JP3157254B2 - Manufacturing method of equalizer for high frequency communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an equalizer which constitutes a demodulation system of an optical communication system using a single mode fiber in a backbone communication line, for example, on the ground or in the sea.
More specifically, the present invention relates to a method for manufacturing an equalizer for a high-frequency communication system applied to optical communication for transmitting information at an ultra-high transfer rate of, for example, 10 Gbits / s.

[0002]

2. Description of the Related Art FIG. 10 shows an optical communication system of this type.
1 shows an example of a system configuration of coherence communication which is one of the two methods. As shown in the figure, an optical signal 1 input from a modulation system and including communication information is supplied to a demodulation system 8 via an optical transmission line 2 composed of a single mode fiber, and received as an output signal 3 as an electric signal. Supplied to the system.

Here, the demodulation system 8 is connected to the optical transmission line 2.
5 that mixes the optical signal from the optical transmitter with the local light signal 4 and photoelectrically converts it into an electric signal of several hundred GHz, an equalizer 6 for compensating and reproducing waveform distortion of the output of the light receiver 5, and a communication signal. The demodulator 7 is generally constituted.

In this case, the equalizer 6 is provided because the electric signal from the light receiver 5 retains the dispersion generated in the optical signal propagating through the optical transmission line 2 as it is. This is because the waveform distortion needs to be reproduced and compensated for in the signal state.

FIG. 11 shows an example of dispersion characteristics of a single mode fiber constituting the optical transmission line 2. As shown in FIG. 11, in the case of the present fiber, the relative delay time ns at a wavelength of 1.3 μm. / Km is 0, in other words, there is no dispersion in the wavelength band. However, the wavelength band with the lowest transmission loss is 1.5
Since it is 5 μm, the optical signal is usually used in the 1.55 micron wavelength band.

On the other hand, when an optical signal propagates in a fiber with a wavelength band of 1.55 μm as a carrier, the propagated optical signal has a relative delay time depending on the wavelength, as shown in FIG. Occurs. The dispersion characteristic of the fiber is 15 ps / km / nm, and at a wavelength of 1.55 μm, it becomes 125 GHz after mixing.
The optical signal propagated through 00 km is subjected to photoelectric conversion, and the electric signal contains waveform distortion corresponding to a relative delay time of about 24 ps / GHz.

In order to compensate for such waveform distortion by reproduction, 2
An equalizer composed of a wideband delay line having a linear frequency dispersion of 4 ps / GHz is required. Further, the frequency band required for such an equalizer is twice the transfer rate, for example, 10 GBits / s at present, so that a delay line that can be used in a wide band of at least 20 GHz is required.

Conventionally, as this type of equalizer, there has been known an equalizer comprising a microstrip type delay line as shown in FIG. As shown in the figure, the equalizer comprises a central conductor 9 made of a normal metal thin film, a 5 cm × 5 cm dielectric substrate 10 to which the center conductor 9 is attached, and a normal metal thin film supporting the dielectric substrate 10. And a ground plane 11.

In this case, in order to avoid frequency dispersion due to coupling on the λ / 4 side, the interval between lines is widened to about 10 mm, and the line length is approximately 21 cm.

FIG. 13 shows the frequency characteristic of the relative delay time of the equalizer configured as described above. As shown in the figure, the relative delay time linearly increases with an increase in the frequency.

This is mainly due to the fact that in the microstrip structure, the high-frequency mode changes from the quasi-TEM to the TM mode as the frequency increases, so that the effective permittivity near the center conductor changes accordingly.

The dispersion characteristic of the fiber is 0.12 ps / GH
z / km, assuming a transfer rate of 10 GBits / s, 2.4 ps / k in a band of 5 to 20 GHz.
m, a relative delay time that varies linearly with frequency is required. Therefore, as shown in FIG. 13, when the line length L of the delay line is 6 cm, the dispersion of the transmission line of about 30 km is
When the line length L is 21 cm, the dispersion of the approximately 100 km fiber can be compensated for reproduction.

