A system and method for optimizing receiving noise floor in optical fiber transmission link

Abstract

The present invention discloses a system and method for optimizing the receiving noise floor in an optical fiber transmission link, belonging to the technical field of optical fiber transmission of analog signals. The system includes a transmitting end and a receiving end, wherein the transmitting end includes a gain compensation circuit for compensating the gain of the signal in the high frequency band, and the receiving end includes a gain compression circuit for compressing the gain of the signal in the high frequency band. The transmitting end of the system of the present invention includes a gain compensation circuit, and the receiving end includes a gain compression circuit. The gain compensation circuit compensates the gain of the signal in the high frequency band, and the gain compression circuit compresses the gain of the signal in the high frequency band, so that the output noise floor of the high frequency band is reduced compared with the original optical fiber link, thereby making the signal flatness of the system small and the signal-to-noise ratio high, thereby ensuring the communication quality.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber transmission of analog signals, and in particular to a system and method for optimizing receiving background noise in an optical fiber transmission link. Background Art

[0002] In modern communication technology, the bandwidth requirements for analog electrical signals in optical fiber transmission links are getting higher and higher, reaching hundreds of megahertz or even several gigahertz. The wider the bandwidth, the higher the total noise floor received, especially the noise floor in the high-frequency band has the largest impact. However, the noise floor of laser devices in the high-frequency band is higher than that in the medium and low-frequency bands. Usually, in links with bandwidths in the gigahertz range, the noise floor in the high-frequency band is several decibels higher than that in the low-frequency band. Therefore, optimizing the noise in the high-frequency band is of great significance to the system noise floor, especially in demanding complex electromagnetic field environment testing applications.

[0003] In existing optical fiber transmission links, the noise floor is optimized by reducing the noise floor of the entire frequency band at the receiving end at the same time. For example, low-noise broadband amplifiers are used, and devices such as reducing the transmitted optical power are used to optimize the noise floor of the entire frequency band of the receiving end so that the system signal flatness is low and a better signal-to-noise ratio is achieved. However, no technical solution for receiving low noise in the high-frequency band of optical fiber transmission links has been proposed. On this basis, the present invention proposes a system and method for optimizing the noise floor of the high-frequency band of optical fiber transmission links. Summary of the invention

[0004] The purpose of the present invention is to overcome the problem in the prior art that it is impossible to optimize low noise reception in high frequency bands in optical fiber transmission links, and to provide an optimization system for receiving background noise in optical fiber transmission links.

[0005] The objective of the present invention is achieved through the following technical scheme: a system for optimizing the receiving noise floor in an optical fiber transmission link, the system specifically comprising a transmitting end and a receiving end, the transmitting end comprising a gain compensation circuit for compensating the gain of the signal in the high frequency band, and the receiving end comprising a gain compression circuit for compressing the gain of the signal in the high frequency band.

[0006] Specifically, the gain compensation circuit includes a first broadband amplifier and a first feedback circuit, and the gain compression circuit includes a second broadband amplifier and a second feedback circuit.

[0007] Specifically, the first feedback circuit includes a first resistor, a second resistor and a first capacitor; one end of the second resistor is connected to the input end of the first broadband amplifier, the other end of the second resistor is connected to one end of the first resistor, the other end of the first resistor is connected to the output end of the first broadband amplifier, and the first capacitor is connected in parallel with the first resistor.

[0008] Specifically, the second feedback circuit includes a third resistor, a fourth resistor and a third capacitor; one end of the third resistor is connected to the input end of the second broadband amplifier, the other end of the third resistor is connected to the output end of the second broadband amplifier, and the fourth resistor is connected in series with the third capacitor and then connected in parallel with the third resistor.

[0009] Specifically, the gain compression circuit further includes a first temperature-compensated attenuator, and the first temperature-compensated attenuator is arranged at the output end of the second broadband amplifier.

[0010] Specifically, as another embodiment, the gain compensation circuit of the system of the present invention includes a third broadband amplifier, an equalizer, a first attenuator, and a DC block connected in sequence; the gain compression circuit of the system of the present invention includes a fourth broadband amplifier, a second attenuator, and a second temperature-compensated attenuator connected in sequence. Specifically, the fourth broadband amplifier includes an amplifier with a full-band flat response and a low-pass filter connected in sequence.

