Function generator for modulating laser beams - Page 1
Forum section: electronics / testgear

author: 3rj4
author_rank: Regular Contributor
timestamp: January 03, 2020, 02:00:49 pm
content: Hi all,I'm building a laser doppler vibrometer for measuring ultrasound frequencies between 2.5-10MHz. I need a function generator (my first) to modulate the laser beam, thereby simulating a real situation where the laser beam would be modulate day the vibration of the measured object.I am seeking recommendations for a function generator that is suitable for this purpose. I'm not sure how much these things typically cost, so I will just say that I want to keep my budget as low as possible, whilst still buying something that successfully achieves my desired outcomes.I was researching some past threads on this subject, and it seems that the HP 3312A is highly recommended, despite its age. I found many second-hand on eBayhttps://www.ebay.com.au/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=HP+Hewlett+Packard+3312A+Function+Generator+&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=3312A.The descriptions all claim seem to claim that they power on, but are untested, and some seem to have buttons missing (although, this seems like a minor inconvenience, assuming you could just use a pen or something instead of the button). And the prices seem reasonable, even with shipping to Australia. However, I have no idea whether this model is suitable for my purposes.I would appreciate it if people would offer recommendations.

author: Yansi
author_rank: Super Contributor
timestamp: January 03, 2020, 02:13:59 pm
content: Jeeez that old thing. Whyyy. Buy at least an Agilent 33120A if you want something decent for a lab or research project. Second hand ones go around the same or less than the HP.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 03, 2020, 02:14:52 pm
content: Quote from: Yansi on January 03, 2020, 02:13:59 pmI'm just using the search function.The Agilent 33120A seems to be quite expensive, even for a used unit.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 03, 2020, 02:38:35 pm
content: What about the Rigol DG1022Z 25 MHz?https://www.tequipment.net/Rigol/DG1022Z/Function-Generator/?Source=googleshopping&gclid=EAIaIQobChMIyc7x4dPn5gIVjw4rCh0mzweBEAYYAiABEgJkK_D_BwEIs this suitable for my purposes?

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2020, 02:42:29 pm
content: One of the generators I have been eyeballing is the TTI TGF4000 series. These have a very low jitter specification. I guess this could be a handy features when dealing with very small frequency shifts.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 03, 2020, 03:01:30 pm
content: Quote from: nctnico on January 03, 2020, 02:42:29 pmThose models seem to be 2K+ AUD -- way outside of my budget.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 03, 2020, 03:04:06 pm
content: The SDG2042X seems to be another popular one on this forum. Although it's quite highly priced, it seems to be better value for money compared to the others in my price range.

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2020, 04:33:16 pm
content: Quote from: 3rj4 on January 03, 2020, 03:01:30 pmThe lowest end model (TGF4042) should be below the 1k AUD mark. But prices may be different at your end. Still the TGF4042 is not much of a stretch compared getting a generator from Rigol or Siglent.

author: Yansi
author_rank: Super Contributor
timestamp: January 03, 2020, 05:27:43 pm
content: Quote from: 3rj4 on January 03, 2020, 02:14:52 pmI wouldn't call a 600 AUD expensive. It is a proper lab tool with all the bells and whistles it can have, including ability to lock to an external 10MHz reference (if you buy one with opt 001) and SCPI interface for automated testing or experiment control.(the only thing it annoys me with is the lack of any output ON/OFF button)

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2020, 05:45:58 pm
content: I have used the 33120A (or similar) and IMHO these aren't the most user friendly generators. If money is an issue then I'd get the Siglent SDG1000 or SDG2000 series.

author: Yansi
author_rank: Super Contributor
timestamp: January 03, 2020, 06:02:57 pm
content: Yes the user interface is a bit weird, but you can say that about almost any Agilent/Keithley 9.75" rack instrument. One can get used to it.

