## 2 Principle and Device of Coherent/Non-Coherent OOK Reception without AL
To reduce the electrical bandwidth, [PERSON] et al. presented a spectrally sliced heterodyne coherent receiver with halved electrical bandwidth [38]. The constellation of coherent reception of the OOK signal is shown in \[\vspace{-0.2 cm}l_{b0}(t)&=R\Big{[}\frac{1}{2}(s(t))^{2}(1-k_{S})P _{S}+\frac{1}{2}(1-k_{LO})P_{\Omega}-\sqrt{1-k_{S}}\sqrt{1-k_{LO}}\sqrt{P_{ \Omega}P_{S}}(t)\cos(\omega st-\omega_{LO}t+\varphi_{S}(t)-\varphi_{LO}(t)) \Big{]}+n_{\Omega}(t),\end{split} \tag{3}\]0  
\[\vspace{-0.2 cm}l_{b0}(t)&=R\Big{[}\frac{1}{2}(s(t))^{2}(1-k_{S})P _{S}+\frac{1}{2}(1-k_{LO})P_{\Omega}-\sqrt{1-k_{S}}\sqrt{1-k_{LO}}\sqrt{P_{ \Omega}P_{S}}(t)\cos(\omega st-\omega_{LO}t+\varphi_{S}(t)-\varphi_{LO}(t)) \Big{]}+n_{\Omega}(t),\end{split} \tag{3}\]1 Constellation of OOK for coherent reception (simulated SNR: 20 dB). The BDs used in the experiment were PDB780 CAC (THORLABS); the typical common mode rejection ratio (CMRR) of the BDs was greater than 25 dB, meeting the experimental requirements. The optical 90\({}^{\circ}\) hybrid was COH24 (Kylia). The oscilloscope was a Lab Master MCM-Zi-A (TELEDYNE LECORY). The I and Q signals of the coherent OOK before algorithm recovery are shown in \[\vspace{-0.2 cm}l_{b0}(t)&=R\Big{[}\frac{1}{2}(s(t))^{2}(1-k_{S})P _{S}+\frac{1}{2}(1-k_{LO})P_{\Omega}-\sqrt{1-k_{S}}\sqrt{1-k_{LO}}\sqrt{P_{ \Omega}P_{S}}(t)\cos(\omega st-\omega_{LO}t+\varphi_{S}(t)-\varphi_{LO}(t)) \Big{]}+n_{\Omega}(t),\end{split} \tag{3}\]2  
The key experimental parameters in this paper are presented in \[\vspace{-0.2 cm}l_{b0}(t)&=R\Big{[}\frac{1}{2}(s(t))^{2}(1-k_{S})P _{S}+\frac{1}{2}(1-k_{LO})P_{\Omega}-\sqrt{1-k_{S}}\sqrt{1-k_{LO}}\sqrt{P_{ \Omega}P_{S}}(t)\cos(\omega st-\omega_{LO}t+\varphi_{S}(t)-\varphi_{LO}(t)) \Big{]}+n_{\Omega}(t),\end{split} \tag{3}\]3  
OOK coherent demodulation is asynchronous reception; the relationship between the BER and the optical signal power under the shot noise limit is expressed as [39]  
\[\vspace{-0.2 cm}l_{b0}(t)&=R\Big{[}\frac{1}{2}(s(t))^{2}(1-k_{S})P _{S}+\frac{1}{2}(1-k_{LO})P_{\Omega}-\sqrt{1-k_{S}}\sqrt{1-k_{LO}}\sqrt{P_{ \Omega}P_{S}}(t)\cos(\omega st-\omega_{LO}t+\varphi_{S}(t)-\varphi_{LO}(t)) \Big{]}+n_{\Omega}(t),\end{split} \tag{3}\]4  
where \(\eta\) is the quantum efficiency, which equals 1 in the ideal state; \(hv\) is the photon energy; \(P_{S}\) is the signal light receiving power; and \(R_{b}\) is the communication rate here. Carrier recovery is required for the coherent reception of phase-shift keying (PSK) signals [40]. Carrier recovery is not required for coherent reception of OOK signals, an advantage of OOK coherent reception. By continuously reducing the optical signal power, the relationship between the BER and the optical signal power for OOK coherent reception is obtained, as shown in \[\vspace{-0.2 cm}l_{b0}(t)&=R\Big{[}\frac{1}{2}(s(t))^{2}(1-k_{S})P _{S}+\frac{1}{2}(1-k_{LO})P_{\Omega}-\sqrt{1-k_{S}}\sqrt{1-k_{LO}}\sqrt{P_{ \Omega}P_{S}}(t)\cos(\omega st-\omega_{LO}t+\varphi_{S}(t)-\varphi_{LO}(t)) \Big{]}+n_{\Omega}(t),\end{split} \tag{3}\]5 \begin{table}
\begin{tabular}{c c c} \hline \hline
**Experimental Parameters** & **Symbol** & **Value** \\ \hline Laser wavelength (signal and LO light) & \(\lambda\) & 1555.74 nm \\ Laser linewidth (signal and LO light) & \(\Delta v\) & 5000 Hz \\ Communication rate & \(R_{b}\) & 1 Gbit/s \\ Received optical signal power & \(P_{S}\) & \(-\)65 to \(-\)30 dBm \\ Detector responsivity & \(R\) & 0.85 A/W \\ Detector transimpedance & \(r\) & 5 k\(\Omega\) \\ Optical 90\({}^{\circ}\) hybrid splitting ratio & \(k_{S}\)\&\(k_{L0}\) & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Key experimental parameters. Figure 5: I and Q signals of coherent OOK (down arrow indicates to I-channel signal, up arrow indicates Q-channel signal). When the OOK signal is coherently received and the BER is \(10^{-3}\), the optical signal power is \(-54.60\) dBm, with a loss of \(3.3\) dB compared to the shot noise limit.