Patent Publication Number: US-2022239401-A1

Title: Spectrum Processing Apparatus and Reconfigurable Optical Add-Drop Multiplexer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/100312, filed on Jul. 5, 2020, which claims priority to Chinese Patent Application No. 201910877927.6 filed on Sep. 17, 2019. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of optical communications, and in particular, to a spectrum processing apparatus and a reconfigurable optical add-drop multiplexer. 
     BACKGROUND 
     In recent years, with the vigorous development of network data services, capacities of optical transmission systems have become increasingly large, and requirements for optical networks have also become increasingly high. High-performance and flexibly configurable optical networks are the development direction of future optical networks, and the use of apparatuses having a spectrum processing capability is required in many cases. 
     These spectrum processing apparatuses having a spectrum processing capability can flexibly change spectral characteristics or can be used to detect a spectrum based on requirements of optical networks. The spectrum processing apparatuses are important components for high-performance intelligent optical networks. A spectrum processing apparatus used for wavelength blocking is used as an example. A dispersive assembly separates wavelengths of an incident light beam, and light beams with different wavelengths are incident onto different positions of a spatial light modulator (SLM). The SLM determines wavelengths of light beams that can be reflected to an output port and wavelengths to be blocked. 
     The spectrum processing apparatus used for wavelength blocking requires bandwidth in each wavelength channel to be as large as possible, and then a light spot formed on the SLM needs to be as small as possible. However, if the spectrum processing apparatus is used for overall spectrum adjustment, small light spots on the SLM may produce glitches in the spectrum, which makes it difficult to form a smooth spectrum. In other words, the spectrum processing apparatus used for wavelength blocking is not suitable for overall spectrum adjustment. Therefore, a current spectrum processing apparatus has a limited function. 
     SUMMARY 
     Embodiments of this application provide a spectrum processing apparatus and a reconfigurable optical add-drop multiplexer, thereby enriching functions of the spectrum processing apparatus. 
     According to a first aspect, an embodiment of this application provides a spectrum processing apparatus, including: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator SLM, and a reflective element, where the port assembly includes N ports, and the lens assembly includes M lenses, where N is an integer greater than 1, and M is an integer greater than or equal to 1 and less than or equal to N. Each port in the port assembly is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the reflective element. The reflective element is configured to reflect the second light beam to the dispersive assembly. The dispersive assembly is configured to decompose the second light beam into a plurality of sub-wavelength light beams, and transmit the plurality of sub-wavelength light beams to the reflective element. The reflective element is further configured to reflect the plurality of sub-wavelength light beams to the SLM. The SLM is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the reflective element. The reflective element is further configured to reflect the at least one sub-wavelength light beam to the dispersive assembly. The dispersive assembly is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the reflective element and the lens assembly to the port assembly. 
     It should be understood that the SLM may be a liquid crystal modulator, a liquid crystal on silicon (LCoS) array, a microelectromechanical system (MEMS) micromirror array, or the like. The SLM changes a reflection direction of the sub-wavelength light beam such that the sub-wavelength light beam can be completely reflected to a port without any loss, or the sub-wavelength light beam cannot be reflected to the port, or a part of the sub-wavelength light beam can be reflected to the port. 
     In this implementation, due to different sizes of light spots on the SLM, corresponding light beams are applicable to different functions. For example, a light beam corresponding to a small light spot is applicable to a wavelength blocking function, while a light beam corresponding to a large light spot is applicable to overall spectrum adjustment. In the spectrum processing apparatus provided in this application, the port assembly includes at least two ports, and each lens in the lens assembly can adjust a width of a light beam from a port. To be specific, a width of a light beam after passing through a lens may become larger or smaller, or may remain unchanged, and sizes of light spots formed by light beams of different widths on the SLM are also different. Therefore, the plurality of ports of the spectrum processing apparatus may be used to implement different functions, thereby enriching functions of the spectrum processing apparatus. 
     Optionally, in some possible implementations, the M lenses are all zoom lenses, for example, variable-focus liquid lenses. A focal length of each lens may be adjusted at any time, and a width of a first light beam passing through a same lens may also be adjusted at any time, so that each port can adapt to a plurality of functions. 
     Optionally, in some possible implementations, each port includes an input port and an output port; and each port in the port assembly being configured to transmit an input first light beam to a lens corresponding to the port includes: each input port being configured to transmit the input first light beam to a lens corresponding to the input port; and the dispersive assembly being further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the reflective element and the lens assembly to the port assembly includes: the dispersive assembly being further configured to multiplex the at least one sub-wavelength light beam, and transmit the multiplexed light beam successively through the reflective element and the lens assembly to the output port corresponding to the input port. 
     In this implementation, each port may include an input port and an output port, and then an input light beam and an output light beam are separated on a transmission path, thereby improving applicability of this solution. 
     Optionally, in some possible implementations, the spectrum processing apparatus further includes a polarization assembly, and the polarization assembly is located between the lens assembly and the reflective element; and the polarization assembly is configured to separate polarizations of the second light beam into a first polarized light beam and a second polarized light beam, and transmit the first polarized light beam and the second polarized light beam to the dispersive assembly, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. 
     In this implementation, the spectrum processing apparatus may further be provided with the polarization assembly, thereby improving scalability of this solution. 
     Optionally, in some possible implementations, the N ports are symmetrically distributed with respect to an optic axis of the reflective element. 
     In this implementation, applicable functions of the spectrum processing apparatus not only have different requirements for sizes of light spots formed on the SLM, but also have different requirements for insertion loss (IL) of each port. In optical design, a shorter distance between a port and the optic axis of the reflective element indicates smaller insertion loss of the port. Therefore, in design of distribution of ports, the ports may be symmetrically distributed with respect to the optic axis of the reflective element, so as to differentiate insertion loss of the ports during use, and select corresponding ports to implement different functions. 
