How can I put the results of a MySQLi prepared statement into an associative array?

I have a sql query and a mysqli prepared statement:

$sql = 'SELECT photographers.photographer_id, photographers.photographer_name
    FROM photographers';

$stmt = $conn->stmt_init(); 
if ($stmt->prepare($sql)) { 
    $stmt->bind_result($photographer_id, $photographer_name);  
    $OK = $stmt->execute(); 
    $stmt->fetch();
}

How can I store the results in an associative array so I can loop it later and get to all the data returned by the sql string?