BABAK MOMENI AND ALI ADIBI
λ2
Stray light
λ1, λ2
λ1
Signal
T
FIGURE 1. Three dispersive properties of photonic crystals (PCs) can be visualized
schematically. In the superprism effect (left), different wavelengths propagate in dif-
he idea of photonic crys- ferent directions within the PC. The negative diffraction effect (center) allows normal
tals (PCs) as synthetic beam broadening to be compensated by propagation in a PC region with negative
optical materials with diffraction, which effectively narrows the beam. And the negative refraction effect
(right) causes the desired signal to be refracted away from the direction of the inci-
“controllable” proper- dent signal, resulting in the separation of the desired signal from the stray signals.
ties has been advanced
by progress in photonic-crystal fabrication technologies (separation of channels with small wavelength difference be-
and improvements in the conceptual understanding of their tween adjacent channels), and low crosstalk (negligible pres-
properties. Besides applications that ence of unwanted chan-
utilize their photonic bandgap mainly Three dispersive properties nels at the location of the
for light confinement, PCs can also be desired channel).
exploited to harness their unique dis- of photonic crystals—the super- Despite these appli-
persive properties.
1,
2,
3 Of particular prism effect, negative diffraction, cation demands, com- interest is the ability of PCs to perform pact WD devices with
parallel demultiplexing in a very small and negative refraction—were the required properties
footprint that is compatible with chip- for practical applications
scale integrated photonic circuits. used in combination to produce have not yet been realized
In addition to applications in optical because of the lack of an
communications, compact optical wave- the most compact photonic- appropriate optical mate-
length-demultiplexing (WD) devices rial with high dispersive
have received increasing attention as crystal demultiplexer to date. properties to allow for
building blocks for spectral analysis in the formation of compact
“lab-on-a-chip” biosensing applications and integrated opti- structures on a chip. But recent advances in dispersion engi-
cal circuits for optical information processing. These com- neering using PCs may be changing this reality.
pact WD devices are used to separate several optical chan-
nels at different wavelengths with high spectral resolution Designing a high-resolution demultiplexer
To realize an efficient spectrometer, in addition to a com-
BABAK MOMENI is a graduate student and ALI ADIBI is an associate pact WD mechanism to achieve spatial separation of differ-
professor in the School of Electrical and Computer Engineering at the Georgia Institute of Technology, Atlanta, GA 30332; e-mail: adibi@ece. ent wavelength channels, special measures must be taken to
gatech.edu; www.ece.gatech.edu achieve high isolation from unwanted wavelength channels.
References:
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