Fine-tuning of a diode laser wavelength with a liquid crystal intracavity element

A novel and simple approach for fine-tuning a laser wavelength is proposed and demonstrated. The key element is a planarly aligned nematic liquid crystal (NLC) cell inserted between the grating and end mirror of an external-cavity semiconductor laser (ECL). Varying the voltage driving the NLC cell, causes its extraordinary index of refraction to change due to field-induced reorientation of the LC director. This is equivalent to tuning the laser cavity length. As a result, the laser wavelength can be continuously tuned. With a 35.5-μm-thick NLC cell, the output frequency of the present laser can be continuously tuned over 4 GHz. The root mean square driving voltage required is 1.5 V or less. The tuning range is in good agreement with the theoretical predictions.