DVD laser and photodiode

J

Jamie Morken

Guest
Hi,

This article says that a typical DVD 16X writer requires 230mW of
optical power, and the wavelength of the laser is around 650nm, red.

"http://www.edn.com/article/CA485669.html"

Also for a 16X DVD the datarate is up to 418 Mbps, so the laser and
photodiode have very fast rise/fall times.

Does anyone know of a site where the DVD optics have been "experimented"
with? :) Is it feasible to use the laser and photodiode for other
purposes than as in a DVD, ie. long distance optical datalink or laser
rangefinding (time of flight and/or phaseshift measurement)

cheers,
Jamie
 
Jamie Morken wrote:
This article says that a typical DVD 16X writer requires 230mW of
optical power, and the wavelength of the laser is around 650nm, red.

"http://www.edn.com/article/CA485669.html"

Also for a 16X DVD the datarate is up to 418 Mbps, so the laser and
photodiode have very fast rise/fall times.

Does anyone know of a site where the DVD optics have been "experimented"
with? :) Is it feasible to use the laser and photodiode for other
purposes than as in a DVD, ie. long distance optical datalink or laser
rangefinding (time of flight and/or phaseshift measurement)
Click to expand...
Jamie,
The fast signals require significant power, a few nA won't
give 500MHz, and neither do just a few photons.
Mreaning long distance, whatever this means, requires some
expensive optics. The narrower the laser beam, the more it
widens over the distance, thus you're quickly at 10cm for
a mile or two.

Yes, I think an optical link is doable. How fast over
which distance require some experiments.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
 
Rene Tschaggelar wrote...
Jamie Morken wrote:
This article says that a typical DVD 16X writer requires 230mW of
optical power, and the wavelength of the laser is around 650nm, red.
"http://www.edn.com/article/CA485669.html"
Also for a 16X DVD the datarate is up to 418 Mbps, so the laser and
photodiode have very fast rise/fall times.

Does anyone know of a site where the DVD optics have been "experimented"
with? :) Is it feasible to use the laser and photodiode for other
purposes than as in a DVD, ie. long distance optical datalink or laser
rangefinding (time of flight and/or phaseshift measurement)
Click to expand...
I've been experimenting with a red Hitachi DVD laser obtained on eBay.
Hitachi's data sheet has a frequency-response plot saying it goes to
700MHz, peaks and drops like a rock. I found that properly wired, it
goes smoothly to 1200MHz, without peaking, and rolls off gradually.
It's possible my detector was primarily responsible for the rolloff.


--
Thanks,
- Win
 
Adrian Jansen wrote:

John Larkin wrote:

On 9 Jan 2005 12:35:44 -0800, Winfield Hill
hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:


Rene Tschaggelar wrote...

Jamie Morken wrote:

This article says that a typical DVD 16X writer requires 230mW of
optical power, and the wavelength of the laser is around 650nm, red.
"http://www.edn.com/article/CA485669.html"
Also for a 16X DVD the datarate is up to 418 Mbps, so the laser and
photodiode have very fast rise/fall times.

Does anyone know of a site where the DVD optics have been
"experimented" with? :) Is it feasible to use the laser and
photodiode for other purposes than as in a DVD, ie. long distance
optical datalink or laser rangefinding (time of flight and/or
phaseshift measurement)


I've been experimenting with a red Hitachi DVD laser obtained on eBay.
Hitachi's data sheet has a frequency-response plot saying it goes to
700MHz, peaks and drops like a rock. I found that properly wired, it
goes smoothly to 1200MHz, without peaking, and rolls off gradually.
It's possible my detector was primarily responsible for the rolloff.




I got some samples of a plastic-packaged Osram IR laser that puts out
about 10 watts peak, and managed to get 1 ns pulses out of it driving
with a gaasfet. You can also get the lasers that have just the chip
soldered to the edge of a little square brass block with a mounting
hole in the middle, which is probably optically superior to the
plastic package. Either one goes for a few dollars in quantity.

The little 850 nm fiber-coupled VCSELS have risetimes around 100 ps...
hard to measure, since the good fast detectors are blind at 850. The
Optek parts are available stock from Newark and are pretty good.

Probably an avalanche transistor driver is easiest to make to do lidar
type stuff. ECL, maybe eclips lite, has enough swing to drive a laser.

John


I have a possible application for lidar, but it wont stand the $200,000
price tag of commercial stuff. The idea is to measure doppler shift on
particles in the air to get the local wind speed. Any info on cheap
lasers, optics and detectors capable of getting a range of the order of
200 metres backscatter in air is welcome.
Click to expand...
LIDAR means measuring backscatter from usually pulsed lasers.
The mentioned pricetag is not just because these guys are expensive.
Consider a backscatter coefficient of say 10^-4, of which by means
of a 30cm reflective mirror you again get only a fraction. Throw
in the r^2 attenuation and you quickly reach 120dB of dynamic range
extending far into the noise. The only way to get the signal out
of the noise is to start with enormous peak power at excitation.
The response is a modulation of the r^2 attenuation, giving a
distance profile of scattering.

