An optical switch comprising: at least one first port , at least one second port , a first wavelength division multiplexing, WDM, apparatus , an optical splitter , an optical monitoring apparatus , and an optical switching apparatus , wherein: • the first port is configured to transmit an input first optical signal to the first WDM apparatus , wherein the first optical signal is a multi-wavelength signal; • the first WDM apparatus is configured to demultiplex the first optical signal, thereby arriving at a demultiplexed first optical signal composed of spatially separated optical signals, thereby spatially separating the multi-wavelength signal into its wavelength component signals; • the optical splitter is configured to split the demultiplexed first optical signal to obtain a first sub-signal and a second sub-signal, wherein the first sub-signal and the second sub-signal are each composed of spatially separated optical signals, wherein each optical signal among the spatially separated optical signals has a different single wavelength among the multiple wavelengths of the multi-wavelength signal; • the optical switching apparatus is configured to perform optical switching on the first sub-signal; • the second port is configured to output an optical signal obtained after the optical switching; • the optical monitoring apparatus is configured to perform optical performance monitoring on the second sub-signal, and • in a first cross-sectional plane at the location of the optical switching apparatus , the cross-sections of the optical signals of the first sub-signal are the same as the cross-sections of the optical signals of the second sub-signal in a second cross-sectional plane at the location of the optical monitoring apparatus , and the distribution of the cross-sections of the optical signals of the first sub-signal in the first cross-sectional plane is the same as the distribution of the cross-sections of the optical signals of the second sub-signal in the second cross-sectional plane. • the first port is configured to transmit an input first optical signal to the first WDM apparatus , wherein the first optical signal is a multi-wavelength signal; • the first WDM apparatus is configured to demultiplex the first optical signal, thereby arriving at a demultiplexed first optical signal composed of spatially separated optical signals, thereby spatially separating the multi-wavelength signal into its wavelength component signals; • the optical splitter is configured to split the demultiplexed first optical signal to obtain a first sub-signal and a second sub-signal, wherein the first sub-signal and the second sub-signal are each composed of spatially separated optical signals, wherein each optical signal among the spatially separated optical signals has a different single wavelength among the multiple wavelengths of the multi-wavelength signal; • the optical switching apparatus is configured to perform optical switching on the first sub-signal; • the second port is configured to output an optical signal obtained after the optical switching; • the optical monitoring apparatus is configured to perform optical performance monitoring on the second sub-signal, and • in a first cross-sectional plane at the location of the optical switching apparatus , the cross-sections of the optical signals of the first sub-signal are the same as the cross-sections of the optical signals of the second sub-signal in a second cross-sectional plane at the location of the optical monitoring apparatus , and the distribution of the cross-sections of the optical signals of the first sub-signal in the first cross-sectional plane is the same as the distribution of the cross-sections of the optical signals of the second sub-signal in the second cross-sectional plane. <EOS>