{"id":1493,"date":"2018-01-31T15:47:00","date_gmt":"2018-01-31T20:47:00","guid":{"rendered":"https:\/\/www.precisionot.com\/?p=1493"},"modified":"2023-06-12T13:10:00","modified_gmt":"2023-06-12T17:10:00","slug":"provoque-un-gazouillis-optique-comment-prevenir","status":"publish","type":"post","link":"https:\/\/www.precisionot.com\/fr\/causes-optical-chirp-how-prevent\/","title":{"rendered":"Causes du chirp optique et comment le r\u00e9duire"},"content":{"rendered":"<p class=\"wp-block-paragraph\">Un chirp optique est un changement soudain de la longueur d&#039;onde centrale d&#039;un laser, caus\u00e9 par l&#039;instabilit\u00e9 du laser. Un chirp est une fr\u00e9quence de signal qui augmente avec le temps, appel\u00e9e \u00ab up-chirp \u00bb, ou diminue, appel\u00e9e \u00ab down-chirp \u00bb. Dans certaines sources, le terme chirp est utilis\u00e9 de mani\u00e8re interchangeable avec le signal de balayage.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Le chirp se produit lorsque le front montant d&#039;une impulsion a une fr\u00e9quence l\u00e9g\u00e8rement diff\u00e9rente de celle du front descendant. Lorsque des impulsions sont g\u00e9n\u00e9r\u00e9es \u00e0 l&#039;extr\u00e9mit\u00e9 transmise, la modulation d&#039;intensit\u00e9 provoque une modulation de phase en raison du changement induit par la porteuse dans l&#039;indice de r\u00e9fraction. Ce changement est intrins\u00e8quement d\u00fb \u00e0 la largeur de raie laser. L&#039;effet de chirp peut \u00eatre r\u00e9duit en utilisant des modulateurs externes.<\/p>\n\n\n\n<figure class=\"wp-block-image alignleft size-large is-resized\"><img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/www.precisionot.com\/wp-content\/uploads\/new.png\" alt=\"tableau des impulsions laser ultrashot\" class=\"wp-image-3328\" width=\"310\" height=\"231\" srcset=\"https:\/\/www.precisionot.com\/wp-content\/uploads\/new.png 451w, https:\/\/www.precisionot.com\/wp-content\/uploads\/new-300x224.png 300w, https:\/\/www.precisionot.com\/wp-content\/uploads\/new-16x12.png 16w\" sizes=\"(max-width: 310px) 100vw, 310px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Lorsque le modulateur envoie des impulsions au laser, une diff\u00e9rence d&#039;indice de r\u00e9fraction de la sortie laser peut provoquer un chirp dans un syst\u00e8me WDM (multiplexage par r\u00e9partition en longueur d&#039;onde). WDM combine divers signaux sur des faisceaux laser \u00e0 diff\u00e9rentes longueurs d&#039;onde infrarouges (IR) pour la transmission sur des supports \u00e0 fibre optique. Chaque laser est modul\u00e9 par un ensemble ind\u00e9pendant de signaux. La modulation peut \u00eatre obtenue en superposant un flux de donn\u00e9es s\u00e9rie sur un signal porteur en modifiant l&#039;un des param\u00e8tres du signal porteur. Dans un r\u00e9seau optique, les donn\u00e9es sont modul\u00e9es sur la lumi\u00e8re \u00e9mise par un laser.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Le terme chirp est \u00e9galement utilis\u00e9 famili\u00e8rement pour d\u00e9signer le d\u00e9calage de fr\u00e9quence obtenu avec certaines sources laser lorsque leur intensit\u00e9 est modifi\u00e9e. Dans un syst\u00e8me optique \u00e0 dispersion chromatique, cela provoque des changements de vitesse de propagation pour diff\u00e9rentes parties d&#039;un signal modul\u00e9 en amplitude.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Un exemple de chirp optique est une diode laser \u00e0 semi-conducteur. L&#039;indice de r\u00e9fraction du mat\u00e9riau semi-conducteur d\u00e9pend du courant traversant le mat\u00e9riau. Ainsi, lorsque le laser est modul\u00e9, la densit\u00e9 de courant change, ce qui modifie la longueur optique (longueur physique&nbsp;<em>\u00d7<\/em>&nbsp;indice de r\u00e9fraction) de la cavit\u00e9, d\u00e9calant ainsi la fr\u00e9quence centrale de la diode laser.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Les signaux chirp sont observ\u00e9s dans de nombreuses applications diff\u00e9rentes allant du radar, du sonar, du spectre \u00e9tal\u00e9, de la communication optique, du traitement d&#039;image, de l&#039;effet Doppler, de la modulation FM ou des ondes de gravitation. Le chirp de fr\u00e9quence peut limiter les performances d&#039;un syst\u00e8me \u00e0 fibre optique car lorsqu&#039;un laser \u00e0 semi-conducteur est modul\u00e9 directement, il s&#039;accompagne g\u00e9n\u00e9ralement d&#039;une modulation de phase. Le spectre d&#039;une impulsion optique est consid\u00e9rablement \u00e9largi du fait du chirp de fr\u00e9quence. L&#039;utilisation d&#039;un modulateur externe tel qu&#039;un laser \u00e0 r\u00e9troaction distribu\u00e9e (DFB) supprimera le chirp de fr\u00e9quence car il est allum\u00e9 en continu\u00a0; il n&#039;y a pas d&#039;activation et de d\u00e9sactivation, ce qui peut provoquer le probl\u00e8me.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Pour plus d&#039;informations sur le chirp optique ou pour en savoir plus sur nos produits,&nbsp;<a href=\"https:\/\/www.precisionot.com\/fr\/contact\/\">Nous contacter<\/a>.&nbsp;<\/p>","protected":false},"excerpt":{"rendered":"<p>Le chirp est un changement soudain de la longueur d&#039;onde centrale d&#039;un laser, caus\u00e9 par l&#039;instabilit\u00e9 du laser.<\/p>","protected":false},"author":33,"featured_media":1494,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"content-type":"","site-sidebar-layout":"default","site-content-layout":"default","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[6,246],"tags":[],"class_list":["post-1493","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","category-operational-technologies"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/posts\/1493","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/comments?post=1493"}],"version-history":[{"count":0,"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/posts\/1493\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/media\/1494"}],"wp:attachment":[{"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/media?parent=1493"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/categories?post=1493"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.precisionot.com\/fr\/wp-json\/wp\/v2\/tags?post=1493"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}