You could make the setup far simpler by measuring forward attenuation,
eg between some highrise buildings, in case you're not interested on a
distance profile.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
 
Jamie Morken wrote:


Any tips on hooking this stuff up? :) I am most interested in the
photodiode as I haven't been able to find any other high speed red light
sensitive photodiodes.
Click to expand...
There are plenty of fast photodiodes around. Their responsivity
is given by the material.
Eg the AEPX65 is recommended.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
 
Rene Tschaggelar wrote...
Jamie Morken wrote:

Any tips on hooking this stuff up? :) I am most interested in the
photodiode as I haven't been able to find any other high speed red
light sensitive photodiodes.

There are plenty of fast photodiodes around. Their responsivity is
given by the material. Eg the AEPX65 is recommended.
Click to expand...
Not so much the material as the size, because high capacitance is a
killer. That part's 4pF is a serious problem, up to 10 times higher
than the detector I used measuring the Hitachi's 1200MHz response.


--
Thanks,
- Win
 
Winfield Hill wrote...
Rene Tschaggelar wrote...

Jamie Morken wrote:

Any tips on hooking this stuff up? :) I am most interested in the
photodiode as I haven't been able to find any other high speed red
light sensitive photodiodes.

There are plenty of fast photodiodes around. Their responsivity is
given by the material. Eg the AEPX65 is recommended.

Not so much the material as the size, because high capacitance is a
killer. That part's 4pF is a serious problem, up to 10 times higher
than the detector I used measuring the Hitachi's 1200MHz response.
Click to expand...
BTW the 664nm red DVD laser was an Hitachi HL6504FM and my detector
an Optek OPF480 PIN diode, biased at -100V, measured into a 25 ohm
load (double-end termination) with an Agilent network analyzer.


--
Thanks,
- Win
 
Winfield Hill wrote:

Rene Tschaggelar wrote...

Jamie Morken wrote:


Any tips on hooking this stuff up? :) I am most interested in the
photodiode as I haven't been able to find any other high speed red
light sensitive photodiodes.

There are plenty of fast photodiodes around. Their responsivity is
given by the material. Eg the AEPX65 is recommended.


Not so much the material as the size, because high capacitance is a
killer. That part's 4pF is a serious problem, up to 10 times higher
than the detector I used measuring the Hitachi's 1200MHz response.
Click to expand...
The responsivity was meant for the spectral color of the light.
You're right, the speed is done with the size. Unfortunately
that calls for some aligned optics unless plenty of light is
available.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
 
Jamie Morken wrote...
Winfield Hill wrote:
Winfield Hill wrote...

I've been experimenting with a red Hitachi DVD laser obtained on eBay.
Hitachi's data sheet has a frequency-response plot saying it goes to
700MHz, peaks and drops like a rock. I found that properly wired, it
goes smoothly to 1200MHz, without peaking, and rolls off gradually.
It's possible my detector was primarily responsible for the rolloff.

BTW the 664nm red DVD laser was an Hitachi HL6504FM and my detector
was an Optek OPF480 PIN diode, biased at -100V, measured into a 25
ohm load (double-end termination) with an Agilent network analyzer.

Could you give more details of your circuit that you used? I can
visualize it several different ways :)
Click to expand...
It was just a quick lash up.

.. bias-tee laser
.. ________| |______,---------,
.. ________|-||-+--|______(-50R-|>|-'
.. 50-ohm |____X__| \\ mirror PD bias
.. coax | \\| optics 100V
.. 50R //| & etc |
.. | // __|____
.. laser // ________| X |___50-ohm
.. current ,-|>|----+-)_______|--+-||-|____ coax
.. supply +-||-50R-' | coax |_______| term.
.. '----------' bias-tee

Components were 1206 SMT hand-soldered with zero-distance spacing.
Bias-tees were 12GHz-bandwidth Picosecond Pulse Labs. A first
attempt at a PCB stripline replacement only goes to 600MHz so far.

Weren't you a bit scared of the laser light too? :)
Click to expand...
One should always be careful of course, but in this case the laser
assembly included optics to spread the beam to 1/4" substantially
lowering its intensity down to a veritable dull glow. :>)


--
Thanks,
- Win
 
Hi,

I posted a conversion of the ascii art circuit to eagle cad pdf:
"http://red79.net/rocketresearch/pics/DVD%20optics/Winfield%20Hill's%20circuit.pdf"

