Showing papers on "Photodiode published in 1994"

Multi-function light sensor for vehicle

Abstract: A system for detecting the presence of rain droplets on a windshield (17) employs a source of light, such as an LED (11), and a photodetector (12) installed on the dashboard (13) of a vehicle. The LED (11) and the photodiode (12) are arranged with respect to one another such that light from the LED (11) cannot reflect directly off the windshield into the photodiode (12). Only when the light from the LED is backscattered by an environmental condition, such as the raindrops (25) on the exterior of the windshield (17), the condensation of moisture on the interior of the windshield (17), or the presence of smoke in the cabin, will the photodiode (12) receive the light from the LED (11). Each of these environmental conditions has a predeterminable characteristic signature which permits the processing of data to detect same. An ambient light signal is subtracted from the combination of the rain and ambient light signals by pulsed operation of the LED (11) and subtracting the ambient light signal, which is detected when the LED (11) is dark, from the combined LED (11) and ambient light signal which is present when the LED (11) is illuminated.

Dual-function semiconducting polymer devices : light-emitting and photodetecting diodes

Abstract: Thin film devices made with poly[2‐methoxy‐5‐(2’‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene], MEH‐PPV, are known to be efficient light‐emitting diodes. The same devices, under reverse bias, exhibit excellent sensitivity as photodiodes. Thus the polymer tunnel diode is a dual‐function device. For the Ca/MEH‐PPV/ITO (indium/tin oxide) layered structure, the external quantum efficiency for electroluminescence is ≊1% photons/electron (forward bias ≳2.5 V). The same device is sensitive as a photodiode: The dc sensitivity (−10 V, reverse bias) is 9×10−2 A/W (at ∼1‐μW/cm2 input) corresponding to a quantum yield of more than 20% electrons/photon.

Semiconducting polymer diodes: Large size, low cost photodetectors with excellent visible‐ultraviolet sensitivity

Abstract: Photodiodes fabricated from conjugated polymers exhibit excellent sensitivity to visible‐UV radiation. The photosensitivity increases with reverse bias voltage. The photoresponse of diodes fabricated from poly(3‐octyl thiophene) is relatively flat in the visible and near UV; for wavelengths shorter than 550 nm, the absolute sensitivity is greater than 0.3 A/W under reverse bias of 15 V, larger than that of commercial UV‐enhanced Si photodiodes. Photodiodes made from poly[2‐methoxy‐5‐(2’‐ethyl‐hexyloxy)‐1,4‐phenylene vinylene], MEH‐PPV, sensitized with C60, show similar sensitivity. The ease of fabrication into large size, arbitrary shapes, and even onto flexible substrates makes the polymer photodiode a novel photodetector with potential for use in a wide range of applications.

Properties of the YAG:Ce scintillator

Abstract: Light yield, light pulse shape due to γ-rays and α-particles, energy resolution and time resolution of the new YAG:Ce scintillator were studied using a light readout by means of the XP2020Q photomultiplier and the S3590-03 photodiode. The light yield of 20 300 ± 2000 photons/MeV was determined using three independent methods. The light pulse produced by γ-rays consists of two components with the decay time constants of 87.9 ns and 302 ns respectively. The light pulse measured for α-particles exhibits a faster and less intense fast component with the decay time constant of 68.4 ns. The energy resolution obtained was 11.1% and 11.7% for the 662 keV γ-rays from a 137 Cs source as measured with the photomultiplier and the photodiode readout, respectively. A time resolution of 1.3 ns was observed for 60 Co γ-rays (at 100 keV threshold) with the crystal coupled to the XP2020Q photomultiplier. The YAG:Ce scintillator with the peak emission at 550 nm is a good candidate to replace CsI(T1) and BGO scintillators in detection of light charged particles when photodiode readout is of importance. The observed difference in the light pulse shape due to γ-rays and α-particles suggests good performance of the crystal in the pulse shape discrimination method for the particle identification.

