Direct Phase Modulation Research Articles

High-precision digital terahertz phase manipulation within a multichannel field perturbation coding chip

Direct phase modulation is one of the most urgent and difficult issues in the terahertz research area. Here, we propose a new method employing a two-dimensional electron gas (2DEG) perturbation microstructure unit coupled to a transmission line to realize high-precision digital terahertz phase manipulation. We induce local perturbation resonances to manipulate the phase of guided terahertz waves. By controlling the electronic transport characteristics of the 2DEG using an external voltage, the strength of the perturbation can be manipulated, which affects the phase of the guided waves. This external control permits electronic manipulation of the phase of terahertz waves with high precision, as high as 2−5° in the frequency range 0.26–0.27 THz, with an average phase error of only 0.36°, corresponding to a timing error of only 4 fs. Critically, the average insertion loss is as low as 6.14 dB at 0.265 THz, with a low amplitude fluctuation of 0.5 dB, so the device offers near-ideal phase-only modulation. A terahertz phase modulator based on the switchable perturbation resonance in two-dimensional electron gas is demonstrated. Phase manipulation with precision ranging from 2° to 5° is obtained at frequencies in the range from 0.26 to 0.27 THz.

Phase and Polarization Modulations Using Radiation‐Type Metasurfaces

AbstractMetasurfaces exhibit promising capacities in the manipulation of electromagnetic (EM) waves, as to diverse dimensions like amplitude, phase, and polarization; even multiple dimensions can be synchronously modulated. Despite the rapid progress in enriching regulatory capabilities of EM waves, primary feeds are integral items however bringing profile elevation, energy obstruction, and leakage, both for reflection‐type and transmission‐type metasurfaces. Aiming at maintaining high operating efficiency and in meantime implementing multiple dimensional manipulations of EM waves, the authors present a concise design of radiation‐type metasurfaces, whose distinctive feature stands that each meta‐atom serves not only as geometry phase provider, but as radiator itself so as to spare primary feeds. To further achieve full phase modulation for arbitrary linear polarized radiations and abate innate conjugacy to orthogonal circular polarized radiations, the propagation phase is introduced irrelevant to geometry ones. Based on the radiation‐type metasurface with 0.07‐wavelength low profile, the authors verify experimentally advanced radiation functions for different polarizations like orbital angular momentum beams, asymmetric beams, and time‐reversed focusing. Compared with traditional planar arrays that rely on feeding networks to realize phase modulation, this design provides the possibility to achieve direct phase and polarization modulation at the element level, thus is with less complexity.

Direct phase modulation via optical injection: theoretical study.

Direct phase modulation via optical injection is a newly developed method for coding the phase of a gain-switched laser, which meets high requirements placed on transmitters for quantum key distribution: compactness, low losses, compatibility with CMOS technologies, and the absence of undesirable effects leading to the side-channel information leakage. Despite the successful implementation and good prospects for the further development of this system, there is still a lack of theoretical investigations of this scheme in the literature. Here, for the first time, we perform its theoretical analysis. We study the influence of the spontaneous emission noise, examine the role of the gain non-linearity, and consider the temperature drift effect. The results obtained reveal that these phenomena significantly affect system performance. We have tried to formulate here practical instructions, which will help to take these features into account when elaborating and employing the optical-injection-based phase modulator.

A Mechanical Antenna With Frequency Multiplication and Phase Modulation Capability

This article reports on a novel direct frequency multiplication and phase modulation (PM) scheme for mechanical antennas operating at the very-low-frequency band (3-30 kHz) and lower. This antenna is intended as a transmitter for underwater and underground communication applications. In mechanical antennas, instead of using signal generators to drive the antenna for radiation, the radiation is induced by accelerating (rotating) electric charges or permanent magnets. One important challenge for mechanical antennas is to find an approach to modulate the information signal with sufficient bandwidth. We propose a novel PM scheme by rotating a permanent magnet which is sandwiched between two pairs of orthogonal bow-tie shape high- μ magnetic material plates. By moving the angular position of the magnetic plates, it is shown that the phase and amplitude of the EM signal can be modulated. The amplitude modulation is significant and this provides an additional important feature, which allows the antenna to generate higher harmonics of the rotation frequency, and thereby it facilitates radiation at a much higher frequency than the rotational frequency of the magnet. Hence, higher range and more radiated power can be achieved. Here, the performance of proposed mechanical antenna with its PM and frequency multiplication capability is first verified analytically and through numerical simulations using ANSYS Maxwell. Then, a prototype of the antenna is fabricated with the aid of low cost 3-D-printing technology and its performance is measured. Measurements are in good agreement with the simulation predictions.

