Researchers develop innovative quantum dot lasers for advanced frequency combs

Researchers at the University of California, Santa Barbara have made significant breakthroughs in laser technology, introducing a groundbreaking quantum dot mode-locked laser that allows for independent generation of amplitude and frequency modulation combs from a single device. This cutting-edge dual mode laser paves the way for the creation of small-sized and energy-efficient frequency combs for silicon photonic integrated circuits in data centers and various other applications.

The UCSB research team led by John Bowers designed the QD platform, which can manufacture devices with bandwidth comparable to the most advanced QD mode-locked lasers currently available. The AM and FM pulse widths generated by UCSB devices meet the latest standards for QD mode-locked lasers.

The significance of this development lies in the potential enhancement of optical frequency combs, which have been proven to have immeasurable value in remote sensing, spectroscopy, and optical communication. However, traditional amplitude modulation frequency combs pose challenges to dense wavelength division multiplexing systems due to their high instantaneous power, resulting in strong thermal nonlinearity. In order to effectively generate a wide and efficient optical frequency comb, precise engineering design of the group velocity dispersion of the waveguide is necessary.

UCSB researchers solved this challenge by utilizing collision pulse structures, which enable QD mode-locked lasers to have impressive fast repetition rates of 60 GHz. This helps to support DWDM systems while minimizing channel crosstalk during data transmission. In addition, the laser cavity is designed with a length of 1.35 mm and a width of 2.6 μ The laser cavity of m achieves a 3 dB optical bandwidth of up to 2.2 THz in the telecommunications O-band, with an impressive electro-optical insertion and removal efficiency of over 12%.

In order to generate FM combs, in addition to the group velocity dispersion of the waveguide, the nonlinear characteristics of the laser active region also play a crucial role. The QD mode-locked laser exhibits an astonishing -5 dB four-wave mixing efficiency, which helps generate FM combs efficiently and robustly. It is fascinating that the gain dynamics of quantum dot lasers determine the mechanism behind the formation of FM and AM combs. The formation of AM combs requires slow gain through low injection current, while FM combs rely on fast gain to generate significant Kerr nonlinearity and four-wave mixing.

In an equally eye-catching discovery, researchers have demonstrated the ability to effectively design Kerr nonlinearity in quantum dot lasers, expanding the FM comb bandwidth without the need for GVD engineering. By applying voltage to the saturable absorber portion of the laser, this method not only improves the performance of the FM comb, but also simplifies the manufacturing process. Compared with traditional quantum well diode lasers, quantum lasers have strong Kerr nonlinearity and four-wave mixing capabilities, making them more suitable for generating FM combs in the optical communication frequency band.

Compared with FM combs produced by other integrated optical frequency comb technologies, the FM combs produced by this new technology have better size, weight, power consumption, and cost characteristics, which demonstrate the strength of QD lasers. The wide range of characteristics of FM combs makes them very suitable for high-capacity optical communication systems, and their performance is superior to traditional AM combs.

Excitingly, the technology developed by UCSB researchers is also compatible with complementary metal oxide semiconductor technology, further highlighting its potential for practical implementation.

This groundbreaking study has been published in "Light: Science and Applications", a renowned scientific journal specializing in the field of optics.

Source: Laser Network