Wavelength demultiplexing heterojunction phototransistor

Experimental and theoretical results on a wavelength demultiplexing receiver composed of an AlGaAs/GaAs heterojunction phototransistor (HPT) integrated within a resonant cavity are reported. A high quality factor cavity was formed using a very thin In/sub 0.05/Ga/sub 0.95/As active absorption layer in the collector depletion region of the HPT. Crosstalk attenuations of 15 dB for dual and 12 dB for triple wavelength demultiplexing were demonstrated. The individual HPTs had an optical gain of 500 at the resonant modes. Theoretical calculations predict crosstalk attenuation levels as high as 40 dB with high reflection mirrors on both ends of the cavity.<>     

Wavelength dispersion in a single-mode fibre

Wavelength dispersion in a single-mode fibre has been evaluated by measuring propagation times of various-wavelength pulses transmitted through a 3.72 km-length fibre. Dispersion in a single-mode fibre is dominated by material dispersion, and is estimated to be 9.1 ps/? dkm at 0.85 ?m wavelength.     

Losses in small-radius bends in single-mode fibres

Refractive index profiles and mode field radii determine small-radius bending losses in single-mode fibres. Losses in six different types of fibres were measured in bends with radii ranging from 1.25 to 8 mm. The results show that a refractive index depression in the core centre reduces the bending-loss sensitivity.<>     

Mode shift at bends in single-mode fibres

The predicted oscillatory field deformation at the onset of a bend in a single-mode fibre, together with the steady-state beam shift, have been confirmed experimentally.     

Wavelength division multiplexing and demultiplexing with photoniccrystal waveguide couplers

A multiplexer-demultiplexer (MUX-DEMUX) based on PC waveguide couplers is proposed, and its wavelength demultiplexing properties are theoretically investigated. First, a two-channel MUX-DEMUX is designed and characterized, and then, by cascading, two stages of photonic crystal (PC) waveguide couplers with different coupling coefficients are constructed. The device sizes are expected to be drastically reduced from a scale of a few tens of micrometers to a scale of a few hundreds of micrometers in a MUX-DEMUX     

Wavelength dispersion characteristics of single-mode fibers in low-loss region

Wavelength dispersion characteristics of single-mode silica fibers in a very low-loss region, including zero dispersion wavelengths, are studied in detail using a "difference method." Wavelength dispersion of single-mode fibers is compared for fibers with same material dispersion but with different waveguide structure. Material dispersion is evaluated by extracting waveguide dispersion from experimental results. Effects of waveguide dispersion on the zero dispersion wavelength of the single-mode fiber in a longer wavelength region are clearly analyzed. Single-mode fiber design consideration is given from the wavelength dispersion point of view.     

Wavelength stabilized single-mode lasers by coupled micro-square resonators

Wavelength stabilized single-mode lasers were realized by on-chip coupling of a ridge waveguide laser with two micro-ring resonators. The micro-ring resonators were fabricated by deeply etching to achieve high lateral optical confinement and to allow small ring diameters in the range between 20-60 /spl mu/m. A square-like ring geometry with 45/spl deg/ facets was used to improve design control and side-wall quality. By using micro rings with two different diameters of 50 and 60 /spl mu/m, a free spectral range of about 18 nm could be obtained which allow a stable single-mode operation with a side-mode suppression ratio of more than 40 dB and a continuous-wave output power of 30 mW per facet at room temperature.     

Wavelength dependence of polarisation mode dispersion in elliptical-core single-mode fibres

Polarisation mode dispersion in elliptical-core single-mode fibres has been measured by a spatial technique based on a visibility maximum position measurement in an interferometer. Using the technique, wavelength dependence of the modal dispersion has been measured by varying optical source wavelengths between 821 and 904 nm. As a result, contribution of geometrical and strain birefringences on the modal dispersion has been evaluated, and normalised frequency dependence of the modal dispersion has been clarified.     

Wavelength-division demultiplexing using graded-index planar structures

In this paper, the authors propose a novel technique for wavelength-division demultiplexing using a graded-index planar structure. The device consists of three layers of the same bulk material: The two outer layers are homogeneous media with refractive indices n/sub 1/ and n/sub 2/, while the inner layer is an inhomogeneous medium where its refractive index is graded according to a certain profile. The proposed technique exploits the spatial shift that results from the material dispersion found in dispersive media such as silicon dioxide (silica). It is found that the graded-index structure produces a spatial shift that is much higher than that encountered in conventional prisms, provided a certain refractive index profile is chosen. Unlike graded-index fibers, it is found that the value of /spl alpha/ of the refractive index profile (/spl alpha/-profile) for the proposed device must be < 1 to get large spatial dispersion. A mathematical expression for the spatial shift between adjacent wavelengths is found by determining the path profiles followed by the different wavelengths as they propagate through the graded-index layer. Theoretically, it is found that any spatial shift can be obtained by either reducing the value of /spl alpha/ far below 1 for a fixed size of the structure or increasing the size of the structure for a fixed value of /spl alpha/.     

