Ten gigabits per second 16-level quadrature amplitude modulated millimeter-wave carrier generation using dual-drive Mach-Zehnder modulators incorporated photonic-vector modulator

A novel photonic-vector modulator architecture for the generation of 16 quadrature amplitude modulation (16 QAM) millimeter-wave carriers using dual-drive Mach-Zehnder modulators is proposed. Experimental generation of 5 Gbits/s 4 amplitude shift-keying (4 ASK) and 10 Gbits/s 16 QAM modulated 42 GHz carriers is reported. The multilevel modulated millimeter-wave signals are demodulated using an electrical receiver and its error-vector magnitude (EVM) estimated from the measurements, obtaining EVMs of -21.04 and -18.33 dB for 4 ASK and 16 QAM modulation formats, respectively.     

10 GHz, 2.4 ps pulse generation using a single-stage dual-drive Mach-Zehnder modulator

This Letter reports on picosecond pulse generation at a repetition of 10 GHz by using a single-stage electro-optic LiNbO(3) Mach-Zehnder modulator, stressing the simplicity of its setup. It is analytically and experimentally proved that dual-arm modulation with in-phase sinusoidal signals having slightly different amplitudes generated a highly coherent optical comb with a great spectral flatness and a parabolic phase relationship in its spectrum. The generated comb was Fourier synthesized and shaped into an ultrashort pulse train with an optical bandpass filter and a dispersive fiber. The pulse source was highly stable, exhibiting an ultralow timing jitter of less than 130 fs.     

Analysis of an optical mm-wave generation scheme with frequency octupling using two cascaded Mach-Zehnder modulators

We propose a novel method to generate optical mm-wave signals with frequency octupling using two cascaded Mach-Zehnder modulators (MZMs). First, the scheme is investigated both theoretically and by simulation, and results show that an 80 GHz mm-wave is generated by a 10 GHz RF oscillator. Then, an analytical expression is developed to describe the performance of the scheme. The influences caused by non-ideal factors are discussed in detail, and undesired sidebands suppression ratios are plotted and analyzed. At last a RoF system using the mm-wave generation scheme is demonstrated and its BER curves indicate that the performance of the system is still good even if the parameters deviate from the ideal values to a certain degree.     

Mach-Zehnder interferometric optical switch with MEMS phase shifter

We propose a novel Mach-Zehnder interferometric optical switching device with micro-electro-mechanical systems (MEMS) phase shifters. Analytical results show that the stretch length per phase shifter is 70 nm at an applied voltage of 100 V. Phase switching can be achieved by the cascade connections of fifteen phase shifters.     

A novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators

We propose a novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators (MZMs) for the first time. First, the scheme is investigated theoretically, which suggests that it can be used for sextupling, 12-tupling, and 18-tupling mm-wave generation. Then simulation results are given, 60 GHz mm-wave is generated from 5 GHz, or 10 GHz RF oscillator based on frequency 12-tupling or sextupling, and 90 GHz mm-wave is generated from 5 GHz RF oscillator based on frequency 18-tupling. The optical sideband suppression ratio (OSSR) and the radio frequency spurious suppression ratio (RFSSR) are analyzed by simulation, in which several non-ideal factors are taken into consideration. Results indicate that all the three mm-wave generation methods are practical and very good performance can be obtained when the extinction ratio of the MZM is 30 dB, even if the extinction ratio of the MZM is 20 dB, the performance is still good, especially for the sextupling mm-wave generation method, whose performance is excellent and insensitive to the extinction ratio of MZM, the non-ideal RF driving voltage and the non-ideal DC bias. At last, we set up a RoF system by simulation to verify the transmission performance of the scheme. The BER performance and eye diagrams are given.     

Idler-free photonic microwave mixer using a broadband optical source and cascaded phase modulators

A method of all-optical microwave mixing and bandpass filtering is proposed to achieve idler-free RF frequency conversion based on cascaded phase modulation of a broadband optical source. The variable optical carrier time-shift method is employed to selectively generate the desired RF mixing components and highly suppress the other idler frequencies. An experimental system that can perform idler-free fundamental and harmonic RF upconversions is demonstrated, and the conversion efficiency is investigated both theoretically and experimentally.     

