RU2778047C1 - Method for receiving optical signals - Google Patents

Abstract

FIELD: optical technology.

SUBSTANCE: invention relates to the reception of optical signals, in particular, to the technique of receiving signals using avalanche photodiodes. The method for receiving optical signals using an avalanche photodiode includes threshold signal processing and the formation of output pulses using a threshold device when the signal from the output of the photodiode exceeds the specified threshold of operation, while the offset voltage of the photodiode is increased from the initial level of U_offs1 to the operating level of U_offsM at a speed of

where ΔU_sm is the stage of regulation of the offset voltage in one control cycle; ΔT=KΔt the duration of the microplasma monitoring cycle;

is the number of control cycles in one cycle; p_p the confidence limit for estimating the probability of microplasma generation; t the reliability of determining p_p; Δt the duration of the microplasma check cycle; at the same time, in the process of regulation, the trigger threshold is continuously adjusted in the mode of noise automatic threshold adjustment, maintaining a preset threshold/noise ratio, and the presence of pulses exceeding the level corresponding to the amplitude of microplasmas is checked, when registering the first such pulse at the moment t_M, the avalanche multiplication coefficient M reached by this moment is set by fixing the offset voltage of the photodiode U_offsM(t_M), the threshold level is simultaneously fixed, after which receiving optical signals starts.

EFFECT: achieving the maximum sensitivity in all operating conditions, taking into account microplasma breakdowns and normal noise with a minimum time to reach the optimal avalanche mode.

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Description

The present invention relates to the reception of optical signals, in particular, to the technique of receiving signals using avalanche photodiodes, and can be used in location, communications and other photoelectronic systems.

A known method of receiving optical signals using avalanche photodiodes [1]. There are also known methods for stabilizing the avalanche mode of the photodiode, for example, by thermal compensation of the operating point of the bias voltage [2].

Closest to the proposed technical solution is a method for receiving pulsed optical signals using an avalanche photodiode, the bias voltage of which is maintained by stabilizing the frequency of noise pulses that occur in the photodiode during avalanche multiplication [3].

The disadvantage of this method is the possibility of introducing a photodiode into the microplasma breakdown mode [4]. Microplasma current pulses have a rectangular shape and a constant amplitude, which increases as the reverse voltage increases. An increase in the amplitude is accompanied by an increase in the duration of the pulses and a decrease in the duty cycle [5]. In this mode, the noise of the avalanche photodiode consists of two independent components - normal noise [6] and "telegraph" noise of microplasmas. The microplasma component of the photodiode noise is not statistically comparable with the normal component, and its participation in the process of controlling the photodiode bias is unpredictable [7]. Under certain temperature conditions, adjusting the avalanche mode according to the frequency of photodiode noise emissions, including microplasmas, can lead to the system reaching a non-optimal avalanche multiplication mode, i.e. to the deterioration of the threshold sensitivity of the photodetector or to the unacceptable probability of false alarms caused by microplasmas.

The objective of the invention is to achieve maximum sensitivity in all operating conditions, taking into account microplasmas and normal noise with a minimum time to reach the optimal avalanche mode.

- количество тактов контроля в одном цикле; р_в - доверительная граница оценки вероятности генерации микроплазмы; t - надежность определения р_в; Δt - длительность такта проверки наличия микроплазмы; при этом в процессе регулирования порог срабатывания непрерывно корректируют в режиме шумовой автоматической регулировки порога, поддерживая заданное отношение порог/шум, и проверяют наличие импульсов, превышающих уровень, соответствующий амплитуде микроплазм, при регистрации первого такого импульса в момент t_M устанавливают достигнутый к этому моменту коэффициент лавинного умножения М путем фиксации напряжения смещения фотодиода U_смМ(t_M), одновременно фиксируют уровень порога, после чего приступают к приему оптических сигналов.This problem is solved due to the fact that in the known method of receiving optical signals using an avalanche photodiode, including threshold processing of signals and the formation of output pulses using a threshold device, when the signal from the output of the photodiode exceeds a predetermined response threshold, the bias voltage of the photodiode is increased from the initial level U _cm1 to the operating level ϕ at a speed of S _cm =ΔU _cm /ΔT, where ΔU _cm is the stage of bias voltage regulation in one control cycle; ΔT=KΔt - duration of the microplasma presence control cycle;

- the number of control cycles in one cycle; p _in - confidence limit of the estimate of the probability of microplasma generation; t is the reliability of the determination of p _in ; Δt - the duration of the step of checking the presence of microplasma; while in the process of regulation, the response threshold is continuously corrected in the noise automatic threshold adjustment mode, maintaining the specified threshold/noise ratio, and the presence of pulses exceeding the level corresponding to the microplasma amplitude is checked, when registering the first such pulse at the moment t _M , the coefficient achieved by this moment is set avalanche multiplication M by fixing the bias voltage of the photodiode U _cmM (t _M ), at the same time fix the threshold level, and then start receiving optical signals.

