A four-level pulse amplitude modulation, PAM4, signal generation apparatus , wherein the PAM4 signal generation apparatus comprises a distributed feedback laser, DFB , a first electro-absorption, EA, modulator , a second EA modulator , a semiconductor optical amplifier, SOA , a polarization beam splitting rotator, PSR , a first electrical-signal generator , a first amplitude-limiting amplifier , a second electrical-signal generator , a second amplitude-limiting amplifier , a first direct-current power source , and a second direct-current power source ; an input port of the DFB is connected to the first direct-current power source , and the DFB is connected to both the first EA modulator and the SOA by using two output ports; the first EA modulator is connected to both the first amplitude-limiting amplifier and the DFB by using two input ports, and an output port of the first EA modulator is connected to the PSR ; the SOA is connected to both the DFB and the second direct-current power source by using two input ports, and an output port of the SOA is connected to the second EA modulator ; the second EA modulator is connected to both the second amplitude-limiting amplifier and the SOA by using two input ports, and an output port of the second EA modulator is connected to the PSR ; the PSR is connected to both the first EA modulator and the second EA modulator by using two input ports; the first electrical-signal generator is connected to the first amplitude-limiting amplifier , and the second electrical-signal generator is connected to the second amplitude-limiting amplifier ; the DFB is configured to: receive a first direct-current bias signal input by the first direct-current power source , generate a first optical signal and a second optical signal according to the first direct-current bias signal separately, transmit the first optical signal to the first EA modulator , and transmit the second optical signal to the SOA , wherein the first optical signal and the second optical signal have a same wavelength; the first EA modulator is configured to: receive a first non-return-to-zero, NRZ, electrical signal input by the first electrical-signal generator by using the first amplitude-limiting amplifier , receive the first optical signal input by the DFB , obtain a first NRZ optical signal by means of modulation according to the first NRZ electrical signal and the first optical signal, and transmit the first NRZ optical signal to the PSR ; the SOA is configured to: receive a second direct-current bias signal input by the second direct-current power source , receive the second optical signal input by the DFB , adjust an optical power of the second optical signal according to the second direct-current bias signal to obtain a second optical signal that is after optical power amplification, and transmit, to the second EA modulator , the second optical signal that is after optical power amplification; the second EA modulator is configured to: receive a second NRZ electrical signal input by the second electrical-signal generator by using the second amplitude-limiting amplifier , receive the second optical signal that is after optical power amplification and that is input by the SOA , obtain a second NRZ optical signal by means of modulation according to the second NRZ electrical signal and the second optical signal that is after optical power amplification, and transmit the second NRZ optical signal to the PSR ; and the PSR is configured to: receive the first NRZ optical signal input by the first EA modulator , receive the second NRZ optical signal input by the second EA modulator , multiplex the first NRZ optical signal and the second NRZ optical signal, and output a PAM4 signal. <EOS>