Abstract: An encoder apparatus including a reflective scale and a readhead. The readhead includes at least one light emitting element, at least one sensor and at least one optical device, which together with the scale form an optical system in which the optical device forms an image of an illuminated region of the reflective scale onto the sensor. The system's optical path, from the light emitting element to the sensor, passes through the optical device on its way toward and after reflection from the scale. and includes an unreflected optical path between the light emitting element and the optical device and an unreflected optical path between the optical device and the sensor.

Abstract: An encoder apparatus including a reflective scale and a readhead. The readhead includes at least one light emitting element, at least one sensor and at least one optical device, which together with the scale form an optical system in which the optical device forms an image of an illuminated region of the reflective scale onto the sensor. The system's optical path, from the light emitting element to the sensor, passes through the optical device on its way toward and after reflection from the scale, and includes an unreflected optical path between the light emitting element and the optical device and an unreflected optical path between the optical device and the sensor.

Abstract: An encoder apparatus including a reflective scale and a readhead. The readhead includes at least one light emitting element, at least one sensor and at least one optical device, which together with the scale form an optical system in which the optical device forms an image of an illuminated region of the reflective scale onto the sensor. The system's optical path, from the light emitting element to the sensor, passes through the optical device on its way toward and after reflection from the scale. and includes an unreflected optical path between the light emitting element and the optical device and an unreflected optical path between the optical device and the sensor.

Abstract: An optical element for generating diffraction orders for an encoder apparatus, in which the optical element includes an array of diffraction features arranged such that the spacing between the centres of adjacent diffraction features varies irregularly from one pair of adjacent features to the next.

Abstract: An encoder apparatus comprising a scale comprising scale features in at least one track which define a series of incremental scale marks and at least one reference mark and a readhead comprising a light source, a diffraction grating, an incremental photodetector and a reference photodetector comprising at least two detector channels. The features defining the at least one reference mark are configured such that the at least one reference mark as resolvable by each of the at least two detector channels comprises a single feature. The optical arrangement of the encoder is such that a non-imaged representation of at least the track in which the at least one reference mark is contained falls onto the detector.

Abstract: An optical element for generating diffraction orders for an encoder apparatus, in which the optical element includes an array of diffraction features arranged such that the spacing between the centres of adjacent diffraction features varies irregularly from one pair of adjacent features to the next.

Abstract: An optical element for generating diffraction orders for an encoder apparatus, in which the optical element includes an array of diffraction features arranged such that the spacing between the centers of adjacent diffraction features varies irregularly from one pair of adjacent features to the next.

Abstract: An encoder apparatus comprising a scale comprising scale features in at least one track which define a series of incremental scale marks and at least one reference mark and a readhead comprising a light source, a diffraction grating, an incremental photodetector and a reference photodetector comprising at least two detector channels. The features defining the at least one reference mark are configured such that the at least one reference mark as resolvable by each of the at least two detector channels comprises a single feature. The optical arrangement of the encoder is such that a non-imaged representation of at least the track in which the at least one reference mark is contained falls onto the detector.

Abstract: An optical element for generating diffraction orders for an encoder apparatus, in which the optical element includes an array of diffraction features arranged such that the spacing between the centres of adjacent diffraction features varies irregularly from one pair of adjacent features to the next.

Abstract: An optical element has a member having features which interact with incident light to produce two or more resultant beams. The configuration of the optical element is such that light which interacts with said features when passing through the member from a first side to produce two or more resultant beams does not interact with said features when returned to another side of the member and/or vice versa. The optical element may be used in a readhead of a scale and readhead apparatus.

Abstract: The present invention provides a polarization separation element comprising a first array of prisms having a wedge-shaped cross-section, and a second array of prisms also having a wedge-shaped cross section. One of the prism arrays is an array of birefringent prisms. The present invention also provides a polarization conversion system having a polarization separation element of the above type for directing light having a first polarization in a first direction and for directing light having a second polarization different from the first polarization in a second direction different from the first direction; and one or more polarization conversion elements for converting light having the first and second polarizations to light having a substantially common output polarization. The polarization conversion system of the invention is suitable for use in a projection display system.

Abstract: The present invention provides a polarization separation element comprising a first array of prisms having a wedge-shaped cross-section, and a second array of prisms also having a wedge-shaped cross section. One of the prism arrays is an array of birefringent prisms.

Abstract: A liquid crystal projector comprises a light source (4), a first lenslet array (6) comprising a plurality of first lenslets (10), a second lenslet array (14) comprising a plurality of second lenslets (12) and being con-focal with said first lenslet array (6), and at least one liquid crystal panel (26, 30, 36), wherein said first and second lenslet arrays (6, 14) are non-identical.