| 摘要 |
PURPOSE:To permit easy control of a change in the focal length of a thin semiconductor film generated by a change in the emission wavelength of a light emitting device such as semiconductor laser by changing the quantity of the carriers to be implanted to the thin film lens. CONSTITUTION:The implantation of the carriers to the thin film lens is permitted by connecting ohmic contacts 4, 5 to a power supply. A band gap expands apparently when the carriers are implanted to the thin film lens and, therefore, the effective refractive index thereof decreases and the focal length thereof increases according to the quantity of the carriers implanted. The focal length can be maintained constant by increasing and decreasing a current value so as to compensate the change in the refractive index when the emission wavelength of the light source changes. Since the refractive index of a semiconductor material generally decreases with an increase in the wavelength, the refractive index of the thin film lens decreases as well when the emission wavelength of the light source increases. The quantity of the current to be supplied to the thin film lens is decreased in order to compensate such decrease. The easy control of the focal length is thus permitted. |
