Dot Distributed Feedback Lasers Research Articles

Design of distributed feedback lasers grown on Si using time-domain traveling wave model combined with mode refractive index method

This paper proposes an optimization method combining the time-domain traveling wave model and the mode refractive index method, employed for characterizing both the transverse and longitudinal modes of quantum dot distributed feedback (DFB) lasers grown on Si. We use this method to optimize the overall performance of the Si-based DFB laser, and determine the material and chip structural parameters, including the ridge width, etching depth, grating thickness and grating position as optimization parameters. Here, the optimal DFB laser operating under fundamental transverse and single longitudinal mode is obtained. Its threshold current is as low as 5 mA, the slope efficiency is as high as 0.77 mW mA−1, and the side mode suppression ratio is up to 48 dB. When the injection current is 150 mA, the output power exceeds 100 mW. The corresponding ridge width, etching depth and grating thickness are 2 μm, 1.3 μm and 20 nm, respectively. The distance from the grating to the active region is 200 nm. Therefore, the novel method presented in this paper offers an effective scheme for the design of DFB lasers grown on Si with excellent performance.

InAs-InAlGaAs quantum dot DFB lasers based on InP [001

The InAs-InAlGaAs quantum dot (QD) lasers with the InAlGaAs-InAlAs material system were fabricated on distributed feedback (DFB) grating structures on InP (001). The single-mode operation of InAs-InAlGaAs QD DFB lasers in continuous-wave mode was successfully achieved at the emission wavelength of 1.564 mum at room temperature. This is the first observation on the InP-based QD lasers operating around the emission wavelength window of 1.55 mum. The threshold current density of the InAs-InAlGaAs QD DFB laser with a cavity length of 1 mm and a ridge width of 3 mum, in which one of the cleaved facets was coated with 95% high-reflection, was 1.23 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (176 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sup> for single QD layer). The sidemode suppression ratio value of the QD DFB laser was as high as 42 dB at the driving current of 100 mA

Fabrication and investigation of nanostructures and their application in new laser devices

In this article, techniques for the realization of exactly positioned nanostructures are presented and the properties of nanometer scale optic laser devices based on GaInAs/GaInAsP/InP heterostructure are discussed. The fabrication of nanometer scale optic devices requires the precise control of the confinement length of carriers as well as the confinement length of photons, which are different by one order of magnitude. Both requirements can be met by the application of high resolution electron beam lithography in combination with low damage etching techniques and planar epitaxial overgrowth. Lateral structures down to 15 nm with high optical quality at periods around 240 nm suitable for distributed feedback (DFB) devices have been obtained. For the first time, these nanofabrication techniques allow the realization of a new class of semiconductor lasers: gain coupled wire and dot DFB lasers. The reduced dimensionality of the active area shows significant improvements of the gain values and the laser thresholds. The precise definition of dot arrays (array size up to some 100 μm) allows the fabrication of a new device: a gain coupled dot DFB laser, consisting of dots forming a two-dimensional DFB grating.

Realization of dot DFB lasers

Dot lasers with first-, second- and third-order gain coupled distributed feedback (DFB) gratings have been realized by low damage dry etching in combination with wet chemical etching and epitaxial over-growth. This technique allows above room temperature (RT) operation of dot DFB lasers with dot diameters down to 85 nm. The laser spectra show the expected emission of gain coupled DFB lasers. Threshold current densities between 1.1 kA/cm/sup 2/ and 2.6 kA/cm/sup 2/ could be obtained depending on size of the active region. An improvement in T/sub 0/ could be demonstrated comparing 0-D/1-D/2-D lasers on the same wafer. Based on the dot grating geometry improvement of the side mode suppression ratio (SMSR) was observed for broad-area dot DFB lasers.