CN213783312U - 1550nm direct dimming transmitter with adjustable dispersion compensation - Google Patents
1550nm direct dimming transmitter with adjustable dispersion compensation Download PDFInfo
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- CN213783312U CN213783312U CN202022916293.1U CN202022916293U CN213783312U CN 213783312 U CN213783312 U CN 213783312U CN 202022916293 U CN202022916293 U CN 202022916293U CN 213783312 U CN213783312 U CN 213783312U
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Abstract
The utility model relates to a 1550nm direct dimming transmitter with adjustable dispersion compensation, which comprises a splitter, a delayer, a combiner, a laser, a CSO generator, an amplifier, an electric control attenuator, an equalizer, a time delay adjuster and a controller; the branching device is divided into a main channel and an auxiliary channel; the splitter is connected with the input end of the time delay unit through the main channel, the output end of the time delay unit is connected with the combiner, the auxiliary channel of the splitter is connected with the input end of the CSO generator, the output end of the CSO generator is connected with the input end of the amplifier, the output end of the amplifier is connected with the input end of the electric control attenuator, the output end of the electric control attenuator is connected with the input end of the equalizer, the output end of the equalizer is connected with the input end of the time delay regulator, the output end of the time delay regulator is connected with the combiner, the combiner is connected with the laser, and the electric control attenuator is connected with the controller. The utility model discloses can set up the distance of optic fibre in a flexible way on the product, the point-to-point application of especially adapted network transmission, the performance index of product can be transferred to the optimal condition.
Description
Technical Field
The application relates to the technical field of cable television networks, in particular to a 1550nm direct dimming transmitter with adjustable dispersion compensation.
Background
In recent years, optical fiber Cable television is developed rapidly in China, with the continuous maturity of 1550nm technology in HFC/FTTX networks, a 1550nm externally-tuned transmitter is widely applied to medium-long distance optical transmission networks with large coverage areas to solve the problem of large-range broadcast coverage, and a 1550nm directly-tuned transmitter is widely applied to short-medium distance optical transmission networks with small-range coverage to solve the problem of Cable Modem data access of local simulation or digital-byte insertion or bidirectional network transformation, namely branch front-end inter-cut.
The dispersion constant of the conventional single mode fiber (ITU-T G.652) at 1550nm wavelength is large, about 17ps/nm/km), and if the laser is directly intensity-modulated, the spectrum is broadened due to the parasitic frequency modulation (chirp) effect caused by the variation of the driving current. The combination of the broad spectrum and the large fiber dispersion causes relative intensity noise in the light waves, particularly combined second order distortion (CSO) of the multi-frequency signal, which is very harmful to the CATV transmission system. Because of this, when the transmission distance of the 1550nm directly-tuned transmitter increases, the CSO degradation caused by the optical fiber dispersion also increases, so that the 1550nm directly-tuned transmitter is only suitable for short-medium distance transmission and is often used for optical fiber transmission within 10-40 km.
A predistortion circuit is arranged in a conventional 1550nm direct modulation transmitter, CSO compensation is performed on a 10km optical fiber link, but in practical application, a transmission distance varies with an installation and use place, and if product customization is performed on a specific transmission distance, for example, the product is classified according to 5km gear, product types are too many, production and product management and control are troublesome, and the product use is very inconvenient, especially when a network is expanded in engineering, because the predistortion compensation of CSO is fixed. Conventional predistortion compensation for CSO is illustrated in fig. 1 below.
The main part of the radio frequency signal (RF input) enters the main channel and a small part of the radio frequency signal enters the auxiliary channel through the splitter, the auxiliary channel is provided with a CSO (combined second-order intermodulation distortion) generator, and the amplitude and the phase are adjusted through attenuation and delay, so that the CSO generated by the auxiliary channel is the same as the inherent CSO amplitude of the laser and opposite in phase, and the aim of pre-distortion compensation is fulfilled.
The predistortion compensation of the structure is fixed, the conventional method is to compensate the dispersion of a 10km optical fiber, and the structure is difficult to adapt to various application scenes in engineering.
