Video signal fiber transmission experimental teaching equipment

Abstract

The utility model belongs to signal optical fiber transmission technical field discloses a kind of video signal optical fiber transmission experiment teaching equipment, it includes camera, video optical signal transmitter, transmission optical fiber, video optical signal receiver and image display connected in turn, image signal collected by camera modulates the laser diode LD light output power of video optical signal transmitter, the light information containing image information emitted by the light outlet of laser diode LD is transmitted to the PIN photoelectric detection diode light inlet of video optical signal receiver by transmission optical fiber, and generates photoelectric current Io containing image information, after photoelectric current Io passes through the conversion resistance Rf of the I-V conversion circuit of video optical signal receiver, it is converted into video voltage signal containing image information, and video voltage signal transmission shows image to image display.The utility model structure is simple, and the physical process of video signal optical fiber transmission is clear and transparent, and adjustment is reasonable and orderly, applicable to teaching.

Description

Technical Field

[0001] This utility model relates to the field of optical fiber signal transmission technology, and in particular to an experimental teaching device for optical fiber transmission of video signals. Background Technology

[0002] Existing video signal fiber optic transmission teaching systems use light-emitting diodes (LEDs) as the light source for the optical signal transmitter. While LEDs require good linearity in their electro-optical characteristics, their output power is low, resulting in low optical power transmitted to the receiver via the fiber optic channel. Therefore, an integrated module containing pins is needed at the receiver as a pre-amplifier for photoelectric conversion, followed by amplification using a video amplifier circuit. Such video signal fiber optic transmission systems are structurally complex, cannot measure the photoelectric characteristics of the devices, and make the physical process of photoelectric conversion unclear and opaque. The debugging process lacks rules and order, easily leading to confusion for students during teaching. Teaching instruments built with this existing structure cannot deeply train students' thinking and hands-on abilities; they only allow students to see the physical phenomenon of video signal fiber optic transmission. Summary of the Invention

[0003] In order to overcome or alleviate one or more of the above technical problems, the purpose of this utility model is to provide an experimental teaching device for video signal fiber optic transmission, which allows students to conduct multiple experiments such as measuring the electro-optical characteristics of LD and the photoelectric characteristics of PIN, and fiber optic transmission of video signals (including audio signals).

[0004] This utility model provides the following technical solution:

[0005] An experimental teaching device for fiber optic transmission of video signals includes a camera, a video optical signal transmitter, a transmission optical fiber, a video optical signal receiver, and an image display connected in sequence. The image signal acquired by the camera modulates the output power of the laser diode (LD) of the video optical signal transmitter. The light information containing image information emitted from the output port of the laser diode (LD) is transmitted through the transmission optical fiber to the input port of the PIN photodetector diode of the video optical signal receiver, generating a photocurrent Io containing image information. After passing through the conversion resistor Rf of the IV conversion circuit of the video optical signal receiver, the photocurrent Io is converted into a video voltage signal containing image information. The video voltage signal is transmitted to the image display to display the image.

[0006] According to some embodiments, the video optical signal transmitter includes a Q9-1 socket. The video signal output terminal of the camera is connected to an input signal amplitude adjustment potentiometer W1 through the Q9-1 socket. The movable end of the input signal amplitude adjustment potentiometer W1 is connected to a capacitor C1 through a jack CK1. The other end of the capacitor C1 is connected to the base b of a high-frequency transistor BG1. A resistor R1 and one end of a potentiometer W2 are also connected to the base b of the high-frequency transistor BG1. The other ends of the resistor R1 and the potentiometer W2 are respectively connected to the GND terminal and the -5V terminal. The GND terminal is connected to the positive terminal of a DC milliammeter mA. The negative terminal of the milliammeter mA is connected to the positive terminal of a laser diode LD. The negative terminal of the laser diode LD is connected to the collector c of the transistor BG1. The emitter e of the transistor BG1 is connected to one end of the resistor R2. The other end of the resistor R2 is connected to -5V. The output port of the laser diode LD is connected to an optical fiber patch cord T1. The other end of the optical fiber patch cord T1 emits a video optical signal.

