# Hi i need to modulate a upto 1MHz green laser

#### somiBabu

Joined Jan 13, 2017
34
Hi any one please help to modulation of a green laser circuit for laser pointer 120mA is threshold current 2.4v threshold voltage.maximum is 200mA

I need it for analog signal modulation for my degree project.

#### BR-549

Joined Sep 22, 2013
4,938
One may put a transformer in series with the laser current. This will allow you to modulate the laser in a number of ways.

The first thing to study is the laser data sheet.

#### somiBabu

Joined Jan 13, 2017
34
its a laser pointer comes with 3V battery.
and characterised with 120mA threshold maximum around 250mA/.

is it possible to modulate with analog signal need current driver laser circuit

#### BR-549

Joined Sep 22, 2013
4,938
It all depends on what you want to do. To modulate with a analog signal can mean a lot of different things.

A laser pointer with a 3 volt battery can mean of lot of different things too.

Do you know what a data sheet is?

What kind of modulation do you want to use?

What is the modulating signal?

Would turning the laser on and off suffice? A key can modulate.

What degree are you working on?

#### somiBabu

Joined Jan 13, 2017
34
sin wave (cw) modulation.
i given info about laser.....! then what is data sheet
engineering student for optical communication

#### joeyd999

Joined Jun 6, 2011
4,376
Would turning the laser on and off suffice?
This likely won't work at 1MHz. A LD takes a bit of time to begin "lasing". The modulation depth should be just above the minimum lasing threshold for 100% modulation.

#### somiBabu

Joined Jan 13, 2017
34
This likely won't work at 1MHz. A LD takes a bit of time to begin "lasing". The modulation depth should be just above the minimum lasing threshold for 100% modulation.
even less frequency is okay 500khz or 100kHz for what ever frequencies i need a circuit

#### Raygl

Joined Dec 3, 2016
10
I modulated an old HeNe laser tube by just putting a vacuum tube audio backwards in the HV line and feeding audio into the 8 Ohm side. It produced a high enough voltage to nicely modulate the laser. We did send audio quite a ways with it.

For a solid state laser it would be only a mater of impedance and using a capacitor because of the high frequency. It would be fun to see how high of a frequency a cheap laser pointer could do.

If you fed the laser through a resister to the midway current point you could see hpw much modulation was needed

#### somiBabu

Joined Jan 13, 2017
34
need circuit

#### BR-549

Joined Sep 22, 2013
4,938
I have never modulated one. Other than a flashlight long ago. I was interested in seeing the device.

Can a laser be AMed? When we AM a carrier......not only does the amplitude change......sidebands are created. Can a laser generate sidebands? Does a laser make an envelope? Can we see a tint change with high levels of AM modulation?

How about FM? Can we FM a laser? What modulation index do we need to see a color change with modulation? Would we need to swing laser many MHz to see modulation?

And if the frequency of the laser changes with modulation.......is it still a laser? Or can we just turn a laser on and off?

Didn't mean to hijack the thread.

I believe the TS just wants to key a laser pointer....not a laser device.

#### EM Fields

Joined Jun 8, 2016
583
Hi any one please help to modulation of a green laser circuit for laser pointer 120mA is threshold current 2.4v threshold voltage.maximum is 200mA

I need it for analog signal modulation for my degree project.

#### ronv

Joined Nov 12, 2008
3,770
need circuit
Not sure what kind of modulation you want. But here is a simple amplitude or frequency modulator.

#### somiBabu

Joined Jan 13, 2017
34
Not sure what kind of modulation you want. But here is a simple amplitude or frequency modulator.
View attachment 122824
Amplitude modulation
Sending an ofdm analog signal through laser
can u send the ltspice file

#### ronv

Joined Nov 12, 2008
3,770
Amplitude modulation
Sending an ofdm analog signal through laser
can u send the ltspice file
Sorry, I don't know about ofdm. Maybe someone else does.
I didn't save the simulation, but I think I used all standard spice parts so you can enter it.

#### EM Fields

Joined Jun 8, 2016
583
One may put a transformer in series with the laser current. This will allow you to modulate the laser in a number of ways.

The first thing to study is the laser data sheet.
In my opinion, the transformer's secondary in series with the laser's supply is the best suggestion offered so far in that if the laser is biased quiescently, through the transformer so that the laser will emit about half power, CW, when the modulator's contribution is nil then, when the transformer starts working, it'll add and subtract voltage / current into the LED, making its output brighter or dimmer.

Voila, amplitude modulation!

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