Tunable DFB laser diode based on high-order surface isolation grooves working at 905nm
Introduction
Distributed feedback Bragg (DFB) laser diodes are important light sources in many applications in modern industry. The DFB laser diodes have the advantages of small size, stable wavelength characteristics, and ease of integration with other devices. They are used as pump sources in both fiber [1] and solid-state [2] lasers. Further, tunable DFB laser diodes are mainly used as light sources in optical modules [3] and many other micro-systems [4], [5], [6]. In particular, 905 nm wavelength DFB laser diodes are important components in photo-electrical sensing and photo-acoustic imaging [7], [8], [9] devices. Owing to the small attenuation in air and a good penetration effect, the 905 nm DFB laser diodes have a great potential for optical phase arrays in laser ranging [10], [11], free-space line-of-sight optical communications, and light detection and ranging (LiDAR) in autonomous vehicles [12], [13].
To the best of our knowledge, existing DFB lasers around a wavelength of 905 nm are all based on the index coupled effect [9], [10]. Most of them are prepared by epitaxial regrowth methods, and such fabrication processes require complicated nanoscale lithography and etching techniques [14], [15], [16], [17].
In our previous work [18], [19], [20], we already proposed some regrowth-free methods for fabricating gain-coupled DFB laser and taper laser diodes. For gain-guided lasers the spontaneous emission factor is taken to be large(as compared with that for index-guided lasers) and the gain profile is taken to be smooth and parabolic [21]. It is suitable for preparing tunable semiconductor lasers. The isolation grooves act as slot inside FP cavity can modulate the emission spectrum, The presence of surface isolation grooves inside the cavity of a semiconductor laser can have a very strong influence on the emission spectrum, It is helpful for the tunable DFB laser to improve the performance of single longitudinal mode [22], [23], [24], [25], [26].
In this paper, We combined surface gratings and periodic p-electrodes structures for fabricating our first 905 nm tunable DFB laser based on isolation grooves and smaller periodic electrode windows, Both gain-coupled mechanism and slot function are considered. By modulating the depth of the isolation grooves, we have recently demonstrated a tunable laser based on surface isolation grooves which completely relies on these grooves to provide necessary reflectivity for the laser operation independent of any etching facets [27]. Compared with the previous work results, the output power and the side-mode suppression ratio (SMSR) is improved, and the novel 905 nm tunable DFB laser can achieve greater tuning range. The central wavelength of this device can be tuned from 899.9 nm to 907.7 nm within a small temperature range. Compared with our previous periodic p-contacts gain-coupled DFB laser diodes, the device in proposed in this study has better thermal stability and wavelength modulation characteristics.
Section snippets
Device structure and fabrication
The laser diode device was prepared by metal–organic chemical vapor deposition. The structure of the wafer is shown in Table 1. The quantum well of the DFB laser is formed by the InGaAs/AlGaAs sandwich layers, and the average peak wavelength of PL spectrum is 891.9 nm.
Fig. 1 shows a schematic diagram of the device structure. The surface isolation grooves can be seen under a scanning electron microscope, as illustrated in Fig. 1(a). The periodic electrode windows were on the top of the mesas,
Results and discussion
A continuous-wave (CW) test was carried out at 20 . The power-voltage-current (P-I-V) and electro-optical efficiency curves of the device are shown in Fig. 2 (measured by Newport PMKIT-15-01). The data in Fig. 2 were obtained by measuring one facet of the device, and the conversion efficiency was calculated by doubling the tested output power of one facet, so as to obtain the total value. The device had a threshold current of 85 mA. The output power reached 145.3 mW/facet at 500 mA. It is
Conclusion
We have presented a 905 nm tunable DFB laser diode with periodic surface isolation grooves. The method of fabrication is cost-effective and does not introduce regrowth technology and the structure is suitable for integration. The uncoated device reached a CW power of 145.3 mW/facet. The SMSR of the device was over 37 dB. We demonstrated that the device realizes a good single longitudinal mode output performance. We achieved the expected tunability within a range of 7.8 nm by controlling the
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work is supported by National Science and Technology Major Project of China (2018YFB2200300); Frontier Science Key Program of the President of the Chinese Academy of Sciences (QYZDY-SSW-JSC006); National Natural Science Foundation of China (NSFC) (11874353, 61935009, 61934003, 61604151, 61674148, 61904179, 61727822, 11604328, 61805236); Dawn Talent Training Program of CIOMP, China .
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