OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 9 — Apr. 27, 2009
  • pp: 7664–7669
« Show journal navigation

A widely tunable wavelength converter based on nonlinear polarization rotation in a carbon-nanotube-deposited D-shaped fiber

K. K. Chow, S. Yamashita, and Y. W. Song  »View Author Affiliations


Optics Express, Vol. 17, Issue 9, pp. 7664-7669 (2009)
http://dx.doi.org/10.1364/OE.17.007664


View Full Text Article

Acrobat PDF (2235 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We demonstrate widely tunable wavelength conversion based on cross-phase modulation induced nonlinear polarization rotation in a carbon nanotubes (CNTs) deposited D-shaped fiber. A 5-centimeter-long CNT-deposited D-shaped fiber is used as the nonlinear medium for wavelength conversion of a 10 Gb/s non-return-to-zero signal. Wavelength tunable converted signal over 40 nm is obtained with around 2.5-dB power penalty in the bit-error-rate measurements.

© 2009 Optical Society of America

1. Introduction

Owing to its unique optical properties, carbon nanotube (CNT) technology has recently drawn much research attention [1–3

1. S. Iijima and T. Ichihashi, “Single shell carbon nanotubes of one nanometer diameter,” Nature 363, 603–605 (1993). [CrossRef]

]. Applications and studies of CNT including mode-locked lasers [4

4. S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, “Ultrafast fiber pulsed lasers incorporating carbon nanotubes,” IEEE J Select. Top. Quantum Electron. 10, 137–146 (2004). [CrossRef]

, 5

5. S. Yamashita, Y. Inoue, S. Maruyama, Y. Murakami, H. Yaguchi, M. Jablonski, and S. Y. Set, “Saturable absorbers incorporating carbon nanotubes directly synthesized onto substrates/fibers and their applications to mode-locked fiber lasers,” Opt. Lett. 29, 1581–1583 (2004). [CrossRef] [PubMed]

], ultra-fast optical response [6

6. Y. C. Chen, N. R. Raravikar, L. S. Schadler, P. M. Ajayan, Y. P. Zhao, T. M. Lu, G. C. Wang, and X. C. Zhang, “Ultrafast optical switching properties of single-walled carbon nanotube polymer composites at 1.55 μm,” App. Phys. Lett. 81, 975–977 (2002). [CrossRef]

, 7

7. S. Tatsuura, M. Furuki, Y. Sato, I. Iwasa, M. Tian, and H. Mitsu, “Semiconductor carbon nanotubes as ultrafast switching materials for optical telecommunications,” Adv. Mater. 15, 534–537 (2003). [CrossRef]

], and optical noise suppression [8

8. S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, “A noise suppressing satiable absorber at 1550 nm based on carbon nanotube technology,” in Proc. OFC 2003, paper FL2, Atlanta, GA, USA (2003).

] had been investigated. In particular, CNTs can be employed as a fiber-based nonlinear medium due to their ultra-high nonlinear coefficient [4

4. S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, “Ultrafast fiber pulsed lasers incorporating carbon nanotubes,” IEEE J Select. Top. Quantum Electron. 10, 137–146 (2004). [CrossRef]

, 9

9. Vl. A. Margulis, E. A. Gaiduk, and E. N. Zhidkin, “Third-order optical nonlinearity of semiconductor carbon nanotubes: third harmonic generation,” Diamond Relat. Mater. 8, 1240–1245 (1999). [CrossRef]

]. Previously, our group had reported optical switching based on a Kerr shutter using a few centimeters of CNT-deposited D-shaped fiber [10

10. Y. W. Song, S. Y. Set, and S. Yamashita, “Novel Kerr shutter using carbon nanotubes deposited onto a 5-cm D-shaped fiber,” in Proc. CLEO 2006, paper CMA4, Long Beach, CA, USA (2006).

] as well as optical loop mirror incorporated with CNT-loaded planar waveguide [11

11. K. Kashiwagi, S. Yamashita, H. Yaguchi, C. S. Goh, and S. Y. Set, “All optical switching using carbon nanotubes loaded planar waveguide,” in Proc. CLEO 2006, paper CMA5, Long Beach, CA, USA (2006).

