KR101029755B1 - Optical transmitter using optoelectronic predistortion method - Google Patents

Abstract

An optical signal transmission apparatus of an optoelectronic line distortion method is disclosed. The first signal branch element branches an input signal supplied from the outside and outputs a first input signal and a second input signal. The second signal branch element branches the second input signal to output the third input signal and the fourth input signal. The first optical signal generating element is mounted in a TO-can to modulate and output the third input signal to the first optical signal. The optical signal detecting element is mounted in a thiocan and coupled to the first optical signal generating element and a stainless steel can (SUS-can). After detecting the first optical signal, the optical signal is output by photoelectric conversion. do. The first distortion signal generation circuit converts the phase of the fourth input signal to be 180 degrees from the phase of the detection signal, converts the magnitude of the fourth input signal corresponding to the magnitude of the detection signal, and converts the phase and magnitude. The fourth input signal and the detection signal are combined to output a first distortion signal included in the detection signal. The second distortion signal generation circuit converts the magnitude of the first distortion signal and combines it with the first input signal to generate a second distortion signal. The second optical signal generating element modulates the second distortion signal into a second optical signal and outputs it. According to the present invention, by using the SUS-can instead of the optical fiber it is possible to reduce the time delay of the optical signal transmission and to minimize the size of the entire optical signal transmission system.

Distortion Signal, Tiocan, SUS-can

Description

Optical transmitter using optoelectronic predistortion method

The present invention relates to an optical signal transmission apparatus of an optoelectronic line distortion method, and more particularly, to an apparatus for transmitting an optical signal by removing noise components and intermodulation distortion components by the optoelectronic line distortion method in an optical transmission system. .

With the advent of the information age, communication forms are evolving into the form of exchanging large-capacity multimedia data including voice, video, and text at the same time. Optical communication technology utilizes the high-speed, high-capacity signal transmission capability of optical fibers, and currently has low service coverage in pico cells or micro cells, mainly in areas with high population densities. We are developing a multimedia service using. The optical transmission and photoreception modules are all-optical and photoelectric conversion apparatuses using laser diodes and photodiodes as all-optical and photoelectric conversion elements, and are required to be compact and inexpensive for the spread of optical transmitters.

A general optical transmission system used in a wireless mobile communication system is an analog subcarrier multiplexing method that directly modulates and demodulates a plurality of RF signals to a light source simultaneously. The main disadvantage of the optical transmission system employing this method is that the analog signal is distorted by the nonlinearity of the system when the signal is transmitted through the optical transceiver and the optical fiber network. These nonlinear distortion components are expressed as intermodulation distortion (IMD). Due to the propagation characteristics in the optical path during the modulation of the semiconductor laser diode used inside the optical transmitter or the long-distance transmission of the optical output signal, new frequencies of the form f _i + f _j and f _i + f _j ± f _k Non-linear components have. And these nonlinear frequency components distort the analog signal and fall within the transmission bandwidth, which degrades the performance of the system. In particular, the intermodulation and dynamic range of the optical transmission system are severely limited by the light source of the optical transmitter. Therefore, a technical breakthrough for solving the nonlinearity problem of an analog optical transmission / reception link is required in a micro / pico cell technology requiring a large number of mobile base stations due to the rapid increase in mobile communication users.

Optical communication is the transmission and reception of information through optical fibers through light. The optical communication system as shown in FIG. 1 is largely composed of a transmitter 110, a transmitter 120, and a receiver 130. The transmitter 110 is an all-optical conversion element (that is, a light source) that converts an electrical signal into an optical signal, and a device in which a laser diode, a light emitting diode, or a laser diode and an external modulator are combined is employed. The transmitter 120 is a light transmitting means such as an optical fiber. The receiver 130 is a photoelectric conversion element (that is, a photo detector) that converts an optical signal into an electrical signal, and includes a PN photodiode, a PIN photodiode, an avalanche photodiode, a phototransistor, and the like. Are employed.