System and method for reading and comparing two-dimensional images

Abstract: A system and method for reading a two-dimensional image, and for comparing the two-dimensional image to stored data representative of a known image. The optical scanning device comprises a sensor for capturing the two-dimensional image, which sensor includes an LED array for projecting an emitted light towards the two-dimensional image. The sensor also includes a lens disposed forward of the LED array for focussing the emitted light and thereby framing the two-dimensional image. The sensor further includes an optical assembly for focussing an ambient light reflected from the framed two-dimensional image. And the sensor includes a CMOS (or CCD) detector for detecting the focussed ambient light, the CMOS detector including a photodiode array for sensing the focussed ambient light and a processor for processing the ambient light to obtain an electrical image signal. The optical scanning device also compresses the electrical image signal. Finally, the optical scanning device decodes the compressed image signal to obtain image data representative of the two-dimensional image. The image data can be compared to the stored data to determine if the two-dimensional image matches the known image.

110-GHz, 50%-efficiency mushroom-mesa waveguide p-i-n photodiode for a 1.55-/spl mu/m wavelength

Abstract: A mushroom-mesa structure is proposed to reduce the CR-time constant which originates from the waveguide photodiode structure. Experimental results at a 1.55-/spl mu/m wavelength show that the multimode waveguide p-i-n photodiode with mushroom-mesa structure has an electrical 3-dB bandwidth of more than 75 GHz in the frequency domain and an electrical 3-dB bandwidth of 110 GHz in the time domain. The external quantum efficiency is 50% or 0.63 A/W, which leads to a record bandwidth-efficiency product of 55 GHz for long wavelength p-i-n photodetectors. >

Design studies for a PET detector module using a PIN photodiode to measure depth of interaction

Abstract: We present design studies of a multi-layer PET detector module that uses an 8/spl times/8 array of 3 mm square PIN photodiodes to both identify the crystal of interaction and measure the depth of interaction. Each photodiode is coupled to one end of a 3/spl times/3/spl times/30 mm BGO crystal, with the opposite ends of 64 such crystals attached to a single 1" square photomultiplier tube that provides a timing signal and energy discrimination. Each BGO crystal is coated with a lossy reflector, so the ratio of light detected in the photodiode and photomultiplier tube depends on the interaction depth in the crystal, and is used to determine this depth of interaction on an event by event basis, A test module with one 3/spl times/3/spl times/30 mm BGO crystal, one 3 mm square PIN photodiode, and one photomultiplier tube is operated at -20/spl deg/C with an amplifier peaking time of 4 /spl mu/s, and a depth of interaction resolution of 5 to 8 mm fwhm measured. Simulations predict that this virtually eliminates radial elongation in a 60 cm diameter BGO tomograph. The photodiode signal corresponding to 511 keV energy deposit varies linearly with excitation position, ranging from 1250 electrons (e/sup -/) at the end closest to the photodiode to 520 e/sup -/ at the opposite end. The electronic noise is a position independent 330 e/sup -/ fwhm, so the signal to noise ratio is sufficient to reliably identify the crystal of interaction in a 64 element module. >

Method of and apparatus for providing offset for light detector

Abstract: The invention provides a solid state light imager or x-ray detector including an array of rows and columns of elements, each element including a photo diode, which converts photons to an electrical signal, and a transistor. Each photo diode has a capacitance associated with it. The cathode of the photo diode in each element is connected to the source of the transistor in the element. The amount of charge removed from each photo diode, after exposure to light, is used to create an image. The image is capable of accurate measurement of charge removed from the photo diodes after the array has been exposed to light, using unipolar measuring circuitry, in spite of charge retention by the transistors and a problem caused by the combination of changes in row voltage and parasitic row to column capacitance.