SUMMERY OF THE UTILITY MODEL
The application provides a 1550nm direct dimming transmitter capable of adjusting dispersion compensation, which aims to solve the problems that the predistortion compensation of the structure of the existing direct dimming transmitter is fixed, the conventional method is to compensate the dispersion of a 10km optical fiber, and the method is difficult to adapt to various application scenes in engineering.
The technical scheme adopted by the application is as follows:
the application provides a 1550nm direct dimming transmitter with adjustable dispersion compensation, which comprises a splitter, a delayer, a combiner, a laser, a CSO generator, an amplifier, an electric control attenuator, an equalizer, a delay adjuster and a controller;
the splitter is used for distributing signals into two paths or multiple paths in proportion and is divided into a main channel and an auxiliary channel;
the branching device is connected with the input end of the time delay device through a main channel, the output end of the time delay device is connected with the input end of the combiner,
the auxiliary channel of the branching device is connected with the input end of the CSO generator, the output end of the CSO generator is connected with the input end of the amplifier, the output end of the amplifier is connected with the input end of the electric control attenuator, the output end of the electric control attenuator is connected with the input end of the equalizer, the output end of the equalizer is connected with the input end of the delay regulator, the output end of the delay regulator is connected with the input end of the combiner,
the output end of the combiner is connected with the input end of the laser,
the electric control attenuator is connected with the controller.
Further, the controller is an MCU.
Further, the system also comprises a human-computer interface, and the human-computer interface is connected with the MCU.
Further, the human-computer interface is a liquid crystal display or a network management system.
The technical scheme of the application has the following beneficial effects:
the utility model discloses a 1550nm direct dimming transmitter of adjustable dispersion compensation adds an automatically controlled attenuator at the back at the CSO generator, can adjust the size of CSO signal, and automatically controlled attenuator is a voltage control's radio frequency signal attenuator, and its attenuation has flat amplitude-frequency characteristic. The control voltage of the attenuator is controlled by a controller, and the controller gives out corresponding control voltage according to the required optical fiber length information. An equalizer is added behind the electrically controlled attenuator, the equalizer is a signal slope controller, and the purpose is to perform amplitude-frequency inclination processing on the CSO predistortion signal after passing through the attenuator, so that the amplitude-frequency response of the predistortion signal is correspondingly the same as the CSO amplitude-frequency response of the laser under the dispersion of a certain length of optical fiber, and the effect of full-band compensation is achieved. Due to the use of the adjustable attenuator, a fixed gain amplifier needs to be added to the side channel to maintain a pre-distorted signal of sufficient amplitude.
The utility model discloses can set up the distance of optic fibre in a flexible way on the product, the point-to-point application of especially adapted network transmission, the performance index of product can be transferred to the optimal condition. Even aiming at a small range of optical fiber coverage, the optimal working point can be set, thereby solving the difficult problem of engineering application.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a block diagram of a 1550nm direct dimming transmitter of the prior art;
FIG. 2 is a schematic diagram of the amplitude-frequency characteristics of CSO levels for different lengths of optical fiber;
FIG. 3 is a block diagram of a 1550nm direct-dimming transmitter with tunable dispersion compensation;
FIG. 4 is a schematic diagram of an electrically controlled attenuator (a pi-type attenuator structure consisting of 4 PIN diodes);
fig. 5 is a graph of attenuation versus voltage for a particular bias circuit.
Detailed Description
The spectral broadening is caused by the parasitic frequency modulation (chirp) effect due to the drive current variation when the laser is directly intensity modulated. The combination of the broad spectrum and the large fiber dispersion causes relative intensity noise in the light waves, particularly combined second order distortion (CSO) of the multi-frequency signal, which is very harmful to the CATV transmission system.
As shown in fig. 2, the CSO amplitude levels of a direct intensity modulated laser are measured under different fiber length dispersions, and it can be seen from fig. 2 that the CSO levels with frequencies from low to high differ a little when the link fiber length is 0km (i.e. the optical transmitting and receiving devices are very close), but under different lengths of fiber, the amplitude-frequency characteristic of the CSO levels is seen to be inclined upward with a certain slope, and the larger the fiber length is, the larger the CSO amplitude is.
