The performance of planar geometry Ge-on-Si single photon avalanche diode (SPAD) detectors of 26 µm diameter are presented. Record low dark count rates are observed, remaining less than 100 k counts per second at 6.6% excess bias and 125 K. Single-photon detection efficiencies are found to be up to 29.4%, and are shown to be temperature insensitive. These performance characteristics lead to a significantly reduced noise equivalent power (NEP) of 7.7 × 10 −17 W Hz − 1 2 compared to prior planar devices, and represent a 2 orders of magnitude reduction in NEP compared to previous Ge-on-Si mesa devices of a comparable diameter. Low jitter values of 134 ± 10 ps are demonstrated.

On-demand indistinguishable single-photon sources are essential for quantum networking and communication. Semiconductor quantum dots are among the most promising candidates, but their typical emission wavelength renders them unsuitable for use in fiber networks. Here, we present quantum frequency conversion of near-infrared photons from a bright quantum dot to the telecommunication C-band, allowing integration with existing fiber architectures. We use a custom-built, tunable 2400 nm seed laser to convert single photons from 942 nm to 1550 nm in a difference-frequency generation process. We achieve an end-to-end conversion efficiency of ≃35%, demonstrate count rates approaching 1 MHz at 1550 nm with g(2)(0)=0.043(1), and achieve Hong-Ou-Mandel (HOM) visibilities of 60%. We expect this scheme to be preferable to quantum dot sources directly emitting at telecom wavelengths for fiber-based quantum networking.

A high repetition rate Q-switched modelocked ~2.1 µm monolithic waveguide laser is reported. Ultrafast laser inscription is used to fabricate 3D depressed cladding channel waveguides in holmium doped yttrium aluminium garnet. This results in a transversely single mode waveguide laser. With the use of a graphene based saturable output coupler, Q-switched modelocking was achieved with a pulse repetition frequency of 5.9 GHz and up to 170 mW of average output power. This first demonstration of multi-GHz repetition rate operation from a Ho:YAG laser provides a compact and convenient source for a number of applications.

Germanium-on-silicon (Ge-on-Si) based single-photon avalanche diodes (SPADs) have recently emerged as a promising detector candidate for ultra-sensitive and picosecond resolution timing measurement of short-wave infrared (SWIR) photons. Many applications benefit from operating in the SWIR spectral range, such as long distance light detection and ranging, however, there are few single-photon detectors exhibiting the high-performance levels obtained by all-silicon SPADs commonly used for single-photon detection at wavelengths <1 µm. This paper first details the advantages of operating at SWIR wavelengths, the current technologies, and associated issues, and describes the potential of Ge-on-Si SPADs as a single-photon detector technology for this wavelength region. The working principles, fabrication and characterisation processes of such devices are subsequently detailed. We review the research in these single-photon detectors and detail the state-of-the-art performance. Finally, the challenges and future opportunities offered by Ge-on-Si SPAD detectors are discussed.

We report fabrication and operation of multi-watt level waveguide lasers utilizing holmium-doped yttrium aluminum garnet (Ho:YAG). The waveguides were fabricated using ultrafast laser inscription, which relies on a chirped pulse ytterbium fiber laser to create depressed cladding structures inside the material. A variety of waveguides were created inside the Ho:YAG samples. We demonstrate output powers of ∼2  W from both a single-mode 50 μm waveguide laser and a multimode 80 μm waveguide laser. In addition, laser action from a co-doped Yb:Ho:YAG sample under in-band pumping conditions was demonstrated.