It's a laser driver. The seven square pads solder to one side of a
14-pin butterfly laser package. This board has a one-shot to make
pulses from 100 ps up to a couple ns maybe, and pots/inputs to adjust
pulse width, laser bias, and laser pulse current. It's pretty common
these days to have a seed laser run at a few hundred mA to make a fast
light pulse, then run that through a few pumped-fiber amplifiers to
get enough optical power for materials processing or some such.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Got the first boards today:
https://dl.dropbox.com/u/53724080/PCBs/T165_6.jpg
Don't know if it works, but the orange LED is sure pretty. My camera
made it look kinda yellow.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Reply by josephkk●September 18, 20122012-09-18
On Tue, 18 Sep 2012 07:06:43 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>On Tue, 18 Sep 2012 00:08:24 -0700, josephkk
><joseph_barrett@sbcglobal.net> wrote:
>
>>On Mon, 17 Sep 2012 12:57:05 -0700, John Larkin
>><jlarkin@highlandtechnology.com> wrote:
>>
>>>On Mon, 17 Sep 2012 12:32:20 -0700 (PDT), whit3rd <whit3rd@gmail.com>
>>>wrote:
>>>
>>>>On Monday, September 17, 2012 7:08:23 AM UTC-7, John Larkin wrote
>>>>\[about ovenized crystal oscillators]
>>>>
>>>>>=20
>>>>> We buy these AT-cut crystals from Lap-Tech, each with its turning
>>>>>=20
>>>>> point temperature marked:
>>>>
>>>>I thought the AT (shear mode) quartz crystals were not preferred for =
reference
>>>>oscillators, because they are sensitive to minor material losses from=
the
>>>>large polished surfaces. There used to be another crystal cut, GC,
>>>>which had some kind of internal-oscillation mode that didn't stress =
or
>>>>accelerate the surfaces, that had better aging characteristics.
>>>>
>>>>Has that changed?
>>>
>>>SC cut (stress compensated) is best, but they are really expensive. I
>>>think they are still shear mode.
>>
>>
>>How odd. I was under the impression that they were standard today, now
>>that the patents have run out. I guess catalog cut sheets and such may
>>reveal the current situation.
>>
>>?-)
>
>
>Top of page 3:
>
>http://www.conwin.com/pdfs/at_or_sc_for_ocxo.pdf
Nice article. It seems that the doubly rotated AT "DRAT" crystals from =
my
teen years were early versions of SC crystals.
?-)
Reply by Phil Hobbs●September 18, 20122012-09-18
On 09/18/2012 04:55 PM, whit3rd wrote:
> On Monday, September 17, 2012 9:42:03 AM UTC-7, Phil Hobbs wrote:
>
>> If you have a baseband signal with a bandwidth of B, and use it to
>>
>> amplitude-modulate a carrier at frequency f, the resulting signal will
>>
>> extend from f-B to f+B, which is twice the bandwidth. (*)
>>
>>
>>
>> As Bill points out, all of the information is present in either sideband
>>
>> alone, so it's possible to use SSB detection to get rid of the 3 dB
>>
>> penalty.
>
> Oh, no you don't! The discussion was about AC and synchronous detection,
> the '3dB penalty' in bandwidth is of no importance because the detector
> rejects the out-of-phase part of the bandwidth in question. You get the
> 3 dB back, it never hits the measurement.
>
Quite right. I corrected that mistake earlier today, actually.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by whit3rd●September 18, 20122012-09-18
On Monday, September 17, 2012 9:42:03 AM UTC-7, Phil Hobbs wrote:
> If you have a baseband signal with a bandwidth of B, and use it to
>
> amplitude-modulate a carrier at frequency f, the resulting signal will
>
> extend from f-B to f+B, which is twice the bandwidth. (*)
>
>
>
> As Bill points out, all of the information is present in either sideband
>
> alone, so it's possible to use SSB detection to get rid of the 3 dB
>
> penalty.
