function UnicodeEncode($str){
    //split word
    preg_match_all('/./u',$str,$matches);

    $unicodeStr = "";
    foreach($matches[0] as $m){
        //拼接
        $unicodeStr .= "&#".base_convert(bin2hex(iconv('UTF-8',"UCS-4",$m)),16,10);
    }
    return $unicodeStr;
}

//$str = "新浪微博";
//echo UnicodeEncode($str);

function unicodeDecode($unicode_str){
    $json = '{"str":"'.$unicode_str.'"}';
    $arr = json_decode($json,true);
    if(empty($arr)) return '';
    return $arr['str'];
}

$unicode_str = "\u65b0\u6d6a\u5fae\u535a";
echo unicodeDecode($unicode_str);