Optical fiber F-P cavity filter frequency response test method and system

Abstract

The invention discloses a frequency response test method and system for an optical fiber F-P cavity filter. The method comprises the following steps: S1, executing the following operations through a signal generator: S11, enabling an approximate linear change region of a transmission peak of the filter to be located near the working wavelength of a narrow linewidth laser; s12, a driving signal x (t) changing periodically is added to the filter, and the center of an approximate linear change area of a rising edge / falling edge of a transmission peak of the filter is made to be close to the working wavelength of the narrow-linewidth laser; s13, enabling the working wavelength of the narrow linewidth laser to be always located in an approximate linear change region of the rising edge / falling edge of the transmission peak; and S2, when the driving mechanism of the filter works at the driving frequency f of the driving signal x (t), detecting the narrow linewidth laser passing through the filter by adopting a photoelectric detector PD, and converting the narrow linewidth laser into a response electric signal y (t). According to the invention, the frequency response of the optical fiber F-P cavity filter can be effectively tested.

Description

Technical Field

[0001] This invention relates to the field of tunable filter manufacturing technology, and in particular to a method and system for testing the frequency response of an optical fiber FP cavity filter. Background Technology

[0002] A fiber FP (Fabry-Pérot) resonator consists of two fiber end faces coated with reflective films and spaced apart. When incident light travels back and forth multiple times within the cavity and undergoes multi-beam interference, it ultimately forms multiple equally spaced comb-shaped transmission peaks. Therefore, a high-precision fiber FP resonator is also called a fiber FP filter. Tunable fiber FP filters (FFP-TF) typically use piezoelectric ceramics (PZT ceramics, i.e., lead zirconate titanate ceramics) to adjust the cavity length. Driven by a voltage signal, the transmission wavelength can be tuned. Due to its high precision, high sensitivity, low insertion loss, fast response speed, and ease of integration, FFP-TF plays an important role in high-precision sensing, swept lasers, optical communication, and quantum optics. In particular, FFP-TF is one of the core components of swept lasers, and its frequency response characteristics are crucial for swept laser design, determining its final performance, such as the sweep range, sweep rate, and instantaneous linewidth. When the FFP-TF operates near its mechanical resonant frequency, it can achieve high responsivity, i.e., a wider scanning range at low voltage, thus enabling the sweep laser based on this filter to achieve a larger sweep range.

[0003] The PZT, a moving element, is essentially a capacitor. It reaches its maximum displacement response at its resonant frequency, where the phase difference between the input and output signals reverses by 180°. The PZT can also be considered an electromechanical transducer, with its electrical resonant frequency approximately equal to its mechanical resonant frequency. Therefore, an impedance analyzer can be used to obtain the electrical resonant frequency of the PZT, or a laser vibrometer can be used to obtain its mechanical resonant frequency. However, these methods cannot reflect the dynamic behavior of its load components (such as the fiber optic ferrule in an FP cavity structure).

[0004] For PZT-driven FFP-TF, the mechanical resonant frequency is generally obtained by manually testing its responsivity. The test optical path is as follows: Figure 1 As shown. First, according to Figure 1 ( Figure 1 In this diagram, the ASE source is a broadband light source, and the OSA is a spectrometer. The optical path is connected, and a signal with an amplitude of 1V, a bias of 1V, and a frequency of 10Hz drives the filter. The resulting transmission peak scanning range is used as the reference response bandwidth. Next, the driving frequency was modified, and the scanning bandwidth of the filter at different frequencies was recorded. , The filter linewidth is calculated using the following formula:

[0005] The relative responsivity at different driving frequencies can be obtained. However, this method requires manually selecting multiple different frequency points for measurement and manually reading the scan bandwidth. The response curve is obtained by calculating according to the above formula. This testing method cannot automate data processing, has significant human measurement errors, cannot accurately obtain resonant frequency information, and lacks phase information. Summary of the Invention

[0006] This invention provides a method for testing the frequency response of an optical fiber FP cavity filter, the method comprising: Step S1: Perform the following operation using a signal generator: Step S11: Make the approximately linear variation region of the filter transmission peak located near the operating wavelength of the narrow linewidth laser. Step S12: Apply a periodically varying drive signal to the filter. x ( t This ensures that the center of the approximately linear variation region of the rising / falling edge of the filter's transmission peak is near the operating wavelength of the narrow-linewidth laser. Step S13: Ensure that the operating wavelength of the narrow linewidth laser is always within the approximately linear variation region of the rising / falling edge of the transmission peak; Step S2: When the filter's driving mechanism operates under the driving signal x ( t ) driving frequency f At that time, a photodetector (PD) is used to detect the narrow-linewidth laser light passing through the filter and convert it into a response electrical signal. y ( t ); Step S3: Acquire the response electrical signal through the data processing module. y ( t and drive signals x ( t ), and process them to obtain the frequency response of the filter.

