DIGITAL OPTICAL MODULATOR

摘要

1,220,486. Light modulators. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 23 Feb., 1968 [25 Feb., 1967], No. 8909/68. Heading H4F. A digital electro-optic or magneto-optic modulation arrangement comprises at least two separate modulators of different construction and/or different electric or magnetic operating characteristics which are successively passed by the radiation to be modulated, each modulator being individually switchable between two operating points in which the electro-optic or magneto-optic material is subject to different electric or magnetic field strengths. The modulators may comprise Kerr or Pockels cells in which the electro-optic material is nitrobenzene, KDP or KTN, the length of the cells, the spacing of the electrodes of the cells, the voltages applied to the cells, or the lengths and voltages of the cells being varied from cell to cell (Figs. 2-4, not shown). Different lengths of magnetooptic material e.g. YIG, may be subjected to a magnetic field (Figs. 5, not shown). To obtain a more homogeneous polarization of the electrooptic material, dielectric plates of material having a small dielectric constant compared to the dielectric constant of the electro-optic material are interposed between adjacent modulators the refractive index of the two materials being substantially equal (Fig. 8, not shown). To produce a system in which the intensity of a radiation beam may be varied in logarithmically equidistant steps, the dielectric plates of Fig. 8 are arranged to comprise plane polarizers or are replaced by plane polarizers (e.g. Nicol prisms or multilayer dielectrics one layer of which comprises a plane polarizer) having the same direction of polarization (Fig. 9, not shown), the direction of polarization being preferably at 45 degrees to the direction of the electric field in the modulators. Each modulator thus changes the intensity of the radiation beam by a factor F i which is less than one. The resulting intensity of the beam after passage through the entire modulator thus equals I = I 0 F 1 F 2 F 3 . . . F n or 1nI= 1nI 0 + 1 n F 1 + 1nF 2 + .... A binary system having logarithmically equidistant stages is obtained, for example, by making F 1 = 0À5, F 2 = 0À52, . . . F i = 0À5i.