147 research outputs found
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Flexible Multimode Polymer Waveguide Arrays for Versatile High-Speed Short-Reach Communication Links
Multimode polymer waveguides have attracted great interest for use in high-speed short-reach communication links as they can be cost-effectively integrated onto standard PCBs using conventional methods of the electronics industry and provide low loss (30 GHz×m) interconnection. The formation of such waveguides on flexible substrates can further provide flexible low-weight low-thickness interconnects and offer additional freedom in the implementation of high-speed short-reach optical links. These attributes make these flexible waveguides particularly attractive for use in low-cost detachable chip-to-chip links and in environments where weight and shape conformity become important, such as in cars and aircraft. However, the highly-multimoded nature of these waveguides raises important questions about their performance under severe flex due to mode loss and mode coupling. In this work therefore, we investigate the loss, crosstalk and bandwidth performance of such waveguides under out-of plane bending and in-plane twisting under different launch conditions and carry out data transmission tests at 40 Gb/s on a 1 m long spiral flexible waveguide under flexure. Excellent optical transmission characteristics are obtained while robust loss, crosstalk and bandwidth performance are demonstrated under flexure. Error-free (BER<10-12) 40 Gb/s data transmission is achieved over the 1 m long spiral waveguide for a 180° bend with a 4 mm radius. The obtained results demonstrate the excellent optical and mechanical properties of this technology and highlight its potential for use in real-world systems.Jaguar Land Rover, CAPE LEAS
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Mode-selective sensing using asymmetric waveguide junctions
Measuring a single analyte in a highly absorptive microfluidic channel has always been a challenge. Even with a highly selective sensing layer, other chemical species can affect the interrogation of the analyte. Matching the evanescent tail with the sensing layer thickness is difficult in case of evanescent field sensing. The tail typically extends beyond the sensing layer, introducing noise and spurious errors in the measurement, which scales up with analyte concentration. In this work therefore, we propose the use of a simple multimode evanescent waveguide sensor that eliminates such common spurious effects. The proposed mode-selective sensing system exploits the sensitivity differences between the different guided modes in detecting the effects of the outer medium in the sensor response. The operation of the sensor device relies on the use of an asymmetric waveguide junction, which enable efficient separation of waveguide modes and therefore detection of their differences in behaviour. The proposed device is shown through simulations to achieve very small estimation errors below 5%, even for very high absorption coefficients of the outer medium of up to 80 times larger than that of the sensing layer.This work is funded by EPSRC UK.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.sna.2015.04.00
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Linearisation Method of DML-Based Transmitters for Optical Communications Part III: Pulse Amplitude Modulation
A new linearization method for optical transmitters based on directly modulated lasers (DMLs), named the Stretched A method, was proposed in Parts I and II of this work. Parts I and II presented the theoretical framework of the method for non-return-To-zero (NRZ) modulation and related detailed simulation and experimental results. Here, we extend the method to pulse amplitude modulation schemes (PAM). Focussing on 4-level PAM (PAM-4), we present the theoretical background and discuss implementation options. A simplified variation of the method for the generation of PAM signals with a significantly lower number of sub-currents is proposed. Simulation studies for PAM-4 transmission at 50 GBaud (100 Gb/s) and an experimental proof-of-principle demonstration at 16 GBaud (32 Gb/s) are reported based on 850 nm vertical-cavity surface-emitting lasers (VCSELs). For PAM-4, products of effective eye diagram areas ({\boldsymbol{PS}}) of 0.6 × 10-5 and 43 × 10-5 before and after applying the Stretched A method were measured, demonstrating an improvement ratio of ∼72. The sensitivity and tolerances of the method are analyzed using simulation and experiment
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Linearisation Method of DML-based Transmitters for Optical Communications Part II: Experimental Demonstration and Implementation Methods
In this paper, we report the first experimental demonstration of the Stretched A linearisation method. The theoretical framework of the method and related simulation studies have been presented in Part I of this work. Here, we apply the method on an 850 nm multimode vertical-cavity surface-emitting laser (VCSEL) specified for operation at 10 Gb/s and demonstrate good quality optical output waveforms with little non-linear distortion at 16 Gb/s using non-return-to-zero (NRZ) modulation. An experimental sensitivity analysis on the generation of the required modulating current components demonstrates large tolerance to parameter mismatch. In addition, it is shown that an adaptive gain scheme can improve the tolerance to the timing offset between the current components. Potential hardware implementations using either analog or digital electronics are also discussed
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Linearisation Method of DML-Based Transmitters for Optical Communications Part I: Theory and Simulation Studies
The performance of directly-modulated lasers (DMLs) is severely impaired by nonlinear behaviour when operating at high symbol rates. We propose a new linearization method for DML-based transmitters which can significantly reduce nonlinearity. This method, named the Stretched A (StrA) method, relies on the generation of an approximation to the ideal modulating current that generates a linear optical output waveform. In Part I of this work, the theoretical framework of the proposed method is presented and detailed simulation studies illustrate its implementation and demonstrate the benefits it offers. Although the method is applicable to any type of DML, the simulation studies presented herein focus on optical links based on vertical-cavity surface-emitting lasers (VCSELs) as these comprise the vast majority of short-reach optical links. Part II of this work presents the proof-of-principle experimental demonstration of this new linearization method and discusses its possible implementations using either analog or digital electronics
