An optical single-sideband frequency shifter and method for generating ultra-high suppression ratio.

Abstract

This invention provides an optical single-sideband frequency shifter and method with ultra-high suppression ratio. The device includes an optical frequency shifting unit, an optical sideband phase modulation interference unit, and a control unit. The device employs an orthogonal Mach-Zehnder modulation structure to achieve optical sideband frequency shifting of a 1.5μm band optical wave. The frequency-shifted optical signal contains residual carrier and residual sidebands, which then enter the optical sideband phase modulation interference unit. The optical sideband phase modulation interference unit uses a two-stage phase modulation structure to achieve destructive suppression of even and odd sidebands. The first stage uses a fiber phase shifter and an adjustable fiber delay line to suppress even-order sidebands, and the second stage uses a fiber phase shifter and an adjustable fiber delay line to suppress odd-order sidebands. The control unit adjusts the phase change of the fiber phase shifter and the delay of the adjustable fiber delay line, respectively, ultimately outputting an optical single-sideband frequency shifter signal with ultra-high suppression ratio. This invention can improve the suppression ratio of each sideband of any modulation format radio frequency signal by more than 20dB.

Description

Technical Field

[0001] This invention belongs to the field of spatial large dynamic range optical information transmission technology, specifically relating to an optical single-sideband frequency shifter and method with ultra-high suppression ratio. Background Technology

[0002] 6G information networks are the next-generation national strategic information infrastructure, enabling high-speed interconnection between information nodes in the air, space, land, and sea. Using lasers as carrier waves for information transmission is a crucial means of achieving this high-speed interconnection. Countries worldwide have developed satellite laser communication technology as a means of high-speed interconnection of space information nodes. For example, the US Starlink constellation deploys numerous laser communication terminals to achieve high-speed space information data transmission. Europe's EDRS relay link system has also established laser communication between high-Earth orbit and low-Earth orbit constellations. China's currently under-construction StarNet constellation will also heavily utilize laser communication transmission networks to achieve high data rate and large-capacity space information transmission.

[0003] Then, since space nodes (such as satellites, airborne platforms, and aircraft) are not fixed nodes in the space network, but move along their orbital paths, the relative motion speed between two space nodes causes a Doppler frequency shift effect in the laser light waves during laser communication or laser detection. Therefore, when testing space laser communication terminals on the ground, it is necessary to simulate the Doppler frequency shift in space for equivalent testing. Currently, single-sideband frequency shift can be achieved using a Mach-Zehnder interferometer structure. This method uses a Mach-Zehnder modulator as the core device. Since the extinction ratio of this device is usually only around 20dB, after generating single-sideband frequency shift, the carrier and other sideband suppression ratios are usually around 20dB. At the same time, if this structure improves the carrier suppression ratio, the suppression ratios of the other sidebands decrease, making it impossible to simultaneously improve the carrier suppression ratio and the suppression ratios of the other sidebands. This has a significant impact on the carrier tracking and transmission sensitivity of the entire communication system. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides an optical single-sideband frequency shifter and method with ultra-high suppression ratio. The technical problem to be solved by this invention is achieved through the following technical solution:

[0005] An optical single-sideband frequency shifter with ultra-high suppression ratio includes an optical frequency shifter unit, an optical sideband phase modulation interference unit, and a control unit;

[0006] The optical frequency shifting unit is used, under the control of the control unit, to perform optical sideband shifting on the input radio frequency signal based on an orthogonal Mach-Zehnder modulation structure to obtain a frequency-shifted optical signal; wherein the frequency-shifted optical signal contains a residual carrier and a residual sideband.

[0007] The optical sideband phase modulation interference unit is used, under the control of the control unit, to suppress the residual carrier and residual sideband contained in the frequency-shifted optical signal using a two-stage phase modulation structure, thereby obtaining an optical single-sideband signal.

