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[SOLVED] Laser's Inputs (please confirm my interpretations)

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LandLack

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Dear Community,
I need to use this Laser: http://www.suncityinc.com.cn/IMAGE/pro/PDF/DC-18GHz_DFB_LD_FIN.pdf ; this is the first time, so I want just to be sure:
1)since the input is said to be matched at 50 ohm, and also since the "input-1db-compression-point" is seen as dBm (power) , I don't need strictly to give current on the input, since power should be enough, right?
2)The input signal should enter through the SMA connector, correct?
3) And the DC current should be entering through pad 3, and should be negative since that connector is "cathode" (while the case is the anode), right?

Please, can you control from the datasheets if at least these simple statements are correct. Thanks

Best Regards,
LandLack
 

FvM

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I don't need strictly to give current on the input
Technically, I don't exactly understand how wideband 50 ohm matching is achieved with about 3 ohm differential diode impedance according to the I/V characteristic. There might be a series resistor.

And the RF input should be AC coupled, or compensated for the diode forward voltage.
 

biff44

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yes it appears that you want to connect a negative voltage to pin 3, and set it up so 75 mA is flowing. I would consider a series current limiting resistor or a current source as the supply of the DC voltage. I would also make sure there were some microwave quality capacitors from pin 3 to ground.

In a fancy setup, you would use the internal photodetector and an analog feedback loop to vary the DC current up or down a little to keep the laser light output power constant.

Also note that there is a thermoelectric cooler inside the box. You probably want to power that sucker up too to keep the diode from overheating.

SMA connector is most likely a DC blocked input.

How they do the broadband match? Maybe there is an internal driver? Maybe a series 47 ohm resistor? Looks good to me.

The light output is infrared, so you will not be able to see it when it is on.
 

FvM

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SMA connector is most likely a DC blocked input.
Would make sense, but shouldn't elementary facts like this appear in a simplified schematic?

How they do the broadband match? Maybe there is an internal driver? Maybe a series 47 ohm resistor? Looks good to me.
Internal driver sounds unlikely (no power supply available). Resistor yes, same thing as before.
 

LandLack

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The suncity... link did not work for me, but the last bit of its title is DC-18GHZ_DFB, DC-> 18 GHZ modulation?
Frank

Yes, it is. Unfortunately I can't find another easy link to the datasheets; it can be seen as "high Bandwidth Analog DFB Laser Module" on google.

yes it appears that you want to connect a negative voltage to pin 3, and set it up so 75 mA is flowing. I would consider a series current limiting resistor or a current source as the supply of the DC voltage. I would also make sure there were some microwave quality capacitors from pin 3 to ground.

In a fancy setup, you would use the internal photodetector and an analog feedback loop to vary the DC current up or down a little to keep the laser light output power constant.

Also note that there is a thermoelectric cooler inside the box. You probably want to power that sucker up too to keep the diode from overheating.

SMA connector is most likely a DC blocked input.

How they do the broadband match? Maybe there is an internal driver? Maybe a series 47 ohm resistor? Looks good to me.

The light output is infrared, so you will not be able to see it when it is on.

I've also planned a good temperature controller and a negative DC current source; can you tell me why are you talking about DC voltage, and not current?
Just to know, how much is the temperature stability should be? The one I want to use gives 0.001°C precision, which seems too good. I'm curious to know what is the limit and the engineering prices.
Also can you tell me if this 3ohm in the I-V characteristics is found from the strobe?
In general, I've understood that at least my first statements seemed good, so thank you very much to you all.

Best Regards,
LandLack
 

biff44

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because you need a negative DC voltage, sufficiently high to turn on the laser diode, to get it to work. Then to keep the diode from blowing up, you need to regulate the current that flows.
 
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