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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 25 — Dec. 10, 2007
  • pp: 17273–17282
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A reconfigurable architecture for continuously variable optical slow-wave delay lines

F. Morichetti, A. Melloni, A. Breda, A. Canciamilla, C. Ferrari, and M. Martinelli  »View Author Affiliations


Optics Express, Vol. 15, Issue 25, pp. 17273-17282 (2007)
http://dx.doi.org/10.1364/OE.15.017273


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Abstract

A novel reconfigurable architecture based on slow-wave propagation in integrated optical ring resonators is proposed for the realization of variable optical delay lines. A continuously variable delay is achieved by combining a coarse discrete (digital) delay, provided by a coupled resonator slow-wave structure, with a fine continuous (analog) delay given by a cascaded ring-resonator phase-shifter. The reflective configuration of the structure enables a simple, accurate and robust tuning of the delay and provides a footprint reduction by a factor 2 with respect to conventional coupled resonator optical waveguides. Proof-of-concept devices realized in 4.4% silicon oxynitride waveguides and activated by a thermal control are discussed. Experimental results demonstrate, in both spectral and time domain, a continuously variable delay, from zero to 800 ps (2 bit fractional delay), on a 2.5 Gbit/s NRZ signal, with less than 8 dB insertion loss and less than 5 mm2 device footprint.

© 2007 Optical Society of America

1. Introduction

The synchronization, buffering and storage of wideband data stream in the optical domain are going to become mandatory tasks in optical networks, in order to remove the bottleneck of electronic processing speed and avoid the cost of electrooptical format conversion. To this aim, optical devices capable of introducing arbitrarily large delays are required1. However, in telecom applications, large delays are of interest only if associated with large bandwidth, low loss and low signal distortion, and if the delay can be tuned finely, continuously and easily with flexible devices. Furthermore, the miniaturization down to chip-scale and the integration with other functionalities undoubtedly represent valuable parameters.

If integration, design flexibility and footprint size have to be taken into account, the exploitation of artificial resonances of optical resonators is expected to outperform slow-light media7. The idea underlying coupled resonator Slow-Wave Structures (SWSs)8 is forcing lightwave to retrace its path, so that it can be trapped inside optical resonators for as much time as the quality factor (or the finesse) of the resonators is high. From a theoretical point of view, different typologies of resonators can be equivalently used as building blocks for SWSs such as Fabry-Perot cavities9,10, coupled-ring resonators11,12 or coupled defect modes in photonic crystals13, the main differences only arising from technological issues. State-of-the art devices have been demonstrated by cascading more than ten ring resonators structured as Coupled Resonator Optical Waveguides (CROW) and made of glass14 and polymer waveguides15. Optical delay lines including up to 100 microring resonators cascaded in either coupled-resonator or all-pass filter (APF) configurations were recently realized also in silicon-on-insulator (SOI) photonic wire waveguides16, showing a fractional group delay exceeding 10 bits at 20 Gb/s rate in a device with a footprint below 0.09 mm2.

In this contribution, we propose a novel coupled resonator architecture for the realization of tunable Slow-Wave Delay Lines (SWDLs). The structure includes a ring resonator SWS, operating in reflective configuration, which is used to introduce a discrete (digital) delay, the time step being provided by the double-transit across the elementary ring of the structure. The SWS is followed by a ring-resonator phase-shifter that adds a fine continuous (analog), contribution to the overall delay. The spectral and time domain characterization of preliminary devices, fabricated in silicon oxynitride (SiON) technology, is reported, demonstrating a continuously tunable delay from zero to 800 ps on a 2.5 Gbit/s NRZ signal, corresponding to a fractional delay of 2 bits. Before the concluding section, an accurate comparison between the presented results and the state-of-the-art integrated devices is presented.

2 Coupled resonator slow-wave delay lines

The architecture of the proposed reconfigurable SWDL is shown in Fig. 1. It comprises two cascaded all-pass structures, namely S 1 and S 2, coupled with the same bus waveguide. The structure S 1 is a SWS made of N directly coupled ring-resonators, while the structure S 2 simply consists of a single ring-resonator phase-shifter. All the rings of the two structures are assumed with the same geometrical length Lr. As explained in the following, the SWDL can be used to introduce a continuously tunable and frequency dependent time delay by controlling the individual resonances of the ring resonators.