[0007] According to some embodiments, the video optical signal receiver includes an IV conversion circuit composed of a PIN photodiode and an operational amplifier integrated circuit CA3140. The negative and positive terminals of the PIN photodiode are connected to the inverting input terminal 2 and the non-inverting input terminal 3 of the operational amplifier integrated circuit CA3140, respectively. The non-inverting input terminal 3 of the operational amplifier integrated circuit CA3140 is connected to GND. An adjustable potentiometer W3 is connected between the inverting input terminal 2 and the output terminal 6 of the operational amplifier integrated circuit CA3140. Pin 7 of the operational amplifier integrated circuit CA3140 is connected to +5V. Pin 4 of the operational amplifier integrated circuit CA3104 is connected to -5V. Pins 1 and 5 of the operational amplifier integrated circuit CA3140 are connected to the two fixed terminals of the zero-adjustment potentiometer W4. Pin 4 of the operational amplifier integrated circuit CA3140 is connected to the movable terminal of W4.

[0008] According to some embodiments, the wavelength of the laser diode LD is either the second window wavelength of the transmission optical fiber, 1310 nm, or the third window wavelength, 1550 nm.

[0009] According to some embodiments, the PIN photodiode has a response wavelength range of 900-1700nm and a responsivity of 0.9A / W; the transmission optical fiber is multimode; and the potentiometer W3 of the IV conversion circuit, i.e., the conversion resistor Rf, has an adjustable resistance value in the range of 0-10K.

[0010] According to some embodiments, the camera is inserted into the Q9-1 socket via a Q9-Q9 connecting cable, the video optical signal generator is connected to the transmission optical fiber via fiber optic patch cord T1, the transmission optical fiber is connected to the video optical signal receiver via fiber optic patch cord T2, the output end of the video optical signal receiver is connected to switch K2, the other end of switch K2 is connected to socket Q92, and the video optical signal receiver is connected to the image display via a Q9-Q9 connecting cable and socket Q92.

[0011] According to some embodiments, the ST plug of the transmission optical fiber is connected to the video optical signal transmitter and the video optical signal receiver respectively via an ST-type flange.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] This invention provides an experimental teaching device for fiber optic transmission of video signals. Its overall structure is simple, allowing for various teaching experiments, including the determination of LD electro-optic and PIN photoelectric characteristics, and fiber optic transmission of video signals (including audio signals). The fiber optic transmission experiment includes the identification and adjustment of the reference video signal at the transmitting end, as well as the measurement of parameters (DC level and peak-to-peak value of the AC component of the video signal), and the regeneration and adjustment of the regenerated video signal parameters at the receiving end. The physical process of fiber optic transmission of video signals presented in this invention is clear, and the regeneration and adjustment of the video signal are logical and orderly. In teaching, it can clearly demonstrate to students the physical processes involved in the determination of LD electro-optic and PIN photoelectric characteristics, and the fiber optic transmission of video signals (including audio signals). Attached Figure Description

[0014] Figure 1 A schematic diagram of the video signal fiber optic transmission experimental teaching equipment provided in this embodiment of the utility model.

[0015] Figure 2 A schematic diagram of the structure of a video optical signal transmitter provided in an embodiment of this utility model.

[0016] Figure 3 A schematic diagram of the transmission optical fiber provided for an embodiment of this utility model.

[0017] Figure 4 This is a circuit diagram and connection schematic diagram of a video optical signal receiver provided in an embodiment of the present invention.

[0018] Figure 5 This is a schematic diagram of the overall connection of the video signal fiber optic transmission system provided in an embodiment of the present invention.

[0019] Figure 6 This is a schematic diagram showing the connection for measuring the electro-optical properties of the LD and the photoelectric properties of the PIN, provided for embodiments of this utility model.

[0020] Figure 7 This is a schematic diagram illustrating the identification, adjustment, and parameter measurement connection of the reference video signal at the transmitting end, as provided in an embodiment of this utility model.

