Optical transmission system and fiber type determination method

Abstract

To reduce labor for determining a type of an optical fiber provided between nodes.SOLUTION: An optical transmission system comprises a first optical node, a second optical node, and an optical fiber provided between the first optical node and the second optical node. The first optical node comprises a signal generation unit and a transmission optical circuit. The signal generation unit generates an optical signal having a plurality of wavelength channels and an idle channel. The transmission optical circuit outputs to the optical fiber the optical signal generated by the signal generation unit. The second optical node comprises an optical channel monitor that measures a reception power of each channel of an optical signal received via the optical fiber. The first optical node or the second optical node further comprises a determination unit that determines a type of the optical fiber on the basis of the reception power of the idle channel measured by the optical channel monitor.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to optical transmission systems and methods for determining the type of optical fiber used in optical transmission systems. [Background technology]

[0002] The type of optical fiber used in an optical communication network is determined based on the application, cost, etc. In recent years, single-mode optical fiber (SMF), dispersion-shifted single-mode optical fiber (DSF), or non-zero dispersion-shifted single-mode optical fiber (NZ-DSF) has been used in optical communication networks.

[0003] SMF is an optical fiber in which only one mode propagates due to its small core diameter. General-purpose SMF has a zero-dispersion wavelength in the 1310 nm band, which means it has low transmission loss and is often used in backbone networks that require high-quality, stable communications. DSF has a zero-dispersion wavelength in the 1550 nm band, which has low transmission loss, so it is often used in long-distance transmission. The zero-dispersion wavelength of NZ-DSF is slightly shifted from the 1550 nm band. For example, NZ-DSF has a zero-dispersion wavelength at approximately 1500 nm. Because nonlinear effects in the 1550 nm band are suppressed, NZ-DSF is well suited to wavelength division multiplexing transmission and is often used in ultra-high-speed long-distance transmission.

[0004] The optical transceivers and optical amplifiers installed at each optical node in an optical transmission system must be designed according to the type of optical fiber. For this reason, telecommunications carriers check the type of optical fiber installed in each span.

[0005] Figure 1 shows an example of a method for detecting the type of optical fiber laid between optical nodes. For example, when detecting the type of optical fiber F1 laid between optical nodes N1 and N2, a light source (LD) is connected to one optical node (N1) and a dispersion measurement device is connected to the other optical node (N2). Light output from the light source propagates from optical node N1 to optical node N2 via optical fiber F1. Then, the dispersion measurement device is used to measure the dispersion of the received light, thereby determining the type of optical fiber F1.

[0006] Also, a method has been proposed for estimating the type of optical fiber based on the power of light reflected from an optical transmission line (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-173969 Summary of the Invention [Problem to be solved by the invention]

[0008] Conventional methods require a great deal of effort to determine the type of optical fiber. For example, the method shown in FIG. 1 requires an operator to be located at both ends of the target optical fiber. Here, each span is several kilometers to 100 kilometers long, and a large-scale optical communication network has a large number of optical nodes. Therefore, determining the type of optical fiber for all spans in an optical communication network requires a great deal of effort.

[0009] An object of one aspect of the present invention is to reduce the effort required to determine the type of optical fiber installed between optical nodes. [Means for solving the problem]

[0010] An optical transmission system according to one embodiment of the present invention includes a first optical node, a second optical node, and an optical fiber provided between the first optical node and the second optical node. The first optical node includes a signal generator that generates an optical signal having a plurality of wavelength channels and an available channel, and a transmitting optical circuit that outputs the optical signal to the optical fiber. The second optical node includes an optical channel monitor that measures the reception power of each channel of the optical signal received via the optical fiber. The first optical node or the second optical node further includes a determination unit that determines the type of the optical fiber based on the reception power of the available channel measured by the optical channel monitor. [Effects of the Invention]

[0011] According to the above-described aspect, it is possible to reduce the effort required to determine the type of optical fiber installed between optical nodes. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 10 is a diagram illustrating an example of a method for detecting the type of optical fiber laid between optical nodes. [Figure 2] 1 is a diagram illustrating an example of an optical transmission system according to an embodiment of the present invention. [Figure 3] FIG. 1 is a diagram illustrating an example of a configuration of an optical node according to an embodiment of the present invention. [Figure 4] FIG. 1 illustrates an example of an OTDR. [Figure 5] FIG. 10 is a diagram showing an example of a measurement result obtained by an OTDR. [Figure 6] FIG. 1 is a diagram showing the relationship between propagation time and wavelength measured by an OTDR. [Figure 7] FIG. 1 is a diagram illustrating the relationship between propagation time, wavelength, and type of optical fiber. [Figure 8] FIG. 1 is a diagram illustrating chromatic dispersion of SMF, DSF, and NZ-DSF. [Figure 9] FIG. 10 is a diagram illustrating an example of a method for determining the type of optical fiber by using a pseudo WDM signal. [Figure 10] FIG. 10 is a diagram illustrating an example of a method for calculating crosstalk. [Figure 11] 1 is a flowchart illustrating an example of a method for determining the type of optical fiber. [Figure 12] FIG. 10 is a diagram illustrating another embodiment of an optical node realized by ROADM. [Figure 13] FIG. 10 is a diagram illustrating another example of an optical transmission system according to an embodiment of the present invention. [Figure 14] FIG. 1 illustrates an example of an optical node that operates as an optical repeater. [Figure 15] FIG. 1 is a diagram illustrating an example of an optical transmission system in which two types of optical fibers are mixed within one span. [Figure 16] FIG. 1 is a diagram showing an example of a method for distinguishing between two types of optical fibers by utilizing crosstalk. [Figure 17] 17 is a diagram illustrating an example of the configuration of an optical node used in the optical transmission system illustrated in FIG. 16. [Figure 18] FIG. 10 is a diagram illustrating an example of a method for controlling the transmission power of a WDM signal depending on the type of optical fiber. [Figure 19] FIG. 10 is a diagram illustrating an example of a sequence of cooperative operations by a pair of optical nodes. [Figure 20] FIG. 1 is a diagram illustrating an example of an arrangement of OSCs. [Figure 21] FIG. 1 is a diagram illustrating an example of an optical node including an OSC processing unit. [Figure 22] 1 is a flowchart illustrating an example of a method for distinguishing between SMF, DSF, and NZ-DSF using a pseudo-WDM signal. [Figure 23] 10A and 10B are diagrams illustrating another example of a method for determining the type of fiber by utilizing crosstalk. DETAILED DESCRIPTION OF THE INVENTION

[0013] FIG. 2 shows an example of an optical transmission system according to an embodiment of the present invention. The optical transmission system 100 according to the embodiment of the present invention includes a plurality of optical nodes 1 (1a to 1n). Each optical node 1 includes an optical transmission device but Here, the optical transmission system 100 is a WDM transmission system that transmits wavelength division multiplexed signals. Therefore, the optical transmission device provided in each optical node 1 is, for example, a ROADM (Reconfigurable Optical Add-Drop Multiplexer). In the following description, the wavelength division multiplexed signal may be referred to as a "WDM signal."

