WO2013143420A1

WO2013143420A1 - Method and device for wavelength label transmission

Info

Publication number: WO2013143420A1
Application number: PCT/CN2013/073092
Authority: WO
Inventors: 华锋; 尚迎春; 陈勋; 刘征; 沈百林
Original assignee: 中兴通讯股份有限公司
Priority date: 2012-03-30
Filing date: 2013-03-22
Publication date: 2013-10-03
Also published as: CN102624479B; CN102624479A

Abstract

The present invention discloses a method and device for wavelength label transmission. The method comprises: packaging wavelength label information as a wavelength label information frame and encoding the wavelength label information frame; determining the low-frequency dither modulation frequency of the wavelength label according to the wavelength channel of the wavelength label information frame, modulating the encoded wavelength label information frame to the low-frequency dither modulation frequency, and sending the encoded wavelength label information frame through the wavelength channel; splitting a received optical signal, and performing the photovoltaic conversion and analog-to-digital conversion on one path of the optical signal; performing spectrum analysis on the converted optical signal , and obtaining the frequency value of the low-frequency dither frequency of the optical signal and the bit information carried by the optical signal; decoding the bit information, obtaining the wavelength label information frame, and thereby obtaining the wavelength label information. According to the present invention, fewer low-frequency dither frequencies are utilized to realize the modulation for a wavelength label signal, information, such as a wavelength signal source address, is sent by data frames carried by the wavelength label, and a check bit is used for timely detecting the situation of transmission errors of the wavelength label.

Description

Wavelength tag transmission method and device

The present invention relates to wavelength label technology, and in particular to a wavelength label transmission method and apparatus. Background technique

The wavelength labeling technique is used to implement the wavelength trace function of a pure optical layer in a wavelength division multiplexing network, especially a wavelength reconfigurable optical add/drop multiplexing system, which can distinguish and identify wavelengths from different addresses in the system. The wavelength labeling technology implements a wavelength label signal for each wavelength signal at the source end of the wavelength path of the wavelength division multiplexing optical switching system, and detects and identifies the label of each wavelength passing through the point at each point of the wavelength path. Wavelength path monitoring and automatic discovery.

The wavelength label can be implemented by adding a topping signal to the wavelength signal. This method can bind the wavelength label to the corresponding wavelength signal and has less influence on the original signal quality. The topping technology involved in the wavelength labeling technology is as follows: In a wavelength division multiplexing system, a pilot tone signal is applied to each wavelength to implement a variety of special applications, which has been studied in the industry. The topping signal is sometimes called the low-frequency dither signal, and the effect of the wavelength signal loading and tuning signal on the transmission performance is almost negligible. For example, in 1993, the British BT laboratory, Sweden Ericsson and other units jointly published in the Journal of Lightwave Technology "A transport network layer based on optical network elements" (a transmission network layer based on optical network elements), proposed the use The grading signal implements acknowledgment and power management of the wavelength channel required for fault management in the wavelength division multiplexing system. There is also a publication of the patent application "Knowledge and apparatus for monitoring performance of optical transmission systems" (published by US Patent No. US005513029A, published on Apr. 30, 1996, the entire disclosure of which is hereby incorporated by Method and apparatus for monitoring), which proposes a method of monitoring the performance of an optical amplifier, that is, monitoring a topping signal of a known modulation depth to achieve light Estimation of the signal and noise components of the amplifier. In addition, in 1996, Fred Heismann et al. at Bell Labs in the United States published "signal tracking and performance monitoring in multi-wavelength optical networks" at the ECOC 96 conference. The paper number is WeB2. .2, discloses a WDM network to achieve online wavelength routing tracking, that is, each wavelength modulation of a unique topping signal, and digital signal encoding by frequency shift keying, in the optical network Any site monitors the tuning signal so that the wavelength routing information of the entire network can be known.

