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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 2 — Jan. 18, 2010
  • pp: 1600–1606
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Synthesis of coupled resonator optical waveguides by cavity aggregation

Pascual Muñoz, José David Doménech, and José Capmany  »View Author Affiliations


Optics Express, Vol. 18, Issue 2, pp. 1600-1606 (2010)
http://dx.doi.org/10.1364/OE.18.001600


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Abstract

In this paper, the layer aggregation method is applied to coupled resonator optical waveguides. Starting from the frequency transfer function, the method yields the coupling constants between the resonators. The convergence of the algorithm developed is examined and the related parameters discussed.

© 2010 Optical Society of America

1. Introduction

Waveguide photonic devices based on the interference of multiple scattered versions of the fundamental mode are instrumental for enabling a wide variety of signal processing functions, such as single and multiple channel filtering and interleaving in WDM systems [1

1. J. Capmany and M. Muriel, “A new transfer matrix formalism for the analysis of fiber ring resonators: compound coupled structures for FDMA demultiplexing,” J. Lightwave Technol. 8, 1904–1919 (1990). [CrossRef]

,2

2. B. Little, S. Chu, H. Haus, J. Foresi, and J.-P. Laine, “Microring resonator channel dropping filters,” J. Lightwave Technol. 15, 998–1005 (1997). [CrossRef]

], linear [3

3. C. Madsen and J. Zhao, “A general planar waveguide autoregressive optical filter,” J. Lightwave Technol. 14, 437–447 (1996). [CrossRef]

] and nonlinear [4

4. V. Van, T. Ibrahim, P. Absil, F. Johnson, R. Grover, and P.-T. Ho, “Optical signal processing using nonlinear semiconductor microring resonators,” IEEE J. Sel. Top. Quantum Electron. 8, 705–713 (2002). [CrossRef]

] digital optics, optical buffering [5

5. F. Xia, L. Sekaric, and Y. Vlasov, “Ultra compact optical buffers on a silicon chip,” Nat. Photonics 1, 65–71 (2007). [CrossRef]

] and modulation [6

6. H. Tazawa and W. Steier, “Analysis of ring resonator-based traveling-wave modulators,” IEEE Photon. Technol. Lett. 18, 211–213 (2006). [CrossRef]

], dispersion compensation [7

7. C. Madsen, G. Lenz, A. Bruce, M. Cappuzzo, L. Gomez, and R. Scotti, “Integrated all-pass filters for tunable dispersion and dispersion slope compensation,” IEEE Photon. Technol. Lett. 11, 1623–1625 (1999). [CrossRef]

] and switching [8

8. B. Little, S. Chu, W. Pan, and Y. Kokubun, “Microring resonator arrays for VLSI photonics,” IEEE Photon. Technol. Lett. 12, 323–325 (2000). [CrossRef]

] which are required in high speed optical communications. Furthermore, novel emerging applications in biophotonics [9

9. H.-C. Ren, F. Vollmer, S. Arnold, and A. Libchaber, “High-Q microsphere biosensor - analysis for adsorption of rodlike bacteria,” Opt. Express 15, 17410–17423 (2007). [CrossRef] [PubMed]

] and quantum communications [10

10. K. Vahala, “Optical microcavities,” Nature (London) 424, 839–846 (2003). [CrossRef]

] are expected to benefit from the functionalities brought by these devices. Each particular application needs a specific device design which can be obtained by a suitable synthesis procedure which, taking as a starting point the impulse response or transfer function that is required, renders the values of the relevant parameters that characterize the device.

