Is this diode driven wrong?

[floppy32]

Hello,

One of my collogue is using the following laser-diode and only using the RF input and applying 5V to 0V short pulsed using a function generator.

He doesn't use the other pins only the RF input by an SMA connector.

Here is the diode pins:

And here is the signal he applies to RF input:

He is till gets some optical output. But isn't he reverse biasing the diode?

 

[barry]

It depends on how the generator is connected, and you don’t show the connection. And what’s the scope reference?

 

[BigBoss]

If you use another RF diode then a capacitor ( rectifier circuit) , you can obtain more efficient result.
This can also work but during half cycle. Also, there will be a RF Power Dissipation over the Resistance.

 

[floppy32]

It depends on how the generator is connected, and you don’t show the connection. And what’s the scope reference?

Function generator is outputting this waveform observed when coupled to a scope https://www.edaboard.com/attachments/1687550647799-png.183510/ And when connected to the laser diode, the function generator is connected to the RF input of the laser I show in question. Isnt the diode reverse biased?

--- Updated Jun 24, 2023 ---

If you use another RF diode then a capacitor ( rectifier circuit) , you can obtain more efficient result.
This can also work but during half cycle. Also, there will be a RF Power Dissipation over the Resistance.

Function generator is outputting this waveform observed when coupled to a scope https://www.edaboard.com/attachments/1687550647799-png.183510/ And when connected to the laser diode, the function generator is connected to the RF input of the laser I show in question. Isnt the diode reverse biased?

 

[FvM]

Looks like the LD would be never forward biased and never lighting. Depending on the LD specs, there's also a risk to damage it by exceeding the reverse breakdown voltage which is typically quite low.

The purpose of the circuit isn't clear. A LD module datasheet could clarify about ratings and intended operation. I guess a negative bias current source is expected at pin 3.

 

[floppy32]

Looks like the LD would be never forward biased and never lighting. Depending on the LD specs, there's also a risk to damage it by exceeding the reverse breakdown voltage which is typically quite low.

The purpose of the circuit isn't clear. A LD module datasheet could clarify about ratings and intended operation. I guess a negative bias current source is expected at pin 3.

Yes exactly thats what I thought so. But he claims he gets some ultrashort optical pulses. Maybe some current passes during diode's recovery due to its capacitance. Yes pin 3 is for biasing but he doesn't use it he leaves it open. He uses only RF connector input with the wave form I provided. I just wanted to be sure if he is reverse biasing it. It seems so isnt it?

 

[Easy peasy]

As the 5V goes to zero there will be some capacitive forward current in the diode - very brief.

 

[floppy32]

As the 5V goes to zero there will be some capacitive forward current in the diode - very brief.

I see and the strange thing is that the max diode reverse voltage of this laser-diode is given as 2V. In this case he is applying 5V reverse voltage and the diode still not damaged. Or maybe it is already damaged since never checked in forward biased way.