[0008] A method for generating an optical single-sideband frequency shifter with ultra-high suppression ratio is disclosed, which utilizes an optical single-sideband frequency shifter with ultra-high suppression ratio. The method includes:

[0009] The control unit generates control voltages to control the optical frequency shifting unit and the optical sideband phase modulation interference unit;

[0010] Using the optical frequency shifting unit, under the action of the control voltage, the input radio frequency signal is optically shifted based on an orthogonal Mach-Zehnder modulation structure to obtain a frequency-shifted optical signal; wherein, the frequency-shifted optical signal contains a residual carrier and a residual sideband;

[0011] By utilizing the aforementioned optical sideband phase modulation interferometry unit, under the influence of the control voltage, a two-stage phase modulation structure is employed to suppress the residual carrier and residual sidebands contained in the frequency-shifted optical signal, thereby obtaining an optical single-sideband signal. Beneficial effects:

[0012] 1) This invention enables optical single-sideband frequency shifting with ultra-high suppression ratio, simulating the Doppler frequency shift process of spatial lasers with extremely high precision. Limited by the extinction ratio performance of conventional optical modulators, using orthogonal Mach-Zehnder modulators to achieve single-sideband frequency shifting in the 1.5μm band will carry residual carrier waves and multiple residual sidebands. Therefore, this invention uses the required +1st order frequency shift as the reference wavelength. Through first-stage optical sideband phase modulation interference, odd-order sideband wavelengths can be significantly suppressed, and through second-stage optical sideband phase modulation interference, even-order sideband wavelengths can be significantly suppressed. Furthermore, after two stages of optical sideband phase modulation interference, the optical power loss of the +1st order frequency shift is theoretically zero, while the optical power of the residual carrier and multiple residual sidebands is greatly attenuated. Therefore, an ultra-high suppression ratio optical single-sideband signal can be achieved. Compared to the traditional method of frequency shifting using only orthogonal Mach-Zehnder modulators, the device of this invention can improve the suppression ratio of the carrier and other sidebands by more than 30dB with the +1st order frequency shift.

[0013] 2) This invention can simulate the Doppler effect of spatial relative motion under strong background noise conditions. Because this invention has extremely high suppression ratios for the carrier wave and residual sidebands, it can still achieve effective Doppler frequency optical signal detection under strong background noise, and can adapt to Doppler simulation of large-scale spatial motion over a wide range.

[0014] 3) This invention supports optical single-sideband frequency shift simulation with ultra-high suppression ratio for various modulation formats. Since this invention uses sideband frequency shifting, there is no loss of modulation information. Therefore, the input 1.5μm band optical signal can be a continuous wave or a signal containing any modulation format.

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an optical single-sideband frequency shifter with ultra-high suppression ratio provided by the present invention;

[0017] Figure 2 This is a schematic diagram of the internal structure of the orthogonal Mach-Zehnder modulator provided by the present invention;

[0018] Figure 3 This is a schematic diagram of the spectrum before and after residual carrier and residual sideband suppression provided by the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0020] In order for laser communication systems to operate normally under space optical Doppler simulation conditions, it is necessary to achieve high suppression ratios for both the carrier and other sidebands during optical single-sideband frequency shifting. However, there is currently no optical single-sideband frequency shifting generation device or method that can simultaneously achieve high suppression ratios for both the carrier and other sidebands.

[0021] refer to Figure 1 and Figure 2 In a first aspect, the present invention provides an optical single-sideband frequency shifting generation device with ultra-high suppression ratio, comprising an optical frequency shifting unit, an optical sideband phase modulation interference unit, and a control unit;

[0022] The optical frequency shifting unit is used, under the control of the control unit, to perform optical sideband shifting on the input radio frequency signal based on an orthogonal Mach-Zehnder modulation structure to obtain a frequency-shifted optical signal; wherein the frequency-shifted optical signal contains a residual carrier and a residual sideband.

[0023] The optical sideband phase modulation interference unit is used, under the control of the control unit, to suppress the residual carrier and residual sideband contained in the frequency-shifted optical signal using a two-stage phase modulation structure, thereby obtaining an optical single-sideband signal.

[0024] refer to Figure 1 As shown, the optical frequency shifting unit of the present invention includes a tunable laser, a frequency shift signal source, a radio frequency phase shifter, a first analog amplifier, a second analog amplifier, a quadrature Mach-Zehnder modulator, and a DC voltage converter; in Figure 1 The first and second analog amplifiers are denoted as analog amplifier A and analog amplifier B, respectively.

