Showing papers on "Photodiode published in 1973"

Light Emitting Diodes and Phototransistors in Photometric Modules

Abstract: The design and construction of photometric modules is discussed. The cell module consists of a cylindrical cell of desired length with a light emitting diode glued to one end window and a phototransistor to the other. Light losses are thus kept at a minimum and power requirements are extremely modest. Invariance of the light path, good monochromacy and sensitivity, ruggedness and extreme light weight are some of the more prominent advantages resulting from this approach. The control module contains power supplies, circuits and a meter. Only a very few components are needed for monitoring the whole system.

Integrated optically coupled light emitter and sensor

Abstract: An optically coupled light emitting diode and photo detector is disclosed, which includes an isolation region made from the same semiconductor material as the light emitting diode and photo detector. The structure involved consists basically of four semiconductor regions, one pair of which is separated from another pair by a semiconductor isolation region. The isolation region is of the same semiconductor material as the pairs of semiconductor regions which form a light emitting diode and a photo detector. By using an isolation region of the same semiconductor material as that of the light emitting diode and the photo diode, an integrated device is provided which eliminates index of refraction and lattice constant mismatches between the light emitter and optical detector. The integrated device is fabricated from a single semiconductor material gallium aluminum arsenide and is fabricated using well known liquid phase or other epitaxial growth techniques. The resulting structure is completely symmetrical and has the unusual feature that it can be operated bidirectionally, i.e., the light emitting and photo detecting functions are completely interchangeable.

HgCdTe varactor photodiode detection of cw CO2 laser beats beyond 60 GHz

Abstract: The simultaneous operation of a HgCdTe photodiode as an optical heterodyne receiver and a varactor microwave harmonic generator and frequency downconverter has made possible the detection of CO2 laser beats to beyond 60 GHz.

Fault detector for paper webs

Abstract: The invention relates to an amplification circuit for a photoelectric device - for example, a phototransistor - whereby the output from such circuit is responsive to percentage changes in the light incident upon said device rather than absolute changes therein or in the condition of the circuit. The device is connected in series with a diode junction across a potential supply and the current passing therethrough controls the bias applied to a transistor connected across a potential supply and having diode junction characteristics similar to those of the first-named junction. The output signal from the circuit is thus dependent upon the current flow through the transistor, which is controlled by the bias applied thereto. Also disclosed and claimed is the application of the circuit to a web fault detector apparatus.

Application of AND and Exclusive-Or (XOR) Logic Operations to the Identification of Elemental Emission Spectra Measured Using a Photodiode Array Direct Reading Spectrometer

Abstract: Direct current arc emission spectra have been measured for 35 elements over a 140 A range in the 3240 to 3380 A region employing a monochromator self-scanned linear silicon photodiode array detector system. Each spectrum was reduced to a binary representation by compressing the spectral intensity information such that a logic 1 and a logic 0 represented the presence and absence of spectral features. It is shown that with the application of the logic operations AND and exclusive-or (XOR) it is possible to identify uniquely each of the 35 elemental emission spectra. The feasibility of extending the procedure to multicomponent spectra is illustrated and discussed.

Factors affecting the ultimate capabilities of high speed avalanche photodiodes and a review of the state-of-the-art

Abstract: The ultimate limitations to the performance of existing and new photodiode structures, which are imposed by both theoretical considerations (noise factor, amplitude distribution of gains, gain-bandwidth product, etc.) and practical limitations (choice of materials, device uniformity, difficulty of designing high speed structures in which most of the light is absorbed in a region of the depletion layer such that the carriers being multiplied are of the more strongly ionizing type, etc.), are examined. It is shown that for a properly designed structure, a useful figure of merit for high-speed (high-gain) operation is given by η/k1/2, where η is the quantum efficiency and k is the effective ratio of the ionization coefficient of the weakly ionizing carrier to that of the strongly ionizing carrier. It is shown further that for various reasons the prospects for achieving low-noise avalanche photodiodes having gain-bandwidth products much above 200 GHz are not too bright.

