Laravel 5.2 Storing an array of values in session

I am trying to store values of file paths during the Ajax upload. This is my code:

public function ajaxUpload() {
  $name = "";
  $path = public_path('files/uploads/articles/');

  if (Input::hasFile('file')) {
    $files = Input::file('file');
    $filePath = [];

  foreach($files as $file){
    $fP = $path.$file->getClientOriginalName();
    Image::make($file)->resize(100, 100)->save($path.'/'.$file->getClientOriginalName());
  }

  if (Session::has('file.Path')){
    Session::push('file.Path', $fP);
    Session::save();
  }
  else {
     Session::put('file.Path', $fP);

     Session::save();
}

return json_encode(Session::get('file.Path'));
}

But then I get an error of:

  LOG.error: Symfony\Component\Debug\Exception\FatalThrowableError: Fatal error: [] operator not supported for strings in /home/vagrant/Projects/myProject/vendor/laravel/framework/src/Illuminate/Session/Store.php:411

And when I try like this:

public function ajaxUpload() {
  $name = "";
  $path = public_path('files/uploads/articles/');

  if (Input::hasFile('file')) {
    $files = Input::file('file');

   foreach($files as $file){
     $filePath[] = $path.'/'.$file->getClientOriginalName();
     Image::make($file)->resize(100, 100)->save($path.'/'.$file->getClientOriginalName());
   }
   Session::put('filePath', $filePath);
   return json_encode($filePath);
   }
   return 'string';
 }

Then it stores each of the paths separately and not in one array, so I only save one path in DB.