Low power all-optical switch in a passive InGaAsP multiple quantum well waveguide

We demonstrate the use of resonant bandfilling nonlinearity in an InGaAsP/InGaAsP Multiple Quantum Well (MQW) waveguide due to photogenerated carriers to obtain switching at pulse powers, which can readily be obtained from an erbium amplified diode laser source. In order to produce gating a polarisation rotation gate was used, which relies on an asymmetry in the nonlinear refraction on the principle axes of the waveguide.

Three band-gap QW intermixing in InP/InGaAs/InGaAsP system for monolithically integrated optical switch

Quantum well intermixing is a key technique for photonic integration. The intermixing of InP/InGaAs/InGaAsP material involving the deposition of a layer of sputtered SiO2 on the semiconductor surface, followed by thermal annealing has allowed good control of the intermixing process and has been used to fabricate extended cavity lasers. This will be used for optimization of the performance of optical switches consisting of passive components, modulators and amplifiers.

Studies on the phytoplankton of inshore and offshore waters off Colombo and some data on the hydrological conditions of these waters

The present paper gives a comparative account of the hydrological conditions and phytoplankton within the Continental Shelf and beyond the Continental Shelf. 54 water samples were taken for hydrological analysis and 18 surface tows for plankton.

Biology of the exploited stock of mackerel tuna E. affinis (Cantor) off the south-west region of Ceylon

According to the statistical data published annually in the Administration Report of the Director of Fisheries, the bloodfish production in 1967-68 showed about 100% increase over a period of five years and the production figures for none of the other groups of fishes have exhibited a parallel to this. Furthermore, the bloodfish group ranks first in the order of production, having displaced the herring and sardine group which had been in the lead for over a decade. This indicates that increasing attention was paid on the production of this group of fishes, in the coastal waters of Sri Lanka.

Apparent abundance of yellowfin and bigeye tuna in the inshore, off shore and near oceanic ranges around Ceylon

Sri Lanka entered oceanic longline fishery in 1967 and have limited the areas of operation to the central equatorial belt, thus limiting their fishery to the yellowfin and bigeye tunas. Sri Lanka while developing her coastal fishery took a leap into oceanic longlining and in view of her programme for accelerated development of the fishing industry, has to fill the gap between the two fisheries by exploiting the intermediate range (off shore and near oceanic) which would chiefly be for tunas and sharks. The present paper has been prepared in this context, utilizing available data and information on the tuna longline fishery in the inshore (approximately 6-15 miles), off shore (approximately 15-100 miles) and near oceanic (approximately 100-300 miles) ranges (Fig, 1).

Process development on the monolithic fabrication of an ultra-compact 4×4 optical switch matrix on InP/InGaAsP material

We have fabricated an ultra-compact 4×4 optical matrix on InP/InGaAsP material. 1×4 MMI couplers and TIR mirrors are employed to produce a compact 1×2 mm2 device. A CH4/H2/O2 RIE dry etch process has been used to realize two-level dry etching: deep-etch for both the MMI couplers and the mirrors and shallow-etch for the rest of the routing waveguides. It was found that a metal/dielectric bilayer mask is essential for multi-dry-etch processes and high profile verticality. We have found a Ti intermediate mask for the deep-etch process which is removable by SF6 dry-etch before the following shallow process. Dry-etch removal of the intermediate mask is necessary to protect the deep-etched mirror sidewall.

All-optical switching in a vertical coupler space switch employing photocarrier-induced nonlinearity

A novel compact integrated nonlinear optical switch is demonstrated. Using a high-power picosecond pulse of 5-ps pulsewidth and 250-MHz repetition rate, all-optical switching with a contrast ratio of 23 dB has been achieved using an in-fiber input power < 14 dBm (100 pJ/pulse). The switch speed depends on the carrier sweep-out time, which can be reduced to the 10 ps range by either applying a reverse bias or by introduction of carrier recombination centers in the active layer.