An optical (Q)PSK-RF-signal transmitter based on two cascaded Mach-Zehnder modulators

This paper proposes an optical transmitter to generate phase-shift-keying (PSK) radio frequency (RF)-signal, using two cascaded single-drive Mach-Zehnder modulators (SDMZMs). With input of a continuous-wave (CW) light, an electrical non-return-to-zero (NRZ) data, and an RF-local oscillator (RF-LO) signal at a frequency of ω_l, the transmitter can simultaneously produce three PSK signals and two CW tones on both sides in spectrum, by employing nonlinear modulation technique. With the help of optical filters, the desired signals can be selected to mix at a photodetector (PD) to obtain a PSK-RF-signal with the carrier frequency of ω_l, 3ω_l, or 5ω_l. Our scheme can be easily extended to generate quadrature PSK-RF-signal. The feasibility of our proposal is experimentally and numerically verified.     

Implentation of optical encoder and multiplexer using Mach-Zehnder inferometer

In this paper a simple all-optical logic device, called Mach-Zhender Interferometer is composed by using a semiconductor optical amplifier (SOA) and an optical coupler. This device is used for generating the logical functions (AND, XOR) and a multiplexer and an Encoder are obtained using this device in Optical Tree Architecture. The simulation of Encoder and Multiplexer is done at a rate of 10 Gb/s and both are simulated for different input logical combinations. Simulations indicate that the device is suitable to operate at much higher bit rate and also for different logical entities.     

Generation of very flat optical frequency combs from continuous-wave lasers using cascaded intensity and phase modulators driven by tailored radio frequency waveforms

We demonstrate a scheme based on a cascade of lithium niobate intensity and phase modulators driven by specially tailored RF waveforms to generate an optical frequency comb with very high spectral flatness. In this Letter, we demonstrate a 10 GHz comb with 38 comb lines within a spectral power variation below 1 dB. The number of comb lines that can be generated is limited by the power handling capability of the phase modulator, and this can be scaled without compromising the spectral flatness. Furthermore, the spectral phase of the generated combs in our scheme is almost purely quadratic, which, as we will demonstrate, allows for high-quality pulse compression using only single-mode fiber.     

Design of millimeter-wave fiber-wireless downlink with remote local-oscillator delivery by using dual-electrode Mach-Zehnder modulators configured for optical single-sideband modulations

An optical fiber-wireless system operating in millimeter-wave (MMW) bands may include numerous optical remote access points (RAPs) of which the cost is critical to implement such systems in real market. In this paper, we design an optical fiber communication system for MMW optical fiber downlink transmission with remote MMW local-oscillator (LO) delivery for intermediate frequency (IF) fiber uplink transmission. The new design is based on two dual-electrode Mach-Zehnder modulators in parallel both configured for optical single-sideband modulations. By using the proposed design, a conventional RAP can be simplified in structure to reduce the cost. Our numerical results show that, with the proposed design, 1-Gbit/s binary-phase-shift-keying (BPSK) data at a 42-GHz sub-carrier frequency can be transmitted over a 20-km standard single-mode optical fiber followed by a wireless transmission of several kilometers. Moreover, a MMW LO at 37-GHz frequency can be remotely delivered over tens of kilometers of a standard single-mode fiber with acceptable deterioration in the LO phase noise for IF uplink fiber transmission.     

A novel wavelength shift keying transmitter using a pair of Mach-Zehnder modulators

A novel and simple method to achieve wavelength shift keying (WSK) modulation is proposed and experimentally demonstrated. The proposed WSK transmitter consists of a pair of Mach-Zehnder modulators (MZMs) that are biased appropriately to achieve complementary operation. When a non-return-to-zero data stream is applied to the two MZMs, thanks to the complementary operation of the MZMs, the WSK-modulated signal can be obtained by combining the two intensity-modulated optical signals. A tunable optical delay line (ODL) is applied to achieve synchronization between the two optical signals. The ODL can also be used to compensate for the dispersion-induced walk-off effect between the two optical carriers. The application of the proposed WSK transmitter in a passive optical network is demonstrated, in which the downstream WSK signal is reused as optical carrier for upstream intensity-modulated data transmission. The proposed approach is experimentally realized; experimental results verify the feasibility of the approach.     

