The ability to measure the orbital angular momentum(OAM)distribution of vortex light is essential for OAM applications.Although there have been many studies on the measurement of OAM modes,it is difficult to quantitatively and instantaneously measure the power distribution among different OAM modes,let alone measure the phase distribution among them.In this work,we propose an OAM complex spectrum analyzer that enables simultaneous measurements of the power and phase distributions of OAM modes by employing the rotational Doppler effect.The original OAM mode distribution is mapped to an electrical spectrum of beat signals using a photodetector.The power and phase distributions of superimposed OAM beams are successfully retrieved by analyzing the electrical spectrum.We also extend the measurement technique to other spatial modes,such as linear polarization modes.These results represent a new landmark in spatial mode analysis and show great potential for applications in OAM-based systems and optical communication systems with mode-division multiplexing.
Two types of 1×2 multi-mode interference （MMI） splitters with splitting ratios of 85：15 and 72：28 are designed. On the basis of a numerical simulation, an optimal length of the MMI section is obtained. Subsequently, the devices are fabricated and tested. The footprints of the rectangular MMI regions are only 3×18.2 and 3×14.3 （#m）. The minimum excess losses are 1.4 and 1.1 dB. The results of the test on the splitting ratios are consistent with designed values. The devices can be applied in ultra-compact photonic integrated circuits to realize the ＂tap＂ function.
All-optical digital logic elementary circuits are the building blocks of many important computational operations in future high-speed all-optical networks and computing systems. Multifunetional and reconfigurable logic units are essential in this respect. Employing the demodulation properties of delay interferometers for input differential phase shift keying signals and the gain saturation effect in two parallel semiconductor optical amplifiers, a novel design of 40 Cbit/s reconfigurable all-optical dual-directional half-subtractor is proposed and demonstrated. All output logic results show that the scheme achieves over 11=dB extinction ratio, clear and wide open eye diagram, as well as low polarization dependence （〈 1 dB）, without using any additional input light beam. The scheme may provide a promising candidate for future ultrafast all-optical signal processing applications.
We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband（UWB） signal generation using a semiconductor optical amplifier（SOA） based nonlinear optical loop mirror（NOLM）.By employing the cross phase modulation（XPM） effect,cross gain modulation（XGM）,or both,multi-shape UWB waveforms are generated including monocycle,doublet,triplet,and quadruplet pulses.Both the shapes and polarities of the generated pulses are flexible to adjust,which may be very useful in UWB pulse shape modulation and pulse polarity modulation.
We theoretically design a power-efficient ultra-wideband pulse generator by combining three monocycle pulses with different weights. We also experimentally demonstrate a feasible scheme to generate such power-efficient ultra-wideband waveforms using cross-phase modulation in a single semiconductor optical amplifier. The designed ultra-wideband pulse fully satisfies the requirements for the spectral mask specified by the Federal Communications Commission with high power efficiency. In the experiment, a power-efficient ultra-wideband waveform with a pulse duration of 310 ps is achieved, and the power efficiency is greatly improved compared with that of a single nlonocycle pulse or a mixture of two monoeycles.
We propose an efficient and low-power second harmonic generation(SHG)process in a silicon-compatible hybrid plasmonic microring resonator.By making the microring resonator doubly resonant at the fundamental wavelength of 3.1μm and second harmonic wavelength of 1.55μm,the SHG efficiency is enhanced by almost two orders of magnitude when compared to the previous result induced in a straight plasmonic waveguide.A SHG efficiency of 13.71%is predicted for a low pump power of 20 mW in a ring with radius of 2.325μm.This device provides a potential route for realizing efficient frequency conversion between mid-infrared and near-infrared wavebands on a chip.
We theoretically propose a multifunctional photonic differentiation （DIFF） scheme based on phase demodulation using two cascaded linear filters. The photonic D1FF has a diversity of output forms, such as the 1 st order intensity DIFF, the 1 st order field DIFF and its inversion, and the 2nd-order field DIFF, depending on the relative shift between the optical carrier and the filter＇s resonant notches. As a proof, we also experimentally demonstrate the DIFF diversity using a phase modulator and two delay interferometers （Dis）. The calculated average deviation is less than 7% for all DIFF waveforms. Our schemes show the advantages of flexible DIFF functions and forms, which may have different optical applications. For example, high order field differentiators can be used to generate complex temporal waveforms, and intensity differentiators are useful for the ultra-wideband pulse generation.
Format conversion is enabling function at the interface of different networks with different optimal modulation formats.Meanwhile,multi-channel signal processing function has its special significance for dense wavelength division multiplexing networks.In this paper,we designed and fabricated a delay interferometer cascaded with an arrayed-waveguide grating based on silicon on insulator.The 4-channel return-to-zero on-off keying(RZ-OOK) to non-return-to-zero on-off keying(NRZ-OOK) and return-to-zero differential phase shift keying(RZ-DPSK) to non-return-to-zero differential phase shift keying(NRZ-DPSK) format conversions at 40 Gbit/s were realized with this integrated device,the output eye diagrams showed a good conversion performance.Thanks to the mature fabrication technology,this device shows great potential for its small size,low power consumption and possibility of monolithic integration.
We propose and demonstrate a silicon-on-insulator （SOI） on-chip optical pulse shaper based on four-tap finite impulse response. Due to different width designs in phase region of each tap, the phase differences for all taps are controlled by an external thermal source, resulting in an optical pulse shaper. We further demonstrate optical arbitrary waveform generation based on the optical pulse shaper assisted by an optical frequency comb injection. Four different optical waveforms are generated when setting the central wavelengths at 1533.78 nm and 1547.1 nm and setting the thermal source temperatures at 23 ℃ and 33 ℃, respectively. Our scheme has distinct advantages of compactness, capability for integrating with electronics since the integrated silicon waveguide is employed.
In this paper, we experimentally demonstrate an all-optical continuously tunable fractional-order differentiator using on-chip cascaded electrically tuned microring resonators （MRRs）. By changing the voltage applied on a MRR, the phase shift at the resonance frequency of the MRR varies, which can be used to implement tunable fractional-order differentiator. Hence fractional-order differentiator with a larger ttmable range can be obtained by cascading more MRR units on a single chip. In the experiment, we applied two direct current voltage sources on two cascaded MRRs respectively, and a tunable order range of 0.57 to 2 have been demonstrated with Gaussian pulse injection, which is the largest tuning range to our knowledge.