     According to a second aspect, an embodiment of this application provides another spectrum processing apparatus, including: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator SLM, and a first lens, where the port assembly includes N ports, and the lens assembly includes M lenses, where N is an integer greater than 1, and M is an integer greater than or equal to 1 and less than or equal to N. Each port in the port assembly is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the dispersive assembly. The dispersive assembly is configured to decompose the second light beam into a plurality of sub-wavelength light beams in a first plane, and transmit the plurality of sub-wavelength light beams to the first lens. The first lens is configured to refract the plurality of sub-wavelength light beams to the SLM in the first plane, and transmit the plurality of sub-wavelength light beams to the SLM in a second plane, where the second plane is perpendicular to the first plane. The SLM is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the first lens. The first lens is further configured to refract the at least one sub-wavelength light beam to the dispersive assembly in the first plane, and transmit the at least one sub-wavelength light beam to the dispersive assembly in the second plane. The dispersive assembly is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam through the lens assembly to the port assembly. 
     Optionally, in some possible implementations, the M lenses are all zoom lenses. 
     Optionally, in some possible implementations, each port includes an input port and an output port; and each port in the port assembly being configured to transmit an input first light beam to a lens corresponding to the port includes: each input port being configured to transmit the input first light beam to a lens corresponding to the input port; and the dispersive assembly being further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam through the lens assembly to the port assembly includes: the dispersive assembly being further configured to multiplex the at least one sub-wavelength light beam, and transmit the multiplexed light beam through the lens assembly to the output port corresponding to the input port. 
     Optionally, in some possible implementations, the spectrum processing apparatus further includes a polarization assembly, and the polarization assembly is located between the lens assembly and the dispersive assembly; and the polarization assembly is configured to separate polarizations of the second light beam into a first polarized light beam and a second polarized light beam, and transmit the first polarized light beam and the second polarized light beam to the dispersive assembly, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. 
     Optionally, in some possible implementations, the N ports are symmetrically distributed with respect to an optic axis of the first lens. 
     According to a third aspect, an embodiment of this application provides another spectrum processing apparatus, including: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator SLM, a first lens, and a second lens, where the port assembly includes N ports, and the lens assembly includes M lenses, where N is an integer greater than 1, and M is an integer greater than or equal to 1 and less than or equal to N. Each port in the port assembly is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the second lens. The second lens is configured to refract the second light beam to the dispersive assembly in a second plane. The dispersive assembly is configured to decompose the second light beam into a plurality of sub-wavelength light beams in a first plane, and transmit the plurality of sub-wavelength light beams to the first lens, where the first plane is perpendicular to the second plane. The first lens is configured to refract the plurality of sub-wavelength light beams to the SLM in the first plane and the second plane. The SLM is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the first lens. The first lens is further configured to refract the at least one sub-wavelength light beam to the dispersive assembly in the first plane and the second plane. The dispersive assembly is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the second lens and the lens assembly to the port assembly. 
     Optionally, in some possible implementations, the second lens is located between the dispersive assembly and the lens assembly, the first lens is located between the dispersive assembly and the SLM, a distance between the first lens and the dispersive assembly is equal to a focal length of the first lens, a distance between the second lens and the dispersive assembly is equal to a focal length of the second lens, and a distance between the first lens and the SLM is equal to the focal length of the first lens. 
     In this implementation, the first lens and the second lens use a standard 4f optical lens configuration, and a transmission path of a light beam is more regular, thereby improving implementability of this solution. 
     Optionally, in some possible implementations, the M lenses are all zoom lenses. 
     Optionally, in some possible implementations, each port includes an input port and an output port; and each port in the port assembly being configured to transmit an input first light beam to a lens corresponding to the port includes: each input port being configured to transmit the input first light beam to a lens corresponding to the input port; and the dispersive assembly being further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the second lens and the lens assembly to the port assembly includes: the dispersive assembly being further configured to multiplex the at least one sub-wavelength light beam, and transmit the multiplexed light beam successively through the second lens and the lens assembly to the output port corresponding to the input port. 
     Optionally, in some possible implementations, the spectrum processing apparatus further includes a polarization assembly, and the polarization assembly is located between the lens assembly and the second lens; and the polarization assembly is configured to separate polarizations of the second light beam into a first polarized light beam and a second polarized light beam, and transmit the first polarized light beam and the second polarized light beam to the first lens, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. 
     Optionally, in some possible implementations, the N ports are symmetrically distributed with respect to an optic axis of the first lens or the second lens. 
     According to a fourth aspect, an embodiment of this application provides a reconfigurable optical add-drop multiplexer (ROADM), including: an add module, a drop module, and the spectrum processing apparatus according to any one of the first aspect to the third aspect. The spectrum processing apparatus is configured to implement a spectrum processing function. The add module is configured to add a local optical wavelength signal from the port assembly of the spectrum processing apparatus. The drop module is configured to drop a local optical wavelength signal from the port assembly of the spectrum processing apparatus. 
     According to a fifth aspect, an embodiment of this application provides a spectrum processing method, applied to a spectrum processing apparatus, where the spectrum processing apparatus includes: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator SLM, and a reflective element, where the port assembly includes N ports, and the lens assembly includes M lenses, where N is an integer greater than 1, and M is an integer greater than or equal to 1 and less than or equal to N. 
     The method includes: transmitting, by each port in the port assembly, an input first light beam to a lens corresponding to each port; adjusting, by each lens in the lens assembly, a width of the first light beam to obtain a second light beam, and transmitting the second light beam to the reflective element; reflecting, by the reflective element, the second light beam to the dispersive assembly; decomposing, by the dispersive assembly, the second light beam into a plurality of sub-wavelength light beams, and transmitting the plurality of sub-wavelength light beams to the reflective element; reflecting, by the reflective element, the plurality of sub-wavelength light beams to the SLM; modulating, by the SLM, the plurality of sub-wavelength light beams, and reflecting at least one modulated sub-wavelength light beam to the reflective element; reflecting, by the reflective element, the at least one sub-wavelength light beam to the dispersive assembly; and multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting a multiplexed light beam successively through the reflective element and the lens assembly to the port assembly. 
     Optionally, in some possible implementations, the M lenses are all zoom lenses. 
     Optionally, in some possible implementations, each port includes an input port and an output port; and the transmitting, by each port in the port assembly, an input first light beam to a lens corresponding to each port includes: transmitting, by each input port, the input first light beam to a lens corresponding to the input port; and the multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting a multiplexed light beam successively through the reflective element and the lens assembly to the port assembly includes: multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting the multiplexed light beam successively through the reflective element and the lens assembly to the output port corresponding to the input port. 
