One more way to use ajax in cakephp. Cakephp provide itself for ajax request. Please see example.
$data = $this->Js->get('#id')->serializeForm(array('isForm' => true, 'inline' => true));
//on click send request to controller and displays response data in view
$this->Js->get('#button-id')->event(
'click', $this->Js->request(
array('controller' => 'Users', 'action' => 'add'), array(
'update' => '#time', // field you wish to update
'data' => $data, // Form Data in serialize form
'async' => true,
'dataExpression'=>true,
'method' => 'POST' // method get or post
)
)
);