1. A quality assessment apparatus for assessing the quality of an optical component, the optical component comprising an arrangement of a first and a second component grating having a component relative orientation angle, wherein the quality is assessed in terms of a deviation of the component relative orientation angle from a desired relative orientation angle, the apparatus comprising: a configurable support system configured to support a master component comprising a substantially matching arrangement of a first and a second master grating having the desired relative orientation angle and to support the optical component with the first and second component gratings in the vicinity of the first and second master gratings, the apparatus further comprising: a light sensor configured to receive light which has interacted with both of the first gratings and light which has interacted with both of the second gratings, and to generate sensor data from the received light; a drive mechanism coupled to the support system; and a controller configured (i) to control the drive mechanism based on the sensor data to reconfigure the support system from a current configuration to a new configuration in which the fringe spacing of a first fringe pattern formed by the first gratings is substantially maximal and (ii) to measure from the sensor data the fringe spacing of a second fringe pattern formed by the second gratings in the new configuration, and to output a quality assessment based on the measured fringe spacing which is indicative of the deviation of the component relative orientation angle from the desired relative orientation angle.