Femtosecond and picosecond mode-locked lasers have been widely used in scientific and industrial areas[
Chinese Optics Letters, Volume. 17, Issue 7, 071404(2019)
Strain compensated robust semiconductor saturable absorber mirror for fiber lasers
We demonstrate a strain compensated long lifetime semiconductor saturable absorber mirror (SESAM) with a high modulation depth for fiber lasers. The SESAM was measured to have a damage threshold of 9.5 mJ/cm2, a modulation depth of 11.5%, a saturation fluence of 39.3 μJ/cm2, and an inversed saturable absorption coefficient of 630 mJ/cm2. The SESAM has been applied to a linear cavity mode-locked Yb-doped fiber laser, which has been working for more than a year without damage of the SESAM.
Femtosecond and picosecond mode-locked lasers have been widely used in scientific and industrial areas[
SESAMs for mode-locked fiber lasers require much higher modulation depth, which means thicker absorption layers or large number of quantum wells (QWs). However, due to the lattice mismatch between the QWs and the substrate, more strain will be accumulated in both the thick layer and multiple QWs in this situation. Such strain can bring defects, misfit locations, as well as poor surface morphology in the epitaxial layers, and also has been one of the main limitations for a higher damage threshold[
In this work, we propose a SESAM structure with strain compensated InGaAs/GaAsP multi-QWs. The SESAM was characterized using femtosecond laser pulses with a modulation depth of 11.5% and a damage threshold of
Sign up for Chinese Optics Letters TOC Get the latest issue of Advanced Photonics delivered right to you!Sign up now
The structure of the SESAM is shown in Fig.
Figure 1.Designed structure of the SESAM.
The SESAM was grown on GaAs (100) substrates by means of metal–organic chemical vapor deposition (MOCVD). The growth temperature was 690°C for GaAs/AlGaAs DBRs, buffers, and caps and 580°C for InGaAs/GaAsP QWs.
The key parameters of the SESAM are the saturation fluence
Based on Eq. (
Following the method in Ref. [
Figure 2.Experimental setup for characterization of the SESAM. Test laser, 1064 nm mode-locked fiber laser with a pulse energy of 5 μJ;
We can adjust the pulse fluence to more than four magnitudes through altering the two attenuation stages. The laser beam was divided into a reference arm and a signal arm using a half-wave plate and a polarization beam splitter. A lens of 30 mm focal length was used to focus the beam onto the SESAM with a spot diameter of 34 μm, which allowed the pulse fluence up to hundreds of millijoules per centimeter squared (
|
Figure 3.Nonlinear reflectivity measurements for the SESAM under test. The reflectivity is fitted with Eq. (
We constructed a linear cavity mode-locked Yb-doped fiber laser to test the SESAM. The structure of the laser is shown in Fig.
Figure 4.Experimental setup of the mode-locked laser based on SESAM. Integrated SESAM including a 1064 nm collimator, a lens with a 15 mm focal length, and a SESAM mounted on a copper heat sink; Yb:fiber, Yb-doped fiber with an absorption coefficient of 5 dB/m at 975 nm; WDM, wavelength division multiplexer; FBG, fiber grating with a center wavelength of 1064 nm; diode laser, with a center wavelength at 975 nm.
Figure 5.Image of the integrated SESAM.
The laser starts mode locking at a pump power of 120 mW, and the mode locking is very stable (Fig.
Figure 6.Pulse sequences from the SESAM mode-locked laser.
Figure 7.(a) Measured pulse spectrum of the pulse train from the laser oscillator. (b) Intensity autocorrelation trace of the pulse train. (c) Measurement of output power as a function of pump power.
In summary, we demonstrated a SESAM by the design of strain compensated InGaAs/GaAsP multi-QWs. The SESAM has a high damage threshold up to
[7] Y. Xue, Q. Wang, Z. Zhang, L. Chai, Z. Wang, Y. Han, H. Sun, J. Li, J. Wang, Y. Wang, X. Ma, Y. Song. Chin. Opt. Lett., 2, 466(2004).
[8] G. Ju, L. Chai, Q. Wang, Z. Zhang, Y. Wang, X. Ma. Chin. Opt. Lett., 1, 695(2003).
[14] L. Chen, M. Zhang, X. Wang, W. Li, Y. Wei, Y. Ma, Z. Fan, G. Niu, J. Yu, Y. Liu, Z. Xue, Z. Zhang. Chin. Sci. Bull., 561, 348(2011).
[18] C. G. E. Alfieri, A. Diebold, M. Kopp, D. Waldburger, M. Mangold, F. Emaury, C. J. Saraceno, E. Gini, U. Keller. Conference on Lasers and Electro-Optics, 1(2016).
[19] T. Diebold, M. Zengerle, M. Mangold, C. Schriber, F. Emaury, M. Hoffmann, C. J. Saraceno, M. Golling, D. Follman, G. D. Cole, M. Aspelmeyer, T. Südmeyer, U. Keller. Opt. Express, 24, 10512(2016).
Get Citation
Copy Citation Text
Yan Wang, Nan Lin, Wanli Gao, Huanyu Song, Minglie Hu, Haiming Li, Wenxia Bao, Xiaoyu Ma, Zhigang Zhang. Strain compensated robust semiconductor saturable absorber mirror for fiber lasers[J]. Chinese Optics Letters, 2019, 17(7): 071404
Category: Letters
Received: Mar. 6, 2019
Accepted: Mar. 28, 2019
Posted: Mar. 29, 2019
Published Online: Jul. 9, 2019
The Author Email: Zhigang Zhang (zhgzhang@pku.edu.cn)