Dual-output Mach-Zehnder Modulator Research Articles

Ultra-wideband instantaneous frequency measurement based on differential photonic time-stretch

A novel technique to perform ultra-wideband instantaneous frequency measurement in real-time based on differential photonic time-stretch is proposed and experimentally demonstrated. Wideband frequency measurement is enabled by time-stretching the RF input signal via the dispersion compensating fiber. Distortion of the measured frequency signal caused by the non-uniformity of the spectrum of the pulsed laser source, which can be found in most of traditional time-stretch systems, is eliminated here by implementing a dual-output Mach–Zehnder modulator (DOMZM) with complementary outputs and a balanced photodetector. Multi-tone tests with a 20 GHz frequency measurement range are conducted to verify the feasibility of the system of measuring multiple frequency signals. Followed by the proposed automated digital signal processing algorithms, our instantaneous frequency measurement system offers an ultra-fast sweep time of 10 ns, a frequency resolution of 660 MHz, and a measurement error within ±380 MHz. A larger frequency measurement range can be realized by implementing a DOMZM with a larger bandwidth.

A ‘DOMZM–Filter–BPD’-Based Microwave Photonic Link for Eliminating Even Harmonics Distortion

The ‘Mach-Zehnder modulator (MZM)–wavelength division demultiplexer (WDM)–photodetector (PD)’ structure in photonic analog-to-digital converters (PADCs) may result in residual even harmonics after photodetection. In this paper, we build the model for the ‘Dual-output MZM (DOMZM)–filter–balanced PD (BPD)’-based microwave photonic link, where the amplitude and the phase responses of the filter can be arbitrary. It is proved that this link can eliminate the aforementioned even harmonics. Theoretical analysis is verified by the simulation and experimental results. By using this structure, the spur-free dynamic range (SFDR) limited by the even harmonics can be improved and the sampling frequency range can be expanded for the PADCs. As the spectrum contains only odd harmonics, the inverse cosine transform for calibrating the nonlinearity of the MZM can be applied to further improve the SFDR.

A Tunable Dual-Passband Microwave Photonic Filter Based on Optically Injected Distributed Feedback Semiconductor Lasers and Dual-Output Mach-Zehnder Modulator

In this paper, a novel approach to achieving a wideband tunable dual-passband microwave photonic filter (MPF) is proposed based on optical-injected distributed feedback (DFB) semiconductor lasers and a dual-output Mach–Zehnder modulator (DOMZM). The fundamental concepts for realizing the MPF are the wavelength-selective amplification effect and the period-one oscillation state under optically injected DFB lasers. These effects provide a widely tunable range of center frequency, along with high flexibility and low insertion loss. The proposed MPF is experimentally demonstrated, showing that the dual-passband center frequency in the MPF can be tuned independently from 19 to 37 GHz by adjusting the detuning frequency and injection ratio. Meanwhile, the insertion loss of the system is about 15 dB when there is no optical or electrical amplifier in the MPF link. The out-of-band suppression ratio of the MPF is more than 20 dB, which can be improved by adjusting the power of the two optical signals.

Compact photonic triangular waveform generator with wideband tunability

A compact triangular waveform generator, consisting of a laser diode, a single dual-output Mach–Zehnder modulator (DOMZM), a variable optical delay line and a balanced photodetector (BPD), is proposed and experimentally demonstrated, using a single-frequency RF signal as the input. The DOMZM is biased at the quadrature point, so that no even-order harmonics of the RF frequency would be generated after the BPD. Then, the modulation index is properly selected to let the generated electrical first- and third-order harmonics approximately equal those of the triangular waveform. The use of the balanced detection not only increases the output power by 6 dB but also removes the DC component and the common-mode noise. No optical filtering is required, which guarantees the simplicity and wide frequency range of the system. A proof-of-concept experiment is carried out. Triangular waveforms with repetition rate tuning from 1 to 13 GHz are successfully generated, with the even-order harmonics suppressed by more than 54 dB.