2. Layer aggregation method

The CROW is a periodic structure as shown in Fig. 1(a), composed of coupled resonators. The coupling constant can be equal for all the couplers (uniform CROW) or different by applying a windowing function (apodized CROW) as described in [25

25. J. Capmany, P. M.ñoz, J. D. Domenech, and M. A. Muriel, “Apodized coupled resonator waveguides,” Opt. Express 15, 10196–10206 (2007). [CrossRef] [PubMed]

]. For the couplers, the well-known matrix [22

22. A. Yariv, Y. Xu, R. K. Lee, and A. Scherer, “Coupled-resonator optical waveguide: a proposal and analysis,” Opt. Lett. 24, 711–713 (1999). [CrossRef]

] relating the input and output electromagnetic field amplitudes is used:

Fig. 1. CROW (a) naming convention, and layer aggregation for h[n] (b) n = 0, (c) n = 1 and (d) n ≥ 2
[bibi+1]=[tiκiκi*ti*][aiai+1]
(1)

where ti and κi are the direct and cross-coupling field coefficients and the subscript i = 0,1,…,N refers to the couplers in the CROW device. A loss-less coupler is assumed hereafter, i.e. |ti|2 + |κi|2 = 1. In practical devices, all the resonators have the same perimeter. Hence, the impulse response of the filter is composed of impulses, or samples, of different amplitudes happening at times multiples of the ring resonator round trip time, T. In this case it is convenient to use a discrete time notation [27

27. A. V. Oppenheim, R. W. Schafer, and J. R. Buck, Discrete-time signal processing, Signal Processing Series (Prentice-Hall International, 1999), 2nd ed.

], i.e. h[n] = h(nT). The layer aggregation method is based upon the analysis of the filter contributions to the impulse response time samples. The approach followed is similar to that developed for Fiber Bragg gratings in [17

17. J. Capmany, M. Muriel, and S. Sales, “Highly accurate synthesis of fiber and waveguide bragg gratings by an impedance reconstruction layer-aggregation method,” IEEE J. Quantum Electron. 43, 889–898 (2007). [CrossRef]

]. Referring to Fig. 1(b) and 1(c), at time n = 0 the impulse response is solely due to the first coupler of the device, while at time n = 1 the response is due to the first two couplers:

h[0]=t0h[1]=-t1[κ0]2
(2)

In both cases the paths followed by the light within the CROWs are non-recursive, i.e. a waveguide section of the device is only traversed once. For n ≥ 2, h[n] is formed by two contributions, one recursive and one non-recursive, as illustrated in Fig. 1(d) for n = 2, with yellow and red lines. In this particular case, the recursive contribution is due to the first resonator (two turns, marked in red as ’x2’), while the non-recursive comes from the direct reflection from coupler number 2. Generalizing, for n ≥ 2:

Fig. 2. CROW (a) target TMM calculated response for m = 9 and m = 14 and (b) synthesized and target responses (inset transmission response).
h[n]=hr[n]+hnr[n]
(3)

where the recursive part at time n is given by the corresponding sample of the impulse response of CROW with n-1 resonators, and the non-recursive part can be derived from the figures:

hnr[n]=(1)ntni=0n1κi2
(4)

3. Reconstruction procedure

  1. Given H[k], calculate its inverse discrete Fourier transform, IDFT, h[n] = IDFTM {H[k]}
  2. For n = 0 and n = 1 use Eq. (2) to solve for (t 0, κ 0) and (t 1, κ 1).
  3. For every n ≥ 2 iterate using the set {ti, κi)} i = 0, …,n - 1 and the method in [25

    25. J. Capmany, P. M.ñoz, J. D. Domenech, and M. A. Muriel, “Apodized coupled resonator waveguides,” Opt. Express 15, 10196–10206 (2007). [CrossRef] [PubMed]

    ] to find the impulse response of a CROW with n - 1 rings, corresponding to hr [n], and eqs. (3)(4) to obtain (tn, κn).
Fig. 3. Reconstructed Ki values for (a) N = 5 and (b) N = 10 rings for a uniform CROW with K = 0.1, and KN for uniform CROWs with K =0.1, 0.2 and 0.3, all vs. IDFT number of points M used.