author: tautech
author_rank: Super Contributor
timestamp: January 03, 2020, 08:35:53 pm
content: Quote from: nctnico on January 03, 2020, 05:45:58 pmYou must mean the X models ?SDG1000 models are discontinued and now replaced by the SDG1000X series.SDG1032X is my pick for budget conscious buyers and apart from the higher BW and 16 bit of SDG2000X models has the same capabilities/features.Trio Test now a division of IPD are the Ozzie agents:https://www.triotest.com.au/store/siglent-technologies/1113-siglent-sdg1032x-30mhz-2-channel-arbitrary-waveform-generator.html

author: Yansi
author_rank: Super Contributor
timestamp: January 03, 2020, 08:39:46 pm
content: Just got me thinking... there's the cheap Hantek generator line: HDG6202B/HDG6162B/HDG6112B/HDG6082B.How well do these compare to the SDG1032X? They both cost about the same, yet the Hantek has a tad better paper spec (16bit D/A, up to 1.25GSa and 200MHz).

author: 3rj4
author_rank: Regular Contributor
timestamp: January 03, 2020, 08:55:25 pm
content: Quote from: nctnico on January 03, 2020, 05:45:58 pmQuote from: tautech on January 03, 2020, 08:35:53 pmDo you guys think that the SDG1032X is suitable for the purposes that I described?

author: unitedatoms
author_rank: Frequent Contributor
timestamp: January 03, 2020, 09:03:33 pm
content: You could by some coincidence already having a wave generator if you have contemporary oscilloscope. Many models can record, replay or arbitrarily generate low MHz signals digitally.Or, for example, Keysight scopes offer the function as option.

author: tautech
author_rank: Super Contributor
timestamp: January 03, 2020, 09:11:53 pm
content: Quote from: 3rj4 on January 03, 2020, 08:55:25 pmOutput drive might be a consideration however you do have+5V into 50 ohms and 200mA available which should be plenty for low power lasers which means you might not need a buffer power stage where you might if using the internal sig gen output from within a scope.Anyways, have a look at the SDG1000X series datasheet:https://int.siglent.com/products-document/20.html?DId=20/

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2020, 10:12:23 pm
content: Quote from: tautech on January 03, 2020, 08:35:53 pmWhateverAll the X-es, E-es and plusses just make things complicated.

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2020, 10:21:00 pm
content: Quote from: 3rj4 on January 03, 2020, 08:55:25 pmI have no idea. You have to create some specifications regarding frequency stability and jitter. Perhaps get a unit on loan and see if it works or not. IIRC you have a good oscilloscope already to do some signal analysis.

author: james_s
author_rank: Super Contributor
timestamp: January 04, 2020, 01:31:47 am
content: Do you even need a fancy function generator for this? If all you want to do is simulate vibrations it seems like something much simpler could be arranged. Of course 10MHz modulation of a laser diode may not be trivial.

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2020, 02:04:28 am
content: Quote from: james_s on January 04, 2020, 01:31:47 amProbably not but these are well enough featured to suit a range of projects and when the OP says he hasn't got a FG he's got the option to get something that will suit his needs maybe forever.I don't generally buy anything for a single job instead look for further functionality I may need later on. My first FG was a 1ch 2 MHz POS Philips that I still have and while it's buried in the garage somewhere I've never used it since acquiring my first AWG.

author: james_s
author_rank: Super Contributor
timestamp: January 04, 2020, 06:40:37 am
content: Sure, but if a $30 ebay function generator would do the job I wouldn't automatically be recommending a $1400 AWG.I've been tempted a few times to buy one of the cheap Chinese AWGs but then I start thinking about whether I actually need one or just want another toy and so far I've realized it's the latter. My ancient 2MHz analog function generator isn't great but it has met my needs so far. I like the idea of arbitrary waveforms but can't actually think of anything to do with one beyond making cool looking waveforms on my scope.

