Abstract:
A label remover, and the method using the same, renders photoelectric conversion becomes unnecessary and improves using conditions and transmission quality. The label remover includes: (a) an oscillator for outputting a driving signal having a third frequency f 3;  (b) a double-sided band converter for (i) receiving an optical signal modulated based on a data signal of an intermediate frequency fm and frequency-modulated based on a label signal so as to indicate a first frequency f 1  and a second frequency f 2;  and (ii) frequency-transiting the received optical signal so that each of the first and second frequencies is transited to at least two frequencies including the intermediate frequency fm; and (c) a band passer filter for filtering the frequency-transited optical signal to remove frequencies except the intermediate frequency fm.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Label Remover and Label Swapper Using the Same”, filed in the Korean Intellectual Property Office on Jan. 28, 2005 and assigned Ser. No. 2005-8179, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an optical network system using labels, and more particularly, to a method of performing label swapping or label switching of an optical signal transmitted through the optical network system.  
         [0004]     2. Description of the Related Art  
         [0005]     Technology using labels in an optical network system having a plurality of nodes is known. Each intermediate node in the optical network system must simultaneously perform the process of reading a label for each input packet and replacing it with a new label, a label swapping process. One of known multi-protocol label switching (MPLS) techniques performs the on-off keying (OOK) modulation of an optical signal based on payload data and frequency shift keying (FSK) modulation of the OOK-modulated optical signal based on label data for routing the optical signal at a lower frequency. In this case, each intermediate node must perform complex processes of converting an input optical signal to an electrical signal, swapping labels, and converting the label-swapped electrical signal to an optical signal again.  
         [0006]     To solve this problem, technology of installing an all-optical label swapper to each intermediate node is used. The all-optical label swapper removes a label from an optical signal using a cross phase modulation (XPM) effect and cross gain modulation (XGM) effect of a semiconductor optical amplifier (SOA), then performs the FSK modulation of the label-removed optical signal using a four wave mixing (FWM) effect of the SOA.  
         [0007]     However, the all-optical label swapper uses non-linear effects, such as the FWM, XPM and XGM, and the efficiency of such effects is poor. Accordingly, transmission quality is deteriorates. In addition, since an extinction ratio, intensity, and a wavelength of an input signal related to non-linear effects of the SOA are limited, the conditions for using the all-optical label swapper are complicated.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a label removing method in which photoelectric conversion is unnecessary and improves working conditions and transmission quality, and a label swapping method using the same.  
         [0009]     One aspect of the present invention provides a label removing method comprising the steps of: (a) receiving an optical signal modulated based on a data signal of an intermediate frequency fm and frequency-modulated based on a label signal so as to indicate a first frequency f 1  and a second frequency f 2 ; (b) frequency-transiting the received optical signal so that each of the first and second frequencies is transited to at least two frequencies including the intermediate frequency fm; and (c) filtering the frequency-transited optical signal to remove frequencies except the intermediate frequency fm.  
         [0010]     Another aspect of the present invention provides a label swapping method comprising the steps of: (a) receiving an optical signal modulated based on a data signal of an intermediate frequency and frequency-modulated based on a label signal so as to indicate a first frequency f 1  and a second frequency f 2 ; (b) frequency-transiting the received optical signal so that each of the first and second frequencies is transited to at least two frequencies including the intermediate frequency; (c) filtering the frequency-transited optical signal to remove frequencies except the intermediate frequency; and (d) modulating the filtered optical signal based on the data signal of the intermediate frequency and frequency-modulating the modulated optical signal based on the label signal so as to indicate the first frequency f 1  or the second frequency f 2 . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The features of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings in which:  
         [0012]      FIG. 1  is a block diagram of an optical network system using labels according to an embodiment of the present invention;  
         [0013]      FIG. 2  is a block diagram of a label swapper shown in  FIG. 1 ;  
         [0014]      FIGS. 3A  to  3 C are diagrams illustrating signals processed by a starting node shown in  FIG. 1 ; and  
         [0015]      FIGS. 4A  to  4 E are diagrams illustrating signals processed by a label remover shown in  FIG. 2 .  
     
    
     DETAILED DESCRIPTION  
       [0016]     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. For the purposes of clarity and simplicity, well-known functions or constructions are not described in detail as they would obscure the invention in unnecessary detail.  
         [0017]      FIG. 1  is a block diagram of an optical network system  100  using labels according to an embodiment of the present invention.  FIG. 2  is a block diagram of a label swapper  220  shown in  FIG. 1 . The optical network system  100  includes a starting node (NODE-S)  110 , at least one intermediate node (NODE-I)  210  and an end node (NODE-E)  330 . The NODE-S  110 , NODE-I  210  and NODE-E  330  are connected to each other through optical fibers  200  and  205 .  
