## Integrated InP-InGaAsP tunable coupled ring optical bandpass filters with zero insertion loss |

Optics Express, Vol. 19, Issue 8, pp. 7816-7826 (2011)

http://dx.doi.org/10.1364/OE.19.007816

Acrobat PDF (1463 KB)

### Abstract

Second and third-order monolithically integrated coupled ring bandpass filters are demonstrated in the InP-InGaAsP material system with active semiconductor optical amplifiers (SOAs) and current injection phase modulators (PMs). Such integration achieves a high level of tunability and precise generation of optical filters in the RF domain at telecom wavelengths while simultaneously compensating for device insertion loss. Passband bandwidth tunability of 3.9 GHz to 7.1 GHz and stopband extinction up to 40 dB are shown for third-order filters. Center frequency tunability over a full free spectral range (FSR) is demonstrated, allowing for the placement of a filter anywhere in the telecom C-band. A Z-transform representation of coupled resonator filters is derived and compared with experimental results. A theoretical description of filter tunability is presented.

© 2011 OSA

## 1. Introduction

2. J. Capmany, B. Ortega, and D. Pastor, “A tutorial on microwave photonic filters,” J. Lightwave Technol. **24**(1), 201–229 (2006). [CrossRef]

## 2. Coupled-ring optical filters and their z-transform representation

### 2.1 Z-transform for optical systems

13. S. Darmawan, Y. M. Landobasa, and M.-K. Chin, “Pole-zero dynamics of high-order ring resonator filters,” J. Lightwave Technol. **25**(6), 1568–1575 (2007). [CrossRef]

14. J. Simon, P. Doussiere, P. Lamouler, I. Valiente, and R. Riou, “Travelling wave semiconductor optical amplifier with reduced nonlinear distortions,” Electron. Lett. **30**(1), 49–50 (1994). [CrossRef]

15. P. Saeung and P. P. Yupapin, “Generalized analysis of multiple ring resonator filters: modeling by using graphical approach,” Optik (Stuttg.) **119**(10), 465–472 (2008). [CrossRef]

*ω*is the normalized frequency,

_{n}*L*is the unit length, taken as the ring length in our devices, and

_{U}*β*is the propagation constant given bywhere

*n*is the effective index of refraction and

_{eff}*λ*is the optical wavelength.

### 2.2 Second-order cascaded and coupled rings

15. P. Saeung and P. P. Yupapin, “Generalized analysis of multiple ring resonator filters: modeling by using graphical approach,” Optik (Stuttg.) **119**(10), 465–472 (2008). [CrossRef]

*c*is the amplitude coupling value of the i

_{i}^{th}coupler, and there is assumed to be no coupler insertion loss, implying

*ϕ*is the phase introduced by the phase modulator in the i

_{i}^{th}ring,

*A*is the fractional amplitude loss in each waveguide segment given bywhere

_{i}*Γg*is the modal power gain and

_{i}*α*is the modal loss from the Semiconductor Optical Amplifier (SOA) in the i

_{a}^{th}waveguide segment,

*L*is the length of the SOAs,

_{SOA}*α*is the passive modal waveguide loss, and

_{p}*L*is the ring length. Equation (3) and (4) are very similar, but result in different behavior due to the coupled nature of the

*z*and

^{−1}*z*terms in the coupled ring equation.

^{−2}*p*. This “intrinsic pole” is the pole obtained from the ring independent of any feedback from other rings, as in the cascaded system. These intrinsic poles are given by Substituting Eq. (10) and (11) into Eq. (4) and solving for the roots of the denominator, the actual poles of the coupled system are determined to bewhere

_{r}*C*is the power coupling in coupler 2 (i.e.

_{2}*C*=

_{2}*c*). If the term under the square root is real, then the poles are complex conjugates of each other. When

_{2}^{2}*ϕ*=

_{1}*ϕ*, the ring resonances are located at the same frequency which is most interesting for the bandpass filter application. For this case,

_{2}*p*and

_{r,1}*p*are real, and the pole magnitudes are both given byThis situation has important implications. The first is that the magnitudes of the two poles are always equal, regardless of the individual intrinsic pole magnitudes. The second is that the pole magnitudes are enhanced above the level of the intrinsic (cascaded) pole magnitudes by a factor of

_{r,2}### 2.3 Third-order coupled rings

*C*and

_{2}*C*, do not need to be equal for the filter to be symmetric, and adjusting just one of them affects both complex conjugate poles.

