Optical gain and absorption of quantum dots measured using an alternative segmented contact method

An alternative segmented-contact method for accurate measurement of the optical gain and absorption of quantum-dot and quantum-dash active materials with small optical gain is reported. The usual error from unguided spontaneous emission is reduced by subtracting signals acquired from three independently controlled sections as opposed to just two found in the conventional technique. The quantum-dot gain spectra are measured to a precision of less than 0.2 cm^-1 at nominal gain values below 2 cm^-1, and gain spectrum of quantum-dash sample is calculated with an error less than 0.3 cm^-1 at a gain less than 1 cm^-1. These accuracies are checked with a self-calibrating method. The internal optical mode loss measurement is also described