[0014] Optical nodes 1 are connected to each other via optical fibers 2. Optical signals are transmitted between the optical nodes in both directions. For example, an optical signal is transmitted from optical node 1a to optical node 1b via optical fiber 2x, and an optical signal is transmitted from optical node 1b to optical node 1a via optical fiber 2y.

[0015] Fig. 3 shows an example of the configuration of an optical node 1 according to an embodiment of the present invention. The optical node 1 includes a wavelength selective switch (WSS) 11, an optical amplifier circuit 12, an optical time domain reflectometer (OTDR) 13, an optical switch 14, an optical channel monitor (OCM) 15, an optical switch 16, an amplified spontaneous emission (ASE) light source 17, and a control unit 18. The optical node 1 may include other elements, circuits, and functions not shown in Fig. 3. An optical fiber TX and an optical fiber RX are connected to the optical node 1.

[0016] The WSS 11 processes a WDM signal having multiple wavelength channels. For example, the WSS 11 can add an optical signal to an unused channel of the WDM signal according to instructions from the control unit 18. The WSS 11 can also extract an optical signal from a wavelength channel specified by the control unit 18. The optical amplifier circuit 12 includes, for example, an erbium-doped fiber amplifier (EDFA) and can amplify the WDM signal. In this example, the optical amplifier circuit 12 amplifies the WDM signal generated by the WSS 11 and also amplifies the WDM signal received via the optical fiber RX. The gain of the optical amplifier circuit 12 is controlled by the control unit 18. The optical amplifier circuit 12 is an example of a transmitting optical circuit that transmits a pseudo-WDM signal, which will be described later.

[0017] The OTDR 13 is an optical measuring instrument that detects discontinuities in optical fibers. Specifically, the OTDR 13 inputs an optical pulse into an optical fiber and detects the reflected light from the optical fiber. The OTDR 13 can then detect the location of the discontinuity in the optical fiber based on the power and timing of the reflected light. Note that discontinuities in optical fibers include breaks and terminations. They also include splices between optical fibers. The optical switch 14 establishes an optical path between the OTDR 13 and the optical fiber. For example, when measuring the optical fiber TX, the optical switch 14 establishes an optical path between the OTDR 13 and the optical coupler C1. When measuring the optical fiber RX, the optical switch 14 establishes an optical path between the OTDR 13 and the optical coupler C2.

[0018] The optical channel monitor 15 can measure the power of each wavelength channel of the WDM signal. The optical switch 16 sets an optical path according to the WDM signal to be measured by the optical channel monitor 15. For example, when monitoring a WDM signal received via the optical fiber RX, the optical switch 16 sets an optical path between the optical channel monitor 15 and the optical coupler C3. When monitoring a received WDM signal amplified by the optical amplifier circuit 12, the optical switch 16 sets an optical path between the optical channel monitor 15 and the optical coupler C4. When monitoring a transmission WDM signal generated by the WSS 11, the optical switch 16 sets an optical path between the optical channel monitor 15 and the optical coupler C5. When monitoring a transmission WDM signal amplified by the optical amplifier circuit 12, the optical switch 16 sets an optical path between the optical channel monitor 15 and the optical coupler C6.

[0019] The ASE light source 17 generates ASE light. Here, the ASE light source 17 is assumed to be capable of generating high-power, broadband ASE light. The ASE light generated by the ASE light source 17 is then guided to the WSS 11. The WSS 11 uses this ASE light to generate a quasi-WDM signal, which will be described later. The ASE light source 17 and the WSS 11 are an example of a signal generator that generates a quasi-WDM signal.

[0020] The control unit 18 includes a determination unit 18a and controls the operation of the optical node 1. For example, the control unit 18 instructs the OTDR 13 to measure the optical fiber. In this case, the determination unit 18a determines the type of optical fiber based on the measurement results by the OTDR 13. The control unit 18 also instructs the WSS 11 to generate a pseudo WDM signal. Furthermore, when the optical node 1 receives a pseudo WDM signal transmitted from an adjacent node, the determination unit 18a may use the pseudo WDM signal to determine the type of optical fiber.

[0021] The control unit 18 is realized by, for example, a CPU including a processor and a memory. In this case, the processor executes a fiber type determination program stored in the memory to determine the type of optical fiber connected to the optical node 1. However, some of the functions of the control unit 18 may be realized by a hardware circuit.

[0022] 4 shows an example of the OTDR 13. In this embodiment, the OTDR 13 includes a pulse generator 13a, a light source circuit 13b, a light receiving circuit 13c, and a signal processing unit 13d. The OTDR 13 measures the optical fiber in accordance with instructions given by the control unit 18.

[0023] The pulse generator 13a generates a pulse signal in response to a generation instruction given by the signal processing unit 13d. The light source circuit 13b generates an optical pulse in synchronization with the pulse signal generated by the pulse generator 13a. This optical pulse is incident on the optical fiber to be measured. The light source circuit 13b also includes two LD light sources (λ1, λ2). That is, the light source circuit 13b can generate an optical pulse with a wavelength of λ1 and an optical pulse with a wavelength of λ2. Note that, although not particularly limited, λ1 and λ2 are, for example, 1310 nm and 1650 nm, respectively.

[0024] When light is incident on the optical fiber from the OTDR 13, Rayleigh scattering occurs, and part of the backscattered light returns to the OTDR 13. In addition, if Fresnel reflection occurs at a discontinuity in the optical fiber, the reflected light also returns to the OTDR 13.

[0025] The light receiving circuit 13c converts the reflected light (backscattered and Fresnel reflected) into an electrical signal. The signal processing unit 13d measures the state of the optical fiber based on the output signal of the light receiving circuit 13c. That is, the signal processing unit 13d measures the state of the optical fiber based on the output signal of the light receiving circuit 13c. of The condition of the optical fiber is measured based on the reflected light.