[0011] Specifically, the transmitting end also includes a laser connected to the output end of the gain compensation circuit, and the receiving end also includes a photodetector and a low-noise amplifier connected in sequence, the output end of the low-noise amplifier is connected to the gain compression circuit, and the transmitting end and the receiving end are connected via an optical cable.

[0012] The present invention also includes a method for optimizing the receiving noise floor in the above optical fiber transmission link, and the method specifically includes:

[0013] A gain compensation circuit is provided at the transmitting end to compensate for the gain of the signal in the high frequency band;

[0014] A gain compression circuit is provided at the receiving end to compress the gain of the signal in the high frequency band.

[0015] Specifically, the gain compensation circuit includes a first broadband amplifier and a first feedback circuit, the gain compression circuit includes a second broadband amplifier and a second feedback circuit, and the method specifically further includes:

[0016] The parameters of the first feedback circuit and the second feedback circuit are adjusted so that the gain slope of the gain compensation circuit and the gain slope of the gain compensation circuit are inverse numbers of each other.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The transmitting end of the system of the present invention includes a gain compensation circuit, and the receiving end includes a gain compression circuit. The gain compensation circuit compensates the gain of the signal in the high frequency band, and the gain compression circuit compresses the gain of the signal in the high frequency band, so that the output noise floor of the high frequency band is lower than that of the original optical fiber link, thereby making the signal flatness of the system small and the signal-to-noise ratio high, thereby ensuring the communication quality.

[0019] (2) The first broadband amplifier of the present invention is used to provide a compensation gain, and the first feedback circuit is used to adjust the gain compensation amount of the full-band signal, so that the low-band gain is low and the high-band gain is high, thereby realizing compensation for the high-band gain of the signal; the second broadband amplifier of the present invention is used to amplify weak signals, and the second feedback circuit is used to adjust the gain compensation amount of the full-band signal, so that the low-band gain is high and the high-band gain is linearly reduced, so that the output background noise of the high-band is lower than that of the original optical fiber link, thereby reducing the signal flatness of the system.

[0020] (3) The first resistor and the second resistor of the first feedback circuit of the present invention are used to adjust the static operating point of the first broadband amplifier so that the first broadband amplifier operates in an amplification state; the first capacitor is used to adjust the gain slope so that the gain of the signal in the low frequency band is lower and the gain of the signal in the high frequency band is higher.

[0021] (4) The third resistor in the second feedback circuit of the present invention is used to adjust the static operating point of the second broadband amplifier so that the second broadband amplifier operates in an amplification state. At the same time, the third resistor is also used to adjust the average gain of the entire frequency band. The fourth resistor is connected in series with the third capacitor to adjust the gain slope. The fourth resistor is used to reduce the Q value to ensure that the signal can present a state in which the gain in the low frequency band is high and the gain in the high frequency band is linearly reduced after passing through the gain compression circuit.

[0022] (5) The gain compression circuit of the present invention further includes a first temperature compensation attenuator for compensating for the fluctuation effect of temperature change on background noise.

[0023] (6) The gain compensation circuit of the present invention comprises a third broadband amplifier, an equalizer, a first attenuator, and a DC block connected in sequence, wherein the third broadband amplifier is used to provide a compensation gain, the equalizer has a large attenuation in the low frequency band and a small attenuation in the high frequency band, so as to ensure the gain compensation of the signal in the high frequency band, the first attenuator is used to make the gain compensation circuit present a good impedance matching circuit, and the DC block is used to protect the static operating point of the laser; the gain compression circuit comprises a fourth broadband amplifier, a second attenuator, and a second temperature-compensated attenuator connected in sequence, the fourth broadband amplifier is used to amplify the signal, so that the entire gain compression circuit presents a frequency response characteristic of a higher gain at the low frequency end and a linearly reduced gain at the high frequency end, the second attenuator is used to make the gain compression circuit present a good impedance matching circuit, and the second temperature-compensated attenuator is used to compensate for the background noise fluctuation caused by high and low temperatures, and improve the high and low temperature performance of the system gain.

[0024] (7) The fourth broadband amplifier of the present invention includes an amplifier with a flat full-band response and a low-pass filter connected in sequence, which is conducive to adjusting the full-band signal gain so that the entire gain compression circuit presents a frequency response characteristic with a higher gain at the low-frequency end and a linearly reduced gain at the high-frequency end.

[0025] (8) The method of the present invention includes setting a gain compensation circuit at the transmitting end and setting a gain compression circuit at the receiving end. The gain compensation circuit compensates for the gain of the signal in the high frequency band, and the gain compression circuit compresses the gain of the signal in the high frequency band, so that the output noise floor of the high frequency band is lower than that of the original optical fiber link, thereby making the signal flatness of the system small and the signal-to-noise ratio high, thereby ensuring the communication quality.

[0026] (9) The gain slope of the gain compensation circuit of the present invention is the inverse of the gain slope of the gain compensation circuit, so as to ensure the gain flatness of the broadband signal and the communication quality of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings. The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to represent the same or similar parts. The exemplary embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application. In the drawings:

[0028] Figure 1 is a circuit schematic diagram of a gain compensation circuit according to Embodiment 1 of the present invention;

[0029] Figure 2 is a circuit schematic diagram of a gain compression circuit according to Embodiment 1 of the present invention;

[0030] Figure 3 is a system block diagram of Embodiment 1 of the present invention;

[0031] Figure 4 is a circuit schematic diagram of a gain compensation circuit according to Embodiment 2 of the present invention;

[0032] Figure 5 4 is a circuit schematic diagram of a gain compression circuit according to Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In the description of the present invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are directions or positional relationships based on the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Example 1

[0038] In order to solve the problem that the prior art cannot optimize the low noise reception in the high frequency band of the optical fiber transmission link, the present embodiment provides an optimization system for the reception noise floor in the optical fiber transmission link. The system includes a transmitting end and a receiving end. The transmitting end includes a gain compensation circuit for compensating the gain of the high frequency band of the signal, so that the gain of the low frequency band is low and the gain of the high frequency band is high. The receiving end includes a gain compression circuit for compressing the gain of the high frequency band of the signal. Even if the gain of the low frequency band is high and the gain of the high frequency band is linearly reduced, the output noise floor of the high frequency band is reduced compared with the original optical fiber link, and the low noise of the full frequency band presents a flat trend, thereby ensuring the gain flatness, making the system signal flatness small, and the signal-to-noise ratio high, thereby ensuring the communication quality.

[0039] As an option, the gain compensation circuit includes a first broadband amplifier A1 and a first feedback circuit, and the gain compression circuit includes a second broadband amplifier A2 and a second feedback circuit. Specifically, the first broadband amplifier A1 is used to provide a compensation gain, and the first feedback circuit is used to adjust the gain compensation amount of the full-band signal, so that the low-band gain is low and the high-band gain is high, thereby achieving compensation for the high-band gain of the signal; the second broadband amplifier A2 is used to amplify weak signals, and the second feedback circuit is used to adjust the gain compensation amount of the full-band signal, so that the low-band gain is high and the high-band gain is linearly reduced, so that the output background noise of the high-band is lower than that of the original optical fiber link, thereby making the signal flatness of the system small.

[0040] As an option, the broadband amplifier is specifically a radio frequency transistor ATF54143, which is used to provide an appropriate amount of compensation gain.

[0041] Furthermore, if Figure 1 As shown, the first feedback circuit includes a first resistor R1, a second resistor R2 and a first capacitor C1. Specifically, one end of the second resistor R2 is connected to the input end of the first broadband amplifier A1, the other end of the second resistor R2 is connected to one end of the first resistor R1, the other end of the first resistor R1 is connected to the output end of the first broadband amplifier A1, and the first capacitor C1 is connected in parallel with the first resistor R1. Specifically, the first resistor R1 and the second resistor R2 of the first feedback circuit are used to adjust the static operating point of the first broadband amplifier A1 so that the first broadband amplifier A1 works in an amplification state; the first capacitor C1 is used to adjust the gain slope so that the gain of the signal in the low frequency band is lower and the gain of the high frequency band is higher. Of course, in order to ensure the gain flatness of the broadband signal, the gain slope of the gain compression circuit and the gain slope of the gain compensation circuit are opposite to each other. More specifically, the value range of the first capacitor C1 is 20-200pF. As a preferred embodiment, the first capacitor C1 is 100pF, the first resistor R1 is 50Ω, and the second resistor R2 is 120Ω. Correspondingly, the high frequency band 3G frequency gain in the gain compensation circuit is increased by about 4.5dB compared with the 0.5G frequency gain.

[0042] It should be further explained that when determining the gain slope of the gain compensation circuit and the gain compression circuit, it should be noted that the gain slope depends on the amount of improvement required for the high-frequency noise floor. The larger the slope, the greater the improvement in the noise floor. However, a large slope means that the compression of the high-frequency gain is large, and excessive compression will affect the power linearity (P-1dB) index of the system output. Suppose the power linearity (P-1dB) margin of the original system is P, the amount of high-frequency noise floor to be improved is S, and the available high and low frequency gain compression or compensation is G. The units of the three indicators are all dB. If P≥S, then determine G=S; if P≤S, then G=P.

[0043] Furthermore, if Figure 2As shown, the second feedback circuit includes a third resistor R3, a fourth resistor R4 and a third capacitor C3. Specifically, one end of the third resistor R3 is connected to the input end of the second broadband amplifier A2, the other end of the third resistor R3 is connected to the output end of the second broadband amplifier A2, and the fourth resistor R4 is connected in series with the third capacitor C3 and then connected in parallel with the third resistor R3, that is, one end of the fourth resistor R4 is connected to the input end of the second broadband amplifier A2, and one end of the third resistor R3 is connected to the output end of the second broadband amplifier A2. Specifically, the third resistor R3 in the second feedback circuit is used to adjust the static operating point of the second broadband amplifier A2 so that the second broadband amplifier A2 works in an amplified state. At the same time, the third resistor R3 is also used to adjust the average gain of the full frequency band; the fourth resistor R4 is connected in series with the third capacitor C3 to adjust the gain slope, and the fourth resistor R4 is used to reduce the Q value to ensure that the signal can present a state where the low-frequency band gain is high and the high-frequency band gain is linearly reduced after passing through the gain compression circuit. More specifically, the value range of the third capacitor C3 is 5pF-20pF, and the value range of the fourth resistor R4 is 100-1000Ω. As a preferred embodiment, the third resistor R3 is 2kΩ, the fourth resistor R4 is 510Ω, and the third capacitor C3 is 10pF. Correspondingly, the high frequency band 3G frequency gain in the gain compression circuit is reduced by about 4.5dB compared with the 0.5G frequency gain.

[0044] As an option, the gain compression circuit also includes a first temperature-compensated attenuator TA1 and a fourth grounding capacitor C4, the fourth grounding capacitor C4 is connected to the output end of the second broadband amplifier A2, and the first temperature-compensated attenuator TA1 is cascaded after the fourth grounding capacitor C4, that is, the first end of the fourth grounding capacitor C4 is connected to the output end of the second broadband amplifier A2, the second end of the fourth grounding capacitor C4 is grounded, and the first end of the fourth grounding capacitor C4 is connected to the first temperature-compensated attenuator TA1. Specifically, the fourth grounding capacitor C4 is used to achieve fine-tuning of the gain slope; since the gain of the broadband amplifier changes with temperature, it directly affects the output noise floor size, so the first temperature-compensated attenuator TA1 can effectively compensate for the noise floor fluctuations caused by high and low temperatures, and improve the high and low temperature performance of the system gain. More specifically, the value range of the fourth grounding capacitor is 0.3pF-1pF. As a preferred embodiment, the fourth grounding capacitor is specifically 0.5pF, and the first temperature-compensated attenuator TA1 model is specifically TCA0604N9.

[0045] Furthermore, if Figure 3 As shown, the transmitting end of the system also includes a laser connected to the output end of the gain compensation circuit, and the receiving end also includes a photodetector and a low-noise amplifier connected in sequence. The output end of the low-noise amplifier is connected to the gain compression circuit, and the transmitting end and the receiving end are connected via an optical cable.

[0046] As an option, the output end of the gain compensation circuit is also connected to a second capacitor C2 for blocking DC and passing AC, and the output end of the first broadband amplifier A1 is connected to the laser via the second capacitor C2 to protect the static operating point of the laser. As a specific embodiment, the second capacitor C2 is 100pF.

[0047] Embodiment 1 of the present invention realizes the noise floor optimization of the analog signal transmission system from 0.5G to 3G. In the original unoptimized analog signal transmission system, the 0.5GHz noise floor is about -136dBm / Hz, the 2GHz noise floor is about -134dBm / Hz, and the 3GHz noise floor is about -132dBm / Hz. After low noise optimization is performed by the system gain compensation circuit and gain compression circuit of the present invention, the 0.5GHz-3GHz noise floor is -136±0.5dBm / Hz, and the signal flatness is small.

[0048] The receiving end of the present invention linearly reduces the gain of the high frequency band, that is, the higher the frequency, the lower the gain, which just offsets the original fiber link's characteristic of higher noise floor as the frequency increases. Therefore, the output noise floor of the high frequency band decreases compared to the original fiber link, and the circuit adjusts it to be consistent with the low frequency band. The transmitting end is used to compensate for the gain reduced in the high frequency band of the receiving end. Although the gain of the high frequency band is relatively increased, its impact on the output noise floor can be ignored. This is because the compensated gain is before the laser. According to the principle of noise cascade, increasing the positive gain in the front stage of the system is conducive to improving the system noise. And because the laser attenuation noise is particularly large, the laser's impact on the noise floor is much greater than that of the front stage. On this basis, the signal flatness of the entire system is small, ensuring the communication quality.

[0049] Example 2

[0050] In order to solve the problem in the prior art that it is impossible to optimize the low noise reception in the high frequency band of the optical fiber transmission link, this embodiment provides an optimization system for the reception noise floor in the optical fiber transmission link, which has the same inventive concept as Example 1. The system includes a transmitting end and a receiving end. The transmitting end includes a gain compensation circuit for compensating the gain of the high frequency band of the signal, even if the gain of the low frequency band is low and the gain of the high frequency band is high. The receiving end includes a gain compression circuit for compressing the gain of the high frequency band of the signal, even if the gain of the low frequency band is high and the gain of the high frequency band is linearly reduced, so that the output noise floor of the high frequency band is lower than that of the original optical fiber link, and the low noise of the full frequency band presents a flat trend, thereby ensuring the gain flatness, making the system signal flat, and the signal-to-noise ratio high, thereby ensuring the communication quality.

[0051] Specifically, Figure 4 As shown, the gain compensation circuit includes a third broadband amplifier A11, a gain equalizer E1, a first attenuator AT1, and a DC block B1 connected in sequence, which can avoid the difficult feedback circuit adjustment process of the gain compensation circuit in Example 1; Figure 5As shown, the gain compression circuit includes a fourth broadband amplifier A22, a second attenuator AT2, and a second temperature-compensated attenuator TA2 connected in sequence. Specifically, the first and third broadband amplifiers A11 are used to provide compensation gain, the gain equalizer E1 has large attenuation in the low frequency band and small attenuation in the high frequency band to ensure gain compensation for the high frequency band of the signal, the first attenuator AT1 is specifically a resistive attenuator, which is used to make the gain compensation circuit present a good impedance matching circuit, and the B1 DC isolation device is used to protect the static operating point of the laser; the fourth broadband amplifier A22 in the gain compression circuit is used to amplify the signal, so that the entire gain compression circuit presents a frequency response characteristic of high gain at the low frequency end and linearly reduced gain at the high frequency end, the second attenuator AT2 is specifically a resistive attenuator, which is used to make the gain compression circuit present a good impedance matching circuit, and the second temperature-compensated attenuator TA2 is used to compensate for the background noise fluctuation caused by high and low temperatures, and improve the high and low temperature performance of the system gain.

[0052] As an option, in an actual application scenario, the fourth broadband amplifier A22 does not have a suitable amplifier model and cannot achieve an ideal signal amplification effect. The fourth broadband amplifier A22 can be split into a combination of an amplifier with a full-band flat response and a low-pass filter in series, that is, the fourth broadband amplifier A22 includes an amplifier with a full-band flat response and a low-pass filter connected in sequence. By adjusting the frequency response of the filter, the entire gain compression circuit presents a frequency response characteristic with a higher gain at the low-frequency end and a linearly reduced gain at the high-frequency end.

[0053] Example 3

[0054] This embodiment solves the problem that the prior art cannot optimize the low noise reception in the high frequency band of the optical fiber transmission link, and provides a method for optimizing the reception noise floor in the optical fiber transmission link. The method has the same inventive concept as that of embodiment 1, and includes:

[0055] A gain compensation circuit is set at the transmitting end and a gain compression circuit is set at the receiving end. The gain compensation circuit compensates the gain of the signal in the high frequency band, and the gain compression circuit compresses the gain of the signal in the high frequency band, so that the output noise floor of the high frequency band is lower than that of the original optical fiber link, thereby making the signal flatness of the system small and the signal-to-noise ratio high, thereby ensuring the communication quality.