Dual-Output Mach–Zehnder Modulator for Optical Access Networks

ABSTRACTThis paper employs dual-output Mach–Zehnder Modulator (MZM) for optical access networks without optical filters. Light waves generated from multiple laser sources are multiplexed and fed into dual-output MZM. Biasing the dual-output MZM at null point generates central carriers in one output port and first-order sidebands in another output port. Reflective semiconductor optical amplifier modulates both the central carriers and sidebands with wired and wireless data, respectively. The modulated optical signals are combined by polarization beam splitter and transmitted through 25-km single-mode fiber. The performance of the proposed scheme is proved by clear eye-diagrams and great bit error rate (BER) curves. Moreover, the power penalty at the BER of 10-9 is less than 1 dB for both wired and wireless signals. Therefore, the proposed system simultaneously transmits wired and wireless signals.

Microwave frequency doubling by synchronising and polarisation multiplexing the optical signals from a dual‐output Mach–Zehnder modulator

A technique is experimentally demonstrated to double the frequency of a microwave signal by synchronising and polarisation multiplexing the optical signals from a dual-output Mach–Zehnder modulator. The frequency-doubled tone at 4 GHz is 41.2 dB stronger than the residual fundamental-frequency tone. The strongest side tone is found at 12 GHz (sixth order) and is suppressed by 32.7 dB. The phase noise of the frequency-doubled signal is −104.1 dBc/Hz at an offset of 10 kHz, an increase of 6.7 dB over that of the initial signal. This technique does not rely on electronic or optical filters or amplifiers and is demonstrated using commercial off-the-shelf components.

Widely Tunable Optoelectronic Oscillator Using a Dispersion-Induced Single Bandpass MPF

A widely frequency tunable optoelectronic oscillator (OEO) based on a dispersion-induced single bandpass microwave photonic filter (MPF) is proposed and demonstrated. The MPF is implemented using a broadband optical source, a dual-output Mach–Zehnder modulator ( $1\times 2$ MZM) with unbalanced output fiber lengths into the upper and lower arms of the $1\times 2$ MZM, and a linearly chirped fiber Bragg grating. Through adjusting the difference between the two output fiber lengths after the $1\times 2$ MZM, the oscillation frequency of the OEO can be tuned by incorporating the MPF into an optical domain dual-loop OEO. A proof-of-concept experiment is performed. A microwave signal with a frequency tunable from 4.078 to 13.05 GHz is generated and its performance is investigated.

Switching response of dual-output Mach–Zehnder modulator in channel-interleaved photonic analog-to-digital converter

This Letter theoretically and experimentally studies the response of photonic switching in a channel-interleaved photonic analog-to-digital converter (PADC) with high sampling rate and wide input frequency range. A figure of merit (FoM) is introduced to evaluate the switching response of the PADC when a dual-output Mach–Zehnder modulator (MZM) serves as the photonic switch to parallelize the sampled pulse train into two channels. After the optimization of the FoM and utilization of the channel-mismatch compensation algorithm, the system bandwidth of PADC is expanded and the signal-to-distortion ratio is enhanced.

Simultaneous transmission of wired and wireless signals based on double sideband carrier suppression

Abstract In this paper, we proposed and experimentally demonstrated simultaneous transmission of wired and wireless signals based on double sideband optical carrier suppression. By properly adjusting the bias point of the dual-output mach-zehnder modulator (MZM), a central carrier in one output port and a pair of first-order sidebands in another output port are generated. The pair of first-order sidebands are fed into a second MZM to generate second-order order sidebands. A wired signal is embedded on the central carrier while a wireless signal is embedded on the second-order sidebands. Unlike other schemes, we did not use optical filter to separate the carrier from the optical sidebands. The measured bit error rate (BER) and eye-diagrams after a 25 km single-mode-fiber (SMF) transmission proved that the proposed scheme is successful for both wired and wireless signals transmission. Moreover, the power penalty at the BER of 10−9 is 0.3 and 0.7 dB for wired and wireless signals, respectively.

Highly sensitive demodulation of a vibration-induced phase shift based on a low-noise OEO.

A highly sensitive demodulation approach of a vibration-induced phase shift based on a low-noise optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The vibration-induced optical phase variation is directly converted to the electrical oscillating signal of the OEO with carrier phase-shifted double-sideband (CPS-DSB) modulation, which is realized by cascading a dual-output Mach-Zehnder modulator (DOMZM) and a fiber interferometer. Theoretically, within a CPS-DSB modulated OEO, the minimum detectable optical phase shift is determined by the phase noise achievable, and the sensitivity of the optical phase shift demodulation no longer depends on its frequency. A proof-of-concept OEO oscillating at 100MHz with ultralow phase noise is built for demonstration. The achieved minimum detectable optical phase shift is 0.58 μrad/√Hz at 1kHz and 0.21 μrad/√Hz at 10kHz, which are the best results ever reported, to the best of our knowledge.

