Target detection plays an important role in the field of autonomous driving. During the driving of the vehicle, the detection system is susceptible to the low illumination of the road at night, resulting in the inability to detect the target. Therefore, night detection becomes a difficult problem in target detection. With the continuous development of sensor types and related algorithms used in night detection systems, how to evaluate the detection capabilities of night detection systems has become an urgent problem to be solved. To solve this problem, an evaluation method for evaluating multi-sensor target detection systems is proposed. It is used to evaluate the target detection ability of the target detection system in the night road environment. This method uses the response characteristics of lidar, depth camera, and RGB camera to the surrounding environment, takes the surface illuminance and BRDF of the target as input variables, and uses the minimum distance classification method to realize the lateral evaluation and comparison of different sensors. And it is obtained that the BRDF limit of the detected samples is 0.057127 sr-1 under the 0.51lx illumination and the BRDF difference limit of the distinguished samples is 0.01953 sr-1 under the 0.98lx illumination of the RGB camera. Finally, the effectiveness of the evaluation method is proved by the test of the response signal of a single sensor.
The photon counting detectors have a wide range of applications in different areas, such as quantum communication, linear-optics quantum computing optical metrology and so on. In this work, a fiber-based 16-channel multiplexer with different time delays was designed based on a construction scheme of 1 (1×4) coupler = 4 (1×4) couplers = 16×optical fibers - 4 (4×1) couplers - 1 (4×1) coupler. The lengths (di, i =1, 2, ...16) of the optical fibers were manufactured to be 0 m, 8.0 m, ... 120.0 m, respectively, with a length difference (Δd) of 8 m. The time delay between the optical fibers (Δt) can then be calculated to be 38.8ns. A pulsed 850 nm laser with a repetition rate of 1 MHz and a pulse duration of 10 ns was adopted to test the time-multiplexing capability of the 16-channel fiber coupler. A 1-GHz Si photodetector and a 1-GHz oscilloscope were used to measure the overall insertion loss and relative power through the 16 different channels. The photoelectric pulse count of the pulsed light passing through the fiber bundle will be measured. According to the loss of optical fiber and the photon detection efficiency of detector, we can roughly the photon detection efficiency of the system. If the fiber bundle with 16 entrances instead of only one, the scheme would be used as a detector array, and for imaging. This is what we're going to do in the future.
An LED-based integrating sphere light source (LED-ISLS) was designed and fabricated for radiance responsivity calibration of microscopes. The LED-ISLS was composed of a miniaturized integrating sphere, an LED chip, a thin circular aperture, and was successfully applied to calibrate the radiance responsivity of a home-built microscope system. Several issues remain to be discussed. Firstly, the area of the circular aperture, which served as an exit port, was measured by comparing the light flux through an area-certified standard aperture and the circular aperture. The measurement uncertainty was smaller than 0.2%. Secondly, the radiance uniformity on the exit port was discussed. Simulations and experiments were conducted to evaluate the effects of circular aperture edge thickness and integrating sphere internal material reflection parameters on the radiance uniformity. From the simulation it was found out that as the edge thickness increases, the radiance uniformity drops drastically; the Bidirectional Reflectance Distribution Function (BRDF) also has impact on the radiance uniformity of the LED-ISLS. By reducing the BRDF from 0.9 to 0.6, the radiance uniformity at the exit port was reduced by about 63%. The radiance uniformity was also evaluated experimentally by using a 1 mm small aperture to scan the different small areas of the exit port. The radiance non-uniformity across the exit port of the LED-ISLS was about 5% from the scanning results. This work further investigated the radiance non-uniformity of the LED-ISLS and offered ideas of technical optimization of the LED-ISLS for better radiance responsivity calibration performance.
Aperture is widely used in optical instruments, for which the area is of importance especially for instruments measuring radiometric or photometric quantities. To measure the radiometric area of the aperture, an optical method using a power stabilized laser to scan the aperture was proposed and investigated by many metrology institutes worldwide. The National Institute of Metrology (NIM) of China has built an apparatus to measure the radiometric area aperture by using the optical method. The scheme of experimental setup and related issues are discussed in this work. Uncertainties are analyzed for an aperture with nominal 6mm diameter. Approaches for further improvements are also discussed.
The wavelength range of a femtosecond laser system can be extended to cover 190 nm ~ 4000 nm via optical parametric oscillation and various harmonic generation processes starting from a Ti:Sapphire mode-locked femtosecond pulsed laser. The laser beams can be well adjusted to be coupled to a galvo scanning system to generate a large-area, uniform light field which is highly suitable for the bi-directional reflectance distribution function (BRDF) measurement of the surface of a large-size objective. The scanning route was carefully designed with a few sub-cycles to provide the same illumination time over different spots on the measurement surface. The irradiance of the light field @ 532 nm was measured using a silicon photodiode with an integration time in the range of 0.1 s ~ 10 s and the non-uniformity was measured to be < 4% over a 60 mm × 60 mm area. The integration time of the radiance sensor for the BRDF measurement sensor was adjusted in the range of 0.1 s ~ 10 s, as well, and the BRDF of a 60 mm × 60 mm surface can be achieved with a standard uncertainty of 5%.
