A stable, single- and dual-wavelength, single-longitudinal-mode operation ring erbium-doped fiber laser with ultranarrow linewidth and high optical signal to noise ratio is proposed and demonstrated experimentally. Different from using traditional fiber Bragg gratings as narrow band filters, a guided-mode resonance reflector with high quality value, fabricated on a silicon-on-insulator wafer, acts as an external reflector to realize optical feedback and wavelength selectivity in the fiber laser. Using unpumped erbium-doped fiber as a saturable absorber, different areas of the guided-mode resonance reflector as mode restricting elements, we obtain a single-wavelength laser with optical signal to noise ratio over 67 dB and ultra-narrow linewidth of 525 Hz, and a dual-wavelength laser with optical signal to noise ratios higher than 61 dB and linewidths less than 800 Hz for both lasing wavelengths. Meanwhile, all the central wavelength variations and power fluctuations of the laser are less than 0.024 nm and 0.106 dB, respectively, showing favorable stability.
The thin film lithium niobate (LNOI) platform has attracted great interest towards integrated photonics devices, featuring high-speed electrooptical responsion and low-loss light propagation. To enhance the function of passive devices in LNOI, the fundamental mode hybridization (TE0, TM0) in an LNOI ridge waveguide is therotically analysed and experimentally demonstrated. A microring resonator with Q-factor of 1.78 million is fabricated, revealing the appearance of the mode hybridization by observing sudden jumps in the FSRs of both fundamentally resonating modes. The central wavelength of the fundamental mode hybridization is designed at 1562nm and observed at 1537nm. Potential applications include fundamental mode conversion, polarization rotation, polarization splitter, and polarization insensitive waveguides in optical receiver module.
Lithium niobate (LN) devices have been used in optical communication and nonlinear optics widely due to its impressive optical properties. Thin-film lithium niobate on insulator (LNOI) improves performances of LN-based devices further. But a high-efficient fiber-chip optical coupler for the LNOI-based devices for practical applications is still absent. In this article, we demonstrate a wide-band, highly efficient and polarization independent edge coupler based on LNOI fabricated by planar semiconductor process. The measured ultra-high numerical aperture fiber (UHNAF)-to-chip optical coupling loss at 1550 nm is 0.54 dB/facet (0.59 dB/facet) for TE(TM). The coupler has the coupling loss lower than 1dB/facet for both TE and TM light at wavelengths longer than 1527nm.
Here we demonstrated a single polarization waveguide and spot size converter for edge coupling working at O band based on Lithium niobate on insulator.The improvement extinction ratio of 35dB/cm is obtained for the single polarization waveguides. The insertion loss of bilayer spot size converters is 3.5dB/facet from our best results at the light length of 1310nm.
Measuring light’s information of polarization and phase in real time is very important in optics. Since metasurfaces enable the wavefront manipulation, which can replace some conventional optical components and make the system extremely compact. Here, we apply the concept of metasurface to system level, creating a generalized Hartmann-Shack array based on 3×2 sub-arrays of silicon-based metalenses for optical multi-parameters detection, which not only measures phase and phase-gradient profiles of optical beams but also measures spatial polarization profiles at the same time. The silicon-based metalenses, with a numerical aperture of 0.32 and a mean measured focusing efficiency in transmission mode of 28% at a wavelength of 1550 nm. Furthermore, we demonstrate detections of a radially polarized beam, an azimuthally polarized beam and a vortex beam.
We present a compact hybrid-integrated 4 × 25.78 Gb/s TOSA based on butt coupling between DFB-LDs and silica-PLC AWG multiplexer. To obtain a low cost TOSA, high-cost conventional hermetic ceramic metal box is replaced with nonhermetic metal box. Experimentally, we demonstrate that the TOSA could achieve error-free operation for a 10 km transmission at 25°C. The packaged CWDM TOSA, which is 15.8 mm × 7.0 mm × 6.0 mm in size, shows a side-mode suppression ratio of >40 dB, a 3-dB bandwidth of >18 GHz, and error-free transmission with an average optical output power of >0 dBm and dynamic extinction ratio of >4.0 dB at 25.78125 Gb/s over a 10-km single-mode fiber for all four lanes.
A four-layered composite silicon nitride waveguide with an asymmetric horizontal slot is proposed. The waveguide exhibits an ultra-flat and low dispersion with four zero dispersion wavelengths over an ultra-wide bandwidth. In the wavelength range from 1269 nm to 2556 nm, the dispersion varies between -3.27 and 3.29 ps/nm/km. Dispersion tailoring is studied by tuning structural parameters of the composite waveguide. Nonlinear coefficient and phasematching condition in four-wave mixing process are explored, which confirm the proposed waveguide is promising in nonlinear applications.
We present a optical phased array antenna with gratings by using shallow ethced grating coupler on silicon-oninsulator for large angle optical beam steering. By decreasing the spacing of antenna to 0.9 μm, The steering range of the antenna can reach as large as 106° with a SNR of -7dB. To prevent crosstalk from grating coupler with small element spacing, we change the width of each grating to cause phase mismatch between adjacent antennas. Specific design is also made to the periods of each antenna in order to make the steering angle of antenna the same. Such grating array superlattices have great potential in LIDAR and free-space communication for its large steering range and small SNR.
Silicon slot waveguides have great potential in hybrid silicon integration to realize nonlinear optical applications. We propose a rectangular-cladding hybrid silicon slot waveguide. Simulation result shows that, with a rectangular-cladding, the slot waveguide can be formed by narrower silicon strips, so the two-photon absorption (TPA) loss in silicon is decreased. When the cladding material is a nonlinear polymer, the calculated TPA figure of merit (FOMTPA) is 4.4, close to the value of bulk nonlinear polymer of 5.0. This value confirms the good nonlinear performance of rectangular-cladding silicon slot waveguides.
We propose a multiwaveguide cavity which can significantly enlarge the mode volume of distributed feedback (DFB) cavity without increasing the cavity length. The cavity is constructed by combining λ/4 shifted DFB cavity with contra-directional couplers. Different from single-waveguide DFB cavity, the resonant mode is oscillating in multiple waveguides. A smaller threshold gain density is also obtained compared to single-waveguide DFB cavity. Theory model of the multiwaveguide cavity is established and finite-difference time-domain simulation is performed to verify the model.
Although slot waveguide structures are widely used in all kinds of optical devices, very few articles focus on the issue of optical isolation of slot waveguides. This article, in an effort to bridge the gap in the available literature, focuses on the aspect of optical isolation of slot waveguides and provides definitive rules for application of different slot waveguides in dense integration of optical links. A slot waveguide with a 48-nm-wide slot was fabricated with electron beam lithography and inductively coupled plasma etching.
In this paper, we present a single microring resonator structure formed by incorporating a reflectivity-tunable loop mirror for the tuning of resonance spacing. Based on the optical mode-splitting in the resonator structure, spacing between two adjacent resonances can be tuned from zero to one whole free spectral range (FSR) by controlling the coupling strength between the two counter-propagating degenerate modes in the microring resonator. In experiment, by integrating metallic microheater, the resonance-spacing tuning over the whole FSR (1.17 nm) is achieved within 9.82 mW heating power dissipation. The device is expected to have potential applications in reconfigurable optical filtering and microwave photonics.