**1. Introduction**

There has been significant growth in the required capacity of the telecommunication systems, which can be attributed to the proliferation of mobile devices, bandwidth-intensive applications, and services [1–3]. As a result, a significant increase in the broadband connections as well as the related multimedia traffic on a yearly basis [4–6] has been progressing. Moreover, the traffic explosion has been one of the challenges being faced in telecommunication systems [2, 7]. Also, it has been observed that the traditional electronic media which are based on copper are unable to meet the system requirements majorly in terms of bandwidth and latency [5, 8–10].

To address the challenges, optical fiber-based transport systems have been employed in different fields of communication systems as viable and reliable solutions. The widely employed optical transport systems are based on single-mode fiber (SMF). To enhance the capacity of single-core SMF, advanced modulation formats and wavelength division multiplexing (WDM) are normally employed. However, the growing demand for further video/image storage capacity and the increase in cloud service adoption, which is as a result of numerous smartphones and other Internet-based gadgets, have led to research on solutions for effective bandwidth optimization [11, 12]. This is due to the fact that the conventional SMFbased transport systems have been observed to be approaching Shannon's limit [13] and the achievable maximum capacity will not be sufficient to support the envisaged massive connection demanded by the next-generation networks [5, 14–16]. Besides the capacity that is expected to be saturated around 100 Tbit/s owing to the physical limits, the conventional SMF schemes with WDM might be unable to meet the power consumption, spatial efficiency, and cost requirements of the communication systems [16, 17].

There has been considerable attention on multicore fiber (MCF) as a feasible solution capable of addressing the capacity limit of a conventional SMF-based scheme [15, 18, 19]. For effective implementation of MCF, the research community has been working diligently on improved cost-efficient and scalable networking infrastructure solutions. A notable optical transport scheme that can exploit the space dimension in order to address the optical system capacity crunch and improve the system performance is spatial division multiplexing (SDM) [19]. Moreover, it has been observed that MCF is an efficient and main enabling technology for the SDM systems [16, 18]. Apart from the MCF, SDM implementation for multimode fiber (MMF) has also been attracting significant attention [17, 18]. Nevertheless, the MCF implementation is susceptible to and can be constrained by the transmission impairments such as nonlinearities and inter-core cross talk (XT) between signals at the neighboring cores that may be presented via multiple optical paths. This may have a significant effect on the system performance regarding the transmission range and the network size [16, 17]. Furthermore, the extent of the presented performance degradation by the transmission impairments varies with the MCF fiber types (i.e., 3-core, 7-core, 13-core, 19-core, 37-core, and 61-core) [16, 20]. A practical solution for addressing the MCF implementation challenges is spatial light modulation.

Spatial light modulators (SLM) can be employed for exciting different cores and/ or modes in order to mitigate the transmission impairments introduced by multiple optical paths, as it enables arbitrary removal or addition of channels with the aid of software, i.e., implementation of a diffractive optical element by computer-generated holograms (CGH). Due to the SLM support for dynamic reconfiguration of optical wave fronts, it can be employed for core and mode multiplexing and demultiplexing [5, 21, 22]. In addition, the use of silicon photonic (SiP) onboard transceivers that are coupled on the MCF for supporting transmissions has been shown to be promising. This is due to the fact that there is no need for fan-in/fan-out or core pitch conversion devices that may give rise to further system complexity [16].

Optical communication evolution has brought about the emergence of improved photonic integrated circuits (PICs) that present economic and sustainable alternative to data transmission [9]. Therefore, it is expected to be an enabling technology, capable of contributing significantly in a number of fields [8]. As a result, various benefits are offered, such as small weight and volume, low power consumption, high mechanical and thermal stability, and the ease of assembling a number of complex systems.

**117**

in Section 5.

