Light Modulators With Phase-change Materials Driven By Transparent Micro-heaters

As an important optical information processing unit,space-based electro-optical modulator is able to dynamically regulate the amplitude,phase,polarization and propagation direction of space incident light by external electric field or bias voltage,and plays an important role in various miniaturized,integrated and compact optical systems.Since the performance of electro-optical modulators essentially depends on the electro-optical effect of the selected tunable materials themselves,the discovery of new electro-optical tunable materials and their regulation mechanisms is an important direction for the development of high-performance electro-optical modulators.In recent years,chalcogenide phase change materials（GST）have attracted extensive attention in the field of integrated electro-optic devices due to their characteristics of crystal-amorphous reversibility,high repeatability,non-volatility and long service life.In general,there are three ways to promote the phase transition of GST:heating annealing,laser pulse and voltage pulse,so that it can be reversibly transformed between high-resistance amorphous and high-conductivity crystalline,accompanied by a significant change in the dielectric constant in the mid-infrared band,showing an efficient optical modulation effect.However,for space light modulation devices,the miniaturization and integration of the devices are greatly limited by the way of hot plate heating or laser pulse induced phase transition,and the electro-induced phase transition technology still faces many technical problems,such as electrode material,shape and arrangement.In this paper,we attempt to use a transparent microheater in the infrared band to drive the crystalline transition of phase change materials,and to design electro-optic tunable devices to solve the light transmission limitations faced by conventional microheaters with metal as the thermal resistance layer.Firstly,a microheater based on semi-metallic two-dimensional material Pt Se₂ thermal resistor is designed and verified.The Pt Se₂ thermal resistor is stacked above the GST nanodisks array to generate heat by electric pulse and induce GST phase transition,so as to realize electro-optic modulation in the transmission direction.The transparent and conductive properties of Pt Se₂ in the infrared band were demonstrated by experimental tests,and the phase change material optical modulation devices with Pt Se₂ microheaters were processed and prepared,and a reflection modulation depth of up to 45%was achieved in the 3～5μm band.However,during the test,it was found that the Pt Se₂ microheater was easy to fuse,resulting in the failure of the modulation device,so the expected reversible modulation was not achieved.Therefore,this paper explores another feasible transparent thermal resistance material,ITO,and improves the microheater configuration by designing a suspended transparent microheater on a self-supporting,highly stressed Si₃N₄ film.The electrical and thermal conduction processes of the microheater are simulated by multi-physics simulation method.It is found that the hot zone of the microheater on the suspended membrane can reach 382.3°C within 100μs,which indicates that the suspended structure of the microheater has extremely high thermal efficiency.In this paper,an electro-optic modulator composed of a suspended ITO microheater and a GST micro-nano structure is also designed.The optical modulators composed of GST nanodisk and nanocube arrays are simulated and optimized.Theoretically,the maximum modulation depth before and after GST phase transition can reach 86.3%,and the extinction ratio of up to 207:1 is achieved.The experimental and theoretical results of this paper can inspire the development of new phase change material electro-optical modulators,which provide a reference for realizing more stable,controllable,fast and reversible electro-optical modulation devices in the mid-infrared band.