Research on photonic generation of quadrupling triangular-shaped waveform using external modulation

In this paper, we study nonlinear effects in the optical communication fibers such as four wave mixing (FWM) in an integration of dense wavelength division multiplexing (DWDM) with radio over fiber (ROF). We used an optical double side band (ODSB) configuration with direct and external modulation using dual drive Mach–Zehnder modulator. A 16-DWDM-ROF link at different data rates is used for information transmission in single mode fiber. Also, the performance analysis of the proposed system under FWM effect with different parameters such as data rate, channel spacing, input power, fiber length and optical amplifier gain is presented. The results of the proposed system are evaluated based on bit error rate (BER) and maximum quality factor (Q). Results show that the external DSB modulation format has better performance rather than the direct modulation. Generally, for 10 dB input power, 100 GHz channel spacing, 10 Gbps bit rate and 20 km link, the Q is about 20 and BER is less than 10−84 for external ODSB modulation format. Also it has been shown that with increasing data transfer rates, output results such as optical signal-to-noise ratio, BER and Q are deteriorated under influence of FWM-effect.

Optical single sideband (OSSB) signals are conventionally generated using a dual-drive Mach–Zehnder modulator (MZM) or by using a single-drive MZM in conjunction with a fibre Bragg grating filter. In this study, the authors propose and mathematically characterise a novel radio over fibre downlink in which an OSSB signal is generated using a single-drive, rather than dual-drive, MZM without any additional filter. Additionally, their proposed scheme can achieve optical upconversion of the electronic signal. Furthermore, in addition to cost advantages, the proposed scheme's bit error ratio (BER) performance is better than the classical OSSB signal generation scheme.

We propose and demonstrate an all-fiber liquid-level sensor using an in-line multimode-single-mode-multimode (MSM) fiber structure. A piece of single-mode fiber (SMF) is spliced to two sections of equivalent multimode fiber (MMF) which are used as both mode splitter and mode coupler. The cladding mode will be excited when the light propagates from MMF to SMF, and then it will be combined with fundamental mode to form a Mach-Zehnder interferometer (MZI) when the light propagates from SMF to the other MMF. The liquid level is detected by the selected resonant dips shift of the transmission spectrum. A sensing sensitivity of 264.6 pm/mm is achieved for the proposed sensor with an SMF length of 26mm. Due to its compact structure, easy fabrication, and high sensitivity, the proposed liquid-level sensor is attractive for practical applications in a variety of fields, such as marine detection and chemical processing.

In the paper, we proposed a simple method to generate two millimeter-wave (MMW) signals for radio-over-fiber (RoF) systems. Firstly, we utilized two cascaded dual-drive Mach-Zehnder modulators (DD-MZMs), both biased at the maximum transmission bias point (MATBP), to implement frequency octupling. And then, a wavelength division multiplexing demultiplexer (WDM Demux) is followed to filter out the −4 order optical carriers of the second DD-MZM's output to enable an optical single side-band (OSSB) modulation by only modulating the baseband data onto the −4 order optical carrier. On the other hand, the +2 order optical carrier of the first DD-MZM's output is filtered out based on an optical splitter (OS) and an optical rectangle band-pass filter (ORBPF). After that, the +2 and the −4 order optical carriers are combined to be transmitted in an identical fiber path. Finally, a 45 GHz and a 60 GHz MMWs were generated simultaneously with a 7.5 GHz local oscillator (LO), by self-heterodyning these optical carriers in a photonic detector (PD). After 50 km single-mode fiber (SMF) transmission distances, the 45 GHz and the 60 GHz MMWs were maintaining good performance with clearly open eye diagrams and power penalties of 0.6 dB and 1.1 dB, respectively, at a bit-error-rate (BER) of 1×10−9.

In this paper, we propose a simulation model to generate an optical single side band (OSSB) signal for 5G modulation format which is called Generalized Frequency Division Multiplexing (GFDM) using semiconductor optical amplifier (SOA). The OSSB and optical double side band (ODSB) signals are investigated.

We proposed an optical 4-ary frequency shift keying (FSK) modulation scheme applying dual-parallel Mach-Zehnder (MZ) modulator. The 4-ary FSK based on the single-side-band modulation scheme can greatly lower the transmission speed in each sub-carriers and increase the transmission performance, comparing with the 2-FSK signal. The transmission performance of the 4-ary FSK was demonstrated after a 50 km single mode fiber. The results showed that the 4-ary FSK can realize error-free transmission. Moreover, we analyzed the influence of factors (such as disperse compensation and demodulation bandwidth) on the transmission performance in this paper. The analysis of the influenced factors can provide a theoretical basic for experiment.

