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Optics Express

Optics Express

  • Vol. 16, Iss. 16 — Aug. 4, 2008
  • pp: 12084–12089
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Ultra high quality factor one dimensional photonic crystal/photonic wire micro-cavities in silicon-on-insulator (SOI)

Ahmad Rifqi Md Zain, Nigel P. Johnson, Marc Sorel, and Richard M. De La Rue  »View Author Affiliations


Optics Express, Vol. 16, Issue 16, pp. 12084-12089 (2008)
http://dx.doi.org/10.1364/OE.16.012084


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Abstract

We present experimental results on photonic crystal/photonic wire micro-cavity structures that demonstrate further enhancement of the quality-factor (Q-factor) - up to approximately 149,000 - in the fibre telecommunications wavelength range. The Q-values and the useful transmission levels achieved are due, in particular, to the combination of both tapering within and outside the micro-cavity, with carefully designed hole diameters and non-periodic hole placement within the tapered section. Our 2D Finite Difference Time Domain (FDTD) simulation approach shows good agreement with the experimental results.

© 2008 Optical Society of America

1. Introduction

In this report, we demonstrate the enhancement of the Quality factor value through the combination of tapering within the cavity and also outside the cavity. For specific cavity design parameters, we have then demonstrated that a usefully large optical transmission level can be obtained. In one case, we have made a comparison of using different numbers of holes in the tapered sections on the outsides of the cavity. The Q- factor value, and the transmission level have also been estimated using a 2D FDTD computational approach.

2. Design optimizations and 2D FDTD approach

We have realized planar 1D PhC/PhW micro-cavity structures consisting of a single row of PhC holes embedded in 500 nm wide photonic wire waveguides based on SOI The waveguides were formed in a 260 nm thick silicon core layer supported by a 1μm-thick silica buffer layer that provided adequate optical isolation of the waveguide core from the silicon substrate. These devices were designed for TE polarization. In order to obtain the required high performance in this device, the correct choice of cavity length, the hole diameters and the combination of periodic and aperiodic hole spacing is necessary.

Fig. 1. Scanning electron micrograph (SEM) image of the tapered PhC micro cavities embedded in PhW waveguide with N number of periodic mirrors, cavity length, c (inside length of the two hole in the middle of the periodic mirrors) and aperiodic mirrors forming the tapered section where NTI is the number of hole for tapered within cavity section and NTO is the number of hole outside the cavity.

Tapering within and outside the cavity through the use of holes of different diameters and aperiodic spacing has been used to enhance the Q-factor, while simultaneously maintaining a useful optical transmission level – i.e. the tapered period and hole diameter transition sections, both outside and within the cavity, were designed to maximize the transmission for light entering or leaving the periodic mirror sections. Tapering outside cavity has an impact primarily to increase the optical transmission.

Fig. 2. Transmission spectra for N = 5 with NTI = 4 and NTO= 3 using 2D FDTD approach with Q of approximately 177 000 at resonance frequency of 1483.54 nm at cavity length, c of 425 nm.

3. Fabrication and optical characterization of the micro cavities

The waveguide patterns were defined using an approximately 200 nm thick layer of hydrogen silsesquioxane (HSQ) negative-tone resist. The devices were fabricated using single-step direct-write electron beam lithography in a Vistec VB6 machine at 100 keV electron energy, with proximity correction at a base dose of 1500 μC/cm2. This VB6 beam writer has the capability of writing a 1.2 mm by 1.2 mm field at 1.25 nm resolution. In addition, extra care has to be taken to reduce the potentially significant impact of field stitching errors on the pattern produced - i.e. to ensure the flatness of the sample during the writing process. The patterns were finally transferred into the silicon guiding layer by using an inductively coupled plasma (ICP) reactive ion etching process. SF6/C4F8 combined chemistry was used to etch the silicon layer, contributing to obtain silicon waveguides with smooth side-walls. The devices were characterized using a tunable laser that was capable of covering the wavelength range from 1.45 μm to 1.58 μm with the spectral resolution of 1 pm measurement step.

Fig. 3. Transmission spectra for N = 4 and NTI = 4 with (a) NTO=1 (b) NTO=2 (c) NTO=3 – with a cavity length, c = 450 nm.

TE polarized light was end-fire coupled into and out of the device waveguide - and the optical signal was detected using a germanium photodiode. The experimental results were normalized with respect to an identical, but unstructured, 500 nm wide wire waveguide without any holes embedded in it. Figure 3 shows measured results for N=4, NTI=4 with a different number of holes used in the tapered section outside the cavity. NTO varies from one to three while retaining a cavity spacer length, c, of 450 nm. The measured Q-factor values were 8000, 21500 and 19000 respectively, with normalized transmission values of 73%, 83% and 65% respectively. It shows that for N=4, the highest Q factor achieved was obtained with NTO=2.