     Optionally, in some possible implementations, the spectrum processing apparatus further includes a polarization assembly, and the polarization assembly is located between the lens assembly and the reflective element; and the method further includes: separating, by the polarization assembly, polarizations of the second light beam into a first polarized light beam and a second polarized light beam, and transmitting the first polarized light beam and the second polarized light beam to the dispersive assembly, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. 
     Optionally, in some possible implementations, the N ports are symmetrically distributed with respect to an optic axis of the reflective element. 
     According to a sixth aspect, an embodiment of this application provides another spectrum processing method, applied to a spectrum processing apparatus, where the spectrum processing apparatus includes: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator SLM, and a first lens, where the port assembly includes N ports, and the lens assembly includes M lenses, where N is an integer greater than 1, and M is an integer greater than or equal to 1 and less than or equal to N. 
     The method includes: transmitting, by each port in the port assembly, an input first light beam to a lens corresponding to each port; adjusting, by each lens in the lens assembly, a width of the first light beam to obtain a second light beam, and transmitting the second light beam to the dispersive assembly; decomposing, by the dispersive assembly, the second light beam into a plurality of sub-wavelength light beams in a first plane, and transmitting the plurality of sub-wavelength light beams to the first lens; refracting, by the first lens, the plurality of sub-wavelength light beams to the SLM in the first plane, and transmitting the plurality of sub-wavelength light beams to the SLM in a second plane, where the second plane is perpendicular to the first plane; modulating, by the SLM, the plurality of sub-wavelength light beams, and reflecting at least one modulated sub-wavelength light beam to the first lens; refracting, by the first lens, the at least one sub-wavelength light beam to the dispersive assembly in the first plane, and transmitting the at least one sub-wavelength light beam to the dispersive assembly in the second plane; and multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting a multiplexed light beam through the lens assembly to the port assembly. 
     Optionally, in some possible implementations, the M lenses are all zoom lenses. 
     Optionally, in some possible implementations, each port includes an input port and an output port; and the transmitting, by each port in the port assembly, an input first light beam to a lens corresponding to each port includes: transmitting, by each input port, the input first light beam to a lens corresponding to the input port; and the multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting a multiplexed light beam through the lens assembly to the port assembly includes: multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting the multiplexed light beam through the lens assembly to the output port corresponding to the input port. 
     Optionally, in some possible implementations, the spectrum processing apparatus further includes a polarization assembly, and the polarization assembly is located between the lens assembly and the dispersive assembly; and the method further includes: separating, by the polarization assembly, polarizations of the second light beam into a first polarized light beam and a second polarized light beam, and transmitting the first polarized light beam and the second polarized light beam to the dispersive assembly, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. 
     Optionally, in some possible implementations, the N ports are symmetrically distributed with respect to an optic axis of the first lens. 
     According to a seventh aspect, an embodiment of this application provides another spectrum processing method, applied to a spectrum processing apparatus, where the spectrum processing apparatus includes: a port assembly, a lens assembly, a dispersive assembly, a spatial light modulator SLM, a first lens, and a second lens, where the port assembly includes N ports, and the lens assembly includes M lenses, where N is an integer greater than 1, and M is an integer greater than or equal to 1 and less than or equal to N. 
     The method includes: transmitting, by each port in the port assembly, an input first light beam to a lens corresponding to each port; adjusting, by each lens in the lens assembly, a width of the first light beam to obtain a second light beam, and transmitting the second light beam to the second lens; refracting, by the second lens, the second light beam to the dispersive assembly in a second plane; decomposing, by the dispersive assembly, the second light beam into a plurality of sub-wavelength light beams in a first plane, and transmitting the plurality of sub-wavelength light beams to the first lens, where the first plane is perpendicular to the second plane; refracting, by the first lens, the plurality of sub-wavelength light beams to the SLM in the first plane and the second plane; modulating, by the SLM, the plurality of sub-wavelength light beams, and reflecting at least one modulated sub-wavelength light beam to the first lens; refracting, by the first lens, the at least one sub-wavelength light beam to the dispersive assembly in the first plane and the second plane; and multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting a multiplexed light beam successively through the second lens and the lens assembly to the port assembly. 
     Optionally, in some possible implementations, the second lens is located between the dispersive assembly and the lens assembly, the first lens is located between the dispersive assembly and the SLM, a distance between the first lens and the dispersive assembly is equal to a focal length of the first lens, a distance between the second lens and the dispersive assembly is equal to a focal length of the second lens, and a distance between the first lens and the SLM is equal to the focal length of the first lens. 
     Optionally, in some possible implementations, the M lenses are all zoom lenses. 
     Optionally, in some possible implementations, each port includes an input port and an output port; and the transmitting, by each port in the port assembly, an input first light beam to a lens corresponding to each port includes: transmitting, by each input port, the input first light beam to a lens corresponding to the input port; and the multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting a multiplexed light beam successively through the second lens and the lens assembly to the port assembly includes: multiplexing, by the dispersive assembly, the at least one sub-wavelength light beam, and transmitting the multiplexed light beam successively through the second lens and the lens assembly to the output port corresponding to the input port. 
     Optionally, in some possible implementations, the spectrum processing apparatus further includes a polarization assembly, and the polarization assembly is located between the lens assembly and the second lens; and the method further includes: separating, by the polarization assembly, polarizations of the second light beam into a first polarized light beam and a second polarized light beam, and transmitting the first polarized light beam and the second polarized light beam to the first lens, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. 
     Optionally, in some possible implementations, the N ports are symmetrically distributed with respect to an optic axis of the first lens or the second lens. 
     It can be learned from the foregoing technical solutions that the embodiments of this application have the following advantages: 