[0026] 5 shows an example of the measurement results obtained by the OTDR 13. The horizontal axis of the graph represents the time elapsed since the OTDR 13 transmitted an optical pulse, and the vertical axis represents the power of the reflected light from the optical fiber detected by the light receiving circuit 13c.

[0027] The intensity of reflected light due to Rayleigh scattering depends on the distance from the OTDR 13. That is, reflected light from a position close to the OTDR 13 is strong, while reflected light from a position far away from the OTDR 13 is weak. Therefore, the power of the reflected light detected by the light-receiving circuit 13c gradually decreases as the time elapsed since the OTDR 13 transmitted an optical pulse increases. However, the light-receiving circuit 13c also detects reflected light due to Fresnel reflection occurring at discontinuities in the optical fiber. The power of the reflected light changes suddenly at the time when the reflected light from the discontinuity is detected. Therefore, by measuring the time from when the OTDR 13 transmitted an optical pulse to when the power of the reflected light suddenly changes, the transmission distance from the OTDR 13 to the discontinuity in the optical fiber can be calculated. Note that the discontinuity in the optical fiber includes the end point of the optical fiber (the adjacent node in FIG. 4).

[0028] In this way, the OTDR 13 can detect discontinuities in the optical fiber by measuring the propagation time from when the optical pulse is transmitted to when the reflected light is received. Here, this propagation time depends on the wavelength of the optical pulse and the type of optical fiber.

[0029] Figure 6 shows the relationship between propagation time and wavelength measured by the OTDR 13. Figure 6(a) shows the case where the optical fiber under measurement is an SMF, and Figure 6(b) shows the case where the optical fiber under measurement is a DSF or NZ-DSF. In this example, the propagation time taken for an optical pulse transmitted from the OTDR 13 to be reflected at a predetermined discontinuity point K and return is measured. The discontinuity point K may be the end point of the optical fiber under measurement (i.e., an adjacent node).

[0030] When the optical fiber to be measured is an SMF, the propagation time of light with a wavelength of 1310 nm (hereinafter referred to as λ1 light) is t1, and the propagation time of light with a wavelength of 1650 nm (hereinafter referred to as λ2 light) is t2. In this example, the propagation time of λ2 light is longer than that of λ1 light. Furthermore, the difference ΔTs between the two propagation times is relatively large.

[0031] On the other hand, if the optical fiber being measured is a DSF or NZ-DSF, the propagation time of the λ1 light is t3, and the propagation time of the λ2 light is t4. In this example, the propagation time of the λ2 light is shorter than the propagation time of the λ1 light. Also, the difference ΔTd between the two propagation times is relatively small.

[0032] Figure 7 shows the relationship between propagation time, wavelength, and type of optical fiber. The horizontal axis represents the wavelength of the optical pulse transmitted from the OTDR 13. The vertical axis represents the propagation time of the optical pulse transmitted from the OTDR 13 until it returns to the OTDR 13. However, this propagation time is a relative value based on the propagation time when the wavelength is 1550 nm. The propagation distance is 100 km. The solid line represents the case where the optical fiber to be measured is SMF. The dashed line represents the case where the optical fiber to be measured is DSF The dashed line indicates the case where the optical fiber under measurement is an NZ-DSF.

[0033] As described above, the OTDR 13 measures the propagation times using the λ1 light and the λ2 light, respectively. In this example, λ1 is 1310 nm and λ2 is 1650 nm.

[0034] When the optical fiber being measured is SMF, the slope of the curve representing the propagation time versus wavelength is steep. Therefore, as indicated by the circle, there is a large difference between the propagation time for λ1 and the propagation time for λ2. Specifically, the difference in propagation time is 3.82 nm / km. In this case, if the distance from the OTDR 13 to the reflection point (i.e., the discontinuity in the optical fiber or the adjacent node) is D [km], then the difference in propagation time is approximately 7.6 × D [nm].

[0035] When the optical fiber being measured is a DSF or NZ-DSF, the slope of the curve showing the propagation time versus wavelength is small. Therefore, as shown by the triangle or square marks, the difference between the propagation time for λ1 and the propagation time for λ2 is small Specifically, for example, the difference in propagation time of DSF is -0.85 nm / km. In this case, the difference in propagation time is approximately 1.9 × D [nm].

[0036] Therefore, by setting a predetermined threshold, it is possible to distinguish between SMF and DSF-based fibers (DSF and NZ-DSF). For example, if a 50% variation is allowed, the threshold range for determining whether the optical fiber under test is SMF is 3.8×D to 11.4×D [nm]. That is, if the difference in propagation time is within the threshold range, the optical fiber under test is determined to be SMF, and if the difference in propagation time is outside the threshold range, the optical fiber under test is determined to be DSF-based fiber. Alternatively, if the difference in propagation time is within the threshold range, the optical fiber under test may be determined to be SMF, and if the difference in propagation time is smaller than the lower limit of the threshold range, the optical fiber under test may be determined to be DSF-based fiber.

[0037] In the example shown in Figures 6 and 7, the two wavelengths used by the OTDR 13 are 1310 nm and 1650 nm, but the embodiment of the present invention is not limited to this configuration. However, if the difference between the two wavelengths is too small, the difference in propagation time also becomes small, and the accuracy of determining the type of optical fiber decreases. Therefore, it is preferable to increase the difference between the two wavelengths within a range that does not increase optical loss. Furthermore, considering the manufacturing cost of the optical node 1, it is preferable to use an inexpensive light source.

[0038] As described above, the fiber type determination method according to the embodiment of the present invention makes it possible to distinguish between SMF and DSF-based fibers. Next, a method for distinguishing between DSF and NZ-DSF will be described.

[0039] Figure 8 shows the chromatic dispersion of SMF, DSF, and NZ-DSF. In this example, the dispersion of DSF is zero at 1550 nm. The zero-dispersion wavelength of NZ-DSF is approximately 1500 nm.

[0040] Here, the nonlinear effect when multiple lightwaves with different wavelengths are input to an optical fiber depends on the amount of dispersion. For example, the amount of crosstalk due to four-wave mixing (FWM) becomes large at the zero-dispersion wavelength. Therefore, the amount of crosstalk occurring at 1550 nm when multiple lightwaves are input to a DSF is larger than the amount of crosstalk occurring at 1550 nm when multiple lightwaves are input to an NZ-DSF. Therefore, the fiber type determination method according to the embodiment of the present invention utilizes this characteristic to distinguish between DSF and NZ-DSF.

