RU2100815C1 - Device which records shape of single optical or electric pulse signals - Google Patents

Abstract

FIELD: investigation of single fast processes, pulses from accelerators and so on. SUBSTANCE: basic and gate pulse sequences for single or scarce signal are generated by optical means. EFFECT: increased bandwidth of signals for investigation, decreased error, simplified design. 2 cl, 2 dwg

Description

 The invention relates to information measuring equipment and can be used in the study of fast processes.

 In many cases, the shape of pulsed signals of the nano- and subnanosecond range is measured by converting the time scale, which is based on the discretization of these signals, i.e., the instantaneous value corresponding to a known time is selected, and each discrete sample is stored (which is registration and allows any operations: measurement, conversion to digital code, etc.) and the subsequent relatively slow reading.

 A known time-scale converter of single signals [1] containing a coaxial delay line with taps, to which are connected mixer keys controlled by pulses from a strobe pulse generator, from the outputs of which discrete sample values of the signal under investigation are sent to amplifiers-extenders that do not violate their amplitude ratio . Using the switch, relatively discrete sampling values are read relatively slowly. At the output of the switch receive the investigated signal in an equivalent time scale.

 The device [1] when measuring the shape of the pulsed signals of the subnano and picosecond range of duration is characterized by a high error, which essentially makes it unsuitable.

 A device [2] is known for developing an applicant for registering single and rarely repeated signals, in which the conversion channel consists of a series-connected threshold element and an interval-code converter connected to a memory unit.

 In the known device [3], the development of the applicant has reduced the conversion error while providing relatively high speed, which is achieved by the introduction of broadband asymmetric voltage dividers.

A common disadvantage of the devices [1 and 2] is the increase in the conversion error when expanding the frequency band of the signal under study. It was experimentally established that when the upper cutoff frequency of the passband f _is reached _{at a} value of 1.5 GHz, the error is 10%
As follows from the above, one of the main problems in the development of digital shape meters and parameters of pulsed signals of the nano and picosecond range is to obtain a sequence of strobe pulses that are rigidly tied to the studied single or periodic signals. This problem applies both to the measurement of single and periodic signals, since the gating mode is possible both in real time and in effective time [1]
In stroboscopic oscilloscopes, this problem is solved by organizing the internal cycle of the formation of strobe pulses, the period of which can be significantly longer than the period of the studied pulses [4]
Digital processing of single pulsed signals of the nano and picosecond range imposes a number of additional difficulties associated with the fact that the signal under study is unique.

 Processing of single optical pulse signals can be carried out as in traditional ways, i.e. conversion at the photodetector and further study of the signal by digital or analog oscillography, and using fiber-optic processing and signal conversion techniques.

 The use of optical means makes it possible to simplify the electronic part of the measuring instrument of the shape and parameters of a single pulse signal, to increase accuracy and improve the time resolution.

 It is promising to use an optical circulation circuit on a fiber-optic cable (FOC), considered in [5] for converting a single pulse signal into a quasiperiodic sequence and to study it in effective time.

 In auth. St. [6] describes a device for measuring the duration of single optical pulses based on an optical circuit, containing a beam splitter, a circulation optical circuit, which includes a two-input optical element And, the first input of which is connected to the beam splitter-bifurcator directly, and the second through an optical delay, and the output radiation of the element And it coincides with the direction of circulation of the measured light pulse, allowing to reduce the measurement error to the value Δt where Δt is the time shift, determined optical delay yaemy inner line.

 The use of an optical circulation circuit on a fiber-optic cable with low attenuation and dispersion and other elements of fiber technology makes it possible to efficiently convert a single pulse signal into a quasiperiodic sequence, to save the shape and parameters of the pulses in a sequence unchanged with a time resolution of up to tens of picoseconds.

The study of the obtained sequence in effective time again poses the problem of obtaining a sequence of gating pulses, rigidly tied to the sequence of main pulses and having a repetition period T _with T _о + Δt where Δt is the sampling step associated with the required time resolution.

So, to study signals in the frequency band up to 1 GHz, it is necessary to have Δt 100 ps, and the instability of the temporary position of the strobe pulses relative to the main ones (jitter) δ _t ≃ 1 ps. In addition, for the formation of a sequence of strobe pulses, it is not possible to organize a long synchronization cycle, as is done in stroboscopic oscilloscopes, since the number of pulses of a quasiperiodic sequence is limited.

 To create a synchronization device that meets the above requirements, using only electronic circuitry and the element base, is not possible.

 Closest to the problem being solved is a device for registering the shape of single pulses [3] by design, a device [6] for measuring the parameters (duration) of optical single pulses, containing the main optical circuit, a beam splitter-splitter, an optical delay element. The optical circulation circuit in it is made using 100% reflective mirrors, a reverse prism, an light intensity amplifier, etc.

