Semiconductor Laser with Electrically Modulated Frequency

TL;DR

This paper introduces a new electrically modulated frequency control method for semiconductor lasers, enabling fast, linear, and wide-range frequency tuning suitable for various laser types, exemplified by quantum cascade lasers at 10μm.

Contribution

A novel electrical modulation technique for semiconductor lasers that achieves fast, linear frequency tuning through space charge effects, applicable to any semiconductor laser type.

Findings

Frequency shift can reach GHz range.

Laser tuning speed limited by external electronics.

Intrinsic linearity between frequency and voltage achieved.

Abstract

We propose a novel method to control the frequency of semiconductor lasers. The new technique allows fabricating three-terminal lasers with fast frequency tuning and the possibility to implement intrinsically the linearization of laser frequency sweep. The electrical contact located between the lower undoped cladding and the waveguide together with the upper laser contact enable pumping for optical gain. A voltage applied between the same contact and the contact located under the lower cladding induces space charge limited current (SCLC) across the lower cladding. Electrons driven into this layer create the space charge. The charge affects the refractive index of the layer and correspondingly the laser frequency. The proposed technique is applicable to any semiconductor lasers. Critical requirements are that free carrier concentration in the lower cladding must be small enough not to affect the SCLC and the laser gain must be high enough to overcome losses introduced by interactivity contact. As an example, we present the calculated characteristics of the QCL operated at 10$\mu$m wavelength. Our calculations show that the laser frequency shift can reach GHz range and the laser tuning speed will be limited by external electronics. Calculations demonstrate that within the range of the selected parameters, the device possesses intrinsically linear relation between the optical frequency and the tuning voltage.