[0025] The output of the tunable laser is connected to the input of the quadrature Mach-Zehnder modulator; the output of the frequency-shift signal source is connected to the input of the radio frequency phase shifter, the input of analog amplifier A, and the input of analog amplifier B; the outputs of analog amplifier A and analog amplifier B are connected to the two radio frequency ports of the quadrature Mach-Zehnder modulator; the input of the quadrature Mach-Zehnder modulator is connected to the output of its corresponding DC voltage transformer; and the input of the radio frequency phase shifter is connected to the output of the control unit.

[0026] The optical frequency shifting unit of this invention functions to achieve optical single-sideband frequency shifting in the 1.5μm band.

[0027] Specifically, under the control of the control unit, the frequency shift signal source generates a time-varying radio frequency signal and sends it to the radio frequency phase shifter;

[0028] The radio frequency phase shifter shifts the radio frequency signal to obtain two orthogonal frequency shift signals, and sends one of the frequency shift signals to the analog amplifier A and the other frequency shift signal to the analog amplifier B;

[0029] Both analog amplifier A and analog amplifier B amplify their own input frequency-shifted signals to obtain two amplified signals, and then send the two amplified signals synchronously into the quadrature Mach-Zehnder modulator.

[0030] The DC voltage generator provides a bias voltage for the quadrature Mach-Zehnder modulator;

[0031] The orthogonal Mach-Zehnder modulator modulates the two amplified signals to obtain a frequency-shifted optical signal, which is then sent to the optical sideband phase-modulation interference unit.

[0032] The DC voltage converter of this invention can provide a voltage that matches the phase operating point of an orthogonal Mach-Zehnder modulator. Simultaneously, the center wavelength is... The 1.5μm band light wave passes through an orthogonal Mach-Zehnder modulator. Based on the orthogonal Mach-Zehnder modulation structure, optical sideband frequency shifting is achieved, and the frequency-shifted optical signal... However, at this time, it contains residual carriers that have not been suppressed and a large number of residual sidebands.

[0033] This invention supports optical single-sideband frequency shift simulation with ultra-high suppression ratios for various modulation formats. Because this invention uses sideband frequency shifting, there is no loss of modulation information; therefore, the input 1.5μm band optical signal can be a continuous wave or a signal containing any modulation format, such as intensity light signals (OOK), phase light signals (BPSK), and higher-order modulated light signals (QPSK, 16QAM, 64QAM).

[0034] refer to Figure 1 The optical sideband phase modulation interference unit of the present invention includes a first optical coupler, a first fiber phase shifter, a first adjustable fiber delay line, a second optical coupler, a third optical coupler, a second adjustable fiber delay line, a second fiber phase shifter, and a fourth optical coupler.

[0035] The first to fourth optical couplers are in Figure 1 In the diagram, optical coupler 1, optical coupler 2, optical coupler 3 and optical coupler 4 are respectively referred to as optical coupler 1 and optical coupler 2, the first fiber phase shifter and the second fiber phase shifter are respectively referred to as fiber phase shifter 1 and fiber phase shifter 2, the first adjustable fiber delay line and the second adjustable fiber delay line are respectively referred to as adjustable fiber delay line 1 and adjustable fiber delay line 2.

[0036] The output of the optical frequency shifting unit is connected to the input of the optical coupler 1. The optical coupler 1 outputs two optical waves to the fiber phase shifter 1 and the adjustable fiber delay line 1, respectively. The outputs of the fiber phase shifter 1 and the adjustable fiber delay line 1 are connected to the input of the optical coupler 2. The output of the optical coupler 2 is connected to the input of the optical coupler 3. The output of the optical coupler 3 is connected to the input of the fiber phase shifter 2 and the adjustable fiber delay line 2. The outputs of the fiber phase shifter 2 and the adjustable fiber delay line 2 are connected to the input of the optical coupler 4. The output of the optical coupler outputs an optical single-sideband signal.

[0037] Specifically, the optical coupler 1 splits the frequency-shifted optical signal into two optical waves, path A and path B;

[0038] The fiber phase shifter 1 shifts the phase of the A-path light wave to obtain the C-path light wave;

[0039] The adjustable fiber delay line 1 delays the B-path light wave to obtain the D-path light wave.

