Optical Single Sideband Modulation Research Articles

Bidirectional radio-over-fiber system based on optical coupling single-sideband modulation

We demonstrate a bidirectional radio-over-fiber system based on optical coupling sing-sideband modulation, which can effectively reduce the impact of nonlinear distortion in transmission. With sidebands heterodyne detection, the system achieves 60-GHz wireless coverage. By optical carrier reusing, the base station can omit the laser source to make the system colorless. Through simulation analysis, the system has the credible transmission property both in downlink and uplink transmissions.

Large-Dynamic Frequency Response Measurement for Broadband Electro-Optic Phase Modulators

A novel method for characterizing the frequency responses of broadband electro-optic phase modulators (PMs) by employing stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. In the proposed method, the SBS amplifies the +1st-order sideband and attenuates the −1st-order sideband of the phase-modulated signal from a PM under test. Thereby, the phase-modulated signal is converted into an optical single-sideband modulation signal. After square-law photodetection, the overall frequency responses are obtained. Removing the frequency responses of the SBS gain and the photodetector from the overall responses, the responses of the PM are thus achieved. Benefitting from the amplification of the SBS, the proposed method possesses a large dynamic range. Sub-Hz resolution and broadband measurement range are also achievable. A commercial broadband PM is experimentally characterized from 10 MHz to 50 GHz with a resolution of 5 MHz. According to the amplification of the SBS, the dynamic range is enhanced by 17.74 dB. The measurement result is verified by the conventional method utilizing optical spectrum analysis.

Low-drift AM–PM based optical single-sideband modulator without 2nd-order sideband with adjustable optical carrier-to-sideband ratio

We propose and theoretically investigated a novel scheme to implement optical single-sideband (OSSB) modulator without 2nd-order sideband with adjustable optical carrier-to-sideband ratio (OCSR). The proposed structure is based on a hybrid concatenated electro-optic amplitude (or intensity) modulator (AM) and phase modulator (PM). The AM consists of a bidirectional PM inside a Sagnac loop (SL). Bias-drift associated problems do not present in the proposed structure because it uses PMs which are bias-free. Furthermore, clockwise (CW) and counter clockwise (CCW) optical signals propagate in the same optical fiber inside the SL, so its robustness against environmental changes increases. The structure is fed by three microwave signals with equal amplitudes and proper phases. The OCSR of the generated OSSB modulated signal can be adjusted by tuning the optical and/or microwave phase shifters and/or the PM modulation indices. The 3rd-order sidebands can also be suppressed by setting the proper optical and microwave phase shifts and adjusting the PM modulation indices.

Feed-forward comb-assisted coherence transfer to a widely tunable DFB diode laser.

The transfer of phase coherence from an ultrastable master laser to a distributed feedback diode laser, using an optical comb as a transfer oscillator, is obtained via a new scheme allowing continuous scanning across the whole tuning range of the slave laser together with absolute frequency determination. This is accomplished without phase lock loops, through a robust high-bandwidth feed-forward control acting directly on the slave laser output radiation. The correction is obtained by means of a dual-parallel Mach-Zehnder interferometer used as an optical single-sideband modulator. Coherence transfer across a master-slave frequency gap of 14 THz yields an ∼10 kHz linewidth providing high injection efficiency of an optical cavity with finesse 250 000. This allows demonstrating a cavity ring-down absorption spectrum of low-pressure ambient air over a 300 GHz spectral window.

Bias-free OSSB modulator with tunable OCSR

Abstract In this paper, a novel approach to realize optical single-sideband (OSSB) modulation with tunable optical carrier-to-sideband ratio (OCSR) is proposed and theoretically demonstrated based on a bidirectional optical phase modulator (PM) in a Sagnac interferometer (SI). In the proposed OSSB modulator, two RF signals with appropriate phase shifts are applied to the bidirectional PM. An OSSB modulated signal with tunable OCSR is obtained by adjusting the optical phase difference between clockwise (CW) and counterclockwise (CCW) propagating lights inside the SI and the PM modulation index. Since no bias is necessary for a PM, the proposed scheme is bias-drift free. In addition, the two counter-propagating lights travel in the same path in the SI so enhances robustness against environmental perturbations. It is shown that the proposed OSSB modulator can operate bidirectionally with dual complementary balanced outputs. It is observed that by using a 120° RF hybrid coupler, the −2nd sideband is suppressed in addition to the + 1 st sideband, results in performance improvement of the proposed OSSB modulator. Besides, effects of the power and phase imbalances of practical non-ideal 90- or 120-degree RF hybrid couplers and lossy Sagnac loop and non-ideal lossy optical coupler with unequal power splitting/combining on the performance of the proposed scheme are investigated.

