In a Mach–Zehnder interferometer, a beam of light traveling through a
waveguide is split into two parallel waveguides of equal length and then
recombined (similar to in a DPI instrument). Applying an electric field to
one arm (or electric fields of opposite polarity to both arms) changes the
refractive index in that arm and causes the light to travel at a different
speed than in the other arm, changing the phase of the light and causing
their electric fields to interfere when they recombine. If the applied
voltage is sufficient to induce a phase shift of 180° (π radians), then the
waves perfectly destructively interfere and no light is emitted. This critical
voltage is called V π , and digital signals can be encoded by rapidly
switching between zero voltage and V π .
One of the most critical parameters in integrating photonic systems with
electronics is the parameter V π L, or the product of the switching voltage
and the device length. This parameter is in turn proportional to the
electro-optic coefficient r 33 , which makes a high electro-optic coefficient
critical for nanoscale devices, such that the device can be run at a
voltage consistent with the electronic components. High hyperpolarizability organic dyes have been demonstrated to give bulk electrooptic coefficents in excess of 500 pm/V, with substantial room for
improvement (Dalton, 2015). Furthermore, organic dyes such as YLD124 (shown in Chapter 8) can be integrated into devices using thinfilm formation methods such as those that we have discussed, and
generate their refractive index shift by electronic polarization (a very
fast process) instead of vibrational motion (much slower), as in inorganic materials.
Integrating organic dyes in a nanoscale silicon (silicon–organic hybrid) or
metal-coated (plasmonic–organic hybrid) waveguide has allowed
shrinking device waveguide widths to 50–200 nm, with electro-optic
coefficients up to about 350 pm/V, operating bandwidths of >100 GHz,
operating voltages of <1 V, and total device footprints with total device
dimensions on the order of microns (Heni, 2017). An example of
plasmonic–organic hybrid modulator is shown in Figure 10.29.
While nanoscale photonic circuitry is currently in its infancy compared to
electronics, continued advances will allow processing data hundreds or
thousand times as fast as in pure electronic circuits, although realization
of this objective will require further advances in materials design,
understanding of interfacial science, and development of nanofabrication
methods, building on the amazing advances that have already occurred in
the electronic domain.
NANOSCALE HYBRID PHOTONICS 431
waveguide is split into two parallel waveguides of equal length and then
recombined (similar to in a DPI instrument). Applying an electric field to
one arm (or electric fields of opposite polarity to both arms) changes the
refractive index in that arm and causes the light to travel at a different
speed than in the other arm, changing the phase of the light and causing
their electric fields to interfere when they recombine. If the applied
voltage is sufficient to induce a phase shift of 180° (π radians), then the
waves perfectly destructively interfere and no light is emitted. This critical
voltage is called V π , and digital signals can be encoded by rapidly
switching between zero voltage and V π .
One of the most critical parameters in integrating photonic systems with
electronics is the parameter V π L, or the product of the switching voltage
and the device length. This parameter is in turn proportional to the
electro-optic coefficient r 33 , which makes a high electro-optic coefficient
critical for nanoscale devices, such that the device can be run at a
voltage consistent with the electronic components. High hyperpolarizability organic dyes have been demonstrated to give bulk electrooptic coefficents in excess of 500 pm/V, with substantial room for
improvement (Dalton, 2015). Furthermore, organic dyes such as YLD124 (shown in Chapter 8) can be integrated into devices using thinfilm formation methods such as those that we have discussed, and
generate their refractive index shift by electronic polarization (a very
fast process) instead of vibrational motion (much slower), as in inorganic materials.
Integrating organic dyes in a nanoscale silicon (silicon–organic hybrid) or
metal-coated (plasmonic–organic hybrid) waveguide has allowed
shrinking device waveguide widths to 50–200 nm, with electro-optic
coefficients up to about 350 pm/V, operating bandwidths of >100 GHz,
operating voltages of <1 V, and total device footprints with total device
dimensions on the order of microns (Heni, 2017). An example of
plasmonic–organic hybrid modulator is shown in Figure 10.29.
While nanoscale photonic circuitry is currently in its infancy compared to
electronics, continued advances will allow processing data hundreds or
thousand times as fast as in pure electronic circuits, although realization
of this objective will require further advances in materials design,
understanding of interfacial science, and development of nanofabrication
methods, building on the amazing advances that have already occurred in
the electronic domain.
NANOSCALE HYBRID PHOTONICS 431