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激光通信的能量链路传输方程可以用以下的通用表达式描述[7]:
式中:
${P_{\rm{r}}}$ 为探测器接收功率;${P_{\rm{t}}}$ 为发射光源的发射功率;${G_{\rm{t}}}$ 为发射光学天线增益;${\eta _{{\rm{ot}}}}$ 为发射光学单元的效率;${L_{\rm{r}}}$ 为自由空间损耗;${\eta _{\rm{s}}}$ 为信道引起的功率损失;${L_{{\rm{APT}}}}$ 为APT对准失配引起的功率损耗;${G_{\rm{r}}}$ 为接收光学天线增益;${\eta _{{\rm{or}}}}$ 为接收光学系统效率;${\eta _{\rm{\alpha }}}$ 为实际束散角与衍射极限角的额外功率损耗。激光通信光源为量子级联中红外激光器[6],可调制功率60 mW,在BER=10−6、1 Gbps时探测器极限灵敏度为−12 dBm;通信距离10 km。接收功率计算表如表1所示。由表1可知,当激光通信有效接收口径为310 mm,通信发射角0.3 mrad,发射光学天线波像差RMS≤λ/10 (λ为通信波长),通信距离可达10 km,留有2.52 dB的裕量。
Parameter Specification Notes Communication transmitting power/dBm 17.78 Laser modulation power is 60 mW,Laser wavelength is 4.7 μm Transmitting antenna gain/dB 85.51 The emission aperture is 290 mm Transmitting antenna loss/dB −2.22 Transmitting optical efficiency is 0.6 Wavefront loss/dB −1.71 Wavefront aberration RMS≤0.1λ,λ= 4.7 μm Space loss/dB −208.5 10 km Alignment adaptation loss/dB −0.01 High alignment precision Atmospheric absorption/dB −3.62 Atmospheric attenuation Receiving antenna gain/dB 106.1 The receiving aperture is 310 mm Receiving antenna loss/dB −2.22 Receiving optical efficiency is 0.6 Detector actual receiving power/ dBm −9.48 Actual arrival power to detector Detector receiving threshold/dBm −12 BER=10−6,1 Gpbs Table 1. Calculation table of midde infrared laser communication link
Development of optical antenna for middle infrared laser communication terminal
doi: 10.3788/IRLA20200331
- Received Date: 2020-12-10
- Rev Recd Date: 2021-01-25
- Publish Date: 2021-06-30
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Key words:
- laser communication /
- middle infrared laser /
- optical antenna /
- wavefront aberration
Abstract: In order to reduce the tolerance of laser communication optical system, save the development cost, and reduce the influence of atmospheric scattering on laser communication link, the middle infrared laser with its wavelength working at the atmosphere window was used as the laser communication light source, and a matching middle infrared laser communication terminal optical system was developed. Firstly, based on the energy link transmission equation of laser communication, the design parameters of the optical antenna, such as aperture and divergence angle, were calculated according to the beam parameters of the middle infrared laser and the detector sensitivity of the receiving terminal, and the wave aberration requirements of the optical transmitting and receiving system of laser communication were given. Then, the design and tolerance analysis of the optical system for the middle infrared laser communication optical antenna were carried out by ZEMAX software, and the system was processed and adjusted to complete the development of the system, and the image quality of the two optical systems was tested. The test results show that the maximum deviation of transmitting optical system MTF from the theoretical value is 9.3%, and the wavefront aberration RMS of the receiving optical system is 0.075λ (λ=4.7 μm), which meets the design requirements. The results show that the difficulty of processing and adjusting optical antenna can be reduced by using the middle infrared laser as the laser communication light source.