Mid-infrared band spatial Doppler frequency shift effect simulation generation device and generation method

Abstract

The present invention discloses a mid-infrared band space Doppler frequency shift effect simulation generation device, including an optical frequency shift unit, the optical frequency shift unit is connected to the input end of the optical amplification unit, and also includes a dichroic mirror, a reflector, and the dichroic mirror is parallel to the reflector. The optical amplification unit also inputs a 1.5 μm band light signal, and the optical frequency shift unit, the optical amplification unit, and the dichroic mirror form a 1 μm band transmission light path, and the optical amplification unit, the reflector, and the dichroic mirror form a 1.5 μm band reflection light path. The 1 μm band transmission light path and the 1.5 μm band reflection light path partially overlap after being emitted by the dichroic mirror to form a coincidence light path, and a periodic polarization crystal is arranged on the coincidence light path, and a filter is arranged at the output end of the periodic polarization crystal; the device of the present invention solves the problem that the prior art is difficult to simulate the real Doppler frequency shift effect of mid-infrared light waves in space. The present invention also discloses a mid-infrared band space Doppler frequency shift effect simulation generation method, which can generate a simulated frequency-shifted mid-infrared frequency-shifted light wave.

Description

Technical Field

[0001] The present invention belongs to the technical field of mid-infrared band spatial light information transmission and detection, and specifically relates to a mid-infrared band spatial Doppler frequency shift effect simulation generation device, and also relates to a mid-infrared band spatial Doppler frequency shift effect simulation generation method. Background Art

[0002] The 6G information network is the next generation of national strategic information infrastructure, which can realize high-speed interconnection between air, space, land and sea information nodes. Using laser as a carrier to realize information transmission is an important means to achieve high-speed interconnection between nodes. At present, optical information transmission and detection based on the near-infrared band have good application effects under vacuum channels and high-visibility atmospheric channels. However, when facing complex time-varying channels such as atmospheric turbulence, rain, snow and fog, its link accessibility 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 proportion of 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 transmission wavelength.

[0003] Therefore, for the atmospheric channels in the space network, the use of mid-infrared bands to realize information transmission in the atmospheric channels (such as laser detection and laser communication) is a very promising new means. In addition, since the space nodes (such as satellites, aerial platforms, and aircraft) are not fixed nodes in the space network, they always move along the orbital route. Therefore, when laser communication or laser detection is performed between two space nodes, the relative movement speed causes the mid-infrared light waves to produce a Doppler shift effect. At present, mid-infrared quantum cascade lasers are used to generate mid-infrared light waves, and the mid-infrared wavelength is adjusted by changing the temperature or current to simulate the Doppler shift effect. However, due to the nonlinearity of the frequency response of the mid-infrared quantum cascade laser, and the large adjustment delay of the temperature and current tuning, the accuracy of the Doppler simulation is very low, the error is large, and the response is slow, making it difficult to simulate the real Doppler shift effect of the mid-infrared light wave in space. At present, there is no high-precision simulation generation device and generation method of the mid-infrared band space Doppler shift effect. Summary of the invention

[0004] The first purpose of the present invention is to provide a device for simulating and generating the spatial Doppler frequency shift effect in the mid-infrared band, which solves the problem that the prior art is difficult to simulate the real Doppler frequency shift effect of mid-infrared light waves in space.

[0005] The second object of the present invention is to provide a method for simulating and generating the spatial Doppler frequency shift effect in the mid-infrared band.

[0006] The first technical solution adopted by the present invention is a mid-infrared band spatial Doppler frequency shift effect simulation generating device, comprising an optical frequency shift unit for generating a 1μm band light wave carrier and single-sideband optical frequency shift, the output end of the optical frequency shift unit is connected to the input end of the optical amplification unit, and also comprises a dichroic mirror, a reflector, and the dichroic mirror is parallel to the reflector. The input end of the optical amplification unit also inputs a 1.5μm band light signal, the optical frequency shift unit, the optical amplification unit, and the dichroic mirror form a 1μm band transmission light path, the optical amplification unit, the reflector, and the dichroic mirror form a 1.5μm band reflection light path, the 1μm band transmission light path and the 1.5μm band reflection light path partially overlap after being emitted by the dichroic mirror to form a coincident light path, a periodically polarized crystal is arranged on the coincident light path, and a filter is arranged at the output end of the periodically polarized crystal; the control unit is connected to the optical frequency shift unit and the temperature control device, and the temperature control device is connected to the periodically polarized crystal.