In the conventional optical communication device as described above, since the signal containing the nonlinear distortion component is transmitted from the light emitting device of the transmitter 110 to the optical detector of the receiver 130 as it is, the optical communication 120 requires most information. Not suitable for networks To solve this problem, a back-off method using a laser diode with better performance than the one to be used, and extracts only the distortion component of the laser diode to generate a signal having the same magnitude and opposite phase as the distortion signal of the main signal. Therefore, a feedforward method for removing only the distortion signal and a line distortion method for generating a signal having the same magnitude and opposite phase as the distortion signal included in the main signal and removing the distortion signal have been proposed. 2 and 3 illustrate a structure of a distortion signal removing device of a line distortion method using a conventional feed forward method and an electric circuit, respectively.

However, the back-off method does not have a high performance improvement compared to the price, and there is a limit in manufacturing a high efficiency laser diode. In addition, the conventional feed forward method increases the size of the device due to the large number of elements required, and it is difficult to apply it to an actual system because of the complexity of the system. There is a limit. Furthermore, in the conventional line distortion method, since the frequency response characteristics of the electric circuit and the laser diode for generating the line distortion signal are different, the characteristics are changed according to external changes, and thus the degree of linearity improvement is changed. There is a limit of linearization degree to 10dB. In addition, the coaxial cable is used as a delay line for canceling the difference in signal delay time transmitted along different paths, which makes it difficult to control the signal delay time and increases the size of the entire apparatus.

An object of the present invention is to provide an optical signal transmission device that is excellent in linearity, can efficiently transmit signals by reducing time delay, and can minimize the size of a system.

In accordance with another aspect of the present invention, there is provided an optical signal transmission apparatus of an optoelectronic ray distortion method, comprising: a first signal branch device for branching an input signal supplied from the outside to output a first input signal and a second input signal; A second signal branch element for branching the second input signal to output a third input signal and a fourth input signal; A first optical signal generating element mounted in a thiocan to modulate and output the third input signal to a first optical signal; An optical signal mounted in a TO-can and coupled to the first optical signal generating element and a stainless steel can (SUS-can), and detecting the first optical signal and then performing photoelectric conversion to output a detection signal. Detection element; Converts the phase of the fourth input signal to be 180 degrees different from the phase of the detection signal, converts the magnitude of the fourth input signal corresponding to the magnitude of the detection signal, and converts the phase and magnitude A first distortion signal generation circuit for combining the input signal with the detection signal to output a first distortion signal included in the detection signal; A second distortion signal generation circuit for converting the magnitude of the first distortion signal and combining the first distortion signal to generate a second distortion signal; And a second optical signal generator for modulating the second distortion signal into a second optical signal, and outputting the second optical signal generator, wherein the second distortion signal generation circuit measures the magnitude of the first distortion signal in the second optical signal generator. Converts to the magnitude of the distortion signal detected in the modulated signal.

According to the optical signal transmission device of the optoelectronic line distortion method according to the present invention, the optical signal generating element and the optical signal detecting element, which are conventionally connected by optical fibers, are integrated in a thiocan and combined by a stainless steel can of which length is minimized. It can reduce the time delay of signal transmission and minimize the size of the entire optical signal transmission system.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the optical signal transmission device of the optoelectronic beam distortion method according to the present invention.

First, a method using a line distortion signal, which is a linearization method used in the optical signal transmission apparatus according to the present invention, will be described.

4 is a diagram for explaining a linearization principle using a line distortion signal. Nonlinear distortion occurs when the RF signal, which is the original signal, is directly modulated by the laser diode LD, which is a nonlinear device. Referring to FIG. 4, an RF signal which is an original signal is directly modulated by the sub laser diode SLD to generate a line distortion signal. These linear distortion signals and nonlinear distortion components due to LD cancel each other out when the magnitude is the same and the phase difference is 180 degrees.

In this way, when the relation of the optical power magnitude P according to the LD input current I ₁ is expressed as a third-order polynomial using the coefficient a, it is expressed as Equation 1 below.

If the size of an input current (I ₁₎ equal to A and the frequency of using the f ₁ and f _2, respectively, the RF signal may be expression of the input current (I ₁₎ expressed by the following equation (2).

Where ω ₁ and ω ₂ are the angular frequencies for f ₁ and f ₂ , respectively.

The magnitude of the optical power output by the LDs from the equations (1) and (2) is equal to the following equation (3).