Therefore, in 1550nm direct modulation transmitter applications, the relationship between CSO degradation and fiber length over a certain range of fiber length dispersion has two characteristics:
(1) as the length of the fiber increases, the CSO amplitude is larger, i.e., the degradation increases;
(2) in a certain length of optical fiber, the amplitude-frequency characteristic of CSO degradation is inclined upward, and exhibits a certain slope.
Therefore, a circuit for dynamically adjusting the CSO compensation according to the length of the optical fiber can be designed to perform targeted adjustment to achieve the optimal compensation.
As shown in fig. 3, the present application provides a 1550nm direct dimming transmitter with adjustable dispersion compensation, which includes a splitter, a delay unit, a combiner, a laser, a CSO generator, an amplifier, an electrically controlled attenuator, an equalizer, a delay adjuster, and a controller.
Specifically, the splitter is used for proportionally distributing the signal into two or more paths, the embodiment is divided into two paths, and the splitter is divided into a main path and an auxiliary path; the splitter is connected with the input end of the time delay unit through the main channel, the output end of the time delay unit is connected with the input end of the combiner, the auxiliary channel of the splitter is connected with the input end of the CSO generator, the output end of the CSO generator is connected with the input end of the amplifier, the output end of the amplifier is connected with the input end of the electric control attenuator, the output end of the electric control attenuator is connected with the input end of the equalizer, the output end of the equalizer is connected with the input end of the time delay adjuster, the output end of the time delay adjuster is connected with the input end of the combiner, the output end of the combiner is connected with the input end of the laser, and the electric control attenuator is connected with the controller.
In this embodiment, the controller is an MCU, and further includes a human-computer interface, and the human-computer interface is connected to the MCU.
Meanwhile, the human-computer interface is a liquid crystal display or a network management system.
Specifically, an amplifier is added on the branch sub-channel line to amplify the sub-channel signal, so that the CSO generator generates a predistortion signal with larger amplitude. As shown in FIG. 4, the electrically controlled attenuator is a voltage controlled attenuator constructed by PIN diodes, and the basic structure is a pi-type attenuator structure. The equalizer compensates for the characteristic that the amplitude-frequency response of CSO generated by optical fiber dispersion is not flat but has slope so as to ensure the index of full frequency band. The man-machine interface can be a liquid crystal display or a network management system, a setting command is issued through the man-machine interface, the length of the optical fiber is set to a certain fixed value, a software program gives out a corresponding voltage according to received data to control the attenuation of the electric control attenuator, so that the amplitude of a predistortion signal of the CSO generator is controlled, the amplitude of the compensation signal is equal to or close to the CSO of the laser under the dispersion of the specific optical fiber length, and the adjustment effect of the time delay device of the main channel and the time delay attenuator of the auxiliary channel is that the signal phases of the two main channels and the auxiliary channel are opposite, so that the two main channels and the auxiliary channel are mutually offset, and the purpose of CSO compensation control is achieved.
As shown in fig. 3, an electrically controlled attenuator is added after the CSO generator to adjust the CSO signal, and the electrically controlled attenuator is a voltage-controlled rf signal attenuator with flat amplitude-frequency characteristics. The control voltage of the attenuator is controlled by software of the MCU, and the software gives out corresponding control voltage according to the optical fiber length information given out by a human-computer interface (a liquid crystal display or network management software). An equalizer is added behind the electrically controlled attenuator, the equalizer is a signal slope controller, and the purpose is to perform amplitude-frequency inclination processing on the CSO predistortion signal after passing through the attenuator, so that the amplitude-frequency response of the predistortion signal is correspondingly the same as the CSO amplitude-frequency response of the laser under the dispersion of a certain length of optical fiber, and the effect of full-band compensation is achieved. Due to the use of the adjustable attenuator, a fixed gain amplifier needs to be added to the side channel to maintain a pre-distorted signal of sufficient amplitude.
