Abstract: Disclosed is a directly modulated distributed feedback laser diode optical transmitter using a vestigial side band modulation. The optical transmitter comprises an electric signal generator converting inputted signals into electric signals; a distributed feedback laser diode converting the electric signals into optical signals; and an optical tunable filter for setting a central wavelength configured to filter the optical signals using a central wavelength, perform a vestigial side band modulation of the optical signals by degenerating a determined band of the optical signals using central wavelength, and reduce the band width of the optical fibers, thereby improving the extinction ratio. By applying an optical tunable filter of a vestigial side band modulation type to an optical transmitter using a directly modulated distributed feedback laser diode, the band width of optical signals for a transmission can be reduced.

Abstract: The present invention relates to a quantitative measuring method of argon impurity contained in high purity oxygen by means of triple point and &ggr;-&bgr; phase transition of oxygen, and also to a cryostat employed in quantitative measuring of argon impurity contained in high purity oxygen.

Abstract: A high temperature platinum resistance thermometer and a method of producing such a thermometer. Both a sensor frame and a protective tube are made of mon-crystalline synthetic sapphire, which has a melting point of about 2050.degree. C. and effectively prevents vaporized metal from transmitting through it. The thermometer is thus effectively operated at a high temperature up to about 1500.degree. C. The thermometer is also provided with platinum wires capable of measuring insulating resistance, thus effectively compensating for measuring errors caused by such an insulating resistance.

Abstract: A thermoelectric refrigerator/warmer using no external power, and a refrigerating/warming method are disclosed. A natural energy such as the solar energy is utilized so as to make an external power needless. Thus a thermoelectric device is made to convert the natural energy into electric power based on the difference between the internal and external temperatures, and this electric energy is converted again into a thermal energy by means of a peltier device, thereby varying the internal temperature of the apparatus. An outer part 4 of a thermoelectric device 3 is attached on the side face of the refrigerator/warmer, and an inner part 5 of it is attached on a bottom plate 7 of the refrigerator/warmer. Thus a thermoelectromotive force is generated based on the temperature difference between outside and inside of the refrigerator/warmer. The voltage thus generated is supplied to a peltier device 6 to cool or heat the bottom plate 7.