Modulated optical signal detection based on cross-correlation algorithm

Thin film lithium niobate optical modulators allow modulation of optical signals up to several THz due to perfect phase matching between RF signal and optical signal that can be achieved using thin film devices. The platform uses a ridge waveguide fabricated by direct etching of lithium niobate thin film fabricated on silicon substrates. The lithium niobate thin film has been developed and optimized in our facility. Transmission spectrum of fabricated micro-ring resonators on this platform shows a linewidth of approximately 7 pm corresponding to a Q value of 2.2×10⁵ and an optical waveguide loss of 2 dB/cm. A coupling loss of -5 dB per coupler is obtained using grating couplers. Measured fiber to fiber insertion loss of the device is -10 dB. The measured 3-dB optical bandwidth of the fiber to fiber optical coupler is 45 nm. A Mach-Zehnder modulator consisting of two MMIs and 6 mm long arms were designed and fabricated on X-cut thin film of lithium niobate. Measured V_π of the device is 7.5 V at low frequencies (i.e. 10KHz) for a device with 7 μm gap between the electrodes. The measured half-wave voltage-length product, V_π.L, is equal to ~4.5 V.cm. High speed measurement results of the device response are presented. A THz electric field of 10kV/mHz^0.5 is detected with a low dynamic range OSA and it is estimated that a THz electric field with a strength as low as ~100V/mHz^0.5 is detectable by modulating the optical signal using these modulators.

A novel satellite on-board processing scheme based on photon frequency conversion is proposed for the purpose of realizing frequency conversion. For the received intermediate frequency signal, a Mach-Zehnder modulator is used to convert it into an optical signal. The modulated optical signal and an optical signal generated by a tunable laser enter the photodiode through a coupler to perform heterodyne beat frequency and generate an intermediate frequency signal of the target carrier frequency, thereby reducing the cost and power consumption of on-board processing. Simulation results show the spectrograms and constellation diagrams of frequency conversion from Q-band to V-band in 8PSK modulation format. The bit error rate(BER) obtained by simulation shows that in a satellite communication system, when the OSNR is higher than 5dB, the BER performance can meet the 2×10^-2 threshold when using 8PSK modulation format, which indicates that error-free transmission can be achieved when using 20% soft-decision FEC. The Q factor obtained by simulation shows that when the OSNR is higher than 5dB, the Q factor can reach more than 6.5 when using QPSK modulation format, which indicates that reliable transmission can be achieved. Compared with existing solutions, this scheme has the advantages of lower cost, lower power consumption and more flexible frequency selection, it can also solve the inflexibility and improve the performance of radio frequency conversion in traditional scheme.

In the era of vigorous development of optoelectronic technology, the high-performance lithium niobate optical beam splitter, as a core component for optical signal processing and transmission, provides an excellent material basis for optical signal modulation with its outstanding electro-optical properties. At present, it has been found in research and application that three-dimensional ridge-shaped strip waveguides can enhance the interaction between light and electric fields. Multimode interferometric couplers (MMI) have the advantages of compact structure, simple fabrication and stable mode conversion. The combination of the two can achieve efficient optical beam splitting and precise modulation, effectively improving the modulation efficiency. Through theoretical analysis and numerical simulation, the light field distribution, mode characteristics and modulation performance parameters of this structure were deeply studied. The results show that compared with the traditional structure, this design significantly improves the modulation efficiency, and can effectively reduce mode crosstalk at the same time, achieving stable optical signal beam splitting and modulation. This research provides a new approach for the application of lithium niobate beam splitters in high-speed optical communication, optical signal processing and other fields, which is conducive to promoting the development of optoelectronic integrated devices.

Integrated photonics is playing an always-increasing role in the development of new technologies and devices, with applications in the fields of optical communications and, more recently, in linear-optical quantum computing and simulations. Actually, the possibility of integrating complex and reconfigurable functionalities inside a small chip allows to develop ultra-stable platforms for the large-scale processing of classical and quantum optical signals [1] , [2] .

Visible Light Communication (VLC) is a rising communication technology which uses Light-Emitting Diode (LED) luminaries for high-speed data transferring; however, the optical signal is usually degraded by the noise in the practical VLC system. In this paper, Allan Variance is introduced for noise analysis and modeling in VLC for the first time, which provides an efficient method to measure different kinds of noise in the VLC systems. By applying Allan variance to analyze the signals collected from the real-world environment, both white noise and random walk are observed in the VLC systems. The observed white noise and random walk are also modeled by using the Allan variance. The noise analysis and modeling based on Allan variance provide a method to improve the performance of VLC.

The repeaterless transmission of an optical duobinary modulated signal at 10 Gbit/s is reported. The power penalty due to the fibre chromatic dispersion is effectively reduced in comparison with conventional binary intensity modulated (IM) signals. In the case of a 164 km standard singlemode fibre, the power penalty is <1.8 dB.

The optical modulation by acoustoelectric domain has been observed in semiconductive CdS single crystal at room temperature. The nature and mechanism for this optical modulation are discussed, as compared with the Franz-Keldysh effect by the high electric field. The electric field in the domain observed here is saturated by 5 kV/cm, while the optical modulation signals rise linearly. There is little shift of the edge, calculated from the experimental and theoretical results of the Franz-Keldysh effect at the saturation field. Furthermore, the optical modulation signals are clearly visible for several nanoseconds after the applied voltage is removed. Therefore, the optical modulation is not caused by the high electric field but is associated with the intense acoustic flux in the domain. Using the optical modulation technique, the acoustic flux reflected at the anode end is observed even for the application of the voltage. The propagation velocity of acoustic domain, where the voltage is applied perpendicul...