[0040] The optical coupler 2 couples the C-path and D-path light waves to obtain the E-path light wave;

[0041] The optical coupler 3 divides the E-path light wave into the F-path and H-path light waves;

[0042] The fiber phase shifter 2 shifts the phase of the F-path light wave to obtain the I-path light wave;

[0043] The adjustable fiber delay line 2 delays the H-path light wave to obtain the G-path light wave.

[0044] The optical coupler 4 couples the I-path and G-path light waves to obtain an optical single-sideband signal.

[0045] The delay amount of the adjustable fiber delay line 1 With the frequency of the radio frequency signal f s satisfy relation;

[0046] The phase change of the fiber phase shifter 1 Phase change introduced by tunable fiber delay line 1 Same; the delay amount of the adjustable fiber delay line 2 and f s satisfy relation;

[0047] The phase change of the fiber phase shifter 2 Phase change introduced by tunable fiber delay line 2 The optical path difference between the optical path from path B to path D and the optical path from path A to path C is equal to the optical delay of adjustable fiber delay line 1; the optical path difference between the optical path from path H to path G and the optical path from path F to path I is equal to the optical delay of adjustable fiber delay line 2.

[0048] The power coupling ratios of optical couplers 1, 2, 3, and 4 are all between 49.5% and 50.5%.

[0049] The delay adjustment range of adjustable fiber delay line 1 and adjustable fiber delay line 2 is between 0 and 1 μs.

[0050] The phase change of fiber phase shifter 1 and fiber phase shifter 2 is between 0° and 360°.

[0051] The phase imbalance range of the RF phase shifter is within ±10°.

[0052] The 1.5μm band tunable laser outputs linearly polarized light with a wavelength tuned between 1.52μm and 1.58μm.

[0053] The adjustable fiber delay line 1 and the adjustable fiber delay line 2 can be either fiber-type or spatial structure.

[0054] The fiber phase shifter 1 and the fiber phase shifter 2 are any one of a phase modulator, a fiber stretcher, and an optical delay line.

[0055] The working process of the optical sideband phase modulation interferometer is as follows: the frequency-shifted optical signal The light waves are split into two paths, A and B, by optical coupler 1. Using the reference wavelength, the remaining residual carrier and residual sideband wavelengths can be considered as sidebands. Path A light wave reaches path C through fiber phase shifter 1, and path B light wave reaches path D through adjustable fiber delay line 1. The odd-numbered sidebands are matched by adjusting adjustable fiber delay line 1, and simultaneously adjusting fiber phase shifter 1 to match... The reference wavelength is used. At this point, the C-path and D-path optical waves, after coupling through optical coupler 2, will have a destructive interference suppression effect on the odd-numbered sidebands. The coupled output E-path optical wave enters optical coupler 3 and is split into F-path and H-path optical waves. The F-path optical wave reaches path I after passing through fiber phase shifter 2, and the H-path optical wave reaches path G after passing through adjustable fiber delay line 2. The even-numbered sidebands are matched by adjusting the adjustable fiber delay line 2, and simultaneously adjusting the fiber phase shifter 2 to match... Using the reference wavelength, the I-path and G-path optical waves are coupled through optical coupler 4. This coupling process will cause destructive interference to the even-order sidebands. Therefore, through two optical sideband phase modulation interferences, the even-order and odd-order sidebands can be suppressed respectively, while the required... Using two reference wavelengths, and with both processes involving constructive interference, an ultra-high suppression ratio optical single-sideband signal is achieved.

[0056] In addition, the control unit controls the delay of adjustable fiber delay line 1 and adjustable fiber delay line 2 to adapt to odd and even sidebands, and controls fiber phase shifter 1 to achieve precise phase adjustment between C-path and D-path optical waves, and controls fiber phase shifter 2 to achieve precise phase adjustment between I-path and G-path optical waves, ultimately achieving ultra-high suppression ratio optical single-sideband signal output.