An optical single sideband modulator without generating both the −2nd- and +2nd-order sidebands is presented. It is based on a parallel operation of two dual-drive Mach–Zehnder modulators (DDMZMs) where one is operated as a conventional single sideband (SSB) modulator and the other is operated as a single-drive Mach–Zehnder modulator (MZM) biased at the maximum transmission point. The 2nd-order sidebands generated by the SSB modulator and the maximum-biased MZM can be cancelled by controlling the sideband amplitude and phase. Canceling the 2nd-order sidebands eliminates the second-order harmonic component presented at the output of a long-reach fiber optic link. The new SSB modulator can be implemented using standard off-the-shelf components and has a wide bandwidth. Experimental results show >20 dB 2nd-order sidebands suppression for different modulation indexes and 22.6 dB reduction in the fiber optic link output second-order harmonic component, compared to using a conventional SSB modulator formed by a DDMZM and a 90° hybrid coupler. Results also demonstrate that the performance of the new SSB modulator is insensitive to the optical carrier frequency and the input RF signal frequency.

We propose a new transmitter for 16QAM generation based on a combination of a dual-drive Mach-Zehnder modulator (DD-MZM) and a dual-parallel Mach-Zehnder modulator (DP-MZM) with electrical binary drive signals. By using the proposed transmitter, we successfully evaluated the performances of 224-Gb/s and 320-Gb/s PDM-RZ-16QAM signals.

Fading cancellation for 60GHz optical double sideband (DSB) signal transmission in a long non-dispersion shifted single mode fibre (SMF) in 1550nm wavelength region is experimentally demonstrated for the first time by using a chirped fibre grating (FGR). Hence, the optical DSB signal transmission will become one of the most practical options for mm-wave radio-on-fiber wireless access systems.

The biconic tapered fiber has been fabricated using flame elongation technique by heating and stretching a piece of single mode fiber (SMF). Intermodal interference occurs in the abrupt biconic tapered fiber. The modulated spectral response was characterized to determine the strain effect. It was found that the shifting of peak modulated spectral response was well matched to the phase change introduced by Michelson-type transmission equation.

We propose and demonstrate an optical single sideband (OSSB) modulation approach with continuously tunable optical carrier-to-sideband ratio (OCSR) theoretically and experimentally. In the proposal, one dual-parallel Mach-Zehnder modulator (DP-MZM) acts as a key component. By properly setting the modulator, three separate sub-modulators inside the DP-MZM can be used to realize the OSSB modulation, optical carrier phase-shift, and lightwave interference. By adjusting the bias voltage of one sub-modulator, the OCSR can be tuned continuously. In the experiment, the tuning range of OCSR is found to be between-20.8 dB and 23.5 dB at modulation index m=0.2. We also analyze the relationship between the OCSR and RF power after detection. It is found that with properly adjusting the OCSR, the receiver sensitivity can be greatly improved.

We demonstrate a radio frequency (RF) phase-stable transmission over fiber based on microwave photonic phase shifter. In the proposed system, both assistant RF signals are applied to drive two arms of a dual-drive Mach-Zehnder modulator (DMZM), respectively. An optical bandpass filter is followed to filter out the first-order sideband of optical modulated signal. Due to the phase independence between two optical sidebands, the phase perturbation caused by fiber-length variations can be compensated automatically via controlling the direct-current bias voltage of the DMZM. We have performed RF transfer in a 155 km single-mode fiber with a frequency instability of 3.05 × 10-17 at 10,000 s averaging time.

Gain switching for the optical generation of modulated millimetre waves

In this paper, a simple image rejection mixer based on the dispersion effect in the single mode fiber is proposed and experimentally demonstrated for the radio-over-fiber (RoF) system. The key idea is to control the DC bias voltages of the dual parallel Mach-Zehnder modulator (DPMZM) to compensate for the desired components and eliminate the image induced components simultaneously during the fiber transmission. The experimental results show, the image rejection ratio (IRR) of ∼50 dB is realized, and the spurious free dynamic range (SFDR) is about 100.75 dB·Hz2/3. In addition, the results also demonstrate an image-free intermediate frequency (IF) range of 0.5 GHz–9.5 GHz. This image-free mixer can be widely employed in the radio-over-fiber (RoF) system, and greatly simplify the receiver structure in the base station.

The trade-off between lateral resolution and depth of focus (DOF) severely limits the capability of endoscopic optical coherence tomography (OCT) for high-resolution deep-tissue imaging. To address this issue, we developed a novel miniature all-fiber axicon OCT probe by inserting a segment of gradient-index (GRIN) fiber between a piece of single-mode fiber (SMF) and an axicon polished from a no-core fiber. The GRIN lens served as a beam expander extending the probe DOF by 5.2 times while maintaining a high lateral resolution of 2 μm. The DOF extension was experimentally verified by measuring the axial profile of the probe output beam and further by imaging multilayered polymer tapes and onion samples. The designed probe with a tight focus over a large DOF holds great potential in endoscopic OCT imaging of deep tissues at the cellular level.