A low-loss, low-power consumption, compact heterodyne acousto-optic modulation module

Abstract

The present invention discloses a low-loss and low-power compact heterodyne acousto-optic modulation module. The 0th-order light output by the first fiber acousto-optic modulator is used as the incident light to connect to the output light position of the 1st-order diffracted light of the second fiber acousto-optic modulator; the 1st-order diffracted light output by the first fiber acousto-optic modulator is used as the incident light to connect to the output light position of the 0th-order light of the second fiber acousto-optic modulator; the incident light position of the second fiber acousto-optic modulator is used as the output light position to output the outgoing light; the two-stage fiber acousto-optic modulators adopt the same drive circuit and the radio frequency signals work alternately. The drive circuit of the present invention adopts a scheme of external clock input, homologous dual channels, adjustable dual-channel delay, and timing control. The present invention does not have a fiber coupler. By controlling the diffraction of the two AOMs relative to the trigger signal to adjust the relative delay between pulses, and controlling the turn-on time of the two AOMs to obtain two pulse signals with different frequencies, it has the advantages of low power consumption, small loss, and arbitrarily adjustable delay.

Description

Technical Field

[0001] The invention relates to a hydrophone, in particular to a heterodyne acousto-optic modulation module in an optical fiber hydrophone, and belongs to the optical technology field of submersibles and shore-based optical fiber hydrophones. Background Art

[0002] The submersible uses fiber-optic hydrophones as a medium for information transmission and sensing to detect and analyze underwater acoustic information. The heterodyne acousto-optic modulation module, as an important component of the optoelectronic preprocessor, is used to modulate and generate optical pulses that meet the needs of the hydrophone probe. On the other hand, it realizes acousto-optic frequency shift of the emitted laser to generate a suitable frequency and realize heterodyne interference. Figure 1 It is a functional block diagram of the existing heterodyne acousto-optic modulation module in the optoelectronic preprocessor system.

[0003] The laser generated by the light source is modulated by a fiber acousto-optic modulator (FAOM) to generate an optical pulse. This optical pulse is divided into two paths through a 1×2 fiber coupler. One path is connected to fiber acousto-optic frequency shifter 1 (FAOFS1) to generate f1 frequency shift, and the other path is connected to fiber acousto-optic frequency shifter 2 (FAOFS2) to generate f2 frequency shift. The f2 frequency shift optical pulse is delayed by the fiber ring, and the coupler synthesizes the two frequency shift signals into a pulse pair. The pulse pair is transmitted to the fiber hydrophone, and the optoelectronic preprocessor uses heterodyne method to obtain the water acoustic information perceived by the fiber hydrophone. FAOM works in the modulation state, with an overall power consumption of 2W and a typical insertion loss of 3dB. FAOFS1 and FAOFS2 work in the equal amplitude state, with an overall power consumption of 10W. In order to ensure that the amplitudes of the two output optical pulses are basically the same, FAOFS1 and FAOFS2 use two devices with similar insertion losses. The typical insertion loss of a single device is 3dB. Coupler 1 and coupler 2 use 3dB couplers, and their own insertion loss is typically 0.5dB. The typical power consumption of the entire heterodyne acousto-optic modulation module is 12W, and the typical insertion loss is 10dB. The overall power consumption of the existing heterodyne acousto-optic modulation module is too high. In order to enable the entire module to work stably for a long time, it is necessary to design a heat dissipation structure for the module, which invisibly increases the installation space of the module. The overall high power consumption has become one of the limiting factors for the wet-end application of the existing heterodyne acousto-optic modulation module. The insertion loss of the existing heterodyne acousto-optic modulation module is too large, so the transmitting end of the optoelectronic preprocessor has to add EDFA devices. The addition of EDFA devices deteriorates the system's reflected light signal-to-noise ratio, limits the transmission of the optoelectronic preprocessor, and inhibits the long-distance transmission of the optical fiber hydrophone detection system to a certain extent. The two-way pulse delay of the existing heterodyne acousto-optic module is controlled by the delay optical fiber. The delay optical fiber is generally tens of meters long and is easily affected by external low-frequency vibrations. It also requires optical fiber fusion coating, which has a complex process and a large volume. Summary of the invention

