Narrow-band tunable optical filters based on cascaded Fabry-Perot cavities.

Narrow-band tunable optical filters (TOF) based on three cascaded Fabry-Perot (FP) cavities are demonstrated. The FP cavities are fabricated with Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), which is a transparent electro-optic ceramic. With a reflective design, the optical signal passes the three FP cavities twice. Thus we can design the FP cavities with a relatively low reflectivity, which enables it more tolerant to the loss in the cavities. Two types of TOF samples are fabricated. The specifications of the transmissive type TOF with dual-ports are tuning range >48nm, FWHM (full width half maximum) <0.06nm, insertion loss <3.87dB, crosstalk <-39dB, which meet the requirements by optical performance monitor (OPM) applications. The specifications of the reflective type TOF with single-port are tuning range >48nm, FWHM (full width half maximum) <0.1nm, insertion loss <2.82dB, crosstalk <-30dB, which can be employed in tunable fiber lasers for wavelength selection and tuning.

A two-in-one Faraday rotator mirror exempt of active optical alignment.

A two-in-one Faraday rotator mirror was presented, which functions as two independent Faraday rotation mirrors with a single device. With the introduction of a reflection lens as substitution of the mirror in traditional structure, this device is characterized by exemption of active optical alignment for the designers and manufacturers of Faraday rotator mirrors. A sample was fabricated by passive mechanical assembly. The insertion loss was measured as 0.46 dB/0.50 dB for the two independent ports, respectively.

A MEMS Variable Optical Attenuator with Ultra-Low Wavelength-Dependent Loss and Polarization-Dependent Loss.

Applications in broadband optical fiber communication system need variable optical attenuators (VOAs) with low wavelength-dependent loss (WDL). Based on analysis on the dispersion of the optical system of a MEMS-based VOA, we provide a method to reduce the WDL significantly with minor revision on the end-face angle of the collimating lens. Two samples are assembled, and the measured WDL is <0.4 dB over the C-band (1.53⁻1.57 µm) at a 0⁻20 dB attenuation range. Meanwhile, the new structure helps to reduce the polarization-dependent loss (PDL) to <0.15 dB, which is only half that of conventional devices.

Generalized Hartmann-Shack array of dielectric metalens sub-arrays for polarimetric beam profiling.

To define and characterize optical systems, obtaining the amplitude, phase, and polarization profile of optical beams is of utmost importance. Traditional polarimetry is well established to characterize the polarization state. Recently, metasurfaces have successfully been introduced as compact optical components. Here, we take the metasurface concept to the system level by realizing arrays of metalenses, allowing the determination of the polarization profile of an optical beam. We use 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. Our system is extremely compact and allows for real-time beam diagnostics by inspecting the foci amplitudes. By further analyzing the foci displacements in the spirit of a Hartmann-Shack wavefront sensor, we can simultaneously detect phase-gradient profiles. As application examples, we diagnose the profiles of a radially polarized beam, an azimuthally polarized beam, and of a vortex beam.

1x8 fiber-optic switch based on an innovative waveguide converter and a micro torsion mirror.

This paper reports a 1x8 fiber-optic switch based on an innovative waveguide converter and a micro torsion mirror. A compact 9-fiber collimator is implemented with the waveguide converter. With the micro torsion mirror aligned to the 9-fiber collimator, light from the central fiber can be steered to any of the other 8 fibers. The introduction of the waveguide converter enables a smaller and faster micro torsion mirror. The switch shows good performance, insertion loss, nonuniformity, and cross talk is <3.02 dB, <0.4 dB, and <-35 dB respectively. Improvements of performance are expected after further optimization.

Design and fabrication of an optical interleaver with cascaded multimode interference couplers.

A lattice-form optical interleaver was designed and fabricated with a silicon-based silica waveguide. Cascaded multimode interference couplers were first employed in the lattice circuit and helped to relax the fabrication tolerance. The device shows good performance, the insertion loss is less than 2.25 dB, the passband ripple is less than 0.15 dB, the cross talk is less than -18.9 dB, and the 0.5 dB passband is more than 100 GHz.