使用 Intervention/image 为照片添加水印 出现乱码空格

$text = $this->to_unicode('科室ID撒水水水水水水水飒飒'); 
$image = Image::make('images/as.jpg')->text($text, 50, 50, function($font) { 
       $font->file(public_path('fonts/FontAwesome.ttf')); 
       $font->size(20); 
       $font->align('center'); 
       $font->valign('top'); 
}); 
$image->save('images/new_avatar.jpg');

function to_unicode($string)
{ 
  $str = mb_convert_encoding($string, 'UCS-2', 'UTF-8'); 
  $arrstr = str_split($str, 2); 
  $unistr = ''; 
  foreach ($arrstr as $n) { 
       $dec = hexdec(bin2hex($n)); 
       $unistr .= '&#' . $dec . ';'; 
  } 
  return $unistr; 
}

请问这是什么情况