], which are significant for various system applications especially wavelength conversion. In a wavelength-routed optical network, wavelength conversion plays a major role in providing the wavelength flexibility and avoiding wavelength blocking [12

12. S. J. B. Yoo, “Wavelength conversion technologies for WDM network applications,” J. Lightwave Technol. 14, 955–966 (1996). [CrossRef]

]. For fiber-based wavelength converter the nonlinear medium usually favors compact, high nonlinearity, and splicable to standard single-mode fiber (SMF). In this paper, we further investigate the optical switching properties of the CNTs and experimentally demonstrate tunable wavelength conversion using a short piece of CNT-deposited D-shaped fiber for the first time. With the cross-phase modulation (XPM) induced nonlinear polarization rotation effect in the fiber, wavelength conversion is obtained with a wavelength tuning range over 40 nm. Also, the D-shaped fiber is fully spliced to standard SMF without free space coupling so that the converter can have a stable operation. A power penalty of 2.5 dB is measured for 10 Gb/s non-return-to-zero (NRZ) signal in the bit-error-rate (BER) measurements.

2. Design and fabrication of CNT-deposited D-shaped fiber for nonlinear applications

The CNT-deposited D-shaped fiber works with the interaction between CNTs and the evanescent field of propagating light in the fiber. Figure 1(a) shows the schematic illustration of the D-shaped fiber and the corresponding SEM image of the deposited CNTs. In our experiment, the CNTs are made by a bulk production method called high-pressure CO conversion. Since the isolation of individual CNT is critical to obtain the maximum nonlinearity, the diameter and the diameter distribution of the CNTs are well controlled. The CNTs are then dispersed in a solvent without any significant agglomeration, and only the homogeneous part is taken after the centrifugal separation before spraying on the D-shaped fiber. The D-shaped fiber is prepared by polishing a segment of standard SMF held by a V-grooved block. The fiber together with the V-grooved block is polished with 4 steps in order to ensure the non-cracked and smooth surface of the D-shaped area, thus minimize the beam scattering through the polished face. The insertion loss is monitored during polishing therefore the amount of optical power leakage through the polished face can also be monitored. The CNTs are then deposited on the D-shaped surface by spray method, and the fiber sample is finalized by adding a protection layer above the deposited CNTs. Figure 1(b) shows the photo of the finished device with the fiber pigtails. The overall insertion loss of the CNT-deposited D-shaped fiber adopted in our experiment is 12 dB with a CNT-light interaction length of around 5 cm. Note that the V-grooved block is a few cm longer as a buffer for protecting the junctions between the D-shaped region and the SMF pigtails. Since the CNTs are randomly sprayed on the D-shaped area, the fiber is polarization sensitive with around 4-dB power variation to the polarization-dependent resonance of individual CNTs. It is worth noting that since the D-shaped fiber is made by standard SMF, the splicing loss of the device to subsystems or laser cavities can be nearly neglected.

Fig. 1. (a) Schematic illustration of D-shaped fiber with carbon nanotubes (CNTs) deposited (SEM image: magnification 50K) and (b) photo showing the CNT-deposited D-shaped fiber in a V-groove block with single-mode fiber pigtails.

3. Experiment and results on wavelength conversion

The experimental setup on wavelength conversion using CNT-deposited D-shaped fiber is shown in Fig. 2. In this session, the modulator is initially turned off and the continuous-wave (cw) output of the external cavity laser (ECL1) serves as the pump for nonlinear effect. The cw pump is then amplified by an erbium-doped fiber amplifier (EDFA) followed by an optical bandpass filter for eliminating ASE from the EDFA. The amplified pump is then combined with a cw probe light from the ECL2 using a 3-dB coupler. The launched optical power of the pump and the probe light into the CNT-deposited D-shaped fiber are estimated to be 21 dBm and -3 dBm, respectively. The combined light then undergoes XPM induced nonlinear polarization rotation in the CNT-deposited D-shaped fiber and the probe light is modulated and filtered out by the polarizer. The switching out of the probe light is originated from the relative states of polarization (SOP) between the probe light and the polarizer. When the SOP of the probe light and the polarizer are orthogonal to each other and the pump light is aligned to have a SOP 45° with respect to that of the polarizer, with appropriate pump power level the birefringence of the fiber is modulated and the probe light will be switched out (on state) or blocked (off state) by the polarizer corresponding to the input signal. The transmittivity of the probe light in such configuration can be expressed as [13

