BLIND PUMP LASER DETECTION

Abstract

Erbium-doped fiber amplifier (EDFA), featuring: an input photodiode (208) configured to generate a control signal based on an input signal; a dummy stage (202) coupled to the input photodiode (208), wherein the dummy stage (202) is configured to generate an amplified signal based on the control signal from the input photodiode (208) and the input signal; a non-reactive stage (204) coupled to the input photodiode (208) and the reactive stage (202), wherein the non-reactive stage (204) is configured to generate an output signal based on the amplified signal of the reactive stage (202), the control signal from the input photodiode (208) and a feedback signal, wherein a driver signal is generated within the non-reactive stage (204) based on the feedback signal and the control signal from the input photodiode (208); a filter (230) coupled to the non-blind stage (204), wherein the filter (230) is configured to generate a filtered signal based on the output signal of the non-blind stage (204); an output photodiode (232) coupled to the filter (230), wherein the output photodiode (232) is configured to generate the feedback signal based on the filtered signal from the filter (230); and an alarm device (231) coupled to the non-blind stage (204), wherein the alarm device (231) is configured to generate an alarm signal when the driver signal within the non-blind stage (204) exceeds a threshold, wherein when the blind stage (202) fails, the amplified signal within the blind stage (202) approaches zero, causing the feedback signal of the output photodiode (232) to approach zero and the driver signal within the non-blind stage (204) to increase and exceed the threshold.

Description

AREA

[0001] The embodiments discussed in this disclosure relate to blind pump detection. US 6,687,049 B1 discloses an optical amplifier based on an optically pumped fiber, wherein a control unit adjusts the pumping power. Furthermore, US 6,671,084 B2 discloses an optical amplifier wherein the output signals of the optical amplifier are controlled using a stylus beam. In addition, DE 10 2004 008 393 A1 describes an optical fiber amplifier with feed-forward and feedback control for controlling the gain. BACKGROUND

[0002] Unless otherwise stated in this disclosure, the materials described in this disclosure are not prior art for the claims of the present application and are not recognized as prior art by inclusion in this section.

[0003] An optical transmission system may include an erbium-doped fiber amplifier (EDFA) configured to amplify an optical signal. The EDFA can extend the transmission path of the optical signal within the optical transmission system. In some embodiments, the EDFA can amplify the optical signal to compensate for losses caused by attenuation in optical cables or other optical losses, enabling data to be transmitted along functional fiber links within the optical transmission system. Amplifying the optical signal to compensate for losses in the optical paths can allow the optical signal to be transmitted over longer distances through the optical transmission system than in transmission systems that do not include an EDFA.

[0004] The subject matter claimed in the present disclosure is not limited to implementations that overcome any disadvantages or function only in environments such as those described above. Rather, this background is provided only to illustrate an exemplary technology domain in which some implementations described in the present disclosure may find application. SUMMARY

[0005] This summary serves to present, in simplified form, a selection of concepts that are described in detail below. This summary is not intended to identify key features or essential characteristics of the claimed subject matter, nor should it be used as an aid in determining the scope of the claimed subject matter.

[0006] Some embodiments described in this disclosure generally relate to the detection of blind pumps.

[0007] One or more embodiments of the present disclosure comprise an EDFA comprising an input photodiode, a dummy stage, a non-dummy stage, a filter, an output photodiode, and an alarm device. The input photodiode is configured to generate a control signal. The control signal is generated based on an input signal. The dummy stage is coupled to the input photodiode and configured to generate an amplified signal. The amplified signal is generated based on the control signal from the input photodiode and the input signal. The non-dummy stage is coupled to the input photodiode and the dummy stage and configured to generate an output signal. The output signal is generated based on the amplified signal from the dummy stage, the control signal from the input photodiode, and a feedback signal.A driver signal within the non-blind stage is generated based on the feedback signal and the control signal from the input photodiode. The filter is coupled to the non-blind stage and configured to generate a filtered signal. This filtered signal is generated based on the output signal from the non-blind stage. The output photodiode is coupled to the filter and configured to generate the feedback signal. This feedback signal is generated based on the filtered signal from the filter. The alarm device is coupled to the non-blind stage. The alarm device is configured to generate an alarm signal when the driver signal within the non-blind stage exceeds a threshold value.

[0008] One or more embodiments of the present disclosure comprise an EDFA comprising an input photodiode, a feed-forward controller, a first pump laser, a first amplifier, a feedback controller, a second pump laser, a second amplifier, a filter, an output photodiode, and an alarm device. The input photodiode is optically coupled to an input of the EDFA. The feed-forward controller is electrically coupled to an output of the input photodiode. The first pump laser is electrically coupled to an output of the feed-forward controller. The first amplifier is optically coupled to an output of the first pump laser and the input of the EDFA. The feedback controller is electrically coupled to the output of the input photodiode. The second pump laser is electrically coupled to an output of the feedback controller.The second amplifier is optically coupled to an output of the second pump laser, an output of the first amplifier, and an output of the EDFA. The filter is optically coupled to an output of the second amplifier. The output photodiode is optically coupled to an output of the filter and electrically coupled to an input of the feedback controller. The alarm device is coupled to the feedback controller.

[0009] One or more embodiments of the present disclosure include a method that involves generating a control signal based on an input signal. The method comprises generating an amplified signal based on the control signal and the input signal. The method comprises generating an output signal based on the amplified signal, the control signal, and a feedback signal. The method comprises generating a filtered signal based on the output signal. The method comprises generating the feedback signal based on the filtered signal. The method comprises generating a driver signal based on the feedback signal and the control signal. The method comprises generating an alarm signal when the driver signal exceeds a threshold value.

