Daniel Mahgerefteh

Chirp Managed Laser and Applications

The chirp managed laser (CML) is an alternative transmitter technology that allows a directly modulated laser (DML) to be used in high-performance applications with a smaller size, lower power consumption, less device complexity, and lower cost. The CML comprises a DML and an isolated, passive optical filter. A key feature of the CML is its large tolerance to fiber dispersion, reaching over 360 km transmission at 10 Gb/s in standard single-mode fiber without dispersion compensation. The combination of adiabatic chirp from the laser and filter edge response produces high extinction ratio pulses with nearly uniform phase, abrupt phase shifts at bit transitions, and a correlation between the 1 bits; 1 bits separated by odd number of 0 bits are out of phase. This results in destructive intersymbol interference after fiber transmission. Other applications of CML are generation of advanced modulation formats, such as return-to-zero (RZ) alternate mark inversion, and RZ differential phase-shift keying. Tunable CML using DFB array, and sampled grating deterministic bit rate (DBR) technologies for 10 Gb/s metro applications have now been demonstrated. A four-element DBR array CML has also been demonstrated for 100 Gb/s metro applications. This paper reviews the principle of operation of CML and its various applications, as well as recent advances in CML-based devices.

Techno-Economic Comparison of Silicon Photonics and Multimode VCSELs

We compare Silicon Photonics and multi-mode short wavelength VCSEL technologies for various optical interconnect applications using addressable volume, relative cost, transmission reach, power consumption, and bandwidth-density as metrics.

Generation and Transmission of 10-Gbaud Optical 3/4-RZ-DQPSK Signals Using a Chirp-Managed DBR Laser

We have demonstrated the generation and transmission of 10-Gbaud optical 3/4-return-to-zero differential quadrature phase-shift-keying (3/4-RZ-DQPSK) signals using a chirp-managed distributed-Bragg-reflector (DBR) laser (CML), without requiring any differential encoder or external modulator. We realized error-free transmission in 60-km standard single-mode fiber without any dispersion compensation. No optical signal-to-noise ratio penalty was induced. We also investigated the impact of different optical spectrum reshaper filters in CML on the transmission performance. The tolerance against the amplitude fluctuation of the electrical driving signal was also studied.

Techno-economic comparison of Silicon Photonics and multimode VCSELs

Recent technical and commercial milestones in Silicon Photonics technology including its introduction into commercial foundries, and successful integration of most optical components, as well as the choice of single mode fiber in some mega data centers have prompted the speculation that Si photonics is the new low cost solution for optical interconnects and that it may replace multi-mode vertical cavity surface emitting lasers (MM VCSEL). We show that the dominant technology has to offer the lowest cost for the single channel transceiver application, which represents 90% of the data center market and which historically dominates sales. We show that Si photonics is currently significantly more expensive than MM VCSEL for single channel, but that it can make a successful entry into the four channel single mode market with significant growth, capturing 20% of the data center market. We discuss the challenges with Si/InP integration; i.e., hybrid lasers for breaking the cost barrier and to enter the market. We show that both MM VCSEL and Si photonics technologies can operate at 50 Gb/s. We discuss the transmission reach limitations of Si photonics and MM VCSEL and show an example of reach extension for 100 Gb/s using MM VCSEL to 300 m of MM fiber. In addition we show that MM VCSEL has fundamentally lower power consumption than Si photonics and is a good candidate for super-computing applications.

Multimode VCSELs vs Si Photonics in the Data Center: A Techno-economical Comparison

Will Si photonics replace MM VCSELs in the data center? We attempt to answer this question by comparing the two technologies based on their application space, cost structure, transmission reach, and power consumption.

Performance of a 56 Gbit/s directly modulated DBR laser with an optimized optical spectrum reshaper

The amplitude and phase responses of an optical spectrum reshaper are optimized for 56 Gbit/s binary intensity modulation using a distributed Bragg reflector laser. An 8 dB extinction ratio and 12 dB loss margin with a pre-amplified receiver are obtained.