opinion photonics
rhombus4
progressing quickly. The graph shows that
by 2010, technology leaders should be in a
position to address very large scale
photonics integration, and perhaps
digitization.
9.0 Metrics for PIC trend maps
and roadmaps
The obvious way to address future trends is
component count, with small, medium, large
and very large scale integration metrics. An
area in which photonics works well is
functional count and functional integration.
In functional count, active and passive
functions are counted separately. Short
definitions of active and passive functional
components are provided below:
“Active” components: These are
optoelectronics functions that require an
electrical contact, such as lasers, PIN
detectors, modulators, switches, VOAs, and Figure 6: Scaling of InP-based transmitter PICs in telecommunication networks
amplifiers. A current (forward potential) may (Infinera, OIDA Photonic Integration Forum, Oct 2008)
be injected into an active device to generate
light by conversion from electrical to optical
at a pn junction. A current may also be and passive functions on a yielded optical passive device is defined as one function
applied to change the local index of a die regardless of the die’s application as a regardless of the number of inputs and
component. A voltage (reverse potential) system or subsystem in an optical network. outputs. For example, an AWG which has 8
may be applied through an electrical contact The philosophical intent is to track the input and 8 output arms counts as one
to enable energy conversion from optical to beneficial effect of reduced defect density. function, as does a similar AWG with 1000
electrical at a pn junction. A voltage can be Counting each device that can have a input and output arms. The larger AWG may
used to change the local index of a different failure mode is an easily applied then have a greater chance of sustaining a
component or to change the optical technique which is independent of the killer defect than the smaller AWG. It may
absorption properties of the material. A method of counting random and systematic seem incorrect to count each device as one;
current may be applied through a resistive “killer” defects. however, as practical circuits get more
medium to change the local temperature of One issue with this approach is that each complex, they will need larger and larger
a device, which may or may not be the same
material as the optical path material system.
Most active elements have separate
contacts for sourcing and sinking current. It
should be clear that it is the function count,
not the contact count that is tracked.
“Passive” components: These components
enable purely passive functions such as
waveguides, filters, power dividers, and
multiplexers. Passive devices may indeed
have electrical contacts in some cases for
tweaking or tuning of the device
performance. These electrical tuning
functions are slow acting relative to the data
rate of information being transported through
them (often thermal in nature) and can be
“set and forget” for the life of the device.
These tuning functions are separate active
elements from the passive device function.
It is possible to measure the technical level
of advancement of the integration platform Figure 7: Moore’s Law component count of functions per die vs. time for research
by aggregating the total number of active prototypes (TU/e, OIDA Photonic Integration Forum, Oct 2008)
October 2009 www.compoundsemiconductor.net 31
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