SU1764174A1 - Analog fiber-optic transmitting device - Google Patents

Abstract

The invention relates to optoelectronics and can be used in fiber optic transmission systems of analog information. The goal is to improve noise immunity by eliminating non-linear distortion. The device contains end LED 1, pump amplifier 2, photodiode 3, photocurrent amplifier 4, optical coupler 5, Peltier micro cooler 6, sinusoidal signal generator 7, nonlinear element 8, band pass filters 9 and 10, multiplier 11, amplifier 12 and adder 13. 3 silt

Description

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The invention relates to optoelectronics and can be used in fiber-optic transmission systems of analog information, implemented on the principle of direct modulation of the radiator by the transmitted analog signal.

An analog fiber-optic transmitting device is known, which contains a pump amplifier, a transmitter, a feedback photodiode with a photocurrent amplifier and a fiber optic coupler connected to the radiator, and the photocurrent amplifier is connected to the input of the pump amplifier in such a way that a negative optical feedback is formed ( application of Germany No. 3726243, class H 01 S3 / 10, 1989).

A disadvantage of the known device is the low throughput of the communication channel organized with its help, due to the increased level of nonlinear distortion due to the small stability margins in broadband systems with chains of common negative feedback.

The closest in technical essence to the present invention is a fiber-optic transmitting device containing a semiconductor laser, a Peltier microcooler, a pump amplifier, a feedback photodiode, a band-pass optical filter, and three processing circuits (German Application No. 3542090, class H 01 S 3 / 10, 1987). The presence of processing schemes that control the level of laser noise and the mismatch of the laser wavelength emitted by the laser from the center frequency of the passband of the filter makes it possible to establish such a constant component of the forward current through the semiconductor laser in order to achieve a wavelength stability no worse than

u; 9.

A disadvantage of the known device is the impossibility of its use for linearization of the amplitude characteristic of analog fiber-optic transmitting devices, the emitting diode of the 1.3 µm range is used as emitters. This is due to the absence in the known device of linearization circuits of the amplitude characteristic and the use of laser noise as a regulating magnitude.

The purpose of the invention is to improve the noise immunity of an analog fiber-optic transmitting device on an end LED of the 1.3 µm range by eliminating non-linear distortion.

To achieve this goal, an analog fiber-optic transmitting device containing serially connected pump amplifier, 1.3 µm end LED and optical coupler, the first output of which is a device output, sequentially connected feedback photodiode and photocurrent amplifier the second output of the coupler is connected to the input of the photodiode, and the micro-refrigerator

0 Peltier, on which the end LED is mounted, introduced in series a sinusoidal signal generator, a nonlinear element, the first band-pass filter tuned to the second

5 harmonic frequency generator, a multiplier and a current amplifier, as well as an adder and a second band-pass filter tuned to the second harmonic of the generator frequency. The output of the photocurrent amplifier is connected to the second input of the multiplier through the second bandpass, the output of the current amplifier is connected to the control input of the Peltier microrefrigerator, the output of the sinusoidal signal generator is connected to the first input of the adder pump. The second input of the adder is the input of the device, and the frequency of the generator of the sinusoidal signal is higher than the upper frequency of the spectrum of the information signal.

FIG. 1 shows the structural scheme of the proposed analog fiber-optic transmitting device; in fig. 2 — the energy characteristics of the end LED of the 1.3 μm range obtained by the authors, measured at different crystal temperatures; in fig. 3 - oscillograms of signals at various points in the analog fiber optic transmitting device circuit.

The analog fiber optic transmitting device comprises an end LED 1, a pump amplifier 2, a feedback photodiode 3 with a photocurrent amplifier 4,

5 optical coupler 5, Peltier micro cooler 6, sine wave generator 7, nonlinear element 8, first 9 and second 10 band-pass filters that are tuned to the second harmonic of generator 7,

0 multiplier 11 analog signals, amplifier 12 current through the Peltier micro-refrigerator 6 and adder 13 of the signal generator 7 and the input signal of the device.

The device works as follows.

