Structural optimizations of SOI-based single-mode rib waveguide bends

Effects of structure parameters on bend loss of rib silicon-on-insulator (Sol) bend waveguides have been analyzed by means of effective index method (EIM) and 2D bend loss formula. The simulation results indicate that the bend loss decreases with the increase of bend radius and waveguide width, as well as with the decrease of the step factor of the rib waveguide. Moreover, the optional structure parameters have been found when bend waveguides are single-mode.

Single-mode holey vertical-cavity surface-emitting laser with ultra-narrow beam divergence

We demonstrated oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs) with a two-dimensional petal-shaped holey structure composed of several annular-sector-shaped holes. Four types of devices with different hole numbers were designed and fabricated. The measured results showed that the larger hole number was beneficial to purifying the lasing mode, and realizing the single-mode operation. The side mode suppression ratio (SMSR) exceeded 30 dB throughout the entire drive current. Mode selective loss mechanism was used to explain the single-mode characteristic. The single-mode devices possessed good beam profiles, and the lowest divergence angle was as narrow as 3.2 degrees (full width at half maximum), attributed to the graded index profile and the shallow etching in the top distributed Bragg reflector (DBR).

Stable single-mode distributed feedback quantum cascade laser with surface metal grating

A design of single-mode distributed feedback quantum cascade lasers (DFB-QCLs) with surface metal grating is described. A rigorous modal expansion theory is adopted to analyse the interaction between the waveguide mode and the surface plasmon wave for different grating parameters. A stable single-mode operation can be obtained in a wide range of grating depths and duty cycles. The single-mode operation of surface metal grating DFB-QCLs at room temperature for lambda = 8.5 mu m is demonstrated. The device shows a side-mode suppression ratio of above 20 dB. A linear tuning of wavelength with temperature indicates the stable single-mode operation without mode hopping.

Theoretical design or single-polarization single-mode microstructured polymer optical fibres

Using the full-vector plane-wave expansion method, a kind of PMMA-based polarization-maintaining microstructured optical fibre (PM-mPOF) is theoretically studied. Dependence of the cutoff wavelengths of the two orthogonal polarization states (polarized along the two principal axes of PM-mPOF) on the structure parameters of the fibre is investigated in detail. A single-polarization single-mode (SPSM) PM-mPOF working in the visible region is designed and optimized with the result of the maximum SPSM bandwidth of 140 nm.

GAAS/GAALAS GRADED INDEX SEPARATE CONFINEMENT SINGLE QUANTUM-WELL SINGLE-MODE WAVE-GUIDE ELECTROABSORPTION LIGHT-MODULATOR

A GaAs/GaAlAs graded-index separate confinement single quantum well heterostructure single-mode ridge waveguide electroabsorption modulator was fabricated and investigated. For the modulator with a quantum well width of 100 angstrom and device length of 700-mu-m, an on/off ratio of 29.7 dB and estimated absorption insertion loss of 3 dB were obtained for TE polarised light with wavelength 8650 angstrom, and for TM polarisation the on/off ratio was 28.5 dB. With a switching voltage of 1 V, an on/off ratio of 15 dB was achieved. Photocurrent spectra exhibited a red shift of 600 angstrom of the absorption edge when the voltage applied to the PIN diode was varied from 0.5 to -7 V. The corresponding shift of the room temperature exciton peak energy was 96 meV.

A Single Mode 980nm InGaAs/GaAs/AlGaAs Large Optical Cavity Quantum Well Laser with Low Vertical Divergence Angle

To achieve high optical power as well as low vertical divergence angle, a new kind of optimized large optical cavity (LOC) structure is applied to a ridge waveguide 980nm InGaAs/GaAs/AlGaAs multi-quantum well laser. The optical power density in the waveguide is successfully reduced. The maximum output power is more than 400mW with a slope efficiency of 0.89W/A and the far-field vertical divergence angle is lowered to 23°.

Single ridge waveguide electroabsorption modulated DFB laser for 2.5Gb/s transmission

In this paper we proposed a single ridge waveguide electroabsorption modulated distributed feedback laser (EML) for long-haul high-speed optical fiber communication system. This EML was successfully fabricated by two step metal organic vapor phase epitaxy (MOVPE) including selective area growth (SAG) and helium partially implantation. No obvious changes of the threshold current (< 0.2 mA), extinction ratio (< 0.1 dB), output power (< 0.2 dBm) and isolation resistance were achieved in the preliminary aging test. With 2.5 Gb/s NRZ modulation, no power penalty was observed after the optical signal was transmitted through 280 Km normal single mode fiber.

The study of single mode 650nm AlGaInP quantum well laser diodes for DVD

Single mode 650nm AlGaInP quantum well laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) was reported in this paper. Selected buried rigewaveguid were applied for single mode operation especially for DVD use. The operating temperature over 90 degree at CW output power 5 mW was achieved.