[0010] As explained above, the invention further comprises the following aspect: The EDFA, wherein the input photodiode is optically coupled to an input of the EDFA; where the blind stage has: a feed-forward controller electrically coupled to an output of the input photodiode; a first pump laser electrically coupled to an output of the feed-forward controller; and a first amplifier optically coupled to an output of the first pump laser and the input of the EDFA; where the non-blind stage has a level: a feedback controller electrically coupled to the output of the input photodiode; a second pump laser electrically coupled to an output of the feedback controller; and a second amplifier optically coupled to an output of the second pump laser, an output of the first amplifier and an output of the EDFA; wherein the filter is optically coupled to an output of the second amplifier; wherein the output photodiode is optically coupled to an output of the filter and electrically coupled to an input of the feedback controller; and wherein the alarm device is coupled to the feedback controller.

[0011] Further features and advantages of the invention are set forth in the following description and are partly evident from the description or can be learned through practical application of the invention. The features and advantages of the invention can be realized or achieved through the instruments and combinations to which reference is made in particular in the appended claims. These and other features of the present invention are clarified by the following description and the appended claims, but can also be conveyed, as explained below, through the embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] To further clarify the above and other advantages and features of the present invention, a more detailed description of the invention is given with reference to specific embodiments illustrated in the accompanying drawings. It is emphasized that the drawings only show typical embodiments of the invention and are therefore not to be considered as limiting the scope of the invention. The invention is described and explained with additional specificity and detail by means of the accompanying drawings, in which: Fig. 1 shows a block diagram of an exemplary optical transmission system; Fig. 2 shows an example of an EDFA that is integrated into the optical transmission system of Fig. 1 can be implemented; Fig. 3 a graphical representation of the measured current of a first driver signal in the EDFA of Fig.2 during the simulations of different operating scenarios of the first pump laser; and Fig. 4 A flowchart of an example procedure for generating an alarm signal shows what happens when a driver signal exceeds a threshold. wherein all are designed in accordance with at least one embodiment described in the present disclosure. DETAILED DESCRIPTION OF SOME VERSIONS

[0013] An optical transmission system may include an EDFA to extend the path over which an optical signal can be transmitted within the system. In some embodiments, the EDFA may include a dummy stage and a non-dummy stage for amplifying the optical signal. In these and other embodiments, the dummy stage may include a feed-forward pump laser, also called a first pump laser, which is controlled in an open-loop (e.g., feed-in) manner. The first pump laser can generate a first pump light. The first pump light from the first pump laser can be combined with the optical signal to drive a first amplifier. In one example, a first combined signal containing the first pump light and the optical signal can drive the first amplifier.More precisely, for example, the first pump light can excite erbium ions in the first amplifier, followed by stimulated emission from the optical signal passing through the first amplifier with the excited erbium ions. Specifically, when the photons of the optical signal interact with the excited erbium ions of the first amplifier, the erbium ions can transfer some of their energy to the optical signal in the form of photons with the same wavelength as the photons of the optical signal, with the erbium ions returning to a lower energy state.

[0014] In some embodiments, the non-blind stage can include a feedback pump laser, also called a second pump laser, which is controlled via a closed-loop system (e.g., feedback). The second pump laser can generate a second pump light. This second pump light from the second pump laser can be combined with an amplified signal generated by the first amplifier to drive a second amplifier. For example, a second combined signal containing the second pump light and the amplified signal can drive the second amplifier. More specifically, the second pump light can, for instance, excite erbium ions in the second amplifier, followed by stimulated emission from the amplified signal passing through the second amplifier with the excited erbium ions.In particular, when the photons of the amplified signal interact with the excited erbium ions of the second amplifier, the erbium ions can transfer some of their energy to the amplified signal in the form of photons with the same wavelength as the photons of the amplified signal, with the erbium ions returning to a lower energy state.

[0015] The second amplifier can generate an output signal based on the second combined signal. This output signal can be a doubly amplified optical signal, such as the optical signal after amplification by both the first amplifier of the dummy stage and the second amplifier of the non-dummy stage. If the first pump laser fails, the first amplifier may operate with losses (e.g., weak optical data signals or non-optical data signals may pass through the first amplifier) ​​because the optical power level of the first pump light approaches zero. Consequently, the optical signal power at the output of the first amplifier may approach or become zero. The low or near-zero optical signal may then enter the second amplifier.The second amplifier can be controlled by both the signal power detected at the input photodiode of the first amplifier and the feedback signal from the output of the second amplifier. It can control the level of the optical pump power of the second pump laser (e.g., the second pump light) fed into the second amplifier to maintain a target signal power at the output photodiode. With little or no optical signal entering the second amplifier, increasing the optical power of the second pump laser can generate significant amplified spontaneous emission (ASE) noise within the second amplifier, resulting in reduced signal power gain. Therefore, although the target total power is achieved at the EDFA output, the optical signal-to-noise ratio (OSNR) at the EDFA output may be below an acceptable level.The reduced OSNR can cause the EDFA and the optical transmission system to malfunction. Since the EDFA's output power may still be achievable, some EDFA technologies may lack methods to determine if the first amplifier is the cause of the system degradation, and a network control scheme may be unable to quickly restore proper system operation.

[0016] Some EDFA technologies may not include suitable monitoring equipment or processes to determine if a part of the EDFA is failing.

[0017] Once an EDFA failure has been identified as being due to a pump laser failure, both the first and second pump lasers may be replaced without attempting to determine which of the two pump lasers is the cause of the EDFA failure. Replacing both the first and second pump lasers every time the EDFA fails can increase the maintenance costs for the optical transmission system containing the EDFA.

[0018] Some EDFA technologies may include an additional photodiode placed before or after the first pump laser to provide a method for monitoring the correct operation of each amplifier. In these EDFA technologies, the additional photodiode can act as a feedback device to directly monitor the operating parameters of the first pump laser (e.g., the optical power level of the first pump light or the optical power level of a driver signal within the dummy stage). However, including the additional photodiode can increase the manufacturing costs associated with the EDFA. Furthermore, the additional photodiode can increase the complexity and difficulty of the EDFA circuit design. Additionally, the extra photodiode can increase the footprint of the EDFA circuit.