[0007] The present invention is also characterized in that:

[0008] The optical frequency shift unit includes a 1μm band tunable laser, the output end of the 1μm band tunable laser is connected to the input end of the IQ modulator, and also includes a frequency signal source, the frequency signal source is connected to the input end of the phase shifter, the output end of the phase shifter is simultaneously connected to the input ends of the RF driver A and the RF driver B, the output ends of the RF driver A and the RF driver B are connected to the two RF ports of the IQ modulator, the RF driver A is connected to the 1μm band tunable laser, the IQ modulator is also connected to the bias voltage module, the control unit is connected to the frequency signal source and the RF driver B, and the IQ modulator is connected to the optical amplification unit.

[0009] The optical amplification unit includes a 1μm band amplifier connected to the optical frequency shift unit, the 1μm band amplifier is connected to the fiber collimating lens A, the 1μm band amplifier, the fiber collimating lens A and the dichroic mirror form a 1μm band transmission light path, and also includes a 1.5μm band amplifier for receiving a 1.5μm band optical signal, the 1.5μm band amplifier is connected to the fiber collimating lens B, the 1.5μm band amplifier, the fiber collimating lens B, the reflector and the dichroic mirror form a 1.5μm band reflection light path.

[0010] The divergence angles of the optical fiber collimating lens A and the optical fiber collimating lens B are between 0.03° and 0.06°.

[0011] The included angle between the output light angle of the fiber collimating lens A and the surface of the dichroic mirror is 45°±0.5°.

[0012] The included angle between the output light angle of the fiber collimating lens B and the reflector surface is 45°±0.5°.

[0013] The material of the 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 period of the periodically poled crystal is any one of a uniform polarization period and a chirped polarization period.

[0014] The dichroic mirror reflects light waves in the range of 1.52μm to 1.56μm, and transmits light waves in the range of 1μm to 1.1μm.

[0015] The second technical solution adopted by the present invention is a method for simulating and generating a spatial Doppler frequency shift effect in a mid-infrared band, which uses a device for simulating and generating a spatial Doppler frequency shift effect in an infrared band, and is specifically implemented according to the following steps: a 1μm band light wave carrier with a central wavelength of λ1 is generated by an optical frequency shift unit and a single-sideband optical frequency shift is realized to obtain a frequency-shifted light signal λ1', the light signal λ1' is input into an optical amplification unit for amplification, collimation, and then emitted to a dichroic mirror, and after being transmitted through the dichroic mirror, a transmitted light is formed, and at the same time, a 1.5μm band light signal λ2 is input into an optical amplification unit for amplification, collimation, and then emitted to a reflector surface, and the reflector reflects the light signal to the dichroic mirror, and after being reflected by the dichroic mirror, a reflected light is formed, and after the reflected light and the transmitted light overlap in the overlapping optical path, they are injected into a periodically polarized crystal for nonlinear frequency conversion, and other stray light waves are filtered out after passing through an optical filter to obtain a frequency-shifted mid-infrared frequency-shifted light wave.

[0016] It also includes: adjusting the frequency shift value, frequency shift change speed, and frequency shift range of the light wave output by the optical frequency shift unit through the control unit, and adjusting the temperature control device through the control unit to achieve the maximum power output of the mid-infrared light wave.

[0017] The beneficial effects of the present invention are:

[0018] 1) High-precision simulation of the spatial Doppler shift effect in the mid-infrared band can be achieved. An IQ modulator is used in the 1μm band to achieve accurate single-sideband light wave frequency shift. The frequency-shifted 1μm band light wave and the 1.5μm band light signal are amplified and then passed through a periodically polarized crystal to generate a difference frequency mid-infrared light wave. Since the response time of the nonlinear optical process is extremely short (fs order) and the information of the conversion process is transparent, the accuracy of the mid-infrared light wave frequency shift and the rate of change of the frequency shift are consistent with the accuracy of the frequency signal source and the rate of change of the frequency shift signal source. Therefore, high-precision simulation of the spatial Doppler shift effect in the mid-infrared band can be achieved. Compared with the frequency shift method of adjusting the temperature and current of the mid-infrared quantum cascade laser, the frequency shift accuracy of the method of the present invention is improved from the GHz order to the Hz order, and the rate of change of the frequency shift is improved from the ms order to the ns order.

