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  • 1. Optical Dest label OLS IP IP Node node Source packet Burst node Dest node Ingress OLS Node Egress Techniques for Labeling of Optical Signals in Burst Switched Source edge router edge router Networks OLS node e OLS Nod Node Optical Source Core Network Dest I. Tafur Monroy (1), node A. M. J Koonen (1), J. Zhang (2), Nan Chi node P. v. Holm-Nielsen (2), C. (2), Peucheret (2), J. J. Vegas Olmos (1), G-D Khoe (1). 1: COBRA Institute, Eindhoven University of Technology P. O. Box 513, 5600 MB Eindhoven, The Netherlands, E-mail: i.tafur@tue.nl 2: Research Center COM, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark Keywords: Optical Burst Switching, Optical Networks, IP-over-WDM, GMPLS. ABSTRACT We present a review of significant issues related to labeled optical burst switched (LOBS) networks and technologies enabling future optical internet networks. Labeled optical burst switching provides a quick and efficient forwarding mechanism of IP packets/bursts over wavelength division multiplexed (WDM) networks due to its single forwarding algorithm, thus yielding low latency, and it enables scaling to terabit rates. Moreover, LOBS is compatible with the general multiprotocol label switching (GMPLS) framework for a unified control plane. We present a review on techniques for labeling of optical signals for LOBS networks, including experimental results, we discuss as well issues for further research. 1. INTRODUCTION In a LOBS network, bursts of data are composed by assembling several IP packets in the ingress LOBS nodes according to their destination or class of service. To each burst a label, of a short, fixed length, is assigned and used by the core nodes to forward the packet through the network . In this way packet forwarding decisions are taken by examining only short optical labels, supported by GMPLS, yielding a low latency, low overhead routing technique that simplifies packet forwarding and enables scaling to terabit rates . This networking strategy is exemplified in Fig. 1. Figure 1: Network architecture of an optical labeled burst switched network. The present contribution focuses on techniques to implement optical labeling of IP bursts and the corresponding technologies for label swapping in the core nodes. Several techniques have been proposed to label optical packets or burst of packets. In this paper we report on five basic methods for labeling packets in a multi-wavelength network: time division multiplexing (TDM) labeling, optical code division multiplexing (OCDM) labeling, sub-carrier multiplexing (SCM) labeling, orthogonal labeling, and WDM labeling. In the
  • 2. first four methods, the label is attached to the payload in the same wavelength channel as the one carrying these payload data, whereas in the fifth method a separate wavelength channel is used to carry the label(s). We make special emphasis on the orthogonal angle/intensity modulation labeling method that is extensively being studied in the framework of the IST–STOLAS (Switching Technologies for Optical Labeled Signals) research project. In this technique, label information is either modulated in FSK (frequency shift keying) or DPSK (differential phase shift keying) format, while the payload is in intensity modulation format . We report on experimental results demonstrating the feasibility of combined FSK/IM modulation for the labeling/payload information. We show also an experimental assessment of the performance of a wavelength converter based on semiconductor optical amplifiers (SOA) in a Mach-Zehnder interferometer (MZI) configuration for optical label swapping operating at a payload data rate of 10 Gbit/s and an FSK label at 312 Mbit/s. Moreover, summary conclusions, design guidelines are presented regarding orthogonal modulation format for labeling of signals. Finally, issues for further research are discussed. 