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Papers by Christof Debaes

Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate ... more Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate optoelectronic interconnects. The target is communication between surface-mounted integrated circuit packages on printed circuit board through embedded optical waveguides. Different kinds of optical elements for coupling between transmitters/receivers and waveguides are studied, including microlens arrays, microlenses integrated on VCSELs, surface-mountable beam deflecting elements, optical pillar structures, and waveguide structures patterned by laser ablation. Integration experiments by the use of ceramic packaging substrate as well as results of the coupling efficiency and alignment tolerance characterizations are presented.

Lecture Notes in Computer Science, 2006

Rapid Prototyping Technology - Principles and Functional Requirements, 2011

SPIE Proceedings, 2010

Optical interconnections have gained interest over the last years, and several approaches have be... more Optical interconnections have gained interest over the last years, and several approaches have been presented for the integration of optics to the printed circuit board (PCB)-level. The use of a polymer optical waveguide layer appears to be the prevailing solution to route optical signals on the PCB. The most difficult issue is the efficient out-of-plane coupling of light between surface-normal optoelectronic devices (lasers and photodetectors) and PCB-integrated waveguides. The most common approach consists of using 45 • reflecting micro-mirrors. The micro-mirror performance significantly affects the total insertion loss of the optical interconnect system, and hence has a crucial role on the system's bit error rate (BER) characteristics. Several technologies have been proposed for the fabrication of 45 • reflector micro-mirrors directly into waveguides. Alternatively, it is possible to make use of discrete coupling components which have to be inserted into cavities formed in the PCB-integrated waveguides. In this paper, we present a hybrid approach where we try to combine the advantages of integrated and discrete coupling mirrors, i.e. low coupling loss and maintenance of the planararity of the top surface of the optical layer, allowing the lamination of additional layers or the mounting of optoelectronic devices. The micro-mirror inserts are designed through non-sequential ray tracing simulations, including a tolerance analysis, and subsequently prototyped with Deep Proton Writing (DPW). The DPW prototypes are compatible with mass fabrication at low cost in a wide variety of high-tech plastics. The DPW micro-mirror insert is metallized and inserted in a laser ablated cavity in the optical layer and in a next step covered with cladding material. Surface roughness measurements confirm the excellent quality of the mirror facet. An average mirror loss of 0.35-dB was measured in a receiver scheme, which is the most stringent configuration. Finally, the configuration is robust, since the mirror is embedded and thus protected from environmental contamination, like dust or moisture adsorption, which makes them interesting candidates for out-of-plane coupling in high-end boards.

SPIE Newsroom, 2009

The heat dissipation in silicon-based Raman lasers and amplifiers could be suppressed by inducing... more The heat dissipation in silicon-based Raman lasers and amplifiers could be suppressed by inducing coherent anti-Stokes Raman scattering in the silicon medium.

Proceedings - 19th IEEE International Parallel and Distributed Processing Symposium, IPDPS 2005, 2005

International Workshop on System Level Interconnect Prediction, SLIP, 2005

Proceedings of SPIE - The International Society for Optical Engineering, 2006

Proceedings of SPIE - The International Society for Optical Engineering, 2008

2009 17th IEEE Symposium on High Performance Interconnects, 2009

2006 First International Conference on Communications and Electronics, 2006

The static interconnection network topologies in the distributed shared memory systems (DSM) have... more The static interconnection network topologies in the distributed shared memory systems (DSM) have several limitations. The reconfigurable interconnection networks may reduce the network congestion, network latency and improve the overall performance. However it is necessary to know when the right moment to perform the reconfiguration is and how to implement it. In this paper, we present our study on communication patterns of parallel scientific and commercial benchmark applications on a simulated but realistic DSM machine and their relation to context switching in the operating system. We also propose a reconfiguration scheme that is triggered by the context switches.

