Large-field-angle underwater optical communication receiver optical system and underwater optical communication receiving device and application thereof

Abstract

A large-field-angle underwater optical communication receiver optical system sequentially comprises an optical window, a composite absorption optical filter and a photoelectric detector along an optical path, the composite absorption optical filter is formed by tightly stacking a band-pass type absorption optical filter and a cut-off type absorption optical filter, and the band-pass type absorption optical filter and the cut-off type absorption optical filter are coupled through spectral characteristics of the band-pass type absorption optical filter and the cut-off type absorption optical filter. The central wavelength of the composite narrow-band-pass filtering structure is in a blue-green light wave band, and the passband characteristic of the composite narrow-band-pass filtering structure is insensitive to an incident angle. By utilizing the angle insensitivity of the absorption optical filter, the problem of performance degradation caused by passband blue shift when a traditional interference optical filter receives at a large field angle is fundamentally solved, background light can be stably and efficiently inhibited within the field angle range larger than or equal to 120 degrees, meanwhile, the high transmittance of communication signal light is ensured, and the communication quality is improved. And the signal-to-noise ratio and the dynamic range of the underwater optical communication receiver are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underwater wireless optical communication, in particular to a large field of view underwater optical communication receiver optical system, underwater optical communication receiving equipment and application thereof. BACKGROUND

[0002] Underwater wireless optical communication has become an important supplement to underwater communication due to its high bandwidth, low delay and other advantages. However, the underwater environment is complex, and the background light (such as sunlight, bioluminescence, artificial light source, etc.) noise is strong, which seriously interferes with the reception of communication signals and reduces the signal-to-noise ratio. In order to suppress the background light, the existing technology often uses optical filters. Among them, although the interference type filter has good out-of-band suppression effect, the center wavelength and bandwidth will shift significantly with the increase of the light incidence angle (i.e. the phenomenon of blue shift of passband), which leads to the decrease of the transmittance of the target signal light and the weakening of the background noise suppression ability. This characteristic seriously limits its application in underwater communication systems that require large field of view reception. Although the absorption type filter has good angle stability, it is usually difficult to achieve narrow bandpass characteristics, and it is difficult to meet the high-precision filtering requirements when used alone.

[0003] Therefore, how to realize wide field of view reception while maintaining stable and efficient suppression of background light is a key problem to improve the performance of underwater optical communication system. SUMMARY

[0004] The purpose of the present application is to overcome the problem of performance degradation of the existing interference filter at large angle of incidence, and to provide a wide-angle underwater optical communication receiving method and system based on double filter superposition. The system combines a specific type of absorption filter to construct an angle-insensitive narrow bandpass light window, which can accurately filter out background light within a field of view angle of more than 120°, while ensuring high transmittance of communication signal light, thereby significantly improving the signal-to-noise ratio and dynamic range of the receiver.

[0005] To achieve the above purpose, the present application adopts the following technical scheme: On the one hand, the present application provides a large field of view underwater optical communication receiver optical system, characterized in that it comprises, in sequence along the light path incidence direction: an optical window; a composite absorption optical filter, arranged behind the optical window, composed of a bandpass type absorption filter and a high-pass cutoff type absorption filter, wherein the passband range of the bandpass type absorption filter covers the target communication waveband, and the cutoff sideband of the high-pass cutoff type absorption filter partially overlaps with the passband of the bandpass type absorption filter, and the two together form a composite narrow bandpass filter structure with spectral characteristics insensitive to incidence angle; and A photoelectric detector is arranged behind the composite absorption optical filter and used to receive the light signal filtered by the composite narrow-bandpass filter.

[0006] Further, the bandpass absorption filter is a filter allowing light in the 350-480 nm wavelength band to pass through, and the high-pass cutoff absorption filter is a filter suppressing light with a wavelength less than 435 nm from passing through.

[0007] Further, the pass-through window of the composite narrow-bandpass filter is 440-480 nm, which is matched with the blue communication laser with a center wavelength of 450 nm.

[0008] Further, the optical subsystem is configured to operate at a receiving field of view angle of no less than 120°, and within the entire operating field of view angle range, the center wavelength shift of the composite narrow-bandpass filter is less than 5 nm.

[0009] In another aspect, the application also provides an underwater optical communication receiving assembly, characterized in that it comprises: The optical system according to any one of claims 1-4; and A signal processing circuit electrically connected to the photoelectric detector and used to process the electrical signal output by the photoelectric detector.

[0010] Further, the signal processing circuit comprises a dual-path gain control module used to adaptively process an input light signal with an intensity dynamic range greater than 60 dB.

[0011] Thirdly, the application also provides a method for suppressing light noise under a large field of view angle receiving, which is applied to the above-mentioned underwater optical communication receiving assembly, and the method comprises: The composite absorption optical filter is used to filter the incident light from a large field of view angle range, and the spectral superposition effect of the bandpass and cutoff absorption filters is used to form an angle-insensitive narrow-bandpass window, so as to uniformly transmit the target communication signal and suppress the out-of-band background noise within a wide angle range; The photoelectric detector is used to convert the filtered light signal into an electrical signal; The signal processing circuit is used to process the electrical signal to recover the communication information.

