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Monolithic cointegration of QD-based InP on SiN as a versatile platform for the demonstration of high performance and low cost PIC transmitters

Periodic Reporting for period 1 - MOICANA (Monolithic cointegration of QD-based InP on SiN as a versatile platform for the demonstration of high performance and low cost PIC transmitters)

Reporting period: 2018-01-01 to 2019-06-30

The wide-spread adoption of optical transceivers in a plethora of application domains is urgently calling for low-cost, high power efficient and large-volume manufacturing integration technology capable of meeting the various specifications required and scaling up to serve the growing telecom and datacom markets.

MOICANA aims to produce the technological background for growing InP QDs directly on Si prior synergizing InP QD structures with the best-in-class, in terms of losses and temperature sensitivity, in a CMOS fab, i.e. the SiN waveguide technology. It aims to shape the necessary framework for the delivery of a low-cost and large volume manufacturing monolithic InP QD-on-SiN transmitter PIC platform, through the demonstrations of a whole new series of cooler-less, energy-efficient and high-performance single-channel and WDM transmitter modules for DataCenter Interconnects, for 5G Mobile fronthaul and for coherent communication applications.

The overall Objectives of MOICANA are :
1. Deploy the process for heterogeneous epitaxy of InP QD on Si towards Selective Area growth (SAG) on SiN technology.
2. Design and develop a monolithic integration process for InP QDs on SiN
3. Design and fabricate InP-to-SiN coupling interfaces
4. Develop and demonstrate a 25Gb/s monolithically integrated InP QD-on-SiN Directly Modulated Laser (DML)
5. Develop and demonstrate a monolithically integrated InP QD External Modulated Laser (EML) on SiN
6. Develop and demonstrate a monolithically integrated tunable wavelength coherence source
7. Design and develop a series of WDM temperature-tolerant monolithic PIC prototype transmitters
8. Validate the monolithic SiN-based PIC Transmitter platform in a wide range of applications
9. Generation of Process Design Kits (PDK) software library for rapid deployment
The main outcomes of MOICANA T=throughout the first half of its lifetime are highlighted below:

Establishment of monolithic integration process of QD InP on Si:
MOICANA partners have managed early in the project to conclude to a process flow that will enable the fabrication and demonstration of all targeted transmitter demonstrators by taking into account the limitations of all involved fabrication partners. The complete integration flow will be executed in 14 main steps and 9-10 lithographic steps, depending on final InP-SiN transition waveguide.

Development of SRN material for interfacing the active InP QD section to the SiN platform:
Within the reporting period MOICANA’s foundry partners have managed to develop a Silicon Rich Nitride (SRN) material to act as a medium for the seamless light transition between the active InP QD section and the targeted SiN platform. This novel SRN material exhibits low stress and variable refractive index that can be tune to match the values of InP and InGaAsP.

Deposition of SRN on SiN achieving adiabatic coupling:
Based on the novel SRN, waveguide structures have been developed revealing propagation losses in the 15dB/cm range. The outcomes of these experimental results together with the measured properties of the material fed the design of efficient interfacing schemes between III-V lasers and SiN waveguides providing coupling losses that can be as low as -0.76dB and back-reflections to the source at -35dB.

Development of a new DFB CW laser with record low linewidth:
A new generation of quantum dot (QD) optical gain material comprising atom-like features, has been also exploited within MOICANA to improve significantly the fundamental spectral characteristics of laser emission. More specifically, the development of a new DFB CW laser exhibiting linewidth as narrow as 60 kHz (30 kHz 10 kHz intrinsic linewidth) at 200C, which broadens to only 280 kHz (80kHz 10kHz intrinsic linewidth) at 800C, has been achieved.
MOICANA will demonstrate for the first time electrically pumped InP-based QD lasers directly grown on Si that will operate under both CW and Directly Modulated mode. Additionally, due to the co-integration with the SiN platform it will feature enhanced WDM capabilities reaching capacities up to 400Gb/s.

The MOICANA DML-DFB laser wil be the first InP-based QD DML encompassing a Bragg Grating for the definition of the emission wavelength, while providing narrow linewidth of 300KHz. Due to the high power emitted from the laser reaching 10dBm at RT and 5.8dBm at 600C, the MOICANA DML will be capable to reach transmission distances up to 40Km error free with dispersion compensation, but without any FEC.

MOICANA will proceed to the demonstration of modulator structures that will enable high modulation depth from short devices that directly affects the required voltage that will up to ±2V for the provision of 6dB modulation depth in a 20nm spectral window, the losses that will be either neutral or 3dB loss and also the 3dB bandwidth that will be at least 7GHz allowing modulation up to 10Gbaud. Finally, this will be the first QD modulator that will be co-integrated with SiN allowing low loss MUX/DEMUX capabilities and easy access to external fibers.

MOICANA SiN platform will rely on the advanced capabilities of LGC’s in the fabrication of crack free waveguides with LPCVD at heights up to 2.5um with their patented DAMASCENE process.

MOICANA will develop for the first time an efficient coupling interface between the InP and the SiN platforms that will allow their co-integration in a monolithic way. The loss imposed in the signal will be lower 2dB/transition without any need for post-processing of the device. Additionally, its appliance will not be limited only to single facets devices like e.g lasers, but it will be also applicable to dual facet one like modulators and SOAs.

MOICANA will demonstrate for the first time a high power (>10dBm) tunable laser source by exploiting the high modal gain provided by the InP based QD active layers. Furthermore, with the novel SiN-to-aSi-to-InP interface it will be possible to insert filters in both sides of the active medium towards exploiting the Vernier effect for the emission of light with very high coherency due to the 20KHz linewidth. The tunability will mainly limited by the DBRs placed at both sides of the laser, but it will exceed 32nm.

ΜOICANA’s unique InP-based QD technology will exploit the low linewidth (<300KHz) due to the overgrown gratings and the low a-factor (<1) stemming from the QD properties towards the demonstration of 1λ- and 4λ- transmitters at 100Gb/s and 400Gb/s, respectively. Each channel will be modulated with a 16QAM signal at 25Gbaud for temperatures up to 600C. With digital dispersion compensation, the 100G and 400G channels will be detected at the receiver side error free under FEC for distances up to 10Km.

MOICANA will demonstrate a 4λ-EML transmitter that will be capable to operate TEC-free up to 600C by exploiting the QD properties of the DFB laser. No EDFA will be required at the receiver side due to the launched power of 4.5dBm/lane. Furthermore, the total power consumption will be only 1.4W.

MOICANA will present for the first time a 1λ- and 4λ-DML transmitters that will be capable to provide error free transmission at distances up to 10Km with NZ-DSF, without any need to add TEC for laser cooling. Considering -18dBm receiver sensitivity (for BER=2e-4 and FEC) from 803.3bs standard, the power budget per link is set to 18.5dB that easily allows PON connections with links up to 40Km if dispersion compensation is employed.