[0019] 2) It can simulate the Doppler effect of mid-infrared light waves under different spatial relative motions. Since the frequency shift characteristics of mid-infrared light waves are consistent with the output characteristics of the front-end frequency signal source, it is possible to simulate different frequency shift changes, frequency change accelerations, frequency ranges and other parameters according to the relative motion characteristics between space terminals.

[0020] 3) It can support Doppler frequency shift simulation of mid-infrared optical signals with multiple modulation formats. Since the nonlinear frequency conversion method based on periodic polarization crystal is adopted, transparent conversion of information can be achieved. Therefore, the input 1.5μm band optical signal can be a signal of any modulation format, and the converted mid-infrared optical signal can also be a corresponding signal of any modulation format, such as intensity optical signal (OOK), phase optical signal (BPSK) and high-order modulated optical signal (QPSK, 16QAM, 64QAM). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the device for simulating and generating the spatial Doppler frequency shift effect in the mid-infrared band of the present invention;

[0022] Figure 2 It is a schematic diagram of the internal structure of the IQ modulator;

[0023] Figure 3 This is a spectral schematic diagram of the Doppler shift from the near-infrared band to the mid-infrared band.

[0024] In the figure, 1. frequency signal source, 2. phase shifter, 3. RF driver A, 4. RF driver B, 5. IQ modulator, 6. 1μm band tunable laser, 7. bias voltage module, 8. 1μm band amplifier, 9. fiber collimating lens A, 10. 1.5μm band amplifier, 11. fiber collimating lens B, 12. dichroic mirror, 13. reflector, 14. periodically polarized crystal, 15. filter, 16. control unit, 17. temperature control device. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] The device for simulating and generating the spatial Doppler frequency shift effect in the infrared band of the present invention is as follows: Figure 1As shown, it includes an optical frequency shift unit, the output end of the optical frequency shift unit is connected to the input end of the optical amplification unit, and also includes a dichroic mirror 12 and a reflector 13. The dichroic mirror 12 is parallel to the reflector 13. The input end of the optical amplification unit also inputs a 1.5 μm band light signal. The optical frequency shift unit, the optical amplification unit, and the dichroic mirror 12 form a 1 μm band transmission light path. The optical amplification unit, the reflector 13, and the dichroic mirror 12 form a 1.5 μm band reflection light path. The 1 μm band transmission light path and the 1.5 μm band reflection light path are emitted by the dichroic mirror 12. The parts of the periodic polarization crystal 14 are overlapped to form an overlapped optical path, and the periodic polarization crystal 14 is arranged on the overlapped optical path, and the filter 15 is arranged at the output end of the periodic polarization crystal 14; the control unit 16 is connected to the optical frequency shift unit and the temperature control device, and the temperature control device is connected to the periodic polarization crystal 14; wherein, the optical frequency shift unit performs single-sideband frequency shifting with carrier suppression on the 1μm band light wave, that is, using the IQ type optical modulation structure and the two orthogonal RF electrical signals, the light wave can produce frequency shift, the frequency shift amount is consistent with the RF signal frequency, and the harmonic frequency is suppressed. The 1μm band light wave after frequency shift is optically amplified, and at the same time, the external input 1.5μm band light signal containing the modulation signal is optically amplified, and the two beams of light are put between 1W and 2W, which is easy to produce nonlinear optical effects in the crystal. Then, the amplified 1μm band light wave is collimated by the fiber collimating lens and then emitted to the dichroic mirror 12, and the dichroic mirror 12 has a transmission effect on it. At the same time, the amplified 1.5μm band optical signal is collimated by the fiber collimating lens B11 and then emitted to the reflector 13. The reflector 13 and the dichroic mirror 12 complete two reflections on it, so that the two beams of light overlap in the spatial optical path, and then the two beams of light are vertically emitted to the surface of the periodic polarization crystal 14. When the two beams of light propagate in the periodic polarization crystal, due to the optical difference frequency nonlinear optical effect, mid-infrared light signals will be continuously generated. The mid-infrared light signal is output at the other end of the periodic polarization crystal 14, which contains unconverted 1μm band and 1.5μm band light waves, so it is filtered out by the filter 15 to obtain a single mid-infrared light signal. The frequency of the mid-infrared light signal satisfies the optical difference frequency formula, that is, the frequency of the 1μm band light wave after frequency shifting is subtracted from the frequency of the 1.5μm band light wave. Therefore, as long as the initial frequency value, frequency change value, frequency range and other values ​​of the RF signal during the frequency shifting process are controlled to meet the spatial Doppler effect parameters, the Doppler effect of the mid-infrared light signal propagating in real space can be simulated with high precision.

