Patent Application
20100129079
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-301979, filed on Nov. 27, 2008, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to an optical wavelength division multiplexer (WDM) transmission apparatus and optical WDM transmission method.
The preamplifier 801 further includes a detector (PD) 811 that is upstream from the amplifier 810 and detects the power of the optical signal input to the amplifier 810 and a detector (PD) 812 that is downstream from the amplifier 810 and detects the power of the optical signal amplified and output by the amplifier 810. The optical amplifier 805 further includes a detector (PD) 851 that is upstream from the post amplifier 850 and detects the power of the optical signal input to the post amplifier 850 and a detector (PD) 852 that is downstream from the post amplifier 850 and detects the power of the optical signal amplified and output by the post amplifier 850.
The optical power varying unit 803 further includes optical receivers (PD1) 831 that are downstream from the VOAs 830 and detect the power of the optical signals transmitted through the VOAs 830.
According to the configuration depicted in
When the power of the optical signals is adjusted, an external variable wavelength optical power source 880 is connected to the ports 860 and optical signals of each wavelength (ch1 to n) are input. A power meter 881 is connected to an output port 845 of the wavelength multiplexing unit 804 and the power of the optical signal passing through the optical power varying unit 803 and the wavelength multiplexing unit 804 is measured.
Control of the power adjustment executed by the monitoring control unit 870 includes:
1) The VOA control unit 874 fully opening (setting to the minimum attenuation level) all of the VOAs (ch1 to n) and measuring, per channel, the optical loss (Ltotal_w, where w is each channel) occurring in the paths from the ports 860 (optical input terminal) to the output port 845 (output terminal of the wavelength multiplexing unit 804). At this time, since measurement is simplified, the power of the optical signal input from the variable wavelength optical power source 880 is 0 dBm/ch.
2) The optical signal power (OP_w) detected by the optical receivers (PD1) 831 respectively provided for each channel being recorded and stored in the storage unit 872.
3) Setting a target power (Otgt_w) per channel to suppress optical power differences between channels in the multiplexed optical signal input to the post amplifier 805. The set values are recorded to the storage unit 872.
4) The calculating unit 873 calculating optical loss (Lmux_w) for each channel of the wavelength multiplexing unit 804. The calculation equation being Lmux_w=Ltotal_w−OP_w.
5) By adding optical loss to the target powers per channel, the calculating unit 873 calculating a range in which the optical receivers (PD1) 831 preferably detect the power of the optical signals. The calculation equation being Opd1_w=Otgt_w+Lmux_w.
6) Subsequently, the attenuation levels of the VOAs 830 being adjusted through the VOA control unit 874 so that the optical signal powers are detected by the optical receivers (PD1) 831 within the range Opd1. Thus, based on the power of each optical signal before multiplexing and preliminarily measured information of the control unit, the power of the optical signal at each wavelength is calculated and control is performed (see, for example, Japanese Laid-Open Patent Publication No. 2007-067759).
However, with the conventional technology above, optical signal power is not appropriately controlled when wideband noise (ASE) is included in the input optical signal.
According to the nature of wavelength multiplexing, the MUX 840 transmits the optical signal λ1 as depicted in (b) of
According to the control of the VOAs 830 based on power detection at such optical receivers (PD1) 831, the difference between target values set for the post amplifier 805 and the actual optical power output by the wavelength multiplexing unit 804 becomes significant. Thus, due to the size of ASE components of the input optical signal and bandwidth of the optical signal, optical signal power is not adjusted to a proper value, for each wavelength after multiplexing. Specifically, the total power of the multiplexed wavelengths is not adjusted to a target value and wavelength deviation in the power of the optical signals of each wavelength occurs inhibiting improvement in the quality of the optical signals.
According to an aspect of an embodiment, an optical WDM transmission apparatus includes plural optical attenuators that respectively attenuate the power of optical signals separated according to wavelength; plural first optical receivers that respectively detect the power of the attenuated optical signals; a multiplexer that multiplexes the optical signals; a second optical receiver that detects the power of the multiplexed optical signal; and a monitoring control unit that includes a first control system that controls the optical attenuators so that the powers detected at the first optical receivers respectively become target values, and a second control system that, based on the power detected by the second optical receiver and information concerning the number of wavelengths corresponding to the optical signals input, controls the optical attenuators so that the powers of the optical signals respectively become the target values.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
Preferred embodiments of the present invention will be explained with reference to the accompanying drawings. An optical WDM transmission apparatus according the present invention includes a control system that, based on the power of each optical signal separated according to wavelength, adjusts the power of each optical signal, and a control system that adjusts the power of each optical signal by detecting the optical signal power after multiplexing and performing a given calculation. The optical power of a multiplexed optical signal id detected using an optical receiver provided in a wavelength mulitplexing unit. Thus, the power of each optical signal separated according to wavelength is adjusted by VOAs to adjust the post-multiplexing optical power.
A first embodiment assumes a configuration that receives input of optical signals separated according to wavelength.
