Cselt-centro Studi E Laboratori Telecomunicazioni S.p.a.

Agilent Technologies, Inc.

Cselt- Centro Studi E Laboratori Telecommunicazioni Spa

Francesco Cisternino

Riccardo Calvani

Renato Caponi

Raffaele Girardi

Andrea De Marchi

Stefania Roemisch

Gianni Coppa

Diego Roccato

Emilio Riccardi

This invention concerns a method of and a device for optical demultiplexing that are based on the four wave mixing between the signals to be demultiplexed and pump signals. The two signals are fed into a polarization maintaining fiber ( ), which divides them into two components with orthogonal polarization, separated in time; and the four wave mixing is performed separately on the two components, thereby originating two separate signals that are polarization-rotated and re-combined. (FIG. ).

Method of and a device for polarization-independent optical demultiplexing

The circuit includes an electro-optical mixer, such as an electro-optical Mach-Zehnder modulator, with non-linear behavior. The modulator receives as input an optical signal (P,) at the frequency to be divided, in addition to an electric signal (e,) at a given frequency, usually corresponding to the frequency deriving from such division. The output optical signal (P,) from modulator exhibits a modulation spectrum containing the frequency difference between the frequency to be divided and at least one harmonic of the frequency of the above electric signal. After having been converted into an electric signal (e,), the output signal of the mixer is subjected to a filtering action to extract the above frequency difference component. This latter one is then used both as electrical signal (e,) for the mixing, and as output signal from the divider (e,). The preferred application is to OTDM systems, to extract a synchronism signal as tributary signal frequency.

Opto-electronic frequency divider circuit and method of operating same

The circuit includes an electro-optical mixer, such as an electro-optical Mach-Zehnder modulator (,), with non-linear behaviour. The modulator (,) receives as input an optical signal (P,) at the frequency to be divided, in addition to an electric signal (e,) at a given frequency, usually corresponding to the frequency deriving from such division. The output optical signal (P,) from modulator (,) exhibits a modulation spectrum containing the frequency difference between the frequency to be divided and at least one harmonic of the frequency of the above electric signal. After having been converted into an electric signal (e,), the output signal of the mixer is subjected to a filtering action (,) to extract the above frequency difference component. This latter one is then used both as electrical signal (e,) for the mixing, and as output signal from the divider (e,). The preferred application is to OTDM systems, to extract a synchronism signal at tributary signal frequency.

Ultra-short transform-limited optical pulses, to be utilized for high bit-rate transmission systems, are obtained through direct modulation of a semiconductor laser by pulses of such duration as to excite only the first peak of the relaxation oscillations of the cavity of laser, tuned to such a length that the pulse portions that overlap inside the cavity interfere constructively. The pulses emitted by the laser then pass upon a fiber with high negative dispersion to compensate for the phase effect due to the chirp.

Method for the generation of ultra-short optical pulses

A constant force perpendicular to the fiber axis is applied to the fiber so as to cause a power coupling from the fundamental mode, which is guided, to a secondary mode which is irradiated, and the intensity of the scattered radiation associated with that secondary mode is measured. Such intensity depends on the local state of polarization. By dispacing the force application point step by step along the fiber axis and by measuring for each point the intensity of the scattered radiation, beat length is obtained as the distance between two consecutive points where the scattered radiation has the same intensity.

Method of measuring polarization and birefringence in single-mode

The interferometer makes use of an acousto-optic device to perform a frequency shift of the beam sent along one of the interferometer branches, so as to allow the determination of the state of polarization by heterodyne radiofrequency detection. The acousto-optic device can be inserted downstream of the device for splitting the beam emitted by the source into the two beams sent along the two interferometer branches, or it can also act as the beam splitter.

Heterodyne michelson interferometer for polarization measurements

Optical-fiber transmission system with heterodyne coherent detection in which, at the transmitting side, the polarization of an optical carrier is modulated, and at the receiving side the beam resulting from a combination of the modulated beam and a beam emitted from a local oscillator is split into two orthogonally-polarized components. The two optical signals are detected and sent to an electronic mixer which receives the two components and carries out a synchronous demodulation eliminating the effects of the linewidth of the source and of the local oscillator.

Optical-fiber transmission system with polarization modulation and

The monochromator presents, in the plane of the slit (5), a mirror (6) which reflects the radiations comprised within the spectrum portion selected by the slit (5) towards the grating (3) dispersing a non-monochromatic beam. The radiations reflected recombine into a single, substantially monochromatic beam on the grating (3), and a suitable optical system (7,8) focuses such a beam forming the substantially monochromatic image of the source (1).

Imaging monochromator

Method and device for realtime measurement of the state of polarization at a quasi-monochromatic light beam. Two quasi-monochromatic radiations with slightly different optical frequencies are generated. A radiation is converted into a 45.degree. linearly polarized radiation, while the other presents the polarization state imposed by a body under test. In each radiation, horizontal and vertical polarization components are separated, and then recombined into two different beams comprising radiations at both frequencies, respectively polarized in the same plane. Beatings between the two components of each beam are originated and from the two electrical signals in the radiofrequency range thus obtained the information is extracted on the relative phase and the amplitude of the two components of the radiation with polarization imposed by the body under test.

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Turin, Italy

Francesco Cisternino