[0028] Example 2

[0029] On the basis of Example 1, the optical frequency shifting unit in this embodiment includes a 1 μm band tunable laser 6, the output end of the 1 μm band tunable laser 6 is connected to the input end of the IQ modulator 5, and also includes a frequency signal source 1, the frequency signal source 1 is connected to the input end of the phase shifter 2, the output end of the phase shifter 2 is simultaneously connected to the input ends of the RF driver A3 and the RF driver B4, the output ends of the RF driver A3 and the RF driver B4 are connected to the two RF ports of the IQ modulator 5, the RF driver A3 is connected to the 1 μm band tunable laser 6, the IQ modulator 5 is also connected to the bias voltage module 7, the control unit 16 is connected to the frequency signal source 1 and the RF driver B4, and the IQ modulator 5 is connected to the optical amplification unit. Among them, 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 full polarization-maintaining amplifier, which can amplify any wavelength between 1μm and 1.1μm; the 1.5μm band amplifier is a full polarization-maintaining amplifier, which can amplify any wavelength between 1530nm and 1565nm. The 1μm band tunable laser 6 passes the 1μm band light wave with a central wavelength of λ1 through the IQ modulator 5, and at the same time, the frequency signal source 1 outputs a frequency-shifted electrical signal and is injected into the IQ modulator 5 after being amplified by the phase shifter 2 and the RF driver A3 and the RF driver B4. Under the configuration of the bias voltage module 7, the IQ modulator 5 generates a single-sideband frequency shift for the 1μm band light wave. The frequency-shifted light wave λ1' is input into the 1μm band amplifier 8 and the fiber collimating lens A9 for amplification and collimation, and then emitted to the surface of the dichroic mirror 12. At the same time, the 1.5μm band light signal λ2 enters the 1.5μm band amplifier 10 and the fiber collimating lens B11 for amplification and collimation, and then emitted to the surface of the reflector 13. After being reflected by the reflector 13, it enters the dichroic mirror 12. The 1.5μm band light wave is reflected by the dichroic mirror 12, and the 1μm band light wave is transmitted through the dichroic mirror 12. The reflected light and the transmitted light overlap in the spatial optical path and are input to the periodically polarized crystal A side. After propagating inside the periodically polarized crystal, they are output from the periodically polarized crystal B side, and other stray light waves are filtered out after passing through the filter 15 to obtain a frequency-shifted mid-infrared frequency-shifted light wave.

[0030] Among them, the accuracy of the frequency shift of the mid-infrared light wave and the rate of change of the frequency shift are consistent with the accuracy of the frequency signal source 1 and the rate of change of the frequency shift signal source. Therefore, according to the relative motion characteristics between the space terminals, the output characteristics of the frequency signal source can be set to simulate different frequency shift changes, frequency change accelerations, frequency ranges and other parameters to achieve high-precision simulation of the spatial Doppler frequency shift effect in the mid-infrared band.

[0031] The divergence angles of the fiber collimating lens A9 and the fiber collimating lens B11 are between 0.03° and 0.06°. The angle between the output light angle of the fiber collimating lens A9 and the surface of the dichroic mirror 12 is 45°±0.5°. The angle between the output light angle of the fiber collimating lens B11 and the surface of the reflector 13 is 45°±0.5°. The above parameters can realize the transmission of optical signals along the preset optical path.