Coherent Ultra-Dense WDM-PON Enabled by Complexity-Reduced Digital Transceivers

Coherent technologies, along with digital signal processing (DSP), have revolutionized optical communication systems, significantly increasing the capacity of the fiber channel owing to transmission of advanced modulation formats and mitigation of propagation impairments. However, commercial solutions for high-capacity core networks are too complex and costly, and therefore hardly feasible, for access networks with high terminal density, where cost, power budget, and footprint are the main limiting factors. This article analyzes the key enabling techniques to implement a complexity-reduced coherent transceiver (CoTRX) by exploiting photonic integration, simplified optical modulation, low-cost DFB lasers, consumer electronics, and low-complexity DSP. Bulk optical modulators are replaced by direct amplitude-and-phase modulation of an integrated electro-absorption modulated laser (EML) with a smaller footprint, generating up to 8-ary modulation formats. Hardware-efficient DSP algorithms for the coherent transmitter and receiver, including pulse-shaping for direct phase modulation, differential detection for optical phase recovery, and digital pre-emphasis with enhanced tolerance to quantization noise, are investigated to face the challenges imposed by low-cost photonic and electronic devices, such as strong phase noise, wavelength drifts, severe bandwidth limitation, and low resolution data converters. Through numerical simulations and real-time experiments, the results indicate that this new class of CoTRX enables effective implementation of wavelength-to-the-user PON with dedicated 1.25–20 Gb/s per user, in an ultra-dense 6.25–25 GHz spaced WDM optical grid, with >30 dB loss budget, outperforming the current competing technologies for access networks.

Design of Galvanic Coupling Intra-Body Communication Transceiver Using Direct Sequence Spread Spectrum Technology

Intra-body communication (IBC) uses the human body as the transmission medium for electrical signals, and it features the following advantages: low power consumption, strong anti-interference ability, high data security, and broad application scenarios. However, some technical issues still need to be addresses, such as the choice of the best modulation and demodulation scheme in different application scenarios, influence of human activity on IBC performance, variable signal-to-noise ratio (SNR), and influence of transmission distance change on different modulation and demodulation methods. This paper adopts direct sequence spread spectrum (DSSS) communication and phase modulation to realize DSSS-differential phase shift keying (DPSK) and DPSK modulation transmission of baseband data. Moreover, the Costas loop method is employed to achieve reliable symbol recovery. Under the same conditions, in vivo experiments were conducted to compare the performance of DSSS-DPSK and DPSK galvanic coupling IBC transceivers. Notably, these transceivers are affected by the changes in SNR, transmission distance, and human activities. Results show that the bit error rate (BER) of the DPSK scheme is 40 times larger than the DSSS-DPSK scheme in a 30 cm channel length and different SNR experiments. When the BER performance changes from extremely poor (1.40 ×10 -1 ) to excellent (1.51×10 -6 ), the SNR of DSSS-DPSK scheme only needs to be improved by 16 dB. In contrast, when the BER performance changes from extremely poor (1.54 ×10 -1 ) to good (1.65 ×10 -5 ), the SNR of DPSK scheme needs to be improved by 25 dB. With a SNR of -5 dB, the BER ratios of the DPSK scheme is 7 times larger than the DSSS-DPSK scheme. Also, DSSS-DPSK scheme is more sensitive to changes in motion status than DPSK.

Novel concept for VCSEL enhanced silicon photonic coherent transceiver

We present a novel concept for an integrated silicon photonic coherent transceiver using vertical-emitting laser sources at 1550 nm. In a state of the art external modulation configuration, we deploy a VCSEL on the transmit and a HCSEL on the receive side. We demonstrate the feasibility of this approach by externally modulating the VCSEL with QPSK at up to 28 Gbaud. We also perform experiments with the VCSEL-HCSEL configuration in a slave-master optical injection locking setup for future data center interconnects. The results show stable locking conditions and the VCSEL is detuned to perform predominant phase modulation. To the best of our knowledge, this is the first time direct phase modulation of a VCSEL under optical injection locking was demonstrated using two vertically emitting laser sources as master - and slave laser.

