"Single Mode" refers to the mode by which power is transmitted by the
fibre. For telecom communications, a wavelength of about 1550nm is commonly
used and the required glass fibre core diameter is about 10um. The required
diameter (mode field diameter) is dependent on the refractive index
difference as well as the wavelength - i.e. the design of the fibre.
Telecom use 1550nm for optical comms because the attenuation is at a
minimum here and it is close to the zero dispersion wavelength. Other
windows used are 1300nm and early (multimode systems) at 850-900 nm.
Typical losses are 0.16dB/km at 1550, 0.32dB/km at 1300nm and 3db/km at
900nm.

Multimode operation will generally have higher losses as the doping levels
are higher and the cores are larger - with the higher order modes
attenuating quicker. But it is easier to launch useful power into a
multimode fibre.

I think the fibre lasers described in the webpage below are lasers
manufactured from optical fibre - not just carrying light  generated by a
laser elsewhere. This requires specially doped fibre and special end
preparation.

Richard P



                    Larry Reynolds
                    <lreynol4@EROL        To:     PICLIST@MITVMA.MIT.EDU
                    S.COM>                cc:
                    Sent by: pic          Subject:     Re: [ot]: laser question
                    microcontrolle
                    r discussion
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                    05/02/03 13:19
                    Please respond
                    to pic
                    microcontrolle
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KreAture,

        In the article cited, look under Program Plans, 3rd bullet down:
It
refers to 10 single mode lasers with a total power out of 1 KW.  From
this, I assumed that each fiber had 100 watts in it. In my experience, a
single mode fiber uses a core of 8-9 um.  What is your understanding of
the comment in the article below?

http://www.darpa.mil/tto/programs/hpfl.html

Larry


Kyrre Aalerud wrote:
>
> They don't use that thin cable for such applications, but the point is
that
> as long as there is little loss, power density doesn't matter.
>
>     KreAture
>
> ----- Original Message -----
> From: "Larry Reynolds" <lreynol4@EROLS.COM>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Tuesday, February 04, 2003 10:07 PM
> Subject: Re: [ot]: laser question
>
> > Consider the optical power densities within a single mode fiber (~8 um)
> > driven with 100 watts of optical power:
> >
> >         Pd = 100/(PI*(8e-6)^2) or 497.4 trillion watts/m^2
> >
> >         egads!!!!!!!!!!!!
> >
> > Larry
> >
> >
> > Mark Perri wrote:
> > >
> > >  From this blurb, it looks like DARPA is trying to make a >100W fiber
> and
> > > eventually 100kW for "speed of light engagement."
> > >
> > > http://www.darpa.mil/tto/programs/hpfl.html

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