CN1588223A - Double pump wide band optical fiber parameter amplifier - Google Patents

Abstract

A dual-pump broadband optical fiber parametric amplifier is composed of two pump lasers, a pump coupler, a signal laser, a signal coupler, a wavelength division multiplexer and three cascaded high nonlinear optical fibers in sequence. The zero dispersion wavelength of the first-stage fiber is close to the center wavelength of the two pump lights, the second-order dispersion of the second-stage fiber is positive at the center wavelength of the pump light, and the second-order dispersion of the third-stage fiber is at the center wavelength of the two pump lights. The second order dispersion is negative. After the two pump light and signal light are coupled by the wavelength division multiplexer, they enter the three-stage optical fiber in turn, and idle light is generated after the first-stage optical fiber. Flat, the unevenness of the gain spectrum curve is reduced after passing through the second-level fiber, and the gain spectrum is corrected after passing through the third-level fiber. The invention can cover the low-loss window of the full-wave optical fiber, thereby making full use of the bandwidth of the full-wave optical fiber and promoting the development of the WDM optical fiber communication system.

Description

Double-pumped Broadband Fiber Parametric Amplifier

technical field

The invention relates to a dual-pump broadband optical fiber parametric amplifier (FOPA), in particular to a three-stage highly nonlinear optical fiber cascaded double-pump broadband optical fiber parametric amplifier, which is suitable for optical fiber communication systems and networks.

Background technique

The current optical fiber communication system widely uses wavelength division multiplexing (WDM), which can effectively use the bandwidth of optical fiber to realize large-capacity, long-distance optical fiber communication, and can increase the number of services in the user distribution system. In the application of these wavelength division multiplexing technologies, multiple amplifiers with larger bandwidths are required to be cascaded to compensate the loss of each channel at the same level, thereby realizing multi-wavelength ultra-long-distance transmission. However, the traditional erbium-doped fiber amplifier (EDFA) can only provide amplification of optical signals in the wavelength range of 1530-1625nm, and cannot meet the further expansion requirements of DWDM (Dense Wavelength Division Multiplexing). Fiber Raman amplifiers pumped by multiple wavelengths can provide broadband amplification of about 100nm, although theoretically analyzed, the flat bandwidth of Raman amplifiers can theoretically cover the entire low-loss window of full-wave optical fibers ( From 1250nm to 1650nm), but it is necessary to use a full-band multiplexer and demultiplexer, which greatly increases the insertion loss, causes the system power cost to increase, and reduces the transmission performance of the system. Therefore, research on new broadband fiber amplifiers, especially fiber amplifiers whose gain bandwidth covers the entire low-loss window of full-wave fibers, is a research topic for wavelength division multiplexing communication systems. The fiber parametric amplifier uses the four-wave mixing effect to amplify the optical signal, and can provide a broadband amplification in any wavelength band. In addition, its noise figure is lower than the quantum limit of 3dB, and can be used as a broadband optical amplifier, wavelength converter, and return-to-zero code pulse generation. device, optical time division multiplexing switch and all-optical signal sampler, etc. The single-pump single-stage fiber parametric amplifier has obtained a gain bandwidth of 200nm in the laboratory, but the gain flatness is very poor, which makes it difficult to apply to the wavelength division multiplexing system. The Chinese invention patent with the application number 200410025214.0 proposes to use four-stage cascaded highly nonlinear optical fibers to form a single-pumped multi-stage optical fiber parametric amplifier. This amplifier can theoretically provide a bandwidth of 320nm, but its bandwidth cannot cover the full-wave optical fiber. Low loss window (1250-1650nm). At the same time, the number of high nonlinear fiber stages used in this amplifier increases the splicing loss.

Therefore, the study of broadband fiber parametric amplifiers, especially fiber amplifiers whose gain bandwidth covers the entire low-loss window of full-wave fibers, is a research topic for WDM communication systems.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art, and propose a double-pumped broadband fiber parametric amplifier, which reduces the number of highly nonlinear fiber stages, and enables the flat bandwidth of the fiber parametric amplifier to cover the low-loss window of the full-wave fiber.

In order to achieve such an object, in the technical solution of the present invention, the dual-pump broadband fiber parametric amplifier consists of two pump lasers, a pump coupler, a signal laser, a signal coupler, a wavelength division multiplexer and sequentially cascaded Three-stage high nonlinear optical fiber composition. The output of the two pump lasers is connected to the wavelength division multiplexer through the pump coupler, the output of the signal laser is connected to the wavelength division multiplexer through the signal coupler, and the output of the wavelength division multiplexer is connected to the cascaded three-stage high nonlinear fiber.

The pump light waves (λ _p1 , λ _p2 ) emitted by the two pump lasers are coupled into the transmission fiber through the pump coupler, and the signal light (λ _s ) emitted by the signal laser is also coupled into the transmission fiber through the signal coupler. Then, the two pump light and the signal light are multiplexed into the sequentially cascaded three-stage high nonlinear optical fiber through the wavelength division multiplexing coupler for four-wave mixing, thereby realizing the effect of parametric amplification. Among them, the zero-dispersion wavelength (λ ₀ ) of the first-stage fiber is close to the center wavelength of the two pump lights (λ _c = (λ _p1 + λ _p2 )/2), and the second-stage fiber is at the center wavelength of the pump light. The first-order dispersion is positive, while the second-order dispersion of the third-order fiber at the central wavelength of the pump light is negative.

The two pump light and the signal light are respectively coupled by the pump coupler and the signal coupler, and then multiplexed by the wavelength division multiplexer, and enter the first stage, the second stage, and the third stage high nonlinear optical fiber in sequence. After the input signal light and the two pump lights enter the first-stage fiber, idle light will be generated, and the gain spectrum at the output end is approximately symmetrically distributed around the center wavelength of the pump light, but not flat. After the signal light, pump light and idle light pass through the second-stage optical fiber, the concave part in the middle of the gain spectrum is reduced, and the unevenness of the gain spectrum curve (the difference between the maximum gain and the minimum gain) is reduced. After passing through the third-level optical fiber, the gain spectrum is corrected, and its flatness reaches within 0.2dB.

The flat bandwidth and the gain of the fiber parametric amplifier of the present invention depend on the physical parameters of the first-stage optical fiber such as zero dispersion wavelength, second-order dispersion and fourth-order dispersion, fiber length and two pumping light wavelengths and pumping light power, the second, The function of the third-stage fiber is to flatten the gain spectrum generated by the first-stage fiber.

The length of the first-stage optical fiber, the second-stage optical fiber and the third-stage optical fiber of the optical fiber parametric amplifier of the present invention is between 0.1-300 meters, and the nonlinear coefficient of the optical fiber is between 1-300W ^- 1.Km ^-1 , four The absolute value of the order dispersion is less than 1.0×10 ^-4 ps ⁴ km ^-1 . The zero-dispersion wavelength of the first-stage fiber is close to the average wavelength of the two pump lights, and the pump light wavelength is selected in the range of 1250-1650nm, which is the low-loss window covering the full-wave fiber. The second-order dispersion of the second-stage fiber at the center wavelength of the pump light is positive, while the second-order dispersion of the third-stage fiber at the center wavelength of the pump light is negative.

The dual-pump fiber parametric amplifier of the present invention can not only provide a broadband flat gain spectrum, but also overcome the idle spectral line broadening caused by pump light jitter, and can also use two orthogonally polarized pump lights to obtain polarization independent characteristics. The double-pumped fiber parametric amplifier using the three-stage highly nonlinear fiber cascade structure can provide a gain bandwidth exceeding 400nm. Compared with the four-stage cascade structure, it not only reduces the number of highly nonlinear fiber stages, but also through the appropriate selection of parameters, The flat bandwidth of the fiber parametric amplifier can cover the low-loss window of the full-wave fiber (from 1250nm to 1650nm), which greatly increases the applicable wavelength range of WDM, so that the bandwidth of the full-wave fiber can be fully utilized and the WDM fiber can be promoted. Development of communication systems.

Description of drawings

Fig. 1 is a schematic structural diagram of the broadband optical fiber parametric amplifier of the present invention.

Figure 2 is a gain spectrum diagram of a broadband fiber parametric amplifier with a bandwidth of 405nm.

In Fig. 2, G ₁ , G ₂ , and G ₃ are the gain spectra after the first, second, and third stages of high nonlinearity respectively.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

The structure of the dual-pump broadband optical fiber parametric amplifier of the present invention is shown in Figure 1, by two pump lasers, pump coupler, signal laser, signal coupler, wavelength division multiplexer, first-order high nonlinear optical fiber , the second level of high nonlinear fiber and the third level of high nonlinear fiber. The output of the two pump lasers is connected to the wavelength division multiplexer through the pump coupler, the output of the signal laser is connected to the wavelength division multiplexer through the signal coupler, and the output of the wavelength division multiplexer is connected to the cascaded three-stage high nonlinear fiber.

The pump light waves (λ _p1 , λ _p2 ) emitted by the two pump light lasers are coupled into the transmission fiber through the pump light coupler, and the signal light (λ _s ) emitted by the signal light laser is also coupled through the signal light coupler Enter the transmission fiber, and then multiplex the two pump lights and the signal light into the sequentially cascaded three-stage high nonlinear fiber through the wavelength division multiplexer to generate nonlinear four-wave mixing, thus realizing the effect of parametric amplification . Among them, the zero-dispersion wavelength (λ ₀ ) of the first-stage fiber is close to the center wavelength of the pump light (λ _c = (λ _p1 +λ _p2 )/2), and the second-order fiber at the center wavelength of the pump light The dispersion is positive, while the second-order dispersion of the third-order fiber is negative at the central wavelength of the pump light.

The two pump light and the signal light are respectively coupled by the pump coupler and the signal coupler, and then multiplexed by the wavelength division multiplexer, and then enter the first stage, the second stage, the third stage high nonlinear fiber, and the third stage Highly nonlinear optical fibers are connected with optical fiber connectors, and the general interface loss is about 0.6dB. After the input signal light and the two pump lights enter the first-stage fiber, idle light will be generated, and the gain spectrum at the output end is approximately symmetrically distributed around the central wavelength of the pump light, but not flat. Then, after the signal light, pump light and idle light pass through the second-stage optical fiber, the concave part in the middle of the gain spectrum is reduced, thereby reducing the gain jitter generated by the first-stage optical fiber. After passing through the third-level optical fiber, the gain spectrum is further corrected, and its flatness reaches within 0.2dB.

Example:

Dual-pump broadband fiber parametric amplifier with 405nm bandwidth. Among them, the powers of the two pumping lights P ₁ =P ₂ =1W, the wavelengths of the two pumping lights λ _p1 =1440nm, λ _p1 =1460nm, the fourth-order dispersion coefficient of the optical fiber β ₄ =-2×10 ^-6 ps ⁴ km ^-1 , the optical fiber Non-linear coefficient γ=60km ^-1 W ^-1 . The length of the first-order highly nonlinear fiber is L ₁ =25m, and the second-order dispersion coefficient β ₂₁ =0 ps ² km ^-1 . The length of the second-level highly nonlinear fiber is L ₂ =2.6m, and the second-order dispersion coefficient β ₂₂ =2.91×10 ^-2 ps ² km ^-1 . The length of the third-level highly nonlinear fiber is L ₃ =2.3m, and the second-order dispersion coefficient β ₂₃ =-11.29×10 ^-2 ps ² km ^-1 . The invention first obtains the gain function of the dual-pump broadband optical fiber parameter amplifier by solving the nonlinear Schrödinger equation, and then obtains the optimal value of the three-level high nonlinear optical fiber parameter by using the genetic algorithm. The zero-dispersion wavelength of the first-stage optical fiber is close to the central wavelength of the pump light, that is, the second-order dispersion β ₂₁ =0 at the central wavelength of the pump light λ ₀ =1450nm; the first-stage optical fiber determines the gain level and gain of the broadband fiber parametric amplifier bandwidth, so in order to generate a large gain, the length of the first-stage fiber is 25m; in order to meet the phase-matching condition, it is necessary to make the fourth-order dispersion β ₄ of the third-stage fiber negative, and take β ₄₁ = β ₄₂ = β ₄₃ - 2×10 ^-6 ps ⁴ km ^-1 . The input signal light and the pump light are coupled into the first-stage optical fiber by a wavelength division multiplexing coupler to generate idle light, and the gain spectrum at the output end is approximately symmetrically distributed around the center wavelength of the pump light, but not flat, as shown in Figure 2 The gain spectrum in _G1 is shown. The second-order dispersion of the second-stage fiber at the central wavelength of the pump light is positive, β ₂₂ =2.91×10 ^-2 ps ² km ^-1 , which utilizes the parametric gain generated in the normal dispersion region when the phase matching condition is not satisfied, and the crossover The result of the modulation will produce a quadratic increase in gain, and the length of this level of fiber is 2.6m. After the signal light, pump light and idle light pass through the second-stage optical fiber, the concave part in the middle of the gain spectrum is reduced, and the unevenness of the gain spectrum curve (the difference between the maximum gain and the minimum gain) is reduced, as shown in the gain spectrum in Figure 2 Line _G2 is shown. The second-order dispersion of the third-stage fiber is negative, β ₂₃ =-11.29×10 ^-2 ps ² km ^-1 , which is used to provide an approximately square gain in an anomalous dispersion fiber, thereby reducing the resulting gain dithering. The fiber length of this grade is 2.3m. Therefore, after passing through the second and third stages of fiber, the gain spectrum of the dual-pump broadband fiber parametric amplifier is further corrected, and its flatness is within 0.2dB, as shown in the gain spectrum line G ₃ in Figure 2. In addition, the loss at the fiber connection at all levels also needs to be considered. Generally, the interface loss of high nonlinear fiber is about 0.6dB, that is to say, the power will be lost by 13%. The pump power should be adjusted as P _k =P ₀ ·α ^(k-1) , α=0.87, where P ₀ =P ₁ +P ₂ =2W. In summary, the first stage of fiber is used to generate a large gain, and the latter two stages of fiber are used to flatten the gain spectrum. Through the optimized design of the three-stage fiber parameters, a broadband fiber parametric amplifier with a gain bandwidth of 405nm is finally obtained, and its gain flatness is less than 0.2dB.