Photonic analog-to-digital conversion using multiple comparators and Mach-Zehnder modulators with identical half-wave voltages

A novel photonic analog-to-digital conversion scheme using Mach-Zehnder modulators (MZMs) with identical half-wave voltages and multiple comparators with improved bit resolution is proposed and demonstrated. Compared with the scheme using MZMs with geometrically scaled half-wave voltages, the proposed scheme has the advantage of using MZMs with identical half-wave voltages which simplify significantly the implementation. The bit resolution is improved based on the use of multiple comparators in each MZM channel, with the digital coding realized based on the symmetrical number system theory. A proof-of-concept experiment is implemented. An analog-to-digital converter with a 4-bit resolution using two MZMs and nine comparators is demonstrated.     

A coherent beam combination system based on double PZT phase modulators

A novel coherent beam combination system based on double piezoelectric ceramics transducer (PZT) phase modulators is presented and demonstrated for the first time. In this system, two different PZT phase modulators are used for high frequency phase modulation and low frequency phase control, respectively, while in previous demonstrated system, LiNbO₃ phase modulators are often employed. The inherent low insert loss and high laser-induced damage threshold of the PZT phase modulator makes the new proposed system more compact and stable. By the way, the experiment of coherent beam combination of two 5-W fiber laser beams based on double PZT phase modulators is done. In the experiment, the PZT phase modulator with 500-kHz frequency response point made in home is used for high frequency phase modulating and another one with 0～30-kHz linear frequency response range for phase controlling. When the phase control system is in the closed loop, the fringe contrast of far-field intensity pattern is improved to be more than 90 % from 5 % in open loop.     

Generation of picosecond optical phase conjugate pulses using cw mode-locked lasers

Low power picosecond optical phase conjugation has been demonstrated using cw mode-locked argon-ion and dye lasers via 4-wave mixing in ruby. Streak camera and power measurements show that the generated pulses are identical to the input pulses.     

Holography,coherent light amplification and optical phase conjugation with photorefractive materials

This paper presents a review of photorefractive effects in electro-optic materials and their applications. Materials properties giving rise to increased photo-sensitivities are discussed and compared with experimental data for a series of newer materials. The formation of volume holograms in these crystals, and accompanying optical effects such as beam coupling and phase conjugation, are discussed. Theoretical results derived from charge transport parameters are compared with our original data obtained in “dynamic holography” experiments with Bi₁₂GeO₂₀, Bi₁₂SiO ₂₀ and KNbO₃:Fe²⁺. The optimum parameters for applications such as volume hologram storage, coherent light amplification, optical phase conjugation etc. have been determined, and possible applications are discussed.     

Higher-order dispersion compensation using phase modulators

The use of electro-optic phase modulation of dispersed optical pulses is investigated for compensating higher-order chromatic dispersion effects. The capability and limitations of the technique are described for compensating third- and fourth-order dispersion terms.     

Optical isolator using two tandem phase modulators

We propose and demonstrate an integrated optical isolator in InP using two phase modulators in series. The phase modulators are driven with a single-frequency signal in quadrature. Theoretically there is no effect on the forward signal, and the carrier of the backward signal can be eliminated, the energy distributed to other frequencies. We achieve a carrier isolation of 11?dB and an excess insertion loss of 2.3?dB. Such an isolator can be monolithically integrated with a laser without extra materials or magnetic fields.     

Generation of three-mode W-type entangled coherent states in free-travelling optical fields

We propose a scheme for generation of three-mode W-type entangled coherent states (ECSs) in freetravelling optical fields by using a single-photon source, coherent state sources, beam splitters, photodetectors, and three-mode cross-Kerr media. The scheme consists of a Mach-Zehnder interferometer (MZI)in which each arm contains a cross-Kerr medium. We calculate the success probability of the generated W-type ECSs, and the total success probability is unity under the ideal conditions.