2. OPTICAL SIGNAL LABELING TECHNIQUES TDM LABELING: In TDM labeling (also called bit-serial labeling) the label information is attached in the time domain, by putting it in front of the payload and header. The payload/header and the attached label are encoded on the same wavelength carrier. Guard time bands are used to separate the label bits from the payload/label and synchronization bits are also used for time-alignment. The guard time may also serve to reduce the buffer time for the payload data, needed to allow completion of the processing of the label and preparing of the new label, before the new label can be attached to the payload. The Advantages of these techniques are related to the coupling of label and payload/header in the same wavelength channel, easing the bookkeeping in the routing node. The Disadvantages are related to the tight synchronization and delineation of payload/header and label that is required. Moreover, label/payload delineation for label erasure is needed; this requirement becomes even more complex as the data rates are increased. It may be noted, that the bit-rate of the label may be the same (synchronous TDM) or of a lower bit-rate (asynchronous TDM) than the payload; commonly a low bit-rate for the label is chosen to allow the use of low speed electronics for label processing and synchronization /delineation at the packet rate. Opto-electronic label swapping is commonly used. In the KEOPS project the following packet format was used: fixed time slot of 1.64 microseconds and a payload of 1.35 microseconds, and 14 bytes for header information . A payload rate of 10 Gbit/s and header rate of 622 Mbit/s was implemented in a lab trial. All-Optical label swapping: the TDM labels can be swapped by optical means. Two techniques have been reported: Wavelength conversion in a fiber loop mirror structure. By using a different pulse format for the header and payload, the header can be suppressed while wavelength conversion of the payload takes place. After removal of the header, a new level can be inserted by opto-electronics means or alternatively the new serial header can be pre-modulated onto the probe signal for the wavelength conversion. Experimental demonstration of label switching by the latter technique of 40 Gbit/s payload and 2.5 Gbit/s header has been reported. A two-hop routing experiments of packets at 80 Gbit/s and 10 Gbit/s has also been reported . Although the header erasure needs no timing information the label insertion does. Optical XOR operations in a SOA-MZI wavelength converter. An optical scheme has been proposed to perform label replacement in a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) wavelength converter by a logical XOR operation. However, tight synchronization at the bit level is required and buffering is required. Experiments of routing by time-serial addressing and XOR label swapping have been demonstrated at 20 Gbit/s payload and 10 Gbit/s label swapping . OCDM LABELING: Optical code division multiplexing (OCDM) has been proposed for labeling in optical networks . The label information is attached by scrambling the payload with a specific code carrying the label 2
  • 3. information. Although OCDM is one of the labeling techniques that allow label recognition for routing instead of look-up table operations, its implementation is still quite complex. For example, if a wavelength supports N OCDM codes, a bank of N optical autocorrelators per wavelength is needed for every channel and a replica of every channel should be provided to every autocorrelator of the bank. However, OCDM labeling offers possibilities to be combined with WDM (WDM sub-bands) and OTDM transmission techniques, and it has inherently a label recognition property. An experiment of WDM-to-OTDM and back of 4x10 Gbit/s OCDM coded channels has been published recently . The OCDM coders and decoders are optical transversal filters in planar lightwave circuit (PLC) technology to perform 8-chips BPSK coding with a chip interval of 5 ps. Although data rates supported are above 10 Gbit/s with label recognition properties, the complexity and the amount of coders and decoders are large as well as the need for dispersion compensation. Large performance penalties are also introduced in each conversion stage, in the order of 8-9 dB for operation at 10 -9 BER. The Advantages of OCDM labeling are the coupling of label and payload/header in the same wavelength channel, easing the bookkeeping in the routing node. To the Disadvantages belongs the sizeable increase of the line rate (by scrambling each payload bit with a label code sequence). SCM LABELING: With subcarrier labeling, the label information is modulated on a subcarrier, which is positioned in the same wavelength channel, well above the baseband spectrum of the payload data. e.g., in the HORNET project the payload data rate is 2.5 Gbit/s, and a subcarrier at 3 GHz carries FSK modulated header data . In a multiwavelength