FR2798779A1 - Wavelength multiplexing fibre optic transmission pumping technique, having laser light source transmitting/producing second wavelength having amplifier pump band stokes separation factor set using Raman effect - Google Patents

Abstract

The optical pumping technique has a laser (1) transmitting a first wavelength to a light source (2) which transmits a second wavelength. The second wavelength is offset from the pump band of the erbium doped fibre optic amplifier by the Stokes separation factor using the Raman effect to reduce losses.

Description

The present invention relates to the field of telecommunications and more particularly to the field of fiber transmission with length-division multiplexing. BACKGROUND OF THE INVENTION 'wave.

To compensate for line losses, it is known to have at regular intervals along the transmission system optical amplifiers, including erbium doped optical fiber amplifiers connected to one of the ports of the repeater placed on the line fiber.

general principle of such transmission systems is described in the article The new windows of amplification Dominique BAYART appeared in OPTICS AND PHOTONICS 2/99, pages 17 and following.

In the state of the art, various solutions have also been proposed for producing a Raman optical amplifier. Such a device is for example described in European Patent EP789432 or US Pat. No. 5,887,093 or US Pat. No. 5,191,628. Patent 89433 discloses an optical fiber Raman amplifier comprising: a) an input port; - a port of exit; c) an optical fiber path connected by signal transmission, said input and output ports, said optical fiber path comprising a silica based amplifier fiber; and d) means for introducing a first pumping radiation of a wavelength 71, p less than one XS signal wavelength in said silica-based amplifier fiber so that the first radiation pumping propagates in said silica-based amplifier fiber only in an upstream direction to said input port; wherein - e) said silica-based amplifier fiber comprises a first amplifier fiber length L1 and a second amplifier fiber length L2, the first length upstream of the second length, and L1 + L2 being at least 200 m; f) the optical fiber Raman amplifier comprises an optical isolator disposed between said first and second amplifier fiber lengths such that the passage of the Xs wavelength radiation from the second to the first length amplifier fiber is substantially blocked by said insulator; g) the optical fiber Raman amplifier further comprises a pump radiation path which is closed on itself and comprises a portion of said silica-based amplifier fiber, said pump radiation path being selected from such that said first pumping radiation is able to flow therethrough and - the pumping radiation path includes means for introducing a second pumping radiation of wavelength it, p, <% lp into the pumping radiation path, and further comprises a first wavelength reflective means adapted to substantially block passage of said second pump radiation through said first reflector means.

The general problem that arises is the power of the pumping source. Multiplexing transmissions currently result in the propagation of 30 to 40 different channels, spaced about 0.8 nanometers apart, in a line fiber. The repeaters are currently implementing erbium doped fiber amplifiers, having a bandwidth of approximately 30 nm, imposing increasing pumping powers with the number of channels.

It has been proposed in the state of the art to use semiconductor lasers emitting at 1480 nm a power limited to about 200 mW.

A first solution that the skilled person could consider is to combine several laser diodes to achieve the required pumping power. Such a solution is however complicated to implement and expensive to industrialize. For example, European Patent EP268523 discloses an optical coupling device for use with an amplifier implementing ef. Raman stimulated comprising: two laser diodes both emitting light of the same wavelength corresponding to a pumping wavelength of the Raman amplifier and each providing a linearly polarized output beam, the respective states of polarization being orthogonal to each other; a first polarization prism arranged to combine the output beams of the two laser diodes and to provide a combined pump beam; a first wavelength multiplexer arranged to receive said combined pump beam and to superimpose a signal light beam having a wavelength different from that of said combined pump beam, thereby to create a pump beam; means for introducing said signal pumping beam into a transmission fiber.

Another solution of the prior art disclosed in Advanced Solid State Laser, OSA Topical Meeting, C # ur Alene, ATuC1 (pp 242-244) February 1998 GRUBB et al. High power fiber laser consists of using a ytterbium doped fiber laser, pumped by a 940 laser diode. Such a laser emits radiation at 1117 nm which is then converted at 1480 nm by five successive steps in silica fiber optic Raman lasers. . Such a solution is not satisfactory because it results in an unfavorable energy balance due to the cascading of several non-linear stages.

The object of the present invention is to provide a powerful laser source overcoming these disadvantages, to allow the pumping of an optical fiber amplifier with the required power, for example a power of the order of Watt.

