VCSEL and Integration Techniques for Wavelength-Multiplexed Optical Interconnects
Doktorsavhandling, 2021

GaAs-based vertical-cavity surface-emitting lasers (VCSELs) are dominating short-reach optical interconnects (OIs) due to their high modulation speed, low power consumption, circular output beam and low fabrication cost. Such OIs provide the high bandwidth connectivity needed for interconnecting servers and switches in data centers. With the rapidly increasing use of Internet-based applications and services, higher bandwidth connectivity and higher aggregate capacity VCSEL-based OIs are needed. Until now, this has been achieved mostly through an increase of the lane rate by higher speed VCSELs and higher order modulation formats. Furthermore, spatial-division-multiplexing has proven effective for increasing the aggregate capacity. Much higher capacity can be achieved by multiple wavelengths per fiber, known as wavelength-divisionmultiplexing (WDM). Moreover, smaller footprint and higher bandwidth density WDM transceivers can be built using monolithic multi-wavelength VCSEL arrays with densely spaced VCSELs. This requires a VCSEL technology where the wavelength of individual VCSELs can be precisely set in a post-epitaxial growth fabrication process and a photonic integrated circuit (PIC) for multiplexing and fiber coupling. Flip-chip integration over grating couplers (GCs) is considered for interfacing VCSELs with waveguides on the PIC.

In this thesis, an intra-cavity phase tuning technique is demonstrated for setting the resonance wavelength of VCSELs in a monolithic array with an accuracy in spacing of <1 nm. Uniform performance over the array is achieved by spectral matching and balancing of mirror reflectances, optical confinement factor and optical gain. Single transverse and polarization mode VCSELs, as required for flip-chip integration over GCs, with a record output power of 6 mW are also demonstrated.

Finally, an investigation of angled flip-chip integration of a VCSEL over a GC on a silicon photonic integrated circuit (Si-PIC) is presented. Dependencies of coupling efficiency and optical feedback on flip-chip angle and size of the VCSEL die are studied using numerical FDTD simulations. Moreover, flip-chip integration of a VCSEL over a GC on a Si-PIC is experimentally demonstrated. The insertion loss from the VCSEL at the input GC to a singlemode fiber, multimode fiber or flip-chip integrated photodetector over the output GC was measured and quantified. The latter forms an on-PIC optical link.

wavelength setting

optical interconnects

mode control

vertical-cavity surface-emitting laser

flip-chip integration


silicon photonics

Room A 423 (Kollektorn), Microtechnology and Nanoscience Department, MC2, Kemivägen 9, Göteborg.
Opponent: Professor James A. Lot, Technical University of Berlin


Mehdi Jahed

Chalmers, Mikroteknologi och nanovetenskap, Fotonik

Precise setting of micro-cavity resonance wavelength by dry etching

Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics,; Vol. 37(2019)

Artikel i vetenskaplig tidskrift

VCSEL Wavelength Setting by Intra-Cavity Phase Tuning - Numerical Analysis and Experimental Verification

IEEE Journal of Quantum Electronics,; Vol. 57(2021)p. 1-7

Artikel i vetenskaplig tidskrift

Monolithic Multi-Wavelength VCSEL Arrays with Uniform Performance by Intra-Cavity Phase Tuning

Conference Digest - IEEE International Semiconductor Laser Conference,; (2021)

Paper i proceeding

High-power single transverse and polarization mode VCSEL for silicon photonics integration

Optics Express,; Vol. 27(2019)p. 18892-18899

Artikel i vetenskaplig tidskrift

Angled Flip-Chip Integration of VCSELs on Silicon Photonic Integrated Circuits

Journal of Lightwave Technology,; Vol. 40(2022)p. 5190-5200

Artikel i vetenskaplig tidskrift

It is difficult to imagine the world without the Internet. The Internet is an important part of everyone’s life. Until March 2021, 65.6% of the world population used the Internet for shopping, listening to music, watching movies, communicating using social media, and many other applications. Two key components of the Internet infrastructure are optical cables and data centers, where data is being processed, stored, and accessed. Moreover, our computers, smartphones, and tablets are mainly used as terminals where we access information, while data storage and processing are located in the data centers. The important component in a data center is a light source which converts electrical signals to optical signals and feed into the optical cables. The light source is called VCSEL (vertical-cavity surface-emitting laser). The VCSEL is a micro-size, energy efficient, and low cost with capability of transmitting data at high speeds. With increasing use of Internet-based applications and cloud computing, the number of the data centers and their size increase rapidly. The largest data center has a size around 120 FIFA football fields. This up-scaling means that present and future data centers need an internal communication network with huge capacity. This thesis deals with how to increase the speed of the VCSELs and capacity of the data centers using a novel technology to meet requirements for high Internet data traffic. Moreover, the thesis shows that it is possible to integrate VCSELs on a small optical circuit to have an ultra-high-capacity board for being used in data centers with a high aggregate capacity.

Integrerade optiska sändare för våglängdsmultiplexering i datacenternätverk

Vetenskapsrådet (VR) (2016-06077), 2017-01-01 -- 2022-12-31.

Optiska datakablar med multi-Tbit/s kapacitet

Stiftelsen för Strategisk forskning (SSF) (SE13-0014), 2014-03-01 -- 2019-06-30.


Nanovetenskap och nanoteknik



Annan teknik

Elektroteknik och elektronik






Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5063



Room A 423 (Kollektorn), Microtechnology and Nanoscience Department, MC2, Kemivägen 9, Göteborg.


Opponent: Professor James A. Lot, Technical University of Berlin

Relaterade dataset

VCSEL and Integration Techniques for Wavelength-Multiplexed Optical Interconnects [dataset]

Mer information

Senast uppdaterat