Femtosecond pulses tunable in (280-540) nm were generated via second and third harmonic generation processes from a Ti:Sapphire femtosecond laser with a 80 MHz pulse repetition rate. The temporal widths of the pulses are ~200 fs and the spectral bandwidths are <10 nm. These pulses can be used for spectral transmittance measurement using an integrating sphere photodetector with less than 0.1% fluorescence effect. The spectral transmittance measurement nonlinearity of the femtosecond pulse laser spectrophotometer was characterized using a double-path scheme for the incident power level from 1 mW to 10 μW. The nonlinearity results were compared with those obtained using a 532 nm continuous wave laser at similar power levels. The spectrophotometer can be well applied for the spectral transmittance measurement of a wide variety of neutral optical materials after nonlinearity corrections.
With the development of lasers, laser sources have been well adopted in spectrophotometry and optical material measurement. Especially in the ultraviolet range, ultraviolet laser has broad application prospects in the fields of optical data storage, lithography, micromachining, photobiology and medical treatment. The previously used xenon lamps have limited reliability, high energy consumption, and poor beam direction stability. NIM's new facility uses Ti: sapphire lasers as a source of monochromatic beams. Femtosecond pulse lasers can be tuned in a wide spectral range via parametric oscillation and high efficiency frequency conversions. For (280-340) nm femtosecond pulses generated via two nonlinear conversion of a (680-1080) nm Ti:Sapphire laser, the average power can be well controlled from 1 mW to sub-nW level using a polarizer-based attenuator. The laser beam quality was significantly improved using a spatial filter consists of an objective lens, a silica optical fiber, and an off-axis parabolic reflective collimator. The spatial filter was mounted on a two-dimension linear stage to accommodate the spatial beam shift. A spatially stabilized, quality beam over (280-340) nm spectral range was obtained and suitable for free-space optical materials measurements.
SQUIDs can be used as amplifiers for superconducting Transition Edge Sensor (TES) photon counting detectors. According to the physical process of photon counting, a TES signal simulator was developed to evaluate the performance of SQUID amplifier for TES detectors. A triangle simulation signal was determined to be a close match to that from a real TES photon counter. The dynamic range for the output voltage versus bias current was first characterized and then the current signals were incrementally coupled to circuit to determine the highest sensitivity of a series-array SQUID amplifier. The sensitivities are obtained by changing the triangle signal amplitude added to the TES signal simulator. The impedance changes can be deduced and further obtain the temperature changes of TES devices. When knowing the photon energy, TES design parameters can be known according to the thermal characteristics. In conclusion, the TES simulator can be well applied to guide the device design for effective readout.
It is important to measure the spectral transmission characteristics of materials when the spatial density of classical optical power (that is, the laser or attenuated light is a small spot, but the optical power hits a fixed position) is different from the spatial density of weak optical power. The most important scientific problem (research or experimental objective) is to distinguish the difference between the probability of photons passing through a sample with a specific absorption rate collectively and the probability of approaching a single photon passing through the same sample. We design an optical fiber system that can measure weak optical power. We use many methods to expand the linear measurement range so that it can measure its linearity in the power range of 1 fA-1 mA. In addition, the system can also verify the linearity of photon counter, starting from 0.1 pA block - essentially, when the detector is adjusted to 0.1 pA, the verification and evaluation of photon counting at the photomultiplier tube level is started. From the power measurement level of cryogenic radiometer to the photon counting level, the optical fiber measurement system covers 12 orders of magnitude, which also shows that the spectral transmittance and reflection ratio can cover a wide range, that is, it can be used to measure the characteristic materials with high transmittance.
A spectrally tunable monochromatic integrating sphere photon source (ISPS) was built based on a laser driven plasma light source, a monochromator, an optical attenuator, and an integrating sphere. The wavelength of ISPS output photons can be tuned from 300 nm to 800 nm with a spectral bandwidth of 1 nm ~ 5 nm; the spectral optical radiant power into the integrating sphere can be adjusted over three decades through the optical attenuator; the diameters of the inner wall and the exit port of the integrating sphere are 100 mm and 50 mm, respectively. The spectral photon radiance of the ISPS can be measured by a photomultiplier-tube (PMT) based photon counter and two precision apertures. An integrating sphere was utilized in front of the PMT-based photon counter and the non-uniformity of the spectral optical radiant power responsivity was reduced to be ~0.5% over a 5-mm-diameter effective detection area. Two precision apertures were adopted to define the effective detection area and the solid angle extended for the field-of-view. The ISPS can be directly applied to calibrate the spectral photon radiance responsivity of a few-photon imaging system, which was demonstrated on a digital color camera and a focusing lens. The spectral photon radiance responsivity of a given imaging system can be effectively validated based on this ISPS apparatus.
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