[0004] Aiming at the deficiencies of the existing heterodyne acousto-optic modulation module, such as high power consumption, large insertion loss, low adjustable precision of delay, complex process, large volume, and susceptibility to external influences, the purpose of the present invention is to provide a low-loss and low-power compact heterodyne acousto-optic modulation module. The present invention does not have a fiber coupler. By controlling the diffraction of two AOMs relative to the trigger signal to adjust the relative delay between pulses, and controlling the turn-on time of the two AOMs to obtain two pulse signals with different frequencies, it has the advantages of low power consumption, small loss, and arbitrarily adjustable delay.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A low-loss and low-power compact heterodyne acousto-optic modulation module includes a laser, two-stage 1×2 fiber acousto-optic modulators, and a driver. The continuous light output by the laser is used as the incident light to connect to the first 1×2 fiber acousto-optic modulator. The first 1×2 fiber acousto-optic modulator outputs the 0th-order light and the 1st-order diffracted light. The output positions of the 0th-order light and the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator are respectively used as the two inputs of the second 1×2 fiber acousto-optic modulator and are connected to the output of the first 1×2 fiber acousto-optic modulator. Among them, the 0th-order light output by the first 1×2 fiber acousto-optic modulator is used as the incident light to connect to the output position of the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator; the 1st-order diffracted light output by the first 1×2 fiber acousto-optic modulator is used as the incident light to connect to the output position of the 0th-order light of the second 1×2 fiber acousto-optic modulator; the incident light position of the second 1×2 fiber acousto-optic modulator is used as the output position to output the output light;

[0007] The two-stage 1×2 fiber acousto-optic modulators share a driver. The driver includes a modulation circuit. The modulation input signal is connected to the input of the modulation circuit through a pulse shaping circuit, and the external clock is connected to the modulation circuit through an oscillation circuit to provide the clock signal for the modulation circuit; the modulation circuit has two outputs, and each output respectively outputs the required radio frequency signal through a delay circuit and a power amplifier circuit. The two radio frequency signals are correspondingly connected to the two-stage 1×2 fiber acousto-optic modulators; the radio frequency signals of the two-stage 1×2 fiber acousto-optic modulators work alternately.

[0008] Furthermore, the two 1×2 fiber acousto-optic modulators generate frequency signals with frequency shifts of f1 and f2 respectively, and the frequency difference between f1 and f2 is the frequency difference required by the hydrophone system.

[0009] Preferably, both of the two-stage 1×2 fiber acousto-optic modulators are provided with parallel prisms for separating the 0th-order light and the 1st-order diffracted light by a required distance.

[0010] Preferably, the optical signals of both the 0th-order light and the 1st-order diffracted light of the two-stage 1×2 fiber acousto-optic modulator are transmitted through optical fibers. The optical fiber corresponding to the 0th-order light of the first 1×2 fiber acousto-optic modulator is fusion-spliced to the optical fiber corresponding to the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator; the optical fiber corresponding to the 1st-order diffracted light of the first 1×2 fiber acousto-optic modulator is fusion-spliced to the optical fiber corresponding to the 0th-order light of the second 1×2 fiber acousto-optic modulator.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1. Low insertion loss. Compared with the prior art, the present invention has no main path AOM and fiber coupler, and the overall insertion loss is more than 6 dB less.

[0013] 2. Low power consumption. Two AOMs of the present invention work in the modulation state, and the overall power consumption is about 6 W, while in the prior art, one AOM works in the modulation state and two AOMs work in the equal-amplitude state, with a power consumption of 12 W; the power consumption of the present invention is significantly reduced.

[0014] 3. High delay accuracy, wide range, flexible adjustment, and little influence by the environment. In the prior art, the frequency shift accuracy is limited by the fiber fusion splicer, and changing the delay requires re-fusion splicing the optical fiber, with a complex process, and special sound insulation and vibration isolation treatment of the delay optical fiber is also required to reduce low-frequency noise. The present invention does not require delay optical fiber, and the entire delay adjustment is changed through a program, without the need for opening the cover for treatment, and is not easily affected by the environment.