Differential 8-APSK monolithically integrated dual-EML transmitter for flexible coherent PONs

We experimentally demonstrate a simultaneous amplitude and phase modulation of a monolithically integrated dual electro-absorption modulated laser. The proposed technique combines a 4-ary direct phase modulation with a two-level amplitude modulation obtaining an 8-ary amplitude phase shift keying external-modulator-free transmitter (Tx). Its performance was tested up to 7.5 Gb/s in a 25 km single-mode fiber link with intradyne coherent detection. A receiver sensitivity of −42.5 dBm was achieved at a forward error correction limit bit error ratio =4×10−3. The results show that the proposed system can be an efficient flexible Tx for next-generation passive optical networks.

Chirped-pulse-amplification seed source through direct phase modulation.

This work presents integration of a directly chirped laser source (DCLS) into a high-energy optical parametric chirped-pulse-amplification (OPCPA) system. DCLS is an all-fiber, chirped laser source that produces nanosecond, linearly chirped laser pulses at 1053 nm for seeding high-energy chirped-pulse-amplification systems. DCLS produces a frequency chirp on an optical pulse through direct temporal phase modulation. A 1-ns, linearly chirped pulse with a 3-nm bandwidth is produced by applying an ~1000-rad (300π) quadratic temporal phase. The chirped pulse is amplified to 76 mJ in an OPCPA system and compressed to close to its Fourier transform limit, producing an intensity autocorrelation trace with a 1.5-ps width.

Vector Modulation by Laser and Electroabsorption Modulator With Digital Pre-Coding and Pre-Compensation

We present a method to achieve vector modulation of lightwave using an electroabsorption modulator intregrated laser. The laser section is used for direct phase modulation followed by an amplitude modulation of the electroabsorption modulator section in a cascade manner, which is an alternative method to conventional IQ modulator. To allow an improved phase demodulation, we propose a digital pre-compensation technique for a transmitter in optical coherent system for the first time, which includes a phase-balanced differential phase shift keying encoding and a digital domain pre-equalization filtering. The phase-balanced encoding technique applies parallel DC-balance coding with a phase-balanced symbol mapping, which results in a bounded cumulative phase and a constant statistical characteristic of the modulating signal in differential M-ary phase shift keying and M-ary quadrature amplitude modulation formats. The digital pre-equalization filter also compensates for the phase response of the laser section. Experimental results show that the pre-digital compensation technique allows the improved complex signal demodulation compared to conventional DQPSK modulation in a back-to-back setup.

High-accuracy vibration sensor based on a Fabry-Perot interferometer with active phase-tracking technology.

A novel position-sensitive Fabry-Perot interferometer was constructed with direct phase modulation by a built-in electro-optic modulator. Pure sinusoidal phase modulation of the light was produced, and the first harmonic of the interference signal was extracted to dynamically maintain the interferometer phase to the most sensitive point of the interferogram. Therefore, the minute vibration of the object was coded on the variation of the interference signal and could be directly retrieved by the output voltage of a photodetector. The operating principle and the signal processing method for active feedback control of the interference phase have been demonstrated in detail. The developed vibration sensor was calibrated through a high-precision piezo-electric transducer and tested by a nano-positioning stage under a vibration magnitude of 60nm and a frequency of 300Hz. The active phase-tracking method of the system provides high immunity against environmental disturbances. Experimental results show that the proposed interferometer can effectively reconstruct tiny vibration waveforms with subnanometer resolution, paving the way for high-accuracy vibration sensing, especially for micro-electro-mechanical systems/nano-electro-mechanical systems and ultrasonic devices.

Chirp-based direct phase modulation of VCSELs for cost-effective transceivers.

A 2.5 Gb/s differential binary phase-shift keying (DPSK) transmitter based on direct phase modulation of a vertical cavity surface emitting lasers (VCSEL) using its own chirp is proposed. The VCSEL, which has a wavelength of 1539.84 nm, has been characterized both statically and dynamically. The sensitivity of a single photodiode heterodyne receiver using the proposed 2.5 Gb/s VCSEL transmitter is -39.5 dBm. Thus, this transmitter is an extremely cost-effective solution for future access networks.

Writing and erasing of temporal cavity solitons by direct phase modulation of the cavity driving field.

