invalid JSON

I have a page with <select> items. I'm getting their values from a AJAX request, as a JSON string :

[{"product_option_1":[{optionValue:1, optionDisplay:S}]},{"product_option_2":[{optionValue:3, optionDisplay:Rouge}]}]

product_option_1 and product_option_2 are the name of my <select> items. and into the brackets, their values.
But Firebug tells me that JSON is not valid.

Where is the mistake ?