*Spatial Light Modulation as a Flexible Platform for Optical Systems*

PIC can be generally characterized as a multiport device with an integrated system of optical elements such as attenuators, modulators, multiplexers, detectors, lasers, and optical amplifiers that are embedded in a single chip using a waveguide (WG) architecture [23]. However, it has been observed that optical component testing is very challenging and time-consuming as well [24]. This can be attributed to the required tight three-dimensional (3D) alignment tolerances, to ensure accurate light coupling. Hence, with notable development and growing adoption of PIC in the communication networks, advanced methods are imperative for an accurate PIC performance testing as well as characterization. As aforementioned, based on the support for dynamic reconfiguration of light, SLM can be employed for optical PIC testing and characterization, by exploring this feature in the feeding and/or receiv-

In this chapter, we focus on the most pertinent applications of phase-only liquid crystal on silicon (LCoS) SLM for optical telecom purposes and the employment of SLM technology in PIC, e.g., field-programmable silicon photonic circuits and integrated SLM application to create versatile reconfigurable elements. Furthermore, a new SLM-based flexible coupling platform for applications in SDM systems and

In Section 2, SLM working principle and their applications in telecom are addressed in more detail. The applied methodology (i.e., algorithms and experimental setup) to create a diffraction optical element through the implementation and optimization of CGH is described in Section 3. In Section 4, discussion on the obtained results from the experimental implementation of CGH for SDM and PIC applications is presented. An overall conclusion regarding the employment of the SLM technology as a flexible platform for optical systems is provided

Optical signal processing has been providing relevant solutions to convert data into spatially modulated coherent optical signals with SLM devices, allowing the effective implementation of digital holograms [25]. One of the most useful properties of the hologram is its ability to control phase and amplitude of light in the far field. The Fourier transform describes the relationship between a hologram (near field) and its corresponding replay field (far field). The far field can be formed at the focal point of a positive lens or an infinite distance from the near field plane in

Holograms can reproduce waveforms from an existing object. With digital advances and optical signal processing, it is possible to numerically calculate interference patterns to generate completely synthetic wave fronts of arbitrary form. These interference patterns can have different denominations, such as CGH, diffractive optical elements (DOE), phase/amplitude masks, diffractive grating, etc. [26]. All operate in the principle of diffraction, so it is somehow an arbitrary

The SLM is a device that can be used to modulate light in accordance with a fixed spatial (pixel) pattern and can be programed electrically. Usually, it can be exploited for incident light phase and/or amplitude control. Subsequently, phase-only, amplitude-only, or the combination of phase-amplitude can be readily realized with SLM. There are a number of modulation mechanisms that can be employed. One of the attractive and widely used ones is electro-optical SLM. The

characterization/testing of photonic processors will be presented.

*DOI: http://dx.doi.org/10.5772/intechopen.88216*

ing the optical signal into the PIC [8, 23].

**2. Spatial light modulator (SLM)**

free space [25, 26], as depicted in **Figure 1**.

choice of terminology.

#### *Spatial Light Modulation as a Flexible Platform for Optical Systems DOI: http://dx.doi.org/10.5772/intechopen.88216*

*Telecommunication Systems – Principles and Applications of Wireless-Optical Technologies*

To address the challenges, optical fiber-based transport systems have been employed in different fields of communication systems as viable and reliable solutions. The widely employed optical transport systems are based on single-mode fiber (SMF). To enhance the capacity of single-core SMF, advanced modulation formats and wavelength division multiplexing (WDM) are normally employed. However, the growing demand for further video/image storage capacity and the increase in cloud service adoption, which is as a result of numerous smartphones and other Internet-based gadgets, have led to research on solutions for effective bandwidth optimization [11, 12]. This is due to the fact that the conventional SMFbased transport systems have been observed to be approaching Shannon's limit [13] and the achievable maximum capacity will not be sufficient to support the envisaged massive connection demanded by the next-generation networks [5, 14–16]. Besides the capacity that is expected to be saturated around 100 Tbit/s owing to the physical limits, the conventional SMF schemes with WDM might be unable to meet the power consumption, spatial efficiency, and cost requirements of the communi-