Photonic generation of multi-frequency phase-coded microwave signal based on a dual-output Mach-Zehnder modulator and balanced detection.

A photonic scheme to generate a multi-frequency phase-coded microwave signal based on a dual-output Mach-Zehnder modulator (DOMZM) and balanced detection is proposed in this paper. The DOMZM driven by an electrical coding data modulates a coherent multi-wavelength light source (CMWL), and a balanced photodetector (BPD) demodulates the output of the DOMZM; as a result, a multi-frequency phase-coded microwave signal is generated. Experiments generate two two-frequency phase-coded signals: one is 5GHz/10GHz signal with a coding rate of 2Gb/s, and the other is 10GHz/20GHz signal with a coding rate of 4Gb/s. Their autocorrelation results show a good pulse compression capability. Each frequency of a two-frequency signal has similar performances with the other in terms of peak-to-side lobe ratio (PSR) and the full width at half-maximum (FWHM) of the main lobe. The proposed scheme can be applied to radar to reduce false detections in adverse conditions. With its potential flexible frequency agility, it can be used for jamming resistance and elimination of the Doppler blind speed during moving target detection.

A Linearized Analog Photonic Link Based on a Single z-Cut LiNbO3 Dual-Output Mach–Zehnder Modulator

We propose a linearized analog photonic link (APL) using a single z-cut LiNbO3 dual-output Mach–Zehnder modulator (MZM) to remove the third-order intermodulation distortion (IMD3). A polarizer, a z-cut LiNbO3 dual-output MZM, and a polarization beam combiner are combined to realize orthogonal polarized complementary intensity modulation with diverse modulation depth. Two IMDs3 with identical amplitude and adverse phase are eliminated destructively via appropriately controlling the optical power between two orthogonal polarized paths. A theoretical analysis is carried out and demonstrated by a simulation. Simulation results show that the spurious-free dynamic range of the proposed linearized APL is 24.5 dB and 18.5 dB higher than that of the conventional optical double sideband modulation link in back-to-back transmission and after 20 km transmission in single-mode fiber, respectively. The proposed scheme features simple structure with good performance.

Microwave photonic link with improved phase noise using a balanced detection scheme

A microwave photonic link (MPL) with improved phase noise performance using a dual output Mach–Zehnder modulator (DP-MZM) and balanced detection is proposed and experimentally demonstrated. The fundamental concept of the approach is based on the two complementary outputs of DP-MZM and the destructive combination of the photocurrent in balanced photodetector (BPD). Theoretical analysis is performed to numerical evaluate the additive phase noise performance and shows a good agreement with the experiment. Experimental results are presented for 4GHz, 8GHz and 12GHz transmission link and an 11dB improvement of phase noise performance at 10MHz offset is achieved compared to the conventional intensity-modulation and direct-detection (IMDD) MPL.

Spectrum-Sliced Microwave-Photonic Filter Based on Fourier Transform of Modified Optical Spectrum

A new technique is presented to reconfigure the dispersion-induced RF fading in a spectrum-sliced microwave photonic filter to an arbitrary spectral shape, including the flat-top response with rectangular shape and operating frequencies beyond conventional baseband. The technique is based on the Fourier transform of the modified optical source power spectrum, which is realized by applying a designed optical amplitude and phase manipulation using a diffraction-based spectral pulse shaper to the ports of a dual-output Mach-Zehnder electro-optic modulator in combination with a broadband light source. This scheme is fundamentally different from earlier finite-impulse-response-based spectrum-sliced microwave-photonic filters that require specific slicing elements for optical taps, but offers the same flexibility in realizing various filter passband characteristics with the added benefit of widely shape-invariant tuning and a single passband response. Experimental results verify the technique and demonstrate a continuously tunable dispersion-induced RF fading up to 20 GHz, exhibiting shape invariance and a flat-top response.

