Description
SM fiber optic cable sc apc simplex coupler
Overview:
Fiber coupler, also known as a splitter, a connector, an adapter, or a fiber flange, is a component used to realize optical signal splitting/combining, or for extending an optical fiber link, and is a passive component. The field is applied in telecommunications networks, cable television networks, subscriber loop systems, and regional networks.
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A directional coupler is a four-port component with directional transmission characteristics that is constructed by two pairs of transmission systems that are coupled together by a coupling device. Firstly, the performance index of the directional coupler is introduced, then the waveguide two-hole directional coupler, the double-branch directional coupler and the parallel coupled microstrip directional coupler are introduced.
1) directional coupler performance indicators
The directional coupler is a four-port network. Port "1" is the input, port "2" is the through output, port "3" is the coupled output, port "4" is the isolated end, and its scattering matrix is [S ]. The performance metrics describing the directional coupler are: coupling degree, isolation, orientation, input standing wave ratio, and operating bandwidth. The following are introduced separately.
2) Isolation
The ratio of the input power P1 of the input terminal "1" to the output power P4 of the isolation terminal "4" is defined as the isolation, which is denoted as I.
(3) Directionality
The ratio of the output power P3 of the coupling terminal "3" to the output power P4 of the isolation terminal "4" is defined as the degree of orientation, denoted as D.
(4) Input standing wave ratio
The standing wave ratio of the input port "1" when the ports "2, 3, 4" are connected to the load is defined as the input standing wave ratio, denoted as ρ.
(5) Working bandwidth
The working bandwidth is the operating frequency range when the above parameters such as C, I, D, and ρ are specified to the coupler.
Waveguide type
The waveguide dual-hole directional coupler is the simplest waveguide directional coupler, with the main and auxiliary waveguides passing through two of its common narrow walls.
A small hole with a distance d=(2n+1)λg0/4 is coupled. λg0 is the wavelength of the waveguide corresponding to the center frequency, and n is a positive integer, generally taking n=0. The coupling holes are generally circular or other shapes. When working at the center frequency, βd=π/2, at this time D→∞; when deviating from the center frequency, secβd has a certain value, and D is no longer infinite. In fact, even at the center frequency, the two-hole coupler is not infinitely directional, but only about 30 dB.
In short, the waveguide two-hole directional coupler relies on the mutual interference of the waves to realize the directional output of the main waveguide, which is superimposed in phase on the coupling port and reversely canceled on the isolation port. In order to increase the coupling degree of the directional coupler and widen the operating frequency band, a porous directional coupler can be used.
Double type
The double-branch directional coupler is composed of a main line, a sub-line and two branch lines, wherein the branch line
The length and spacing are 1/4 of the center wavelength, as shown in Figure 5-15. Let the characteristic impedance of the main line inlet line "1" be that the characteristic impedance of the main line exit line "2" is (k is the impedance conversion ratio), the characteristic impedance of the sub-line isolation end "4" is, and the sub-line coupling end "3" The characteristic impedance is that the characteristic impedance of the parallel connection line is Z0p, and the characteristic impedances of the two branch lines are respectively sum.
Parallel species
The parallel coupled microstrip directional coupler is a reverse directional coupler whose coupling output is on the same side as the main input. As shown in the right figure, the port in is the input port, the port out is the through port, and the port ocup is the coupling. Port, port "4" is the isolation port.