Temporal cavity solitons (CSs) are persisting pulses of light that can manifest themselves in continuously driven passive resonators, such as macroscopic fiber ring cavities and monolithic microresonators. Experiments so far have demonstrated two techniques for their excitation, yet both possess drawbacks in the form of system complexity or lack of control over soliton positioning. Here we experimentally demonstrate a new CS writing scheme that alleviates these deficiencies. Specifically, we show that temporal CSs can be excited at arbitrary positions through direct phase modulation of the cavity driving field, and that this technique also allows existing CSs to be selectively erased. Our results constitute the first experimental demonstration of temporal CS excitation via direct phase modulation, as well as their selective erasure (by any means). These advances reduce the complexity of CS excitation and could lead to controlled pulse generation in monolithic microresonators.

25 Gbit/s differential phase-shift-keying signal generation using directly modulated quantum-dot semiconductor optical amplifiers

Error-free generation of 25-Gbit/s differential phase-shift keying (DPSK) signals via direct modulation of InAs quantum-dot (QD) based semiconductor optical amplifiers (SOAs) is experimentally demonstrated with an input power level of −5 dBm. The QD SOAs emit in the 1.3-μm wavelength range and provide a small-signal fiber-to-fiber gain of 8 dB. Furthermore, error-free DPSK modulation is achieved for constant optical input power levels from 3 dBm down to only −11 dBm for a bit rate of 20 Gbit/s. Direct phase modulation of QD SOAs via current changes is thus demonstrated to be much faster than direct gain modulation.

Performance comparison of analogue inter‐satellite microwave photonics link using intensity modulation with direct detection and phase modulation with interferometric detection

The performance of optical inter-satellite communications using microwave photonics technologies employing intensity modulation with direct detection (IMDD) and phase modulation (PM) with interferometric detection are investigated and demonstrated with a numerical example. The theoretical model considering the saturated gain and amplifier spontaneous emission noise of optical booster amplifier and optical preamplifier is constructed for both architectures. Furthermore, the authors compare the performance of PM with interferometric detection to optimum biased IMDD in terms of radio frequency (RF) gain, RF noise figure and compression dynamic range (CDR). The numerical results show that the PM with interferometric detection can achieve better RF gain, RF noise figure and CDR than the optimum biased IMDD link as the laser output power is lower than 14.34, 12.45 and 4.2 dBm, respectively.

All-fiber arbitrary and precise pulse spectral shaping

A fiber-loop-based electro-optic (EO) modulation system is proposed and demonstrated to realize both broadband and high-resolution spectral shaping of laser pulses through direct phase modulation. With this fiber-loop EO modulator, arbitrary spectral shape can be carved and the modulation precision is up to 0.004 nm. The laser spectral bandwidth can be steadily broadened from several MHz to several nanometers through tuning the pulse cycle times and the programmable driving signal. One representative shaped spectrum is presented with a <0.01 nm mismatch to the simulated results, which is used to effectively pre-compensate the pulse spectral distortion during amplification.

直接相位调制产生线性啁啾脉冲特性研究

直接相位调制产生线性啁啾脉冲特性研究

全光纤多程直接相位调制实现光谱控制技术研究

全光纤多程直接相位调制实现光谱控制技术研究

Periodic linear chirped pulse generation based on direct phase modulation

A new method of generating periodic linear chirped pulse is proposed, and a 0.52 nm bandwidth periodic chirped pulse is generated. Numerical simulation shows that the gain saturation, group velocity dispersion and synchronization jitter have great influences on chirped pulse; and self-phase modulation has little influence since the peak power stays at a low level. The experimental results indicate that the polarization mode dispersion will lead to a great intensity modulation, and the amplified spontaneous emission will break the light stability, which leads to the fewer round-trips of light. Research shows that the direct phase modulation is a novel method of generating periodic linear chirped pulse, which could be used for smoothing the spectral dispersion.

Efficient direct magneto-optical phase modulation of light waves in spun microstructured fibres

We have proposed a phase modulator of optical radiation for an interferometric electric-current sensor. The modulator takes advantage of the Faraday effect in spun microstructured optical fibres. Such fibres enable small-diameter multiturn fibre coils to be produced, which is necessary for achieving a preset phase modulation amplitude at a moderate drive current. The principal characteristics of the modulator have been studied experimentally: frequency response, magneto-optical sensitivity and output signal contrast. The results demonstrate that the modulator ensures high efficiency, approaching the theoretical one, provided the modulation period exceeds the time it takes light to pass through the fibre. We have examined the influence of spun fibre parameters on the performance of the modulator.