[0056] Further, the gain compensation circuit is specifically the gain compensation circuit in Example 1, and the gain compression circuit is specifically the gain compression circuit in Example 1. The value of the first capacitor C1 in the first feedback circuit, the value of the fourth resistor R4 and the third capacitor C3 in the second feedback circuit are changed so that the gain slope of the gain compensation circuit and the gain slope of the gain compensation circuit are inversely proportional to each other, so as to ensure the gain flatness of the broadband signal and the communication quality of the system. As a preferred embodiment, the first capacitor C1 is specifically 100pF, the fourth resistor R4 is 510Ω, and the third capacitor C3 is 10pF. Correspondingly, the gain compensation circuit has a high frequency band 3G frequency gain that is about 4.5dB higher than the 0.5G frequency gain, and the gain compression circuit has a high frequency band 3G frequency gain that is about 4.5dB lower than the 0.5G frequency gain.

[0057] Furthermore, the value of the fourth grounding capacitor C4 in the second feedback circuit is adjusted to fine-tune the slope of the gain compression circuit. As a preferred embodiment, the fourth grounding capacitor C4 is 0.5 pF.

[0058] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A system for optimizing receiving noise floor in an optical fiber transmission link, characterized in that: The system comprises a transmitting end and a receiving end, wherein the transmitting end comprises a gain compensation circuit for compensating the gain of the signal in the high frequency band, and the receiving end comprises a gain compression circuit for compressing the gain of the signal in the high frequency band; The gain compensation circuit includes a third broadband amplifier, an equalizer, a first attenuator, and a DC block connected in sequence. The third broadband amplifier is used to provide a compensation gain. The equalizer has a large attenuation in the low frequency band and a small attenuation in the high frequency band to ensure gain compensation for the high frequency band of the signal. The first attenuator is used to make the gain compensation circuit present a good impedance matching circuit. The DC block is used to protect the static operating point of the laser. The gain compression circuit includes a fourth broadband amplifier, a second attenuator, and a second temperature-compensated attenuator connected in sequence. The fourth broadband amplifier is used to amplify the signal so that the entire gain compression circuit presents a frequency response characteristic of higher gain at the low frequency end and linearly reduced gain at the high frequency end. The second attenuator is used to make the gain compression circuit present a good impedance matching circuit. The second temperature-compensated attenuator is used to compensate for the background noise fluctuations caused by high and low temperatures and improve the high and low temperature performance of the system gain.

2. The system for optimizing receiving noise floor in an optical fiber transmission link according to claim 1, characterized in that: The fourth broadband amplifier includes an amplifier with a full-band flat response and a low-pass filter connected in sequence.

3. The system for optimizing receiving noise floor in an optical fiber transmission link according to claim 1, characterized in that: The transmitting end also includes a laser connected to the output end of the gain compensation circuit, and the receiving end also includes a photodetector and a low-noise amplifier connected in sequence. The output end of the low-noise amplifier is connected to the gain compression circuit. The transmitting end and the receiving end are connected via an optical cable.

4. A method for optimizing the receiving noise floor in an optical fiber transmission link, characterized in that: The method comprises: A gain compensation circuit is provided at the transmitting end to compensate for the gain of the signal in the high frequency band; A gain compression circuit is provided at the receiving end to compress the gain of the signal in the high frequency band; The gain compensation circuit includes a first broadband amplifier and a first feedback circuit, and the gain compression circuit includes a second broadband amplifier and a second feedback circuit; The first feedback circuit includes a first resistor, a second resistor and a first capacitor; One end of the second resistor is connected to the input end of the first broadband amplifier, the other end of the second resistor is connected to one end of the first resistor, the other end of the first resistor is connected to the output end of the first broadband amplifier, and the first capacitor is connected in parallel with the first resistor; The second feedback circuit includes a third resistor, a fourth resistor and a third capacitor; One end of the third resistor is connected to the input end of the second broadband amplifier, the other end of the third resistor is connected to the output end of the second broadband amplifier, and the fourth resistor is connected in series with the third capacitor and then connected in parallel with the third resistor; The method specifically also includes: Adjusting the parameters of the first feedback circuit and the second feedback circuit so that the gain slope of the gain compression circuit and the gain slope of the gain compensation circuit are inverse numbers of each other; Adjusting the parameters of the first feedback circuit and the second feedback circuit includes: The value of the first capacitor in the first feedback circuit, the value of the fourth resistor and the third capacitor in the second feedback circuit are changed.

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