Dither signal filtering and sampling method based on TFLN laser

Abstract

A dither signal filtering and sampling method based on a TFLN laser. The method comprises: step 1, loading a fundamental wave / second harmonic of a low-frequency dither signal into a photo-generated current of an optical module; step 2, amplifying, by means of an operational amplifier circuit, a photo-generated current signal loaded with the fundamental wave / second harmonic of the dither signal, and then splitting the amplified photo-generated current signal into two outputs; step 3, passing a first output of the two outputs through a low-pass RC filter circuit and then performing optical power sampling to monitor an output optical power, and splitting a second output of the two outputs into a fundamental wave branch and a second harmonic branch; and step 4, passing the fundamental wave branch and the second harmonic branch through corresponding frequency-selective filtering and amplification circuits and subsequent amplification and biasing circuits, respectively, so as to obtain a fundamental wave signal and a second harmonic signal, and outputting the fundamental wave signal and the second harmonic signal to an ADC sampling module for sampling. The present invention achieves effective sampling of a fundamental wave and a second harmonic of dither.

Description

A method for dither signal filtering and sampling based on TFLN laser Technical Field

[0001] This invention relates to the field of optical modules, and more specifically to a dither signal filtering and sampling method based on a TFLN laser. Background Technology

[0002] Since 2020, with the advent of 800G / 1.6T single-mode high-end optical modules, the single-channel modulation rate of optical modules has increased from 100G to 200G per wave. Traditional DML lasers (Directly Modulated Lasers) are no longer sufficient to meet the new application requirements, and TFLN MZ modulators (thin-film lithium niobate MZ) have become the best choice for applications with single-wavelength rates of 200G and above. However, quad locking of TFLN modulators has become a technical challenge in their application, and the prerequisite for quad locking is the effective detection of the quad point. Summary of the Invention

[0003] In view of the technical defects and drawbacks existing in the prior art, embodiments of the present invention provide a dither signal filtering and sampling method based on a TFLN laser to overcome or at least partially solve the above problems, thereby solving the difficulties of amplifying and detecting dither signals. The specific solution is as follows:

[0004] A method for dither signal filtering and sampling based on a TFLN laser, the method comprising:

[0005] Step 1: Load the fundamental / second harmonic of the low-frequency dither signal into the photocurrent of the optical module;

[0006] Step 2: The fundamental / second harmonic photocurrent signal loaded with the dither signal is amplified by the operational amplifier circuit and then output in two paths.

[0007] Step 3: After passing the first output of the two outputs through a low-pass RC filter circuit, the optical power is sampled to monitor the output optical power. The second output of the two outputs is then divided into a fundamental frequency branch and a second harmonic frequency branch.

[0008] Step 4: After passing the fundamental frequency branch and the second harmonic branch through the corresponding frequency selection filtering and amplification circuits and the back-end amplification and biasing circuits, the fundamental frequency signal and the second harmonic signal are obtained and output to the ADC sampling module for sampling.

[0009] Furthermore, in step 1, a low-frequency dither signal is coupled at the input of the heater modulator of the optical module, so that the fundamental / second harmonic of the dither signal is carried in the photocurrent of the MPD.

[0010] Furthermore, in step 2, the operational amplifier circuit is a front-end optoelectronic signal amplification circuit, which includes a first integrated operational amplifier MAX4233ABC+T and its peripheral circuits.

[0011] Further, the peripheral circuit includes resistors R3, R9, R10, R11, R14, R15, and R16, capacitors C4, C9, C8, and C13, and an LED PD1; the positive input terminal of the first integrated operational amplifier MAX4233ABC+T is grounded through resistor R16 and connected to power supply VCC_2V5 through resistor R14; one end of resistor R3 is connected to the negative terminal of LED PD1, and the other end is connected to power supply VCC_2V5; the positive terminal of LED PD1 is connected to ground GND_POWER; the common point of LED PD1 and resistor R3 is connected to the negative input terminal of the first integrated operational amplifier MAX4233ABC+T through resistor R9; capacitor C4 and resistor R10 are connected in parallel to form a feedback circuit, one end of which is connected to the first integrated operational amplifier MAX4233ABC+T. The negative input terminal of C+T is connected to the output terminal of the first integrated operational amplifier MAX4233ABC+T. The resistor R11 and capacitor C8 form a low-pass RC filter circuit. The output of the first integrated operational amplifier MAX4233ABC+T is divided into two paths. The first output is sampled for optical power to monitor the output optical power after passing through the low-pass RC filter circuit. The other output is sent to the frequency selection filter and amplification circuit. The control terminal of the first integrated operational amplifier MAX4233ABC+T is connected to the power supply VCC_2V5 through the resistor R15. The positive power supply terminal and the negative power supply terminal of the first integrated operational amplifier MAX4233ABC+T are connected to the power supplies VCC_2V5 and VCC_-2V5, respectively. The positive power supply terminal of the first integrated operational amplifier MAX4233ABC+T is also connected to ground GND_POWER through the capacitor C13, and the negative power supply terminal is connected to ground GND_POWER through the capacitor C13.