We present how a custom reconfigurable optical network can be incorporated into Distributed Share... more We present how a custom reconfigurable optical network can be incorporated into Distributed Shared-memory (DSM) multiprocessor machines, and show the potential speed improvement of the interprocessor communication, even when the limits associated to opto-electronics are included. We find that for 32 processors connected in a torus topology, slowly reconfiguring interconnects can provide up to 30% reduction in communication delay. For larger 64-node networks, the expected gain can rise up to 40%. We also introduce the elements for a possible reconfigurable optical network implementation: a selective broadcasting system using focusing-splitting diffractive lenses is described.

Progress In Electromagnetics Research, 2013

Physical Review Letters, 2007

We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman las... more We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman lasers. The basic principle of this so-called ''coherent anti-Stokes Raman scattering (CARS)-based heat mitigation'' is to suppress the phonon creation in the Raman medium by increasing the number of outcoupled anti-Stokes photons with respect to the number of out-coupled Stokes photons. We demonstrate with the aid of numerical simulations that for a hydrogen and a silicon Raman laser, CARS-based heat mitigation efficiencies of at least 30% and 35%, respectively, can be obtained.

IEEE Photonics Technology Letters, 2007

We propose discrete out-of-plane coupling components as a versatile alternative to current approa... more We propose discrete out-of-plane coupling components as a versatile alternative to current approaches used to couple light in and out of the propagation plane in waveguide-based printed circuit board (PCB)-level optical interconnections. The out-of-plane couplers feature a 45 micromirror and are fabricated using deep proton writing as a rapid prototyping technology. Their fabrication is compatible with replication techniques and shows all the potential of low-cost mass fabrication. In a first configuration, we use the component in a fiber-to-fiber coupling scheme. Coupling losses as small as 0.77 dB were achieved. In a second configuration, the out-of-plane coupler is plugged into a laser ablated cavity in optical waveguides integrated on a PCB. Here a total link loss between out-of-plane fiber and in-plane fiber of 3.00 dB was achieved when using it at the transmitter side and 5.69 dB when using it at the receiver side.

IEEE Photonics Technology Letters, 1998

IEEE Journal of Selected Topics in Quantum Electronics, 2003

We present a new method of latency reduction in optical interconnects: using very low duty cycle ... more We present a new method of latency reduction in optical interconnects: using very low duty cycle return-to-zero encoding (i.e., subpicosecond pulses). An analytical comparison of three different receiver architectures, including transimpedance, integrating, and totem-pole diode pair, is presented. For all three receivers, we demonstrate that using short pulses instead of nonreturn-to-zero (NRZ) shortens the circuit delay. We also experimentally demonstrate a 65% reduction in latency of a transimpedance receiver by using short optical pulses. Finally, we show that the latency of optical interconnects can be comparable to or even less than electrical interconnects for global on-chip communication. Index Terms-Complementary metal-oxide-semiconductor (CMOS) integrated circuits, integrating receivers, latency, multiple quantum well (MQW) modulator, optical interconnects, short optical pulses, totem-pole diode pair, trans-impedance receivers. I. INTRODUCTION M ODERN computer processors run at the clock speeds of many gigahertz but the processor to memory interface typically runs at only a few hundred megahertz. A key reason for this difference, and a problem for computing in general, is that the interface connection speeds are not able to keep up with the increase in the processor speeds. This is mainly because of design issues of electrical busses and their underlying physical properties. Due to the capacity limitations of electrical wires, most long distance communication is now done via optics. For medium distance communication, e.g., local-area network (LAN), metropolitan area networks (MAN), wide area network (WAN) (about 300 m-100 km), optics is making inroads, specifically, because only optics can support the high data rates required by these applications. At shorter distances (a few meters-few hundred meters), primarily in data links, optics is rapidly gaining entry. Recently, a lot of research has been done Manuscript

IEEE Journal of Selected Topics in Quantum Electronics, 2003

IEEE Journal of Selected Topics in Quantum Electronics, 2003

Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate ... more Hybrid integration of polymer-based micro-optical technologies allows implementing high-bit-rate optoelectronic interconnects. The target is communication between surface-mounted integrated circuit packages on printed circuit board through embedded optical waveguides. Different kinds of optical elements for coupling between transmitters/receivers and waveguides are studied, including microlens arrays, microlenses integrated on VCSELs, surface-mountable beam deflecting elements, optical pillar structures, and waveguide structures patterned by laser ablation. Integration experiments by the use of ceramic packaging substrate as well as results of the coupling efficiency and alignment tolerance characterizations are presented.

