An all-fiber high-speed photodetector impulse response measurement device and method

Abstract

The application discloses a kind of all-fiber high-speed photoelectric detector impulse response measuring device and method, it is characterized in that, including femtosecond laser, optical fiber polarizer, optical fiber delay line, optical fiber circulator, first optical fiber polarization controller, second optical fiber polarization controller, electro-optic sampling head, optical fiber polarization beam splitter, balanced photoelectric detector and lock-in amplifier.Femtosecond laser is branched, and is coupled to photoelectric detector to generate electric pulse signal.A bundle is coupled to optical fiber polarizer, and is sent into optical fiber delay line, first optical fiber polarization controller, optical fiber circulator in turn.Electro-optic sampling head reflects polarized light from optical fiber circulator, while detecting electric pulse signal.It is sent into lock-in amplifier after being converted into electrical signal by balanced photoelectric detector after being sent into optical fiber polarization beam splitter.By connecting each device with polarization maintaining optical fiber, the shortcomings of traditional electro-optic sampling space light system, such as the need for optical alignment, system complexity and instability, are overcome.The measuring system is simple, stable and highly practical.

Description

Technical Field

[0001] This application relates to the field of optoelectronic instrument measurement technology, and in particular to a device and method for measuring the impulse response of an all-fiber high-speed photodetector. Background Technology

[0002] As a fundamental photosensitive sensor, the accurate measurement of the impulse response of photodetectors enables their adaptation to specific application requirements. With the widespread use of high-speed photodetectors in optical communication, signal processing, and measurement systems, the requirements for impulse response measurement are gradually increasing. However, the bandwidth of sampling oscilloscopes used in traditional methods can only reach a maximum of 100 GHz. Optical measurement methods offer a 2-3 order of magnitude higher bandwidth than electrical measurements, with electro-optic sampling methods achieving even lower time resolution. Traditional electro-optic sampling systems primarily rely on spatial light, which requires optical alignment during setup and suffers from relatively poor stability. Therefore, this measurement method has certain limitations in practical applications. Summary of the Invention

[0003] This application proposes an all-fiber high-speed photodetector impulse response measurement device and method to solve the problems of traditional electro-optic sampling spatial light systems requiring optical alignment, system complexity and instability, and bandwidth limitations when using sampling oscilloscopes to measure the impulse response of high-speed photodetectors.

[0004] This application provides an impulse response measurement device for an all-fiber high-speed photodetector, including a femtosecond laser, a fiber polarizer, a fiber delay line, a fiber circulator, a first fiber polarization controller, a second fiber polarization controller, an electro-optic sampling head, a fiber polarization beam splitter, a balanced photodetector, and a lock-in amplifier.

[0005] After the femtosecond laser outputs a split beam, one beam is coupled to the photodetector under test to generate an electrical pulse signal. The other beam is coupled to the fiber polarizer and then fed successively into the fiber delay line and the first fiber polarization controller. After the polarization direction is made parallel to the tangent of the electro-optic material of the electro-optic sampling head, it is fed into the fiber circulator.

[0006] The electro-optic sampling head is attached to the fiber optic port, and a high-reflectivity film is coated on the end face perpendicular to the fiber transmission direction to reflect polarized light from the fiber optic circulator, while simultaneously detecting the electrical pulse signal generated by the photodetector.

[0007] The reflected light is elliptically polarized by the second fiber polarization controller and sent to the fiber polarization beam splitter. The reflected light is then converted into an electrical signal by the balanced photodetector and sent to the lock-in amplifier.

[0008] Preferably, it further includes a control and calculation unit, which is connected to the optical fiber delay line and the lock-in amplifier respectively, and is used to control the delay amount of the optical fiber delay line and the sample-by-sample sampling of the lock-in amplifier respectively.

[0009] A further preferred embodiment includes a transmission line, which is connected to the output of the photodetector under test and serves as a transmission carrier for electrical pulse signals.

[0010] Preferably, the present invention further includes a load connected to the transmission line for reducing reflection of the power-on pulse signal on the transmission line.