[0012] Furthermore, let the voltage of the common point signal MPD_IN between LED PD1 and resistor R3 be U. MPD_IN The voltage of the negative input signal U1A_IN1- of the first integrated operational amplifier MAX4233ABC+T is U U1A_IN1-The voltage of the positive input signal U1A_IN1+ of the first integrated operational amplifier MAX4233ABC+T is U U1A_IN1+ The voltage of the second output signal U1A_OUT is U U1A_OUT The voltage of the first output signal PD1_MON, which passes through the low-pass RC filter circuit, is U. PD1_MON The current i on the optical module MPD satisfies:

[0013] Eliminating intermediate values ​​yields U. U1A_OUT The relationship between i and i is:

[0014] Where R9 = R14 and R10 = R16, we can conclude that:

[0015] Furthermore, the frequency selective filtering and amplification circuit includes a first frequency selective filtering and amplification circuit and a second frequency selective filtering and amplification circuit. The first frequency selective filtering and amplification circuit is used to perform frequency selective filtering and amplification on the fundamental frequency branch to select the fundamental frequency component in the dither signal. The second frequency selective filtering and amplification circuit is used to perform frequency selective filtering and amplification on the second harmonic branch to select the second harmonic component in the dither signal.

[0016] Further, the first frequency selection filtering and amplification circuit includes a second integrated operational amplifier MAX4233ABC+T, resistors R4, R6, R7, R12, capacitor C2, and capacitor C6; the fundamental branch is connected to the negative input terminal of the second integrated operational amplifier MAX4233ABC+T via R6 and capacitor C6; the positive input terminal of the second integrated operational amplifier MAX4233ABC+T is grounded to GND_POWER, and the control terminal is connected to the power supply VCC_2V5 via resistor R7; one end of resistor R12 is grounded, and the other end is connected to the common terminal of resistor R6 and capacitor C6; one end of capacitor C2 is connected to the output terminal of the second integrated operational amplifier MAX4233ABC+T, and the other end is connected to the common terminal of resistor R6 and capacitor C6; one end of resistor R4 is connected to the output terminal of the second integrated operational amplifier MAX4233ABC+T, and the other end is connected to the negative input terminal of the second integrated operational amplifier MAX4233ABC+T; the output terminal of the second integrated operational amplifier MAX4233ABC+T is connected to the back-end amplification and biasing circuit;

[0017] The second frequency selection filtering and amplification circuit includes a third integrated operational amplifier MAX4233ABC+T, resistors R19, R21, R23, and R24, capacitors C12 and C15; the second harmonic branch is connected to the negative input terminal of the third integrated operational amplifier MAX4233ABC+T via R21 and capacitor C15; the positive input terminal of the third integrated operational amplifier MAX4233ABC+T is grounded to GND_POWER, and the control terminal is connected to the power supply VCC_2V5 via resistor R24; resistors... One end of R23 is grounded, and the other end is connected to the common terminal of resistor R21 and capacitor C15; one end of capacitor C12 is connected to the output terminal of the third integrated operational amplifier MAX4233ABC+T, and the other end is connected to the common terminal of resistor R21 and capacitor C15; one end of resistor 19 is connected to the output terminal of the third integrated operational amplifier MAX4233ABC+T, and the other end is connected to the negative input terminal of the third integrated operational amplifier MAX4233ABC+T; the output terminal of the third integrated operational amplifier MAX4233ABC+T is connected to the back-end amplification and biasing circuit.

[0018] Furthermore, in step 4, the fundamental frequency branch is connected to the corresponding frequency selective filter and amplifier circuit through the first DC blocking and AC passing capacitor C5, and the second harmonic frequency branch is connected to the corresponding frequency selective filter and amplifier circuit through the second DC blocking and AC passing capacitor C14.

[0019] Furthermore, the back-end amplification and biasing circuit includes a first back-end amplification and biasing circuit and a second back-end amplification and biasing circuit. The first back-end amplification and biasing circuit is used to amplify and bias the fundamental frequency branch after frequency selection filtering and amplification, and the second back-end amplification and biasing circuit is used to amplify and bias the second harmonic frequency branch after frequency selection filtering and amplification.

