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.     

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.     

Resonant detectors and focal plane arrays for infrared detection

We are developing resonator-QWIPs for narrowband and broadband long wavelength infrared detection. Detector pixels with 25 μm and 30 μm pitches were hybridized to fanout circuits and readout integrated electronics for radiometric measurements. With a low to moderate doping of 0.2–0.5 × 10¹⁸ cm⁻³ and a thin active layer thickness of 0.6–1.3 μm, we achieved a quantum efficiency between 25 and 37% and a conversion efficiency between of 15 and 20%. The temperature at which photocurrent equals dark current is about 65 K under F/2 optics for a cutoff wavelength up to 11 μm. The NEΔT of the FPAs is estimated to be 20 mK at 2 ms integration time and 60 K operating temperature. This good performance confirms the advantages of the resonator-QWIP approach.     

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.     

4 × 10 Gb/s wavelength multicasting with tunable NRZ-to-RZ pulse format conversion using time- and wavelength-interleaved pulses

We demonstrate 4 × 10 Gb/s simultaneous wavelength multicasting and NRZ-to-RZ pulse format conversion with tunable duty cycle. Multicasting is achieved by four-wave mixing of the input signal with a time- and wavelength-interleaved laser source, while the format conversion is obtained through the use of a pulsed probe. The input data are copied to four multicast outputs with a common relative delay time. Error-free operations have been obtained in all the outputs with power penalties ranging from ? 0.5 to 0.5 dB. Output duty cycles with a tuning range of 4.3 ps have been achieved.     

Tunable single-longitudinal-mode operation of a sandwich-type YAG/Ho:YAG/YAG ceramic laser

We present a 2.09 μm single-longitudinal-mode sandwich-type YAG/Ho:YAG/YAG ceramic laser pumped by a Tm-doped fiber laser for the first time. A pair of F-P etalons was used to achieve tunable single-longitudinal-mode operation. The maximum single-longitudinal-mode output power of 530 mW at 2091.4 nm was obtained with an absorbed pump power of 8.06 W, corresponding to an optical conversion efficiency of 6.6% and a slope efficiency of 12.7%. Wavelength tunable was achieved by tuning the angle of etalons and the wavelength could be tuned from 2091.1 nm to 2092.1 nm, corresponding to a tuning frequency of 68 GHz. The M² factor was measured to be 1.23.     

High efficiency on-chip charge pump DC–DC converter for LCD drivers

An on-chip charge pump (CP) DC–DC converter applicable to potable displays is described. A merged 2×/3× booster eligible for both single-phase pumping and dual-phase pumping is developed. A closed-loop sensing scheme with analog/digital mixed-mode voltage regulation helps to ensure a low ripple output voltage and high power transfer efficiency. A test vehicle was implemented for a DC input range of 2.2–3.6 V and the DC output of 5 V with a load condition of 20 mA in a standard 0.35-μm 2poly-4metal CMOS process. The test results reveal output ripple of less than 80 mV and efficiency of 77.4% in the 2× dual phase mode.     

Integrated wavelength monitoring in a photonic-crystal tunable laser diode

A photonic-crystal tunable 1.55 μm laser diode is fitted with a wavelength monitor on its rear side. The 250-μm long laser based on a coupled-cavity design has approximately 15 nm tunability. The wavelength monitor collects and differentially feeds two-photodetecting areas, thanks to a mode conversion to a higher-order mode (a mini-stopband), followed by tunneling through a thin clad. The layout is numerically optimized to minimize unwanted reflections. Electrical cross-talk was prevented through guard rings and trenches. The correlation between wavelength and the monitor photocurrent ratio demonstrates a 10–20 GHz stabilization capability, or a 15 nm monitoring range.     

Er/Yb co-doped fiber amplifier with wavelength-tuned Yb-band ring resonator

Erbium-ytterbium co-doped fiber amplifier with wavelength-tuned Yb-band loop resonator is presented. The amplified spontaneous emission (ASE) from Yb ions is utilized to stimulate a laser emission at several wavelengths from the 1 μm band in the 1550 nm amplifier. The wavelength of this lasing is tuned by introducing a fiber Bragg grating (FBG). The results show, that the overall efficiency of the amplifier at nominal 1550 nm wavelength can be increased by introducing a feedback loop with 1040 nm and 1050 nm FBG. This loop also protects the Er/Yb amplifier from parasitic lasing at 1 μm and allows significant output power scaling without risk of self-pulsing.     

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.     

1/f Noise QWIPs and nBn detectors

The low-frequency noise is a ubiquitous phenomenon and the spectral power density of this fluctuation process is inversely proportional to the frequency of the signal. We have measured the 1/f noise of a 640 × 512 pixel quantum well infrared photodetector (QWIP) focal plane array (FPA) with 6.2 μm peak wavelength. Our experimental observations show that this QWIP FPA’s 1/f noise corner frequency is about 0.1 mHz. With this kind of low frequency stability, QWIPs could unveil a new class of infrared applications that have never been imagined before. Furthermore, we present the results from a similar 1/f noise measurement of bulk InAsSb absorber (lattice matched to GaSb substrate) nBn detector array with 4.0 μm cutoff wavelength.     

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.     

Passively Q-switched diode-pumped Raman laser with third-order Stokes eye-safe oscillation

We demonstrate a passively Q-switched all-solid-state laser system with intracavity Raman frequency conversion to the eye-safe spectral region. Laser oscillation at the 1.064 μm wavelength with a pulse repetition rate of several kilohertz was provided by a Nd:YAG crystal and a Cr:YAG passive absorber. Third Stokes oscillations at the 1.599 and 1.494 μm wavelengths were obtained in Ba(NO₃)₂ and PbWO₄ crystals with output pulse energies of 5 μJ and 6 μJ, respectively. The results of the numerical simulation of the pulse dynamics are in good agreement with the experimental data.     

