incandescent lamp vs laser diode

Posted on 2014-07-14
Last Modified: 2014-07-15
It is a continuation of, where we establish 150W incandescent lamp probably emits some 1000+ times more of 5mW laser diode in 1260-1360 nm range.

Now, is it feasible to use regular lamp to pump same amount of light as using 5mW laser diode into a fiber? The lamp can be upgraded to 1KW lamp as far as I'm concerned. Can add some rudimentary optics, it has to be IR-transparent though, so perhaps a mirror of some kind.
Question by:gremwell
    LVL 26

    Expert Comment

    There are infrared lenses (and mirrors).

    There are also infrared LED's that might work very well and inexpensively.

    What are you tring to do?
    LVL 26

    Expert Comment

    This one is $52 from Digi-Key and is designed to couple to a fiber.
    LVL 3

    Author Comment

    For testing purposes I need to inject substantial amount light into a fiber. Substantial means more than existing transmitter based on a laser diode.

    Using LEDs might be an option, do you think it is more effective than an incandescent lamp? If I read the datasheet correctly, LED you refer to seems to produce only -11dbm. I am not an expert in this field, just figured incandescent lamp is probably the most powerful source of IR radiation one can easily get. It scales up to 1.5KW [2] so I will get 75W in the range I care about. I guess it is extremely hard to beat using LED.

    Now, back to the objective of pumping up light into the core of the fiber. I guess if I just point the fiber to the lamp, not much will enter into the core. Assuming 50 micron core (don't care about reflection), its surface is just 3.14*(0.000050*0.000050)/4 = .000000001962 m^2. You've brought the topic of low power density of the lamp in the previous question. Do you have any suggestions how to practically solve the problem? I would rather not build a complicated optics system.

    LVL 26

    Accepted Solution

    >>  substantial amount light into a fiber
    You need to specify an actual value.

    What do you hope to do with the light once you get it into the fiber?
    And why have you chosen this particular band of  wavelengths?

    Pointing the fiber at the lamp will capture a tiny fraction of the power (as your calculations indicate).

    >> I would rather not build a complicated optics system . . .
    >> I don't care about reflection . . .

    I don't thank any optical system, no matter how complicated, will be particularly effective.
    To get substantial power into the fiber, you would have to form a low divergence beam and focus it down to 50u.
    The broadband, incoherent nature of the source makes this somewhere between horribly inefficient and impossible.
    Managing reflection from the face of the fiber would be crucial in any case.

    I don't think brute force can work here.  You really need a laser.

    There are Power-over-fiber products that work at the watt level:   (I have one of these)

    And there are fiber laser cutting tools that work at the kilowatt level:
    LVL 26

    Expert Comment

    This company has some interesting products and expertise.  You might want to contact them.

    Kilowatt IR lamps:
    (the Omega Emitter in particular)

    Fiber/Lamp Interfacing:
    (but not for IR)
    LVL 3

    Author Comment

    Thanks for the responses, you are being very helpful.

    > >>  substantial amount light into a fiber
    >You need to specify an actual value.
    I've already mentioned "Substantial means more than existing transmitter based on a laser diode".
    I can't be more precise. I imagine 50mW would be good test already.

    > I don't thank any optical system, no matter how complicated, will be particularly effective.

    You probably right. I hope to overcome it with brute force of kilowatt light source ;).
    I understand this applies to both IR LED and incandescent lamp, so the only real option is laser?
    Can sunlight be used? I guess it has low divergence beam already, not sure about the intensity.

    > There are Power-over-fiber products that work at the watt level:
    Interesting, but 830nm. I can't find any info if there are other options in IR range.

    In general, availability of 1300nm laser diodes seems to be very limited. I've found this diode, 110mW output, . It is an option, but a bit pricey.
    LVL 26

    Expert Comment

    Thorlabs has nine devices at 1310 nm from 2.5 to 300 mW.

    The one you found at Digi-Key is probably a better deal.

    As you probably know, the wavelength you are looking for is in the Near Infrared (NIR) band.
    The telecom designation is O band.
    LVL 3

    Author Comment

    All new modules I saw are $200+. There are some low-power ones for less than $100, but even those are with 4+ weeks lead time, not sure what delay will it be in practice.

    So the laser diode from Digi-key is the easiest option, price is not prohibitive.

    Another option I'll investigate is to buy some second-hand device with suitable optics on ebay and harvest laser from there. I've already found some, will cost me some $100. Not sure if it worth it, unless I'll find something noticeably cheaper I'll probably buy one from Digikey.

    Anyway, I guess we can end our quest here. Thanks for all your input.

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