[0020] Further, the first back-end amplification and biasing circuit includes a fourth integrated operational amplifier MAX4233ABC+T, resistors R1, R2, R5, R8, and R13, and capacitors C1, C3, C7, and C10. The positive input terminal of the fourth integrated operational amplifier MAX4233ABC+T is connected to the fundamental frequency branch, and the negative input terminal is grounded to GND_POWER through resistor R1. Resistor R2 and capacitor C1 are connected in parallel to form a feedback circuit, with one end of the feedback circuit connected to the negative input terminal of the fourth integrated operational amplifier MAX4233ABC+T and the other end connected to the output terminal of the fourth integrated operational amplifier MAX4233ABC+T. Resistor R5 and resistor R13 are connected in series to form a biasing circuit. One end of the bias circuit is connected to power supply VCC_2V5, and the other end is grounded to GND_POWER; the common terminal of resistors R5 and R13 is connected to the output terminal of the fourth integrated operational amplifier MAX4233ABC+T through C17; the control terminal of the fourth integrated operational amplifier MAX4233ABC+T is connected to power supply VCC_2V5 through resistor R8; the positive and negative power supply terminals of the fourth integrated operational amplifier MAX4233ABC+T are connected to power supplies VCC_2V5 and VCC_-2V5, respectively; the positive power supply terminal of the fourth integrated operational amplifier MAX4233ABC+T is also connected to ground GND_POWER through capacitor C3, and the negative power supply terminal is connected to ground GND_POWER through capacitor C10.

[0021] The second back-end amplification and biasing circuit includes a fifth integrated operational amplifier MAX4233ABC+T, resistors R17, R18, R20, R22, and R25, and capacitors C11 and C16. The positive input terminal of the fifth integrated operational amplifier MAX4233ABC+T is connected to the fundamental frequency branch, and the negative input terminal is grounded to GND_POWER through resistor R17. Resistor R18 and capacitor C11 are connected in parallel to form a feedback circuit, and one end of the feedback circuit is connected to the fifth integrated operational amplifier MAX4233ABC+T. The negative input terminal is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T, and the other end is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T. The resistors R20 and R25 are connected in series to form a bias circuit. One end of the bias circuit is connected to the power supply VCC_2V5, and the other end is grounded GND_POWER. The common terminal of the resistors R20 and R25 is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T through C16. The control terminal of the fifth integrated operational amplifier MAX4233ABC+T is connected to the power supply VCC_2V5 through the resistor R22.

[0022] The present invention has the following beneficial effects:

[0023] This invention couples a low-frequency dither signal at the input of the heater (TFLN modulator). The fundamental / second harmonic of this signal appears in the photocurrent generated by the output MPD. The photocurrent is then amplified and debiased, and then passed through a capacitor DC blocking and dither fundamental / second harmonic frequency selective filter amplification circuit. Finally, it is operationally amplified and DC biased to achieve effective sampling of the fundamental and second harmonics of the dither. Attached Figure Description

[0024] Figure 1 is a flowchart of a dither signal filtering and sampling method based on a TFLN laser provided in an embodiment of the present invention;

[0025] Figure 2 is a circuit diagram of the dither signal filtering and sampling circuit based on a TFLN laser provided in an embodiment of the present invention;

[0026] Figure 3 shows the gain-frequency curve (including normalization) of the fundamental 1kHz selective amplification provided in the embodiment of the present invention;

[0027] Figure 4 shows the second harmonic 2kHz frequency selective amplification gain-frequency curve (including normalization) provided in the embodiment of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an,” “a,” or “the,” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising,” “including,” or “including,” and similar terms mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “connected,” “linked,” and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. “Up,” “down,” “left,” “right,” etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly; R in the formula of this invention… i Represented as resistance Ri, C iIt is represented as capacitance Ci.

[0030] In the various figures, the same elements are represented by similar reference numerals. For clarity, not all parts in the figures are drawn to scale. Furthermore, some well-known parts may not be shown in the figures.

[0031] Many specific details of this disclosure are described below to provide a clearer understanding of it. However, as those skilled in the art will understand, this disclosure may be implemented without following these specific details.

[0032] Figure 1 is a flowchart of a dither signal filtering and sampling method based on a TFLN laser provided in an embodiment of the present invention. Referring to Figure 1, the dither signal filtering and sampling method based on a TFLN laser provided in an embodiment of the present invention includes:

[0033] Step 1: Load the fundamental / second harmonic of the low-frequency dither signal into the photocurrent of the optical module;

[0034] Step 2: The fundamental / second harmonic photocurrent signal loaded with the dither signal is amplified by the operational amplifier circuit and then output in two paths.

[0035] Step 3: After passing the first output of the two outputs through a low-pass RC filter circuit, the optical power is sampled to monitor the output optical power. The second output of the two outputs is then divided into a fundamental frequency branch and a second harmonic frequency branch.