The role of an optical receiver is to convert an optical signal into an electrical signal. The goal of an optical transmitter is to convert an electrical signal into a modulated optical signal. These requirements define digital transceivers as well as analog receivers and transmitters. However, they differ from each other in respect of design requirements and design considerations, irrespective of digital or analog. The digital transceivers deal with large signals, while the analog receivers handle smaller signals per channel and overall large loading due to multi tone transport. On the other hand, both topologies have common requirements that can be analyzed similarly, such as sensitivity and jitter, with minor differences. Digital transceivers, however, differ from analog with respect to interfaces, controls, status, reports, and indications due to the differences in mode of operation. As for transmission, an analog transmitter handles fewer signals per channel since the optical modulation index (OMI) is low, about 4% per channel at maximum. But it has to transmit many channels; hence, the loading is similar to that of a large signal. The modulation depth for a digital transmitter is that of a large signal, driving the laser between threshold to high conduction and high optical power. Further discussion on OMI is provided in Secs. 6.9, 8.2.4, and 21.2. Additional material about community access TV (CATV) signals, standards, and broadcast methods are provided in Chapter 3.

This work involves in transmitting of intermediate frequency (IF) signal over fiber utilizing photonics frequency conversion, which, the main focus is the development of optical front-end receiver. The system uses photodiode and heterojunction bipolar transistor (HBT) to detect and up-convert the received IF modulated optical signal. The photodiode (PD) and HBT are very useful devices for photonics frequency conversion technique with high internal gain and frequency up conversion of optical signal. Through simulation, the optimum device parameters and characteristics were determined. The system was implemented to detect a 0.4 GHz of IF carriers signal and up-converted to 3.4 GHz of radio frequency (RF) signal. The optimum conversion gain that has been obtained from the measurement and simulation were about -11 dB and -8 dB, respectively, at V BE = 0.7 V, P LO = 4 dBm, and -25 dBm of IF optical input power. The system has been practically demonstrated and shown to agree reasonably well with both the theory and simulation. This article also refers to some recent patents on frequency conversion techniq.

We propose a microwave signal generation device using difference frequency generation in a periodically-poled LiTaO3 rectangular waveguide. In the experiment, a microwave signal was successfully generated at the designed frequency of 15 GHz from the intensity modulated optical signal. The measured frequency response of the fabricated proto-type device was in good agreement with the theoretically expected ones. We expect the proposed device can be useful for high-frequency signal generation, detections of the vector modulation optical signal, and the optical clock signal.

An approach to transmitting two independent microwave vector signals on a single optical carrier with one polarization state based on coherent detection and digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, two independent microwave vector signals are modulated on an optical carrier via a dual-drive Mach-Zehnder modulator (DD-MZM). The modulated optical signals are transmitted over a single-mode fiber (SMF) and sent to a coherent receiver. At the receiver, the optical signals are detected where a local oscillator (LO) optical wave generated by a second free-running laser source is also applied. To recover the two microwave vector signals, a novel digital signal processing (DSP) algorithm is developed and applied to eliminate the joint phase noise terms from the transmitter and the LO laser sources as well as the unstable offset frequency between the two laser sources. An experiment is performed. The transmission of two independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals at 4 GHz with a symbol rate of 1 GSymb/s over a 9-km SMF is demonstrated. The transmission performance in terms of error vector magnitudes (EVMs) and bit error rates (BERs) is also evaluated.

Space laser communication has attracted closely attention to the improvement in laser technology and communication now. Space laser communication technology is comprehensive and covers many fields. The emitting and receiving of optical signals between satellites and AlT (acquiring, tracking, pointing) of target-signals between satellites or space stations are the crucial techniques in space laser communication. It's necessary to analyze the influencing on the bit error rate from space transmission environment and other factors when discussing some problems in technique scheme of space laser communication. This paper discusses the space laser communication system in which semiconductor laser acts as light source and photoelectric sensor acts as receiver. The chief factors influencing the bit error rate in space laser communication such as the posture of satellite, vibration, the degradation of optical energy, background light and the corresponding solvent are analyzed.

For radio-over-fiber (RoF) systems, optical single-sideband modulation (SSB) signals are preferred over optical double-sideband modulation (DSB) signals due to the microwave power fading effect. Direct or external modulation scheme typically adopted in RoF systems, however, generates optical DSB signals, thus requiring optical DSB-to-SSB conversion. In this study, period-one nonlinear dynamics of semiconductor lasers is investigated for such conversion. Only a typical laser is required as the conversion unit. An operating microwave frequency up to least 70 GHz with improved detection sensitivity is feasible, showing the system reconfigurability for different networks.

A second-order finite-difference time-domain (FDTD) large signal model for silicon phonics (SiP) modulators is compared against a first-order large signal model, via studies of both electrical RF driving signals and optical modulated signals.

We propose and demonstrate a silicon photonics electro-absorption-modulator (EAM) based transmitter architecture for generating high-speed optical PAM4 modulation signals. The adopted push-pull-interference approach can take the advantages of differential driving for suppressing common-mode noises.