Microwave photon dual orthogonal mirror frequency suppression mixing method and device

Abstract

The present invention discloses a microwave photon dual orthogonal mirror frequency suppression mixing method, comprising the following steps: S1, using a radio frequency signal and a local oscillator signal to perform carrier suppressed single sideband modulation on a cognate optical carrier, respectively, to obtain a light-carrying radio frequency signal and an optical local oscillator signal, respectively; S2, dividing the light-carrying radio frequency signal and the optical local oscillator signal into two paths, and respectively undergoing a phase shift, and then dividing the two paths of optical local oscillator signals / optical radio frequency signals that have undergone a phase shift into four paths, and respectively undergoing a secondary phase shift, and then coupling them with the light-carrying radio frequency signal / optical local oscillator signal that has undergone a phase shift; S3, selecting four paths of coupled optical signals and converting them into electrical signals respectively; S4, respectively phase shifting the four paths of electrical signals and then coupling them, to obtain an intermediate frequency signal that achieves image frequency suppression. The present invention also discloses a microwave photon dual orthogonal mirror frequency suppression mixing device. Compared with the prior art, the present invention can greatly improve the image frequency suppression ratio.

Description

Technical Field

[0001] The invention relates to a mirror frequency suppression mixing method, in particular to a microwave photon mirror frequency suppression mixing method. Background Art

[0002] Image rejection mixing is mainly used in the receiver of the system to achieve down-conversion reception without image interference. L The RF signal with frequency ω L -ω I The RF signal is input into the mixer together with the frequency ω L The local oscillator signal is mixed, and the intermediate frequency output signal obtained will be down-converted into a useful RF signal, and the intermediate frequency signal down-converted by the useless image frequency signal will be suppressed. This mixer can effectively suppress the interference caused by the image frequency, improve the signal-to-noise ratio of the receiver, and thus reduce the pressure of signal processing. The main performance indicators of the image frequency suppression mixer are the operating frequency range and the image frequency suppression ratio. The image frequency suppression ratio refers to the ratio of the intermediate frequency signal down-converted from the useful RF signal to the intermediate frequency signal down-converted from the useless image frequency signal. In actual RF systems, wideband mixers with high image frequency suppression ratios can effectively reduce the structural complexity of the RF system, improve the performance of the entire RF system, and reduce the difficulty of signal processing. Figure 1 It is the most commonly used image suppression mixer structure. The implementation method of this structure is to mix the input RF signal with a pair of mutually orthogonal local oscillator signals to obtain a pair of orthogonal intermediate frequency signals. However, the image suppression bandwidth of the image suppression mixer based on electronic technology is usually narrow, only in the order of hundreds of MHz, and the suppression ratio of the sideband to the image frequency is usually less than 30dB, which cannot meet the needs of higher performance RF systems. For many instances, the image interference is larger than the desired useful signal (J.Crols, and MSJ Steyaert, IEEE Trans.Circuits Syst.II, Analog Digit.Signal Process.45,269,(1998). B.Li, and K.P.Pun, IEEE Trans.Circuits Syst.Regul.Pap.61,92(2014). Varun, D., and G.R.Kadambi, IEEE Annual India Conference(INDICON,2016)), so a larger image suppression ratio is required to ensure a large signal-to-noise ratio.

[0003] Due to the characteristics of large bandwidth and flat response of photonic technology, microwave photonic image suppression mixing has wider bandwidth and larger image suppression ratio compared with traditional electrical methods. Figure 2The general structure of a microwave photon mirror frequency suppression mixer is shown. This structure is realized by using the optical sideband amplitude and phase control method based on traditional microwave photon mixing.

[0004] Will Figure 1 The mixer in the Hartley structure is replaced by a 90° optical mixer and a balanced photodetector, and the 90° phase shifter and adder are replaced by a 90° bridge, and the following is obtained: Figure 3 The microwave photon mirror frequency suppression mixing structure shown in FIG. Compared with the traditional electric domain mirror frequency suppression mixing scheme, the suppression ratio of the microwave photon mirror frequency suppression mixing scheme has been greatly improved. However, the suppression ratio of the existing microwave photon mirror frequency suppression mixing scheme still has room for improvement. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a microwave photon double orthogonal mirror frequency suppression mixing method with a higher suppression ratio.