system, the subcarrier frequencies may be chosen to be unique per wavelength channel, which allows easy recognition by direct detection and bandpass filtering. By intensity-modulating the subcarrier label on the optical carrier, two subcarrier sidebands next to the baseband will occur, centered around the optical carrier. The wavelength channels need to be spaced by twice the subcarrier frequency at least. Due to fibre dispersion, fading of the subcarrier signal in a fibre link may occur. More complicated optical single-sideband modulation techniques have been explored to avoid the fading problem. The Advantages of SCM labeling are related to the coupling of label and payload/header in the same wavelength channel, easing the bookkeeping in the routing node. Moreover, the label data can be completely asynchronous to the payload data; no strict synchronisation issues. Futhermore, by optical direct detection by a single photodiode, the different subcarriers belonging to different wavelength channels can be detected without wavelength demultiplexing. Some Disadvantages are related to the fading of the subcarrier that may occur due to fibre dispersion. Moreover, non-linearities may cause intermodulation distortions, causing interference into other channels by direct simultaneous optical detection of the subcarriers. In addition the issues above, for high payload data rates, the subcarrier needs to be positioned at a very high frequency, which requires complicated electronics, and which enlarges the minimum allowed wavelength channel spacing Reading the SCM label: Reading the SCM label can be done in two ways: 1) optical direct detection by means of tapping off part of the multiwavelength signal and converting it to an electrical signal. When the subcarrier frequencies are chosen such that each wavelength channel uses a unique subcarrier frequency, this electrical signal contains all the individual labels, and each can be inspected separately by electronic bandpass filtering. No (complex) wavelength demultiplexing is needed. The demodulation of the subcarrier label information can be done by means of envelope detection, which requires a carrier to be present. 2) alternatively, a narrow optical bandpass filter may be centred at the spectral location of a subcarrier band. The filter may pass just one of the subcarrier bands, and thus no carrier fading effects are noticeable. Then, the filter output signal is the label baseband signal, so no high frequency receiver is needed. Swapping of a subcarrier label is done in two steps: firstly erasure of the old label, and subsequently insertion of the new label. The sub-carrier can be suppressed by using a notch filter while the payload is left intact. Subcarrier erasure: A subcarrier suppression of 25- 32 dB and a payload loss of 2 dB by using a FP filter have been demonstrated . Label suppression has also been realized by using a fiber Bragg grating (FBG) . This technique is also pursued in the IST LABELS project. Alternatively, a fibre non-linear mirror can be 3
  • 4. used for subcarrier suppression. SCM erasure can also be performed by wavelength conversion by XGM in a SOA . If the corner frequency of the low-pass wavelength conversion response is located at a higher frequency than the upper frequency of the baseband payload but far enough below the subcarrier channel, the SOA will efficiently convert the baseband payload to the new wavelength while suppressing the SCM header signal. SCM Label insertion: Using a MZI LiNbO3 dual drive modulator. The data payload can thus be differentially modulated, eliminating chirp effects. To achieve optical SSB modulation of the subcarrier, the subcarrier with the label information is added to the payload and fed to one modulator port, and after shifting by π/2 and adding to the inverted payload fed to the other modulator port . Another technique is to use a MZI- SOA wavelength converter, by modulation of the current of one of the SOAs in the MZI structure. A two- stage scheme using XGM + XPM in a MZI-SOA has been demonstrated for a payload at 2.5 Gbit/s and a SCM label up to 10 GHz . Alternatively, using a MZI-SOA wavelength converter and a tunable laser, the new SCM label can be pre-modulated by means of an external modulator onto the output of the tunable laser that delivers the probe signal for the wavelength converter. ORTHOGONAL LABELING: Label information can be conveyed in the phase or frequency of the payload – carrier by orthogonal modulation to the amplitude modulated of the payload information. In the STOLAS project, the payload data at 10 Gbit/s is intensity-modulated, and the label data at 155 Mbit/s is modulated orthogonally in FSK (or DPSK) format on the same wavelength channel. Label erasure is accomplished by using an MZI-SOA wavelength converter, where only the IM payload information is transposed to a new wavelength channel, not the label information. Label rewriting in FSK format is done by FSK modulation of the tunable laser at the wavelength converter; in DPSK format by means of a phase modulator following the wavelength converter. The Advantages of this approach are related to the fact that the data payload is coupled to the label in the same wavelength channel, which eases the bookkeeping in the routing nodes. Moreover, the label and data payload are decoupled regarding timing, and thus do not need strict synchronisation, only synchronisation at packet level is needed, not at the bit level. Furthermore, no header/payload delineation is needed for label erasure and rewriting. Addition of label information does not increase the channel’s bandwidth. The Disadvantages of orthogonal modulation scheme are related mainly to crostalk: crosstalk of payload to label by chirp in the wavelength converter used for the label swapping. Also, crosstalk of label to payload by FM-to-IM conversion, due to e.g. dispersion and interferometric effects in the fiber links during propagation. WDM LABELING: The labels of the packets in every wavelength channel can be time-multiplexed in a separate common wavelength channel. Careful synchronisation of the individual label signals with the respective payload channels needs to be maintained. Therefore, time-slotted operation in all wavelength channels with careful synchronisation among the channels is required. Chromatic dispersion in the fibre links may, however, affect the strict synchronisation, by introducing group velocity differences between the label- channel and the various payload channels. Orthogonal SCM Synchronous Aynchronous OCDM WDM labeling labeling TDM TDM labeling labeling labeling labeling 4
  • 5. Synchronisation Not strict, at Not strict, at Strict, at bit Not strict, at Strict, at bit Not strict, at of payload and packet level packet level level packet level level packet level label Channel Payload rate + Highest Payload Slightly larger Multiple of Payload rate bandwidth * FSK tone subcarrier freq. rate+label rate than payload payload rate spacing rate Net payload Line rate Line rate Line rate – Reduces when Fraction of line Line rate rate * label rate label rate rate decreases Label reading Demuxing of OE detection Demuxing of Demuxing of Demuxing of Demuxing of all λ-channels for all λ- all λ-channels + all λ-channels + all λ-channels labels in channels, no λ- high-speed optical switch + common λ- demuxing electronics low-speed channel electronics Label erasing λ-demuxing, + λ-demuxing, + λ-demuxing, + Separate label λ-demuxing, + OE conversion λ-converter XGM λ- OE conversion from payload OE conversion + time (XGM or XPM) converter, or of by slow optical of demuxing of optical notch payload+label switch, payload+label, labels in filter required triggered by + decoding common λ- label sync bits channel Label rewriting By FSK By dual-drive EO conversion Multiplex EO conversion OE conversion modulation of external of payload and and decoding of + time muxing tunable laser in modulator, or payload+label new label with payload+label of new labels on λ-conv., or driving SOA in required, + time slow optical required, + common λ- DPSK external MZI-SOA λ- muxing of new switch encoding with channel modulation conv. label new label code after λ-conv. Transmission IM-to-FM Fading of Payload + label Large guard High line rate Multi-channel issues conversion and subcarriers delineation bands between delineation of v.v. among channels payload and payload, label chromatic dispersion Table 1. Comparison of techniques for labeling of optical signals. * neglecting guard bands, and assuming label rate is much smaller than payload rate 5
  • 6. Label, 312 Mb/s a) FSK DFB+EAM SOA-MZI Label detection Label generation Label erasure Laser ECL Label, 312 Mb/s b) Label generation FSK DFB+EAM Label detection SOA-MZI IM Label insertion ECL AM Payload, 10Gb/s Figure 2: Experimental setups for FSK label (a) erasure and (b) insertion using a SOA-MZI wavelength converter. ECL: external cavity laser. From . One advantage of this approach is that only the common label-wavelength channel needs to be inspected for label processing and routing. However, a disadvantage is the fact that strict synchronisation of time- multiplexed labels in the dedicated label-wavelength channel with the payload data in the various data- wavelength channels required; also header/payload delineation for label erasure is needed, which becomes more complex at higher data rates. Moreover, the data payload is not closely coupled to the label, requiring careful bookkeeping when routing in a node. In Table 1 is presented a comparative study of techniques to label optical signals. 3. EXPERIMENTAL RESULTS ON FSK/IM LABEL SWAPPING In this section we present experimental results on the generation of FSK/IM orthogonal labeling of signals. We present as well results on the performance of a SOA-MZI based wavelength converter label swapping for a payload rate of 10 Gbit/s and a FSK label rate of 312 Mbit/s. The experimental setup for the label erasure and label insertion is depicted in Figure 2. The optical FSK modulation can be achieved simply by directly modulating the electrical current of a distributed feedback (DFB) laser diode at 1549.3nm. However, the drive current variation always results in a simultaneous intensity modulation of the emitted light. To remove the intensity variation of the laser’s output, the inverse electrical data is injected into the integrated electro-absorption modulator (EAM) with appropriate time delay and modulation voltage. In this way, a constant amplitude optical FSK signal is generated. The payload 6
  • 7. 10-5 back-to-back label back-to-back payload inserted label -6 10 converted payload payload after label erasure BER 10-7 10-8 10-9 10-10 -36 -32 -28 -24 -20 -16 Average received power (dBm) Figure 3: BER versus receiver input power for the IM payload and the FSK label a) ■ label in the back-to- back configuration b) ▼ payload back-to-back c) ∇ payload after wavelength conversion and FSK label insertion d) □ inserted FSK label, e)  payload after label erasure. From . information at 10Gbit/s is added by a subsequent Mach-Zehnder modulator, thus producing an optically FSK labeled signal. This signal is then injected into the SOA-MZI with a CW light at 1554.1 nm, which is generated by a tunable external cavity laser (ECL). With the above setup, label insertion and erasure has been experimentally verified and its performance assessed. More details on the experimental setup and transmission issues will be presented during the talk and they can also be found in . Because of the wavelength conversion process in the SOA-MZI, the 10 Gbit/s IM payload is copied onto the CW light while the FSK label will not be converted to the new wavelength. Hence the label erasure is accomplished. For an input payload with extinction ratio of 4.5 dB, the output signal has an extinction ratio of 12.9 dB, resulting in an increase in receiver sensitivity of 2 dB compared to back–to-back case, clearly demonstrating the 2R regeneration due to the SOA-MZI. Fig. 3 shows the dependence of the BER on the received power for a back-to back configuration of the FSK/IM combined modulation format. We can see that the receiver sensitivity at a BER of 10-9 is –32.6 dBm and –24.2 dBm, for the FSK label and IM payload respectively (curves marked with ■, and ▼, respectively). A label insertion scheme was realized using a FSK modulated signal instead of a CW signal at the SOA-MZI converter. The signal output of the SOA-MZI device is then the original payload data, converted to the FSK signal wavelength, with the superimposed FSK label modulation. After splitting the signal for FSK and IM detection, the BER was measured as a function of the average received power. The results are presented in Fig. 3. As we can see the receiver sensitivity at a BER of 10-9 is –31 dBm and -23.5 dBm, for the label and payload, respectively (curves marked □ and ∇, respectively). We observe that no substantial degradation of the receiver sensitivity takes place in the label insertion process. In fact, the SOA-MZI has a regenerative character. However, for a proper detection of the FSK signal, a certain power level in the ‘zeros’ bit should be present. The extinction ratio of the input signal was measured to be 5.1 dB and an extinction ratio of 4 dB was 7