Starting from the structure S 1, an optical signal, incoming from the In port, can propagate along the chain of resonators only if its spectrum is entirely contained within the passing band B=2FSRsin-1(t1)/π of the structure8, FSR being the rings’ Free Spectral Range and t1 the field coupling coefficient between two adjacent resonators. If the signal spectrum lies outside B, the signal is directly transferred to the output port without entering S1 and without any significant delay. When inside the SWS, pulse propagation is slowed down by the factor8 S=cos(kLr2)t12sin2(kLr2), k being the propagation constant in the ring’s waveguide. With the aim to explain the working principle of the structure, let us assume that the first M rings have been set to the same resonant frequency f0 (M=4 in Fig. 1). The optical signal can propagate along the ring chain only up to the M-th ring, because all the M+n-th (n≥1) offresonance rings act as mirrors. Once arrived at the M-th ring, the signal is reflected backward to the input/output bus waveguide. The delay experienced by the signal is roughly Td=2M/πB, where Tr=2/πB is the group delay given by the double transit through every elementary resonator of the folded structure. The number of rings resonating at f 0, and hence the overall delay, can be arbitrarily selected by controlling the round-trip phase-shift of the rings of S1. Depending on the waveguide technology, this can be conveniently obtained by a thermo-optic, electro-optic or even all-optic control. By selecting M, a discrete, or digital, tunable delay between zero and Td,max=NTr=2 N/πB and with a minimum time-step equal to Tr can be achieved. Note that the folded layout enables an easy and complete reconfiguration of the S1 structure as well as the reduction of the overall dimensions by a factor 2. A remarkable advantage of the proposed structure is that, whatever the desired delay is, the optical signal always propagates at the centre of the SWS bandwidth, where the effects of either dispersion8,17 or disorder18 have been demonstrated to be minimum.

Fig. 1. Scheme of a continuously tunable SWDL, the coupled resonator SWS S1 providing a ‘digital’ tunable delay and the all-pass ring S2 giving an additional ‘analog’ tunable delay.

The phase-shifter S2 is cascaded to the coupled resonator SWS S1 in order to add a continuously variable analog delay. The S2 delay is selected by simply detuning its resonant frequency with respect to the signal carrier frequency. In this way, it is possible to make the optical signal experience any delay between T2,max=(1+r2)/(1-r2)/FSR at the resonance and T2,min=(1-r2)/(1+r2)/FSR at the anti-resonance frequency, where r2 is the through port field coupling coefficient of the ring S2. Straightforwardly, the condition to guarantee a continuously variable delay by the combination of the two cascaded structures S1 an S2 is T2,max-T2,min>Tr.

3. Experimental results

The reconfigurable SWDL of Fig. 1 was fabricated in integrated optical technology by using high index contrast silicon oxynitride (SiON) waveguides19. The cross sectional SEM picture of the optical channel waveguide is shown in Fig. 2(a). The waveguide has a square cross section with 2.2 µm×2.2 µm PECVD SiON core with refractive index n SION=1.513, deposited on a thermal silicon dioxide substrate (n Si02=1.4456) and covered by BPSG glass (n BPSG=1.45) as upper-cladding material. By means of cut back measurements, propagation losses of α=0.35 dB/cm at 1550nm were measured for the SWDL waveguide. Lower losses, down to 0.15 dB/cm, have been recently reached on subsequent fabrications by reducing sidewall roughness and improving the thermal annealing process. Fiber to waveguide coupling losses of 0.2 dB per facet can be achieved by using small core fiber with 3.6 µm mode field diameter. The 4.4% index contrast guarantees a minimum bending radius of 500 µm with negligible radiation losses, enabling the realization of ring resonators with a FSR of 100 GHz. Note that, from the point of view of the SWDL performance, the FSR limitation only concerns the minimum achievable device footprint and does not affect neither the group delay per ring Tr (only depending on the SWS bandwidth) nor the insertion loss per ring, of about 2cα/πBng, with ng the waveguide group effective index.