[0007] Furthermore, before performing step S11, the following steps are also included: A DC bias voltage is applied to the filter's drive mechanism via a signal generator. U 0.

[0008] Furthermore, the driving signal x ( t The signal is a sine wave, and is represented by the following formula: x ( t )= A sin(2 πf· t + φ )+ D in, t For time, A The amplitude of the driving signal, f For driving frequency, φ For phase shift, D This is the bias value.

[0009] Furthermore, step S12 also includes: Apply a periodically varying driving signal to the filter. x ( t After that, the signal generator is used according to... U 0 Change the drive signal x ( t bias amount D This is to ensure that the center of the approximately linear variation region of the rising / falling edge of the filter transmission peak is near the operating wavelength of the narrow-linewidth laser.

[0010] Furthermore, step S13 also includes: Control the drive signal via a signal generator x ( t The amplitude A is adjusted to control the scanning range of the transmission peak so that the operating wavelength of the narrow linewidth laser is always within the approximately linear variation region of the rising / falling edge of the transmission peak.

[0011] Furthermore, the frequency response of the filter is expressed by the following formula:

[0012] in, H ( f ) represents the frequency response of the filter.

[0013] Furthermore, in step S3, the data processing module also performs the following steps: According to the response electrical signal y ( t and drive signals x ( t The amplitude-frequency response of the frequency response is obtained, and this amplitude-frequency response is expressed by the following formula:

[0014] in, The amplitude-frequency response is described above.

[0015] Furthermore, in step S3, the data processing module also performs the following steps: According to the response electrical signal y ( t and drive signalsx ( t The phase frequency response is obtained from the frequency response, and this phase frequency response is expressed by the following formula:

[0016] in, The amplitude-frequency response is described above.

[0017] On the other hand, the present invention also provides a frequency response testing system for fiber optic FP cavity filters, the system comprising a narrow linewidth laser, a signal generator, a photodetector (PD), and a data processing module, wherein... The narrow-linewidth laser is electrically connected to the filter, and both the signal generator and the photodetector (PD) are electrically connected to the filter. Both the signal generator and the photodetector (PD) are electrically connected to the data processing module. The narrow linewidth laser is used to output narrow linewidth laser light to the filter; The signal generator is used to control the approximately linear variation region of the filter's transmission peak to be located near the operating wavelength of the narrow-linewidth laser; and is also used to apply a periodically varying drive signal to the filter. x ( t After that, the center of the approximately linear change region of the rising / falling edge of the transmission peak of the filter is located near the operating wavelength of the narrow linewidth laser; and the operating wavelength of the narrow linewidth laser is always located within the approximately linear change region of the rising / falling edge of the transmission peak. The photodetector PD is used to operate the filter's driving mechanism under a driving signal. x ( t ) driving frequency f At that time, the narrow-linewidth laser light passing through the filter is detected and converted into a response electrical signal. y ( t ); The data processing module is used to acquire response electrical signals. y ( t and drive signals x ( t ), and process them to obtain the frequency response of the filter.

[0018] Furthermore, the signal generator is also used to apply a DC bias voltage to the filter's drive mechanism. U 0.

[0019] This invention provides a method and system for testing the frequency response of fiber optic FP cavity filters, which can automatically simplify the testing method for tunable fiber optic FP filters. Furthermore, the driving signal acquired through the data acquisition module... x ( t and response electrical signals y (t It can simultaneously obtain the amplitude frequency response and the phase frequency response. By using the corresponding curves of the amplitude frequency response and the phase frequency response, the resonant frequency of the filter can be obtained. Furthermore, by using the phase frequency response curve, the magnitude of the phase delay at different tuning frequencies can be obtained. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a structural diagram of an existing fiber optic FP cavity filter frequency response testing system.

[0022] Figure 2 This is a flowchart of a fiber optic FP cavity filter frequency response testing method according to an embodiment of the present invention; Figure 3 This is a structural diagram of a fiber optic FP cavity filter frequency response testing system according to an embodiment of the present invention; Figure 4 This is a diagram showing the positional relationship between the filter transmission spectrum and the 1550nm narrow linewidth laser in an embodiment of the present invention. Figure 5 This is a frequency response curve diagram of an embodiment of the present invention.