4. Results and discussion

As a first example, the reconstruction is applied for the target transfer functions corresponding to uniform CROW devices with power coupling constant K = |κ|2 = 0.1 of N = 5 and N = 10 rings. The target transfer functions were calculated using the Transfer Matrix Method, TMM, from [25

25. J. Capmany, P. M.ñoz, J. D. Domenech, and M. A. Muriel, “Apodized coupled resonator waveguides,” Opt. Express 15, 10196–10206 (2007). [CrossRef] [PubMed]

]. Figure 2(a) shows the response for N = 10 sampled with 2m points (m = 9 and m = 14). The coupling constants Ki, i = 0,…,N obtained through reconstruction are shown in Fig. 3(a) and 3(b), for 5 and 10 rings respectively, for different number of samples in H(ωd).

Fig. 4. Hamming (H=0.2) apodized CROW with nominal K = 0.1 (a) target TMM calculated response for m = 9 and m = 14, (b) synthesized and target responses (inset transmission response) and reconstructed Ki values for (c) N = 5 and (d) N = 10 rings, all vs. IDFT number of points M used.

The convergence of the reconstruction for uniform CROWs with different K values, 0.1, 0.2 and 0.3, is shown in Fig. 3(c) and 3(d) for N = 5 and N = 10 rings respectively. The graphs show the value of the coupling constant for the last coupler in the CROW, KN. For 5 rings, convergence is achieved for K = 0.2 and K = 0.3 with m ≥ 10 and m ≥ 9 respectively, while K = 0.1 requires m ≥ 11. The convergence worsens for 10 rings, where m ≥ 13 and m ≥ 12 are needed for K = 0.2 and K = 03 respectively, while K = 0.1 needs m > 14.

The reconstruction was also applied to a CROW device with apodized coefficients, where the ti values are modified following a weight (window) function. Starting with a nominal coupling constant K = 0.1, a Hamming window with parameter H = 0.2 was used as described in [25

25. J. Capmany, P. M.ñoz, J. D. Domenech, and M. A. Muriel, “Apodized coupled resonator waveguides,” Opt. Express 15, 10196–10206 (2007). [CrossRef] [PubMed]

]. Hence, the coupler values for the target response calculation using the TMM are:

ti=1K1+Hcos(2πi0.5(N1)N)1+Hi=0,,N

that correspond to Ki = {0.5728, 0.3750, 0.1397, 0.1397, 0.3750, 0.5728} and Ki = {0.5919, 0.5280, 0.4101, 0.2668, 0.1470, 0.1000, 0.1470, 0.2668, 0.4101, 0.5280, 0.5919} for 5 and 10 rings respectively. The TMM calculated target responses, sampled with the same points as in the uniform case of Fig. 2(a), are shown in Fig. 4(a).

Consequently, this results in less error on the impulse response approximation, since the differences between the samples of h[n], using m = 9 and m = 14, are of the order of 10-14. The convergence of all the coupling constants vs m is shown in Fig. 4(c) and 4(d) for 5 and 10 rings respectively. As outlined before, lower sampling is required for the apodized cases, since for theses cases convergence is achieved for m ≥ 7 and m ≥ 9, for 5 and 10 rings respectively.

Finally, the responses calculated using the reconstructed coupling coefficients and the TMM, are compared with the targeted responses in Figs. 2(b) and 4(b). An inset shows also the reconstructed transmission response. In both cases, uniform and apodized, the match between the target and reconstructed responses is excellent.

5. Conclusion

Acknowledgement

The authors acknowledge financial support from the Spanish MICINN project TEC2008-06145 and the GVA through project PROMETEO/2008/092. J.D. Doménech acknowledges the FPI research grant BES-2009-018381.

References and links

1.

J. Capmany and M. Muriel, “A new transfer matrix formalism for the analysis of fiber ring resonators: compound coupled structures for FDMA demultiplexing,” J. Lightwave Technol. 8, 1904–1919 (1990). [CrossRef]

2.

B. Little, S. Chu, H. Haus, J. Foresi, and J.-P. Laine, “Microring resonator channel dropping filters,” J. Lightwave Technol. 15, 998–1005 (1997). [CrossRef]

3.

C. Madsen and J. Zhao, “A general planar waveguide autoregressive optical filter,” J. Lightwave Technol. 14, 437–447 (1996). [CrossRef]

4.

