The Signal Path - 2021-07-12
In this video Shahriar dives into the world of tuneable semiconductor lasers. First, a Santec TSL-200 source is presented and repaired. The performance of the instrument is verified using a multi-wavelength meter. A DFB gold box laser module is then presented along with a demonstration showing the sensitivity of the laser diode to temperature variations. The entire wavelength locking mechanism of the DFB laser is presented in details along with the principle operation of an Etalon wavelength interferometer. The teardown of the module shows all its inner workings. The LightSquare product and its teardown is also shown which includes a diffraction wavelength measurement system. Finally the operation of the TSL-200 tuneable semiconductor laser is presented which uses a tuneable external cavity Fabry-Perot laser. Finally the teardown of the multi-wavelength meter is shown along with the operation of the Michelson Interferometer inside. www.TheSignalPath.com www.YouTube.com/TheSignalPath www.Patreon.com/TheSignalPath
The quality of content in the signal path is unmatchable.
The signal to noise ratio is excellent!
Startup caps on a SMPS are such a common failure that I just replace them first without doing any further tests. The classic symptom is a device that was working, but then failing to come on again after power has been removed.
I see this failure mode all the time as well, although I often find a design will splurge on a name brand 400 V bulk filter capacitor, but the bootstrap capacitor will be some Dongguan back alley special in the smallest and highest ESR package they can find (much smaller than the ones in this video). Makes me rethink where I should be spending my BOM.
The reason the startup cap has such a high voltage rating is that if the power supply doesn't start for any reason/fault the voltage in the cap can go way higher that 50V
You are an inspiration for so many. Thank you Shahriar, I love you and your work, so glad I found you years ago.
Thank you!
Wow! A miniature F-P! We had a bench sized one in the mid 80s for Alexandrite work. This is mind blowing.
Very interesting breakdown of how tunable lasers work. This is what YouTube should be about. Thanks
"Jump to 9:30 if you like to skip the repair" why on earth would someone wanted to do that? Amazing as always, specially the smps caps... hey! that's something i do! you know... not everyone own an xray machine....lol Greetings from Argentina!
Great video as always, I really enjoyed the experiments and teaching!
Very nice, I love it when you do these optical subjects! The substrate that the tunable laser diode was mounted on looked like something special, maybe Zerodur or some other low CTE glass-ceramic material?
Looks like AIN to me
AlN is quite common for these types of applications. You can find it almost in every mass product butterfly-like assemblies. Zerodur will be overkill.
@Konstantin Akmarov yes also from the color, an i think it is hard on other material to make solder contact surfaces that hold well. Zerodur is way too expensive ^^
Thanks for the amazing videos. Obviously laser cooling is cooler than laser hammers...
Amazing knowledge and well put in understandable manner. Thank you for the effort. Keep them coming! :)
This video was all over the place, in the best way possible. I think the only thing missing from this channel is something with magnets, like a MOT.
I loved the fact that the last instrument was based in another measuring method, so we learned still something different. So much information in one video! Just great! Make more like this!
Great video. I would like to to see some more videos about magnetic levitation.
We have on campus a monochromator, which uses 2 Diffraction gratings in series, which was used with a non-coherent light source of high intensity which was then passed through an unknown color filter, and it was set up to scan through from Mid IR to UVA to a sensitive optical sensor that measured power and we got a characteristic curve showing the band pass of the filter. It was also used to test CCDs, CMOS, and and other photo detectors and check their photon conversion based on wavelength.
I have never heard of using laser to punch the components into position in photonics and micro-optics packaging. I can imaging there are several reasons not to do that. One would be the power required and the debris generated during the process would be very bad for those free space optics. Do you have any references on how this is done? Single mode fiber coupling in integrated optics package are typically done with nano positioning stages during glueing. Fiber coupling are sensitive, but not that sensitive. You can be off by a um and still have acceptable coupling efficiency.
I was trying to see how an optical silicon microprocessor could use the frequency deviations for mathematical functions especially in a Pico wavelength measure. I can see how it would be faster than electrons because it could be instantly read globally on the face at a moment.
Out of curiosity, how much current did that diode take? Are these systems relatively efficient?
At 50mA it was putting out about -3dBm.
Always enjoy your videos.
I work in a synchrotron facility building and testing undulator magnets, which ARE the ultimate laser sources producing kWs of coherent X-ray beams.
Good video as always, somehow it seems you are getting even better and concise at explaining all of these concepts.
Loved this, lots of explanations and details: good job!
Great video, thanks!
I actually laughed out loud seeing the values for the second start up capacitor xD
Great video! Do you know of any devices that utilize the magneto optical Kerr effect, or (maybe entering rf territory) evanescent waves to do calibration (or for any other reasons)?
I think any device utilizing those would be fascinating to look into!
Woooooow I learned a lot of new stuff This episode was great .
Until today I had no idea you could make a tuneable laser source of such precision. Amazing.
In a previous career I serviced and supported commercial laser printers. In a consumer or midrange printer, the laser is a sealed unit which is not serviced. In the highest-speed printing environments, they were made with 15-50mW gas lasers (usually argon), or with laser diodes. This video covered so much of the similar technologies. The components in these types of laser arrays would all be replaceable and adjustable, much larger than a sealed wire-bonded unit. I miss the art and science of adjusting those units. Such happy memories :)
7:12 It'll blow up your scope even if you probe the negative pin of that capacitor, or in fact any pin after the rectifier. Because of the way full bridge rectifiers work, both DC rails end up floating around with amplitude of the mains Vpk.
Every time I start watching one of Shariar's videos, I wonder what will the fault be today ? Fuse or just a connector come off 😀
Hey! Not so easy this time...
