Semiconductor Lasers and Photonic Integrated Circuits

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Applications
Overview

Tunable Distributed Amplification DFB (TDA-DFB) laser

Description

Wavelength-tunable lasers are key devices in WDM systems. They can be integrated, for instance, with an electro-absorption (EA) section or in a more complex structure such as an Optical Phase-Locked Loop (OPLL). The performance of such structures may vary significantly for relatively small changes of the physical device parameters and can also influence the system performance tremendously.
In this application example, we show a design of a tunable distributed amplification (TDA) DFB laser [1]. The schematic of the modeled device is represented in Figure 1. It is implemented by a module which models a multi-section semiconductor device consisting of a DFB cavity with 280 um total length. The cavity contains a grating and is formed by alternate gain (SOA) and passive (tuning) sections. The active region type of the gain and tuning sections are MQW and bulk, respectively. One current contact is applied to each of the sections, where the injected current is divided for the gain and tuning sections.

Typical Results

The first design is formed by 8 sections that perform alternating gain and tuning functions. The length of the gain sections (Lsoa) is 40 um, and 30 um of the tuning sections (Ltune). In order to study the wavelength tunability and mode-hopping response of the laser, a continuous ramp current from 0 to 100 mA is applied to the tuning sections; the current of the SOA sections is swept in steps from 50 to 100 mA. The output frequency of the laser versus output power is displayed in Figure 2.
In the next test, the length of the sections is varied while the total length of the device is kept constant. Figure 3 represents the results for lasers with 8 sections of different lengths. It can be seen that the laser presents mode-hopping when the SOA sections are shorter than the tuning ones.
For the results represented in Figure 4, all sections have the same length, but the number of sections is varied. We observe that when increasing the number of sections, i.e. using sections with smaller length, the wavelength tunability and the output power increase. For the case of 4 sections or less, the laser shows mode-hopping.

Keywords

PICs, semiconductors, multi-section laser, tunable laser, TDA-DFB-LD