Formation of a Diffractional Grating by Magnetic Lithograph
A new method to make an optical diffraction grating has been developed using the Bitter method. A periodic magnetic pattern like 0101 ... is written in a magnetic memory medium, and a magnetic fluid is used as magnetic toner to visualize this pattern. To enhance the contrast of the grating, an interfacial active agent in the magnetic fluid is destroyed by a certain organic solvent, and a DC magnetic bias field is applied to the memory medium to thicken the pattern. When a transparent grating is required, Au film is deposited on it as a parting agent after the formation of a magnetic toner pattern. After separation of the epoxy resin film from the memory medium, Au film is chemically etched. A sharp diffraction image is observed by projecting a laser diode onto the diffraction grating. Using this method, an optical grating can easily be made even on a convex or concave surface.
High-resolution laser linear encoder with numerical error compensation
Metrological feasibilities of the prototype of a high-resolution displacement encoder with a laser diode light beam focused on the scale surface are investigated. Resolution of 0.01 µm has been obtained. The repeatability of the system ranges from 0.02 to 0.03 µm. A new simple reference point detection method that uses a scale grating edge as a reference point has been proposed. We suggest two possible ways of implementation of this method: analog by dc signal component extraction and digital by signal amplitude extraction. The proposed reference point detection technique allows significant reduction of nonlinearity errors of the measuring system. Nonlinearity of the prototype device does not exceed 0.1 µm in the 48-mm measuring range. Due to the application of a focused laser beam, the proposed optical system is extremely insensitive to disturbing shifts and tilts of the scale. The acceptable tilts of the encoder detection head relative to the grating in the prototype device reach about 0.5 arcdeg in all directions. The tolerance of the distance between detection head and the grating is approximately equal to 0.1 mm.
Criteria for designing V-groove lasers
For designing V -groove lasers, the influence of the width of current injection w and the distance d of the diffusion front from the active layer is considered. Two laser designs with stable emission properties have been found: the first possibility consists of using a narrow current injection ( w \approx 3 \mu m) while, alternatively, a wider current injection ( w \approx 5...8 \mu m) can be used if d is less than about 0.5 μm, since a built-in antiwaveguide is then formed and this antiwaveguide stabilizes laser emission.