 The aim of the invention is to expand the bandwidth of the recorded signals while providing a satisfactorily low error.

 The purpose of the invention is a device for recording single optical and electrical pulsed signals, comprising a main optical circulation circuit connected to an optical coupler, a beam splitter, an optical delay element, is achieved by introducing an additional optical circulation circuit connected to an additional optical coupler into the device , a block for generating strobe pulses and a block for sampling and storage, wherein the input of the beam splitter-splitter through comm the ator is connected to the information inputs of the device, the first and second outputs with the main and additional coupler, the output of the additional coupler directly, and the main output through the optical delay element connected to the first and second photodetectors, respectively, the output of the second photodetector is connected to the first input of the sampling and storage unit, output the first photodetector through the gate pulse generation unit with the second input of the sampling and storage unit, the output of which is the information output of the device.

The essence of the invention lies in the fact that in the proposed device, the formation of the main and gate sequences of pulses from a single or rare signal is carried out by optical means, and the pulse repetition period of the gate sequence is shifted by an unknown and fixed time relative to the pulse repetition period of the main sequence. In this case, the main delay time T t _о • i, where t is _the pulse repetition period of the main or gating sequence, i 1 N, where N is the maximum number of pulses in one of these sequences, is formed by optical means, i.e., practically without distorting the shape of the investigated signal. The amount of additional delay is also generated by optical means, by the optical delay element.

 The electrical signals generated from optical signals by conversion on broadband photodetectors carry out the operation of temporal reference, discretization, and storage of the obtained samples, which can be performed without distorting the shape of the signal under study with a temporal resolution of about 50 ps.

 In FIG. 1 presents a diagram of the proposed device; in FIG. 2 is a timing diagram illustrating its operation.

 The device consists of a switch 1, an optical splitter 2, directional couplers 3 and 4, optical circulation loops 5 and 6, an optical delay element 7, high-speed photodetectors 8 and 9, a sampling and storage unit 10, a gate pulse generating unit 11, and a laser diode 12.

 Switch 1 is a fiber-optic switch 2 of channel 1, for which, for example, the optical relay PKO-PB05-T1X2, produced by Radio Relay, can be used. In order to use it to switch the signal from the electrical input, the signal must be converted into an optical signal by applying to a high-speed laser diode 12, for example, of the ILPN-206 type (STC "Microlaser", "Polyus" plant).

 Optical splitter 2 is an optical splitter 1 • 2, made for fiber lines. Such a splitter is produced by a number of enterprises, for example, NPK advanced technologies. The directional couplers 3 and 4, together with the optical circulation circuits 5 and 6, are a fiber optic assembly made, for example, by alloy technology with a fiber optic cable for the circulating circuit. A directional coupler with a circulation circuit described in [5] allows you to get the number of circulations of at least 30 pcs.

 High-speed photodetectors 8 and 9 are also currently available from a number of enterprises. For example, you can use the avalanche photodiode LFDG-70 with a rise time of 70 ps, produced by MP “Metek” at the factory “Polyus”. The sampling and storage unit 10 is a known device implemented, for example, on a storage capacitor, which generates signal samples when exposed to the strobe pulses generated in the strobe pulse generating unit 11, which may consist of a limiter amplifier, a high-speed comparator, a time delay circuit, and pulse sharpener. Such devices are implemented in serial stroboscopic oscilloscopes and are considered, for example, in the technical description for the C1-122 stroboscopic oscilloscope; YaChS-100 block of the two-channel stroboscopic converter GV2.206.120 TO.

 The device operates as follows.

At the input of the device there is a switch 1, which allows you to feed either an optical pulse or an optical analogue of an electrical pulse converted to a laser diode 12. The input signal in the form of a single optical pulse is bifurcated by an optical splitter 2 and fed through the directional couplers 3 and 4 to the main optical circulation loop 5 and an additional optical circulation loop 6, which are closed rings of fiber optic cable with different lengths. The quasiperiodic sequences of optical pulses formed as a result of the circulation of a single signal in closed optical circuits are output through the directional couplers 3 and 4 from the optical circuits 5 and 6. The sequence of optical pulses from the main circuit 5 having the pulse repetition period To (Fig. 2a) is delayed optical delay element 7 by a value of t ₃₁ is converted into electrical signals by a high-speed photodetector 8 and enters the sampling and storage unit 10 (Fig. 2, c). The sequence of optical pulses from the additional circuit 6, having a pulse repetition period T _with T _o + Δt (Fig. 2, b), is converted into an electrical signal by a silent photodetector 9 and enters the block for generating strobe pulses 11, where a sequence of strobe pulses with the same period T _with and also enters the sampling and storage device 10 (Fig. 2, d).