  • 8. observed at the output of the SOA-MZI. The error free detection of the FSK data experimentally demonstrates that the chirp introduced by the SOA-MZI wavelength converter has no detrimental influence on the FSK detection. FSK label swapping: The complete operation of label swapping (i.e. label erasure and insertion of a new FSK label) can be performed with the SOA-MZI under study provided a second FSK signal is available at a different wavelength than the old FSK label to be erased. This second FSK signal is then used instead of the CW input into the SOA-MZI wavelength converter. Although, a counter-propagation mode of operation could be used, the SOA-MZI device under study shows insufficient performance for data rates above 5 Gbit/s. To study the chirp and linewidth properties of the IM converted signal after FSK erasure, and to assess its suitability for FSK label re-insertion, the experimental setup shown in Fig. 4 was used. The output of the SOA-MZI wavelength converter was amplified and fed into an EAM where FSK label insertion took place by cross-absorption modulation (XAM) using an FSK modulated pump signal. Experimental details on the label swapping process and transmission propertied are presented in . The results for the BER measurements for the FSK and IM signals after a complete label swapping stage are shown in Fig. 5. We can compare these results with the back-to-back measurements presented in Fig. 3. As we can see, there is no substantial observed power penalty for both signals (below 0.5 dB). The chirp introduced by the SOA-MZI has shown no effect on the performance, as confirmed by the error free detection of the FSK signal. This is in accordance with the previous chirp measurements and simulations results presented . Figure 4: SetupPacket generation swapping of FSK/IM labeled signal. OC: optical circulator. From . for a complete label Label, 320 Mb/s Label generation FSK/IM FSK DFB+EAM AM SOA-MZI Optical filter Label erasure and 2R Payload, 10Gb/s ECL OC EAM Payload detection label detection 8
  • 9. label insertion w EAM 1.00E-05 1.00E-06 payload 1.00E-07 label 1.00E-08 BER 1.00E-09 1.00E-10 -38 -36 -34 -32 -30 -28 -26 -24 -22 -20 Received power, dBm Figure 5: BER versus input power for a FSK/IM combined modulation scheme after a complete label swapping stage. The results are to be compared with the back-to-back curves of Fig. 2. From DISCUSSION OF RESULTS: The extinction ratio of the IM is a crucial design parameter for a combined FSK/IM system. Namely, there should be enough optical power in the IM ‘”zero”’ binary symbols so that the FSK data still can be recovered. Experimentally, it has been shown that an ER of 4-5 dB gives proper performance, this value is in accordance with simulations results . Using the above value for the IM extinction ratio, transmission of FSK/IM has shown to be feasible over a link of 88 km of standard single mode fiber with pre-and post dispersion compensation. Another aspect relevant to the design of the combined modulation format may be the synchronization between the FSK bit and the IM bit. With the reported generation method of the FSK signal, if the FSK and the IM bits are not perfectly synchronized, the eye pattern may be distorted and errors are detected . This effect is accumulative in the case of label swapping, and therefore the performance degradation may be severe. However, in recent experiments with other methods to generate FSK optical signal this effect has not been observed; correspondent details will be published elsewhere. 4. CONCLUSIONS Several optical labeling techniques have been reviewed with emphasis on their advantages and weaknesses for applications in LOBS networks. We have presented an experimental validation of the feasibility of FSK/IM labeling scheme. A label swapper based on a SOA-MZI has been employed. The presented results show that the orthogonal labeling scheme is a promising technique for LOBS that offers the possibility for building label swapping nodes in integrated photonic circuits based on SOA technologies. 9