Is the laser current supply used to keep the laser always lasing, and
then a small signal modulation is fed to the laser through the coax?
Does the laser need to always be lasing to be able to achieve high
frequency operation? I was thinking of turning the laser on and off to
send 0's and 1's (but this is probably slower than just changing the
lasing brightness. I don't know what Win's application is, but the next
step seems to be getting this signal into digital logic :)

cheers,
Jamie
 
Jamie Morken wrote...
I posted a conversion of the ascii art circuit to eagle cad pdf:
"http://red79.net/rocketresearch/pics/DVD%20optics/Winfield%20Hill's%20circuit.pdf"

Is the laser current supply used to keep the laser always lasing, and
then a small signal modulation is fed to the laser through the coax?
Does the laser need to always be lasing to be able to achieve high
frequency operation? I was thinking of turning the laser on and off
to send 0's and 1's (but this is probably slower than just changing
the lasing brightness.
Click to expand...
Yes, at very high frequencies like 1GHz, it's best not to attempt to
fully turn the laser on and off. At 300MHz or under, that's OK, but
may still not be the best approach.

I don't know what Win's application is, but the next step seems to
be getting this signal into digital logic :)
Click to expand...
Not my next step - one of our scientists will be using it to evaluate
nanowire FETs.

The circuit I posted (and you wrote up) doesn't look much like a
typical laser driver or optical receiver circuit, certainly not like
most of the ones I design. The primary goal throughout, which you
didn't show or analyze on your little writeup, it to maintain a very
clean 50-ohm impedance at all points for the drive signal and for the
received signal, and double terminated as well. As I mentioned, when
one of us attempted to translate the lashup to a PCB, the performance
dropped from 1200MHz to 600MHz despite being very careful, indicating
the important of avoiding any impedance discontinuities.


--
Thanks,
- Win
 
Winfield Hill wrote:


Not my next step - one of our scientists will be using it to evaluate
nanowire FETs.

The circuit I posted (and you wrote up) doesn't look much like a
typical laser driver or optical receiver circuit, certainly not like
most of the ones I design. The primary goal throughout, which you
didn't show or analyze on your little writeup, it to maintain a very
clean 50-ohm impedance at all points for the drive signal and for the
received signal, and double terminated as well. As I mentioned, when
one of us attempted to translate the lashup to a PCB, the performance
dropped from 1200MHz to 600MHz despite being very careful, indicating
the important of avoiding any impedance discontinuities.
Click to expand...
There are laserdiode drivers at Analog Devices doing 1.25 to 10GBit.
Yes, at some point, impedance drops towards the laser.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
 
Rene Tschaggelar wrote:


LIDAR means measuring backscatter from usually pulsed lasers.
The mentioned pricetag is not just because these guys are expensive.
Consider a backscatter coefficient of say 10^-4, of which by means
of a 30cm reflective mirror you again get only a fraction. Throw
in the r^2 attenuation and you quickly reach 120dB of dynamic range
extending far into the noise. The only way to get the signal out
of the noise is to start with enormous peak power at excitation.
The response is a modulation of the r^2 attenuation, giving a
distance profile of scattering.

You could make the setup far simpler by measuring forward attenuation,
eg between some highrise buildings, in case you're not interested on a
distance profile.

Rene
Thanks for the thoughts, but the app requires the source and receiver at
Click to expand...
the same location ( moving vehicle ). And we cant have high power, the
laser must be eye-safe. Guess its one of those expensive solutions, but
I would still like to know what sources and detectors are around.


--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.
 
Adrian Jansen wrote:

Rene Tschaggelar wrote:



LIDAR means measuring backscatter from usually pulsed lasers.
The mentioned pricetag is not just because these guys are expensive.
Consider a backscatter coefficient of say 10^-4, of which by means
of a 30cm reflective mirror you again get only a fraction. Throw
in the r^2 attenuation and you quickly reach 120dB of dynamic range
extending far into the noise. The only way to get the signal out
of the noise is to start with enormous peak power at excitation.
The response is a modulation of the r^2 attenuation, giving a
distance profile of scattering.

You could make the setup far simpler by measuring forward attenuation,
eg between some highrise buildings, in case you're not interested on a
distance profile.

Rene

Thanks for the thoughts, but the app requires the source and receiver at
the same location ( moving vehicle ). And we cant have high power, the
laser must be eye-safe. Guess its one of those expensive solutions, but
I would still like to know what sources and detectors are around.
Click to expand...
AFAIK, the pulsed lasers are still considered eye save when the
rep rate is sufficiently low, say 1 Hz or lower. I've seen a
handheld Q switched YAG issuing single pulses of say 20kW with a
pulsetime of 1ns or below. At least at that time, the regulations
didn't cover it. Such a laser is still doable in the size of
two fists. The optics is much bigger. I'd suggest a 20 to 30cm
parabol mirror for the receiver. I'd don't know the angular margin of
the backscatter, but it could be sufficiently narrow, especially
on short range such that you have to use the same mirror for the
sending.
Your receiving electronics then would have to be fast enough to
get the 1ns pulse and its distance square decay. There are
wonderful logamps that make the exponential appear linear.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
 
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