[0019] Some EDFA technologies can implement a back-facet monitor (BFM) to monitor the first pump laser. In these EDFA technologies, the BFM can detect the optical power level of an optical signal emitted by the first pump laser. However, the BFM can produce inconsistent results because it is significantly affected by temperature, polarization states, and the lifetime of the reflected light. Therefore, the BFM can lead to false alarms (e.g., false failures). Furthermore, in some implementations, a single BFM detects the light from two laser chips in one package. If one of the two laser chips fails, it may not be possible to identify which one has failed using the single BFM. BFMs can also increase the manufacturing costs or the complexity of the circuit design for EDFAs.

[0020] Some embodiments described in this disclosure may include systems, methods, or devices for reliably verifying the proper operation of the EDFA (e.g., the first pump laser) without significantly increasing production costs or circuit design complexity. According to at least one embodiment described in this disclosure, the EDFA may include a filter coupled to the non-blind stage. The filter may be configured to generate a filtered signal based on the output signal. In some embodiments, the filter may be a passband filter configured to allow portions of the output signal within an L-frequency band (e.g., L-band) to pass through the filter. An output photodiode may be coupled to the filter. The output photodiode may generate a feedback signal based on the filtered signal.The L-band can cover a wavelength range from approximately 1565 nanometers to 1605 nanometers.

[0021] A driver signal within the non-blind stage can be generated, at least partially, based on the feedback signal. In some embodiments, when the first pump laser fails, the output signal of the second amplifier may contain mainly ASE in a C-frequency band (e.g., C-band ASE), which is filtered out. This can cause the current of the feedback signal to approach zero amperes. Consequently, the current of the driver signal can increase to compensate for the decreasing current of the feedback signal. The C-band can cover a wavelength range of approximately 1528 nanometers to 1565 nanometers. In some examples, the filter can be a C / L-band filter, blocking frequencies in the C-band and allowing frequencies in the L-band to pass.

[0022] In some embodiments, the EDFA may include an alarm device configured to monitor the current of the driver signal within the non-blind stage. In these and other embodiments, the alarm device may generate an alarm signal when the current of the driver signal within the non-blind stage exceeds a threshold. Therefore, at least one embodiment described in this disclosure may indirectly monitor the blind stage (e.g., the first pump laser) and enable the generation of the alarm signal to indicate that the EDFA has failed.

[0023] Accordingly, at least one embodiment described in this disclosure can enable a network operator (e.g., an entity providing or maintaining the optical transmission system) to reliably determine whether the EDFA has failed, even if the first pump laser is the cause of the failure. Furthermore, in some embodiments, the filter can be implemented as a passive thin-film component, which is cost-effective and does not increase the complexity or difficulty of the EDFA circuit design. Additionally, in some embodiments, the filter can be integrated into an output photodiode to further reduce the circuit complexity. At least one embodiment described in this disclosure can have a circuit footprint that is smaller than that of EDFA technologies implementing an additional photodiode.At least one embodiment described in the present disclosure can be implemented in the EDFA within operating conditions ranging from high optical power levels to low optical power levels or without wavelength dependence.

[0024] Therefore, some embodiments may include a C / L-band filter upstream of the output photodiode. If the first pump laser fails, the inversion level of the first amplifier (which may, for example, contain a first erbium-doped fiber) of the dummy stage can drop sharply, resulting in strong absorption of the optical signal. If the amplified signal is not received at the second amplifier (which may, for example, contain a second erbium-doped fiber) due to the strong absorption of the optical signal by the first amplifier, the second amplifier can only, or primarily, generate C-band stimulated spontaneous emission under excitation of the second pump laser and does not produce an effective L-band signal. Thus, by adding the C / L-band filter upstream of the output photodiode, the C-band stimulated spontaneous emission can be prevented from reaching the output photodiode.As a result, the output photodiode, due to the lack of signal power in the L-band, can cause the alarm device to issue an error message, e.g., an alarm signal.

[0025] As explained above, the invention further comprises: The EDFA according to one of the preceding embodiments, wherein the input photodiode is optically coupled to an input of the EDFA; where the blind stage has: a feed-forward controller electrically coupled to an output of the input photodiode; a first pump laser electrically coupled to an output of the feed-forward controller; and a first amplifier optically coupled to an output of the first pump laser and the input of the EDFA; where the non-blind stage has: a feedback controller electrically coupled to the output of the input photodiode; a second pump laser electrically coupled to an output of the feedback controller; and a second amplifier optically coupled to an output of the second pump laser, an output of the first amplifier and an output of the EDFA; wherein the filter is optically coupled to an output of the second amplifier; wherein the output photodiode is optically coupled to an output of the filter and electrically coupled to an input of the feedback controller; and wherein the alarm device is coupled to the feedback controller.

[0026] Reference is now made to the drawings to describe various aspects of some embodiments of the invention. The drawings are to be understood as diagrams and schematic representations of the embodiments and neither limit the present invention nor are they necessarily drawn to scale.

[0027] Fig.Figure 1 shows a block diagram of an exemplary optical transmission system 100 according to at least one embodiment described in the present disclosure. The optical transmission system 100 can comprise a transmitter 101, a booster amplifier 103, a first optical cable 105, an EDFA 107, a second optical cable 109, a preamplifier 111, and a receiver 113. The transmitter 101 can be optically coupled to the booster amplifier 103. The booster amplifier 103 can be optically coupled to the EDFA 107 via the first optical cable 105. The EDFA 107 can be optically coupled to the preamplifier 111 via the second optical cable 109. The preamplifier 111 can be optically coupled to the receiver 113.

