How does the iRobot create IR beacon work?

[Razor Concepts]

I have worked with the iRobot create, a plain version of the roomba. Like the roomba, the create has some kind of 360 degree IR sensor:


That little disc has a inverted cone-shaped mirror to presumably deflect the horizontal IR beam down vertically. But how does it detect around 360 degrees? Is there just a circle of small IR receivers?

[waltr]

What I recall reading is that there are four small mirrors that reflect the beacon light down to four photodetectors one for each direction.