Magento – How to return a JSON object with a custom REST API in Magento 2

I'm writing a custom REST API demo; now it can return numbers and strings in my demo, but I want it to return a JSON object like other REST APIs.

In my demo, I call the Magento 2 API (i.e. get customer info: http://localhost/index.php/rest/V1/customers/1) with curl, and it returns a JSON string:

"{\"id\":1,\"group_id\":1,\"default_billing\":\"1\",\"created_at\":\"2016-12-13
14:57:30\",\"updated_at\":\"2016-12-13
15:20:19\",\"created_in\":\"Default Store
View\",\"email\":\"75358050@qq.com\",\"firstname\":\"azol\",\"lastname\":\"young\",\"store_id\":1,\"website_id\":1,\"addresses\":[{\"id\":1,\"customer_id\":1,\"region\":{\"region_code\":\"AR\",\"region\":\"Arad\",\"region_id\":279},\"region_id\":279,\"country_id\":\"RO\",\"street\":[\"abc\"],\"telephone\":\"111\",\"postcode\":\"1111\",\"city\":\"def\",\"firstname\":\"azol\",\"lastname\":\"young\",\"default_billing\":true}],\"disable_auto_group_change\":0}"

The response is a JSON string, but all the keys have a slash within. I know I can remove the slash with str_replace, but it's a stupid way. Is there any other way to return a JSON object without slashes within keys?

************ UPDATE 2016.12.27 ************

I pasted my test code here:

   $method = 'GET';
    $url = 'http://localhost/index.php/rest/V1/customers/1';

    $data = [
        'oauth_consumer_key' => $this::consumerKey,
        'oauth_nonce' => md5(uniqid(rand(), true)),
        'oauth_signature_method' => 'HMAC-SHA1',
        'oauth_timestamp' => time(),
        'oauth_token' => $this::accessToken,
        'oauth_version' => '1.0',
    ];

    $data['oauth_signature'] = $this->sign($method, $url, $data, $this::consumerSecret, $this::accessTokenSecret);

    $curl = curl_init();

    curl_setopt_array($curl, [
        CURLOPT_RETURNTRANSFER => 1,
        CURLOPT_URL => $url,
        CURLOPT_HTTPHEADER => [
            'Authorization: OAuth ' . http_build_query($data, '', ','),
            'Content-Type: application/json'
        ], 
    ]);

    $result = curl_exec($curl);
    curl_close($curl);

    // this code has slash still
    //return stripslashes("hi i\" azol"); 

    // has slashes still
    //return stripcslashes("{\"id\":1,\"group_id\":1,\"default_billing\":\"1\",\"created_at\":\"2016-12-13 14:57:30\",\"updated_at\":\"2016-12-13 15:20:19\",\"created_in\":\"Default Store View\",\"email\":\"75358050@qq.com\",\"firstname\":\"azol\",\"lastname\":\"young\",\"store_id\":1,\"website_id\":1,\"addresses\":[{\"id\":1,\"customer_id\":1,\"region\":{\"region_code\":\"AR\",\"region\":\"Arad\",\"region_id\":279},\"region_id\":279,\"country_id\":\"RO\",\"street\":[\"abc\"],\"telephone\":\"111\",\"postcode\":\"1111\",\"city\":\"def\",\"firstname\":\"azol\",\"lastname\":\"young\",\"default_billing\":true}],\"disable_auto_group_change\":0}");

    // has slashes still
    //return json_encode(json_decode($result), JSON_UNESCAPED_SLASHES);

    // this code will throw and expcetion:
    // Undefined property: *****\*****\Model\Mycustom::$_response
    //return  $this->_response->representJson(json_encode($data));

    return $result;