[0028] The first optical cable 105 or the second optical cable 109 can be multimode fiber (MMF), single-mode fiber (SMF), multi-fiber ribbon cable, or any other suitable optical signal transmission medium. The optical transmission system 100 can be configured for optical signal transmission at a variety of data rates, including 1.25 Gb / s, 2.125 Gb / s, 2.5 Gb / s, 4.25 Gb / s, 8.5 Gb / s, 10.3 Gb / s, 10.5 Gb / s, 11.3 Gb / s, 14.025 Gb / s, 25 Gb / s, 50 Gb / s, 100 Gb / s, or other suitable data rates. Furthermore, the optical transmission system 100 can be configured for optical signal transmission at various wavelengths, including 850 nm, 1310 nm, 1470 nm, 1490 nm, 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm, 1610 nm or other suitable wavelengths.

[0029] Transmitter 101 can generate an optical signal to be transmitted to receiver 113. Transmitter 101 can forward the optical signal to booster amplifier 103. Booster amplifier 103 can be configured to increase the optical power level of the optical signal before it reaches the first optical cable 105. EDFA 107 can receive the optical signal via the first optical cable 105. Due to losses occurring in the first optical cable 105, EDFA 107 may receive the optical signal at a reduced optical power level. The loss occurring in the first optical cable 105 may be due to attenuation in the first optical cable 105.

[0030] The EDFA 107 can operate as an inline amplifier to compensate for losses occurring in the first optical cable 105. Furthermore, the EDFA can operate as an inline amplifier to compensate for losses occurring in the second optical cable 109. The EDFA 107 can amplify the optical power level of the optical signal before it reaches the second optical cable 109. The EDFA 107 can then transmit the optical signal via the second optical cable 109 to the preamplifier 111. The preamplifier 111 can be configured to increase the optical power level of the optical signal to a level that can be received and processed by the receiver 113. The optical transmission system 100 can then transmit data from the transmitter 101 to the receiver 113 using the optical signal.Integrating the EDFA 107 into the optical transmission system 100 can extend the distance over which the optical signal can be properly transmitted without data loss. Fig. Figure 1 shows the optical transmission system 100 with a single EDFA 107. In other implementations, the optical transmission system 100 can contain any number of EDFAs inline to further extend the distance over which the optical signal can be transmitted.

[0031] Fig. Figure 2 shows an example of an EDFA 107, which is integrated into the optical transmission system 100 of Fig.1 can be implemented in accordance with at least one embodiment described in the present disclosure. The EDFA 107 can comprise a first optical splitter 206, an input photodiode 208, a blanking stage 202, a non-blinding stage 204, a second optical splitter 228, a filter 230, an output photodiode 232, and an alarm device 231. The blanking stage 202 can comprise a feed-forward controller (FFC) 210, a first pump laser 212, a first optical combiner 214, a first amplifier 216, and an optical isolator 218. The non-blinding stage 204 can comprise a feedback controller 224, a second pump laser 222, a second optical combiner 220, and a second amplifier 226.

[0032] An input 255 of the first optical divider 206 can be optically coupled to an input 209 of the EDFA 107. A first output 239 of the first optical divider 206 can be optically coupled to a first input 259 of the first optical combiner 214. A second output 257 of the first optical divider 206 can be optically coupled to an input 235 of the input photodiode 208. An output of the input photodiode 208 can be split into several connections. For example, the output of the input photodiode can be divided into a first output (in Fig. 2, designated as 211) and a second exit (in Fig.The outputs of the first optical combiner 210 (designated as 213) can be divided. The first output 211 can be electrically coupled to an input 247 of the FFC 210. An output 215 of the FFC 210 can be electrically coupled to an input 251 of the first pump laser 212. An output 217 of the first pump laser 212 can be optically coupled to a second input 261 of the first optical combiner 214. An output 271 of the first optical combiner 214 can be optically coupled to an input 237 of the first amplifier 216. An output 223 of the first amplifier 216 can be optically coupled to an input 263 of the optical isolator 218. An output 243 of the optical isolator 218 can be optically coupled to a first input 265 of the second optical combiner 220.

[0033] The second output 213 can be electrically coupled to a first input 249 of the feedback controller 224. An output 219 of the feedback controller 224 can be electrically coupled to an input 253 of the second pump laser 222. An output 221 of the second pump laser 222 can be optically coupled to a second input 267 of the second optical combiner 220. An output 269 of the second optical combiner 220 can be optically coupled to an input 241 of the second amplifier 226. An output 227 of the second amplifier 226 can be optically coupled to an input 273 of the second optical divider 228. A first output 275 of the second optical divider 228 can be optically coupled to an output 225 of the EDFA 107. A second output 277 of the second optical divider 228 can be optically coupled to an input 245 of the filter 230. An output 229 of the filter 230 can be optically coupled to an input 279 of the output photodiode 232.An output 281 of the output photodiode 232 can be electrically coupled to a second input 233 of the feedback controller 224.

[0034] In some embodiments, the EDFA 107 can be configured to operate as an optical amplifier, amplifying the optical signal. In these and other embodiments, the EDFA 107 can operate in the C-band, the L-band, or both. The dummy stage 202 (e.g., the first pump laser 212) can be controlled in an open-loop system, and the non-dummy stage 204 (e.g., the second pump laser 222) can be controlled in a closed-loop system. In some embodiments, the dummy stage 202 can operate without a direct fault detection device. In these and other embodiments, the alarm device 231 can act as an indirect fault detection device for the dummy stage 202 to determine whether the dummy stage 202 is operating correctly.

[0035] The first optical splitter 206 can receive the optical signal (e.g., an input signal) from the input 209 of the EDFA 107. The first optical splitter 206 can split the input signal and forward it to the input photodiode 208 and the first optical combiner 214. In some embodiments, the first optical splitter 206 can divide the optical power level of the input signal between the first output 239 and the second output 257 of the first optical splitter 206. In these and other embodiments, the first optical splitter 206 can divide the optical power level of the input signal between the first output 239 and the second output 257 of the first optical splitter 206 evenly or unevenly. Additionally or alternatively, the input photodiode 208 and the first optical combiner 214 can receive the input signal with divided optical power levels.

