Fujitsu Corporation

Tomoyuki Otsuka

Norio Nagase

Motoyoshi Sekiya

Hiroyuki Furukawa

Tetsuya Kiyonaga

Yuji Tamura

Setsuo Misaizu

Hisaya Sakamoto

Akimitsu Miyazaki

Akihiko Hayashi

Takashi Kurooka

Shinichiro Sano

Hiroshi Kuwahara

A constant current driving circuit for supplying a constant current to a load circuit includes: a first driver circuit having a pulse width converting circuit for converting a first difference detection signal into a pulse signal having a pulse width corresponding to a signal level of the first difference detection signal, a switch turned on/off on a basis of the pulse signal, and a smoothing circuit for supplying a smoothed first load current to the load circuit; a first current detecting circuit for converting the first load current into a first voltage corresponding to the first load current, and outputting a first current detection signal; a second driver circuit for supplying a second load current to the load circuit on a basis of a signal level of a second difference detection signal; a second current detecting circuit for converting the second load current into a second voltage corresponding to the second load current, and outputting a second current detection signal; a first difference detecting circuit for calculating the first difference detection signal to make zero a difference between the first current detection signal and an input voltage; a second difference detecting circuit for detecting a difference voltage between the first current detection signal and the input voltage, and outputting a third difference detection signal; and a third difference detecting circuit for detecting a difference voltage between the third difference detection signal and the second current detection signal, and outputting the second difference detection signal.

Constant current driving circuit

The optical receiver includes: an optical input port for receiving WDM signals; a transmittable-wavelength-variable filtering unit which transmits, of the received WDM signals, a light signal in a predetermined transmittable wavelength bandwidth with a desired central wavelength of &#x3bb;i (i=1 to n: n is an integer number greater than 2); an optical output port which outputs the remaining light signals at wavelengths (&#x3bb;i) (k=1 to n; k&#x2260;i) untransmittable through the transmittable-wavelength-variable filtering unit; and a control unit which controls the central wavelength so that the level of the light signal passing through the transmittable-wavelength-variable filtering unit is the maximum. It is whereby possible to flexibly accommodate changes in number of channels combined in a WDM system, and to adaptively minimize ASE light leaking into the photoreceptor of the optical receiver even in a CWDM system with wide channel spacing.

Optical receiver and optical transmission apparatus

In a receiving apparatus, there are included a compensation characteristic variable type waveform degradation compensating unit capable of compensating for waveform degradation of a received signal stemming from a transmission line, a received waveform measuring unit for measuring waveform data on the received signal (which will be referred to hereinafter as &ldquo;received waveform data), and a control unit for controlling a compensation characteristic of the waveform degradation compensating unit to minimize a difference between frequency data on the received signal, obtained by converting the received waveform data acquired by the received waveform measuring unit into a frequency domain, and frequency data on a reference waveform free from waveform degradation. With this configuration, certain compensation for the waveform degradation of the received signal stemming from chromatic dispersion or the like becomes feasible without using a dispersion compensation fiber.

Receiving apparatus, method of compensating for waveform degradation of received signal, apparatus and method for detecting waveform degradation, and apparatus and method for measuring waveform

The invention relates to a modulation controlling circuit for supplying a modulating signal to an external modulator that outputs a modulated optical signal, while setting a proper operating point in the external modulator. The external modulator that operates in cooperation with the modulation controlling circuit of the invention enables high-quality modulation at a wide bit rate range. Therefore, in an optical transmission system or a measuring instrument to which the invention is applied, the characteristics and the performance are improved and the operation is made stable without loss of advantages of the external modulator.

Modulation controlling circuit

The optical transmission apparatus for multiple wavelengths according to the present invention comprises; a light source, a temperature control section for controlling the temperature of the light source, a temperature control (ATC) loop for controlling the operation of the temperature control section, and a wavelength control (AFC) loop. The ATC loop detects the temperature of the light source and feedback controls the operation of the temperature control section, so that the optical output wavelengths of the light source fall within a wavelength capture range corresponding to a target wavelength of the AFC loop. The AFC loop has a wavelength detection filter having a periodic transmission wavelength characteristic. After the operation of the ATC loop has stabilized, a wavelength capture operation is commenced, and the operation of the temperature control section is controlled so that the optical output wavelength of the light source is captured at a stable point corresponding to a target wavelength, among a plurality of stable points.

Growing community of inventors

Kawasaki, Japan

Tomoyuki Otsuka