[0021] Figure 8 This is a connection diagram illustrating the parameter adjustment of the regenerated video signal at the receiving end, as provided in an embodiment of the present invention.

[0022] Figure 9 A schematic diagram of the actual structure of an IV converter circuit with distributed capacitance provided in an embodiment of this utility model. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. However, it should be understood that the embodiments and accompanying drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations that fall within the inventive spirit of the present invention are within the scope of protection of the present invention.

[0024] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "front," and "rear," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model; the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In addition, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this utility model can be understood according to the specific circumstances.

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] Example

[0027] Figure 1 The diagram shown is a structural schematic of an experimental teaching device for video signal fiber optic transmission (hereinafter referred to as the teaching device) provided in this embodiment. The teaching device includes a camera, a video optical signal transmitter, a transmission optical fiber, a video optical signal receiver, and an image display.

[0028] like Figure 2 The diagram shown is a detailed circuit diagram of the video optical signal transmitter in this embodiment. The video signal output terminal of the camera is connected to the input signal amplitude adjustment potentiometer W1 via a Q9-1 socket. The movable end of the input signal amplitude adjustment potentiometer W1 is connected to capacitor C1 via jack CK1. The other end of capacitor C1 is connected to the base (b) of high-frequency transistor BG1. Resistor R1 and one end of potentiometer W2 are also connected to the base (b) of high-frequency transistor BG1. The other ends of resistor R1 and potentiometer W2 are connected to GND and -5V respectively. GND is connected to the positive terminal of a DC milliammeter mA. The negative terminal of the milliammeter mA is connected to the positive terminal of laser diode LD. The negative terminal of LD is connected to the collector (c) of transistor BG1. The emitter (e) of transistor BG1 is connected to one end of resistor R2. The other end of R2 is connected to -5V. The output port of LD is connected to fiber optic patch cord T1, and the other end of fiber optic patch cord T1 emits the video optical signal. Figure 2 In this configuration, potentiometer W1 adjusts the amplitude of the input video signal, and the DC level and peak-to-peak value of the AC component of the input video signal can be observed through jack CK1. Potentiometer W2 adjusts the bias current of the LD. Switch K1, connected in parallel with the LD, protects the LD; switch K1 is closed before the power is turned on and open after the power is turned on. It is particularly important to note that in this embodiment, in... Figure 2 In the video optical signal transmitter shown, a laser diode (LD) must be used as the light source device so that the video receiver, which will be introduced later, can achieve photoelectric conversion of the video signal using a simple IV conversion circuit.

[0029] like Figure 3 The diagram shown is a schematic representation of the transmission optical fiber in this embodiment. The multimode optical fiber, with a secondary tight-fitting, is approximately 60m long and has ST-type connectors at both ends. The ST connectors of the transmission optical fiber are connected to ST-type flanges F1 and F2, respectively. The other ports of flanges F1 and F2 serve as the input and output ports for optical signals, respectively.

[0030] like Figure 4The diagram shown is a detailed circuit diagram of the video optical signal receiver in this embodiment. It is a simple IV converter circuit, with pins 1 to 7 of the diagram representing the pins of the operational amplifier integrated circuit CA3140. The video optical signal receiver includes an IV converter circuit composed of a PIN photodiode and the operational amplifier integrated circuit CA3140. The negative and positive terminals of the PIN photodiode are connected to the inverting input terminal 2 and the non-inverting input terminal 3 of the operational amplifier integrated circuit CA3140, respectively. The non-inverting input terminal 3 of the operational amplifier integrated circuit CA3140 is connected to GND. A 0-10K potentiometer W3 is connected between the inverting input terminal 2 and the output terminal 6 of the operational amplifier integrated circuit CA3140. Pin 7 of the operational amplifier integrated circuit CA3140 is connected to +5V; pin 4 of the operational amplifier integrated circuit CA3104 is connected to -5V; pins 1 and 5 of the operational amplifier integrated circuit CA3140 are connected to the two fixed terminals of the zero-adjustment potentiometer W4; and pin 4 of the operational amplifier integrated circuit CA3140 is connected to the movable terminal of W4.

