Optical Vector Network Analyzer Research Articles

A DFB-SOA Based Optical Vector Network Analyzer for Characterization of Bandpass Optical Devices

In this paper a novel optical vector network analyzer (OVNA) utilizing a distributed feedback semiconductor optical amplifier (DFB-SOA) is introduced. The proposed OVNA is implemented by converting the transmission response of the optical device under test (ODUT) into the electrical domain. The main principle of the OVNA is predicated on the optical carrier restoration facilitated by the wavelength-selective amplification attribute of the DFB-SOA. The implemented OVNA effectively determined the transmission spectrum of an optical filter possessing a passband of 9-GHz bandwidth, achieving a commendable resolution of 25 MHz in the measurement process. The dynamic range of the OVNA can be broadened by adjust the driven current under the DFB-SOA. Additionally, the detection range of our system can be expanded through the utilization of broadband optoelectronic devices. Furthermore, the OVNA possesses considerable potential for integration onto a single chip.

High-accuracy optical vector network analyzer for optical notch and bandpass responses

A high-accuracy optical vector network analyzer (OVNA) based on optical carrier-suppressed double sideband (CS-DSB) modulation is proposed and experimentally demonstrated. The ±1st-order sideband signals are generated by CS-DSB modulation and then pass through the symmetric optical device under test (DUT). The band-stop or band-pass responses can be realized by detecting and processing the double frequency of the driven RF signal. Compared with the conventional symmetrical DSB-based OVNA, the measurement accuracy is improved by eliminating the errors caused by the even-order sidebands, and the complexity is reduced as the proposed method with only one step measurement can avoid the complex postprocessing. In addition, the optical carrier is aligned to the center frequency of the DUT by employing the Pound–Drever–Hall (PDH) technique, which provides stable measurement. At the same time, the limitation that the band-pass responses cannot be measured by the traditional single-sideband (SSB)-based OVNA is overcome. Additionally, accurate magnitude and phase responses of the DUT near the optical carrier can be also achieved since the proposed OVNA is optical filter-immune. The proposed method is theoretically analyzed and verified by experiment. A Fabry–Perot (FP) interferometer serves as the symmetric DUT; the band-stop responses in a frequency range of 6 GHz are obtained with a resolution of 1.2 MHz; and the band-pass responses with the range from 0 to 13 GHz offsetting the optical carrier are also obtained. The measurement time can reach up to 30 min with high stability. The proposed OVNA offers enhanced accuracy and a stable approach for applications in photonic systems and other innovations.

Fast optical vector network analysis based on dual optical frequency comb

An ultrafast optical vector network analysis (OVNA) based on dual optical frequency comb (OFC) and I/Q demodulation technology is proposed and demonstrated. The responses of the DUT with broadband are characterized by propagating the signal OFC through the DUT, and then detecting interference signals using digital signal processor with retrieval algorithm. Without the need of the acousto-optic modulator or optical filter in the scheme, the frequency aliasing can be eliminated by using the I/Q demodulation module, so that the spectral utilization efficiency of the OFC is improved significantly. Meanwhile, the wideband measurement with high acquisition rates can also be achieved. In simulation process, the single spectrum of HCN molecule with linewidth of 1 GHz and bandwidth of 10 GHz can be rapidly measured, and the measurement time is only 1μs in theory. Our proposed OVNA opens the door to realize a real-time detection in the field of trace molecular sensing.

Fully Automatic In-Situ Reconfiguration of Optical Filters in a CMOS-Compatible Silicon Photonic Process

Automatic reconfiguration of optical filters is the key to novel flexible RF photonic receivers and Software Defined Radios (SDRs). Although silicon photonics (SiP) is a promising technology platform to realize such receivers, process variations and lack of in-situ tuning capability limit the adoption of SiP filters in widely-tunable RF photonic receivers. To address this issue, this work presents a first ‘in-situ’ automatic reconfiguration algorithm and demonstrates a software configurable integrated optical filter that can be reconfigured on-the-fly based on user specifications. The presented reconfiguration scheme avoids the use of expensive and bulky equipment such as an Optical Vector Network Analyzer (OVNA), does not use simulation data for reconfiguration, reduces the total number of thermo-optic tuning elements required, and eliminates several time-consuming configuration steps as in the prior art. This makes this filter ideal in a real-world scenario where the user specifies the filter center frequency, bandwidth, required rejection, and filter type (Butterworth, Chebyshev, etc.), and the filter is automatically configured regardless of process, voltage, and temperature (PVT) variations. We fabricated our design in AIM Photonics' Active SiP process and have demonstrated our reconfiguration algorithm for a second-order filter with a 3 dB bandwidth of 3 GHz, 2.2 dB insertion loss, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 30 dB out-of-band rejection using only two reference laser wavelength settings. Since the filter photonic integrated circuit (PIC) is fabricated using a CMOS-compatible SiP foundry, the design is manufacturable with repeatable and scalable performance suited for its integration with electronics to realize complex chip-scale RF photonic systems.