Fig. 4. Measured transmission spectra for N = 5 with NTI = 4 and NTO= 3 corresponded to simulation result in Fig. 2 with Q of approximately 147 000 at resonance frequency of 1479.705 nm.

Further enhancement of the Q-factor value has been obtained through the use of N=5, together with three hole aperiodic tapering outside the cavity and NTO as shown in Fig. 1. Figure 4 shows the measured transmission spectrum of the device with a cavity length of 425 nm - corresponding to the simulation result in Fig. 2, with NTO = 3. The estimated experimental quality factor value of ∼147 000 was at the resonance wavelength of 1479.705 nm, with full width half maximum (FWHM) of ∼ 0.01 nm- see inset in Fig. 4(b). A normalized transmission of approximately 34% has been measured for this particular resonance. The effect of Fapy-Perot (FP) ripple in Fig. 4(b) is clearly small.

Table 1. Comparison of Simulated and Experimental value of different taper outside cavity, NTO for N=5 and NTI=4

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4. Conclusions and discussions

We have successfully demonstrated substantial further enhancement of the quality factor value achieved in one dimensional PhC/PhW micro-cavities based on silicon-on-insulator. A high Q-factor value (approaching 147 000), together with a useful transmission level of 34%, has been measured at a cavity spacer length of 425 nm. It should be noted that this performance has been obtained in structures with a supporting lower cladding. Further device enhancement is possible through more attention to the design of the tapered sections, together with the use of a larger number of holes in the periodic parts of the cavity mirrors. This combination will contribute increases in both the Q-factor and the transmission coefficient.

Acknowledgements

The authors would like to acknowledge financial support through the ePIXnet European Community project and Universiti Teknologi Malaysia (UTM) Skudai, Johor, Malaysia.

References and links

1.

Ahmad RU, Pizzuto F, Camarda GS, Espinola RL, Rao H, and Osgood RM, ‘Ultra compact corner-mirrors and T branches in silicon-on- insulator,’ IEEE Photon. Technol. Lett. 14, no 1, January, 2002.

2.

Ohno F., T. Fukuzawa, and T. Baba,‘Mach-Zehnder Interferometers Composed of μ-Bends and μ-Branches in a Si Photonic Wire Waveguide,’ Jpn.J.Appl.Phys. 44, No. 7A, 2005, pp. 5322–5323. [CrossRef]

3.

Richard De La Rue, Harold Chong, Marco Gnan, Nigel Johnson, Iraklis Ntakis, Pierre Pottier, Marc Sorel, Ahmad Md Zain, Hua Zhang, Edilson Camargo, Chongjun Jin, Mario Armenise, and Caterina Ciminell ‘Photonic crystal and photonic wire nano-photonics based on silicon-on-insulator,’ New J. Phys , 8, (2006) 256. [CrossRef]

4.

E. A. Camargo, H. M. H. Chong, and R. M. De La Rue, ‘Highly compact asymmetric Mach-Zehnder device based on channel guides in a two-dimensional photonic crystal,’ Appl. Opt. , 45, pp. 6507–6510, 1st Sept (2006). [CrossRef] [PubMed]

5.

E.A. Camargo, H.M.H. Chong, and R.M. De La Rue, ‘Four-port coupled channel-guide device based on 2D photonic crystal structure,’ Photonics and Nanostructures - Fundamentals and Applications, 2 (3), pp 207–213, December (2004).

6.

Hua Zhang, M. Gnan, N.P. Johnson, and R.M. De La Rue, ‘Ultra-Small Mach-Zehnder Interferometer Devices in Thin Silicon-on-Insulator,’ Integrated Photonics Research and Applications (IPRA), Uncasville, Conn., USA, April (2006).

7.

H. M. H. Chong and R. M. De La Rue, ‘Tuning of photonic crystal waveguide microcavity by thermooptic effect,’ IEEE Photon. Technol. Lett. , 16, no. 6, pp. 1528–1530, Jun. 2004. [CrossRef]

8.

M. W. Geis, S. J. Spector, R. C. Williamson, and T. M. Lyszczarz, ‘Submicrosecond submilliwatt siliconon- insulator thermooptic switch,’ IEEE Photon. Technol. Lett. , 16, no. 11, pp. 2514–2516, Nov. 2003. [CrossRef]

9.

T. F. Krauss and R. M. De La Rue, ‘Photonic crystals in the optical regime—Past, present and future,’ Progress Quantum Electron. , vol.23, no. 2, pp. 51–96, Mar. 1999. [CrossRef]

10.