         [0018]     The NODE-S  110  includes an optical transmitter (TX)  120  and a label modulator (LABEL MOD)  130 .  
         [0019]     The TX  120 , which outputs an OOK-modulated optical signal S 1  based on payload data of an intermediate frequency fm, may include a typical laser diode. That is, the OOK-modulated optical signal S 1  represents every “1” bit of the payload data as a power of an “A” level and every “0” bit of the payload data as a power of a “B” level. This OOK modulation scheme is one of intensity modulation schemes. The optical signal output from the TX  120  can be arbitrary-non-frequency-modulated signal based on the payload data, and this non-frequency modulation scheme includes the intensity modulation schemes and polarization modulation schemes. The intermediate frequency fm corresponds to a mean frequency (f 1 +f 2 )/2 of separated first and second frequencies f 1  and f 2 .  
         [0020]     The LABEL MOD  130 , which performs FSK modulation of the OOK-modulated optical signal S 1  based on label data, includes first and second optical couplers (OCs)  140  and  170 , an oscillator (OSC)  180 , a 90° hybrid coupler  190  and first and second intensity modulators (IMs)  150  and  160 .  
         [0021]     The first OC  140  includes a root waveguide  142  and coupled to first and second branch waveguides  144  and  146  that branch off in two directions from the root waveguide  142  and first to third ports. The first port is connected to the TX  120 , the second port is connected to the first IM  150 , and the third port is connected to the second IM  160 . The first OC  140  power-splits the OOK-modulated optical signal S 1  input through the first port (generates first and second split optical signals S 2 A and S 2 B) and outputs the power-split first and second split optical signals S 2 A and S 2 B to the second and third ports, respectively. The first OC  140  may be a typical Y-branch waveguide.  
         [0022]     The OSC  180  outputs a sinusoidal wave electrical signal having a predetermined frequency and controls a frequency difference between the first and second frequencies f 1  and f 2 , which are output frequencies of the LABEL MOD  130 , by controlling the predetermined frequency.  
         [0023]     The 90° hybrid coupler  190  generates first and second driving signals S 3 A and S 3 B having a 90° phase difference from the electrical signal input from the OSC  180 .  
         [0024]     The first IM  150  includes first and second arms  152  and  154  that at coupled to each other at both ends and an electrode  156  for supplying the first driving signal S 3 A. First end of the first IM  150  is coupled to the second port of the first OC  140  and second end is coupled to a second port of the second OC  170 . The first IM  150  inputs the first split optical signal S 2 A from the first OC  140  and outputs a first intensity-modulated optical signal S 4 A generated by intensity-modulating the first split optical signal S 2 A based on the input first driving signal S 3 A. Each of the first and second IMs  150  and  160  may be a LiNbO 3  MachZehnder modulator.  
         [0025]     The second IM  160  includes first and second arms  162  and  164  that are coupled to each other at both ends and an electrode  166  for supplying the second driving signal S 3 B. First end of the second IM  160  is coupled to the third port of the first OC  140  and a second end is coupled to a third port of the second OC  170 . The second IM  160  inputs the second split optical signal S 2 B from the first OC  140  and outputs a second intensity-modulated optical signal S 4 B generated by intensity-modulating the second split optical signal S 2 B based on the input second driving signal S 3 B.  
         [0026]     The second OC  170  includes a root waveguide  172  that are coupled to first and second branch waveguides  174  and  176  that branch off in two directions from the root waveguide  172 , an electrode  178 , and a first to third ports. The electrode  178  is deployed between the first and second branch waveguides  174  and  176  and provides label data. The first port is coupled to the optical fiber  200 , the second port is coupled to the first IM  150 , and the third port is coupled to the second IM  160 . The second OC  170  controls a phase difference between the first intensity-modulated optical signal S 4 A passing through the first branch waveguide  174  and the second intensity-modulated optical signal S 4 B passing through the second branch waveguide  176  based on the label data. Thereafter, the second OC  170  outputs an FSK-modulated optical signal S 5  generated by coupling the two phase-controlled optical signals. The label data has a lower frequency than the intermediate frequency fm of the payload data. The FSK-modulated optical signal S 5  represents every “1” bit of the label data as the first frequency f 1  and every “0” bit of the label data as the second frequency f 2 . In addition, as described above, since the FSK-modulated optical signal S 5  is OOK-simulated, every “1” bit of the payload data is represented as the power of the “A” level and every “0” bit of the payload data is represented as the power of the “B” level.  
