A programmable, multi-format photonic transceiver platform enabling flexible optical networks

Development of programmable photonic devices for future flexible optical networks is ongoing. To this end, an innovative, multi-format QAM transmitter design is presented. It comprises a segmented-electrode InP IQ-MZM to be fabricated in InP, which can be directly driven by low-power CMOS logic. Arbitrary optical QAM format generation is made possible using only binary electrical signals, without the need for high-performance DACs and high-swing linear drivers. The concept enables a host of Tx-side DSP functionality, including the spectral shaping needed for Nyquist-WDM system concepts. In addition, we report on the development of an optical channel MUX/DEMUX, based on arrays of microresonator filters with reconfigurable bandwidths and center wavelengths. The device is intended for operation with multi-format flexible transceivers, enabling Dense (D)WDM superchannel aggregation and arbitrary spectral slicing in the context of a flexible grid environment

Segmented optical transmitter comprising a CMOS driver array and an InP IQ-MZM for advanced modulation formats

Segmented Mach-Zehnder modulators are promising solutions to generate complex modulation schemes in the migration towards optical links with a higher-spectral efficiency. We present an optical transmitter comprising a segmented-electrode InP IQ-MZM, capable of multilevel optical signal generation (5-bit per I/Q arm) by employing direct digital drive from integrated, low-power (1W) CMOS binary drivers. We discuss the advantages and design tradeoffs of the segmented driver structure and the implementation in a 40 nm CMOS technology. Multilevel operation with combined phase and amplitude modulation is demonstrated experimentally on a single MZM of the device for 2-ASK-2PSK and 4-ASK-2-PSK, showing potential for respectively 16-QAM and 64-QAM modulation in future assemblies