Wavelength tunability and polarization characteristics of twistedpolarization beamsplitting single-mode fiber couplers

The wavelength tunability and the polarization characteristics of twisted polarization beamsplitting fiber couplers are investigated experimentally and analyzed theoretically. The measured spectrum transmissions and polarization characteristics agree well with the theoretical results. The wavelength working as a polarization beamsplitter can be tuned in the 1.3-1.75 μm wavelength range without significant degradation. Splitting ratios for orthogonally polarized light are more than 20 dB and less than -20 dB     

Wavelength conversion using a T-gate laser

Wavelength conversion from 830 nm to 837 nm of a 250 Mb/s NRZ optical signal has been demonstrated at 10/sup -9/ bit-error rate and a detector sensitivity of -29 dBm using a semiconductor power amplifier monolithically integrated at 90/spl deg/ with a GaAs-AlGaAs SQW semiconductor laser. This device offers a high degree of isolation between the input and the output and has the potential for high-speed operation with a wide continuous-wavelength conversion range.     

All-optical demultiplexing of a signal using collision and waveguiding of spatial solitons

The basic principle of a new all-optical demultiplexer is experimentally demonstrated. It relies on the interaction between an input signal and two colliding spatial solitons of a different wavelength in a planar nonlinear waveguide.     

160-Gb/s all-optical demultiplexing using a gain-transparentultrafast-nonlinear interferometer (GT-UNI)

We report on an all-optical demultiplexer based on gain-transparent operation of a semiconductor optical amplifier (SOA) in an ultrafast-nonlinear interferometer (GT-UNI). The GT-UNI comprises a robust fiber-chip setup in a folded geometry. For switching window widths of 5.2 ps and 6.0 ps, error-free demultiplexing of 160-10 Gb/s is demonstrated     

16 Gbit/s all-optical demultiplexing using four-wave mixing

A novel, purely optical technique for demultiplexing high-speed time-division multiplexed data is proposed and demonstrated. The technique uses optical fibre nonlinearity induced four-wave mixing with a data signal and a probe signal located at different wavelengths. Using only semiconductor laser light sources, 1:4 demultiplexing of 20 ps long, subpicojoule, 2/sup 15/-1 RZ pulses at a data rate of 16 Gbit/s with less than 1 dB penalty is demonstrated.<>     

Adiabatic coupling in tapered air-silica microstructured opticalfiber

We study adiabatic mode propagation in tapered air-silica microstructured optical fibers and demonstrate efficient coupling into a robust high-delta microstructured fiber. In the waist region of the taper, the core mode is tightly confined by the air holes and exhibits properties similar to a high-delta waveguide such as enhanced peak intensity and widely flattened anomalous dispersion. We exploit these properties to generate tunable self-frequency shifting Raman solitons over the communications window from 1.3 μm to 1.65 μm, with over 60% conversion efficiency These fiber devices are practical for several reasons: they can be fusion spliced to standard single-mode fibers with relatively low loss, they are mechanically strong, due to the supporting cladding, and because the mode is isolated from the surrounding air interface, they can potentially be recoated allowing for packaging     

Suppression of galloping oscillation for a self-supporting opticalfiber cable

Estimation formulas for wind force coefficients for self-supporting (SS) optical fiber cable are derived. Using these formulas, a procedure for evaluating the critical wind velocity that triggers galloping oscillation is provided. An SS cable with projections is designed to increase the critical wind velocity     

Compensation of microstrip bends by using square cutouts

An alternative to the commonly used technique of mitring for compensation of microstrip bends is described. Experimental data are presented for the case where a square cutout is removed, at either the inner or outer corner of the 90° bend. This approach eases artwork generation.     

Simultaneous time- and wavelength-domain optical demultiplexing ofNRZ signals by using a side-injection-light-controlled bistable laserdiode

The authors have demonstrated direct optical demultiplexing of NRZ signals with simultaneous wavelength conversion by using a side-injection-light-controlled bistable laser diode module. The 250 Mbit/s demultiplexed output signals are each selected once every four bits from 1 Gbit/s NRZ optical input signals. Then each signal is regenerated and its bit width and wavelength are converted on one chip     

40 Gbit/s all-optical demultiplexing using a monolithicallyintegrated Mach-Zehnder interferometer with semiconductor laseramplifiers

The authors demonstrate all-optical error-free demultiplexing of 10, 20 and 40 Gbit/s to 5 Gbit/s data signals by using a monolithically integrated Mach-Zehnder interferometer with two semiconductor laser amplifiers     

Interferometric demultiplexing experiment using linear coherentcorrelation with modulated local oscillator

A novel optical demultiplexing method is experimentally demonstrated using the coherent linear correlation between the signal light and a modulated local oscillator. Although the bit-rate is only 2.4 Gbit/s in this preliminary experiment, the method is applicable to faster signals, and features high sensitivity similar to that of coherent detection