You might want to clarify your question a bit: On one hand you imply by the statement "since in ancient and mediaeval periods science and philosophy weren't clearly distinguished as disciplines" that by modern period, you mean starting with the Enlightenment. But on the other hand, you specifically call out philosophy of science, which only appeared in the 20th century. So it is not clear what you mean by modern period.
If by modern period, you mean starting with the enlightenment, then DesCartes (epistemology, physics, math) and Kant (epistemology, astronomy) would count as examples. Here I am considering epistemology to be the "ancestor" of philosophy of science.
On the other hand if you are looking for those who contributed strictly to the field of philosophy of science (so starting from the 20th century) - the only well known example I can think of is Hilary Putnam, who contributed to philosophy of science (multiple-realizability and scientific realism), and also made significant contributions to computer science (The DP and DPLL algorithms).
Less known is Massimo Pigliucci, who holds doctorates in genetics, botany and in philosophy of science, and has held positions both as professor of evolutionary biology and as professor of philosophy of science. I don't know if his contributions are considered major, but he has contributed enough that he qualifies as a working biologist and as a working academic philosopher of science.
Sam Harris hold degrees in both philosophy (undergraduate ) neuroscience (Ph.D), and has written on both topics, but he isn't considered a major contributor to either. His main claims to fame are as a critic of religion (one of the New Atheists) and as a TV pundit, not as a philosopher of science.