WO2024099578A1

WO2024099578A1 - Optical apparatus and method for selective wavelength switching of light

Info

Publication number: WO2024099578A1
Application number: PCT/EP2022/081659
Authority: WO
Inventors: Aurelian Dodoc
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2022-11-11
Filing date: 2022-11-11
Publication date: 2024-05-16

Abstract

An optical apparatus (100) for selective wavelength switching of light is disclosed. The optical apparatus (100) comprises a first spatial light modulator, SLM, (120) configured to receive and redirect a plurality of demultiplexed light input waveband channels and a second SLM (160) positioned along an optical axis at a distance D from the first SLM (120) and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM (160). The optical axis defines a first plane of symmetry and a second plane of symmetry perpendicular to the first plane of symmetry of the optical apparatus (100). Moreover, the optical apparatus (100) comprises a plurality of lens arrangements positioned between the first SLM (120) and the second SLM (160) to redirect the plurality of demultiplexed light input channels received from the first SLM (120) in the direction of the second SLM (160). The plurality of lens arrangements comprise a first lens arrangement with a refractive power primarily in the first plane of symmetry, a second lens arrangement with a first refractive power in the first plane of symmetry and a second refractive power different from the first refractive power in the second plane of symmetry, and a third lens arrangement with a refractive power primarily in the first plane of symmetry and being positioned on the optical axis between the second lens arrangement and the second SLM (160) within about a quarter of the distance D from an intersection point with the optical axis of a light beam propagating from a point on the optical axis on the first SLM (120) in the first plane of symmetry towards the second SLM (160).

Description

Optical apparatus and method for selective wavelength switching of light

TECHNICAL FIELD

The present disclosure relates to optical technology for optical fiber communication networks. More specifically, the present disclosure relates to an optical apparatus and method for selective wavelength switching (also referred to as cross-connecting) of light.

BACKGROUND

Optical networks are networks that use optical signals to carry data. Light sources such as lasers generate optical signals. Modulators modulate the optical signals with data to generate modulated optical signals. Various components transmit, propagate, amplify, receive, and process the modulated optical signals, such as optical fibers and optical multiplexers/demultiplexers allowing to achieve higher bandwidths for optical networks. More details about switching architectures in optical networks can be found in the review article “Survey of Photonic Switching Architectures and Technologies in Support of Spatially and Spectrally Flexible Optical Networking”, Marom Dan, et. al., JOSA, VOL. 8, No. 1 , 2017.

SUMMARY

It is an objective of the present disclosure to provide an improved optical apparatus (herein also referred to as an optical multiplexer/demultiplexer) and method for selective wavelength switching of light.

The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect an anamorphic optical apparatus for selective wavelength switching of light is provided. The optical apparatus comprises a first spatial light modulator, SLM, configured to receive and redirect a plurality of demultiplexed light input waveband channels, wherein each light input waveband channel comprises a plurality of light beams. Moreover, the optical apparatus comprises a second SLM positioned along an optical axis at a distance D from the first SLM and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM, wherein the optical axis defines a first plane of symmetry and a second plane of symmetry perpendicular to the first plane of symmetry of the optical apparatus. The optical apparatus further comprises a plurality of lens arrangements positioned between the first SLM and the second SLM to redirect the plurality of demultiplexed light input waveband channels received from the first SLM in the direction of the second SLM. The plurality of lens arrangements comprises a first lens arrangement with a refractive power primarily in the first plane of symmetry and a second lens arrangement with a first refractive power in the first plane of symmetry and a second refractive power different from the first refractive power in the second plane of symmetry. Moreover, the plurality of lens arrangements comprises a third lens arrangement with a refractive power primarily in the first plane of symmetry and being positioned on the optical axis between the second lens arrangement and the second SLM within about a quarter of the distance D from an intersection point with the optical axis of a light beam propagating from a point on the optical axis on the first SLM in the first plane of symmetry towards the second SLM. The optical apparatus for selective wavelength switching of light has a compact design. Moreover, the optical apparatus is configured for beam steering in both directions, thus X-Y steering. This allows the input ports to be arranged in a multi-dimension array further reducing the optical active diameters and so the general size of the optical apparatus.

