I need to couple the light emerging a VCSEL into a single mode fibre. I searched the internet, and I couldn't find any out-of-box commercial product to buy.
Are there any particular tool like a receptacle I could use to achieve a high coupling efficiency?
PS: I tried the traditional way, i.e., focusing the VCSEL beam into a single mode fibre using an objective lens. However, the setup sensitivity to vibrations and other impacts makes it impractical.
The most important aspect for coupling losses is the mode-field overlap. There are different VCSELs on the market. In order to reduce the losses you should find a VCSEL that matches best with the mode-field diameter (MFD) of the fibre. You may use single-mode VCSELs with diameters of 4-5µm so larger one should improve the coupling efficiency for ordinary SMFs (in case we are talking about 1.55µm operational wavelength).
I also know that there are VCSELs with integrated ball lens on the market.
And the easiest way should be a laser with a fibre pigtail.
Dear Mojtoba,
10 years ago I worked on the fibre coupling from a monomode VCSEL (850nm) to a single-mode fibre (4.5 µm). There was a company in UK : Afonics which was selling the fibre pigtailing for lasers and they did some pigtailing for us (we provided them the VCSELs). But the company doesn't exist anymore to the best of my knowledge.. On the other hand, we also worked on fibre lensing using graded-index multimode fibres and it worked quite well, and we had achieved better results than Afonics. The idea here is to lens the tip of a fibre such way : Single-mode - coreless fibre - Graded index fibre. The lengths are to be calculated in order to match the input and output numerical apertures (from VCSEL to single-mode fibre..). But you will need to align and approach the lensed fibre very close to the laser chip in order to have the minimum beam diameter and hence increase as much as possible the coupling efficiency. It sounds maybe a bit difficult, but it's not really..
I attach you three files here : One of our recent publication which makes use of lensed fibres for a rotating fibre coupling system (look at chapter 2), another one which is a good reference for the lensing using graded index fibres, and finally a third one which is a graph that shows the results we've obtained with this technique for making the VCSEL coupling to a single-mode fibre.
Do not hesitate to ask if you want more details.. And i hope that it will help a bit.. :)
Good luck !
Miguel
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