High power 980 nm Al-free strained quantum-well lasers for erbium-doped fiber amplifiers

In this paper, we reported on the fabrication of 980 nm InGaAs/InGaAsP strained quantum-well (QW) lasers with broad waveguide. The laser structure was grown by low-pressure metalorganic chemical vapor deposition on a n(+)- GaAs substrate. For 3 mu m stripe ridge waveguide lasers, the threshold current is 30 mA and the maximum output power and the output power operating in fundamental mode are 350 mW and 200 mW, respectively. The output power from the single mode fiber is up to 100 mW, the coupling efficiency is 50%. We also fabricated 100 mu m broad stripe coated lasers with cavity length of 800 mu m, a threshold current density of 170 A/cm(2), a high slope efficiency of 1.03 W/A and a far-field pattern of 40 x 6 degrees are obtained. The maximum output power of 3.5 W is also obtained for 100 mu m wide coated lasers. (C) 2000 Elsevier Science B.V. All rights reserved.

Tunable and switchable multiwavelength fiber lasers with broadband range based on nonlinear polarization rotation technique

Switchable multiwavelength fiber laser outputs with a wide tuning range are experimentally observed in an ultralong cavity. Because of the long spooled single-mode fiber and filter effect of the cavity, multiwavelength lasers with the spacing of similar to 14.5 nm are obtained. The proposed fiber laser has the capacity of simultaneously emitting the three wavelengths. By means of adjusting the polarization controllers, the arbitrary single- and dual-wavelength operations are achieved in our laser. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3485754]

Size-Dependent Adhesion Strength of a Single Viscoelastic Fiber

Nano-fibrillar adhesives can adhere strongly to surfaces as a gecko does. The size of each fiber has significant effects on the adhesion enhancement, especially on rough surfaces. In the present study, we report the size effects on the normal and shear strength of adhesion for a single viscoelastic fiber. It is found that there exists a limited region of the critical sizes under which the interfacial normal or tangential tractions uniformly attain the theoretical adhesion strength. The region for a viscoelastic fiber under tension with similar material constants to a gecko's spatula is 135-255 nm and that under torque is 26.5-52 nm. This finding is significant for the development of artificial biomimetic attachment systems.

Modal correction for fiber-coupling efficiency in free-space optical communication systems through atmospheric turbulence

High-speed free-space optical communication systems have recently used fiber-optical components. The coupling efficiency with which the received laser beam can be coupled into a single-mode fiber is noticeably limited by atmospheric turbulence due to the degradation of its spatial coherence. Fortunately, adaptive optics (AO) can alleviate this limitation by partially correcting the turbulence-distorted wavefront. The coupling efficiency improvement provided by Zernike modal AO correction is numerically evaluated. It is found that the first 3-20 corrected polynomials can considerably improve the fiber-coupling efficiency. The improvement brought by AO is compared with that brought by a coherent fiber array. Finally, a hybrid technique that integrates AO and a coherent fiber array is proposed. Results show that the hybrid technique outperforms each of the two above-mentioned techniques. (C) 2009 Elsevier GmbH. All rights reserved.

Single mode and multimodes lasing emission from MEH-PPV doped polystyrene thin films with surface ripples formed by vapour-induced phase separation

We report single mode and multimodes lasing emission from conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) doped polystyrene ( PS) thin films with surface ripples. Surface ripples were formed by water vapour-induced phase separation. A single mode lasing emission at 606 nm with a line-width of less than 0.4 nm was obtained. The laser threshold was as low as 3.5 mu J pulse(-1). The side mode suppression ratio was 5.76 dB. The periodic changes of the refraction index in the MEH-PPV : PS blending film due to the phase separation should be attributed to the lasing actions.

Single Mueller matrix description of the propagation of degree of polarisation in a uniformly anisotropic single-mode optical fibre

R. Zwiggelaar and M.G.F. Wilson, 'Single Mueller matrix description of the propagation of degree of polarisation in a uniformly anisotropic single-mode optical fibre', IEE Proceedings Optoelectronics 141 (6), 367-372 (1994)

Calibrating single-ended fiber-optic Raman spectra distributed temperature sensing data.

Hydrologic research is a very demanding application of fiber-optic distributed temperature sensing (DTS) in terms of precision, accuracy and calibration. The physics behind the most frequently used DTS instruments are considered as they apply to four calibration methods for single-ended DTS installations. The new methods presented are more accurate than the instrument-calibrated data, achieving accuracies on the order of tenths of a degree root mean square error (RMSE) and mean bias. Effects of localized non-uniformities that violate the assumptions of single-ended calibration data are explored and quantified. Experimental design considerations such as selection of integration times or selection of the length of the reference sections are discussed, and the impacts of these considerations on calibrated temperatures are explored in two case studies.