Optimizing Performance of DFB Lasers: Pin Connections and Cooling Considerations

[fuyejun]

Hi：


I'm going to buy a DFB laser for my project, when I looked for Datasheet of such kind of laser, They give dimensions and equivalent schematic, and pin connections.

For example: A 14 pin butterfly[NEC LASER DIODE NX8563LA Series], from the datasheet, pin 1 and 2 functions thermistor and pin 6 pin7 are cooler anode and cooler cathode .

So, if I buy this laser ,should I need add resistor and pin 1 and 2. Do I need to buy some TEC module connect to pin 6 and 7 ?

 

[dlgoff]

I appears that this type requires cooling in order to function properly. And this cooling is accomplished by controlling the current to the built-in cooling circuit. It has a built-in thermistor (measures the lasers internal temperature and provides a variable resistance reading) which you would use to determine what current to provide to the cooler. In other words, you will need to build a circuit to take this thermistor resistance value (temperature) as your input and produces the appropriate current output for the cooler. Probably a few op-amps or maybe an "of the shelf" unit for these types of applications.

 

[Mike_In_Plano]

Some fiber optics lasers have very controlled wavelengths so that multiple lasers can be transmitted down the same fiber and the signals separated by using optical filters on the receiving end. To ensure that these lasers stay within their designated wavelength, their temperature must be regulated - hence thermoelectric coolers are used.

If you're just using such a laser as a wideband signal source, then there probably isn't a need for the cooler. I'd call the manufacturer.

- Mike

 

[fuyejun]

Some fiber optics lasers have very controlled wavelengths so that multiple lasers can be transmitted down the same fiber and the signals separated by using optical filters on the receiving end. To ensure that these lasers stay within their designated wavelength, their temperature must be regulated - hence thermoelectric coolers are used.

If you're just using such a laser as a wideband signal source, then there probably isn't a need for the cooler. I'd call the manufacturer.

- Mike

Hi Mike:

I am using such laser for a narrow band wavelength at 1550nm, So the cooler is needed. Do you know, when datasheet says pin 1 2 functions thermistor. Does it means it inbuilt a thermistor in the module.

-Johnny

 

[dlgoff]

You may be right Mike about the temperature not mattering in his application. But I would think that the thing would still get hot and need some kind of cooling to keep it from destroying itself. It does have a rather large operating temperature range. i.e. operating case temperature from −20 to +85°C. And they say one of the cooler current conditions is ΔT = 85 − Tset

Edit: you beat me posting fuyejun so you application does require cooling.

 

[dlgoff]

Hi Mike:

I am using such laser for a narrow band wavelength at 1550nm, So the cooler is needed. Do you know, when datasheet says pin 1 2 functions thermistor. Does it means it inbuilt a thermistor in the module.

-Johnny

Yes. It's built in and at 25°C it's typically 10kΩ.

 

[fuyejun]

You may be right Mike about the temperature not mattering in his application. But I would think that the thing would still get hot and need some kind of cooling to keep it from destroying itself. It does have a rather large operating temperature range. i.e. operating case temperature from −20 to +85°C. And they say one of the cooler current conditions is ΔT = 85 − Tset

Edit: you beat me posting fuyejun so you application does require cooling.

Hi Dlgoff:

I am reading a book at library it's named "fiber optics" by Robert j.Hoss at the page 55 there is a figure names conceptual drawing of a packaged laser transmitter. Fiber cable coupled with a laser diode then there is a Back-facet detector ( I think it is a photo detector) then there is a inbuilt thermal sensor( thermal resistor) all of these components are based on a Heat sink( thermoelectric cooler).


To now, I think TEC and thermal resistor are inbuilt. Like you said thermal resistor give a temperature change to control the current which is supply for laser diode. Do you know how the TEC （thermoelectric cooler) contribute for such application. I mean how TEC works?




thanks a lot
Fuyejun

 

[fuyejun]

I appears that this type requires cooling in order to function properly. And this cooling is accomplished by controlling the current to the built-in cooling circuit. It has a built-in thermistor (measures the lasers internal temperature and provides a variable resistance reading) which you would use to determine what current to provide to the cooler. In other words, you will need to build a circuit to take this thermistor resistance value (temperature) as your input and produces the appropriate current output for the cooler. Probably a few op-amps or maybe an "of the shelf" unit for these types of applications.

From above opinion the thermistor is used to TEC to cooling . So the current for Laser diode is fixed for example 85mA, it will not change.

 

[dlgoff]

From above opinion the thermistor is used to TEC to cooling . So the current for Laser diode is fixed for example 85mA, it will not change.

Yes. The actual laser current should be fairly constant. The current to the cooler (TEC) however will be constantly changing depending on the chips temperature (measured by the thermistor). As the chip heats up (thermistor resistance increases), your controlling circuit will have to increase the current to the cooler. The opposite happens for a decreasing chip temperature.

The temperature control circuit will be more or less a "stand alone" circuit. For a introduction to temperature control, check out how a PID controller works. http://en.wikipedia.org/wiki/PID_controller"

 

[pavel_ivanov]

So, if I buy this laser ,should I need add resistor and pin 1 and 2. Do I need to buy some TEC module connect to pin 6 and 7 ?

I agree with Dlgoff.
I just want to add that some laser diode controllers have slots for connecting the thermistor (pins 1 and 2) and measuring the temperature.

 

[Redbelly98]

If the built-in TEC is used, you'll also want to mount the laser on a heat sink.