A Radio over Fiber (RoF) Based Single Sideband Modulated Passive Optical Network (PON) Using Mach Zender Modulator Based on Different Electrical Phase Shifts

Abstract This research work provides an insight on a radio over fiber (RoF) based passive optical network (RoF-PON) utilizing two diverse electrical phase shifts with optical single sideband modulation (OSSB) by exploiting Mach Zender modulator. The influence of chromatic dispersion (CD) in PONs employing single mode fiber (SMF) is a noteworthy issue and should be limited. The two techniques of OSSB modulation, in view of the two distinct angles of the hybrid coupler are employed for the design and implementation of RoF-PON. The RF signal is partitioned into two ways equally before applying it to the dual drive Mach Zender modulator input, utilizing an electrical hybrid coupler that imparts two discrete phase shifts of 90° and 120° to generate two OSSB signals individually. By utilizing traditional OSSB technique having 90° phase shift, either of the first-order sideband (lower or upper first order) suppression occurs yet second-order harmonics are still existent in the system. As opposed to this, the OSSB technique using 120° phase shift causes the suppression of either lower first order and higher second order sideband or vice versa. When contrasted to the PON based on traditional technique (90° phase shift technique), the suppression of second order sideband in PON using 120° technique lessens the system CD. Hence the PON based on 120° phase shift technique has enhanced functionality in terms of system BER, received power and power losses as compared to that with traditional OSSB technique.

Millimeter-wave band optical single-sideband modulator using array-antenna-electrode and polarization-reversed structures with asymmetric Mach–Zehnder waveguide

The radio-over-fiber (RoF) technology is effective in millimeter-wave (MMW) wireless systems for future broadband massive mobile communication. In constructing MMW RoF systems, a device for converting MMW signals into lightwave signals is important. In particular, a conversion device for optical single-sideband (SSB) modulation is rather attractive since the signal fading caused by the chromatic dispersion effect of an optical fiber does not occur. We have proposed a new optical SSB modulator using array-antenna-electrode and polarization-reversed structures with an asymmetric Mach–Zehnder waveguide for MMW band RoF systems. By introducing polarization-reversed structures in electro-optic modulators, it is possible to control the optical modulation phase arbitrarily. Therefore, by combining with an asymmetric Mach–Zehnder waveguide, we can obtain the SSB optical modulation in the MMW band without an external power supply. In the experiment, SSB modulation characteristics and the switching of enhanced sidebands were successfully demonstrated in the 60 GHz band.

Optical Single Sideband Modulator Without Second-Order Sidebands

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.

Conversion from non-orthogonally to orthogonally polarized optical single-sideband modulation using optically injected semiconductor lasers.

This Letter investigates an optically injected semiconductor laser for conversion from non-orthogonally to orthogonally polarized optical single-sideband modulation. The underlying mechanism relies solely on nonlinear laser characteristics and, thus, only a typical semiconductor laser is required as the key conversion unit. This conversion can be achieved for a broadly tunable frequency range up to at least 65GHz. After conversion, the microwave phase quality, including linewidth and phase noise, is mostly preserved, and simultaneous microwave amplification up to 23dB is feasible.

High-Resolution Optical Vector Analysis Based on Symmetric Double-Sideband Modulation

An optical vector analyzer (OVA) based on symmetric optical double-sideband (ODSB) modulation using a phase modulator (PM) and an intensity modulator (IM) is proposed and demonstrated. In the symmetric-ODSB-based OVA, frequency response measurements are implemented by transmitting the phase-modulated and intensity-modulated ODSB signals through an optical device-under-test (DUT), respectively. Then, removing the responses of the two electro-optic modulators and processing the measured responses, accurate frequency responses of the DUT on both sides of the optical carrier are obtained. Comparing with the conventional OVA based on optical single-sideband (OSSB) modulation, the proposed ODSB-based OVA has the doubled measurement range and the simple wavelength-independent configuration. Moreover, the measurement system inherently has large dynamic range and high accuracy, which is difficult to achieve for the OSSB-based OVA due to the restriction of the limited sideband suppression ratio. An experiment for measuring the magnitude and the phase responses of a programmable optical filter is carried out. The responses in a range of 100 GHz are measured with a resolution of 10 MHz by using 50-GHz components.