[0041] 9 shows an example of a method for determining the type of optical fiber using a pseudo WDM signal. The pseudo WDM signal is generated by the ASE light source 17 and the WSS 11 in the optical node 1 shown in FIG. 3 based on instructions from the control unit 18.

[0042] 9(a) shows the ASE light generated by the ASE light source 17. The ASE light has a large power over a wide band. This ASE light is then guided to a predetermined input port of the WSS 11.

[0043] FIG. 9(b) shows an example of a pseudo-WDM signal output from WSS 11. The pseudo-WDM signal is realized by multiple wavelength channels CH1 to CH10 and CH12 to CH21 arranged at a predetermined wavelength interval. The predetermined wavelength interval (frequency interval) is not particularly limited, but may be 50 GHz, for example. Alternatively, these wavelength channels may be arranged on a frequency grid specified by ITU-T. Each wavelength channel has a transmission power equal to or greater than a predetermined level. However, no wavelength channel is set at the zero-dispersion wavelength of DSF. In other words, an empty channel is set at the zero-dispersion wavelength of DSF. The empty channel must be set to a transmission power at least lower than that of the wavelength channel (i.e., the signal channel) that transmits the signal. In this embodiment, the zero-dispersion wavelength of DSF is 1550 nm. Therefore, as shown in FIG. 9(b), no wavelength channel is set at 1550 nm. Note that although it is preferable to set the empty channel at the zero-dispersion wavelength of DSF, it may also be set near the zero-dispersion wavelength of DSF.

[0044] The control unit 18 issues an instruction to the WSS 11 to pass the light of wavelength channels CH1 to CH10 and CH12 to CH21 and block the light of other wavelengths. The WSS 11 then processes the ASE light in accordance with this instruction. As a result, a quasi-WDM signal is generated that transmits wavelength channels CH1 to CH10 and CH12 to CH21 and has substantially zero optical power at 1550 nm. Note that in the following description, wavelengths for which no wavelength channel is set and whose optical power is controlled to substantially zero may be referred to as "free channel wavelengths."

[0045] Optical node 1 transmits the generated pseudo WDM signal to an adjacent node. The adjacent node receives the pseudo WDM signal via an optical fiber. The received pseudo WDM signal is then guided to an optical channel monitor 15 at the adjacent node. The configuration of the adjacent node is assumed to be the same as that of optical node 1 shown in FIG.

[0046] When the above-mentioned quasi-WDM signal propagates through an optical fiber, crosstalk due to four-wave mixing occurs. The amount of crosstalk due to four-wave mixing depends on the chromatic dispersion of the optical fiber. Specifically, large crosstalk occurs at the zero-dispersion wavelength of the optical fiber. Here, the zero-dispersion wavelength of DSF is 1550 nm. Therefore, when the optical fiber propagating the quasi-WDM signal is DSF, the optical power detected at 1550 nm is large, as shown in Figure 9(c). In contrast, the zero-dispersion wavelength of NZ-DSF is shifted from 1550 nm. Therefore, when the optical fiber propagating the quasi-WDM signal is NZ-DSF, the optical power detected at 1550 nm is small, as shown in Figure 9(d). Although not specifically shown, when the optical fiber propagating the quasi-WDM signal is SMF, the optical power detected at 1550 nm is also small.

[0047] In this way, when optical node 1 transmits a pseudo WDM signal to an adjacent node, it can determine whether the optical fiber between optical node 1 and the adjacent node is DSF based on the optical power detected at the available channel wavelength at the adjacent node. Specifically, when the optical power detected at the available channel wavelength is greater than a predetermined threshold, it is determined that the optical fiber between optical node 1 and the adjacent node is DSF. On the other hand, when the optical power detected at the available channel wavelength is less than the predetermined threshold, it is determined that the optical fiber between optical node 1 and the adjacent node is a fiber other than DSF (NZ-DSF or SMF).

[0048] In a fiber type determination method according to an embodiment of the present invention, large crosstalk occurring at the zero-dispersion wavelength of DSF is utilized to distinguish between DSF and NZ-DSF. If a wavelength channel were set at the zero-dispersion wavelength of DSF, it would be difficult to detect crosstalk occurring due to four-wave mixing. Therefore, by using a pseudo-WDM signal in which the optical power at the zero-dispersion wavelength of DSF is substantially zero, crosstalk occurring at the zero-dispersion wavelength of DSF can be accurately detected.

[0049] Furthermore, instead of using a pseudo-WDM signal in which the optical power at the zero-dispersion wavelength of DSF is substantially zero, a pseudo-WDM signal in which the optical power at the zero-dispersion wavelength of NZ-DSF is substantially zero may be used. In this case, it is possible to determine whether the optical fiber between optical node 1 and the adjacent node is NZ-DSF or another fiber (DSF or SMF).

[0050] FIG. 10 shows an example of a method for calculating crosstalk. In this example, a quasi-WDM signal shown in FIG. 9(b) is transmitted from optical node 1a to optical node 1b. Then, in optical node 1b, optical channel monitor 15 measures the ratio between the average power of the wavelength channels (e.g., CH1 to CH10, CH12 to CH21) of the quasi-WDM signal and the power of the idle channel wavelength. Here, the optical component of the idle channel wavelength corresponds to noise with respect to wavelength channels CH1 to CH10, CH12 to CH21. Therefore, in the following description, the above ratio may be referred to as "OSNR_OCM."

[0051] The determining unit 18a calculates the crosstalk due to four-wave mixing based on the OSNR_OCM obtained by measurement. Specifically, the crosstalk FWMXT is expressed by equation (1). Note that equation (1) is a calculation using antilogarithms.

number

[0052] OSNR_AMP represents the optical signal-to-noise ratio of the amplifier circuit 12 that operates as a preamplifier in the receiving node, and is calculated using equation (2). Note that equation (2) is calculated in dB.

number

[0053] P_in represents the input power at the receiving node. For example, light arriving at the optical node via the optical fiber RX shown in FIG. 3 is guided to the optical channel monitor 15 by the optical coupler C3. Therefore, the optical channel monitor 15 can measure the input power. NF is the noise figure of the amplifier circuit 12 and is a function of the input power P_in. It is assumed that the characteristics of NF are known. Then, the noise figure NF can be calculated by measuring the input power P_in.