[0015] 4. Small volume. In the prior art, a fixed position for coiling and fixing the delay optical fiber needs to be reserved inside the housing, while the present invention does not require delay optical fiber, so the volume is smaller and it is easier to integrate. Description of the Drawings

[0016] Figure 1 is a functional block diagram of the prior heterodyne acousto-optic modulation module in the optoelectronic preprocessor system.

[0017] Figure 2 is a schematic structural diagram of a 1×2 fiber acousto-optic modulator.

[0018] Figure 3 is a schematic structural diagram of the heterodyne acousto-optic modulation module of the present invention.

[0019] Figure 4 is a schematic diagram of the external clock + homologous dual-channel + two-channel delay adjustable driver of the present invention.

[0020] Figure 5 is a schematic circuit diagram of the driver of the present invention.

[0021] Figure 6 is a timing diagram corresponding to the embodiment of the present invention. Detailed Embodiments

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] The present invention realizes the coupling of the optical path by connecting two 1×2 fiber acousto-optic modulators in series. The first 1×2 fiber acousto-optic modulator couples the incident light into the 0th-order light and the 1st-order diffracted light. The second 1×2 fiber acousto-optic modulator utilizes the reversibility of light to couple the 0th-order light and the 1st-order diffracted light into the output light again, thereby eliminating the two fiber couplers in the existing module. The two 1×2 fiber acousto-optic modulators share a driving circuit, and the driving circuit adopts a scheme of external clock input, dual paths from the same source, adjustable dual-path delay, and timing control, achieving the effects of high delay accuracy, wide range, and flexible adjustment.

[0024] The structure of the 1×2 fiber acousto-optic modulator involved in the present invention is as Figure 2 shown. The radio frequency electrical signal output by the driving circuit is applied to the piezoelectric transducer of the acousto-optic medium through an impedance matching network. The piezoelectric transducer converts this signal into ultrasonic waves and propagates them in the acousto-optic medium to form a refractive index grating. When the laser passes through at a certain angle, Bragg diffraction occurs, and the input light and the 1st-order diffracted light are coupled and output through the fiber. By modulating the electrical signal, the modulation function of the optical signal can be realized. The 1×2 fiber acousto-optic modulator uses a parallel prism to separate the 0th-order light and the 1st-order diffracted light by a certain distance, so that the 0th-order light and the 1st-order diffracted light can be coupled and output respectively, ensuring the output function of the 0th-order light while realizing the modulation function of the 1st-order diffracted light, that is, realizing the 1×2 fiber acousto-optic modulator.

[0025] A low-loss, low-power, and compact heterodyne acousto-optic modulation module of the present invention uses two 1×2 fiber acousto-optic modulators, and their connection method is as Figure 3 shown. It includes a laser, two-stage 1×2 fiber acousto-optic modulators, and a driver. The continuous light output by the laser is used as the incident light and is connected to the first 1×2 fiber acousto-optic modulator. The first 1×2 fiber acousto-optic modulator outputs the 0th-order light and the 1st-order diffracted light. The output positions of the 0th-order light and the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator are respectively used as the two inputs of the second 1×2 fiber acousto-optic modulator and are connected to the output of the first 1×2 fiber acousto-optic modulator. Among them, the 0th-order light output by the first 1×2 fiber acousto-optic modulator is used as the incident light and is connected to the output position of the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator; the 1st-order diffracted light output by the first 1×2 fiber acousto-optic modulator is used as the incident light and is connected to the output position of the 0th-order light of the second 1×2 fiber acousto-optic modulator; the incident light position of the second 1×2 fiber acousto-optic modulator is used as the output position to output the output light.

[0026] See Figure 4 and Figure 5, the two-stage 1×2 fiber optic acousto-optic modulators share a driver. The driver includes a modulation circuit. The modulation input signal is connected to the input of the modulation circuit through a pulse shaping circuit, and the external clock is connected to the modulation circuit through an oscillation circuit to provide the clock signal for the modulation circuit. The modulation circuit has two outputs, and each output respectively outputs the required radio frequency signal through a delay circuit and a power amplifier circuit. The two radio frequency signals are correspondingly connected to the two-stage 1×2 fiber optic acousto-optic modulators. The radio frequency signals (driving circuits) of the two-stage 1×2 fiber optic acousto-optic modulators work alternately.

