Field
The present disclosure relates to techniques for optically coupling an optical signal. More specifically, the present disclosure relates to a lens-integrated vertical laser that optically couples an optical signal into an optical waveguide using a grating coupler, and that includes an isolator to reduce or eliminate back reflection.
Related Art
Advances in CMOS technologies are enabling integrated circuits with very large-scale integration of billions of transistors on a single chip. However, because of thermal constraints and other physical limits, the performance scaling of such large-scale integrated circuits may not be associated with increased clock rates. Instead, parallel architectures that aggregate large numbers of function units are increasingly being used to scale the capabilities of integrated circuits. With more and more processing power being integrated onto a semiconductor chip, integrated circuits often need commensurate increases in the communication bandwidth to fully utilize the increased processing performance.
In particular, over the last decade the off-chip input/output (I/O) bandwidth of advanced processors has increased at a rate of about 2× every two years. Consequently, a total I/O bandwidth of a few Tbps is fairly common for current chips. However, in order to maintain this growth rate, an I/O bandwidth of tens of Tbps may soon be needed for a single chip. Similar communication bandwidth scaling is also occurring at the server level and networking level. Given the limited physical resources, interconnect solutions with lower power consumption, larger bandwidth, and larger bandwidth density are, therefore, needed to meet the communication bandwidth scaling demand of high-performance electrical systems.
Silicon photonics is a promising technology that can provide efficient and dense large bandwidth system interconnects for future computing systems. Significant progress has been made toward achieving low-cost practical applications, including components such as: high-bandwidth efficient silicon modulators, low-loss optical waveguides, wavelength division multiplexing (WDM) components, as well as high-speed CMOS optical waveguide photo-detectors. However, low-cost and reliable array laser sources integrated with silicon photonics remain an obstacle to implementing large-scale integrated silicon photonic links
While individual external III-V laser sources are commercially available, low-cost integration of an array of external laser sources onto a silicon photonics chip remains a challenge. In principle, an optical fiber array can be used to bring many-channel laser sources onto silicon photonics chips. However, in practice this approach is prohibitively expensive.
A variety of approaches are being investigated to make integrated laser source arrays. For example, an electrical pumped distributed feedback laser has been demonstrated by heterogeneous integration of III-V materials on silicon. However, the yield and reliability of this distributed feedback laser remain obstacles to low-cost optical sources. Moreover, III-V materials and processes are usually not defect-free. Consequently, the yield of III-V lasers remains much lower compared to silicon CMOS circuits. Furthermore, burn-in is also typically required to weed out the infant failures. Therefore, it is not typically ideal to integrate III-V lasers with silicon photonics circuits before component qualification, especially for applications such as large bandwidth system interconnects in which large integration scale is typically required.
Another approach uses a single high-power laser source packaged with free-space optics supported by a silicon bench for integration with silicon photonics chips. This approach may allow power sharing so that multiple optical links can be supported in parallel. However, the scaling of such an optical source is often limited given the limited maximum power of an individual laser die. Moreover, integration of many laser packages onto a single silicon photonics chip may be needed for large bandwidth system interconnects, such as applications with tens and hundreds of optical links, which represents a significant challenge for packaging and integration.
Hence, what is needed is an optical source without the above-described problems.