         [0027]      FIGS. 3A  to  3 C are diagrams illustrating signals processed by the starting node (NODE-S)  110  shown in  FIG. 1 .  FIG. 3A  illustrates the payload data input to the TX  120 , where the payload data is a bitstream composed of “0” bits and “1” bits. The payload data has the intermediate frequency fm.  FIG. 3B  illustrates the label data supplied to the second OC  170 , where the label data is a bitstream composed of “0” bits and “1” bits. The label data has the lower frequency than the intermediate frequency fm of the payload data.  FIG. 3C  illustrates a frequency spectrum of the FSK-modulated optical signal S 5  output from the LABEL MOD  130 . The FSK-modulated optical signal S 5  represents every “1” bit of the label data as the first frequency f 1  and every “0”bit of the label data as the second frequency f 2 .  
         [0028]     Returning to  FIG. 1 , the NODE-I  210  includes the label swapper  220 . As shown in  FIG. 2 , the label swapper  220  includes a label remover (LABEL REM)  230  and a label modulator (LABEL MOD)  260 .  
         [0029]     The LABEL REM  230  in  FIG. 2  removes the label data from the FSK-modulated optical signal S 5  by removing the first and second frequencies f 1  and f 2  included in the FSK-modulated optical signal S 5  and restoring the intermediate frequency fm. The LABEL REM  230  includes an oscillator (OSC)  255 , a double side band converter (DSB)  240  and a band pass filter (BPF)  250 .  
         [0030]     The OSC  255  outputs a sinusoidal third driving signal having a third frequency f 3 , which corresponds to a half of difference between the first and second frequencies (f 1 −f 2 )/2.  
         [0031]     The DSB  240  includes first and second arms  242  and  244  coupled to each other at both ends and an electrode  246  for supplying the third driving signal. A first end of the DSB  240  is also coupled to the optical fiber  200  and a second end is also coupled to the BPF  250 . The DSB  240  receives the FSK-modulated optical signal S 5  from the optical fiber  200  and receives double-side-band-converts the FSK-modulated optical signal S 5  based on the third driving signal from the OSC  255 . Accordingly, the first frequency f 1  is transited to a frequency (f 1 −f 3 ) and a frequency (f 1 +f 3 ), and the second frequency f 2  is transited to a frequency (f 2 −f 3 ) and a frequency (f 2 +f 3 ). Herein, the frequency (f 1 +f 3 ), the frequency (f 2 −f 3 ) and the intermediate frequency fm are identical. That is, the DSB  240  double-side-band-converts the FSK-modulated optical signal S 5  having two frequencies to an optical signal S 6  having three frequencies. The DSB  240  may be the LiNbO 3  Mach-Zehnder modulator.  
         [0032]     The BPF  250  frequency-filters the input double-side-band-converted optical signal S 6 , where the filtering frequency is set equally to the intermediate frequency fm. That is, the BPF  250  removes the frequencies (f 1 −f 3 ) and (f 2 +f 3 ) except the intermediate frequency fm by filtering the double-side-band-converted optical signal S 6 .  
         [0033]      FIGS. 4A  to  4 E are diagrams illustrating signals processed by the label remover (LABEL REM)  230  shown in  FIG. 2 .  FIG. 4A  illustrates a frequency spectrum of the FSK-modulated optical signal S 5  input to the DSB  240 . As shown in  FIG. 4A , the FSK-modulated optical signal S 5  has the first and second frequencies f 1  and f 2 .  FIG. 4B  illustrates a frequency spectrum of the double-side-band-converted optical signal S 6  output from the DSB  240 .  FIG. 4C  illustrates a state in which the first frequency f 1  is converted to the frequencies (f 1 −f 3 ) and (f 1 +f 3 ).  FIG. 4D  illustrates a state in which the second frequency f 2  is converted to the frequencies (f 2 −f 3 ) and (f 2 +f 3 ).  FIG. 4E  illustrates a frequency spectrum of a frequency-filtered (or existing-label-data-removed) optical signal S 7  output from the BPF  250 .  
         [0034]     Returning to  FIG. 2 , the LABEL MOD  260 , which FSK-modulates the frequency-filtered optical signal S 7  based on a new label data, includes first and second OC  270  and  300 , an OSC  310 , a 90° hybrid coupler  320 , and first and second IMs  280  and  290 . The LABEL MOD  260  has the equal configuration as the LABEL MOD  130  of the NODE-S  110 .  