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2020, 07:13:47 am
content: I mentioned SDG1032X, a $320 14 bit 2ch 30 MHz AWGnota $1500 16 bit 2ch 200 MHz SDG6022X.I have both but the SDG6022X (hacked to 500 MHz) stays in its box except for the rare occasions when the BW might be needed.

author: nctnico
author_rank: Super Contributor
timestamp: January 04, 2020, 10:21:37 am
content: Quote from: james_s on January 04, 2020, 06:40:37 amTrue. I don't think I have ever used the AWG functionality. However the biggest advantage of a digital function generator is that the output signal is more stable and the parameters are easier to set (especially if there is a graphic display). And you can buy such a device for very little money. Maybe one of the Feeltech generators fits the OP's purpose as well if stability/jitter isn't much of a concern. The Feeltech FY6900 is pretty much on par with the Siglent SDG1000 series when it comes to features and performance.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 04, 2020, 11:09:54 am
content: Quote from: tautech on January 04, 2020, 02:04:28 amYes, that's true. Although this particular project deals with a laser doppler vibrometer, I'm also undertaking a lot of other projects, many of which use lasers. So I'm certainly looking for something that is also good for general use.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 04, 2020, 11:16:32 am
content: Quote from: nctnico on January 04, 2020, 10:21:37 amReally? I came across discussion of Feeltech generators when I was browsing past threads, and the overwhelming consensus seemed to be very negative. In fact, I saw that the Feeltech customer service rep. who came onto this forum was lambasted and promptly banned. I'm not sure it's a good idea to buy Feeltech?

author: nctnico
author_rank: Super Contributor
timestamp: January 04, 2020, 11:22:43 am
content: Quote from: 3rj4 on January 04, 2020, 11:16:32 amIf it works it works. Many people make too much fuss about a cheap device (expecting to get $1000 worth for $50). It is a cheap tool so treat it as such. Get one from Ebay so at least you have buyer protection. I have an older Feeltech model (FY3200) and it works just fine.

author: qft1967
author_rank: Contributor
timestamp: January 04, 2020, 12:07:34 pm
content: In a laser doppler vibrometer you also need a function generator to apply the frequency shift to the reference (or signal) beam. Or how are you going to apply the frequency shift between the reference and signal arm? Here also phase noise might be important, depending on how sensitive you want to get!

author: 3rj4
author_rank: Regular Contributor
timestamp: January 04, 2020, 12:17:56 pm
content: Quote from: nctnico on January 04, 2020, 11:22:43 amBut that's just it, it seems that people have had a lot of problems with the Feeltech models, so it might not be a good idea for a beginner to purchase one. I'm looking at the Siglent SDG1032X 30MHz at the moment. Will have to request prices for both the Siglent SDG1025 25MHz and Siglent SDG1032X 30MHz for comparison.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 04, 2020, 12:19:36 pm
content: Quote from: qft1967 on January 04, 2020, 12:07:34 pmDo you think the models that I mentioned above are suitable for this task?

author: nctnico
author_rank: Super Contributor
timestamp: January 04, 2020, 01:04:06 pm
content: Quote from: 3rj4 on January 04, 2020, 12:17:56 pmBecause of the low price lots of people buy them. The FY3200S model is OK but the models after that did had firmware issues. The newer FY6900 seems to be a good one though in which Feeltech has fixed all the issues (as far as I can see). The Siglent SDG1000 series had a similar rough start.Still you really need to do some math on what your requirements are otherwise you don't know whether you are looking at the jitter of the generator or a doppler shift effect. Before doing any measurement you have to determine what kind of accuracy is required / what kind of result you can expect. Just hooking something up and look at the signals is not going to work. You might find yourself in a rabbit hole chasing an effect which is caused by the instruments you are using and not the device under test.

author: qft1967
author_rank: Contributor
timestamp: January 04, 2020, 01:16:26 pm
content: Quote from: 3rj4 on January 04, 2020, 12:19:36 pmAs others have been saying, you need to work on your requirements. If you cannot give that, describe a bit more in detail the experiment and the results you want to get!

author: TurboTom
author_rank: Super Contributor
timestamp: January 04, 2020, 03:13:34 pm
content: @3rj4 - to me, the combination of your recently acquired very substantial scope and one of these "tinkerer's delight" AWG's (sorry, not meant as an offense...) looks a little funny. I'ld at least get something proven from a reputable "B brand". The SDG2042X - hacked -, as mentioned before, is probably the sweet spot.If this is out of your financial comfort zone for that kind of instrument, I'ld wait a little until a way to hack the recent firmware version of the Rigol DG800 has been figured out (I've got the feeling that this won't take long) and then get a DG811 and hack it to (almost) DG992 capabilities (just lacking a level calibration over the full frequency range, it's accurate to approx. 70MHz). That's quite a potent generator despite its somewhat toyish casing style. I think, this resembles the clear winner of bang-per-buck currently when it comes to AWGs if hacking is an option for you.Well, just my two (euro-) cents

author: nctnico
author_rank: Super Contributor
timestamp: January 04, 2020, 05:27:59 pm
content: Quote from: TurboTom on January 04, 2020, 03:13:34 pmWhy would that be? If it does the job it does the job. I have both very expensive equipment and very cheap equipment.