[0012] Further, the step of forming an angle-insensitive narrow-bandpass window specifically comprises: within a field of view angle range of no less than 120°, the transmittance of the communication light with a center wavelength of 450 nm is controlled to be within 3 dB, and the average suppression rate of the background light in the 500-700 nm wavelength band is maintained to be more than 90%.

[0013] Compared with the prior art, the application has the beneficial effects that: 1) High-efficiency background light suppression: through the innovative combination of two absorption filters 259116 and 259051, a narrow bandpass (440-480 nm) highly matched with the communication laser wavelength (450 nm) is accurately constructed. The combination can effectively filter out main background noise sources such as warm light lamps (spectrum concentrated in 500-700 nm) and cold light lamps (spectrum concentrated in 440 nm), greatly improving the receiving signal-to-noise ratio.

[0014] 2) Stable operation in a large field of view: since the function of the absorption filter is based on the absorption characteristics of a specific material to a specific spectrum, its filtering characteristics are not affected by the incident angle of light, fundamentally solving the problem of performance degradation caused by the passband shift (blue shift) of traditional interference filters at large angles of incidence. This feature makes it particularly suitable for use with a 120° wide-angle receiving system, achieving stable and efficient filtering in a large field of view.

[0015] 3) Wide dynamic range reception: the signal processing module adopts a dual-channel design, which can adaptively process light signals with a large intensity variation range, ensuring the communication reliability of the system in complex underwater channels. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of the spectral characteristics of the body of the dual-filter assembly; Figure 2 is a schematic diagram of the spectral characteristics of the body of the dual-filter assembly; Figure 3 is a schematic diagram of the spectral characteristics of the dual-filter assembly after superposition. DETAILED DESCRIPTION

[0017] The application will be further described in detail below in conjunction with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application.

[0018] Example 1: Construction and spectral verification of the dual-filter assembly Referring to Figures 1-3 , the spectral superposition effect of the dual-filter is shown. Figure 1 The middle curve represents the transmittance characteristics of the 259116 filter (350-480 nm), Figure 2 The middle curve represents the transmittance characteristics of the 259051 filter (suppressing <435 nm). After superposition, the final passband Figure 3 The middle curve, with a transmittance window of 440 nm to 480 nm, has the highest transmittance at the center wavelength of 450 nm.

[0019] The 259116 type glass produced by SCHOTT company is used as a band-pass type absorption filter, and the 259051 type glass is selected as a cut-off type absorption filter.

[0020] A double filter assembly is arranged on the light path between the transparent dome and the wide-angle photodetection array, for accurately filtering out background light. The double filter assembly is composed of a 259116 type band-pass absorption filter and a 259051 type high-pass absorption filter. The 259116 filter is used to transmit light in the 350nm to 480nm waveband, and the 259051 filter is used to suppress light with a wavelength less than 435nm. After superposition, the two filters form a narrow band-pass filter with a transmission window of 440nm to 480nm, and the center of the passband is highly matched with the center wavelength 450nm of the communication laser.

[0021] The spectral transmittance curves of the single filters and the combined filter after stacking are measured at normal incidence (0°) and large incidence angles (such as 30°, 45°, and 60°) using an ultraviolet-visible-near infrared spectrophotometer.

[0022] As shown in Figure 1 , the 259116 type filter has a high transmittance in the range of 350nm to 480nm. As shown in Figure 2 , the 259051 type filter has a sharp decrease in transmittance when the wavelength is less than 435nm, effectively cutting off short-wave light.

[0023] After stacking, as shown in Figure 3 , a composite narrow band-pass with a transmission window of 440nm to 480nm is formed. The key is that, through testing, the center wavelength (about 460nm, with slight fluctuations due to specific glass batch) and the passband shape of the composite passband change very little within the incidence angle range of 0° to 60°. Specifically, the center wavelength offset is less than 3nm, and the transmittance at the target wavelength of 450nm decreases by less than 5%. This fundamentally solves the problem that interference filters may have a blue shift of more than 15nm at large angles (such as more than 30°) and cause serious signal attenuation.

[0024] Example Two: Integration of Large Field Angle Underwater Receiver This embodiment describes how to integrate the above composite filter into a complete underwater optical communication receiving device.

[0025] Referring to the schematic diagram of the receiver structure not shown, the receiving device includes, along the light path direction: Pressure-resistant optical window: a hemispherical cover made of sapphire or high-strength optical glass, providing a receiving field of view (FOV) of more than 120° and capable of withstanding underwater pressure.

[0026] Composite absorption optical filter: as described in Example One, placed closely or in close proximity behind the optical window.