[0006] The microwave photon double orthogonal mirror frequency suppression mixing method proposed in the present invention comprises the following steps:

[0007] S1, using the radio frequency signal and the local oscillator signal to perform carrier suppressed single sideband modulation on the same source optical carrier, to obtain the optical radio frequency signal and the optical local oscillator signal respectively;

[0008] S2, the optical radio frequency signal and the optical local oscillator signal are divided into two paths, and pass through θ1, θ2 and The first phase shift is then performed, and the two optical local oscillator signals / optical radio frequency signals that have undergone the first phase shift are divided into four paths respectively and are phase shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then coupled with the optical radio frequency signal / optical local oscillator signal that has undergone the first phase shift respectively. The relationship between the phase shifts θ1 and θ2 satisfies: θ2=θ1+π / 2+2πm, and the phase shift The relationship between them satisfies: The relationship between phase shifts α1, α2, α3 and α4 satisfies: α2=α1+π+2πa1, α3=α1+π / 2+2πa2, α4=α1+3π / 2+2πa3, phase shift β 1. The relationship between β2, β3 and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where m, n, a i (i=1,2,3),b i (i=1,2,3) are all integers;

[0009] S3, from the four coupled optical signals including the optical local oscillator signal / optical radio frequency signal that has undergone a primary phase shift of θ1, select two coupled optical signals whose optical local oscillator signal / optical radio frequency signal is orthogonal to each other after a secondary phase shift; from the four coupled optical signals including the optical local oscillator signal / optical radio frequency signal that has undergone a primary phase shift of θ2, select two coupled optical signals whose optical local oscillator signal / optical radio frequency signal is orthogonal to each other after a secondary phase shift; and then convert the selected four coupled optical signals into electrical signals respectively;

[0010] S4, after phase shifting the four electrical signals by ε1, ε2, ε3, and ε4 respectively, the intermediate frequency signal with image frequency suppression is obtained. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

[0011] Preferably, step S2 is implemented by two 90° optical directional couplers and two 90° optical mixers, the optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two 90° optical directional couplers, and the two output ends of each 90° optical directional coupler are respectively connected to one input end of each of the two 90° optical mixers.

[0012] Preferably, step S2 is implemented by two directional couplers, four beam splitters, four optical couplers, and two 90° phase shifters. The optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two directional couplers, the four output ends of the two directional couplers are respectively connected to the input ends of the four beam splitters, the input ends of the four beam splitters are cross-connected with the input ends of the four optical couplers in pairs, and a 90° phase shifter is respectively connected in series in two of the connecting lines.

[0013] Preferably, step S3 and step S are implemented by two balanced photodetectors and a 90° microwave bridge, the selected four coupled optical signals are respectively connected to the four input ends of the two balanced photodetectors, the two output ends of the two balanced photodetectors are respectively connected to the two input ends of the 90° microwave bridge, and the 90° microwave bridge outputs the two intermediate frequency signals.

[0014] Preferably, the carrier suppressed single sideband modulation is implemented by dual parallel Mach-Zehnder modulators or Mach-Zehnder modulator cascade optical filters.

[0015] Based on the same inventive concept, the following technical solutions can also be obtained:

[0016] A microwave photon double orthogonal mirror frequency suppression mixing device, comprising:

[0017] A modulation module, used to perform carrier suppressed single sideband modulation on a co-source optical carrier using a radio frequency signal and a local oscillator signal, respectively, to obtain an optically carried radio frequency signal and an optical local oscillator signal;

[0018] The dual orthogonal mixer module is used to divide the optical RF signal and the optical local oscillator signal into two paths, and pass through θ1, θ2 and The first phase shift is then performed, and the two optical local oscillator signals / optical radio frequency signals that have undergone the first phase shift are divided into four paths respectively and are phase shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then coupled with the optical radio frequency signal / optical local oscillator signal that has undergone the first phase shift respectively. The relationship between the phase shifts θ1 and θ2 satisfies: θ2=θ1+π / 2+2πm, and the phase shift The relationship between them satisfies: The relationship between phase shifts α1, α2, α3 and α4 satisfies: α2=α1+π+2πa1, α3=α1+π / 2+2πa2, α4=α1+3π / 2+2πa3, phase shift β 1. The relationship between β2, β3 and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where m, n, a i (i=1,2,3),b i (i=1,2,3) are all integers;

[0019] The optoelectronic conversion module is used to select two coupled optical signals whose optical local oscillator signals / optical radio frequency signals are orthogonal to each other after secondary phase shift from four coupled optical signals including optical local oscillator signals / optical radio frequency signals that have undergone a primary phase shift of θ1; select two coupled optical signals whose optical local oscillator signals / optical radio frequency signals are orthogonal to each other after secondary phase shift from four coupled optical signals including optical local oscillator signals / optical radio frequency signals that have undergone a primary phase shift of θ2; and then convert the selected four coupled optical signals into electrical signals respectively;

[0020] The electrical phase coupling module is used to couple the four electrical signals after phase shifting ε1, ε2, ε3, and ε4 respectively to obtain an intermediate frequency signal that achieves image frequency suppression. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

[0021] Preferably, the dual orthogonal mixing module includes two 90° optical directional couplers and two 90° optical mixers, the optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two 90° optical directional couplers, and the two output ends of each 90° optical directional coupler are respectively connected to one input end of each of the two 90° optical mixers.

