**9. Design of an holographic router with λ conversion and losses compensation**

Fig. 18 shows a device composed of a Semiconductor Optical Amplifier (SOA) and a holographic wavelength router. The SOA performs the wavelength conversion by a non linear operation using the Cross Gain Modulation (XGM) method. An incident wavelength, *λi,* modulated by a digital signal is combined with the wavelength *λCWj* generated by a tunable laser (CW) into the SOA. At the amplifier output, according to different CWj wavelengths, *λCWj* signals are obtained modulated with the digital signal from the incident *λi* wavelength. These *λCWj* signals are also amplified and inverted.

The holographic wavelength router, depending on the input signal, *λCWj,*, and the generated hologram *(nij)* stored in the SLM, addresses this signal to the assigned output. As has been stated, this technology has the drawback of high insertion losses (less than 10 dB, using an optimized device). In order to solve this problem, by combining a SOA with the holographic router, this insertion loss is compensated with the amplifier gain in the saturation zone of operation. A parameter to control in the SOA operation, is related to the amplified spontaneous emission (ASE) because of the impact on the signal distortion.

The use of tunable holographic devices in Access and Metro networks, like demultiplexers or routers has been studied in different papers (Koonen, 2006), (Martin Minguez & Horche, 2010). In Fig. 17 an application for the equalized holographic ROADM is represented.

**Node**

A double ring CWDM METRO topology is used to connect this primary access network, through an Optical Line Termination (OLT), with some Fiber to the Office (FTTO) or Fiber to the Home (FTTH) networks with Passive Optical Network (PON) structure; on the other side, a connection to a DWDM METRO network, by an OXC (Optical Cross Connect) with λ conversion, is provided. The target is to address the wavelengths of the double ring network,

Fig. 18 shows a device composed of a Semiconductor Optical Amplifier (SOA) and a holographic wavelength router. The SOA performs the wavelength conversion by a non linear operation using the Cross Gain Modulation (XGM) method. An incident wavelength, *λi,* modulated by a digital signal is combined with the wavelength *λCWj* generated by a tunable laser (CW) into the SOA. At the amplifier output, according to different CWj wavelengths, *λCWj* signals are obtained modulated with the digital signal from the incident *λi*

The holographic wavelength router, depending on the input signal, *λCWj,*, and the generated hologram *(nij)* stored in the SLM, addresses this signal to the assigned output. As has been stated, this technology has the drawback of high insertion losses (less than 10 dB, using an optimized device). In order to solve this problem, by combining a SOA with the holographic router, this insertion loss is compensated with the amplifier gain in the saturation zone of operation. A parameter to control in the SOA operation, is related to the amplified

**LONG HAUL network**

**OXC: Optical Cross-Connect OLT: Optical Line Termination PON: Passive Optical Network**

**DWDM METRO network**

} **Access Networks**

**FTTH: Fiber to the Home FTTO: Fiber to the Office**

**Primary path Spare path**

\*

**oxc**

**CWDM METRO network**

**Node**

**\***

**OLT**

λ1, λ2, λ3 and λ4 to four different PONs with the possibility of wavelength reallocation.

**9. Design of an holographic router with λ conversion and losses** 

spontaneous emission (ASE) because of the impact on the signal distortion.

wavelength. These *λCWj* signals are also amplified and inverted.

**Node**

**\***

**OLT**

**ROADM: Reconfigurable Optical Add-Dropp Multiplexer**

**FTTO**

**FTTH**

Fig. 17. Application of an EH\_ROADM in a CWDM METRO network

**\* : location for tunable holographic devices use**

λ1 λ<sup>2</sup>

**ROADM**

λ3 λ<sup>4</sup>

**\***

**8.2.6 CWDM METRO networks application** 

**PON 1**

λ1

λ2

λ3

λ4

**PON 2**

**PON 3**

**PON 4**

**compensation** 

Fig. 19 shows the simulation of this device, composed of three different blocks: a CW tunable laser, a wavelength conversion semiconductor optical amplifier and a wavelength holographic router. In Fig. 20, the response of the Wavelength Conversion and Routing Holographic Device (WCR-HD) is represented for a 2.5 Gb/s input signal, λi = 1540 nm, which is converted to an output signal, λo = 1520 nm, where the losses of the holographic router are compensated by the gain of the SOA.

