Abstract: Apparatus for use with an imaging optical system, to indicate both the direction and magnitude of focus adjustment, includes a diffractive optical element exposed to a broad spectrum of radiation. The element filters out a narrow spectrum of the radiation and directs it into a path centered on detectors in a circuit that indicates the required focus adjustment. According to one feature of the invention, two detectors are used, and the focusing adjustment signal is determined by the difference in signal between the two detectors, eliminating absolute intensity and reflectivity from the focusing determination. Still another feature employs a holographic diffractive element transparent to most of the broad spectrum, but reflective in a narrow spectrum corresponding to detector sensitivity. This permits positioning of the holographic element between the optical system and its focal plane without significantly degrading the focused image. The focusing element can remain in position during imaging.

Abstract: A laser diode comprises an optically active planar waveguide and a volume refractive index grating for providing distributed optical feedback of stimulated radiation to the waveguide. According to the invention, the grating comprises a stack of alternating thin layers each layer being less than 300 nm. thick) of two materials having different indices of refraction. At least one side of the stack provides a smooth, planar surface composed of the respective edges of each grating layer. The active waveguide, together with optional cladding and separate-confinement heterostructure (SCH) layers, are epitaxially grown atop the smooth grating surface, whereby the respective planes of such layers are substantially perpendicular to the respective planes of the grating layers. The smooth surface of the grating is advantageous in that it promotes good crystalline growth of the subsequently grown layers of the laser diode structure and reduces the number of non-radiative recombination sites.

Abstract: Two novel structures of a high-quantum efficiency, wavelength-tunable, surface-emitting, low threshold laser diode which optimally utilizes certain advantages of a distributed feedback (DFB) structure. The preferred embodiments combine a separate confinement heterostructure (SCH), surface-emitting distributed feedback laser diode structure with a multiple quantum well (MQW) active layer and an index-guiding buried heterostructure. A wave-length tuning section is included in the device structure for wavelength adjustment, and an arrangement of transparent electrodes useable for ohmic contacts to the device provide anti-reflection coatings for the emitting portion of the device. A first preferred embodiment is termed the SELTH laser diode (surface emitting, low threshold). A second, related preferred embodiment combines the SELTH laser diode structure with additional optical elements to provide a collimated output beam and is termed the COSELTH laser diode (collimated, surface emitting, low threshold).

Abstract: An electrophotographic copier/duplicator having a 17".times.11" wide endless photoconductor includes single imaging apparatus for forming and processing a single 17".times.11" image at a time, within a 17".times.11 " image frame of its photoconductor, and dual imaging apparatus for simultaneously forming and processing two 8.5".times.11" images at a time, within a 17".times.11" image frame of such photoconductor.

Abstract: A light scanning system for moving a light beam across a straight surface. The system includes a laser light source, a rotating holographic disk deflection system, and a multielement F.theta. lens constructed entirely of holographic plates. The holographic plates are offset from each other in the beam path and have parameters which cause the holographic plates to optically cooperate with each other to produce uniform spot size and scan velocity. Specific construction parameters and methods are outlined along with particular materials and parameter ranges.

Abstract: A method and apparatus is provided for line scanning a beam receiving member, wherein a scanning beam is angularly or laterally displaced to compensate for scan line spacing error. The beam is displaced according to error arising from variation (flutter) in the relative motion of the beam and the beam receiving member, or according to error arising from movement of the receiving member while the scanning beam travels to a start of scan position, or both. Embodiments of beam displacement means include a refracting tilt plate, a reflecting tilt plate, a diffracting tilt plate, and a tilt prism.