M. Gnan, S. Thoms, D.S. Macintyre, R.M. De La Rue, and M. Sorel, ‘Fabrication of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,’ Electron. Lett. , 44 (2), 115 – 116, 17th Jan (2008). [CrossRef]

11.

M. Gnan, D.S. Macintyre, M. Sorel, R.M. De La Rue, and S. Thoms, ‘Enhanced stitching for the fabrication of photonic structures by electron beam lithography,’ J. Vac. Sci. Technol. B, 25, pp. 2034, 2007. [CrossRef]

12.

J. S. Foresi, P. R. Villeneuve, J. Ferrera, E. R. Thoen, G. Steinmeyer, S. Fan, J. D. Joannopoulos, L. C. Kimerling, Henry I. Smith, and E. P. Ippen, ‘Photonic-bandgap microcavities in optical waveguides,’ Nature 390, 143 (1997)

13.

P. Lalanne and J. P. Hugonin, ‘Bloch-wave engineering for high-Q, small-V microcavities,’ IEEE J. Quantum Electron. , 39, no. 11, pp. 1430–1438, Nov. 2003. [CrossRef]

14.

C. Sauvan, G. Lecamp, P. Lalanne, and J. P. Hugonin, ‘Modal reflectivity enhancement by geometry tuning in photonic crystal micro-cavities,’ Opt. Express , 3, no. 1, pp. 245–255, Jan. 2005. [CrossRef]

15.

T. Asano, B.S. Song, and S. Noda,’ Analysis of the experimental Q factors (∼1 million) of photonic crystal nanocavities,’ Opt. Express 14, 1996–2002 (2006) [CrossRef] [PubMed]

16.

P. Velha, E. Picard, T. Charvolin, E. Hadji, J. C. Rodier, P. Lalanne, and D. Peyrade, ‘Ultra-High Q/V Fabry-Perot microcavity on SOI substrate,’ Opt. Express, 15 (24), 16090–16096, 26th November (2007). [CrossRef]

17.

P. Velha, J. C. Rodier, P. Lalanne, J. P. Hugonin, D. Peyrade, E. Picard, T. Charvolin, and E. Hadji, ‘Ultra high reflectivity photonic bandgap mirrors in a ridge SOI waveguide,’ New J. Phys. (IOP) , 8, no. 204, pp. 1–13, Sep. 2006.

18.

Ahmad Rifqi Md Zain, Marco Gnan, Harold M. H. Chong, Marc Sorel, and Richard M. De La Rue, ‘Tapered Photonic Crystal Microcavities Embedded in Photonic Wire Waveguides with Large Resonance Quality-Factor and High Transmission,’ IEEE Photon.Technol. Lett. 20(1), 6 – 8, 1st January (2008). [CrossRef]

19.

B.S. Song, S. Noda, T. Asano, and Y. Akahane,’Ultra-high-Q photonic double-heterostructure nanocavity,’ Nature materials 4, March 2005.

OCIS Codes
(130.0130) Integrated optics : Integrated optics
(250.5300) Optoelectronics : Photonic integrated circuits
(230.5298) Optical devices : Photonic crystals

ToC Category:
Photonic Crystals

History
Original Manuscript: May 7, 2008
Revised Manuscript: July 21, 2008
Manuscript Accepted: July 21, 2008
Published: July 28, 2008

Citation
Ahmad R. Md Zain, Nigel P. Johnson, Marc Sorel, and Richard M. De La Rue, "Ultra high quality factor one dimensional photonic crystal/photonic wire micro-cavities in silicon-on-insulator (SOI)," Opt. Express 16, 12084-12089 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-16-12084


