An optical receiver's structure is very simple. It consists of a photodiode that produces the electric current and an amplifier. It is much more difficult to create a high-performance optical receiver. We will now discuss some criteria for actual receivers.
There are many factors that go into the process. Signal current noise, noise coming from the photodiode (such as an avalanche dimming diode), noise from the amplifier electronics, thermal noise and dark current are all important factors.
How do you choose the right photodiode
For optical receiver applications, there are two main types of photodiodes: Avalanche and PIN.
PIN photodiode can be extended to PN diode. But PN diode is not without its flaws. The PN diode's depletion area is too small, so the received PON Optical Receiver power must not be very high in order to generate enough current. The second flaw of PN diode is its slow response, which limits it to kilohertz applications.
These limitations were solved by PIN photodiode. The depletion area has been increased to the maximum extent possible, with most photons being absorbed in the depletion area. The intrinsic layer reduces the function capability, which increases the switching speed and photon capture area.
This improved design has the added benefit of a faster opto-electro conversion rate and more efficiency.
Each photon absorbed by a PIN photodiode produces an electron hole pair, which then sets one electron flowing in the circuit.
A few incident photons can result in many carriers being created and an increase in external current in Avalanche photodiodes. This is how an Avalanche photodiode does it.
This phenomenon is called avalanche multiplication. This is because a strong electric field accelerates current carriers to such an extent that they knock out valence electrons from the semiconductor lattice. With a sufficient bias voltage, an avalanche will occur.
All of these are great, but there is a downside. The carriers amplify, but the uneven nature and multiplication creates noise.
Avalanche photodiodes, while non-linear, are quite unstable. However, they perform very similarly to regular silicon photodiodes, except that they require a lower operating voltage to achieve good multiplication.
Other important performance parameters for a photodiode
Below are some key parameters for your reference.
Photodiode responsiveness is the ratio between incident light power and generated current. This is often expressed in Amp/Watt. This is sometimes referred to as quantum efficiency.
The photodiode produces dark current when there is no incident sunlight. Dark current also includes current that is generated by background radiation or the saturation current at the semiconductor junction. When used in optical communication systems, dark current can be a source for noise. Read more here: https://www.premlink.net/pl150d-3-ftth-optical-receiver-pon-pass/