In this paper, we propose a bio-sensing method using optical heterodyne detection for ultra-high Q micro-disk laser (MDL) sensor platform. MDL structure with ultra-high Q-factor (> 108) has advantage in detecting a small variation of the lasing wavelength. For example, when a single molecule is attached to sidewall of MDL, the lasing wavelength is changed by sub-pm. Optical spectrum analyzer (OSA) has limits to detect sub-pm variation in the resonant wavelength because of the spectral resolution. In order to overcome this limitation, we used a heterodyne detection method which needs two MDLs with the same characteristics.
In this paper, an effective quality-factor is analyzed for asymmetric Mach-Zehnder interferometer (AMZI) with ring resonator sensor. The device is designed with AMZI to interference with the optical input of the ring resonator based on silica semiconductor process. The design of device satisfy a critical resonance at out of phase condition through asymmetric power split ratio. According to operation principle of Mach-Zehnder interferometer, the critical resonance occurs when the power passing through asymmetric arm is in a range of ring resonator power variation. Our simulation shows that the Q-factor of the device is enhanced from 1161.9 to 5342.5 if a RR is coupled to an arm of AMZI.
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.
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.
KEYWORDS: Diodes, Radio over Fiber, Intermodulation, Modulation, Nonlinear optics, Semiconductor lasers, Signal attenuation, Distortion, Transmitters, Signal detection
In this paper, we propose a simple and efficient predistortion method using schottky diodes to compensate the nonlinearity of RoF systems. L-I curve in LD is compared with I-V curve in schottky diode and the nonlinear characteristics are analyzed. The predistortion circuit has been designed with two paths. One path is the nonlinearity generation circuit with schottky diode, while the other path has only a time delay. Then, these two paths are recombined to suppress the IMD3 (3rd inter - modulation distortion) of LD. Experimental results show that the enhancements of about 26 dBc in the IMD3 and about 8.5 dB in the SFDR are achieved at 2.4 GHz.
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