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is about 50%, and we found that the optical absorptance does not decrease with a double side cavity structure even when the lling factor is less than 25%[7][12]. e length of the nanowire become shorter if the lling factor becomes smaller, so a higher count rate can be achieved.e last pulse generation probability is the probability that the superconducting state of the nanowire collapses due to photon absorption according to the theory shown in Fig. 1. If there is nonuniformity in the quality of the membrane or line width somewhere in the superconductive nanowire on a photosensitive area, the superconducting critical current density become lower, hence sucient bias current cannot be supplied to other normal areas because the bias current supplied to the nanowire is limited at this minimum area of critical current. In this case, the probabil-ity that the superconducting state does not collapse due to absorption of a photon by the superconductive nanowire becomes higher. In order to achieve high pulse generation probability, it is important to manufacture a very thin, ne, and long superconducting nanowire uniformly. We used a nitride (NbN, NbTiN) superconducting substance whose thin-membrane surface is not easily oxidized and realized a super-thin membrane with a thickness of 5 nm of which uniformity of properties is excellent. Electron beam draw-ing of acceleration voltage of 125 kV was adopted for patterning and we succeeded to manufacture nanowire of width 100 nm with high patterning accuracy. As a result, pulse generation probability reached over 90%.e view and performance of the 6-channel SSPD system developed by NICT is summarized in Fig. 3. We achieved detection eciency of 80% at 1,550 nm by maxi-mizing the value of each of the three factors mentioned above [7]. is value is much superior compared with 20% of the APD made of InGaAs. As for dark count rate; it is more than 10,000 (counts/sec) for InGaAs APD; however, it is less than 100 (counts/sec) for SSPD that is much smaller than APD.ere exists a noise called aer-pulse in InGaAs APD that has correlation with detector response. In order to suppress this noise, gate bias is necessary that synchro-nizes with the photo signal. On the other hand, the dark count is small and the aer-pulse does not exist in SSPD, so this device can be driven by bias current of direct cur-rent, which is a large advantage.In order to supply SSPD to users in a more convenient manner by maximizing its performance, we mounted the 6-channel SSPD on a small mechanical cryocooler (0.1 W Giord McMahon cryocooler) that operates by 100 V power and developed a multi-channel SSPD system en-closed in a 19-inch rack [6]. is mechanical cryocooler does not require a water cooling system and it can cool SSPD down to 2.5 K only by turning on the cryocooler. As it is a mechanical cryocooler, coolant such as liquid helium is not necessary. So, long-time continuous running is pos-sible without maintenance. e system is already used in many experiments in the quantum information eld such as the Tokyo QKD network system, as a photon detection system that anybody can use easily at anytime and any-where [8]–[10].3Challenge of extending application field3.1Broadband detectionAlthough we have optimized the device structure of SSPD for optical absorptance at the 1,550 nm wavelength assuming to be applied in the quantum information eld, the photon detector is applied in various elds from com-munication and measurement to biology and medical treatment (Fig. 4). Because the wavelength used in such applications varies by eld, it is important for an SSPD to be sensitive to not only at 1,550 nm but to other various wavelengths in order for it to be applied in other elds. Considering the theory of photon detection of SSPD where the superconducting state collapses by photon energy, shorter wavelength light with high energy is advantageous to realize higher pulse generation eciency. However, as incident light irradiates from the backside of the silicon substrate in the case of the double-side cavity structure shown in Fig. 2(b), light of a wavelength shorter than 1μm is absorbed in the substrate because the energy of the photon is larger than the band gap of silicon. en, we FiF36-channel SSPD system and its specification and performanceSpecification & performanceSystem DE(λ=1550nm)80% @1550nmDark CR （c/s）100 cpsTiming jitter68 ps# of channel6 Gate operatingNot requiredRefrigeratorAir cooling compact GMDriving voltage and power consumptionAC 100V・Max. 1.2 kWLiquid heliumNot required570 mm1850 mm594-2 Development of Superconducting Nanowire Single-Photon Detector