Abstract

We present an optical pulse multiplication and temporal coding method for OCDMA systems. The true time delay among the pulses was obtained by utilizing the difference in the propagation speeds of the core mode and a co-propagating cladding mode coupled by a long-period fiber grating. By cascading gratings we could get an equally spaced 40-GHz pulse train from a 10-GHz input train. The dispersion compensating fiber having an inner cladding structure enabled us to have the gratings that were not sensitive to the polymer jacket on the cladding surface, and also allowed shortening the device length. Various coding and decoding of a pulse train are possible by controlling the separations among the gratings.

© 2004 Optical Society of America

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References

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  1. A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia. T. Erdogan, and J. E. Sipe, �??Long-period fiber gratings as band-rejection filters,�?? J. Lightwave Technol. 14, 58-64 (1996).
    [CrossRef]
  2. B. H. Lee and J. Nishii, �??Bending sensitivity of in-series long-period fiber gratings,�?? Opt. Lett. 23, 1624- 1626 (1998).
    [CrossRef]
  3. P. Petropoulos, M. Ibsen, M. Z. Zervas, and D. J. Richardson, �??Generation of a 40-GHz pulse stream by pulse multiplication with a sampled fiber Bragg grating,�?? Opt. Lett. 25, 521-523 (2000).
    [CrossRef]
  4. N. K. Berger, B. Levit, S. Atkins, and B. Fischer, �??Repetition rate multiplication of optical pulses using fiber Bragg gratings,�?? in Optical Fiber Communication Conference �??2002, Optical Society of America, Anaheim, USA, ThGG34 (2002).
  5. L. R. Chen, �??Flexible fiber Bragg grating encoder/decoder for hybrid wavelength-time optical CDMA,�?? IEEE Photon. Technol. Lett. 13, 1233 �??1235 (2001).
    [CrossRef]
  6. P. Petropoulos, N. Wada, P. C. Teh, M. Ibsen, W. Chujo, K. -I. Kitayama, and D. J. Richardson, �??Demonstration of a 64-chip OCDMA system using superstructured fiber gratings and time-gating detection,�?? IEEE Photon. Technol. Lett. 13, 1239�??1241 (2001).
    [CrossRef]
  7. T. J. Eom, S. J. Kim, C. S. Park, and B. H. Lee, �??Generation of high-repetition-rate optical pulse using cascaded long-period fibre gratings,�?? Electron Lett. 40, 981-982 (2004).
    [CrossRef]
  8. S. J. Kim, T. J. Eom, B. H. Lee, and C. S. Park, �??Optical temporal encoding/decoding of short pulses using cascaded long-period fiber gratings,�?? Opt. Express 11, 3034-3040 (2003).
    [CrossRef] [PubMed]
  9. B. H. Lee, T. J. Eom, M. J. Kim, U. C. Paek, and T. Park, �??Mode coupling within inner cladding fibers,�?? J. of the Optical Society of Korea 7, 53-58 (2003).
    [CrossRef]
  10. S. Ramachandran, Z. Wang, and M. Yan, �??Bandwidth control of long-period fiber grating-based mode converters in few-mode fibers,�?? Opt. Lett. 27, 698-700 (2002).
    [CrossRef]
  11. J. Kim and D. Y. Kim, �??An efficient dispersion calculation for axially symmetric optical fibers,�?? Fiber and Integrated Optics 21, 13-30 (2002).
    [CrossRef]
  12. E. M. Dianov, S. A. Vasiliev, A. S. Kurkov, O. I. Medvedkov, and V. N. Protopopov, �??In-fiber Mach- Zehnder interferometer based on a pair of long-period gratings,�?? Proc. European Conf. Optical Communication, 65-68 (1996).
  13. B. H. Lee and J. Nishii, �??Dependence of fringe spacing on the grating separation in a long-period fiber grating pair,�?? Appl. Opt. 38, 3450-3459 (1999).
    [CrossRef]
  14. B. H. Lee and U. C. Paek, �??Multislit interpretetion of cascaded long-period fiber gratings,�?? J. Lightwave Technol. 20, 1750-1761 (2002).
  15. W.C Kwong, G.C. Yang, Prime Codes with Applications to CDMA Optical and Wireless Networks (Artech House, Boston, MA, 2002).
  16. B. H. Lee, J. Cheong, and U. C. Paek, �??Spectral polarization-dependent loss of cascaded long-period fiber gratings,�?? Opt. Lett. 27, (2002).
    [CrossRef]
  17. S. T. Oh, W. T. Han, U. C. Paek, and Y. Chung, �??Reduction of Birefringence and Polarization- Dependent Loss of Long-Period Fiber Gratings Fabricated Using KrF Excimer Laser,�?? Opt. Express 11 (2003).
    [CrossRef] [PubMed]

Appl. Opt. (1)

Electron Lett. (1)

T. J. Eom, S. J. Kim, C. S. Park, and B. H. Lee, �??Generation of high-repetition-rate optical pulse using cascaded long-period fibre gratings,�?? Electron Lett. 40, 981-982 (2004).
[CrossRef]

Fiber and Integrated Optics (1)

