Highstocks的JSON日期格式

I am trying to retrieve data from database using json and use it to build highstocks chart but problem is date format, i am getting unix timestamps in milliseconds . Its stored as float type but when i fetch it , it displays as string . i even used int conversion but then it gives 2147483647 (because its a big number. please help
Here is the output for PHP page (json callback)

[
["1380648572000",224],
["1380648594000",223]
]

Here is jsfiddle

http://jsfiddle.net/c8mKp/

It looks like incorrect json encoding, but you should use JSON_NUMERIC_CHECK as flag or use string and then parse by parseFloat() each x value.