Abstract: An optical multiplexer/demultiplexer with an improved spectral characteristic is provided by two diffraction gratings (61, 60) arranged optically in tandem, the gratings being arranged to provide free spectral ranges differing by a factor of at least two, and having a coupling between them that carries over into the second grating information concerning the dispersion afforded by the first grating.

Abstract: A two-sided display for changeably displaying identical indicia, such as letters or numbers, on each side of the display. Two or more rolls of indicia are located in a housing, the housing having openings on each side for display of the numbers or characters. The rolls vary in width, and the smallest roll bears the left-most information to be displayed. Succeeding rolls have their printed information straddling the next preceding roll so that information appears serially and identically on both sides of the display. Due to use of rolls, changing of the indicia on one side of the display automatically changes the indicia identically on the other side of the display.

Abstract: An integral cover for a hardback book is disclosed. The book has an edge binding and a pair of stiff side panels, and the cover includes and features a thermoplastic sheet comprising between about 60 to about 85% by weight of a polypropylene homopolymer, between about 12 and about 32% by weight calcium carbonate, and between about 3 to about 12% by weight of a low density polyethylene carrier for the calcium carbonate. The edges of the thermoplastic sheet are turned over the edges of the stiff side panels of the book and adhesively secured thereto and smooth, wrinkle-free gutters are formed in the thermoplastic sheet between the edge binding of the book and each of the stiff side panels to provide hinges for the covered side panels. The cover is a substitute for book covers made of cloth, paper or vinyl and the formulation permits the sheet material to be easily cut, smoothly formed in the gutters and reduces the tendency of blocking and of sticking to the hot lettering stamp.