Highly Linear Broadband Photonic-Assisted Q-Band ADC

A highly linear broadband photonic-assisted analog-to-digital converter (ADC) based on high-frequency optical sampling utilizing a dual output Mach–Zehnder modulator operating with signal frequencies up to 50 GHz is presented. The pulses employed in the optical sampling were generated by a cavity-less pulse source operated at 10 GHz in preference to conventional mode-locked lasers. The optical sampling front-end greatly extends the operational frequency range of the Nyquist limited electronic digitization back-end. The performance of the sampling system is characterized with 7.1 effective number of bits (ENOBs) at 40 with 5 GHz fully accessible bandwidth, and greater than 99 dB·Hz2/3 spurious free dynamic range for the 30–40 GHz frequency range. Furthermore, more than 8 ENOB was achieved by reducing the effective bandwidth to 1 GHz with a digital filter, demonstrating the additional advantage of using a higher sampling rate compared to previous demonstrations. A new figure of merit of photonic-assisted sub-sampled ADCs is also presented accompanied with a comparison to previous implementations.

A Frequency-Doubling Optoelectronic Oscillator using a Three-Arm Dual-Output Mach-Zehnder Modulator

This paper proposes a frequency-doubling optoelectronic oscillator employing a novel three-arm dual-output Mach-Zehnder modulator (MZM). One output of the MZM generates the fundamental-frequency signal which is recycled by the microwave optical fiber link for oscillation, and the other output can generate the frequency-doubled signal. Experiment was conducted using a commercial two-arm MZM, a phase modulator, and an optical fiber link of 89 meters in length. A 19-GHz frequency-doubled signal was successively obtained with fundamental signal suppression more than 36 dB.

Photonic preprocessor for analog-to-digital-converter using a cavity-less pulse source

A photonic preprocessor for analog to digital conversion is demonstrated and characterized using a cavity-less optical pulse source. The pulse source generates high fidelity pulses at 2 GHz repetition rate with temporal width of 3 ps. Chirped pulses are formed by cascaded amplitude and phase modulators, and subsequently compressed in dispersion compensating fiber. Sampling operation is performed with a dual-output Mach-Zehnder modulator, where the complimentary output enables a reduction of noise by 3 dB. Phase noise characterization shows that the phase noise of the generated pulses is fully dictated by the RF source. The high quality of the pulse source used in a sampling preprocessor experiment was verified by measuring 8 effective number of bits at 10 GHz and 7.0 effective number of bits at 40 GHz.

The Performance of a Fiber-Optic Link Using Unbiased Balanced Photodiodes for Antenna Array Calibration

A quadrature-biased dual-output Mach-Zehnder modulator is used to drive unbiased balanced photodiodes for use in antenna array applications. The RF gain is measured as a function of frequency and photocurrent. Balanced photodiode two-tone measurements at 6 GHz are compared with those of a single photodiode to show 26-dB suppression of the second-order distortion. This results in a second-order limited spur-free dynamic-range improvement of 12 dB. The phase error introduced in unbiased photodiodes is compared to that of the biased case to demonstrate that it would have minimal effect on the performance of the antenna array system.

Photonic Instantaneous Frequency Measurement System Using Complementary Modulation

A novel photonic instantaneous frequency measurement system based on complementary modulation is proposed and experimentally demonstrated. A dual-electrode dual-output Mach-Zehnder modulator is used to simultaneously achieve electrooptical modulation and complementary modulation sideband (MS) filtering. By suppressing the optical carrier at one of the modulator outputs, complementary MS filtering is mapped into two complementary average optical powers from which the RF frequency is derived. The obtained frequency measurement is independent of both optical and RF powers, and is also robust to electrical circuitry imperfections.

Even-order harmonic cancellation for off-quadrature biased Mach-Zehnder modulator with improved RF metrics using dual wavelength inputs and dual outputs

We present a technique using a dual-output Mach-Zehnder modulator (MZM) with two wavelength inputs, one operating at low-bias and the other operating at high-bias, in order to cancel unwanted even-order harmonics in analog optical links. By using a dual-output MZM, this technique allows for two suppressed optical carriers to be transmitted to the receiver. Combined with optical amplification and balanced differential detection, the RF power of the fundamental is increased by 2 dB while the even-order harmonic is reduced by 47 dB, simultaneously. The RF noise figure and third-order spurious-free dynamic range (SFDR(3)) are improved by 5.4 dB and 3.6 dB, respectively. Using a wavelength sensitive, low V(pi) MZM allows the two wavelengths to be within 5.5 nm of each other for a frequency band from 10 MHz to 100 MHz and 10 nm for 1 GHz.