author: TurboTom
author_rank: Super Contributor
timestamp: January 04, 2020, 07:04:37 pm
content: Quote from: nctnico on January 04, 2020, 05:27:59 pmOf course, I also (probably like most members here) have cheaper and more expensive gear. Some of this cheap stuff - in hindsight - was way more expensive than anticipated, considering the time spent on it to make it half-way useful, some was a real steal.Obviously, I don't own any of the Feeltech AWGs, but from what i read and watched about them, at least their power supply appears to be sub-par. The waveform generation engine of the FY6900 appears to be quite decent, compared to their previous models. Yet, it's somewhat disappointing that Feeltech didn't implement the "Magic Pulse" technology for all the possible waveforms but only for square.One detail that is a complete no-go for me is the absence of a decimal keypad (neither physical nor simulated on a touch panel). While in case of power supplies, it's an annoyance if this input option is missing, on a generator with two channels and the multitude of parameters that can be adjusted, I consider this just inacceptable. But that's my own view of the situation. For someone who rarely needs to change a setting, or always operates the generator via the PC-interface, the FY6900 may be just okay.But taking into account the alternatives, I'ld rather spend twohundred bucks more than always getting annoyed when I had to fiddle with this user interface. I'ld consider this money well spent for my mental health (...if there is any left that is...)

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2020, 07:56:15 pm
content: Quote from: 3rj4 on January 04, 2020, 12:17:56 pmFYI, I saw SDG1000 models listed on Trio's website too and they might have some old stock but more likely they haven't kept their website up to date as this range is now discontinued.While they were a bit cheaper than SDG1032X they were missing a LAN I/O and ch2 didn't have the output drive of ch1.All the official Siglent websites now show them as discontinued:https://int.siglent.com/products-overview/sdg1000/And the US website specifically points to SDG1000X models as suitable/better replacements:https://siglentna.com/waveform-generators/sdg1000-series-functionarbitrary-waveform-generators/Keep me in the loop as to how you get on with Trio as you can contact their top guy Mark if you have issues with the sales dept.https://www.eevblog.com/forum/testgear/where-to-buy-the-siglent-sds1202x-in-asutralia/

author: 3rj4
author_rank: Regular Contributor
timestamp: January 04, 2020, 11:08:00 pm
content: Quote from: tautech on January 04, 2020, 07:56:15 pmQuote from: TurboTom on January 04, 2020, 03:13:34 pmIamleaning more-so towards the SDG2042X, since it is a high quality device and seems to be powerful enough to be useful for the foreseeable future. I will contact Trio for a quote.Thank you all for taking the time to advise me on this! I really appreciate it!

author: tautech
author_rank: Super Contributor
timestamp: January 04, 2020, 11:17:09 pm
content: Quote from: 3rj4 on January 04, 2020, 11:08:00 pmThe UI is almost identical to SDG1032X except for the touch display (yes occasionally it is handy) however the SDG1000X models do square and sinewave to the same max frequency. This may not matter to you but it's easily overlooked when studying datasheets.Still, the SDG2000X series is an excellent mid range choice.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 04, 2020, 11:49:32 pm
content: Quote from: tautech on January 04, 2020, 11:17:09 pmYes, I intend to also ask for a quote for the SDG1032X.

author: Performa01
author_rank: Super Contributor
timestamp: January 05, 2020, 06:24:18 pm
content: Quote from: 3rj4 on January 04, 2020, 11:49:32 pmJust to alienate you a little more:If high frequency accuracy and stability, lowest jitter, ultra low phase noise and/or long memory for arbitrary waveforms are of any importance for you, then get the SDS2000X.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 05, 2020, 10:39:51 pm
content: Quote from: Performa01 on January 05, 2020, 06:24:18 pmThe SDG2042X was quoted at over 300AUD more than the SDG1032X. I'm not sure that the SDG2042X is worth the extra 300+ AUD. What do you guys think?

