Optical Vector Analysis Research Articles

High-resolution optical vector analysis based on single sideband modulation using a dual port Mach–Zehnder modulator

High-resolution optical vector analysis based on single sideband modulation using a dual port Mach–Zehnder modulator

High-Accuracy Optical Vector Analysis Based on Dual-Polarization MZM and Polarization Control

High-Accuracy Optical Vector Analysis Based on Dual-Polarization MZM and Polarization Control

Large Dynamic and Precision Optical Vector Analysis Assisted by SBS Processing

Large Dynamic and Precision Optical Vector Analysis Assisted by SBS Processing

Wideband Optical Vector Analysis Based on Microwave Photonic Frequency Downconversion

Wideband Optical Vector Analysis Based on Microwave Photonic Frequency Downconversion

Hyperfine optical vector analysis of ultra- narrowband optical bandpass filters based on coherent two-tone sweeping and fixed low-frequency detection

A hyperfine optical vector analyzer (OVNA) is proposed and experimentally demonstrated to characterize ultra-narrowband optical bandpass filters (OBPFs). In this scheme, a coherent two-tone optical signal (TTOS) with a small frequency interval is generated to act as a probe light. Through finely sweeping the TTOS across the passband of the OBPF via electro-optic modulation, the magnitude and phase responses of the OBPF under test can be measured with a high signal-to-noise ratio based on fixed low-frequency detection. The frequency response measurement is immune to external disturbance. In the experiment, the magnitude and group delay responses of a fiber-based Fabry-Perot tunable filter (FFP-TF) and a fiber-based Fabry-Perot interferometer (FFP-I) with 3-dB bandwidths of 1.5 GHz and 60 MHz, respectively, are successfully measured. In addition, the measurement uncertainty is theoretically and experimentally analyzed. This method paves a way to characterize ultra-narrowband OBPFs with high out-of-band rejection ratios.

Research on Ultra-Fast Optical Vector Analysis Based on Microwave Photonic Frequency Sweeping

An ultra-fast and high-resolution optical vector analysis scheme has been proposed and experimentally demonstrated. In the scheme, a broadband optical frequency-sweeping signal is generated by injecting a linearly frequency-modulated signal into one radio-frequency (RF) port of a dual-drive Mach-Zehnder electro-optic modulator, which is used to achieve fast scanning of the frequency response characteristic of the device under test (DUT). A single-tone microwave signal is injected into the other RF port of the modulator to realize down-conversion of the frequency-sweeping signal. The down-converted signal is then digitized by an analog-to-digital converter, and is processed through Hilbert transform to extract the amplitude- and phase-frequency response of the DUT. In the proof-of-concept experiment, the amplitude- and phase-frequency response of the Brillouin gain in a section of non-zero dispersion shifted fiber with a length of 3 km is accurately measured, where the measurement time is only 20 μs, and the frequency resolution reaches 20 kHz.

High-Resolution Optical Vector Analysis With Enhanced Sensitivity

High-resolution and high-sensitivity optical vector analysis (OVA) is highly desired by many applications, such as optical sensors and photonic integrated circuits (PICs). However, it is difficult to achieve high resolution and high sensitivity simultaneously. Here, we propose and experimentally demonstrate a high sensitivity OVA using coherent detection to achieve the complex frequency responses (including magnitude and phase responses) of a device under test (DUT). Carrier phase noise (CPN) cancellation is employed to eliminate the carrier phase fluctuation induced by the coherent detection. In an experiment, the frequency responses of a fiber Bragg grating (FBG) is accurately measured by the proposed method when the probe light is suppressed by ~18 dB. As a comparison, the method using coherent detection without CPN cancellation can only achieve the magnitude response, and the method using direct detection cannot obtain an effective measurement. The influence of the linewidth and time delay on the measurement is discussed. The proposed OVA provides a stable, high resolution, high sensitivity and low cost approach for characterizing optical devices with arbitrary response, especially for optical devices with large loss or bandpass response.