13. G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (New York: Academic, 210–216, 2001).

]:

T=sin2(Δϕ2)
(1)

where T is the transmittivity of the probe light and ∆ϕ is the phase different between the pump and the probe light. T becomes 100% when ∆ϕ = π or an odd multiple of π where the probe light is blocked completely when ∆ϕ equals to even multiples of π. In our experiment, the SOP of the pump and the probe light are optimized by the polarization controllers in order to obtain π phase shift and maximize the switching efficiency. Finally, we use an optical bandpass filter to completely filter out the pump light and wavelength conversion is obtained.

Fig. 2. Experimental setup on wavelength conversion using CNT-deposited D-shaped fiber. ECL: external cavity laser; EDFA: erbium-doped fiber amplifier; BERT: bit-error rate test set.
Fig. 3. Output spectra obtained after the CNT-deposited D-shaped fiber and the polarizer with (a) pump turned off and (b) pump turned on.

Figure 3 shows the spectra obtained after the polarizer. In our experiment the pump and the probe light are set at 1555.0 nm and 1545.0 nm, respectively. Figure 3(a) depicts the spectrum with the pump light turned off. Note that the probe light power is suppressed to minimum by adjusting its SOP orthogonal to that of the polarizer by the polarization controllers. With the input pump turned on and polarization appropriately adjusted, the probe light experiences XPM induced nonlinear polarization rotation and its SOP becomes parallel with that of the polarizer, leading to the power increase of the probe light output as shown in Fig. 3(b). From the spectra it is observed that the maximum extinction ratio obtained between on and off state is 16 dB.

Fig. 4. Plot of probe light transmittivity against input pump power.

The normalized transmittivity of the probe light against input pump power is plotted in Fig. 4. A theoretical fitting of Eq. 1 is also depicted. The results show that with the launched pump power of around 125 mW π phase shift between the pump and the probe light is obtained and the characteristics is consistent with the theoretical fitting. The pump power required for 100% probe light transmission can be expressed as [13

13. G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (New York: Academic, 210–216, 2001).

]:

P=λAeff2n2L
(2)

where Aeff is the effective core area, n2 is the Kerr coefficient, and L is the fiber length. With the launched pump power of around 125 mW and fiber length of 5 cm, by Eq. 2 the estimated nonlinear coefficient of our sample can be as high as 5.02×105 W-1km-1, which is attractive for numerous nonlinear applications. Note that this estimation is concerning the effective nonlinear coefficient of the fabricated fiber device instead of the nonlinear coefficient of the deposited CNTs only. It is worth noting that four-wave mixing effect is also observed in another experiment using the same piece of CNT-deposited D-shaped fiber, which indicates that phase matching between the pump and the probe light is able to obtain. From Eq. 2, it is suggested that adopting a smaller core fiber such as dispersion-shifted fiber or dispersion compensating fiber for fabricating the D-shaped fiber can in principle decrease the required pump power. However, it is a trade off concerning the mechanical difficulties of precise polishing of the D-shaped fiber.

Fig. 5. Optical spectra obtained (a) after the CNT-deposited D-shaped fiber and the polarizer with 10 Gb/s NRZ input signal; and corresponding close up of (b) input signal and (c) converted signal.
Fig. 6. Plot of bit-error rate against received optical power. Inset (upper) and (lower) show the 10 Gb/s eye-diagrams of input and converted signal, respectively.

Fig. 7. Plot of extinction ratio and power penalty at 10-9 BER level against different converted wavelength.

