Design of a thin-film-based optical filter for broadband multichannel communication systems R.K. Sinha ∗ ), Shalini Garg, K.L. Deori Departmentof Applied Physics, Delhi College of Engineering (Faculty of Technology, University of Delhi), Bawana Road, Delhi – 110042, India Received 8 December 2002; final version 31 March 2003 This paper is concerned with the design of an optical filter, based on thin-film inter- ference, for multichannel optical communication systems with Ta2O5 and MgF2 materials for 1550 nm operation. The performance of the filter configuration is analyzed and the numerical results of the optimization parameters, such as central wavelength, 3-dB band- width, figure of merit and ripple in the passband, are reported. The variation of these parameters is also studied for various modified filter configurations. The angular perfor- mance of the filter is investigated in terms of the polarization-dependent loss and spectral shift of transmittance towards shorter wavelengths. PACS : 42.79.Sz, 42.79 Wc, 42.25.Hz, 42.82.Bq, 42.79.Ci Key words : dense wavelength-division multiplexing, thin film, interference, 3-dB band- width, ripple 1 Introduction Multichannel optical communication systems, such as wavelength-division mul- tiplexing (WDM) and dense wavelength-division multiplexing (DWDM) [1,2] was made possible by the realization of several optical components. An optical filter is one of the most critical component. In order to increase the channel information capacity of the optical fiber, the bandpass filter [3] must have a wide bandwidth, covering the wavelength deviation of the signal light. For optical telecommunication applications, the 1300nm and 1550nm wavelength windows are mainly considered. Recently, there has been a growing interest in the application of the interference filter [4] in DWDM broadband optical communication systems. Since the informa- tion carried in the fiber is modulated at high bit rate and because the source lasers are inherently unstable in wavelength, the DWDM filter must have a flat response and a large spectral width. In this paper, a bandpass filter for application in broadband DWDM systems, based on thin-film interference, is designed. The performance of the filter is eval- uated in terms of its central wavelength, 3-dB bandwidth, quality factor, ripple in the passband and polarization-dependent loss at various angle of incidences. * ) E-mail: dr rk sinha@yahoo.com, sgupta90@yahoo.com Czechoslovak Journal of Physics, Vol. 53 (2003), No. 5 417