Method and device for measuring frequency response of optoelectronic detector based on optical LFM signal

Abstract

The present application relates to the technical fields of optoelectronic device measurement and microwave photonics, and discloses a method and device for measuring the frequency response of a photodetector based on an optical LFM signal, comprising an optical linear frequency modulation (LFM) signal generation module, an optical coupler, a time-domain signal acquisition module and a low-frequency detection module; the optical LFM signal generation module is used to generate an optical LFM signal; the optical coupler is used to divide the optical LFM signal into two paths, i.e., an upper path and a lower path; the time-domain signal acquisition module is used to extract beat frequency information of a carrier and a swept first-order sideband input into a photodetector to be measured; and the low-frequency detection module is used to extract low-frequency information generated by the beat frequency of the original first-order sideband and the first-order sideband after time delay. The method and device for measuring the frequency response of a photodetector based on an optical LFM signal realize one shot detection by using an optical LFM signal, so the measurement speed is extremely fast, and the measurement efficiency can be greatly improved; the present application has a simple structure, can be built by using existing shelf products, and has a low implementation cost.

Description

Technical Field

[0001] This invention relates to the fields of optoelectronic device measurement and microwave photonics technology, specifically to a method and apparatus for measuring the frequency response of a photodetector based on optical LFM signals. Background Technology

[0002] Optical fiber communication boasts numerous advantages, including resistance to electromagnetic interference, corrosion resistance, light weight, and large capacity, making it widely used in high-energy physics, nuclear radiation-resistant communication systems, submarines, warships, aircraft, missile control communication systems, and the Internet, among many other fields. Currently, optical fiber communication is developing towards higher speeds, higher efficiency, larger capacity, and longer-distance transmission. With increasing informatization, corresponding demands are being placed on the speed of optical fiber communication transmission systems.

[0003] Photodetectors are one of the key components of fiber optic communication systems, and their development, testing, and application require the measurement of their spectral response. Currently, numerous methods for testing the spectral response of photodetectors have been developed, which can be broadly classified into two categories: time-domain methods and frequency-domain methods.

[0004] The key device for measuring the frequency response of a photodetector using the time-domain method is a sampling oscilloscope. However, the limitation of the time-domain method is that the frequency range of the photodetector is limited by the bandwidth of the sampling oscilloscope.

[0005] Frequency domain methods can be further divided into two main categories: heterodyne beat frequency and external modulation. Typical measurement methods include vector network analysis (limited bandwidth, low accuracy), white noise measurement using semiconductor optical amplifiers (insufficient sensitivity), and optical heterodyne method (high requirements for phase, amplitude, and polarization state matching).

[0006] Therefore, there is an urgent need to study new measurement methods to improve the measurement accuracy, efficiency and bandwidth of photodetector frequency response measurement technology. Thus, a photodetector frequency response measurement method and device based on optical LFM signal is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method and apparatus for measuring the frequency response of a photodetector based on optical LFM signals, so as to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for measuring the frequency response of a photodetector based on optical LFM signals, comprising the following steps:

[0009] Step 1: Split a linear frequency modulated signal into two paths, upper and lower, using an optical coupler;

[0010] Step 2: The upper path is used as the detection path. The input is directly to the photodetector under test. After the photodetector under test beats the frequency, the beat frequency information of the carrier and the first-order sideband of the sweep frequency is extracted by the time domain signal acquisition module.

[0011] Step 3: The lower path is used as a reference path. After passing through the time delay module, it is sent to a low-frequency detection module to extract the beat frequency information of the original first-order sideband and the first-order sideband after the time delay.

[0012] Step 4: Combining the results of the detection path and the reference path, calculate the amplitude and phase information of the photodetector under test, that is, obtain the frequency response of the photodetector under test.

[0013] Preferably, the optical frequency modulation signal can be achieved by loading an electrical frequency modulation signal onto an electro-optic modulator, or by directly linearly sweeping the frequency of the light source.

[0014] A photodetector frequency response measurement device based on optical LFM signal includes an optical frequency modulation signal generation module, an optical coupler, a time-domain signal acquisition module, and a low-frequency detection module.

[0015] The optical frequency modulation signal generation module is used to generate an optical frequency modulation signal;

[0016] The optical coupler is used to split the optical frequency modulated signal into upper and lower paths;

[0017] The time-domain signal acquisition module is used to extract the carrier and beat frequency information of the first-order sideband of the input photodetector under test.

[0018] The low-frequency detection module is used to extract low-frequency information generated by the beat frequency of the original first-order sideband and the first-order sideband after time delay.

[0019] Preferably, the optical frequency modulation signal generation module can be implemented by modulating an electrical frequency modulation signal onto an electro-optic modulator, or by directly linearly sweeping the frequency of the light source.