A method of identifying a wavelength channel, namely by two or more low frequencies, is described in US Patent Application Publication No. US20030067647 A1, issued on Apr. 10, 2003, the disclosure of which is incorporated herein in The topping frequency is used to identify a wavelength channel. Although the number of wavelength channels that the wavelength division multiplexing optical switching system can support is certain, the number of network elements included in the system should be determined according to the requirements of the application. For a wavelength division multiplexing optical switching network with multiple network elements, the method of the patent is used to identify the wavelength channel, and the required low frequency frequency resources increase as the number of system wavelengths increases, and also increases with the number of network elements. And increase, so the scalability of this wavelength identification system is not very good. In addition, due to the high frequency of the low frequency required by the patented method, the interval between the low frequency frequencies in the low frequency band is small, and the precision required for the spectrum analysis transformation at the receiving end is high, so that the calculation amount of the spectrum analysis is performed. Larger, the receiving end needs more time to perform spectrum analysis, and more hardware resources are required.

An optical identification and modulation and demodulation method and apparatus are disclosed in the patent application with the publication number CN101330485A, published on December 24, 2008, and the applicant is Huawei Technologies Co., Ltd., which describes the implementation of a wavelength label, ie Different frequencies are used for different wavelengths to distinguish; the same frequency of different nodes is distinguished by the same frequency and different interval time. According to the method of the patent, it is achieved that the unique identification of each wavelength of the entire network only needs to be equal to the number of frequencies of the network wavelength. However, the method still has the following drawbacks: The length of the wavelength label at the receiving end increases as the number of network elements of the system increases, and the number of network elements having the same wavelength is greater in the entire network. In the case of 64 network elements, at least 64 intervals are required to distinguish the same wavelengths from the 64 network elements, so the detection efficiency and detection time of the receiving end are not well controlled.

In addition, the prior art represented by the above patent has the following defects: in the case where there is noise in the actual system, the receiving end may be misjudged, and the wavelength of the wavelength label and/or its source address information is incorrect. The analysis, but the receiving end can not actively detect and correct the error in the case of receiving errors. In summary, the existing wavelength labeling technology cannot fully meet the requirements for reliable and scalable transmission of wavelength labels in large-scale WDM optical switching networks. Summary of the invention

In view of this, the main object of the present invention is to provide a wavelength label transmission method and apparatus, which can effectively support wavelength path monitoring and automatic discovery in a wavelength division multiplexing system, and can also timely detect the reception error of a wavelength label.

In order to achieve the above object, the technical solution of the present invention is achieved as follows:

A method for transmitting a wavelength label, comprising: encapsulating wavelength label information into a wavelength label information frame; determining a low frequency perturbation modulation frequency of the wavelength label according to a wavelength channel of the wavelength label information frame, and modulating the wavelength label information frame And to the low frequency perturbation modulation frequency, and transmitted through the wavelength channel.

Before modulating the wavelength label information frame onto the low frequency perturbation modulation frequency, the method further comprises: encoding the wavelength label information frame.

The encapsulating the wavelength label information into a wavelength label information frame is: encapsulating the frame into a frame by adding a frame header and a frame parity bit to the wavelength label information.

The encoding the wavelength label information frame is: encoding the remaining information except the frame header of the wavelength label information frame.

The method further includes: separately setting a low frequency perturbation modulation frequency for carrying the wavelength label information frame for each wavelength channel.

A wavelength tag transmission method, comprising: splitting a received optical signal, and One of the optical signals is subjected to photoelectric conversion and analog-to-digital conversion; spectral analysis is performed on the converted optical signal to obtain a frequency value of the low-frequency perturbation frequency in the optical signal and bit information carried therein; and the wavelength is obtained from the bit information A label information frame, and obtaining wavelength label information from the wavelength label information frame.

Obtaining a wavelength label information frame from the bit information, if: the sender encodes the wavelength label information frame, and then decodes the bit information to form a wavelength label information frame; If the wavelength label information frame is not encoded, the bit information is directly framing to obtain a wavelength label information frame.

Before performing photoelectric conversion on one of the optical signals, the method further includes: amplifying and sampling the one of the optical signals.

A wavelength tag transmission device includes a package unit, a frequency generation unit, a modulation unit, and a force port unit; wherein:

a packaging unit, configured to encapsulate the wavelength label information into a wavelength label information frame;

a frequency generating unit, configured to generate a low frequency perturbation modulation frequency corresponding to a wavelength channel of the wavelength label information frame;

a modulating unit configured to modulate the wavelength label information frame onto the low frequency perturbation modulation frequency;

And a loading unit, configured to load the modulated wavelength label information frame signal into the wavelength channel for transmission.