이고, 이를 제어하기 위해 입력전류를 선 왜곡시킨 신호(I₂)는 다음의 수학식 4와 같이 주파수가 2f₁-f₂ 및 2f₂-f₁, 크기가 B이고 위상변화가 φ인 IMD3 성분을 가진다.Here, the magnitude of the third order intermodulation distortion component (IMD3 component), which is a nonlinear component,

In order to control this, the signal I ₂ pre-distorted with the input current has an IMD3 component having a frequency of 2f ₁ -f ₂ and 2f ₂ -f ₁ , a magnitude of B, and a phase change of φ as shown in Equation 4 below. Has

The IMD3 component among the optical power magnitudes of the LD by the original signal I ₁ and the line distorted signal I ₂ is expressed by Equation 5 below.

및

의 조건을 만족할 때 비선형 성분이 제거되어 높은 성능 향상을 볼 수 있다.Referring to Equation 5,

And

When the condition is satisfied, the nonlinear component is removed to show a high performance improvement.

5 is a block diagram showing the configuration of a preferred embodiment of the optical signal transmission apparatus of the optoelectronic line distortion method according to the present invention.

Referring to FIG. 5, the optical signal transmission apparatus according to the present invention includes a signal branch unit 510, an optical component unit 520, a first distortion signal generation circuit 530, and a second distortion signal generation circuit 540. .

The signal branch unit 510 includes a first signal branch element 512 and a second signal branch element 514. The first signal branch element 512 branches the input signal supplied from the outside to output the first input signal and the second input signal. The second signal branch element 514 branches the second input signal to output the third input signal and the fourth input signal. As the signal branching elements 512 and 514, a divider which is a passive element for branching or combining electrical signals is used. In the present invention, a power divider that operates in a desired frequency band includes a high frequency monolithic integrated circuit (MMIC). It can be produced in the form of. The first to fourth input signals are input to the optical component unit 520, the first distortion signal generation circuit 530, and the second distortion signal generation circuit 540 and used to remove the distortion signal.

The optical component unit 520 includes a first optical signal generator 522, an optical signal detector 524, and a second optical signal generator 526.

The first optical signal generating element 522 modulates and outputs the third input signal branched by the second signal branching element 514 into a first optical signal, and the second optical signal generating element 526 is provided according to the present invention. Outputs the final output signal of the optical signal transmitter according to the invention. Laser diodes are used as the first optical signal generator 522 and the second optical signal generator 526. The optical signal detecting element 524 detects the first optical signal, photoelectrically converts the detected first optical signal and outputs the detection signal. As the optical signal detecting device 524, a PN photodiode, a PIN photodiode, an Everanche photodiode, a phototransistor, or the like is used. In addition, the first optical signal generating element 522 and the optical signal detecting element 524 are integrated in a package of a thiocan type and disposed on a dielectric substrate, and are formed through a stainless steel can (hereinafter referred to as SUS-can). Combined.

The conventional optical signal generating device and the optical signal detecting device are connected by an optical fiber, and even if the length of the optical fiber is shortened as much as 20 cm to 30 cm, the size of the optical signal transmission system becomes large. However, if the optical signal generating element and the optical signal detecting element can be directly connected by means other than the optical fiber, the optical signal transmitting apparatus can be implemented with a minimized size.

FIG. 6 illustrates a first optical signal generator 522 and an optical signal detector 524 mounted in a thiocan and coupled through a SUS-can. Referring to FIG. 6, the first optical signal generating element 522 and the optical signal detecting element 524 are respectively integrated in the thiocans 610 and 620, and each of the thiocans 610 and 620 is formed of SUS-can ( 630 is compactly coupled. SUS-can performs a function of fixing the first optical signal generating element 522 and the optical signal detecting element 524, and the position between the first optical signal generating element 522 and the optical signal detecting element 524 is This is because the signal is not transmitted correctly when it is misaligned, causing problems in optical communication. As such, when the first optical signal generator 522 and the optical signal detector 524 are coupled through the SUS-can, the length of the SUS-can can be shortened to at least 1.5 cm, compared to the case where the optical fiber is connected by an optical fiber. The size of the optical signal transmission system can be minimized. 6 shows an actual implementation of a module in which the first optical signal generating device 522 and the optical signal detecting device 524 are mounted in the thiocans 610 and 620 and combined by the SUS-can 630. .