J. Kim and D. Y. Kim, �??An efficient dispersion calculation for axially symmetric optical fibers,�?? Fiber and Integrated Optics 21, 13-30 (2002).
[CrossRef]

IEEE Photon. Technol. Lett. (2)

L. R. Chen, �??Flexible fiber Bragg grating encoder/decoder for hybrid wavelength-time optical CDMA,�?? IEEE Photon. Technol. Lett. 13, 1233 �??1235 (2001).
[CrossRef]

P. Petropoulos, N. Wada, P. C. Teh, M. Ibsen, W. Chujo, K. -I. Kitayama, and D. J. Richardson, �??Demonstration of a 64-chip OCDMA system using superstructured fiber gratings and time-gating detection,�?? IEEE Photon. Technol. Lett. 13, 1239�??1241 (2001).
[CrossRef]

J. Lightwave Technol. (2)

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia. T. Erdogan, and J. E. Sipe, �??Long-period fiber gratings as band-rejection filters,�?? J. Lightwave Technol. 14, 58-64 (1996).
[CrossRef]

B. H. Lee and U. C. Paek, �??Multislit interpretetion of cascaded long-period fiber gratings,�?? J. Lightwave Technol. 20, 1750-1761 (2002).

J. of the Optical Society of Korea (1)

B. H. Lee, T. J. Eom, M. J. Kim, U. C. Paek, and T. Park, �??Mode coupling within inner cladding fibers,�?? J. of the Optical Society of Korea 7, 53-58 (2003).
[CrossRef]

Opt. Express (2)

S. J. Kim, T. J. Eom, B. H. Lee, and C. S. Park, �??Optical temporal encoding/decoding of short pulses using cascaded long-period fiber gratings,�?? Opt. Express 11, 3034-3040 (2003).
[CrossRef] [PubMed]

S. T. Oh, W. T. Han, U. C. Paek, and Y. Chung, �??Reduction of Birefringence and Polarization- Dependent Loss of Long-Period Fiber Gratings Fabricated Using KrF Excimer Laser,�?? Opt. Express 11 (2003).
[CrossRef] [PubMed]

Opt. Lett. (4)

Other (3)

N. K. Berger, B. Levit, S. Atkins, and B. Fischer, �??Repetition rate multiplication of optical pulses using fiber Bragg gratings,�?? in Optical Fiber Communication Conference �??2002, Optical Society of America, Anaheim, USA, ThGG34 (2002).

E. M. Dianov, S. A. Vasiliev, A. S. Kurkov, O. I. Medvedkov, and V. N. Protopopov, �??In-fiber Mach- Zehnder interferometer based on a pair of long-period gratings,�?? Proc. European Conf. Optical Communication, 65-68 (1996).

W.C Kwong, G.C. Yang, Prime Codes with Applications to CDMA Optical and Wireless Networks (Artech House, Boston, MA, 2002).

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Figures (10)

Fig. 1.
Fig. 1.

The schematic diagram of realization of a true time delay with a cladding mode by using cascaded LPGs. Inset figures are the measured near-field patterns of the core mode and a cladding mode of a DCF.

Fig. 2.
Fig. 2.

The refractive index profile of the DCF used for the experiment. It had an inner cladding layer.

Fig. 3.
Fig. 3.

(a) The measured near-field image of the inner cladding mode coupled by a single LPG fabricated in the DCF and (b) the simulation result of the modal field distribution of the inner cladding mode.

Fig. 4.
Fig. 4.

The transmission spectrum of the LPGP made in the DCF. The poly-acrylate coating between two gratings was not removed. The first peak, left most, has good contrast interference fringes, but the third peak, right most, has no interference fringes. The middle one is between.

Fig. 5.
Fig. 5.

The differential effective group index (left) and the differential effective index (right) calculated from the interference fringes in the first resonant peak of Fig. 3.

Fig. 6.
Fig. 6.

The experimental setup for optical pulse multiplication by using the cascaded LPGs made in DCF. An active mode lock fiber laser was used as an initial optical pulse train. AMFRL, actively mode locked fiber ring laser. PC, polarization controller. PD, 45-GHz photodetector.

Fig. 7.
Fig. 7.

The temporal responses of the proposed device: (a) Initial pulse train with a 10-GHz repetition rate, (b) Two times multiplied pulse train obtained by LPGP-1. It has a 50 ps repetition period, (c) 25 ps time delayed pulse train obtained with LPGP-2 only, (d) Four times multiplied pulse train obtained by using both LPGPs. It has a 25 ps repetition period or 40-GHz repetition rate.

Fig. 8.
Fig. 8.

The experimental setup for the OCDMA application. AMFRL, actively mode locked fiber ring laser. PC, polarization controller. PD, 45-GHz photodetector. τ, the chip spacing (τ=4.16 ps).

Fig. 9.
Fig. 9.

The temporal responses of the encoded signals with (a) the code of C1 (100100100100) and (b) the code of C2 (1000010100001).

Fig. 10.
Fig. 10.

Decoded signals of the pulse train encoded by (a) only the matched encoder; C1∗C1, (b) only the unmatched encoder; C1∗C2, and (c) both encoders; (C1+C2)∗C1.

Equations (1)

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Δ T = L c Δ m eff

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