Photo-sensors switching speed

[neptune]

Hi,

i want to know what is the max. switching speed of photo sensors available.

I have heard that maximum capacity of fiber optic is not fully utilised because the process of conversion of light into electric current and vice-versa is very slow process.

 

[MrAl]

Hi,

Some devices have data sheets that give some useful information, but now that you mention it i was thinking briefly about this a while back too where i wanted to use a light dependent resistor and laser to measure fan speed. It worked just fine, but i never looked into what the limit of the fan speed would be due to the LDR. I know they are slower than other types, but how much slower im not sure and never bothered to measure. Perhaps i should do this or look for some better data sheets. But sometimes i also like to use surplus parts that dont come with data sheets or even part numbers, so i guess a test or two is in order.

 

[neptune]

i have seen while Googling maximum speed of photosensors to be 500Khz, lol although data transfer is much faster.

I think photo sensors are inherently slow devices then switches. !

 

[dpj]

Generally for photo devices datasheets give rise time and fall time.
OSRAM SFH4510 950nm Photo Emitters has rise time tr=fall time=tf= 0.5uSeconds.
Hence maximum transition rate can be 1MHz.
Most of the devices are nearby this range only.

 

[neptune]

So which photosensors are used in optical communication

 

[RichTheDude]

PIN photodiodes are typically used in optical communications and they can have very large bandwidths ( GHz ).

For reference **broken link removed**

Please note, such parts are not cheap

 

[Jaguarjoe]

I poked around through Mouser, they have 349 photodiodes, many around $3.00 or so. Here is a $3 device with 20/25 ns response:

https://www.electro-tech-online.com/custompdfs/2012/04/QS2FQSE1103.pdf

They can't be too expensive because I was able to buy some affordable ones 45 years ago when I made a muzzle velocity gizmo.

 

[MrAl]

Hello again,


Yes the higher speed diode sensors are much faster and can be used when a faster response is needed. The LDR's are good for audio compressor work where a resistor works better to adjust the gain than a light sensitive diode because of the symmetrical current conduction.

Most glass diodes are light sensitive too and actually put out a (rather high impedance) voltage when illuminated. That's basically a solar cell.

Solar cells are pretty fast too i think, but it's been years since i looked at them for light detection applications.

LED's too of course, generate a small voltage when illuminated. Their higher capacitance would probably make them slower than the si diodes.