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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 20 — Sep. 26, 2011
  • pp: 19078–19083
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All-optical modulation using two-photon absorption in silicon core optical fibers

P. Mehta, N. Healy, T. D. Day, J. R. Sparks, P. J. A. Sazio, J. V. Badding, and A. C. Peacock  »View Author Affiliations


Optics Express, Vol. 19, Issue 20, pp. 19078-19083 (2011)
http://dx.doi.org/10.1364/OE.19.019078


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Abstract

All-optical modulation based on degenerate and non-degenerate two-photon absorption (TPA) is demonstrated within a hydrogenated amorphous silicon core optical fiber. The nonlinear absorption strength is determined by comparing the results of pump-probe experiments with numerical simulations of the coupled propagation equations. Subpicosecond modulation is achieved with an extinction ratio of more than 4dB at telecommunications wavelengths, indicating the potential for these fibers to find use in high speed signal processing applications.

© 2011 OSA

1. Introduction

Hydrogenated amorphous silicon (a-Si:H) is emerging as an increasingly promising material for photonics applications as it offers simple and flexible fabrication and possesses a large optical nonlinearity [1

1. K. Narayanan and S. F. Preble, “Optical nonlinearities in hydrogenated amorphous silicon waveguides,” Opt. Express 18, 8998–9005 (2010). [CrossRef] [PubMed]

]. To date, a number of important photonic functions have been demonstrated in a-Si:H waveguides on-chip including all-optical modulation [2

2. Y. Shoji, T. Ogasawara, T. Kamei, Y. Sakakibara, S. Suda, K. Kintaka, H. Kawashima, M. Okano, T Hasama, H Ishikawa, and M. Mori, “Ultrafast nonlinear effects in hydrogenated amorphous silicon wire waveguide,” Opt. Express 18, 5668–5673 (2010). [CrossRef] [PubMed]

, 3

3. K. Narayanan, A. W. Elshaari, and S. F. Preble, “Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides,” Opt. Express 18, 9809–9814 (2010). [CrossRef] [PubMed]

], photon pair generation [4

4. S. Clemmen, A. Perret, S. K. Selvaraja, W. Bogaerts, D. van Thourhout, R. Baets, P. Emplit, and S. Massar, “Generation of correlated photons in hydrogenated amorphous-silicon waveguides,” Opt. Lett. 35, 3483–3485 (2010). [CrossRef] [PubMed]

], and parametric amplification [5

5. B. Kuyken, S. Clemmen, S. K. Selvaraja, W. Bogaerts, D. van Thourhout, P. Emplit, S. Massar, G. Roelkens, and R. Baets, “On-chip parametric amplification with 26.5 dB gain at telecommunications wavelengths using CMOS-compatible hydrogenated amorphous silicon waveguides,” Opt. Lett. 36, 552–554 (2011). [CrossRef] [PubMed]

]. The ability to incorporate silicon materials into the optical fiber geometry not only provides a route towards integrating such devices within existing fiber networks [6

6. L. Lagonigro, N. Healy, J. R. Sparks, N. F. Baril, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Low loss silicon fibers for photonics applications,” Appl. Phys. Lett. 96, 041105 (2010). [CrossRef]

, 7

7. J. Ballato, T. Hawkins, P. Foy, R. Stolen, B. Kokuoz, M. Ellison, C. McMillen, J. Reppert, A. M. Rao, M. Daw, S. Sharma, R. Shori, O. Stafsudd, R. R. Rice, and D. R. Powers, “Silicon optical fiber,” Opt. Express 16, 18675–18683 (2008). [CrossRef]

], but also opens up the potential for the waveguiding properties of the devices to be manipulated in ways not possible on-chip [8

8. N. Healy, J. R. Sparks, M. N. Petrovich, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Large mode area silicon microstructured fiber with robust dual mode guidance,” Opt. Express 17, 18076–18082 (2009). [CrossRef] [PubMed]

, 9

9. N. Healy, J. R. Sparks, R. He, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “High index contrast semiconductor ARROW and hybrid ARROW fibers,” Opt. Express 19, 10979–10985 (2011). [CrossRef] [PubMed]

]. As such, a-Si:H core fibers can be expected to offer new capabilities in future generations of semiconductor photonic devices.

