Position-sensitive photomultiplier tubes (PSPMTs) in array are used as gamma ray position detector. Each PMT converts the light of wide spectrum range (100 nm ~ 2500 nm) to electrical signal with amplification. Because detection system size is determined by the number of output channels in the PSPMTs, resistive network has been used for reducing the number of output channels. The photo-generated current is distributed to the four output current pulses according to a ratio by resistance values of resistive network. The detected positions are estimated by the peak value of the distributed current pulses. However, due to parasitic capacitance of PSPMTs in parallel with resistor in the resistive network, the time constants should be considered. When the duration of current pulse is not long enough, peak value of distributed pulses is reduced and detected position error is increased. In this paper, we analyzed the detected position error in the resistive network and variation of time constant according to the input position of the PSPMTs.
Lock-in amplifier (LIA) has been proposed as a detection technique for optical sensors because it can measure low signal in high noise level. LIA uses synchronous method, so the input signal frequency is locked to a reference frequency that is used to carry out the measurements. Generally, input signal frequency of LIA used in optical sensors is determined by modulation frequency of optical signal. It is important to understand the noise characteristics of the trans-impedance amplifier (TIA) to determine the modulation frequency. The TIA has a frequency range in which noise is minimized by the capacitance of photo diode (PD) and the passive component of TIA feedback network. When the modulation frequency is determined in this range, it is possible to design a robust system to noise. In this paper, we propose a method for the determination of optical signal modulation frequency selection by using the noise characteristics of TIA. Frequency response of noise in TIA is measured by spectrum analyzer and minimum noise region is confirmed. The LIA and TIA circuit have been designed as a hybrid circuit. The optical sensor is modeled by the laser diode (LD) and photo diode (PD) and the modulation frequency was used as the input to the signal generator. The experiments were performed to compare the signal to noise ratio (SNR) of the minimum noise region and the others. The results clearly show that the SNR is enhanced in the minimum noise region of TIA.
In this paper, hybrid optical delay line (HODL) which is demanded on automotive radar test system (RTS) is proposed and demonstrated. HODL is composed with coaxial cable in short delay time (< 32 nsec) and optical fiber in long delay time (≥ 32 nsec) which are considering the volume, loss and frequency characteristics. Also, the optical transceiver that has the bandwidth of 1 GHz is designed for frequency modulated continuous wave (FMCW). Experimental results show that the S21 is ± 0.5 dB in the optical transceiver and ± 1.7 dB in the whole system at 3.7 GHz ~ 4.7 GHz. The resolution of delay time is 1 ns and the delay flatness is ± 0.23 ns.
Surface plasmon resonance (SPR) sensor has been studied for high sensitivity optical biosensor as a single molecule
detection, virus detection, DNA sequencing etc. SPR sensor requires an ultra-small signal detection system that measures
very small intensity variation of reflected light along with the change of a refractive index near the sensor surface. In this
reason, lock-in detection method which is able to detect small signal buried in noise has been applied to SPR sensor. In
general lock-in detection method using multiplier and low pass filter measures DC value of output, and its sensitivity is
determined by 1/f noise at DC. Unlike the DC measurement we have proposed 2ω harmonic lock-in detection method
using multiplier and band pass filter. Sensitivity of the proposed lock-in detection method is much lower than 1/f noise at
DC. In this paper we will show that 2ω harmonic lock-in detection method for SPR sensor system providing the