For this purpose, the invention relates in its most general sense to a pumping means of a doped optical fiber amplifier erbium requiring pumping at a wavelength, e or a line fiber of a link by optical fiber requiring pumping at a wavelength λ e, said pumping means comprising a laser diode emitting at a wavelength λ p, said diode pumping a light source emitting at a wavelength λ e , characterized in that X'e is different from the pumping band%, e of an erbium-doped fiber amplifier and in that the e is chosen to be, by Raman effect, transformed into e by an offset Unique stocks in a silica fiber.

Advantageously, the light source comprises a doped neodymium crystal emitting at εe.

According to a particular embodiment, said pump laser diode is a diode emitting at a wavelength λ, of about 808 nanometers.

According to one variant, the light source comprises an Nd: YAP crystal.

Preferably, a silica fiber forming a Raman laser producing a single stagger shift of about 440 cm -1, said silica fiber being disposed between the light source and the output of the pumping means for exciting the fiber amplifier. erbium doped optics. According to another variant, the light source comprises an Nd: YAP crystal placed in a cavity tuned to the Ee formed by two mirrors, the input mirror having a maximum transmission at about 808 nm and a maximum reflection in the range 1300. at 1400 nm and the output mirror having a 1340 nm transmission greater than the transmission at 1385 nm.

The invention also relates to an optical fiber amplifier for the regeneration of a wavelength multiplexed signal propagating in a connecting fiber, comprising an erbium doped optical fiber and a pumping means emitting at Xe, characterized in that the The pumping means is composed of an emitting laser diode 4 associated with a Nd: YAP laser emitting Xe which, by Raman effect in a silica fiber, produces a single Stokes shift equal to this amplifier constitutes a first application of pumping means according to the invention. Advantageously, the pumping means emits at about 1480 nm and comprises a laser diode emitting at about 808 nm associated with a Nd: YAP laser emitting at about 1385 nm which, by Raman effect in a silica fiber, achieves a unique Stokes shift. about 440 cm -1.

The invention also relates to an optical fiber amplifier for the regeneration of a multiplexed signal propagating in a line fiber of a link comprising a silica optical fiber and a pumping means emitting at X ', characterized in that the pumping means is composed of a laser diode emitting at% l, p associated with a Nd: YAP laser emitting at X'e.

This amplifier constitutes a second application of a pumping means according to the invention. Advantageously, the pumping means is composed of a laser diode emitting at about 808 nm associated with a Nd: YAP laser emitting at about 1385 nm. Other features and advantages of the invention will appear on reading the description which follows the embodiments of the invention, given by way of non-limiting example and with reference to the accompanying drawings, in which - Figure 1 shows a schematic view. the light source for the pumping means of a device according to the invention; FIG. 2 represents a schematic view of the pumping means, for a first application concerning the erbium doped fiber amplifiers; FIG. 3 represents a schematic view of the pumping means, for a second application concerning Raman amplifiers.

The device according to the invention is described schematically with reference to FIG.

It comprises a laser diode (1) emitting radiation at about 808 nm. For example, such a diode may be a fiber laser diode SDL P7 (trade name) which can provide a power of 14.3 Watts. The beam of the diode at about 808 nm is then transported and concentrated in a light source (2) comprising a Nd: YAP crystal (12).

This light source (2) is constituted by a crystal (12) Nd: YAP (Ya103: Nd3 +) placed between two mirrors (10, 11). The crystal (12) is a neodymium doped Perovskite (Ya103) cylinder 7 mm long and 3 mm in section, cut along the optical axis A.

Such a crystal (12) has a transition 4F3 / 2 -> 4I1 3/2 creating lines associated with Stark sub-levels, including a doublet at 1378 nm and 1385.4 nm.

The presence of this doublet has several advantages with regard to the application to amplification for telecommunication signals of the S band (1470 - 1500 nm). It first produces an enlargement of the amplification window. This spectral spread resulting from the presence of a doublet will also promote the Raman effect in the fiber at the expense of the Brillouin effect, the latter producing a counter-propagative wave that can cause disturbances.

The crystal (12) is placed in a plane-plane cavity comprising a plane input mirror (10) processed to have a high transmission rate at 808 nm and a high reflection ratio in the range 1300 to 0 nm.

The exit mirror (11) is a plane mirror, with 12% transmission at 1340 nm and 1.2% at 85 nm.