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High-bandwidth and low-loss multimode polymer waveguides and waveguide components for high-speed board-level optical interconnects
Multimode polymer waveguides are being increasingly considered for use in short-reach board-level optical interconnects as they exhibit favourable optical properties and allow direct integration onto standard PCBs with conventional methods of the electronics industry. Siloxane-based multimode waveguides have been demonstrated with excellent optical transmission performance, while a wide range of passive waveguide components that offer routing flexibility and enable the implementation of complex on-board interconnection architectures has been reported. In recent work, we have demonstrated that these polymer waveguides can exhibit very high bandwidth-length products in excess of 30 GHz×m despite their highly-multimoded nature, while it has been shown that even larger values of > 60 GHz×m can be achieved by adjusting their refractive index profile. Furthermore, the combination of refractive index engineering and launch conditioning schemes can ensure high bandwidth (> 100 GHz×m) and high coupling efficiency (< 1 dB) with standard multimode fibre inputs with relatively large alignment tolerances (~17×15 μm^2 ). In the work presented here, we investigate the effects of refractive index engineering on the performance of passive waveguide components (crossings, bends) and provide suitable design rules for their on-board use. It is shown that, depending on the interconnection layout and link requirements, appropriate choice of refractive index profile can provide enhanced component performance, ensuring low loss interconnection and adequate link bandwidth. The results highlight the strong potential of this versatile optical technology for the formation of high-performance board-level optical interconnects with high routing flexibility.The authors would like to acknowledge Dow Corning for the provision of the polymer samples and the UK EPSRC for supporting this work . Additional data related to this publication is available at the University of Cambridge data repository ( https://www.repository.cam.ac.uk/handle/1810/253542).This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by SPIE
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Bandwidth studies on multimode polymer waveguides for ≥ 25 Gb/s optical interconnects
Multimode polymer waveguides constitute a promising technology for use in board-level optical interconnects. However, the continuous improvements in high-speed performance of VCSELs raise important questions about their ability to support such high data rates due to their inherent highly-multimoded nature. Thorough experimental studies on the bandwidth of a 1.4 m long multimode spiral waveguide are presented in this paper, indicating a bandwidth-length product of at least 35 GHz×m even in the case of an overfilled launch. No significant transmission impairments are observed for spatial input offsets, while error-free (BER<10⁻¹²) data transmission over the 1.4 m long spiral waveguide is demonstrated at 25 Gb/s.This is the final version of the article. It first appeared from IEEE Photonics Technology Letters via http://dx.doi.org/10.1109/LPT.2014.2342881. © © 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works
A new equalizer structure for high-speed optical links based on carrierless amplitude and phase modulation
© 2020 IEEE. Spectral efficient modulation formats can enable the transmission of higher data rates than conventional on-off keying (OOK). Carrierless amplitude and phase modulation (CAP) is such an attractive modulation scheme that has been widely considered for use in different types of optical links. The scheme however can suffer from intersymbol interference (ISI) and channel crosstalk (CCI) when the frequency response of the channel is not ideal. Conventional equalizers based on feedforward (FFE) and decision feedback (DFE) equalizers are easy to implement in practice and can mitigate some of the induced ISI. However, they fail to suppress the induced CCI in the link as each channel is equalized independently. As a result, we have recently proposed the use of a new equalizer structure for use in CAP-based optical links to mitigate these transmission impairments. This new equalizer, named CAP equalizer, can be formed with conventional FFEs and DFEs with minimal additional complexity whilst providing significant performance advantages. In this paper therefore, we review the equalizer structure and report recent demonstrations of its use in short-reach optical links. We present experimental studies on a 112 Gb/s CAP-16 VCSEL-based OM4 MMF link and a 4 Gb/s CAP-16 LED-based POF link and compare the performance of the links when both a conventional FFE and DFE equalizer and the newly proposed CAP equalizer are used. The results clearly demonstrate that the CAP equalizer offers improved receiver sensitivity and enables successful data transmission over longer fibre reaches.UK EPSRC via the UP-VLC (EP/K00042X/1) and TOWS (EP/S016570/1) project
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Single-lane > 100 Gb/s CAP-based data transmission over VCSEL-MMF links using low-complexity equalization
In this paper, we review recent work on the development of a novel low-complexity equalizer that can enable single-lane <100 Gb/s short-reach optical links based on carrierless amplitude and phase modulation. This equalizer, named the CAP equalizer, can mitigate the transmission impairments in the link due to a non-ideal channel frequency response, providing significant performance advantage over conventional FFE and DFE equalizers and enabling higher data rates and longer reach. Its use is demonstrated in a VCSEL-based MMF link achieving data transmission of 112 and 124 Gb/s over 100 m OM4 MMF
40 Gb/s data transmission over a 1 m long multimode polymer spiral waveguide
We report record error-free data transmission of 40Gb/s over a 1m-long multimode polymer spiral waveguide. The waveguide imposes no significant transmission impairments in the link despite its highly-multimoded nature and long length, demonstrating its potential in high-speed board-level optical interconnections
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