An optical encoder is provided. The encoder includes an optical disc mounted on a shaft, the optical disc containing pit and land markings; an optical pickup unit for an optical disc that receives light from the optical disc and supplies as an output an electrical signal representative of the received light, comprising: a reading head objective lens, and dynamic steering actuators that control the focus and tracking of the reading head objective lens; a processor that receives as an input the electrical signal from the optical pickup unit and reports motion of the substrate based on the received at least one electrical signal.

The present disclosure is to provide a photopolymer composition including a polymer matrix or a precursor thereof including a reaction product of a reactive isocyanate compound having a hydrogen bonding functional group capable of forming multiple hydrogen bonds and at least one isocyanate group, and a polyol having at least two hydroxyl groups; a photoreactive monomer; and a photoinitiator, a hologram recording medium produced from the photopolymer composition, an optical element including the photopolymer composition and a holographic recording method using the photopolymer composition.

A method of aligning a first and a second structure, the first structure comprising one or more first surface relief features and a channel system communicating with a surface of the first structure at one or more of the first surface relief features, the second structure comprising one or more second surface relief features shaped complementarily to the first surface relief features; the method comprising: generating suction in the channel system to draw the first and second structures together in a drawing direction; wherein, when the first and second structures are drawn together, the interaction between one or more of the first surface relief features and one or more of the second surface relief features aligns the structures in a plane perpendicular to the drawing direction such that the first and second surface relief features mate.

A method of aligning a first and a second structure, the first structure comprising one or more first surface relief features and a channel system communicating with a surface of the first structure at one or more of the first surface relief features, the second structure comprising one or more second surface relief features shaped complementarily to the first surface relief features; the method comprising: generating suction in the channel system to draw the first and second structures together in a drawing direction; wherein, when the first and second structures are drawn together, the interaction between one or more of the first surface relief features and one or more of the second surface relief features aligns the structures in a plane perpendicular to the drawing direction such that the first and second surface relief features mate.

An improved optical encoder uses an optical pick-up unit that provides for degrees of freedom in the tracking and focus axes that are unavailable in conventional optical encoders thereby improving the encoders' performance. In an embodiment the encoder employs an optical disc marked with pits and lands which may be arranged in a spiral pattern. The optical disc is mounted on the shaft whose motion is to be monitored by the optical encoder. The encoder may be arranged to read the markings on the optical disc using the three-beam pickup method.

For evaluating navigation information based on line-of-sight measurements, a method measures a line-of-sight measurement with an imager. The method further calculates an information metric based on the line-of-sight measurement. The information metric is a function of imager pixel measurement noise and a relative position vector for an imager frame aligned with a focal plane frame for the imager. The method evaluates navigation information using the information metric.

For evaluating navigation information based on line-of-sight measurements, a method measures a line-of-sight measurement with an imager. The method further calculates an information metric based on the line-of-sight measurement. The information metric is a function of imager pixel measurement noise and a relative position vector for an imager frame aligned with a focal plane frame for the imager. The method evaluates navigation information using the information metric.

For evaluating navigation information based on line-of-sight measurements, a method measures a line-of-sight measurement with an imager. The method further calculates an information metric based on the line-of-sight measurement. The information metric is a function of imager pixel measurement noise and a relative position vector for an imager frame aligned with a focal plane frame for the imager. The method evaluates navigation information using the information metric.

In one embodiment, a self-describing fiducial includes a communication element that optically communicates navigation-aiding information. The navigation-aiding information may include a position of the self-describing fiducial with respect to one or more coordinate systems and the communication element communicates the navigation-aiding information to one or more navigating objects in the vicinity of the self-describing fiducial.

In one embodiment, a self-describing fiducial includes a communication element that optically communicates navigation-aiding information. The navigation-aiding information may include a position of the self-describing fiducial with respect to one or more coordinate systems and the communication element communicates the navigation-aiding information to one or more navigating objects in the vicinity of the self-describing fiducial.