Infrared Heterodyne Detection of the Moon, Planets and Stars at 10 µm

Abstract: THE possibility of applying heterodyne detection techniques in astronomy is now becoming well known1-3. Earlier observations made in this way in the visible region of the spectrum4,5 have indicated that its importance for astronomy lies primarily in the infrared. Preliminary measurements with a 10 µm system for solar heterodyne interferometry were recently published by Gay and Journet6. In August and September 1973 we carried out heterodyne detection measurements of planets, stars and the Moon at wavelengths around 10.5 µm. The observations were made at the Coude focus of the 1.5-m spectrographic telescope of the European Southern Observatory at La Silla in Chile. Figure 1 shows a block diagram of the experimental equipment. The local oscillator was a linearly polarised single line, single mode CO2 laser (Sylvania, model P941) tunable to different laser transitions around 10.5 µm. Tuning is achieved by changing the temperature of the cooling water and thereby varying the cavity length of the laser tube. Two different types of detectors were available as photomixing elements: a liquid nitrogen-cooled HgCdTe photodiode (Societe Anonyme de Telecommunications, quality B1) and a liquid helium-cooled Ge : Cu photoconductor (Santa Barbara Research Center, type HS). The detector signals were amplified by radiofrequency amplifiers and subsequently rectified by a quadratic detector. For amplifying the diode signals we used two CA1003 E + M amplifiers with a pass band between 10 and 300 MHz; the photoconductor signals were amplified by two AWL-1200 M Avantek amplifiers having a pass band between 0.1 and 1,200 MHz. A high-pass filter was used to produce a flat frequency response over the largest possible bandwidth. This resulted in an effective bandwidth of about 250 MHz for the photodiode system and of 1,000 MHz for the photoconductor system. The application of a chopper allowed synchronous detection. A rotating mirror (MC in Fig. 1), which chopped the source against the sky background, was used when observing planets or stars, whereas a plastic chopper (PC) was used in the calibration measurements and in the observations of the Moon to chop against room temperature (291 K). The sensitivities of both heterodyne detection systems were measured with the aid of a calibrated blackbody source. Heterodyne detection with a photodiode of an extended blackbody of absolute temperature T should have an associated signal-to-noise ratio (SNR)

High speed light detector amplifier

Abstract: A light detector amplifier preferably fabricated as a monolithic integrated circuit has high speed of response (in the order of 1 microsecond) at low and high illumination levels, uses low quiescent power and supply voltage, and has an optional thyristor or power transistor output. A transistor preamplifier conducts in the quiescent state and reverse biases a photodiode. Upon illumination, current is diverted to the photodiode and a power amplifier is energized to produce an output which can also provide gating current for a thyristor output. Enhanced performance is obtained by the use of special components, and unique placement of components within the circuit. Voltage excursions are limited in the circuit at several points by current steering, pre-biasing and diode clamping techniques.

Photodiode with patterned structure

Abstract: A monolithic or discrete photodiode has a patterned region, preferably in the form of elongated strips or fingers, with a spacing less than the diffusion length to obtain low capacitance without loss of photo response. Enhanced efficiency is achieved by the use of surface skin regions and/or a buried layer to confine generated carriers, and by a structure that effects combination of the epitaxial layer-substrate photodiode with the finger photodiode. The low capacitance photodiode is sensitive to visible and infrared light and is useful in high speed circuit applications.

Isolated photodiode array

Abstract: Low impurity concentration planar anode regions are formed without a mask in a plurality of cathode regions which are isolated from each other on their lateral edge by an insulating barrier and connected to each other by a low resistivity polycrystalline body. Metal contacts to the anode regions and the common cathode polycrystalline body are coplanar.

Laser Doppler instrument for measurement of vibration of moving turbine blades

Abstract: A laser Doppler instrument using a 1 mW laser has been developed for the measurement of the vibration of moving objects. Particular interest has been taken in rotating turbine blades. The design and optimisation of the instrument are described, and details given of its performance and resolution. It is shown that resolution is limited by signal/noise ratio and by Doppler broadening, both of which can be predicted. A coherence loss factor is established which enables the expected signal/noise ratio to be estimated from simple ‘noncoherent’ measurements of light scattered from a target. Experiments are described which compare the performance of photomultipliers and avalanche photodiodes. The instrument has been used successfully on a turbine having blade-tip velocities up to 300 m/s, equivalent to Doppler shifts up to 1000 MHz. At the lower frequencies, photomultipliers and avalanche photodiodes are comparable in performance, but at the top end of the range only the latter is satisfactory. Resolution in velocity of about one part in 104 is achieved with an output bandwidth of 1 kHz.

