A new semiconductor laser structure with digitally switchable wavelength is proposed. The device comprises two coupled c.avities with different optical path lengths, which form V-shaped branches with a reflective 2 × 2 half-wave optical coupler at the closed end. The reflective 2 × 2 coupler is designed to have a π-phase difference between cross-coupling and self-coupling so as to produce synchronous power transfer functions. High single-mode selectivity is achieved by optimizing the coupling coefficient. The switchable wavelength range is greatly increased by using Vernier effect. Using deep-etched trenches as partial reflectors, additional waveguide branch structures are used outside the laser cavities to form a complete Mach-Zehnder interferometer, allowing space switching, variable attenuation, or high speed modulation to be realized simultaneously. Detailed design principle and numerical results are presented.

We demonstrate an ultrahigh sensitivity silicon photonic biosensor based on cascaded Mach–Zehnder interferometer (MZI) and ring resonator with the Vernier effect using wavelength interrogation. Experimental results show that the sensitivities reached 2870 nm/RIU and 21,500 nm/RIU for MZI sensor and MZI-ring sensor, respectively. A biosensing application was demonstrated by monitoring the interaction between goat and antigoat immunoglobulin G (IgG) pairs. The measured results show that 1 ng/ml IgG resulted in 0.035 nm and 0.5 nm wavelength shift for MZI sensor and MZI-ring sensor, respectively. This high performance sensor is promising for medical diagnostic applications.

A highly sensitive optical waveguide sensor based on simple intensity interrogation with a broadband light source is proposed and investigated. It consists of two cascaded microring resonators with the same or slightly different free spectral ranges. The variation of the refractive index of the analyte sample results in a large shift in the envelope function of the transmission peaks of the sensor, and, consequently, a large change in the transmitted power. The low-cost sensing scheme can achieve an ultrahigh sensitivity of $2\times {10}^4\mathrm{dB}/\mathrm{RIU}$. Experimental results on the intensity interrogated double-ring sensor using a broadband source are presented, demonstrating its operation principle and potential for low-cost practical applications.

A silicon nitride waveguide is a promising platform for integrated photonics, particularly due to its low propagation loss compared to other complementary metal–oxide–semiconductor compatible waveguides, including silicon-on-insulator. Input/output coupling in such thin optical waveguides is a key issue for practical implementations. Fiber-to-chip grating couplers in silicon nitride usually exhibit low coupling efficiency because the moderate index contrast leads to weak radiation strengths and poor directionality. Here, we present the first, to the best of our knowledge, experimental demonstration of a recently proposed apodized-imaging fiber-to-chip grating coupler in silicon nitride that images an in-plane waveguide mode to an optical fiber placed at a specific distance above the chip. By employing amplitude and phase apodization, the diffracted optical field of the grating is matched to the fiber mode. High grating directionality is achieved by using staircase grating teeth, which produce a blazing effect. Experimental results demonstrate an apodized-imaging grating coupler with a record coupling efficiency of $-1.5\mathrm{dB}$ and a 3 dB bandwidth of 60 nm in the C-band.

We propose a highly-sensitive temperature sensor employing a Mach-Zehnder interferometer (MZI) based on silicon-on-insulator (SOI) platform. The waveguide widths in the two MZI arms are tailored to have different temperature sensitivities but nearly the same group refractive indices. A temperature sensor with an enhanced sensitivity of larger than 438pm/°C is experimentally demonstrated, which is over seven times larger than that of conventional silicon optical temperature sensor (about 60pm/°C for quasi-TM mode). Moreover, the sensor is easy to fabricate, only by a single mask, and no need of any polymer cladding, which makes it more robust, and can be used in lab-on-chip systems as a temperature monitor.

We report the first experimental demonstration of a single-electrode-controlled digitally wavelength switchable V-coupled-cavity laser with high side-mode-suppression-ratio (SMSR) in the $40\mathrm{dB}$ range. Sixteen-channel and twenty-six channel wavelength switchable lasers with $100\mathrm{GHz}$ spacing are demonstrated with the maximal SMSR of $40\mathrm{dB}$ and $37\mathrm{dB}$, respectively. They do not require complex gratings, multiple epitaxial growths, or complex tuning algorithms. The device size is only $500\mathrm{\mu m}\times 300\mathrm{\mu m}$. Such a simple, compact, and high-performance laser has great potential as a low-cost alternative to existing complex tunable lasers for wide deployment in optical networks and beyond.