The device also includes:

a coding unit, configured to encode the wavelength label information frame;

The modulating unit is further configured to modulate the encoded wavelength label information frame onto the low frequency perturbation modulation frequency.

The encapsulating unit is further configured to add a frame header and a frame check bit to the wavelength label information to encapsulate the frame. The coding unit is further configured to encode the remaining information of the wavelength label information frame except the frame header.

A wavelength label transmission device includes a beam splitting unit, a processing unit, a spectrum analyzing unit, and a framing unit; wherein:

a light splitting unit configured to split the received optical signal;

The processing unit is configured to perform photoelectric conversion and analog-to-digital conversion on one of the optical signals; and the spectrum analyzing unit is configured to perform spectrum analysis on the converted optical signal to obtain a frequency value of the low frequency perturbation frequency in the optical signal and carry it Bit information;

The framing unit is configured to obtain the wavelength label information frame from the bit information group frame, and obtain the wavelength label information from the wavelength label information frame.

The apparatus further includes: a decoding unit configured to decode the bit information when the bit information is decoded.

The processing unit is further configured to amplify and sample the one of the optical signals before performing analog-to-digital conversion on the optical signals of one of the optical signals.

In the present invention, at the transmitting end, the wavelength label information is encapsulated into a wavelength label information frame, and the wavelength label information frame is encoded; the low frequency perturbation modulation frequency of the wavelength label is determined according to the wavelength channel of the wavelength label information frame, and the encoded The wavelength label information frame is modulated onto the low frequency perturbation modulation frequency and transmitted through the wavelength channel. At the receiving end, splitting the received optical signal, and performing photoelectric conversion and analog-to-digital conversion on one of the optical signals; performing spectrum analysis on the converted optical signal to obtain a frequency value of the low-frequency perturbation frequency in the optical signal and Bit information carried by the bit information; decoding the bit information to obtain a wavelength label information frame, thereby acquiring wavelength label information. The data frame carried on the wavelength label transmits information such as the wavelength signal source address, and the wavelength tag transmission error is detected in time by the check bit in the data frame. DRAWINGS

1 is a flowchart of a method for transmitting a wavelength label according to an embodiment of the present invention;

2 is a schematic structural diagram of a wavelength label transmission apparatus according to an embodiment of the present invention; and FIG. 3 is a schematic structural diagram of another wavelength label transmission apparatus according to an embodiment of the present invention. detailed description

The basic idea of the present invention is: encapsulating wavelength label information into a wavelength label information frame, encoding a wavelength label information frame; determining a low frequency perturbation modulation frequency of the wavelength label according to a wavelength channel of the wavelength label information frame, and encoding the encoded wavelength The tag information frame is modulated onto the low frequency perturbation modulation frequency and transmitted over the wavelength channel.

The present invention will be further described in detail below with reference to the accompanying drawings.

FIG. 1 is a flowchart of a method for transmitting a wavelength label according to an embodiment of the present invention. As shown in FIG. 1, the wavelength label transmission method of this example includes the following steps:

Step 101: Encapsulate a wavelength label information frame.

At the wavelength label transmitting end, the source address information of the wavelength label to be transmitted is filled in the frame data, and the upper frame header and the frame check bit are added to form a wavelength label information frame. The header is a special sequence that does not appear in subsequent encoded frame data, so the start of a wavelength label information frame can be identified by this special sequence. For example, if the frame data is encoded by 4B5B encoding, the frame header may take the illegal codeword in the 4B5B encoding, such as 11000 01101. The frame check in this example uses a simple Cyclic Redundancy Check (CRC), and other error detection/correction methods such as Forward Error Correction (FEC).

Step 102: Encode the wavelength label information frame.

For the above-mentioned wavelength label information frame, except for the byte outside the frame header, that is, the data part and the frame check bit, the encoding is performed according to the encoding rule, so that the phenomenon of long connection 0 and long connection 1 does not occur after the coding, which is convenient. Subsequent receivers process. In this example, the encoding method uses 4B5B encoding, and other methods, such as 8B10B, scrambling code, etc., may also be used.

Step 103: Determine a modulation frequency according to the wavelength channel.

