We demonstrated low cost and power-efficient a 2.5 Gb/s optical wireless transmission system at 10 cm distance, which should be employed in high-energy physics experiments such as Compact Muon Solenoid. The system uses an off-the-shelf VCSEL and a PIN photodiode with proper ball lens. Its most attractive feature is that it does not need a complex active tracking system because its measured tolerance to misalignment is around +/-1mm at Bit Error Rate of 10^-12. The experimental results show that this can be a viable solution for future HEP experiments.