Some questions related to Opto Electronics

[Waqas]

optoelectronics version

Hi,

anybody please give me answers of these basic opto electronics questions

1. Why LED is called current optical modulator??
2. What is CTR(Current Transfer Ratio) and why it should be constant??
3. What is spontaneous mean lifetime for HeNe laser?
4. What is meta stable state & why it has larger mean lifetime than spontaneous?

some other questions i wanna ask
5. Why Germanium diode has larger size than Silicon diode?
6. What is the function of External Trigger on an Oscilloscope?

Thanks in advance.

 

[Waqas]

optoelectronics questions

what ?? no reply in 1 day 8O

it seems i m not the only one having problem finding answers to these questions. :roll:

PLz help me.

 

[laktronics]

ctr opto

Hi,
1.Why LED called current optical modulator:
I suppose it should be because it produces light intensities proprtional to apllied forward current.
2. CTR ( Current Transfer Ratio):
Opto couplers produce an output collector current proportional to the applied input current.
The ratio between the output current to input current is called current transfer ratio. Inside the optocoupler, the input LED converts the forward current to light intesity and the output opto transistor converts this light back to its base current and β times this base current appears at its collector as output current. Thus current transfer ratio is a product of these three conversion factors which will be a constant depending on the physical and electrical parameters of the opto.
6. External trigger in oscilloscope:
One of the basic problems in the usage of oscilloscopes is synchronisation of nonperiodic signals to get a steady wave form on the screen. Since the internal trigger may not have any time relations with such wave forms, it will difficult to synchronise using the internal trigger. In such cases by applying a signal having definite time relations with the monitored signal at the external trigger input, we can get a steady wave form on the screen.
Since to answer other questions, I have to refer some documents, I leave it to you under self help category.
Regards,
Laktronics.

 

[boonrider]

wiki current transfer ratio in an optocoupler

Have a look here:

https://en.wikipedia.org/wiki/Metastable

It provides a good explanation of metastability