[0057] The working principle of the optical single-sideband frequency shifter with ultra-high suppression ratio provided by this invention is as follows:

[0058] In the optical frequency shifting unit, a 1.5μm band tunable laser is set to output a continuous optical carrier, the wavelength of which is defined as λ1 (corresponding to a frequency of...). f 1. Angular frequency is The frequency of the radio frequency signal generated by the frequency shift signal source is set to... f s (angular frequency is) Since the 1.5μm laser outputs a continuous optical carrier, its optical field expression can be given as:

[0059] (1)

[0060] in, This represents the amplitude of the light field. For example... Figure 2 As shown, the quadrature Mach-Zehnder modulator contains two sub-modulators, 1 and 2, and an optical phase shifter. To achieve carrier-suppressed single-sideband frequency shift, the two sub-modulators operate at the minimum power transmission point. The DC voltage converter outputs three voltages, two of which are applied to the two sub-modulators, and the DC bias voltage is equal to the half-wave voltage. V π The RF phase shifter outputs two RF signals of the same frequency with a 90° phase difference. One of these signals, after being amplified by analog amplifier A, has a voltage of... V A The electrical signal loaded onto the upper arm of sub-modulator 1 is:

[0061] (2)

[0062] The phase change of this voltage can be obtained as follows:

[0063] (3)

[0064] in, It is the modulation index. The output optical field expression after modulation by the upper arm of sub-modulator 1. for:

[0065] (4)

[0066] According to the identity of the Bessel function, it is as follows:

[0067] (5)

[0068] Substituting equation (5) into equation (4) simplifies the process, considering the smaller order ( n (Less than 3), and other values ​​can be ignored, resulting in the following simplified expression for the light field:

[0069] (6)

[0070] Similarly, the sampling of the lower arm of sub-modulator 1 is carried out in the same way, and the voltage applied to the lower arm is... The phase change is as follows:

[0071] (7)

[0072] The resulting output light field is:

[0073] (8)

[0074] Typically, the extinction ratio of a quadrature Mach-Zehnder modulator is around 15-25 dB. The extinction ratios of the main modulator, sub-modulator 1, and sub-modulator 2 are defined as follows: , and The refraction ratios are respectively , and The spectrophotometer ratio and extinction ratio are related as follows:

[0075] (9)

[0076] Therefore, the output optical signal after sub-modulator 1 and sub-modulator 2 and It can be represented as:

[0077] (10)

[0078] (11)

[0079] Simultaneously, the phase shift between sub-modulator 1 and sub-modulator 2 is set to... The final superimposed light field expression is shown in the following equation:

[0080] (12)

[0081] Substituting equations (10) and (11) into equation (12), and using Bessel function expansion, while ignoring higher-order sidebands above the fourth order, we can obtain the optical field output by the orthogonal Mach-Zehnder modulator. The expression is as follows:

[0082] (13)

[0083] In the formula, for Bessel function of order 1, This is the modulation index.

[0084] As can be seen from equation (13), in addition to generating the required +1 order, the frequency shifting process also generates additional sidebands of order 0 (carrier), -1, ±2, and ±3. When the optical field The light wave is split into path A and path B by optical coupler 1. The phase change introduced by fiber phase shifter 1 for path A is: The light wave in path B, after passing through the tunable fiber delay line 1, experiences a delay of [value missing]. The phase change introduced at the same time is The two-port optical field output after the C-path light wave and the D-path light wave are coupled through optical coupler 2. It can be represented as follows:

[0085] (14)

[0086] In the formula, The splitting ratio of fiber coupler 1. This represents the splitting ratio of fiber coupler 2. This refers to the frequency corresponding to the +1 order frequency shift sideband mentioned above. Let n be the frequency of other sidebands, where n can take values ​​of 0, -1, ±2, ±3, and ±4. Further simplification yields:

[0087] (15)

[0088] Since the E-path light wave is a single-port wave, the upper part of the factor in equation (14) is taken as the light field of the E-path light wave, which is:

[0089] (16)

[0090] When the frequency of the frequency shift signal source outputs the radio frequency signal is f s At that time, with the +1st order sideband frequency Interval is f s Even-numbered sidebands are defined as type I sidebands, with frequencies of . Ignoring higher-order sidebands, where k The value can be -2, -1, 1, 2, etc.; similarly, it is the same as the +1st order sideband frequency. Interval is f s Odd-numbered double-sided bands are defined as second-type sidebands, with frequencies of . Ignoring higher-order sidebands, where k The values ​​can be -3, -2, -1, 0, 1, 2, etc. Adjusting the delay of adjustable fiber optic delay line 1. and f s satisfy At that time, the phase change of fiber phase shifter 1 Phase change introduced by tunable fiber delay line 1 When they are the same, substitute the first and second type sideband frequencies into equation (16) respectively. This yields the following formula:

[0091] (17)

[0092] (18)

[0093] Due to the splitting ratio and Both are close to 50%, therefore we can obtain:

[0094] (19)

[0095] (20)

[0096] It can be seen that the optical field of the first type of sideband is almost zero, while the optical field of the second type of sideband hardly changes. Therefore, the E-path optical field formed by coupling through fiber phase shifter 1 and tunable fiber delay line 1 suppresses the first type of sideband. Similarly, adjusting the delay of tunable fiber delay line 2... and f s satisfy At the same time, adjust the phase change of fiber phase shifter 2. Phase change introduced by tunable fiber delay line 2 At the same time, the optical field output by optical coupler 4 will suppress the second type of sideband, i.e. Therefore, through two-stage phase modulation interference, the optical fields of the first and second type sidebands are suppressed sequentially, retaining only the required +1 order sideband, thus comprehensively improving the sideband suppression ratio.

[0097] refer to Figure 3 As shown, Figure 3 The spectrum before and after suppression of residual carrier and residual sideband is shown, which can verify that the optical single-sideband frequency shifter with ultra-high suppression ratio of the present invention can effectively suppress residual carrier and residual sideband.

[0098] In a second aspect, the present invention provides a method for generating an optical single-sideband frequency shifter with ultra-high suppression ratio, implemented using the optical single-sideband frequency shifter with ultra-high suppression ratio described in the first aspect. The method for generating the optical single-sideband frequency shifter with ultra-high suppression ratio includes:

[0099] The control unit generates control voltages to control the optical frequency shifting unit and the optical sideband phase modulation interference unit;

[0100] Using the optical frequency shifting unit, under the action of the control voltage, the input radio frequency signal is optically shifted based on an orthogonal Mach-Zehnder modulation structure to obtain a frequency-shifted optical signal; wherein, the frequency-shifted optical signal contains a residual carrier and a residual sideband;

[0101] By utilizing the optical sideband phase modulation interference unit, under the action of the control voltage, a two-stage phase modulation structure is used to suppress the residual carrier and residual sideband contained in the frequency-shifted optical signal, thereby obtaining an optical single-sideband signal.

[0102] This invention discloses an optical single-sideband frequency shifting generation method with ultra-high suppression ratio, using an optical single-sideband frequency shifting generation device with ultra-high suppression ratio. The process is as follows: in the optical frequency shifting unit, the center wavelength is... A 1.5μm band light wave passes through an orthogonal Mach-Zehnder modulator. Simultaneously, a frequency shift signal source outputs a time-varying frequency signal. This signal, after passing through an RF phase shifter, becomes two orthogonal frequency-shifted signals. These two orthogonal frequency-shifted signals are then simultaneously fed into the orthogonal Mach-Zehnder modulator after passing through analog amplifiers A and B, respectively. A DC voltage converter provides the phase-adaptive operating point voltage to the orthogonal Mach-Zehnder modulator. Based on this, the output of the orthogonal Mach-Zehnder modulator will generate an optical single-sideband frequency shift process containing residual sidebands and residual carrier waves. In the optical sideband phase-modulation interference unit, the frequency-shifted light wave... After passing through optical coupler 1, the light waves are split into two equal paths, A and B. Path A passes through fiber phase shifter 1 and reaches path C, while path B passes through tunable fiber delay line 1 and reaches path D. Paths C and D are coupled through optical coupler 2 and output through path E. The light wave in path E reaches optical coupler 3 and splits into two paths, F and H. Path F passes through fiber phase shifter 2 and reaches path I, while path H passes through tunable fiber delay line 2 and outputs through path G. Paths I and G are coupled through optical coupler 4 and output as an ultra-high suppression ratio optical single-sideband signal. The control unit controls the frequency shift signal source to simulate the current frequency shift value and rate of change, controls the output frequency of the 1.5μm band tunable laser, and controls the phase change of the fiber phase shifter and the delay of the tunable fiber delay line.

