Optical Single Sideband Modulation and Optical Carrier Power Reduction and CATV Networks

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1 Optical Single Sideband Modulation and Optical Carrier Power Reduction and CATV Networks by: Hatice Kosek

2 Outline Optical Single Sideband Modulation Techniques Optical Carrier Power Reduction Techniques An overview of CATV fiber optical networks

3 The Need for Optical Single Sideband (SSB) Modulation Chromatic dispersion is a major problem in double side band modulation especially at 1550nm. RF signal can be completely eliminated at the receiver if phase difference between the USB and LSB is 180 o.

4 SSB Modulation Techniques G.H. Smith et al.(1997) suggested use of dualelectrode Mach-Zehnder Modulator. Sideband is not completely suppressed J. Park et al.(1997) and C. Marra et al.(2001) experimentally showed the feasibility of Fiber Bragg Gratings as optical filters. Compatible with fiber Has potential low cost However, adds dispersion

5 My Objectives Single Sideband modulation using the ultra-narrow fiber Bragg grating RF signal de-multiplexing with fiber Bragg grating Rx1 Laser Rx2

6 Optical Power Reduction Weak modulation of the optical carrier is needed in Sub Carrier Multiplexing (SCM). However, weak modulation results in high optical power and therefore large DC. Large DC can saturate and even damage the photo-detector. Therefore, high modulation depth is needed.

7 Techniques to Decrease the Carrier Power Optical Filters (1995) Distortion to the RF signal Stimulated Brillouin Scattering (1994,2000) Instabilities in frequency response Noise FBGs as optical filters (2005) M. Attygalle et al. used FBGs with different reflectivities Sensitivity and dynamic range increased up to 7dB in DSB and SSB modulation

8 FBGs as optical filters continued FBGs with 80% reflectivity 10 GHz DSB signal using MZM 35 GHz SSB signal using Dual-Electrode MZM

9 Results BER vs. receiver optical power for 10 GHz DSB and 35 GHZ SSB with and without FBG of 80 % reflectivity

10 Results Continued.. 35 GHz SSB signal (squares). Point A (no grating), B(80%), C(95%), D(98.5%)

11 CATV Fiber Optical Networks Coaxial Based Cable TV Networks Issues - Too many amplifiers - Addition of noise and distortion - Large coaxial cable attenuation - Low quality and reliability

12 Coaxial-Fiber CATV Network

13 Advantages of hybrid fiber/coaxial CATV Number of amplifiers is reduced down significantly. Fiber has less loss than coaxial cable Fiber (0.25 db/km) Coaxial cable (1dB/300m) Cable bandwidth is increased therefore more video channels can be transmitted over the link. The quality and the reliability of the network is increased.

14 Features of CATV Fiber Optical Network Up to 80 video channels in a frequency range of 120 to 550 MHz can be delivered. Modulation techniques: AM modulation (6MHz/channel) Simple and cost effective S/N of 47 db FM modulation (30 MHz/channel) Has higher S/N than AM modulation Sub Carrier Multiplexing Multiplexing of both analog and digital signals Intermodulation products Composite Second Order (CSO) (f 1 ±f 2 ) Composite Third Order (CTB) (f 1 ±f 2 ±f 3 ) Cross Modulation

15 Possible Research Topic Investigation of embedding cellular service in CATV networks. Effect of one system on the other. Maximum number of video and voice channels that can be transmitted simultaneously. Modification needed to accommodate both systems. SNR analysis, fiber length, cell size and etc.

16 Conclusion Fiber Bragg Gratings offer a simple and cost effective solution in SSB modulation and carrier power reduction. The implementation of fiber in CATV networks has improved the system performance. Re-definition of the current network can support cellular service.