Gain-switched dynamics of tapered waveguide bow-tie lasers

The use of tapered waveguide lasers and amplifiers for enhanced picosecond pulse generation has led to order-of-magnitude peak power and pulse energy improvements. Monolithic pulse generation schemes have so far relied on a double-tapered bow-tie structure. The modeling of tapered lasers has so far been limited to steady-state operation or has lacked experimental comparison. This paper considers both experimentally and theoretically the gain-switched performance of bow-tie lasers of various taper angles. The role of transverse-mode spatial hole burning in tapered waveguide lasers is thereby investigated.

Effects of pedestal suppression on gain-switched laser sources for 40 Gbit/s OTDM transmission

The performance of 40 Gbit/s optical time-division multiplexed (OTDM) communication systems can be severely limited when the extinction ratio of the optical pulses is low. This is a consequence of the coherent interference noise between individual OTDM channels. When taken alone, the multiple quantum well-distributed feedback laser+dispersion compensating fiber source exhibits a relatively poor extinction ratio which impairs its potential for use in a 40 Gbit/s OTDM system. However, with the addition of an electroabsorption modulator to suppress the pulse pedestals to better than 30 dB extinction, coherent interference noise is reduced, the bit-error-rate performance is greatly improved, and the source shows good potential for 40 Gbit/s OTDM communication.

Spatial emission control of vertical cavity surface emitting lasers to provide bandwidth gain in multimode fibre links using a simple alignment technique

Etched VCSEL sources are reported which avoid bandwidth collapse in multimode fibre using a simple coupling technique to control the launch. These devices have allowed better than over-filled launch bandwidth for alignment tolerances of ±7 microns.

10-Gbits/s all-optical 3R regeneration and format conversion using a gain-switched DFB laser

A strain-compensated multiple quantum well device is used as a DFB laser, this has been optimized for low jitter gain switched operation at 10 GHz. The signal is transmitted down 80 km of standard fiber then amplified, filtered and polarization controlled before being injected into a DFB laser. The purpose of this regeneration process is to gain switch the DFB with the extracted clock signal in order to retime the converted signal. This process also simultaneously converts the input NRZ format to an output RZ data to format and results in a signal whose optical power and extinction ratio are considerably improved by the regeneration process.

Role of the state and financial institutions in financing the fishing industry

The experience of the Government in the recovery of loans for 28 foot mechanized vessels has been unsatisfactory. The author examines the various aspects which have contributed to this situation, and considers arrangements for financing purchase of such vessels. The risks associated with the investment in 38 foot vessels are high, and it seems that the reluctance of private investors to make the required contribution from personal funds is a result of fear of the unknown. Current incentives provided by the Government to the private sector for the purchase of 38 foot vessels are considered to be adequate.

Financial assistance for purchase of large fishing vessels

The Government of Sri Lanka is improving off-shore and deep-shore fishing by introducing more sophisticated and larger vessels into the Sri Lanka waters, together with the offer of subsidies, tax holidays and other concessions to those who seek to operate such fishing vessels. As a first step, some thirty 38 foot class fishing vessels are to be introduced. The requisite variety and quantity of fishing gear is supplied together with the vessels, and operators will be given further assistance to either export or market their catches locally by provision of insulated fish transport vans, jeeps with trailers, crushed ice plants, fish storage cabinets and adequate spares for at least the next few years. A description is given of the credit terms offered for the purchase of such vessels, pre-shipment finance, and loans and hire purchase facilities.