Evaluation of daylight background noise for satellite-to-ground free-space optical communication during daytime operation

Fig. 1. Schematic showing the ADD-OGS. (a) Schematic illustration of the ADD-OGS operating during the day in the horizontal coordinate system. (b) Photograph and (c) optical configuration of the ADD-OGS. (d) Optical configuration of a beacon optical system on a piggyback. (e) Optical configuration of a communication optical system on a Coudé table. M, mirror; DFB-LD, distributed feedback laser diode; C, collimator; L, lens; FSM, fast steering mirror; W, window; MZM, Mach–Zehnder modulator; MBC, modulator bias controller; PAM, point-ahead angle mirror; BS, beam splitter; FM, folding mirror; F, filter; APD, avalanche photodiode; and QPD, quadrant photodiode.

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Fig. 2. Satellite tracking and solar noise measurement tests. (a) Satellite tracking test conducted during the evening. The satellite tracking test aimed at the satellite SL-16 R/B was conducted on August 28, 2024. (b) Solar noise measurement test during the day while the ADD-OGS was following the satellite trajectory. The satellite trajectory calculated from the TLE data of the satellite STARLINK-31539 on August 13, 2024; inset: solar noise measurement setup using a QPD-based system. (c) Image-based tracking of the satellite using an SWIR camera. (d) Altitude angles, (e) right ascension angles (RAs), and (f) declination angles (DECs) of the satellite and ADD-OGS during the satellite tracking test (gray indicates measurement data of the ADD-OGS’s position, and blue indicates calculation results using the TLE data). (g) Measurement results of the solar noise incident on the ADD-OGS and angular changes. (h) Altitude angles, (i) RAs, and (j) DECs of the satellite and ADD-OGS during the solar noise measurement test (gray indicates measurement data of the ADD-OGS’s position, and blue indicates calculation results using the TLE data).

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Fig. 3. Solar noise measurements of the ADD-OGS during the day. (a) Measurement setup for the solar noise incident on the ADD-OGS for 12 h. (b) Measurement setup for the solar noise incident on the ADD-OGS in different spatial positions. (c) Temporal dependence of solar noise. The data were measured on August 30, 2024. (d) Altitude angles, (e) right ascension angles, and (f) declination angles of the sun and the ADD-OGS during the day (gray indicates the position of the ADD-OGS, and red indicates the solar position). (g) Angular dependence of solar noise. The data were measured on September 5, 2024. (h) 3D spatial map of solar noise at different RAs and DECs of the ADD-OGS relative to the sun at noon. (i) 2D contour map overlaid with satellite trajectory from Fig. 2(g) (gray indicates the trajectory, and black highlights the regions of highest noise).

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Fig. 4. Noise, SNR, beacon detection, and communication performance analysis based on the measured background noise data. (a) Noise variance in the QPD as a function of the received power (simulation). (b) SNR of the QPD as a function of the received power (simulation). (c) Beacon detection performance as a function of the received power (simulation). (d) Noise variance in the APD as a function of the received power (simulation). (e) SNR of the APD as a function of the received power (simulation). (f) Bit error rate performance as a function of the received power (simulation). (g) Error rate data (experimental results) and (h) error count data obtained from the communication test at 7-km ground-to-ground links (experimental results).

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Table 1. Link Budget Design

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Table 1. Link Budget Design

Parameter	Downlink	Uplink	Unit
Channel data rate	2.5	2.5	Gbps
Modulation	NRZ-OOK	NRZ-OOK
Wavelength	1536.61	1553.33	nm
Tx power	33.98	44.31	dBm
Tx gain	104.31	95.05	dB
Tx optical loss	−4.50	−1.32	dB
Free-space loss	−256.31	−256.22	dB
Atmospheric loss	−7.48	−10.16	dB
Pointing loss	−3.0	−3.0	dB
Rx gain	122.79	106.12	dB
Rx optical loss	−2.70	−4.84	dB
Rx power	−12.91	−30.06	dBm
Rx sensitivity	−36.6	−43.9	dBm
Link margin	23.69	13.84	dB

Table 2. Parameters and Constants Used in the Detectors

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Table 2. Parameters and Constants Used in the Detectors

Parameters	Symbol	Value	Unit
Receiving wavelength	$λ$	1536	nm
Optical bandwidth	$Δ λ$	8.6	nm
APD electrical bandwidth	$B_{APD}$	2.5	GHz
QPD electrical bandwidth	$B_{QPD}$	7	kHz
APD responsivity	$R_{APD}$	11.0	A/W
QPD responsivity	$R_{QPD}$	1.05	A/W
APD gain	$M_{APD}$	11
APD excess noise factor	$F_{APD}$	6.3
APD dark current	$I_{D, APD}$	10	nA
QPD dark current	$I_{D, QPD}$	2	nA
APD load resistance	$R_{L, APD}$	50	Ω
QPD load resistance	$R_{L, QPD}$	100	MΩ
Temperature	$T$	300	K
Electric charge	$q$	$1.6 \times 10^{- 19}$	C
Boltzmann constant	$k_{B}$	$1.38 \times 10^{- 23}$	J/K
Planck constant	$h$	$6.626 \times 10^{- 34}$	$J \cdot s$

Table 3. Mean Link Margin Comparison between the Terrestrial Test Link and the GSL (Downlink)^a

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Table 3. Mean Link Margin Comparison between the Terrestrial Test Link and the GSL (Downlink)^a

	Tx. Power	Gain		Free-Space Loss	Atmospheric Loss		Optical Loss		Pointing Loss	Link Margin
	Tx. Power	Tx.	Rx.	Free-Space Loss	Attenuation	Scintillation	Tx.	Rx.	Pointing Loss	Link Margin
GSL	33.98	104.31	122.79	−256.31	−0.27	−7.21	−4.50	−2.70	−3.00	23.69
Test link	−7.96	79.49	122.79	−215.16	−0.24	−5.28	−4.00	−2.70	−3.00	0.54

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Heesuk Jang, Hajun Song, Hansol Jang, "Evaluation of daylight background noise for satellite-to-ground free-space optical communication during daytime operation," Photonics Res. 13, 2630 (2025)

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