We present experimental results showing a reduction of relative intensity noise (MN) in partly gaincoupled InGaAsPIInP multiquantum-well DFB lasers. By comparing with conventional index-coupled lasers, it is found that even a small gain-coupling improves significantly the feedback insensitivity of DFB lasers. The mechanism of the KIN reduction and the less feedback sensitivity are believed to be a combined effect of the high relaxation frequency and heavy damping rate, the stronger internal mode discrimination, the facet reflectivity immunity, and the flatter carrier distribution in the gain-coupling structure. . IntroductionToday's high-capacity and long-haul fiber optic communication systems use distributed feedback (DFB) semiconductor lasers as the light sources because of their narrow spectral linewidth. However, these commonly used DFB lasers were found very sensitive to external optical feedback (EOF) [1, 2]. For instance, even a small amount of EOF can cause significantly linewidth broaderning and extra frequency and relative intensity noises (RIN) in such lasers. The direct consequences of the EOF-induced problems are increased "bit errors" in digital communication systems and signal distortion in analog communication systems.There are several approaches to solving the EOF problems. A most effective and popularly utilized approach is to use a discrete optical isolator with above 60 dB isolation. The usage of isolators not only increases the production-cost but also hampers the laser being integrated monolithically with other optical devices. Another approach is to conduct high-reflectivity coating on laser front facet (facet reflectance R >70%) to diminish the amount of EOF into the laser cavity. An obvious shortcoming of doing this is the lower optical output from the facet. Recently, a more sophisticated approach by DFB laser internal mode stabilization has attracted considerable attention. In practice, this kind of mode stabilization can be realized with different methods, such as using larger icL or introducing gain-coupling in a DFB structure. Unfortunately, the lager icL often induces spacial hole-burning effects in DFB laser. Therefore, the DFB laser incorporating a gaincoupled (GC) structure has been considered more advantageous in reducing the operation sensitivity of the laser to EOF [3]. There are very few data supporting this consideration either experimentally or theoretically. In this paper, we present the experimental results on a partly GC multiquantum-well (MQW) DFB laser [4]. As RIN of a laser is a very sensitive parameter and directly related to system application issues, we use the R1N to evaluate the EOF sensitivity of the lasers. A clear reduction of RIN in partly GC DFB lasers at various EOF levels was observed. By comparing with conventional index-coupled (IC) DFB lasers, it is found that even a small gain-238 ISPIE Vol. 2148 O8194-144331941$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 07/03/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
A simplified technique has been developed for fabricating ultrafine GaAs gratings, exploiting electron-beam lithography, SiCl4 reactive ion etching (RIE) and single-layer masking. A 50-nm-thick single PMMA (polymethylmethacrylate) layer, directly exposed and not postbaked, is used as the etching mask. Using this technique, ultrafine diffraction gratings (period 60, 80, 120 nm) with good profile have been successfully fabricated on GaAs substrates. It is expected that the present technique will be applicable to the fabrication of finer structures such as quantum wires and dots.
Light sources capable of emitting multiple wavelengths are key components for the implementation of wavelength division multiplexing (WDM) systems. Over the past several years, there has been remarkable progress in developing such sources. Today's WDM sources include solitary distributed feedback (DFB) lasers selected by operation wavelength, tunable singlemode lasers, multi-wavelength laser arrays, and various integrated laser devices made with different technologies. This paper presents an overview of present WDM lasers, and discusses the pros and cons of the different fabrication technologies in conjunction with device performance, manufacturability, reliability and overall cost. Commercial availability ofthe lasers will also be reviewed.
We have fabricated 1 .55 im ridge waveguide DFB lasers consisting of p-doped, 1.5% compressive strained-layer all quaternary MQW active region by two-step MOCVD with a first-order grating located in the upper GRINSCH region. By optimizing the p-doped carrier concentration in the barrier layers, ii and detuning, the measured -3 dB bandwidth was 13 GHz with flat frequency response and very little RC roll-off in this structure.From RIN measurements, the intrinsic bandwidth was calculated to be 18 GHz.Furthermore, by changing the position of the grating to the MQW active region, partly gain-coupled DFB lasers were formed; these devices exhibit very stable single mode operation and narrow spectral linewidths. The -3 dB electrical bandwidth was measured around 22 GHz and the intrinsic bandwidth was estimated to be 28-30 GHz. Experimental results show that the devices have small wavelength chirps and clear eye patterns under 10 Gbit/s NRZ direct modulation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.