Can anyone identify this mystery photo-interrupter?

Dear All, Can anyone identify this

mystery photo-interrupter for me? It comes from a custom laboratory instrument made at a German university, for which I have no documentation :-{. The interrupting device is a 'spoked' code wheel. That and the device's six pins make me fairly sure it must be an encoder type. The closest looking devices I could find browsing RS, Farnell, Mouser & DigiKey websites are the Honeywell HOA0901 & HOA0902 but their 4 sensor side pins are arranged to define a parallelogram rather than truncated pyramid mine has. Any ideas?

Many thanks Tom Crane

Ps. The email address in the header is just a spam-trap.

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Tom Crane, Dept. Physics, Royal Holloway, University of London, Egham Hill, 
Egham, Surrey, TW20 0EX, England.  
Email:  T dot Crane at rhul dot ac dot uk