Modeling and design of a single photon detector and its various characteristics are presented. It is a type of avalanche photo diode (APD) designed to suit the requirements of a Quantum Key Distribution (QKD) detection system. The device is modeled to operate in a gated mode at liquid nitrogen temperature for minimum noise and maximum gain. Different types of APDs are compared for best performance. The APD is part of an optical communication link, which is a private channel to transmit the key signal. The encrypted message is sent via a public channel. The optical link operates at a wavelength of 1.55μm. The design is based on InGaAs with a quantum efficiency of more than 75% and a multiplication factor of 1000. The calculated dark current is below 10-12A with an overall signal to noise ratio better than 18 dB. The device sensitivity is better than -40 dBm, which is more than an order of magnitude higher than the dark current, corresponding to a detection sensitivity of two photons in pico-second pulses.
Modeling and design of a single photon detector and its various characteristics are presented. It is a type of avalanche photo diode (APD) designed to suit the requirements of a Quantum Key Distribution (QKD) detection system. The device is modeled to operate in a gated mode at liquid nitrogen temperature for minimum noise and maximum gain. Different types of APDs are compared for best performance. The APD is part of an optical communication link, which is a private channel to transmit the key signal. The encrypted message is sent via a public channel. The optical link operates at a wavelength of 1.55μm. The design is based on InGaAs with a quantum efficiency of more than 75% and a multiplication factor of 1000. The calculated dark current is below 10-12A with an overall signal to noise ratio better than 18 dB. The device sensitivity is better than -40 dBm, which is more than an order of magnitude higher than the dark current, corresponding to a detection sensitivity of two photons in pico-second pulses.
The application of quantum key distribution (QKD) has raised particular demands for single-photon detectors. One of the most promising candidates at the low-loss optical fibre communications windows is the planar geometry InGaAs/InP single-photon avalanche diode. These detectors have been modelled, fabricated and characterised at 1.55 µm wavelength. Their performance in terms of single-photon detection efficiency, dark count rate, timing jitter and afterpulsing behaviour are reported and compared with the best commercially available, linear multiplication avalanche photodiodes operated in Geiger-mode. Their use in the application of QKD is discussed.
In our experiment, two InGaAs/InP avalanche photodiodes (APD) were used in the quantum key distribution (QKD) system for single-photon detection at telecom communication wavelength (1310/1550 nm). By using properly designed passive-quenching circuit, the photo-detection efficiency of the APD could reach 10% at 1550 nm. In order to decrease the dark count rate efficiently, we designed a coincident counting circuits for single-photon detection. Before the APD signals were sent to the signal processing circuit, the avalanche signals were amplified and shaped into the TTL pulses. In order to obtain an accurate and efficient data acquisition and to transfer synchronically several signals such as the TTL signals and pulses from Random generators, we designed a signal processing circuit with the parallel port whose speed limitation is about 100Kb/s. In our experiments of single-photon interference and quantum cryptography, the electronic designs presented us satisfactory performance and results. To achieve much higher speed for the data acquisition, we also employed the Universal Serial Bus System (USB2.0) to interface our single-photon avalanche detectors and random generators used in our QKD system, which was believed to improve the performance of QKD such as the key distribution speed.
We provide a direct comparison between the InGaAs avalanche photodiode (APD) and the NbN superconducting single photon detector (SSPD) for applications in fiber-based quantum cryptography. The quantum efficiency and dark count rate were measured for each detector, and used to calculate the quantum bit error rate (QBER) and shared key rate for a QKD link. The results indicate that, despite low quantum efficiency, the speed of the SSPD makes it a superior detector for quantum information applications. Finally, we present results of an initial integration of an SSPD into a receiver node of the DARPA quantum network to perform quantum key distribution. Encoding quantum information on single photons has enabled the realization of a number of unique communication schemes such as the implementation of the BB84 protocol for quantum key distribution 1 and quantum dense coding. 2 Furthermore, the implementation of these schemes using photons at telecommunication wavelengths has permitted their extension to fiber optic networks, 3,4 drastically increasing the practicality of quantum information processing. To date, the state of the art in commercially available single photon detection at telecommunication wavelengths (1550 nm) has been the thermo-electrically cooled InGaAs avalanche photodiode (APD). The cooled InGaAs APD is generally operated at T = -60°C in the reverse-biased Geiger mode. Though these detectors have been successfully implemented in operating QKD links in optical fiber, the InGaAs APD suffers from afterpulsing effects that limit the key exchange rates. New SPD (single photon detector) technologies based on superconducting materials are emerging that hold tremendous promise for drastically increasing the photon counting rate and eliminating dark noise.57 The SSPD consists of a NbN thin film (t ∼ 5 nm) patterned into a narrow (w ∼ 100 nm) microstrip meander that is ∼ 500μm in length. The detector is cooled to T < 4K in a closed cycle refrigeration unit and a bias current I b is supplied to the device just below the superconducting critical current (I c ). When a photon is incident upon the microstrip superconductivity is broken in the region local to photon absorption and a normal state region is formed in the device. The current passing through the device causes a measurable voltage pulse in the detector that can be amplified and shaped to act as an input for traditional logic circuitry. Due to the unique electronic bandstructure in a superconducting material the intrinsic response time of the device is on the order of picoseconds, so that the repetition rate may be increased above 1 GHz 8 without being susceptible to afterpulsing effects that plague the InGaAs APD. 9 To make a direct comparison between the InGaAs APD and the SSPD both were placed in a SPD characterization testbed to measure quantum efficiency and dark count rate at a variety of bias conditions. The QBER for a QKD link is calculated from the measured parameters and then compared to requirements for a provably secure QKD link. Following detector characterization, one of the nodes of the DARPA Quantum Network operated by BBN Technologies 3 utilized an SSPD in the receiver to transmit key material. The demonstration provides an in situ comparison between the InGaAs APD, normally operated in the BBN link, and the SSPD.
It is the closest technology to practice in the quantum communication at present to apply single-photon scheme to implement the quantum key distribution (QKD), and may achieve the absolute security in principle. Because of the limit of the response speed of the present single-photon detector, the code rate is still too low to come into practical use. The paper has put up a new idea to design a quick single-photon detector with a multi-port optic-fiber splitter or an optical switch array and many avalanche photo diodes (APD). All of the ports with APD work on time division and cooperate with the logic discrimination and deciding unit by the clock signal, thus the quick detection can come true to high repetition-rate pulses with a single photon. The multiple of the detection rate is decided by the number of the port. The optoelectronic integration can be adopted for the reliable detector. The applying of this detector will largely raise the code rate of the QKD, and stimulate the commercial use.
Due to the limit of response speed of the present single-photon detector, the
code rate is still too low to come into practical use for the present quantum key
distribution (QKD) system. A new idea is put up to design a quick single-photon
detector. This quick single-photon detector is composed of a multi-port optic-fiber
splitter and many avalanche photo diodes (APDs). All of the ports with APDs work on
the time division and cooperate with a logic discriminating and deciding unit driven
by the clock signal. The operation frequency lies on the number N of ports, and can
reach N times of the conventional single-photon detector. The single-photon prompt
detection can come true for high repetition-rate pulses. The applying of this
detector will largely raise the code rate of the QKD, and boost the commercial use.
In any quantum communication system, such as a quantum key distribution (QKD) system, data rates are mainly limited by the system clock rate and the various link losses. While the transmission clock rate is limited by the temporal resolution of the single-photon detectors, losses in a fiber-based quantum communication system can be minimized by operating in the near infrared range (NIR), at 1310 nm or 1550 nm. Commercially available InGaAs-based avalanche photo-diodes (APDs) can be operated as single-photon detectors in this wavelength range [Hadfield, 2009]. Due to the severe after-pulsing, InGaAs APDs are typically used in a gated mode and this can limit their application in high-speed quantum communications systems. Superconducting single-photon detectors (SSPDs) can work in the NIR wavelength range with good performance [Gol’tsman et al. 2001; Hadfield, 2009]. However, SSPDs require cryogenic temperatures, and are not widely available on the commercial market at present. In addition, InGaAs/InP based photomultiplier tubes (PMT) can operate in the NIR range, but its performance is limited by very low detection efficiency (1 % at 1600 nm) and large timing jitter (1.5 ns) [Hamamatsu, 2005]. Microchannel plates (MCP) are micro-capillary electron multipliers coated with an electron-emissive material and multiply photon-excited electrons from a photon cathode [Wiza, 1979]. MCPs usually have faster rise times and lower timing jitter than is achievable with PMTs. InGaAs MCPs can work in the NIR range. These MCPs, but are limited by low detection efficiency (~1 %) [Martin, J. & Hink P. 2003]. On the other hand, silicon based avalanche photo-diodes (Si APDs) are compact, relatively inexpensive, and can be operated at ambient temperatures with high detection efficiency and low noise in the visible or near-visible range. Unfortunately they do not work at wavelengths longer than 1000 nm. For those wavelengths, an up-conversion technique has been developed that uses sum-frequency generation (SFG) in a non-linear optical medium to convert the signal photons to a higher frequency (shorter wavelength) in the visible or near visible range. The up-converted photons can then be detected by a Si APD. Up-conversion detectors use commercially available components and devices, and are a practical solution for many applications in quantum communications. To date, several groups have successfully developed highly efficient up-conversion single-photon detectors in the nearinfrared range using periodically poled lithium niobate (PPLN) waveguides [Diamanti et al., 2005; Langrock et al., 2005; Thew et al., 2006; Tanzilli et al., 2005; Xu et al., 2007;] and bulk crystals [Vandevender & Kwiat, 2004].