We propose a novel silicon on-line monitor of orthogonal modes/polarization, which consists of a Polarization Rotator (PR) and two location-specified photodiodes. The PR converts two polarization states to TE0 and TE1 state, which has different field distributions. Two photodiodes located in the different places on the waveguide are designed to analyze the modes. The experiment reveals that the p-n junctions which are located in the different places on the waveguide show different photo responsivity of both the TE0 and TE1 modes, because the responsivity is sensitive to optical power density around the depletion area. The power consumptions of both two modes are analyzed by the two sets of orthogonal photocurrent signals acquired from two location-specified photodiodes. The result matches well with the theory. The mode/polarization detector can also be expanded when more orthogonality states and more photodiodes are induced.
We demonstrate 32-channel dispersive optical phased arrays on a Si3N4-on-SOI integration platform. The phase difference is introduced by the arrayed waveguide. Beam steering in phased-array direction with an aliasing-free range of 22.4° and free spectrum ranges of ∼ 60 nm and ∼ 6 nm is achieved. Meanwhile, the main lobe is deflected simultaneously by 19.67° in the other direction by tuning the wavelength from 1500 nm to 1630 nm. Measurement results show that the dispersive optical phased array provides a compact, low-power and massively parallel solution for LiDAR applications.
Multimode waveguide Bragg gratings filters with square shape amplitude responses and well-controlled dispersion characteristics are achieved by the Time-Domain Layer Peeling method for the first time, the Bragg grating structures can be mapped by the complementary lateral-misalignment modulation apodization. Three filters with different amplitude and phase responses are demonstrated. For the dispersion-less filter, the dispersion compensation filter and the three-channel dispersionless filter, the 3 dB bandwidth and the group delay of the realizable spectral responses are 4.0 nm, 4.7 nm, 2.1 nm and 0 ps/nm, 5.7 ps/nm, 0 ps/nm, the group delay ripples have a standard deviation of 1.7 ps, 1.5 ps, and 2.0 ps. The multimode relaxes the fabrication requirement in terms of both the lithography resolution and minimum feature size/spacing while maintaining the advantages of low insertion loss.
A polarization-insensitive optical filter based on silicon and silicon nitride film is demonstrated. The lateral-shift apodization is introduced to suppress the sidelobes. The fabricated optical filter shows polarization-insensitive performances with large 3dB-bandwidths of 3.5–5.1 nm, low losses of 1.72-1 dB, decent SLSRs of 18.5-19.1 dB for both polarizations.
We demonstrate a 63-channel grating-lobe-free optical phased array, in which end-fire antennas were fabricated with a pitch of 775 nm to eliminate grating lobe. Phase mismatch was configured to suppress the optical crosstalk in the dense waveguides. Two-dimensional beam steering within 16°× 2.7° were presented by thermal phase shifting and wavelength tuning.
KEYWORDS: Sensors, Signal to noise ratio, Wavelets, Temperature metrology, Convolutional neural networks, Sensing systems, Reflectometry, Optical fibers, Modulation, Signal processing
We propose an instantaneous temperature measurement method based on wavelet convolutional neural network (wavelet-CNN) to extract Brillouin frequency shift (BFS) in Brillouin optical time domain reflectometer (BOTDR) sensor and map the BFS to the temperature. Compared to Lorentzian curve fitting (LCF), both the simulation and experimental results show the wavelet-CNN has better accuracy and shorter processing time.
ultra-compact silicon mode (de)multiplexers are demonstrated based on asymmetric directional couplers with subwavelength structure (ADCWSS), the subwavelength structure is a series of corrugation on the sidewalls of waveguides, and the two arrays of corrugation extend into the gap region between the waveguides and interlace with each other. The coupling length of ADCWSS are 5.6μm, 6.5μm, and 7.9μm for TE0-TE1, TE0-TE2, TE0-TE3 mode (de)multiplexers, respectively. The four-mode mode-division-multiplexing (MDM) link was fabricated and measured. The insertion losses of TE0-TE0-TE0, TE0-TE1-TE0, TE0-TE2-TE0, and TE0-TE3-TE0 are 0.2dB, 0.7dB, 0.7dB and 0.9dB (around 1.55μm). The maximum insertion losses and crosstalk are 2.4dB, 2.9dB, 3.0dB, 4.0dB and -18dB, -19dB, -16dB, -18dB for the TE0, TE1, TE2 and TE3-mode channels over a 50-nm bandwidth.
A dual-microring resonator replaces one of the couplers of the Mach-Zehnder interferometer (MZI) to achieve a widely tunable twin-fano resonance, which originates from the interference and coupling of mode in a dual-microring resonator. The slope can be tuned in a wide range from -84.2 dB/nm to 91.0 dB/nm by metal heaters integrated on one arm of the MZI, and the resonant wavelength fixes when slope changes. The “X-type” spectrum is shown by self-alignment, which means manual alignment to form “X-type” line is unnecessary after tuning dual-microrings because the “X-type” line can be produced easily by the difference of two correlated spectrums rather than two independent spectra. Meanwhile, it shows high wavelength resolution of 1 pm with an ideal resolution of 0.4 pm in the region of the slope of 127.4 dB/nm, which can be applied to wavelength monitoring with ultra-high resolution.
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