[0036] The input photodiode 208 can receive the input signal from the first optical splitter 206. The input photodiode 208 can generate a control signal based on the input signal. In some embodiments, the input photodiode 208 can generate the control signal as an electrical signal corresponding to the input signal. In these and other embodiments, the current of the control signal can be based on the split optical power level of the input signal received by the input photodiode 208.

[0037] The FFC 210 can receive the control signal from the input photodiode 208. The FFC 210 can generate a driver signal within the reactive stage 202, also referred to as the second driver signal, as an electrical signal based on the control signal. In some embodiments, the current of the second driver signal can be based on the current of the control signal. For example, the FFC 210 can increase the current of the second driver signal when the current of the control signal increases. Conversely, when the current of the control signal decreases, the FFC 210 can decrease the current of the second driver signal. In some embodiments, the FFC 210 can apply a gain level to the control signal to generate the second driver signal as an amplified version of the control signal.

[0038] The first pump laser 212 can receive the second driver signal from the FFC 210. The first pump laser 212 can generate a first pump light based on the second driver signal. In some embodiments, the first pump laser 212 can generate the first pump light according to the second driver signal. In these and other embodiments, the optical power level of the first pump light can be based on the current of the second driver signal.

[0039] The first optical combiner 214 can receive the input signal with the split optical power level from the first optical splitter 206. Furthermore, the first optical combiner 214 can receive the first pump light from the first pump laser 212. The first optical combiner 214 can combine the input signal and the first pump light into a first combined signal. Additionally, the first optical combiner 214 can supply the first combined signal to the first amplifier 216. In some embodiments, the optical power level of the first combined signal can be equal to the sum of the optical power levels of the input signal and the first pump light received by the first optical combiner 214.In other embodiments, the optical power level of the first combined signal can be greater than the individual optical power level of the input signal or the first pump light, but less than the sum of these optical power levels.

[0040] The first amplifier 216 can receive the first combined signal from the first optical combiner 214. The first amplifier 216 can generate an amplified signal based on the first combined signal. For example, the first pump light of the first combined signal can excite erbium ions in the first amplifier 216, which can amplify the input signal by stimulated emission, thereby generating the amplified signal. In some embodiments, the first amplifier 216 can be configured to apply amplification to the first combined signal, so that the amplified signal is generated as an amplified version of the first combined signal. In these and other embodiments, the first combined signal can drive the first amplifier 216. The optical isolator 218 can allow the amplified signal from the first amplifier 216 to reach the first input 265 of the second optical combiner 220.Furthermore, the optical isolator 218 can be configured to prevent or at least reduce the back reflection of light from the second optical combiner 220 to the first amplifier 216.

[0041] The feedback controller 224 can receive the control signal from the input photodiode 208. Additionally, the feedback controller 224 can receive a feedback signal as an electrical signal from the output photodiode 232. The feedback controller 224 can generate a driver signal within the non-reactive stage 204, also referred to as the first driver signal, as an electrical signal based on the control signal and the feedback signal. In some embodiments, the feedback controller 224 can be configured as a PI controller. In these and other embodiments, the current of the first driver signal can be based on the current of the control signal or the current of the feedback signal. In some embodiments, the current of the first driver signal can be based on a difference between the current of the control signal and the current of the feedback signal.

[0042] The second pump laser 222 can receive the first driver signal from the feedback controller 224. The second pump laser 222 can generate a second pump light based on the first driver signal. In some embodiments, the second pump laser 222 can generate the second pump light according to the first driver signal. In these and other embodiments, the optical power level of the second pump light can be based on the current of the first driver signal.

[0043] The second optical combiner 220 can receive the amplified signal from the optical isolator 218 and the second pump light from the second pump laser 222. The second optical combiner 220 can combine the amplified signal and the second pump light into a second combined signal. Furthermore, the second optical combiner 220 can supply the second combined signal to the second amplifier 226. In some embodiments, the optical power level of the second combined signal can be equal to the sum of the optical power levels of the amplified signal and the second pump light. In other embodiments, the optical power level of the second combined signal can be greater than the individual optical power levels of the amplified signal or the second pump light, but less than the sum of these optical power levels.

[0044] The second amplifier 226 can receive the second combined signal from the second optical combiner 220. The second amplifier 226 can generate the output signal as an optical signal based on the second combined signal. In some embodiments, the second amplifier 226 can be configured to apply amplification to the second combined signal, so that the output signal is generated as an amplified version of the second combined signal. For example, the second pump light of the second combined signal can excite erbium ions in the second amplifier 226, which can amplify the amplified signal by stimulated emission, thereby generating the output signal. In these and other embodiments, the second combined signal can drive the second amplifier 226.

[0045] The second optical splitter 228 can receive the output signal from the second amplifier 226. The second optical splitter 228 can divide the output signal and supply it to the filter 230 and the output 225 of the EDFA 107. In some embodiments, the second optical splitter 228 can divide the optical power level of the output signal between the first output 275 and the second output 277 of the second optical splitter 228. In these and other embodiments, the second optical splitter 228 can divide the optical power level of the output signal between the first output 275 and the second output 277 of the second optical splitter 228 evenly or unevenly. Additionally or alternatively, the filter 230 and the output 225 of the EDFA 107 can receive the output signal with divided optical power levels.

[0046] The filter 230 can receive the output signal with the divided optical power level from the second optical splitter 228. The filter 230 can generate a filtered signal based on the output signal. In some embodiments, the filter 230 can be a pass-through filter configured to allow portions of the output signal to pass through the filter 230. For example, the filter 230 can be configured as an L-band pass-through filter, configured to allow optical signals within the L-band to pass through the filter 230, while blocking optical signals with wavelengths outside the L-band. In some embodiments, the filter 230 can be implemented as a device separate from the output photodiode 232. In other embodiments, the filter 230 can be implemented as a device integrated in or with the output photodiode 232. In some embodiments, the filter 230 can be implemented as a thin-film filter.

[0047] The output photodiode 232 can receive the filtered signal from the filter 230. The output photodiode 232 can generate the feedback signal based on the filtered signal. In some embodiments, the output photodiode 232 can generate the feedback signal as an electrical signal corresponding to the filtered signal. In these and other embodiments, the current of the feedback signal can be based on the optical power level of the filtered signal.

[0048] The alarm device 231 can be configured to measure (e.g., monitor) the current of the first driver signal generated by the feedback controller 224. The alarm device 231 can be configured to generate an alarm signal when the current of the first driver signal exceeds a threshold. In some embodiments, the threshold can be a current value equal to twice the current of the first driver signal during the proper operation of the EDFA 107 (e.g., the current of the first driver signal when the EDFA 107 is operating properly). In other embodiments, the threshold can be a current value equal to 1090 milliamperes (mA) or some other value. In some embodiments, the alarm signal can indicate that the dummy stage 202 (e.g., the first pump laser 212) has failed.In other embodiments, the alarm signal can indicate that a target optical power level of the output signal from the non-blind stage 204 cannot be reached. Additionally or alternatively, the alarm signal can indicate that the EDFA 107 has failed and needs to be replaced, or that a system implementing the EDFA 107 (e.g., System 100) needs to be replaced. Fig. 1) needs to be reconfigured to maintain proper operation.

[0049] If the first pump laser 212 fails, the amplified signal generated by the first amplifier 216 approaches zero—or the first pump laser 212 may cease to generate any amplified signal at all, which may result in the output signal generated by the second amplifier 226 being primarily ASE in the C-band. In these and other embodiments, the filter 230 may be configured to filter out the C-band. For example, the filter 230 may be configured to prevent ASE in the C-band from passing through the filter 230, which may also cause the filtered signal to approach zero. Additionally or alternatively, the filtered signal approaching zero may cause the current of the feedback signal to approach zero amperes.Consequently, the feedback controller 224 can attempt to compensate for the decreasing optical power levels and current by increasing the current of the first driver signal for the second pump laser 222. Increasing the current of the first driver signal by the feedback controller 224 can cause the current of the first driver signal to exceed the threshold. The alarm device 231 can generate the alarm signal if the feedback controller 224 increases the current of the first driver signal to such an extent that the current exceeds the threshold.

[0050] Fig.Figure 3 shows a graphical representation 300 of the measured current of the first driver signal during simulations of various operating scenarios of the first pump laser 212 according to at least one embodiment described in this disclosure. The graphical representation 300 was obtained by measuring the current of the first driver signal using different combinations of optical power level and gain within the EDFA 107. Table I contains the data used to generate the graphical representation 300. Fig. 3 were used, in tabular form.

[0051] Each point along the horizontal axis of Fig. 3 and the first column of Table I is formatted to indicate the optical power entering the EDFA 107 and the gain for the corresponding currents. For example, the first point in Fig.3 and Table I are labelled “Pin-20G9”, which means that the optical power entering the EDFA is -20 decibel milliwatts (dBm) and the gain is 9 decibels (dB) for the corresponding currents of 64 mA or 145 mA. Another example: The last point in Fig. 3 and Table I is “Pin1G23”, which means that the optical power entering the EDFA is 1 dBm and the gain is 23 dB for the corresponding currents of 542 mA or 1092 mA.

[0052] The various combinations of optical power levels and gains are listed in Table I below for each point, along with the corresponding currents for proper operation and the corresponding currents for faulty operation. Curve 338 in Fig. Figure 3 graphically represents the current strength of the first driver signal, measured in the simulations of the faulty operating scenarios. Curve 340 in Fig.Figure 3 graphically represents the current strength of the first driver signal, which was measured in the simulations of the scenarios for proper operation.

[0053] As in Fig. As shown in Figure 3 and Table I, the current of the first driver signal in the simulations of the faulty operating scenarios exceeds 1000 mA for most combinations of optical power level and gain. As shown in Fig. As shown in Figure 3 and Table I, the current of the first driver signal in the simulations of the faulty operation scenarios also exceeds twice the corresponding current of the first driver signal in the simulations of the proper operation scenarios for each of the combinations of optical power level and gain. Table I Optical power level [dBm] Gain [dB] Current [mA] proper operation Current [mA] faulty operation Pin-20G9 -20 9 64 145 Pin-15G9 -15 9 63 788 Pin-10G9 -10 9 65 1094 Pin-5G9 -5 9 70 1094 Pin0G9 0 9 83 1094 Pin5G9 5 9 117 1094 Pin10G9 10 9 222 1093 Pin15G9 15 9 637 1092 Pin-25G14 -25 14 62 178 Pin-20G14 -20 14 62 997 Pin-15G14 -15 14 64 1094 Pin-10G14 -10 14 69 1094 Pin-5G14 -5 14 80 1094 Pin0G14 0 14 112 1094 Pin5G14 5 14 208 1093 Pin10G14 10 14 594 1092 Pin-29G18 -29 18 61 329 Pin-24G18 -24 18 62 1094 Pin-19G18 -19 18 64 1094 Pin-14G18 -14 18 68 1094 Pin-9G18 -9 18 79 1094 Pin 4G18 -4 18 109 1094 Pin1G18 1 18 201 1002 Pin6G18 6 18 566 1092 Pin-29G23 -29 23 67 1094 Pin-24G23 -24 23 68 1094 Pin-19G23 -19 23 75 1094 Pin-14G23 -14 23 81 1094 Pin-9G23 -9 23 110 1094 Pin 4G23 -4 23 197 629 Pin1G23 1 23 542 1092

[0054] Fig.Figure 4 shows a flowchart of an example method 400 for generating an alarm signal when a driver signal exceeds a threshold, in accordance with at least one embodiment described in this disclosure. The method 400 can be performed by any suitable system, apparatus, or device. For example, the EDFA 107 of Fig. 2. Execute or instruct the execution of one or more of the operations associated with Procedure 400. Procedure 400 may include one or more of blocks 402, 404, 406, 408, 410, 412, or 414. Although represented by discrete blocks, the steps and operations associated with one or more of the blocks of Procedure 400 may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the specific implementation.

[0055] A control signal can be generated in block 402. In some embodiments, the control signal can be generated based on an input signal. For example, the input photodiode 208 can be controlled by Fig. 2. Generate the control signal based on the input signal.

[0056] An amplified signal can be generated in block 404. In some embodiments, the amplified signal can be generated based on the control signal and the input signal. For example, the dummy stage 202 of Fig. 2. Generate the amplified signal based on the control signal and the input signal.

[0057] An output signal can be generated in block 406. In some embodiments, the output signal can be generated based on the amplified signal, the control signal, and a feedback signal. For example, the non-blind stage 204 can generate the output signal based on the amplified signal, the control signal, and the feedback signal.

[0058] A filtered signal can be generated in block 408. In some embodiments, the filtered signal can be generated based on the output signal. For example, filter 230 of Fig. 2. Generate the filtered signal based on the output signal.

[0059] A feedback signal can be generated in block 410. In some embodiments, the feedback signal can be generated based on the filtered signal. For example, the output photodiode 232 can be made from Fig.2. Generate the feedback signal based on the filtered signal.

[0060] A driver signal can be generated in block 412. In some embodiments, the driver signal can be generated based on the feedback signal and the control signal. For example, the feedback controller 224 of Fig. 2. Generate the driver signal (e.g., the first driver signal) based on the feedback signal and the control signal.

[0061] In block 414, an alarm signal can be generated if the driver signal exceeds a threshold. The alarm signal can be generated, for example, by the alarm device 231 if the current of the first driver signal exceeds the threshold. In some embodiments, the alarm signal can indicate that the EDFA (e.g., the dummy stage) has failed.

[0062] Method 400 may be modified, supplemented, or omitted without departing from the scope of this disclosure. For example, the operations of Method 400 may be performed in different sequences. Additionally or alternatively, two or more operations may be performed simultaneously. Furthermore, the outlined operations and actions are given only as examples, and some of the operations and actions may be optional, combined into fewer operations and actions, or extended to include additional operations and actions without deviating from the fundamental concept of the described embodiments.

[0063] An exemplary method for detecting the failure of a feed-forward pump laser (e.g., the first pump laser 212) in an L-band fiber amplifier (e.g., the EDFA 107) may involve adding a C / L-band filter before the input (e.g., input 279) of an output photodiode (e.g., output photodiode 232). The method may include obtaining a current value (e.g., a driver signal) of a feed-back pump laser (e.g., the second pump laser 222) and a normal operating current value at a corresponding time. The normal operating current value can be obtained during a production test and recorded in a modular memory for determination by modular software of the L-band fiber amplifier. The method may include determining whether the obtained current value of the feed-back pump laser is greater than a current threshold. The threshold current value can represent a maximum nominal operating current of the feedback pump.The procedure may include determining whether the current value of the feedback pump is greater than twice the normal operating current value. The procedure may also include triggering an alarm signal if the current value of the feedback pump is greater than the threshold current value or greater than twice the normal operating current value.

[0064] Provided that certain arrangements described herein are not mutually exclusive, the various implementations described herein can be combined to improve system functionality or to generate complementary functions. Likewise, aspects of the implementations can be implemented in independent arrangements. Therefore, the above description is given only as an example, and modifications to details can be made within the scope of the present invention.

[0065] Regarding the use of plural or singular terms, professionals may translate from plural to singular or vice versa as appropriate to the context or application. The various singular / plural permutations may be explicitly listed here for clarity. A reference to an element in the singular should not mean "one and only one" unless explicitly stated, but rather "one or more." Furthermore, nothing disclosed herein is intended for public release, regardless of whether such disclosure is explicitly mentioned in the description above.

[0066] In general, the terms used here, and in particular in the appended claims (e.g., in the bodies of the appended claims), are to be understood as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "with" as "with at least", the term "comprises" as "comprises but is not limited to", etc.). Furthermore, where a composition is used analogously to "at least one of A, B, and C, etc.", it generally refers to a construction in the sense that a person skilled in the art would understand the composition (e.g., "a system with at least one of A, B, and C" would include systems comprising A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, etc., without being limited thereto).A phrase containing two or more alternative terms, whether in the description, claims, or drawings, should be understood to include one of the terms, one or the other, or both. For example, the phrase "A or B" should be understood to include the possibilities "A" or "B" or "A and B".

[0067] The present invention can be embodied in other specific forms without deviating from its basic concept or essential features. The described embodiments are to be considered in every respect merely illustrative and not limiting. The scope of the invention is therefore more readily apparent from the appended claims than from the preceding description. All modifications that fall within the scope and equivalence of the claims are to be included within their scope.