Photonic Generation of Triangular-shaped Waveform Based on External Modulation

We present a novel approach for triangular-shaped waveform generation by applying optical single sideband (OSSB) modulation and optical carrier suppression (OCS) modulation to an input signal. Firstly, an OSSB modulated signal consists of an optical carrier and +1st-order sideband, is initially generated with a dual-drive Mach-Zehnder modulator (DD-MZM1) driven by a quadruple frequency RF signal. By tuning the amplitude of the RF signal and the bias of the DD-MZM1, the power ratio between the carrier and the +1st-order sideband is controlled as 19 dB. These two components are then transmitted to a DD-MZM2 which is driven by a fundamental frequency. After OCS modulation, four sidebands are existed in optical spectra of the modulated signal. By utilizing a fiber Bragg grating (FBG) to remove the undesired sideband, an output signal that features a triangular-shaped waveform is finally achieved.

Single-chip Si optical single-sideband modulator

We demonstrate an integrated Si optical single-sideband (OSSB) modulator composed of a parallel dual-ring modulator (PDRM) and a quadrature hybrid coupler (QHC). Both the PDRM and the QHC are carefully designed for 30 GHz opearation, and their operations are verified by measurement. The Si OSSB modulator successfully generates a single sideband with larger than 15 dB suppression of the undesired sideband.

Photonic Measurement of Microwave Frequency With Low-Error based on an Optomechanical Microring Resonator

We propose and experimentally demonstrate photonic measurement of microwave frequency by utilizing an optomechanical microring resonator (MRR). The pump powers injected into the MRR would result the resonance red-shifts based on nonlinear effects. In the case of optical single sideband modulation, the frequency intervals between the optical carrier and the corresponding MRR resonance are tunable. Then microwave photonic filters with tunable central frequency could be achieved. Through using two microwave photonic filter responses with different central frequencies, an amplitude comparison function (ACF) (i.e., microwave power ratios) could be obtained. The microwave frequency could be calculated through the frequency-to-power mapping in the monotonic increasing region of the ACF. Moreover, the frequency resolution could be effectively improved by multiple measurement steps, so as to reduce the measurement errors. In the experiment, the microwave frequency could be measured from 8 to 18 GHz with errors lower than 0.035 GHz. The required highest pump power is low as −3.9 dBm. In the future, the measurement range could be largely increased by employing vector network analyzer with a larger bandwidth. The significant optomechanical device and measurement method are competent to measure microwave frequency with dominant advantages, such as all-optical control, compact footprint, low-error, and low-power consumption.

A reconfigurable photonic microwave mixer using a dual-polarization modulator

A novel reconfigurable photonic microwave mixer using an integrated dual-polarization binary phase shift keying modulator is proposed. In the modulator, one dual-drive Mach–Zehnder modulator (DMZM) is driven by an RF signal to perform optical single sideband modulation, while another DMZM is driven by a local oscillator (LO) signal. Thanks to the orthogonal-polarization property of the integrated modulator, the optical carriers from the two DMZMs can be cancelled out each other. By adjusting the phase difference of the two LO signals applied to the modulator and the bias phase of the DMZM, the photonic microwave mixer can be worked as a single sideband mixer or harmonic mixer. The scheme is simple, compact and filter-free. The reconfigurable photonic microwave mixer is verified by simulation. The results show that the electrical spurs suppression ratios for both the single sideband mixer and the harmonic mixer are 31 dB.

Precise tuning of single-photon frequency using an optical single sideband modulator

Frequency translation of single photons while preserving their quantum characteristics is an important technology for flexible networking of photonic quantum communication systems. Here we demonstrate a flexible scheme to interface different-color photons using an optical single sideband (OSSB) modulator. By changing the radio-frequency signal that drives the modulators, we can easily shift and precisely tune the frequency of single photons. Using the OSSB modulator, we successfully erased the frequency distinguishability of non-degenerated photon pairs to obtain the Hong-Ou-Mandel interference with a visibility exceeding 90%. We also demonstrated that the level of distinguishability can be precisely controlled by the OSSB modulator. We expect that the OSSB modulator will provide a simple and flexible photonic interface for realizing advanced quantum information systems.

Influence of Unwanted First-Order Sideband on Optical Vector Analysis Based on Optical Single-Sideband Modulation

Optical vector analyzer (OVA) based on optical single-sideband (OSSB) modulation is attractive due to its potential sub-Hz resolution. However, the accuracy and dynamic range are limited by the unwanted sidebands of the OSSB signal, including the high-order sidebands and the unwanted first-order sideband. Previously, the influence of the high-order sidebands has been studied and several methods to suppress the errors induced by the high-order sidebands have been proposed. However, the investigation of the influence of the unwanted first-order sideband is still insufficient. In this paper, an analytical model is established and a numerical simulation is performed to comprehensively study the impact of the unwanted first-order sideband on the accuracy and dynamic range of the OSSB-based OVA. Then the simulation results are verified by experiment, which indicates that the unwanted first-order sideband has evident influence on the measurement accuracy and places a restriction on the dynamic range. Given that some prior information of the transmission responses is known, certain parameters of the device under test may still be achievable with high accuracy even when large unwanted first-order sideband is presented. This study may provide guidance in design and application of the OSSB-based OVA.