[0027] Specifically, for the 0th-order light and the 1st-order diffracted light of the two-stage 1×2 fiber optic acousto-optic modulators of the present invention, the optical signal transmission is realized through optical fibers. The optical fiber corresponding to the 0th-order light of the first 1×2 fiber optic acousto-optic modulator is fused with the optical fiber corresponding to the 1st-order diffracted light of the second 1×2 fiber optic acousto-optic modulator; the optical fiber corresponding to the 1st-order diffracted light of the first 1×2 fiber optic acousto-optic modulator is fused with the optical fiber corresponding to the 0th-order light of the second 1×2 fiber optic acousto-optic modulator.

[0028] The incident light of the present invention passes through the first 1×2 fiber optic acousto-optic modulator. When the driving circuit works, the light is output from the 1st-order diffracted light. When the driving circuit does not work, the light is output from the 0th-order light. The two 1×2 fiber optic acousto-optic modulators generate frequency signals with frequency shifts of f1 and f2 respectively (the frequency difference is determined by the hydrophone system). According to the characteristics of the fiber optic hydrophone array, by controlling the timing of the driving circuits of the two 1×2 fiber optic acousto-optic modulators, pulses with fixed delay and frequency difference are obtained. For example, for a fiber optic hydrophone system with a pulse width of 120 ns, a repetition frequency of 200 KHz, and an optical pulse delay of 150 ns, the two fiber optic acousto-optic modulators of the present invention and the finally output optical pulse are as Figure 6 shown.

[0029] The driving circuit of the present invention adopts a scheme of external clock input, homologous dual channels, adjustable dual-channel delay, and timing control. When an external trigger signal with a repetition frequency of 200 KHz and a pulse width of 120 ns acts on the driving circuit, the first 1×2 fiber optic acousto-optic modulator generates diffracted light after time t, and the pulse width of the diffracted light is 120 ns. At this time, the driving circuit of the second modulator does not work, the second modulator does not diffract, and the 0th-order light is coupled and output. Finally, an optical pulse signal with a frequency shift of f1 and a pulse width of 120 ns is output. After the trigger signal t + 150 ns, the driving circuit of the first 1×2 fiber optic acousto-optic modulator does not work, does not diffract, the 0th-order light is output, and no frequency shift is generated. The driving circuit of the second modulator works, generates diffracted light, the pulse width of the light pulse is 120 ns, and finally an optical pulse signal with a frequency shift of f2 and a pulse width of 120 ns is output. The optical pulses output within one cycle are as Figure 6As shown in the figure. The radio frequency signals (driving circuits) of the two fiber optic acousto-optic modulators of the present invention need to work alternately, that is, when the driving circuit of the first 1×2 fiber optic acousto-optic modulator works, the driving circuit of the second 1×2 fiber optic acousto-optic modulator does not work; when the driving circuit of the first 1×2 fiber optic acousto-optic modulator does not work, the driving circuit of the second 1×2 fiber optic acousto-optic modulator works. The heterodyne acousto-optic modulation module of the present invention has no fiber optic coupler and no delay fiber compared with the existing module, and only has two devices. The typical value of the overall loss is 3.5 dB, and the typical value of the power consumption is 6 W.

[0030] The present invention keeps the user system clock consistent with the acousto-optic module clock through an external clock input, adopts a homologous dual-channel scheme to achieve consistent two-channel driving clocks, and the adjustable dual-channel delay can achieve high-precision (highest precision 0.1 ns), large-range (maximum μs level) (depending on the delay adjustment range selected by the user) adjustment of the delay of two pulses relative to the external modulation trigger signal. The present invention can provide a low-loss and low-power compact heterodyne acousto-optic modulation module with different delays in the range of 0-1 μs and different frequency differences in the range of 0-1 GHz according to user requirements.