[0020] The electro-optic modulator can be a Mach-Zehnder modulator operating at a linear operating point.

[0021] Preferably, the direct linear frequency sweep of the light source can be achieved using a linear frequency sweep laser source.

[0022] Preferably, the time-domain signal acquisition module can be an oscilloscope.

[0023] Preferably, the low-frequency detection module can be a low-frequency photodetector with a known frequency response.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0025] This invention uses optical frequency modulation signals to achieve one-shot detection, resulting in extremely fast measurement speed and significantly improved measurement efficiency. The invention also has a simple structure that can be built using existing shelving products, resulting in low cost. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the frequency response measurement device for a photodetector based on a light-induced frequency-modulated signal according to the present invention.

[0027] Figure 2 This is a schematic diagram of a specific embodiment of the measuring device 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 some embodiments of the present invention, and not all 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] Please see Figure 1-2

[0030] Example 1

[0031] This embodiment is a specific implementation of a photodetector frequency response measurement method based on optical LFM signals.

[0032] The method for measuring the frequency response of a photodetector based on optical LFM signals includes the following steps:

[0033] Step 1: Split a linear frequency modulated signal into two paths, upper and lower, using an optical coupler;

[0034] Step 2: The upper path is used as the detection path. The input is directly to the photodetector under test. After the photodetector under test beats the frequency, the beat frequency information of the carrier and the first-order sideband of the sweep frequency is extracted by the time domain signal acquisition module.

[0035] Step 3: The lower path is used as a reference path. After passing through the time delay module, it is sent to a low-frequency detection module to extract the beat frequency information of the original first-order sideband and the first-order sideband after the time delay.

[0036] Step 4: Combining the results of the detection path and the reference path, calculate the amplitude and phase information of the photodetector under test, that is, obtain the frequency response of the photodetector under test.

[0037] Specifically, the optical frequency modulation signal can be achieved by loading an electrical frequency modulation signal onto an electro-optic modulator, or by directly linearly sweeping the frequency of the light source.

[0038] Example 2

[0039] This embodiment is a specific implementation of a photodetector frequency response measurement device based on optical LFM signals.

[0040] A photodetector frequency response measurement device based on optical LFM signal includes an optical frequency modulation signal generation module, an optical coupler, a time-domain signal acquisition module, and a low-frequency detection module.

[0041] The optical frequency modulation signal generation module is used to generate an optical frequency modulation signal;

[0042] The optical coupler is used to split the optical frequency modulated signal into upper and lower paths;

[0043] The time-domain signal acquisition module is used to extract the carrier and beat frequency information of the first-order sideband of the input photodetector under test.

[0044] The low-frequency detection module is used to extract low-frequency information generated by the beat frequency of the original first-order sideband and the first-order sideband after time delay.

[0045] Specifically, the optical frequency modulation signal generation module can be implemented by modulating an electrical frequency modulation signal onto an electro-optic modulator, or by directly linearly sweeping the frequency of the light source.

[0046] Specifically, the electro-optic modulator can be a Mach-Zehnder modulator operating at a linear operating point.

[0047] Specifically, the direct linear frequency sweep of the light source can be achieved using a linear frequency sweep laser source.

[0048] Specifically, the time-domain signal acquisition module can be an oscilloscope.

[0049] Specifically, the low-frequency detection module can be a low-frequency photodetector with a known frequency response.

[0050] Example 3

[0051] This embodiment is a specific implementation plan of a photodetector frequency response measurement method and device based on optical LFM signals.

[0052] An operational example of a photodetector frequency response measurement method and device based on optical LFM signals is as follows: Figure 1 A specific embodiment of the photodetector frequency response measurement device of the present invention is shown. For example... Figure 2 As shown, the measuring device in this specific embodiment includes: a laser, an arbitrary waveform generator, a Mach-Zehnder modulator, an oscilloscope, a long optical fiber, a standard low-frequency detector with a known frequency response, and a photodetector under test.

[0053] The frequency of the optical frequency modulated signal at time t is set to...

[0054]

[0055] Among them, f c Let t be the carrier frequency, k be the chirp rate of the linear frequency modulated signal, and θ(t) represent the phase error introduced by the non-ideal nature of linear frequency modulation.

[0056] The optical frequency modulated signal is split into two paths by an optical coupler. The upper path probe signal is directly input to the photodetector under test to extract the carrier and the beat frequency signal of the first-order sideband of the sweep frequency.

[0057] The expressions for the carrier and the first-order sideband of the frequency sweep are as follows:

[0058]

[0059] Where E0(t) and E1(t) correspond to the amplitudes of the carrier and the first-order sideband as a function of time, respectively.