In a further possible implementation form, the plurality of lens arrangements positioned between the first SLM and the second SLM define an afocal optical system between the first SLM and the second SLM in the first plane of symmetry.

In a further possible implementation form, each of the plurality of lens arrangements has a first focal length and corresponding front and rear focal points in the first plane of symmetry and a second focal length and corresponding front and rear focal points in the second plane of symmetry.

In a further possible implementation form, the second lens arrangement comprises a microlens array positioned within about a quarter of the distance D from a point on the optical axis halfway between the first SLM and the second SLM. The micro-lenses in the micro-lens array may be implemented with an optical power based on refractive or diffractive effects, for instance, a liquid crystal.

In a further possible implementation form, the micro-lens array is positioned in the vicinity of the rear focal point of the first lens arrangement in the first plane of symmetry within about a quarter of the focal length of the first lens arrangement in the first plane of symmetry and/or the micro-lens array is positioned in the vicinity of the front focal point of the third lens arrangement in the first plane of symmetry within about a quarter of the focal length of the third lens arrangement in the first plane of symmetry. In a further possible implementation form, the first SLM is positioned in the vicinity of the front focal point of the second lens arrangement in the second plane of symmetry within about a quarter of the focal length of the second lens arrangement in the second plane of symmetry and the second SLM is positioned in the vicinity of the rear focal point of the second lens arrangement in the second plane of symmetry within about a quarter of the focal length of the second lens arrangement in the second plane of symmetry.

In a further possible implementation form, the first SLM is positioned in the vicinity of the front focal point of the first lens arrangement in the first plane of symmetry within about a quarter of the focal length of the first lens arrangement in the first plane of symmetry and the second SLM is positioned in the vicinity of the rear focal point of the third lens arrangement in the first plane of symmetry within about a quarter of the focal length of the third lens arrangement in the first plane of symmetry.

In a further possible implementation form, the first SLM is positioned in the vicinity of the front unit magnification point at about a distance of twice the focal length of the first lens arrangement in the first plane of symmetry within about a quarter of the focal length of the first lens arrangement in the first plane of symmetry and the second SLM is positioned in the vicinity of the rear unit magnification point at about twice the focal length of the third lens arrangement in the first plane of symmetry within about a quarter of the focal length of the third lens arrangement in the first plane of symmetry.

In a further possible implementation form, the micro-lenses of the micro-lens array have a first refractive power in the first plane of symmetry and a second refractive power in the second plane of symmetry different from the first refractive power.

In a further possible implementation form, the refractive power of the micro-lenses of the micro lens array in the second plane of symmetry is a zero refractive power and the micro-lenses of the micro lens array are cylindrically shaped micro-lenses.

In a further possible implementation form, the first and third lens arrangement have refractive power primarily in the first plane of symmetry.

In a further possible implementation form, the first SLM and/or the second SLM comprises a liquid crystal on silicon device and/or a digital mirror device. In a further possible implementation form, the optical apparatus further comprises: a first dispersive optical element configured to disperse one or more input light beams into the plurality of light input waveband channels and to direct the plurality of light input waveband channels onto the first SLM; and/or a second dispersive optical element configured to receive a plurality of light output waveband channels from the second SLM and combine the plurality of light output waveband channels from the second SLM into one or more output light beams.

In a further possible implementation form, the first dispersive optical element and/or the second dispersive optical element comprises a grating, a prism and/or a grism.

According to a second aspect a method for selective wavelength switching of light by an optical apparatus is provided. The optical apparatus comprises a first SLM configured to receive and redirect a plurality of demultiplexed light input waveband channels, wherein each light input waveband channel comprises a plurality of light beams, and a second SLM positioned along an optical axis at a distance D from the first SLM and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM, wherein the optical axis defines a first plane of symmetry and a second plane of symmetry perpendicular to the first plane of symmetry of the optical apparatus. The method comprises a step of redirecting, by a plurality of lens arrangements of the optical apparatus positioned between the first SLM and the second SLM, the plurality of demultiplexed light input waveband channels received from the first SLM in the direction of the second SLM, wherein the plurality of lens arrangements comprise: a first lens arrangement with a refractive power primarily in the first plane of symmetry; a second lens arrangement with a first refractive power in the first plane of symmetry and a second refractive power, different from the first refractive power in the second plane of symmetry; and a third lens arrangement with a refractive power primarily in the first plane of symmetry and being positioned on the optical axis between the second lens arrangement and the second SLM within about a quarter of the distance D from an intersection point with the optical axis of a light beam propagating from a point on the optical axis on the first SLM in the first plane of symmetry towards the second SLM.

