How to Design a High Performance Optical Receiver?

The structure of an optical receiver is simple: consisting of only producing a photodiode to the electrical current and an amplifier. But do not be fooled: It is far more complex, a really high performance optical receiver design. So we'll talk about some of the criteria of the actual recipients.

They are a number of factors involved in the process. They have in the amount of signal current noise, noise from the photodiode, such as by an avalanche diode, the noise of the amplificationElectronics, thermal noise, dark current and signal to noise ratio for high data bit rate.

How to choose the correct photodiode?

Essentially two types of photodiodes are commercially available for optical receiver applications: PIN photo diode and avalanche photodiode.

PIN photodiode

PIN photodiode is an extension of the PN diode. But PN diode has many crucial mistakes. PN diode is too small, depletion region, allowing the received optical power needs to be fairly high toto generate enough electricity. The second mistake is PN diode slow reaction, which is only for applications kilohertz limits.

PIN photodiode solved these restrictions on PN diode. The degradation in the region were as large as possible and included most of the photons in the depletion region. And the inclusion of the inner layer decreases the function of capacity, the switching speed and the photon capture area increased.

The advantage of the improved design is an efficientopto-electronic conversion and more speed.

Avalanche photodiodes (APD)

Produced in a PIN photodiode, each absorbed photon creates an electron-hole pair, which flows one electron in the external circuit sets.

But in an avalanche photodiode, a few photons are produced too many winners and a strengthened external current. How does it achieve an avalanche diode?

This is evidenced by the phenomenon produced in avalanche multiplication. As this is a strongelectric field will accelerate the current carrier, so much that they knock out valence electrons of the semiconductor lattice and with a high enough bias leads an avalanche of carriers.

While all are good, there is also a dark side to this issue. While strengthening the institutions, is the uneven nature of the propagation and noise.

In conclusion, although avalanche photodiodes are non-linear and relatively unstable, they are very similar to normal siliconPhotodiodes except that they can reach a slightly lower operating voltage for a good reproduction.

Other critical performance parameters of a photodiode

For your information some of the most important parameters are listed.

Sensitivity

Photodiode sensitivity is the ratio of the generated current on incident light power. This is usually expressed in amperes / watt. Sometimes this is referred to as quantum yield.

DarkCurrent

Dark current is the current generated by the photodiode when there is no incident light at all. The dark current includes background information generated radiation and the saturation of the current semiconductor junction. Dark current is a source of noise when they already used in optical communications.

Noise equivalent power

Noise equivalent power is the minimum input voltage necessary to produce optical power to photocurrent. This corresponds to the current RMS Noisein a 1Hz bandwidth.