GaAs Ridge Waveguide Research Articles

On-Chip Generation, Routing, and Detection of Resonance Fluorescence.

Quantum optical circuits can be used to generate, manipulate, and exploit nonclassical states of light to push semiconductor based photonic information technologies to the quantum limit. Here, we report the on-chip generation of quantum light from individual, resonantly excited self-assembled InGaAs quantum dots, efficient routing over length scales ≥1 mm via GaAs ridge waveguides, and in situ detection using evanescently coupled integrated NbN superconducting single photon detectors fabricated on the same chip. By temporally filtering the time-resolved luminescence signal stemming from single quantum dots we use the quantum optical circuit to perform time-resolved excitation spectroscopy on single dots and demonstrate resonance fluorescence with a line-width of 10 ± 1 μeV; key elements needed for the use of single photons in prototypical quantum photonic circuits.

Quantum dot spontaneous emission control in a ridge waveguide

We investigate the spontaneous emission (SE) of self-assembled InAs quantum dots (QDs) embedded in GaAs ridge waveguides that lay on a low index substrate. In thin enough waveguides, the coupling to the fundamental guided mode is vanishingly small. A pronounced anisotropy in the coupling to non-guided modes is then directly evidenced by normal-incidence photoluminescence polarization measurements. In this regime, a measurement of the QD decay rate reveals a SE inhibition by a factor up to 4. In larger wires, which ensure an optimal transverse confinement of the fundamental guided mode, the decay rate approaches the bulk value. Building on the good agreement with theoretical predictions, we infer from calculations the fraction β of SE coupled to the fundamental guided mode for some important QD excitonic complexes. For a charged exciton (isotropic in plane optical dipole), β reaches 0.61 at maximum for an on-axis QD. In the case of a purely transverse linear optical dipole, β increases up to 0.91. This optimal configuration is achievable through the selective excitation of one of the bright neutral excitons.

A carrier relaxation bottleneck probed in single InGaAs quantum dots using integrated superconducting single photon detectors

Using integrated superconducting single photon detectors, we probe ultra-slow exciton capture and relaxation dynamics in single self-assembled InGaAs quantum dots embedded in a GaAs ridge waveguide. Time-resolved luminescence measurements performed with on- and off-chip detection reveal a continuous decrease in the carrier relaxation time from 1.22 ± 0.07 ns to 0.10 ± 0.07 ns upon increasing the number of non-resonantly injected carriers. By comparing off-chip time-resolved spectroscopy with spectrally integrated on-chip measurements, we identify the observed dynamics in the rise time (τr) as arising from a relaxation bottleneck at low excitation levels. From the comparison with the temporal dynamics of the single exciton transition with the on-chip emission signal, we conclude that the relaxation bottleneck is circumvented by the presence of charge carriers occupying states in the bulk material and the two-dimensional wetting layer continuum. A characteristic τr ∝ P−2∕3 power law dependence is observed suggesting Auger-type scattering between carriers trapped in the quantum dot and the two-dimensional wetting layer continuum which circumvents the phonon relaxation bottleneck.

On-chip time resolved detection of quantum dot emission using integrated superconducting single photon detectors

We report the routing of quantum light emitted by self-assembled InGaAs quantum dots (QDs) into the optical modes of a GaAs ridge waveguide and its efficient detection on-chip via evanescent coupling to NbN superconducting nanowire single photon detectors (SSPDs). The waveguide coupled SSPDs primarily detect QD luminescence, with scattered photons from the excitation laser onto the proximal detector being negligible by comparison. The SSPD detection efficiency from the evanescently coupled waveguide modes is shown to be two orders of magnitude larger when compared with operation under normal incidence illumination, due to the much longer optical interaction length. Furthermore, in-situ time resolved measurements performed using the integrated detector show an average QD spontaneous emission lifetime of 0.95 ns, measured with a timing jitter of only 72 ps. The performance metrics of the SSPD integrated directly onto GaAs nano-photonic hardware confirms the strong potential for on-chip few-photon quantum optics using such semiconductor-superconductor hybrid systems.

Integrated autocorrelator based on superconducting nanowires

We demonstrate an integrated autocorrelator based on two superconducting single-photon detectors patterned on top of a GaAs ridge waveguide. This device enables the on-chip measurement of the second-order intensity correlation function g(2)(τ). A polarization-independent device quantum efficiency in the 1% range is reported, with a timing jitter of 88 ps at 1300 nm. g(2)(τ) measurements of continuous-wave and pulsed laser excitations are demonstrated with no measurable crosstalk within our measurement accuracy.

Waveguide superconducting single-photon detectors for integrated quantum photonic circuits

The monolithic integration of single-photon sources, passive optical circuits, and single-photon detectors enables complex and scalable quantum photonic integrated circuits, for application in linear-optics quantum computing and quantum communications. Here, we demonstrate a key component of such a circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (∼20%) at telecom wavelengths, high timing accuracy (∼60 ps), and response time in the ns range and are fully compatible with the integration of single-photon sources, passive networks, and modulators.

Selective disordering of InAs/InGaAs dots-in-a-well structure patterned with sol-gel derived SiO2 strips imprinted by soft mold technique

Selective impurity free vacancy disordering of InAs/InGaAs quantum dot (QD) structures imprinted with sol-gel derived SiO2 strips via a polyethylene terepthalate soft mold has been investigated. Wavelength blueshift of up to 220 nm for areas capped with the sol-gel derived SiO2 is demonstrated. The imprinted SiO2 strips were used as hard mask for plasma etching of GaAs ridge waveguide structures and were found to have similar hardness as the SiO2 prepared by plasma-enhanced chemical vapor deposition. QD intermixing using sol-gel derived SiO2 with step-thickness profile was demonstrated, and a one-step SiO2 imprinting technique for multiple band gap QD intermixing is proposed.

Attenuation losses in electron cyclotron resonance plasma etched AlGaAs waveguides

AlGaAs GaAs ridge waveguides with fundamental mode attenuation ≤ 1 dBcm −1 at a wavelength of 1.32 μm and channel widths of 4–4.5 μm are realized by ECR (Electron Cyclotron Resonance) plasma etching in BCl 3/Cl 2/Ar/N 2 chemistries. The choice of both plasma chemistry and initial mask scheme (single layer photoresist or trilevel resist) has a significant effect on the attenuation losses.

Low loss GaAs optical waveguides

To realize an optical integrated circuit, various losses in the semiconductor waveguide such as absorption loss, waveguide loss, bending loss, and coupling loss, have to be minimized. Theoretical and experimental considerations for the reduction of these losses have been presented. A propagation loss of less than 0.5 dB/cm has been observed for a well-designed GaAs ridge waveguide. Moreover its coupling loss with a polarization-maintaining optical fiber decreased below 1.5 dB.

Low loss GaAs optical waveguides

To realize an optical integrated circuit, various losses in the semiconductor waveguide such as absorption loss, waveguide loss, bending loss, and coupling loss, have to be minimized. Theoretical and experimental considerations for the reduction of these losses have been presented. A propagation loss of less than 0.5 dB/cm has been observed for a well-designed GaAs ridge waveguide. Moreover its coupling loss with a polarization-maintaining optical fiber decreased below 1.5 dB.