Menghao Huang

Linearized analog photonic links based on a dual-parallel polarization modulator

A linearized analog photonic link (APL) is proposed based on an integratable electro-optic dual-parallel polarization modulator (DPPolM), which consists of two polarization beam splitters and two polarization modulators (PolMs). Theoretical analysis shows that the APL is potentially free from the third-order nonlinear distortion if a polarization controller placed before the DPPolM is carefully adjusted. A proof-of-concept experiment is carried out. A reduction of the third-order intermodulation components as high as 40 dB and an improvement of the spurious-free dynamic range as large as 15.5 dB is achieved as compared with a single PolM-based link. The DPPolM-based APL is simple, compact, and power efficient since it requires only one laser, one modulator, and one photodetector.

Polarization-modulated analog photonic link with compensation of the dispersion-induced power fading

A novel integrable modulator consisting of a polarization modulator and a polarizer is proposed for constructing a high-performance analog photonic link. By adjusting a polarization controller placed before the modulator, both amplitude modulation and phase modulation with adjustable ratio between them are implemented. This feature is used to shift the peak of the frequency response of a dispersive link to any desired frequency, so the dispersion-induced power fading around the frequency is compensated. A proof-of-concept experiment is performed. The compensation of the dispersion-induced power fading in the proposed analog photonic link increases the spur-free dynamic range as large as 12.5 dB.

Measurement of optical magnitude response based on double-sideband modulation

A novel approach to perform high-resolution optical magnitude response measurements, using optical double-sideband (ODSB) modulation, is proposed and experimentally demonstrated. As compared with a conventional optical single-sideband modulation-based optical magnitude response measurement, the proposed method based on ODSB modulation features not only simple configuration and doubled measurement range, but also immunity to modulation nonlinearity. A proof-of-concept experiment is carried out. The magnitude response of a fiber Bragg grating (FBG), in the range of 40 GHz, was measured with a resolution of 10 MHz, by using a 20 GHz microwave signal source.

Photonic microwave bandpass filter based on optical single-sideband polarization modulation for long-reach radio over fiber applications

A two-tap dispersion-insensitive photonic microwave bandpass filter based on optical single-sideband (SSB) polarization modulation is proposed for long-reach radio over fiber applications. The optical SSB polarization modulation, which generates two complementary intensity-modulated signals along two orthogonal polarization directions, is implemented by a polarization modulator (PolM) followed by an optical filter. With a polarization maintaining fiber (PMF) to introduce a time delay, a two-tap dispersion-insensitive photonic microwave bandpass filter is obtained. The proposed filter is used to shape a Gaussian pulse to an ultra-wideband (UWB) signal. After 40-km fiber transmission, no distortion in the waveform of the UWB signal is observed.

Reflective-type ring resonators for flat-top optical filter and wideband true time delay line

Optical ring resonators have attracted great interests in integrated photonics, since they can be employed for a variety of applications, such as filters, multi/demultiplexers, true time delay lines, optical routers, optical signal processers, and so on. Here, we propose our recent progress on reflective-type ring resonators in both theoretical analysis and experimental results, which can be used as flat-top optical filters and wideband true time delay lines. In the reflective-type ring resonators, the drop port is cascaded by a reflector and the light from the drop port can be reflected back into the ring. Hence, there are two light propagating in the opposite direction in the ring cavity. The output port of the device is the add port of a conventional ring resonator. It can be considered that the reflective-type ring is a superposition of two ring resonators with the same radii, but one propagating in clockwise direction and the other propagating in counterclockwise direction. The input port of clockwise direction ring resonator is the drop port of the other one. These two ring resonators produce peak response and notch response in the output port, respectively. By tuning the coupling coefficients, the strong peak response can be offset the weak notch response. As a result, the device can be used as a flat-top bandpass filter. In another respect, ring resonators can be used as the true time delay line, but the delay bandwidth of a ring resonator is limited by large group delay dispersion. In such reflective-type ring resonator, with suitable coupling coefficients, the light propagating counterclockwise is strong slow light, while the one propagating clockwise is weak fast light. Due to the group delay dispersion of fast light can offset that of the slow light, the total group delay dispersion can be reduced. Hence, wideband optical true time delay can be obtained.

A bandwidth-tunable flat-top optical filter based on a single reflective-type microring resonator

An optical filter with flat-top spectral response and tunable bandwidth is proposed and numerically demonstrated based on a single reflective-type microring resonator (MRR). The reflective-type MRR consists of a MRR and a reflector in the drop port of the MRR, which is equivalent to two cascaded rings with one creates a strong passband response and the other one produces a weak notch response. The combination of the two responses leads to a flat-top bandpass response. By adjusting the coupling coefficients of the two optical couplers in the MRR, the 1-dB bandwidth can be continuously tuned from 0.025 to 0.121 nm for a reflective-type MRR with a radius of 100 μm, while the insertion loss is varied within 0.63 dB.