Claims

[1] Erbium-doped fiber amplifier (EDFA), comprising: an input photodiode (208) configured to generate a control signal based on an input signal; a dummy stage (202) coupled to the input photodiode (208), the dummy stage (202) configured to generate an amplified signal based on the control signal from the input photodiode (208) and the input signal; a non-dummy stage (204) coupled to the input photodiode (208) and the dummy stage (202), the non-dummy stage (204) configured to generate an output signal based on the amplified signal of the dummy stage (202), the control signal from the input photodiode (208) and a feedback signal, a drive signal being generated within the non-dummy stage (204) based on the feedback signal and the control signal from the input photodiode (208); a filter (230) coupled to the non-dummy stage (204), the filter (230) configured to generate a filtered signal based on the output signal of the non-dummy stage (204); an output photodiode (232) coupled to the filter (230), the output photodiode (232) configured to generate the feedback signal based on the filtered signal from the filter (230); and an alarm device (231) coupled to the non-dummy stage (204), the alarm device (231) being configured to generate an alarm signal when the drive signal within the non-dummy stage (204) exceeds a threshold, wherein, when the dummy stage (202) fails, the amplified signal within the dummy stage (202) approaches zero, causing the feedback signal of the output photodiode (232) to approach zero and the drive signal within the non-dummy stage (204) to rise and exceed the threshold. [2] The EDFA of claim 1, wherein when the dummy stage (202) fails, the non-dummy stage (204) produces the output signal as amplified spontaneous emission (ASE) and the filter (230) is configured to filter out the ASE, wherein the filtered signal from the filter (230) and the feedback signal from the output photodiode (232) approach zero and the drive signal within the non-dummy stage (204) increases and exceeds the threshold. [3] EDFA according to claim 1, wherein: the EDFA is configured as an L-band amplifier; and the filter comprises a C / L filter configured to filter out signals in a C-band. [4] The EDFA of claim 1, wherein the alarm device (231) is configured to measure a current of the drive signal within the non-dummy stage (204). [5] The EDFA of claim 1, wherein the dummy stage comprises a feed-forward controller (210) coupled to the input photodiode (208), and the feed-forward controller (210) is configured to generate a drive signal within the dummy stage (202) based on the control signal from the input photodiode (208), and the amplified signal within the dummy stage (202) is based on the drive signal within the dummy stage (202) and the input signal. [6] The EDFA of claim 5, wherein the non-dummy stage (204) comprises a feedback controller (224) coupled to the input photodiode (208) and the output photodiode (232), the feedback controller (224) configured to generate the drive signal within the non-dummy stage (204) based on the control signal from the input photodiode (208) and the feedback signal from the output photodiode (232), and the output signal is based on the drive signal within the non-dummy stage (204) and the amplified signal within the dummy stage (202). [7] The EDFA of claim 6, wherein the dummy stage (202) further comprises: a first pump laser (212) coupled to the feed-forward controller (210), the first pump laser (212) configured to generate a first pump light based on the drive signal within the dummy stage (202); a first combiner (214) coupled to the first pump laser (212), the first combiner (214) configured to generate a first combined signal based on the input signal and the first pump light from the first pump laser (212); and a first amplifier (216) coupled to the first combiner (214), the first amplifier (216) configured to amplify the first combined signal from the first combiner (214) to generate the amplified signal. [8] The EDFA of claim 7, wherein the non-blind stage (204) further comprises: a second pump laser (222) coupled to the feedback controller (224), the second pump laser (222) configured to generate a second pump light based on the drive signal within the non-dummy stage (204); a second combiner (220) coupled to the second pump laser (222) and the first amplifier (216), the second combiner (220) configured to generate a second combined signal based on the amplified signal from the first amplifier (216) and the second pump light from the second pump laser (222); and a second amplifier (226) coupled to the second combiner (220), the second amplifier (226) configured to amplify the second combined signal from the second combiner (220) to generate the output signal. [9] An erbium-doped fiber amplifier (EDFA) comprising: an input photodiode (208) optically coupled to an input (209) of the EDFA (107); a feed-forward controller (210) electrically coupled to an output of the input photodiode (208); a first pump laser (212) electrically coupled to an output (215) of the feed-forward controller (210); a first amplifier (216) optically coupled to an output (217) of the first pump laser (212) and the input (209) of the EDFA (107); a feedback controller (224) electrically coupled to the output of the input photodiode (208); a second pump laser (222) electrically coupled to an output (215) of the feedback controller (224); a second amplifier (226) optically coupled to an output (221) of the second pump laser (222), an output (223) of the first amplifier (216) and an output (225) of the EDFA (107); a filter (230) optically coupled to an output (227) of the second amplifier (226); an output photodiode (232) optically coupled to an output (229) of the filter (230) and electrically coupled to an input (233) of the feedback controller (224); and an alarm device (231) coupled to the feedback controller (224), wherein, when the first pump laser (212) fails, an amplified signal generated by the first amplifier (216) decreases, resulting in a feedback signal generated by the output photodiode (232) decreasing and a drive signal generated by the feedback controller (224) increasing. [10] The EDFA of claim 9 further comprising an optical splitter (206) optically coupled to the input (209) of the EDFA (107), an input of the input photodiode (208) and an input (237) of the first amplifier (216). [11] The EDFA of claim 10 further comprising an optical combiner (214) optically coupled to an output (239) of the optical splitter (206), the output (217) of the first pump laser (212) and the input (237) of the first amplifier (216). [12] The EDFA of claim 9 further comprising an optical isolator (218) optically coupled to the output (223) of the first amplifier (216) and an input (241) of the second amplifier (226). [13] The EDFA of claim 12 further comprising an optical combiner (220) optically coupled to an output (243) of the optical isolator (218), the output (221) of the second pump laser (222) and the input (241) of the second amplifier (226). [14] The EDFA of claim 9 further comprising an optical splitter (228) optically coupled to the output (227) of the second amplifier (226), an input (245) of the filter (230) and the output (225) of the EDFA (107). [15] A method comprising: Generating a control signal based on an input signal; Generating an amplified signal based on the control signal and the input signal; Generating an output signal based on the amplified signal, the control signal and a feedback signal; Generating a filtered signal based on the output signal; Generating the feedback signal based on the filtered signal; Generating a drive signal based on the feedback signal and the control signal; and Generating an alarm signal when the drive signal exceeds a threshold, wherein as the amplified signal approaches zero, the feedback signal approaches zero and the drive signal increases and exceeds the threshold. [16] The method of claim 15, wherein, as the amplified signal approaches zero, the output signal is produced as amplified spontaneous emission (ASE), causing the filtered signal and the feedback signal to approach zero and the drive signal to increase and exceed the threshold. [17] The method of claim 15, further comprising determining a current of the drive signal, wherein the threshold is a current. [18] The method of claim 15, wherein the drive signal is a first drive signal, and the method further comprises generating a second drive signal based on the control signal, and the amplified signal is generated based on the second drive signal and the input signal. [19] The method of claim 18 further comprising generating a first pump light based on the second drive signal, wherein the amplified signal is based on the first pump light. [20] The method of claim 19 further comprising generating a second pump light based on the first drive signal, wherein the output signal is based on the second pump light and the amplified signal.

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