Progress in CMOS active pixel image sensors

Abstract: Recent research results regarding the investigation of CMOS active pixel image sensors (APS) are reported. An investigation of various designs for the pixel, including photogate devices of various geometries and photodiode devices, has been performed. Optoelectronic performance including intrapixel photoresponse maps taken using a focused laser scanning apparatus are presented. Several imaging arrays have also been investigated. A 128 X 128 image sensor has been fabricated and characterized. Both p-well and n-well implementations have been explored. The demonstrated arrays use 2 micrometers CMOS design rules and have a 40 X 40 micrometers pixel pitch. Typical design fill-factor is 26%. Output sensitivity is 3.7 (mu) V/e- for the p-well devices and 6.5 (mu) V/e- for the n-well devices. Read noise is less than 40 e- rms for the baseline designs. Dynamic range has been measured to be over 71 dB using a 5 V supply voltage. The arrays are random access with TTL control signals. Results regarding on-chip suppression of fixed pattern noise also are presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Single-photon detection beyond 1 µm: performance of commercially available germanium photodiodes.

Abstract: Germanium avalanche photodiodes (APD’s) working biased above the breakdown voltage detect single optical photons in the near-infrared wavelength range. We give guidelines for the selection of devices suitable for photon-counting applications among the commercial samples, and we discuss in detail how the devices should be operated to achieve the best performance, both in terms of noise-equivalent power (NEP) and the timing-equivalent bandwidth. We introduce the driving electronics and we show that, in the measurements of fast optical signals, the adoption of single-photon techniques is very favorable, notwithstanding that presently available photodiodes are not designed for this purpose. On the contrary, in the detection of cw signals, the lower NEP values achieved in photon counting may not be sufficient to justify the replacement of conventional analog p-i-n germanium detectors, which offer comparable performance with a definitely larger sensitive area. Finally, we show that, by properly choosing the operating conditions, some selected APD’s achieve an 85-ps time resolution in the detection of optical photons at a 1.3-μm wavelength, which corresponds to a timing-equivalent bandwidth of 1.8 GHz. To the best of our knowledge, this time resolution is the lowest reported to date for single-photon detectors in the near infrared.

Method of making a compound semiconductor having metallic inclusions

Abstract: A doped or undoped photoresponsive material having metallic precipitates, and a PiN photodiode utilizing the material for detecting light having a wavelength of 1.3 micrometers. The PiN photodiode includes a substrate having a first compound semiconductor layer disposed thereon. The PiN photodiode further includes an optically responsive compound semiconductor layer disposed above the first compound semiconductor layer. The optically responsive layer includes a plurality of buried Schottky barriers, each of which is associated with an inclusion within a crystal lattice of a Group III-V material. The PiN device also includes a further compound semiconductor layer disposed above the optically responsive layer. For a transversely illuminated embodiment, waveguiding layers may also be disposed above and below the PiN structure. In one example the optically responsive layer is comprised of GaAs:As. The GaAs:As exhibits a very low room temperature dark current, even under forward bias conditions, and a responsivity to 1.3 micrometer radiation modulated at frequencies greater than 1 GHz.

Optical sensing of combustion dynamics

Abstract: An optical radiation detector, such as a silicon carbide photodiode ultraviolet radiation detector, is employed for real time, noninvasive monitoring and diagnosis of combustion dynamics in gas turbine engines. The SiC photodiode responds to flame ultraviolet emission, and a Fast Fourier Transform spectrum analyzer peak acoustic frequency components of the detector signal as indicators of systematic gas pressure vibrations related to combustion. The combustion may be modified in accordance with the monitored acoustic frequency components.

Optical sensor array in an artificial compound eye

Abstract: Optical systems of compound eyes are of great interest in the study of micro-optics. We propose an artificial visual sensor in a model of the apposition eye of an insect. As a key component unit of the visual sensor, a sensor array consisting of 16 x 16 individual optical sensors each with a small view field is fabricated and examined. To achieve both the practical assembly and the compact size of the sensor array, a photodiode array, a glass substrate with a pinhole array, and a group of rod-type gradient-index microlenses are stacked. The optical thickness of the sensor array is 2.9 mm. Because of the low intensity of light received by the photodiode the photocurrent is amplified 107 times in current-to-voltage conversion efficiency. The fabricated sensor array produces a mosaic image with 16 x 16 pixels and eight shades of gray scale. By arranging several of these sensor arrays along a circumference, a wide-field-angle visual sensor similar to a compound eye could be realized.