Oh, no you don't! The discussion was about AC and synchronous detection,
the '3dB penalty' in bandwidth is of no importance because the detector
rejects the out-of-phase part of the bandwidth in question. You get the
3 dB back, it never hits the measurement.
Reply by Phil Hobbs●September 18, 20122012-09-18
On 09/18/2012 12:51 PM, John Devereux wrote:
> George Herold<gherold@teachspin.com> writes:
>
>> On Sep 18, 8:23 am, John Devereux<j...@devereux.me.uk> wrote:
>>> George Herold<gher...@teachspin.com> writes:
>>>
>>> [...]
>>>
>>>
>>>
>>>> OK I'll go look it over... can you quote me the chapter and verse?
>>>
>>> Old testament or new? :)
>>>
>>>> (ie Hobbs 7:16) (I hope the slight profanity does not offend.)
>>>
>>> Likewise
>>>
>>> --
>>>
>>> John Devereux
>>
>> Oh I've got the first edition.. (old testemant? :^)
>
> I've got both Books :)
>
>
The really old one is way better--it's by the guy that invented light
and electrons and silicon and everything. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by John Devereux●September 18, 20122012-09-18
George Herold <gherold@teachspin.com> writes:
> On Sep 18, 8:23 am, John Devereux <j...@devereux.me.uk> wrote:
>> George Herold <gher...@teachspin.com> writes:
>>
>> [...]
>>
>>
>>
>> > OK I'll go look it over... can you quote me the chapter and verse?
>>
>> Old testament or new? :)
>>
>> > (ie Hobbs 7:16) (I hope the slight profanity does not offend.)
>>
>> Likewise
>>
>> --
>>
>> John Devereux
>
> Oh I've got the first edition.. (old testemant? :^)
I've got both Books :)
--
John Devereux
Reply by Phil Hobbs●September 18, 20122012-09-18
On 09/18/2012 05:08 AM, Bill Sloman wrote:
> On 9/17/2012 6:42 PM, Phil Hobbs wrote:
>> On 09/17/2012 09:49 AM, George Herold wrote:
>>> On Sep 16, 5:21 pm, Phil Hobbs
>>> <pcdhSpamMeSensel...@electrooptical.net> wrote:
>>>> whit3rd wrote:
>>>>
>>>>> On Saturday, September 15, 2012 7:02:27 PM UTC-7, Phil Hobbs wrote:
>>>>>> Bill Sloman wrote:
>>>>
>>>>>>>>>>>>>>>>> With AC excitation, you can amplify everything and rely
>>>>>>>>>>>>>>>>> on the
>>>>
>>>>>>>>>>>>>>>>> demodulator to get rid of the 1/f components.
>>>>
>>>>>> The amps now are, roughly, 120 dB more stable, 50 dB smaller, and
>>>>>> dissipate 40 dB less power than the ones Neubert knew about back in
>>>>>> the
>>>>>> '40s. That makes the tradeoffs very different now.
>>>>
>>>>>> Today it would be replaced by a chop amp, a sensor, four resistors,
>>>>>> and
>>>>>> a capacitor, all in less than 1 square centimetre, inside the
>>>>>> controlled
>>>>>> volume, would work at least as well, and nobody would think it was
>>>>>> anything unusual.
>>>>
>>>>> But, Bill's point remains. The use of AC excitation buys your way
>>>>> out of
>>>>> several traps. If Johnson noise is higher than the temperature
>>>>> signal,
>>>>> the AC method works. The best chopamp doesn't.
>>>>
>>>> That's not true. An AC measurement has an inherent 3 dB bandwidth
>>>> penalty, so for the same transient response, the SNR will be 3 dB
>>>> lower. Johnson noise is white--do the math. AC measurements help with
>>>> DC drifts and 1/f noise, if you do them well, but are no help
>>>> whatsoever
>>>> in the flatband.
>>>
>>> Still loving this thread!
>>>
>>> (I've done both AC and DC.. and DC is easier, electronics-wise :^)
>>>
>>> Phil can you elucidate the 3dB loss in the AC measurement?