V. Van, T. Ibrahim, P. Absil, F. Johnson, R. Grover, and P.-T. Ho, “Optical signal processing using nonlinear semiconductor microring resonators,” IEEE J. Sel. Top. Quantum Electron. 8, 705–713 (2002). [CrossRef]

5.

F. Xia, L. Sekaric, and Y. Vlasov, “Ultra compact optical buffers on a silicon chip,” Nat. Photonics 1, 65–71 (2007). [CrossRef]

6.

H. Tazawa and W. Steier, “Analysis of ring resonator-based traveling-wave modulators,” IEEE Photon. Technol. Lett. 18, 211–213 (2006). [CrossRef]

7.

C. Madsen, G. Lenz, A. Bruce, M. Cappuzzo, L. Gomez, and R. Scotti, “Integrated all-pass filters for tunable dispersion and dispersion slope compensation,” IEEE Photon. Technol. Lett. 11, 1623–1625 (1999). [CrossRef]

8.

B. Little, S. Chu, W. Pan, and Y. Kokubun, “Microring resonator arrays for VLSI photonics,” IEEE Photon. Technol. Lett. 12, 323–325 (2000). [CrossRef]

9.

H.-C. Ren, F. Vollmer, S. Arnold, and A. Libchaber, “High-Q microsphere biosensor - analysis for adsorption of rodlike bacteria,” Opt. Express 15, 17410–17423 (2007). [CrossRef] [PubMed]

10.

K. Vahala, “Optical microcavities,” Nature (London) 424, 839–846 (2003). [CrossRef]

11.

E. Peral, J. Capmany, and J. Marti, “Iterative solution to the Gel’fand-Levitan-Marchenko coupled equations and application to synthesis of fiber gratings,” IEEE J. Quantum Electron. 32, 2078–2084 (1996). [CrossRef]

12.

R. Feced, M. Zervas, and M. Muriel, “An efficient inverse scattering algorithm for the design of nonuniform fiber Bragg gratings,” IEEE J. Quantum Electron. 35, 1105–1115 (1999). [CrossRef]

13.

L. Poladian, “Simple grating synthesis algorithm,” Opt. Lett. 25, 787–789 (2000). [CrossRef]

14.

J. Skaar, L. Wang, and T. Erdogan, “On the synthesis of fiber Bragg gratings by layer peeling,” IEEE J. Quantum Electron. 37, 165–173 (2001). [CrossRef]

15.

J. Skaar, L. Wang, and T. Erdogan, “Synthesis of thick optical thin-film filters with a layer-peeling inverse-scattering algorithm,” Appl. Opt. 40, 2183–2189 (2001). [CrossRef]

16.

A. Rosenthal and M. Horowitz, “Inverse scattering algorithm for reconstructing strongly reflecting fiber bragg gratings,” IEEE J. Quantum Electron. 39, 1018–1026 (2003). [CrossRef]

17.

J. Capmany, M. Muriel, and S. Sales, “Highly accurate synthesis of fiber and waveguide bragg gratings by an impedance reconstruction layer-aggregation method,” IEEE J. Quantum Electron. 43, 889–898 (2007). [CrossRef]

18.

J. E. Heebner, P. Chak, S. Pereira, J. E. Sipe, and R. W. Boyd, “Distributed and localized feedback in microres-onator sequences for linear and nonlinear optics,” J. Opt. Soc. Am. B 21, 1818–1832 (2004). [CrossRef]

19.

J. Poon, J. Scheuer, S. Mookherjea, G. Paloczi, Y. Huang, and A. Yariv, “Matrix analysis of microring coupled-resonator optical waveguides,” Opt. Express 12, 90–103 (2004). [CrossRef] [PubMed]

20.

Y. Landobasa, S. Darmawan, and M.-K. Chin, “Matrix analysis of 2-D microresonator lattice optical filters,” IEEE J. Quantum Electron. 41, 1410–1418 (2005). [CrossRef]

21.