[0054] The crosstalk FWMXT is calculated by the above equations (1) and (2). If the crosstalk FWMXT is greater than a predetermined threshold, the determining unit 18a determines that the optical fiber between the optical nodes 1a and 1b is DSF.

[0055] Here, the transmission distance between optical nodes 1a and 1b is known. Then, for this transmission distance, the relationship between fiber input power and crosstalk is assumed to be determined in advance, as shown in Fig. 10. Note that the fiber input power corresponds to the transmission power at the sending node (optical node 1a in Fig. 10).

[0056] For example, when the fiber input power is 4 dBm, the crosstalk of the DSF is -26 dBm, and the crosstalk of the other optical fibers is -33 dBm. The intermediate value between the two values ​​is set as the threshold. That is, the threshold is -29.5 dBm. In this case, if the crosstalk is greater than -29.5 dBm, the optical fiber between optical nodes 1a and 1b is determined to be DSF. On the other hand, if the crosstalk is less than -29.5 dBm, the optical fiber between optical nodes 1a and 1b is determined to be an optical fiber other than DSF.

[0057] The zero-dispersion wavelength of DSF can vary. Therefore, when the idle channel wavelength is set to 1550 nm, the idle channel of the quasi-WDM signal may deviate from the zero-dispersion wavelength of the DSF. If the idle channel of the quasi-WDM signal deviates from the zero-dispersion wavelength of the DSF, the receiving node cannot accurately detect crosstalk. Therefore, optical node 1 transmits the quasi-WDM signal while gradually changing the idle channel wavelength near 1550 nm. The receiving node then detects crosstalk using this quasi-WDM signal. This allows crosstalk to be detected accurately even when the zero-dispersion wavelength of the DSF varies, thereby improving the accuracy of determining the type of optical fiber.

[0058] 11 is a flowchart showing an example of a method for determining the type of optical fiber. The processing of this flowchart is executed by a pair of optical nodes. In the following, it is assumed that the processing is executed by the optical nodes 1a and 1b shown in FIG. 2.

[0059] In S1, the control unit 18 activates the optical amplifier circuit (EDFA) 12, the ASE light source 17, the WSS 11, the OTDR 13, and the optical channel monitor (OCM) 15. This operation is performed in each of the optical nodes 1a and 1b.

[0060] In S2, the OTDR 13 of the optical node 1a measures the propagation times between the optical node 1a and a predetermined discontinuity point using the wavelengths λ1 and λ2, respectively, resulting in propagation times T1 and T2 for the wavelengths λ1 and λ2, respectively.

[0061] In S3, the determination unit 18a of the optical node 1a determines whether the difference ΔT between the propagation time T1 and the propagation time T2 is greater than a predetermined threshold TH1. If the difference ΔT is greater than the threshold TH1, the determination unit 18a determines that the optical fiber between the optical nodes 1a and 1b is SMF. On the other hand, if the difference ΔT is smaller than the threshold TH1, the determination unit 18a determines that the optical fiber between the optical nodes 1a and 1b is a fiber other than SMF (i.e., DSF or NZ-DSF).

[0062] If the difference ΔT is smaller than the threshold TH1, the control unit 18 of the optical node 1a generates a quasi-WDM signal in S4. Specifically, the control unit 18 instructs the WSS 11 to generate a WDM signal including an available channel. Here, the wavelength of the available channel is the same as or approximately the same as the zero-dispersion wavelength of the DSF. The WSS 11 then processes the ASE light in accordance with the instruction from the control unit 18 to generate the quasi-WDM signal. Thereafter, the optical node 1a amplifies the quasi-WDM signal using the amplifier circuit 12 and transmits it to the optical node 1b.

[0063] At S5, optical node 1b receives the quasi-WDM signal. Then, at optical node 1b, optical channel monitor 15 measures the power of each wavelength channel of the quasi-WDM signal and the power of free channels. Furthermore, control unit 18 calculates the crosstalk FWMXT occurring in the optical fiber between optical nodes 1a and 1b based on the measurement results by optical channel monitor 15. Optical node 1b then reports the calculated crosstalk FWMXT to optical node 1a.

[0064] In S6, the determination unit 18a of the optical node 1a determines the type of optical fiber between the optical nodes 1a and 1b based on the crosstalk FWMXT reported from the optical node 1b. Specifically, when the crosstalk FWMXT is larger than a predetermined threshold TH2, the determination unit 18a determines that the optical fiber between the optical nodes 1a and 1b is DSF. On the other hand, when the crosstalk FWMXT is smaller than the predetermined threshold TH2, the determination unit 18a determines that the optical fiber between the optical nodes 1a and 1b is a fiber other than DSF (i.e., SMF or NZ-DSF). However, in S3, it was determined that the optical fiber was not SMF. Therefore, when the crosstalk FWMXT is smaller than the predetermined threshold TH2, the optical fiber is determined to be NZ-DSF.

[0065] 11, it is determined whether the optical fiber is an SMF or not, and then it is determined whether the optical fiber is a DSF or not, but the embodiment of the present invention is not limited to this procedure. That is, it may be determined whether the optical fiber is an SMF or not, after it is determined whether the optical fiber is a DSF or not.

[0066] In the above example, optical node 1b detects crosstalk and optical node 1a determines the type of optical fiber based on the value of the crosstalk, but the embodiment of the present invention is not limited to this procedure. For example, optical node 1b, which receives a pseudo WDM signal, may determine the type of optical fiber based on the crosstalk and report the determination result to optical node 1a.

[0067] As described above, according to the embodiment of the present invention, a pair of optical nodes work together to determine the type of optical fiber between the optical nodes. Therefore, the type of optical fiber can be determined without an operator visiting the nodes at both ends of the optical fiber to be determined, thereby reducing the labor and costs of the telecommunications carrier. Furthermore, in many cases, optical nodes such as ROADMs are equipped with an ASE light source, a WSS, and an optical channel monitor, so there is no need to add dedicated components or circuits for transmitting and receiving pseudo-WDM signals.

[0068] Fig. 12 shows another embodiment of an optical node realized by ROADM. The configuration and operation of the optical node shown in Fig. 12 are substantially the same as those of the optical node 1 shown in Fig. 3. Note that the control unit 18 is omitted in Fig. 12.