[0011] Preferably, the femtosecond laser has an output wavelength of 1550nm, a pulse width of 100fs, and a signal repetition frequency of 100MHz.

[0012] Preferably, the signal output by the femtosecond laser is connected to a lock-in amplifier as its reference signal.

[0013] Preferably, the electro-optic sampling head is located 5-10 μm above the transmission line.

[0014] Preferably, the electro-optic sampling head is made of LiTaO3 material coated with a high-reflectivity film and is directly attached to the fiber optic port using optical curing adhesive.

[0015] This application also provides a method for measuring the impulse response of an all-fiber high-speed photodetector, characterized by the following steps:

[0016] The femtosecond laser outputs a split beam into a first beam and a second beam.

[0017] The first beam is used as the excitation beam and applied to the photodetector under test to generate an electrical pulse signal;

[0018] The second light is converted into linearly polarized light, and its delay and polarization direction are changed so that the polarization direction is parallel to the tangent of the electro-optic material before being sent into the electro-optic material.

[0019] Electro-optic materials detect electrical pulse signals, reflect polarized light passing through the electro-optic materials, and then separate the light into two beams with mutually perpendicular polarization directions. These beams are then converted into electrical signals and amplified using phase-locked loop amplification.

[0020] Preferably, the method further includes: controlling the delay amount and sampling point by point respectively, and processing the sampled signal to obtain the time-domain waveform of the electrical pulse signal.

[0021] The above-mentioned at least one technical solution adopted in the embodiments of this application can achieve the following beneficial effects: it has a large test bandwidth, can measure the impulse response of high-speed photodetectors more accurately and conveniently, and the measurement system is simple, stable and highly practical. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0023] Figure 1 A schematic diagram of the connection of the impulse response measurement device for an all-fiber high-speed photodetector.

[0024] Figure 2 This is a structural diagram of the electro-optic sampling head;

[0025] Figure 3 This is a flowchart of the impulse response measurement method for an all-fiber high-speed photodetector. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0028] Figure 1 This is a schematic diagram of the connection of the impulse response measurement device for an all-fiber high-speed photodetector.

[0029] The impulse response measurement device for an all-fiber high-speed photodetector includes a femtosecond laser 1, an optical fiber polarizer 2, an optical fiber delay line 6, an optical fiber circulator 7, a first optical fiber polarization controller 8, a second optical fiber polarization controller 9, an electro-optic sampling head 10, an optical fiber polarization beam splitter 11, a balanced photodetector 12, and a lock-in amplifier 13.

[0030] A femtosecond laser is a pulsed laser with a pulse duration on the order of femtoseconds, used as a light source. For example, in one embodiment, the femtosecond laser has a wavelength of 1550 nm, a pulse width of 100 fs, and a signal repetition frequency of 100 MHz.

[0031] The measuring device consists of fiber optic components, which are interconnected by fiber optic cables. For example, the modules are connected by polarization-maintaining fiber optic cables, making it an all-fiber optic device.

[0032] For example, one embodiment includes a femtosecond laser source, an optical fiber beam splitter, a linear polarizer, a high-speed photodetector, a transmission line, a load, an optical fiber delay line, an optical fiber circulator, an optical fiber polarization control loop, an electro-optic sampling probe, a polarization beam splitter, a balanced photodetector, a lock-in amplifier, and a control and computing unit.

[0033] After the femtosecond laser outputs a split beam, one beam is coupled to the photodetector 3 under test to generate an electrical pulse signal.

[0034] Beam splitting can be achieved using fiber optic beam splitters or other beam splitters, dividing the laser into two beams: an excitation beam loaded onto a high-speed photodetector and a probe beam used for electro-optic sampling.

[0035] A beam is coupled to the fiber polarizer and successively fed into the fiber delay line and the first fiber polarization controller. After the polarization direction is made parallel to the tangent of the electro-optic material of the electro-optic sampling head, it is fed into the fiber circulator.

