Xiuyou Han

Athermal Silicon-on-insulator ring resonators by overlaying a polymer cladding on narrowed waveguides

Athermal silicon ring resonators are experimentally demonstrated by overlaying a polymer cladding on narrowed silicon wires. The ideal width to achieve athermal condition for the TE mode of 220 nm-height SOI waveguides is found to be around 350 nm. After overlaying a polymer layer, the wavelength temperature dependence of the silicon ring resonator is reduced to less than 5 pm/degrees C, almost eleven times less than that of normal silicon waveguides. The optical loss of a 350-nm bent waveguide (with a radius of 15 microm) is extracted from the ring transmission spectrum. The scattering loss is reduced to an acceptable level of about 50 dB/cm after overlaying a polymer cladding.

Bandstop-to-Bandpass Microwave Photonic Filter Using a Phase-Shifted Fiber Bragg Grating

A bandstop-to-bandpass microwave photonic filter (MPF) using a phase-shifted fiber Bragg grating (PS-FBG) and a dual-drive Mach-Zehnder modulator (DD-MZM) is proposed and experimentally demonstrated. The PS-FBG has an ultra-narrow notch in the reflection band. The DD-MZM is employed to generate a phase-modulated or a quasi-single-sideband (QSSB) optical signal by controlling the bias voltage. By applying the phase-modulated or QSSB signal to the PS-FBG to suppress one sideband, a bandpass or a bandstop MPF is implemented. The MPF can be continuously tuned from bandstop to bandpass or vice versa by controlling the bias voltage applied to the DD-MZM. The frequency tuning can be simply done by tuning the wavelength of the optical carrier. The proposed MPF is experimentally evaluated. Continuous tuning from a bandstop to bandpass filter with a bandstop rejection as high as 60 dB and frequency tuning with a frequency tunable range as large as 10 GHz are demonstrated.

A PSQ-L Polymer Microring Resonator Fabricated by a Simple UV-Based Soft-Lithography Process

Photonic integrated circuits based on polymer waveguides have great potential as low-cost optical devices. A novel inorganic-organic hybrid polymer polysiloxane-liquid (PSQ-L) is introduced for defining the waveguides and for use as both core and cladding layer for the waveguides. The waveguide circuits are replicated by a simple ultraviolet-based soft lithography method consisting of two steps. All-polymer microring resonators are fabricated by this approach and characterized. About 6-dB extinction ratio at the through port and 18-dB extinction ratio at the drop port is demonstrated. A Q-factor of 4.2 times 104 is obtained. Extracted from the measured spectrum, the scattering loss of the ring waveguides is estimated to be about 1.6 dB/cm. This easy fabrication technique can be easily extended to fabricate other devices.

Tunable Single Bandpass Microwave Photonic Filter With an Improved Dynamic Range

A tunable single bandpass microwave photonic filter (MPF) with an improved spurious free dynamic range (SFDR) using a dual-parallel Mach-Zehnder modulator (DP-MZM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. The DP-MZM is employed to generate an equivalent phase-modulated (EPM) signal with an adjustable optical carrier to sideband ratio. The PS-FBG is used as an optical notch filter to remove one sideband of the EPM signal to convert the EPM signal to a single-sideband intensity-modulated signal. At the output of a photodetector, a microwave signal is detected. The entire operation is equivalent to a single passband MPF. The tunability is achieved by tuning the wavelength the optical carrier. The SFDR of the MPF is improved due to the gain enhancement by a partial suppression of the optical carrier. An experiment is performed. A single bandpass MPF with a passband width of 150 MHz and a frequency-tunable range of ~5.5 GHz with an improved SFDR by 11 dB is demonstrated.

Tunable Dual-Passband Microwave Photonic Filter Using Orthogonal Polarization Modulation

A microwave photonic filter (MPF) with two independently tunable passbands using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. By applying two orthogonally polarized optical waves from two tunable laser sources (TLSs) to the PolM, two phase-modulated optical signals that are orthogonally polarized are generated, which are sent to the PS-FBG that acts as an optical notch filter to suppress one sideband of the orthogonally polarized phase-modulated signals. Thus, the two phase-modulated signals are converted to two intensity-modulated single-sideband signals. The overall operation corresponds to a dual-passband MPF with the central frequencies of the two passbands independently tunable by changing the wavelengths of the optical carriers from the two TLSs. The proposed MPF is experimentally evaluated. A dual-passband MPF with a bandwidth for each passband of 140 MHz and a frequency tunable range of ~6 GHz is demonstrated. The insertion loss and the dynamic range of the filter are also studied and measured experimentally.