2. Theory

Since we are primarily concerned with the temporal characteristics induced on the probe via the XAM process, it is convenient to use a simplified pulse propagation model that accounts for the rate of change in the carrier density but neglects the effects of spectral modulation. Under these conditions, the coupled equations for the input fields and the carrier density are [13

13. J. Y. Lee, L. H. Yin, G. P. Agrawal, and P. M. Fauchet, “Ultrafast optical switching based on nonlinear polarization rotation in silicon waveguides,” Opt. Express 18, 11514–11523 (2010). [CrossRef] [PubMed]

]:
A2(t,z)z=αl,22A2(t,z)12σFCAN(t,z)A2(t,z)βTPAI1(t,z)A2(t,z),
(1a)
I1(t,z)z=αl,1I1(t,z)σFCAN(t,z)I1(t,z)βTPAI12(t,z),
(1b)
N(t,z)t=βTPA2hν1I12(t,z)N(t,z)τ.
(1c)
Equation (1a) describes the propagation of a weak probe field amplitude A 2(t, z), where αl ,2 is the linear transmission loss at the probe wavelength, σ FCA is the FCA coefficient, N(t, z) is the free-carrier density, βTPA is the non-degenerate TPA coefficient, and I 1(t, z) is the intensity profile of the pump. The evolution of the pump is described by Eq. (1b) where αl ,1 is the linear transmission loss at the pump wavelength and β TPA is the degenerate TPA coefficient. In these equations we have assumed that the probe is so weak that it does not induce any nonlinear effects and that the value of σ FCA is constant for the closely spaced wavelengths of the pump and probe. Finally, the time varying TPA-induced free-carrier density N(t, z) is determined by the rate equation Eq. (1c) where h is Planck’s constant, ν 1 is the pump frequency, and τ is the carrier lifetime. We solve this set of equations for two different scenarios as investigated experimentally in the following section. The first assumes a strong pump and weak probe, both of which are at λ 1 ∼ 1540nm so that βTPA = β TPA, i.e., a degenerate TPA process with β TPA the only free parameter. The second scenario involves a pump at λ 1 ∼ 1540nm and weak probe signal at λ 2 ∼ 1570nm, where βTPA is now the free parameter.

3. Experiment and Characterization

Fig. 1 (a) Degenerate TPA experiment. AC Autocorrelator, PD Photodiode, LA Lock-in amplifier, FD Frequency driver. (b) Measured degenerate absorption (blue crosses) together with the simulated fit (black line).

To investigate non-degenerate TPA, the experimental setup was modified to generate a weak probe at a wavelength shifted from the pump as shown in Fig. 2(a). Here the pulses that propagate through the highly nonlinear fiber (HNLF) experience strong spectral broadening and the output is filtered by a bandwidth variable tunable filter (BVF) to select the desired wavelength. A minimum probe pulse width of 1ps is achieved by maximizing the bandwidth of the filter centered at 1570nm. After propagation through the a-Si:H fiber the pump and probe were separated using a blazed diffraction grating and a pinhole was positioned to isolate the 1570nm probe. The non-degenerate absorption curves are plotted in Fig. 2(b) for three different pump powers, as labeled in the legend. We obtain a good fit for all the selected powers with βTPA ∼ 0.49cm/GW at 1570nm. This estimated value is slightly lower than that obtained for the degenerate TPA parameter due to the lower photon energy of the probe, as predicted by the two-parabolic band model [17

17. M. Sheik-Bahae, J. Wang, and E. W. Van Stryland, “Non-degenerate optical Kerr effect in semiconductors,” IEEE J. Quantum Electron. 30, 249–255 (1994). [CrossRef]

]. Again, from the levels of the depressed floors we can estimate the carrier densities as N ∼ 1.1 × 1021 m−3, 0.7 × 1021 m−3, and 0.4 × 1021 m−3, for the highest to lowest pump powers, respectively. Compared to the degenerate experiment, there is almost twice the number of carriers generated in the non-degenerate case for the 250W pump, whilst a similar number are generated for the lower pump powers. We also note that for the higher pump powers, an elongated carrier relaxation feature can be seen that is not reproduced by the simulations. At this stage the precise cause of this elongation is not known, though it could be due in part to the difference in the pump-probe pulse widths and/or the generated carrier densities, and further investigations are currently ongoing. The modulated absorption width is estimated to be ∼ 1.1ps, indicating only a minor temporal broadening relative to the incident probe pulse, and the measured extinction ratio for a pump peak power of 250W is ∼ 3.5dB. This observed reduction in the extinction ratio, relative to the degenerate experiment, can be primarily attributed to the lower value of the non-degenerate TPA parameter. Thus, as βTPA is predicted to increase for a decreasing probe wavelength [17

17. M. Sheik-Bahae, J. Wang, and E. W. Van Stryland, “Non-degenerate optical Kerr effect in semiconductors,” IEEE J. Quantum Electron. 30, 249–255 (1994). [CrossRef]

], we expect that larger modulation depths could be obtained by simply using a shorter probe wavelength. By measuring the band edge of our a-Si:H material it should be possible to obtain an accurate estimate for the TPA cutoff, allowing for the extinction ratio to be optimized.

Fig. 2 (a) Non-degenerate TPA experiment. HNLF Highly nonlinear fiber, BVF Bandwidth variable tunable filter. (b) Measured non-degenerate absorption (crosses) as a function of pump power together with the simulated fits (solid lines).

Fig. 3 Non-degenerate TPA experiment for a CW probe.
Fig. 4 (a) Impulse response of pump pulse and modulated probe. (b) Carrier relaxation where the fitted (red) curve reveals τ ∼ 87ns.

4. Conclusion

Acknowledgments

The authors acknowledge EPSRC ( EP/G051755/1 and EP/G028273/1), NSF ( DMR-0806860) and the Penn State Materials Research Science and Engineering Center ( NSF DMR-0820404) for financial support. A. C. Peacock holds a Royal Academy of Engineering fellowship.

References and links

1.

K. Narayanan and S. F. Preble, “Optical nonlinearities in hydrogenated amorphous silicon waveguides,” Opt. Express 18, 8998–9005 (2010). [CrossRef] [PubMed]

2.

Y. Shoji, T. Ogasawara, T. Kamei, Y. Sakakibara, S. Suda, K. Kintaka, H. Kawashima, M. Okano, T Hasama, H Ishikawa, and M. Mori, “Ultrafast nonlinear effects in hydrogenated amorphous silicon wire waveguide,” Opt. Express 18, 5668–5673 (2010). [CrossRef] [PubMed]

3.

K. Narayanan, A. W. Elshaari, and S. F. Preble, “Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides,” Opt. Express 18, 9809–9814 (2010). [CrossRef] [PubMed]

4.

S. Clemmen, A. Perret, S. K. Selvaraja, W. Bogaerts, D. van Thourhout, R. Baets, P. Emplit, and S. Massar, “Generation of correlated photons in hydrogenated amorphous-silicon waveguides,” Opt. Lett. 35, 3483–3485 (2010). [CrossRef] [PubMed]

5.

B. Kuyken, S. Clemmen, S. K. Selvaraja, W. Bogaerts, D. van Thourhout, P. Emplit, S. Massar, G. Roelkens, and R. Baets, “On-chip parametric amplification with 26.5 dB gain at telecommunications wavelengths using CMOS-compatible hydrogenated amorphous silicon waveguides,” Opt. Lett. 36, 552–554 (2011). [CrossRef] [PubMed]

6.

L. Lagonigro, N. Healy, J. R. Sparks, N. F. Baril, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Low loss silicon fibers for photonics applications,” Appl. Phys. Lett. 96, 041105 (2010). [CrossRef]

7.

J. Ballato, T. Hawkins, P. Foy, R. Stolen, B. Kokuoz, M. Ellison, C. McMillen, J. Reppert, A. M. Rao, M. Daw, S. Sharma, R. Shori, O. Stafsudd, R. R. Rice, and D. R. Powers, “Silicon optical fiber,” Opt. Express 16, 18675–18683 (2008). [CrossRef]

8.