Figure 7 further plots the output extinction ratio between on and off state against different converted wavelength with the input signal fixed at 1555.0 nm. Note that the conversion range has covered all the C-band over 40 nm while maintaining over 14 dB extinction ratio. The Fig. also depicts the power penalty at 10-9 BER level against different converted wavelength in the 10 Gb/s BER measurements. It is observed that the power penalty is kept at around 2.5 dB for the whole tuning range with less than 1 dB variation. Note that the large increase of the power penalty approaching the shorter wavelength side is originated from the converted wavelength being outside the gain bandwidth of the EDFA for BER measurements. The wavelength tuning range is actually limited by the performance of the ECL adopted in the experiment and it is expected that wider conversion range with similar BER performance can be obtained with suitable tunable laser source.

4. Conclusion

A widely tunable wavelength converter has been experimentally demonstrated using cross-phase modulation induced nonlinear polarization rotation in a carbon nanotubes deposited D-shaped fiber. The converted signal has over 14 dB extinction ratio all over C-band. Also, a power penalty of 2.5 dB with less than 1 dB variation for the whole tuning range is measured in the 10 Gb/s BER measurements. It is expected if the polishing of the D-shaped fiber can be further improved, lower power penalty can be obtained. Owing to the ultra-fast response properties of the CNTs, future work on high repetition rate RZ signal pulse processing is also expected. The results show that such compact fiber device with a length of 5 cm is promising for wavelength conversion applications in all-optical networks and other nonlinear applications.

Acknowledgment

This work was supported by Strategic Information and Communications R&D Promotion Programme (SCOPE) of The Ministry of Internal Affairs and Communications (MIC).

References and links

1.

S. Iijima and T. Ichihashi, “Single shell carbon nanotubes of one nanometer diameter,” Nature 363, 603–605 (1993). [CrossRef]

2.

A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petit, J. Robert, C. Xu, Y. H. Lee, S. G. Kim, D. T. Colbert, G. Scuseria, D. Tománek, J. E. Fischer, and R. E. Smalley, “Crystalline ropes of metallic carbon nanotubes,” Science 273, 483–487 (1996). [CrossRef] [PubMed]

3.

Ph. Avouris, M. Freitag, and V. Perebeinos, “Carbon Nanotube Optics and Optoelectronics,” Nat. Phton. 2, 341–350 (2008). [CrossRef]

4.

S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, “Ultrafast fiber pulsed lasers incorporating carbon nanotubes,” IEEE J Select. Top. Quantum Electron. 10, 137–146 (2004). [CrossRef]

5.

S. Yamashita, Y. Inoue, S. Maruyama, Y. Murakami, H. Yaguchi, M. Jablonski, and S. Y. Set, “Saturable absorbers incorporating carbon nanotubes directly synthesized onto substrates/fibers and their applications to mode-locked fiber lasers,” Opt. Lett. 29, 1581–1583 (2004). [CrossRef] [PubMed]

6.

Y. C. Chen, N. R. Raravikar, L. S. Schadler, P. M. Ajayan, Y. P. Zhao, T. M. Lu, G. C. Wang, and X. C. Zhang, “Ultrafast optical switching properties of single-walled carbon nanotube polymer composites at 1.55 μm,” App. Phys. Lett. 81, 975–977 (2002). [CrossRef]

7.

S. Tatsuura, M. Furuki, Y. Sato, I. Iwasa, M. Tian, and H. Mitsu, “Semiconductor carbon nanotubes as ultrafast switching materials for optical telecommunications,” Adv. Mater. 15, 534–537 (2003). [CrossRef]

8.

S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, “A noise suppressing satiable absorber at 1550 nm based on carbon nanotube technology,” in Proc. OFC 2003, paper FL2, Atlanta, GA, USA (2003).

9.

Vl. A. Margulis, E. A. Gaiduk, and E. N. Zhidkin, “Third-order optical nonlinearity of semiconductor carbon nanotubes: third harmonic generation,” Diamond Relat. Mater. 8, 1240–1245 (1999). [CrossRef]

10.

Y. W. Song, S. Y. Set, and S. Yamashita, “Novel Kerr shutter using carbon nanotubes deposited onto a 5-cm D-shaped fiber,” in Proc. CLEO 2006, paper CMA4, Long Beach, CA, USA (2006).

11.

K. Kashiwagi, S. Yamashita, H. Yaguchi, C. S. Goh, and S. Y. Set, “All optical switching using carbon nanotubes loaded planar waveguide,” in Proc. CLEO 2006, paper CMA5, Long Beach, CA, USA (2006).