Fluoroscopic x-ray imaging with amorphous silicon thin-film arrays

Abstract: The dream of an all-solid state large area x-ray image sensor with digital readout and full dynamic performance will most probably find a first realization in 2D thin-film amorphous silicon arrays. In this paper we address in particular the evaluation of the limits of the signal/noise ratio in this concept. Using small prototype detectors measurements of MTF and noise power spectra have been made as a function of x-ray dose. The results are given in terms of the detective quantum efficiency as a function of dose and spatial frequency. We further present an analysis of the different noise sources and their dependence on the detector parameters, and we provide estimates on the maximum signals that may be achieved per unit dose. The intrinsic lag of the amorphous silicon photodiodes causes a second problem area with this type of x-ray detectors. Especially in radiography/fluoroscopy mixed applications, memory effects may not be negligible.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Photon-counting with passively quenched germanium avalanche

Abstract: We demonstrate photon counting in germanium avalanche photodiodes biased beyond breakdown and quenched with a simple series resistance circuit. The devices show moderate (> 7%) quantum efficiency with limited afterpulsing and dark counts and subnanosecond jitter.

Optocoupler made from semiconducting polymers

Abstract: Optocouplers (optoisolators) were fabricated using semiconducting polymers. The input unit is a polymer light emitting diode with an external quantum efficiency of ∼1% photons/electron. The output unit is a polymer photodiode with a quantum yield of ∼35% electrons/photon at 590 nm. Both units can be operated at bias voltages sufficiently low to be compatible with TTL and complementary metal-oxide semiconductor logic circuits. Since the transfer characteristic is nearly linear, the polymer optocoupler can be used in analogue circuits as well. The current transfer ratio reaches 2 × 10−3 under-10V reverse bias, comparable to that of commercial inorganic optocouplers.

LED-based fibre optic oxygen sensor using sol-gel coating

Abstract: An intrinsic evanescent wave fibre optic sensor for oxygen is reported. The sensor is based on the quenching of fluorescence from a ruthenium complex trapped in the cage-like structure of a sol-gel-derived porous film on a de-clad section of multimode optical fibre. The sensor exhibits excellent performance using blue LED excitation and silicon photodiode detection, and establishes the viability of low-cost portable sensor devices based on the sol-gel process. Gas phase measurement data over the range 0-100% oxygen exhibit high signal-to-noise ratio ( approximately 150), good repeatability and short response time (<5 s).

PET detector modules based on novel detector technologies

Abstract: A successful PET detector module must identify 511 keV photons with: high efficiency (> 85%), high spatial resolution (< 5 mm fwhm), low cost (<$600/in.2), low dead time (< 4 μs in.2), good timing resolution (< 5 ns fwhm for conventional PET, < 200 ps fwhm for time of flight), and good energy resolution (< 100 keV fwhm), where these requirements are listed in order of decreasing importance. The “high efficiency” requirement also implies that the detector modules must pack together without inactive gaps. Several novel and emerging radiation detector technologies could improve the performance of PET detectors. Avalanche photodiodes, PIN photodiodes, metal channel dynode photomultiplier tubes, and new scintillators all have the potential to improve PET detectors significantly.

Wide wavelength and low dark current lattice‐mismatched InGaAs/InAsP photodiodes grown by metalorganic vapor‐phase epitaxy

Abstract: Using a very thin InP/InAsP cap layer and InAsP strained superlattices in a buffer layer, a lattice‐mismatched InGaAs/InAsP photodiode with low dark current and very wide wavelength spectral response was fabricated by metalorganic vapor‐phase epitaxy. External quantum efficiencies as high as 55% at 0.6 μm, 80%–90% at 0.8–1.9 μm, and 65% at 2.1 μm was obtained. For the 1‐mm‐diam photodiodes, typical dark current measured at 274 K and at a reverse bias voltage of 0.1 V was as low as 1×10−7 A.

