Optocoupler basics

Optocoupler is the coupling device used to couple the optical signal. Optical coupler is basically used to combine and to split the signals in the optical network. It is also referred as directional coupler.

Optocoupler-Optical coupler

Figure depicts 2X2 coupler with two input ports and two output ports. The simplest and most common coupler is made by fusing two optical fibers at the middle parts. These types of fibers are referred as fused fiber couplers.

As shown in the figure, fractional part(say α) of power from IN1 port is passed through OUT1 port and remaining part of 1- α is taken out form OUT2. Here α is the coupling ratio. The fraction 1-α of the power from IN2 is distributed to the OUT1 port and the left over power to the OUT2.

The optical coupler is designed either as wavelength selective type or as wavelength independent type. They usually operate over a wide range of wavelengths referred as bandwidth. In wavelength selective type α depends on wavelength and in wavelength independent type α does not depend on wavelength.

Wavelength selective type of optical couplers are widely used to combine signals at wavelengths of 1310 nm and 1550 nm into a optic fiber without loss. Wavelength-dependent type of couplers are used to combine 980 nm or 1480 nm pump signals along with a 1550 nm signal into an EDFA.

4N46 opto-coupler from Avago technologies is one of the optical coupler having High gain with darlington output .

Optical Coupler Features

•  High isolation
•  No signal reflectivity
•  Low coupling power loss
•  No added polarization effects
•  No added dispersion effects
•  No signal absorption
•  No added noise
•  No through-phase shift

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