[0022] Preferably, the dual orthogonal mixing module includes two directional couplers, four beam splitters, four optical couplers, and two 90° phase shifters. The optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two directional couplers, and the four output ends of the two directional couplers are respectively connected to the input ends of the four beam splitters. The input ends of the four beam splitters are cross-connected with the input ends of the four optical couplers in pairs, and a 90° phase shifter is respectively connected in series in two of the connecting lines.

[0023] Preferably, the photoelectric conversion module includes two balanced photodetectors, the electrical phase coupling module is a 90° microwave bridge, the selected four coupled optical signals are respectively connected to the four input ends of the two balanced photodetectors, the two output ends of the two balanced photodetectors are respectively connected to the two input ends of the 90° microwave bridge, and the 90° microwave bridge outputs the two intermediate frequency signals.

[0024] Preferably, the modulation module implements the carrier suppressed single sideband modulation through dual parallel Mach-Zehnder modulators or Mach-Zehnder modulator cascade optical filters.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] The present invention adopts a microwave photonic dual-orthogonal structure, passes both the optical local oscillator signal and the optically-carried radio frequency signal through an orthogonal network to form four output signals, which are then mixed separately. By introducing the orthogonal characteristics of the optical local oscillator and the optically-carried radio frequency signal, the image frequency suppression ratio can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the image frequency suppression mixing structure based on the Hartley structure;

[0028] Figure 2 It is the general structure of microwave photon mirror frequency suppression mixing;

[0029] Figure 3 It is an existing microwave photon mirror frequency suppression mixing structure based on 90° optical mixer;

[0030] Figure 4 It is a schematic diagram of the principle of the microwave photon double orthogonal mirror frequency suppression mixing device of the present invention;

[0031] Figure 5 It is a specific implementation structure of the microwave photon double orthogonal mirror frequency suppression mixing device of the present invention;

[0032] Figure 6 It is another specific implementation structure of the microwave photon double orthogonal mirror frequency suppression mixing device of the present invention;

[0033] Figure 7 for Figure 3 The effects of amplitude imbalance and phase imbalance of the image suppression mixing scheme shown in the figure on the image suppression ratio; wherein (a) is the effect of the phase imbalance θ1 of the 90° optical mixer and the phase imbalance θ2 of the 90° bridge on the image suppression ratio; (b) is the effect of the amplitude imbalance R and phase deviation θ1 on the single orthogonal image suppression ratio; (c) is the effect of the amplitude imbalance R and phase deviation θ2 on the single orthogonal image suppression ratio;

[0034] Figure 8 The effects of amplitude imbalance and phase imbalance on the image suppression ratio of the microwave photonic dual-orthogonal mirror frequency suppression mixing scheme of the present invention are shown; wherein, (a) is the effect of the phase imbalances θ1 and θ2 of two 90° optical mixers on the image suppression ratio; (b) is the effect of the amplitude imbalance R=R1=R2 and the phase deviation θ1 on the dual-orthogonal mirror frequency suppression ratio; (c) is the effect of the amplitude imbalance R=R1=R2 and the phase deviation θ2 on the dual-orthogonal mirror frequency suppression ratio. DETAILED DESCRIPTION

[0035] Figure 3 The existing microwave photonic mirror frequency suppression mixing structure based on a 90° optical mixer shown in the figure can greatly improve the suppression ratio compared with the electrical domain mirror frequency suppression mixing scheme, but the 90° optical mixer it uses will cause amplitude and phase inconsistency, which in turn affects the improvement of the mirror frequency suppression ratio.

[0036] Let E1(t) and E2(t) represent the optical radio frequency signal and the optical local oscillator signal respectively, then the expression is:

[0037]

[0038] The four signals output by the 90° optical mixer are:

[0039]

[0040] Where η and φ are 90°, and the mixer brings amplitude imbalance and phase imbalance between the I (in-phase) path and the Q (quadrature) path.

[0041] From equation (2), it can be seen that the 90° optical mixer generates two pairs of orthogonal local oscillator-signal pairs. The output signal after balanced photoelectric detection is:

[0042]

[0043] where 2ω s =ω f -ω m =2(ω f -ω l )=2(ω l -ω m ).

