Narrowing Linewidth of Wavelength-Swept Active Mode Locking Laser Based on Cross Gain Modulation

Se Jin Park,Gyeong Hun Kim,Minsik Jo,Chang-Seok Kim,Hwi Don Lee

doi:10.3390/app9194029

Abstract

We demonstrate a novel narrow-linewidth configuration of a wavelength-swept active mode locking (AML) fiber laser. The frequency response of the modulation depth of a semiconductor optical amplifier can be improved in a higher modulation frequency region by adapting the cross gain modulation (XGM) configuration, compared to that of the conventional direct gain modulation (DGM) configuration. As a sufficient modulation depth is implemented for an AML at higher modulation frequencies at around gigahertz order, it results in a narrower linewidth of lasing output. For the same modulation frequency of 1361.25 MHz, the linewidth of 0.25 nm with DGM becomes narrower up to 0.113 nm with XGM, which corresponds to an improved point spread function with 1.41 mm of 6-dB roll-off.

Highlights

Over the last decade, the wavelength-swept laser has been used as a powerful tool in biomedical imaging and various sensing application areas [1,2,3,4,5,6]
Wavelength-swept active mode locking (AML) lasers have been developed by exploiting a radio frequency (RF) signal generator to modulate the gain of a semiconductor optical amplifier (SOA) using an electric current pump directly, which can implement an output wavelength tuning from the AML condition matching in a chromatic dispersion cavity [8,9,10]
Under the direct gain modulation (DGM) configuration used for most wavelength-swept AML laser schemes, this linewidth narrowing approach by increasing the modulation frequency is mostly limited below the region of a few hundred MHz

Summary

Introduction

The wavelength-swept laser has been used as a powerful tool in biomedical imaging and various sensing application areas [1,2,3,4,5,6]. Wavelength-swept active mode locking (AML) lasers have been developed by exploiting a radio frequency (RF) signal generator to modulate the gain of a semiconductor optical amplifier (SOA) using an electric current pump directly, which can implement an output wavelength tuning from the AML condition matching in a chromatic dispersion cavity [8,9,10].

Results

Conclusion