UV-soft Imprinted Tunable Polymer Waveguide Ring Resonator for Microwave Photonic Filtering

A tunable polymer waveguide ring resonator is proposed and demonstrated for microwave photonic filtering. The ring resonator consists of a Mach-Zehnder interferometer (MZI) as the tunable coupler and two micro-heaters as the thermo-optic phase shifters. It was fabricated with inorganic-organic hybrid optical material polysiloxane-liquid series by a novel and simple UV-soft selective imprint technique. The coupling conditions, over-, critical- and under-coupling, were obtained with the micro-heater on the arm of MZI and the maximum notch depth of about 18 dB was achieved. The resonant wavelength was also tuned with the micro-heater on the ring waveguide. The dispersion induced power fading of radio over fiber link was overcome by the tunable ring resonator with its notch filtering function.

Optical RF Self-Interference Cancellation by Using an Integrated Dual-Parallel MZM

An optical approach to implement radio-frequency (RF) self-interference cancellation using an integrated dual-parallel Mach–Zehnder modulator (DP-MZM) is proposed and demonstrated experimentally. The received signals and the reference signal are converted into optical domain via the sub-MZMs (MZM1 and MZM2) in the DP-MZM, which are biased at the quadrature point and the minimum point with the output of double sideband with carrier signal and double sideband with carrier-suppressed signal, respectively. It avoids the optical interference at the combining Y branch waveguide. The time and the amplitude matching conditions for cancellation between the reference signal and the interference signal are completed by the electrical tunable time delay line and the phase shifter in the MZM2 path. A cancellation depth larger than 80 dB is obtained for the single-frequency signal of 2.4, 5, 8, and 10 GHz. For the bandwidth of 100 MHz, cancellation depths as high as 35.8, 33.1, and 38.3 dB are realized at frequencies of 2.4, 5, 8, and 10 GHz, respectively.

Simultaneous even- and third-order distortion suppression in a microwave photonic link based on orthogonal polarization modulation, balanced detection, and optical sideband filtering.

A microwave photonic link (MPL) with simultaneous suppression of the even-order and third-order distortions using a polarization modulator (PolM), an optical bandpass filter (OBPF), and a balanced photodetector (BPD) is proposed and experimentally demonstrated. The even-order distortions are suppressed by utilizing orthogonal polarization modulation based on the PolM and balanced differential detection based on the BPD. The third-order distortions (IMD3) are suppressed by optimizing the spectral response of the OBPF with an optimal power ratio between the optical carrier and the sidebands of the phase-modulated signals from the PolM. Since the suppression of the IMD3 is achieved when the MPL is optimized for even-order distortion suppression, the proposed MPL can operate with simultaneous suppression of the even-order and third-order distortions. The proposed MPL is analyzed theoretically and is verified by an experiment. For a two-tone RF signal of f1 = 10 GHz and f2 = 19.95 GHz, the spurious-free dynamic range (SFDR2) is enhanced by 23.4 dB for the second harmonic (2f1), and 29.1 and 27.6 dB for the second intermodulation (f2-f1 and f1 + f2), as compared with a conventional MPL. For a two-tone RF signal of f1 = 9.95 GHz and f2 = 10 GHz, the SFDR3 is increased by 13.1 dB as compared with a conventional MPL.

A low cost photonic biosensor built on a polymer platform

Planar integrated optical biosensors are becoming more and more important as they facilitate label-free and real time monitoring biosensing with high sensitivity. In this paper, the systematic research on one kind of optical biosensor, based on a resonant principle in a polymer ring resonator, will be presented. Reduced footprint and high sensitivity are advantages of this kind of biosensor. Rather than expensive CMOS fabrication, the device with high performance is fabricated through a simple UV based soft imprint technique utilizing self-developed low loss polymer material. The measurement results for the bulk sensing of a NaCl solution and the surface sensing of a minimal amount of avidin molecules in a buffered solution will be presented.

RF self-interference cancellation using phase modulation and optical sideband filtering

A novel optical approach to implement RF self-interference cancellation for full-duplex communication using phase modulation and optical sideband filtering is proposed and demonstrated experimentally. Based on the inherent out-of-phase property between the left and right sidebands of phase-modulated signal and optical sideband filtering, the RF self-interference cancellation is achieved by tuning the delay time and amplitude in the optical domain. RF self-interference cancellation for single frequency and microwave with various bandwidths of 1, 5, and 10 MHz is experimentally demonstrated to verify the proposed technique.