A 2011 Optics Express experiment established the feasibility of recognizing optical packet labels built from double two-dimensional optical orthogonal codes (2D-OOCs) entirely in the optical domain, using fiber Bragg grating decoders followed by cascaded first- and second-order four-wave mixing (FWM) in semiconductor optical amplifiers to generate a unique identification tone per label. The demonstration was limited to two codes, three wavelengths, and a single node, with no quantified identification error rates, and with recognition quality degraded by wide-bandwidth demultiplexing, polarization misalignment, and finite pulse extinction ratio. The open problem is to advance this recognition scheme toward a reliable, scalable optical packet switching label processor: quantify the minimum detectable identification-tone power and the false-positive/false-negative identification rates under realistic amplifier, filter, and traffic noise; overcome the demonstrated degradation mechanisms; and assess operation with larger codebooks, realistic payload wavelength plans, and multi-node network scenarios.

Background

Optical packet switching (OPS) is a network architecture in which data packets are routed and forwarded entirely in the optical domain, avoiding electronic conversion at intermediate nodes; each packet carries a short optical label (header) that a switching node must read to decide where to forward the payload. All-optical label swapping (AOLS) denotes the set of techniques for generating, recognizing, erasing, and rewriting such labels optically at line rate. One label family encodes the address as an optical code: a two-dimensional optical orthogonal code (2D-OOC) places kk pulses (the code weight) at kk chosen wavelengths out of a set of carrier wavelengths, in kk chosen time slots out of a frame of LL slots (the code length), with code families designed so that the matched-filter autocorrelation peak of the correct code is sharp while cross-correlation against wrong codes stays low; these constraints are the same correlation properties used in optical code-division multiple access. A 'double' 2D-OOC label concatenates two such codes into one label, multiplying the number of distinguishable labels for a given wavelength resource.

In the scheme of Zhang et al. (Opt. Express 19(16), 14937, 2011), each 2D-OOC label is generated by serial fiber Bragg grating (FBG) encoders — an FBG is a length of optical fiber with a periodic refractive-index modulation that reflects one narrow wavelength band — and decoded by matched FBG decoders that produce a narrow autocorrelation peak (about 2 ns in the experiment) only for the correct code. The decoded multi-wavelength pulses are injected into semiconductor optical amplifiers (SOAs), in which four-wave mixing (FWM) — a third-order nonlinear interaction in which two or three input waves generate new waves at combination frequencies — creates first-order mixing products, and selected first-order tones are re-injected into a second SOA to create second-order products; one second-order wavelength is filtered out with a wavelength-division-multiplexing (WDM) demultiplexer and serves as the unique optical identification signal for the label. The experiment used two codes (C11 and C12 with L=19L=19, k=3k=3), three carrier wavelengths (1552.5, 1554.1, 1557.3 nm), erbium-doped fiber amplifiers (EDFAs) for amplification, and payloads at 2.5 and 5 Gbit/s transmitted over 25 km, with bit-error-rate (BER) power penalties of at most about 0.9 dB at BER 10−910^{-9}. Predecessor label schemes in the same research program used multiple one-dimensional optical orthogonal code sequences with FBG-based processing, and FWM-based recognition of spectral-amplitude-code (SAC) labels in a single nonlinear element had been shown earlier by Rosas-Fernandez et al. (ECOC 2006).

The 2011 paper validated feasibility only. As the paper reports, the recognition signal-to-noise ratio was degraded by the wide bandwidth (about 1.6 nm) of the WDM demultiplexer used for tone selection, which spectrally broadened the pulses and increased beat noise; the FWM efficiency and repeatability were undermined by polarization misalignment between the interacting waves and by an insufficient extinction ratio (the ratio of pulse peak power to the residual 'zero' level) of the input pulses; the code set was a specific small pair of codes under single-node laboratory conditions; and the identification-performance margins — the minimum detectable identification-tone power and the false-positive and false-negative identification rates under realistic noise and traffic — were never quantified. Whether FWM-based recognition of double 2D-OOC labels can operate reliably at larger codebook sizes, with realistic payload wavelength plans and in multi-node networks, therefore remained undetermined.