_{3}## 3. Design of the monolithically integrated filter

### 3.1 System design

### 3.2 Active/passive integration and waveguide design

17. J. W. Raring, M. N. Sysak, A. T. Pedretti, M. Dummer, E. J. Skogen, J. S. Barton, S. P. Denbaars, and L. A. Coldren, “Advanced integration schemes for high-functionality/high-performance photonic integrated circuits,” Proc. SPIE **6126**, 61260H, 61260H-20 (2006). [CrossRef]

17. J. W. Raring, M. N. Sysak, A. T. Pedretti, M. Dummer, E. J. Skogen, J. S. Barton, S. P. Denbaars, and L. A. Coldren, “Advanced integration schemes for high-functionality/high-performance photonic integrated circuits,” Proc. SPIE **6126**, 61260H, 61260H-20 (2006). [CrossRef]

18. T. Darcie, R. Jopson, and R. Tkach, “Intermodulation distortion in optical amplifiers from carrier-density modulation,” Electron. Lett. **23**(25), 1392–1394 (1987). [CrossRef]

17. J. W. Raring, M. N. Sysak, A. T. Pedretti, M. Dummer, E. J. Skogen, J. S. Barton, S. P. Denbaars, and L. A. Coldren, “Advanced integration schemes for high-functionality/high-performance photonic integrated circuits,” Proc. SPIE **6126**, 61260H, 61260H-20 (2006). [CrossRef]

_{2}/Cl

_{2}/Ar ICP-RIE recipe [21

21. J. S. Parker, E. J. Norberg, R. S. Guzzon, S. C. Nicholes, and L. A. Coldren, “High verticality InP/InGaAsP etching in Cl_{2}/H_{2}/Ar inductively coupled plasma for photonic integrated circuits,” J. Vac. Sci. Technol. B **29**(1), 011016 (2011). [CrossRef]

### 3.3 Fabrication

_{2}hardmask was defined with photo-resist [21

21. J. S. Parker, E. J. Norberg, R. S. Guzzon, S. C. Nicholes, and L. A. Coldren, “High verticality InP/InGaAsP etching in Cl_{2}/H_{2}/Ar inductively coupled plasma for photonic integrated circuits,” J. Vac. Sci. Technol. B **29**(1), 011016 (2011). [CrossRef]

## 4. Measured filter results

### 4.1 Measurement setup

_{2}O

_{3}carrier and light was coupled in and out via lensed fiber.

### 4.2 Measured filters

*A*and decreasing

_{2}*A*such that

_{1}*A*remains the same. The results are also normalized in frequency, but are tunable across a full FSR, indicating the ability to place a filter anywhere in the c-band.

_{1}A_{2}## 5. Conclusion

## Acknowledgments

## References and links

1. | C. K. Madsen and J. H. Zhao, |

2. | J. Capmany, B. Ortega, and D. Pastor, “A tutorial on microwave photonic filters,” J. Lightwave Technol. |

3. | P. Dong, N. N. Feng, D. Feng, W. Qian, H. Liang, D. C. Lee, B. J. Luff, T. Banwell, A. Agarwal, P. Toliver, R. Menendez, T. K. Woodward, and M. Asghari, “GHz-bandwidth optical filters based on high-order silicon ring resonators,” Opt. Express |

4. | N. N. Feng, P. Dong, D. Feng, W. Qian, H. Liang, D. C. Lee, J. B. Luff, A. Agarwal, T. Banwell, R. Menendez, P. Toliver, T. K. Woodward, and M. Asghari, “Thermally-efficient reconfigurable narrowband RF-photonic filter,” Opt. Express |

5. | M. Rasras, K. Tu, D. Gill, Y. Chen, A. White, S. Patel, A. Pomerene, D. Carothers, J. Beattie, M. Beals, J. Michel, and L. Kimerling, “Demonstration of a tunable microwave-photonic notch filter using low-loss silicon ring resonators,” J. Lightwave Technol. |

6. | B. E. Little, S. T. Chu, P. P. Absil, J. V. Hryniewicz, F. G. Johnson, F. Seiferth, D. Gill, V. Van, O. King, and M. Trakalo, “Very high-order microring resonator filters for WDM applications,” IEEE Photon. Technol. Lett. |

7. | M. S. Dahlem, C. W. Holzwarth, A. Khilo, F. X. Kärtner, H. I. Smith, and E. P. Ippen, “Reconfigurable multi-channel second-order silicon microring-resonator filterbanks for on-chip WDM systems,” Opt. Express |