The method according to the second aspect of the present disclosure can be performed by the optical apparatus according to the first aspect of the present disclosure. Thus, further features of the method according to the second aspect of the present disclosure, result directly from the functionality of the optical apparatus according to the first aspect of the present disclosure as well as its different implementation forms described above and below. Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

Fig. 1 shows a schematic diagram illustrating an optical apparatus for selective wavelength switching of light according to an embodiment;

Figs. 2a-d show tables illustrating some examples of input ports arrangements and possible waveband channels distributions on a first SLM of an optical apparatus according to an embodiment;

Fig. 3 shows two schematic cross-sectional side views of an optical apparatus for selective wavelength switching of light according to an embodiment;

Fig. 4 shows two schematic cross-sectional side views of an optical apparatus for selective wavelength switching of light according to a further embodiment; and

Fig. 5 shows a flow diagram illustrating steps of a method for operating an optical apparatus for selective wavelength switching of light according to an embodiment.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1 shows a schematic diagram illustrating an optical apparatus (also referred to as optical multiplexer/demultiplexer) 100 for selective wavelength switching of light according to an embodiment from a plurality of input ports to a plurality of output ports. Each input and output port may contain one or more data carrying waveband channels so that the optical apparatus 100 is configured to recombine and redirect a plurality of input data channels to the plurality of output ports. The input ports may be connected to optical fibers, wherein each optical fiber transmits the one more data carrying waveband channels. As will be described in more detail below, the optical apparatus 100 shown in figure 1 is adapted for the exemplary waveband channel distribution illustrated in figure 2c. In this embodiment, as illustrated in figure 1 , the plurality of input ports are arranged in a two-dimensional array with multiple rows, particularly two rows and multiple columns. Because of this compact arrangement of the input ports two rows of channels with the same wavelength are generated on a first spatial light modulator, SLM, 120 of the optical apparatus 100 and steered by an optical system 180 of the optical apparatus 100 in two dimensions X and Y to a second SLM 160 of the optical apparatus 100 in order to interconnect all input channels to corresponding output channels.

More specifically, the optical apparatus 100 comprises the first SLM 120 configured to receive and redirect a plurality of demultiplexed light input waveband channels, for instance, the eight exemplary waveband channels An to 24 illustrated in figure 1. As will be appreciated, each light input waveband channel comprises a plurality of light beams. The optical apparatus 100 further comprises the second SLM 160 positioned along a main optical axis OA at a distance D from the first SLM 120 and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM 120. In an embodiment, the first SLM 120 and/or the second SLM 160 may be implemented as a liquid crystal on silicon device (also referred to as a LCOS device) and/or a digital mirror device. As schematically indicated in figure 1 , the optical apparatus 100 further comprises the optical system 180 arranged between the first SLM 120 and the second SLM 160 for guiding the light emitted by a respective portion of the first SLM 120 to a selectable desired portion of the second SLM 160. By way of example, as illustrated in figure 1 , the optical system 180 of the optical apparatus 100 is configured to guide a first light input waveband channel An provided by a first input port In to a portion of the second SLM 160 associated with a first light output waveband channel connected with one of the output ports. Detailed embodiments of the optical system 180 of the optical apparatus 100 will be described below.

For generating the plurality of demultiplexed light input waveband channels based on the light input ports li._N, the optical apparatus 100 may further comprise a first dispersive optical element 110 (shown in figures 3 and 4) configured to disperse one or more input light beams into the plurality of light input waveband channels and to direct the plurality of light input channels onto the first SLM 120. Additionally, the optical apparatus 100 may further comprise a second dispersive optical element 170 (also shown in figures 3 and 4) configured to receive the plurality of light output waveband channels from the second SLM 160 and combine the plurality of light output waveband channels from the second SLM 160 into one or more output light beams, further directed to a specific output port of the N output ports OI-N. In an embodiment, the first dispersive optical element 110 and/or the second dispersive optical element 170 may comprise a grating, a prism and/or a grism.