As shown in fig. 5, the relationship between the attenuation and the control voltage of the electrically controlled attenuator is a curve, the larger the control voltage is, the smaller the attenuation is, the lower fig. 4 is a graph of the attenuation and the voltage under a specific bias circuit, it can be seen that the slope of the curve has a "turning point" when the attenuation is 4dB, for the convenience of data processing, the minimum value of the attenuation and the maximum value of the control voltage take the point of 4dB, for the simplification of the processing, the linearization processing can be adopted for the control voltage.
When the length of the optical fiber is 0 kilometer, no optical fiber dispersion exists, the predistortion signal should be attenuated to the minimum, the attenuation of the attenuator should be kept at the maximum, the corresponding control voltage is minimum, and V is assumed to be0. At maximum Lm km of fiber length, the predistortion signal should remain at maximum, the attenuation of the attenuator should remain at minimum, and the corresponding control voltage is at maximum, assumed to be Vm. If the length variable of the optical fiber is x and the corresponding control voltage is y, the relationship between the control voltage y and the length x of the optical fiber is:
(y-V0)/(x-0)＝(Vm-V0)/(Lm-0)
can obtain the product
y＝V0+(Vm-V0)/Lm*x
Because the chirp parameters of different lasers are distributed in a larger range, the CSO degradation generated by different lasers with the same maximum length of the optical fiber Lm is also distributed in a larger range, and therefore, for Vm, the correction setting is carried out on each device in the production process, namely Vm is made into a production setting parameter.
According to experimental tests, the slope of the equalizer is maintained to be about 15dB, and the optical fibers with various lengths can be considered.
The 1550nm direct dimming transmitter with adjustable dispersion compensation, which is provided by the embodiment, can flexibly set the distance of an optical fiber on a product, is very suitable for point-to-point application of network transmission, and the performance index of the product can be adjusted to an optimal state. Even aiming at a small range of optical fiber coverage, the optimal working point can be set, thereby solving the difficult problem of engineering application.
The embodiments provided in the present application are only a few examples of the general concept of the present application, and do not limit the scope of the present application. Any other embodiments extended according to the scheme of the present application without inventive efforts will be within the scope of protection of the present application for a person skilled in the art.
Claims (4)
1. A1550 nm direct dimming transmitter with adjustable dispersion compensation is characterized by comprising a splitter, a delayer, a combiner, a laser, a CSO generator, an amplifier, an electric control attenuator, an equalizer, a delay adjuster and a controller;
the splitter is used for distributing signals into two paths or multiple paths in proportion and is divided into a main channel and an auxiliary channel;
the branching device is connected with the input end of the time delay device through a main channel, the output end of the time delay device is connected with the input end of the combiner,
the auxiliary channel of the branching device is connected with the input end of the CSO generator, the output end of the CSO generator is connected with the input end of the amplifier, the output end of the amplifier is connected with the input end of the electric control attenuator, the output end of the electric control attenuator is connected with the input end of the equalizer, the output end of the equalizer is connected with the input end of the delay adjuster, the output end of the delay adjuster is connected with the input end of the combiner,
the output end of the combiner is connected with the input end of the laser,
the electric control attenuator is connected with the controller.
2. The tunable dispersion compensated 1550nm direct dimming transmitter according to claim 1, wherein the controller is an MCU.
3. The tunable dispersion compensated 1550nm direct dimming transmitter according to claim 2, further comprising a human-machine interface, wherein the human-machine interface is connected to the MCU.
4. The tunable dispersion compensated 1550nm direct dimming transmitter of claim 3, wherein the human-machine interface is a liquid crystal display or a network management system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202022916293.1U CN213783312U (en) | 2020-12-04 | 2020-12-04 | 1550nm direct dimming transmitter with adjustable dispersion compensation |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202022916293.1U CN213783312U (en) | 2020-12-04 | 2020-12-04 | 1550nm direct dimming transmitter with adjustable dispersion compensation |
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| CN213783312U true CN213783312U (en) | 2021-07-23 |
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| CN202022916293.1U Active CN213783312U (en) | 2020-12-04 | 2020-12-04 | 1550nm direct dimming transmitter with adjustable dispersion compensation |
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