[0023] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and the accompanying drawings. Detailed Implementation

[0024] 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 embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that all directional indications in the embodiments of the present invention, such as up, down, left, right, front, back, etc., are only used to explain the relative positional relationship and movement of the components in a specific posture as shown in the attached figure. If the specific posture changes, the directional indication will also change accordingly.

[0026] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0027] like Figure 2 As shown, the present invention provides a method for testing the frequency response of an optical fiber FP cavity filter, such as... Figure 3 As shown, the present invention also provides a frequency response testing system for fiber optic FP cavity filters. The testing method can be performed based on the system built by the present invention. The system of the present invention will be described below.

[0028] In some embodiments of the present invention, such as Figure 3 As shown, the system includes a narrow-linewidth laser, a signal generator, a photodetector (PD), and a data processing module. The narrow-linewidth laser is electrically connected to a filter, the signal generator is electrically connected to the filter, and the photodetector (PD) is electrically connected to the filter. Both the signal generator and the photodetector (PD) are electrically connected to the data processing module. The narrow-linewidth laser transmits narrow-linewidth laser signals to the filter. The signal generator sends control signals to the filter. Additionally, the control signals sent by the signal generator to the filter can also be sent to the data processing module. The photodetector (PD) detects the signals from the filter, processes them, and then sends them to the data processing module. The data processing module receives the outputs of the photodetector (PD) and the signal generator, processes them, and ultimately obtains the frequency response of the filter, as well as the corresponding amplitude-frequency and phase-frequency response curves.

[0029] Based on the above system, the frequency response testing method of an optical fiber FP cavity filter of the present invention will be described in detail below.

[0030] like Figure 2 As shown, the method includes: Step S1: Perform the following operation using a signal generator: Step S11: Make the approximately linear variation region of the filter transmission peak located near the operating wavelength of the narrow linewidth laser. Step S12: Apply a periodically varying drive signal to the filter. x ( t This ensures that the center of the approximately linear variation region of the rising / falling edge of the filter's transmission peak is near the operating wavelength of the narrow-linewidth laser. Step S13: Ensure that the operating wavelength of the narrow linewidth laser is always within the approximately linear variation region of the rising / falling edge of the transmission peak; Step S2: When the filter's driving mechanism operates under the driving signal x ( t ) driving frequency f At that time, a photodetector (PD) is used to detect the narrow-linewidth laser light passing through the filter and convert it into a response electrical signal. y ( t ); Step S3: Acquire the response electrical signal through the data processing module. y ( t and drive signals x ( t ), and process them to obtain the frequency response of the filter.

[0031] The present invention will now be described in detail.

[0032] In some embodiments of the present invention, before performing step S11, the following step is further included: applying a DC bias voltage to the drive mechanism of the filter through a signal generator. U After this step, proceed to step S11. You can observe with instruments such as a spectrometer that when the approximately linear change region of the filter transmission peak is located near the working wavelength of the narrow linewidth laser, proceed to the next step, namely step S12.

[0033] In some embodiments of the present invention, step S12 specifically involves: the signal generator sending a periodically varying drive signal to the filter. x ( t In addition, this drive signal x ( t The drive signal can also be sent to the data processing module, wherein, for example, the drive signal... x ( t The signal is a sine wave, and is represented by the following formula: x ( t )= A sin(2 πf · t + φ )+ D in, t For time, A The amplitude of the driving signal, f For driving frequency, φ For phase shift, D This is the bias value.

[0034] A periodically changing drive signal is applied to the signal generator.x ( t After passing through the filter, it is then passed through the signal generator according to... U 0 Change the drive signal x ( t bias amount D This is to ensure that the center of the approximately linear variation region of the rising / falling edge of the filter transmission peak is near the operating wavelength of the narrow-linewidth laser.

[0035] In some embodiments of the present invention, step S13 specifically involves controlling the drive signal via a signal generator. x ( t The amplitude A is adjusted to control the scanning range of the transmission peak so that the operating wavelength of the narrow linewidth laser is always within the approximately linear variation region of the rising / falling edge of the transmission peak.

[0036] In some embodiments of the present invention, after completing step S13, step S3 is performed, that is, when the filter driving mechanism is operating under the driving signal... x ( t ) driving frequency f At that time, a photodetector (PD) is used to detect the narrow-linewidth laser light passing through the filter and convert it into a response electrical signal. y ( t The data is then sent to the data acquisition module for processing, which is step S3.

