Doing a second doctorate to get back on a research track? I graduated with a Ph.D. in Physics (specialized in studying protein dynamics via laser light and coherent X-rays) from a U.S. university in May 2014. However, could not continue with research/post-doc due to a medical condition with my infant child. We had to move to a different state for  his medical treatment. Over there I did not have any contacts to secure even a post-doc position and ended up as a part-time community college instructor for more than two years. 

Now my child is okay, and I want to continue my research, but when I submit my CV to research positions, no one seems to care about it. My Ph.D. supervisor has no funding, so no hope there. As a result, I was thinking of doing a Ph.D. in biomedical engineering specializing in biophotonics and/or optical radiology. Is this possible ? Will graduate schools in U.S. accept my application since I already have a Ph.D. in Physics ? 

Hopefully, someone can shed some light on my concern.

Thank you in advance!
A second Ph.D. is generally a bad idea, as noted elsewhere in other answers.  

Instead, there are several other paths that you can pursue to get back into research, depending on your goals.  The main ones that I would think of are: getting a postdoc, joining a lab as research staff, or joining an industrial lab.  All of these will lead you back into research in some form or other, thought probably not your same line of research that you were working on in your Ph.D.

You've got a gap on your CV, but not an unusually large one, so I don't think that needs to be a major barrier.  More concerning is the fact that you don't seem to have a professional network: the thing that you want from your old advisor is not for them to hire you, but for them to connect you with other different professors or industrial folks who might be interested in hiring you.  Going to conferences in your field is another good opportunity for networking, but it will be more effective if you can get help from your advisor or other professors who you have gotten to know during your doctoral program.