[0013]

However, in the equalizer having the above-mentioned conventional configuration, the applicable maximum frequency is the cut-off frequency of the TE mode having the microstrip structure, which is 3 dB lower than that of DC. Assuming that the transfer rate is 10 GBits / s and the fiber dispersion is 15 ps / km / nm because the frequency is determined by the frequency, the fiber length is 256 km even when the delay line is made of an ideal normal metal. Can only deal with things.

Accordingly, since the equalizer using a normal metal conductor as described above has a large loss and a relatively low cutoff frequency, it is applied to a long-distance repeaterless optical transmission communication system having a high transfer rate. Had technical limitations.

In the conventional equalizer, although a relatively large dielectric substrate having a size of 5 cm × 5 cm is used, only a line length of about 20 cm is obtained in order to prevent line-to-line coupling. As a result, a single equalizer can only compensate for reproduction of a fiber dispersion of 100 km.

Furthermore, in order to equalize the optical fiber line dispersion, the frequency dispersion of the delay time using the mode change with the increase in the frequency is performed. Therefore, it is necessary to change the line length of the delay line according to the situation, and the degree of freedom in design is small.

The present invention has been made to solve the above-mentioned problems of the prior art, and is applicable to an optical communication system capable of long-distance transmission at a high transfer rate and can be applied to a wide band with low loss. It is an object of the present invention to provide a method for manufacturing an equalizer for a demodulation system.

[0018]

According to the present invention, there is provided a method of manufacturing an equalizer for a high-frequency communication system, wherein a high-frequency signal delay line is interposed between a pair of ground planes and a dielectric on one of the ground planes. A method of manufacturing an equalizer for a high-frequency communication system configured by a strip line structure provided as a conductor on a substrate, or a microstrip structure provided as a conductor on a dielectric substrate on one ground plane, While at least the conductor is formed of a superconducting thin film, the entire signal path of the high-frequency signal delay line is meandered, and the signal path is formed of a number of basic unit coupled lines formed in a meander shape, It is characterized in that the degree of coupling of the coupling line is adjusted by adjusting the mutual interval between the coupling lines to obtain a wide range of relative delay time.

[0019]

Since at least the center conductor is made of an oxide superconducting thin film, low loss can be realized, the entire delay line is formed in a meandering state, and the basic unit coupling line constituting the delay line is formed in a meander shape. Therefore, miniaturization can be realized, the degree of coupling of the transmitted high-frequency signal can be set to an appropriate value, and the signal delay line can have frequency dispersion, so that the relative required for the equalizer can be set. A delay time can be obtained, thereby enabling reproduction compensation of optical fiber dispersion over a wide band.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a method of manufacturing an equalizer according to the present invention.
This figure shows the configuration of the applied equalizer, and FIG.
As shown in (b), the arrangement of the high-frequency delay line is a strip line structure. The center conductor pattern 15
Is formed in a meandering state in which a square well type is repeated, and as shown in an enlarged portion 14 of FIG. 3C, its signal path is formed of a number of basic unit coupling lines 20 and 21 formed in a meander shape. , 22 and the like. Here, the center conductor 15 is formed of an oxide superconducting thin film.

One end of the center conductor 15 is an input section 12 and the other end is an output section 13. The center conductor 15 is mounted on a dielectric substrate 19 on a lower ground plane 17, and is located above the center conductor 15. Is provided with an upper ground plane 16 having a dielectric substrate 18.

Here, the center conductor is 0.16
An EuBaCuO oxide superconducting thin film having a width of 2 mm is used, a copper thin film having a thickness of 3 μm is used as a ground plane, and the dielectric substrates 18 and 19 are, for example, 0.5 mm thick and 2.5 mm thick.
A 4 cm × 2.54 cm MgO substrate is used.

As described above, the signal path is composed of the basic units of the coupling lines 20, 21, 22 and the like. Assuming that the total length of the signal path is 28 cm and the length of the basic unit of the coupling line is 1 mm, The frequency at which the first dispersion peak appears using this coupled line as a λ / 4 coupler is about 24 GHz.

Further, the line interval of the coupling line is set to 0.64.
mm, the degree of coupling of the coupling line is about 24 dB from the relationship shown in FIG. Further, the delay time per unit length in this coupled line is about 8.9 from the relationship shown in FIG.
ns / m. Further, from the relationship shown in FIG. 3, the relative delay time can be obtained by about 25%, and the total length of the effective coupling line is about 1%.
Considering that the distance is 5 cm, 8.9 ns / m × 0.
15m × 0.25 = 330ps relative delay time 20G
It can be expected in the band below Hz.

The degree of coupling can be easily adjusted by adjusting the distance between the coupling lines 20, 21, 22.

The signal delay line for the equalizer for compensating the dispersion of the optical fiber is required to have a low loss and a wide band. As a basic method for obtaining the relative delay time depending on the frequency,
(1) dispersion by a coupling line, (2) dispersion of a dielectric substrate,
(3) Dispersion of effective permittivity due to mode change accompanying higher frequency is used.

Among them, in the case of (1) due to the dispersion of the coupling line, the relative delay time can be selected widely in a band of 50 GHz or less, which is suitable for use as a demodulation system equalizer. Also used this.

Next, an equalizer having a stripline structure will be supplementarily described.

FIG. 2 shows an example of the frequency characteristic of the delay time in the distributed delay line. The coupling line length is 6 mm, the degree of coupling is 23 dB, and the peak of dispersion when this is λ / 4 is repeated at about 4.1 GHz. The ratio (Δt / t ₀ ) of the relative delay time of the coupled line to the delay time of all the lines caused by the coupled line is about 24%. The smaller the degree of coupling, the narrower the line spacing and the stronger the coupling.

As shown in FIG. 3, the relationship between the ratio of the relative delay time obtained from the delay line having various degrees of coupling and the degree of coupling can be understood, and the degree of coupling can be adjusted by adjusting the meander line interval of the strip line structure. Is changing. By increasing the coupling to about 15 dB, a relative delay time of about 80% is obtained.

From FIG. 4, the dependence of the delay time on the coupling line in the coupling degree can be understood, and the capacitance and the inductance of the mutual line change due to the coupling between the lines, which shows the delay time dependence as shown in FIG. As shown in FIG. 5, by reducing the line interval to 0.2 mm, 10 dB
The above coupled line can be easily realized.

Assuming that 0.5 mm thick MgO (relative dielectric constant: 9.4) is used as the dielectric substrate and the line width of the center conductor is 0.16 mm, the characteristic impedance is 50 mm.
Ω.

When the signal delay line is formed of a superconducting thin film, the loss is about 0.7 dB at 10 GHz and 77K, which is extremely small, about 1/10 of the loss of the copper delay line. In the case of a superconducting delay line, the loss is 2 dB even at 20 GHz.
It is as follows. Also, when the ground plane is formed of a superconductive thin film, the loss can be further reduced, and the loss and the bandwidth can be further reduced as compared with the conventional equalizer.

FIG. 7 shows the relationship between the relative delay time and the frequency. With a coupling degree of 24 dB set in the configuration of the present embodiment, a relative delay time of about 340 ps is obtained in a band of 20 GHz or less, and with a coupling degree of 29 dB, a relative delay time of about 120 ps is obtained. Each equalizer has a total line length of approximately 28 cm, and the line intervals of the coupled lines are different.
Since the dispersion characteristic of the fiber is 0.12 ps / GHz / km, the equalizer having a coupling degree of 24 dB can compensate for the dispersion of about 140 km fiber, and the equalizer having the coupling degree of 29 dB can compensate for the dispersion of about 50 km fiber. It is possible. Coupling degree 2
The 4 dB equalizer is about 1.4 times as large as the conventional microstrip type equalizer (5 cm x 5 cm, which can compensate 100 km fiber), but the fiber distance that can be compensated is about 1.4 times. It was confirmed that the device was small and had an excellent equalizing function.