[0031] like Figure 5 The diagram shown is a schematic diagram of the overall connection in this embodiment.

[0032] In this embodiment, the center wavelength of the laser diode (LD) should be the second and third window wavelengths (1310nm and 1550nm) of the transmission fiber. At the optimal bias current, the output power is greater than 1mW. The PIN photodiode has a response wavelength range of 900-1700nm and a responsivity of 0.9A / W. The resistance Rf of the multimode and IV conversion circuit in the transmission fiber is adjustable from 0-10KΩ. This invention features a simple structure, a clear and transparent physical process for video signal fiber optic transmission, and rational and systematic adjustments. The receiving end produces good visual image quality, and the transmission distance can reach approximately 2km.

[0033] The following experiments can be conducted using the video signal fiber optic transmission experimental teaching equipment provided in this embodiment:

[0034] 1. Experiment on the determination of electro-optic properties of LD

[0035] according to Figure 6 The connection is shown. The optical power meter and the video optical signal receiver's IV conversion circuit share a single PIN photodiode. When measuring the LD's electro-optical characteristics, the PIN switch K3 is turned to the left. Adjust the LD current adjustment potentiometer W2 and record the optical power meter readings corresponding to different mA current values. Based on the measurement data, plot the LD's electro-optical characteristic curve and determine the optimal bias current for the LD.

[0036] 2. Experiment on the determination of photoelectric properties of PIN photodiodes

[0037] according to Figure 6Connect the circuit. Adjust potentiometer W3 until its resistance Rf equals 1KΩ. Keep switch K2 closed. Then, first turn switch K3 to the left, and adjust potentiometer W2 to obtain optical power meter readings of 100μW, 200μW, 300μW, ..., 1000μW sequentially. After each adjustment of the optical power meter reading, turn switch K3 to the right and record the corresponding DC voltmeter reading. Based on the measurement data and the Rf resistance value, plot the photoelectric characteristic curve of the PIN and calculate the PIN's responsivity.

[0038] 3. Fiber optic transmission experiment of video signals

[0039] 3.1 Adjustment and determination of the reference video signal at the transmitting end and measurement of parameters (DC level and AC component)

[0040] according to Figure 7 Connect the following steps: Switch K2 is in the off position. Short-circuit the video signal input jack CK1 and the video signal output jack CK2 using connecting wire 1. This allows the image display to connect directly to the output of the video signal amplitude adjustment potentiometer W1 at the transmitting end, bypassing the video signal fiber optic transmission system. Connect the oscilloscope and DC voltmeter to jack CK2 using connecting wires 2 and 3, respectively.

[0041] Adjust potentiometer W1 until the image quality on the image display screen is satisfactory. Read and record the reading of the DC voltmeter (the DC level of the reference video signal V-) and the amplitude of the video signal on the oscilloscope screen (i.e., the peak-to-peak value of the AC component of the reference video signal V-). PP ).

[0042] The adjustment and determination of the reference video signal is not unique. The result of a lower DC level and better image quality is used as a reference value for subsequent adjustment and regeneration of the video signal. Practice shows that a DC level V- = 300mV and an AC component peak-to-peak value V... PP An input video signal of 300mV is recommended.

[0043] 3.2 Parameter Adjustment of Regenerated Video Signal at the Receiver

[0044] according to Figure 8 Connect the circuit. Switch K2 is in the closed position. The video signal input amplitude potentiometer W1 is turned to zero. The LD bias current is adjusted to the optimal value. After completing the above connections and settings, a photocurrent Io flows from the negative to the positive terminal of the receiving end. This current also flows through the IV conversion resistor Rf, generating an ohmic voltage drop. According to the working principle of the IV conversion circuit, this voltage drop is equal to the output voltage Vo of the IV conversion circuit, and its value is:

[0045] Vo=Io*Rf (1)

[0046] In equation (1), under the conditions that the LD bias current, the transmission fiber length, and the optical coupling state of each component of the optical path system remain unchanged, the photocurrent Io has a definite value. Therefore, by adjusting potentiometer W3 (i.e., changing the resistance value of Rf), Vo can be made equal to the DC level of the reference video signal. Then, keeping the resistance value of Rf constant, adjust the amplitude adjustment potentiometer W1 of the input video signal at the transmitting end so that the peak-to-peak value of the video signal displayed on the oscilloscope is equal to the peak-to-peak value of the AC component of the reference video signal.