Amplitude detection scheme for optical transmitter control

Abstract: An amplitude control scheme for a high bit rate digital optical transmitter is disclosed. The data to be transmitted by the laser is pulse-width modulated by a low frequency signal (MOD). The pulse-width modulated signal is applied to the laser via a laser driver (14) and to a mark density reference generator (15). The magnitude of the low frequency components from the mark density reference generator is a signal (ARS) indicative of the desired amplitude of the laser light pulses. A back-face photodiode (20) converts a portion of the laser light into an electrical signal, the magnitude of the low frequency portion thereof being a signal (ACS) indicative of the actual amplitude of the laser light pulses. The actual amplitude of the laser light pulses is compared to the desired amplitude and the laser driver output amplitude may then adjusted to compensate for variations in the laser performance.

155 Mbit/s optical wireless link using a bootstrapped silicon APD receiver

Abstract: A 155 Mbit/s optical wireless link has been implemented using a large-area silicon APD, bootstrapped, transimpedance receiver and a hologram-based laser transmitter. The receiver gives high sensitivity and high transimpedance while providing a large photodiode collection area.

Silicon carbide photodiode with improved short wavelength response and very low leakage current

Abstract: A silicon carbide photodiode exhibiting high short-wavelength sensitivity, particularly in the ultraviolet spectrum, and very low reverse leakage current includes a p type conductivity 6H crystalline substrate. A first p- silicon carbide crystalline layer is epitaxially grown on the body. A second n+ silicon carbide crystalline layer is epitaxially grown on the first layer and forms a p-/n+ junction with the first layer. A metallic upper contact layer is formed on a predetermined surface region of the second layer oppositely situated from the junction. The second layer is of a uniform minimum thickness, generally less than 1000 Angstroms, with a greater thickness, typically 3000-4000 Angstroms, beneath the predetermined surface region. The thicker portion of the second layer occupies less than 10% and generally less than 1% of the total second layer surface area. Hence optical sensitivity of the photodiode is essentially determined by the thinner portion of the second layer, while the thicker portion of this layer is made sufficiently large to prevent diffusion of upper contact layer metal into the vicinity of the junction during contact sintering or alloying operations.

Solid state image sensor having a high photoelectric conversion efficiency

Abstract: In a solid state image sensor comprising a first impurity layer of a first conductivity type forming a photodiode, the impurity layer is composed of a first impurity region formed of a low concentration at a deep level, and a second impurity region formed of a high concentration at a shallow level. The first impurity region extends under a second impurity layer of a second conductivity type formed for device isolation, and also extends under a gate region of a transistor for transferring an electric charge from the photodiode to a CCD channel.

Electro-optic characterisation of ultrafast photodetectors using adiabatically compressed soliton pulses

Abstract: The response of ultrafast photodetectors at 1.55 mu m wavelength has been measured by electro-optic sampling using adiabatically compressed soliton pulses. 750 fs-duration pulses with no wings were used to both pump and probe the waveguide pin photodiode. The measured bandwidth of the photodiode is more than 110 GHz, which is the highest value for a detector operating at 1.55 mu m.

Signal multiplexing system for an image sensor array

Abstract: A photosensitive apparatus comprising a plurality of sets of photodiodes and a plurality of amplifiers, each amplifier being operatively connected to one set of photodiodes. A transfer circuit is associated with each photodiode for loading a charge from the photodiode to a storage node associated therewith. Readout means sequentially unload charges from each storage node in the set of transfer circuits through the amplifier, so that multiple photodiodes may operate through a single amplifier.

