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What Is Optical Modulation?}

  • Posted on November 26, 2017 at 4:40 am

What is Optical Modulation?


Mary Bush

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Simply put, optical modulation is the process of impressing information on a light carrier; it involves varying one or more of the features that define the optical wave, such as its power level, frequency, or phase.nnOur current fiber optic communication systems almost exclusively use semiconductor laser as the light source, and by far the easiest way to modulate the light is to modulate its power level. The amount of light power the emerges from the device depends on the electric current that is injected into it. The greater the current, the more light power.nnBut, the relationship between the input electric current and the output light power is not directly proportional: doubling the current does not produce double light power.nnOptical fiber supports the following modulation schemes, known as optical modulation.nn1. Continuous: in optics, we usually call this intensity modulation, similar to analog modulation, with the only difference being in the nature of the optical carrier signal.nn2. Discrete: Here, it is known as optical on-off keying similar to shift keying with a sinusoidal carrier. The modulated signal is comprised of pulses (on/off) of constant amplitude.nnThese techniques are based on the variation of optical power according to electric signals applied to the electro-optical transducers. It is recommended to use frequency pulse modulation for analog transmission of a television channel by optical fiber.nnThe use of optical fiber as a transmission medium in a network for data communication offers very high data rates in the range of gigabits per second. All the high speed LANs and integrated networks use a fiber transmission medium for data transfer.nnThe optical transmission medium offers very low attenuation and very high bandwidth. Two of the high data rate user-networks interfaces of 155.720 Mbps and 622.080 Mbps for ATM-based B-ISDN have been defined.Technology Advisory Board

The New Technology of Fiber Optics

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