     In the embodiments of this application, due to different sizes of light spots on the SLM, corresponding light beams are applicable to different functions. For example, a light beam corresponding to a small light spot is applicable to a wavelength blocking function, while a light beam corresponding to a large light spot is applicable to overall spectrum adjustment. In the spectrum processing apparatus provided in this application, the port assembly includes at least two ports, and each lens in the lens assembly can adjust a width of a light beam from a port. To be specific, a width of a light beam after passing through a lens may become larger or smaller, or may remain unchanged, and sizes of light spots formed by light beams of different widths on the SLM are also different. Therefore, the plurality of ports of the spectrum processing apparatus may be used to implement different functions, thereby enriching functions of the spectrum processing apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a structure of a first spectrum processing apparatus according to an embodiment of this application; 
         FIG. 2  is a schematic diagram of a structure of a lens assembly; 
         FIG. 3  is a schematic diagram of changes in a beam waist radius after a light beam passes through a lens; 
         FIG. 4  is a side view of a structure of a second spectrum processing apparatus according to an embodiment of this application; 
         FIG. 5  is a top view of the structure of the second spectrum processing apparatus according to the embodiment of this application; 
         FIG. 6  is a schematic diagram of a structure of a first lens; 
         FIG. 7  is a side view of a structure of a third spectrum processing apparatus according to an embodiment of this application; 
         FIG. 8  is a top view of the structure of the third spectrum processing apparatus according to the embodiment of this application; 
         FIG. 9  is a schematic diagram of a structure of a second lens; 
         FIG. 10  is a top view of a structure of a fourth spectrum processing apparatus according to an embodiment of this application; 
         FIG. 11  is a side view of a structure of a fifth spectrum processing apparatus according to an embodiment of this application; 
         FIG. 12  is a top view of the structure of the fifth spectrum processing apparatus according to the embodiment of this application; 
         FIG. 13  is a side view of a structure of a sixth spectrum processing apparatus according to an embodiment of this application; 
         FIG. 14  is a schematic diagram of a structure of a ROADM according to an embodiment of this application; 
         FIG. 15  is a schematic diagram of an embodiment of a signal transmission method using a spectrum processing apparatus according to an embodiment of this application; 
         FIG. 16  is a schematic diagram of an embodiment of another signal transmission method using a spectrum processing apparatus according to an embodiment of this application; and 
         FIG. 17  is a schematic diagram of an embodiment of another signal transmission method using a spectrum processing apparatus according to an embodiment of this application. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Embodiments of this application provide a spectrum processing apparatus and a reconfigurable optical add-drop multiplexer, thereby enriching functions of the spectrum processing apparatus. In the specification, claims, and accompanying drawings of this application, the terms “first”, “second”, “third”, “fourth”, and the like (if existent) are intended to distinguish between similar objects but do not necessarily indicate a specific order or sequence. It should be understood that data termed in such a way are interchangeable in proper circumstances so that the embodiments described herein can be implemented in other orders than the order illustrated or described herein. Moreover, the terms “include”, “have” and any other variants thereof mean to cover the non-exclusive inclusion, for example, a process, method, system, product, or device that includes a list of steps or units is not necessarily limited to the clearly listed steps or units, but may include other steps or units not clearly listed or inherent to such a process, method, product, or device. 
       FIG. 1  is a top view of a structure of a first spectrum processing apparatus according to an embodiment of this application. The spectrum processing apparatus includes: a port assembly  101 , a lens assembly  102 , a dispersive assembly  103 , a spatial light modulator (SLM)  104 , and a reflective element  105 . The port assembly  101  includes N ports, where N is an integer greater than 1. The lens assembly  102  consists of M lenses, where M is an integer greater than or equal to 1 and less than or equal to N. Therefore, not all ports have their respective lenses. 
     Each port in the port assembly  101  is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly  102  is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the reflective element  105 . The reflective element  105  is configured to reflect the second light beam to the dispersive assembly  103 . The dispersive assembly  103  is configured to decompose the second light beam into a plurality of sub-wavelength light beams, and transmit the plurality of sub-wavelength light beams to the reflective element  105 . The reflective element  105  is further configured to reflect the plurality of sub-wavelength light beams to the spatial light modulator  104 . The spatial light modulator  104  is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the reflective element  105 . The reflective element  105  is further configured to reflect the at least one sub-wavelength light beam to the dispersive assembly  103 . The dispersive assembly  103  is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the reflective element  105  and the lens assembly  102  to the port assembly  101 . 
     It should be noted that the ports in the port assembly  101  may have a plurality of arrangements. For example, the ports may be sequentially arranged in the plane shown in  FIG. 1 ; or the ports may be sequentially arranged in a plane perpendicular to the plane shown in  FIG. 1 ; or the ports are distributed in both planes, that is, the port assembly  101  may also be an array with ports arranged in both rows and columns. This is not specifically limited herein. For example, when seen from the perspective shown in  FIG. 1 , the port assembly  101  may include a first column in which a first port  101   a  is located and a second column in which a second port  101   b  is located. In the first column, a plurality of other ports may be sequentially arranged following the first port  101   a . Similarly, in the second column, a plurality of other ports may be sequentially arranged following the second port  101   b.    
       FIG. 2  is a schematic diagram of a structure of a lens assembly. It may be understood that different lenses (including convex lenses, concave lenses, and the like) may converge or diverge light beams, and therefore may cause changes in a size of a light spot formed by a light beam striking the spatial light modulator  104 . For example, the lens assembly  102  in  FIG. 2  includes an A lens  102   a  and a B lens limb, where the A lens  102   a  is a convex lens, and after a first light beam passes through the A lens  102   a , a width of the light beam decreases; and the B lens  102   b , is a concave lens, and after a first light beam passes through the B lens  102   b , a width of the light beam increases. 
     It should be noted that, if a width of a first light beam emitted from some port meets requirements, no lens may be arranged on a transmission path of the first light beam to change the width of the light beam, or a plane mirror may be placed at a corresponding position of the lens assembly  102  only to transmit the first light beam. In practical applications, the lens assembly  102  may be a combination of M separate lenses. Certainly, another design may also be possible. For example, the lens assembly  102  may alternatively be an integral light transmitting surface structure, and different positions of the integral light transmitting surface structure are formed with different curvatures, to adjust the width of the first light beam. A structure of the lens assembly  102  is not specifically limited herein. 
     It should be noted that a focal length of a lens meeting requirements may be pre-calculated based on an actual required width of a light beam. A possible implementation is provided below, where a width of a light beam is represented by a beam waist radius.  FIG. 3  is a schematic diagram of changes in a beam waist radius after a light beam passes through a lens. If a first light beam does not pass through a lens or a curvature of the lens is infinite, a beam waist radius of a second light beam is ω. If the first light beam passes through a lens with a focal length f, the beam waist radius of the second light beam is ω′. According to Gaussian optics, the focal length f of the lens may be selected according to the following formula: 
     