A single-frequency signal (diagram 1 in Fig. 3) from the output of the generator 7 is fed to the input of the pump amplifier 2 and to the nonlinear element 8, as which can be used the usual semiconductor

diode. The volt-ampere characteristic of a semiconductor diode, regardless of the temperature of its crystal, has the form of a convex downward function, whereby when setting the operating point in the forward current region, the second harmonic signal on the nonlinear element 8 removed from the output of the first band-pass filter 9 will look like shown in diagram 2 of FIG. 3

The character of the convexity of the function describing the energy characteristics of end 1.3-µm LEDs (GaAIAsP system) determines the temperature dependence of the amplification factor of spontaneous photons in the bulk of the structure and the intensity of nonradiative Auger recombination. At the same time, as the temperature decreases, the gain of the spontaneous photons increases and the energy characteristic becomes superlinear, i.e. takes the form of a convex downward function. As the temperature increases, the Auger recombination rate begins to increase and the energy characteristic becomes sublinear, i.e. takes the form of a convex up function. For LEDs with a working wavelength of 1.3 µm, Auger recombination starts to manifest at temperatures above 270 K and the temperature at which the mechanisms under consideration compensate each other will lie within the range of operating temperatures. The type of the power characteristic of the end LED of the 1.3 μm range, depending on the temperature of its crystal, is shown in Fig. 2

The proposed device uses this circumstance to minimize non-linear distortion and improve noise immunity. For this, the output signal of the generator 7 is fed to the first input of the adder 13 and together with the information signal arriving at the second input of the adder 13 after amplification in the pump amplifier 2 modulates the emission intensity of the LED 1. To eliminate the effect of the information signal on the device, the frequency of the sinusoidal signal is selected above the upper frequency spectrum of the information signal.

A part of the optical output of the LED 1 passes through the optical tap 5 and is fed to the feedback photodiode 3. The photocurrent flowing through the photodiode 3, proportional to the output signal of the LED 1, is amplified by the amplifier 4 and is fed to the input of the second band-pass filter 10, which is configured, as well as the first band-pass filter 9, on

the second harmonic frequency generator 7 sinusoidal signal. If the temperature ti of the crystal of LED 1 is lower than the optimum temperature t2, at which nonlinear

signal distortion is minimal, the energy characteristic of the LED 1 has the form of a convex down function and the signal at the output of the second band-pass filter 10 has the form shown in diagram 4 of FIG.

0 3. As a result of multiplying both signals at the output of the multiplier 11, Vits is a positive voltage. This voltage is fed to the control input of the current amplifier 12 through the microcooler.

5 Peltier, the current through the microcooler is reduced and the LED 1 crystal is then heated to the optimum in terms of minimum non-linear temperature distortion t2

0 In the event that the temperature ts of the crystal of the LED 1 is higher than optimal, the signal at the output of the second POLESOPE filter 10 has the form shown in diagram 3 of FIG. 3. Output multiplier

5, a negative voltage arises, the current through the microcooler increases, and the crystal is cooled to an optimum from the point of view of the minimum of nonlinear temperature distortions t2.

0 Thus, the proposed analog fiber optic transmitting device allows to obtain minimal non-linear distortions of the transmitted signal in a wide range of operating temperatures, increase the noise immunity and achieve the goal.

Claims (1)

Analog fiber optic transmitting device containing successively connected pump booster, end LED and optical coupler, the first output of which is the device output, serially connected feedback photodiode and 5 photocurrent amplifier, the second output of the coupler is connected to the photodiode input, and the Peltier microcooler, the end LED is located on the Peltier microcooler, characterized in that 0 in order to reduce out-of-band emissions, a series-connected sinusoidal signal generator, nonlinear element, first band-pass filter, 5 tuned to the second harmonic frequency of the sinusoidal signal generator connected to the second input of the multiplier, the output of the current amplifier is connected to the control input of the Peltier micro-refrigerator, the output of the sinusoidal signal generator is connected to the first input of the adder, the output of which is connected to the input of the adder, Editor O. Stenina. Compiled by A.Semenov Tehred M. Morgental the output of which is connected to the input of the pump amplifier, the second input of the adder is the input of the device, and the frequency of the sinusoidal signal generator is higher than the upper frequency of the spectrum of the information signal. J F, S.3 Proofreader A.Dolinich