[0103] The method of the present invention can be implemented according to the following steps:

[0104] Step 1: The control unit sets the frequency shift value of the frequency shift signal source output, and can also set the rate and direction of frequency shift change. Additionally, the control unit controls the output wavelength of the 1.5μm band tunable laser to be... Continuous light.

[0105] Step 2: The frequency shift signal source outputs an RF signal and inputs it to the input terminal of the RF phase shifter. The RF phase shifter outputs two quadrature RF signals with a 90° phase difference. These two quadrature RF signals are amplified by analog amplifiers A and B, respectively, and then connected to the RF port of the quadrature Mach-Zehnder modulator. Continuous light is also input to the optical input port of the quadrature Mach-Zehnder modulator. The output voltage of the DC voltage converter is supplied to the DC port of the quadrature Mach-Zehnder modulator, causing it to operate in single-sideband frequency-shift mode and generate a frequency-shifted light wave. It also carries residual carriers and residual sidebands.

[0106] Step 3, Frequency-shifting light wave The light waves are split into two identical paths, path A and path B, by optical coupler 1. Path A passes through fiber phase shifter 1 and reaches path C, while path B passes through adjustable fiber delay line 1 and reaches path D. The two light waves, path C and path D, are coupled by optical coupler 2 and output from path E.

[0107] Step 4: The E-path light wave reaches optical coupler 3 and splits into two light waves, namely the F-path and H-path light waves. The F-path light wave passes through fiber phase shifter 2 and reaches the I-path, while the H-path light wave passes through adjustable fiber delay line 2 and is output to the G-path. The two light waves, I-path and G-path, are coupled through optical coupler 4 and output as one optical signal.

[0108] Step 5: The control unit controls the phase change of the fiber phase shifter 1 and the delay of the adjustable fiber delay line 1 to suppress even-numbered sidebands, and controls the phase change of the fiber phase shifter 2 and the delay of the adjustable fiber delay line 2 to suppress odd-numbered sidebands, ultimately achieving ultra-high suppression ratio optical single-sideband signal output.

[0109] It is worth noting that the terms "first" and "second" in this invention are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0110] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. An optical single-sideband frequency shifter with ultra-high suppression ratio, characterized in that, It includes an optical frequency shifting unit, an optical sideband phase modulation interference unit, and a control unit; The optical frequency shifting unit is used, under the control of the control unit, to perform optical sideband shifting on the input radio frequency signal based on an orthogonal Mach-Zehnder modulation structure to obtain a frequency-shifted optical signal; wherein the frequency-shifted optical signal contains a residual carrier and a residual sideband. The optical sideband phase modulation interference unit is used, under the control of the control unit, to suppress the residual carrier and residual sideband contained in the frequency-shifted optical signal using a two-stage phase modulation structure, thereby obtaining an optical single-sideband signal. The optical sideband phase modulation interference unit includes a first optical coupler, a first fiber phase shifter, a first adjustable fiber delay line, a second optical coupler, a third optical coupler, a second adjustable fiber delay line, a second fiber phase shifter, and a fourth optical coupler. The output of the optical frequency shifting unit is connected to the input of the first optical coupler. The first optical coupler outputs two optical waves to the first fiber phase shifter and the first adjustable fiber delay line, respectively. The outputs of the first fiber phase shifter and the first adjustable fiber delay line are correspondingly connected to the input of the second optical coupler. The output of the second optical coupler is connected to the input of the third optical coupler. The output of the third optical coupler is correspondingly connected to the inputs of the second fiber phase shifter and the second adjustable fiber delay line. The outputs of the second fiber phase shifter and the second adjustable fiber delay line are connected to the input of the fourth optical coupler. The output of the optical coupler outputs an optical single-sideband signal. The delay of the first adjustable fiber delay line With the frequency of the radio frequency signal f s satisfy relation; Phase change of the first fiber phase shifter Phase change introduced by the first adjustable fiber delay line Same; the delay of the second adjustable fiber delay line and f s satisfy relation; Phase change of the second fiber phase shifter Phase change introduced by the second adjustable fiber delay line same.

