An optical device (32) transfers an optical signal to or from an electronics unit (30) used in relation to downhole equipment of a drilling operation. The device includes a body (38) and an optical signal direction or light path altering means (40), the body having a light path arranged to allow the optical signal from a light source (16,18) associated with the electronics unit to pass to the optical signal direction altering means, the optical signal direction altering means arranged to cause the optical signal to change direction of travel within the body of the optical device.