In an optical receiver, the unity-gain current responsivity of the photodetector is given by:
eta.e
Ri = ------
hf
where:
| eta | = quantum efficiency (0.5), |
| e | = electronic charge (1.6 x 10-19 C), |
| h | = Planck's constant (6.63 x 10-34 J.s), |
| f | = optical frequency (c/Wl = 4.57 x 1014 Hz), |
| c | = velocity of light (3 x 108 m/s), |
| Wl | = wavelength (656 x 10-9 m). |
Substituting the values given above in parentheses into the expression for reception at 656 nm, we find that:
Ri = 0.26 mA/mW
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