diameter mPOFs of the standard polymer PMMA we found the optimum temperatures to be 77.5 °C for both blade and fiber. For 280 μm in diameter mPOFs of the humidity insensitive polymer TOPAS® (grade 8007) the optimum temperature was 40° for both blade and fiber. A 100 μm thick flat-edge blade was found to minimize the core-shift by the cleaving to only 298 nm or 5% of the pitch for the PMMA mPOF at the optimal temperature.     

Nonlinear optics in glasses: How can we analyze?

Maximal optical nonlinearity obtainable in amorphous materials at telecommunication wavelengths of ∼1.5 μm is predicted. Applying a semiconductor concept, we suggest that nonlinear properties become greater in the materials with smaller optical gaps. This trend makes the chalcogenide glass such as As₂Se₃ promising for fiber devices (∼1 m), including optical switches, intensity stabilizers, and stimulated Raman amplifiers. However, for integrated devices with optical path lengths of ∼1 cm, greater nonlinearity is needed.     

Development of an efficient coherent optical source at 6.04 μm

Efficiency as high as 26% is obtained for generation of mid-infrared radiation at 6.04 μm by frequency doubling of ammonia laser emission at 12.08 μm in a 15 mm long type-I cut AgGaSe₂ crystal. The NH₃ laser used for this work is optically pumped by a commercial TEA CO₂ laser operating on 9.22 μm and produces pulsed output of ∼210 mJ with a duration of ∼200 ns at 12.08 μm. The generated radiation at 6.04 μm is separated out from the residual radiation at 12.08 μm by exploiting the principle of polarization dependent diffraction of reflection grating.     

Picosecond laser cutting and drilling of thin flex glass

We investigate the feasibility of cutting and drilling thin flex glass (TFG) substrates using a picosecond laser operating at wavelengths of 1030 nm, 515 nm and 343 nm. 50 μm and 100 μm thick AF32^®Eco Thin Glass (Schott AG) sheets are used. The laser processing parameters such as the wavelength, pulse energy, pulse repetition frequency, scan speed and the number of laser passes which are necessary to perform through a cut or to drill a borehole in the TFG substrate are studied in detail. Our results show that the highest effective cutting speeds (220 mm/s for a 50 μm thick TFG substrate and 74 mm/s for a 100 μm thick TFG substrate) are obtained with the 1030 nm wavelength, whereas the 343 nm wavelength provides the best quality cuts. The 515 nm wavelength, meanwhile, can be used to provide relatively good laser cut quality with heat affected zones (HAZ) of <25 μm for 50 μm TFG and <40 μm for 100 μm TFG with cutting speeds of 100 mm/s and 28.5 mm/s, respectively. The 343 nm and 515 nm wavelengths can also be used for drilling micro-holes (with inlet diameters of ⩽75 µm) in the 100 μm TFG substrate with speeds of up to 2 holes per second (using 343 nm) and 8 holes per second (using 515 nm). Optical microscope and SEM images of the cuts and micro-holes are presented.     

A tunable and single-longitudinal-mode Ho:YLF laser

A 1.94 μm Tm-doped fiber laser pumped tunable single-longitudinal-mode Ho:YLF laser with double etalons was reported for the first time. The maximum single-longitudinal-mode output power of 345 mW at 2051.6 nm was achieved at the absorbed pump power of 11.9 W, corresponding to a slope efficiency of 5.5% and an optical conversion efficiency of 2.9%. By regulating the angle of the F–P etalons, the output wavelength of the laser can be tuned from 2051.6 nm to 2063.3 nm. The single-longitude-mode Ho:YLF laser operating at 2 μm can be used as the seed laser source of coherent Doppler lidar, differential absorption lidar and so on.