[0037] In some embodiments of the present invention, step S3 specifically involves: the photodetector PD detecting the narrow-linewidth laser light passing through the filter and converting it into a response electrical signal. y ( t After being sent to the data acquisition module, the data processing module will also process the drive signal transmitted by the acquired signal generator. x ( t The filter is processed to obtain its frequency response. For example, the frequency response of the filter can be expressed by the following formula:

[0038] in, H ( f ) represents the frequency response of the filter.

[0039] In some embodiments of the present invention, the data acquisition module acquires the response electrical signal. y ( t and drive signals x ( t After that, it also responds to the electrical signal. y ( t and drive signals x ( tThe amplitude-frequency response of the frequency response is obtained, and this amplitude-frequency response is expressed by the following formula:

[0040] in, The amplitude-frequency response is described above.

[0041] In some embodiments of the present invention, the data acquisition module acquires the response electrical signal. y ( t and drive signals x ( t After that, it also responds to the electrical signal. y ( t and drive signals x ( t The phase frequency response is obtained from the frequency response, and this phase frequency response is expressed by the following formula:

[0042] in, The amplitude-frequency response is described above.

[0043] In this invention, the data acquisition module can be designed based on the aforementioned frequency response and its corresponding amplitude and phase frequency response calculation methods. Furthermore, according to the above analysis, when the piezoelectric ceramic PZT operates at its resonant frequency, To obtain the maximum value, and A 180° reversal occurs.

[0044] In some embodiments of the present invention, the filter can operate in multiple frequency bands, and all filters operating in multiple frequency bands can utilize the testing method and system of the present invention. The present invention provides an exemplary description of a frequency response testing method for an optical fiber FP cavity filter, using a 1550 nm frequency band filter as an example: First, apply a DC bias voltage to the PZT. U 0. Use a spectrometer to observe the transmission peak of the filter (please refer to...). Figure 4 The approximately linear variation region of the transmission peak in the transmission spectrum of the medium filter is located near the operating wavelength of a narrow-linewidth laser at 1550 nm, such as... Figure 4 As shown.

[0045] Apply a periodically varying sinusoidal drive signal to the filter x ( t ).according to U 0. Adjust the corresponding bias appropriately. D This ensures that the center of the approximately linear variation region of the rising / falling edge of the filter's transmission peak is precisely near the operating wavelength of the narrow-linewidth laser. Control drive signal x ( tThe amplitude A can be adjusted to control the scanning range of the transmission peak, so that the operating wavelength of the narrow linewidth laser, 1550nm, is always within the approximately linear variation region of the rising / falling edge of the transmission peak.

[0046] Depend on Figure 4 Analysis shows that when 1550nm is closer to the center wavelength of the filter's transmission spectrum, the output power of the 1550nm narrow-linewidth laser is also greater. Because the displacement response of PZT differs under different frequency signal driving, the tuning range of the tunable filter driven by the PZT also varies, and the degree to which 1550nm approaches the center wavelength of the filter's transmission spectrum differs, resulting in different maximum powers of the 1550nm narrow-linewidth laser transmitted by the filter. When the PZT operates at its resonant frequency, its displacement response is maximum, corresponding to the largest filter tuning range, thus resulting in the strongest maximum power of the 1550nm narrow-linewidth laser transmitted by the filter.

[0047] When PZT operates at frequency f At that time, a photodetector (PD) is used to detect the narrow-linewidth laser light passing through the filter and convert it into a response electrical signal. y ( t The frequency response of a filter can be expressed as the ratio of the response electrical signal to the driving signal, based on the driving signal. x ( t and response electrical signals y ( t The corresponding amplitude frequency response and phase frequency response can be calculated.

[0048] according to Figure 3 By setting up a testing platform, one can obtain results such as Figure 5 The frequency response curve shown is shown, where, Figure 5 Figure (a) shows the amplitude-frequency response curve. Figure 5 Figure (b) shows the phase frequency response curve. It can be seen from the figure that the amplitude frequency response of the filter reaches its maximum value at 50kHz, and the phase is reversed by 180°. The resonant frequency of the filter is measured to be 50kHz.

[0049] In summary, the fiber optic FP cavity filter frequency response testing method and system provided by this invention simplifies the frequency response testing method of tunable fiber optic FP filters, and can obtain both amplitude frequency response and phase frequency response. The resonant frequency of the filter can be obtained through the corresponding curves of amplitude frequency response and phase frequency response, and the magnitude of its phase delay at different tuning frequencies can also be obtained through the phase frequency response curve.