         [0035]     The first OC  270 , which includes a root waveguide  272  coupled to first and second branch waveguides  274  and  276  that branch off in two directions from the root waveguide  272 , and first to third ports. The first port is coupled to the BPF  250 , the second port is coupled to the first IM  280 , and the third port is coupled to the second IM  290 . The first OC  270  power-splits the frequency-filtered optical signal S 7  input from the first port (generates first and second split optical signals S 8 A and S 8 B) and outputs the power-split first and second split optical signals S 8 A and S 8 B to the second and third ports, respectively.  
         [0036]     The OSC  310  outputs a sinusoidal electrical signal having a predetermined frequency and controls a frequency difference between the first and second frequencies f 1  and f 2  by controlling the predetermined frequency. The first and second frequencies f 1  and f 2  are output frequencies of the LABEL MOD  260 .  
         [0037]     The 90° hybrid coupler  320  generates first and second driving signals having a 90° phase difference from the electrical signal input from the OSC  310 .  
         [0038]     The first IM  280  includes first and second arms  282  and  284  coupled to each other at both ends and an electrode  286  for supplying the first driving signal. The first end of the first IM  280  is coupled to the second port of the first OC  270  and the second end is coupled to a second port of the second OC  300 . The first IM  280  inputs the first split optical signal S 8 A from the first OC  270  and outputs a first intensity-modulated optical signal S 9 A generated by intensity-modulating the first split optical signal S 8 A based on the input first driving signal. Each of the first and second IMs  280  and  290  may be a LiNbO 3  Mach-Zehnder modulator.  
         [0039]     The second IM  290  includes first and second arms  292  and  294  coupled to each other at both ends and an electrode  296  for supplying the second driving signal First end of the second IM  290  is connected to the third port of the first OC  270  and second end is connected to a third port of the second OC  300 . The second IM  290  inputs the second split optical signal S 8 B from the first OC  270  and outputs a second intensity-modulated optical signal S 9 B generated by intensity-modulating the second split optical signal S 8 B based on the input second driving signal.  
         [0040]     The second OC  300  includes a root waveguide  302  coupled to first and second branch waveguides  304  and  306  that branch off in two directions from the root waveguide  302 , an electrode  308 , and first to third ports. The electrode is deployed between the first and second branch waveguides  304  and  306   r  and provides label data. The first port is coupled to the optical fiber  205 , the second port is coupled to the first IM  280 , and the third port is coupled to the second IM  290 .  
         [0041]     The second OC  300  controls a phase difference between the first intensity-modulated optical signal S 9 A passing through the first branch waveguide  304  and the second intensity-modulated optical signal S 9 B passing through the second branch waveguide  306  based on the label data. Thereafter, the second OC  300  outputs an FSK-modulated optical signal S 10  generated by coupling the two phase-controlled optical signals. The label data has a lower frequency than the intermediate frequency fm of the payload data. The FSK-modulated optical signal S 10  represents every “1” bit of the label data as the first frequency f 1  and every “0” bit of the label data as the second frequency f 2 . In addition, since the FSK-modulated optical signal S 5  is OOK-simulated, every “1” bit of the payload data is represented as the power of the “A” level, and every “0” bit of the payload data is represented as the power of the “B” level.  
         [0042]     Returning to  FIG. 1 , the NODE-E  330  includes an OC  340 , a BPF  350  and first and second optical detectors  360  and  370 .  
         [0043]     The OC  340  has first to third ports, where the first port is coupled to the optical fiber  205 , the second port is coupled to the BPF  350 , and the third port is coupled to the second optical detector  370 . The OC  340  power-splits the FSK-modulated optical signal S 10  input from the first port (generates first and second split optical signals S 11 A and S 11 B) and outputs the power-split first and second split optical signals S 11 A and S 11 B to the second and third ports, respectively.  
         [0044]     The BPF  350 , which is connected to the second port of the OC  340 , converts a frequency component of the FSK-modulated first split optical signal S 11 A to an amplitude component. That is, a first frequency of the first split optical signal S 11 A is converted to a power of a “C” level, and a second frequency is represented as a power of a “D” level.  
         [0045]     The first optical detector  360  detects an amplitude-converted first split optical signal S 12  passed through the BPF  350  as an electrical signal and demodulates the label data from the electrical signal.  
         [0046]     The second optical detector  370 , which is connected to the third port of the OC  340 , detects the input second split optical signal S 11 B as an electrical signal and demodulates the payload data from the electrical signal.  
         [0047]     As described above, according to a label remover, a method using the label remover, a label swapper, and a method using the label swapper according to the embodiment of the present invention, photoelectric conversion becomes unnecessary. The present invention renders the conversion unnecessary by removing label data through a process of double-side-band-converting an input FSK-modulated optical signal. Since a non-linear effect of an SOA is not used, using conditions and transmission quality are improved compared to prior arts.  
         [0048]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.