Controllable Bistability in Dual-Fiber Optical Trap in Air

TL;DR

This paper investigates bistability in a dual-fiber optical trap, demonstrating how optical interference causes multiple equilibrium states and how misalignment can improve positional stability to thermal noise limits.

Contribution

It reveals the origin of bistability due to optical interference and proposes a method to suppress it using transverse misalignment, enhancing trapping stability.

Findings

Bistability arises from optical interference between fiber ends and the microsphere.

Adjusting laser power modulates the transition rate between states.

Transverse misalignment eliminates bistability, reaching thermal noise limit stability.

Abstract

The dual-fiber optical trap, owing to its high sensitivity and facile miniaturization, holds significant actual application value in fields such as high-precision metrology of mechanical quantities and biological manipulation. The positional stability of the trapped particle is pivotal to system performance, directly setting the measurement noise floor and operational precision. In this work, we observe bistability and hysteresis in the axial equilibrium position of a 10-um diameter SiO2 microsphere. This bistability arises from optical interference between the fiber ends and the microsphere, creating multiple potential wells. Experimental results demonstrate that the microsphere's transition rate can be effectively modulated through precise control of the trapping laser power. Furthermore, the incorporation of transverse misalignment has effectively eradicated bistability, thereby substantially improving positional stability throughout the entire optical trapping region. This suppression successfully reduced the system's residual positional uncertainty to the thermal noise limit. Consequently, this research will enhance the precision of microparticle manipulation and the sensitivity of sensing in dual-fiber optical trap systems.