[0036] A fiber optic polarizer is an optical device that uses a special fiber structure to convert input light into linearly polarized light. A femtosecond laser, when coupled to a fiber optic polarizer, becomes linearly polarized light. For example, it is used to adjust the polarization state of fiber optic light.

[0037] The fiber delay line changes the relative delay between the excitation light and the probe light, enabling point-by-point sampling of the electrical pulse signal.

[0038] Fiber polarization controller, also known as fiber polarization control loop.

[0039] The first fiber polarization controller can use a half-wave plate, and the second fiber polarization controller can use a quarter-wave plate, to change the polarization direction or polarization state of polarized light. For example, the fiber polarization controller uses a half-wave plate to control the polarization direction of the probe light to be parallel to the tangent of the electro-optic material, and uses a quarter-wave plate to make the output light elliptically polarized.

[0040] Fiber optic circulators enable bidirectional optical signal transmission over a single optical fiber. The signal transmission direction of a circulator is irreversible; it can only guide an optical signal from one port to another in one direction at a time. For example, a fiber optic circulator transmits probe light to an electro-optic sampling probe and separates the output light reflected from the probe.

[0041] The reflected light is elliptically polarized by the second fiber polarization controller and sent to the fiber polarization beam splitter. The reflected light is then converted into an electrical signal by the balanced photodetector and sent to the lock-in amplifier.

[0042] Fiber polarization beam splitters are used to separate elliptical polarized output light into two beams with mutually perpendicular polarization states.

[0043] Balanced photodetectors can achieve low-noise common-mode suppression output for two beams, ensuring that the intensity of the two beams is the same when there is no electrical pulse signal. For example, a balanced photodetector receives two beams of light from a polarization beam splitter and converts them into electrical signals.

[0044] A lock-in amplifier, also known as a phase detector, is an amplifier that can extract a specific carrier frequency signal from a highly interference-prone environment. It is used to amplify the electrical signal from a balanced photodetector in a lock-in manner. For example, a lock-in amplifier uses the optical signal from a femtosecond laser as a reference signal to amplify the electrical signal from a balanced photodetector in a lock-in manner.

[0045] Preferably, it further includes a control and calculation unit 14, which is connected to the optical fiber delay line and the lock-in amplifier respectively, and is used to control the delay amount of the optical fiber delay line and the sample-by-sample sampling of the lock-in amplifier respectively.

[0046] The control and calculation unit is used to precisely control the delay of the fiber delay line, thereby changing the relative delay of the probe light and the excitation light. For example, the control and calculation unit controls the delay of the fiber delay line and the sample-by-sample sampling of the lock-in amplifier, respectively, and processes the sampled signal to obtain the time-domain waveform of the ultrafast electrical pulse signal.

[0047] More preferably, it also includes a transmission line 4, which is connected to the output of the photodetector under test and serves as a transmission carrier for electrical pulse signals.

[0048] A transmission line is used to transmit electrical pulse signals generated by a photodetector under test. For example, it serves as a carrier for the propagation of electrical pulse signals; another example is when a high-speed photodetector generates an ultrafast electrical pulse signal that is then loaded onto the transmission line after being excited by excitation light.

[0049] Preferably, the present invention further includes a load 5, which is connected to the transmission line and is used to reduce the reflection of the power-on pulse signal on the transmission line.

[0050] A load is used to reduce reflections of electrical pulse signals and improve measurement accuracy. For example, in one embodiment, the load is a 50Ω resistor.

[0051] Preferably, the signal output by the femtosecond laser is connected to a lock-in amplifier as its reference signal.

[0052] A femtosecond laser is connected to a lock-in amplifier as a reference signal for phase detection, improving measurement accuracy.

[0053] Figure 2 This is a structural diagram of the electro-optic sampling head.

[0054] The electro-optic sampling head is attached to the fiber optic port, and a high-reflectivity film is coated on the end face perpendicular to the fiber transmission direction to reflect polarized light from the fiber optic circulator, while simultaneously detecting the electrical pulse signal generated by the photodetector.