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References

  1. R.U. Ahmad, F. Pizzuto, G. S. Camarda, R. L. Espinola, H. Rao, and R. M. Osgood, "Ultra compact corner-mirrors and T branches in silicon-on- insulator," IEEE Photon. Technol. Lett. 14,no 1, January, 2002.
  2. F. Ohno, T. Fukuzawa and T. Baba,"Mach-Zehnder Interferometers Composed of μ-Bends and μ-Branches in a Si Photonic Wire Waveguide,"Jpn.J.Appl.Phys. 44, No. 7A, 2005, pp. 5322-5323. [CrossRef]
  3. Richard De La Rue, Harold Chong, Marco Gnan, Nigel Johnson, Iraklis Ntakis, Pierre Pottier, Marc Sorel, Ahmad Md Zain, Hua Zhang, Edilson Camargo, Chongjun Jin, Mario Armenise and Caterina Ciminell �??Photonic crystal and photonic wire nano-photonics based on silicon-on-insulator,"New J. Phys,  8, (2006) 256. [CrossRef]
  4. E. A. Camargo, H. M. H. Chong, and R. M. De La Rue, "Highly compact asymmetric Mach-Zehnder device based on channel guides in a two-dimensional photonic crystal," Appl. Opt.,45, pp. 6507-6510, 1st Sept (2006). [CrossRef] [PubMed]
  5. E.A.  Camargo, H.M.H.  Chong and R.M.  De La Rue, "Four-port coupled channel-guide device based on 2D photonic crystal structure," Photonics and Nanostructures - Fundamentals andApplications, 2 (3), pp 207-213, December (2004).
  6. Hua Zhang, M.  Gnan, N.P. Johnson and R.M. De La Rue, "Ultra-Small Mach-Zehnder Interferometer Devices in Thin Silicon-on-Insulator," Integrated Photonics Research and Applications (IPRA), Uncasville, Conn., USA, April (2006).
  7. H. M. H. Chong and R. M. De La Rue, "Tuning of photonic crystal waveguide microcavity by thermooptic effect," IEEE Photon. Technol. Lett.,  16, no. 6, pp. 1528-1530, Jun. 2004. [CrossRef]
  8. M. W. Geis, S. J. Spector, R. C. Williamson, and T. M. Lyszczarz, "Submicrosecond submilliwatt silicon-on-insulator thermooptic switch," IEEE Photon. Technol. Lett., 16, no. 11, pp. 2514-2516, Nov. 2003. [CrossRef]
  9. T. F. Krauss and R. M. De La Rue, "Photonic crystals in the optical regime�??Past, present and future," Progress Quantum Electron., vol. 23, no. 2, pp. 51-96, Mar. 1999. [CrossRef]
  10. M. Gnan, S. Thoms, D.S. Macintyre, R.M. De La Rue and M. Sorel, "Fabrication of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist," Electron. Lett.,  44 (2), 115 - 116, 17th Jan (2008). [CrossRef]
  11. M. Gnan, D.S. Macintyre, M. Sorel, R.M. De La Rue, and S. Thoms, "Enhanced stitching for the fabrication of photonic structures by electron beam lithography," J. Vac. Sci. Technol. B,  25, pp. 2034, 2007. [CrossRef]
  12. J. S. Foresi, P. R. Villeneuve, J. Ferrera, E. R. Thoen, G. Steinmeyer, S. Fan, J. D. Joannopoulos, L. C. Kimerling, HenryI. Smith & E. P. Ippen, �??Photonic-bandgap microcavities in optical waveguides,"Nature 390, 143 (1997)
  13. P. Lalanne and J. P. Hugonin, "Bloch-wave engineering for high-Q, small-V microcavities," IEEE J. Quantum Electron.,  39, no. 11, pp. 1430-1438, Nov. 2003. [CrossRef]
  14. C. Sauvan, G. Lecamp, P. Lalanne, and J. P. Hugonin, "Modal reflectivity enhancement by geometry tuning in photonic crystal micro-cavities," Opt. Express,  3, no. 1, pp. 245-255, Jan. 2005. [CrossRef]
  15. T. Asano, B.S. Song, S. Noda," Analysis of the experimental Q factors (~1 million) of photonic crystal nanocavities,"Opt. Express 14, 1996-2002 (2006) [CrossRef] [PubMed]
  16. P. Velha, E. Picard, T. Charvolin, E. Hadji, J. C. Rodier, P. Lalanne and D. Peyrade, "Ultra-High Q/V Fabry-Perot microcavity on SOI substrate," Opt. Express,  15 (24), 16090-16096, 26th November (2007). [CrossRef]
  17. P. Velha, J. C. Rodier, P. Lalanne, J. P. Hugonin, D. Peyrade, E. Picard, T. Charvolin, and E. Hadji, "Ultra high reflectivity photonic bandgap mirrors in a ridge SOI waveguide,' New J. Phys. (IOP), 8, no. 204, pp. 1-13, Sep. 2006.
  18. Ahmad Rifqi Md Zain, Marco Gnan, Harold M. H. Chong, Marc Sorel and Richard M. De La Rue, "Tapered Photonic Crystal Microcavities Embedded in Photonic Wire Waveguides with Large Resonance Quality-Factor and High Transmission," IEEE Photon.Technol. Lett.20(1), 6 - 8, 1st January (2008). [CrossRef]
  19. B.S. Song, S. Noda, T. Asano and Y. Akahane,"Ultra-high-Q photonic double-heterostructure nanocavity,"Nature materials 4, March 2005.

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