1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｔｈｅｉｎｆｒａｒｅｄｔｏｖｉｓｉｂｌｅｕｐｃｏｎｖｅｒｓｉｏｎｐｒｏｃｅｓｓｅｓｉｎｒａｒｅｅａｒｔｈｄｏｐｅｄｆｉｂｅｒｈａｖｅｂｅｅｎａｔｔｒａｃｔｉｎｇｇｒｅａｔｉｎｔｅｒｅｓｔｂｅｃａｕｓｅｏｆｉｔｓａｐｐｌ?.. 1 Introduction Theinfraredtovisibleupconversionprocessesinrareearthdopedfiberhavebeenattractinggreatinterest......