The deep crab - Geryon quinquedens: first notes on its biology off Mozambique

The deep crab Geryon quinquedens was the objective of an exploratory fishing operation with long lines of baited traps along the slope of southern Mozambique and was caught between 250 and 850 m. Data were analysed from the start of the operation in May, 1979 until March, 1980. The availability of the resource is discussed on the basis of catch rates. Size composition of the catches shows the bigger size of the males and suggests a stratification of the resource by area. Females dominate in shallower waters whereas the interval at which the sex-ratio equals one is identified at 400-450 m. Reproduction is discussed in connection with recruitment and an hypothesis is advanced for an exponential growth rate of about 10 mm per month.

Stock assessment of Haliporoides triarthrus (Fam. Solenoceridae) off Mozambique: a preliminary analysis

The pink shrimp, Haliporoides triarthrus, is an important species in the deep-water shrimp fishery in Mozambique. Total catches are in the range of 1,500 to 2,700 tons, with the pink shrimp accounting for 70-90%. Estimates of growth parameters and of natural mortality are used for a preliminary assessment of the fishery, based on length-structured virtual population analysis and yield-per-recruit analyses. With an arbitrarily chosen terminal fishing mortality F, the results indicate a situation of overfishing, but realistic parameters must be acquired in order to diagnose the state of the stock

Stock assessment of the deep-water spiny lobster Palinurus delagoae, off Mozambique

Preliminary estimates of growth parameters and mortality are presented for the deep-water spiny lobster Palinurus delagoae fished off Mozambique. The length-converted catch curve shows three levels of total mortality (year-1): Z=2.9 for the smaller sizes; Z=1.4 for intermediate, and Z=0.6 for the larger lobsters. These results are confirmed by a length-structured virtual population analysis. Yield-per-recruit analysis suggests that a long-term yield, at least 50% higher than the present one, could be obtained by increasing the mean size at first capture from about 6 cm (carapace length) to about 10 cm.

Growth of the buccaneer anchovy Encrasicholina punctifer off Mozambique, based on samples collected in research surveys

Growth of Encrasicholina punctifer (Engraulididae) is estimated, based on samples obtained during five surveys on Sofala Bank (central Mozambique). The estimated values of the von Bertalanffy growth function, TL∞=12 cm and K=2.0 yearˉ¹ are compared with results of growth studies elsewhere in the Indo-Pacific region, based mainly on the index Φ=log(sub)10 K+2*log(sub)10L∞ assumed to be constant within species. This comparison is rendered difficult by the uncertain taxonomical status of stolephorid anchovies.

A preliminary assessment of the shallow water prawn stocks off Mocambique, North of Beira

At present, the trawl fishery for shallow water prawns is the only industrialized national fishery in Mozambique. Most of the catch is exported. Plans are laid for expansion of the fishery, and this report is an attempt to make a preliminary assessment of the potential yields from the stocks occupying the shallow water areas between Beira and Angoche.

The biology and availability of the spiny lobster Palinurus delagoae Barnard, off the coast of Mozambique

Catch and effort data and some biological characteristics of the deep water spiny lobster P. delagoae collected between August 1980 and December 1981, are presented. The work was conducted on board a commercial vessel off the coast of Mozambique.

Circulation system and areas of potentially successful tuna fishing with surface methods off Mozambique

Charts with 3-months running means of thermal data collected during 1977-1982 are used to describe the seasonal variability of the circulation pattern off Mozambique, and to identify the areas of tuna vulnerability to surface gears. The main conclusions reached by Sætre and Jorge da Silva (1984) have received further support. Areas of potentially successful exploitation of tunas by surface methods have been identified during the whole year, with emphasis for November-April.

Development of off-shore and deep-sea fishing in Sri Lanka

Since 1950 onwards, a practice has grown in Sri Lanka of dividing the marine fisheries into three different classes depending on the location of the resource to be exploited viz. coastal fishing, off-shore fishing and deep-sea fishing. The author describes commercial fishing activities, paying attention to changes emerged and future prospectives.