With the rapid development of high-level road traffic system and the implementation of autonomous mobility system, smart driving has become an important work toward the realization of intelligent society. Large capacity of imaging data acquired by imaging sensors and large surrounding traffic information data are required to be transferred to vehicles via in-vehicle transmission lines. Plastic optical fiber (POF) has potential for this type of next generation automotive data networks due to its relatively high bandwidth compared to current coaxial cables, easy connection due to relatively large core diameter, low cost, and immunity to electromagnetic interference. However, due to fiber mode dispersion, the bandwidth of large core POF is limited to several hundred Mega-Hertz for a hundred-meter-long transmission line. Equalization (including linear equalization and feedback equalization) was proposed to be used for eliminating inter symbol interference introduced by the limited bandwidth of the POF. In the past, fiber transfer function was supposed to be a Gaussian shape in simulations, which is not the actual situation. In this work, we first calculate the POF transfer function based on the power flow equation and the real fiber parameters. Then, we evaluate the transmission quality of raised cosine pulse sequence by observing the eye-pattern at the receiving end, which shows clear eye closure. Next, we designed a decision feedback equalizer and applied it to improve the bit rate of the transmission line. The result showed that transmission quality is improved, but the speed cannot achieve Gbps by equalizer alone.
We propose a method for developing small all-fiber vehicle laser rangefinders that is based on pulse position modulation (PPM) and data integration and present a theoretical study on its performance. Compared with spatial coupling, which is employed by most of the current commercial vehicle laser rangefinders, fiber coupling has the advantage that it can guide laser echoes into the interior of a car, so the electronic components following the photodiode can operate in a moderate-temperature environment. However, optical fibers have numerical apertures (NAs), which means that a laser beam from a receiving lens cannot be coupled into an optical fiber if its incident angle exceeds the critical value. Therefore, the effective size of the receiving lens is typically small since it is limited by its focal length and the NA of the fiber, causing the power of the laser echoes gathered by the receiving lens to be insufficient for performing target identification. Instead of increasing the peak transmitting laser power unrestrictedly, PPM and data integration effectively compensate for the low signal-to-noise ratio that results from the effective receiving lens size reduction. We validated the proposed method by conducting numerical simulations and performance analysis. Finally, we compared the proposed method with pseudorandom noise (PN) code modulation and found that, although the two methods perform equally well in single-target measurement scenarios, PPM is more effective than PN code modulation for multitarget measurement. In addition, PPM enables the transmission of laser beams with higher peak powers and requires less computation than PN code modulation does.
A pulsed coherent vehicle laser radar system basing on the measurement of light flight time and Doppler frequency shift is demonstrated for the first time, which features a simple design that uses one photodiode (PD) as its optical detector. Pseudo random noise (PN) code is used for modulating the amplitude of transmitting light. Correlation function of the received echoes and the local modulating codes is calculated for measuring the light flight time. Due to PN code modulation, beat signal output from PD is piecewise continuous, which causes equidistant sampling of Doppler sine wave not feasible. In order that Doppler frequency be correctly measured by using fast Fourier transform (FFT), a simple signal amplitude modification method is derived from the definition of Fourier transform.
We have developed a LIDAR system with a sensor head which, although it includes a scanning mechanism, is less than
20 cc in size. The system is not only small, but is also highly sensitive.
Our LIDAR system is based on time-of-flight measurements, and incorporates an optical fiber. The main feature of our
system is the utilization of optical amplifiers for both the transmitter and the receiver, and the optical amplifiers enable
us to exceed the detection limit set by thermal noise. In conventional LIDAR systems the detection limit is determined
by the thermal noise, because the avalanche photo-diodes (APD) and trans-impedance amplifiers (TIA) that they use
detect the received signals directly. In the case of our LIDAR system, the received signal is amplified by an optical fiber
amplifier before reaching the photo diode and the TIA. Therefore, our LIDAR system boosts the signal level before the
weak incoming signal is depleted by thermal noise. There are conditions under which the noise figure for the
combination of an optical fiber amplifier and a photo diode is superior to the noise figure for an avalanche photo diode.
We optimized the gains of the optical fiber amplifier and the TIA in our LIDAR system such that it would be capable of
detecting a single photon. As a result, the detection limit of our system is determined by shot noise.
We have previously demonstrated optical pre-amplified LIDAR with a perfect co-axial optical system[1]. For this we
used a variable optical attenuator to remove internal reflection from the transmission and receiving lenses. However, the
optical attenuator had an insertion loss of 6dB which reduced the sensitivity of the LIDAR. We re-designed the optical
system such that it was semi-co-axial and removed the variable optical attenuator. As a result, we succeeded in scanning
up to a range of 80 m.
This small and highly sensitive measurement technology shows great potential for use in LIDAR.
We developed a LIDAR system with a sensor head as small as 22 cc, in spite of the inclusion of a scanning mechanism.
This LIDAR system not only has a small body, but is also highly sensitive.
Our LIDAR system is based on time-of-flight measurements, and it incorporates an optical fiber. The main feature of our
system is the utilization of optical amplifiers for both the transmitter and the receiver, and the optical amplifiers enabled
us to exceed the detection limit of thermal noise. In conventional LIDAR systems the detection limit is determined by
thermal noise, because the avalanche photo-diodes (APD) and trans-impedance amplifiers (TIA) that they use detect the
received signals directly. In the case of our LIDAR system, received signal is amplified by an optical fiber amplifier in
front of the photo diode and the TIA. Therefore, our LIDAR system can boost the signal level before the weak incoming
signal is depleted by thermal noise. There are conditions under which the noise figure for the combination of an optical
fiber amplifier and a photo diode is superior to the noise figure for an avalanche photo diode.
We optimized the gain of the optical fiber amplifier and TIA in our LIDAR system such that it is capable of detecting a
single photon. As a result, the detection limit of our LIDAR system is determined by shot noise.
This small and highly sensitive measurement technology shows great potential for use in LIDAR with an optical
preamplifier.
Pseudo Random Noise (PN) coded laser radar can improve the target detection ability without the demand on high power
laser. However, the reflected echoes are generally so weak that they are buried in the thermal noise of the receiver, which
raises the problem of choosing an optimal threshold for correctly decoding them since the power of echoes varies from
time to time, and the voltage of light generated electrical signal by photo diode (PD) is always positive. In this work, we
firstly show the problem we are going to discuss. Then, a novel method basing on Inter Symbol Interference (ISI) is
proposed for solving the problem. Next, numerical simulations and experiments are performed to validate the method.
Finally, we discuss the obtained results theoretically.
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