It's a special RF remote. It works directly with the dock. It is rather short range too, likely because it uses a button cell battery. On the plus side, the dock enables USB host, allowing for use of flash drives, keyboards and mice.
I got mine for $55 on ebay. Keep in mind that it doesn't come with the hdmi cable(I know), but you can get one from amazon for like $5.
[Edit] It looks like I was wrong. It is IR. Just checked it with my camera app. Most camera sensors detect IR and translate it into white light.
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