[0032] The material of the periodically poled crystal 14 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 period of the periodically poled crystal 14 is any one of a uniform polarization period and a chirped polarization period.

[0033] The dichroic mirror 12 reflects light waves in the range of 1.52 μm to 1.56 μm and transmits light waves in the range of 1 μm to 1.1 μm, so that the two optical signals can overlap after being reflected and transmitted respectively.

[0034] like Figure 1 As shown in FIG. 1 , in the optical frequency shift unit, the 1 μm band tunable laser 6 is set to output a light wave with a central wavelength of λ1 (corresponding to a frequency of f1 and an angular frequency of ω1), and the frequency of the RF signal generated by the frequency signal source 1 is set to f doppler (angular frequency is ω doppler ). Since the 1 μm band tunable laser 6 outputs a continuous optical carrier, its optical field expression can be expressed as:

[0035]

[0036] Where A1 is the amplitude of the light field. Figure 2 As shown, since the IQ modulator 5 works in push-pull mode, it has two sub-modulators I and II, as well as an optical phase shifter. To achieve single-sideband frequency shifting with carrier suppression, the two sub-modulators work at the minimum power transmission point, and the DC bias voltage loaded on the two sub-modulators is equal to the half-wave voltage V π . Assume that the voltage after RF driver A3 amplifies is V A , the RF signal uses a cosine signal, and the electrical signal loaded to the upper arm of sub-modulator I is:

[0037] V1(t)=V A cos(ω doppler t)+V π (2)

[0038] The phase change of this voltage is:

[0039]

[0040] in, is the modulation index. After the upper arm modulation of sub-modulator I, the output light field expression E1'(t) is:

[0041]

[0042] The identity of the Bessel function is as follows:

[0043]

[0044] Substituting equation (5) into equation (4) and simplifying it, by considering a smaller order (n is less than 3), the others can be ignored, and the simplified expression of the light field is obtained as follows:

[0045]

[0046] Similarly, the sampling of the lower arm of sub-modulator I is carried out in the same way. The voltage applied to the lower arm is V1'(t), and its phase change is:

[0047]

[0048] The output light field obtained is:

[0049]

[0050] The output of sub-modulator I is obtained by adding E1'(t) and E1"(t):

[0051]

[0052] It can be seen that the light beam output by sub-modulator I should have ±1-order and ±3-order sidebands. Similarly, another sub-modulator II is derived using the same method, and there is an optical phase shifter in the optical path of sub-modulator II. Assuming that the upper arm voltage of sub-modulator II is V2(t), the lower arm voltage is V2'(t), and the voltage applied to the optical phase shifter is V3(t), the optical field expression of the output of the superposition of sub-modulator II and the phase shifter is obtained as follows:

[0053]

[0054] The total output light field is:

[0055]

[0056] The optical field finally output by the IQ modulator 5 only contains +1-order and -3-order frequency-shifted optical waves. The amplitude of the -3-order frequency-shifted optical wave is much smaller than that of the +1-order. Therefore, the +1-order frequency-shifted optical wave is mainly considered, and this wavelength is recorded as λ1'.

[0057] The power of the 1μm band optical wave after frequency shift is set to P1, and the gain of the 1μm band amplifier 8 is set to G1. The power of the 1.5μm band optical signal is set to P2, and the gain of the 1.5μm band amplifier 10 is set to G2. After amplification, the power of the 1μm band optical wave is P 1-out and 1.5μm band optical signal P 2-out The relationship is shown as follows:

[0058]

[0059] The gains G1 and G2 of the 1.5 μm band amplifier 10 and the 1 μm band amplifier 8 can be adjusted by the control unit, and the adjustment range is between 30 and 33 dB.

[0060] The two amplified light waves pass through the optical fiber collimating lens and enter the dichroic mirror 12 and the reflector 13. The 1μm band light wave is transmitted and output from the dichroic mirror 12. The 1.5μm band light signal is reflected twice by the reflector 13 and the dichroic mirror 12, overlaps with the 1μm band light wave on the spatial optical path, and is incident on the periodic polarization crystal 14. The duty cycle of the polarization period of the periodic polarization crystal 14 is set to Λ.