[0069] Fig. 13 shows another example of an optical transmission system according to an embodiment of the present invention. The optical transmission system shown in Fig. 13 includes optical nodes 1 (1a, 1b) realized by the ROADM shown in Fig. 2, as well as an optical node 3 realized by an ILA (In-Line Amplifier). Here, the optical node 3 operates as an optical repeater. That is, the optical node 3 amplifies the optical signal transmitted from the optical node 1a and transmits the amplified optical signal to the optical node 1b. Similarly, the optical node 3 amplifies the optical signal transmitted from the optical node 1b and transmits the amplified optical signal to the optical node 1a.

[0070] 14 shows an example of an optical node operating as an optical repeater station. The optical node 3 operating as an optical repeater station includes an optical amplifier circuit 32, an OTDR 33, an optical switch 34, an optical channel monitor 35, an optical switch 36, and a control unit 38. The OTDR 33, the optical switch 34, the optical channel monitor 35, and the optical switch 36 are substantially the same as the OTDR 13, the optical switch 14, the optical channel monitor 15, and the optical switch 16 shown in FIG. 3. Note that the optical node 3 does not include the ASE light source 17 shown in FIG. 3. Therefore, the optical node 3 cannot generate the pseudo-WDM signal shown in FIG. 9(b).

[0071] 14, the optical amplifier circuit 32 includes an optical amplifier such as an EDFA and a dynamic gain equalizer (DGE) 39. The DGE 39 can individually control the power of each wavelength channel according to instructions given from the control unit 38. In this embodiment, the optical node 3 outputs the pseudo WDM signal shown in FIG. Reception When this occurs, the DGE 39 controls the power of the vacant channel to substantially zero, i.e., the DGE 39 cuts off or blocks the vacant channel.

[0072] For example, as shown in Figure 13, when optical node 1a transmits a quasi-WDM signal to optical node 1b, this quasi-WDM signal is relayed by optical node 3. At this time, crosstalk occurs in optical fiber RX1 between optical node 1a and optical node 3. Therefore, optical channel monitor 35 of optical node 3 measures the power (i.e., crosstalk) of the idle channel of the quasi-WDM signal. Therefore, based on the magnitude of this crosstalk, it can be determined whether optical fiber RX1 is DSF or not.

[0073] Furthermore, in optical node 3, DGE 39 controls the power of the vacant channels of the quasi-WDM signal to zero. Then, optical node 3 transmits the quasi-WDM signal, in which the power of the vacant channels has been controlled to zero, to optical node 1b. That is, the signal transmitted from optical node 3 to optical node 1b is substantially the same as the quasi-WDM signal transmitted from optical node 1a to optical node 3. Therefore, optical node 1b can determine whether the optical fiber between optical node 3 and optical node 1b is DSF.

[0074] <Variation 1> In the optical transmission system 100B shown in FIG. 15, two types of optical fibers are laid in the span between the optical nodes 1a and 1b. That is, the optical fiber 2x for propagating an optical signal from the optical node 1a to the optical node 1b is composed of an optical fiber F1 and an optical fiber F2. The same is true for the optical fiber 2y for propagating an optical signal from the optical node 1b to the optical node 1a. In this case, simply measuring the propagation time using the OTDR 13 mounted on the optical node 1a or the optical node 1b only obtains the average propagation time of the two optical fibers, making it difficult to identify the type of optical fiber. Therefore, in variation 1, the type of optical fiber is identified using a forward OTDR and a backward OTDR.

[0075] For example, the OTDR 13 installed in the optical node 1a inputs an optical pulse into the optical fiber F1 and measures the propagation time using the light reflected from the discontinuity in the optical fiber. Similarly, the OTDR 13 installed in the optical node 1b inputs an optical pulse into the optical fiber F2 and measures the propagation time using the light reflected from the discontinuity in the optical fiber. Here, the connection point between the optical fibers F1 and F2 is a discontinuity in the optical fiber, which generates Fresnel reflection. Therefore, the optical node 1a can determine whether the optical fiber F1 is an SMF. Similarly, the optical node 1b can determine whether the optical fiber F2 is an SMF.

[0076] In the optical transmission system 100C shown in Figure 16, an optical fiber 2x is laid for transmitting an optical signal from optical node 1a to optical node 1b. The optical fiber 2x is composed of an optical fiber F1 and an optical fiber F2. In the example shown in Figure 16(a), a quasi-WDM signal is transmitted from optical node 1a to optical node 1b, and the optical channel monitor of optical node 1b detects crosstalk. In the example shown in Figure 16(b), a quasi-WDM signal is transmitted from optical node 1b to optical node 1a, and the optical channel monitor of optical node 1a detects crosstalk.

[0077] Here, when the optical fiber F1 and the optical fiber F2 are of the same type (or when the optical nodes 1a and 1b are connected by a single optical fiber), the crosstalk detected at the optical node 1a and the crosstalk detected at the optical node 1b are substantially the same. However, in the example shown in Figure 16, the crosstalk detected at the optical node 1a and the crosstalk detected at the optical node 1b are different from each other. In this case, it is considered that the optical fiber F1 and the optical fiber F2 are of different types from each other.

[0078] The magnitude of crosstalk that occurs in optical fibers due to four-wave mixing depends on the intensity of the propagating light. Specifically, crosstalk that occurs in areas with high optical power is dominant.

[0079] In the case shown in Figure 16(a), the quasi-WDM signal generated by optical node 1a is input to optical fiber F1, so the power of the quasi-WDM signal propagating through optical fiber F1 is higher than the power of the quasi-WDM signal propagating through optical fiber F2. In this case, the magnitude of crosstalk detected at optical node 1b depends on the type of optical fiber F1. In this embodiment, the crosstalk detected at optical node 1b is sufficiently large. Therefore, in this case, optical fiber F1 is determined to be DSF.

[0080] In the case shown in Figure 16(b), the quasi-WDM signal generated by optical node 1b is input to optical fiber F2, so the power of the quasi-WDM signal propagating through optical fiber F2 is higher than the power of the quasi-WDM signal propagating through optical fiber F1. In this case, the magnitude of crosstalk detected at optical node 1a depends on the type of optical fiber F2. In this embodiment, the crosstalk detected at optical node 1a is sufficiently small. Therefore, in this case, optical fiber F2 is determined to be not DSF.

[0081] As described above, whether each of the optical fibers F1 and F2 is an SMF or not is determined by the procedure shown in Fig. 15. Therefore, by combining the procedure shown in Fig. 15 and the procedure shown in Fig. 16, it is possible to determine whether each of the optical fibers F1 and F2 is an SMF, DSF, or NZ-DSF.