8. | J. Park, T. Lee, D. Lee, S. Kim, W. Hwang, and Y. Chung, “Widely tunable coupled-ring-reflector filter based on planar polymer waveguide,” IEEE Photon. Technol. Lett. |

9. | H.-W. Chen, A. W. Fang, J. D. Peters, Z. Wang, J. Bovington, D. Liang, and J. E. Bowers, “Integrated microwave photonic filter on a hybrid silicon platform,” IEEE Trans. Microw. Theory Tech. |

10. | R. S. Guzzon, E. J. Norberg, J. S. Parker, L. A. Johansson, and L. A. Coldren, “Monolithically integrated programmable photonic microwave filter with tunable inter-ring coupling,” |

11. | D. M. Baney, P. Gallion, and R. S. Tucker, “Theory and measurement techniques for the noise figure of optical amplifiers,” Opt. Fiber Technol. |

12. | C. K. Madsen and J. H. Zhao, |

13. | S. Darmawan, Y. M. Landobasa, and M.-K. Chin, “Pole-zero dynamics of high-order ring resonator filters,” J. Lightwave Technol. |

14. | J. Simon, P. Doussiere, P. Lamouler, I. Valiente, and R. Riou, “Travelling wave semiconductor optical amplifier with reduced nonlinear distortions,” Electron. Lett. |

15. | P. Saeung and P. P. Yupapin, “Generalized analysis of multiple ring resonator filters: modeling by using graphical approach,” Optik (Stuttg.) |

16. | R. S. Guzzon, E. J. Norberg, J. S. Parker, and L. A. Coldren, “Highly programmable optical filters integrated in InP-InGaAsP with tunable inter-ring coupling,” |

17. | J. W. Raring, M. N. Sysak, A. T. Pedretti, M. Dummer, E. J. Skogen, J. S. Barton, S. P. Denbaars, and L. A. Coldren, “Advanced integration schemes for high-functionality/high-performance photonic integrated circuits,” Proc. SPIE |

18. | T. Darcie, R. Jopson, and R. Tkach, “Intermodulation distortion in optical amplifiers from carrier-density modulation,” Electron. Lett. |

19. | E. Norberg, R. Guzzon, and L. Coldren, “Programmable photonic filters fabricated with deeply etched waveguides,” in |

20. | G. P. Agrawal, |

21. | J. S. Parker, E. J. Norberg, R. S. Guzzon, S. C. Nicholes, and L. A. Coldren, “High verticality InP/InGaAsP etching in Cl |

**OCIS Codes**

(230.5750) Optical devices : Resonators

(250.5300) Optoelectronics : Photonic integrated circuits

(350.2460) Other areas of optics : Filters, interference

(130.7408) Integrated optics : Wavelength filtering devices

**ToC Category:**

Integrated Optics

**History**

Original Manuscript: February 11, 2011

Revised Manuscript: March 18, 2011

Manuscript Accepted: March 30, 2011

Published: April 7, 2011

**Citation**

Robert S. Guzzon, Erik J. Norberg, John S. Parker, Leif A. Johansson, and Larry A. Coldren, "Integrated InP-InGaAsP tunable coupled ring optical bandpass filters with zero insertion loss," Opt. Express **19**, 7816-7826 (2011)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-8-7816