[0027] Wide-angle photodetection array: using a silicon photomultiplier (SiPM) array or large-area avalanche photodiode (APD), with its photosensitive surface behind the composite filter, responsible for converting the filtered optical signal into an electrical signal. The receiving angle of the array itself is matched with the optical system, ensuring that the overall FOV ≥ 120°.

[0028] Signal processing module: electrically connected to the detection array. The core of this module is its dual-channel adaptive processing circuit: High-gain channel: used to process weak light signals, using high-transimpedance amplifiers and possibly integrating time-gating technology to further suppress scattered background light.

[0029] Low-gain channel: used to process strong light signals to prevent saturation.

[0030] The two-channel signals are automatically switched or fused by subsequent comparators or digital signal processors (DSPs), ensuring that the system can reliably receive signals in complex underwater channels from turbid shallow water (strong background light) to clear deep water (weak signal), with an effective dynamic range of up to 80dB.

[0031] System workflow and beneficial effect verification: In implementation and deployment, the receiver is installed on an underwater vehicle or observation platform. Signal light from a 450nm laser communication source, as well as sunlight, bioluminescence and other background light, enters through the optical window.

[0032] Composite absorption optical filter: using the absorption characteristics of BG-3 and GG-435, a "optical channel" is stably created within the entire 120° field of view. This channel only allows 440-480nm light to pass efficiently, while simultaneously and efficiently blocking 500-700nm warm background light (such as sunlight attenuated by water layers) and 435nm or below shortwave background light (such as some bioluminescence and cold light). Actual measurements show that in strong environmental light, this filter can improve the signal-to-noise ratio (SNR) of the receiver by 15-20dB.

[0033] The "pure" 450nm signal light after filtering is captured by the wide-angle photodetection array and converted into an electrical signal. This electrical signal is then sent to the signal processing module, where the dual-channel circuit overcomes the fluctuations in underwater channel light intensity, ultimately outputting stable, low-error-rate digital signals.

[0034] The application realizes stable, reliable and high-speed light communication signal receiving with high signal-to-noise ratio in a wide underwater space. In addition, the method can be applied to deep sea environment monitoring, underwater laser communication, underwater three-dimensional terrain detection and the like, and can provide a method for background light suppression under a large field of view.

Claims

1. An optical system for a large field-of-view underwater optical communication receiver, characterized in that, Along the incident direction of the light path, the following are included in sequence: Optical window; A composite absorptive optical filter, disposed behind the optical window, is composed of a bandpass absorber filter and a high-pass cutoff absorber filter stacked together. The passband of the bandpass absorber filter covers the target communication band, and the cutoff sideband of the high-pass cutoff absorber filter overlaps with a portion of the passband of the bandpass absorber filter. Together, they form a composite narrowband pass filter structure whose spectral characteristics are insensitive to the incident angle. A photodetector is disposed behind the composite absorption optical filter to receive the optical signal filtered by the composite narrow-bandpass filter structure.

2. The optical system according to claim 1, characterized in that, The bandpass absorption filter is a filter that allows light in the 350nm to 480nm wavelength range to pass through, and the high-pass cutoff absorption filter is a filter that suppresses light with a wavelength less than 435nm from passing through.

3. The optical system according to claim 2, characterized in that, The transparent window of the composite narrowband pass filter structure is 440nm to 480nm, which is used to match the blue communication laser with a center wavelength of 450nm.

4. The optical system according to claim 1, characterized in that, The optical subsystem is configured to operate at a receiving field of view of not less than 120°, and the center wavelength shift of the composite narrowband pass filter structure is less than 5 nm over the entire operating field of view.

5. An underwater optical communication receiving component, characterized in that, include: The optical system as described in any one of claims 1 to 4; as well as A signal processing circuit, electrically connected to the photodetector, is used to process the electrical signal output by the photodetector.

6. The underwater optical communication receiving component according to claim 5, characterized in that, The signal processing circuit includes a dual-path gain control module for adaptively processing input optical signals with an intensity dynamic range greater than 60dB.

7. A method for suppressing optical noise in a large field-of-view receiving background, characterized in that, The method, applied to the underwater optical communication receiving component as described in claim 5 or 6, comprises: The composite absorption optical filter filters incident light from a wide field of view. By utilizing the spectral superposition effect of the bandpass and cutoff absorption filters, an angle-insensitive narrow bandpass window is formed to consistently transmit target communication signals over a wide angle range and suppress out-of-band background noise. The filtered optical signal is converted into an electrical signal using the photodetector. The signal processing circuit processes the electrical signal to recover the communication information.

8. The method for suppressing optical noise in a large field-of-view receiving background according to claim 7, characterized in that, The step of forming an angle-insensitive narrowband pass window specifically includes: controlling the transmittance variation of the communication light with a center wavelength of 450nm to within 3dB within a field of view of not less than 120°, while maintaining the average suppression rate of background light in the 500nm to 700nm band at more than 90%.

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