Graded bandgap semiconductor photodetector for equalization of optical fiber material delay distortion

Abstract: In optical fiber transmission, one of the causes of signal distortion (pulse broadening) stems from the fact that energy at different optical wavelengths travels at different velocities in the fiber material (material dispersion), and hence these wavelength components undergo different time delays while propagating through the fiber. In order to reduce this optical distortion, a p-n junction photodiode made of a graded bandgap semiconductor material is disclosed as a delay equalizing detector. The gradient of the bandgap is made in such a manner that the different time delays of drifting charge carriers, generated by the absorption of different wavelengths at different depths in the graded bandgap semiconductor, can be made to compensate for the time delays suffered by the optical energy at different wavelengths while propagating through the fiber.

Optical detection using photodiodes

Abstract: Linear photodiode-amplifier combinations will be required for optical communication systems, in particular for those using fibre optics as the transmission medium. The noise performance of photodiode-amplifier combinations is derived and presented, and some parameters affecting photodiode and first stage amplifier design are reviewed. It is shown that, of foreseen devices, silicon JFETs will be quietest as amplifier first stages for base bandwidths of up to 10 MHz, GaAs FETs up to 100 MHz and bipolar transistors will be preferred for broader bandwidths. In tuned applications the JFET is to be preferred up to 8 MHz and GaAs FETs will be the best devices above that frequency.

High speed photodiode mount

Abstract: A small, easily constructed, high speed, coaxially connected, photodiode mount is constructed by modifying two conventional seven-millimeter coaxial connectors so as to position the diode in the end of one connector. The flanges of the connectors are positioned in back-to-back relationship with insulation between them to form a coupling capacitor. The photodiode bias potential is impressed on the photodiode by making electrical connections to the flanges. A coaxial cable signal lead is conventionally connected to the other flange. The mount is held in a light and electric field shielding tube by insulating screws through holes in the flanges.

Analysis and measurement of the speed and linearity of silicon photodiodes for measuring short laser pulses

Abstract: The principles of operation of the different classes of silicon photodiodes are given together with a discussion of the importance of various parameters when using the diodes for measuring the power and energy of short laser pulses. A theoretical analysis is made of the speed of response and maximum linear current to be expected from a photodiode of known area, thickness and bulk sensitivity for various bias voltage, pulse lengths and wavelengths.

The design, fabrication, and evaluation of a silicon junction field-effect photodetector

Abstract: A new device for photodetection is introduced in this study that is capable of responsivities comparable to devices operating in the charge-storage mode. Since the physical process involved corresponds to a photodiode in series with a high value of resistance, the device operates in real time and hence avoids the problems of switching encountered in the charge-storage mode at low light levels. The device utilizes this physical process in a new technique that significantly reduces the required surface area. Although the junction field-effect transistor (FET) serves as the prototype for the device, considerations for improving the magnitude of the output response and its linearity along with the responsivity-bandwidth product lead to a device having a very low transconductance _{m} and a large cutoff voltage V GC . Field-effect photodetectors fabricated in accordance with the principles developed for optimum photodetection are evaluated. Epitaxial silicon of conventional doping was used in the fabrication. The devices are found to exhibit the photodetecting characteristics expected from theoretical considerations. A simple two-lump approximation of the distributed gate-channel interface is found to adequately describe the frequency response of the devices. In contrast to the area-independent responsivity of the charge-storage mode, it is shown that the responsivity of the field-effect photodetector is proportional to the square of the device surface area. Depending upon the illumination level and the deviation from linearity that is tolerable, this area dependence presents one of the fundamental drawbacks of the field-effect photodetector for applition in dense arrays.

Light measuring process and apparatus

Abstract: A photodiode and a signal storing capacitor are cyclically operated in alternate connection to an output circuit. A synchronized shutter alternately shields the photodiode from the light being measured while the capacitor is being charged and uncovers it to generate a light measuring signal. The capacitor discharges into the output circuit together with the light measuring signal to cancel the error portion of the signal from that corresponding to the amount of light being measured. The output from the photodiode is connected into an amplifier which is connected to a switching circuit including a charge-storing capacitor. The shutter is mechanically or electronically operated through a pulse generator, which also synchronizes the charging and discharging of the storage capacitor and the phase of connection of the output signal to an accumulator which provides a stationary indicating signal. An electronic shutter for alternately covering and uncovering the photodiode is provided by a liquid crystal.