Ok I’ll bite. If you want intuition about optics (and laser phenomena), watch @Huygens Optics videos about photon sieves (essentially phonon ring resonator interactions). A collaboration between you two would be fascinating.
Maan we need to figure out an excuse to get more spinning things in RF equipment.
We make phased arrays to not have to do that! ;)
This was highly interesting. I kinda want to build my own crude tunable diode laser with closed-loop feedback now. *hm*
Wow things I studied right there on the bench. Fantastic channel
Many thanks for this, Ive been using Sm Fibre in my work, and never really understood it ("All Smoke and Mirrors..." is the usual description....... fantastic insight....
Very nice and I liked the detour to the Linksquare thingy. Perhaps a new video about that?
Was wondering about the Pico wavelength pizo-chrystal controlled laser. Does it turn the mirror slanting or the spacing of the incident light dots?
Quite increadable. How on earth would you make the parts that are on this assembly let alone actually assemble and align them. And for peanuts! Stunning stuff
Curious about how the LD will somehow synchronise with the frequency of light reflected back into it.
This is due to a phenomenon called stimulated emission. It is the fundamental thing that makes lasers work and produce coherent radiation. Basically, a photon that is reflected back into the LD will stimulate the recombination of electrons and holes inside the LD. The photons emitted in the recombination are in phase and of the same wavelength as that original photon, and they stimulate further recombination and so on. Eventually, the large majority of the photons are produced this way and you get laser light.
Fascinating tutorial....cheers.
Fabulous video. Many thanks.
This was so interesting! Thanks!
The shiny bare machined optical enclosure of the Agilent multi-wavelength meter makes me uncomfortable! But I do see this somewhat often in certain optical test instruments, I would have thought you'd always want it matt black? From what I understand the geometry of the Michelson interferometer doesn't inherently reject dynamic scatted light, I would assume it would just raise the noise floor?
Very good content !!!!!!
Those old HeNe lasers stop working after a while because their gas tube fails and needs to be replaced. This is true of all gas lasers, which is why most instruments now use diode or other solid state laser technologies. If it is indeed the gas tube that has failed in that laser, it might be difficult to source a compatible one that still works.
Yep. Our applications of gas lasers would have a simple ammeter on the driver input. Once the gas started to get very low, you’d see a high draw of current and know it was soon to fail. In our case, we went through hundreds of the exact same unit, so the OEM would remanufacture them - however the reman units had a substantially shorter life.
Most wavemeters nowadays still use HeNe lasers because a stabilized HeNe laser has a relatively precise absolute wavelength to ~ppm level. Most solid state laser are not absolute and can vary up to several nm so it’s easier to use a HeNe as a light source so the instrument doesn’t need to be designed to accommodate calibration over several nm.
@Wade Hsu Solid states laser can be made as frequency stable as HeNe lasers, but those are extremely expensive and HeNe lasers also have very tight beam that is hard to get on solid state lasers. So thus its way cheaper to get a HeNe laser which it very stable as is, only disadvantage is that is bulky and need HV but they can be made quite small if not need any real power from them.
dtiydr yes, solid state laser can be frequency stable, but they are not inherently accurate and not as stable as stabilized HeNe laser. So each laser will need to be measured and calibrated and the range of that calibration can vary up to 10nm. Unless the laser diode are lock to an atomic reference then the accuracy becomes absolute, but that come with a price of complexity and wavelength typically in the IR for common atomic reference such as Cs or Rb. Also, long term stability of single frequency diode laser are poor if not locked and they are also temperature sensitive. So to maintain the wavelength stability the temperature and current of the laser diode will need to be regulated to better than 1mK and ppm stability.
@Wade Hsu All correct and thus their price and in many case a HeNe is easier to control that part but not as wide band and also bulkier which could be a constrain sometimes but otherwise its pretty much the best choice and no doubt cheapest.
I want to capture still shots of the J 11 process delided! what would you suggest for capturing the images? What camera are you using?
And yes that’s the best sight all day. Nice and mate black/gold 👍
God Bless.
20:32 ... and imagine all those discrete optical parts integrated like transistors in a chip, then you would get a PIC like this:
https://effectphotonics.com/nasa-acknowledges-effect-photonics-pic-as-a-state-of-art-commercial-example/
wait, the way diffraction grates split one laser into multiple dots is the same mathematics that causes grating lobes in an antenna array, right? That's where the name comes from?
Out standing content here. Greetings from France.
Nice repair and discussion
This had me thinking of Newton's famous prism experiment.
Interesting video. Another expensive piece of equipment rendered inoperable by a few dollars worth of capacitors. I think l know what is causing the Hubble grief....
Also interesting that some agency (government funded lab or possibly college lab) disposed of an instrument that any reasonably experienced tech could have easily repaired. Hey, the taxpayers have endless amounts of cash available!
The Signal Path - 2021-07-12
Some of you have advised against putting an oscilloscope on an isolation transformer. The main reason is that by "floating" your scope with respect to earth, the outer conductor of the BNCs also float and can therefore rise to dangerous voltages due to probing. This is good advice and safety measure. Always place the DUT on the isolation transformer and never the instrument! This is how all my setups are done.
cjs819 - 2021-07-12
Or use a memory recorder. Memory recorders have isolated inputs.
NiHaoMike - 2021-07-13
Or use isolated probes, but those aren't cheap. Probably the cheapest but safe solution for hobbyists is to use an inverter powered by an isolated DC source.
Dmitry Orlov - 2021-07-13
I use two isolating transformers, one for DUT and another one for instruments.
cjs819 - 2021-07-13
@Dmitry Orlov that is certainly possible. Get the right tool for the job! Or as my friend Ed always said: ‘because you could doesn’t mean you should’
Dmitry Orlov - 2021-07-13
@NiHaoMike Transformer is much chipper and reliable, and doesn't create noise (EMI).