Tandem electroabsorption modulators integrated with DFB laser by ultra-low-pressure selective-area-growth MOCVD for 10 GHz optical short pulse generation - art. no. 60200O

A novel device of tandem multiple quantum wells (MQWs) electroabsorption modulators (EAMs) monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 mbar) selective area guowth (SAG) MOCVD technique. Experimental results exhibit superior device characteristics with low threshold of 19 mX output light power of 4.5 mW and over 20 dB extinction ratio when coupled into a single mode Fiber. Moreover, over 10 GHz modulation bandwidth is developed with a driving voltage of 2 V. Using I this sinusoidal voltage driven integrated device, 10GHz repetition rate pulse with a width of 13.7 ps without any compression elements is obtained.

Wavelength-selectable DFB laser with wide gain bandwidth realized in nonidentical quantum well - art. no. 60200W

Width varied quantum wells show a more flat and wide gain spectrume (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an selectable DFB laser based on this material grown identical chip using traditional holographic exposure. A wavelength by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.

Microwave packaging for 10 Gb/s EML modulators - art. no. 60201O

A novel microwave packaging technique for 10Gb/s electro-absorption modulator integrated with distributed feedback laser (EML) is presented. The packaging parasitics and intrinsic parasitics are both well considered, and the packaging circuit was synthetically designed to compensate for the intrinsic parasitic of the chip. A butterfly-packaged EMI module has been successfully developed to prove that. The small-signal modulation bandwidth of the butterfly-packaged module is about 10 GHz. Optical fiber transmission experiments have shown that the module can be used for 10Gb/s optical transmission system. After transmission through 40km,. the power penalty is less than 1 dBm at a bit-error-rate of 10-12.

Recent progresses of SOI-based photonic devices - art. no. 60201R

SOI (Silicon on Insulator) based photonic devices, including stimulated emission from Si diode, RCE (Resonant Cavity Enhanced) photodiode with quantum structure, MOS (Metal Oxide Semiconductor) optical modulator with high frequency, SOI optical matrix switch and wavelength tunable filter are reviewed in the paper. The emphasis will be played on our recent results of SOI-based thermo-optic waveguide matrix switch with low insertion loss and fast response. A folding re-arrangeable non-blocking 4x4 matrix switch with total internal reflection (TIR) mirrors and a first blocking 16 x 16 matrix were fabricated on SOI wafer. The extinction ratio and the crosstalk are better. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length and more bend and intersecting waveguides. The insertion losses are expected to decrease 2-3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.

Subtraction of S-parameters for adiabatic small-signal modulation characteristics of laser diode - art. no. 60201V

An extended subtraction method of scattering parameters for characterizing laser diode is introduced in this paper. The intrinsic small-signal response can be directly extracted from the measured transmission coefficients of laser diode by the method. However the chip temperature may change with the injection bias current due to thermal effects, which causes inaccurate intrinsic response by our method. Therefore, how to determine the chip temperature and keep the laser chip adiabatic is very critical when extracting the intrinsic response. To tackle these problems, the dependence of the lasing wavelength of the laser diode on the chip temperature is investigated, and an applicable measurement setup which keeps the chip temperature stable is presented. The scattering parameters of laser diode are measured on diabatic and adiabatic conditions, and the extracted intrinsic responses for both conditions are compared. It is found that the adiabatic intrinsic responses are evidently superior to those without thermal consideration. The analysis indicates that inclusion of thermal effects is necessary to acquire accurate intrinsic response.

Leakage current analysis in AlGaInP/GaInP multi-quantum well lasers by the electrical derivative method - art. no. 60202F

In AlGaInP/GaInP multi-quantum well (MQW) lasers, the electron leakage current is a much more serious problem than that in laser diodes with longer wavelength. To further improve the output performance, the leakage current should be analyzed. In this letter, the temperature dependence of electrical derivative characteristics in AlGaInP/GaInP multi-quantum well lasers was measured, and the potential barrier for electron leakage was obtained. With the help of secondary ion mass spectroscopy (SIMS) measurement, theoretical analysis of the potential barrier was presented and compared with the measurement result. The influence of p-cladding doping level and doping profile on the potential barrier was discussed, and this can be helpful in metalorganic chemical vapor deposition (MOCVD) growth.

Novel compact SOI-based reconfigurable optical add/drop multiplexer using microring resonators - art. no. 60190L

Novel compact design for 4-channel SOI-based reconfigurable optical add/drop multiplexer using microring resonators is presented and analyzed. Microring resonators have two important attributes as a key new technology for future optical communications, namely functionality and compactness. Functionality refers to the fact that a wide range of desirable filter characteristics can be synthesized by coupling multiple rings. Compactness refers the fact that ring resonators with radii about 30 mu m can lead to large scale integration of devices with densities on the order of 10(4) similar to 10(5) devices per square centimeter. A 4-channel reconfigurable optical add/drop multiplexer comprises a grid-like array of ridge waveguides which perpendicularly cross through each other. SOI-based resonators consisted of multiple rings at each of the cross-grid nodes serve as the wavelength selective switch, and they can switch an optical signal between two ports by means of tuning refractive index of one of the rings. The thermo-optic coefficient of silicon is 1.86x 10(-4) /K. Thus a temperature rise of 27K will increase the refractive index by 5 x 10(-3), which is enough to cause the switching of our designed microring resonators. The thermo-optic effect is used to suppress the resonator power transfer, rather than to promote loss. Thus, the input signal only suffers small attenuation and simultaneously low crosstalk can be achieved by using multiple rings.

