Abstract: A device and method for stabilizing the polarization of polarization multiplexed optical radiation includes an identified channel which is provided with a pilot signal.

Abstract: Optical telecommunications system, comprising: a transmitting station capable of emitting an optical signal having a power of between 18 and 30 dBm; an optical fibre transmission line capable of transmitting the said optical signal, comprising dispersion shifted fibre with a length of between 100 km and 1000 km; an optical receiving station, capable of receiving the said optical signal; which comprises, between the said transmission line and the said optical receiver, a chromatic dispersion compensator. Preferably the said optical fibre transmission line has a length of between 200 and 400 km.

Abstract: An optical fiber power amplifier, particularly for telecommunication lines with optical fibers, including an active fiber doped with Erbium as a fluorescing substance, and with Al.sub.2 O.sub.3 as refraction index modifying dopant. The fiber is pumped with a laser providing a wavelength higher than 520 nm and preferably, 980 nm. The amplifier has a particularly high amplification efficiency close to the theoretical maximum efficiency.

Abstract: An optical signal generator for telecommunication systems, comprising at least a single-frequency active optical fiber laser as an optical signal source at a signal transmission wavelength, at least an active optical fiber optical amplifier operatively connected to said laser and at least one source of pumping optical power at a pumping wavelength, the pumping optical power source being operatively connected to at least one of said active fibers of said laser and amplifier and transfer-means for said pumping optical power being connected to said active fibers of said laser and amplifier, in order to transfer unabsorbed optical power at the pumping wavelength from one of said active fibers to the other of said active fibers.

Abstract: The telecommunication line comprises at least one terminal station having an optical-signal transmitter and an optical-signal receiver, which are operationally connected by an automatic protection device suitable for shutting down said transmitter in the absence of a received optical signal, at least one opticalfibre line for the transmission of the optical signals transmitted by said transmitter and received by said receiver, and at least one optical amplifier included in said line. With said optical amplifier there are associated means for the detection of the presence of light energy at input and means for causing the shut down of the amplifier, which in the absence of light energy at input are caused by said detection means to interrupt substantially any emission of light energy on the part of said optical amplifier.

Abstract: An optical fiber telecommunications system having two terminals interconnected by optical fibers and active-fiber optical amplifiers. Each terminal has an optical telecommunication signal transmitter associated with an optical signal receiver which are interconnected by a protective device which causes the transmitter to be inoperative when its associated receiver does not receive an optical signal. Optical switches are provided at the downstream sides of active-fiber optical amplifiers and are controlled by detecting devices coupled to amplifier outputs, each of which detecting devices opens the associated switch in the absence of a signal having the characteristics, e.g. an alternating component, of the optical telecommunication signal whereby the protective devices are operated.

Abstract: An optical fiber and an optical amplifier, in particular for optical fiber telecommunication lines operating with a transmission signal in a predetermined wavelength range. The amplifier comprises laser emitting active optical fiber doped with erbium and a further doping substance, distributed along the fiber. The further doping substance has an absorption for a light having a wavelength lower than 1,540 nm substantially higher than the absorption that the further doping substance shows for a light having a wavelength varying from 1,540 nm to the upper limit of the predetermined wavelength range of the transmission signal. Preferably, the further doping substance is samarium.

Abstract: The optical amplifier (1) comprises two amplifying stages, an upstream amplifying stage (S.sub.M) and a downstream amplifying stage (S.sub.V). The former stage comprises an upstream active fiber (9) doped with a fluorescent dopant and connected serially to the optical fiber line (2), an upstream optical coupler (10) connected serially downstream from the upstream section of active fiber (9), a laser diode (11) for supplying pumping energy towards the upstream active fiber (9) through the coupler (10), said coupler being oriented to cause pump energy travel towards said upstream active fiber (9) in the opposite direction from the predetermined signal direction (S); the latter stage (S.sub.

Abstract: Active-fiber optical amplifier connected to optical fiber lines or a telecommunication signal source through energy reflection limiting means, such as optical isolators, for limiting the reflected energy, due to Rayleigh scattering, which reaches the active fiber, to permit increased amplifier gain. The input of the active fiber is connected to a dichroic coupler which is also connected to a pumping energy source by an optical fiber having a bevelled end surface or an antireflection coating at the energy source end to limit reflection of energy to the active fiber. Also, a telecommunication system including one or more of such protected amplifiers.

Abstract: A unit for amplifying light signals in optical fiber transmission lines includes a fiber optical amplifier to which light signals are transmitted through an input optical fiber line, and from which the signals, after having been amplified, are introduced into an output optical fiber line. First and second optical insulators are interposed between the fiber optical amplifier and the input and output lines to prevent the transmission of optical noise signals from the input and output lines, respectively, to the amplifier.

Abstract: An optical amplifier, particularly useful for optical fiber telecommunication lines, which includes an active fiber doped with a fluorescent dopant which provides light energy emission at the wavelength of the transmission signals when the latter signals are applied thereto. One section of telecommunication line is connected to one input of a dichroic coupler, the output of which is connected to one end of the active fiber and the other input of which is connected to a source of pumping energy at a wavelength lower than that of the transmission signals. The other end of the active fiber is connected to another section of the telecommunication line. In rectilinear form, the active fiber provides single-mode propagation of the energy at the signal wavelength and multi-mode propagation of energy at the pumping energy wavelength.

Abstract: An optical, low-noise amplifier of the active-fiber type, which fiber contains a laser light emitting substance, adapted to be connected to an optical telecommunication fiber and receiving light therefrom at the transmission wavelength. The active fiber is also fed from a light source at a pumping wavelength and has a length corresponding to a partial absorption of the pumping light. Downstream of active fiber, there is a selective mirror device which reflects the light at the pumping wavelength and is transparent to the transmission wavelength light. Preferably, the mirror device consists of an optical demultiplexer adapted to separate the transmission wavelength and the pumping wavelength on two output fibers. A mirror which reflects the pumping wavelength is present at the end of the fiber carrying the pumping wavelength.

Abstract: An optical amplifier (3) in accordance with the invention consists of the assembly of a length of active-core optical fiber (8), single-mode to both pumping and signal optical radiations, and a dichroic coupler (6) which includes two optical fiber lengths (9, 10), both single-mode to pumping and signal optical radiations, coupled to each other over one portion (11) by fusion of the respective claddings and substantial setting in common of the respective cores in the fused portion (11).

Abstract: An optical fiber telecommunication line composed of a number of series connected optical cables arranged end-to-end includes an active core optical fiber amplifier for the transmitted signals between each adjacent pair of optical cables. Two pumping optical radiation sources are connected to each active core optical fiber within each of the amplifiers, one source for each end of a single active core optical fiber. One of these two sources is placed into service and the second one is kept in reserve to be placed into service if the first one fails. A microprocessing circuit causes the sources to send distinctive recognizable alarm signals indicative of the state of an associated amplifier to terminal stations at the ends of the line and to receive therefrom control signals to control and exchange the functions between the two sources as necessary.

Abstract: A unit for amplifying light signals in optical fiber transmission lines includes a fiber optical amplifier to which light signals are transmitted through an input optical fiber line, and from which the signals, after having been amplified, are introduced into an output optical fiber line. First and second optical insulators are interposed between the fiber optical amplifier and the input and output lines to prevent the transmission of optical noise signals from the input and output lines, respectively, to the amplifier.