  • 10. ACKNOWLEDGMENT This work was performed in the framework of the IST-STOLAS project, which is partially funded by the IST Program of the European Community. The authors would like to acknowledge the contributions of their colleagues within the STOLAS consortium. REFERENCES [1] Chunming Qiao, “Labeled Optical Burst Switching for IP over WDM Integration”, IEEE Communication Magazine, September 2000, pp.104-114. [2] A. Banerjee, et al., “Generalized Multiprotocol Label Switching: An Overview of Routing and Management Enhancements”, IEEE Communication Magazine, Jan. 2001, pp.144-150. [3] Ton Koonen, Geert Morthier, Jean Jennen, Huug de Waardt and Piet Demeester, "Optical packet routing in IP-over- WDM networks deploying two-level optical labeling”, Proc. of ECOC'01, Amsterdam, Sep.30-Oct.4, 2001, paper Th.L.2.1. [4] Guillemot, C.; Henry, M.; Clerot, F.; Le Corre, A.; Kervaree, J.; Dupas, A.; Gravey, P., KEOPS optical packet switch demonstrator: architecture and testbed performance, Proc. of Optical Fiber Communication Conference 2000, Vol. 3, pp. 204 -206 [5] Blumenthal, D.J.; Olsson, B.-E.; Rossi, G.; Dimmick, T.E.; Rau, L.; Masanovic, M.; Lavrova, O.; Doshi, R.; Jerphagnon, O.; Bowers, J.E.; Kaman, V.; Coldren, L.A.; Barton, J., All-optical label swapping networks and technologies, J. of Lightwave Technology, Vol. 18, No. 12 , Dec 2000, pp. 2058 –2075 [6] Rau, L.; Rangarajan, S.; Blumenthal, D.J.; Chou, H.-F.; Chiu, Y.-J.; Bowers, J.E., Two-hop all-optical label swapping with variable length 80Gb/s packets and 10Gb/s labels using nonlinear fiber wavelength converters, unicast/multicast output and a single eam for 80- to 10Gb/s packet demultiplexing, Proc. of Optical Fiber Communication Conference 2002, 17-22 Mar 2002 [7] Fjelde, T.; Wolfson, D.; Kloch, A.; Dagens, B.; Coquelin, A.; Guillemot, I.; Gaborit, F.; Poingt, F.; Renaud, M., Demonstration of 20 Gbit/s all-optical logic XOR in integrated SOA-based interferometric wavelength converter, Electronics Letters, Vol. 36, No. 22, 26 Oct 2000 [8] Y. G. en, Y. Zhang, L. K. Chen, On Architecture and Limitations of Optical Multiprotocol Label Switching (MPLS) Networks Using Optical-Orthogonal-Code (OCC)/Wavelength Label, OTF, Vol. 8, pp. 43-70, 2002 [9] Hideyuki Sotobayashi ; Wataru Chujo ; Ken-ichi Kitayama, Photonic Gateway: Multiplexing Format Conversions of OCDM-to-WDM and WDM-to-OCDM at 40 Gbit/s (4 x10 Gbit/s) , Journal of Lightwave Technology, accepted for future publication , 2002, pp. 1 [10] Kapil V. Shrikhande, I. M. White, M. S. Rogge, F-T. An, A. Srivatsa, E.S. Hu, S. S-H. Yam and Leonid G. Kazovsky, “Performance Demonstration of a Fast-Tunable Transmitter and Burst-Mode Packet Receiver for HORNET,” Optical Fiber Communication Conference (OFC), paper ThG2, Anaheim, California, February 2001. [11] Meagher, B.; Chang, G.K.; Ellinas, G.; Lin, Y.M.; Xin, W.; Chen, T.F.; Yang, X.; Chowdhury, A.; Young, J.; Yoo, S.J.; Lee, C.; Iqbal, M.Z.; Robe, T.; Dai, H.; Chen, Y.J.; Way, W.I., Design and implementation of ultra-low latency optical label switching for packet-switched WDM networks, Journal of Lightwave Technology, Vol. 18, No. 12, Dec 2000, pp. 1978-1987 [12] H.J. Lee, V. Hernandez, V. K. Tsui, S. J. B. Yoo, Simple, polarization-independent, and dispersion-insensitive SCM signal extraction technique for optical switching systems applications, Elec. Letters, Vol. 37, No. 20, 2001, pp. 1240 [13] Y. M. Lin, W. I. Way, and G. K. Chang, A Novel Optical Label Swapping Technique Using Erasable Optical Single-Sideband Subcarrier Label, IEEE Photonics Technology Letters, Vol. 12, No. 8, pp. 1088-1090, August 2000. [14] I. Tafur Monroy, E. J. M. Verdurmen, Sulur, A. M. J. Koonen, H. de Waardt, G. D. Khoe, N. Chi, P. V. Holm- Nielsen, J. Zhang and C. Peucheret, “Performance of a SOA-MZI wavelength converter for label swapping using combined FSK/IM modulation format”, to appear in Optical Fiber Technology, invited paper. 10
  • 11. [15] N. Chi, J. Zhang, P. V. Holm-Nielsen, C. Peucheret and P. Jeppesen, “Transmission and transparent wavelength conversion of an optically labelled signal using ASK/DPSK orthogonal modulation”, IEEE Photonics Technology Letters, Vol. 15, No. 5, pp. 760-762, May 2003. [16] J. Zhang, N. Chi, P. V. Holm-Nielsen, C. Peucheret and P. Jeppesen, “An optical FSK transmitter based on an integrated DFB laser/EA modulator and its application in optical labeling, to appear in IEEE Photonics Technology Letters. [17] N. Chi, L. Xu, L. J. Christiansen, K. Yvind, J. Zhang, P. V. Holm-Nielsen, C. Peucheret, C. Zhang and P. Jeppesen, “Optical label swapping and packet transmission based on ASK/DPSK orthogonal modulation format in IP-over- WDM networks, in Technical Digest Optical Fiber Communication Conference, OFC’03, Atlanta, Georgia, U.S.A., paper FS2, vol. 2, pp. 792-794. 11