Single-photon avalanche diodes (SPADs) are widely used for practical applications requiring single-photon detection. The readout circuit, or quenching electronics, plays an important role for the operations of SPADs. Sine wave gating (SWG) is one of the key techniques for synchronous single-photon detection that can easily operate SPADs with a gating frequency as high as GHz level. Here we present a monolithic readout circuit for 1.25 GHz SWG SPADs. The monolithic chip, including a low-noise amplifier and two low-pass filters inside, is designed for weak avalanche extraction in the SWG scheme and fabricated using the technology of low temperature co-fired ceramic with a size of 15 mm × 15 mm. We then apply the monolithic chip into an InGaAs/InP single-photon detector (SPD). After the characterization both on the monolithic chip and the InGaAs/InP SPD, the functionality of the monolithic readout circuit is effectively verified. Implementing the monolithic integration of readout circuit is a key step towards developing miniaturized InGaAs/InP SPDs.
We demonstrate a high-power pulse laser with extremely high pulse extinction ratio (ER). This laser module is designed
for the experiment of 217 km long distance photon-counting optical time-domain reflectometry (ν-OTDR) using an upconversion
single photon detector. The maximum peak power of laser pulse is over 24dBm with an extremely high pulse
extinction ratio of more than 100dB.
With the optical phase lock loop (OPLL) we made, we can achieve phase locking at frequency differences ranging from
0.5GHz to 7.5 GHz. This OPLL is fully applicable in atomic physics experiments, mostly in coherent lasers frequency
locking. Two kinds of modulation modes were brought to ensure the frequency range and precision: the fast feedback
current as the injection current and the slow feedback current to adjust the piezo-electric transducer. This device has been
put into an optical lattice platform to lock a laser used for cooling and trapping atoms. The beat signal has a -3dB band
width of 1Hz at 6.834GHz, corresponding to the hyperfine splitting of the ground state <sup>87</sup>Rb atom.
A readout electronics system is presented for the mobile direct detection Doppler Wind LIDAR (DWL). The structure of
the readout electronics is compact to fit the mobile DWL which is fixed on a truck. According to the wind measurement
principle of double-edge technique with triple-channel Fabry-Perot etalon, the readout electronics system is designed
adjustable for wind speed detection due to the multi-channel technique and reconfiguration of the FPGA. The
experimental results indicate that there is good consistency between the readout electronics and the current commercial
devices. The detection range of the experiments can cover the troposphere and low stratosphere even in daylight.
Ghost interference with entangled photon pairs are studied theoretically. The pump beam in parametric down-conversion is treated as the Gaussian profile, while for the function describing phase matching in the longitudinal direction, both a Gaussian and a sinc function are considered. The numerical results show that the transverse size of the pump beam and transverse coherence width of the parametric fluorescence strongly influence the interference pattern. With the increase of the pump transverse size and the decrease of transverse coherence width, the interference pattern becomes more and more prominent. When the transverse coherence width is small to 0.01 mm category, the Gaussian and sinc models give the same results.
The effect of pump focusing on the performance of ghost imaging is studied experimentally on an entangled source. Theoretical results show that the correlation properties of the entangled photon source are destroyed when the conversion crystal is pumped by a focused laser beam. The experiment is performed on a compact entangled source produced by type-II non-collinear degenerate SPDC, and the results demonstrate that the “walk off” effects almost have no effect on the image, while the pump focusing greatly degrades the visibility of the image. However, a sharp image could be reproduced in the configuration first proposed in Ref.  for the case with pump focusing.
32 scientific CCD cameras within 16 low-dispersion spectrographs of LAMOST are used for object spectra. This paper
introduced the CCD Master system designed for camera management and control based on UCAM controller. The layers
of Master, UDP and CCD-end daemons are described in detail. The commands, statuses, user interface and spectra
viewer are discussed.
A programmable workflow environment grants more flexibility to conduct an observation. This paper provides an easy
way to develop visual workflow control. Users can drag and drop command elements to make up a workflow. The
workflow supports sequence and parallel patterns. When a workflow starts to run automatically, a full set of manual
interventions is supplied, which enable users to cope with unpredictable online situation. Beside this, rule check is
implemented to workflows, which ensures there is no incorrect operation sequence in a user-defined workflow. Rules are
not permanent. They can be modified or added if necessary.
Terahertz Time Domain Spectroscopy (TDS) provides a new way presenting
the 'fingerprint' vibrational or rotational absorption spectra of a lot of molecules. For
some molecules, their pure rotational spectra within far infrared wavelength range are
much easier to be recognized and discriminated than their vibrational spectra in
middle infrared. Especially, vapor molecules have obvious absorption lines in the THz
range since it has permanent dipole moment while N<sub>2</sub>, O<sub>2</sub> ,CO<sub>2</sub> have none permanent
dipole moment. So it is possible to detect the vapor content in atmosphere and study
dynamics process with terahertz TDS. We measure the vapor's absorption lines in the
range of 0.3-2.0THz at different humidity from 10% to 85% at room temperature. The
strengths of the vapor absorption lines within this frequency range have been
quantitative measured and the absorption coefficients of these absorption lines at
different humidity have been calculated. In addition, the THz absorption spectrum has
a frequency resolution of 0.004THz so that the locations of most absorption lines can
be defined properly and different absorption lines can be distinguished. Seventeen
different lines have been identified consistent with previous work. But it is found that
the changes of the lines' intensities with humidity do not obey the same trend.
Especially, the absorption coefficients of two lines located at 1.6625THz and
1.6735THz have apparently different behavior when the humidity increases. This
phenomenon may be due to the interaction between the vapor molecules. Nevertheless,
the ratio of the absorptance of these lines can be used in humidity identification for
The 4 m large aperture, 5 degrees field of view and 4000 fibers make LAMOST an important optical
spectrum astronomical telescope in the world. It will take a survey observation on about 10,000,000
stars in 20,000 square degrees field of view of north celestial sphere within several years. In order to
fully utilize the advantages of a large number of goal optic fibers of LAMOST, carry out the survey
observation with better efficiency, and economize valuable astronomical observation time, it is very
essential and worthy to make a series of observation plans with utilization ratio of optic fiber as high as
possible, which is exactly the scientific goal of Survey Strategy System (SSS) of LAMOST. Various
kinds of static and dynamic restraint conditions affecting a survey observation are analyzed and
modeled. On the basis of looking for tile with the largest density, the Mean-Shift algorithm is adopted,
effectively improving the utilization ratio of optic fiber. With the progress of LAMOST project, new
restraints and algorithms will be involved.