{
    "53a6e02221360e263e000000": {
        "_id": {
            "$id": "53a6e02221360e263e000000"
        },
        "title": "1"
    },
    "53a6e02221360e263e000001": {
        "_id": {
            "$id": "53a6e02221360e263e000001"
        },
        "title": "2"
    }
}

[
    {
        "id": "53a6e02221360e263e000000",
        "title": "1"
    },
    {
        "id": "53a6e02221360e263e000001",
        "title": "2"
    }
]

// MongoDB init before it
$cursor = $mongo->db->collection->find();
// For not large data
$result = iterator_to_array( $cursor );
$json = json_encode($result);
var_dump($json);