Ultranarrow resonance peaks in the transmission and reflection spectra of a photonic crystal cavity with Raman gain

TL;DR

This paper theoretically investigates how Raman gain in a photonic crystal cavity can produce ultranarrow resonance peaks in transmission and reflection spectra, with potential for high coefficients at low pump intensities.

Contribution

It demonstrates the existence of a specific pump intensity range where narrow resonance peaks occur due to Raman gain, revealing a new mechanism for controlling light in photonic crystals.

Findings

Narrow peaks in spectra occur at specific pump intensities.

Transmission and reflection coefficients can exceed unity.

Resonance peaks are due to drastic dispersion near Raman transition.

Abstract

The Raman gain of a probe light in a three-state $\Lambda $-scheme placed into a defect of a one-dimensional photonic crystal is studied theoretically. We show that there exists a pump intensity range, where the transmission and reflection spectra of the probe field exhibit \textit{simultaneously} occurring narrow peaks (resonances) whose position is determined by the Raman resonance. Transmission and reflection coefficients can be larger than unity at pump intensities of order tens of $\mu$W/cm$^{2}$. When the pump intensity is outside this region, the peak in the transmission spectrum turns into a narrow dip. The nature of narrow resonances is attributed to a drastic dispersion of the nonlinear refractive index in the vicinity of the Raman transition, which leads to a significant reduction of the group velocity of the probe wave.