Determining, according to the wavelength channel corresponding to the wavelength label information frame, a low frequency perturbation modulation frequency corresponding to the wavelength channel, the frequency may be generated by a digital frequency synthesizer, and modulating the encoded wavelength label information frame signal to the low frequency perturbation modulation In frequency, the modulation method can be selected from an amplitude modulation that is easier to implement, or other modulation methods, such as frequency modulation. Since the number of frequencies required in the present invention is at least the same as the number of wavelengths of the system, a larger frequency interval can be taken in the optional low frequency band 10 ΚΗζ ~ 1 ,, which requires lower frequency accuracy for the digital frequency synthesizer.

Step 104: Load a wavelength label information frame signal onto the optical channel.

Use a modulated low frequency perturbation signal to control a wavelength tag loading device such as a dimmable attenuator, with a suitable modulation depth (ranging from 3% to 8%, either empirically or by simulation) to low frequency perturbation The signal is loaded into the corresponding wavelength channel and transmitted.

The above steps are methods for transmitting wavelength labels, and the above methods are applicable to the transmitting ends of various optical communication systems.

In the present invention, the wavelength label transmission method described with reference to the flowchart shown in Fig. 1 is inexpensive, and the transmission method and reception method of the wavelength label are collectively described.

Hereinafter, a method of receiving a wavelength tag will be described.

Step 105: split, photoelectrically convert, amplify, and sample the received optical signal.

At the receiving end of the wavelength tag, the received optical signal is split by a coupler, a small part (such as 5%) of the optical signal is taken out, sent to the PIN receiver for photoelectric conversion, and then amplified and sampled and modulo Number conversion.

Step 106: Perform frequency analysis on the converted optical signal. The sampled signal is subjected to spectrum analysis by a chirp Z transform (CZT, Chirp Z Transform) transform or a Fast Fourier Transform (FFT) transform, and the frequency value of the low frequency perturbation frequency is obtained according to the result of the spectrum analysis. The bit information carried by the bit recovers the wavelength channel information corresponding to the low frequency perturbation frequency.

Step 107: Decode the parsed bit information.

Find the special bit sequence corresponding to the frame header in the bit information obtained after the spectrum analysis, here is 11000 01101, and then decode the frame data after the frame header according to the decoding rule; corresponding to the data encoded by the transmitting end using 4B5B, The decoding process is performed here with the corresponding 4B5B decoding rule. If a codeword is not in the code table of 4B5B, if the error code occurs, the frame data is discarded and a decoding error is reported. If there is no error in decoding, the decoded data is framing.

Step 108: Restore the wavelength label information frame.

The decoded information is framing and verified. Corresponding to the frame check byte generated by the CRC check by the sender, where the frame check is performed by the CRC check rule. If the intraframe data passes the CRC check, the frame of the wavelength source address byte in the frame is used. The internal payload is extracted as valid information. Otherwise, the CRC check error is reported and the error frame is discarded. If the sender uses FEC check, the receiver verifies with the FEC check rule. Since the FEC and CRC check methods are all prior art, the implementation details will not be described here.

1 is a schematic structural diagram of a wavelength label transmission apparatus according to an embodiment of the present invention. As shown in FIG. 1, the wavelength label transmission apparatus of this example includes a packaging unit 20, an encoding unit 21, a frequency generating unit 22, a modulation unit 23, and a loading unit. 24; where:

The encapsulating unit 20 is configured to encapsulate the wavelength label information into a wavelength label information frame. The encapsulating unit 20 adds a frame header and a risk information bit to the wavelength label information to be sent to form a wavelength label information frame, and the frame check in this example. Other error detection/correction methods, such as FEC, can also be used to implement a simple CRC. Wavelength tag information frame data except for completing wavelength tracking and wave In addition to the source address information of the wavelength signal necessary for long path discovery, the corresponding extended information may also be added to the frame data of the wavelength label information frame according to other applications.

The encoding unit 21 is configured to encode the wavelength label information frame;

The encoding unit 21 encodes the content of the frame other than the frame header of the wavelength label information frame. In this example, 4B5B encoding is used, and other encoding formats such as 8B10B, scrambling code, and the like may be used as needed. When 4B5B encoding is used, the frame header can be set to 11000 01101, which is an illegal codeword in 4B5B encoding, and thus does not appear in the encoded frame data.

In this example, the coding unit 21 is not a necessary technical feature of the implementation solution. In the case that the wavelength channel performance is better, the wavelength label information frame is directly modulated by the modulation unit 23 to the corresponding one without encoding the wavelength label information frame. Low frequency perturbation modulation frequency.

