Eight-element polarisation independent transmission trap detector with high attenuation

A polarisation-insensitive transmission trap detector was constructed from two identical polarisation-dependent transmission trap detectors, each containing four 10 mm × 10 mm silicon photodiodes. The performance of the 8-element polarisation-independent and coaxial input-output transmission trap detector has been characterised at laser wavelengths of 635 nm and 850 nm. The measured transmittances are lower than 10⁻⁴ and are in agreement with values calculated from the reflectances of single photodiodes. The measured relative transmittances and responsivities are independent of polarisation within 0.12%. The spectral responsivity is spatially uniform within 0.1% across an area of 4 mm × 4 mm , consistent with the expected variations due to the oxide layer thickness of the photodiodes.