       
         
           
             
               
                 
                   ω 
                   ′ 
                 
                 ω 
               
               = 
               
                 1 
                 
                   
                     1 
                     - 
                     
                       
                         ( 
                         
                           d 
                           f 
                         
                         ) 
                       
                       2 
                     
                     + 
                     
                       
                         ( 
                         
                           
                             z 
                             R 
                           
                           f 
                         
                         ) 
                       
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     where ω is a beam waist radius of the first light beam, ω′ is a beam waist radius of the second light beam, f is the focal length of the lens, d is a distance between a beam waist position of the second light beam and the lens, z R  is a Rayleigh distance of the first light beam, z R =πω 2 /λ, and λ is a wavelength of the first light beam. 
     Optionally, the lenses in the lens assembly  102  may be zoom lenses, for example, variable-focus liquid lenses. A focal length of each lens may be adjusted at any time, and a width of a first light beam passing through a same lens may also be adjusted at any time, so that each port can adapt to a plurality of functions. 
     It should be noted that, the dispersive assembly  103  may usually be a structure such as a grating or a prism, and can decompose the second light beam into a plurality of sub-wavelength light beams by wavelength, where each sub-wavelength light beam has a different wavelength. It may be understood that each sub-wavelength light beam is transmitted to a different position of the spatial light modulator  104 . For example, after passing through the dispersive assembly  103 , each second light beam is decomposed into two sub-wavelength light beams. Specifically, a quantity of sub-wavelength light beams decomposed from the second light beam after the second light beam passes through the dispersive assembly  103  is subject to practical applications. This is not limited herein. 
     Optionally, the spatial light modulator  104  may be specifically a plurality of different structures, for example, a liquid crystal modulator, a liquid crystal on silicon (LCoS) array, and a microelectromechanical system (MEMS) micromirror array. This is not specifically limited herein. 
     For example, the spatial light modulator  104  is specifically an LCoS. The LCoS has a pixelated region for modulation, and a reflection direction of each sub-wavelength light beam can be changed by modulating pixels of a corresponding wavelength region. For example, the spatial light modulator  104  is specifically a MEMS micromirror array. The MEMS micromirror array consists of a plurality of rotatable reflectors, and a reflection direction of a sub-wavelength light beam is adjusted by rotating the reflectors. Specifically, after a sub-wavelength light beam is incident onto the spatial light modulator  104 , the spatial light modulator  104  changes a reflection direction of the sub-wavelength light beam such that the sub-wavelength light beam can be completely reflected to a port without any loss, or the sub-wavelength light beam cannot be reflected to the port, or a part of the sub-wavelength light beam can be reflected to the port. A specific modulation scheme of the spatial light modulator  104  is subject to practical applications, and this is not limited herein. 
     Optionally, each port in the port assembly  101  may be classified as an input port and an output port. It may be understood that each input port is configured to transmit the input first light beam to a lens corresponding to the input port, and after the dispersive assembly  103  multiplexes the sub-wavelength light beam reflected by the spatial light modulator  104 , a multiplexed light beam is transmitted successively through the reflective element  105  and the lens assembly  102  to the output port. 
     In this embodiment of this application, due to different sizes of light spots on the SLM, corresponding light beams are applicable to different functions. For example, a light beam corresponding to a small light spot is applicable to a wavelength blocking function, while a light beam corresponding to a large light spot is applicable to overall spectrum adjustment. In the spectrum processing apparatus provided in this application, the port assembly includes at least two ports, and each lens in the lens assembly can adjust a width of a light beam from a port. To be specific, a width of a light beam after passing through a lens may become larger or smaller, or may remain unchanged, and sizes of light spots formed by light beams of different widths on the SLM are also different. Therefore, the plurality of ports of the spectrum processing apparatus may be used to implement different functions, thereby enriching functions of the spectrum processing apparatus. 
       FIG. 1  elaborates on the structure of the first spectrum processing apparatus in this application. The following describes other possible structures of the spectrum processing apparatus in this application. 
     Referring to  FIG. 4  and  FIG. 5 ,  FIG. 4  is a side view of a structure of a second spectrum processing apparatus according to an embodiment of this application, and  FIG. 5  is a top view of the structure of the second spectrum processing apparatus according to the embodiment of this application. The spectrum processing apparatus includes: a port assembly  101 , a lens assembly  102 , a dispersive assembly  103 , a spatial light modulator  104 , and a first lens  106 . Descriptions of the port assembly  101 , the lens assembly  102 , the dispersive assembly  103 , and the spatial light modulator  104  are similar to the related descriptions of the embodiment shown in  FIG. 1 . Details are not described herein again. 
     Each port in the port assembly  101  is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly  102  is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the dispersive assembly  103 . The dispersive assembly  103  is configured to decompose the second light beam into a plurality of sub-wavelength light beams in a first plane ( FIG. 5  shows light beams in the first plane), and transmit the plurality of sub-wavelength light beams to the first lens  106 . The first lens  106  is configured to refract the plurality of sub-wavelength light beams to the spatial light modulator  104  in the first plane, and transmit the plurality of sub-wavelength light beams in a second plane ( FIG. 4  shows light beams in the second plane) to the spatial light modulator  104 , where the first plane is perpendicular to the second plane. The spatial light modulator  104  is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the first lens  106 . The first lens  106  is further configured to refract the at least one sub-wavelength light beam to the dispersive assembly  103  in the first plane, and transmit the at least one sub-wavelength light beam to the dispersive assembly  103  in the second plane. The dispersive assembly  103  is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam through the lens assembly  102  to the port assembly  101 . 
