High speed 8PSK optical modulator using silicon/electro-optic polymer hybrid coupled ring resonator

Characteristics optimization in single and dual coupled silicon-on-insulator ring (disk) photonic biosensors

A novel in-band OSNR monitoring technique based on fractional Fourier transform of LFM signal

We have proposed an 8PSK modulator based on three microring modulators (MRM). The design consists of three MRMs, each with a radius of 11.1 μm. Of these three, two MRMs are connected in parallel and they together generate a quadrature phase shift keying (QPSK) signal. While at the output port of the QPSK, a third MRM is connected in series works as an angle modulator, which is basically a 45° phase shift modulator; that is, the output of the MRM varies by 45° depending on the bit pattern fed to it, ‘0’or ‘1’ respectively. We have simulated and shown the performance of the proposed 8PSK modulator after transmitting the modulated signal through various lengths of optical. Constellation diagrams and eye diagrams at different fiber lengths are analyzed. Bit error rate (BER) versus optical signal to noise ratio curve shows that, 10−3 BER has been achieved at 13.5 dB optical signal to noise ratio.

We propose and fabricate an ultrafast and high extinction ratio 1×4 optical switch based on a cascade, dual-output Mach–Zehnder interferometer (MZI) on the lithium niobate platform. The optical switch consists of cascaded, identical, dual-output MZI structures, and each of them includes a Y-branch waveguide, two parallel interference arms (electrode action area), and a 3 dB directional coupler. Four output optical paths can be switched through three groups of electrode hierarchical modulation. The test results of the fabricated device show that the insertion loss of each port is less than 7.1 dB and that the maximum extinction ratio is higher than 39.3 dB. The optical switch can achieve a high extinction ratio greater than 20 dB within the 50 nm wavelength range. The measured half-wave voltage is less than 4.13 V, and the minimum switching rise and fall times reach 125 ps and 250 ps, respectively. This result shows that the proposed and fabricated 1×4 integrated optical switch on a lithium niobate platform has the advantages of a fast response rate, high extinction ratio, and low switching voltage.

Joint modulation format identification and OSNR estimation method based on trajectory information analysis

Electro-optic Mach-Zehnder interferometer (MZI) switches are well known devices in optical systems for their high speed of operation. In next generation optical network, such switches have wide applications due to their high switching capability and great reliability. In this paper we have investigated the enhanced performance of an electro-optic switch made by titanium diffused lithium niobate (Ti:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) functioned as waveguide medium based on integrated Mach-Zehnder interferometer (MZI) at 1.55 μm wavelength. The performance of the switch is optimized for low switching voltage, low insertion loss, high extinction ratio. This is done by varying the strip thickness of titanium, interferometer arm length, arm gap, waveguide width, gap in the coupling region of the 3 dB couplers, and center position of second electrode deposited on integrated Mach-zehnder Interferometer arm with respect to the original axis of the switch. The designed switch gives lowest insertion loss of 0.00881dB and highest extinction ratio of 33.581 dB at 8.8 V.

We demonstrate a multiwavelength semiconductor optical amplifier (SOA) fiber ring laser with a dual- pass Mach- Zehnder interferometer (MZI) filter. Two SOAs provide enough gain and wider gain spectrum for more wavelength lasing. The dual-pass MZI with a high extinction ratio (ER) serves as comb filter. 82 wavelengths within a power deviation of 5 dB with the signal-to-noise ratio of 30 dB oscillate simultaneously.

An all-fiber Mach-Zehnder interferometer (MZI) interleaver using one planar 3×3 fiber coupler, one 2×2 fiber coupler and one 8-shaped fiber ring resonator is developed by the new configuration. Based on its structure, the output spectrum expression is established and described by using the principle of fiber transmission and the matrix transfer function. The results of numerical simulation indicate that when the length difference of interference arms and the coupling coefficients of the couplers are some certain values, it obtains a uniform flat-top passband and similar to rectangular output spectrum. Compared with the traditional MZI interleaver, the isolation in stopband and the rolloff in transition band are strengthen, the 25dB stopband bandwidth and 0.5dB passband bandwidth are simultaneously remarkably improved. Compared with the asymmetrical ring resonator MZI interleaver, the influence of transmission loss on extinction ratio can be effectively reduced. The device has a certain ability to resist the deviation, which reduces the difficulties in fabricating it. The experiment results agree with the theoretical analysis well. The interleaver designed by the proposed approach has favorable performance, which has the potential application value in optical fiber communication system.

