An optical instrument for splitting optical spectrum, comprising a series
of hollow core optical wave guides (12, 22, and so on) connected by
optical couplers (16, 26, and so on) transporting broad band incident
optical wave from one stage to another, a narrow band optical wave guide
(14, 24, and so on) made of photonic crystal materials mounted inside
each of said hollow core optical wave guide and along it, and specified
for confining certain portion of the incident optical spectrum. Said
inner narrow band optical wave guides bend out at the ends of said outer
hollow core optical wave guides to extract and guide out the selected
component of the incident optical spectrum. Said optical couplers couple
the output optical waves of said outer hollow core wave guides of the
previous stages into said inner optical wave guides of the next stages
for further splitting.