Next, an equalizer having a microstrip structure will be described. FIG. 8 shows the relationship between the degree of coupling and the line spacing in a 50Ω microstrip line having an MgO substrate having a thickness of 0.5 mm and a line width of 0.5 mm. As in the case of the stripline structure, by adjusting the line spacing, the degree of coupling of the coupled line can be easily changed.

FIG. 9 shows the relationship between the delay time and the degree of coupling. Thus, it can be understood that the delay time per unit length becomes shorter as the coupling between lines becomes stronger, similarly to the strip line structure. Since the relationship between the relative delay time and the degree of coupling is almost the same as the case of the stripline structure shown in FIG. 3, basically, the same performance as that of the stripline structure equalizer can be obtained even in the microstrip structure. Can understand.

[0038]

As described above, according to the present invention,
By using an oxide superconducting thin film for the center conductor and the ground plane of the equalizer, the loss is greatly reduced, thereby enabling a wider band. In addition, the entire signal path is meandered, and the basic unit coupling line arranged in the center conductor is formed in a meandering shape, so that a wideband distributed delay line can be realized.

Regardless of the stripline or microstrip structure, the frequency dispersion of the delay characteristics due to the coupling lines can be obtained over a wide range of relative delay time by changing the distance between the coupling lines and the total length of the coupling lines. Since it can be used, it can be used for dispersion compensation of optical fibers at various distances. As a result, the communication system using optical fiber,
The degree of freedom in design is increased, and an excellent effect of enabling a higher transfer rate and longer non-repeated optical transmission is achieved. Further, a small equalizer can be realized by the above configuration.

[Brief description of the drawings]

FIG. 1 is a plan view showing a preferred embodiment of the present invention,
It is sectional drawing (b) along the AA 'line, and its partial enlarged view (c).

FIG. 2 is a graph showing a characteristic example of a distributed delay line.

FIG. 3 is a graph showing a relationship between a ratio of a relative delay time and a coupling degree.

FIG. 4 is a graph showing a relationship between a delay time and a coupling degree;

FIG. 5 is a graph showing the line spacing dependency of the coupling degree.

FIG. 6 is a graph showing the relationship between insertion loss and frequency in a distributed delay line for an equalizer.

FIG. 7 is a graph showing a characteristic example of a superconducting equalizer.

FIG. 8 is a graph showing the dependency between the degree of coupling and the line spacing in the microstrip structure.

FIG. 9 is a graph showing the dependence of the delay time on the coupling degree.

FIG. 10 is a block diagram illustrating an example of typical coherent communication.

FIG. 11 is a graph showing an example of characteristics of an optical fiber.

FIG. 12 is a perspective view showing a configuration example of a conventional microstrip type delay line equalizer.

FIG. 13 is a graph showing a relationship between a relative delay time and a frequency of the microstrip type equalizer.

[Explanation of symbols]

 Reference Signs List 12 signal input part, 13 signal output part, 14 part of coupling line, 15 center conductor, 16 upper ground plane, 17 lower ground plane, 18 upper dielectric substrate, 19 lower dielectric substrate, 20, 21, 22 coupling line.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Naofumi Suzuki 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-3-205904 (JP, A) JP-A Hei 2-19013 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01P 1/00 ZAA H01P 9/00 ZAA H04B 3/14

Claims (1)

(57) [Claims] 1. A strip line structure in which a high-frequency signal delay line is interposed between a pair of ground planes and provided as a conductor on a dielectric substrate on one of the ground planes, or on a single ground plane. In a method of manufacturing an equalizer of a high-frequency communication system configured by a microstrip structure provided as a conductor on a dielectric substrate, at least the conductor is formed of a superconductive thin film, and the high-frequency signal delay line is formed. Meandering the entire signal path, and configuring the signal path with a number of basic unit coupling lines formed in a meander shape, and adjusting the coupling degree of the coupling line by adjusting the mutual interval between the coupling lines. A method for producing an equalizer for a high-frequency communication system, characterized in that a wide range of relative delay time is obtained by using the same .