The insertion loss of a fiber optical rotary joint depends on the mechanical misalignments of the collimating lenses. To achieve 3-dB or lees insetion loss, the lateral misalignment of the braded-index (GRIN) lenses should be less than 100μm, and the angular tilt of these lenses is limited to 0.1 deg. These requirements cause a high mechanical abrication and assembly cost. To solve this problem. We design a singlechannel optical rotary joint using a bulk optical detector. The requirement on lateral misalignment is relaxed to 500μm, and the angular tilting is relaxed to 2 deg. Using this method, the cost of the optical rotary joint can be dramatically reauced.