42 research outputs found
Ultrafast, low-power, all-optical switching via birefringent phase-matched transverse mode conversion in integrated waveguides
We demonstrate the potential of birefringence-based, all-optical, ultrafast
conversion between the transverse modes in integrated optical waveguides by
modelling the conversion process by numerically solving the multi-mode coupled
nonlinear Schroedinger equations. The observed conversion is induced by a
control beam and due to the Kerr effect, resulting in a transient index grating
which coherently scatters probe light from one transverse waveguide mode into
another. We introduce birefringent phase matching to enable efficient
all-optically induced mode conversion at different wavelengths of the control
and probe beam. It is shown that tailoring the waveguide geometry can be
exploited to explicitly minimize intermodal group delay as well as to maximize
the nonlinear coefficient, under the constraint of a phase matching condition.
The waveguide geometries investigated here, allow for mode conversion with over
two orders of magnitude reduced control pulse energy compared to previous
schemes and thereby promise nonlinear mode switching exceeding efficiencies of
90% at switching energies below 1 nJ
Fully on-chip photonic turnkey quantum source for entangled qubit/qudit state generation
Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust and scalable chip formats, with applications in long-distance quantum-secured communication, quantum-accelerated information processing and nonclassical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers, making them impractical prototype devices that are not reproducible, hindering their scalability and transfer out of the laboratory into real-world applications. Here we demonstrate a fully integrated quantum light source that overcomes these challenges through the integration of a laser cavity, a highly efficient tunable noise suppression filter (>55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon-pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically pumped InP gain section and a Si3N4 low-loss microring filter system, and demonstrates high performance parameters, that is, pair emission over four resonant modes in the telecom band (bandwidth of ~1 THz) and a remarkable pair detection rate of ~620 Hz at a high coincidence-to-accidental ratio of ~80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), as verified by quantum interference measurements with visibilities up to 96% (violating Bell’s inequality) and by density matrix reconstruction through state tomography, showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables scalable, commercially viable, low-cost, compact, lightweight and field-deployable entangled quantum sources, quintessential for practical, out-of-laboratory applications such as in quantum processors and quantum satellite communications systems
Photo-induced second-order nonlinearity in stoichiometric silicon nitride waveguides
We report the observation of second-harmonic generation in stoichiometric
silicon nitride waveguides grown via low-pressure chemical vapour deposition.
Quasi-rectangular waveguides with a large cross section were used, with a
height of 1 {\mu}m and various different widths, from 0.6 to 1.2 {\mu}m, and
with various lengths from 22 to 74 mm. Using a mode-locked laser delivering
6-ps pulses at 1064 nm wavelength with a repetition rate of 20 MHz, 15% of the
incoming power was coupled through the waveguide, making maximum average powers
of up to 15 mW available in the waveguide. Second-harmonic output was observed
with a delay of minutes to several hours after the initial turn-on of pump
radiation, showing a fast growth rate between 10 to 10 s,
with the shortest delay and highest growth rate at the highest input power.
After this first, initial build-up, the second-harmonic became generated
instantly with each new turn-on of the pump laser power. Phase matching was
found to be present independent of the used waveguide width, although the
latter changes the fundamental and second-harmonic phase velocities. We address
the presence of a second-order nonlinearity and phase matching, involving an
initial, power-dependent build-up, to the coherent photogalvanic effect. The
effect, via the third-order nonlinearity and multiphoton absorption leads to a
spatially patterned charge separation, which generates a spatially periodic,
semi-permanent, DC-field-induced second-order susceptibility with a period that
is appropriate for quasi-phase matching. The maximum measured second-harmonic
conversion efficiency amounts to 0.4% in a waveguide with 0.9 x 1 {\mu}m
cross section and 36 mm length, corresponding to 53 {\mu}W at 532 nm with 13 mW
of IR input coupled into the waveguide. The according amounts to
3.7 pm/V, as retrieved from the measured conversion efficiency.Comment: 20 pages, 10 figure
High confinement, high yield Si3N4 waveguides for nonlinear optical application
In this paper we present a novel fabrication technique for silicon nitride
(Si3N4) waveguides with a thickness of up to 900 nm, which are suitable for
nonlinear optical applications. The fabrication method is based on etching
trenches in thermally oxidized silicon and filling the trenches with Si3N4.
Using this technique no stress-induced cracks in the Si3N4 layer were observed
resulting in a high yield of devices on the wafer. The propagation losses of
the obtained waveguides were measured to be as low as 0.4 dB/cm at a wavelength
of around 1550 nm.Comment: 10 pages, 4 figure
Quantum photo-thermodynamics on a programmable photonic quantum processor
One of the core questions of quantum physics is how to reconcile the unitary evolution of quantum states, which is information-preserving and time-reversible, with the second law of thermodynamics, which is neither. The resolution to this paradox is to recognize that global unitary evolution of a multi-partite quantum state causes the state of local subsystems to evolve towards maximum-entropy states. In this work, we experimentally demonstrate this effect in linear quantum optics by simultaneously showing the convergence of local quantum states to a generalized Gibbs ensemble constituting a maximum-entropy state under precisely controlled conditions, while using a new, efficient certification method to demonstrate that the state retains global purity. Our quantum states are manipulated by a programmable integrated photonic quantum processor, which simulates arbitrary non-interacting Hamiltonians, demonstrating the universality of this phenomenon. Our results show the potential of photonic devices for quantum simulations involving non-Gaussian states
Hybrid integrated semiconductor lasers with silicon nitride feedback circuits
Hybrid integrated semiconductor laser sources offering extremely narrow
spectral linewidth as well as compatibility for embedding into integrated
photonic circuits are of high importance for a wide range of applications. We
present an overview on our recently developed hybrid-integrated diode lasers
with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to
provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage
around 1.55 um wavelength, and an output power above 100 mW. We show
dual-wavelength operation, dual-gain operation, laser frequency comb
generation, and present work towards realizing a visible-light hybrid
integrated diode laser.Comment: 25 pages, 16 figure