Interferometric Technique for the Spectral Characterization of High Frequency Current-Modulated Mid-Infrared Semiconductor Lasers

Marc-Simon Bahr,Marcus Wolff

doi:10.3390/photonics8100443

Abstract

We describe two methods, based on Michelson interferometery, that enable the determination of the absolute wavelength of current-modulated semiconductor lasers. By non-linear regression of the instantaneous frequency of the interference signal, the rate of change of the wavelength of the radiation can be inferred. Alternatively, the absolute wavelength can be directly calculated from the maxima and minima of the interference signal. In both cases a reference absorption line enables the determination of the absolute wavelength. Both methods offer respective advantages. The methods allow a highly resolved wavelength measurement under lower kilohertz range current-modulation with relatively little effort. As a result, we present the rates of wavelength change and absolute wavelengths exemplarily for a specific interband cascade laser. It is furthermore shown that the spectral dynamic range of the laser decreases with increasing modulation frequency.

Highlights

The exact knowledge of the emission wavelength is one of the fundamental parameters in laser spectroscopy
The determination of the momentary wavelength becomes extraordinarily difficult if the semiconductor laser emitting in the mid-infrared is modulated with a higher frequency
2 shows thatthat the direct evaluation of of fringes requires fewer physical quantities for the calculation of the absolute wavelength fringes requires fewer physical quantities for the calculation of the absolute wavelength andless lesscomputational computational effort compared to the non-linear regression method

Summary

Introduction

The exact knowledge of the emission wavelength is one of the fundamental parameters in laser spectroscopy. Several spectroscopic techniques such as photoacoustics require a modulation of the radiation as a matter of principle [1]. Semiconductor lasers can be modulated by variation of the operating current. In doing so amplitude as well as wavelength modulation are possible. Assuming a simple, frequency-independent proportionality between wavelength and current, as it is observable in continuous wave (cw) operation, can lead to significant measurement errors [2]. The determination of the momentary wavelength becomes extraordinarily difficult if the semiconductor laser emitting in the mid-infrared (e.g., an interband cascade laser or ICL) is modulated with a higher frequency

Methods

Results

Conclusion