[0082] Fig. 17 shows an example of the configuration of the optical node 1 used in the optical transmission system 100C shown in Fig. 16. In this case, the optical node 1 includes not only an optical fiber (optical fiber TX in Fig. 17) that transmits an optical signal, but also an optical signal 17. Therefore, the optical node 1 is provided with optical switches 41 and 42.

[0083] When a pseudo WDM signal is input to the optical fiber TX, the optical switch 41 is controlled to guide the pseudo WDM signal generated by the WSS 11 to the optical fiber TX. When a pseudo WDM signal is input to the optical fiber RX, the optical switch 41 is controlled to guide the pseudo WDM signal generated by the WSS 11 to the optical switch 42, and the optical switch 42 is controlled to guide the pseudo WDM signal to the optical fiber RX. The optical switches 41 and 42 are controlled by the control unit 18.

[0084] <Variation 2> As described above, optical node 1 can determine the type of optical fiber connected to optical node 1. Then, the carrier sets each wavelength channel of the WDM signal according to the type of optical fiber to improve communication quality. In variation 2, optical node 1 performs this setting automatically.

[0085] 18 shows an example of a method for controlling the transmission power of a WDM signal according to the type of optical fiber. In this embodiment, optical node 1 transmits a WDM signal. Then, control unit 18 sets the average transmission power of multiple wavelength channels constituting the WDM signal and the amount of tilt compensation for the WDM signal according to the type of optical fiber connected to optical node 1. The amount of tilt compensation is set, for example, so that the spectrum of the WDM signal becomes flat at the receiving node.

[0086] The optical node 1 has a parameter table shown in Fig. 18(a). The parameter table stores the transmission power value of each wavelength channel for each type of optical fiber. In this case, a transmission power value may be prepared for each combination of optical fiber type and transmission distance. In addition, in cases where two types of optical fiber are mixed within one span, a transmission power value may be prepared for each combination of the two types of optical fiber.

[0087] For example, when the optical fiber connected to optical node 1 is an SMF, tilt is formed so that the power of long-wavelength channels is smaller than that of short-wavelength channels in each signal wavelength band (C-band, L-band), as shown in Figure 18(b). In the following description, the transmission power pattern set for an SMF may be referred to as the "standard pattern."

[0088] When the optical fiber connected to optical node 1 is DSF, the transmission power in the C band is set lower than the standard pattern, and the transmission power in the L band is set higher than the standard pattern, as shown in Figure 18(c).When the optical fiber connected to optical node 1 is NZ-DSF, the transmission power in the C band is set equal to the standard pattern, and the transmission power in the L band is set lower than the standard pattern, as shown in Figure 18(d).

[0089] The setting of the transmission power is realized by the WSS 11 and the amplifier circuit 12. That is, the control unit 18 sets parameters for the WSS 11 and the amplifier circuit 12, thereby controlling the transmission power. In this case, the control unit 18 sets parameters for the WSS 11 that control the power of each wavelength channel. This setting forms the tilt of the WDM signal. The control unit 18 also controls the gain of the amplifier circuit 12, thereby controlling the average power of the WDM signal.

[0090] <Variation 3> As described above, when determining the type of optical fiber using a pseudo WDM signal, a pair of optical nodes 1 installed at both ends of the optical fiber in question operate in cooperation with each other. At this time, the optical nodes 1 transmit control signals using an OSC (Optical Supervisory Channel).

[0091] 19 shows an example of a sequence of cooperative operations by a pair of optical nodes. In this example, the optical node 1a determines the type of optical fiber between the optical nodes 1a and 1b.

[0092] First, optical node 1a transmits a command to start crosstalk measurement to optical node 1b. This command is transmitted using an OSC. For example, as shown in FIG. 20, the OSC is set outside the signal band for transmitting the WDM signal. Upon receiving the command, optical node 1b prepares to receive the pseudo WDM signal. Thereafter, optical node 1b transmits a response signal to optical node 1a using the OSC.

[0093] Upon receiving the response signal, optical node 1a transmits a pseudo WDM signal to optical node 1b. As described above, the pseudo WDM signal is generated by the ASE light source 17 and WSS 11 based on instructions from the control unit 18. Optical node 1b uses the pseudo WDM signal to measure crosstalk due to four-wave mixing. Then, optical node 1b reports the crosstalk measurement results to optical node 1a using OSC.

[0094] The optical node 1a determines the type of optical fiber between the optical nodes 1a and 1b based on the crosstalk measurement results reported from the optical node 1b. The determination result is displayed, for example, on a computer of the telecommunications carrier. After this, the optical node 1a may set parameters of the transmitting optical circuit (WSS 11, amplifier circuit 12, etc.) of the optical node 1a according to the type of optical fiber.

[0095] 19, optical node 1b reports the crosstalk measurement results of optical node 1a, and optical node 1a determines the type of optical fiber based on the crosstalk measurement results, but the embodiment of the present invention is not limited to this sequence. For example, optical node 1b may measure crosstalk and then determine the type of optical fiber based on the measurement results. In this case, optical node 1b uses OSC to report the determination result regarding the type of optical fiber to optical node 1a.

[0096] FIG. 21 shows an example of an optical node including an OSC processing unit. The optical node 1 shown in FIG. 21 includes an OSC processing unit 51 in addition to the configuration shown in FIG. 3. The OSC processing unit 51 transmits an optical signal representing a control signal generated by the control unit 18. In the example shown in FIG. 19, the OSC processing unit 51 transmits an OSC optical signal representing a start instruction. In addition, the OSC processing unit 51 receives an OSC optical signal transmitted from another node, extracts the control signal from this OSC optical signal, and passes it to the control unit 18. In the example shown in FIG. 19, the OSC processing unit 51 receives a response and crosstalk measurement results from optical node 1b.

[0097] <Variation 4> 8 to 10, the crosstalk is measured using a pseudo WDM signal to determine whether the target optical fiber is a DSF. In contrast, in variation 4, the configuration of the pseudo WDM signal is changed to determine whether the target optical fiber is an SMF, DSF, or NZ-DSF.

[0098] FIG. 22 is a flowchart showing an example of a method for identifying SMF, DSF, and NZ-DSF using a pseudo-WDM signal. Note that steps S11 to S13 are substantially the same as steps S4 to S6 in the flowchart shown in FIG. 11. That is, the control unit 18 uses the ASE light source 17 and the WSS 11 to generate a pseudo-WDM signal having an empty channel near the zero-dispersion wavelength of the DSF. This pseudo-WDM signal is transmitted to an adjacent node via the target optical fiber. The adjacent node calculates crosstalk by measuring the power of the empty channel. Then, as described with reference to FIG. 9, if this crosstalk is greater than a predetermined threshold, the target optical fiber is determined to be DSF.