There has been considerable attention on multicore fiber (MCF) as a feasible solution capable of addressing the capacity limit of a conventional SMF-based scheme [15, 18, 19]. For effective implementation of MCF, the research community has been working diligently on improved cost-efficient and scalable networking infrastructure solutions. A notable optical transport scheme that can exploit the space dimension in order to address the optical system capacity crunch and improve the system performance is spatial division multiplexing (SDM) [19]. Moreover, it has been observed that MCF is an efficient and main enabling technology for the SDM systems [16, 18]. Apart from the MCF, SDM implementation for multimode fiber (MMF) has also been attracting significant attention [17, 18]. Nevertheless, the MCF implementation is susceptible to and can be constrained by the transmission impairments such as nonlinearities and inter-core cross talk (XT) between signals at the neighboring cores that may be presented via multiple optical paths. This may have a significant effect on the system performance regarding the transmission range and the network size [16, 17]. Furthermore, the extent of the presented performance degradation by the transmission impairments varies with the MCF fiber types (i.e., 3-core, 7-core, 13-core, 19-core, 37-core, and 61-core) [16, 20]. A practical solution for addressing the MCF implementation challenges is spatial light modulation.

Spatial light modulators (SLM) can be employed for exciting different cores and/ or modes in order to mitigate the transmission impairments introduced by multiple optical paths, as it enables arbitrary removal or addition of channels with the aid of software, i.e., implementation of a diffractive optical element by computer-generated holograms (CGH). Due to the SLM support for dynamic reconfiguration of optical wave fronts, it can be employed for core and mode multiplexing and demultiplexing [5, 21, 22]. In addition, the use of silicon photonic (SiP) onboard transceivers that are coupled on the MCF for supporting transmissions has been shown to be promising. This is due to the fact that there is no need for fan-in/fan-out or core pitch conversion devices that may give rise to further system complexity [16].

Optical communication evolution has brought about the emergence of improved photonic integrated circuits (PICs) that present economic and sustainable alternative to data transmission [9]. Therefore, it is expected to be an enabling technology, capable of contributing significantly in a number of fields [8]. As a result, various benefits are offered, such as small weight and volume, low power consumption, high mechanical and thermal stability, and the ease of assembling a number of

**116**

complex systems.

cation systems [16, 17].

PIC can be generally characterized as a multiport device with an integrated system of optical elements such as attenuators, modulators, multiplexers, detectors, lasers, and optical amplifiers that are embedded in a single chip using a waveguide (WG) architecture [23]. However, it has been observed that optical component testing is very challenging and time-consuming as well [24]. This can be attributed to the required tight three-dimensional (3D) alignment tolerances, to ensure accurate light coupling. Hence, with notable development and growing adoption of PIC in the communication networks, advanced methods are imperative for an accurate PIC performance testing as well as characterization. As aforementioned, based on the support for dynamic reconfiguration of light, SLM can be employed for optical PIC testing and characterization, by exploring this feature in the feeding and/or receiving the optical signal into the PIC [8, 23].

In this chapter, we focus on the most pertinent applications of phase-only liquid crystal on silicon (LCoS) SLM for optical telecom purposes and the employment of SLM technology in PIC, e.g., field-programmable silicon photonic circuits and integrated SLM application to create versatile reconfigurable elements. Furthermore, a new SLM-based flexible coupling platform for applications in SDM systems and characterization/testing of photonic processors will be presented.

In Section 2, SLM working principle and their applications in telecom are addressed in more detail. The applied methodology (i.e., algorithms and experimental setup) to create a diffraction optical element through the implementation and optimization of CGH is described in Section 3. In Section 4, discussion on the obtained results from the experimental implementation of CGH for SDM and PIC applications is presented. An overall conclusion regarding the employment of the SLM technology as a flexible platform for optical systems is provided in Section 5.