N. Healy, J. R. Sparks, M. N. Petrovich, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Large mode area silicon microstructured fiber with robust dual mode guidance,” Opt. Express 17, 18076–18082 (2009). [CrossRef] [PubMed]

9.

N. Healy, J. R. Sparks, R. He, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “High index contrast semiconductor ARROW and hybrid ARROW fibers,” Opt. Express 19, 10979–10985 (2011). [CrossRef] [PubMed]

10.

D. J. Won, M. O. Ramirez, H. Kang, V. Gopalan, N. F. Baril, J. Calkins, J. V. Badding, and P. J. A. Sazio, “All-optical modulation of laser light in amorphous silicon-filled microstructured optical fibers,” Appl. Phys. Lett. 91, 161112 (2007). [CrossRef]

11.

T. Liang, L. Nunes, T. Sakamoto, K. Sasagawa, T. Kawanishi, M. Tsuchiya, G. Priem, D. Van Thourhout, P. Dumon, R. Baets, and H. Tsang, “Ultrafast all-optical switching by cross-absorption modulation in silicon wire waveguides,” Opt. Express 13, 7298–7303 (2005). [CrossRef] [PubMed]

12.

P. Mehta, N. Healy, N. F. Baril, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Nonlinear transmission properties of hydrogenated amorphous silicon core optical fibers,” Opt. Express 18, 16826–16831 (2010). [CrossRef] [PubMed]

13.

J. Y. Lee, L. H. Yin, G. P. Agrawal, and P. M. Fauchet, “Ultrafast optical switching based on nonlinear polarization rotation in silicon waveguides,” Opt. Express 18, 11514–11523 (2010). [CrossRef] [PubMed]

14.

R. Dekker, A. Driessen, T. Wahlbrink, C. Moormann, J. Niehusmann, and M. Först, “Ultrafast Kerr-induced all-optical wavelength conversion in silicon waveguides using 1.55 μm femtosecond pulses,” Opt. Express 14, 8336–8346 (2006). [CrossRef] [PubMed]

15.

P. Mehta, N. Healy, R. Slavík, R. T. Watts, J. R. Sparks, T. D. Day, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Nonlinearities in silicon optical fibers,” in Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2011), paper OThS3.

16.

N. Minamikawa and K. Tanaka, “Nonlinear optical properties of hydrogenated amorphous Si films probed by a novel z-scan technique,” Jpn. J. Appl. Phys. 45, L960–L962 (2006). [CrossRef]

17.

M. Sheik-Bahae, J. Wang, and E. W. Van Stryland, “Non-degenerate optical Kerr effect in semiconductors,” IEEE J. Quantum Electron. 30, 249–255 (1994). [CrossRef]

OCIS Codes
(060.2290) Fiber optics and optical communications : Fiber materials
(160.6000) Materials : Semiconductor materials
(190.4370) Nonlinear optics : Nonlinear optics, fibers

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: June 30, 2011
Revised Manuscript: July 26, 2011
Manuscript Accepted: July 26, 2011
Published: September 15, 2011

Citation
P. Mehta, N. Healy, T. D. Day, J. R. Sparks, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, "All-optical modulation using two-photon absorption in silicon core optical fibers," Opt. Express 19, 19078-19083 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-20-19078


