In order to solve the limitation of data transmission speed and transmission distances of the communication system due to the accumulated dispersion in Orbital Angular Momentum (OAM) transmission system, a Ge-doped Sandwich Ring-core Photonic Crystal fiber (SR-PCF) is proposed for OAM modes’ broadband dispersion compensation. SR-PCF is divided by the Ge-doped sandwich ring-core into two regions of the inner and outer claddings, which is conducive to negative dispersion. By optimizing structural parameters and doping percentages, the dispersion compensation properties of SR- PCF are improved. The proposed SR-PCF are numerically analyzed by the finite element method. The results show that SR-PCF has high negative dispersion of -63.31 and -62.14ps/(nm·km) of the OAM1,1~2,1 modes at 1.55μm with negative dispersion slope in the range of 1530~1570nm. In addition, its maximum confinement loss is only 2.18×10 -7dB/km. The proposed SR-PCF can be used for high order of orbital angular momentum modes’ broadband dispersion compensation in the mode division multiplexing systems and the construction of passive all-optical networks.
A novel two-dimensional photonic crystal broadband Y-shaped 1 × 2 beam splitter is proposed. Broadband performance of the 1 × 2 beam splitter can be greatly improved by optimizing the z-axis offset of the dielectric rods adjacent to the input and output waveguides, and the offset along the V-shaped oblique waveguide of the dielectric rods at the junction area. To enhance the optimization efficiency and achieve excellent splitting performance of the 1 × 2 beam splitter, the genetic algorithm is applied to inversely design the above offsets of the 1 × 2 beam splitter. The results show that, in the bandwidth range of 1515 to 1587 nm, the highest and lowest transmittance of the 1 × 2 beam splitter are 99.6% and 97.9%, respectively, the additional loss is <0.1 dB, and the uniformity tends to 0 dB. Finally, the tolerance analysis of the 1 × 2 beam splitter is carried out. When the deviation of each variable reaches ±10 nm, the total transmittance of the 1 × 2 beam splitter in the bandwidth range of 1515 to 1587 nm is still higher than 95.2%, with the additional loss <0.22 dB. Due to the virtues of broad operating bandwidth, high transmittance, good uniformity, and strong robustness, the proposed 1 × 2 beam splitter will have great application prospects in the field of photonic integrated circuits, all-optical communication network, and so on.
KEYWORDS: Modulation, Frequency combs, Modulators, Lithium, Optical engineering, Superposition, Binary data, Signal to noise ratio, Continuous wave operation, Signal attenuation
We propose a scheme of optical frequency comb (OFC) generation based on cascaded Mach–Zehnder modulator (MZM) and electroabsorption modulator (EAM) with Gaussian-shaped pulse signal. In the proposed scheme, the MZM and the nonzero-chirp EAM are driven by a periodic Gaussian-shaped pulse signal that is controlled with binary sequences, and then an OFC is output from EAM. The theoretical model of the OFC generation is developed by improving the theory of electroabsorption modulation. The performance of OFC is investigated. The results show that the frequency spacing of the OFC can be tuned in the range of 1 to 10 GHz, the number of effective comb-lines is 35, and the power variation of comb-lines is 2.14 dB.
KEYWORDS: Microsoft Foundation Class Library, Microwave radiation, Frequency combs, Binary data, Modulation, Lithium, Modulators, Optical engineering, Phased array optics, Signal to noise ratio
We propose a scheme of a digitally controlled microwave frequency comb (MFC) based on a Mach–Zehnder modulator (MZM) and pulse signals. In the proposed scheme, an MZM is driven by a periodic pulse signal that is controlled with binary sequences and then outputs an optical frequency comb (OFC). After the beat frequency occurs among modes of the OFC, an MFC with a wide spectrum coverage and small power variation is obtained using a photodetector. The theoretical model of the MFC generation based on pulse signals is developed. The performance of the MFC generation scheme is investigated. The results show that the minimum power variation and maximum spectrum bandwidth of the generated MFC are 0.31 dB and 300 GHz, respectively. By programming the binary sequence, the frequency spacing of MFC and the number of microwave signals can be tuned in the range of 1.25 to 10 GHz and 31 to 255, respectively.
