Which IC design field is more challenging: optics or RF?

i am interested in IC design for one of these fields. which one is more challenging? which has more job opportunities? are there alot of similarities between the two? i did my undergrad thesis in rf (bluetooth transceiver 0.18u), i am not very familiar with optical IC, i have just taken communications class on optics. i would like to do masters in either RF or optical IC. please some advice. any good books to get started in optical IC? razavis optics book is as good as his analog and rf books?

I would say the analog ic design for RF and optical IC design are very similar.
They are designed based on the same theory in circuit theory, signal and systmes,
communication theory. For job opportunity, I would say RF gives you more, but
it looks the fiber comm is in recovery recently. For your reference.