Repetitive Switching of Optical Gate Switch
Using Phase-Change Material and Si Waveguide
Tatsuya Toyosaki1, Daiki Tanaka1, Yuichiro Ikuma1, Yuya Shoji2, Masashi Kuwahara2,
Xiaomin Wang2, Kenji Kintaka2, Hitoshi Kawashima2 and Hiroyuki Tsuda1
1: Graduate School of Science and Technology, Keio University
2: National Institute of Advanced Industrial Science and TechnologyABSTRACT
In this paper, we reported repetitive switching of two types of optical gate switch using
phase-change material and Si waveguide; with a channel waveguide and with a ribwaveguide. 1,000 times of repetitive switching was observed, and an average extinction
ratio of channel waveguide and rib waveguide type switch was 9.7 dB and 15 dB,respectively.
Key word: Optical switch, Silicon photonics, Phase-change material
INTRODUCTION
Fast and low power consumption optical switches are required for photonic networks.
For that purpose, we have proposed the optical gate switches using phase-changematerial (PCM) and silicon wire waveguide [1-6]. PCM has two different stable states ofcrystalline and amorphous at room temperature. We used the large difference in theimaginary part of the complex refractive index of these two states for the optical gateswitches. This optical gate switch has three advantages; 1) small size, 2) fast switching,and 3) low power consumption. In this paper, we reported repetitive switching of two
types of optical gate switch using PCM and Si waveguide.
STRUCTURE OF THE OPTICAL GATE SWITCH
Figure 1 shows the structure of the channel waveguide type switch. We used Ge2Sb2Te5(GST-225) as PCM. A GST-225 film with a thickness of 25 nm and a length of 5 m wasdeposited on wire waveguide in a gate region. ZnS/SiO2 with a thickness of 50 nm wasdeposited on GST-225 as a passivation layer. The core dimensions of the Si waveguidewere 520 x 200 nm2, but they were 410 x 180 nm2 in a gate region.
Figure 2 shows a structure of the rib type switch. A GST-225 film with a thickness of 50nm and a length of 1 m was deposited on rib waveguide. A thickness of over cladding
was about 2 m.

EXPERIMENTAL
Figure 3 shows the experimental setup for laser pulse irradiation. A laser diode (LD)with a wavelength of 660 nm was used to irradiate the material. A light was guided by asingle mode optical fiber and focused on to the sample. An object lens with a numericalaperture (NA) of 0.8 was used. The full-width at half-maximum (FWHM) of the focused
spot size was about 1.2 m.
Figure 4 shows the transmittance change of the channel waveguide type switch for 950
to 1,000 irradiation cycles. 1,000 times of repetitive switching with an average
extinction ratio of 9.7 dB was observed. We used a laser pulse with a width of 400 ns anda peak power of 15 mW for crystallization, and a laser pulse with a width of 12 ns and apeak power of 70 mW for amorphization.
Figure 5 shows the transmittance change of the rib waveguide type switch for 950 to
1,000 irradiation cycles. 1,000 times of repetitive switching with an average extinction
ratio of 15 dB was observed. We used a laser pulse with a width of 400 ns and a peak
power of 25 mW for crystallization, and a laser pulse with a width of 12 ns and a peak
power of 160 mW for amorphization.
CONCLUSION
In this paper, we have reported repetitive switching of two types of optical gate switch
using phase-change material and Si waveguide; with a channel waveguide and with arib waveguide. In a channel waveguide type switch, 1,000 times of repetitive switchingwith an average extinction ratio of 9.7 dB was observed. In a rib waveguide type switch,
1,000 times of repetitive switching with an average extinction ratio of 15 dB wasobserved.
ACKNOWLEDGEMENT
This work was supported by the Strategic Information and Communications R&DPromotion Programme (SCOPE) from the Ministry of Internal Affairs and Communications.

REFERENCES[1] H. Tsuda, et al., PCOS2007, Atami, pp. 39-42, 2007.
[2] Y. Ikuma, et al., IEICE Electron. Express, vol. 5, no. 12, pp. 442-445, 2008.
[3] Y. Ikuma, et al., Electron. Lett., vol. 46, no. 5, pp. 368-369, 2010.
[4] Y. Ikuma, et al., IPR 2010, IWA6, July 25-28, Monterey, U.S.A., 2010.
[5] Y. Ikuma, et al., Electron. Lett., vol. 46, no. 21, pp. 1460-1462, 2010.
[6] D. Tanaka, et al., Electron. Lett., vol. 47, no. 4, pp. 416-417, 2011.

Fig. 1. Structure of the channel waveguide type switch

Fig. 2. Structure of the rib waveguide type switch

Fig. 3. Experimental setup for switching operation.

Transmittance [dB]-40

ON state-45-50-55

OFF state
-60
950

960

970
980
Number of irradiation

990

1000

Fig. 4. Transmittance change with pulse irradiation for the channel waveguide typeswitch

Transmittance [dB]-25

ON state-30-35-40-45-50

OFF state

-55
950

960

970
980
Number of irradiation

990

1000

Fig. 5. Transmittance change with pulse irradiation for the rib waveguide type switch