[0060] For ease of derivation, we will use g(t) = πkt 2 +θ(t), equation (2) can be expressed as,

[0061]

[0062] At time t, the instantaneous frequencies of the optical carrier and the first-order sideband of the frequency sweep are ft and ft, respectively. c f c +f(t).

[0063] At this point, after the photodetector under test beats, we assume that the amplitude and phase changes introduced by the device under test are represented as a[f(t)] and φ[f(t)], respectively. Then, the electrical signal after passing through the device under test is expressed as follows:

[0064] i dut (t)=a[f(t)]E0(t)E1(t)cos(g(t)+φ[f(t)]) (4)

[0065] By performing a Hilbert transform on equation (3), we can obtain...

[0066]

[0067] According to equations (3) and (4), we can obtain that

[0068]

[0069]

[0070] The lower reference path uses a delay interferometer to split the reference path signal into two paths, one of which is introduced with a delay τ0 through a long optical fiber. The time-domain expression of the first-order sidebands of the two outputs can be expressed as follows:

[0071]

[0072] After passing through a low-frequency photodetector, the beat frequency signals of the two first-order sidebands are extracted, and the output signal can be expressed as follows:

[0073]

[0074] We assume that the amplitudes of the first-order sidebands at time t and time t-τ0 are the same, i.e., E1(t-τ0) = E1(t), then equation (9) can be expressed as follows:

[0075] i ref (t)=η ref (τ0)·E1(t) 2 cos(2πktτ0-πkτ0 2 +2πf c τ0+θ(t)-θ(t-τ0)) (10)

[0076] By performing a Hilbert transform on equation (10), we can obtain...

[0077]

[0078] According to equations (10) and (11), we can obtain that

[0079]

[0080]

[0081] Taking a Fourier transform of equation (13) yields the following:

[0082]

[0083] Where F(x(t)) represents the Fourier transform of x(t).

[0084] According to equations (6) and (12), the amplitude response of the photodetector under test can be obtained as follows:

[0085]

[0086] According to equations (7) and (14), the phase response of the photodetector under test can be obtained as follows:

[0087]

[0088] in

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0090] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 measuring the frequency response of a photodetector based on optical LFM signals, characterized in that: Includes the following steps: Step 1: Split a linear frequency modulated signal into two paths, upper and lower, using an optical coupler; Step 2: The upper path is used as the detection path. The input is directly to the photodetector under test. After the photodetector under test beats the frequency, the beat frequency information of the carrier and the first-order sideband of the sweep frequency is extracted by the time domain signal acquisition module. Step 3: The lower path is used as a reference path. After passing through the time delay module, it is sent to a low-frequency detection module to extract the beat frequency information of the original first-order sideband and the first-order sideband after the time delay. Step 4: Combining the results of the detection path and the reference path, calculate the amplitude and phase information of the photodetector under test, that is, obtain the frequency response of the photodetector under test.

2. The method for measuring the frequency response of a photodetector based on an optical LFM signal according to claim 1, characterized in that: The optical frequency-modulated signal can be achieved by loading an electrical frequency-modulated signal onto an electro-optic modulator, or by directly linearly sweeping the frequency of the light source.

3. A photodetector frequency response measurement device based on optical LFM signals, characterized in that: It includes a light-frequency modulated signal generation module, an optical coupler, a time-domain signal acquisition module, and a low-frequency detection module; The optical frequency modulation signal generation module is used to generate an optical frequency modulation signal; The optical coupler is used to split the optical frequency modulated signal into upper and lower paths; The time-domain signal acquisition module is used to extract the carrier and beat frequency information of the first-order sideband of the input photodetector under test. The low-frequency detection module is used to extract low-frequency information generated by the beat frequency of the original first-order sideband and the first-order sideband after time delay.

4. The photodetector frequency response measurement device based on optical LFM signal according to claim 3, characterized in that: The optical frequency modulation signal generation module can be implemented by modulating an electrical frequency modulation signal onto an electro-optic modulator, or by directly linearly sweeping the frequency of the light source.

5. The photodetector frequency response measurement device based on optical LFM signal according to claim 4, characterized in that: The electro-optic modulator can be a Mach-Zehnder modulator operating at a linear operating point.

6. The photodetector frequency response measurement device based on optical LFM signal according to claim 4, characterized in that: The direct linear frequency sweep of the light source can be achieved using a linear frequency sweep laser source.

7. The photodetector frequency response measurement device based on optical LFM signal according to claim 3, characterized in that: The time-domain signal acquisition module can be an oscilloscope.

8. The photodetector frequency response measurement device based on optical LFM signal according to claim 3, characterized in that: The low-frequency detection module can be a low-frequency photodetector with a known frequency response.

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