Abstract
We present a novel concept for an integrated silicon photonic coherent transceiver using vertical-emitting laser sources at 1550 nm. In a state of the art external modulation configuration, we deploy a VCSEL on the transmit and a HCSEL on the receive side. We demonstrate the feasibility of this approach by externally modulating the VCSEL with QPSK at up to 28 Gbaud. We also perform experiments with the VCSEL-HCSEL configuration in a slave-master optical injection locking setup for future data center interconnects. The results show stable locking conditions and the VCSEL is detuned to perform predominant phase modulation. To the best of our knowledge, this is the first time direct phase modulation of a VCSEL under optical injection locking was demonstrated using two vertically emitting laser sources as master - and slave laser.
Highlights
There is an intense debate about how far coherent communication will be deployed for short-reach intra data center interconnects in the future, which are presently entirely served by direct detect systems
We propose the use of VCSEL and horizontal-cavity surface-emitting DFB laser (HCSEL) sources integrated with a silicon photonics platform such as photonic BiCMOS to enable coherent transmission
The predominant phase modulation changes in this domain to amplitude modulation. This can be explained by assuming that part of the HCSEL signal is reflected at the VCSEL’s mirror and is interfering with the locked VCSEL signal causing a complex offset.13. While this is working towards the phase modulation for smaller detunings, we find it to be the cause of a unwanted shift in the complex offset and the amplitude modulation for increasingly higher detunings
Summary
There is an intense debate about how far coherent communication will be deployed for short-reach intra data center interconnects (up to 10 km) in the future, which are presently entirely served by direct detect systems. Coherent communication generally requires a more complex modulation scheme It offers a scalable technology, able to support highly spectral efficient modulation formats commonly used for longer link distances. It is a viable approach for supporting the increasing data rate demands of future intra data center interconnects. The rationale behind the use of VCSEL and HCSEL sources are as follows Both are vertical emitters and intrinsically compatible with flip-chip soldering on silicon photonic grating couplers, which is at present a comparatively mature integration technology. Due to their generally larger linewidth in comparison to edge-emitters Both issues can be addressed by deploying a vertically emitting DFB laser in combination with VCSELs
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