[0044] It can be seen from equation (3) that the signals at the two output ends are orthogonal. Inputting this pair of orthogonal signals into a 90° bridge, we get:

[0045]

[0046] It can be seen from formula (4) that based on the mirror frequency suppression mixing structure of the 90° optical mixer, the signals on both sides of the optical local oscillator are down-converted to the same intermediate frequency and output from two output ports respectively. The outputs each include two intermediate frequency signals of the optically-carried RF signal located on the left side of the optical local oscillator and the down-converted signal on the right side.

[0047] The image frequency rejection ratio can be calculated from the intermediate frequency signal output by the 90° bridge (taking the output signal i1 as an example), and its expression is:

[0048]

[0049] It can be found that although the suppression ratio of this type of microwave photonic mirror suppression mixer is greatly improved compared with the traditional mirror suppression mixer, the amplitude and phase inconsistency of the 90° optical mixer affects the improvement of the mirror suppression ratio.

[0050] To solve this problem, the present invention proposes the following technical solutions:

[0051] A microwave photon double orthogonal mirror frequency suppression mixing method comprises the following steps:

[0052] S1, using the radio frequency signal and the local oscillator signal to perform carrier suppressed single sideband modulation on the same source optical carrier, to obtain the optical radio frequency signal and the optical local oscillator signal respectively;

[0053] S2, the optical radio frequency signal and the optical local oscillator signal are divided into two paths, and pass through θ1, θ2 and The first phase shift is then performed, and the two optical local oscillator signals / optical radio frequency signals that have undergone the first phase shift are divided into four paths respectively and are phase shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then coupled with the optical radio frequency signal / optical local oscillator signal that has undergone the first phase shift respectively. The relationship between the phase shifts θ1 and θ2 satisfies: θ2=θ1+π / 2+2πm, and the phase shift The relationship between them satisfies: The relationship between phase shifts α1, α2, α3 and α4 satisfies: α2=α1+π+2πa1, α3=α1+π / 2+2πa2, α4=α1+3π / 2+2πa3, phase shift β 1. The relationship between β2, β3 and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where m, n, a i(i=1,2,3),b i (i=1,2,3) are all integers;

[0054] S3, from the four coupled optical signals including the optical local oscillator signal / optical radio frequency signal that has undergone a primary phase shift of θ1, select two coupled optical signals whose optical local oscillator signal / optical radio frequency signal is orthogonal to each other after a secondary phase shift; from the four coupled optical signals including the optical local oscillator signal / optical radio frequency signal that has undergone a primary phase shift of θ2, select two coupled optical signals whose optical local oscillator signal / optical radio frequency signal is orthogonal to each other after a secondary phase shift; and then convert the selected four coupled optical signals into electrical signals respectively;

[0055] S4, after phase shifting the four electrical signals by ε1, ε2, ε3, and ε4 respectively, the intermediate frequency signal with image frequency suppression is obtained. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

[0056] like Figure 4 As shown, the microwave photon double orthogonal mirror frequency suppression mixing device of the present invention comprises:

[0057] A modulation module, used to perform carrier suppressed single sideband modulation on a co-source optical carrier using a radio frequency signal and a local oscillator signal, respectively, to obtain an optically carried radio frequency signal and an optical local oscillator signal;

[0058] The dual orthogonal mixer module is used to divide the optical RF signal and the optical local oscillator signal into two paths, and pass through θ1, θ2 and The first phase shift is then performed, and the two optical local oscillator signals / optical radio frequency signals that have undergone the first phase shift are divided into four paths respectively and are phase shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then coupled with the optical radio frequency signal / optical local oscillator signal that has undergone the first phase shift respectively. The relationship between the phase shifts θ1 and θ2 satisfies: θ2=θ1+π / 2+2πm, and the phase shift The relationship between them satisfies: The relationship between phase shifts α1, α2, α3 and α4 satisfies: α2=α1+π+2πa1, α3=α1+π / 2+2πa2, α4=α1+3π / 2+2πa3, phase shift β 1. The relationship between β2, β3 and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where m, n, a i (i=1,2,3),b i (i=1,2,3) are all integers;

[0059] The optoelectronic conversion module is used to select two coupled optical signals whose optical local oscillator signals / optical radio frequency signals are orthogonal to each other after secondary phase shift from four coupled optical signals including optical local oscillator signals / optical radio frequency signals that have undergone a primary phase shift of θ1; select two coupled optical signals whose optical local oscillator signals / optical radio frequency signals are orthogonal to each other after secondary phase shift from four coupled optical signals including optical local oscillator signals / optical radio frequency signals that have undergone a primary phase shift of θ2; and then convert the selected four coupled optical signals into electrical signals respectively;