раз, где f₀ - частота пересечения шумом нулевого уровня; f_п - установившаяся частота шумовых превышений порога в подготовительном режиме; f_p - заданная частота ложных тревог в рабочем режиме.Before receiving signals, the threshold can be increased by

times, where f ₀ - the frequency of crossing the noise level zero; f _p - steady frequency of noise exceeding the threshold in the preparatory mode; f _p - the specified frequency of false alarms in the operating mode.

In FIG. 1 shows a diagram of a photodetector device that implements this method. In FIG. 2a), b) - examples of the implementation of noise at the input of the threshold device. In FIG. 3 shows graphs of the signal-to-noise ratio ηM) for germanium (Fig. 3a) and silicon (Fig. 3b) avalanche photodiodes.

The photodetector implementing the method comprises an avalanche photodiode 1, an amplifier 2 and a threshold device 3 connected in series. The bias voltage is supplied to the photodiode 1 from a power source 4 and a bias enhancement circuit 5 connected in series. The threshold device 3 is covered by a feedback circuit in the form of a noise automatic threshold adjustment circuit. (SHARP) 6 connected between the output of the threshold device and its control input. The bias boost circuit 5 is controlled by the second threshold device 7 connected to the output of the amplifier 2. Mode synchronization is carried out by the control unit 8 associated with blocks 6 and 7.

The method is carried out as follows.

гдеOn command from the control unit 8, the bias increase circuit 5 and the SHARP circuit 6 are switched on. The bias increase circuit provides a gradual increase in the bias voltage at a rate of S _cm V/s. The Threshold Threshold device responds to an increase in the RMS value of normal noise

where

K _y - transmission coefficient of the path from the photodiode to the input of the threshold device;

- квадрат неумножаемого шумового тока;

is the square of the non-multipliable noise current;

e is the electron charge;

I ₁ - primary reverse current of the photodiode;

Δf is the bandwidth of the linear path to the input of the threshold device;

M - coefficient of avalanche multiplication;

M ^α - noise factor of avalanche multiplication;

α - coefficient determined by the material of the photodiode [6].

The speed (time constant) of the SHARP circuit must provide a constant threshold/noise ratio at a given rate of change

As the bias voltage of the photodiode increases, not only the normal component of the multiplied noise I _m ² increases, but also the probability of occurrence of microplasma breakdowns [7]. After registering the first microplasma using the second threshold device 7, the signal from the output of this device stops the increase in bias voltage, carried out by the bias increase circuit 5, and the threshold stabilization process, carried out by the SHARP circuit 6.

The required rate of rise of the bias voltage is determined as follows.

When assessing the probability p of a false event (generation of microplasma) by calculating the relative frequency of false events [10, p. 226] as the ratio w of the number m of false events and the total volume k of tests, there is a confidence limit p _in the probability estimate p for m=1.

where w=1/k;

t - confidence factor (reliability of the assessment); for example, a confidence level of 0.95 corresponds to a reliability of t=1.96 [10, p. 226].

From (3) follows the required amount of tests k=K at m=1 to ensure a given probability p _in with reliability t.

Example 1

p=0.0001; t=2.

According to (4) K=3 ⋅ 10 ⁴ .

Statistical volume K is required for each step ΔU _cm of bias voltage regulation.

Duration T ₁ control cycle at each stage ΔU _cm

where Δt is the duration of the cycle of checking the presence of microplasma, corresponding to the discreteness of measuring the delay of the received pulse.

Example 2

K= ¹⁰⁴ ; Δt=10 ^-8 s.

T ₁ \u003d 10 ⁴ ⋅ 10 ^-8 \u003d 10 ^-4 s.

Number Q steps of bias voltage regulation

where U _cm1 - the initial level of the bias voltage;

U _cmM - the maximum final level of the bias voltage.

Example 3

U _cm0 -U _cmM \u003d 20V: ΔU _cm \u003d 1 V.

Q=20/1=20.

The maximum time to reach the operating mode of displacement

Example 4

Under the conditions of examples 2-3

Т=20⋅10 ^-4 =2⋅10 ^-3 s.

раз [9], где f₀ - частота пересечения шумом нулевого уровня. Такой процесс стабилизации режима порогового устройства также занимает время не более 10^-3 с [9].If the process of stabilization of the threshold/noise ratio occurs at a frequency f _p of noise exceeding the threshold exceeding the frequency f _p of such events in the operating mode, then before switching to signal reception, the threshold is increased by

times [9], where f ₀ is the frequency of noise crossing the zero level. Such a process of stabilization of the threshold device mode also takes no more than 10 ^-3 s [9].