author: nctnico
author_rank: Super Contributor
timestamp: January 06, 2020, 09:10:38 am
content: We can't tell. Again, we don't know the requirements. It may be that the SDG2042X isn't good enough or total overkill. We can keep throwing model numbers at you and see what sticks but I don't think this is doing you much good.Can you tell us something about the experiment setup you want to create and what kind of frequency shifts you expect?

author: tggzzz
author_rank: Super Contributor
timestamp: January 06, 2020, 10:27:21 am
content: The phrasing of the original question makes me wonder whther the OP intending to drive the laser more or less directly with the function generator. Given that lasers are highly nonlinear, a sinusoidal drive signal won't result in a sinusoidal light output.If, OTOH, it is driving a laser module with an analogue input, then it would work.Personally I would consider using a function generator to mimic the expected output of an optical receiver, and simply test the linearity of the optical tx and rx components.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 02:07:12 pm
content: Quote from: nctnico on January 06, 2020, 09:10:38 amQuote from: tggzzz on January 06, 2020, 10:27:21 amThe laser diode itself is connected to a function generator. The laser beam is modulated by the function generator to simulate a real situation where the laser beam would be modulated by the vibration of the measured object. The laser beam is directed on the photodiode.

author: nctnico
author_rank: Super Contributor
timestamp: January 06, 2020, 02:58:13 pm
content: I'm not sure whether that test will work because you won't be generating a doppler shift. A better test may be to build the laser doppler setup and drive a piezo disc from the function generator.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 03:36:23 pm
content: Quote from: nctnico on January 06, 2020, 02:58:13 pmSo which model of generator is suitable for this? Although, Ihaveseen other experiments use this setup, so I think it does work (unless they made a mistake).

author: nctnico
author_rank: Super Contributor
timestamp: January 06, 2020, 03:41:10 pm
content: The cheapest one will do just fine to drive a piezo disc.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 03:54:08 pm
content: Quote from: nctnico on January 06, 2020, 03:41:10 pmBut what if I want to run the experimental setup that I described?

author: nctnico
author_rank: Super Contributor
timestamp: January 06, 2020, 03:59:55 pm
content: Quote from: 3rj4 on January 06, 2020, 03:54:08 pmYou could but you'll be mostly testing the optic sensor without having an idea of what kind of light intensities it receives from an actual doppler application. The laser diode may be sensitive to overvoltage / reverse voltages so if you want to modulate the laser then I recommend getting a driver board with a modulation input.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 04:40:25 pm
content: Quote from: nctnico on January 06, 2020, 03:59:55 pmHmm, well the experiments who did this used a HAMEG HM 8030-5 generator for this purpose. It seems that this is a pretty old generator. Is it capable of doing something that the one's that I'm looking at cannot? Unless this is the case or the experimenters made a mistake, then I'm guessing it will work with these newer scopes too?

author: james_s
author_rank: Super Contributor
timestamp: January 06, 2020, 04:43:42 pm
content: Modulating a laser diode at high speed is not trivial. As has been mentioned they are highly nonlinear, the lasing threshold is often not that far from the point at which it fails from catastrophic optical damage, though newer more powerful diodes are a lot more robust than early ones. You still have to bias them so they stay above the lasing threshold with any input signal that you want producing an output. Then you need to avoid any overshoot in the drive current so you need to watch the step response of your driver.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 04:53:10 pm
content: Quote from: james_s on January 06, 2020, 04:43:42 pmGiven that experimenters were apparently able to accomplish this with a HAMEG HM 8030-5 generator, would I be able to do it with an SDG2042X or SDG1032X?

