| 摘要 |
PURPOSE:To control the quantity of diffracted light, and to form a half tone picture by using an optical modulation element which is capable of modulating an incident luminous flux in a prescribed time by a modulating signal, and utilizing an attenuation curve part of the quantity of diffracted light. CONSTITUTION:When a video signal is inputted to a pulse generating circuit 31, a semiconductor laser 20 oscillates a pulse through a driving circuit 34. A pulse phase modulating circuit 32 modulates a phase of a pulse signal from the circuit 31 basing on information of variable density of the video signal, and applies a pulse voltage to a heating resistor of an optical modulating device LM. A luminous flux from the laser 20 forms a linear image on the optical modulation element LM by a lens system 21, and a luminous flux diffracted by a refractive index distribution generated on the heating resistor forms an image on a photodetecting medium 24. The light quantity A for illuminating the heating resistor is varied in the form of pulse at a constant period and intensity, but the applied pulse voltage B is subjected to phase modulation DELTA in proportion to the density of a picture, a generation time of the refractive index distribution is also varied in accordance therewith, and the diffracted light quantity C becomes a part shown by an oblique line, and is varied in proportion to the phase modulation quantity DELTA. |
