DP-QPSK Modulator Research Articles

UWB quadruplet signal generation based on a DP-QPSK modulator and a delay-line filter: publisher's note.

This publisher's note corrects two sentences in Appl. Opt.59, 4404 (2020)APOPAI0003-693510.1364/AO.390663.

UWB quadruplet signal generation based on a DP-QPSK modulator and a delay-line filter.

A photonic ultra-wideband (UWB) quadruplet signal generation based on a dual-polarization quadrature phase shift keying (DP-QPSK) modulator is presented. A Gaussian sequence is split into four parts and input to the four driving ports of the DP-QPSK. Through polarization rotation and polarization combination, a pair of polarization-orthogonal, polarity-reversed doublet signals are generated from the output of the DP-QPSK modulator. Subsequently, they are injected into a balanced photodetector (BPD) for further differentiation. After the heterodyne detection, a UWB quadruplet signal can be obtained. In this system, four electrical amplifiers are incorporated into the four electrical driving paths to adjust the modulation indices of the DP-QPSK. To attain the optimal spectral power efficiency (SPE), a relationship among the SPE, pulse width, delay time, and the two main modulation indices is created. Consequently, the optimal point is found with an SPE of 53.46%. Then, several impairments brought by the nonideal devices are considered in the simulation system. The distortion caused by impairments is compensated by properly adjusting the devices. The generated spectrum has a SPE of 53.38% and efficiently complies with the Federal Communications Commission (FCC) mask without any low-frequency components exceeding the FCC mask. In addition, on-off keying and pulse position modulation are realized in the system.

Quadruple-frequency optical two-tone signal generation using a DP-QPSK modulator

Quadruple-frequency optical two-tone signal generation using a DP-QPSK modulator

Microwave photonic image rejection mixer based on a DP-QPSK modulator

A simple image rejection mixer based on a dual-polarization quadrature phase shift keying modulator is presented without a 90° hybrid coupler in electrical field. By properly adjusting DC bias points in the integrated modulator and performing balanced photo-detection, the influence of image components can be well rejected. The simulation results show that a 52.24 dB image suppression ratio (ISR) and a conversion efficiency (CE) of −9.17 dB can be achieved by the proposed mixer. Besides, another research on the ISR and CE against non-ideal parameters is carried out. According to the simulation results, it can be figured that the main factor to influence the ISR and CE is the DC drifting which results both of them changed rapidly as the DC bias points deviate from the settled values. On the other hand, with different extinction ratios and LO signal powers and RF signal powers, the mixer still performs good ISR and CE.

Photonic microwave multi-band frequency conversion based on a DP-QPSK modulator for satellite communication

We propose and demonstrate a simple, flexible and stably operated multi-band frequency conversion approach based on a dual-polarization quadrature phase shift keying modulator (DP-QPSK). The modulator incorporating two dual parallel Mach–Zehnder modulators (DPMZMs) which perform as OFC generator and +1st carrier suppressed single sideband generator, respectively, to achieve the purpose of frequency conversion. The theoretical analysis indicates that by properly adjusting six DC bias points in the integrated modulator and two modulation indices, a frequency of received RF signal can be directly converted into different frequencies that cover different bands simultaneously. The simulation results verified the possibility. For example, the received C band frequency of 3.8 GHz can be converted into X, Ku, K and Ka bands. An X band frequency of 9.6 GHz can be down-converted to C band and up-converted to Ku, K, Ka band. In addition, the simulation also focuses on how the adjustable parameters (such as DC bias points and modulation index) influence the conversion results. It demonstrates stable conversion efficiency against the DC drafting.

Rebuttal to “Photonic Microwave Generation With Frequency Octupling Based on a DP-QPSK Modulator”

In the title paper, Gao et al. have experimentally demonstrated a scheme for filter-less photonic millimetre-wave (mm-wave) generation using a dual polarization quadrature phase shift keying modulator (DP-QPSK). For frequency octo-tupling generation, the X-QPSK modulator is biased such that all the harmonics are suppressed except those that are order of ${4l}$ , where ${l}$ is an integer and combined with the output of the non-modulated Y-QPSK modulator using a polarization beam combiner. Precise setting of the polarizer angle suppresses the carrier, leaving the ±4th sidebands as the strongest harmonics, which is the innovative part of their design. However, a demerit of the design is that, following any change in modulation index, a precise readjustment of the polarizer angle is required in order to suppress the unwanted harmonics (e.g. carrier) without undue suppression of the wanted harmonics. The goal of this comment is to show that, for an appropriate modulation of the Y-QPSK modulator with the design presented by Gao for a fixed polarizer angle, all the harmonics can be suppressed except those that are order of $4{l}$ , where ${l}$ is an odd integer. Hence, a filter-less frequency octo-tupling can be generated without restricting its operation by the careful adjustment of the RF drive signal; rather the circuit can function for a broad range of modulation index ( $m\sim 2.5 \to 7.25)$ . Moreover, the unwanted harmonics suppressed by design mandate 6.66 dB optical and 11 dB electrical advantages over the design presented by Gao and the precise setting of the polarizer angle can be avoided.

Photonic Microwave Generation With Frequency Octupling Based on a DP-QPSK Modulator

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated using a dual-polarization quadrature phase shift keying modulator. By properly setting the phase difference between the two drive signals, the working points of the modulator, and the polarization state of the light wave after the modulator, an optical signal with only ±4th order sidebands is generated. A pure 24-GHz microwave signal with low-phase noise is experimentally obtained using a 3-GHz local oscillator signal. The proposed photonic frequency octupling system also exhibits good frequency tunability as no electrical or optical filter is used.

Functional integrated modulators and receivers utilizing PLC hybrid integration technology for coherent transmission

We review our recent progress toward transmission speeds per channel of 100Gbit/s and beyond, focusing on optical modulators and receivers for coherent transmission using PLC integration technology. We have used PLC-LiNbO3 hybrid integration technology to develop optical multilevel modulators, including a DP-QPSK modulator and a 64QAM modulator for 100Gbit/s and post 100Gbit/s. This technology provides practical performance and scalability for various advanced modulations. We have also developed flexible-format modulators for future elastic networks, which will enable the efficient use of the spectral resource. This modulator can select an optimum carrier number and modulation level according to the transmission conditions. In terms of receivers, we have developed integrated optical receiver front-ends for 100Gbit/s DP-QPSK based on hermetically sealed O/E converters. PLC hybrid-integration technologies are promising for compact, practical, cost-effective, and highly reliable coherent optical modulators and receivers.