The frequency generating unit 22 is configured to generate a low frequency perturbation modulation frequency corresponding to the wavelength channel of the wavelength label information frame;

The frequency generating unit 22 first determines the corresponding low frequency perturbation frequency based on the wavelength information of the wavelength signal, and then controls the digital frequency synthesizer to generate the low frequency. Since the number of frequencies required in the present invention is at least the same as the number of wavelengths of the system, a larger frequency interval can be taken in the optional low frequency band 10 ΚΗζ 1 ΜΗζ, which requires lower frequency accuracy for the digital frequency synthesizer.

a modulating unit 23 configured to modulate the wavelength label information frame onto the low frequency perturbation modulation frequency;

The modulating unit 23 modulates the encoded or uncoded wavelength label information frame signal into the low frequency perturbation frequency by amplitude modulation, and the modulation method herein may also adopt other modulation methods such as frequency modulation.

The loading unit 24 is configured to load the modulated wavelength label information frame signal into the wavelength channel for transmission.

The loading unit 24 loads the modulated signal onto the wavelength channel signal with a suitable modulation depth, and controls the stability of the modulation depth. Specifically, the loading unit 24 can be modulated by Signal controlled tunable attenuators and other devices to achieve.

In the present invention, a low frequency perturbation modulation frequency carrying the wavelength label information frame needs to be separately set for each wavelength channel.

It should be understood by those skilled in the art that FIG. 2 is a wavelength label transmission apparatus mainly used for a transmitting end of an optical network according to an embodiment of the present invention.

It will be understood by those skilled in the art that the implementation functions of the various units in the wavelength label transmission apparatus shown in Fig. 2 can be understood by referring to the related description of the aforementioned wavelength label transmission method. It will be understood by those skilled in the art that the functions of the various processing units in the wavelength tag transmission device shown in Figure 2 can be implemented by a program running on the processor or by a specific logic circuit.

FIG. 3 is a schematic structural diagram of another wavelength label transmission apparatus according to an embodiment of the present invention. As shown in FIG. 3, the wavelength label transmission apparatus of this example includes a beam splitting unit 30, a processing unit 31, a spectrum analyzing unit 32, a decoding unit 33, and Framing unit 34; where:

The light splitting unit 30 is configured to split the received optical signal;

The beam splitting unit 30 is composed of a fiber coupler that takes out 5% of the optical power for wavelength tag detection and reception.

The processing unit 31 is configured to perform photoelectric conversion and analog-to-digital conversion on one of the optical signals (such as 5% of the entire optical signal);

The processing unit 31 includes a PIN tube, an amplifier, and an analog-to-digital converter (ADC) for realizing photoelectric conversion. One of the optical signals is taken out, sent to a PIN tube for photoelectric conversion, then amplified (amplified by an amplifier) and sampled and analog-to-digital converted (analog-to-digital conversion by an analog-to-digital converter).

The spectrum analyzing unit 32 is configured to perform spectrum analysis on the converted optical signal to obtain a frequency value of the low frequency perturbation frequency in the optical signal and bit information carried thereby;

The spectrum analysis unit 32 reads the output signal of the ADC in the processing unit 31, and performs spectral analysis using a chirped Z-transform (CZT) to obtain a low-frequency perturbation frequency existing in the signal. The frequency value and the frequency signal amplitude information, and recover the wavelength channel information corresponding to the low frequency perturbation frequency and the code stream information thereon.

The decoding unit 33 is arranged to decode the bit information when the bit information is decoded.

When decoding unit 33 decodes, it first looks for a frame header in the code stream signal. In this example, the frame header is 11000 01101, and then the frame data following the frame header is 4B5B decoded. At the time of decoding, if a certain codeword is not in the coding table of 4B5B, that is, when the error code occurs, the frame data is lost, and a decoding error is reported.

In this example, the decoding unit 33 is not a necessary technical feature for implementing the technical solution. In the case where the sender does not encode the wavelength label information frame, it is not necessary to decode the demodulated bit information.

The framing unit 34 is configured to obtain the wavelength label information frame from the bit information group frame, and obtain the wavelength label information from the wavelength label information frame.