[0055] The electro-optic sampling head is made of electro-optic materials, which are optical functional materials with electro-optic effects. Under the action of an external electric field, changes in the polarization state and phase of the transmitted light beam are generated, thereby achieving modulation of the light wave.

[0056] The electro-optic sampling head is located above the transmission line. The high-speed electrical pulse signal generated by the photodetector is detected by the electro-optic sampling head, causing a change in the refractive index of the electro-optic material. The incident linearly polarized light is modulated by the electrical pulse signal, resulting in a change in its polarization state. For example, the polarization state remains unchanged when there is no electrical pulse signal, but changes when an electrical pulse signal is present.

[0057] High-reflectivity films are used to reflect incoming linearly polarized light. For example, they reflect linearly polarized light transmitted through an optical fiber to an optical fiber circulator.

[0058] The electro-optic sampling head uses LiTaO3 material coated with a high-reflectivity film and is directly attached to the fiber optic port using optical curing adhesive.

[0059] LiTaO3 is an electro-optic material that changes the polarization state of passing light after an electro-optic effect occurs.

[0060] Preferably, the electro-optic sampling head is located 5-10 μm above the transmission line.

[0061] An electro-optic sampling head is positioned above the transmission line to accurately detect ultrafast electrical pulse signals generated by a high-speed photodetector when excited by excitation light, thus producing an electro-optic effect. For example, an electro-optic sampling probe is positioned above the transmission line to detect electrical pulse signals propagating along the transmission line.

[0062] Figure 3 This is a flowchart of the impulse response measurement method for an all-fiber high-speed photodetector.

[0063] This application also provides a method for measuring the impulse response of an all-fiber high-speed photodetector, including the following steps:

[0064] Step 101: The femtosecond laser output beam is split into a first beam and a second beam.

[0065] For example, a femtosecond laser source outputs a first beam and a second beam.

[0066] For example, a femtosecond laser source splits the laser into two beams using an optical fiber beam splitter.

[0067] Step 102: The first light source is applied as excitation light to the photodetector under test to generate an electrical pulse signal.

[0068] For example, the first beam of light is applied as excitation light to the high-speed photodetector under test to obtain an ultrafast electrical pulse signal that propagates on the transmission line, or a beam of light is applied to the high-speed photodetector under test to excite an ultrafast electrical pulse signal that propagates on the transmission line.

[0069] Step 103: The second light path is converted into linearly polarized light, and its delay and polarization direction are changed so that the polarization direction is parallel to the tangent of the electro-optic material before being sent into the electro-optic material.

[0070] For example, another beam of light passes through an optical fiber delay line to change the relative delay between the excitation light and the probe light, passes through an optical fiber circulator and a first optical fiber polarization controller, and is transmitted to an electro-optic sampling probe with its polarization direction fixed parallel to the tangent of the electro-optic material.

[0071] For example, the second light path passes through a linear polarizer and an optical fiber delay line and is incident on an electro-optic sampling probe located above the transmission line to obtain reflected output light.

[0072] Step 104: The electro-optic material detects the electrical pulse signal. The electro-optic material reflects the polarized light that has passed through the electro-optic material, and then separates it into two beams of light with mutually perpendicular polarization directions. These beams are then converted into electrical signals and amplified by phase lock-in.

[0073] Electro-optic materials detect electrical pulse signals and reflect polarized light that has passed through them. If no electrical pulse signal is detected, the polarization state of the polarized light remains unchanged. However, if an electrical pulse signal is detected, the polarization state changes due to the electro-optic effect, thus modulating the femtosecond pulse laser. For example, the polarization state of the reflected output light changes under the influence of the electrical pulse signal.

[0074] To separate the reflected light into two beams with mutually perpendicular polarization directions, a polarization beam splitter or other polarization beam splitting devices can be used. For example, a polarization beam splitter can be used to split the reflected output light into two beams with mutually perpendicular polarization directions.