Fig. 2. Photograph of (a) the SiON waveguide cross section and (b) the first rings of a SWDL realized with directly coupled ring resonators. The diameter of the rings is approximately 1.24 mm, corresponding to FSR=50 GHz.
Fig. 3. (solid line) experimental and (dashed line) simulated (a) spectral intensity and (b) group delay characteristic of a SWDL with M=2 (blue), 3 (black) and 4 (red) tuned rings. The group delay, normalized to 2.5 Gbit/s NRZ pulse width (400 ps), is referred to as fractional delay.

Figure 2(b) is a photograph of the initial section of the SiON SWDL. The input waveguide is on the top left and the output port on the bottom right of the photograph. All the rings have the same nominal resonance. The different shape of the first rings is a consequence of the apodization of the coupling coefficients of the directional couplers, which is required to achieve the impedance matching condition between the SWS and the bus waveguide. By this strategy, a flat intensity spectral response as well as a ripple free group delay characteristic can be obtained20. Chromium resistors, acting as thermo-heaters, were deposited on the top of the waveguides to finely control the resonance of every ring by thermo-optic effect. Every resistor is 2 mm long, 9 µm wide, 200 nm thick, giving a measured resistance of about 600 Ω (+/- 10 Ω). The gold electric pads are clearly visible in the middle of the rings. The delay line can be reconfigured simply by changing the voltage applied to the heaters at the typical velocity of thermo-controllers, that has been demonstrated to be well below 1 ms21.

Figure 3 discloses in solid lines both the measured spectral intensity (a) and the group delay (b) of the SWDL of Fig. 2(b), for an increasing number of tuned resonators (M=2, 3, 4). With reference to Fig. 1, these measurements give the transmission from the In to the Out port, when only the S1 section is concerned. The delay line has a useful bandwidth larger than 2.5 GHz over a FSR=50 GHz, corresponding to a finesse 16 and a slowing ratio S=10. The SWDL spectral response of Fig. 3(a) is normalized to the insertion loss of the 2-cm-long bus waveguide, amounting to about 1.2 dB, where 0.25 dB/facet is the contribution of the fiber-to-waveguide coupling loss and 0.7 dB is the bus propagation loss. The transmission spectra of a lossless SWDL would be unitary at any wavelength and for any number of resonators. Under the effect of losses, dips in the spectrum of Fig. 3(a) appear. The insertion loss increases with the number M of tuned resonators, that is with the increasing effective length, or delay, of the SWDL. Higher attenuation is observed at the band-edges, where the group delay of coupled-resonator structures exhibits sharp peaks, which are as much pronounced as the number of resonator increases22. A good agreement between experimental data and the simulations of the nominal structure (dashed lines) was found. The agreement gets worse in the neighbourhood of the band edges, where the delay peaks are expected to be very sensitive to any inaccuracies or disorder, like tolerances on rings coupling coefficients and frequency detuning18.

The group delay of Fig. 3(b) is normalized to the 400 ps temporal width of a NRZ 2.5 Gbit/s pulse. The reference zero-delay is attributed to the minimum delay of the SWDL, achieved when all the resonators are tuned off-resonance. When four resonators are tuned at the carrier frequency f0 of the input signal (red line in Fig. 3), the folded SWS induces a delay equal to 2 bit lengths (Td=800 ps), corresponding to an effective geometrical length of about 15.6 cm., with an insertion loss lower than 8 dB. From the measured insertion loss, a ring round-trip loss of 0.2 dB/turn was inferred, where 0.15 dB/turn is the waveguide propagation loss contribution and 0.05 dB is due to excess loss of directional couplers and radiation loss in the ring’s bend. By increasing the number M of tuned rings, both the delay and the insertion loss increase but the intensity spectral shape remains roughly the same obtained with four rings.

Thermal measurements showed that, to shift the rings resonances, the power required by every thermo-heater is about 12 mW/GHz, corresponding to 1.45 °C/GHz for a 2-mm long heater. Despite of the presence of a Peltier thermo-cooler placed below the chip, a small thermal crosstalk was observed during the reconfiguration of the structure. However, thanks to the quite high finesse of the resonators, a small temperature variation (<4 °C to induce a frequency shift of 2.5 GHz) is sufficient to drive resonators outside the SWS passing band, thus limiting the effects of the thermal cross-talk.

Time domain measurements were carried out to evaluate the time delay and the envelope distortion given by the SWDL. To this aim, a SWS with bandwidth B=6.25 GHz (FSR=50 GHz) was used to entirely accommodate the spectrum of a 2.5 Gbit/s NRZ data stream. The structure has finesse F=8 and provides a slowing ratio S=6. Figure 4 shows in the right column the measured eye diagrams at the output of the SWDL for the case M=0 (a), M=1 (b), M=2 (c) and M=3 (d). In the left column, the results of numerical simulations are reported, where the input signal (blue line) is described by a supergaussian envelope of order 5. The simulated output pulses (red line) of Fig. 4(a)–4(d) are in very nice agreement with the experimental data with respect to both the delay and the distortion experienced by the pulse. As predicted by the theory, each additional resonator provides a delay Tr=2/πB≈100 ps. Despite of the distortion of the leading and trailing pulse edges, which increases with the length M of the SWDL, the measured eye remains well open, with a small intersymbol interference and only slightly attenuated (less than 3 dB for 300 ps delay). These distortions are mainly due to the peaks of group delay and attenuation at the band edges of the SWDL and are expected to disappear if a smoother input pulse is used, for instance by filtering the electric signal sent to the electro-optical modulator. The best way to finely tune the various rings to the correct position is in the time domain by maximizing the eye opening rather than impose a flat intensity spectral response. In this way also the group delay characteristic is optimized and the pulse shape preserved.

As discussed in Sec. 2, the continuous delay is achieved with the addition of a single resonator phase shifter, named S2 in Fig. 1, cascaded to the coupled resonator SWS S1. As shown in Fig. 5(a), a resonator with FSR=50 GHz and field coupling coefficient r2=0.65 can introduce a delay comprised between T2,max=94 ps at resonance (no frequency detuning) and T2,min=4 ps at anti-resonance frequencies (FSR/2 frequency detuning). The 90 ps range of tunability almost covers the 100 ps time step of the digital SWDL described in Fig. 4. Figure 5(b) shows the eye pattern of a 2.5 Gbit/s NRZ signal propagating through the resonator whose spectral group delay is reported in Fig. 5(a). Three frequency detunings of the ring’s resonant frequency with respect to the signal carrier are reported, 3.5 GHz (b1), 2 GHz (b2) and 0 (b3), introducing 50 ps, 69 ps and 90 ps delay, respectively. For more than 4 GHz frequency detuning, the pulse experiences less than 50 ps delay with no envelope distortion, because of the smoothness of the ring’s frequency response far from resonance. In the linear part of the group delay characteristic, the slope of the delay versus frequency is around 10 ps/GHz. Therefore, in order to achieve 1 ps resolution in the delay tunability, the resonator temperature must be controlled with an accuracy of ΔT 1ps=ngΔf/KThf≈0.1 °C, where ng=1.534 and Kth=1.04e-5 are the measured SiON waveguide effective group index and thermooptic coefficient, respectively. Note that this temperature accuracy is typically guaranteed by the state-of-the-art thermo-heaters, thus enabling both the stability and the fine adjustment of the delay. As shown by Fig. 5(b3), the envelope distortion is maximum at the resonance, where a small oscillation in the leading edge of the pulse and a sharp overshoot in the trailing edge appear. These effects are the consequence of the third order dispersion, which is the dominant dispersion contribution at ring’s resonance. Nonetheless, the eye diagram aperture remains practically unaffected. Figures 5(b1) and 5(b2) show also that the second order dispersion, arising where the group delay slope versus frequency is different from zero, carries negligible pulse envelope distortion.

Fig. 4. Simulated pulse propagation (left column) and experimental eye pattern (right column) of a 2.5 Gbit/s NRZ optical signal delayed by a SWDL for an increasing number of rings tuned to resonance: M=0 (a), M=1 (b), M=2 (c) and M=3 (d). A total delay of 300 ps is induced without significant pulse distortion.
Fig. 5. (a) Theoretical group delay of a ring resonator phase-shifter with FSR=50 GHz and r2=0.65; (b) Experimental eye pattern of a 2.5 Gbit/s NRZ optical signal delayed by the resonator shown in (a) for three different detuning of the ring’s resonant frequency with respect to the signal carrier: 3.5 GHz (b1), 2 GHz (b2) and 0 (b3).

4. Discussion

It is interesting to compare the performance of the proposed reconfigurable SWDL with the state-of-the-art architectures based on integrated ring-resonators and employed as optical buffers or delay lines. The main properties of the devices under investigation are summarized in Tab. 1. In Ref. [15

15. J. K. S. Poon, L. Zhu, G.A. De Rose, and A. Yariv, “Transmission and group delay of microring coupledresonator optical waveguides,” Opt. Lett. 31, 456 (2006). [CrossRef] [PubMed]

], a CROW with 12 coupled ring resonators realized in polymethyl methacrylate (PMMA) was presented, showing a maximum delay of 110 ps over a bandwidth of 17 GHz. In Ref. [16

16. F. Xia, L. Sekaric, and Y. Vlasov, “Ultracompact optical buffers on a silicon chip,” Nature Photonics 1, 65 (2006). [CrossRef]

] optical delay lines based on silicon wire waveguides in either CROW or APF configurations were reported. The figures of merit reported here refer to the APF configuration only, enabling more than 500 ps delay with 56 resonators and significantly outperforming the SOI CROW architecture.

Three figures of merit can be defined to compare the proposed structures:

- the ratio Td/IL [ns/dB] between the delay and the insertion loss;

- the ratio Td/A [ns/mm2] between the delay and the device footprint;

- the ratio Td/Tb N between the delay and the bit time duration, normalized to the number N of resonators (normalized fractional delay).

As shown in Tab. 1, SOI APFs largely show the best footprint parameter (5.6 ns/mm2, more than 30 times higher than the SiON SWDL one), thanks to the ultra tight waveguide bending enabled by silicon photonic wires. Note that the footprint parameter scales up with the waveguide index contrast (around 140 % in SOI waveguides, 11 % in PMMA waveguides and 4.4% SiON waveguides); therefore, it is mainly dependent on the employed technology rather than on the circuit design.

If losses are concerned, the best result is achieved by SiON SWDL, where Td/IL=0.1 ns/dB, more than 4 times higher than the SOI APS one. The poor value of the PMMA CROW (<0.003 ns/dB) is due to the extremely high loss of the waveguide (>17 dB/cm) mainly arising from sidewall roughness. It is worthwhile to point out here that, for any structure (not necessarily involving slow light), the theoretical upper limit for the delay to insertion loss ratio is fixed by (Td/IL)max=ng/cα. Therefore, it only depends on the ratio between the waveguide group index and the waveguide propagation loss. For the SiON waveguide discussed in this work, this condition gives 0.146 ns/dB, very close to measured value 0.1 ns/dB. As mentioned in Sec. 3, the discrepancy is probably due to the additional loss carried by ring-to-ring couplers and waveguide bending. In recent fabrications, propagation losses have been reduced down to 0.15 dB/cm, so that a delay-loss ratio higher than 0.2 ns/dB (reported in brackets in Tab. 1) is expected to be reached in future SWDLs. From the point of view of pulse attenuation, it corresponds to an attenuation per bit delay equal to 2 dB/bit in a 2.5 Gbit/s system, or even better 0.5 dB/bit in a 10 Gbit/s system. It is easy to verify that SOI structures can reach the same performance only if losses are reduced below 0.6 dB/cm, three times less than the state-of-the art value of 1.7 dB/cm [16

16. F. Xia, L. Sekaric, and Y. Vlasov, “Ultracompact optical buffers on a silicon chip,” Nature Photonics 1, 65 (2006). [CrossRef]

].

