Abstract
At present, amplitude modulation is preferred for the distribution of cable television signals, although it places stringent requirements on carrier-to-noise ratio (CNR) and linearity.1 For example, consider a system consisting of a 200-mW laser with relative intensity noise of −165 dB/Hz, fiber coupling of −35 dB, external interferometric modulator with 6-dB insertion loss, link loss of 5 dB, and receiver with rms noise current of 15 pA/(Hz)1/2 and operating at an optical modulation depth (OMD) of 1% per channel. In principle this system limits the broadcasting of 40 channels with a desired CNR of 50 dB (4-MHz bandwidth) and composite triple beat of 62 dB below the carrier (dBc) to two locations. We have analyzed the distortion characteristics of a variety of modulators based on coupled waveguides and variable phase mismatch to look for a passive means of reducing the distortion, thus allowing us to broadcast to more sites. Here we show analytically that these structures exhibit intermodulation distortion similar to the interferometric modulator.2 Measured 3IM distortion levels for samples of Ti:LiNbO3 interferometric, uniform Δβ, Δβ reversal, and weighted coupling3 projected to an OMD of 4% are in the range of −74 to −72 dBc and confirm the models.
© 1990 Optical Society of America
PDF ArticleMore Like This
R. M. De RIDDER and S. K. KOROTKY
WH5 Optical Fiber Communication Conference (OFC) 1990
Richard B. Childs and Vincent A. O’Byrne
PD23 Optical Fiber Communication Conference (OFC) 1990
Masayuki Shigematsu, Kouji Nakazato, Toshio Okita, Yasushi Tagami, and Kiyoshi Nawata
WB3 Optical Amplifiers and Their Applications (OAA) 1990