The delay time t ₃₂ in block 11 is set so that the first gating pulse falls on the initial section of the first pulse of the signal under study in the range from 0 to Δt, i.e., t ₁ t ₃₂ t ₃₁ ≅ Δt. In the above description, the value of Δt, equal to the difference between the periods of the circulation of pulses in the primary and secondary circuits, is equivalent to the sampling step of the input pulse signal with a period t _d = Δt.
Thus, the processed signal in the form of a quasiperiodic sequence of pulses of copies of the input pulse with a period T _o and a sequence of strobe pulses with a period T _with T _o + Δt are supplied to the sample and storage unit 10, which ensures the correct operation of the sample and storage block 10 with a sampling step Δt.
At the output of the sampling and storage unit 10, there is a sequence of extended pulse samples from the input signal (Fig. 2, e) taken with a step Δt and subjected to a time-scale transformation with a transformation coefficient q = T _c / Δt, which will allow to convert the samples into subsequent blocks digital view, filed on a personal computer (PC) for mathematical software processing. As a result of such processing, the shape of the studied pulse P _in (t) will be restored, and its parameters such as amplitude, half-maximum duration, rise time, and others will be calculated.

где l₁ длина основного оптического контура;
l₂ длина дополнительного оптического контура;
V_р скорость распространения света в волокне оптических контуров.A positive effect arising from the use of the proposed device is the expansion of the bandwidth of the registration path of single optical and electrical pulsed signals, achieved with a significant simplification of the recording part: the entire device can be made in the form of a small block, interfaced with a PC via a standard highway. The achievable time resolution is determined by Δt, which is actually determined by the difference in the length of the main and additional circulation circuits

where l _{1 the} length of the main optical circuit;
l _{2 the} length of the additional optical circuit;
V _{p is the} speed of light propagation in the fiber of the optical circuits.

If l ₂ l ₁ 1 cm, V _p 2 • August ¹⁰ m / s, then Δt 50 ps, which corresponds to the upper limiting frequency f _in the spectrum of the test using the proposed device signal in accordance with the theorem Kotel'nikova f _s = 1 / 2Δt = 10 GHz
Due to the use of fiber elements and delay lines in the signal path, the bandwidth of which is no less than an order of magnitude greater than the bandwidth of the corresponding electrical analogs, the main component of the measurement error of the shape and parameters of the signal under study is the proposed device is the error of the time-scale transformation similar to the measurement error signal parameters with stroboscopic oscilloscopes. So for the C1-122 oscilloscope with YaChS-100 and YaChS-101 blocks, the basic error of the deviation and sweep coefficients is 4 10% depending on the values of these coefficients.

 The measurement error using the proposed device will be small, since it is mainly associated with the generation of a time shift Δt in the optical circuits 5, 6 and the optical delay in block 7 and is determined by the stability of the propagation speed of optical waves in the fiber optic cable, which is very high. In the block forming the strobe pulses 11 is also a small adjustable delay of the signal electronically, but it does not significantly affect the error of the entire device.

 The error value of 10% can be taken as the upper estimate of the error in measuring signal parameters using the proposed device.

 Thus, the proposed device is characterized by the best basic parameters in comparison with the known, solving the same problem.

Literature
1. Gryaznov M. I. Gurevich M. L. and Ryabinin Yu. A. Measurement of pulse parameters. Radio and communications, 1991.

 2. Copyright certificate N 501363, cl. G 01 R 19/04, 1973.

 3. Patent N 1422857, cl. G 01 R 29/02.

 4. Naydenov A. I. and Novopolsky V. A. Electron beam oscilloscopes. Energoatomizdat, 1983.

 5. Newton S. A. Howland R. S. Jackson K. P. and Shaw H. J. Hight-speed pulse generator using single mode fiber reciculating delay lines. - Electron.Lett. vol. 19, p. 756, 1983.

 6. Copyright certificate N 571788, cl. G 04 F 13/02, 1973.

Claims (2)

 1. A device for recording the shape of a single optical and electrical pulsed signals, comprising a main optical circulation circuit connected to the main optical coupler, a beam splitter-splitter, an optical delay element, characterized in that an optical switch, photodetectors, an additional optical circulation circuit are introduced therein, connected to an additional optical coupler, a gate pulse generation unit and a sampling and storage unit, the beam splitter input being divided the carrier through the optical switch is connected to the information inputs of the device, the first and second outputs are with the main and additional optical couplers, respectively, the output of the additional optical coupler is directly, and the output of the main optical coupler through the optical delay element is connected to the first and second photodetector, respectively, the output of the second photodetector is connected to the first input of the sampling and storage unit, the output of the first photodetector through the gate generating unit with the second input ohm block sampling and storage, the output of which is the information output of the device. 2. The device according to claim 1, characterized in that the primary and secondary optical circuits are made on fiber optic cables (FOC) in the form of closed rings and have circulation periods determined by the length of the FOC in the ring T ₀ and T ₀ + Δt, respectively.

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