A tunable dual-frequency optoelectronic oscillator (OEO) based on a tunable dual-passband microwave photonic filter (DPMPF) is proposed and demonstrated. The DPMPF is based on phase-to-intensity modulation (PM-IM) conversion and stimulated Brillouin scattering (SBS). Two pump lightwaves are generated through carrier-suppression doublesideband modulation (CS-DSB) in a Mach-Zehnder modulator (MZM) to generate two SBS gain regions in a single mode fiber. Two SBS gain regions act on the phase modulation signal to achieve a dual-passband filter. Through simply varying the frequency of the radio frequency (RF) signal used for CS-DSB, the two central frequencies of the OEO can be tuned with the frequency interval kept constant. In addition, adjusting the frequency of tunable optical source launched to the MZM, the frequency interval of the OEO can be tuned. In the experiment, the dual-frequency OEOs with frequency intervals of 0.2 GHz and 1.2 GHz are achieved, respectively. The frequency tuning range from 3 to 8 GHz is demonstrated. The dual-frequency OEO with the frequency interval tuned is also achieved.
A polarization independent 1 × 3 equal optical power splitter (OPS) based on the self-collimation effect in two-dimensional (2-D) photonic crystal (PC) is proposed. Two splitter structures are introduced in the self-collimation 2-D PC, both of which have an air layer and a row of defect air holes. The proposed OPS is simulated using Rsoft software combined with plane wave expansion method and two finite-difference time-domain method. The results show that the beam for transverse electric (TE) mode and transverse magnetic (TM) mode can be self-collimated and divided equally into three outputs at the operating wavelength of 1310 nm. The transmission efficiencies are 95% for TE mode and 93% for TM mode, and the corresponding additional losses are 0.223 and 0.315 dB for TE mode and TM mode, respectively. The steady times are lower than 1.4 ps. The proposed polarization independent 1 × 3 equal OPS will have potential applications in optical fiber communication system.
A coherence-free and reconfigurable filter based on semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. A high coherent RF-modulated light source is converted to an incoherent light source by employing the cross-gain modulation of amplified spontaneous emission (ASE) of the SOA. The inversely modulated ASE is sliced by an optical wavelength demultiplexer to realize a stable transversal microwave filter. Reconfigurability of the filter can be achieved by controlling the number and apodization of the taps. The filters with two, three and four taps are experimentally demonstrated.
A reconfigurable microwave photonic filter based on a polarization modulator (PolM) is proposed and experimentally demonstrated. The PolM together with a polarization controller (PC) and a polarization beam splitter (PBS) implements two complementary intensity modulations in two separated branches. Then, optical components are inserted in the two branches to realize a bandpass filter and an allpass filter, respectively. When the two branches are combined by a second PBS, a filter with a frequency response that equals the subtraction of the frequency responses of the allpass filter and bandpass filter is achieved. By adjusting the PCs placed before the second PBS, a notch filter with a tunable notch depth or a bandpass filter can be achieved.
A new cascaded microwave photonic filter consisting of two or more infinite impulse response (IIR) filters based on
active loops. is presented. Owing to wavelength conversion, the interference between the modulated optical signals of
different taps from different active loops can be avoided and the stable transmission characteristic of the cascaded filter
can then be achieved. The cascaded filter can increase the free spectral range (FSR) and the Q value significently by
designing the FSR differences of the IIR filters. The cascaded filter with two IIR filters is demonstrated, and the
measured results of a high Q of 3338 and rejection ratio of about 40 dB are obtained. The tunability can also be realized.