12.

S. J. B. Yoo, “Wavelength conversion technologies for WDM network applications,” J. Lightwave Technol. 14, 955–966 (1996). [CrossRef]

13.

G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (New York: Academic, 210–216, 2001).

OCIS Codes
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers
(070.4340) Fourier optics and signal processing : Nonlinear optical signal processing

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: January 22, 2009
Revised Manuscript: April 22, 2009
Manuscript Accepted: April 23, 2009
Published: April 24, 2009

Citation
K. K. Chow, S. Yamashita, and Y. W. Song, "A widely tunable wavelength converter based on nonlinear polarization rotation in a carbon-nanotube-deposited D-shaped fiber," Opt. Express 17, 7664-7669 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-9-7664


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. S. Iijima and T. Ichihashi, "Single shell carbon nanotubes of one nanometer diameter," Nature 363, 603-605 (1993). [CrossRef]
  2. A. Thess, R. Lee, P. Nikolaev, H. Dai, P. Petit, J. Robert, C. Xu,Y. H. Lee, S. G. Kim, D. T. Colbert, G. Scuseria, D. Tománek, J. E. Fischer, and R. E. Smalley, "Crystalline ropes of metallic carbon nanotubes," Science 273, 483-487 (1996). [CrossRef] [PubMed]
  3. Ph. Avouris, M. Freitag, and V. Perebeinos, "Carbon Nanotube Optics and Optoelectronics," Nat. Phton. 2, 341-350 (2008). [CrossRef]
  4. S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, "Ultrafast fiber pulsed lasers incorporating carbon nanotubes," IEEE J Select.Top. Quantum Electron. 10, 137-146 (2004). [CrossRef]
  5. S. Yamashita, Y. Inoue, S. Maruyama, Y. Murakami, H. Yaguchi, M. Jablonski, and S. Y. Set, "Saturable absorbers incorporating carbon nanotubes directly synthesized onto substrates/fibers and their applications to mode-locked fiber lasers," Opt. Lett. 29, 1581-1583 (2004). [CrossRef] [PubMed]
  6. Y. C. Chen, N. R. Raravikar, L. S. Schadler, P. M. Ajayan, Y. P. Zhao, T. M. Lu, G. C. Wang, and X. C. Zhang, "Ultrafast optical switching properties of single-walled carbon nanotube polymer composites at 1.55 ?m," App. Phys. Lett. 81, 975-977 (2002). [CrossRef]
  7. S. Tatsuura, M. Furuki, Y. Sato, I. Iwasa, M. Tian, and H. Mitsu, "Semiconductor carbon nanotubes as ultrafast switching materials for optical telecommunications," Adv. Mater. 15, 534-537 (2003). [CrossRef]
  8. S. Y. Set, H. Yaguchi, Y. Tanaka, and M. Jablonski, "A noise suppressing satiable absorber at 1550 nm based on carbon nanotube technology," in Proc. OFC 2003, paper FL2, Atlanta, GA, USA (2003).
  9. Q3Q4. Vl. A. Margulis, E. A. Gaiduk, and E. N. Zhidkin, "Third-order optical nonlinearity of semiconductor carbon nanotubes: third harmonic generation," Diamond Relat. Mater. 8, 1240-1245 (1999). [CrossRef]
  10. Y. W. Song, S. Y. Set, and S. Yamashita, "Novel Kerr shutter using carbon nanotubes deposited onto a 5-cm D-shaped fiber," in Proc. CLEO 2006, paper CMA4, Long Beach, CA, USA (2006).
  11. K. Kashiwagi, S. Yamashita, H. Yaguchi, C. S. Goh, and S. Y. Set, "All optical switching using carbon nanotubes loaded planar waveguide," in Proc. CLEO 2006, paper CMA5, Long Beach, CA, USA (2006).
  12. S. J. B. Yoo, "Wavelength conversion technologies for WDM network applications," J. Lightwave Technol. 14, 955-966 (1996). [CrossRef]
  13. G. P. Agrawal, Nonlinear Fiber Optics, 3rd ed. (New York: Academic, 210-216, 2001).

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited