The temporal behavior of the optical frequency emitted by several DFB lasers under direct square wave modulation was measured using an all-fiber implementation of a Mach-Zender interferometer with an imbalance of 30 ps. The impulse response of the optical frequency to injection current modulation was found to contain a time constant as short as 10-20 ns, together with a few longer ones. The existence of such a short time constant is consistent with a thermal analysis of a laser structure with finite thermal impedance of the active region and should be taken into consideration in various wide bandwidth applications of direct modulated semiconductor lasers.
Bibliographical noteFunding Information:
Manuscript received March 2, 1998; revised June 26, 1998. This work was supported in part by the UK-Israel science and technology research fund. H. Shalom, A. Zadok, and M. Tur are with the Faculty of Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel. P. J. Legg, W. D. Cornwell, and I. Andonovic are with the Department of Electronic and Electrical Engineering, University of Strathclyde, Glasgow G1 1XW, U.K. Publisher Item Identifier S 0018-9197(98)07162-0.
- Distributed feedback lasers
- Optical communications
- Optical modulation/demodulation
- Thermal analysis