A logical study of local and global graded similarities

In this work we study the relationship between global and local similarities in the graded framework of fuzzy class theory (FCT), in which there already exists a graded notion of similarity. In FCT we can express the fact that a fuzzy relation is reflexive, symmetric, or transitive up to a certain degree, and similarity is defined as a first-order sentence, which is the fusion of three sentences corresponding to the graded notions of reflexivity, symmetry, and transitivity. This allows us to speak in a natural way of the degree of similarity of a relation. We consider global similarities defined from local similarities using t-norms as aggregation operators, and we obtain some results in the framework of FCT that, adequately interpreted, allow us to say that when we take a t-norm as an aggregation operator, the properties of reflexivity, symmetry, and transitivity of fuzzy binary relations are inherited from the local to the global level, and that the global similarity is a congruence if some of the local similarities are congruence

Frequency dynamics of gain-switched injection-locked semiconductor lasers

The frequency dynamics of gain-switched single-mode semiconductor lasers subject to optical injection is investigated. The requirements for low time jitter and reduced frequency chirp operation are studied as a function of the frequency mismatch between the master and slave lasers. Suppression of the power overshoot, typical during gain-switched operation, can be achieved for selected frequency detunings.This work was supported by the program Human Capital and Mobility, Refs. CHRX-CT93- 0331 & CHRX-CT94-0594 and by Comision Interministerial de Ciencia y ´ Tecnolog´ıa under Project PB93-0769 and Project PB94-1167Peer Reviewe

Low-Cost Feedback-Insensitive DFB Laser/ Electroabsorption Modulator Package

The design of a feedback insensitive DFB Laser/electroabsorption modulator package is presented. The device is shown to be appropriate for short pulse generation. The performance of the proposed device is numerically checked. Monolithically integrated CW DFB lasers coupled to electroabsorption modulators (EAMs) are one of the best configurations for high speed and low chirp pulse generation [1, 2]. Modulation frequencies up to 40 Gb/s has been achieved and soliton-like shaped pulses of a few picoseconds duration have been successfully generated [2]. However, due to the high sensitivity of DFB lasers to optical feedback, the package window has to be anti-reflection (AR) coated. Moreover, sometimes it is also necessary to include optical isolators which considerably increases the size and the cost of the package. In addition, if the package is coupled to an optical fiber, the latter has to be AR coated or specially cut (tapered). Optical feedback from short external cavities modifies t..