PCDD/F-s, PCBs, HCHs and HCB in sediments and soils of Ya-Er lake area in China: Results on residual levels and correlation to the organic carbon and particle size

Sediments and soils collected from the Ya-Er Lake area in China were analysed for the polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyl (PCBs), hexachlorocyclohexane (HCHs) and hexachlorobenzene (HCB). The results indicated the main pollution problems in the Ya-Er Lake area, which was heavily polluted by HCHs and chlorobenzenes, now is dominantly polluted by PCDD/Fs, PCBs and HCB. The occurrence of PCDD/Fs and PCBs with relatively high levels of HpCDDs, OCDD and low chlorinated-substituted PCBs, is attributed to the discharge of waste water and biodegradation. The vertical distributions of HCH-residues are related with the content of organic carbon and particle size. Copyright (C) 1996 Elsevier Science Ltd

Monolithic integration of sampled grating DBR with electroabsorption modulator by combining selective-area-growth MOCVD and quantum-well intermixing

We present the monolithic integration of a sampled-grating distributed Bragg reflector (SC-DBR) laser with a quantum-well electroabsorption modulator (QW-EAM) by combining ultra-low-pressure (55 mbar) selective-area-growth (SAG) metal-organic chemical vapour deposition (MOCVD) and quantum-well intermixing (QWI) for the first time. The QW-EAM and the gain section can be grown simultaneously by using SAG MOCVD technology. Meanwhile, the QWI technology offers an abrupt band-gap change between two functional sections, which reduces internal absorption loss. The experimental results show that the threshold current I-th = 62 mA, and output power reaches 3.6 mW. The wavelength tuning range covers 30 nm, and all the corresponding side mode suppression ratios are over 30 dB. The extinction ratios at available wavelength channels can reach more than 14 dB with bias of -5 V.

Stable multiplication gain in GaN p-i-n avalanche photodiodes with large device area

Visible-blind p-i-n avalanche photodiodes (APDs) were fabricated with high-quality GaN epilayers deposited on c-plane sapphire substrates by metal-organic chemical vapour deposition. Due to low dislocation density and a sophisticated device fabrication process, the dark current was as small as similar to 0.05 nA under reverse bias up to 20V for devices with a large diameter of 200 mu m, which was among the largest device area for GaN-based p-i-n APDs yet reported. When the reverse bias exceeded 38V the dark current increased sharply, exhibiting a bulk avalanche field-dominated stable breakdown without microplasma formation or sidewall breakdown. With ultraviolet illumination (360 nm) an avalanche multiplication gain of 57 was achieved.

A selective area growth double stack active layer electroabsorption modulator integrated with a distributed feedback laser

A new method for fabricating electroabsorption modulator integrated with a distributed feedback laser (EML) was proposed. With the method we fabricated a selective area growth double stack active layer EML (SAG-DSAL-EML). Through comparing with other fabrication methods of EMLs, the characters and the merits of the new method presented in this paper were discussed.

Microorganisms linked to Neoproterozoic microspar carbonate sedimentation in the Jilin-Liaoning area

Molar-tooth carbonate refers to a sort of rock that has ptygmatical folded structure comparable to the ivory. This kind of carbonate exists in a special time range (from Middle to Neoproterozoic). Its origin and the possibility to use it in stratigraphic correlation of the paleocontinent is the key task of the IGCP447, a project on Proterozoic molar tooth carbonates and the evolution of the earth (2001-2005). The importance lies in that the molar-tooth structure is the key to solving problems related to Precambrian biological and global geochemical events. The molar-tooth structure is associated with microorganisms. Development and recession of such carbonates have relations with the evolution process of early lives and abrupt changes in sea carbonate geochemistry. In recent years, based on researches on petrology, geochemistry and Sr isotope of molar-tooth carbonate in the Jilin-Liaoning and Xuzhou-Huaiyang area, the authors hold that it can be used as a marker for stratigraphic sequence and sedimentary facies analyses.

10 Gbit s(-1) electroabsorption-modulated laser light-source module using selective area MOVPE

A distributed-feedback (DFB) laser and a high-speed electroabsorption (EA) modulator are integrated, on the basis of the selective area MOVPE growth (SAG) technique and the ridge waveguide structure, for a 10 Gbit s(-1) optical transmission system. The integrated DFB laser/EA modulator device is packaged in a compact module with a 20% optical coupling efficiency to the single-mode fibre. The typical threshold current is 15 mA, and the side-mode suppression ratio is over 40 dB with the single-mode operation at 1550 nm. The module exhibits 1.2 mW fibre output power at a laser gain current of 70 mA and a modulator bias voltage of 0 V. The 3 dB bandwidth is 12 GHz. A dynamic extinction ratio of over 10 dB has been successfully achieved under 10 Gbit s(-1) non-return to zero (NRZ) operation, and a clearly open eye diagram is obtained.

Tandem electroabsorption modulators integrated with DFB laser by ultra-low-pressure selective-area-growth MOCVD for 10 GHz optical short pulse generation

　

A 10-GHz bandwidth electroabsorption modulated laser by ultra-low-pressure selective area growth

A novel integration technique has been developed using band-gap energy control of InGaAsP/InGaAsP multi-quantum-well (MQW) structures during simultaneous ultra-low-pressure (22 mbar) selective-area-growth (SAG) process in metal-organic chemical vapour deposition. A fundamental study of the controllability of band gap energy by the SAG method is performed. A large band-gap photoluminescence wavelength shift of 83nm is obtained with a small mask width variation (0-30 mu m). The method is then applied to fabricate an MQW distributed-feedback laser monolithically integrated with an electroabsorption modulator. The experimental results exhibit superior device characteristics with low threshold of 19 mA, over 24 dB extinction ratio when coupled into a single mode fibre. More than 10GHz modulation bandwidth is also achieved, which demonstrates that the ultra-low-pressure SAG technique is a promising approach for high-speed transmission photonic integrated circuits.