Optical vector analysis with attometer resolution, 90-dB dynamic range and THz bandwidth

Optical vector analysis (OVA) capable of achieving magnitude and phase responses is essential for the fabrication and application of emerging optical devices. Conventional OVA often has to make compromises among resolution, dynamic range, and bandwidth. Here we show an original method to meet the measurement requirements for ultra-wide bandwidth, ultra-high resolution, and ultra-large dynamic range simultaneously, based on an asymmetric optical probe signal generator (ASG) and receiver (ASR). The ASG and ASR remove the measurement errors introduced by the modulation nonlinearity and enable an ultra-large dynamic range. Thanks to the wavelength-independence of the ASG and ASR, the measurement range can increase by 2 N times by applying an N-tone optical frequency comb without complicated operation. In an experiment, OVA with a resolution of 334 Hz (2.67 attometer in the 1550-nm band), a dynamic range of > 90 dB and a measurement range of 1.075 THz is demonstrated.

Optical Vector Analysis With Improved Accuracy and Enhanced Dynamic Range

An optical vector analyzer (OVA) based on phase-shift (PS) technique is proposed and experimentally demonstrated, which enables improved accuracy and enhanced dynamic range. A carrier-suppressed optical double-sideband (ODSB) signal achieved by external modulation is used as the probe signal, which is then transmitted through a device under test (DUT). By photodetecting, a photocurrent carrying the frequency responses is generated. By scanning the wavelength of the optical carrier while extracting the magnitude and phase information of the photocurrent, the responses of the optical DUT are thus acquired. Since the carrier-suppressed ODSB signal has lower sensitivity to the nonlinearity and generates larger photocurrent than the intensity modulated ODSB signal, the proposed OVA has improved accuracy and enhanced dynamic range compared to the conventional PS-based OVA, which is comprehensively investigated in analytical analysis and simulation. In an experiment, the accuracy improvement is confirmed, and the enhancement of the dynamic range is evidently observed, which agrees well with the simulation results.

Rectangular domain curl polynomial set for optical vector data processing and analysis

Rectangular pupils are employed in many optical applications such as lasers and anamorphic optics, as well as for detection and metrology systems such as some Shack−Hartmann wavefront sensors and deflectometry systems. For optical fabrication, testing, and analysis in the rectangular domain, it is important to have a well-defined set of polynomials that are orthonormal over a rectangular pupil. Since we often measure the gradient of a wavefront or surface, it is necessary to have a polynomial set that is orthogonal over a rectangular pupil in the vector domain as well. We derive curl (called C) polynomials based on two-dimensional (2-D) versions of Chebyshev polynomials of the first kind. Previous work derived a set of polynomials (called G polynomials) that are obtained from the gradients of the 2-D Chebyshev polynomials. We show how the two sets together can be used as a complete representation of any vector data in the rectangular domain. The curl polynomials themselves or the complete set of G and C polynomials has many interesting applications. Two of those applications shown are systematic error analysis and correction in deflectometry systems and mapping imaging distortion.

Ultrafast and ultrahigh-resolution optical vector analysis using linearly frequency-modulated waveform and dechirp processing.

We propose and experimentally demonstrate an ultrafast and ultrahigh-resolution optical vector analyzer (OVA) using linearly frequency-modulated (LFM) waveform and dechirp processing. An optical LFM signal, achieved by modulating an electrical LFM signal on an optical carrier via carrier-suppressed optical single-sideband (OSSB) modulation, is separated into two portions. One portion (denoted as the reference signal) directly goes through the reference path, and the other (denoted as the probe signal) undergoes magnitude and phase changes by an optical device under test (DUT) in the measurement path. After balanced photodetection, the reference signal and the probe signal are mixed to perform a dechirp operation. A relatively low-frequency electrical signal is generated, which can be sampled by a low-speed analog-to-digital converter. As a result, the frequency responses of the DUT can be extracted at a high speed by post digital signal processing. Thanks to the large chirp rate of the electrical LFM signal and the dechirp processing, the proposed LFM-based OVA enables ultrafast measurement speed and ultrahigh frequency resolution. We perform an experiment in which a narrowband tunable optical filter is characterized. The measurement speed reaches 1ns/point, and the frequency resolution is 1.6MHz.