author: nctnico
author_rank: Super Contributor
timestamp: January 06, 2020, 05:10:15 pm
content: Even the Feeltech FY6900 is better compared to the HM 8030-5.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 05:36:52 pm
content: Quote from: nctnico on January 06, 2020, 05:10:15 pmHaha, ok. I guess that tilts it in favour of the SDG1032X.... But then again, given that Iwilleventually be doing higher frequency work than what the authors did, I suspect that I might need something that is closer to what Performa01 describes.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 07:37:23 pm
content: Ok, I think I'll go with the SDG1032X. I have to buy a lot of other items for my work as well, so I'm going to stick with the lower-cost piece of good quality hardware that I know will at least be sufficient for the foreseeable future, rather than going for something 300+ AUD more that might, for all I know, be overkill.Once again, thank you all for taking the time to help me! I greatly appreciate it!

author: nfmax
author_rank: Super Contributor
timestamp: January 06, 2020, 07:49:12 pm
content: Buthowdo you propose modulating the laser diode? Do you want to modulate the output intensity or the output (optical) frequency? You can vary the intensity by varying the drive current, but this variation needs to be about a steady drive current level, that must be carefully controlled to avoid damage. Generally, you would use a 'diode laser driver', which might be a piece of stand-alone test equipment or a purpose-designed chip: these generally have a convenient 'modulation' input you could drive with almost anything, even a very simple oscillator or function generator. You can vary a diode laser's frequency, to some extent, by changing its temperature, but only slowly. To get frequency modulation at the modulating frequencies you mention (MHz) you will need some sort of electro-optic device. Is this what you had in mind?

author: TurboTom
author_rank: Super Contributor
timestamp: January 06, 2020, 08:14:32 pm
content: An amplitude modulation of an LD also causes sidebands to appear in the spectrum, so in theory, it would be possible to modulate the frequency of a highly stable LD by modulating its drive current and varying the modulation frequency, if "looking" at such a side band. But I guess the direct effect of the changing drive current on the LD's frequency/wavelength would outweigh the side band modulation by far. If the sideband modulation actually works, you would need a pretty fast AWG, though.And then, there are those open-cavity LDs that require an external mirror to "lase". Of course, these permit all kinds of modulation schemes that you can find in "conventional" lasers but I'm not sure if these LDs available as a stock item. They won't be cheap for sure...I can also well imagine that it's possible to drive a small(ish) LD directly with an AWG. If using a properly dimensioned series resistor, even output voltage excursions (i.e. when switching the relays in the output signal attenuator), wouldn't cause any harm to the LD. Every AWG (that I know of) permits superimposing an offset with the output voltage so the LD can very well be properly biased. For most LDs, the output power, once above the threshold, increases pretty linearly with the drive current, almost up to its power limits.Of course, using a "proper" LD driver with modulation input is a much safer way to go. But if you (@3rj4) propose such a modulation scheme, you should pretty well know what you're doing and what kind of equipment you need to get it done. I cannot get rid of the impression that you're actaully just wanting to play around a little with your new oscilloscope and now you need a signal source. A source, that you may possibly, some considerable time in the future when you actually have learned more about the things you've got in mind now, can re-purpose for that application. If that is the case, I'ld rather recommend to now go and get an Analog Discovery or a ADALM-2k and start by playing around with this and at the same time gaining valuable experience in the sphere of signal theory and electronics.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 10:04:02 pm
content: Quote from: nfmax on January 06, 2020, 07:49:12 pmYes, I also plan to design the laser diode driver module myself. Do you think the SDG1032X is sufficient for this purpose?And as I said, the researchers used the HM 8030-5 to do what I have described, so unless they made an mistake, I'm presuming that I'd be able to do anything they did with the SDG1032X.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 10:12:46 pm
content: Quote from: TurboTom on January 06, 2020, 08:14:32 pmIt's not so much that I want to "play" with these devices for the sake of it; rather, I'm trying to go through the same process for building a (from what I can tell, relatively simple) LDV that some researchers went through. I've already specified what they mentioned they did in this process, and, as I said, they used a HM 8030-5 generator, so it seems reasonable to expect that an SDG1032X will be more than enough for at least this project (and any I have for the foreseeable future), no?