[0061] 1μm band light wave λ1' (corresponding angular frequency is ω1+ω doppler ) and the 1.5μm band optical signal λ2 (corresponding to the angular frequency ω2) are incident on the periodically polarized crystal 14, and an optical difference frequency effect will occur. The corresponding difference frequency light wavelength is λ3 (corresponding to the angular frequency ω3), and the difference frequency effect satisfies the following formula:

[0062]

[0063] By replacing the wavelength in the above formula with frequency, we can get the following formula:

[0064] ω3=(ω1+ω doppler )-ω2 (14)

[0065] It can be seen from equation (14) that the angular frequency of the generated mid-infrared band light signal is equal to the angular frequency of the 1μm band light wave with frequency shift minus the angular frequency of the 1.5μm band light signal. doppler When relative changes occur, the mid-infrared light signal will also synchronously follow the angular frequency ω doppler The Doppler shift in the near-infrared band is copied to the mid-infrared band.

[0066] Example 3

[0067] The method for simulating and generating the spatial Doppler frequency shift effect in the mid-infrared band of the present invention uses a device for simulating and generating the spatial Doppler frequency shift effect in the mid-infrared band, and is specifically implemented according to the following steps:

[0068] Step 1, generating a 1 μm band optical wave carrier with a central wavelength of λ1 through an optical frequency shift unit and realizing single-sideband optical frequency shifting to obtain a frequency-shifted optical signal λ1′;

[0069] Specifically, in the optical frequency shift unit: the 1μm band tunable laser emits a 1μm band continuous light wave with a central wavelength of λ1 (corresponding frequency f1, angular frequency ω1), the light field amplitude is A1, and the RF signal frequency generated by the frequency signal source is set to f doppler (angular frequency is ω doppler ) is connected to the input port of the IQ modulator 5. At the same time, the frequency signal source 1 outputs a frequency-shifted electrical signal and is injected into the two RF ports of the IQ modulator 5 after being amplified by the phase shifter 2 and the RF driver A3 and the RF driver B4. The bias voltage module 7 outputs a voltage to the IQ modulator 5 to make it work at the lowest point of power transmission and generate a frequency-shifted optical wave λ1';

[0070] Since the IQ modulator works in push-pull mode, Figure 2 As shown, there are two sub-modulators I and II inside. The two sub-modulators work at the minimum power transmission point to achieve single-sideband frequency shift. The DC bias voltage loaded on the two sub-modulators is equal to the half-wave voltage V π , the RF voltage loaded to the modulator is V A , modulation index The light field expression after frequency shift is as follows:

[0071]

[0072] The output light field only contains +1-order and -3-order frequency-shifted light waves, and the amplitude of the -3-order frequency-shifted light wave is much smaller than that of the +1-order, so the +1-order frequency-shifted light wave is mainly considered.

[0073] Step 2, the frequency-shifted light wave λ1' is input into the 1μm band amplifier 8 to amplify the output power to between 1 and 2W, and then collimated by the fiber collimating lens A9 and emitted to the surface of the dichroic mirror 12; the input 1.5μm band optical signal λ2 is amplified by the 1.5μm band amplifier, the amplified output power is between 1 and 2W, and then collimated by the fiber collimating lens B and emitted to the surface of the reflector 13.

[0074] The power of the 1μm band optical wave after frequency shift is set to P1, and the gain of the 1μm band optical amplifier is set to G1. The power of the 1.5μm band optical signal is set to P2, and the gain of the 1.5μm band amplifier is set to G2. After amplification, the power of the 1μm band optical wave is P 1-out and 1.5μm band optical signal P 2-out The relationship is shown as follows:

[0075]

[0076] Step 3, the frequency-shifted light wave λ1' is transmitted and output through the dichroic mirror 12, and the 1.5μm band light signal λ2 is reflected to the surface of the dichroic mirror 12 after passing through the reflector 13. The dichroic mirror 12 reflects the λ2 light signal again. The two light beams overlap in the spatial optical path and are incident on the A side of the periodic polarization crystal 14. They are output from the B side of the periodic polarization crystal 14 and enter the filter 15.