InP segmentierte Mach-Zehnder Modulatoren mit erweiterten EO-Funktionalitäten

Thema dieser Arbeit sind segmentierte Indium Phosphid (InP) Mach-Zehnder Modulatoren (SEMZMs). Diese elektro-optischen Komponenten werden verwendet um Digital Analog Wandler (DACs) und digitale Signalverarbeitung zu implementieren, ohne jedoch die herkömmlichen dafür vorgesehenen platzraubenden elektronischen Komponenten mit hoher Leistungsaufnahme zu verwenden. Der hier vorgeschlagene und umgesetzte Ansatz adressiert hauptsächlich die Thematik des kleineren Platz- und Leistungsbedarf. Von den zu ersetzenden Einsatzmöglichkeiten des DAC werden hier drei näher untersucht: Frequenzentzerrung (frequency equalization), Nyquist spektrale Profilformung (spectral shaping) und Digital-zu-Analog-Konversion. Als Erstes wird ein segmentierter Modulator mit Bandbreitenerhöhung präsentiert. Diese wird verwendet um eine möglichst hohe elektro-optische Übertragungsbandbreite zu erzielen bei gleichzeitiger Verwendung von elektrischen Komponenten mit niedriger Bandbreite. Konkret wurde ein Transmitter mit Bandbreite von 30 GHz realisiert und für eine fehlerfreie Übertragung bei 56 GBd OOK genutzt, obwohl die elektrischen Komponenten maximal 22 GHz Bandbreite besitzen, dies entspricht einer Bandbreitenerhöhung von 36%. Die Vergleichsmessung unter Verwendung eines Lithiumniobat Modulators statt eines SEMZM zeigt die Vorteile des SEMZM bezüglich der Bit-Fehler-Rate (BER). Als Zweites wird der SEMZM verwendet, um die spektrale Bandbreite eines modulierten 40 GBd 4-Niveau Signals zu halbieren. Dank der spektral-formenden Eigenschaften des SEMZM können zwei Dual-Polarisations modulierte Subträger, mit einem Abstand von nur 50 GHz, fehlerfrei über 80 km Standard Einmoden-Faser (SSMF) übertragen werden. Mit einer genutzten spektralen Bandbreite von insgesamt 100 GHz beträgt die spektrale Effizienz 3,2 b/s/Hz. BER Messungen zeigen keinen Einfluss der beiden eng beieinanderliegenden Subträger aufeinander. Im letzten Abschnitt der Arbeit werden segmentierte Modulatoren für die optische digital analog Konversion betrachtet. Zwei verschiedene InP SEMZM Bauelemente wurden entwickelt, für den Einsatz mit BiCMOS oder CMOS Elektronik. Der SEMZM in Intensität-Quadratur-Konfiguration mit BiCMOS Treiber zeigt eine fehlerfreie Übertagung über 80 km SSMF mit einem Dual-Polarisation 64-Symbol Quadratur-Amplituden modulierten Signal bei einer Symbolrate von 32 Gbd. Diese Symbolrate zusammen mit einem Leistungsverbrauch von nur 1.5 W ergibt eine totale Datenrate von 384 Gb/s und eine Energie pro Bit von 7,8 pJ/b. Unter Verwendung des CMOS Treibers zeigte der entwickelte SEMZM fehlerfrei transmittierte amplituden- und phasenmodulierte Signale bei 15 Gbd.This work covers indium phosphide (InP) segmented Mach-Zehnder modulators (SEMZMs). These electro-optical components are proposed as a means to implement digital-to-analog converters (DACs) and digital signal processing functionalities without the need of bulky and power-hungry dedicated electrical components. The proposed approach shows its advantage in terms of reduced area and power consumption. Among the different DAC-enabled features, bandwidth enhancement by frequency equalization, Nyquist-space spectral shaping, and optical-DAC are identified and discussed. First, a segmented modulator with bandwidth enhancement capability is presented. When the modulator is driven by electronics of 22 GHz bandwidth, the electro-optical bandwidth of the complete transmitter is measured to be 30 GHz. Hence, a bandwidth broadening of 36 % is measured. With this setup, error-free transmission of a 56 GBd on-off keying signal is demonstrated. The experiment is repeated by replacing the SEMZM with a lithium niobate modulator driven by the same electronics. Bit error ratio (BER) measurements show the SEMZM performs better, both in presence of chromatic dispersion and in presence of noise. Afterwards, a Nyquist-space spectral shaping SEMZM is used to halve the occupied bandwidth of a 40 GBd 4-level modulated signal. Thanks to this shaping, two dual-polarization modulated subcarriers, spaced at only 50 GHz, are transmitted error-free over 80 km of standard single mode fiber (SSMF). With an overall occupied bandwidth of 100 GHz, the overall measured gross spectral efficiency is 3.2 b/s/Hz. BER measurements show no influence of the closely spaced adjacent subcarrier. Lastly, optical digital-to-analog conversion by segmented modulators is demonstrated. Two different InP devices are developed to be driven by either BiCMOS or CMOS dedicated electronics. For the first time, error-free transmission of a 32 GBd dual-polarization 64-symbol quadrature amplitude modulated (64-QAM) signal over 80 km of SSMF without the use of a DAC is demonstrated. The speed of 32 GBd and the low power consumption of 1.5 W translate to a total gross data rate of 384 Gb/s and energy per bit of 7.8 pJ/b. Alternatively, using a CMOS driver, the developed segmented modulator is shown to transmit error-free a 15 GBd 4-ASK-2-PSK signal with a power consumption of 1 W and corresponding energy per bit of 22.2 pJ/b

The role of competitive learning in the generation of DG fields from EC inputs

We follow up on a suggestion by Rolls and co-workers, that the effects of competitive learning should be assessed on the shape and number of spatial fields that dentate gyrus (DG) granule cells may form when receiving input from medial entorhinal cortex (mEC) grid units. We consider a simple non-dynamical model where DG units are described by a threshold-linear transfer function, and receive feedforward inputs from 1,000 mEC model grid units of various spacing, orientation and spatial phase. Feedforward weights are updated according to a Hebbian rule as the virtual rodent follows a long simulated trajectory through a single environment. Dentate activity is constrained to be very sparse. We find that indeed competitive Hebbian learning tends to result in a few active DG units with a single place field each, rounded in shape and made larger by iterative weight changes. These effects are more pronounced when produced with thousands of DG units and inputs per DG unit, which the realistic system has available, than with fewer units and inputs, in which case several DG units persists with multiple fields. The emergence of single-field units with learning is in contrast, however, to recent data indicating that most active DG units do have multiple fields. We show how multiple irregularly arranged fields can be produced by the addition of non-space selective lateral entorhinal cortex (lEC) units, which are modelled as simply providing an additional effective input specific to each DG unit. The mean number of such multiple DG fields is enhanced, in particular, when lEC and mEC inputs have overall similar variance across DG units. Finally, we show that in a restricted environment the mean size of the fields is unaltered, while their mean number is scaled down with the area of the environment