It should be noted that, although the finesse of the resonators used in the APF structure [16

16. F. Xia, L. Sekaric, and Y. Vlasov, “Ultracompact optical buffers on a silicon chip,” Nature Photonics 1, 65 (2006). [CrossRef]

] (F=100) is much higher than those of the SiON SWDL (F=16), the effective slowing ratio S is almost the same. The reason is that, in the APF case, the overall transmission resonance is much wider than that of the single resonator, this broadening resulting from a spread of individual resonances caused by imperfections in the width of the waveguides and the resonators’ lengths. The high slowing factor of the PMMA CROW demonstrates that, even in the absence of an active control of the waveguide refractive index, the rings resonances are very close to their nominal value.

The reflective architecture enables also an easy and complete reconfiguration of the proposed SWDL. From this point of view, it is worthwhile to stress that full reconfiguration and continuously variable delays have not been demonstrated so far in neither APF nor CROW, both operating in transmission configuration.

Table 1. Figure of merits of state-of -the art slow-wave delay lines

table-icon
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5. Conclusion

Acknowledgement

Authors would like to thank the European project SPLASH (6th FP) for the partial financial support and Alessandro Cabas, Melissa Di Muri and Giorgio Mutinati, from Pirelli Labs, for the fabrication of the integrated optical circuits.

References and links

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R. S. Tucker, P.-C. Ku, and C. J. Chang-Hasnain, “Slow-light optical buffers: capabilities and fundamental limitations,” J. Lightwave Technol. 23, 4046 (2005). [CrossRef]

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L. Vestergaard Hau, S. E. Harris, Z. Dutton, and C.H. Behroozi, “Light speed reduction to 17 metres per second in an ultracold atomic gas,” Nature 397, 594 (1999). [CrossRef]

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M. Bajcsy, A.S. Zibrov, and M.D. Lukin, “Stationary pulses of light in an atomic medium,” Nature 426, 638 (2003). [CrossRef] [PubMed]

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Y. Okawachi, M.S. Bigelow, J.E. Sharping, Z. Zhu, A. Schweinsberg, D.J. Gauthier, R.W. Boyd, and A.L. Gaeta, “Tunable all-optical delays via Brillouin slow light in an optical fiber,” Phys. Rev. Lett. 94, 153902 (2005). [CrossRef] [PubMed]

5.

K.Y. Song and K. Hotate, “25 GHz bandwidth Brillouin slow light in optical fibers,” Opt. Lett. 32, 217 (2007). [CrossRef] [PubMed]

6.

R.M. Camacho, M.V. Pack, J.C. Howell, A. Schweinsberg, and R.W. Boyd, “Wide-bandwidth, tunable, multiple-pulse-width optical delays using slow light in cesium vapour,” Phys. Rev. Lett. 98, 153601 (2007). [CrossRef] [PubMed]

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J. B. Khurgin, “Optical buffers based on slow light in electromagnetically induced transparent media and coupled resonator structures: comparative analysis,” J. Opt. Soc. Am. B 22, 1062 (2005). [CrossRef]

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M. Ghulinyan, M. Galli, C. Toninelli, J. Bertolotti, S. Gottardo, F. Marabelli, D. Wiersma, L. Pavesi, and L. Andreani, “Wide-band transmission of non-distorted slow waves in one-dimensional optical superlattices,” Appl. Phys. Lett. 88, 241103 (2006). [CrossRef]

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F. Morichetti, A. Melloni, J. Čáp, J. Petráćek, P. Bienstman, G. Priem, B. Maes, M. Lauritano, and G. Bellanca, “Self-phase modulation in slow-wave structures: A comparative numerical analysis,” Opt. Quantum. Electron. 38, 761 (2006). [CrossRef]

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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]

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F. Morichetti, A. Melloni, C. Canavesi, F. Persia, M. Martinelli, and M. Sorel, “Tunable Slow-Wave Optical Delay-Lines,” Slow and Fast Light, Washington DC, MB2 (2006).

13.

A. L. Reynolds, U. Peschel, F. Lederer, P. J. Roberts, T. F. Krauss, and P. J. I. De Maagt, “Coupled defects in photonic crystals,” IEEE Trans. Microwave Theory Tech. 49,1860 (2001). [CrossRef]

14.

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, 2263 (2004). [CrossRef]

15.