Design of a compact polarization splitter based on the dual-elliptical-core photonic crystal fiber

We propose a compact polarization splitter based on dual-elliptical-core photonic crystal fiber. Two elliptical cores are introduced to increase the difference of effective index between x-polarized and y-polarized mode and three elliptical modulation air holes are used to control the power transfer between the two cores. By optimizing the structure parameters, the length of the polarization splitter is distinctly shortened. Numerical results demonstrate that the compact splitter has the length of 775 μm and up to 50 dB extinction ratio at the central wavelength of 1.55 μm. The corresponding bandwidth of 32 nm could be achieved from the wavelength of 1.534–1.566 μm with the extinction ratio over 20 dB     

Submicron-scale spatial compression of light beam through two-stage photonic crystals spot-size converter

Photonic crystals spot-size converter that achieved the controlling of the spot-size through two-stage conversions was proposed. The pre-conversion depended on the efficient coupling between the high quality factor resonator and photonic crystal waveguide. Nearly unity transmission efficiency of the pre-conversion can be achieved through optimizing the radii of the rods located surrounding the resonator. Nanowire waveguide with width of 0.14 μm at a distance 1.05 μm from the resonator was introduced to realize the second stage conversion. Through two-stage conversions, the light beam width was converted to 0.16 μm. The transmission efficiency and conversion ratio reached to 94.6% and 14.875 respectively in theory.     

Realization of compatible stealth material for infrared,laser and radar based on one-dimensional doping-structure photonic crystals

To inhibit the radiant infrared energy between 8 and 14 μm, which is the infrared atmospheric window, and decrease the echo power of detecting laser and radar, to achieve compatible stealth, a doping structural one-dimensional photonic crystal (1-D PC) with Ge, ZnSe and Si was fabricated; and then combine it with radar absorbing material (RAM) to make a compound. After that, the reflection spectra of this compound was tested, and the result shows a high average reflectance (89.5%) in 8–14 μm waveband, and a reflective valley (39.8%) in the wavelength of 10.6 μm, which is the wavelength of CO₂ laser; and the reflectance in radar band shows that at high frequency, especially between 7.8 and 18 GHz, the radar power is strongly absorbed by this material and the reflected energy attenuate over 10 dB within the range from 11.1 GHz to 18.3 GHz, even 24.5 dB to the most in the frequency of 14.6 GHz.     

Bias-selectable mid-/long-wave dual band infrared focal plane array based on Type-II InAs/GaSb superlattice

In this paper, a mid-/long-wave dual-band detector which combined PπMN structure and unipolar barrier was developed based on type-II InAs/GaSb superlattice. A relevant 320 × 256 focal plane array (FPA) was fabricated. Unipolar barrier and PπMN structure in our dual band detector structure were used to suppress cross-talk and dark current, respectively. The two channels, with respective 50% cut-off wavelength at 4.5 μm and 10 μm were obtained. The peak quantum efficiency (QE) of mid wavelength infrared (MWIR) band and long wavelength infrared (LWIR) band are 53% at 3.2 μm under no bias voltage and 40% at 6.4 μm under bias voltage of −170 mV, respectively. And the dark current density under 0 and −170 mV of applied bias are 1.076 × 10⁻⁵ A/cm² and 2.16 × 10⁻⁴ A/cm². The specific detectivity of MWIR band and LWIR band are 2.15 × 10¹² cm·Hz^1/2/W at 3.2 μm and 2.31 × 10¹⁰ cm·Hz^1/2/W at 6.4 μm, respectively, at 77 K. The specific detectivity of LWIR band maintains above 10¹⁰ cm·Hz^1/2/W at the wavelength range from 4.3 μm to 10.2 μm under −170 mV. The cross-talk, selectivity parameter at 3.0 μm, about 0.14 was achieved under bias of −170 mV. Finally, the thermal images were taken by the fabricated FPA at 77 K.     

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).     

Laser welding of structural steels: Influence of the edge roughness level

Laser welding continues to become more extensively used in many industrial applications and in the last 10 years an increasing number of studies have examined ways to increase the efficiency of the process. This study investigates the influence of joint edge surface roughness on weld quality and penetration depth. The characteristics are investigated of welded samples of two low alloyed steels, S355 and St 3, of 20 mm thickness with various joint edge surface roughness levels in butt joint configuration. Welding was performed with different fiber lasers with a wavelength of 1070 nm at power levels from 10 to 15 kW. The absorption characteristics were evaluated at 10 kW power level using a calorimeter. There was a significant positive correlation between edge surface roughness level and the penetration depth. Optimum roughness levels to provide maximum penetration depth are presented. The highest penetration depth at power levels of 14 and 10 kW was achieved at R_a=6.3 μm.     

A novel polarization splitter based on dual-core elliptical-holes hybrid photonic crystal fiber

A novel kind of polarization splitter in dual-core elliptical holes hybrid photonic crystal fiber is proposed. Numerical results show that the splitter can reach small coupling length ratio of 0.5, for wavelength from 1.15 μm to 1.9 μm. At wavelength 1.55 μm, the extinction ratio can achieve ?64 dB and the 1.92-mm-long splitter is suggested to achieve extinction ratio better than ?10 dB, a bandwidth of 150 nm. The fiber has small coupling length ratio, small coupling length and high extinction ratio and it is more suitable for fabricating polarization splitter.