Laser Instant Switch

[goldperson2005]

Hi guys
I need Laser Instant Switch for my project . I've searched about it trough the web , but the laser switching time were about ms(fall and rise time ) , and in phototransistors it was about us .
In my project rise/fall time shouldn't be more than 499ps .
Please let me know how should I figure it out ?

[mixedgas]

One, please complete your user profile.

OK, so as I understand it, you have a picosecond laser at some unstated wavelength and you would like to use it to trigger some event? I do not have enough data to answer your question, if I can.

What is a laser instant switch supposed to do? Is this a photodiode to create a signal or something else?

Steve

[goldperson2005]

Thanks
I want to use laser to measure the time between two events . The time that I try to measure is about 3.5ns to 1ms ( the resolution should be at least 0.5ns ) .
The response time (both Rise/Fall) of the laser instant switch should be at least 499ps ( ; 499ps after receiving the spectrums of laser it should trigger other part of circuit ) .

[mixedgas]

Are your events repetitive?

The picosecond photodetector is not expensive, in fact 499 pS is long. What is difficult is processing the timing.

You need a detector and something like a constant fraction discriminator to process the detector signal.

The nuclear physics, nuclear medicine, and chemistry people have long had this problem and there are some well developed methods of processing the signal.

So you need a start/stop gate for a period counter or a time to digital converter?

Please tell me more about your experiment, there is still not enough detail.

Does the event block or adsorb the laser beam?

Steve

[goldperson2005]

Yes ,
Isn't it expensive ? May you present some of these laserdiodes ?
As you realized , I want to use LaserDiode to trigger the start and stop of TDC ( Time to Digital Converter ) .
start with Not buffer and stop directly .
By breaking the laser beam , must start & by receiving the beam again , it must stop .

[goldperson2005]

Dear friend
My other question is :
If I use optical fiber will the dispersion of light in fiber have unwanted influence on the operation of the LaserDiode ?
I couldn't able to find the laserdiode with ps response time up to now ?
please help me !

[danielbriggs]

The LaserComponents HSA-X-S might work?

[goldperson2005]

Thanks Daniel
What should I do with out put impedance ( < 50 ohm ) .
I want use it , to trigger start and stop of the TDC-GP22 . ( NegEdge : start , PosEdge : stop )
Also I can't understand what is the response time of the chip ;
in page 7 :

as you see it defines the response time : 200ns .
I do not know that the maximum response time of the chip is 200ns Or the maximum response time of input signal should be less than 200ns .

[mixedgas]

I'd talk to John Larkin at Highland Technologies before you try to develop your own photo diode interface to anything. Perhaps Dr. Phil Hobbs at ElectroOptical Consulting. You can spend three months verifying photodiode designs or you can just buy the design expertise or devices.


The difficult part is getting the Transimpedance amplifier and Comparator right. You have to get from the photodiode signal to ECL or PECL logic levels. Then from ECL/PECL to what ever the chip needs. This requires some form of Transimpedance converter, and one of very small physical size and high speed, because of propagation delays. The reason for this is to select a constant point on the edges of the photodiode signal to trigger from.

If you have a reasonable signal repetition rate of tens of Hertz or more you can use a CFD to find the pulse edge and condition the signal.

If your application is single shot you need either modules made for CAMAC crates, or some other specialized signal processing hardware.

Re-inventing the wheel is not advised in this area, you are dealing with signals of Gigahertz Bandwidth, and that requires "Controlled Impedance" circuit design techniques. A small error in circuit board design can set you back months at this pulse rise time.

This is not expensive if you find an expert. it is widely available for high speed fiber optics techniques such as SONET.

Even if you cannot afford their services, Mr. Larkin or Dr. Hobbs are very likely to point you in the right direction.

http://www.highlandtechnology.com/
http://www.electrooptical.net
www.ThinkSRS.com Stanford Research Systems also works in this area.

Steve

[goldperson2005]

I'd talk to John Larkin at Highland Technologies before you try to develop your own photo diode interface to anything. Perhaps Dr. Phil Hobbs at ElectroOptical Consulting. You can spend three months verifying photodiode designs or you can just buy the design expertise or devices.


The difficult part is getting the Transimpedance amplifier and Comparator right. You have to get from the photodiode signal to ECL or PECL logic levels. Then from ECL/PECL to what ever the chip needs. This requires some form of Transimpedance converter, and one of very small physical size and high speed, because of propagation delays. The reason for this is to select a constant point on the edges of the photodiode signal to trigger from.

If you have a reasonable signal repetition rate of tens of Hertz or more you can use a CFD to find the pulse edge and condition the signal.

If your application is single shot you need either modules made for CAMAC crates, or some other specialized signal processing hardware.

Re-inventing the wheel is not advised in this area, you are dealing with signals of Gigahertz Bandwidth, and that requires "Controlled Impedance" circuit design techniques. A small error in circuit board design can set you back months at this pulse rise time.

This is not expensive if you find an expert. it is widely available for high speed fiber optics techniques such as SONET.

Even if you cannot afford their services, Mr. Larkin or Dr. Hobbs are very likely to point you in the right direction.

http://www.highlandtechnology.com/
http://www.electrooptical.net
www.ThinkSRS.com Stanford Research Systems also works in this area.

Steve

Thanks a lot for guidance ,