Light detector using reverse biased photodiodes with dark current compensation

Abstract: Light intensity detecting circuits using reverse biased photodiodes are disclosed. Two photodiodes are fabricated with essentially the same structure in close enough proximity to each other on a single semiconductor substrate so that they both experience the same environment. In one scheme the cathode of the first photodiode is common with the anode of the second photodiode and an inverting terminal of an operational amplifier with negative feedback. A negative voltage is applied to the anode of the first photodiode and a positive voltage of the same magnitude is applied to the cathode of the second photodiode. The output of the operational amplifier is proportional to the incident light provided the intensity on each photodiode are proportional to each other. In another circuit one of either the anodes or cathodes of each diode is common and the other is input into the inverting terminal of a separate operational amplifier. The outputs of each operational amplifier is input into a subtracter circuit to subtract common dark or photocurrent components so the output of the subtracter circuit is proportional to the difference in light incident on the photodiodes. The reverse bias across the photodiodes may be varied and this is of particular use for detectors whose spectral response may be shifted by means of, for instance the Franz-Keldysh or quantum confined Stark effects.

Millimetre-wave signal generation using pulsed semiconductor lasers

Abstract: A novel technique for millimetre-wave signal generation using a pulsed semiconductor laser is proposed and demonstrated. Optical filtering is used to select only two modes and suppress all other modes in the optical spectrum of the laser. The two selected modes beat together in a photodiode to generate a millimetre-wave signal with 100 % modulation depth.

Solid-state image pickup device having a photoelectric conversion detection cell with high sensitivity

Abstract: A photoelectric conversion detection cell includes a photodiode; a storage capacitor for storing a photo-induced charge induced in the photodiode; and a transfer transistor for transferring the photo-induced charge induced in the photodiode to the storage capacitor, the source of the transfer transistor being connected to the photodiode, the drain of the transfer transistor being connected to the storage capacitor; an inverting amplifier, the input of the inverting amplifier being connected to the photodiode, the output of the inverting amplifier being connected to the gate of the transfer transistor. Also, the photo-induced charge stored in the storage capacitor may be reset and an amplified output corresponding to the photo-induced charge stored in the storage capacitor may be generated by an amplifier. The photoelectric conversion detection cell is used as a pixel to form a low noise and high sensitivity solid state image pickup device. In a further embodiment, a current mirror is connected in parallel to the storage capacitor.

The TIMED solar EUV experiment

Abstract: The Solar EUV Experiment (SEE) investigation contributes primarily to the NASA Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics (TIMED) mission goal to characterize the sources of energy responsible for the thermal structure of the mesosphere, the lower thermosphere, and the ionosphere (MLTI). These energy sources include solar radiation, solar energetic particles, Joule heating, conduction, dynamical forcing, and chemical energy release. Of these energy inputs, the solar vacuum ultraviolet (VUV) radiation below 200 nm is the dominant global energy source for heating of the thermosphere, creating the ionosphere, and driving the diurnal cycles of wind and chemistry. The Solar EUV Experiment selected for the NASA TIMED mission will measure the solar vacuum ultraviolet (VUV) spectral irradiance from 0.1 to 200 nm. To cover this wide spectral range two different types of instruments are used: a grating spectrograph for spectra above 25 nm and an avalanche photodiode for spectra below 25 nm. As part of the in-flight calibration plan, silicon XUV photodiodes with thin film filters are used as stable broadband photometers between 0.1 and 40 nm. In addition, redundant spectrograph and avalanche photodiode capabilities provide calibration checks on the time scale of a month, and annual rocket underflight measurements provide absolutemore » calibration checks traceable to NIST photometric standards. All three types of instruments have been developed and flight proven as part of a NASA solar EUV irradiance rocket experiment.« less

An optoelectric transducer

Abstract: A transducer (1) for use in a hybrid optical and radio communications system comprises a zero electrical power photodetector (2), and a radio antenna (3) The photodetector (2) is directly electrically connected to the radio antenna (3) so that in use optical signals are received and radio signals are transmitted by the transducer (1) without the use of electrical power The transducer (1) can thus be remotely sited at locations in communications systems not having a supply of electrical power In a first embodiment the photodetector comprises a zero-bias photodiode, and in a second embodiment the transducer (1) comprises a self-biasing photodetector