The first distortion signal generation circuit 530 converts the phase of the fourth input signal to be 180 degrees from the phase of the detection signal, and converts the magnitude of the fourth input signal corresponding to the magnitude of the detection signal. The fourth input signal whose magnitude is converted and the detection signal are combined to output the first distortion signal included in the detection signal. To this end, the first distortion signal generation circuit 530 includes a first size adjusting unit 532 and a hybrid coupler 534. In addition, the first distortion signal generation circuit 530 is each RF component is manufactured in the form of a high frequency single integrated circuit.

The first size adjusting unit 532 is electrically coupled to the second signal branch element 514 and branched by the second signal branch element 514 to match the strength of two signals input to the hybrid coupler 534. 4 The magnitude of the input signal is attenuated by the magnitude of the detection signal. This is because a nonlinear component included in the detection signal can be extracted by combining a signal having the same magnitude as that of the detection signal and the opposite phase with the detection signal. The attenuation amount of the fourth input signal is determined from the ratio of the intensity of the detection signal to the intensity of the fourth input signal. Further, the ratio of the intensity of the detection signal to the intensity of the signal of the fourth input signal is experimentally determined by operating characteristics related to signal attenuation of the first optical signal generating element 522 and the optical signal detecting element 524. As a device for attenuation, a mechanical attenuator, an electrical attenuator, or the like may be used.

Next, the hybrid combiner 534 converts the phase of the output signal of the first size adjusting unit 532 to be 180 degrees from the phase of the detection signal, and combines the detection signal to output the first distortion signal. The hybrid coupler 534 may use a 180 ° hybrid coupler. The 180 ° hybrid coupler is a device that allows the phases of two signals to differ by 180 ° when two signals with the same phase come in. The 180 ° hybrid coupler is operable in a frequency range of 1.3 GHz to 2.6 GHz and has an error range of about 0.4 dB in the magnitude of the signal and about 8 ° in the phase difference. However, by using two 90 ° hybrid couplers instead of the 180 ° hybrid coupler as the hybrid coupler 534, the phase difference between the two signals may be 180 °. Referring to FIG. 5, the magnitude and phase of two signals coupled and adjusted to have opposite phases by the hybrid combiner 534 may be confirmed. Finally, the first distortion signal output from the hybrid combiner 534 corresponds to a nonlinear component included in the detection signal. This nonlinear component is used to remove the distortion component of the signal which is combined with the first input signal and modulated by the second optical signal generating element 526.

As described above, even if the distance between the first optical signal generating element 522 and the optical signal detecting element 524 is combined by SUS-can to minimize the distance between the two, there is a minimum distance of 1.5 cm due to a process problem. There may be some phase delay. As a result, when the phase difference between the output signal of the first size adjusting unit 532 and the detection signal adjusted by the hybrid coupler 534 is not exactly 180 °, the first size adjusting unit 532 and the hybrid coupler 534 may be replaced. The phase difference may be adjusted to 180 ° by adjusting the length of the first delay line 550 to be electrically coupled.

That is, the length of the first delay line 550 passes through the detection signal generated by the time delay characteristics of the first optical signal generating element 522 and the optical signal detecting element 524 and the first delay line 550. The phase difference corresponding to the difference in time delay of the output signal of the first scale controller 532 is determined to fall within the phase shift range of the hybrid coupler 534. Since the distance between the first optical signal generating element 522 and the optical signal detecting element 524 is minimized, the length of the first delay line 550 can also be significantly shortened as compared with the conventional optical signal transmitting apparatus.

7 is a graph illustrating the phases of two signals input to the hybrid coupler 534. Referring to FIG. 7, it can be seen that the phase difference between the detection signal output from the optical signal detecting element 524 and the signal passing through the first delay line 550 is 180 °.

The second distortion signal generation circuit 540 converts the magnitude of the first distortion signal and combines the first distortion signal to generate a second distortion signal. To this end, the second distortion signal generation circuit 540 includes an amplifier 542, a second size controller 544, and a signal combiner 546. Like the first distortion signal generation circuit 530, each of the second distortion signal generation circuit 540 may be manufactured in the form of a high frequency single integrated circuit.