We propose an ultrahigh-speed all-optical wavelength conversion for polarization-shift-keying (PolSK) signal, based on
parallel dual-pump four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). A comprehensive broad-band
dynamic model of this kind of all-optical wavelength converter is developed. By numerical simulation, using the
broad-band dynamic model, the effects of input waves powers and wavelengths on the output performance of
wavelength conversion for PolSK signal are theoretically investigated in detail. This scheme is suitable for wide
wavelength range of input PolSK signal. It is simple, compact, and feasible for ultrahigh-speed operation.
We proposed a simultaneous three-wavelength conversion based on the cross-gain modulation (XGM) in the
multi-wavelength semiconductor fiber ring laser (SFRL). It is easily implemented owing to the simple structure.
Furthermore, it has realized multi-channel wavelength conversion, which reduces the cost of network expansion. A
comprehensive broadband dynamic model is presented. By numerical simulation, the proposed multi-wavelength
conversion is theoretically realized using the broadband dynamic model. Moreover, the dependences of conversion
efficiency and extinction ratio on the input signal power, signal wavelength and injection current are investigated in
detail.
We propose and experimentally demonstrate a novel all-optical microwave filter with high quality factor (Q). It is based
on a recirculating delay line (RDL) loop in which a semiconductor optical amplifier (SOA) is followed by a tunable
narrow-band optical filter and a 1x2 10:90 optical coupler. Converted signal used as a negative tap is generated through
wavelength conversion employing the cross-gain modulation (XGM) of the amplified spontaneous emission (ASE)
spectrum of the SOA. The converted signal can circulate in the RDL loop so that the proposed filter realizes a high Q
factor response after photo-detection. The 1x2 10:90 coupler is employed to extract 10% optical power from the loop as
output. A frequency response with a high Q factor of 543, a rejection ratio of 40 dB is experimentally demonstrated.
A novel scheme for 40Gb/s all-optical nonreturn-to-zero (NRZ) to polarization-shift-keying (PolSK) format conversion,
based on transient cross-phase modulation (T-XPM), is proposed and experimentally demonstrated using a single
semiconductor optical amplifier (SOA) assisted by optical bandpass filter (BPF). This proposed NRZ-PolSK format
conversion is robust in terms of simple structure and high bit rate operation. In addition, it can be realized without
wavelength change.
A novel scheme for an ultrahigh-speed all-optical full adder based on dual-pump four-wave mixing (FWM), including parallel dual-pump FWM and orthogonal dual-pump FWM, in two semiconductor optical amplifiers (SOAs) is proposed. In this scheme, the polarization-shift-keying (PolSK) modulation format is used, so pattern-dependent degradation can be reduced. The proposed all-optical full adder is simple, compact, and can accommodate ultrahigh-speed operation. By numerical simulation, it is theoretically investigated using the broad-band dynamic model.
Semiconductor optical amplifier (SOA)-based all-optical XNOR and AND gates using four-wave mixing (FWM) and
cross-gain modulation (XGM) with improved dynamics are simultaneously realized. The effects of the input optical
wave powers and injection current on the critical factors of the logic gate performances, such as the ON-OFF contrast
ratio, the output power level of the logic "1", and the output power difference of the logic "1", are theoretically
investigated in detail. In addition, the effect of the
counter-propagating CW pump on the gain recovery is analyzed.
Ultrahigh-speed all-optical AND and NOR gates for three-input polarization-shift-keying (PolSK) signals, based on
orthogonal dual-pump four-wave mixing (FWM) in semiconductor optical amplifier (SOA), is proposed and theoretically
investigated. This scheme is simple, compact, and feasible for ultrahigh-speed operation.
In this paper, a comprehensive broad-band model of tunable wavelength converter based on four-wave mixing (FWM) in semiconductor fiber ring laser (SFRL) is presented. Critical factors, eg., the material gain profile, the longitudinal variation of the optical field, the carrier density and the broad-band spontaneous noise emission are considered in the model. By numerical simulation, the effects of the input signal power, injection current, the coupling of the output couplers and the lasing wavelength on the performances of the wavelength converter, such as the conversion efficiency and the SBR, are investigated. Simulation results are in agreement with the experimental results in literatures.
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