[0060] The electrical phase coupling module is used to couple the four electrical signals after phase shifting ε1, ε2, ε3, and ε4 respectively to obtain an intermediate frequency signal that achieves image frequency suppression. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

[0061] To facilitate public understanding, the specific principles of the present invention are described as follows:

[0062] Assume that the modulation module generates a frequency of ω c +ω f and ω c +ω m The light carries the RF signal and is symmetrical about the optical local oscillator signal, where ω c is the angular frequency of the optical carrier, ω f ,ω m is the angular frequency of the RF signal. At this time, the optically-carried RF signal can be expressed as:

[0063] E1(t)∝a m expj(ω c t+ω m t)+a1 expj(ω c t+ω f t) (6)

[0064] where a m , a1 are the two amplitude information of the RF signal.

[0065] Assume that the modulation module generates a frequency of ω c +ω l The optical local oscillator signal, where ω l is the angular frequency of the optical local oscillator signal. At this time, the expression of the optical local oscillator signal is:

[0066] E2∝b1 expj(ω c t+ω l t) (7)

[0067] Where b1 is the amplitude of the optical local oscillator signal.

[0068] The optical radio frequency signal and optical local oscillator signal in equations (6) and (7) are divided into two paths, and pass through θ1, θ2 and A phase shift of , we get:

[0069]

[0070] The relationship between the phase shifts θ1 and θ2 satisfies: θ2 = θ1 + π / 2 + 2πm, where m is an integer; the phase shift The relationship between them satisfies: Where n is an integer.

[0071] The optical local oscillator signal E after a phase shift 21 (t) and E 22 (t) are divided into four paths and phase-shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then combined with the optical radio frequency signal E after the primary phase shift. 11 (t), E 12 (t) are coupled respectively, and we can get:

[0072]

[0073] Among them, α1, α2, α3, and α4 are phase shifted The secondary phase shift of the 4 optical local oscillator signals, β1, β2, β3, β4 are the first phase shift The secondary phase shift of the four optical local oscillator signals, the relationship between the phase shifts α1, α2, α3, and α4 satisfies: α2 = α1 + π + 2πa1, α3 = α1 + π / 2 + 2πa2, α4 = α1 + 3π / 2 + 2πa3, where a i (i=1,2,3) is an integer; the relationship between phase shifts β1, β2, β3, and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where b i (i=1,2,3) is an integer.

[0074] From the four coupled optical signals including the optical local oscillator signal after the first phase shift θ1, two coupled optical signals including the optical local oscillator signals after the second phase shift are orthogonal to each other are selected; from the four coupled optical signals including the optical local oscillator signal after the first phase shift θ2, two coupled optical signals including the optical local oscillator signals after the second phase shift are orthogonal to each other are selected; in this case, e 11 、e 13 and e 22 、e 24 For example, e 11 、e 22 、e 13 、e24 Injected into the photoelectric conversion module probe, set ω f >ω l ,ω m <ω l , the electrical signal is:

[0075]

[0076] The four electrical signals are coupled and output as one signal after phase shifts of ε1, ε2, ε3, and ε4 are performed by the electrical phase coupling module. The expression is:

[0077]

[0078] Among them, ε1, ε2, ε3, and ε4 represent the different phase shifts of the four electrical signals in the electrical phase coupling module. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

[0079] In the above process, the optically carried radio frequency signal and the optical local oscillator signal can be interchanged, and the results are the same.

[0080] When the above phase shifts satisfy their phase shift conditions, that is, the relationship between the phase shifts θ1 and θ2 satisfies: θ2 = θ1 + π / 2 + 2πm, where m is an integer; The relationship between them satisfies: Where n is an integer; the relationship between the phase shifts α1, α2, α3, and α4 satisfies: α2 = α1 + π + 2πa1, α3 = α1 + π / 2 + 2πa2, α4 = α1 + 3π / 2 + 2πa3, where a i (i=1,2,3) is an integer; the relationship between phase shifts β1, β2, β3, and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where b i (i=1,2,3) is an integer; the relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2=ε1+π+2πk1, ε3=ε1+π / 2+2πk2, ε4=ε1+3π / 2+2πk3, where k i (i=1,2,3) is an integer, we can get:

[0081]

[0082] It can be seen from formula 13 that the final output signal only includes the output component of the down-converted RF signal on one side of the optical local oscillator, and the image signal on the other side is suppressed. This structure can suppress multiple spurious components, and the mixing output is output as the maximum term.