Ultrahigh-Resolution Optical Vector Analysis for Arbitrary Responses Using Low-Frequency Detection

We propose and experimentally demonstrate an ultrahigh-resolution optical vector analyzer (OVA) for arbitrary responses measurement by using microwave photonic frequency down-conversion and fixed low-frequency detection. It avoids high-speed photodetection and ultrawideband electrical phase-magnitude detection, which are the key challenges to the previous OVAs based on microwave photonics (MWPs). Additionally, the proposed OVA has the capability of measuring arbitrary spectral responses. A high-resolution optical frequency-swept signal generated by using MWP-based techniques is separated into two parts. One portion propagates through an optical device under test (DUT) and then directs to a photodetector (PD), which carries out the spectral responses. In the other branch, the optical signal is accurately shifted by a small frequency and then sent to the PD. By square-law detection, the spectral responses of the optical DUT are thus transferred to a low-frequency photocurrent with a frequency equaling to the shifted frequency. Thus, the spectral responses can be obtained by detecting the photocurrent using a low-frequency electrical phase-magnitude detector working at a fixed frequency. In the experiment, a measurement system is established, by which the magnitude and phase responses of optical devices, such as an optical Hilbert transformer and an optical bandpass filter, are successfully measured. The measurement results are verified by the previous MWP-based OVAs and a commercial instrument.

Ultrahigh-resolution optical vector analysis using fixed low-frequency electrical phase-magnitude detection.

An ultrahigh-resolution optical vector analyzer (OVA) is proposed and experimentally demonstrated based on microwave photonic frequency downconversion and fixed low-frequency electrical phase-magnitude detection. In the proposed OVA, two optical single-sideband (OSSB) signals are generated by two RF signals with a fixed frequency spacing. One propagates through an optical device under test (DUT) and is then combined with the other before entering to a low-speed photodetector. By photodetection, a low-frequency and frequency-fixed photocurrent carrying the spectral responses is achieved. Hence, a low-frequency electrical phase-magnitude detector is sufficient to extract the magnitude and phase. Sweeping the frequency of the RF signals, the spectral responses of the DUT can be obtained. As compared with the conventional OSSB- and optical double-sideband-based OVA, the proposed OVA avoids the use of high-speed photodetection and broadband electrical phase-magnitude detection. In addition, it is inherently immune to the measurement errors induced by high-order sidebands and has the capability of measuring arbitrary spectral responses. In an experiment, the proposed OVA is implemented based on an electrical phase-magnitude detector working at 10MHz. The measurement resolution is 1MHz, and the measurement range is larger than 45GHz.

Ultrahigh-resolution and wideband optical vector analysis for arbitrary responses.

An ultrahigh-resolution and wideband optical vector analyzer (OVA) with the simplest architecture, to the best of our knowledge, is proposed and demonstrated based on chirped optical double-sideband (ODSB) modulation in a single-drive Mach-Zehnder modulator (MZM). To distinguish the magnitude and phase information carried by the two sidebands in the ODSB signal, a two-step measurement, in which biasing, respectively, the MZM at two different points is applied. Because no optical filtering is required in the scheme, the optical carrier can be located at any wavelength that is suitable for accurate measurement, e.g., close to the notch of a notch response or within the passband of a bandpass response, so the proposed OVA has the capability to measure an arbitrary response. An experiment is carried out, which achieves the magnitude and phase responses of a programmable optical processor with bandpass, notch, or falling-edge responses. The measurement bandwidth is 134GHz, and the measurement resolution is 1.12MHz.

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.

Optical vector analysis based on double-sideband modulation and stimulated Brillouin scattering.

A high-resolution and high-accuracy optical vector analysis based on optical double-sideband modulation and stimulated Brillouin scattering is proposed and experimentally demonstrated. Different from the conventional OVA based on optical single-sideband modulation, in which the measurement range is limited by the bandwidth of the microwave and optoelectronic components, and the measurement accuracy is restricted by the high-order sidebands, the proposed technique measures the magnitude and phase responses by making use of both ±1st-order sidebands without spectrum response aliasing. As a result, the measurement range is doubled, and the high-order, sideband-induced errors only appear at specific frequencies that are predictable and removable. A proof-of-concept experiment is carried out. The transmission response of a fiber Bragg grating, in a range of 80GHz, is measured with a resolution of less than 667kHz by using 40GHz microwave components.