[0075] Optical signals can be converted into electrical signals using photoelectric conversion devices. For example, a balanced photodetector can be used to convert the polarization state change of reflected output light into an electrical signal for detection.

[0076] For example, after the reflected output light passes through an optical fiber circulator and an optical fiber polarization control loop, it is split into two beams with mutually perpendicular polarization states by a polarization beam splitter and then injected into a balanced photodetector.

[0077] Preferably, the method further includes:

[0078] Step 105: Control the delay amount and sample point by sample respectively, and process the sampled signal to obtain the time-domain waveform of the electrical pulse signal.

[0079] The delay amount and sample-by-sample sampling can be controlled by a control and calculation unit to precisely control the delay amount of the fiber delay line, change the relative delay of the probe light and the excitation light, realize the sample-by-sample sampling of the lock-in amplifier, and process the sampled signal to obtain the time-domain waveform of the ultrafast electrical pulse signal.

[0080] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. An all-fiber high-speed photodetector impulse response measurement apparatus, characterized by, It includes a femtosecond laser, fiber polarizer, fiber delay line, fiber circulator, first fiber polarization controller, second fiber polarization controller, electro-optic sampling head, transmission line, fiber polarization beam splitter, balanced photodetector, and lock-in amplifier; After the femtosecond laser outputs a split beam, one beam is coupled to the photodetector under test to generate an electrical pulse signal; the other beam is coupled to the fiber polarizer and then fed into the fiber delay line and the first fiber polarization controller in sequence. After the polarization direction is made parallel to the tangent of the electro-optic material of the electro-optic sampling head, the beam is fed into the fiber circulator. It also includes a transmission line, which is connected to the output of the photodetector under test and serves as a transmission carrier for electrical pulse signals; The electro-optic sampling head is located 5-10 μm above the transmission line. The electro-optic sampling head is made of LiTaO3 material coated with a high-reflectivity film and is attached to the fiber port using optical curing adhesive. The end face perpendicular to the fiber transmission direction is coated with a high-reflectivity film to reflect polarized light from the fiber circulator, while simultaneously detecting the electrical pulse signal generated by the photodetector. The reflected light is elliptically polarized by the second fiber polarization controller and sent to the fiber polarization beam splitter. The reflected light is then converted into an electrical signal by the balanced photodetector and sent to the lock-in amplifier.

2. Impulse response measuring apparatus as defined in claim 1, characterized in that It also includes a control and computing unit, which is connected to the optical fiber delay line and the lock-in amplifier respectively, and is used to control the delay amount of the optical fiber delay line and the sample-by-sample sampling of the lock-in amplifier respectively.

3. The impulse response measuring apparatus of claim 1, wherein It also includes a load, which is connected to the transmission line to reduce the reflection of the power-on pulse signal on the transmission line.

4. The impulse response measuring apparatus of claim 1, wherein The femtosecond laser has an output wavelength of 1550nm, a pulse width of 100fs, and a signal repetition frequency of 100MHz.

5. The impulse response measuring apparatus of claim 1 wherein, The signal output from the femtosecond laser is connected to a lock-in amplifier as its reference signal.

6. An all-fiber high-speed photodetector impulse response measurement method, implemented by the impulse response measurement device according to any one of claims 1-5, characterized in that, Includes the following steps: The femtosecond laser outputs a split beam into a first beam and a second beam. The first beam is used as the excitation beam and applied to the photodetector under test to generate an electrical pulse signal; The second light is converted into linearly polarized light, and its delay and polarization direction are changed so that the polarization direction is parallel to the tangent of the electro-optic material before being sent into the electro-optic material. Electro-optic materials detect electrical pulse signals, reflect polarized light passing through the electro-optic materials, and then separate the light into two beams with mutually perpendicular polarization directions. These beams are then converted into electrical signals and amplified using phase-locked loop amplification.

7. The impulse response measurement method of claim 6, wherein, Also includes: By controlling the delay amount and sampling point by point, the sampled signal is processed to obtain the time-domain waveform of the electrical pulse signal.

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