[0083] Figure 5 A specific implementation structure of the microwave photon double orthogonal mirror frequency suppression mixing device of the present invention is shown, which includes: a narrow linewidth laser, two double-balanced Mach-Zehnder modulators, two 90° directional couplers, two 90° optical mixers, two balanced detectors and a 90° microwave bridge.

[0084] The narrow linewidth laser output frequency is ω c The optical carrier is divided into two paths, one of which is injected into the Mach-Zehnder modulator (MZM) with a frequency of ω m and ω f The RF signal is modulated to obtain a carrier-suppressed single-sideband signal, from which the expression of the optically-carried RF signal is:

[0085] E RF (t)∝a m expj(ω c t+ω m t)+a1 expj(ω c t+ω f t) (14)

[0086] where a m , a1 is the amplitude of the positive first-order sideband.

[0087] The other optical carrier is injected into the dual parallel Mach-Zehnder modulator (DPMZM), which is composed of a frequency of ω l By modulating the local oscillator signal, a carrier-suppressed single-sideband signal can be obtained (taking the upper sideband as an example), and the expression of the optical local oscillator signal can be obtained as follows:

[0088] E LO (t)∝b1 expj(ω c t+ω l t) (16)

[0089] Where b1 is the amplitude of the sideband signal.

[0090] Then, the optical RF signal and the optical local oscillator signal are injected into the 90° optical directional coupler respectively, at which θ1 = 0° and θ2 = 90°. The optical phase shift condition is met. At this time, the expressions of the two optically-carried RF signals and the two optical local oscillator signals output are:

[0091]

[0092] E 11(t), E 21 (t) and E 12 (t), E 22 (t) are injected into a 90° mixer respectively. The corresponding phase shifts are α1 = 0°, α2 = 180°, α3 = 90°, α4 = 270° and β1 = 0°, β2 = 180°, β3 = 90°, β4 = 270°. The optical output expression is:

[0093]

[0094] I1', I2' and Q1', Q2' are the in-phase output signals of 90° optical mixer 1 and 90° optical mixer 2, and I1", I2", Q1", Q2" are the quadrature output signals of 90° optical mixer 1 and 90° optical mixer 2. η1, η2 and φ1, φ2 are the amplitude and phase imbalances brought by the two 90° optical mixers to the I (in-phase) path and the Q (quadrature) path.

[0095] Select two orthogonal mixing signals from the upper 4 channels, and select two orthogonal mixing signals from the lower 4 channels. Take I1', Q1' and I2", Q2" as examples, and inject I1', I2" and Q1', Q2" into the balanced detector. Assume ω f >ω l ,ω m <ω l , the electrical signal is:

[0096]

[0097] where ω f -ω m =2ω s =2(ω f -ω l )=2(ω l -ω m ), the signal output by the balanced detector is input into a 90° microwave bridge, and finally a dual output signal is obtained, and its expression is:

[0098]

[0099] The image frequency suppression ratio of the dual orthogonal structure can be calculated from the electrical signal output by the 90° microwave bridge. Here, we take i1 as an example:

[0100]

[0101] When only orthogonal optical local oscillators are used, the expression for the image frequency suppression ratio is:

[0102]

[0103] because,

[0104]

[0105] Therefore |IRR 双 ∣>∣IRR 单 ∣, in particular, when η1=η2=η, φ1=φ2=φ, ∣IRR 双 ∣=2∣IRR 单 ∣.

[0106] Figure 6 Another specific implementation structure of the microwave photon double orthogonal mirror frequency suppression mixing device of the present invention is shown, which includes: a laser, two Mach-Zehnder modulators, two optical filters, two directional couplers, a beam splitter, an optical coupler, a balanced detector, a 90° phase shifter and a 90° bridge, etc.