Figure 2 shows four tables illustrating some examples of input port arrangements and possible waveband channels distributions on the first SLM 120. In a first table shown in figure 2a the input port arrangement is in a one-dimensional array of N input ports li._N. Correspondingly the demultiplexed input light waveband channels are arranged in a two-dimensional array on the first SLM 120. The columns correspond to the different input ports ._N and the rows corresponds to the different waveband channels AI-L. In the following tables shown in figure 2b to 2d, the N input ports ._N are arranged in an array comprising multiple rows particularly two rows I11-1N/2 and I21-2N/2 with N/2 columns but with different waveband channel arrangements. In figure 2b the waveband channels from two input ports arranged in the same column are interleaved represented on the first SLM 120 in one column, so that two waveband channels with the same waveband but from different input ports are adjacent, thus 21 is following An and A2L/2 is following A1L/2. As a consequence, the wavebands An and A12 from port In and correspondingly A21 and A22 from port I21 are not connected in this configuration, because in between the two subsequent waveband channels there is a wavelength gap as long as a waveband channel itself. So, in an input port, the carrying waveband channels may be individual and not connected to each other. This arrangement corresponds to the optical system 180 shown figure 1 . In figure 2c the sequence of connected waveband channels in an input port is larger comprising two connected wavebands so that for example the connected wavebands A21 and A22 are adjacent to the connected wavebands An and A12. In this particular case, the gap is as large as two connected wavebands. In figure 2d all the waveband channels from an input port are connected but the waveband channels from an input port in the first row are different from the waveband channels of the second input port in the same input ports column. So, if the optical apparatus 100 is working for example in the C and L wavebands, the first row of input ports may contain the C band, while the second row of input ports may contain the L band. This case corresponds also with the arrangement in table 2a where the input ports contain all C and L waveband channels. On the second SLM 160 the channel distribution may be the same. The advantage of the multi row distribution of input ports is a more compact size in one dimension of the optical apparatus 100.

An important consequence of port distribution is the type of steering. While the one row distribution involves one-dimensional steering, the multirow distribution usually requires a two- dimensional steering.

In the following embodiments of the optical switching system 180 of the optical apparatus 100 will be described under further reference to figures 3 and 4. Both figure 3 and 4 show two schematic cross-sectional side views of the optical switching system 180 of the optical apparatus 100 for two different embodiments in a first plane of symmetry, namely the Y-Z plane and in a second plane of symmetry, namely the X-Z plane. As will be appreciated, both embodiments shown in figures 3 and 4 illustrate an anamorphic optical switching system 180 having different optical properties in the Y-Z plane and the X-Z plane. More specifically, in the embodiments shown in figures 3 and 4 the X-Z plane defines the switching direction, while the Y-Z plane defines the dispersion direction of the optical apparatus 100. The embodiments disclosed in figures 3 and 4 allow providing a small switching angle in the switching direction, while keeping the beam structure in the dispersion direction. Although the X direction in the X- Z plane is called switching direction, beam steering may be done in both X and Y directions, i.e. the steering may be two-dimensional.

In the embodiments of figures 3 and 4 the optical switching system 180 of the optical apparatus 100 comprises a plurality of lens arrangements positioned between the first SLM 120 and the second SLM 160 to redirect the plurality of demultiplexed light input waveband channels received from the first SLM 120 in the direction of the second SLM 160. The plurality of lens arrangements comprises a first lens arrangement 130 along the optical axis OA with a refractive power primarily in the first plane of symmetry, i.e. the Y-Z plane. As indicated in figures 3 and 4, in an embodiment the first lens arrangement 130 may be implemented as a biconvex Y-lens, i.e. a lens having refractive power only in the first plane of symmetry, i.e. the Y-Z plane.

Moreover, the plurality of lens arrangements comprises a second lens arrangement 140a-c along the optical axis OA with a first refractive power in the first plane of symmetry, i.e. the Y- Z plane and a second refractive power different from the first refractive power in the second plane of symmetry, i.e. the X-Z plane.

The plurality of lens arrangements further comprise a third lens arrangement 150 with a refractive power primarily in the first plane of symmetry, i.e. the Y-Z plane and being positioned on the optical axis OA between the second lens arrangement 140a-c and the second SLM 160 within about a quarter of the distance D from an intersection C point with the optical axis OA of a light beam propagating from a point on the optical axis OA on the first SLM 120 in the first plane of symmetry, i.e. the Y-Z plane towards the second SLM 160.