Thus, the proposed method provides the time to enter the regime of the order of T=1 ms and work with a maximum repetition rate of 1/T=1 kHz. Existing technical solutions [8] provide access to the mode in 1-6 s. The speed gain of the proposed method is 1000-6000 times.

удовлетворяющем требованиям по частоте микроплазм. При этом отношение сигнал/шум практически не ухудшается.Microplasmas can appear when the avalanche multiplication factor M is less than the optimal M _opt [6]. Fig. 2a) shows the implementation of noise at M=M _opt , and Fig. 2b) - at

meeting the requirements for the frequency of microplasmas. In this case, the signal-to-noise ratio practically does not deteriorate.

Example 5 (Fig. 3a).

germanium photodiode. I ₁ \u003d 10 ^-7 A. I _m ² \u003d 3.2⋅10 ^-19 A ² . α=1. The area of microplasmas starts from M=3.5. The operating point of the photodiode is maintained at M=2.5...3.5. In this case, the maximum signal-to-noise ratio provided by the method differs from the maximum value provided at M=M _opt = 3 by no more than 2%.

Example 6 (Fig. 3b).

Silicon photodiode. I ₁ \u003d 10 ^-9 A. I _m ² \u003d 3.2⋅10 ^-21 A ² . α=0.5. The area of microplasmas starts from M=25. The operating point of the photodiode is maintained at a factor of M=25, corresponding to the appearance of individual microplasmas. In this case, the maximum signal-to-noise ratio provided by the method differs from the maximum value provided at M=M _opt = 30 by no more than 2%.

It should be noted that discreteness Δt is not directly involved in the operations of the method, but determines only the duration T _1. Due to this, the method is easy to implement - a smooth increase in U _cm and waiting for the first microplasma, through which the preparatory mode switches to the working one.

Thus, the objective of the invention is ensured - the achievement of maximum sensitivity in all operating conditions, taking into account microplasma breakdowns and normal noise with a minimum time to reach the optimal avalanche mode.

Sources of information

1. Ross M. Laser receivers. - "Mir", M., 1969

2. Patent of the Russian Federation No. 2 248670. A device for switching on an avalanche photodiode in an optical radiation receiver. 2005

3 US Pat. 4,077,718. Receiver for optical radar. 1978. - prototype.

4. Filachev A.M., Taubkin I.I., Trishenkov M.A. Solid state photoelectronics. Physical bases. Moscow, Fizmatgiz. 2007.

5. Vishnevsky A.I., Rudenko V.S., Platonov A.P. Power ion and semiconductor devices. Textbook for universities. Edited by B.C. Rudenko. Moscow, Higher School, 1975.

6. Vilner V.G., Leichenko Yu.A., Motenko B.N. Analysis of the input circuit of a photodetector with an avalanche photodiode and anti-noise correction. Optical-mechanical industry, 1981, No. 9, - p. 59.

7. Shashkina A.S. Avalanche breakdown of a p-n-junction in radio engineering problems. - Scientific and technical bulletin of information technologies, mechanics and optics, 2016, volume 16, no. 5, p. 864-871.

8. Vilner V.G. Design of threshold devices with noise threshold stabilization. - Optical-mechanical industry, 1984, No. 5, p. 39-41.

9. RF patent No. 2718856. A method for automatically stabilizing the frequency of crossing the threshold level by noise process emissions, 2020

10. Gmurman V.E. Theory of Probability and Mathematical Statistics. Moscow, Higher School, 1977, - 480 p.

Claims (2)

1. A method for receiving optical signals using an avalanche photodiode, including threshold processing of signals and the formation of output pulses using a threshold device when the signal from the output of the photodiode exceeds a predetermined response threshold, characterized in that the bias voltage of the photodiode is increased from the initial level U _cm1 to the operating level U _cmm with speed

where ΔU _cm is the bias voltage regulation step for one control cycle; ΔТ=KΔt - duration of the microplasma presence control cycle;

- the number of control cycles in one cycle; p _in - confidence limit of the estimate of the probability of microplasma generation; t is the reliability of the determination of p _in ; Δt - the duration of the step of checking the presence of microplasma; while in the process of regulation, the response threshold is continuously corrected in the noise automatic threshold adjustment mode, maintaining the specified threshold/noise ratio, and the presence of pulses exceeding the level corresponding to the microplasma amplitude is checked, when registering the first such pulse at the moment t _M , the coefficient achieved by this moment is set avalanche multiplication M by fixing the bias voltage of the photodiode U _cmM (t _M ), at the same time fix the threshold level, and then start receiving optical signals. 2. The method according to p. 1, characterized in that before the start of signal reception, the threshold is increased by

times, where f ₀ - the frequency of crossing the noise level zero; f _p - steady frequency of noise exceeding the threshold in the preparatory mode; f _p - the specified frequency of false alarms in the operating mode.

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