Doppler-shift velocity measurement system using a two-frequency laser

Abstract: A system for determining the velocity of a moving object, including a laser that emits light at two original frequencies to impinge on a reflector included on the object; a beam splitter and a mirror for directing the light emitted from the laser and the light reflected from the object to a photodiode; and a device for displaying an electrical signal generated in the diode that is the difference between one original frequency and the dopplershifted frequency of the other original frequency, the difference in frequency being a function of the velocity of the object and being in a range of values that are conveniently measured.

Influence of the charge pumping effect on an integrated solid-state image sensor using MOST switches

Abstract: The charge pumping in image sensors with MOST switches is simulated experimentally and discussed. It is found that photodiode potential is changed with no illumination, that photoelectric characteristics are degraded, and that a storage mode operation cannot be achieved. A desirable treatment available to diminish this effect is proposed.

Light-measuring systems

Abstract: A light-measuring system in which a photodiode is electrically connected with a logarithmic compression element in a circuit which includes a voltage source and a source follower circuit connected between the voltage source on the one hand and the photodiode and the logarithmic compression element on the other hand for providing approximately zero voltage across the photodiode.

Limitations of the Use of Vacuum Photodiodes in Instruments for the Measurement of Laser Power and Energy

Abstract: The effect of the variation in the area sensitivity upon the calibration of instruments incorporating biplanar vacuum photodiodes for the measurement of laser power and energy is discussed. A technique for the measurement of the area sensitivity is described, and the experimental results for several tubes are given. At the present time it would appear to be difficult to use biplanar vacuum phctodiodes in devices to measure laser energy or power.

A new grating-type gold-n-type silicon Schottky-barrier photodiode

Abstract: The new grating-type Au-n-type Si Schottky-barrier photodiode has been fabricated and analyzed. The device is constructed with a new structure of contact mask. The mask forms a grating of gold film over the contacting silicon substrate. The grating spacing is so chosen that even at zero bias the interfacial layer between the silicon substrate and the gold gratings is completely depleted. The device is fabricated on an n-type silicon wafer of ∼1300-Ω.cm resistivity, and the grating spacing is 12.5 µm. An analysis is performed to determine the I-V characteristics, the spectral dependence of the quantum yield, the responsivity, and the noise characteristics of the photodiode. It is found that without optimization the device has a bandwidth of ∼1 GHz and responsivity of 0.63 A/W at λ =0.9 µm.

Limitations of the use of vacuum photodiodes in instruments for the measurement of laser power and energy.

Abstract: The effect of the variation in the area sensitivity upon the calibration of instruments incorporating biplanar vacuum photodiodes for the measurement of laser power and energy is discussed. A technique for the measurement of the area sensitivity is described, and the experimental results for several tubes are given. At the present time it would appear to be difficult to use biplanar vacuum phctodiodes in devices to measure laser energy or power.

Scintillation camera brightness calibrating apparatus

Abstract: Circuitry is disclosed for calibrating the brightness level of the cathode ray tube associated with a scintillation camera. The apparatus disclosed includes circuitry for generating a raster over a small area of the cathode ray tube face. A photodiode is mounted closely adjacent that face area and produces an output voltage related to the brightness of the emitted light. That voltage is amplified and applied to a comparator circuit which compares the amplitude thereof with that of a reference voltage. The cathode ray tube beam intensity is altered until the comparator output achieves a desired state. The raster is chopped to produce a series of dots on the cathode ray tube face and minimize problems of aging of the tube phospher. In one embodiment, the output of the photodiode is processed to minimize the effects of light and electrical noise.

Investigation of responsivity and noise in a direct-coupled photodetector-preamplifier for facsimile cameras

Abstract: The direct-coupled (DC) mode of detector operation is evaluated for use in a facsimile camera. Photodiode-preamplifier sensitivity is described in terms of photodiode responsivity and possible noise sources resulting from the photodiode and preamplifier. Responsivity and noise limitations are experimentally verified and used to predict photodiode-preamplifier sensitivity under a wide range of operating conditions. Results demonstrate that the DC mode offers advantages in sensitivity and reduced mechanical complexity for facsimile cameras over the more common technique of chopping the radiation and ac amplifying the resultant signal.

Impulse rise and fall times of biplanar vacuum photodiodes.

Abstract: The impulse rise and fall times of biplanar vacuum photodiodes are experimentally investigated by the use of a single ultrashort laser pulse from a train of mode-locked pulses. It was confirmed that the impulse rise time is a function of the photoelectrons' transit time from photocathode to anode, and that the impulse fall time is 2.2 times the capacitance of the photodiode and the resistive component of the load.