ptical fiber is the medium of choice for high capacity digital transmission systems and high speed local area network. Besides these applications, optical fiber also can be used to transmit microwave signals for cable television, cellular radio, WLAN and microwave antenna remoting. To transmit microwave over optical fiber, the microwave signal is converted into optical form at the input of the fiber and at the output of the fiber, it is converted back to electrical signal. The main advantage of fiber transmission of microwave is reduced losses relative to metallic media (e.g. copper coaxial cable). This results in longer transmission distance without signal amplification or use of repeaters.
There are two approaches to optical signal modulation and recovery. The first type is IMDD (Intensity Modulation Direct Detection) and the second type is Coherent Detection. In IMDD, the optical source intensity is modulated by the microwave signal and the resulting intensity modulated signal passes through the optical fiber to a photodiode where the modulation microwave signal is converted back to electrical domain. In Coherent Detection, the optical source is modulated in intensity, frequency or phase by the microwave signal. The modulated signal passes through the optical fiber to the receiver where it is mixed with the output of a local oscillator (LO) laser. The combined signal is converted to electrical domain using a photodiode. This produces an electrical signal centered on the difference frequency between the optical source and the LO laser (i.e. intermediate frequency). This signal is further processed to recover the analog microwave signal.
RFoG (Radio Frequency over Glass) is the cable operators’ implementation of microwave transmission over optical fiber in which the coax portion of the HFC (Hybrid Fiber Coax) is replaced by a single fiber, passive optical network architecture (PON). RFoG allows cable operators to deploy fiber connectivity to customer premises (FTTP) while keeping its existing HFC and DOCSIS infrastructure. Like the HFC architecture, video controllers and data networking services are fed through a CMTS/edge router.
.
Related reading:Optical Isolator filmgear 銉夈儵銈偍10 rmt car sunshade