D. L. MacFarlane and E. M. Dowling, “Z-domain techniques in the analysis of Fabry-Perot étalons and multilayer structures,” J. Opt. Soc. Am. A 11, 236–245 (1994). [CrossRef]

22.

A. Yariv, Y. Xu, R. K. Lee, and A. Scherer, “Coupled-resonator optical waveguide: a proposal and analysis,” Opt. Lett. 24, 711–713 (1999). [CrossRef]

23.

A. Melloni and M. Martinelli, “Synthesis of direct-coupled-resonators bandpass filters for WDM systems,” J. Lightwave Technol. 20, 296–303 (2002). [CrossRef]

24.

R. Orta, P. Savi, R. Tascone, and D. Trinchero, “Synthesis of multiple-ring-resonator filters for optical systems,” IEEE Photon. Technol. Lett. 7, 1447–1449 (1995). [CrossRef]

25.

J. Capmany, P. M.ñoz, J. D. Domenech, and M. A. Muriel, “Apodized coupled resonator waveguides,” Opt. Express 15, 10196–10206 (2007). [CrossRef] [PubMed]

26.

A. Yariv, “Universal relations for coupling of optical power between microresonators and dielectric waveguides,”, Electron. Lett. 36, 321–322 (2000). [CrossRef]

27.

A. V. Oppenheim, R. W. Schafer, and J. R. Buck, Discrete-time signal processing, Signal Processing Series (Prentice-Hall International, 1999), 2nd ed.

OCIS Codes
(130.2790) Integrated optics : Guided waves
(130.3120) Integrated optics : Integrated optics devices
(230.5750) Optical devices : Resonators

ToC Category:
Integrated Optics

History
Original Manuscript: November 19, 2009
Revised Manuscript: January 8, 2010
Manuscript Accepted: January 9, 2010
Published: January 13, 2010

Citation
Pascual Muñoz, José David Doménech, and José Capmany, "Synthesis of coupled resonator optical waveguides by cavity aggregation," Opt. Express 18, 1600-1606 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-2-1600


