Christopher J. K. Richardson

A stable smoothly wavelength-tunable picosecond pulse generator

Smooth wavelength tuning over 10 nm has been realized in a dispersion-tuned harmonically mode-locked fiber ring laser. Supermode noise is suppressed by 13 dB by adding a semiconductor optical amplifier (SOA) into the cavity and the suppression improves as the SOA gain increases. 5.3-ps pulses are obtained at a repetition rate of 10 GHz. A simple numerical model demonstrates the effects of the intracavity dispersion and the SOA on the pulse characteristics.

Two-photon interference from a bright single-photon source at telecom wavelengths

Long-distance quantum communication relies on the ability to efficiently generate and prepare single photons at telecom wavelengths. In many applications these photons must also be indistinguishable such that they exhibit interference on a beamsplitter, which implements effective photon-photon interactions. However, deterministic generation of indistinguishable single photons with high brightness remains a challenging problem. We demonstrate two-photon interference at telecom wavelengths using an InAs/InP quantum dot in a nanophotonic cavity. The cavity enhances the quantum dot emission, resulting in a nearly Gaussian transverse mode profile with high out-coupling efficiency exceeding 36% after multi-photon correction. We also observe Purcell enhanced spontaneous emission rate up to 4. Using this source, we generate linearly polarized, high purity single photons at 1.3 micron wavelength and demonstrate the indistinguishable nature of the emission using a two-photon interference measurement, which exhibits indistinguishable visibilities of 18% without post-selection and 67% with post-selection. Our results provide a promising approach to generate bright, deterministic single photons at telecom wavelength for applications in quantum networking and quantum communication.

Implementation of discrete unitary transformations by multimode waveguide holograms.

Integration of holograms into multimode waveguides allows the implementation of arbitrary unitary mode transformations and unitary matrix-vector multiplication. Theoretical analysis is used to justify a design approach to implement specific functions in these devices. Based on this approach, a compact mode-order converter, a Hadamard transformer, and a spatial pattern generator-correlator are proposed and analyzed. Beam propagation simulations are used to verify the theoretical calculations and to address bandwidth, scalability, and fabrication criteria. Optical pattern generators were successfully fabricated using standard photolithographic techniques to demonstrate the feasibility of the devices.

Optical clock recovery using SOA for relative timing extraction between counterpropagating short picosecond pulses

A technique that determines the relative arrival timing difference between two counterpropagating picosecond pulses in a nonlinear waveguide is presented. Optical clock recovery experiment constructed around a semiconductor optical amplifier demonstrates a recovered clock with less than 100 fs of jitter. The bit-error-rate measurement at 10 GHz, using 2/sup 31/-1 long pseudorandom bit sequence data, revealed error free operation.

Low-loss suspended quantum well waveguides.

We have used surface micromachining to fabricate suspended InGaAs/InGaAsP quantum well waveguides that are supported by lateral tethers. The average measured TE propagation loss in our samples is 4.1 dB/cm, and the average measured TE loss per tether pair is 0.21 dB. These measurements are performed at wavelengths in the optical L-band, just 125 nm below the quantum well band gap.

Enhanced continuous-wave four-wave mixing efficiency in nonlinear AlGaAs waveguides

Enhancements of the continuous-wave four-wave mixing conversion efficiency and bandwidth are accomplished through the application of plasma-assisted photoresist reflow to reduce the sidewall roughness of sub-square-micron-modal area waveguides. Nonlinear AlGaAs optical waveguides with a propagation loss of 0.56 dB/cm demonstrate continuous-wave four-wave mixing conversion efficiency of -7.8 dB. Narrow waveguides that are fabricated with engineered processing produce waveguides with uncoated sidewalls and anti-reflection coatings that show group velocity dispersion of +0.22 ps²/m. Waveguides that are 5-mm long demonstrate broadband four-wave mixing conversion efficiencies with a half-width 3-dB bandwidth of 63.8-nm.

Conversion of RZ-OOK to RZ-BPSK by XPM in a Passive AlGaAs Waveguide

The conversion of data modulation format from 10-Gb/s return-to-zero on-off keying (RZ-OOK) to 10-Gb/s RZ binary phase-shift keying (RZ-BPSK) has been successfully carried out for the first time utilizing cross-phase modulation (XPM) in a passive AlGaAs waveguide. A 10-9-bit-error-rate (BER) preamplified receiver sensitivity gain of ≈ 1 dB was measured for the converted RZ-BPSK relative to baseline RZ-OOK, whereas a penalty of ≈ 2.7 dB relative to baseline RZ-BPSK is explained to be due to cross-absorption modulation induced by nondegenerate two-photon absorption (ND-TPA), as well as to an insufficient nonlinear phase shift.

Two-Photon Interference from the Far-Field Emission of Chip-Integrated Cavity-Coupled Emitters

Interactions between solid-state quantum emitters and cavities are important for a broad range of applications in quantum communication, linear optical quantum computing, nonlinear photonics, and photonic quantum simulation. These applications often require combining many devices on a single chip with identical emission wavelengths in order to generate two-photon interference, the primary mechanism for achieving effective photon-photon interactions. Such integration remains extremely challenging due to inhomogeneous broadening and fabrication errors that randomize the resonant frequencies of both the emitters and cavities. In this letter we demonstrate two-photon interference from independent cavity-coupled emitters on the same chip, providing a potential solution to this long-standing problem. We overcome spectral mismatch between different cavities due to fabrication errors by depositing and locally evaporating a thin layer of condensed nitrogen. We integrate optical heaters to tune individual dots within each cavity to the same resonance with better than 3 {\mu}eV of precision. Combining these tuning methods, we demonstrate two-photon interference between two devices spaced by less than 15 {\mu}m on the same chip with a post-selected visibility of 33%. These results pave the way to integrate multiple quantum light sources on the same chip to develop quantum photonic devices.

Mid-infrared difference-frequency generation in suspended GaAs waveguides

We experimentally demonstrate mid-infrared difference frequency generation in suspended 181-nmthick GaAs waveguides. The extreme form-birefringence in the nanoslab waveguide enables phase-matching between the CW signal (1550 nm), pump (1025 nm), and idler (3000 nm).

Metamorphic growth of III-V semiconductor bicrystalsa)

The authors report on the structural properties of III-V semiconductor films that are not lattice matched to the GaAs substrates on which they are grown. Using molecular beam epitaxy, a uniform two-dimensional edge dislocation network is formed that abruptly relaxes the misfit strain at the film/substrate interface. The nucleation and initial growth of a GaSb film on GaAs are analyzed using reflection high-energy electron diffraction to show growth that becomes two dimensional in approximately five monolayers. Comparisons of the experimental reciprocal space map peak shapes and theoretical shapes show that some of these films are approaching the theoretical limit where all of the strain is completely relaxed at the interface.