2. The optical single-sideband frequency shifter with ultra-high suppression ratio according to claim 1, characterized in that, The optical frequency shifting unit includes a tunable laser, a frequency shifting signal source, a radio frequency phase shifter, a first analog amplifier, a second analog amplifier, a quadrature Mach-Zehnder modulator, and a DC voltage converter. The output of the tunable laser is connected to the input of the quadrature Mach-Zehnder modulator, and the output of the frequency-shift signal source is connected to the input of the radio frequency phase shifter, the input of the first analog amplifier, and the input of the second analog amplifier. The outputs of the first and second analog amplifiers are connected to the two radio frequency ports of the quadrature Mach-Zehnder modulator, the input of the quadrature Mach-Zehnder modulator is connected to the output of its corresponding DC voltage transformer, and the input of the radio frequency phase shifter is connected to the output of the control unit.

3. The optical single-sideband frequency shifter with ultra-high suppression ratio according to claim 2, characterized in that, The frequency shift signal source, under the control of the control unit, generates a radio frequency signal that varies with time and sends it to the radio frequency phase shifter; The radio frequency phase shifter shifts the radio frequency signal to obtain two orthogonal frequency shift signals, and sends one of the frequency shift signals to the first analog amplifier and the other frequency shift signal to the second analog amplifier; Both the first analog amplifier and the second analog amplifier amplify their own input frequency-shifted signals to obtain two amplified signals, and then synchronously send the two amplified signals into the quadrature Mach-Zehnder modulator. The DC voltage generator provides a bias voltage for the quadrature Mach-Zehnder modulator; The orthogonal Mach-Zehnder modulator modulates the two amplified signals to obtain a frequency-shifted optical signal, which is then sent to the optical sideband phase-modulation interference unit.

4. The optical single-sideband frequency shifter with ultra-high suppression ratio according to claim 1, characterized in that, The first optical coupler splits the frequency-shifted optical signal into two optical waves, path A and path B; The first fiber phase shifter shifts the phase of the A-path light wave to obtain the C-path light wave; The first adjustable fiber delay line delays the B-path light wave to obtain the D-path light wave. The second optical coupler couples the C-path and D-path light waves to obtain the E-path light wave; The third optical coupler splits the E-path light wave into the F-path and H-path light waves; The second fiber phase shifter shifts the phase of the F-path light wave to obtain the I-path light wave; The second adjustable fiber delay line delays the H-path light wave to obtain the G-path light wave; The fourth optical coupler couples the I-path and G-path light waves to obtain an optical single-sideband signal.

5. The optical single-sideband frequency shifter with ultra-high suppression ratio according to claim 4, characterized in that, The optical path difference between the optical path from path B to path D and the optical path from path A to path C is equal to the optical delay of the first adjustable fiber delay line; the optical path difference between the optical path from path H to path G and the optical path from path F to path I is equal to the optical delay of the second adjustable fiber delay line.

6. The optical single-sideband frequency shifter with ultra-high suppression ratio according to claim 1, characterized in that, The power coupling ratios of the first, second, third, and fourth optical couplers are all between 49.5% and 50.5%.

7. The optical single-sideband frequency shifter with ultra-high suppression ratio according to claim 1, characterized in that, The first adjustable fiber delay line and the second adjustable fiber delay line are either fiber-type or spatial structure; the first fiber phase shifter and the second fiber phase shifter are either phase modulators, fiber stretchers, or optical delay lines.

8. A method for generating an optical single-sideband frequency shifter with ultra-high suppression ratio, characterized in that, The method of generating an optical single-sideband frequency shifter with ultra-high suppression ratio, as described in any one of claims 1 to 7, comprises: The control unit generates control voltages to control the optical frequency shifting unit and the optical sideband phase modulation interference unit; Using the optical frequency shifting unit, under the action of the control voltage, the input radio frequency signal is optically shifted based on an orthogonal Mach-Zehnder modulation structure to obtain a frequency-shifted optical signal; wherein, the frequency-shifted optical signal contains a residual carrier and a residual sideband; By utilizing the optical sideband phase modulation interference unit, under the action of the control voltage, a two-stage phase modulation structure is used to suppress the residual carrier and residual sideband contained in the frequency-shifted optical signal, thereby obtaining an optical single-sideband signal.

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