We review the current status of single-photon-source and single-photon-detector technologies operating at wavelengths from the ultraviolet to the infrared. We discuss applications of these technologies to quantum communication, a field currently driving much of the development of single-photon sources and detectors.

/pdf/invited-review-article-single-photon-sources-and-detectors-5bsn8auo37.pdf

Invited review article: Single-photon sources and detectors

The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity.

pdf/new-frontiers-in-time-domain-diffuse-optics-a-review-4ka88szoxn.pdf

New frontiers in time-domain diffuse optics, a review

The invention discloses a device and method for controlling the bias voltage of an electrooptical modulator. The device and method are used for controlling the bias voltage of the electrooptical modulator, not only can enable the stable working of the electrooptical modulator to resist the external interference, but also can control the electrooptical modulator to work in different states according to the need. The method comprises the following steps of: inputting a continuous-sine bias voltage signal with the known period into the electrooptical modulator, then demodulating the response of the electrooptical modulator to the signal to judge and determine the working point of the electrooptical modulator and the drift of the working point caused by external influence, and finally adjusting the bias voltage of the electrooptical modulator and enabling the electrooptical modulator to work on the set working point stably.

Device and method for controlling bias voltage of electrooptical modulator

A QKD system used to securely exchange encryption keys between an emitter (100) and a receiver (200) modified to accept an additional customization parameter. Said QKD system consists of a QKD transmitter (120) and a QKD receiver (220) capable of implementing a plurality of QKD protocols forming a family of protocols. The QKD transmitter (120) and receiver (220) connected through a quantum channel (500) consist of optical and electronic components adapted to produce and detect a stream of qubits. The qubits (520) exchanged over the quantum channel (500) are grouped into blocks (510) consisting of at least one qubit and whose length is L i (511). For each, block (510) of qubits (520), one of the QKD protocol (530), selected from the family of protocols can be implemented using the emitter (100) and transmitter (200) is used.

Apparatus and method for quantum key distribution with enhanced security and reduced trust requirements

A separate absorption, grading, charge and multiplication InGaAs/InP avalanche photodiode with ultra low dark current and high responsivity is demonstrated. It has a thin multiplication layer and a planar structure. Through the use of a well and a single floating guard ring to suppress edge breakdown, the device can easily be fabricated by one step epitaxial growth and one step diffusion. The dark current of a 30 μm diameter device is as low as 0.028 nA at punch-through and 0.1 nA at 90% of the breakdown voltage. The responsivity at 1.55 μm is 0.93 A/W at unity gain and the multiplication layer is estimated to be less than 300 nm.

Ultra Low Dark Current, High Responsivity and Thin Multiplication Region in InGaAs/InP Avalanche Photodiodes

The invention discloses a control device of the bias voltage of an electro-optical intensity modulator for quantum private communication and a control method thereof The control device is a high-accuracy closed-loop control device The output of the electro-optical intensity modulator is converted into electric signals by an optical detector; and low-frequency signals for direct-current point drifting are extracted by utilizing a lock-in amplifier circuit module The invention has the advantages that the drifting condition is monitored by a microprocessor, so that the circuit module is driven to change the bias voltage of the electro-optical intensity modulator, and the electro-optical intensity modulator is positioned at a proper working point The control device has the advantages that the automatic control of the bias voltage of the electro-optical intensity modulator is realized, so that the electro-optical intensity modulator can work continuously by stable extinction ratio, and the working stability of the system for the quantum private communication is improved

Control device of bias voltage of electro-optical intensity modulator and control method thereof

We demonstrate an integral gated mode single photon detector at telecom wavelengths. The charge number of an avalanche pulse rather than the peak current is monitored for single photon detection. The transient spikes in conventional gated mode operation are cancelled completely by integrating, which enables one to effectively improve the performance of single photon detector with the same avalanche photodiode. This method achieved a detection efficiency of 29.9% at the dark count probability per gate equal to 5.57 × 10−6/gate (1.11 × 10−6 ns−1) at 1550 nm.

https://iopscience.iop.org/article/10.1088/0022-3727/40/22/011/pdf

An integral gated mode single photon detector at telecom wavelengths

We demonstrate an integral gated mode single photon detector at telecom wavelengths. The charge number of an avalanche pulse rather than the peak current is monitored for single-photon detection. The transient spikes in conventional gated mode operation are canceled completely by integrating, which enables one to improve the performance of single photon detector greatly with the same avalanche photodiode. This method has achieved a detection efficiency of 29.9% at the dark count probability per gate equal to 5.57E-6/gate (1.11E-6/ns) at 1550nm.

The invention discloses a four-state quantum encoder and decoder for phase modulation polarization encoding and a quantum key distribution system. The encoder and the decoder have intrinsic stability, namely, the working stability is not influenced by the external environment or connecting optical fibers which can be common mono-mode optical fibers. The quantum encoder and decoder can be applied to the field of quantum key distribution, the whole system comprises a transmitting end and a receiving end, and the transmitting end and the receiving end are connected through a quantum channel to complete the key distribution process. The quantum encoder and decoder can achieve BB84 protocol four-state quantum key encoding and decoding with intrinsic stability. The common mono-mode optical fibers can be used as all the connecting optical fibers without using polarization-maintaining optical fibers, and interference with the phase drift and polarization change of the system from the external environment has no influence on the encoding or decoding process at all.

Four-state quantum encoder and decoder for phase modulation polarization encoding and quantum key distribution system

A rigorous theoretical model for In0.53Ga0.47As/InP single photon avalanche diode is utilized to investigate the dependences of single photon quantum efficiency and dark count probability on structure and operation condition. In the model, low field impact ionizations in charge and absorption layers are allowed, while avalanche breakdown can occur only in the multiplication layer. The origin of dark counts is discussed and the results indicate that the dominant mechanism that gives rise to dark counts depends on both device structure and operating condition. When the multiplication layer is thicker than a critical thickness or the temperature is higher than a critical value, generation—recombination in the absorption layer is the dominative mechanism; otherwise band-to-band tunneling in the multiplication layer dominates the dark counts. The thicknesses of charge and multiplication layers greatly affect the dark count and the peak single photon quantum efficiency and increasing the multiplication layer width may reduce the dark count probability and increase the peak single photon quantum efficiency. However, when the multiplication layer width exceeds 1 μm, the peak single photon quantum efficiency increases slowly and it is finally saturated at the quantum efficiency of the single photon avalanche diodes.

Numerical analysis of In 0:53 Ga 0:47 As/InP single photon avalanche diodes ⁄

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Control device of bias voltage of electro-optical intensity modulator and control method thereof

An integral gated mode single photon detector at telecom wavelengths

An integral gated mode single photon detector at telecom wavelengths

Four-state quantum encoder and decoder for phase modulation polarization encoding and quantum key distribution system

Numerical analysis of In 0:53 Ga 0:47 As/InP single photon avalanche diodes ⁄