The amplifier 542 amplifies the first distortion signal and outputs the first distortion signal to the second scale controller 544. If the magnitude of the first distortion signal corresponding to the non-linear component included in the detection signal is too small, it is difficult to perform a subsequent signal processing process, so that the magnitude of the first distortion signal is amplified and then adjusted.

The second size adjusting unit 544 modulates the output signal of the amplifying element 542 to the magnitude of the distortion signal detected in the signal modulated by the second optical signal generating element 526 and outputs the modulated signal. When the first input signal is input to the second optical signal generator 526 via the second delay line 560, the distortion signal is generated while being modulated by the second optical signal generator 526. In order to remove the distortion signal, the output signal of the amplifying element 542 is adjusted to be equal to the magnitude of the distortion signal according to the characteristics of the second optical signal generating element 526, thereby the second optical signal generating element 526. When coupled to the first input signal is input to the distortion signal included in the signal modulated by the second optical signal generating element 526 can be canceled and eliminated. However, in order to cancel the distortion signal, the phase of the output signal of the second size adjusting unit 544 coupled to the first input signal is a distortion signal generated by the second optical signal generating element 526, that is, in the case of the present invention The phase of the first input signal must have a difference of 180 °.

Referring to the magnitude and phase of the signal passing through each element shown in FIG. 5, the first distortion signal and the second delay line, which are amplified by the amplifier 542 and adjusted by the second scaler 544, are adjusted. It can be confirmed that the phase of the first input signal passing through 560 is reversed. Accordingly, the second distortion signal generation circuit 540 does not have to include a device for inverting phase. However, the phase difference may be adjusted by adjusting the length of the second delay line 560 so that the phase difference between the output signal of the second size adjusting unit 544 and the first input signal does not become 180 °.

The length of the second delay line 560 that electrically couples the first signal branch element 512 and the signal combiner 546 is generated by the time delay characteristics of the amplifier 542 and the second size adjuster 544. The phase difference corresponding to the difference in time delay between the output signal of the second size adjusting unit 544 and the first input signal passing through the second delay line 560 is determined to be 180 degrees.

The output signal and the first input signal of the second size adjusting unit 544 whose phase difference is reversed by the length adjustment of the second delay line 560 are combined by the signal combining unit 546 and output as the second distortion signal. . The magnitude of the output second distortion signal is equal to the magnitude of the distortion signal included in the signal modulated by the second optical signal generating element 526, and the phases are opposite to each other.

Finally, the second optical signal generating element 526 modulates the second distortion signal into the second optical signal and outputs the second optical signal. Since a signal having the same magnitude and opposite phase as the nonlinear component generated when the first input signal is modulated by the second optical signal generator 526 modulates the second distortion signal generated by being coupled to the first input signal, Nonlinear components are canceled out. This can be confirmed from the magnitude and phase of the signal shown in FIG.

FIG. 8 is a graph showing the magnitudes of the non-linear components included in the optical signal generated by the first input signal being modulated by the second optical signal generating elements 526 and LD2 and the output signal of the second scale controller 544. . Referring to FIG. 8, it can be seen that the aspect of the change in the magnitude of the two signals according to the frequency change is similar. In particular, in the frequency range of 2.0 to 2.4 GHz, since the magnitudes of the two signals are almost the same, the removal performance of the nonlinear component is the corresponding frequency. It can be seen that it is excellent in the range.

9A and 9B are graphs showing the results of performing signal linearization in the frequency range of 1.9 to 2.6 GHz. Referring to FIG. 9A, it can be seen that the magnitude difference between the third order intermodulation distortion component (IMD3 component) included in the linearized signal and the signal without the nonlinear component is larger than that of the linearized signal. . This means that the linearity of the signal is excellent when the nonlinear component is removed by the first distortion signal generation circuit 530 and the second distortion signal generation circuit 540 in the optical signal transmission apparatus according to the present invention. In addition, referring to Figure 9b, it can be seen that the frequency range in which the size of the reduced IMD3 component is 10dB or more is in the range of 1.97 ~ 2.48GHz, and thus it is possible to obtain a performance improvement of 10dB or more over the conventional range in the 510MHz range.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific preferred embodiments described above, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