J. K. S. Poon, L. Zhu, G.A. De Rose, and A. Yariv, “Transmission and group delay of microring coupledresonator optical waveguides,” Opt. Lett. 31, 456 (2006). [CrossRef] [PubMed]

16.

F. Xia, L. Sekaric, and Y. Vlasov, “Ultracompact optical buffers on a silicon chip,” Nature Photonics 1, 65 (2006). [CrossRef]

17.

J.B. Khurgin, “Dispersion and loss limitations on the performance of optical delay lines based on coupled resonant structures,” Opt. Lett. 32, 133 (2007). [CrossRef]

18.

S. Mookherjea and A. Oh, “Effect of disorder on slow light velocity in optical slow-wave structures,” Opt. Lett. 32, 289 (2007). [CrossRef] [PubMed]

19.

A. Melloni, F. Morichetti, G. Cusmai, R. Costa, A. Breda, C. Canavesi, and M. Martinelli, “Progress in large integration scale circuits in SiON technology,” Proc. of 9th International Conference on Transparent Optical Networks , vol. 1, 223 (2007).

20.

A. Melloni and M. Martinelli, “Synthesis of Direct-Coupled-Resonators Bandpass Filters for WDM Systems,” IEEE J. Lightwave Technol. 20, 296 (2002). [CrossRef]

21.

C.K. Madsen, M. Cappuzzo, E.J. Laskowski, E. Chen, L. Gomez, A. Griffin, A. Wong-Foy, S. Chandrasekhar, L. Stulz, and L. Buhl, “Versatile integrated PMD emulation and compensation elements,” IEEE J. Lightwave Technol. 22, 1041 (2007). [CrossRef]

22.

A. Melloni, F. Morichetti, F. Persia, C. Canavesi, R. Siano, and M. Martinelli, “Optical processing with slow wave structures: properties and applications,” Proc. of 8th International Conference on Transparent Optical Networks , vol. 2, 199 (2006).

23.

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OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(200.4490) Optics in computing : Optical buffers
(230.4555) Optical devices : Coupled resonators

ToC Category:
Rings, Disks, and Other Cavities

History
Original Manuscript: September 28, 2007
Revised Manuscript: October 17, 2007
Manuscript Accepted: October 18, 2007
Published: December 10, 2007

Virtual Issues
Physics and Applications of Microresonators (2007) Optics Express

Citation
F. Morichetti, A. Melloni, A. Breda, A. Canciamilla, C. Ferrari, and M. Martinelli, "A reconfigurable architecture for continuously variable optical slow-wave delay lines," Opt. Express 15, 17273-17282 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-25-17273


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References

  1. R. S. Tucker, P.-C. Ku, C. J. Chang-Hasnain, "Slow-light optical buffers: capabilities and fundamental limitations," J. Lightwave Technol. 23, 4046 (2005). [CrossRef]
  2. L. Vestergaard Hau, S. E. Harris, Z. Dutton, C.H. Behroozi, "Light speed reduction to 17 metres per second in an ultracold atomic gas," Nature 397, 594 (1999). [CrossRef]
  3. M. Bajcsy, A.S. Zibrov, M.D. Lukin, "Stationary pulses of light in an atomic medium," Nature 426, 638 (2003). [CrossRef] [PubMed]
  4. Y. Okawachi, M.S. Bigelow, J.E. Sharping, Z. Zhu, A. Schweinsberg, D.J. Gauthier, R.W. Boyd, A.L. Gaeta, "Tunable all-optical delays via Brillouin slow light in an optical fiber," Phys. Rev. Lett. 94, 153902 (2005). [CrossRef] [PubMed]
  5. K.Y. Song and K. Hotate, "25 GHz bandwidth Brillouin slow light in optical fibers," Opt. Lett. 32, 217 (2007). [CrossRef] [PubMed]
  6. R.M. Camacho, M.V. Pack, J.C. Howell, A. Schweinsberg and R.W. Boyd, "Wide-bandwidth, tunable, multiple-pulse-width optical delays using slow light in cesium vapour," Phys. Rev. Lett. 98, 153601 (2007). [CrossRef] [PubMed]
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