- Table of contents
- 2.1 Elements
2.1.1 Optical link : Radio Frequency Over Fiber¶
On optical link consists of :
Figure 1. Optical Link (source Miteq).
- an optical transmitter ; it modulates input Radio Frequency (RF) signal onto the optical wavelength intensity.
Optical intensity is varied either directly by varying Laser Diode current or indirectly through a Mach-Zehnder Modulator modulating a constant laser source.
- fiber optic : in general, monomode fiber optic is used to avoid dispersion especially for long link. Morever, wavelengths around 1300 nm are used as dispersion is minimum in this region.
- an optical receiver : it is based on a photodectector. It detects RF modulation on the optical wavelength and outputs the RF signal.
Such an optical link is referred to as Radio Over Fiber (RoF), as well.
The main parameters for an optical link are gain, bandwidth, Noise Figure (NF) and Spurious Free Dynamic Range (SFDR).
These parameters are described in the document from MITEQ : MITEQ, Fiber optic products : https://www.miteq.com/docs/MITEQ_FiberOptic_c40.pdf.Main applications are
- Antenna remoting :
for satellite broadcast TV, signal is received on the antenna on the roof but actually demodulated in the tuner in the living room.
for teleports, Radio-frequency signal transport through optical fibres from Antenna to the main building (containing Modulator/Demodulator, Network Equipments).
- Signal distribution :
for phased array radar application, it could be used to distribute the Local Oscillator to the different array elements.
for cable television (CATV : Community Antenna TeleVision) : to distribute the TV channels to the homes.
2.1.2 Antenna remoting : IF transport from Antenna Low Noise Block to Tuner/Demodulator for Satellite Broadcast TV¶
Earth stations are based on an indoor/outdoor unit architecture. In our system we will count on:
- Outdoor: Ku-band reception antenna, Low Noise Block (LNB) transposing Ku-Band to Intermediate Frequency at L-Band, a short coaxial cable, the modulator transmitter (allows to convert from L-band to optic frequencies) and the 30m of Monomode FO.
- Indoor: consists of the receiver L-band/optic receiver and the coaxial cable to connect it to the satellite tuner/demodulator (connected to the TV).
Both the coaxial cable and the optical link have been put on the graph. This is to show what the optical link will actually replace in the traditional implementation with the coaxial cable.
Remark:The choice of L-Band has been made to have cable with reasonable loss at affordable cost. Optical link will have to meet similar cost constraints.