Lauri Hallman

A sub-ns time-gated CMOS single photon avalanche diode detector for Raman spectroscopy

A time-gated single photon avalanche diode (SPAD) has been designed and fabricated in a standard high voltage 0.35 μm CMOS technology for Raman spectroscopy. The sub-ns time gating window is used to suppress the fluorescence background typical of Raman studies, and also to minimize the dark count rate in order to maximize the signal-to-noise ratio of the Raman signal. The proposed time-gating technique is applied for measuring the Raman spectra of olive oil with a gate window of 300 ps, and shows significant fluorescence suppression.

On Laser Ranging Based on High-Speed/Energy Laser Diode Pulses and Single-Photon Detection Techniques

This paper discusses the construction principles and performance of a pulsed time-of-flight (TOF) laser radar based on high-speed (FWHM ~100 ps) and high-energy (~1 nJ) optical transmitter pulses produced with a specific laser diode working in an “enhanced gain-switching” regime and based on single-photon detection in the receiver. It is shown by analysis and experiments that single-shot precision at the level of 2W3 cm is achievable. The effective measurement rate can exceed 10 kHz to a noncooperative target (20% reflectivity) at a distance of > 50 m, with an effective receiver aperture size of 2.5 cm2. The effect of background illumination is analyzed. It is shown that the gating of the SPAD detector is an effective means to avoid the blocking of the receiver in a high-level background illumination case. A brief comparison with pulsed TOF laser radars employing linear detection techniques is also made.

3 nJ, 100 ps laser pulses generated with an asymmetric waveguide laser diode for a single-photon avalanche diode time-of-flight (SPAD TOF) rangefinder application

An asymmetric waveguide laser diode with a thick active layer operated with enhanced gain switching is shown to be able to produce ?100 ps, ?25 W optical pulses in fundamental transverse mode with ?15 A, ?1.5 ns injection current pulses. A pulsed time-of-flight distance measurement demonstration utilizing this laser diode and a SPAD detector indicates centimetre-level precision and compensated accuracy from uncooperative targets at tens to hundreds of metres in a measurement time of a fraction of a second.

A high-speed/power laser transmitter for single photon imaging applications

A compact laser pulser emitting ~100 ps, ~10 W pulses at >100 kHz is presented. The high pulsing frequency is achieved using a MOSFET-based current driver, whereas the high pulse power is a merit of the used laser diode with an asymmetric waveguide structure leading to enhanced gain switching. The pulsing frequency is higher than with avalanche transistor based current pulsing circuits due to lower heating, and the current pulse width is shown to be even shorter than with avalanche transistor based circuits. The laser diode transmitter was developed especially for the pulsed time-of-flight laser radar application utilizing a single photon avalanche diode (SPAD) matrix as the detector element. A demonstration measurement is done enabling centimeter-precision distance measurement to 50 m in a measurement time of ~5 ms outdoors in sunny weather.

Compact laser pulser for TOF SPAD rangefinder application

Fundamental mode, ~100 ps, ~40 W optical pulses are demonstrated from a laser diode with a strongly asymmetric waveguide structure and a relatively thick (~0.1 μm) active layer driven with ~15 A, ~1.5 ns injection current pulses produced by a simple avalanche transistor circuit. Using this compact laser source, pulsed time-of-flight laser rangefinding measurements were performed utilizing a single-photon avalanche detector. The results show the feasibility of a very compact overall device with centimeter-level distance measurement precision and walk-error compensated accuracy to passive targets at tens to hundreds of meters in a measurement time of about ten milliseconds.

Effect of signal quantum shot noise on the jitter of leading edge detected and high-pass discriminated laser pulse signals

Effects of signal quantum shot noise on the jitter properties of laser pulses detected by a typical time-of-flight laser radar receiver channel configuration have been studied. Simulation and measurement results show that the optimal leading edge detection level in a typical industrial measurement situation with a PIN-diode detector is at the maximum point of the timing pulse slew rate. For avalanche photodiodes (APD) at the same signal to noise ratio, defined at the input of the preamplifier, the optimum detection level is lower due to the effect of signal quantum shot noise. In high-pass discrimination the optimum timing discrimination time constant is higher with an APD receiver than with a PIN-diode receiver due to signal quantum shot noise. In addition, it was noted that the optimum APD gain from the jitter point of view is less than the maximum gain in certain measurement situations.

An 80 × 25 pixel CMOS single-photon range image sensor with a flexible on-chip time gating topology for solid state 3D scanning

A solid state 3D scanner based on a pulsed laser diode source and narrow time gating of a 2D CMOS single photon avalanche diode (SPAD) detector array is presented. The imager uses an on-chip delay-locked loop to program the time gating of 40 sub-arrays individually. The prototype detector has 80 × 25 pixels with a fill factor of 32 % in the sensor area. The chip has been fabricated in a 0.35 μm high-voltage process and occupies a 5.69 × 5.02 mm2 area. A 3D range image rate of ∼5 frames/second with centimeter level precision is demonstrated to passive targets within a range of ∼1 meter and FOV of 36 × 57 degrees.

Comparison of the leading-edge timing walk in pulsed TOF laser range finding with avalanche bipolar junction transistor (BJT) and metal-oxide-semiconductor (MOS) switch based laser diode drivers

Timing walk error in pulsed time-of-flight based laser range finding was studied using two different types of laser diode drivers. The study compares avalanche bipolar junction transistor (BJT) and metal-oxide-semiconductor field-effect transistor switch based laser pulse drivers, both producing 1.35 ns current pulse length (full width at half maximum), and investigates how the slowly rising part of the current pulse of the avalanche BJT based driver affects the leading edge timing walk. The walk error was measured to be very similar with both drivers within an input signal dynamic range of 1:10 000 (receiver bandwidth of 700 MHz) but increased rapidly with the avalanche BJT based driver at higher values of dynamic range. The slowly rising part does not exist in the current pulse produced by the metal-oxide-semiconductor (MOS) based laser driver, and thus the MOS based driver can be utilized in a wider dynamic range.