We propose a novel method to generate photonic quadrature-phase-shift-keying (QPSK) vector signal by using only one Mach-Zehnder modulator (MZM). Because of the 'square-law' by the photo-detector, the amplitudes and the phase of the driving radio-frequency (RF) signal changed after detection. So the amplitude and the phase of the driving radio-frequency (RF) signal should be pre-coded before used to drive the MZM. Turbo equalization is investigated in vector signal system to improve the system transmission performance. We experimentally demonstrate and investigate the transmission performance with rates of 1-Gbaud over 40-km single-mode fiber (SMF) transmission. Our experimental results shows that this concept of the generation of QPSK vector signal can be employed in our transmission system architecture based on Turbo equalization. The received sensitivity of QPSK vector signal with code rate 1/2 and 2/3 Turbo equalization at the bit error rate (BER) of 10−4 after 40km SMF transmission are 4dB and 3dB better than the original QPSK signal, respectively. The experimental results show that the QPSK signal with Turbo equalization has better dispersion compensation and error-correcting ability.

Ultra-dense wavelength division multiplexing (UDWDM) free-space optical (FSO)-fiber-to-the-x (FTTx) hybrid networks were investigated as a critical enabler for nextgeneration <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 G / 6 G$</tex> backhaul systems. However, dynamic atmospheric turbulence and weather-induced impairments were identified as significant challenges. To solve these issues, a machine learning (ML)-based system that employs the eXtreme Gradient Boosting (XGBoost) algorithm for real-time cross-layer prediction of optical signal-to-noise ratio (OSNR), quality factor (QF), and bit error rate (BER) under different weather conditions was developed. Four modulation formats-on-off keying non-return-to-zero (OOK-NRZ), quadrature phase-shift keying (QPSK), polarization-division multiplexed QPSK (PDM-QPSK), and polarization shift keying (PolSK)-across input power levels (20 to 5 dBm), FSO link distances (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1-12.5 \text{km}$</tex>), and weather conditions (clear, fog, haze, and rain) were created using numerical simulations. While BER <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(R^{2}=0.6980\right.$</tex>, MAE <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$=1.56 \times 10^{-} { }^{1}$</tex>) had intermediate prediction accuracy, OSNR <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(R^{2} \geqslant 0.99\right., R M S E=0.0238)$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q F\left(R^{2} \geqslant 0.99\right., \left.M A E=0.0039\right)$</tex> had good prediction accuracy. The final predictive node used a greedy approach that prioritizes reduced power consumption and higher modulation orders to dynamically find optimal configurations. This allows for dependable high-speed communication by repeatedly adjusting to the conditions of the channel. Shapley Additive Explanations (SHAP) analysis revealed that the main factors influencing performance were link length and weather intensity. The proposed model shown by statistical testing (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$p&lt;$</tex> 0.05), indicates how the model is reliable. Thus, the theoretical machine learning models and real-world FSO network optimization were bridged by using the proposed study, which offers a scalable implementation technique.

In future wavelength-division multiplexed (WDM) reconfigurable networks, the ability to shift a signal from one wavelength to another may be an essential function due to a limited number of available wavelengths. The Mach-Zehnder interferometer (MZI) has sparked the interest of the WDM community because ofits ability to wavelength convert signals at high speed, in both inverting and noninverting configurations with a high output extinction ratio, and with low chirp. In this paper, we assess the stability of the extinction ratio of the MZI with variations in the SOA bias currents, as well as with the wavelength and the power of the pump and probe. We characterize the operating point stability of the MZI and find ranges for the bias currents and for the input parameters, in order to minimize the sensitivity of the extinction ratio (ER).

Suppression of optical beat interference-noise in orthogonal frequency division multiple access-passive optical network link using self-homodyne balanced detection

Differential phase-shift keying (DPSK) has been widely implemented and developed in high-speed optical communication systems. The low error rate detection at high access rate is one of the considerable issues in practical engineering application. Balanced detection based on fiber Mach-Zehnder delay interferometer (MZDI) is the typical optical DPSK signal detecting method. It requires that the free spectrum range (FSR) of the MZDI equals the reciprocal of symbol period of the DPSK signal. For the reasons of ambient temperature variation and nonlinear phase noise, a dynamic frequency offset always exists between the FSR and the reciprocal of symbol period. That may introduce some optical signal-to-noise ratio (OSNR) costs and fault detections. Therefore, it is significant to inhibit the frequency offset on DPSK detection. In this paper, firstly, we discuss the effects of frequency offset on DPSK detection, and realize the conclusion that frequency offset is virtually equivalent to an additional phase difference between adjacent symbols. Secondly, through simulation, we analyze the feasibility of DPSK detection in the presence of a definite range of frequency offset, and present the quantitative computation of effective coverage, duty cycle, and optimal sampling time of symbol interference. Some issues which should be considered in practical implementation are also discussed. Finally, according to the relationship among phase difference, temperature and voltage, we propose a phase difference compensation scheme which can automatically adjust the voltage for optimal detections, and dynamically track the changing of ambient temperature and nonlinear phase noise. Furthermore, we ascertain the performance of the voltage requested for implementing the scheme. The scheme can be also developed to quadrature phase-shift keying (QPSK) and differential QPSK (DQPSK) modulation situations.

Analytical Treatment of Parametric Effects in a Ring Resonator

We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications.