photonics opinion
rhombus4
an integrated photonic circuit are generally
best made from materials of different
bandgaps and junction placements. For
example, laser material must enable efficient
light emission under forward bias, modulator
material should allow low and high
attenuation in the “on” and “off” states
under reverse bias, and passive waveguides
require a material with minimal absorption. A
multitude of successful material integration
methods exist for photonic integration.
Optical components are built using many
materials including indium phosphide (InP),
gallium arsenide (GaAs), lithium niobate
(LiNbO3), silicon (Si), and silica-on-silicon.
Photonic integration derives its value from
the ability to unify as many disparate
functions into a single material platform, and
thereby deliver maximum impact on system
cost and functionality.
Figure 2: Prototype PM-DPSK transmitter with 282 functional elements (Infinera)
Lithium niobate has, to date, allowed small-
scale photonic integration of several
addition of several functions for a single integrated into a single monolithic substrate. components. Devices have been built that
wavelength channel and even some small This could include the integration of integrate multiple Mach-Zehnder modulators
level of parallelism (i.e., multiple functions functions as well as wavelengths, but and associated waveguides and couplers
duplicated across multiple channels). nevertheless is probably the barrier to on a single substrate, for example. Complex
Large-scale PICs: These circuits will be digital-based PICs, and thus might be processing requirements and size
above 100 functions or components referred to as the Holy Grail for PICs. limitations, however, may preclude it from
integrated into a single monolithic substrate, being a material of choice for scaling to
which may imply the integration of several 6.0 Materials platforms for medium or large-scale integration.
functions for a single wavelength channel as photonic integration Furthermore, lithium niobate faces severe
well as a high degree of parallelism (i.e., A wide variety of materials platforms exist technical challenges to practically implement
10+ channels per PIC). A good example is which offer the possibility of photonic active optoelectronics functions like lasers
shown in Figure 2, a 282 functional element integration, and these generally mirror the and detectors, thus limiting its potential to
prototype PM-DQPSK transmitter in InP. materials used in the construction of both integrate the entire range of desired
active and passive optical components. photonic functions.
Very large-scale PICs: These circuits will be
above 1000 functions or components Individual component devices that make up Silicon, or silicon-on-insulator (SOI), has
shown promise as a materials platform for
the large-scale integration of passive optical
devices such as arrayed waveguide gratings
(AWG), optical switches, and VOAs. In
recent years, integration of active devices
have been commercialized—such as lasers,
amplifiers, modulators, and photodetectors—
which offer potential for low cost PICs. In
addition, silicon photonic integrated circuits
can be built using standard CMOS
processes and therefore hold the promise
for enabling both optical and electronic
integration.
Figure 3: Commercial PLC-based
integrated ROADMs showing integrated
switch/VOA arrays packaged into a
ROADM sub-system module
(NeoPhotonics)
28 www.compoundsemiconductor.net October 2009
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44