103 research outputs found
Highly efficient coupling between a monolithically integrated photonic crystal cavity and a bus waveguide
We experimentally demonstrate a new optical filter design comprising of a photonic crystal cavity and a low index bus waveguide which are monolithically integrated on a silicon-on-insulator (SOI) platform. We have fabricated oxide clad PhC cavities with a silicon nitride waveguide positioned directly above, such that there is an overlap between the evanescent tails of the two modes. We have realised an extinction ratio of 7.5dB for cavities with total Q of 50,000.Postprin
Ultra-compact modulators based on novel CMOS-compatible plasmonic materials
We propose several planar layouts of ultra-compact plasmonic waveguide
modulators that utilize alternative CMOS-compatible materials. The modulation
is efficiently achieved by tuning the carrier concentration in a transparent
conducting oxide layer, thereby tuning the waveguide either in plasmonic
resonance or off-resonance. Resonance significantly increases the absorption
coefficient of the plasmonic waveguide, which enables larger modulation depth.
We show that an extinction ratio of 86 dB/um can be achieved, allowing for a
3-dB modulation depth in less than one micron at the telecommunication
wavelength. Our multilayer structures can potentially be integrated with
existing plasmonic and photonic waveguides as well as novel semiconductor-based
hybrid photonic/electronic circuits
Optical time reversal from time-dependent Epsilon-Near-Zero media
Materials with a spatially uniform but temporally varying optical response
have applications ranging from magnetic field-free optical isolators to
fundamental studies of quantum field theories. However, these effects typically
become relevant only for time-variations oscillating at optical frequencies,
thus presenting a significant hurdle that severely limits the realisation of
such conditions. Here we present a thin-film material with a permittivity that
pulsates (uniformly in space) at optical frequencies and realises a
time-reversing medium of the form originally proposed by Pendry [Science 322,
71 (2008)]. We use an optically pumped, 500 nm thick film of epsilon-near-zero
(ENZ) material based on Al-doped zinc oxide (AZO). An incident probe beam is
both negatively refracted and time-reversed through a reflected
phase-conjugated beam. As a result of the high nonlinearity and the refractive
index that is close to zero, the ENZ film leads to time reversed beams
(simultaneous negative refraction and phase conjugation) with near-unit
efficiency and greater-than-unit internal conversion efficiency. The ENZ
platform therefore presents the time-reversal features required e.g. for
efficient subwavelength imaging, all-optical isolators and fundamental quantum
field theory studies
CMOS compatible integrated all-optical radio frequency spectrum analyzer
We report an integrated all-optical radio frequency spectrum analyzer based on a ~4cm long doped silica glass waveguide, with a bandwidth greater than 2.5 THz. We use this device to characterize the intensity power spectrum of ultrahighrepetition rate mode-locked lasers at repetition rates up to 400 GHz, and observe dynamic noise related behavior not observable with other technique
Self-locked optical parametric oscillation in a CMOS compatible microring resonator: a route to robust optical frequency comb generation on a chip
We report a novel geometry for OPOs based on nonlinear microcavity resonators. This approach relies on a self-locked scheme that enables OPO emission without the need for thermal locking of the pump laser to the microcavity resonance. By exploiting a CMOS-compatible microring resonator, we achieve oscillation featured by a complete absence of “shutting down”, i.e. the self-terminating behavior that is a very common and detrimental occurrence in externally pumped OPOs. Further, our scheme consistently produces very wide bandwidth (>300nm, limited by our experimental set-up) combs that oscillate at a spacing equal to the FSR of the micro cavity resonance
Engineering Waveguide Nonlinear Effective Length via Low Index Thin Films
Novel photonic nanowires were fabricated using low-index materials and tested
in the near-infrared spectrum to assess their nonlinear optical properties. In
this work, we argue the need to redefine the standard nonlinear figure of merit
in terms of nonlinear phase shift and optical transmission for a given
propagation distance. According to this new metric, our devices largely
outperform all established platforms for devices with a linear footprint in the
range of 50 to 500 um, which is demonstrated to be an outstanding technological
gap. For 85 fs pulses, with carrier wavelength at 1480nm and sub-uW power
levels, a spectral broadening exceeding 80% of the initial bandwidth was
recorded over a propagation length of just 50 um. Leveraging on CMOS-compatible
processes and well-established materials such as silicon, silica, and indium
tin oxide, our devices bring great promise for developing alternative
all-optical devices with unparalleled nonlinear performances within the
aforementioned range
- …