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### References

- C. K. Madsen and J. H. Zhao, Optical Filter Design and Analysis: A Signal Processing Approach (Whiley-Interscience, 1999), Chap. 1.
- J. Capmany, B. Ortega, and D. Pastor, “A tutorial on microwave photonic filters,” J. Lightwave Technol. 24(1), 201–229 (2006). [CrossRef]
- P. Dong, N. N. Feng, D. Feng, W. Qian, H. Liang, D. C. Lee, B. J. Luff, T. Banwell, A. Agarwal, P. Toliver, R. Menendez, T. K. Woodward, and M. Asghari, “GHz-bandwidth optical filters based on high-order silicon ring resonators,” Opt. Express 18(23), 23784–23789 (2010). [CrossRef] [PubMed]
- N. N. Feng, P. Dong, D. Feng, W. Qian, H. Liang, D. C. Lee, J. B. Luff, A. Agarwal, T. Banwell, R. Menendez, P. Toliver, T. K. Woodward, and M. Asghari, “Thermally-efficient reconfigurable narrowband RF-photonic filter,” Opt. Express 18(24), 24648–24653 (2010). [CrossRef] [PubMed]
- M. Rasras, K. Tu, D. Gill, Y. Chen, A. White, S. Patel, A. Pomerene, D. Carothers, J. Beattie, M. Beals, J. Michel, and L. Kimerling, “Demonstration of a tunable microwave-photonic notch filter using low-loss silicon ring resonators,” J. Lightwave Technol. 27(12), 2105–2110 (2009). [CrossRef]
- B. E. Little, S. T. Chu, P. P. Absil, J. V. Hryniewicz, F. G. Johnson, F. Seiferth, D. Gill, V. Van, O. King, and M. Trakalo, “Very high-order microring resonator filters for WDM applications,” IEEE Photon. Technol. Lett. 16(10), 2263–2265 (2004). [CrossRef]
- M. S. Dahlem, C. W. Holzwarth, A. Khilo, F. X. Kärtner, H. I. Smith, and E. P. Ippen, “Reconfigurable multi-channel second-order silicon microring-resonator filterbanks for on-chip WDM systems,” Opt. Express 19(1), 306–316 (2011). [CrossRef] [PubMed]
- J. Park, T. Lee, D. Lee, S. Kim, W. Hwang, and Y. Chung, “Widely tunable coupled-ring-reflector filter based on planar polymer waveguide,” IEEE Photon. Technol. Lett. 20(12), 988–990 (2008). [CrossRef]
- H.-W. Chen, A. W. Fang, J. D. Peters, Z. Wang, J. Bovington, D. Liang, and J. E. Bowers, “Integrated microwave photonic filter on a hybrid silicon platform,” IEEE Trans. Microw. Theory Tech. 58(11), 3213–3219 (2010). [CrossRef]
- R. S. Guzzon, E. J. Norberg, J. S. Parker, L. A. Johansson, and L. A. Coldren, “Monolithically integrated programmable photonic microwave filter with tunable inter-ring coupling,” Proc. IEEE Conf. Microwave Photonics (IEEE, Montreal, Canada, 2010).
- D. M. Baney, P. Gallion, and R. S. Tucker, “Theory and measurement techniques for the noise figure of optical amplifiers,” Opt. Fiber Technol. 6(2), 122–154 (2000). [CrossRef]
- C. K. Madsen and J. H. Zhao, Optical Filter Design and Analysis: A Signal Processing Approach (Whiley-Interscience, 1999), Chap. 3.
- S. Darmawan, Y. M. Landobasa, and M.-K. Chin, “Pole-zero dynamics of high-order ring resonator filters,” J. Lightwave Technol. 25(6), 1568–1575 (2007). [CrossRef]
- J. Simon, P. Doussiere, P. Lamouler, I. Valiente, and R. Riou, “Travelling wave semiconductor optical amplifier with reduced nonlinear distortions,” Electron. Lett. 30(1), 49–50 (1994). [CrossRef]
- P. Saeung and P. P. Yupapin, “Generalized analysis of multiple ring resonator filters: modeling by using graphical approach,” Optik (Stuttg.) 119(10), 465–472 (2008). [CrossRef]
- R. S. Guzzon, E. J. Norberg, J. S. Parker, and L. A. Coldren, “Highly programmable optical filters integrated in InP-InGaAsP with tunable inter-ring coupling,” Conf. Integrated Photonics Research, Silicon and Nanophotonics (Optical Society of America, Monterey, CA, 2010).
- J. W. Raring, M. N. Sysak, A. T. Pedretti, M. Dummer, E. J. Skogen, J. S. Barton, S. P. Denbaars, and L. A. Coldren, “Advanced integration schemes for high-functionality/high-performance photonic integrated circuits,” Proc. SPIE 6126, 61260H, 61260H-20 (2006). [CrossRef]
- T. Darcie, R. Jopson, and R. Tkach, “Intermodulation distortion in optical amplifiers from carrier-density modulation,” Electron. Lett. 23(25), 1392–1394 (1987). [CrossRef]
- E. Norberg, R. Guzzon, and L. Coldren, “Programmable photonic filters fabricated with deeply etched waveguides,” in Proc. of IEEE Conf. on Indium Phosphide and Related Materials (IEEE Photonics Society, Newport beach, CA, 2009), pp. 163–166.
- G. P. Agrawal, Fiber-Optic Communication Systems (Whiley-Interscience, 2002), Chap. 6.
- J. S. Parker, E. J. Norberg, R. S. Guzzon, S. C. Nicholes, and L. A. Coldren, “High verticality InP/InGaAsP etching in Cl2/H2/Ar inductively coupled plasma for photonic integrated circuits,” J. Vac. Sci. Technol. B 29(1), 011016 (2011). [CrossRef]

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