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Large delay-bandwidth product and tuning of slow light pulse in photonic crystal coupled waveguide

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Abstract

This paper reports two advances in a slow light device consisting of chirped photonic crystal slab coupled waveguide on SOI substrate. One is concerning the delay-bandwidth product, indicating the buffering capacity of the device. We experimentally evaluated a record high value of 57 (a 40 ps delay and a 1.4 THz bandwidth). We also observed ~1 ps wide optical pulse transmission in the cross-correlation measurement. Regarding the pulse as a signal and considering the broadening of the pulse width due to the imperfect dispersion compensation in the device, storage of more than 12 signal bits was confirmed. The other is a wide-range tuning of the pulse delay. We propose a technique for externally controlling the chirping to permit variable delay. We demonstrate tuning of the pulse delay up to 23 ps, corresponding to a ~7 mm extension of the free space length.

©2008 Optical Society of America

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Figures (5)

Fig. 1.
Fig. 1. Chirped PCCW connected with I/O PCWs. (a) Scanning electron microscope image of the device fabricated on a SOI substrate and the measured airhole diameter 2r. (b) Magnified image of the branch between the input PCW and PCCW. (c) Schematic photonic band diagram (ω-k) and group index spectrum (ω-n g) in unchirped structure (left) and chirped structures (center and right). Here illustrates the case that the band shifts to higher frequencies with increasing 2r.
Fig. 2.
Fig. 2. Transmission characteristics of chirped PCCW. Design is the same as in Fig. 1. (a) Transmission spectrum. (b) Group delay measured using modulation phase shift method (black line). Circles denote the delay evaluated from the pulse peak in d. (c) Spectrum of input optical pulse. A shoulder-like bump is a nature of the used mode-locked fiber laser. (d) Cross-correlation trace of output optical pulse. Top one is the self-correlation trace of input pulse. Pulse widths Δτi and Δτo are evaluated from the FWHM of the trace Δτc. In (b)–(d), the same color indicates pulses having the same wavelength.
Fig. 3.
Fig. 3. Delay and group index spectra in unchirped PCCW with laser heating centered at the branch. Modulation phase-shift method was used. The airhole diameter 2r was fixed at 0.25 µm.
Fig. 4.
Fig. 4. Cross-correlation trace of output optical pulse in chirped PCCW with laser heating. Device used is the same as for Fig. 1. Colors correspond to those in Fig. 2.
Fig. 5.
Fig. 5. Cross-correlation trace of output optical pulse at λp=1.546 µm in chirped PCCW (another sample) with heating by the smallest spot. The heating was centerd (a) at the branch and (b) at the confluence. Compared with the previous sample, the absolute delay was small because of slightly larger chirping and the short I/O PCWs.
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