[0031] The present invention has the following characteristics:

[0032] 1. The optical path coupling is realized by connecting two 1×2 fiber optic acousto-optic modulators in series. Compared with the traditional scheme, the loss is greatly reduced;

[0033] 2. The two 1×2 fiber optic acousto-optic modulators are used to modulate the frequency shift function, reducing the loss and power consumption of the heterodyne acousto-optic modulation module, and laying a foundation for the miniaturization and low power consumption of the system;

[0034] 3. The driver adopts an external clock input and a homologous dual-channel output scheme to ensure the consistency of the user system clock and the AOM clock, laying a foundation for the phase stability of the heterodyne detection optical pulses;

[0035] 4. The high-precision delay adjustment function of the two-channel pulse of the heterodyne acousto-optic modulation module is realized by adjusting the delay of the two-channel pulsed light through a circuit chip, reducing the overall size of the system, improving the delay adjustment accuracy, and reducing the complexity of the delay adjustment process.

[0036] The above embodiments of the present invention are only examples for explaining the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes and modifications can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A low-loss, low-power compact heterodyne acousto-optic modulation module for fiber optic hydrophones, characterized in that: It includes a laser, a two-stage 1×2 fiber acousto-optic modulator, and a driver. The continuous light output by the laser is used as the incident light to connect to the first 1×2 fiber acousto-optic modulator. The first 1×2 fiber acousto-optic modulator outputs the 0th-order light and the 1st-order diffracted light. The output positions of the 0th-order light and the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator are respectively used as the two inputs of the second 1×2 fiber acousto-optic modulator and are connected to the output of the first 1×2 fiber acousto-optic modulator. Among them, the 0th-order light output by the first 1×2 fiber acousto-optic modulator is used as the incident light to connect to the output position of the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator; the 1st-order diffracted light output by the first 1×2 fiber acousto-optic modulator is used as the incident light to connect to the output position of the 0th-order light of the second 1×2 fiber acousto-optic modulator; the incident light position of the second 1×2 fiber acousto-optic modulator is used as the output light position to output the output light. The two-stage 1×2 fiber acousto-optic modulators share a driver. The driver includes a modulation circuit. The modulation input signal is connected to the input of the modulation circuit through a pulse shaping circuit, and the external clock is connected to the modulation circuit through an oscillation circuit to provide the clock signal for the modulation circuit; the modulation circuit has two outputs, and each output respectively outputs the required radio frequency signal through a delay circuit and a power amplifier circuit. The two radio frequency signals are correspondingly connected to the two-stage 1×2 fiber acousto-optic modulators; the radio frequency signals of the two-stage 1×2 fiber acousto-optic modulators work alternately; by controlling the timing of the two 1×2 fiber acousto-optic modulator drivers, a pulse pair with fixed delay and frequency difference is obtained.

2. The low-loss and low-power compact heterodyne acousto-optic modulation module for an optical fiber hydrophone according to claim 1, wherein: The two 1×2 fiber acousto-optic modulators generate frequency signals with frequency shifts of f1 and f2 respectively, and the frequency difference between f1 and f2 is the required frequency difference of the hydrophone system.

3. A low-loss and low-power compact heterodyne acousto-optic modulation module for an optical fiber hydrophone, characterized in that: Parallel prisms are provided in both stages of the 1×2 fiber acousto-optic modulators to separate the 0th-order light and the 1st-order diffracted light by the required distance.

4. A low-loss and low-power compact heterodyne acousto-optic modulation module for an optical fiber hydrophone, characterized in that: The 0th-order light and the 1st-order diffracted light of the two-stage 1×2 fiber acousto-optic modulators both use optical fibers to realize the transmission of optical signals. The optical fiber corresponding to the 0th-order light of the first 1×2 fiber acousto-optic modulator is fused with the optical fiber corresponding to the 1st-order diffracted light of the second 1×2 fiber acousto-optic modulator; the optical fiber corresponding to the 1st-order diffracted light of the first 1×2 fiber acousto-optic modulator is fused with the optical fiber corresponding to the 0th-order light of the second 1×2 fiber acousto-optic modulator.

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