     It should be noted that  FIG. 6  is a schematic diagram of a structure of the first lens. The first lens  106  is a cylindrical lens. As can be seen from  FIG. 6 , when passing through the first lens  106 , a sub-wavelength light beam is refracted only in the first plane, and is not refracted in the second plane. Therefore, when seen from the perspective of the first plane, the first lens  106  can transmit the sub-wavelength light beams to the spatial light modulator  104  by means of refraction, and when seen from the perspective of the second plane, the sub-wavelength light beams are not projected together onto a same position of the spatial light modulator  104  due to the refraction. This avoids a disorder caused by projection of the sub-wavelength light beams onto the same position of the spatial light modulator  104 , while ensuring that the sub-wavelength light beams can be transmitted to the spatial light modulator  104 . For example, as can be seen from  FIG. 4 , light beams emitted from a first port iota, a second port  101   b , and a third port low are finally projected onto different positions of the spatial light modulator  104 , so that a light beam reflected by the spatial light modulator  104  can be transmitted to a corresponding port. 
     Referring to  FIG. 7  and  FIG. 8 ,  FIG. 7  is a side view of a structure of a third spectrum processing apparatus according to an embodiment of this application, and  FIG. 8  is a top view of the structure of the third spectrum processing apparatus according to the embodiment of this application. The spectrum processing apparatus includes: a port assembly  101 , a lens assembly  102 , a dispersive assembly  103 , a spatial light modulator  104 , a first lens  106 , and a second lens  107 . Descriptions of the port assembly  101 , the lens assembly  102 , the dispersive assembly  103 , and the spatial light modulator  104  are similar to the related descriptions of the embodiment shown in  FIG. 1 . Details are not described herein again. 
     Each port in the port assembly  101  is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly  102  is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the second lens  107 . The second lens  107  is configured to refract the second light beam to the dispersive assembly  103  in a second plane ( FIG. 7  shows light beams in the second plane). The dispersive assembly  103  is configured to decompose the second light beam into a plurality of sub-wavelength light beams in a first plane ( FIG. 8  shows light beams in the first plane), and transmit the plurality of sub-wavelength light beams to the first lens  106 , where the first plane is perpendicular to the second plane. The first lens  106  is configured to refract the plurality of sub-wavelength light beams to the spatial light modulator  104  in the first plane and the second plane. The spatial light modulator  104  is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the first lens  106 . The first lens  106  is further configured to refract the at least one sub-wavelength light beam to the dispersive assembly  103  in the first plane and the second plane. The dispersive assembly  103  is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the second lens  107  and the lens assembly  102  to the port assembly  101 . 
     Optionally, the first lens  106  and the second lens  107  may use a standard 4f optical lens configuration. Specifically, the second lens  107  is located between the dispersive assembly  103  and the lens assembly  102 , the first lens  106  is located between the dispersive assembly  103  and spatial light modulator  104 , a distance between the first lens  106  and the dispersive assembly  103  is equal to a focal length of the first lens  106 , a distance between the second lens  107  and the dispersive assembly  103  is equal to a focal length of the second lens  107 , and a distance between the first lens  106  and spatial light modulator  104  is equal to the focal length of the first lens  106 . 
     It should be noted that the first lens  106  in this embodiment is different from the first lens  106  in the embodiment shown in  FIG. 4  and  FIG. 5 . In this embodiment, the first lens  106  may be a common convex lens, which refracts the second light beam in both the first plane and the second plane. 
     In addition, the second lens  107  is a cylindrical lens, and  FIG. 9  is a schematic diagram of a structure of the second lens. Different from the cylindrical lens shown in  FIG. 6 , when passing through the second lens  107 , the first light beam is refracted only in the second plane, and is not refracted in the first plane. 
     The three possible structures of the spectrum processing apparatus have been described above, and in all the foregoing three structures, a circulator may be used for each port to separate an input signal and an output signal. Optionally, each port in the port assembly  101  may also be classified as an input port and an output port. There may also be some changes in a structure of the spectrum processing apparatus in which the input port is distinguished from the output port. The following provides a description by using an example. 
     The second spectrum processing apparatus provided in  FIG. 5  is used as an example.  FIG. 10  is a top view of a structure of a fourth spectrum processing apparatus according to an embodiment of this application. Specifically, an input port and an output port are placed side by side in a first plane. In an input direction, each input port is configured to transmit an input first light beam to a lens corresponding to the input port. In an output direction, a light beam multiplexed by a dispersive assembly  103  is transmitted through a lens assembly  102  to an output port corresponding to the input port. As can be seen from  FIG. 10 , each port is classified as an input port and an output port, but the structure of the lens assembly  102 , the dispersive assembly  103 , a spatial light modulator  104 , and a first lens  106  remains the same as the structure of the embodiment shown in  FIG. 5 , except that the SLM adjusts a reflection direction of each sub-wavelength light beam such that a light beam multiplexed by the dispersive assembly  103  can be transmitted to the output port corresponding to the input port. For the several other spectrum processing apparatuses provided in the foregoing embodiments, an input port and an output port may also be distinguished in the manner shown in  FIG. 10 . Details are not described herein again. 
     It should be noted that the spectrum processing apparatus may further have a plurality of other structures different from the foregoing example, and structure variations based on the foregoing idea all fall within the protection scope of this application. The following further provides a possible structure of the spectrum processing apparatus. 
     Referring to  FIG. 11  and  FIG. 12 ,  FIG. 11  is a side view of a structure of a fifth spectrum processing apparatus according to an embodiment of this application, and  FIG. 12  is a top view of the structure of the fifth spectrum processing apparatus according to the embodiment of this application. 
     The spectrum processing apparatus includes: a port assembly  101 , a lens assembly  102 , a dispersive assembly  103 , a spatial light modulator  104 , a first lens  106 , a second lens  107 , and a third lens  108 . Descriptions of the port assembly  101 , the lens assembly  102 , the dispersive assembly  103 , and the spatial light modulator  104  are similar to the related descriptions of the embodiment shown in  FIG. 1 . Details are not described herein again. 