>>> Is this just the rms value of the sine wave? So square wave
>>> excitation would reduce that advantage? Or something more subtle?
>>> And if you were to do a lockin measurement, don�t you get a 3dB
>>> improvement because you get rid of the noise in the other
>>> quadrature?
>>> Maybe even square wave modulation and then switched gain (+1/-1) phase
>>> detection.
>>>
>>> George H.
>>>
>>> (still planning to use DC excitation for the next temperature thing I
>>> have to do.)
>>
>> If you have a baseband signal with a bandwidth of B, and use it to
>> amplitude-modulate a carrier at frequency f, the resulting signal will
>> extend from f-B to f+B, which is twice the bandwidth. (*)
>>
>> As Bill points out, all of the information is present in either sideband
>> alone, so it's possible to use SSB detection to get rid of the 3 dB
>> penalty. However, the circuitry required has a strong tendency to be
>> both complicated and drift-prone,
>
> Traditional analog SSB uses a "sequence asymmetric polyphase filter" to
> get a more or less constant 90 degree phase shift over a couple of
> decades of frequency. "The Art of Electronics" spells out the gory
> detail, or you can go to
>
> M.J. Gingell �Single Sideband Modulation using Sequence Asymmetric
> Polyphase Networks� Electrical Communication 48 21-25 (1973). See also
> http://traktoria.org/files/electronics/networks/polyphase_networks.pdf
>
> This isn't going to be all that practical for the fractional-Hz
> bandwidths you end up with in temperature control, and you are much more
> likely to be doing most of your processing in the digital domain, where
> complexity isn't much of a problem and drifts are non-existent.
>
> There's also the point that SSB radio is all about rejecting strong
> signals in adjacent channels, whereas in this application the "adjacent
> channel" has precisely the same strength as the channel you want to
> detect. In this application, 90% rejection is going to be almost as good
> as 99% rejection, when it would be a total disaster in a radio receiver.
>
> <snip>
>
The other thing I should have pointed out about SSB is that the filter
you'd need (either Hilbert or bandpass) has to cut off infinitely
sharply at f0, and so will have infinite group delay.
However, I do have a correction to make.
I'm so used to the usual optical AM case that I wasn't really thinking
about the phase sensitive detection step, which of course gets you the 3
dB back for free--half the noise is in the quadrature phase, and so goes
away when you mix and filter. So the 3 dB is a red herring--AC and DC
are theoretically equivalent when you're using a 1-phase lock-in technique.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by John Larkin●September 18, 20122012-09-18
On Tue, 18 Sep 2012 00:08:24 -0700, josephkk
<joseph_barrett@sbcglobal.net> wrote:
>On Mon, 17 Sep 2012 12:57:05 -0700, John Larkin
><jlarkin@highlandtechnology.com> wrote:
>
>>On Mon, 17 Sep 2012 12:32:20 -0700 (PDT), whit3rd <whit3rd@gmail.com>
>>wrote:
>>
>>>On Monday, September 17, 2012 7:08:23 AM UTC-7, John Larkin wrote
>>>\[about ovenized crystal oscillators]
>>>
>>>>
>>>> We buy these AT-cut crystals from Lap-Tech, each with its turning
>>>>
>>>> point temperature marked:
>>>
>>>I thought the AT (shear mode) quartz crystals were not preferred for reference
>>>oscillators, because they are sensitive to minor material losses from the
>>>large polished surfaces. There used to be another crystal cut, GC,
>>>which had some kind of internal-oscillation mode that didn't stress or
>>>accelerate the surfaces, that had better aging characteristics.
>>>
>>>Has that changed?
>>
>>SC cut (stress compensated) is best, but they are really expensive. I
>>think they are still shear mode.
>
>
>How odd. I was under the impression that they were standard today, now
>that the patents have run out. I guess catalog cut sheets and such may
>reveal the current situation.
>
>?-)
Top of page 3:
http://www.conwin.com/pdfs/at_or_sc_for_ocxo.pdf
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators