Terabit capacity mid-infrared optical signal generating device and signal generating method

Abstract

The present invention discloses a terabit-capacity mid-infrared optical signal generating device, which includes a dual-wavelength optical amplification unit and an ultra-wideband matching frequency conversion unit. The ultra-wideband matching frequency conversion unit adopts a step chirped polarization period method with matching design and a matching crystal temperature control. A terabit-capacity optical signal in the 1.5 μm band enters the dual-wavelength optical amplification unit, is coupled with a continuous pump optical signal in the 1 μm band with a wavelength of λ2, and then enters the ultra-wideband matching frequency conversion unit. Through the non-linear frequency conversion of ultra-wideband quasi-phase matching, a terabit-capacity mid-infrared optical signal is generated. Due to the adoption of the step chirped polarization period method with matching design and the matching crystal temperature control, the optical domain conversion bandwidth from the 1.5 μm band to the mid-infrared band can be increased to more than 50 nm, while the bandwidth occupied by the terabit signal is usually about 20 nm. Therefore, it is fully capable of realizing the generation of terabit-capacity optical signals in the mid-infrared band.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-high-speed mid-infrared space laser communication, and relates to a device for generating a terabit-capacity mid-infrared optical signal, and specifically to a method for generating a terabit-capacity mid-infrared optical signal. Background Art

[0002] The 6G communication network is the next generation of national strategic information infrastructure, which can realize high-speed interconnection between air, space, land and sea information nodes, and space laser communication technology is an important communication means to achieve high-speed interconnection between nodes. At present, space laser communication based on the near-infrared band has a good application effect under vacuum channel and high-visibility atmospheric channel conditions. However, when facing complex time-varying channels such as atmospheric turbulence, rain, snow and fog, its link access rate is only about 32%. Correspondingly, the 3-5μm mid-infrared light wave has obvious advantages in atmospheric channel transmission, such as strong resistance to atmospheric turbulence, low solar background noise and high transmittance under low visibility. For example, the French Aerospace Research Agency has released the "SCALPEL" research plan, which plans to target new spectral band communication methods that are more suitable for atmospheric transmission and weak turbulence effects. By comparing the various characteristics of near-infrared and mid-infrared in atmospheric transmission, the mid-infrared band (3-5μm) is selected as the communication wavelength. Therefore, for the indispensable atmospheric links in the space network, the use of the mid-infrared band to achieve atmospheric communication is a very promising new communication method. Currently, the use of nonlinear optical frequency conversion technology is an effective means to generate high-speed mid-infrared optical signals. It can convert near-infrared optical signals to the mid-infrared band and retain the original modulation information. However, it is currently limited by the single polarization period characteristics of nonlinear crystals and temperature sensitivity. The conversion bandwidth is generally a few nanometers, which leads to bottlenecks in further improving the capacity of mid-infrared optical signals and makes it difficult to generate mid-infrared optical signals with a capacity of more than ~100Gbps. Therefore, in order to further break through the transmission capacity of the mid-infrared band and move towards the generation of mid-infrared optical signals with a terabit (~Tbps) capacity, it is necessary to greatly improve the bandwidth and gain flatness characteristics of the nonlinear frequency conversion process. However, there is currently no method for generating mid-infrared optical signals with a terabit capacity. Summary of the invention

[0003] The purpose of the present invention is to provide a terabit capacity mid-infrared optical signal generating device, which solves the problem that the prior art is difficult to achieve terabit capacity optical signal generation in the mid-infrared band.

[0004] Another object of the present invention is to provide a method for generating a terabit capacity mid-infrared optical signal.

[0005] The first technical solution adopted by the present invention is a terabit capacity mid-infrared optical signal generating device, including a dual-wavelength optical amplification unit and an ultra-wideband matching frequency conversion unit. The ultra-wideband matching frequency conversion unit adopts a matching designed step-chirp polarization period mode and matching crystal temperature control. The 1.5μm band terabit capacity optical signal enters the dual-wavelength optical amplification unit, is coupled with a 1μm band continuous pump light with a wavelength of λ2, and then enters the ultra-wideband matching frequency conversion unit. After nonlinear frequency conversion of ultra-wideband quasi-phase matching, a terabit capacity mid-infrared optical signal is generated.

[0006] The present invention is also characterized in that:

[0007] The specific structure of the dual-wavelength optical amplification unit is as follows: it includes a 1.5μm band amplifier for receiving 1.5μm band terabit optical signals, the 1.5μm band amplifier is connected to a high-power optical isolator a, and also includes a 1μm band tunable laser, a 1μm band amplifier, and a high-power optical isolator b connected in sequence, the high-power optical isolator a and the high-power optical isolator b are both connected to the input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to a fiber collimating lens, the output end of the fiber collimating lens is connected to an ultra-wideband matching frequency conversion unit, and the four ports of the control unit are respectively connected to the 1μm band tunable laser, the 1μm band amplifier, the 1.5μm band amplifier, and the crystal heating device.

[0008] The specific structure of the ultra-wideband matching frequency conversion unit is as follows: it includes a step-chirp periodic polarization crystal, a crystal heating device, a filter, and a mid-infrared band optical power meter. The side of the step-chirp periodic polarization crystal close to the dual-wavelength optical amplification unit is called the A side, and the side of the step-chirp periodic polarization crystal away from the dual-wavelength optical amplification unit is called the B side. The A side of the step-chirp periodic polarization crystal is connected to the dual-wavelength optical amplification unit, the B side of the step-chirp periodic polarization crystal is connected to the filter, the filter is connected to the mid-infrared band optical power meter, the crystal heating device is connected to the step-chirp periodic polarization crystal, and the crystal heating device is also connected to the control unit in the dual-wavelength optical amplification unit. The step-chirp periodic polarization crystal and the output end of the optical fiber collimating lens are located on the same optical path.

[0009] The polarization period of the step-chirp periodic polarization crystal is a periodic step increase. The specific design is: the crystal length L is divided into n regions, each region contains k identical polarization periods Λ, and the period in the nth region is Λ n , the polarization period difference between adjacent regions △Λ=Λ n -Λ n-1 , the polarization duty cycle is 0.5.

[0010] The angle at which the output light of the optical fiber collimating lens is incident on the surface of the step-chirp periodically polarized crystal is between 89° and 91°.

[0011] The output wavelength of the 1μm band tunable laser is tuned between 1μm and 1.1μm, and the output is linearly polarized light; the 1μm band amplifier is a fully polarization-maintaining amplifier that can amplify any wavelength between 1μm and 1.1μm; the 1.5μm band amplifier is a fully polarization-maintaining amplifier that can amplify any wavelength between 1530nm and 1565nm.

[0012] The modulation format of the 1.5μm band terabit optical signal is any one of an intensity optical signal, a phase optical signal and a high-order modulated optical signal; the high-power optical isolator a, the high-power optical isolator b and the wavelength division multiplexer are all polarization-maintaining devices, and can withstand a maximum optical power of 10W; the temperature range of the crystal heating device is 20℃~100℃.

[0013] The step-chirp periodically poled crystal is any one of magnesium oxide-doped periodically poled lithium niobate crystal, magnesium oxide-doped periodically poled lithium tantalate crystal, and periodically poled lithium niobate crystal; the filter is any one of a germanium window, a silicon window, and a barium fluoride window.

[0014] The second technical solution adopted by the present invention is a method for generating a terabit-capacity optical signal in the mid-infrared band, using a terabit-capacity mid-infrared optical signal generating device. The process is as follows: a terabit-capacity optical signal with a central wavelength of λ1 in the 1.5μm band and an optical signal output by a tunable laser in the 1μm band are respectively input into a dual-wavelength optical amplification unit, and after amplification, filtering, coupling, and collimation, spatial light is obtained. The spatial light is input into an ultra-wideband matching frequency conversion unit, and after nonlinear frequency conversion of ultra-wideband quasi-phase matching, a terabit-capacity mid-infrared optical signal is generated.

[0015] The method for generating a terabit-capacity optical signal in the mid-infrared band is specifically implemented according to the following steps:

[0016] Step 1, the control unit sets the 1 μm band tunable laser to output a pump light with a wavelength of λ2 in the range of 1 μm to 1.1 μm, and the output power range of the 1.5 μm band amplifier and the 1 μm band amplifier is 1 W to 5 W;

[0017] Step 2, the terabit capacity optical signal with a central wavelength of λ1 in the 1.5μm band enters the 1.5μm band amplifier for amplification, and then enters the wavelength division multiplexer after passing through the high-power optical isolator a; at the same time, the 1μm band tunable laser outputs pump light with a wavelength range of λ2 between 1μm and 1.1μm, and enters the wavelength division multiplexer after being amplified by the 1μm band amplifier and passing through the high-power optical isolator b;

[0018] Step 3: After the two optical signals are coupled in the wavelength division multiplexer, they enter the fiber collimating lens for collimation and output spatial light. The spatial light is incident on the surface of the step-chirp periodic polarization crystal at a certain angle from the A side, and then output from the B side of the step-chirp periodic polarization crystal and enters the filter.

[0019] Step 4, after passing through the filter, only the 3-5μm mid-infrared light signal output is retained, and the output mid-infrared band terabit capacity light signal enters the mid-infrared band optical power meter for power monitoring; the control signal of the control unit sets the corresponding temperature to adapt to the phase matching process of the optical difference frequency process, and monitors the power of the mid-infrared band terabit capacity light signal in the mid-infrared band optical power meter. When the power reaches the maximum, the surface achieves the best phase matching of the nonlinear frequency conversion process at this temperature.

[0020] The beneficial effects of the present invention are:

[0021] 1) It can realize the generation of ultra-large capacity mid-infrared optical signals at the terabit level. Due to the matched step-chirp polarization cycle method and the matched crystal temperature control, the optical domain conversion bandwidth from the 1.5μm band to the mid-infrared band can be increased to more than 50nm, while the bandwidth occupied by the terabit signal is usually about 20nm. Therefore, it is fully capable of realizing the generation of terabit capacity optical signals in the mid-infrared band, which is 5 to 10 times higher than the conversion bandwidth using a single polarization cycle method. This lays a technical foundation for terabit capacity mid-infrared optical communication light sources.

[0022] 2) It can realize the generation of mid-infrared band terabit capacity optical signals with flat wavelength power. Since the 1.5μm band terabit capacity optical signals are usually composed of wavelength division multiplexing, they contain many independent wavelengths. The step-chirp periodic polarization method using the toe-cut method can still maintain a relatively flat gain curve within a wide conversion bandwidth. Therefore, the power difference between all wavelengths converted to the mid-infrared band is small, ensuring the power balance between the various wavelengths of the mid-infrared band terabit capacity optical signals.

[0023] 3) The device is simple and easy to operate. Since the nonlinear frequency conversion method based on periodic polarization crystal quasi-phase matching is adopted, the principle is that the periodic phase reversal allows the conversion efficiency to be accumulated step by step with the increase of propagation distance, so the accuracy of the angle position of the incident light is relatively low. Although traditional birefringence phase matching can also achieve nonlinear frequency conversion, it has strict requirements on the angle of the incident light to meet the phase matching. Therefore, the device and method are relatively simple and easy to generate terabit capacity mid-infrared high-speed optical signals, and the accuracy requirements for angle control and adjustment are relatively low.

[0024] 4) It can support the generation of mid-infrared high-speed optical signals in various modulation formats. Due to the use of nonlinear frequency conversion based on periodically polarized crystals, transparent conversion of various modulation formats can be achieved, such as intensity optical signals (OOK), phase optical signals (BPSK), and high-order modulated optical signals (QPSK, 16QAM, 64QAM). BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the infrared optical signal generating device with terabit capacity and the signal generating process of the present invention;

[0026] Figure 2 It is a detailed design structure diagram of the step-chirp periodically polarized crystal;

[0027] Figure 3 This is a schematic diagram of the spectrum of a terabit-capacity optical signal converted from the near-infrared band to the mid-infrared band. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The terabit capacity mid-infrared optical signal generating device of the present invention proposes a step-chirp type periodic polarization mode to match the quasi-phase matching of ultra-large bandwidth optical signals in the nonlinear frequency conversion process, thereby realizing the generation of ultra-large capacity (terabit) mid-infrared optical signals. Figure 1 As shown, it includes a dual-wavelength optical amplification unit and an ultra-wideband matching frequency conversion unit. The ultra-wideband matching frequency conversion unit adopts a matching designed step-chirp polarization period mode and matching crystal temperature control. The 1.5μm band terabit capacity optical signal enters the dual-wavelength optical amplification unit, is coupled with the 1μm band continuous pump light with a wavelength of λ2, and then enters the ultra-wideband matching frequency conversion unit. After the nonlinear frequency conversion of the ultra-wideband quasi-phase matching, a terabit capacity mid-infrared optical signal is generated.

[0030] Among them, the ultra-wideband matched frequency conversion unit adopts a matching step-chirp polarization period method and matching crystal temperature control, which can support the optical domain conversion bandwidth from 1.5μm band to mid-infrared band to be increased to more than 50nm. The bandwidth occupied by terabit signals is usually about 20nm. Therefore, it is fully capable of realizing the generation of terabit capacity optical signals in the mid-infrared band, which is 5 to 10 times higher than the conversion bandwidth using a single polarization period method.

[0031] Since 1.5μm-band terabit-capacity optical signals are usually composed of wavelength division multiplexing, they contain many independent wavelengths. The step-chirp periodic polarization method using the toe-cut method can still maintain a relatively flat gain curve within a very wide conversion bandwidth. Therefore, the power difference between all wavelengths converted to the mid-infrared band is small, ensuring the power balance between the various wavelengths of the mid-infrared band terabit-capacity optical signals.

[0032] The specific structure of the dual-wavelength optical amplification unit is as follows: it includes a 1.5μm band amplifier for receiving 1.5μm band terabit optical signals, the 1.5μm band amplifier is connected to a high-power optical isolator a, and also includes a 1μm band tunable laser, a 1μm band amplifier, and a high-power optical isolator b connected in sequence, the high-power optical isolator a and the high-power optical isolator b are both connected to the input end of a wavelength division multiplexer, the wavelength division multiplexer is used to couple two optical signals, the output end of the wavelength division multiplexer is connected to a fiber collimating lens, the coupled optical signal is collimated by the fiber collimating lens, the output end of the fiber collimating lens is connected to an ultra-wideband matching frequency conversion unit, and the four ports of the control unit are respectively connected to the 1μm band tunable laser, the 1μm band amplifier, the 1.5μm band amplifier, and the crystal heating device. The control unit can control the wavelength tuning of the 1μm band tunable laser, can control the output pump light power of the 1μm band amplifier to be adjusted within the range of 1W to 5W, and can control the output pump light power of the 1.5μm band amplifier to be adjusted within the range of 1W to 5W.

[0033] The specific structure of the ultra-wideband matching frequency conversion unit is as follows: it includes a step-chirp periodic polarization crystal, a crystal heating device, a filter, and a mid-infrared band optical power meter. The side of the step-chirp periodic polarization crystal close to the dual-wavelength optical amplification unit is called the A side, and the side of the step-chirp periodic polarization crystal away from the dual-wavelength optical amplification unit is called the B side. The A side of the step-chirp periodic polarization crystal is connected to the dual-wavelength optical amplification unit, the B side of the step-chirp periodic polarization crystal is connected to the filter, the filter is connected to the mid-infrared band optical power meter, the crystal heating device is connected to the step-chirp periodic polarization crystal, and the crystal heating device is also connected to the control unit in the dual-wavelength optical amplification unit. The step-chirp periodic polarization crystal and the output end of the optical fiber collimating lens are located on the same optical path.

[0034] Among them, the input end of the ultra-wideband matching frequency conversion unit is connected to the fiber collimating lens. The pump light and signal light after the output coupling of the fiber collimating lens enter the step-chirp periodic polarization crystal. Due to the effect of the optical difference frequency nonlinear effect, the two beams of light generate new difference frequency light waves when propagating in the step-chirp periodic polarization crystal. Due to the step chirp design that matches the polarization period of the crystal, the input ultra-large bandwidth terabit capacity optical signal meets the quasi-phase matching condition in the optical difference frequency effect, and thus has the conditions for generating a mid-infrared band terabit capacity optical signal. The output mid-infrared band terabit capacity optical signal is connected to a filter to filter out the residual 1μm band pump light and 1.5μm band signal light, and only retain the mid-infrared band terabit capacity optical signal output. One end of the crystal heating device is connected to the control unit of the dual-wavelength optical amplification unit, and the other end is connected to the periodic polarization crystal. The optimal matching temperature of the periodic polarization crystal is set according to the control signal of the control unit.

[0035] The polarization period of the step-chirp periodic polarization crystal is a periodic step increase, and the specific design is as follows: Figure 2 As shown, the crystal length L is divided into n regions, each region contains k identical polarization periods Λ, and the period in the nth region is Λ n , the polarization period difference between adjacent regions △Λ=Λ n -Λ n-1 , the polarization duty cycle is 0.5.

[0036] The angle at which the output light of the optical fiber collimating lens is incident on the surface of the step-chirp periodically polarized crystal is between 89° and 91°.

[0037] The output wavelength of the 1μm band tunable laser is tuned between 1μm and 1.1μm, and the output is linearly polarized light; the 1μm band amplifier is a fully polarization-maintaining amplifier that can amplify any wavelength between 1μm and 1.1μm; the 1.5μm band amplifier is a fully polarization-maintaining amplifier that can amplify any wavelength between 1530nm and 1565nm.

[0038] The modulation format of the 1.5μm band terabit optical signal is any one of intensity optical signal, phase optical signal and high-order modulated optical signal; high-power optical isolator a, high-power optical isolator b and wavelength division multiplexer are all polarization-maintaining devices, and can withstand a maximum optical power of 10W; the temperature range of the crystal heating device is 20℃~100℃, and the control accuracy can be as low as 0.1℃.

[0039] The step-chirp periodically poled crystal is any one of magnesium oxide-doped periodically poled lithium niobate crystal, magnesium oxide-doped periodically poled lithium tantalate crystal, and periodically poled lithium niobate crystal; the filter is any one of a germanium window, a silicon window, and a barium fluoride window.

[0040] The working principle of the mid-infrared band terabit capacity optical signal generation device is:

[0041] like Figure 1 As shown in FIG. 1 , in the dual-wavelength optical amplifier unit, the input center wavelength λ1 of the 1.5 μm band terabit capacity optical signal power is set to P 1-in , 3dB signal bandwidth is △λ, covering the wavelength range from λ 1-L to λ 1-R , that is, satisfying λ 1-L -λ 1-R =△λ. Set the output wavelength of the 1μm band tunable laser to λ2 and the power to P 2-in After the 1.5μm band terabit capacity optical signal passes through the 1.5μm band amplifier, the output power is P 1-out , the gain of the 1.5μm band amplifier is G1, then P 1-out and P 1-in The relationship is shown as follows:

[0042] P 1-out =P 1-in G1 (1)

[0043] Similarly, after the 1μm band pump light passes through the 1μm band amplifier, the output power is P 2-out , the gain of the 1μm band amplifier is G2, then P 2-out and P 2-in The relationship is shown as follows:

[0044] P 2-out =P 2-in G2 (2)

[0045] The gains G1 and G2 of the 1.5μm band amplifier and the 1μm band amplifier can be adjusted by the control unit, and the adjustment range is between 30 and 37dB. Assuming that the total loss of the signal light by the high-power optical isolator a, the wavelength division multiplexer, and the fiber collimating lens is α1, and the total loss of the pump light by the high-power optical isolator b, the wavelength division multiplexer, and the fiber collimating lens is α2, then the 1.5μm band signal light power P' emitted from the fiber collimating lens is 1-out and 1μm band pump light power P' 2-out They are shown as follows:

[0046] P' 1-out =P 1-out α1 (3)

[0047] P' 2-out =P 2-out α2 (4)

[0048] The polarization period of the step-chirp periodic polarization crystal increases step by step along the propagation direction. The specific design is as follows: Figure 2 As shown, the crystal length L is divided into n regions, each region contains k identical periods Λ, and the period in the nth region is Λ n , the period difference between adjacent regions is △Λ=Λ n -Λ n-1 , the duty cycle of the polarization period is 0.5.

[0049] Since the wavelength range of 1.5μm band terabit capacity optical signal covers from λ 1-L to λ 1-R , that is, satisfying λ 1-L -λ 1-R =△λ. All wavelengths within this △λ bandwidth need to meet the quasi-phase matching condition in the crystal to achieve the generation of terabit capacity mid-infrared optical signals. When the 1.5μm band terabit capacity optical signal and the pump light λ2 are incident on the periodically polarized crystal, an optical difference frequency effect will occur. For the left wavelength λ 1-L Theoretically, the wavelength of the difference frequency light generated is λ 3-L , for the right wavelength λ 1-R Theoretically, the wavelength of the difference frequency light generated is λ 3-R , and satisfies the following formula:

[0050]

[0051]

[0052] From equations (5) and (6), it can be seen that the wavelength range of the generated mid-infrared band terabit capacity optical signal is from λ 3-L to λ 3-R , in quasi-phase matching, the phase mismatch corresponding to each wavelength is The calculation of is as follows:

[0053]

[0054] In the formula, and are the wave vectors of signal light, pump light and idler light respectively, is the phase compensation introduced by periodic polarization. If the three beams are collinear, the wave vector can be expressed as a scalar. In addition, under the condition of three beams being collinear, equation (7) can also be expressed in the form of wavelength as shown below:

[0055]

[0056] Where λ1, λ2 and λ3 are the wavelengths of the signal light, pump light and idler light, respectively, and n1, n2 and n3 are the refractive indices of the signal light, pump light and idler light in the periodically polarized crystal, respectively. When the three beams of light propagate in the periodically polarized crystal, the refractive index n in the crystal is related to the wavelength λ and the temperature T, which satisfies the Sellmeier equation, as shown in the following equation:

[0057]

[0058] In the formula, coefficients a1~a6 and b1~b4 are the parameters of the periodically poled crystal, and different materials correspond to different parameters. Taking 5% magnesium oxide doped periodically poled lithium niobate crystal (MgO:PPLN) as an example, its parameters are shown in Table 1:

[0059] Table 1

[0060] <![CDATA[a1]]> <![CDATA[a2]]> <![CDATA[a3]]> <![CDATA[a4]]> <![CDATA[a5]]> <![CDATA[a6]]> <![CDATA[b1]]> <![CDATA[b2]]> <![CDATA[b3]]> <![CDATA[b4]]> 5.756 0.098 0.202 189.32 12.52 1.32E-02 2.86E-06 4.70E-08 6.11E-08 1.51E-04

[0061] In addition, in formula (9), f is a temperature-related function, and its expression is shown as follows:

[0062] f=(T-24.5)(T+570.82) (10)

[0063] Under the combined formula (8) to (10), it can be calculated that when the temperature is T, the wavelength of the signal light is λ 1-L and λ 1-R When the phase mismatch △k = 0, the corresponding polarization period Λ value is as shown in equations (11) and (12):

[0064]

[0065]

[0066] Therefore, when the polarization period of the step-chirp periodic polarization crystal changes from Λ 1-L Gradually increase to Λ 1-R When 1-L to λ 1-R The phase mismatch of all wavelengths will encounter the situation of △k=0, so the conversion of near-infrared optical signals with terabit capacity to the mid-infrared band can be achieved.

[0067] Take the following parameters as an example: crystal temperature T = 50 ° C, 1.5 μm band terabit capacity optical signal bandwidth covers the entire band (limit case), that is, λ 1-L =1530nm,λ 1-R =1565nm, the corresponding signal bandwidth is △λ=35nm. When the frequency points λ on both sides of the signal 1-L and λ 1-RWhen the quasi-phase matching conditions are met in the crystal, the two corresponding periodic polarization values ​​calculated are Λ 1-L =30.1467μm, Λ 1-R =30.6571μm, so when the polarization period of the two sides of the step-chirp periodic polarization crystal is set to Λ 1-L and Λ 1-R , the polarization period of the middle region is increased step by step at equal intervals to satisfy the 1-L to λ 1-R The quasi-phase matching of all wavelengths between the two wavelengths can be achieved. The incremental factor △Λ can be set between 0.001 and 0.005 μm. Taking 0.005 μm as an example, the number of polarization period regions n designed is as follows:

[0068] n=30.6571μm-30.1467μm / 0.005μm=102 (12)

[0069] If the number of periodic repetitions of each region k = 10, the length L of the entire crystal is calculated as follows:

[0070] L = k(Λ 1-L +Λ 1-L +0.005+Λ 1-L +0.005+0.005+...Λ 1-R )≈31mm (13)

[0071] It can be seen that when the wavelength coverage of the 1.5μm band optical signal is determined from λ 1-L to λ 1-R , crystal temperature T, step increment factor △Λ, and period repetition number k, the polarization period Λ on both sides of the step-chirped periodic polarization crystal can be completely calculated. 1-L and Λ 1-R , the number of periodic polarization regions n and the length L of the crystal. The calculation of these parameters provides effective input for the production of the crystal, which can meet the conversion of near-infrared optical signals with terabit capacity into the mid-infrared band.

[0072] The method for generating a terabit capacity optical signal in the mid-infrared band of the present invention uses a terabit capacity mid-infrared optical signal generating device, and the process is: inputting a terabit capacity optical signal with a central wavelength of λ1 in the 1.5μm band and a tunable laser output optical signal in the 1μm band into a dual-wavelength optical amplification unit respectively, amplifying, filtering, coupling, and collimating to obtain spatial light, inputting the spatial light into an ultra-wideband matching frequency conversion unit, and generating a terabit capacity mid-infrared optical signal through nonlinear frequency conversion of ultra-wideband quasi-phase matching. It is implemented specifically according to the following steps:

[0073] Step 1, the control unit sets the 1 μm band tunable laser to output a pump light with a wavelength of λ2 in the range of 1 μm to 1.1 μm, and the output power range of the 1.5 μm band amplifier and the 1 μm band amplifier is 1 W to 5 W;

[0074] Step 2, the terabit capacity optical signal with a central wavelength of λ1 in the 1.5μm band enters the 1.5μm band amplifier for amplification, and then enters the wavelength division multiplexer after passing through the high-power optical isolator a; at the same time, the 1μm band tunable laser outputs pump light with a wavelength range of λ2 between 1μm and 1.1μm, and enters the wavelength division multiplexer after being amplified by the 1μm band amplifier and passing through the high-power optical isolator b;

[0075] Step 3: After the two optical signals are coupled in the wavelength division multiplexer, they enter the fiber collimating lens for collimation and output spatial light. The spatial light is incident on the surface of the step-chirp periodic polarization crystal at a certain angle from the A side, and then output from the B side of the step-chirp periodic polarization crystal and enters the filter.

[0076] Step 4, after passing through the filter, only the 3-5μm mid-infrared light signal output is retained, and the output mid-infrared band terabit capacity light signal enters the mid-infrared band optical power meter for power monitoring; the control signal of the control unit sets the corresponding temperature to adapt to the phase matching process of the optical difference frequency process, and monitors the power of the mid-infrared band terabit capacity light signal in the mid-infrared band optical power meter. When the power reaches the maximum, the surface achieves the best phase matching of the nonlinear frequency conversion process at this temperature.

[0077] Example 1

[0078] The invention discloses a mid-infrared band terabit capacity optical signal generating device to generate mid-infrared band terabit capacity optical signals, that is, firstly, the 1.5μm band signal light and the 1μm band pump light are subjected to optical fiber amplification processing, so that the power of the 1.5μm band optical signal and the 1μm band pump light can be adjusted between 1 and 5W, and it is easy to generate nonlinear optical effects in the crystal. The two amplified light beams are respectively isolated by high-power light and then enter the wavelength division multiplexer to couple to one optical fiber, and then collimated by the optical fiber collimating lens and emitted at a vertical angle to the surface of the step-chirp periodic polarization crystal. When the two light beams propagate in the step-chirp periodic polarization crystal, mid-infrared idler light will be continuously generated due to the optical difference frequency nonlinear optical effect. In order to achieve quasi-phase-matched frequency conversion of ultra-wide bandwidth optical signals with terabit capacity in the crystal, the minimum value of the designed crystal polarization period can correspond to the optimal phase matching at the upper frequency edge of the terabit capacity optical signal, and the maximum value of the crystal polarization period can correspond to the optimal phase matching at the lower frequency edge of the terabit capacity optical signal. The polarization period in the middle area of ​​the crystal increases in a step-like manner from the minimum value to the maximum value, satisfying the phase matching of all frequencies from the upper frequency edge to the lower frequency edge, so that the input ultra-wide bandwidth terabit capacity optical signal satisfies the quasi-phase matching conditions in the optical difference frequency effect, and thus has the conditions to generate terabit capacity optical signals in the mid-infrared band.

[0079] Example 2

[0080] Reference Figure 1 The specific operation process of the mid-infrared band terabit capacity optical signal generating device of the present invention is as follows:

[0081] (1) Signal light and pump light power amplification: In the dual-wavelength optical amplification unit, the input 1.5μm band terabit capacity optical signal is first amplified to between 1W and 5W by configuring a 1.5μm band amplifier. Similarly, the pump light output by the 1μm band tunable laser is amplified to between 1W and 5W by configuring a 1μm band amplifier. The power of the two beams after amplification is expressed as follows:

[0082] P 1-out =P 1-in G1 (1)

[0083] P 2-out =P 2-in G2 (2)

[0084] (2) Coupling of signal light and pump light: The two amplified light beams are coupled through a wavelength division multiplexer and then enter a fiber collimator lens. The fiber collimator lens expands and collimates the light beams. The outgoing light is vertically incident on the surface of a step-chirp periodically polarized crystal. When the two strong light beams propagate inside the periodically polarized crystal, idler light is generated due to the optical difference frequency effect.

[0085] (3) Phase mismatch in the optical difference frequency process: Since the wavelength range of the 1.5 μm band terabit capacity optical signal is from λ 1-L to λ 1-R , that is, the bandwidth is λ 1-L -λ 1-R =△λ. All wavelengths within this △λ bandwidth need to meet the quasi-phase matching condition in the crystal to achieve the generation of terabit capacity mid-infrared optical signals. For the left wavelength λ 1-L Theoretically, the wavelength of the difference frequency light generated is λ 3-L , for the right wavelength λ 1-R Theoretically, the wavelength of the difference frequency light generated is λ 3-R , and satisfies the following formula:

[0086]

[0087]

[0088] When the 1.5 μm band terabit capacity optical signal and the pump light λ2 are incident on the periodically polarized crystal, an optical difference frequency effect will occur. From equations (5) and (6), it can be seen that the wavelength range of the generated terabit mid-infrared optical signal is from λ 3-L to λ 3-R In order to obtain the matching polarization period result, the following calculations need to be completed. In quasi-phase matching, the signal light wave vector Pump light wave vector and idler wave vector Phase mismatch The relationship calculation is shown as follows:

[0089]

[0090] When the three beams of light propagate in the periodically poled crystal, the refractive index n in the crystal is related to the wavelength λ and the temperature T, which satisfies the Sellmeier equation. Therefore, by substituting the coefficients a1~a6 and b1~b4 of the periodically poled crystal into the Sellmeier equation, the refractive indices n1, n2, and n3 of the signal light, the pump light, and the idler light in the periodically poled crystal can be calculated. Then, equation (7) can be further expressed as follows:

[0091]

[0092] (4) Step-chirp periodic polarization crystal matching design: In order to achieve a wavelength range from λ 1-L to λ 1-R Quasi-phase matching of terabit capacity optical signals requires the design of corresponding polarization periodic structures. The specific design is as follows: Figure 2As shown, the structure is a step-chirp periodic polarization mode, which is divided into n regions on the crystal length L. Each region contains k identical polarization periods Λ, and the polarization period in the nth region is Λ n , the polarization period difference between adjacent regions is △Λ=Λ n -Λ n-1 , along the propagation direction, the polarization period increases step by step, and the duty cycle of the polarization period is 0.5. When the temperature is T, the wavelengths of the signal light are λ 1-L and λ 1-R When the phase mismatch △k = 0, the corresponding polarization period Λ value is calculated as shown in equations (9) and (10):

[0093]

[0094]

[0095] Therefore, when the polarization period of the step-chirp periodic polarization crystal changes from Λ 1-L Gradually increase to Λ 1-R When 1-L to λ 1-R The phase mismatch of all wavelengths between them will encounter the situation of △k = 0, so it is possible to convert the near-infrared optical signal with a terabit capacity to the mid-infrared band. Its frequency conversion spectrum is as follows: Figure 3 shown.

[0096] Example 3

[0097] Take the following parameters as an example: crystal temperature T = 50 ° C, 1.5 μm band terabit capacity optical signal bandwidth covers the entire band (limit case), that is, λ 1-L =1530nm,λ 1-R =1565nm, the corresponding signal bandwidth is △λ=35nm. When the frequency points λ on both sides of the signal 1-L and λ 1-R When the quasi-phase matching conditions are met in the crystal, the two corresponding periodic polarization values ​​calculated are Λ 1-L =30.1467μm, Λ 1-R =30.6571μm, so when the polarization period on both sides of the step-chirp periodic polarization crystal is set to Λ 1-L and Λ 1-R , the polarization period of the middle region is increased step by step at equal intervals to satisfy the 1-L to λ 1-R The quasi-phase matching of all wavelengths between them can be achieved. The incremental factor △Λ can be set between 0.001 and 0.005μm. Taking 0.005μm as an example, the number of the entire periodic polarization region n designed is as follows:

[0098] n=30.6571μm-30.1467μm / 0.005μm=102 (11)

[0099] The number of periodic repetitions of each region is k = 10, and the length of the entire crystal is calculated as follows:

[0100] L = k(Λ 1-L +Λ 1-L +0.005+Λ 1-L +0.005+0.005+...Λ 1-R )≈31mm (12)

[0101] From the above example, it can be seen that when the wavelength range λ of the 1.5μm band signal is determined 1-L to λ 1-R , crystal temperature T, step increment factor △Λ, period repetition number k, the polarization period Λ on both sides of the step-chirped periodic polarization crystal can be completely calculated 1-L and Λ 1-R , the number of periodic polarization regions n and the length L of the crystal. The calculation of these parameters provides effective input for the production of the crystal, which can meet the conversion of near-infrared optical signals with terabit capacity into the mid-infrared band.

[0102] So far, through the above steps, the process of generating terabit-capacity optical signals in the mid-infrared band has been realized.

[0103] Through the above method, the terabit capacity mid-infrared optical signal generating device of the present invention proposes a step-chirp periodic polarization method to match the quasi-phase matching of ultra-large bandwidth optical signals in the process of nonlinear frequency conversion, thereby realizing the generation of ultra-large capacity (terabit) mid-infrared optical signals.