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 10:26:19 pm
content: The researchers did not give further details, so I'm unsure of precisely what they did. However, It sounds like it was similar to this:https://www.newport.com/medias/sys_master/images/images/h1b/heb/8797049913374/AN22-Modulating-Laser-Diodes.pdf"Throughout this discussion, oscilloscope traces will be presented to help explain many aspects of laser modulation. These traces were generated using an ILX Lightwave LDC- 3724B laser diode controller as the current source and viewed with a Tektronix TDS 3014 oscilloscope. The output was modulated with an Agilent 33120A function generator."From what I can tell, the Agilent 33120A generator seems to be less powerful than the SDG1032X, so, again, it seems that for this purpose, the SDG1032X should be more than capable?

author: TurboTom
author_rank: Super Contributor
timestamp: January 06, 2020, 10:56:42 pm
content: Thanks for providing this document. It's basically ILX engineers demonstrating and characterizing the modulation capabilities of one of their laser diode current sources. It's always worth having a look at the issue date of such papers, this one originates from 2005! This explains the less-than-stellar performance of their setup. Today's integrated laser drivers easily modulate fiber laser transmitters far into the gigahertz range.With a setup like shown in the paper, you can probably still learn a lot but from today's point of view, you won't compete against current technology, so it may not be a good idea to use such publications as a guidline, also for choosing equipment. If you would like to duplicate their setup with similar frequencies, and you're not sure what kind of signals you will need in future (so any spendings on the AWG right now may be needless later), I can only suggest to get the cheapest generator that you feel comfortable to use and replace it with a model that suits your "real" application when the time has come.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 06, 2020, 11:47:17 pm
content: Quote from: TurboTom on January 06, 2020, 10:56:42 pmThat document is not the experiment that I am looking to perform; I just posted it as an example, since what they described sounds similar to what the researchers described for their LDV setup. I apologise for any confusion.Here's some of the things I plan to do:Build laser modules for <100mW CW lasers.Build low power (2-10 mJ per pulse), nanosecond pulsed (anywhere from 1-100 ns) lasers.Build LDV systems for measuring ultrasound frequencies between 2.5-10MHz.My main concern now is whether the SDG1032X is going to be sufficient for performing this type of work, or whether I need the SDG2042X? I don't want to spend 400 AUD on the SDG1032X, and then realise a year later that I need the SDG2042X (which is 300+ AUD more).

author: nctnico
author_rank: Super Contributor
timestamp: January 07, 2020, 12:44:18 am
content: Then buy the Feeltech FY6900If it turns out to be inadequate you can always upgrade to the SDG2042X or Tti TGF4000 series without losing any sleep over it.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 01:35:20 am
content: Quote from: nctnico on January 07, 2020, 12:44:18 amThat's true. I could also modify/repair it without fear of (further) destroying an expensive piece of hardware. But what happens if the FY6900 malfunctions and destroys whatever I'm working on (which could be an expensive piece of hardware)?

author: nctnico
author_rank: Super Contributor
timestamp: January 07, 2020, 01:44:46 am
content: Well... the same thing can happen with any function generator. Just make sure you have some form of circuit protection in place even on a prototype. Accidents do happen.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 01:48:04 am
content: Quote from: nctnico on January 07, 2020, 01:44:46 amThe point is not that it cannot happen with other function generators; rather, it is that it is more likely to happen with a poorly built piece of hardware, such as the FY6900.And what do you mean circuit protection? How do you have circuit protection against function generator malfunctions?

author: nctnico
author_rank: Super Contributor
timestamp: January 07, 2020, 01:55:03 am
content: Quote from: 3rj4 on January 07, 2020, 01:48:04 amI wouldn't say it is poorly build. The chance of operator error is infinitely higher.QuoteTVS/ zener diodes for example which limit the voltage across a device. The stuff you also use on inputs/outputs of circuits. They also help against static discharges.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 02:00:05 am
content: Quote from: nctnico on January 07, 2020, 01:55:03 amHmm, maybe I should get it. I wouldn't mind opening it up at some point and replacing parts to improve it. This seems like an excellent way to gain experience for repairs/improvements. Then I could eventually start opening up my 54845A.

author: nctnico
author_rank: Super Contributor
timestamp: January 07, 2020, 02:07:02 am
content: I would leave it as-is unless it is broken.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 02:12:11 am
content: Quote from: nctnico on January 07, 2020, 02:07:02 amThat's probably the best course of action -- at least, until I become more experienced with electronics. SteveyG posted this video review in a past thread:https://youtu.be/FaNvHQW_CsQ

author: bdunham7
author_rank: Super Contributor
timestamp: January 07, 2020, 02:26:02 am
content: Quote from: 3rj4 on January 06, 2020, 10:26:19 pmI had to read this far to make sure you weren't trying to power the diode itself directly from the FG. If you aren't and you intend to use a proper controller, then any FG should work fine. I have both the FY6900 and the SDG2042X so I can give you a simple comparison. They both work fine, the FY6900 is a light, cheap toy while the SDG2042X is a near-pro unit that works pretty well as long as you have later firmware--features were added that improved it over the first shipped units. Owning both and having used both, I can say that if I needed to use one for what you are doing, I would simply grab the one that was closest to me. HTH.I am curious though--what system allows you to physically convert vibrations into an intensity modulation of a laser? Or am I misunderstanding something?

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 02:34:21 am
content: Quote from: bdunham7 on January 07, 2020, 02:26:02 amThanks for the information.I'm not sure. My plan is to just attempt to follow what the researchers did and hope it works. Such is all a newbie to electronics can do. If I encounter problems, then I guess that's when the real learning begins.

author: tggzzz
author_rank: Super Contributor
timestamp: January 07, 2020, 08:25:28 am
content: Quote from: 3rj4 on January 06, 2020, 10:04:02 pmGood luck with that. It isn't trivial.Make sure you have a ready supply of laser diodes.Make sure everybody in the vicinity is wearing good eye protection.

author: nctnico
author_rank: Super Contributor
timestamp: January 07, 2020, 11:05:48 am
content: Quote from: 3rj4 on January 07, 2020, 02:12:11 amBut he is wrong about the grounding wire. Just leave it; don't make it worse. If you watch close enough you can see the wire says it is rated for 300V.

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 03:02:27 pm
content: Quote from: tggzzz on January 07, 2020, 08:25:28 amThanks for the advice. Yes, I anticipate burning through a number of diodes, and have already purchased safety glasses (rated for the particular wavelength).

author: 3rj4
author_rank: Regular Contributor
timestamp: January 07, 2020, 03:03:37 pm
content: Quote from: nctnico on January 07, 2020, 11:05:48 amUnderstood. Thank you for all of the help!

author: JohnG
author_rank: Frequent Contributor
timestamp: January 07, 2020, 06:40:16 pm
content: Quote from: 3rj4 on January 06, 2020, 11:47:17 pmI would take a careful look at these numbers. A rectangular laser pulse of 100 ns width and 2 mJ/pulse is a 20 kW (20,000 W!) peak power pulse. This is the best case, a 10 mJ, 1 ns pulse will be 10 MW peak power. Not of the generators listed will do this. I have not bothered to factor in laser diode efficiency.Even if you mean uJ (1e-6 J) instead of mJ (1e-3 J), none of these signal generators can do this.John

author: 3rj4
author_rank: Regular Contributor
timestamp: January 08, 2020, 12:46:32 am
content: Quote from: JohnG on January 07, 2020, 06:40:16 pmUnderstood. It will be a while until I get to the pulsed laser, so I'll worry about that then. Thanks again for the advice!

author: JUNCE LEE
author_rank: Newbie
timestamp: January 18, 2020, 05:51:17 am
content: The output current of most function signal generators is relatively small, which means that it cannot carry a large load. I don't know if your laser debugging has enough current of 0.1A in actual use.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: January 18, 2020, 09:15:22 am
content: What area of Australia are you in? I’m in WA and have a few function generators in a pile that I need to list for sale because I’ve upgraded.If you’re over this side of the country it can definitely save on postage costs

author: 3rj4
author_rank: Regular Contributor
timestamp: January 24, 2020, 10:26:10 pm
content: Quote from: PTR_1275 on January 18, 2020, 09:15:22 amHa, I'm actually also in WA. But I already ordered the FY6900, so I'm done with function generators for the time being. Thanks for the offer, though.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: January 24, 2020, 11:40:44 pm
content: No worries