Noninvasive glucose meters are the Holy Grail in glucose testing. To be able to get a glucose value without a finger stick would be a tremendous benefit to the millions of people who have to test themselves several times each day.
So there have scores of scientists who have worked on the problem, backed by diagnostic companies since the profit potential is huge.
I remember while at Ciba Corning, attending a lecture on near infrared spectroscopy given by a professor whom I think we were supporting to try to come up with a noninvasive glucose meter.
On a website devoted to diabetes, I became aware of a book which chronicles the quest for a noninvasive glucose meter. It is recent (2015 publication date), free, and written by a former chief scientific officer and VP of LifeScan who has been involved in this search for years.
I found it fascinating.