[0047] Similarly, the parameters that enable the receiver to obtain a high-quality regenerated video signal are not unique. A certain range of fluctuation is allowed based on the reference video signal parameters.

[0048] Because the input video signal at the transmitting end is DC-blocked and coupled to the LD driver modulation circuit via capacitor C1, the DC level of the regenerated video signal is only related to the LD bias current, and the AC component of the regenerated video signal is only related to the amplitude of the input video signal. Within the linear adjustment range, adjusting the AC component of the regenerated video signal does not affect the DC level adjustment result.

[0049] Under normal circumstances, the incident light power Po of the video signal fiber optic transmission technology experimental teaching equipment provided in this embodiment is better than 1mW to the PIN. The responsivity R of the PIN is approximately 0.9μA / μW. The photocurrent Io flowing through the PIN is:

[0050] Io=Po*R=900μA (2)

[0051] According to equation (1), when adjusting the DC level of the regenerated video signal, the required IV conversion resistor Rf is calculated as follows: Rf = Vo / Io = V- / Io = 300mV / 900μA = 333.3Ω.

[0052] In this case, the final image quality obtained at the receiving end in this embodiment is satisfactory.

[0053] To further demonstrate the beneficial effects of this invention, the following alternative feasible solution is compared:

[0054] As discussed in most sources, video signals are analog signals. Due to the excellent linearity of LEDs' electro-optical characteristics, they are commonly used as the light source in optical signal transmitters in analog signal fiber optic transmission systems. Under optimal bias, the maximum light output power of an LED pigtail is only around 100μW. The center wavelength of LED emission is approximately 860nm, and the responsivity R of the accompanying photodiode (SPD) is only 0.25–0.3μA / μW. If an IV-conversion circuit is used for the photoelectric conversion of the video optical signal, the photocurrent flowing through the conversion resistor Rf will not exceed 30μA. The resistance value of the conversion resistor Rf required for video signal regeneration and adjustment will not be less than 10KΩ. At this point, the spectrum of the output signal from the IV-conversion circuit narrows, losing much of the image information from the original video signal at the transmitting end, resulting in a blurry or even nonexistent image at the receiving end. Such a transmission system can only transmit audio signals, not video signals. This indicates that the resistance value of Rf in the video optical signal receiver has a significant impact on the amplitude-frequency characteristics of the IV-conversion circuit.

[0055] Theoretically, the IV converter circuit is a purely resistive circuit with infinite bandwidth. However, in actual construction, a distributed capacitance C exists between the output and inverting input of the operational amplifier circuit (the size of which depends on the manufacturing process). Therefore, the structure of the IV converter circuit in actual devices is as follows: Figure 9 Show. In the face of Figure 9 After theoretical analysis of the amplitude-frequency characteristics of the circuit, it can be seen that the smaller the resistance value of Rf, the better the amplitude-frequency characteristics of the IV conversion circuit. Therefore, only by using a high-power LD in the video optical signal generator and a high-efficiency PIN in the video optical signal receiver, as in this embodiment, can the IV conversion resistor Rf have a sufficiently small resistance value, so that the bandwidth of the IV conversion circuit's amplitude-frequency characteristics meets the requirements for transmitting video optical signals. This is also the most innovative and noteworthy feature of this invention.

[0056] The above embodiments are merely preferred embodiments of this utility model, and the protection scope of this utility model is not limited to the above embodiments. All technical solutions falling within the scope of this utility model's concept are within its protection scope. It should be noted that improvements and modifications made by those skilled in the art without departing from the principle of this invention should also be considered within the protection scope of this utility model.

Claims

1. An experimental teaching device for fiber optic transmission of video signals, characterized in that: It includes a camera, a video optical signal transmitter, a transmission optical fiber, a video optical signal receiver, and an image display connected in sequence. The image signal acquired by the camera modulates the output power of the laser diode LD of the video optical signal transmitter. The light information containing image information emitted from the output port of the laser diode LD is transmitted through the transmission optical fiber to the input port of the PIN photodetector diode of the video optical signal receiver, generating a photocurrent Io containing image information. After passing through the conversion resistor Rf of the IV conversion circuit of the video optical signal receiver, the photocurrent Io is converted into a video voltage signal containing image information. The video voltage signal is transmitted to the image display to display the image.

2. The video signal fiber optic transmission experimental teaching equipment according to claim 1, characterized in that: The video optical signal transmitter includes a Q9-1 socket. The video signal output terminal of the camera is connected to the input signal amplitude adjustment potentiometer W1 through the Q9-1 socket. The movable end of the input signal amplitude adjustment potentiometer W1 is connected to the capacitor C1 through the jack CK1. The other end of the capacitor C1 is connected to the base b of the high-frequency transistor BG1. The base b of the high-frequency transistor BG1 is also connected to the resistor R1 and one end of the potentiometer W2. The other ends of the resistor R1 and the potentiometer W2 are respectively connected to the GND terminal and the -5V terminal. The GND terminal is connected to the positive terminal of the DC milliammeter mA. The negative terminal of the milliammeter mA is connected to the positive terminal of the laser diode LD. The negative terminal of the laser diode LD is connected to the collector c of the transistor BG1. The emitter e of the transistor BG1 is connected to one end of the resistor R2. The other end of the resistor R2 is connected to -5V. The output port of the laser diode LD is connected to the fiber optic patch cord T1. The other end of the fiber optic patch cord T1 emits the video optical signal.

3. The video signal fiber optic transmission experimental teaching equipment according to claim 2, characterized in that: The video optical signal receiver includes an IV conversion circuit composed of a PIN photodiode and an operational amplifier integrated circuit CA3140. The negative and positive terminals of the PIN photodiode are connected to the inverting input terminal 2 and the non-inverting input terminal 3 of the operational amplifier integrated circuit CA3140, respectively. The non-inverting input terminal 3 of the operational amplifier integrated circuit CA3140 is connected to GND. An adjustable potentiometer W3 is connected between the inverting input terminal 2 and the output terminal 6 of the operational amplifier integrated circuit CA3140. Pin 7 of the operational amplifier integrated circuit CA3140 is connected to +5V. Pin 4 of the operational amplifier integrated circuit CA3104 is connected to -5V. Pins 1 and 5 of the operational amplifier integrated circuit CA3140 are connected to the two fixed terminals of the zero-adjustment potentiometer W4. Pin 4 of the operational amplifier integrated circuit CA3140 is connected to the movable terminal of W4.

4. The video signal fiber optic transmission experimental teaching equipment according to claim 2, characterized in that: The wavelength of the laser diode (LD) is either 1310 nm (the second window wavelength) or 1550 nm (the third window wavelength) of the transmission optical fiber.

5. The video signal fiber optic transmission experimental teaching equipment according to claim 3, characterized in that: The PIN photodiode has a response wavelength range of 900-1700nm; the transmission optical fiber is multimode; the potentiometer W3 in the IV conversion circuit has an adjustable resistance Rf in the range of 0-10K.

6. The video signal fiber optic transmission experimental teaching equipment according to claim 3, characterized in that: The camera is inserted into the Q9-1 socket via a Q9-Q9 connecting cable. The video optical signal generator is connected to the transmission optical fiber via fiber optic patch cord T1. The transmission optical fiber is connected to the video optical signal receiver via fiber optic patch cord T2. The output end of the video optical signal receiver is connected to switch K2. The other end of switch K2 is connected to socket Q92. The video optical signal receiver is connected to the image display via a Q9-Q9 connecting cable and socket Q92.

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