[0036] Step 4: After passing the fundamental frequency branch and the second harmonic branch through the corresponding frequency selection filtering and amplification circuits and the back-end amplification and biasing circuits, the fundamental frequency signal and the second harmonic signal are obtained and output to the ADC sampling module for sampling.

[0037] Specifically, the fundamental frequency branch passes through a first frequency-selective filtering and amplification circuit to select and amplify the fundamental frequency signal in the dither signal. The amplified fundamental frequency signal then passes through a first back-end amplification and biasing circuit to obtain a 1kHz fundamental frequency. The second harmonic frequency branch passes through a second frequency-selective filtering and amplification circuit to select and amplify the second harmonic signal in the dither signal. The amplified second harmonic signal then passes through a second back-end amplification and biasing circuit to obtain a 1kHz fundamental frequency.

[0038] In step 1, a low-frequency dither signal is coupled at the input of the heater modulator of the optical module, so that the fundamental / second harmonic of the dither signal is carried in the photocurrent of the MPD.

[0039] This invention starts with the backlight MPD (monitoring diode) at the light output end of the module detecting weak light signals containing dither. After amplification and de-DC biasing of the front-end photocurrent, it passes through a capacitor for DC blocking and a dither fundamental / second harmonic frequency selective filter amplification circuit. After operational amplification and DC biasing, the fundamental and second harmonic signals of dither are effectively sampled separately.

[0040] In some embodiments, the operational amplifier circuit is a front-end optoelectronic signal amplification circuit, which includes a first integrated operational amplifier MAX4233ABC+T and its peripheral circuits, as shown in Figure 2.

[0041] Specifically, the peripheral circuit includes resistors R3, R9, R10, R11, R14, R15, and R16, capacitors C4, C9, C8, and C13, and an LED PD1. The positive input terminal of the first integrated operational amplifier MAX4233ABC+T is grounded through resistor R16 and connected to power supply VCC_2V5 through resistor R14. One end of resistor R3 is connected to the negative terminal of LED PD1, and the other end is connected to power supply VCC_2V5. The positive terminal of LED PD1 is connected to ground GND_POWER. The common point of LED PD1 and resistor R3 is connected to the negative input terminal of the first integrated operational amplifier MAX4233ABC+T through resistor R9. Capacitor C4 and resistor R10 are connected in parallel to form a feedback circuit, one end of which is connected to the first integrated operational amplifier MAX4233ABC+T. The negative input terminal of C+T is connected to the output terminal of the first integrated operational amplifier MAX4233ABC+T. Resistor R11 and capacitor C8 form a low-pass RC filter circuit. The output of the first integrated operational amplifier MAX4233ABC+T is divided into two paths: the first output is sampled for optical power monitoring after passing through the low-pass RC filter circuit, and the other output is sent to the frequency selection filter and amplification circuit. The control terminal of the first integrated operational amplifier MAX4233ABC+T is connected to power supply VCC_2V5 through resistor R15. The positive and negative power supply terminals of the first integrated operational amplifier MAX4233ABC+T are connected to power supplies VCC_2V5 and VCC_-2V5, respectively. The positive power supply terminal of the first integrated operational amplifier MAX4233ABC+T is also connected to ground GND_POWER through capacitor C13, and the negative power supply terminal is also connected to ground GND_POWER through capacitor C13.

[0042] In some embodiments, the voltage of the common point signal MPD_IN between the light-emitting diode PD1 and the resistor R3 is set to U. MPD_INThe voltage of the negative input signal U1A_IN1- of the first integrated operational amplifier MAX4233ABC+T is U U1A_IN1- The voltage of the positive input signal U1A_IN1+ of the first integrated operational amplifier MAX4233ABC+T is U U1A_IN1+ The voltage of the second output signal U1A_OUT is U U1A_OUT The voltage of the first output signal PD1_MON, which passes through the low-pass RC filter circuit, is U. PD1_MON The current i on the optical module MPD satisfies:

[0043] Among them, U ref The reference voltage for the integrated operational amplifier is used to eliminate intermediate values, resulting in U. U1A_OUT The relationship between i and i is:

[0044] Where R9 = R14 and R10 = R16, we can conclude that:

[0045] In this embodiment, U ref =2.5V, R3=120Ω, R9=R14=24.9KΩ, R10=R16=100KΩ, U U1A_OUT The first term in the square brackets can be ignored due to the resistance relationship, that is:

[0046] so:

[0047] The results show that the output voltage of the front-end photoelectric signal amplifier circuit is directly proportional to the photocurrent generated by the MPD. When the photocurrent is 1mA, U U1A_OUT The voltage output is approximately 0.48V. If the photocurrent generated by the dither disturbance is approximately 50uA, then the resulting dither AC voltage amplitude is approximately 24mV.

