In this work, a transverse magnetic (TM)-pass polarizer based on subwavelength grating (SWG) on the emerging potential hybrid silicon-LNOI platform is proposed. By integrating silicon material onto the LNOI platform, the optical power of TE0 and TM0 modes is judiciously distributed to distinct regions. This design not only effectively blocks the TE0 mode but also enables low-loss transmission of the TM0 mode, thereby achieving a balanced manipulation of both polarizations. Due to the strong reflection of TE0 mode by SWG, a polarizer is realized with a high polarization extinction ratio (PER) and low insertion loss (73 dB and 0.37 dB respectively at 1550 nm) in a compact size (device length is 23.38 μm). Moreover, the PER is beyond 50 dB and the insertion loss is under 0.46 dB in a broad wavelength range of 1525 to 1585 nm.
We theoretically analyze the performances of the anti-PT-symmetric gyroscope near the exceptional point (EP). The results show that the frequency splitting caused by rotation is proportional to the square root of the fraction of power coupled from the bus to the ring. To fully exploit the potential of the EP, one needs to overcome two aspects of challenges. The first one is the preparation of sensitive unit, to detect the angular velocity of 104 deg / h with a micron-scale sensor; the allowable variation in the ratio of cavities’ radii is within the order of 10 − 16, which is exceedingly challenging in current nano fabrication. The other is controlling environmental disturbances. A temperature variation of 0.002°C would make the minimum detectable rotation rate up to 1010 deg / h, which is far beyond practically applications. Our analysis points out the difficulties in realizing this gyroscope, which has significant referential values to future work.
We propose a monolithic integrated cavity optomechanical accelerometer based on push-pull photonic crystal zipper cavity. The accelerometer integrates grating couplers, phase modulators, acceleration sensing unit, and electrostatic force feedback module on a chip. We use push-pull structure to eliminate the coupling crosstalk caused by paraxial acceleration and extend its range using electrostatic force feedback module. The transmissive photonic crystal zipper cavity structure is adopted to improve the integration and stability of the system. Accurate results are demonstrated as follows: the bandwidth is larger than 20 kHz, the mechanical sensitivity is 369 pm/g, the measuring range is ±100 g, and the noise equivalent acceleration is 5.06 μg / Hz. With its advantages, the accelerometer can be used in consumer electronics, aerospace, resource exploration, and other fields.
In this paper, a new method for analyzing the states of polarization (SOP) distribution characteristics is proposed, which combines the Poincaré sphere measurement method with the improved Delaunay triangulation algorithm, and the specific components and proportions of the SOP of the beam can be quantitatively obtained. On this basis, a numerical parameter, called polarization separation degree (PSD), is introduced to characterize the spatial random dispersion level of partially polarized or unpolarized light. Experimentally, the output SOP distribution of the depolarized erbium-doped superfluorescent fiber source (SFS) is tested, the results show that the PSD of the SFS output light within 2.5 hours is 96.856%, and the proportion of right-handed (left-handed) elliptically polarized light is 49.21% and 50.53%, the proportions of righthanded (left-handed) circularly polarized light and linearly polarized light are 0.05%, 0.11%, and 0.1%, respectively, which provides a valuable numerical reference for further optimizing its structural design and reducing its polarization-dependent wavelength shift. Moreover, the evaluation method proposed in the paper provides an effective way to analyze the dynamic evolution and distribution characteristics of the SOP, and can effectively promote the development and application of polarization imaging and detection, optical fiber communication and sensing technology.
We present a design of a laterally tapered optical waveguide mode-size converter from super luminescent diode (SLD) to silica-based planar lightwave circuit (PLC). The mode-size converter is based on silica-based PLC. By using three dimensional semi-vectorial beam propagation methods, laterally tapered waveguides with different boundaries are simulated and compared with each other, where the factors of polarization-dependent loss and coupling loss are mainly focused on. The results show that the most influential factor for polarization-dependent loss is the ratio of the divergence angle of SLD in the horizontal direction and the vertical direction. The refractive index difference Δ between core layer and cladding layer, core width of endface and taper length influence coupling loss mostly, while the effect of all side boundaries is within 0.05 dB. We also investigate the SLD misalignment tolerance and wavelength bandwidth’s impact on coupling loss. Furthermore, we examine the performance of the mode-size converter based on a particular SLD which has a divergence angle of 30°×45°. By optimizing the parameters of the tapered waveguide, the coupling efficiency is increased to 62.4% and the polarization-dependent loss is reduced to 0.035 dB. Meanwhile, it eΔnables us to reduce the coupling loss variation to 0.05dB with core width of endface fabrication tolerance of ±0.5 μm and taper length tolerance of ±0.5 mm. The proposed mode-size converter has been demonstrated to be well performed, implying its application in the optical transceiver module using SLD as light source and hybrid integration of III–V semiconductor waveguiding devices and PLCs.
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