     Each input port in the port assembly  101  is configured to transmit an input first light beam to a lens corresponding to the port. Each lens in the lens assembly  102  is configured to adjust a width of the first light beam to obtain a second light beam, and transmit the second light beam to the third lens  108 . The third lens  108  is configured to refract the second light beam to the second lens  107  in a first plane ( FIG. 11  shows light beams in the first plane). The second lens  107  is configured to refract the second light beam to the dispersive assembly  103  in a second plane ( FIG. 10  shows light beams in the second plane), where the first plane is perpendicular to the second plane. The dispersive assembly  103  is configured to decompose the second light beam into a plurality of sub-wavelength light beams in the first plane, and transmit the plurality of sub-wavelength light beams to the first lens  106 . The first lens  106  is configured to refract the plurality of sub-wavelength light beams to the spatial light modulator  104  in the first plane and the second plane. The spatial light modulator  104  is configured to modulate the plurality of sub-wavelength light beams, and reflect at least one modulated sub-wavelength light beam to the first lens  106 . The first lens  106  is further configured to refract the at least one sub-wavelength light beam to the dispersive assembly  103  in the first plane and the second plane. The dispersive assembly  103  is further configured to multiplex the at least one sub-wavelength light beam, and transmit a multiplexed light beam successively through the second lens  107 , a third lens  108 , and the lens assembly  102  to an output port corresponding to the input port. 
     It should be noted that the first lens  106  in this embodiment is similar to the first lens  106  in the embodiment shown in  FIG. 7  and  FIG. 8 . Details are not described herein again. The second lens  107  in this embodiment is different from the second lens  107  in the embodiment shown in  FIG. 7  and  FIG. 8 . In this embodiment, the second lens  107  may be a common convex lens, which refracts the second light beam in both the first plane and the second plane. 
     In addition, the third lens  108  is a cylindrical lens, and a structure of the third lens  108  is similar to that of the cylindrical lens shown in  FIG. 6 . Details are not described herein again. 
     Optionally, on the basis of the various spectrum processing apparatuses listed above, the spectrum processing apparatus may further be provided with a polarization assembly  109 . The polarization assembly  109  is adjacent to the lens assembly  102 , and when seen from an input direction of a light beam, the polarization assembly  109  is located behind the lens assembly  102 . Specifically, in the input direction of the light beam, the polarization assembly  109  is configured to separate polarizations of the second light beam to obtain a first polarized light beam (o light) and a second polarized light beam (e light), and further transmit the first polarized light beam and the second polarized light beam along the input direction, where the first polarized light beam and the second polarized light beam have mutually orthogonal polarization components. Correspondingly, in an output direction of the light beam, the polarization assembly  109  is configured to restore the first polarized light beam and the second polarized light beam into a state before the separation, and further transmit a restored light beam along the output direction. 
     The following describes the spectrum processing apparatus including the polarization assembly  109  by using the structure of the second spectrum processing apparatus shown in  FIG. 4  as an example.  FIG. 13  is a side view of a structure of a sixth spectrum processing apparatus according to an embodiment of this application. The spectrum processing apparatus includes: a port assembly  101 , a lens assembly  102 , a dispersive assembly  103 , a spatial light modulator  104 , a first lens  106 , and a polarization assembly  109 . Descriptions of the port assembly  101 , the lens assembly  102 , the dispersive assembly  103 , and the spatial light modulator  104  are similar to the related descriptions of the embodiment shown in  FIG. 1 . Details are not described herein again. Specifically, the polarization assembly  109  decomposes a second light beam into a first polarized light beam (as shown by the solid line in  FIG. 13 ) and a second polarized light beam (as shown by the dashed line in  FIG. 13 ) in a second plane ( FIG. 13  shows light beams in the second plane). In addition, for the structures of the several other spectrum processing apparatuses listed above, the polarization assembly  109  may also be arranged with reference to the manner shown in  FIG. 13 . Details are not described herein again. 
     It should be noted that, applicable functions of the spectrum processing apparatus not only have different requirements for sizes of light spots formed on the SLM, but also have different requirements for insertion loss (IL) of each port. The spectrum processing apparatus shown in  FIG. 4  is used as an example. In optical design, a shorter distance between a port and an optic axis of the first lens  106  indicates smaller insertion loss of the port. Therefore, in design of distribution of ports, the ports may be symmetrically distributed with respect to the optic axis of the first lens  106 , so as to differentiate insertion loss of the ports during use, and select corresponding ports to implement different functions. It may be understood that, corresponding to the different structures of the foregoing spectrum processing apparatuses, symmetrical distribution of the ports may also be different. Specifically, in the spectrum processing apparatus shown in  FIG. 1 , the ports may be symmetrically distributed with respect to an optic axis of the reflective element  105  in a plane perpendicular to the plane shown in  FIG. 1 . In the spectrum processing apparatus shown in  FIG. 7 , the ports may be symmetrically distributed with respect to an optic axis of the first lens  106  or the second lens  107 . In the spectrum processing apparatus shown in  FIG. 11 , the ports may be symmetrically distributed with respect to an optic axis of the first lens  106 , the second lens  107 , or the third lens  108 . 
     For example, the port assembly  101  has a total of five ports that are distributed in sequence, namely, ports  1  to  5 . It is assumed that three different functions in total need to be allocated to the five ports, where one port is for wavelength blocking, two ports are for dynamic spectrum adjustment, and the other two ports are for spectrum scanning. According to insertion loss requirement analysis, because the port  3  is located in the middle position and has the smallest insertion loss for being closest to the optic axis, the port  1  is for wavelength blocking. In addition, because of the wavelength blocking to be implemented, a light spot of a light beam projected from the port  1  onto the spatial light modulator  104  should be relatively small. The port  1  and the port  5  are located at edge positions and have the largest insertion loss. Therefore, the port  1  and the port  5  are for spectrum scanning that is not sensitive to insertion loss. In addition, to improve accuracy of the spectrum scanning of the spectrum processing apparatus, light spots of light beams projected from the port  1  and the port  5  onto the spatial light modulator  104  should be relatively small. The port  2  and the port  4  are located between the middle port and the edge ports and have relatively moderate insertion loss. Therefore, the port  2  and the port  4  are for dynamic spectrum adjustment. In addition, dynamic spectrum adjustment requires that a spectrum curve be relatively smooth after adjustment, and light spots of light beams projected from the port  2  and the port  4  onto the spatial light modulator  104  should be relatively large. 
     It may be understood that, functions allocated to the ports in the port assembly  101  are subject to practical applications. This is not specifically limited herein. 
       FIG. 14  is a schematic diagram of a structure of a reconfigurable optical add-drop multiplexer (ROADM) according to an embodiment of this application. The ROADM includes an add module  201 , a drop module  202 , and a spectrum processing apparatus  203 . The spectrum processing apparatus  203  may be any one of the structures shown in  FIG. 1 ,  FIG. 4 ,  FIG. 5 ,  FIG. 7 ,  FIG. 8 ,  FIG. 10 ,  FIG. 11 ,  FIG. 12 , and  FIG. 13 . The spectrum processing apparatus  203  is configured to implement spectrum processing functions such as dynamic spectrum adjustment, spectrum scanning, and wavelength blocking. The add module  201  may include a plurality of transmitters, and is configured to add a local optical wavelength signal from the port assembly of the spectrum processing apparatus  203 . The drop module  202  may include a plurality of receivers, and is configured to drop a local optical wavelength signal from the port assembly of the spectrum processing apparatus  203 . 
     Referring to  FIG. 15  below, an embodiment shown in  FIG. 15  provides a signal transmission method using a spectrum processing apparatus. 
     Specifically, the spectrum processing apparatus in this embodiment of this application is the structure of the spectrum processing apparatus in the embodiment shown in  FIG. 1 . Details are not described herein again. 
     The method includes the following steps. 
       1501 : Each port in a port assembly transmits an input first light beam to a lens corresponding to the port. 
       1502 : Each lens in a lens assembly adjusts a width of the first light beam to obtain a second light beam, and transmits the second light beam to a reflective element. 
       1503 : The reflective element reflects the second light beam to a dispersive assembly. 
       1504 : The dispersive assembly decomposes the second light beam into a plurality of sub-wavelength light beams, and transmits the plurality of sub-wavelength light beams to the reflective element. 
       1505 : The reflective element reflects the plurality of sub-wavelength light beams to an SLM. 
       1506 : The SLM modulates the plurality of sub-wavelength light beams, and reflects at least one modulated sub-wavelength light beam to the reflective element. 
       1507 : The reflective element reflects the at least one sub-wavelength light beam to the dispersive assembly. 
       1508 : The dispersive assembly multiplexes the at least one sub-wavelength light beam, and transmits a multiplexed light beam successively through the reflective element and the lens assembly to the port assembly. 
     In this embodiment of this application, due to different sizes of light spots on the SLM, corresponding light beams are applicable to different functions. For example, a light beam corresponding to a small light spot is applicable to a wavelength blocking function, while a light beam corresponding to a large light spot is applicable to overall spectrum adjustment. In the spectrum processing apparatus provided in this application, the port assembly includes at least two ports, and each lens in the lens assembly can adjust a width of a light beam from a port. To be specific, a width of a light beam after passing through a lens may become larger or smaller, or may remain unchanged, and sizes of light spots formed by light beams of different widths on the SLM are also different. Therefore, the plurality of ports of the spectrum processing apparatus may be used to implement different functions, thereby enriching functions of the spectrum processing apparatus. 
     Referring to  FIG. 16  below, an embodiment shown in  FIG. 16  provides another signal transmission method using a spectrum processing apparatus. 
     Specifically, the spectrum processing apparatus in this embodiment of this application is the structure of the spectrum processing apparatus in the embodiment shown in  FIG. 4  and  FIG. 5 . Details are not described herein again. 
     The method includes the following steps. 
       1601 : Each port in a port assembly transmits an input first light beam to a lens corresponding to the port. 
       1602 : Each lens in a lens assembly adjusts a width of the first light beam to obtain a second light beam, and transmits the second light beam to a dispersive assembly. 
       1603 : The dispersive assembly decomposes the second light beam into a plurality of sub-wavelength light beams in a first plane, and transmits the plurality of sub-wavelength light beams to a first lens. 
       1604 : The first lens refracts the plurality of sub-wavelength light beams to an SLM in the first plane, and transmits the plurality of sub-wavelength light beams to the SLM in a second plane, where the second plane is perpendicular to the first plane. 
       1605 : The SLM modulates the plurality of sub-wavelength light beams, and reflects at least one modulated sub-wavelength light beam to the first lens. 
       1606 : The first lens refracts the at least one sub-wavelength light beam to the dispersive assembly in the first plane, and transmits the at least one sub-wavelength light beam to the dispersive assembly in the second plane. 
       1607 : The dispersive assembly multiplexes the at least one sub-wavelength light beam, and transmits a multiplexed light beam through the lens assembly to the port assembly. 
     Referring to  FIG. 17  below, an embodiment shown in  FIG. 17  provides another signal transmission method using a spectrum processing apparatus. 
     Specifically, the spectrum processing apparatus in this embodiment of this application is the structure of the spectrum processing apparatus in the embodiment shown in  FIG. 7  and  FIG. 8 . Details are not described herein again. 
     The method includes the following steps. 
       1701 : Each port in a port assembly transmits an input first light beam to a lens corresponding to the port. 
       1702 : Each lens in a lens assembly adjusts a width of the first light beam to obtain a second light beam, and transmits the second light beam to a second lens. 
       1703 : The second lens refracts the second light beam to a dispersive assembly in a second plane. 
       1704 : The dispersive assembly decomposes the second light beam into a plurality of sub-wavelength light beams in a first plane, and transmits the plurality of sub-wavelength light beams to a first lens, where the first plane is perpendicular to the second plane. 
       1705 : The first lens refracts the plurality of sub-wavelength light beams to an SLM in the first plane and the second plane. 
       1706 : The SLM modulates the plurality of sub-wavelength light beams, and reflects at least one modulated sub-wavelength light beam to the first lens. 
       1707 : The first lens refracts the at least one sub-wavelength light beam to the dispersive assembly in the first plane and the second plane. 
       1708 : The dispersive assembly multiplexes the at least one sub-wavelength light beam, and transmits a multiplexed light beam successively through the second lens and the lens assembly to the port assembly. 
     It should be noted that the foregoing embodiments are merely used to describe the technical solutions of this application, but are not intended to limit this application. Although this application is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features thereof, without departing from the spirit and scope of the technical solutions of the embodiments of this application.