The plurality of lens arrangements 130, 140a-c, 150 positioned between the first SLM 120 and the second SLM 160 of the embodiments shown in figures 3 and 4 define an afocal optical system between the first SLM 120 and the second SLM 160 in the first plane of symmetry, i.e. the Y-Z plane, and this allows the conservation of the waveband channel structure from the first SLM 120 to the second SLM 160 so that parallel beams emerging from the first SLM 120 will infringe in parallel on the second SLM 160. Each of the plurality of lens arrangements may 130, 140a-c, 150 have a first focal length and corresponding front and rear focal points in the first plane of symmetry and a second focal length and corresponding front and rear focal points in the second plane of symmetry.

In the embodiment shown in figure 3, the optical switching system 180 of the optical apparatus 100 of figure 1 with the first, second and third lens arrangement between the first SLM 120 and the second SLM 160 defines in the first symmetry plane, i.e. the Y-Z dispersion plane a “4Fi” system and in the second symmetry plane, i.e. the X-Z plane a “2F2” system, meaning that the distance D between the first SLM 120 and the second SLM 160 is four times the first focal length F1 of the first lens arrangement 130 or the third lens arrangement 150 in the Y-Z plane and two times the second focal length F2 of the second lens arrangement 140 in the X-Z plane. Both the first lens arrangement 130 and the second lens arrangement 150 have a positive refractive power in the Y-Z plane and may be implemented as a biconvex Y lens 130, 150 with refractive power only in the Y-Z plane with the focal length Fi. Moreover, in the embodiment shown in figure 3, the third lens arrangement 150 is positioned on the optical axis OA substantially at the intersection point C with the optical axis OA of a light beam propagating from a point on the optical axis OA on the first SLM 120 in the first plane of symmetry, i.e. the Y-Z plane towards the second SLM 160. As will be appreciated, in the embodiment shown in figure 3, the first lens arrangement 130 is positioned substantially at a distance Fi from the first SLM 120, the second lens arrangement 140a-c is positioned substantially at a distance 2Fi from the first SLM 120 and the third lens arrangement 150 is positioned substantially at a distance 3Fi from the first SLM 120 (and at a distance Fi from the second SLM 160).

In the embodiment shown in figure 3, the second lens arrangement 140a-c with a first refractive positive power in the first plane of symmetry, i.e. the Y-Z plane, which may be implemented as a biconvex Y lens 140c with positive refractive power in the Y-Z plane, and a second positive refractive power different from the first refractive power in the second plane of symmetry, i.e. the X-Z plane, which may be implemented as a biconvex X lens 140b with positive refractive power in the X-Z plane, further comprises (in that order along the optical axis OA) a onedimensional multi-lens array 140a (comprising a plurality of micro-lenses) with negative refractive power lenslets in the Y-Z plane only. As will be appreciated, the one-dimensional multi-lens array 140a has only the effect of focusing the light beams on the second SLM 160. For the embodiment of the optical apparatus 100 shown in figure 1 with two rows of input ports the one-dimensional multi-lens array 140a may comprise three micro-lenses, in particular three long cylindrical micro-lenses with negative refractive power in the dispersion direction i.e. the Y-Z plane and no refractive power in the switching direction i.e. the X-Z plane. As will be appreciated, the proper selection of the refractive power for these micro lenses allows focusing of the beams on the second SLM 160 without influencing the beam direction.