A flexible millimeter-wave radio-over-fiber system for various transmission bit rate

In this paper, we propose a flexible scheme to generate millimeter-waves (MMWs) for millimeter-wave radio-over-fiber (MMW-RoF) system. The proposed scheme has two configurations to adapt to various transmission bit rate by slightly rearranging the allocation of the system. The main structure of the system is cascaded LiNbO3 Mach-Zehnder modulators (LiNbO3-MZMs). The first configuration is cost effective method, where we utilize a wavelength division multiplexing de-multiplexer (WDM Demux) and an optical splitter (OS) to generate two unmodulated optical signals and a modulated optical signal. Each unmodulated optical signal and the modulated signal will form an optical single sideband (OSSB) modulation and therefore we simultaneously achieve a Q-band (45GHz) and a V-band (60GHz) MMWs in the receiver. The bit-error-ratio (BER) curves show that the power penalties of 45GHz and 60GHz are 0.6dB and 1.1dB at a BER of 1×10−9 with 2.5Gb/s transmission data rate and 50km fiber transmission distances. The second configuration can accommodate high bit rate, where few optical devices is rearranged to only generate a 60GHzMMW with 40Gb/s 4 quadrature amplitude modulation orthogonal frequency division multiplexing (4-QAM OFDM) signals. The power penalty is 1.1dB at a BER of 1×10−9 with 50km fiber transmission distances. Therefore, the proposed scheme can flexibly generate either two Q&V-band MMWs (45GHz and 60GHz) for the applications of the low data-rate transmission systems or one V-band MMW (60GHz) for the applications of the high data-rate transmission systems.

Hilbert superposition and modified signal-to-signal beating interference cancellation for single side-band optical NPAM-4 direct-detection system.

We propose a Hilbert superposition and modified signal-to-signal beating interference (SSBI) cancellation scheme in an optical single side-band (SSB) modulation and direct-detection system. The optical SSB signal is generated by a relatively low-cost dual-drive Mach-Zehnder modulator (DDMZM). The two driving signals are a pair of Hilbert signals with Nyquist pulse-shaped four-level pulse amplitude modulation (NPAM-4). In addition to the transmitted baseband signal, both its Hilbert transform and the SSBI can also be detected by direct-detection, which introduce the interference to the transmitted signal. We use the first-stage Hilbert superposition cancellation (HSC) to cancel the unwanted Hilbert transform signal and a modified single-stage linearization filter which contains the second-stage HSC to deduct the SSBI in the receiver. We experimentally demonstrate that 40 Gb/s optical SSB NPAM-4 signal transmission over 80 km standard single mode fiber (SSMF).

A novel method to realize optical single sideband modulation with tunable optical carrier to sideband ratio

AbstractAn optical single sideband (OSSB) modulation method with tunable optical carrier to sideband ratio (OCSR) is proposed and experimentally demonstrated based on a dual‐polarization Mach–Zehnder modulator (DPol‐MZM). An orthogonally polarized double sideband (DSB) signal output from the DPol‐MZM is filtered out the carrier and one sideband utilizing an optical bandpass filter (OBPF). Then the orthogonally polarized OSSB signal is transformed into a linear polarized OSSB signal by a polarizer (Pol). By changing the polarization direction of the Pol utilizing a polarization controller (PC), the tunable OCSR can be achieved. In the demonstrated experiments, an OSSB modulation is implemented over the wide microwave frequency range of 5–30 GHz. The OCSR is tuned from −30 dB to infinity. The proposed OSSB modulation method is advantageous in many respects as large tunable OCSR range, wide operation bandwidth, and simple structure.

Optical vector analysis based on asymmetrical optical double-sideband modulation using a dual-drive dual-parallel Mach-Zehnder modulator.

A novel approach to perform optical vector analysis (OVA) is proposed and experimentally demonstrated with carrier-shifted optical double-sideband (ODSB) modulation based on a dual-drive dual-parallel Mach-Zehnder modulator (DD-DPMZM). The proposed method has a doubled measurement range as compared with the conventional OVA based on optical single sideband modulation (OSSB), and a much simpler and more robust configuration as compared with the previously-reported ODSB-based OVA. In addition, the proposed scheme does not generate any undesirable spikes in the measurement results. The transmission response of a sampled fiber Bragg grating in a range of 80 GHz is measured with a resolution of less than 667 kHz by using 40-GHz microwave components. The influence of the unideal frequency-shifted optical carrier generation in the DD-DPMZM on the measurement error is also investigated.