Monolithic integration of an InGaAsP-InP strained DFB laser and an electroabsorption modulator by ultra-low-pressure selective-area-growth MOCVD

The design and basic characteristics of a strained InGaAsP-InP multiple-quantum-well (MQW) DFB laser monolithically integrated with an electroabsorption modulator (EAM) by ultra-low-pressure (22 mbar) selective-area-growth (SAG) MOCVD are presented. A fundamental study of the controllability and the applicability of band-gap energy by using the SAG, method is performed. A large band-gap photoluminescence wavelength shift of 88 mn. was obtained with a small mask width variation (0-30 mu m). The technique is then applied to fabricate a high performance strained MQW EAM integrated with a DFB laser. The threshold current of 26 mA at CW operation of the device with DFB laser length of 300 mu m and EAM length of 150 mu m has been realized at a modulator bias of 0 V. The devices also exhibit 15 dB on/off ratio at an applied bias voltage of 5 V.

Electroabsoorption-modulated laser light-source module using selective area growth for 10 Gb/s transmission

In this work, a novel light source of strained InGaAsP/InGaAsP MQW EAM monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 x 10(2) Pa) selective area growth ( SAG) MOCVD technique. Superior device performances have been obtained, sue h as low threshold current of 19 mA, output light power of about 7 mW, and over 16 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3 dB bandwidth in EAM part is developed with a driving voltage of 3 V. After the chip is packaged into a 7-pin butterfly compact module, 10-Gb/s NRZ transmission experiments are successfully performed in standard fiber. A clearly-open eye diagram is achieved in the module output with over 8.3 dB dynamic extinction ratio. Power penalty less than 1.5 dB has been obtained after transmission through 53.3 km of standard fiber, which demonstrates that high-speed, low chirp EAM/DFB integrated light source can be obtained by ultra-low-pressure (22 x 102 Pa) SAG method.

10 GHz optical short pulse generation using tandem electroabsorption modulators monolithically integrated with distributed feedback laser by ultra-low-pressure selective area growth

In this work, a novel light source of tandem InGaAsP/InGaAsP multiple quantum well electroabsoption modulator( EAM ) monolithically integrated with distributed feedback laser is fabricated by ultra-low-pressure ( 22 x 10(2) Pa ) selective area growth metal-organic chemical vapor diposition technique. Superior device performances have been obtained, such as low threshold current of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3dB bandwidth in EAM part is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10 GHz repetition rate pulse with an actual width of 13.7 ps without any compression elements is obtained due to the gate operation effect of tandem EAMs.

Improving response speed of electrooptical switch in silicon-on-insulator by modifying modulation area structure

This paper reports on the simulation of two 2 x 2 electrooptical switches with different modulation area structures in silicon-on-insulator (SOI). A two-dimensional (2D) semiconductor device simulation tool PISCES-II has been used to analyze the dc and transient behaviors of the two devices. The modeling results show that the switch with an N+-I-P+-I-N+ modulation structure has a much faster response speed than the device with a P+-I-N+ modulation structure, although the former requires slightly stronger injection power.

Selective area growth of GaN on GaAs(001) substrates by metalorganic vapor-phase epitaxy

Selective area growth (SAG) of GaN on SiO2 stripe-patterned GaN/GaAs(001) substrates was carried out by metalorganic vapor-phase epitaxy. The SAG samples were investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). SEM observations showed that the morphology of SAG GaN is strongly dependent on the window stripe orientation and slightly affected by the orientation relationship between the window stripes and the gas flow. The (I 1 1)B sidewalls formed on the SAG GaN stripes are found to be stable. XRD measurements indicated the full-widths at half-maximum (FWHMs) of cubic GaN (0 0 2) rocking curves are reduced after SAG. The measured FWHMs with omega-axis parallel to [1(1) over bar 0] are always larger than the FWHM values obtained with omega-axis parallel to [I 10], regardless of the orientation relationship between the w-axis and the GaN stripes. (C) 2003 Elsevier Science B.V. All rights reserved.

Selective-area MOCVD growth for distributed feedback lasers integrated with vertically tapered self-aligned waveguide

The growth pressure and mask width dependent thickness enhancement factors of selective-area MOCVD. grow th were investigated in this article. A, high enhancement of 5.8 was obtained at 130 mbar with the mask width of 70 mum. Mismatched InGaAsP (-0.5%) at the maskless region which could ensure the material at butt-joint region to be matched to InP was successively grown by controlling the composition and mismatch modulation in the selective-area growth. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously in separated confined heterostructure 1.55 gm distributed feedback laser, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. A narrow beam of 9degrees and 12degrees in the vertical and horizontal directions, a low threshold current of 6.5 mA was fabricated by using this technique. (C) 2003 Elsevier Science B.V. All rights reserved.

Design, simulation and testing of large area silicon drift detectors and detector array for X-ray spectroscopy

Large area (25 mm(2)) silicon drift detectors and detector arrays (5x5) have been designed, simulated, and fabricated for X-ray spectroscopy. On the anode side, the hexagonal drift detector was designed with self-biasing spiral cathode rings (p(+)) of fixed resistance between rings and with a grounded guard anode to separate surface current from the anode current. Two designs have been used for the P-side: symmetric self-biasing spiral cathode rings (p(+)) and a uniform backside p(+) implant. Only 3 to 5 electrodes are needed to bias the detector plus an anode for signal collection. With graded electrical potential, a sub-nanoamper anode current, and a very small anode capacitance, an initial FWHM of 1.3 keV, without optimization of all parameters, has been obtained for 5.9 keV Fe-55 X-ray at RT using a uniform backside detector.