In the embodiment shown in figure 4, the optical switching system 180 of the optical apparatus 100 of figure 1 with the first, second and third lens arrangement between the first SLM 120 and the second SLM 160 defines in the first symmetry plane, i.e. the Y-Z dispersion plane a “6F1” system and in the second symmetry plane, i.e. the X-Z switching plane a “2F2” system, meaning that the distance D between the first SLM 120 and the second SLM 160 is six times the first focal length Fi of the first lens arrangement 130 or the third lens arrangement 150 in the Y-Z plane and two times the second focal length F2 of the first lens arrangement 130 or the third lens arrangement 150 in the Y-Z plane. As in the embodiment shown in figure 3, both the first lens arrangement 130 and the third lens arrangement 150 may be implemented as a biconvex Y lens 130, 150 with refractive power only in the Y-Z plane with the focal length Fi. Moreover, also in the embodiment shown in figure 4, the third lens arrangement 150 is positioned on the optical axis OA substantially at the intersection point C with the optical axis OA of a light beam propagating from a point on the optical axis OA on the first SLM 120 in the first plane of symmetry, i.e. the Y-Z plane towards the second SLM 160. As will be appreciated, in the embodiment shown in figure 4, the first lens arrangement 130 is positioned substantially at a distance 2Fi from the first SLM 120, the second lens arrangement 140a-c is positioned substantially at a distance 3Fi from the first SLM 120 and the third lens arrangement 150 is positioned substantially at a distance 4Fi from the first SLM 120 (and at a distance 2Fi from the second SLM 160). In the X-Z plane, the second lens arrangement 140a-c is positioned at a distance F2 from the first SLM 120 and the second SLM 160.

In the embodiment shown in figure 4, the second lens arrangement 140a, b with a first refractive power in the first plane of symmetry, i.e. the Y-Z plane and a second refractive power different from the first refractive power in the second plane of symmetry, i.e. the X-Z plane comprises (in that order along the optical axis OA) a one-dimensional multi-lens array 140a (comprising a plurality of micro-lenses) with negative refractive power in the Y-Z plane only, and a biconvex X lens 140b with positive refractive power in the X-Z plane. The one-dimensional multi-lens array 140a may be configured in the same way as the one-dimensional multi-lens array 140a of the embodiment shown in figure 3.

As illustrated in figures 3, in this embodiment the first and third lens arrangement 130, 150 may also be used to focus the optical path between the first dispersive element 110 and the first SLM 120 and the optical path between the second dispersive element 170 and the second SLM 160, respectively. In the embodiment shown in figure 4 two supplementary lens arrangements 115 and 165 may be used to focus the optical beams between the first dispersive element 110 and the first SLM 120 and the optical beams between the second dispersive element 170 and the second SLM 160, respectively.

According to a variant of the embodiments shown in figures 3 and 4, in further embodiments of the optical apparatus the micro-lens array 140a may be positioned within about a quarter of the distance D from a point on the optical axis OA halfway between the first SLM 120 and the second SLM 160. In a further embodiment, the micro-lens array 140a may be positioned in the vicinity of the rear focal point of the first lens arrangement 130 in the first plane of symmetry within about a quarter of the focal length F1 of the first lens arrangement 130 in the first plane of symmetry and/or the micro-lens array 140a may be positioned in the vicinity of the front focal point of the third lens arrangement 150 in the first plane of symmetry within about a quarter of the focal length F1 of the third lens arrangement 150 in the first plane of symmetry. According to a further embodiment, the first SLM 120 may be positioned in the vicinity of the front focal point of the second lens arrangement 140a-c in the second plane of symmetry within about a quarter of the focal length of the second lens arrangement 140a-c in the second plane of symmetry and the second SLM 160 may be positioned in the vicinity of the rear focal point of the second lens arrangement 140a-c in the second plane of symmetry within about a quarter of the focal length of the second lens arrangement 140a-c in the second plane of symmetry.

According to a further embodiment, the first SLM 120 may be positioned in the vicinity of the front focal point of the first lens arrangement 130 in the first plane of symmetry within about a quarter of the focal length Fi of the first lens arrangement 130 in the first plane of symmetry and the second SLM 160 may be positioned in the vicinity of the rear focal point of the third lens arrangement 150 in the first plane of symmetry within about a quarter of the focal length Fi of the third lens arrangement 150 in the first plane of symmetry.

In a further embodiment, the first SLM 120 may be positioned in the vicinity of the front unit magnification point at about a distance of twice the focal length of the first lens arrangement 130 in the first plane of symmetry within about a quarter of the focal length Fi of the first lens arrangement 130 in the first plane of symmetry and the second SLM 160 may be positioned in the vicinity of the rear unit magnification point at about twice the focal length Fi of the third lens arrangement 150 in the first plane of symmetry within about a quarter of the focal length Fi of the third lens arrangement 150 in the first plane of symmetry.