[0107] After the RF signal and the local oscillator signal pass through the modulator and the optical filter, the optically transmitted RF signal (E RF (t)) and the optical local oscillator signal (E LO (t)), injecting the optical RF signal into the directional coupler yields (E RF (t)) and (jE RF (t)), injecting the optical local oscillator signal into the directional coupler yields (E LO (t)) and (jE LO (t). RF (t) and E LO (t), are injected into a 1×2 beam splitter and divided into two parts with equal power. Then, a part of the optical RF signal and a part of the optical local oscillator signal are directly coupled through a 2×2 optical coupler to obtain the in-phase output signal I1' (I1'∝E RF (t)+E LO (t)) and I2'(I2'∝E RF (t)-E LO (t)), the other part of the optical RF signal and the optical local oscillator signal after 90° phase shift pass through a 2×2 optical coupler to obtain the orthogonal output signal Q1' (Q1'∝E RF (t)+jE LO (t)) and Q2'(Q2'∝E RF (t)-jE LO (t)), similarly, by jE RF (t) and jE LO signal, we can get the same-phase output signal I1”(I1”∝jE RF (t)+jE LO (t)) and I2”(I2”∝jE RF (t)-jE LO(t)), the quadrature output signal Q1”(Q1”∝jE RF (t)-E LO (t)) and Q2”(Q2”∝jE RF (t)+E LO (t)). The in-phase output signals I1' and I2" are injected into a balanced detection module, and the orthogonal output signals Q1' and Q2" are injected into another photoelectric detection module, which can convert the optical signal into an electrical signal output. After the output electrical signal passes through a 90° bridge, the down-conversion component of the optically-carried RF signal with mirror frequencies at both ends of the output optical local oscillator is output.

[0108] According to the above principle, a model is constructed and simulation is performed to verify the influence of amplitude and phase inconsistency of single orthogonal structure and dual orthogonal structure on the image frequency suppression ratio.

[0109] Figure 7 Shows Figure 3 The effects of amplitude imbalance and phase imbalance of the image suppression mixing scheme on the image suppression ratio are shown in the figure; wherein, (a) is the effect of the phase imbalance θ1 of the 90° optical mixer and the phase imbalance θ2 of the 90° bridge on the image suppression ratio; (b) is the effect of the amplitude imbalance R and phase deviation θ1 on the single orthogonal image suppression ratio; (c) is the effect of the amplitude imbalance R and phase deviation θ2 on the single orthogonal image suppression ratio.

Claims

1. A microwave photon dual orthogonal mirror frequency suppression mixing method, characterized in that: The following steps are involved: S1, using the radio frequency signal and the local oscillator signal to perform carrier suppressed single sideband modulation on the same source optical carrier, to obtain the optical radio frequency signal and the optical local oscillator signal respectively; S2, the optical radio frequency signal and the optical local oscillator signal are divided into two paths, and pass through θ1, θ2 and The first phase shift is then performed, and the two optical local oscillator signals / optical radio frequency signals that have undergone the first phase shift are divided into four paths respectively and are phase shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then coupled with the optical radio frequency signal / optical local oscillator signal that has undergone the first phase shift respectively. The relationship between the phase shifts θ1 and θ2 satisfies: θ2=θ1+π / 2+2πm, and the phase shift The relationship between them satisfies: The relationship between phase shifts α1, α2, α3 and α4 satisfies: α2=α1+π+2πa1, α3=α1+π / 2+2πa2, α4=α1+3π / 2+2πa3, phase shift β 1. The relationship between β2, β3 and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where m, n, a i (i=1,2,3),b i (i=1,2,3) are all integers; S3, from the four coupled optical signals including the optical local oscillator signal / optical radio frequency signal that has undergone a primary phase shift of θ1, select two coupled optical signals whose optical local oscillator signal / optical radio frequency signal is orthogonal to each other after a secondary phase shift; from the four coupled optical signals including the optical local oscillator signal / optical radio frequency signal that has undergone a primary phase shift of θ2, select two coupled optical signals whose optical local oscillator signal / optical radio frequency signal is orthogonal to each other after a secondary phase shift; and then convert the selected four coupled optical signals into electrical signals respectively; S4, after phase shifting the four electrical signals by ε1, ε2, ε3, and ε4 respectively, the intermediate frequency signal with image frequency suppression is obtained. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

2. The microwave photon dual orthogonal mirror frequency suppression mixing method according to claim 1, characterized in that: The step S2 is implemented by two 90° optical directional couplers and two 90° optical mixers. The optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two 90° optical directional couplers, and the two output ends of each 90° optical directional coupler are respectively connected to one input end of each of the two 90° optical mixers.

3. The microwave photon dual orthogonal mirror frequency suppression mixing method as claimed in claim 1, characterized in that: The step S2 is implemented by two directional couplers, four beam splitters, four optical couplers, and two 90° phase shifters. The optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two directional couplers, and the four output ends of the two directional couplers are respectively connected to the input ends of the four beam splitters. The input ends of the four beam splitters are cross-connected with the input ends of the four optical couplers in pairs, and a 90° phase shifter is respectively connected in series in two of the connecting lines.

4. The microwave photon dual orthogonal mirror frequency suppression mixing method as claimed in claim 1, characterized in that: Step S3 and step S4 are implemented by two balanced photodetectors and a 90° microwave bridge. The selected four coupled optical signals are respectively connected to the four input ends of the two balanced photodetectors, and the two output ends of the two balanced photodetectors are respectively connected to the two input ends of the 90° microwave bridge, and the 90° microwave bridge outputs the two intermediate frequency signals.