[0077] Step 4: After passing through the filter 15, only the mid-infrared Doppler frequency shift optical signal output is retained. The temperature control device 17 outputs the corresponding temperature according to the setting of the control unit 16 to adapt the phase matching process of the optical difference frequency process to generate the best mid-infrared light power.

[0078] 1μm band light wave λ1' (corresponding angular frequency is ω1+ω doppler ) and the 1.5μm band optical signal λ2 (corresponding to the angular frequency ω2) are incident on the periodically polarized crystal, and the optical difference frequency effect will occur. The corresponding difference frequency light wavelength is λ3 (corresponding to the angular frequency ω3), and the difference frequency effect satisfies the following formula:

[0079]

[0080] By replacing the wavelength in the above formula with frequency, we can get the following formula:

[0081] ω3=(ω1+ω doppler )-ω2 (18)

[0082] It can be seen from formula (18) that the angular frequency of the generated mid-infrared band light signal is equal to the angular frequency of the 1μm band light wave with frequency shift minus the angular frequency of the 1.5μm band light signal. Figure 3 As shown, when the angular frequency ω corresponding to the Doppler effect doppler When relative changes occur, the mid-infrared light signal will also synchronously follow the angular frequency ω doppler The Doppler shift in the near-infrared band is copied to the mid-infrared band.

[0083] The function of the control unit is to control the wavelength output by the 1μm band tunable laser, control the speed and range of the frequency shift of the 1μm band light wave, and control the temperature control device of the periodically polarized crystal to ensure good conversion efficiency.

[0084] In this embodiment, the control unit 16 adjusts the frequency shift value, frequency shift change speed, and frequency shift range of the optical frequency shift unit output light waves, and the control unit 16 adjusts the temperature control device 17 to achieve maximum power output of mid-infrared light waves.

[0085] Through the above-mentioned method, the mid-infrared band spatial Doppler frequency shift effect simulation generation device of the present invention can realize high-precision mid-infrared band spatial Doppler frequency shift effect simulation. In the 1μm band, an IQ modulator is used to realize accurate single-sideband light wave frequency shift. The frequency-shifted 1μm band light wave and the 1.5μm band light signal are amplified and then passed through a periodically polarized crystal to generate a difference frequency mid-infrared light wave. Since the nonlinear optical process response time is extremely short (fs order of magnitude) and the conversion process information is transparent, the accuracy of the mid-infrared light wave frequency shift and the rate of change of the frequency shift are consistent with the accuracy of the frequency signal source and the rate of change of the frequency shift signal source. Therefore, it is completely possible to realize high-precision simulation of the mid-infrared band spatial Doppler frequency shift effect. Compared with the frequency shift method of adjusting the temperature and current of the mid-infrared quantum cascade laser, the frequency shift accuracy of the method of the present invention is increased from the GHz order of magnitude to the Hz order of magnitude, and the rate of change of the frequency shift is increased from the ms order of magnitude to the ns order of magnitude. The Doppler effect of mid-infrared light waves under different spatial relative motions can be simulated. Since the frequency shift characteristics of mid-infrared band light waves are consistent with the output characteristics of the front-end frequency signal source, different frequency shift changes, frequency change accelerations, and frequency ranges can be simulated according to the relative motion characteristics between space terminals. Doppler frequency shift simulation of mid-infrared optical signals of multiple modulation formats can be supported. Since the nonlinear frequency conversion method based on periodically polarized crystals is adopted, transparent conversion of information can be achieved. Therefore, the input 1.5μm band optical signal can be a signal of any modulation format, and the converted mid-infrared optical signal can also be a corresponding signal of any modulation format, such as intensity optical signal (OOK), phase optical signal (BPSK), and high-order modulated optical signal (QPSK, 16QAM, 64QAM).