Figure 5 shows a flow diagram illustrating steps of a method 500 for operating the optical apparatus 100 for selective wavelength switching of light according to an embodiment. As already described above, the optical apparatus 100 comprises a first SLM 120 configured to receive and redirect a plurality of demultiplexed light input channels, wherein each light input channel comprises a plurality of light beams, and a second SLM 160 positioned along an optical axis OA at a distance D from the first SLM 120 and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM 120. The optical axis OA defines a first plane of symmetry (for instance, the Y-Z plane indicated in figures 3 and 4) and a second plane of symmetry (for instance, the X-Z plane indicated in figures 3 and 4) perpendicular to the first plane of symmetry of the optical apparatus 100. The method 500 comprises a step 501 of redirecting, by a plurality of lens arrangements positioned between the first SLM 120 and the second SLM 160, the plurality of demultiplexed light input waveband channels received from the first SLM 120 in the direction of the second SLM 160. The plurality of lens arrangements comprise: a first lens arrangement 130 with a refractive power primarily in the first plane of symmetry; a second lens arrangement 140a-c with a first refractive power in the first plane of symmetry and a second refractive power different from the first refractive power in the second plane of symmetry; and a third lens arrangement 150 with a refractive power primarily in the first plane of symmetry and being positioned on the optical axis OA between the second lens arrangement 140a-c and the second SLM 160 within about a quarter of the distance D from an intersection point C with the optical axis OA of a light beam propagating from a point on the optical axis OA on the first SLM 120 in the first plane of symmetry towards the second SLM 160.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

1. An optical apparatus (100) for selective wavelength switching of light, wherein the optical apparatus (100) comprises: a first spatial light modulator, SLM, (120) configured to receive and redirect a plurality of demultiplexed light input waveband channels, each light input waveband channel comprising a plurality of light beams; a second SLM (160) positioned along an optical axis (OA) at a distance D from the first SLM (120) and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM (120), wherein the optical axis (OA) defines a first plane of symmetry and a second plane of symmetry perpendicular to the first plane of symmetry of the optical apparatus (100); and a plurality of lens arrangements positioned between the first SLM (120) and the second SLM (160) to redirect the plurality of demultiplexed light input waveband channels received from the first SLM (120) in the direction of the second SLM (160), wherein the plurality of lens arrangements comprise: a first lens arrangement (130) with a refractive power primarily in the first plane of symmetry; a second lens arrangement (140a-c) with a first refractive power in the first plane of symmetry and a second refractive power, different from the first refractive power in the second plane of symmetry; and a third lens arrangement (150) with a refractive power primarily in the first plane of symmetry and being positioned on the optical axis (OA) between the second lens arrangement (140a-c) and the second SLM (160) within about a quarter of the distance D from an intersection point (C) with the optical axis (OA) of a light beam propagating from a point on the optical axis (OA) on the first SLM (120) in the first plane of symmetry towards the second SLM (160).

2. The optical apparatus (100) of claim 1 , wherein the plurality of lens arrangements positioned between the first SLM (120) and the second SLM (160) define an afocal optical system between the first SLM (120) and the second SLM (160) in the first plane of symmetry.

3. The optical apparatus (100) of any one of the preceding claims, wherein each of the plurality of lens arrangements has a first focal length and corresponding front and rear focal points in the first plane of symmetry and a second focal length and corresponding front and rear focal points in the second plane of symmetry.

4. The optical apparatus (100) of claim 3, wherein the second lens arrangement (140a-c) comprises a micro-lens array (140a) positioned within about a quarter of the distance D from a point on the optical axis (OA) halfway between the first SLM (120) and the second SLM (160).

5. The optical apparatus (100) of claim 4, wherein the micro-lens array (140a) is positioned in the vicinity of the rear focal point of the first lens arrangement (130) in the first plane of symmetry within about a quarter of the focal length of the first lens arrangement (130) in the first plane of symmetry and/or the micro-lens array (140a) is positioned in the vicinity of the front focal point of the third lens arrangement (150) in the first plane of symmetry within about a quarter of the focal length of the third lens arrangement (150) in the first plane of symmetry.

