Two-wavelength wdm analog catv transmission with low crosstalk

Abstract

A two-wavelength WDM analog CATV transmission system which utilizes wavelength channel spacing of about 2.2 nm and laser-dithering. The system includes a pair of optical transmitters (DBF lasers), a pair of modulators, a dithering device, a polarization controller, a 3-dB combiner, an optical amplifier (EDFA), an attenuator, a length of optical fiber, a filter and a CATV receiver. The two lasers have wavelengths of .lambda.1 and .lambda.2, where the difference between .lambda.1 and .lambda.2 is approximately 2.2 nm. The modulators are driven with analog signals comprising 77 NTSC channels between 55.25 and 535.25 MHz A 2-GHz dithering tone is applied to the .lambda.1 laser and the output of the .lambda.2 laser is passed through the polarization controller to align the polarization of the two transmitters. The two modulated and aligned outputs are combined by the 3-dB combiner and launched into the EDFA The output of the EDFA is divided by the splitter four ways and one of the four outputs is passed through the attenuator and launched into the transmitting end of the optical fiber. The receiving end of the fiber is connected to a filter, which provides input into the CATV receiver. By utilizing a wavelength channel spacing of about 2.2 nm and dithering one of the lasers, worst-channel Composite Triple Beat distortion is reduced to -60 dBc, an acceptable level for deployment of WDM analog CATV systems.