Problem Statement

Advance four-wave-mixing-based all-optical recognition of double two-dimensional optical orthogonal code (2D-OOC) labels from its demonstrated feasibility point — two codes (L=19L=19, k=3k=3), three wavelengths, single node — to a reliable and scalable optical packet switching label processor. Concretely, the unresolved questions left by the 2011 demonstration are: (1) quantification of identification performance under realistic conditions — the minimum detectable identification-tone power and the false-positive and false-negative label-identification rates under realistic EDFA amplified-spontaneous-emission noise, filter bandwidths, SOA operating points, and traffic conditions — including how these degrade as the codebook grows; (2) removal of the demonstrated performance limitations, namely the signal-to-noise degradation caused by wide-bandwidth (about 1.6 nm) WDM demultiplexing of the mixing tones, the loss of FWM efficiency and repeatability caused by polarization misalignment and insufficient input-pulse extinction ratio, and the impurity of the generated mixing tones; and (3) operation with larger codebooks, denser spectral packing compatible with realistic payload wavelength plans, and in multi-node network scenarios rather than a single laboratory node. Items (1) and (2) are the required contributions: a resolution must quantify the identification performance and identify and justify remedies for the named degradation mechanisms. Item (3) may be discharged by an analysis- or simulation-based scalability assessment — for example, by extending the error-rate quantification of (1) to larger codebooks and multi-node traffic under stated parameter ranges — rather than by a new experimental multi-node demonstration.

References

  1. Chongfu Zhang, Leyang Wang, Sathishkumar Perumal, Kun Qiu, Heng Zhou, "All-optical recognition method of double two-dimensional optical orthogonal codes-based labels using four-wave mixing," Optics Express 19(16), 14937 (2011). DOI: 10.1364/OE.19.014937, https://doi.org/10.1364/OE.19.014937
  2. J. B. Rosas-Fernandez, S. Ayotte, S. LaRochelle, L. A. Rusch, "A Single All-Optical Processor for Multiple Spectral Amplitude Code Label Recognition Using Four Wave Mixing," Proceedings of the 32nd European Conference on Optical Communication, ECOC 2006. DOI: 10.1109/ECOC.2006.4800973, https://doi.org/10.1109/ECOC.2006.4800973
  3. Chongfu Zhang, Kun Qiu, Heng Zhou, Yun Ling, Yawei Wang, Bo Xu, "Experimental demonstration of tunable multiple optical orthogonal codes sequences-based optical label for optical packets switching," Optics Communications 283(6), 932–938 (2010). DOI: 10.1016/j.optcom.2009.11.036, https://doi.org/10.1016/j.optcom.2009.11.036
  4. S. Alireza Nezamalhosseini, Mohammad Rezagholipour Dizaji, Kerim Fouli, Lawrence R. Chen, Farokh Marvasti, "Novel FWM-Based Spectral Amplitude Code Label Recognition for Optical Packet-Switched Networks," IEEE Photonics Journal 5(4), 6601510 (2013). DOI: 10.1109/JPHOT.2013.2274769, https://doi.org/10.1109/JPHOT.2013.2274769
  5. Koji Morita, Gihan Weerasekara, Takahiro Kodama, Satoshi Shimizu, Naoya Wada, Ken-ichi Kitayama, "Massive Generation/Recognition of 2-D Label Using Optical Code and Wavelength," 18th OptoElectronics and Communications Conference held jointly with 2013 International Conference on Photonics in Switching (OECC/PS 2013). DOI: 10.1364/OECC_PS.2013.MT2_4, https://doi.org/10.1364/OECC_PS.2013.MT2_4
  6. Kai-Sheng Chen, Chung-Lien Pan, "Operating Characteristic Curves of Optical Packet-Switching Using Optical Code-Division Multiplexing for Label Switching," Photonics 10(6), 613 (2023). DOI: 10.3390/photonics10060613, https://doi.org/10.3390/photonics10060613
  7. Efthymios N. Lallas, "A survey on all optical label swapping techniques: Comparison and trends," Optical Switching and Networking 31, 22–38 (2019). DOI: 10.1016/j.osn.2018.08.002, https://doi.org/10.1016/j.osn.2018.08.002
  8. Franco Callegati, Davide Careglio, Luiz Henrique Bonani, Mario Pickavet, Josep Solé-Pareta, "Why Optical Packet Switching failed and can Elastic Optical Networks take its place?," Optical Switching and Networking 44, 100664 (2022). DOI: 10.1016/j.osn.2021.100664, https://doi.org/10.1016/j.osn.2021.100664