An optical power varying unit 103 includes an optical attenuator (VOA) 130 for each wavelength and adjusts (attenuates) the power of the optical signals of each wavelength. Optical receivers (PD1) 131 downstream from the VOAs 130 detect the power of the optical signals after attenuation. A wavelength multiplexing unit 104 includes a MUX 140 and multiplexes the optical signals output from the optical power varying unit 103. An optical receiver (PD2) 143 detects the total power of the multiplexed signal.
Thus, the attenuation level of each of the VOAs 130 is controlled by the detection by the optical receivers (PD1) 131 respectively provided immediately downstream from the VOAs 130 and for each wavelength. Additionally, the detection value of the optical receiver (PD2) 143 provided downstream from the MUX 140 is used. Specifically, the power of the optical signal at each wavelength is obtained. Consequently, loss at the MUX 140 and the ASE of each wavelength is considered and the attenuation level of each of the VOAs 130 is appropriately controlled.
A monitoring control unit 170 acquires the detection values of the optical receivers (PD1) 131 that detect the power of the optical signals at each wavelength of the optical power varying unit 103, and the detection value of the optical receiver (PD2) 143 that detects the power of the multiplexed optical signal. The monitoring control unit 170 includes a monitoring unit 171; a storage unit 172 storing therein power control parameters; a calculating unit 173 that, based on the parameters stored in the storage unit 172 and a monitoring value of the monitoring unit 171, calculates a control value for optical signal power; and a VOA control unit 174 that, based on the calculated control value, variably controls the attenuation level of the VOAs 130. An external terminal 182 outputs a per-channel, target input power value for a post amplifier; the storage unit 172 stores target input power value as a parameter.
When the power of the optical signal is adjusted, an external variable wavelength optical power source 180 is connected to the ports 160 and optical signals of each wavelength (ch1 to n) are input. The optical signals are separated according to wavelength, i.e., the power of each of the optical signals before multiplexing is detected by the optical receivers (PD1) 131 and the power of the multiplexed signal is detected by the optical receiver (PD2) 143.
Control of the optical signal power according to the configuration above is roughly separated into pre-operation preparation and control during operation, and is executed by the monitoring control unit 170.
The optical receivers (PD1, PD2) 131, 143 respectively detect the power of the light received. The optical receiver (PD2) 143 detects an optical power Opd2_w (step S203). The optical receivers (PD1) 131 detect an optical power Opd1_w (step S204). w is a given wavelength. The optical power Opd1_w and Opd2_w are stored in the storage unit 172.
The calculating unit 173, based on the difference between the optical power Opd1_w and the optical power Opd2_w, calculates, for each wavelength, optical loss (Lomux_w) occurring in the wavelength multiplexing unit 104 (step S205). Here, optical loss occurring in paths from the ports 160 to the optical receiver (PD2) 143 is calculated, for each wavelength, using the difference of the input power and the optical power Opd2_w; optical loss occurring in paths from the ports 160 to the optical receivers (PD1) 131 is calculated, for each wavelength, using the difference of the input power and the optical power Opd1_w; and based on the differences between the above calculation results, optical loss Lomux_w at the MUX 140 is obtained for each wavelength.
The calculating unit 173 calculates loss VOALoss at the VOAs 130 (step S206). The calculation is performed using the difference of the power of the optical signal input to one of the ports 160 and the optical power Opd1_w detected by the optical receivers (PD1) 131; i.e., 1 mW-Opd1_w. The value obtained indicates the minimum loss (min) at the corresponding VOA 130. The loss at the VOA VOALoss (min) is stored in the storage unit 172.
The target input power Otgt for the post amplifier provided downstream from the wavelength multiplexing unit 104 is set (step S207). The target input power Otgt is stored in the storage unit 172.
The optical receivers (PD1) 131 detect the optical power for each wavelength input (step S502). The calculating unit 172 reads the loss VOALoss at the VOAs 130 from the storage unit 172 (step S503-1), and calculates the input optical power Opin_w for each wavelength (step S503-2). Here, processing is executed with respect to each wavelength in ascending order of wavelength.
input optical power for each wavelength Opin—w=Opd1+VOALoss(min)+VOAλ
Where, VOAλ is the VOA attenuation level.
The calculating unit 173 reads the target input power Otgt from the storage unit 172 (step S504-1), and calculates a VOA control target value VOAtgt_w for each wavelength (step S504-2).
VOA control target value for a given wavelength VOAtgt—w=Opin—w−(Otgt+(Opd1—w−Opd2—w))
The VOA control unit 174 executes VOA control for adjusting the attenuation level of the VOAs 130 (step S505). Here, it is determined whether the difference of the optical power Opd1_w detected for a wavelength by an optical receiver (PD1) 131 and the target input power Otgt_w is below a predetermined allowable margin of error (step S506).
power Opd1—w−Otgt>allowable margin of error
If the result of the comparison at step S506 exceeds the allowable margin of error (step S506: NO), processing returns to step S502 and VOA control is executed again. If the result is within the allowable margin of error (step S506: YES), the following processing is executed.