When there is no error in decoding, the framing unit 34 framing the decoded data, composing the data decoded by 4B5B into one frame, and performing CRC check. If there is an error, a CRC check error is reported. If no error is found, the wavelength source address in the frame data is extracted for source address identification of the wavelength signal and other applications. Finally, other information such as wavelength information and address information contained in the wavelength label is recovered at the receiving end.

It should be understood by those skilled in the art that FIG. 3 is a wavelength label transmission apparatus mainly used for a receiving end of an optical network according to an embodiment of the present invention.

It will be understood by those skilled in the art that the implementation functions of the various units in the wavelength label transmission apparatus shown in Fig. 3 can be understood by referring to the related description of the aforementioned wavelength label transmission method. It will be understood by those skilled in the art that the functions of the various processing units in the wavelength label transmission device shown in Figure 3 can be implemented by a program running on the processor or by a specific logic circuit.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Range of protection.

Industrial applicability

The invention encapsulates the wavelength label information into a wavelength label information frame, determines a low frequency perturbation modulation frequency of the wavelength label according to the wavelength channel of the wavelength label information frame, and modulates the wavelength label information frame to the low frequency perturbation modulation frequency. Sending, in this way, the modulation of the wavelength label signal can be completed with less low frequency perturbation frequency, and the information such as the wavelength signal source address can be transmitted through the data frame carried on the wavelength label, and the wavelength can be found in time through the check bit in the data frame. The condition of the tag transmission error.

Claims

Claim

1. A method for transmitting a wavelength tag, comprising:

Encapsulating the wavelength label information into a wavelength label information frame;

Determining a low frequency perturbation modulation frequency of the wavelength label according to a wavelength channel of the wavelength label information frame, modulating the wavelength label information frame to the low frequency perturbation modulation frequency, and transmitting by using the wavelength channel.

2. The method according to claim 1, wherein before the modulating the wavelength label information frame to the low frequency perturbation modulation frequency, the method further comprises:

The wavelength label information frame is encoded.

The method according to claim 1 or 2, wherein the encapsulating the wavelength label information into a wavelength label information frame is:

A frame header and a frame syndrome are respectively added to the wavelength label information to be encapsulated into a frame.

4. The method according to claim 3, wherein the encoding the wavelength label information frame is:

The remaining information of the wavelength label information frame except the frame header is encoded.

The method according to claim 1 or 2, wherein the method further comprises: separately setting a low frequency perturbation modulation frequency for carrying the wavelength label information frame for each wavelength channel.

6. A wavelength label transmission method, comprising:

Performing splitting on the received optical signal, and performing photoelectric conversion and analog-to-digital conversion on one of the optical signals;

Performing spectrum analysis on the converted optical signal to obtain a frequency value of the low frequency perturbation frequency in the optical signal and bit information carried thereby;

Obtaining a wavelength label information frame from the bit information, and acquiring wavelength label information from the wavelength label information frame.

7. The method according to claim 6, wherein the wavelength tag information frame is obtained from the bit information, as follows:

If the sender encodes the wavelength label information frame, the frame information is framed into a wavelength label information frame by decoding the bit information; if the sender does not encode the wavelength label information frame, directly The bit information is framing to obtain a wavelength label information frame.

8. The method according to claim 6, wherein, before performing photoelectric conversion on the optical signal of one of the optical signals, the method further comprises:

One of the optical signals is amplified and sampled.

9. A wavelength tag transmission device comprising a packaging unit, a frequency generating unit, a modulating unit and a loading unit; wherein:

10. The device according to claim 9, wherein the device further comprises:

a coding unit, configured to encode the wavelength label information frame;

The device according to claim 9 or 10, wherein the encapsulating unit is further configured to add a frame header and a frame parity bit to the wavelength label information to encapsulate the frame.

12. The apparatus according to claim 11, wherein the encoding unit is further configured to encode the remaining information of the wavelength label information frame except the frame header.

13. A wavelength label transmission apparatus, comprising: a beam splitting unit, a processing unit, a spectrum analyzing unit, and a framing unit; wherein:

a light splitting unit configured to split the received optical signal;

14. The apparatus according to claim 13, wherein the apparatus further comprises: a decoding unit configured to decode the bit information when the bit information is decoded.

The device according to claim 13 or 14, wherein the processing unit is further configured to amplify and sample the one of the optical signals before performing analog-to-digital conversion on the optical signals of one of the optical signals.