5. The microwave photon dual orthogonal mirror frequency suppression mixing method as claimed in claim 1, characterized in that: The carrier suppressed single sideband modulation is realized by dual parallel Mach-Zehnder modulators or Mach-Zehnder modulator cascade optical filters.

6. A microwave photon dual orthogonal mirror frequency suppression mixing device, characterized in that: include: A modulation module, used to perform carrier suppressed single sideband modulation on a co-source optical carrier using a radio frequency signal and a local oscillator signal, respectively, to obtain an optically carried radio frequency signal and an optical local oscillator signal; The dual orthogonal mixer module is used to divide the optical RF signal and the optical local oscillator signal into two paths, and pass through θ1, θ2 and The first phase shift is then performed, and the two optical local oscillator signals / optical radio frequency signals that have undergone the first phase shift are divided into four paths respectively and are phase shifted twice by α1, α2, α3, α4 and β1, β2, β3, β4 respectively, and then coupled with the optical radio frequency signal / optical local oscillator signal that has undergone the first phase shift respectively. The relationship between the phase shifts θ1 and θ2 satisfies: θ2=θ1+π / 2+2πm, and the phase shift The relationship between them satisfies: The relationship between phase shifts α1, α2, α3 and α4 satisfies: α2=α1+π+2πa1, α3=α1+π / 2+2πa2, α4=α1+3π / 2+2πa3, phase shift β 1. The relationship between β2, β3 and β4 satisfies: β2=β1+π+2πb1, β3=β1+π / 2+2πb2, β4=β1+3π / 2+2πb3, where m, n, a i (i=1,2,3),b i (i=1,2,3) are all integers; The optoelectronic conversion module is used to select two coupled optical signals whose optical local oscillator signals / optical radio frequency signals are orthogonal to each other after secondary phase shift from four coupled optical signals including optical local oscillator signals / optical radio frequency signals that have undergone a primary phase shift of θ1; select two coupled optical signals whose optical local oscillator signals / optical radio frequency signals are orthogonal to each other after secondary phase shift from four coupled optical signals including optical local oscillator signals / optical radio frequency signals that have undergone a primary phase shift of θ2; and then convert the selected four coupled optical signals into electrical signals respectively; The electrical phase coupling module is used to couple the four electrical signals after phase shifting ε1, ε2, ε3, and ε4 respectively to obtain an intermediate frequency signal that achieves image frequency suppression. The relationship between the phase shifts ε1, ε2, ε3, and ε4 satisfies: ε2 = ε1 + π + 2πk1, ε3 = ε1 + π / 2 + 2πk2, ε4 = ε1 + 3π / 2 + 2πk3, where k i (i=1,2,3) is an integer.

7. The microwave photon dual orthogonal mirror frequency suppression mixing device as claimed in claim 6, characterized in that: The dual orthogonal mixing module includes two 90° optical directional couplers and two 90° optical mixers. The optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two 90° optical directional couplers, and the two output ends of each 90° optical directional coupler are respectively connected to one input end of each of the two 90° optical mixers.

8. The microwave photon dual orthogonal mirror frequency suppression mixing device as claimed in claim 6, characterized in that: The dual orthogonal mixing module includes two directional couplers, four beam splitters, four optical couplers, and two 90° phase shifters. The optically-carried radio frequency signal and the optical local oscillator signal are respectively connected to the input ends of the two directional couplers, and the four output ends of the two directional couplers are respectively connected to the input ends of the four beam splitters. The input ends of the four beam splitters are cross-connected with the input ends of the four optical couplers in pairs, and a 90° phase shifter is respectively connected in series in two of the connecting lines.

9. The microwave photon dual orthogonal mirror frequency suppression mixing device as claimed in claim 6, characterized in that: The photoelectric conversion module includes two balanced photodetectors, and the electrical phase coupling module is a 90° microwave bridge. The selected four-way coupled optical signals are respectively connected to the four input ends of the two balanced photodetectors, and the two output ends of the two balanced photodetectors are respectively connected to the two input ends of the 90° microwave bridge, and the 90° microwave bridge outputs the two intermediate frequency signals.

10. The microwave photon dual orthogonal mirror frequency suppression mixing device as claimed in claim 6, characterized in that: The modulation module realizes the carrier suppressed single sideband modulation through dual parallel Mach-Zehnder modulators or Mach-Zehnder modulator cascade optical filters.

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