Insertion losses: 0 dB

Fig. 18. Device composed of an optical λ converter and a holographic λ router

Fig. 19. Wavelength Conversion and Routing Holographic Device (WCR-HD) simulation

Application of Holograms in WDM Components for Optical Fiber Systems 281

been obtained allowing the full routing of several channels from the input fiber to the outputs. As it is possible to change the active pixels in the SLM for each hologram, in order to maintain a fixed output power level, channel equalization has been reached. Intrinsic losses of the device have been optimized using 4-phases holograms whose diffraction

Also, the ROADM size has been minimizing by using a "2f-folded" instead of a "linear-4f" for the optical structure. To reduce the total insertion losses of the holographic device a SOA has been added increasing the input power range for equalization. An example of use of these ROADM devices in CWDM Metro and Access Networks (PONs) has been reviewed. Another example of application is dealing with the design of a holographic router with losses compensation and wavelength conversion, whose main application is in the interconnection nodes of Metro networks. This device uses a SOA (Semiconductor Optical Amplifier), in the non-linear region, to do the wavelength conversion and, in addition, to supply the gain in order to compensate for the intrinsic losses of the holographic router. Other applications in Metro networks like path protection between nodes or switch matrix for ring networks interconnection could be implemented showing the versatility of these

Laboratory experiments testing the capability of a phase FLC-SLM to be used in these devices have been carried out and results show that, for different types of holograms, the possibility of distributing several wavelengths depends on the diffracted angle and,

The authors gratefully acknowledge the support of the MICINN (Spain) through project

Ahderom S.; Raisi M. et al.. (Jul 2002) "Applications of Liquid Crystal Spatial Light

Agrawal, G.P. (2002) "Fiber-Optic Communication Systems" (Third Edition), Wiley

Alarcón A., (2004) "Dynamic holography applications in SLMs based systems", Master

Broomfield S.; Neil M. et al. (1992)"Programmable binary phase-only optical device based on ferroelectric liquid crystal SLM", Electronics Letters, vol. 28 (1), pp. 26-28 Crossland W. A. et al.. (Dec 2000)"Holographic Optical Switching: The ROSES Demostrator"

Dames M.; R. Dowling et al. (1991) "Efficient optical elements to generate intensity weighted

Homa J. & Bala K., (Jul 2008) "ROADM Architectures and Their Enabling WSS Technology"

Horche P.R.; Alarcón A. et al.. (2004), "Spatial Light Modulator holographic filter for WDM

spot arrays: design and fabrication", Applied Optics vol. 30, no (19), pp. 2685-2691

Modulators in Optical Communications", 5th International Conference on High

therefore, enabling the building of filters, demultiplexers or wavelength routers.

Speed Networks and Multimedia Comm., 3-5, pp 239-242

IEEE/OSA, J. of Lightwave Tech., vol 18 , no 12, pp 1845-1853

Thesis, ETSITM, Universidad Politécnica de Madrid

IEEE Communications Magazine, pp 150-153

systems", International Union of Radio Science URSI'04

efficiency, for the 1st order, is twice that of binary holograms.

devices (Tibuleac & Filer, 2010).

**11. Acknowledgment** 

**12. References** 

TEC2010-18540 (ROADtoPON).

Interscience

Fig. 20. WCR-HD response for a 2.5 Gbit/s input signal: a) λi = 1540 nm, with wavelength conversion λo = 1520 nm, and losses compensation, b) Q factor ≈ 100 and c) BER ≈ 0.