The crystal (12) can be rotated a few degrees relative to the horizontal autocollimation plane, to reveal the desired lines.

A light source (2) according to the invention makes it possible to deliver a power of about Watts at about 85 nm.

The laser diode (1) and the light source (20) constitute the base brick (20) for producing amplifiers operating in the C (1520 - 1550 nm) or L (1550 - 0 nm) band (application described with reference to FIG. Figure 2) and S-band (1470 - 1500 nm) application described reference to Figure 3).

FIG. 2 represents a schematic view of the pumping means, for a first application concerning erbium doped fiber amplifiers.

The base brick (20) according to that described in reference to Figure 1, is connected upstream of the amplifier. The light emitted by the base brick (20) injected into a Raman laser (21) of known performing a single Stokes shift and producing radiation at about 1480 nm. This radiation for pumping an erbium-doped fiber amplifier (22) in the so-called conventional or L (1550- 1600 nm) C-band (1520-1550 nm). FIG. 3 represents a schematic view of the pumping means, for a second application concerning Raman amplifiers.

The base brick (20) according to that described with reference to Figure 1, is connected to a silica fiber (30) using a Y coupler (31).

In this case, the light source is used directly at about 1385 nm as a pumping source to amplify the band signals S (1470 - 1500) by means of the Raman effect. The same light source (20), and of the invention, can therefore without modification, be used for two different applications, requiring different wavelengths.

Claims (1)

1 - Pumping means either an erbium-doped optical fiber amplifier requiring pumping at a wavelength λ e, or an amplifier by Raman effect in a line fiber of a link by optical fiber requiring pumping at a wavelength λ e, said pumping means comprising a laser diode emitting at a wavelength λ p, said diode pumping a light source emitting at a wavelength λ e , characterized in that% 'e is different from the pumping band Xe of an erbium doped fiber amplifier and in that #,' e is chosen to be, by Raman effect, transformed into X, e by a shift unique in a silica fiber. 2 - pumping means of an optical fiber according to claim 1 characterized in that the light source comprises a doped neodymium crystal emitting X 'e. 3 - pumping means according to claim 1 or 2 characterized in that said pump laser diode is a diode emitting at a wavelength X.p of about 808 nanometers. - Pumping means according to at least one of the preceding claims characterized in that the light source comprises a crystal Nd: YAP. 5 - pumping means according to claim 1, 2 or 3 characterized in that it further comprises a Raman laser comprising a silica fiber producing a single Stokes shift of about 440 cm-1, said silica fiber being disposed between the light source and the output of the pumping means for exciting the erbium doped optical fiber amplifier. 6 - Pumping means according to at least one of the preceding claims, characterized in that the light source comprises an Nd: YAP crystal placed in a cavity provided at k ', formed by two mirrors, the input mirror having a transmission maximum at about 808 nm and maximum reflection in the range 1300 to 1400 nm and the output mirror having a transmission at about 1340 nm greater than the transmission at about 1385 nm. 7 - Optical fiber amplifier for the regeneration of a wavelength multiplexed signal propagating in a connecting fiber, comprising an erbium doped optical fiber and a pumping means emitting at Xe characterized in that the pumping means is composed of by a laser diode emitting at%, p associated with a Nd: YAP laser emitting at k ', which, by Raman effect in a silica fiber, makes a single Stokes shift equal to 8 - Optical fiber amplifier for the regeneration of a wavelength multiplexed signal according to claim 8 characterized in that the pumping means emits at about 1480 nm and has a laser diode emitting at about 808 nm associated with a Nd: YAP laser emitting at about 1385 nm which, by effect Raman in a silica fiber, achieves a unique Stokes shift of about 440 cm-1. 9 - Optical fiber amplifier for regeneration by Raman effect of a wavelength multiplexed signal propagating in a line fiber of a link comprising a silica optical fiber and a pumping means emitting at X 'characterized by the pumping means is composed of a laser diode emitting at%, p associated with a Nd: YAP laser emitting at X 'e. 10 - Optical fiber amplifier for regeneration by Raman effect of a wavelength multiplexed signal propagating in a line fiber of a link comprising a silica optical fiber and a pumping means emitting at the e according to the claim 10 characterized in that the pumping means is composed of a laser diode emitting at about 808 nm associated with a Nd: YAP laser emitting at about 1385 nm.