Laser Diodes
Laser diodes are forward biased p-n junctions. Photos are generated from recombining of holes and electronics that are injected into semiconductor material.
Photon Energy
Energy of a photon:
Where: h = Planks Constant = 6.626*10^-34 Js
f = frequency (Hz)
c = Speed of Light = 3*10^8 m/s
Therefore:
Laser Diode Type | Wavelength |
AlGaAs | 800 – 900 nm |
InGaAsP | 1310 – 1550 nm |
Relative Intensity Noise
Relative intensity noise (RIN) is caused by random power fluctuations in laser diodes. RIN is given by:
RIN is defined in terms of power fluctuations of 1 Hz bandwidth.
The noise current in photo detector that results from RIN is given by:
Where: Ro = Responsivity (A/W)
A way to reduce the RIN is to increase the laser bias current, Ib above threshold current, Ith:
