A near-infrared spectroscopy (NIRS) sensor assembly for measuring a characteristic of a biological tissue is provided. The NIRS sensor assembly includes a light source (22), at least one light detector (24,26), and a layer (32) disposed within the sensor assembly. The light source (22) is operable to emit light at one or more predetermined wavelengths. The at least one light detector (24,26) has an active area for detecting light emitted by the light source (22) and passed through the biological tissue. The light detector (24,26) is operable to produce signals representative of the detected light. The layer (32) disposed within the sensor assembly has at least one deflection element (98).