Claims

1. A device for simulating and generating spatial Doppler frequency shift effect in the mid-infrared band, characterized in that: The invention comprises an optical frequency shift unit for generating a 1μm band light wave carrier and performing single-sideband optical frequency shifting, wherein the output end of the optical frequency shift unit is connected to the input end of an optical amplifying unit, and further comprises a dichroic mirror and a reflector, wherein the dichroic mirror is parallel to the reflector, and the input end of the optical amplifying unit also inputs a 1.5μm band light signal, wherein the optical frequency shift unit, the optical amplifying unit and the dichroic mirror form a 1μm band transmission light path, and the optical amplifying unit, the reflector and the dichroic mirror form a 1.5μm band reflection light path, wherein the 1μm band transmission light path and the 1.5μm band reflection light path partially overlap after being emitted by the dichroic mirror to form a coincident light path, a periodically polarized crystal is arranged on the coincident light path, and a filter is arranged at the output end of the periodically polarized crystal; a control unit is connected to the optical frequency shift unit and a temperature control device, and the temperature control device is connected to the periodically polarized crystal.

2. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 1, characterized in that: The optical frequency shift unit includes a 1 μm band tunable laser, the output end of the 1 μm band tunable laser is connected to the input end of the IQ modulator, and also includes a frequency signal source, the frequency signal source is connected to the input end of the phase shifter, the output end of the phase shifter is simultaneously connected to the input ends of the RF driver A and the RF driver B, the output ends of the RF driver A and the RF driver B are connected to two RF ports of the IQ modulator, the RF driver A is connected to the 1 μm band tunable laser, the IQ modulator is also connected to a bias voltage module, the control unit is connected to the frequency signal source and the RF driver B, and the IQ modulator is connected to the optical amplification unit.

3. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 1, characterized in that: The optical amplification unit includes a 1 μm band amplifier connected to the optical frequency shift unit, the 1 μm band amplifier is connected to the fiber collimating lens A, the 1 μm band amplifier, the fiber collimating lens A and the dichroic mirror form a 1 μm band transmission light path, and also includes a 1.5 μm band amplifier for receiving a 1.5 μm band optical signal, the 1.5 μm band amplifier is connected to the fiber collimating lens B, the 1.5 μm band amplifier, the fiber collimating lens B, the reflector and the dichroic mirror form a 1.5 μm band reflection light path.

4. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 3, characterized in that: The divergence angles of the optical fiber collimating lens A and the optical fiber collimating lens B are between 0.03° and 0.06°.

5. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 3, characterized in that: The included angle between the output light angle of the optical fiber collimating lens A and the surface of the dichroic mirror is 45°±0.5°.

6. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 3, characterized in that: The included angle between the output light angle of the optical fiber collimating lens B and the reflector surface is 45°±0.5°.

7. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 1, characterized in that: The material of the 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 period of the periodically poled crystal is any one of a uniform polarization period and a chirped polarization period.

8. The mid-infrared band spatial Doppler frequency shift effect simulation generation device according to claim 1, characterized in that: The dichroic mirror reflects light waves in the range of 1.52 μm to 1.56 μm, and transmits light waves in the range of 1 μm to 1.1 μm.

9. A method for simulating and generating the spatial Doppler shift effect in the mid-infrared band, characterized in that: The mid-infrared band spatial Doppler frequency shift effect simulation generation device described in claim 1 is used, and is specifically implemented according to the following steps: a 1μm band light wave carrier with a central wavelength of λ1 is generated by an optical frequency shift unit and a single-sideband optical frequency shift is realized to obtain a frequency-shifted light signal λ1', the light signal λ1' is input into an optical amplification unit for amplification, collimated and then emitted to a dichroic mirror, and transmitted through the dichroic mirror to form transmitted light, and at the same time, a 1.5μm band light signal λ2 is input into an optical amplification unit for amplification, collimated and then emitted to a reflector surface, and the reflector reflects the light signal to the dichroic mirror, and reflected light is formed after reflection by the dichroic mirror, and the reflected light and the transmitted light are overlapped in the overlapping optical path and injected into a periodically polarized crystal for nonlinear frequency conversion, and other stray light waves are filtered out after passing through an optical filter to obtain a frequency-shifted mid-infrared frequency-shifted light wave.

10. The method for simulating and generating the spatial Doppler shift effect in the mid-infrared band according to claim 9, characterized in that: Also includes: The control unit is used to adjust the frequency shift value, frequency shift change speed, and frequency shift range of the light wave output by the optical frequency shift unit, and the control unit is used to adjust the temperature control device to achieve the maximum power output of the mid-infrared light wave.

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