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 demonstrate a temperature-insensitive waveguide sensor based on a silicon-on-insulator platform. The sensor consists of a ring resonator and a Mach–Zehnder interferometer (MZI). A free spectral range of the sensing ring is designed to be slightly different from that of the MZI; hence, the Vernier effect can be employed to improve sensitivity. By optimizing structural parameters of the MZI, the envelope peak position of a cascaded transmission spectrum can be immune to the temperature variation, and only dependent on analyte change in the sensing area. The experimental results show that bulk refractive index (RI) sensitivity of the proposed sensor is 3552 nm/RI unit, while its temperature sensitivity is less than 4 pm/K, which is two orders of magnitude smaller than the conventional cascaded sensor structure without temperature compensation. The proposed temperature-insensitive waveguide sensor does not need polymer cladding or extra thermal stabilization, making it more robust in practical applications.

Two Edge-input arrayed waveguide gratings (AWGs) with star couplers of Confocal and Rowland configurations, respectively, are experimentally investigated and the one with Rowland configuration shows better performance in terms of insertion loss and crosstalk. Based on the optimized Rowland configuration, two 64 × 0.4 nm ultra-compact on-chip spectrometers using bidirectional AWGs with two side inputs and different lengths of free propagation region (FPR) are designed and fabricated. Due to the utilization of two side inputs, the footprint of AWG spectrometer is significantly reduced compared to a conventional one center-input AWG spectrometer with the same resolution. The reduced footprint contributes to the performance improvement for an AWG spectrometer on high index contrast platforms, which is verified in our fabricated spectrometers on silicon-on-insulator platform. The demonstrated ultra-compact on-chip spectrometer has large potential applications in miniaturized spectral analysis systems on a chip.

We analyze the impact of aberration on spectral performance of silicon-based arrayed waveguide grating (AWG) router with the conventional design using a constant pitch along the grating circle for the array waveguides near the free propagation region (FPR), and simulation results show that due to existence of large aberration, side lobes occur in spectral responses of peripheral output channels for the center input light while more serious side lobes appear in most output channels within a free spectral range (FSR) for the edge channel input. Therefore, there is a high crosstalk in conventional N × N silicon AWG, which is very detrimental for router applications. In order to address it, a simple design with a constant projected period on a line tangent to the grating at its pole for the array waveguides near the FPR is proposed, and aberrations of all output wavelengths within a FSR are kept at a rather low level both for the center and edge input. Then we fabricate two kinds of AWG routers with the conventional and proposed design respectively on a SOI wafer, and experimental results show that spectral responses of the AWG router with the proposed design are significantly improved compared to those obtained in the conventional design, especially for the edge channel input.

Ultra-compact on-chip spectrometers with high resolution and large bandwidth play a crucial role in miniaturized spectroscopic analysis systems. Here we present a novel polarization-insensitive micro-spectrometer with high resolution and large bandwidth based on a ( N + 3) × ( N + 3) arrayed waveguide grating (AWG) on silicon-on-insulator (SOI) platform. The proposed AWG can be viewed as two same 3 × N AWGs with each one having three input waveguides with channel spacing of 4/3 Δ λ and N output waveguides with channel spacing of Δ λ . The three input waveguides are time division multiplexed, i.e., they are excited one by one in sequence. As a result, combining all spectral responses of each input, a micro-spectrometer with channel wavelength spacing enhanced to one-third Δ λ and channel number enlarged to 3 × ( N – 2) is achieved, only using N output channels. The polarization diversity scheme is utilized to address the polarization sensitive issue of silicon nano-waveguide, i.e., the AWG operates at a counter-propagating manner to process each polarization, respectively. In experiment, we demonstrate a micro-spectrometer with 81 channels and channel wavelength spacing of 0.4 nm by employing a 32 × 32 AWG on the SOI platform. The footprint of the fabricated micro-spectrometer is only 1.1 × 2.35 mm ² . Experimental results show that the spectrometer has on-chip losses ranging from –5.8 to –2.5 dB, noise level of better than 17 dB, polarization dependent wavelength shift (PD λ ) of less than 0.07 nm and polarization dependent loss (PDL) of less than 1.5 dB, for all 81 wavelength channels. The resolution of the micro-spectrometer is mainly dependent on the 3-dB bandwidth of each channel and is simulated to be ∼0.65 nm. The proposed ultracompact and polarization insensitive high-resolution on-chip spectrometer provides a very promising approach for achieving miniaturized spectrometer-on-a-chip with good performance for applications such as in fiber Bragg grating (FBG) sensor readout unit and optical waveguide sensor systems.

We propose an ultra-compact novel wavelength multiplexer employing a ( N + 1) × ( N + 1) arrayed waveguide grating (AWG) and a polarization-combiner-rotator (PCR) on the SOI platform, to realize a multiplexing for 2 N wavelengths with a spacing of Δλ. The ( N + 1) × ( N + 1) AWG works at a bidirectional way to provide two groups of N × 1 wavelength multiplexing with each group having a channel spacing of 2×Δλ, and the central wavelengths of all input channels in one group have a wavelength shift of Δλ with respect to those in the other group. The double channel spacing results in a significant decrease on the footprint of the ( N + 1) × ( N + 1) AWG-based multiplexer compared with a conventional 2 N × 1 AWG multiplexer with the same wavelength spacing Δλ. Due to the fact that a single mode fiber is insensitive to the polarization of input light, if we consider short reach datacom applications such as 100/400 GbE, the two separate multiplexing outputs of the ( N + 1) × ( N + 1) AWG can be combined as one output with one half wavelengths working at TE polarization and the other at TM polarization by employing a low loss and broadband PCR. In the experiment, we demonstrate a 16 × 200 GHz multiplexer based on a 9 × 9 AWG. The experimental results show that the on-chip loss of the fabricated multiplexer is 2.7 dB and the loss uniformity is 0.5 dB. The 1-dB and 3-dB bandwidths are >0.56 nm (i.e., 35% of the wavelength spacing) and >1.1 nm (i.e., 69% of the wavelength spacing), respectively. They can also be further increased by decreasing the gap between adjacent input waveguides at the interfaces of star couplers of the designed AWG without inducing an excess loss. The proposed multiplexer has great potential for application to future super large capacity (> Tb/s) data transmission systems.