Reflecting method and device for performing the receiving function of an optical access network using wavelength division multiplexing

Abstract

The invention relates to a receiving device (Rx1_b) capable of receiving an optical signal emitted by an emitting device including a light source for emitting the optical signal, the optical signal being transmitted by a passive optical network having wavelength division multiplexing, the receiving device including: an optical amplifier (Amp_b) for amplifying the optical signal received from the emitting device; an optical detector (D_b) capable of detecting data in the amplified optical signal; an optical reflector (Ref_b) configured to return the amplified optical signal toward the emitting device, such as to tune the wavelength of the optical signal emitted by the emitting device by means of a round trip of the optical signal between the emitting device and the optical reflector.

Claims

1. A receiver device (Rx1_a, Rx1_b, Rx1_c, Rx1_d) designed to receive an optical signal (1) emitted by a transmitter device (Tx1) comprising a light source for emission of the optical signal, the optical signal being transmitted by a passive optical network with wavelength division multiplexing, the receiver device being characterized in that it comprises: an optical amplifier (Amp_a, Amp_b, Amp_c, Amp_d) for amplifying the optical signal received from the transmitter device; an optical detector (D_b, D_d) designed to detect data in the amplified optical signal; an optical reflector (Ref_a, Ref_b) configured for reflecting the amplified optical signal toward the transmitter device, in order to seed the wavelength of the optical signal emitted by the transmitter device by means of a return path followed by the optical signal between the transmitter device and the optical reflector.

2. The receiver device (Rx1_a, Rx1_c) as claimed in claim 1, characterized in that the optical detector is integrated into the optical amplifier (Amp_a, Amp_c).

3. The receiver device (Rx1_b, Rx1_d) as claimed in claim 1, characterized in that the optical detector (D_b, D_d) is integrated into the optical reflector (Ref_b).

4. The receiver device (Rx1_c, Rx1_d) as claimed in claim 1, characterized in that the optical reflector comprises a polarization separator (Sep_c, Sep_d) and a polarization rotator by 180 (Rot_c, Rot_d), and in that the optical signal (1) received is separated along axes of polarization so as to form a first separate signal (1_1) and a second separate signal (1_2), the polarization rotator and the optical amplifier (Amp_c, Amp_d) being disposed so as to form a loop with the polarization separator, the first separate signal running in one direction and the second separate signal running in the other direction, the two separate signals being re-united in the polarization separator so as to form an amplified optical signal sent back to the transmitter device.

5. The receiver device (Rx1_d) as claimed in claim 4, characterized in that the loop comprises a coupler disposed between the amplifier (Amp_d) and the rotator (Rot_d) in order to extract a part of the light and to direct it toward the optical detector (D_d).

6. An optical terminal comprising: a receiver device (Rx1_a, Rx1_b, Rx1_c, Rx1_d) designed to receive a received optical signal (1) emitted by an external transmitter device (Tx1) comprising an external light source for emission of the received optical signal, the received optical signal being transmitted by a passive optical network with wavelength division multiplexing, the receiver device being characterized in that it comprises: an optical amplifier (Amp_a, Amp_b, Amp_c, Amp_d) for amplifying the received optical signal received from the external transmitter device forming an amplified received optical signal; an optical detector (D_b, D_d) designed to detect data in the amplified received optical signal; an optical reflector (Ref_a, Ref_b) configured for reflecting the amplified received optical signal toward the external transmitter device, in order to seed the wavelength of the received optical signal emitted by the external transmitter device by means of a return path followed by the received optical signal between the external transmitter device and the optical reflector; and an internal transmitter device comprising an internal light source for the emission of a transmitted optical signal.

7. An optical transmission system comprising: a transmitter device (Tx1) comprising a light source for the emission of an optical signal (1), a passive optical network with wavelength division multiplexing transmitting the optical signal; and a receiver device (Rx1_a, Rx1_b, Rx1_c, Rx1_d) designed to receive the optical signal (1) emitted by the transmitter device (Tx1), the receiver device being characterized in that it comprises: an optical amplifier (Amp_a, Amp_b, Amp_c, Amp_d) for amplifying the optical signal received from the transmitter device forming an amplified optical signal; an optical detector (D_b, D_d) designed to detect data in the amplified optical signal; and an optical reflector (Ref_a, Ref_b) configured for reflecting the amplified optical signal toward the transmitter device, in order to seed the wavelength of the received optical signal emitted by the transmitter device by means of a return path followed by the optical signal between the transmitter device and the optical reflector.

8. A method for receiving an optical signal emitted by a transmitter device comprising a light source for emission of the optical signal, a passive optical network with wavelength division multiplexing transmitting the optical signal, the method comprising the following steps: reception (E1, F1, G1, H1) of the optical signal from the passive optical network; amplification (E2, E5, F2, F5, G3, G6, H3, H6) of the optical signal received; detection (E4, F4, G8, H9) of data in the amplified optical signal; reflection (E3, F3) of the amplified signal toward the transmitter device, in order to seed the wavelength of the optical signal emitted by the transmitter device by means of a return journey of the optical signal with the transmitter device.