6. The optical apparatus (100) of claim 4 or 5, wherein the first SLM (120) is positioned in the vicinity of the front focal point of the second lens arrangement (140a-c) in the second plane of symmetry within about a quarter of the focal length of the second lens arrangement (140a- c) in the second plane of symmetry and the second SLM (160) is positioned in the vicinity of the rear focal point of the second lens arrangement (140a-c) in the second plane of symmetry within about a quarter of the focal length of the second lens arrangement (140a-c) in the second plane of symmetry.

7. The optical apparatus (100) of any one of claims 4 to 6, wherein the first SLM (120) is positioned in the vicinity of the front focal point of the first lens arrangement (130) in the first plane of symmetry within about a quarter of the focal length of the first lens arrangement (130) in the first plane of symmetry and the second SLM (160) is positioned in the vicinity of the rear focal point of the third lens arrangement (150) in the first plane of symmetry within about a quarter of the focal length of the third lens arrangement (150) in the first plane of symmetry.

8. The optical apparatus (100) of any one of claims 4 to 6, wherein the first SLM (120) is positioned in the vicinity of the front unit magnification point at about a distance of twice the focal length of the first lens arrangement (130) in the first plane of symmetry within about a quarter of the focal length of the first lens arrangement (130) in the first plane of symmetry and the second SLM (160) is positioned in the vicinity of the rear unit magnification point at about twice the focal length of the third lens arrangement (150) in the first plane of symmetry within about a quarter of the focal length of the third lens arrangement (150) in the first plane of symmetry.

9. The optical apparatus (100) of any of claims 4 to 8, wherein the micro-lenses of the micro-lens array (140a) have a first refractive power in the first plane of symmetry and a second refractive power in the second plane of symmetry different from the first refractive power.

10. The optical apparatus (100) of any one of claims 4 to 8, wherein the micro-lenses of the micro-lens array (140a) have a first refractive power in the first plane of symmetry and substantially no refractive power in the second plane of symmetry different from the first refractive power.

11 . The optical apparatus (100) of any one of the preceding claims, wherein the first and third lens arrangement (130, 150) have refractive power primarily in the first plane of symmetry.

12. The optical apparatus (100) of any one of the preceding claims, wherein the first SLM (120) and/or the second SLM (160) comprises a liquid crystal on silicon device and/or a digital mirror device.

13. The optical apparatus (100) of any one of the preceding claims, wherein the optical apparatus (100) further comprises: a first dispersive optical element (110) configured to disperse one or more input light beams into the plurality of light input waveband channels and to direct the plurality of light input waveband channels onto the first SLM (120); and/or a second dispersive optical element (170) configured to receive a plurality of light output channels from the second SLM (160) and combine the plurality of light output channels from the second SLM (160) into one or more output light beams.

14. The optical apparatus (100) of claim 12, wherein the first dispersive optical element (110) and/or the second dispersive optical element (170) comprises a grating, a prism and/or a grism.

15. A method (500) for selective wavelength switching of light by an optical apparatus (100), the optical apparatus (100) comprising a first spatial light modulator, SLM, (120) configured to receive and redirect a plurality of demultiplexed light input waveband channels, wherein each light input waveband channel comprises a plurality of light beams, and a second SLM (160) positioned along an optical axis (OA) at a distance D from the first SLM (120) and configured to receive and redirect the plurality of demultiplexed light input waveband channels redirected by the first SLM (120), wherein the optical axis (OA) defines a first plane of symmetry and a second plane of symmetry perpendicular to the first plane of symmetry of the optical apparatus (100), wherein the method (500) comprises: redirecting (501), by a plurality of lens arrangements positioned between the first SLM (120) and the second SLM (160), the plurality of demultiplexed light input waveband channels received from the first SLM (120) in the direction of the second SLM (160), wherein the plurality of lens arrangements comprise: a first lens arrangement (130) with a refractive power primarily in the first plane of symmetry; a second lens arrangement (140a-c) with a first refractive power in the first plane of symmetry and a second refractive power, different from the first refractive power in the second plane of symmetry; and a third lens arrangement (150) with a refractive power primarily in the first plane of symmetry and being positioned on the optical axis (OA) between the second lens arrangement (140a-c) and the second SLM (160) within about a quarter of the distance D from an intersection point (C) with the optical axis (OA) of a light beam propagating from a point on the optical axis (OA) on the first SLM (120) in the first plane of symmetry towards the second SLM (160).