Abstract: This invention provides the easy and consistent displacement control of a piezo-electric actuator for driving the variable wavelength filter used for wavelength multiplexed optical communication, wherein the piezo-electric actuator is controlled once to the initial displacement condition and, thereafter, a driving voltage is applied to the piezo-electric actuator based on the displacement characteristic data stored in a memory circuit for obtaining a desired displacement.

Abstract: An apparatus and a method for performing hitless switching between optical transmission lines such as optical fiber circuits are provided. An optical switch or optical switching network having input terminals and output terminals for selecting optical signals inputted to the input terminals to the output terminals with a selection ratio which can be varied continuously is used. An optical signal converter for generating an optical signal of light which does not interfere with another optical signal is attached to the optical switch. Further, a signal loop interconnecting one of the output terminals of the switch and the input of the optical signal converter is provided.

Abstract: The output light of a variable-wavelength light source 101 is brought to incidence on an optical resonator 103 having a periodic transmitting characteristic, and the transmitted light is detected by an optical intensity detector 105 and, having the difference from a reference level as the error signal, fed back by an operational amplifier 106 to the variable-wavelength light source 101. Therefore the output light frequency of the variable-wavelength light source 101 is stabilized at the shoulder of the peak of the transmitting characteristic (the point where the transmittance varies) of the optical resonator 103. Wavelength switching is accomplished by selecting one out of two variable current sources built into a wavelength control circuit 108. This variable current source switching forcibly shifts the stabilization point to the shoulder of the peak of another transmittance of the optical resonator 103.

Abstract: A frequency stabilization method of a semiconductor laser is provided. A driving current, a forward voltage and an output light power of the laser mounted on a heat sink is detected. A temperature of the heat sink is also detected. A consumption power of the laser is obtained from the driving current and voltage thus detected, providing a relationship between the output light power and the consumption power. The driving current is controlled so that the output light power is kept constant, and the temperature of the heat sink is controlled based on the relationship so that a temperature of an active layer of the laser is maintained. The output light power is kept constant and at the same time, any temperature change of the active layer is cancelled through the temperature control of the heat sink.

Abstract: An apparatus for controlling an acousto-optic filter includes a high-frequency oscillator, a beam intensity detector, a first and a second oscillator, and a first and a second controller. The high-frequency oscillator drives the acousto-optic filter and the frequency of the driving signal is finely modulated by oscillation frequency f.sub.0 of the first oscillator. The detector detects an output signal beam intensity of the acousto-optic filter. An output of the detector is synchronously detected at the frequency f.sub.0 and the frequency of the driving signal is controlled by the first controller so that the resultant detected output becomes zero. Similarly, the amplitude of the driving signal is finely modulated by the oscillation frequency f.sub.1 of the second oscillator. The output of the detector is synchronously detected at the frequency f.sub.1 and the amplitude of the driving signal is controlled by the second controller so that the resultant detected output becomes zero. The frequency f.sub.

Abstract: An optical scanning device comprising a transmission or reflection hologram disk, wherein recording beams, such as an object and a reference beam which are used in preparing holograms, and a reconstructing beam which is used in reconstructing or scanning, are spherical waves having different wavelengths; and wherein the sources of recording beams and reconstructing beams are located at different positions for enabling the beams to fall obliquely on the hologram disk to cause a reconstructed image on a focusing or scanning plane to be subjected to linear aberration free scanning. The incident angle of the reconstructing beam on the hologram disk meets the Bragg condition for high diffraction efficiency.