Study of monolithic integrable directional coupler structures as pulse compressors in InGaAsP Martín López García , Horacio Lamela and Guillermo Carpintero Escuela Politecnica, Univ. Carlos III, Av. De la Universidad 30, 28911 Leganes Madrid (SPAIN) ABSTRACT An integrable device for pulse compression based in a directional coupler is presented. InGaAsP/ InP materials have been used in order to design an integrable structure. The length of the device is calculated in vertical and lateral guides. Each of the supermodes in the total structure presents a giant Group Velocity Dispersion (GVD) which make possible to obtain total pulse chirp compensation if the pulse propagates enought distance into the guides. In case of vertical structures, two guides of InGaAsp have been used to obtain GVD`s of 10 5 ps 2 /Km wich allow high compression rates. Secondly we have designed a directional coupler using lateral coupled guides calculated with Efective Index Method (EIM) , and values arround 4*10 4 ps 2 /Km have been achieved. Both designs are compared between then taking into account several important parameters as device length or fabrication issues. 1.-Introduction Pulse compression is one of the most important issues in optical comunications systems. In many cases, such as pulses generated by diode lasers or pulses propagated a long distance, it is neccesary to compress or recompress the pulses to obtain better transmission bit-rates because of broad pulses in high-bit rate communications systems limits the máximum number of pulses without superposition by time unit. Work presented in this paper study linear pulse compression based in chirp compensation. Chirp elimination (or máximum reduction) provoque pulse to narrow, but represents too an important condition to obtain goods compressions using no-lineal compression devices such as non-linear loops mirrors. Manipulation of Group Velocity Dispersion (GVD) is the usual way to obtain chirp compensation with a relative easy to fabricate structure. There is a lot of devices to obtain linear compression, but many of them presents large structures not suitables for integration. As a example, DCF needs several meters to obtain high compensation because of the relative low GVD (10 2 -10 3 ps 2 /Km). Other way, gratings allow compensation but although it presents integrable caracteristics the reflections provoque power looses and especial technics as apodiced [1]. In this article we study several solutions based in directional couplers structures wich allow high compression ratios in integrable lengths (about the milimmeter) [2] and without high losses what represents a good structure to be integrated with diode lasers designs. Directional coupling are usually used to switch power between guides as a filter or a ligth router . However, aplications in pulse compression are an important field where coupled theory can be useful. In our case, we will use a typicall directional coupler formed by two guides separated by a distance short enougth to achieve coupling but long enougth to use perturbation theory [3] given that perturbation can only be used if the guides are weakly coupled. In agreenment with coupled mode theory [3] total field in the structure described avobe can be descibed as the superposition of two supermodes (symmetric and antisymmetric). Each of the supermodes has his own dispersion parameters (including GVD) depending in the structure caracteristics. In this work we have studied two directional coupling structures which presents very differents fabrication difficults. Because of that design parameters in both cases have been obtained for a total chirp compensation device and compared taking into account the lengths of the devices and their integration capabilities.