Jan Nissinen

Integrated Receiver Including Both Receiver Channel and TDC for a Pulsed Time-of-Flight Laser Rangefinder With cm-Level Accuracy

An integrated receiver that includes both the time-to-digital converter (TDC) and the receiver channel and is intended for a pulsed time-of-flight laser rangefinder with a measurement range of approximately 10 m has been designed and fabricated in a standard 0.13 mum CMOS process. The receiver operates by detecting the current pulse of an optical detector and producing a stop timing mark for the TDC by means of a leading edge timing discriminator. The TDC is used to measure the actual time interval between the start and stop pulses and the slew-rate of the stop pulse, to compensate for a walk error produced in the discriminator. The single-shot precision of the whole receiver is 250 ps for a minimum detectable signal, and its accuracy and power consumption are plusmn 37 ps with compensation within a dynamic range of at least 1:10,000 and less than 45 mW, respectively. The size of the die is 1300 mum times1300 mum including pads.

Fluorescence suppression in Raman spectroscopy using a time-gated CMOS SPAD

A Raman spectrometer technique is described that aims at suppressing the fluorescence background typical of Raman spectra. The sample is excited with a high power (65W), short (300ps) laser pulse and the time position of each of the Raman scattered photons with respect to the excitation is measured with a CMOS SPAD detector and an accurate time-to-digital converter at each spectral point. It is shown by means of measurements performed on an olive oil sample that the fluorescence background can be greatly suppressed if the sample response is recorded only for photons coinciding with the laser pulse. A further correction in the residual fluorescence baseline can be achieved using the measured fluorescence tails at each of the spectral points.

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.

High-Energy Picosecond Pulse Generation by Gain Switching in Asymmetric Waveguide Structure Multiple Quantum Well Lasers

A multiple quantum well laser diode utilizing an asymmetric waveguide structure with a large equivalent spot size of ~3 μm is shown to give high energy (~1 nJ) and short (~100 ps) isolated optical pulses when injected with <;10 A and ~1-ns current pulses realized with a MOS driver. The active dimensions of the laser diode are 30 μm (stripe width) and 3 mm (cavity length), and it works in a single transversal mode at a wavelength of ~0.8 μm. Detailed investigation of the laser behavior at elevated temperatures is conducted; it is shown that at high enough injection currents, lasers of the investigated type show low temperature sensitivity. Laser diodes of this type may find use in accurate and miniaturized laser radars utilizing single photon detection in the receiver.

A Multitime-Gated SPAD Line Detector for Pulsed Raman Spectroscopy

A time-gated 2 × (4) × 128 single photon avalanche diode line detector for pulsed laser Raman spectroscopy has been developed and fabricated in a 0.35-μm high-voltage CMOS technology. The sample is illuminated with short laser pulses (~100 ps) at a rate of ~50 kHz and four time gates synchronized with these pulses and having selectable widths within the subnanoseconds range are used to measure the Raman photons and fluorescence background simultaneously. The fluorescence background measurement is used to suppress the residual fluorescence level to improve the quality of the Raman spectrum. The variation in the width of the time window was measured to be approximately ±17.5 ps along the spectral axis when set externally to a nominal value of 100 ps. Measurements with a reference sample demonstrate the effect of nonhomogeneities in the time gates on the quality of the recorded Raman spectrum and the residual fluorescence correction.

A CMOS receiver for a pulsed time-of-flight laser rangefinder

An integrated CMOS 0.35/spl mu/m receiver channel with a wide dynamic range for a pulsed time-of-flight laser rangefinder was designed and tested. The circuit uses a leading edge timing discrimination technique. The measured bandwidth, transimpedance and an input referred noise current are 80 MHz, 122 k/spl Omega/ and 6.1 pA//spl radic/Hz. The measured walk error is 0.6 ns in 1:1000 dynamic range. The time-to-digital converter (TDC) is also implemented on the same chip.

A High Repetition Rate CMOS Driver for High-Energy Sub-ns Laser Pulse Generation in SPAD-Based Time-of-Flight Range Finding

An integrated 0.35-μm HV-CMOS driver has been designed for a gain-switched quantum well laser diode to generate short, energetic (100 ps/~0.5 nJ) optical pulses for a pulsed time-of-flight (TOF) laser radar, operating on the single-photon detection principle. The driver can produce a current pulse with a peak amplitude of ~2 A, a pulsewidth of 1 ns, and a pulsing rate of 500 kHz. The peak optical power and pulsewidth of the transmitter output with these parameters are 3 W and 100 ps, respectively. A single-shot precision of 2-3 cm is achieved in the TOF measurements of a non-cooperative target at 25 m with a reflectivity of 8% and a receiver aperture of 18 mm using a CMOS SPAD as the receiver.

2×(4×)128 time-gated CMOS single photon avalanche diode line detector with 100 ps resolution for Raman spectroscopy

A 2×(4×)128 multiphase time-gated single photon avalanche diode (SPAD) line detector has been designed and fabricated in a high voltage 0.35 μm CMOS technology for Raman spectroscopy. The time positions of the photons can be measured with the resolution of 100 ps using four time gates over the whole line detector simultaneously. This approach enables to reduce the fluorescence background of the Raman spectrum markedly. Measurements showed that the time gates can be distributed over the whole line detector with the accuracy of ± 35 ps which is adequate for a time-gated pulsed Raman spectroscopy using a laser pulse width of approximately 150 ps.

Wide dynamic range CMOS receivers for a pulsed time-of-flight laser range finder

Two integrated CMOS 0.18 /spl mu/m receiver channels, with wide dynamic range, for a pulsed time-of-flight laser range finder were designed. The circuits use a timing discriminator based on a high-pass CR-filter at the input of the receiver to produce a bipolar pulse from a unipolar one. This pulse has a zero-crossing point that is amplitude independent and thus a wide dynamic range can be achieved by detecting it. Two different structures for the front-end have been presented. The simulated bandwidths and transimpedances are 370 MHz, 280 MHz and 3.4 M/spl Omega/, 5 M/spl Omega/. The simulated walk error is under 100 ps over a 1:1000 dynamic range for typical process parameters in both channels.