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References

  1. K. Narayanan and S. F. Preble, “Optical nonlinearities in hydrogenated amorphous silicon waveguides,” Opt. Express 18, 8998–9005 (2010). [CrossRef] [PubMed]
  2. Y. Shoji, T. Ogasawara, T. Kamei, Y. Sakakibara, S. Suda, K. Kintaka, H. Kawashima, M. Okano, T Hasama, H Ishikawa, and M. Mori, “Ultrafast nonlinear effects in hydrogenated amorphous silicon wire waveguide,” Opt. Express 18, 5668–5673 (2010). [CrossRef] [PubMed]
  3. K. Narayanan, A. W. Elshaari, and S. F. Preble, “Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides,” Opt. Express 18, 9809–9814 (2010). [CrossRef] [PubMed]
  4. S. Clemmen, A. Perret, S. K. Selvaraja, W. Bogaerts, D. van Thourhout, R. Baets, P. Emplit, and S. Massar, “Generation of correlated photons in hydrogenated amorphous-silicon waveguides,” Opt. Lett. 35, 3483–3485 (2010). [CrossRef] [PubMed]
  5. B. Kuyken, S. Clemmen, S. K. Selvaraja, W. Bogaerts, D. van Thourhout, P. Emplit, S. Massar, G. Roelkens, and R. Baets, “On-chip parametric amplification with 26.5 dB gain at telecommunications wavelengths using CMOS-compatible hydrogenated amorphous silicon waveguides,” Opt. Lett. 36, 552–554 (2011). [CrossRef] [PubMed]
  6. L. Lagonigro, N. Healy, J. R. Sparks, N. F. Baril, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Low loss silicon fibers for photonics applications,” Appl. Phys. Lett. 96, 041105 (2010). [CrossRef]
  7. J. Ballato, T. Hawkins, P. Foy, R. Stolen, B. Kokuoz, M. Ellison, C. McMillen, J. Reppert, A. M. Rao, M. Daw, S. Sharma, R. Shori, O. Stafsudd, R. R. Rice, and D. R. Powers, “Silicon optical fiber,” Opt. Express 16, 18675–18683 (2008). [CrossRef]
  8. N. Healy, J. R. Sparks, M. N. Petrovich, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Large mode area silicon microstructured fiber with robust dual mode guidance,” Opt. Express 17, 18076–18082 (2009). [CrossRef] [PubMed]
  9. N. Healy, J. R. Sparks, R. He, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “High index contrast semiconductor ARROW and hybrid ARROW fibers,” Opt. Express 19, 10979–10985 (2011). [CrossRef] [PubMed]
  10. D. J. Won, M. O. Ramirez, H. Kang, V. Gopalan, N. F. Baril, J. Calkins, J. V. Badding, and P. J. A. Sazio, “All-optical modulation of laser light in amorphous silicon-filled microstructured optical fibers,” Appl. Phys. Lett. 91, 161112 (2007). [CrossRef]
  11. T. Liang, L. Nunes, T. Sakamoto, K. Sasagawa, T. Kawanishi, M. Tsuchiya, G. Priem, D. Van Thourhout, P. Dumon, R. Baets, and H. Tsang, “Ultrafast all-optical switching by cross-absorption modulation in silicon wire waveguides,” Opt. Express 13, 7298–7303 (2005). [CrossRef] [PubMed]
  12. P. Mehta, N. Healy, N. F. Baril, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Nonlinear transmission properties of hydrogenated amorphous silicon core optical fibers,” Opt. Express 18, 16826–16831 (2010). [CrossRef] [PubMed]
  13. J. Y. Lee, L. H. Yin, G. P. Agrawal, and P. M. Fauchet, “Ultrafast optical switching based on nonlinear polarization rotation in silicon waveguides,” Opt. Express 18, 11514–11523 (2010). [CrossRef] [PubMed]
  14. R. Dekker, A. Driessen, T. Wahlbrink, C. Moormann, J. Niehusmann, and M. Först, “Ultrafast Kerr-induced all-optical wavelength conversion in silicon waveguides using 1.55 μm femtosecond pulses,” Opt. Express 14, 8336–8346 (2006). [CrossRef] [PubMed]
  15. P. Mehta, N. Healy, R. Slavík, R. T. Watts, J. R. Sparks, T. D. Day, P. J. A. Sazio, J. V. Badding, and A. C. Peacock, “Nonlinearities in silicon optical fibers,” in Optical Fiber Communication Conference , OSA Technical Digest (CD) (Optical Society of America, 2011), paper OThS3.
  16. N. Minamikawa and K. Tanaka, “Nonlinear optical properties of hydrogenated amorphous Si films probed by a novel z-scan technique,” Jpn. J. Appl. Phys. 45, L960–L962 (2006). [CrossRef]
  17. M. Sheik-Bahae, J. Wang, and E. W. Van Stryland, “Non-degenerate optical Kerr effect in semiconductors,” IEEE J. Quantum Electron. 30, 249–255 (1994). [CrossRef]

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