Intra-cavity stimulated emissions of photons in almost pure spin states without imposed nonreciprocity

Shu-Wei Chang

doi:10.1364/oe.20.002516

Abstract

We propose a chiral Fabry-Perot cavity in which only the cavity modes in almost pure spin (circular polarization) states lase in the presence of gain. In absence of imposed nonreciprocal environments and time-reversal symmetry breaking of emitter states to favor the emission of circularly-polarized photons, only the resonance of modes with a specific spin orientation remains in the cavity. We demonstrate a prototype of the cavity using distributed Bragg reflectors and cholesteric liquid crystals. This reciprocal cavity may provide a method to control the angular momentum state of emitters based on stimulated emissions.

Highlights

Nonvanishing angular momenta in quantum mechanical systems often come along with the time-reversal symmetry (T symmetry) breaking
Only one circular polarization stands out in the presence of gain. We show that such a FP laser is realizable using isotropic distributed Bragg reflectors (DBRs) and cholesteric liquid crystals (CLCs), of which a few combinations had been considered in literature [26,27,28]
We begin with a reciprocal condition, we show that the feedback from circularly polarized (CP) stimulated emissions may turn the cavity nonreciprocal

Summary

Introduction

Nonvanishing angular momenta in quantum mechanical systems often come along with the time-reversal symmetry (T symmetry) breaking. In addition to nonreciprocal responses such as the magneto-optic effect which distinguishes the two circular polarization (spin) states in a time-irreversible way, we gain another access to angular momenta of optical fields via reciprocal photonic structures. Such examples include quarterwave plates which transform linearly polarized (LP) beams into circularly polarized (CP) ones, or cholesteric liquid crystals (CLCs) in the chiral phase that filter CP components of incident waves [1, 2]. A conclusion will be given at the end (section 6)

Time-reversal symmetry breaking from photon emissions in reciprocal cavities

Fabry-Perot cavities with a special chiral reflector

Construction of the chiral cavity

Effect of circularly-polarized stimulated emissions on reciprocity

Conclusion