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References

  1. J. Capmany and M. Muriel, "A new transfer matrix formalism for the analysis of fiber ring resonators: compound coupled structures for FDMA demultiplexing," J. Lightwave Technol. 8, 1904-1919 (1990). [CrossRef]
  2. B. Little, S. Chu, H. Haus, J. Foresi, and J.-P. Laine, "Microring resonator channel dropping filters," J. Lightwave Technol. 15, 998-1005 (1997). [CrossRef]
  3. C. Madsen and J. Zhao, "A general planar waveguide autoregressive optical filter," J. Lightwave Technol. 14, 437-447 (1996). [CrossRef]
  4. V. Van, T. Ibrahim, P. Absil, F. Johnson, R. Grover, and P.-T. Ho, "Optical signal processing using nonlinear semiconductor microring resonators," IEEE J. Sel. Top. Quantum Electron. 8, 705-713 (2002). [CrossRef]
  5. F. Xia, L. Sekaric, and Y. Vlasov, "Ultra compact optical buffers on a silicon chip," Nat. Photonics 1, 65-71 (2007). [CrossRef]
  6. H. Tazawa and W. Steier, "Analysis of ring resonator-based traveling-wave modulators," IEEE Photon. Technol. Lett. 18, 211-213 (2006). [CrossRef]
  7. C. Madsen, G. Lenz, A. Bruce, M. Cappuzzo, L. Gomez, and R. Scotti, "Integrated all-pass filters for tunable dispersion and dispersion slope compensation," IEEE Photon. Technol. Lett. 11, 1623-1625 (1999). [CrossRef]
  8. B. Little, S. Chu, W. Pan, and Y. Kokubun, "Microring resonator arrays for VLSI photonics," IEEE Photon. Technol. Lett. 12, 323-325 (2000). [CrossRef]
  9. H.-C. Ren, F. Vollmer, S. Arnold, and A. Libchaber, "High-Q microsphere biosensor - analysis for adsorption of rod like bacteria," Opt. Express 15, 17410-17423 (2007). [CrossRef] [PubMed]
  10. K. Vahala, "Optical microcavities," Nature (London) 424, 839-846 (2003). [CrossRef]
  11. E. Peral, J. Capmany, and J. Marti, "Iterative solution to the Gel’fand-Levitan-Marchenko coupled equations and application to synthesis of fiber gratings," IEEE J. Quantum Electron. 32, 2078-2084 (1996). [CrossRef]
  12. R. Feced, M. Zervas, and M. Muriel, "An efficient inverse scattering algorithm for the design of nonuniform fiber Bragg gratings," IEEE J. Quantum Electron. 35, 1105-1115 (1999). [CrossRef]
  13. L. Poladian, "Simple grating synthesis algorithm," Opt. Lett. 25, 787-789 (2000). [CrossRef]
  14. J. Skaar, L. Wang, and T. Erdogan, "On the synthesis of fiber Bragg gratings by layer peeling," IEEE J. Quantum Electron. 37, 165-173 (2001). [CrossRef]
  15. J. Skaar, L. Wang, and T. Erdogan, "Synthesis of thick optical thin-film filters with a layer-peeling inverse scattering algorithm," Appl. Opt. 40, 2183-2189 (2001). [CrossRef]
  16. A. Rosenthal and M. Horowitz, "Inverse scattering algorithm for reconstructing strongly reflecting fiber bragg gratings," IEEE J. Quantum Electron. 39, 1018-1026 (2003). [CrossRef]
  17. J. Capmany, M. Muriel, and S. Sales, "Highly accurate synthesis of fiber and waveguide bragg gratings by an impedance reconstruction layer-aggregation method," IEEE J. Quantum Electron. 43, 889-898 (2007). [CrossRef]
  18. J. E. Heebner, P. Chak, S. Pereira, J. E. Sipe, and R. W. Boyd, "Distributed and localized feedback in microresonator sequences for linear and nonlinear optics," J. Opt. Soc. Am. B 21, 1818-1832 (2004). [CrossRef]
  19. J. Poon, J. Scheuer, S. Mookherjea, G. Paloczi, Y. Huang, and A. Yariv, "Matrix analysis of microring coupled resonator optical waveguides," Opt. Express 12, 90-103 (2004). [CrossRef] [PubMed]
  20. Y. Landobasa, S. Darmawan, and M.-K. Chin, "Matrix analysis of 2-D microresonator lattice optical filters," IEEE J. Quantum Electron. 41, 1410-1418 (2005). [CrossRef]
  21. D. L. MacFarlane and E. M. Dowling, "Z-domain techniques in the analysis of Fabry-Perot ´etalons and multilayer structures," J. Opt. Soc. Am. A 11, 236-245 (1994). [CrossRef]
  22. A. Yariv, Y. Xu, R. K. Lee, and A. Scherer, "Coupled-resonator optical waveguide: a proposal and analysis," Opt. Lett. 24, 711-713 (1999). [CrossRef]
  23. A. Melloni and M. Martinelli, "Synthesis of direct-coupled-resonators bandpass filters for WDM systems," J. Lightwave Technol. 20, 296-303 (2002). [CrossRef]
  24. R. Orta, P. Savi, R. Tascone, and D. Trinchero, "Synthesis of multiple-ring-resonator filters for optical systems," IEEE Photon. Technol. Lett. 7, 1447-1449 (1995). [CrossRef]
  25. J. Capmany, P. Muñoz, J. D. Domenech, and M. A. Muriel, "Apodized coupled resonator waveguides," Opt. Express 15, 10196-10206 (2007). [CrossRef] [PubMed]
  26. A. Yariv, "Universal relations for coupling of optical power between microresonators and dielectric waveguides," Electron. Lett. 36, 321-322 (2000). [CrossRef]
  27. A. V. Oppenheim, R. W. Schafer, and J. R. Buck, Discrete-time signal processing, Signal Processing Series, 2nd ed. (Prentice-Hall International, 1999).

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