Claims

1. A terabit capacity mid-infrared optical signal generating device, characterized in that: It includes a dual-wavelength optical amplification unit and an ultra-wideband matching frequency conversion unit. The ultra-wideband matching frequency conversion unit adopts a matching step-chirp polarization period mode and matching crystal temperature control. The 1.5μm band terabit capacity optical signal enters the dual-wavelength optical amplification unit, is coupled with the 1μm band continuous pump light with a wavelength of λ2, and then enters the ultra-wideband matching frequency conversion unit. After the nonlinear frequency conversion of the ultra-wideband quasi-phase matching, a terabit capacity mid-infrared optical signal is generated. The specific structure of the dual-wavelength optical amplification unit is as follows: it includes a 1.5μm band amplifier for receiving 1.5μm band terabit optical signals, the 1.5μm band amplifier is connected to a high-power optical isolator a, and also includes a 1μm band tunable laser, a 1μm band amplifier, and a high-power optical isolator b connected in sequence, the high-power optical isolator a and the high-power optical isolator b are both connected to the input end of a wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to a fiber collimating lens, the output end of the fiber collimating lens is connected to an ultra-wideband matching frequency conversion unit, and the four ports of the control unit are respectively connected to the 1μm band tunable laser, the 1μm band amplifier, the 1.5μm band amplifier, and the crystal heating device; The specific structure of the ultra-wideband matching frequency conversion unit is as follows: it includes a step-chirp periodic polarization crystal, a crystal heating device, a filter, and a mid-infrared band optical power meter. The side of the step-chirp periodic polarization crystal close to the dual-wavelength optical amplification unit is called the A side, and the side of the step-chirp periodic polarization crystal away from the dual-wavelength optical amplification unit is called the B side. The A side of the step-chirp periodic polarization crystal is connected to the dual-wavelength optical amplification unit, the B side of the step-chirp periodic polarization crystal is connected to the filter, and the filter is connected to the mid-infrared band optical power meter. The crystal heating device is connected to the step-chirp periodic polarization crystal, and the crystal heating device is also connected to the control unit in the dual-wavelength optical amplification unit. The step-chirp periodic polarization crystal and the output end of the optical fiber collimating lens are located on the same optical path; the polarization period of the step-chirp periodic polarization crystal is periodically increased in steps, and the specific design is as follows: at the length of the crystal, the step-chirp periodic polarization crystal is connected to the output end of the optical fiber collimating lens. L The upper part is divided into n regions, each containing k The same polarization period Λ, n The period in the region is Λ n , the polarization period difference between adjacent regions , the polarization duty cycle is 0.5; the angle at which the output light of the fiber collimating lens is incident on the surface of the step-chirp periodically polarized crystal is between 89° and 91°.

2. The terabit capacity mid-infrared optical signal generating device according to claim 1, characterized in that: The output wavelength of the 1 μm band tunable laser is tuned between 1 μm and 1.1 μm, and the output is linearly polarized light; the 1 μm band amplifier is a full polarization-maintaining amplifier, which can amplify any wavelength between 1 μm and 1.1 μm; The 1.5μm band amplifier is a fully polarization-maintaining amplifier that can amplify any wavelength between 1530 nm and 1565 nm.

3. The terabit capacity mid-infrared optical signal generating device according to claim 1, characterized in that: The modulation format of the 1.5μm band terabit optical signal is any one of an intensity optical signal, a phase optical signal and a high-order modulated optical signal; the high-power optical isolator a, the high-power optical isolator b and the wavelength division multiplexer are all polarization-maintaining devices and can withstand a maximum optical power of 10W; the temperature range of the crystal heating device is 20℃~100℃.

4. The terabit capacity mid-infrared optical signal generating device according to claim 1, characterized in that: The step-chirp periodically-poled crystal is one of a magnesium oxide-doped periodically-poled lithium tantalate crystal or a periodically-poled lithium niobate crystal; and the optical filter is one of a silicon window plate or a barium fluoride window plate.

5. A method for generating a terabit capacity optical signal in the mid-infrared band, characterized in that: The process of using the terabit capacity mid-infrared optical signal generating device according to claim 1 is as follows: a terabit capacity optical signal with a central wavelength of λ1 in the 1.5 μm band and an optical signal outputted by a tunable laser in the 1 μm band are respectively inputted into a dual-wavelength optical amplification unit, and spatial light is obtained after amplification, filtering, coupling and collimation, and the spatial light is inputted into an ultra-wideband matching frequency conversion unit, and a terabit capacity mid-infrared optical signal is generated after nonlinear frequency conversion of ultra-wideband quasi-phase matching; the process is specifically implemented in the following steps: Step 1, the control unit sets the 1 μm band tunable laser to output a pump light with a wavelength of λ2 in the range of 1 μm to 1.1 μm, and the output power range of the 1.5 μm band amplifier and the 1 μm band amplifier is 1 W to 5 W; Step 2, the terabit capacity optical signal with a central wavelength of λ1 in the 1.5μm band enters the 1.5μm band amplifier for amplification, and then enters the wavelength division multiplexer after passing through the high-power optical isolator a; at the same time, the 1μm band tunable laser outputs pump light with a wavelength of λ2 in the wavelength range of 1μm to 1.1μm, and enters the wavelength division multiplexer after being amplified by the 1μm band amplifier and passing through the high-power optical isolator b; Step 3: After the two optical signals are coupled in the wavelength division multiplexer, they enter the fiber collimating lens for collimation and output spatial light. The spatial light is incident on the surface of the step-chirp periodic polarization crystal at 89°~91° from the A side, and then output from the B side of the step-chirp periodic polarization crystal and enters the filter. Step 4, after passing through the filter, only the 3~5μm mid-infrared optical signal output is retained, and the output mid-infrared band terabit capacity optical signal enters the mid-infrared band optical power meter for power monitoring; the control signal of the control unit sets the corresponding temperature to adapt to the phase matching process of the optical difference frequency process, and monitors the power of the mid-infrared band terabit capacity optical signal in the mid-infrared band optical power meter. When the power reaches the maximum, it indicates that the optimal phase matching of the nonlinear frequency conversion process is achieved at this temperature.

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