Lecture Notes in Computer Science, 2006

Rapid Prototyping Technology - Principles and Functional Requirements, 2011

SPIE Proceedings, 2010

Optical interconnections have gained interest over the last years, and several approaches have be... more Optical interconnections have gained interest over the last years, and several approaches have been presented for the integration of optics to the printed circuit board (PCB)-level. The use of a polymer optical waveguide layer appears to be the prevailing solution to route optical signals on the PCB. The most difficult issue is the efficient out-of-plane coupling of light between surface-normal optoelectronic devices (lasers and photodetectors) and PCB-integrated waveguides. The most common approach consists of using 45 • reflecting micro-mirrors. The micro-mirror performance significantly affects the total insertion loss of the optical interconnect system, and hence has a crucial role on the system's bit error rate (BER) characteristics. Several technologies have been proposed for the fabrication of 45 • reflector micro-mirrors directly into waveguides. Alternatively, it is possible to make use of discrete coupling components which have to be inserted into cavities formed in the PCB-integrated waveguides. In this paper, we present a hybrid approach where we try to combine the advantages of integrated and discrete coupling mirrors, i.e. low coupling loss and maintenance of the planararity of the top surface of the optical layer, allowing the lamination of additional layers or the mounting of optoelectronic devices. The micro-mirror inserts are designed through non-sequential ray tracing simulations, including a tolerance analysis, and subsequently prototyped with Deep Proton Writing (DPW). The DPW prototypes are compatible with mass fabrication at low cost in a wide variety of high-tech plastics. The DPW micro-mirror insert is metallized and inserted in a laser ablated cavity in the optical layer and in a next step covered with cladding material. Surface roughness measurements confirm the excellent quality of the mirror facet. An average mirror loss of 0.35-dB was measured in a receiver scheme, which is the most stringent configuration. Finally, the configuration is robust, since the mirror is embedded and thus protected from environmental contamination, like dust or moisture adsorption, which makes them interesting candidates for out-of-plane coupling in high-end boards.

SPIE Newsroom, 2009

The heat dissipation in silicon-based Raman lasers and amplifiers could be suppressed by inducing... more The heat dissipation in silicon-based Raman lasers and amplifiers could be suppressed by inducing coherent anti-Stokes Raman scattering in the silicon medium.

Proceedings - 19th IEEE International Parallel and Distributed Processing Symposium, IPDPS 2005, 2005

International Workshop on System Level Interconnect Prediction, SLIP, 2005

Proceedings of SPIE - The International Society for Optical Engineering, 2006

Proceedings of SPIE - The International Society for Optical Engineering, 2008

2009 17th IEEE Symposium on High Performance Interconnects, 2009

2006 First International Conference on Communications and Electronics, 2006

The static interconnection network topologies in the distributed shared memory systems (DSM) have... more The static interconnection network topologies in the distributed shared memory systems (DSM) have several limitations. The reconfigurable interconnection networks may reduce the network congestion, network latency and improve the overall performance. However it is necessary to know when the right moment to perform the reconfiguration is and how to implement it. In this paper, we present our study on communication patterns of parallel scientific and commercial benchmark applications on a simulated but realistic DSM machine and their relation to context switching in the operating system. We also propose a reconfiguration scheme that is triggered by the context switches.

