return an unescaped json

Hi, i have some strings like 

["000"]

and with the classic $this->respond($mydata, 200) i can't unescape this. the json output is always "[\"000\"]"
I've also try

PHP Code:

    return $this->response->setStatusCode(200)
    ->setHeader('Content-Type', 'application/json')
    ->setBody(json_encode($mydata, JSON_UNESCAPED_SLASHES)); 


but the result is the same.

Any suggestion?
Thanks in advance