High-sensitivity And Large-dynamic-range Optical Power Measurement System Based On SPAD

Power measurement is one of the most commonly used and fundamental techniques among various optical measurement techniques.Accurate and reliable intensity measurement of the incident light signal is crucial for the tuning,calibration,and validation of most optical systems.For example,in optical communication applications,accurate calibration of optical signals with a wide range of intensity spans is necessary;in the field of biomedical imaging,the intensity of very weak bioluminescent signals needs to be measured to optimize the imaging system’s state and observe the structure and function of biological tissues;in space optical sensing applications,stable detection and analysis of optical signals with a large dynamic range of intensity are required to achieve precise perception of targets with different distances and optical properties.In many of these applications,the measurement of optical power needs to achieve high measurement sensitivity at the level of sparse photons and direct power measurement within the dynamic range from femtowatts to hundreds of microwatts.However,the sensitivity of currently available commercial optical power measurement devices is usually only at the level of nanowatts,which cannot meet the demands of many application scenarios.In this paper,we conduct research on the development of high-sensitivity and large-dynamic-range optical power measurement technology and systems,which have significant practical value for tuning many optical systems and developing new optical systems.To achieve both high sensitivity and a large dynamic range,this paper proposes a scheme that combines a high-performance electronically-controlled attenuator with a single-photon avalanche diode(SPAD)based on avalanche photodiode for optical power measurement.Firstly,two technical methods,namely polymer dispersed liquid crystal film and electronically-controlled aperture,are discussed and compared in detail for their ability to attenuate light intensity.In order to meet the requirements for light attenuation performance,the preparation process and material selection of the polymer dispersed liquid crystal film were studied,and its voltage-transmittance performance,time stability,repeatability,and attenuation dynamic range were tested.The advantages,disadvantages,and applicable range of polymer dispersed liquid crystal film in achieving high-performance light attenuation are demonstrated.A precision optical intensity control system based on the electronically-controlled aperture was developed,which achieves a dynamic range of greater than 100 d B for accurate light intensity control,and the relative standard deviation of the attenuation repeatability is less than2%.This proves the reliability and applicability of the electronically-controlled aperture scheme in the optical power measurement system developed in this paper.Using SPAD as the photoelectric detection element and combining an electrically controlled aperture with a scattering plate for precise control of the incident light intensity,power measurement experiments were performed on a 705 nm signal light.The results show that the developed optical power measurement system can achieve accurate power measurement in the range of 20 f W to 300 μW,with a relative standard deviation of less than 2% for repeated measurements,a measurement error of less than3.5% for accuracy,and a zero drift of ±0.23%/15 min,all meeting the design requirements.In addition,tests were conducted on the system’s response to different wavelength signal lights and intensity,further verifying the reliability and stability of the system.The study shows that the developed optical power measurement system has the advantages of large dynamic range,high accuracy,high sensitivity,and high stability,and has great potential for application in various optical system tests and calibrations,especially in the field of long-distance laser sensing and measurement.