Description

4. BRIEF DESCRIPTION OF THE FIGURES

(1) Other advantages and features of the invention will become more clearly apparent upon reading the following description of particular embodiments of the invention, given simply by way of illustrative and non-limiting example, and of the appended drawings, amongst which:

(2) FIG. 1 shows a self-seeded WDM PON optical transmission system according to the prior art,

(3) FIG. 2 shows a self-seeded WDM PON optical transmission system, according to one particular embodiment of the invention,

(4) FIG. 3 shows the receiver device according to a first embodiment of the invention,

(5) FIG. 4 shows the method for receiving an optical signal implemented by the receiver device according to the first embodiment of the invention,

(6) FIG. 5 shows the receiver device according to a second embodiment of the invention,

(7) FIG. 6 shows the method for receiving an optical signal implemented by the receiver device according to the second embodiment of the invention,

(8) FIG. 7 shows the receiver device according to a third embodiment of the invention,

(9) FIG. 8 shows the method for receiving an optical signal implemented by the receiver device according to the third embodiment of the invention,

(10) FIG. 9 shows the receiver device according to a fourth embodiment of the invention,

(11) FIG. 10 shows the method for receiving an optical signal implemented by the receiver device according to the fourth embodiment of the invention.

5. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

(12) In the following part of the description, several embodiments of the invention in the case of passive optical networks (PON) with wavelength division multiplexing (WDM) are presented, but the invention is also applicable to point-to-point networks.

(13) FIG. 2 shows a self-seeded WDM PON optical transmission system, according to one particular embodiment of the invention.

(14) In this particular embodiment of the invention, a mirror Ref is placed in the receiver device Rx1 of the optical terminal ONT1. In comparison with the system according to the prior art described with reference to FIG. 1, there is no longer any mirror M in the PON between the multiplexer/demultiplexer mdx1 and mdx2. Thus, no modification is introduced into the passive infrastructure of the WDM PON for it to be self-seeded. Moreover, it is possible to implement the invention for certain transmitter/receiver pairs and not to do it for other pairs. It is not necessary to equip the receiver device of the optical terminal ONT2 for example.

(15) In one variant, a second mirror Ref may also be placed in the receiver device Rx1 of the optical terminal OLT1, in order to obtain a self-seeded WDM PON in both directions.

(16) FIG. 3 shows the receiver device according to a first embodiment of the invention.

(17) In this embodiment, the device Rx1_a comprises an optical amplifier Amp_a and an optical reflector Ref_a, amplifying and reflecting all of the polarization states of the incident light. The device Rx1_a may be implemented either by means of a RSOA integrating both Amp_a and Ref_a, or by means of a SOA and of a Faraday mirror in order to respectively implement Amp_a and Ref_a. The SOA, like the RSOA, can advantageously emit along a single axis of polarization for a higher efficiency in terms of optical power.

(18) The optical signal is photo-detected directly across the terminals of the optical amplifier Amp_a. The measurement of the electrical current generated by the photons yields the electrical signal ES1 which can subsequently be demodulated into a data signal.

(19) FIG. 4 shows the steps of the method for receiving an optical signal implemented by the receiver device according to the first embodiment of the invention.

(20) During a step E1, the receiver device Rx1_a receives from the WDM PON the optical signal, represented here by its wavelength 1, emitted by the transmitter Tx1 of a remote optical terminal such as OLT1 for example.

(21) During a step E2, the optical signal received is amplified by the optical amplifier Amp_a.

(22) During a step E3, the amplified optical signal is reflected by the optical reflector Ref_a.

(23) During a step E4, the amplified optical signal is photo-detected across the terminals of the optical amplifier Amp_a, in order to generate the electrical signal ES1.

(24) During a step E5, the reflected optical signal goes back through the optical amplifier Amp_a, before being re-emitted toward the WDM PON.

(25) FIG. 5 shows the receiver device according to a second embodiment of the invention.

(26) In this embodiment the device Rx1_b comprises an optical amplifier Amp_b and a partial optical reflector Ref_b, amplifying and reflecting all of the polarization states of the incident light. The device Rx1_b may be implemented either by means of an RSOA with a partial reflector incorporating both Amp_b and Ref_b, or by means of an SOA and of a partial Faraday mirror for respectively implementing Amp_b and Ref_b. The SOA, like the RSOA, can advantageously emit along a single axis of polarization for a higher efficiency in terms of optical power.

(27) The optical signal passing through the partial mirror Ref_b without being reflected is photo-detected by a diode D_b arranged behind Ref_b. The diode D_b generates the electrical signal ES1 which can subsequently be demodulated into a data signal.

(28) FIG. 6 shows the steps of the method for receiving an optical signal implemented by the receiver device according to the second embodiment of the invention.

(29) During a step F1, the receiver device Rx1_b receives from the WDM PON the optical signal, represented here by its wavelength 1, emitted by the transmitter Tx1 of a remote optical terminal such as OLT1 for example.

(30) During a step F2, the optical signal received is amplified by the optical amplifier Amp_b.