We present how a custom reconfigurable optical network can be incorporated into Distributed Share... more We present how a custom reconfigurable optical network can be incorporated into Distributed Shared-memory (DSM) multiprocessor machines, and show the potential speed improvement of the interprocessor communication, even when the limits associated to opto-electronics are included. We find that for 32 processors connected in a torus topology, slowly reconfiguring interconnects can provide up to 30% reduction in communication delay. For larger 64-node networks, the expected gain can rise up to 40%. We also introduce the elements for a possible reconfigurable optical network implementation: a selective broadcasting system using focusing-splitting diffractive lenses is described.

Progress In Electromagnetics Research, 2013

Physical Review Letters, 2007

We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman las... more We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman lasers. The basic principle of this so-called ''coherent anti-Stokes Raman scattering (CARS)-based heat mitigation'' is to suppress the phonon creation in the Raman medium by increasing the number of outcoupled anti-Stokes photons with respect to the number of out-coupled Stokes photons. We demonstrate with the aid of numerical simulations that for a hydrogen and a silicon Raman laser, CARS-based heat mitigation efficiencies of at least 30% and 35%, respectively, can be obtained.

IEEE Photonics Technology Letters, 2007

We propose discrete out-of-plane coupling components as a versatile alternative to current approa... more We propose discrete out-of-plane coupling components as a versatile alternative to current approaches used to couple light in and out of the propagation plane in waveguide-based printed circuit board (PCB)-level optical interconnections. The out-of-plane couplers feature a 45 micromirror and are fabricated using deep proton writing as a rapid prototyping technology. Their fabrication is compatible with replication techniques and shows all the potential of low-cost mass fabrication. In a first configuration, we use the component in a fiber-to-fiber coupling scheme. Coupling losses as small as 0.77 dB were achieved. In a second configuration, the out-of-plane coupler is plugged into a laser ablated cavity in optical waveguides integrated on a PCB. Here a total link loss between out-of-plane fiber and in-plane fiber of 3.00 dB was achieved when using it at the transmitter side and 5.69 dB when using it at the receiver side.

IEEE Photonics Technology Letters, 1998

IEEE Journal of Selected Topics in Quantum Electronics, 2003

We present a new method of latency reduction in optical interconnects: using very low duty cycle ... more We present a new method of latency reduction in optical interconnects: using very low duty cycle return-to-zero encoding (i.e., subpicosecond pulses). An analytical comparison of three different receiver architectures, including transimpedance, integrating, and totem-pole diode pair, is presented. For all three receivers, we demonstrate that using short pulses instead of nonreturn-to-zero (NRZ) shortens the circuit delay. We also experimentally demonstrate a 65% reduction in latency of a transimpedance receiver by using short optical pulses. Finally, we show that the latency of optical interconnects can be comparable to or even less than electrical interconnects for global on-chip communication. Index Terms-Complementary metal-oxide-semiconductor (CMOS) integrated circuits, integrating receivers, latency, multiple quantum well (MQW) modulator, optical interconnects, short optical pulses, totem-pole diode pair, trans-impedance receivers. I. INTRODUCTION M ODERN computer processors run at the clock speeds of many gigahertz but the processor to memory interface typically runs at only a few hundred megahertz. A key reason for this difference, and a problem for computing in general, is that the interface connection speeds are not able to keep up with the increase in the processor speeds. This is mainly because of design issues of electrical busses and their underlying physical properties. Due to the capacity limitations of electrical wires, most long distance communication is now done via optics. For medium distance communication, e.g., local-area network (LAN), metropolitan area networks (MAN), wide area network (WAN) (about 300 m-100 km), optics is making inroads, specifically, because only optics can support the high data rates required by these applications. At shorter distances (a few meters-few hundred meters), primarily in data links, optics is rapidly gaining entry. Recently, a lot of research has been done Manuscript

IEEE Journal of Selected Topics in Quantum Electronics, 2003

IEEE Journal of Selected Topics in Quantum Electronics, 2003