[0048] After the front-end photoelectric signal is amplified, it is split into two paths. One path is sampled by a low-pass RC filter circuit, where the low-pass filter cutoff frequency is:

[0049] The other path is further divided into two branches, named the fundamental frequency branch and the second harmonic frequency branch. The fundamental frequency branch and the second harmonic frequency branch are respectively fed into the frequency selective filtering and amplification circuit through DC blocking and AC passing capacitors, resulting in two branches with frequencies of 1KHz and 2KHz. Specifically, the first frequency selective filtering and amplification circuit is used to perform frequency selective filtering and amplification on the fundamental frequency branch to select the fundamental frequency signal in the dither signal, i.e., the 1KHz signal. The second frequency selective filtering and amplification circuit is used to perform frequency selective filtering and amplification on the second harmonic frequency branch to select the second harmonic signal in the dither signal, i.e., the 2KHz signal.

[0050] The first frequency selection filtering and amplification circuit includes a second integrated operational amplifier MAX4233ABC+T, resistors R4, R6, R7, R12, capacitor C2, and capacitor C6. The fundamental branch is connected to the negative input terminal of the second integrated operational amplifier MAX4233ABC+T via R6 and capacitor C6. The positive input terminal of the second integrated operational amplifier MAX4233ABC+T is grounded to GND_POWER, and the control terminal is connected to the power supply VCC_2V5 via resistor R7. One end of resistor R12 is grounded, and the other end is connected to the common terminal of resistor R6 and capacitor C6. One end of capacitor C2 is connected to the output terminal of the second integrated operational amplifier MAX4233ABC+T, and the other end is connected to the common terminal of resistor R6 and capacitor C6. One end of resistor R4 is connected to the output terminal of the second integrated operational amplifier MAX4233ABC+T, and the other end is connected to the negative input terminal of the second integrated operational amplifier MAX4233ABC+T. The output terminal of the second integrated operational amplifier MAX4233ABC+T is connected to the back-end amplification and biasing circuit.

[0051] The second frequency selection filtering and amplification circuit includes a third integrated operational amplifier MAX4233ABC+T, resistors R19, R21, R23, and R24, capacitors C12 and C15; the second harmonic branch is connected to the negative input terminal of the third integrated operational amplifier MAX4233ABC+T via R21 and capacitor C15; the positive input terminal of the third integrated operational amplifier MAX4233ABC+T is grounded to GND_POWER, and the control terminal is connected to the power supply VCC_2V5 via resistor R24; resistors... One end of R23 is grounded, and the other end is connected to the common terminal of resistor R21 and capacitor C15; one end of capacitor C12 is connected to the output terminal of the third integrated operational amplifier MAX4233ABC+T, and the other end is connected to the common terminal of resistor R21 and capacitor C15; one end of resistor 19 is connected to the output terminal of the third integrated operational amplifier MAX4233ABC+T, and the other end is connected to the negative input terminal of the third integrated operational amplifier MAX4233ABC+T; the output terminal of the third integrated operational amplifier MAX4233ABC+T is connected to the back-end amplification and biasing circuit.

[0052] Referring to Figure 2, the 1kHz frequency selective filter and amplifier circuit (i.e., the first frequency selective filter and amplifier circuit) is the upper part. Let the input signal be U. in1 The output signal is U out1 The common point voltage of C6 / R6 / C2 / R12 is U. x The voltage at the negative input terminal of op-amp U1B is U U1B_IN2- The voltage at the positive input terminal of op-amp U1B is U U1B_IN2+ The voltage can be represented using the vector method, derived from the laws of Kirchhoff's Law (KCL) and Kirchhoff's Voltage Law (KVL):

[0053] Eliminate U x The output transfer function with respect to the input is obtained as follows:

[0054] The transfer function can be written in the standard form of a bandpass filter:

[0055] The standard form of a bandpass filter is as follows;

[0056] The transfer function, compared with its standard form, has the following:

[0057] This design involves a bandpass filter and amplification, requiring a narrow bandwidth. The bandwidth is designed to be 12.5Hz, and the resonant gain is designed to be |H|. 0BP |=20, since Q=W0 / BW, W0=2πf 0，f0 = 1kHz, therefore Q = 80. Designing C2 and C6 as 10nF, we can theoretically calculate: R4 = 2547.7KΩ, R6 = 63.694KΩ, R12 = 0.099KΩ. Using actual 1% precision resistors: R4 = 2.55MΩ, R6 = 63.4KΩ, R12 = 100Ω.