1 is a view showing the configuration of a general optical transmission and reception system;

2 is a diagram illustrating a configuration of a feedforward distortion signal removing device in a general optical transmission / reception system;

3 is a view showing the configuration of a distortion signal removing device of the line distortion method using an electric circuit in a general optical transmission and reception system;

4 is a view for explaining a linearization principle using a line distortion signal;

5 is a block diagram showing the configuration of a preferred embodiment of the optical signal transmission device of the optoelectronic line distortion method according to the present invention,

6 is a view showing a first optical signal generating element and an optical signal detecting element mounted in a thiocan and coupled through SUS-can;

7 is a graph illustrating phases of two signals input to a hybrid coupler;

FIG. 8 is a graph showing the magnitudes of the nonlinear components included in the optical signal generated by modulating the first input signal by the second optical signal generating element and the output signal of the second scale controller;

9A and 9B are graphs showing the results of linearization of signals in the frequency range of 1.9 to 2.6 GHz.

Claims (6)

A first signal branch element for branching an input signal supplied from the outside to output a first input signal and a second input signal; A second signal branch element for branching the second input signal to output a third input signal and a fourth input signal; A first optical signal generating element mounted in a thiocan to modulate and output the third input signal to a first optical signal; An optical signal mounted in a TO-can and coupled to the first optical signal generating element and a stainless steel can (SUS-can), and detecting the first optical signal and then performing photoelectric conversion to output a detection signal. Detection element; Converts the phase of the fourth input signal to be 180 degrees different from the phase of the detection signal, converts the magnitude of the fourth input signal corresponding to the magnitude of the detection signal, and converts the phase and magnitude A first distortion signal generation circuit for combining the input signal with the detection signal to output a first distortion signal included in the detection signal; A second distortion signal generation circuit for converting the magnitude of the first distortion signal and combining the first distortion signal to generate a second distortion signal; And And a second optical signal generator for modulating and outputting the second distortion signal to a second optical signal. The second distortion signal generation circuit converts the magnitude of the first distortion signal into a magnitude of a distortion signal detected in a signal modulated by the second optical signal generating element. Device. The method of claim 1, The first distortion signal generation circuit, A first size adjusting unit converting the magnitude of the fourth input signal into a magnitude of the detection signal and outputting the converted magnitude; A first delay line electrically coupled to the first size adjusting unit and converting a phase of the fourth input signal to be equal to a phase of the detection signal; And A hybrid combiner for converting the phase of the output signal of the first size adjusting unit passing through the first delay line so as to be 180 degrees from the phase of the detection signal, and combining the detection signal to output the first distortion signal. Optical signal transmission apparatus of the optoelectronic ray distortion method comprising a. 3. The method of claim 2, The length of the first delay line is the length of the detection signal generated by the time delay characteristics of the first optical signal generating element and the optical signal detecting element and the output signal of the first size adjusting unit passing through the first delay line. And a phase difference corresponding to a difference in time delay falls within a phase shift range of the hybrid coupler. The method according to any one of claims 1 to 3, The second distortion signal generation circuit, An amplifier for amplifying and outputting the first distortion signal; A second size adjusting unit converting the magnitude of an output signal of the amplifying element into a magnitude of a distortion signal detected in a signal modulated by the second optical signal generating element; A second delay line electrically coupled to the first signal branch element, for converting a phase of the first input signal to be equal to a phase of an output signal of the second scale controller; And And a signal combiner configured to combine the output signal of the second size adjusting unit passing through the second delay line with the first input signal to output the second distortion signal. Signal transmitter. The method of claim 4, wherein The length of the second delay line is a time delay of the output signal of the second size adjusting unit and the first input signal passing through the second delay line generated by the time delay characteristic of the amplifier and the second size adjusting unit. The optical signal transmission device of the opto-ray distortion method, characterized in that the phase difference corresponding to the difference is determined to be 180 degrees. The method according to any one of claims 1 to 3, And the first distortion signal generation circuit is made of a high frequency single integrated circuit.

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