Design and Fabrication of Low-microwave loss Coplannar Waveguide and precise V groove on Silicon Substrate for Optoelectronic Packaging - art. no. 601938

Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0 similar to 26GHz, and V groove has the accuracy in micro level and smooth surface. These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.

Nonradiative recombination effect on photoluminescence decay dynamics in GaInNAs/GaAs quantum wells - art. no. 61180Z

The nonradiative recombination effect on the photoluminescence (PL) decay dynamics in GaInNAs/GaAs quantum wells is studied by photoluminescence and time-resolved photoluminescence under various excitation intensities and temperatures. It is found that the PL decay dynamics strongly depends on the excitation intensity. In particular, under the moderate excitation levels the PL decay curves exhibit unusual non-exponential behavior and show a convex shape. By introducing a new concept of the effective concentration of nonradiative recombination centers into a rate equation, the observed results are well simulated. In the cw PL measurement, a rapid PL quenching is observed even at very low temperature and is of the excitation power dependence. These results further demonstrate that the non-radiative recombination process plays a very important role on the optical properties of GaInNAs/GaAs quantum wells.

Narrow stripe selective growth of InGaAlAs waveguides used for buried heterostructure lasers - art. no. 63210I

The narrow stripe selective growth of the InGaAlAs bulk waveguides and InGaAlAs MQW waveguides was first investigated. Flat and clear interfaces were obtained for the selectively grown InGaAlAs waveguides under optimized growth conditions. These selectively grown InGaAlAs waveguides were covered by specific InP layers, which can keep the waveguides from being oxidized during the fabrication of devices. PL peak wavelength shifts of 70 nm for the InGaAlAs bulk waveguides and 73 nm for the InGaAlAs MQW waveguides were obtained with a small mask stripe width varying from 0 to 40 gm, and were interpreted in considering both the migration effect from the masked region (MMR) and the lateral vapor diffusion effect (LVD). The quality of the selectively grown InGaAlAs MQW waveguides was confirmed by the PL peak intensity and the PL FWHM. Using the narrow stripe selectively grown InGaAlAs MQW waveguides, then the buried heterostructure (BH) lasers were fabricated by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good performance characteristics, with a high internal differential quantum efficiency of about 85% and an internal loss of 6.7 cm(-1).

Suspended particulate matter fluxes through the Straits of Dover, English Channel: observations and modelling

Suspended Particulate Matter (SPM) concentrations at various levels within the water column, together with salinity and temperature, were measured using water samples collected from six stations across the Straits of Dover. The sampling programme covered a 16-month period, undertaken during 23 cruises. On the basis of the spatial variability in the concentrations, the water bodies are divided by several boundaries, controlled by tidal and wind conditions. Within the water column, SPM concentrations were higher near the sea bed than in the surface waters. Throughout the cross-section, maximum concentrations occurred adjacent to the coastlines. Temporal variability in the SPM concentration exists on daily and seasonal scales within the coastal waters (4.2 to 74.5 mg L-1): resuspension processes, in response to semi-diurnal tidal cycles (with a period of around 12.4 h) and spring-neap cycles (with a period of 15 days) make significant contributions. Distinctive seasonal/annual concentration changes have also been observed. In the offshore waters, such variability is much less significant (0.9 to 6.0 mg L-1). In the summer the English Coastal Zone is associated with relatively high SPM concentrations: the Central Zone has a low and stable SPM concentration between these zones, there is a Transitional Zone, where there is a rapid response of SPM concentration to wind forcing. Finally, the French Coastal Zone is characterized by variable (sometimes high) SPM concentrations. Because of the zonation, SPM fluxes within the Dover Strait are controlled by different transport mechanisms. Within the Central Zone, the flux can be represented by the product of mean water discharges and SPM concentrations. However, within the coastal zones fluctuations in SPM concentrations on various time-scales must be considered. In order to calculate the maximum and minimum SPM fluxes, 10 cells were divided in the strait. A simple modelling calculation has been proposed for this complex area. The effect of spring-neap tidal cycles and seasonal changes can contribute significantly to the overall flux, which is of the order of 20 x 10(6) t.yr(-1) (through the Dover Strait, towards the North Sea). Such an estimate is higher than most obtained previously. (C) 2000 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.

Resuspension and advection processes affecting suspended particulate matter concentrations in the central English Channel

Suspended particulate matter (SPM) measurements obtained along a cross-section in the central English Channel (Wight-Cotentin transect) indicate that the area may be differentiated into: (1) an English coastal zone, associated with the highest concentrations; (2) a French coastal zone, with intermediate concentrations; and (3) the offshore waters of the Channel, characterised by a very low suspended-sediment load. The SPM particle-size distribution was modal close to the English coast (main mode 10-12 mu m); the remainder of the area was characterised by flat SPM distributions. Examination of the diatom communities in the SPM suggest:; that material resuspended in the intertidal zone and the estuarine environments was advected towards the offshore waters of the English Channel. Considerable variations in SPM concentrations occurred during a tidal cycle: maximum concentrations were sometimes up to 3 times higher than the minimum concentrations, Empirical orthogonal function (EOF) analysis of the SPM concentration time series indicates that, although the bottom waters were more turbid than the surficial waters, this was not likely to be the result of in situ sediment resuspension. Instead, the observed variations appear to be controlled mainly by advective mechanisms. The limited resuspension was probably caused by: (1) the limited availability of fine-grained material within the bottom sediments, and (2) 'bed-armouring' processes which protect the finer-grained fractions of the seabed material from erosion and entrainment within the overlying flow during the less energetic stages of the tide.