[0058] Similarly, for the design of the second harmonic bandpass filter, the bandwidth is also set to 12.5Hz, and the resonant gain is designed to be |H 0BP |=20, since Q=W0 / BW, W0=2πf 0， f0 = 2KHz, so Q = 160. Designing C12 and C15 as 10nF, we can theoretically calculate: R19 = 2547.7KΩ, R21 = 63.694KΩ, R23 = 0.02489KΩ. Using actual 1% precision resistors: R19 = 2.55MΩ, R21 = 63.4KΩ, R23 = 24.9Ω.

[0059] In some embodiments, the back-end amplification and biasing circuit includes a first back-end amplification and biasing circuit and a second back-end amplification and biasing circuit. The first back-end amplification and biasing circuit is used to amplify and bias the fundamental branch after frequency selective filtering and amplification, and the second back-end amplification and biasing circuit is used to amplify and bias the second harmonic branch after frequency selective filtering and amplification.

[0060] The first back-end amplification and biasing circuit includes a fourth integrated operational amplifier MAX4233ABC+T, resistors R1, R2, R5, R8, and R13, and capacitors C1, C3, C7, and C10. The positive input terminal of the fourth integrated operational amplifier MAX4233ABC+T is connected to the fundamental frequency branch, and the negative input terminal is grounded to GND_POWER through resistor R1. Resistor R2 and capacitor C1 are connected in parallel to form a feedback circuit, with one end of the feedback circuit connected to the negative input terminal of the fourth integrated operational amplifier MAX4233ABC+T and the other end connected to the output terminal of the fourth integrated operational amplifier MAX4233ABC+T. Resistor R5 and resistor R13 are connected in series to form a biasing circuit. One end of the circuit is connected to power supply VCC_2V5, and the other end is grounded to GND_POWER. The common terminal of resistors R5 and R13 is connected to the output terminal of the fourth integrated operational amplifier MAX4233ABC+T through C17. The control terminal of the fourth integrated operational amplifier MAX4233ABC+T is connected to power supply VCC_2V5 through resistor R8. The positive and negative power supply terminals of the fourth integrated operational amplifier MAX4233ABC+T are connected to power supplies VCC_2V5 and VCC_-2V5, respectively. The positive power supply terminal of the fourth integrated operational amplifier MAX4233ABC+T is also connected to ground GND_POWER through capacitor C3, and the negative power supply terminal is connected to ground GND_POWER through capacitor C10.

[0061] The second back-end amplification and biasing circuit includes a fifth integrated operational amplifier MAX4233ABC+T, resistors R17, R18, R20, R22, and R25, and capacitors C11 and C16. The positive input terminal of the fifth integrated operational amplifier MAX4233ABC+T is connected to the fundamental frequency branch, and the negative input terminal is grounded to GND_POWER through resistor R17. Resistor R18 and capacitor C11 are connected in parallel to form a feedback circuit, and one end of the feedback circuit is connected to the fifth integrated operational amplifier MAX4233ABC+T. The negative input terminal is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T, and the other end is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T. The resistors R20 and R25 are connected in series to form a bias circuit. One end of the bias circuit is connected to the power supply VCC_2V5, and the other end is grounded GND_POWER. The common terminal of the resistors R20 and R25 is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T through C16. The control terminal of the fifth integrated operational amplifier MAX4233ABC+T is connected to the power supply VCC_2V5 through the resistor R22.

[0062] Considering the frequency selection filtering and amplification are 20 times (26dB), and the input fundamental and second harmonic amplitudes of the back-end circuit are around 0.5V, further amplification is needed to facilitate ADC sampling. Setting it to 2 times is reasonable. A 5pF capacitor is connected in parallel with the feedback resistor to solve the operational amplifier stability problem. Then, it is coupled to a 1.25V bias through a 2.2uF capacitor, thus realizing the back-end amplification and biasing. Since this part of the circuit is relatively simple to implement, it will not be described in detail here.

[0063] Referring to Figures 3 and 4, the following are the gain-frequency curves (including normalization) of the fundamental 1kHz frequency selective amplification and the second harmonic 2kHz frequency selective amplification (including normalization) provided in the embodiments of the present invention.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for dither signal filtering and sampling based on a TFLN laser, characterized in that, The method includes: Step 1: Load the fundamental / second harmonic of the low-frequency dither signal into the photocurrent of the optical module; Step 2: The fundamental / second harmonic photocurrent signal loaded with the dither signal is amplified by the operational amplifier circuit and then output in two paths. Step 3: After passing the first output of the two outputs through a low-pass RC filter circuit, the optical power is sampled to monitor the output optical power. The second output of the two outputs is then divided into a fundamental frequency branch and a second harmonic frequency branch. Step 4: After passing the fundamental frequency branch and the second harmonic branch through the corresponding frequency selection filtering and amplification circuits and the back-end amplification and biasing circuits, the fundamental frequency signal and the second harmonic signal are obtained and output to the ADC sampling module for sampling.