(31) During a step F3, the amplified optical signal is reflected by the optical reflector Ref_b.

(32) During a step F4, the optical signal amplified and filtered by the partial optical reflector Ref_b is photo-detected by a diode D_b, in order to generate the electrical signal ES1.

(33) During a step F5, the reflected optical signal goes back through the optical amplifier Amp_b, prior to being re-emitted toward the WDM PON.

(34) FIG. 7 shows the receiver device according to a third embodiment of the invention.

(35) In this embodiment, the device Rx1_c comprises an optical amplifier Amp_c, a polarization separator Sep_c and a polarization rotator by 180 Rot_c, forming a bi-directional optical loop. The optical amplifier Amp_c may be implemented by means of an SOA. The SOA can advantageously emit along a single axis of polarization for a higher efficiency in terms of optical power.

(36) The optical signal is photo-detected directly across the terminals of the optical amplifier Amp_c. The measurement of the electrical current generated by the photons yields the electrical signal ES1 which can subsequently be demodulated into a data signal.

(37) FIG. 8 shows the steps of the method for receiving an optical signal implemented by the receiver device according to the third embodiment of the invention.

(38) During a step G1, the receiver device Rx1_c receives from the WDM PON the optical signal, represented here by its wavelength 1, emitted by the transmitter Tx1 of a remote optical terminal such as OLT1 for example.

(39) During a step G2, the optical signal received is separated into two signals, 1_1 and 1_2, by the polarization separator Sep_c.

(40) During a step G3, the signal 1_1 is amplified by the optical amplifier Amp_c.

(41) During a step G4, the signal 1_2 is processed by the polarization rotator Rot_c which flips its axes of polarization by 180.

(42) During a step G5, the amplified signal 1_1 passes in turn through the polarization rotator Rot_c but in the other direction.

(43) During a step G6, the signal 1_2, whose polarization is now opposite, is amplified by the optical amplifier Amp_c.

(44) During a step G7, the signals 1_1 and 1_2, amplified and flipped, go back through the separator Sep_c but in the other direction, in order to be re-united and re-emitted toward the WDM PON.

(45) During a step G8, the amplified and flipped optical signal is photo-detected across the terminals of the optical amplifier Amp_c, in order to generate the electrical signal ES1.

(46) FIG. 9 shows the receiver device according to a fourth embodiment of the invention.

(47) In this embodiment the device Rx1_d comprises an optical amplifier Amp_d, a polarization separator Sep_d and a polarization rotator by 180 Rot_d, forming a bidirectional optical loop. The optical amplifier Amp_d may be implemented by means of a SOA. The SOA can advantageously emit along a single axis of polarization for a higher efficiency in terms of optical power.

(48) The device Rx1_d also comprises a coupler Cpl_d extracting a part of the optical signal carried by the bidirectional optical loop. The extracted signal is photo-detected by a diode D_d generating the electrical signal ES1 which can subsequently be demodulated into a data signal.

(49) FIG. 10 shows the steps of the method for receiving an optical signal implemented by the receiver device according to the fourth embodiment of the invention.

(50) During a step H1, the receiver device Rx1_d receives of the WDM PON the optical signal, represented here by its wavelength 1, emitted by the transmitter Tx1 of a remote optical terminal such as OLT1 for example.

(51) During a step H2, the optical signal received is separated into two signals, 1_1 and 1_2, by the polarization separator Sep_d.

(52) During a step H3, the signal 1_1 is amplified by the optical amplifier Amp_d.

(53) During a step H4, the signal 1_2 is processed by the polarization rotator Rot_d which flips its axes of polarization by 180.

(54) During a step H5, the amplified signal 1_1 passes in turn through the polarization rotator Rot_d but in the other direction.

(55) During a step H6, the signal 1_2, whose polarization is now opposite, is amplified by the optical amplifier Amp_d.

(56) During a step H7, the signals 1_1 and 1_2, amplified and flipped, go back through the separator Sep_d but in the other direction, in order to be re-united and re-emitted toward the WDM PON.

(57) During a step H8, a part of the amplified and flipped optical signal, carried by the bidirectional optical loop, is extracted between the amplifier Amp_d and the rotator Rot_d by the optical coupler Cpl_d.

(58) During a step H9, the extracted optical signal is photo-detected by a diode D_d, in order to generate the electrical signal ES1.

(59) A receiver device such as the device Rx_a, Rx_b, Rx_c, or Rx_d, whose descriptions have just been presented, may be incorporated into a receiver module forming part of optical line termination equipment (OLT) or of an optical network (ONT). Such a device may also be implemented in a piece of equipment distinct from the optical termination equipment, within equipment of the network dedicated or otherwise to the reception of signals from an optical distribution network.

(60) The exemplary embodiments of the invention that have just been presented are only a few of the embodiments that may be envisioned. They show that the invention allows the reflector device needed for the operation of the wavelength self-seeding to be eliminated from the passive infrastructure of a self-seeded WDM PON. The reflector device according to the invention is moved to the termination equipment at the opposite end to the light source, and offers other advantages allowing the optical losses suffered along the light path to be reduced.