[0099] In S14, the control unit 18 generates a quasi-WDM signal having an empty channel near the zero-dispersion wavelength of the NZ-DSF using the ASE light source 17 and the WSS 11. In this example, as shown in Figure 23(a), the zero-dispersion wavelength of the NZ-DSF is approximately 1500 nm, and the wavelength of the empty channel is 1525 nm. This quasi-WDM signal is transmitted to an adjacent node via the target optical fiber.

[0100] In S15, the control unit 18 of the adjacent node calculates crosstalk due to four-wave mixing by measuring the power of the vacant channel using the optical channel monitor 15. In S16, the determination unit 18a of the optical node 1 or the adjacent node compares the crosstalk obtained in S15 with a predetermined threshold. This threshold is preferably set independently of the threshold used in S13. Then, as shown in FIG. 23(b), if the crosstalk obtained in S15 is greater than the threshold, the target optical fiber is determined to be an NZ-DSF. On the other hand, as shown in FIG. 23(c), if the crosstalk obtained in S15 is less than the threshold, the target optical fiber is determined to be an SMF. In this way, in variation 4, it is possible to identify whether the optical fiber installed between optical nodes is an SMF, DSF, or NZ-DSF without using an OTDR. [Explanation of symbols]

[0101] 1 (1a~1n) Optical Node (ROADM) 2 (2x, 2y) optical fibers 11 Wavelength Selective Switch (WSS) 12, 32 Optical amplifier circuit 13, 33 Optical time domain reflectometer (OTDR) 13b Light source circuit 13c Photodetector circuit 13d Signal processing section 14, 16, 34, 36 Optical switches 15, 35 Optical Channel Monitor (OCM) 17 ASE light source 18, 38 Control section 18a Judgment part 39 Dynamic Gain Equalizer (DGE) 41, 42 Optical switch 51 OSC processing section

Claims

1. An optical transmission system comprising a first optical node, a second optical node, and an optical fiber provided between the first optical node and the second optical node, The first optical node a signal generating unit that generates an optical signal having a plurality of wavelength channels and an empty channel; a transmitting optical circuit that outputs the optical signal to the optical fiber, the second optical node includes an optical channel monitor that measures the received power of each channel of the optical signal received via the optical fiber; The first optical node or the second optical node further includes a determination unit that determines the type of the optical fiber based on the reception power of the free channel measured by the optical channel monitor. An optical transmission system comprising:

2. the idle channel is located at or near the zero-dispersion wavelength of the dispersion-shifted single-mode optical fiber, The determining unit determines whether the optical fiber is a dispersion-shifted single-mode optical fiber based on the received power of the free channel.

2. The optical transmission system according to claim 1.

3. the empty channel is located at or near the zero-dispersion wavelength of the non-zero dispersion-shifted single-mode optical fiber; The determining unit determines whether the optical fiber is a non-zero dispersion shifted single mode optical fiber based on the received power of the empty channel.

2. The optical transmission system according to claim 1.

4. The determination unit calculating crosstalk at wavelengths at which the unused channels are arranged, the crosstalk occurring in the optical fiber due to the plurality of wavelength channels based on a ratio between the reception power of the plurality of wavelength channels and the reception power of the unused channels; The type of the optical fiber is determined based on the magnitude of the crosstalk.

2. The optical transmission system according to claim 1.

5. The signal generation unit an ASE light source that generates ASE light; a wavelength selective switch that generates the optical signal from the ASE light; 2. The optical transmission system according to claim 1.

6. the determining unit is provided in the first optical node, the second optical node reports a measurement result by the optical channel monitor to the first optical node; The determining unit determines the type of the optical fiber based on the measurement result reported from the second optical node.

2. The optical transmission system according to claim 1.

7. the first optical node further includes an optical measuring instrument that inputs a first optical pulse having a first wavelength and a second optical pulse having a second wavelength into the optical fiber and detects reflected light of the first optical pulse and the second optical pulse from a discontinuity point in the optical fiber; The determination unit determines whether the optical fiber is a single-mode optical fiber based on a difference between a first propagation time representing a period from when the first optical pulse is transmitted until reflected light from the discontinuity point for the first optical pulse is detected, and a second propagation time representing a period from when the second optical pulse is transmitted until reflected light from the discontinuity point for the second optical pulse is detected.

2. The optical transmission system according to claim 1.

8. an optical repeater is provided between the first optical node and the second optical node; The optical repeater blocks the idle channel when repeating the optical signal transmitted from the first optical node to the second optical node.

2. The optical transmission system according to claim 1.

9. The second optical node a second signal generating unit that generates a second optical signal having a plurality of wavelength channels and an empty channel; a second optical transmission circuit that outputs the second optical signal to the optical fiber; the first optical node includes a second optical channel monitor that measures the received power of each channel of the second optical signal received via the optical fiber; The determining unit determines the type of the optical fiber based on the reception power of an empty channel of the optical signal measured by the optical channel monitor and the reception power of an empty channel of the second optical signal measured by the second optical channel monitor.

2. The optical transmission system according to claim 1.

10. When the reception power of the empty channel of the optical signal measured by the optical channel monitor is different from the reception power of the empty channel of the second optical signal measured by the second optical channel monitor, the determination unit: determining that the optical fiber is composed of a first optical fiber and a second optical fiber of a different type than the first optical fiber; determining the type of the first optical fiber and the type of the second optical fiber based on the reception power of the empty channel of the optical signal measured by the optical channel monitor and the reception power of the empty channel of the second optical signal measured by the second optical channel monitor; 10. The optical transmission system according to claim 9.

11. The first optical node further includes a control unit that controls transmission power of each wavelength channel of a wavelength division multiplexed signal to be transmitted to the second optical node in accordance with the type of the optical fiber determined by the determination unit.

2. The optical transmission system according to claim 1.

12. 1. A fiber type determination method for determining a type of optical fiber provided between a first optical node and a second optical node, comprising: transmitting an optical signal having a plurality of wavelength channels and an empty channel from the first optical node to the second optical node over the optical fiber; measuring, at the second optical node, the reception power of each channel of the optical signal received via the optical fiber; The type of the optical fiber is determined based on the received power of the free channel measured at the second optical node. A fiber type determination method comprising:

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