2. The dither signal filtering and sampling method based on a TFLN laser according to claim 1, characterized in that, In step 1, a low-frequency dither signal is coupled at the input of the heater modulator of the optical module, so that the fundamental / second harmonic of the dither signal is carried in the photocurrent of the MPD.

3. The dither signal filtering and sampling method based on a TFLN laser according to claim 1, characterized in that, In step 2, the operational amplifier circuit is a front-end optoelectronic signal amplification circuit, which includes a first integrated operational amplifier MAX4233ABC+T and its peripheral circuits.

4. The dither signal filtering and sampling method based on a TFLN laser according to claim 3, characterized in that, The peripheral circuit includes resistors R3, R9, R10, R11, R14, R15, and R16, capacitors C4, C9, C8, and C13, and an LED PD1. The positive input terminal of the first integrated operational amplifier MAX4233ABC+T is grounded through resistor R16 and connected to power supply VCC_2V5 through resistor R14. One end of resistor R3 is connected to the negative terminal of LED PD1, and the other end is connected to power supply VCC_2V5. The positive terminal of LED PD1 is connected to ground GND_POWER. The common point of LED PD1 and resistor R3 is connected to the negative input terminal of the first integrated operational amplifier MAX4233ABC+T through resistor R9. Capacitor C4 and resistor R10 are connected in parallel to form a feedback circuit, one end of which is connected to the first integrated operational amplifier MAX4233ABC+T. The negative input terminal of T is connected to the output terminal of the first integrated operational amplifier MAX4233ABC+T. The resistor R11 and capacitor C8 form a low-pass RC filter circuit. The output of the first integrated operational amplifier MAX4233ABC+T is divided into two paths. The first output is sampled for optical power to monitor the output optical power after passing through the low-pass RC filter circuit. The other output is sent to the frequency selection filter and amplification circuit. The control terminal of the first integrated operational amplifier MAX4233ABC+T is connected to the power supply VCC_2V5 through the resistor R15. The positive power supply terminal and the negative power supply terminal of the first integrated operational amplifier MAX4233ABC+T are connected to the power supply VCC_2V5 and VCC_-2V5, respectively. The positive power supply terminal of the first integrated operational amplifier MAX4233ABC+T is also connected to ground GND_POWER through the capacitor C13, and the negative power supply terminal is connected to ground GND_POWER through the capacitor C13.

5. The dither signal filtering and sampling method based on a TFLN laser according to claim 4, characterized in that, Let the voltage of the common point signal MPD_IN of LED PD1 and resistor R3 be U. MPD_IN The voltage of the negative input signal U1A_IN1- of the first integrated operational amplifier MAX4233ABC+T is U U1A_IN1- The voltage of the positive input signal U1A_IN1+ of the first integrated operational amplifier MAX4233ABC+T is U U1A_IN1+ The voltage of the second output signal U1A_OUT is U U1A_OUT The voltage of the first output signal PD1_MON, which passes through the low-pass RC filter circuit, is U. PD1_MON The current i on the optical module MPD satisfies: Among them, U ref The reference voltage for the integrated operational amplifier is used to eliminate intermediate values, resulting in U. U1A_OUT The relationship between i and i is: Where R9 = R14 and R10 = R16, we can conclude that:

6. The dither signal filtering and sampling method based on a TFLN laser according to claim 1, characterized in that, The frequency selective filtering and amplification circuit includes a first frequency selective filtering and amplification circuit and a second frequency selective filtering and amplification circuit. The first frequency selective filtering and amplification circuit is used to perform frequency selective filtering and amplification on the fundamental frequency branch to select the fundamental frequency signal in the dither signal. The second frequency selective filtering and amplification circuit is used to perform frequency selective filtering and amplification on the second harmonic branch to select the second harmonic signal in the dither signal.

