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3Multi-level phase transitions in GST225 thin film coated on a
fiber end face
D. Guryev1*, I. Zhluktova1, V. Kamynin1, P. Lazarenko2, D. Terekhov2, S. Kozyukhin3,
V. Tsvetkov1
1-Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia 2- National Research University of Electronic Technology, Moscow, Russia 3- Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, Moscow, Russia
Phase-change materials (PCMs) are ideal candidates for nonvolatile memories, in particular, the Ge2Sb2Te5 (GST225) has the best performance in terms of speed and stability. Also, GST225 have large contrast in electrical/optical properties between the crystalline state and the amorphous state, furthermore, it has been shown that GST225 has opportunity to procced partial phase transitions (multilevel transitions) [1]. This is a good opportunity for producing all-optical devices for logic computing [2].
In this work, we have demonstrated an all-fiber system for performing and observing phase transitions in a GST225. The endface of a SMF28 fiber (core diameter 9 ^m) was coated with GST225 film by magnetron sputtering of Ge2Sb2Te5 polycrystalline target. According to the results of atomic force microscopy the film thickness was 458 nm.
An all-fiber system was assembled to perform phase transitions in the GST225 film and to observe the change in the optical properties of GST (fig. 1(a)). A pulsed amplified fiber laser [3] operating at a wavelength of 1070 nm was used as the writing laser. The repetition rate of the writing pulses was 1 MHz, the pulse energy could be varied from 1 to 14 nJ, and the pulse duration was ~ 50 ps. A single pulse from a pulse train, or several pulses with a repetition rate of 1 MHz (fig. 1(c)), could be extracted with the acousto-optic modulator (AOM). Continuous-wave laser diode with a wavelength of 1550 nm and emission power < 4 mW was used as the probe laser.
Figure 1. (a) - Scheme of the experimental setup: ISO - optical isolator, AOM - acousto-optic modulator, WDM - wave division multiplexer, PD 1-3 - photodetectors connected with fiber endfaces; PD 1 - registering of writing pulses; PD 2 - registering of the probe laser radiation reflected from the GST sample; PD 3 - registering of the probe radiation passed through the GST225 film; (b) - oscilloscope trace of the reflected radiation of the probe laser; (c) - oscilloscope trace of a series of writing pulses.
We were able to observe partial phase transitions (partial crystallization or partial amorphization) due to changes in film reflectance (increased reflectance-crystallization, decreased reflectance-amorphization). The possibility of multi-level phase transition (>10 reflection levels) was also demonstrated due to the effect on the film of several consecutive writing pulses (fig. 1(b)).
This research may be useful for the development of optical modulators compatible with fiber systems and integrated circuits. In particular, this research may be useful for the development of allfiber circuits for all-photonic computing, information storage and logic elements.
[1] G.P. Lazarenko, et al, Low power reconfigurable multilevel nanophotonic devices based on Sn-doped Ge2Sb2Te5 thin films, Acta Materialia, vol. 234, pp. 117994, (2022).
[2] Z. Liu, et al, Intelligent all-fiber device: storage and logic computing, Photon. Res., vol. 10 (1), pp.357-363, (2022).
[3] I. Zhluktova, S. Filatova, A. Trikshev, V. Kamynin, V. Tsvetkov, All-Fiber 1125 Nm Spectrally Selected Subnanosecond Source, Appl. Opt., 59, pp. 9081, (2020).