The optical output power Opd2 after multiplexing is detected by the optical receiver (PD2) 143 of the wavelength multiplexing unit 104 (step S507). An average power per wavelength Opd2w_ave is calculated (step S508). The optical receiver (PD2) 143 is disposed downstream from the MUX 140 and hence, the power for only one wavelength cannot be detected, i.e., the total power for all of the wavelengths in the multiplexed optical signal is detected by the optical receiver (PD2) 143. Thus, by dividing the total power detected Opd2 by the number of wavelengths n, an average power per wavelength is obtained.
average power per wavelength Opd2w—ave=Opd2/n(mw)
Next, it is determined whether the difference of the average power per wavelength Opd2w_ave and the target input power Otgt of the post amplifier 150 is below a predetermined allowable margin of error (step S509).
average power per wavelength Opd2w—ave−target input power Otgt>allowable margin of error
If the result of the comparison at step S509 indicates the difference to be within the allowable margin of error (step S506: YES), a series of the processing ends. On the other hand, if the result indicates the difference to exceed the allowable margin of error (step S506: NO), processing proceeds to step S510, and reset processing is executed.
At step S510, the wavelength (ch) to be subject to reset processing is confirmed (step S510). The larger of the average power per wavelength Opd2w_ave and the target input power Otgt of the post amplifier 150 is determined (step S511). Reset processing for the wavelength (ch) is executed in ascending order of wavelength.
the average power per wavelength Opd2w—ave−the target input power Otgt
If the result of the comparison at step S511 indicates the average power per wavelength Opd2w_ave to be less than the target input power Otgt (step S511: <0), the VOA control unit 174 reduces the attenuation level of the VOA 130 (step S512); if the average power per wavelength Opd2w_ave is greater than the target input power Otgt (step S511: >0), the VOA control unit 174 increases the attenuation level of the VOA 130 (step S513). After steps S512 and S513, the number of the wavelength (ch) to be reset is updated by adding 1 (step S514), flow returns to step S507 and processing from step S507 is executed. Thus, the processing at step S509, i.e., control whereby the difference of the average power per wavelength Opd2w_ave and the target input power Otgt is within the predetermined allowable margin of error, is executed.
According to the control processing above, irrespective of optical signal bandwidth, or more specifically regardless of whether ASE is included, a wavelength multiplexed optical signal may be controlled to a desirable value for each wavelength included, wavelength deviation is eliminated, and the optical signal power for each wavelength may be made uniform and output. Further, with the configuration above, detection at the optical receiver (PD2) 143 after wavelength multiplexing and calculation of optical power per wavelength by the monitoring control unit 170 is used in VOA attenuation control; therefore, connection of an optical spectrum analyzer, optical channel monitor, optical power meter, etc. to the ports 160 is unnecessary.
A second embodiment assumes a configuration that multiplexes optical signals demultiplexed by a DMUX and newly inserted (ADD) optical signals.
As depicted in
The external terminal 182 outputs the number of input wavelengths, information concerning the optical signals (“a”) being transmitted in the apparatus, and information concerning the optical signals added (“b”) to the apparatus. The monitoring control unit 170, based on the above information, determines the input state of the optical signals. Processing for pre-operation preparation is identical to that of the first embodiment depicted in
Thus, when the determination at step S509 indicates that the allowable margin of error is exceeded, because the ASE power has been removed by a filter property of the DMUX 120 from the optical signals in the paths “a” (THROUGH), the cause of the allowable margin of error being exceeded is determined to be optical signal inserted (path “b”) from the ports 160. The reset processing from step S510 may be attenuation control of the VOAs 130 performed with respect to the inserted optical signals and in ascending order of wavelength.
According to the processing above, irrespective of optical signal bandwidth, whether optical signals are transmitted through the apparatus or optical signals are inserted, a wavelength multiplexed optical signal may be controlled to a desirable value for each wavelength included, wavelength deviation is eliminated, and the optical signal power at each wavelength may be made uniform and output. The optical WDM transmission apparatus 100 is not limited to transmitting input optical signals, and may output (DROP) optical signals from the ports 160, receive new optical signals (ADD) through the ports 160, etc. Further, transmission paths in the network may vary from short distances to long distances. Although power associated with ASE components varies according to such factors, the above configuration enables the optical signal power for each wavelength to be made uniform and output.
As described, according to the embodiments, optical signal power may be appropriately adjusted for each wavelength and consequently, wavelength deviation of the wavelengths in a multiplexed optical signal is eliminated and signal quality is improved. Additionally, long distance transmission is enabled. The embodiments disclosed are applicable to optical WDM transmission apparatuses having at least VOAs and an MUX, and improve adjustment precision with respect to the optical power of the multiplexed optical signal output.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-301979 | Nov 2008 | JP | national |