7. The dither signal filtering and sampling method based on a TFLN laser according to claim 6, characterized in that, The first frequency selection filtering and amplification circuit includes a second integrated operational amplifier MAX4233ABC+T, resistors R4, R6, R7, R12, capacitor C2, and capacitor C6. The fundamental branch is connected to the negative input terminal of the second integrated operational amplifier MAX4233ABC+T via R6 and capacitor C6. The positive input terminal of the second integrated operational amplifier MAX4233ABC+T is grounded to GND_POWER, and the control terminal is connected to the power supply VCC_2V5 via resistor R7. One end of resistor R12 is grounded, and the other end is connected to the common terminal of resistor R6 and capacitor C6. One end of capacitor C2 is connected to the output terminal of the second integrated operational amplifier MAX4233ABC+T, and the other end is connected to the common terminal of resistor R6 and capacitor C6. One end of resistor R4 is connected to the output terminal of the second integrated operational amplifier MAX4233ABC+T, and the other end is connected to the negative input terminal of the second integrated operational amplifier MAX4233ABC+T. The output terminal of the second integrated operational amplifier MAX4233ABC+T is connected to the back-end amplification and biasing circuit. The second frequency selection filtering and amplification circuit includes a third integrated operational amplifier MAX4233ABC+T, resistors R19, R21, R23, and R24, capacitors C12 and C15; the second harmonic branch is connected to the negative input terminal of the third integrated operational amplifier MAX4233ABC+T via R21 and capacitor C15; the positive input terminal of the third integrated operational amplifier MAX4233ABC+T is grounded to GND_POWER, and the control terminal is connected to the power supply VCC_2V5 via resistor R24; resistors... One end of R23 is grounded, and the other end is connected to the common terminal of resistor R21 and capacitor C15; one end of capacitor C12 is connected to the output terminal of the third integrated operational amplifier MAX4233ABC+T, and the other end is connected to the common terminal of resistor R21 and capacitor C15; one end of resistor 19 is connected to the output terminal of the third integrated operational amplifier MAX4233ABC+T, and the other end is connected to the negative input terminal of the third integrated operational amplifier MAX4233ABC+T; the output terminal of the third integrated operational amplifier MAX4233ABC+T is connected to the back-end amplification and biasing circuit.

8. The dither signal filtering and sampling method based on a TFLN laser according to claim 1, characterized in that, In step 4, the fundamental frequency branch is connected to the corresponding frequency selective filter and amplifier circuit through the first DC blocking and AC passing capacitor C5, and the second harmonic frequency branch is connected to the corresponding frequency selective filter and amplifier circuit through the second DC blocking and AC passing capacitor C14.

9. The dither signal filtering and sampling method based on a TFLN laser according to claim 1, characterized in that, The back-end amplification and biasing circuit includes a first back-end amplification and biasing circuit and a second back-end amplification and biasing circuit. The first back-end amplification and biasing circuit is used to amplify and bias the fundamental frequency branch after frequency selection filtering and amplification, and the second back-end amplification and biasing circuit is used to amplify and bias the second harmonic frequency branch after frequency selection filtering and amplification.

10. The dither signal filtering and sampling method based on a TFLN laser according to claim 9, characterized in that, The first back-end amplification and biasing circuit includes a fourth integrated operational amplifier MAX4233ABC+T, resistors R1, R2, R5, R8, and R13, and capacitors C1, C3, C7, and C10. The positive input terminal of the fourth integrated operational amplifier MAX4233ABC+T is connected to the fundamental frequency branch, and the negative input terminal is grounded to GND_POWER through resistor R1. Resistor R2 and capacitor C1 are connected in parallel to form a feedback circuit, with one end of the feedback circuit connected to the negative input terminal of the fourth integrated operational amplifier MAX4233ABC+T and the other end connected to the output terminal of the fourth integrated operational amplifier MAX4233ABC+T. Resistor R5 and resistor R13 are connected in series to form a biasing circuit. One end of the circuit is connected to power supply VCC_2V5, and the other end is grounded to GND_POWER. The common terminal of resistors R5 and R13 is connected to the output terminal of the fourth integrated operational amplifier MAX4233ABC+T through capacitor C17. The control terminal of the fourth integrated operational amplifier MAX4233ABC+T is connected to power supply VCC_2V5 through resistor R8. The positive and negative power supply terminals of the fourth integrated operational amplifier MAX4233ABC+T are connected to power supplies VCC_2V5 and VCC_-2V5, respectively. The positive power supply terminal of the fourth integrated operational amplifier MAX4233ABC+T is also connected to ground GND_POWER through capacitor C3, and the negative power supply terminal is connected to ground GND_POWER through capacitor C10. The second back-end amplification and biasing circuit includes a fifth integrated operational amplifier MAX4233ABC+T, resistors R17, R18, R20, R22, and R25, and capacitors C11 and C16. The positive input terminal of the fifth integrated operational amplifier MAX4233ABC+T is connected to the fundamental frequency branch, and the negative input terminal is grounded to GND_POWER through resistor R17. Resistor R18 and capacitor C11 are connected in parallel to form a feedback circuit, and one end of the feedback circuit is connected to the fifth integrated operational amplifier MAX4233ABC+T. The negative input terminal is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T, and the other end is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T. The resistors R20 and R25 are connected in series to form a bias circuit. One end of the bias circuit is connected to the power supply VCC_2V5, and the other end is grounded GND_POWER. The common terminal of the resistors R20 and R25 is connected to the output terminal of the fifth integrated operational amplifier MAX4233ABC+T through C16. The control terminal of the fifth integrated operational amplifier MAX4233ABC+T is connected to the power supply VCC_2V5 through the resistor R22.

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