Advances in Photonic Devices Based on Optical Phase-Change Materials

Abstract

Phase-change materials (PCMs) are important photonic materials that have the advantages of a rapid and reversible phase change, a great difference in the optical properties between the crystalline and amorphous states, scalability, and nonvolatility. With the constant development in the PCM platform and integration of multiple material platforms, more and more reconfigurable photonic devices and their dynamic regulation have been theoretically proposed and experimentally demonstrated, showing the great potential of PCMs in integrated photonic chips. Here, we review the recent developments in PCMs and discuss their potential for photonic devices. A universal overview of the mechanism of the phase transition and models of PCMs is presented. PCMs have injected new life into on-chip photonic integrated circuits, which generally contain an optical switch, an optical logical gate, and an optical modulator. Photonic neural networks based on PCMs are another interesting application of PCMs. Finally, the future development prospects and problems that need to be solved are discussed. PCMs are likely to have wide applications in future intelligent photonic systems.

On-Chip Integrated Photonic Devices Based on Phase Change Materials

“…To achieve these features, other than the design parameters, the device is also dependent upon the fabrication processes adopted. As no method is perfect and each method has its own advantages and disadvantages [147]. 4 Operating wavelength: 1530-1650 nm.…”

An Investigation into the Kinetics and Mechanism of Phase Transitions in Optical Phase Change Ternary Alloy $Ge_2Sb_2Te_5$

“…[12] [55] Such a mechanism requires the laser irradiated GST spot not losing heat fast enough to induce rim to centre growth, but instead causing the formation of randomly distributed crystal nucleation sites, facilitated by low thermal conductivity of the rim-ambient interface, spot-substrate interface and GST alloys in general. [31] This is observed in GST − 415, GST − 124 and GST − 225 where the crystallization time t n is independent of the radius of the spot, which is expected of such a mechanism. [31] [63] [67] The rate at which nucleation sites are formed inside the irradiated spot is dependent on the temperature, which in-turn is determined by the laser power and pulse width.…”

“…[12] [31] The application of a preconditioning short laser pulse (t p ∼ 100ns) can help as-deposited films mimic the speed of melt-quench films. [31] Laser power is another important factor influencing the kinetics of GST films that has been extensively studied in literature. [12] [31] [51] [62] The evolution of crystallinity in the samples as the laser power is increased is clearly visible in the XRD measurements shown in Figure 8(a) & 8(e).…”

“…[12] (b) Ternary phase diagram for the Ge-Sb-Te system. [31] hexagonal phase (h−GST ).Then we will move on to study how various factors such as laser power, pulse width, quench time & cooling rate affect both the (c → a) and (a → c) transitions and the macroscopic kinetics and mechanism of phase change namely nucleation and rim to centre growth. We will also investigate the atomistic mechanism of the phase change and look at bond distortions in the structure which when coupled with atomic migrations and carrier collisions facilitate phase change in GST − 225 upon stimulation.…”

“…Experiments in which the concentrations of Ge/Sb atoms were increased showed that the excess Ge/Sb did not occupy the octahedral vacancies but accumulates at the grain boundary. [31] [32] [36] [37] [43] It is proposed that this is due to the need for vacancies to maintain the long range order in the crystal structure and thus maintain crystal stability. [32] [36] [37] It is also proposed that vacancies are usually formed at the sites that would have been occupied by the Ge atoms, which has been experimentally verified and reported.…”