The flat bandwidth and gain of the dual-pump broadband fiber parametric amplifier of the present invention depend on the physical parameters of the first-stage optical fiber such as zero dispersion wavelength, second-order dispersion and fourth-order dispersion, fiber length, pump light wavelength and pump light power, The role of the second and third grade fibers is to flatten the gain spectrum generated by the first grade fiber. Proper selection of these parameters can obtain a fiber parametric amplifier with a flat bandwidth covering the low-loss window of the full-wave fiber, so that the bandwidth of the full-wave fiber can be fully utilized to promote the development of WDM fiber optic communication systems.

Table 1 shows the optimized parameters of the dual-pump broadband fiber parametric amplifier with a bandwidth of 405nm. In the table, L is the length of the fiber, β ₂ is the second-order dispersion coefficient, β ₄ is the fourth-order dispersion coefficient, P ₁ and P ₂ are the two pumps γ is the fiber nonlinear coefficient, λ _p1 and λ _p2 are the wavelengths of the two pump lights, λ ₀ is the zero dispersion wavelength of the fiber, and bandwidth is the gain bandwidth of the obtained broadband fiber parametric amplifier. optical fiber Level 1 level 2 level 3 L(m) 25 2.6 2.3 β ₂ (×10 ^-2 ps ² km ^-1 ) 0 2.91 -11.29 P ₁ =P ₂ =1W, β ₄ =-2×10 ^-6 ps ⁴ km ^-1 , γ = 60km ^-1 W ^-1 , λ _p1 = 1440nm, λ _p2 = 1460nm, λ ₀ = 1450nm, bandwidth = 405nm .

Claims (2)

1, a kind of double pump wide band optical fiber parameter amplifier, by pump laser, pumping coupler, signal laser, signal coupler, wavelength division multiplexer and highly nonlinear optical fiber are formed, the output that it is characterized in that two pump lasers connects wavelength division multiplexer through pumping coupler, the output of signal laser connects wavelength division multiplexer through signal coupler, the output of wavelength division multiplexer is connected to three grades of highly nonlinear optical fibers of cascade successively, the pumping light wave that two pump light laser instruments are launched is coupled into Transmission Fibers through pumping coupler, the flashlight that the flashlight laser instrument is launched also is coupled into Transmission Fibers through signal coupler, and then by wave division multiplex coupler two pump lights and flashlight are multiplexed in three grades of highly nonlinear optical fibers of cascade successively the four-wave mixing effect takes place, realize that parameter amplifies.

2, according to the double pump wide band optical fiber parameter amplifier of claim 1, the length that it is characterized in that described first order optical fiber, second level optical fiber, third level optical fiber is between 0.1-300 rice, and the nonlinear factor of optical fiber is at 1-300W ^-1.Km ^-1Between, the fourth-order dispersion absolute value is less than 1.0 * 10 ^-4Ps4km ^-1The centre wavelength of the zero-dispersion wavelength of first order optical fiber and two pump lights is approaching, the pump light wavelength is positioned at the 1250-1650nm scope, second level optical fiber the 2nd order chromatic dispersion of pump light central wavelength be on the occasion of, the 3rd optical fiber is negative value in the 2nd order chromatic dispersion of pump light central wavelength.

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