[0050] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made under the concept of the present invention using the description and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for testing the frequency response of an optical fiber FP cavity filter, characterized in that, The method includes: Step S1: Perform the following operation using a signal generator: Step S11: Make the approximately linear variation region of the filter transmission peak located near the operating wavelength of the narrow linewidth laser. Step S12: Apply a periodically varying drive signal to the filter. x ( t This ensures that the center of the approximately linear variation region of the rising / falling edge of the filter's transmission peak is near the operating wavelength of the narrow-linewidth laser. Step S13: Ensure that the operating wavelength of the narrow linewidth laser is always within the approximately linear variation region of the rising / falling edge of the transmission peak; Step S2: When the filter's driving mechanism operates under the driving signal x ( t ) driving frequency f At that time, a photodetector (PD) is used to detect the narrow-linewidth laser light passing through the filter and convert it into a response electrical signal. y ( t ); Step S3: Acquire the response electrical signal through the data processing module. y ( t and drive signals x ( t ), and process them to obtain the frequency response of the filter.

2. The method for testing the frequency response of an optical fiber FP cavity filter as described in claim 1, characterized in that, Before performing step S11, the following steps are also included: A DC bias voltage is applied to the filter's drive mechanism via a signal generator. U 0.

3. The method for testing the frequency response of an optical fiber FP cavity filter as described in claim 2, characterized in that, The driving signal x ( t The signal is a sine wave, and is represented by the following formula: x ( t )= A sin(2 πf · t + φ )+ D Among them, t For time, A The amplitude of the driving signal, f For driving frequency, φ For phase shift, D This is the bias value.

4. The method for testing the frequency response of an optical fiber FP cavity filter as described in claim 3, characterized in that, Step S12 also includes: Apply a periodically varying driving signal to the filter. x ( t After that, the signal generator is used according to... U 0 Change the drive signal x ( t bias amount D This is to ensure that the center of the approximately linear variation region of the rising / falling edge of the filter transmission peak is near the operating wavelength of the narrow-linewidth laser.

5. The method for testing the frequency response of an optical fiber FP cavity filter as described in claim 3, characterized in that, Step S13 also includes: Control the drive signal via a signal generator x ( t The amplitude A is adjusted to control the scanning range of the transmission peak so that the operating wavelength of the narrow linewidth laser is always within the approximately linear variation region of the rising / falling edge of the transmission peak.

6. A method for testing the frequency response of an optical fiber FP cavity filter as described in any one of claims 3-5, characterized in that, The frequency response of a filter is expressed by the following formula: in, H ( f ) represents the frequency response of the filter.

7. The method for testing the frequency response of an optical fiber FP cavity filter as described in claim 5, characterized in that, In step S3, the data processing module also performs the following steps: According to the response electrical signal y ( t and drive signals x ( t The amplitude-frequency response of the frequency response is obtained, and this amplitude-frequency response is expressed by the following formula: in, The amplitude-frequency response is described above.

8. A method for testing the frequency response of an optical fiber FP cavity filter as described in any one of claims 4 or 5, characterized in that, In step S3, the data processing module also performs the following steps: According to the response electrical signal y ( t and drive signals x ( t The phase frequency response is obtained from the frequency response, and this phase frequency response is expressed by the following formula: in, The amplitude-frequency response is described above.

9. A frequency response testing system for fiber optic FP cavity filters, characterized in that, The system includes a narrow-linewidth laser, a signal generator, a photodetector (PD), and a data processing module, wherein... The narrow-linewidth laser is electrically connected to the filter, and both the signal generator and the photodetector (PD) are electrically connected to the filter. Both the signal generator and the photodetector (PD) are electrically connected to the data processing module. The narrow linewidth laser is used to output narrow linewidth laser light to the filter; The signal generator is used to control the approximately linear variation region of the filter's transmission peak to be located near the operating wavelength of the narrow-linewidth laser; and is also used to apply a periodically varying drive signal to the filter. x ( t After that, the center of the approximately linear change region of the rising / falling edge of the transmission peak of the filter is located near the operating wavelength of the narrow linewidth laser; and the operating wavelength of the narrow linewidth laser is always located within the approximately linear change region of the rising / falling edge of the transmission peak. The photodetector PD is used to operate the filter's driving mechanism under a driving signal. x ( t ) driving frequency f At that time, the narrow-linewidth laser light passing through the filter is detected and converted into a response electrical signal. y ( t ); The data processing module is used to acquire response electrical signals. y ( t and drive signals x ( t ), and process them to obtain the frequency response of the filter.

10. The fiber optic FP cavity filter frequency response testing system as described in claim 9, characterized in that, The signal generator is also used to apply a DC bias voltage to the filter's drive mechanism. U 0.

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