Distinct strategy for the improvement of conductivity and electromagnetic shielding properties of MWCNTs/PLA/PBS composites: Synergistic effects of double percolation structure and UV aging

AbstractTo reveal a relationship among crystallization, conductivity and electromagnetic shielding properties of full biodegradable polymer after ultraviolet (UV) aging, polybutylene succinate (PBS)‐based composites with different weight ratios of multi‐wall carbon nanotubes (MWCNTs)/polylactic acid (PLA) /PBS masterbatch were processed via melt‐compounding approach. Morphology of the MWCNTs/PLA/PBS masterbatch prepared by Pickering emulsion method was confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM) observation. Comprehensive effects of different content of masterbatch and UV aging time on the morphology, crystallization, and electrical and electromagnetic shielding properties of MWCNTs/PLA/PBS composites were shown by Fourier transform infrared spectroscopy (FTIR), SEM, wide angle X‐ray diffraction (WAXD), differential scanning calorimeter (DSC), polarizing microscope (POM), ultra‐depth of field optical microscope, resistance tester, and vector network analyzer. Compared with PBS composite with 0.1 wt% MWCNTs, the electrical conductivity of PBS composite with the MWCNTs/PLA/PBS masterbatch increased by two orders of magnitude, and dispersed morphology for the composite showed double percolation structure. After UV aging, both MWCNTs/PBS composites and the PBS composites with the MWCNTs/PLA/PBS masterbatch, their surface presented burnt yellow and parts of flaws, while both their electrical conductivity and total electromagnetic shielding effectiveness gradually increased. Moreover, with the increasing of UV aging time, not only crystal size of these PBS‐based composites became large, but also their crystal interface became clearer. Furthermore, when UV aging time reached 528 h, the tensile strength of 0.6 M/PLA/PBS composite decreased by 12.6%, while its total electromagnetic shielding effectiveness increased by 39.8%, compared with the composite without UV aging.

Impulse Response Measurement of Spooled and Twisted Few-Mode Multi-Core Fiber for Short-Range Optical Links

The impact of bending and twisting on the impulse response matrix is investigated using optical vector network analysis. The heterogeneous 36-core 3-mode fiber under test is spooled at bending radii of 8 cm to 50 cm and additionally up to 4 twists per meter along the longitudinal direction are applied. The by-design large differential mode group delay of the fiber enables comprehensive measurement of the inter-mode-group cross-talk of the fiber impulse response matrix, which is directly measured with an optical vector network analyzer. A maximal inter-mode-group cross-talk of −28.1 dB is observed over all 36 cores. Furthermore, no significant changes related to the bending radii or additional strain by twisting the fiber were detected. These results demonstrate that the transmission characteristics of few-mode fibers with large differential mode group delay are fairly unaffected by bend- and twist-related perturbations which may prove beneficial for short-range mode-group multiplexed transmission systems using partial multiple-input multiple-output equalization in conjunction with mode-selective multiplexers.

Ultrafast single-shot optical vector network analyzer based on coherent time-stretch

Ever-increasing demands for a higher bandwidth of data in the optical communications augment the operating frequency of components and systems. To accelerate the development of these large-bandwidth technologies, there is a growing demand to characterize the frequency response of optical devices in real time. In this work, we report a method to significantly improve the measurement speed of an optical vector network analyzer (OVNA) with coherent time-stretch (CTS). Single-shot frequency spectrum measurements are enabled by time-stretch technology that maps the spectrum of an optical pulse to the time domain. Compared to single-ended detection, the implementation of coherent detection enables the acquiring of accurate phase information of the signal and also provides the digital processed cancellation of dispersion-induced impairments. By utilizing dispersive time-stretch and digital coherent detection techniques, we demonstrate an ultrafast and wide bandwidth OVNA. We successfully characterize its performance by measuring the frequency response of a micro-ring cavity and a silicon Mach–Zehnder interferometer with 0.07-nm spectral resolution and 0.156-rad phase accuracy over 10-nm bandwidth. Meanwhile, the dynamic responses of the magnitude and phase, and the drift of the resonance wavelength of the micro-ring modulator under thermal tuning, were fully recorded by the CTS-OVNA at a 20-MHz frame rate.

Electromagnetically induced transparency in a mono-isotopic 167Er:7LiYF4 crystal below 1 Kelvin: microwave photonics approach.

Electromagnetically induced transparency allows for the controllable change of absorption properties, which can be exploited in a number of applications including optical quantum memory. In this paper, we present a study of the electromagnetically induced transparency in a 167Er:7LiYF4 crystal at low magnetic fields and ultra-low temperatures. The experimental measurement scheme employs an optical vector network analysis that provides high precision measurement of amplitude, phase and group delay and paves the way towards full on-chip integration of optical quantum memory setups. We found that sub-Kelvin temperatures are the necessary requirement for observing electromagnetically induced transparency in this crystal at low fields. A good agreement between theory and experiment is achieved by taking into account the phonon bottleneck effect.

Polarization Equalization in Optical Vector Network Analysis for SDM Fiber Characterization

Precise characterization of space division multiplexing fibers is a key requirement for their further development and deployment in the field. Optical vector network analysis allows to measure all linear parameters of such fibers in a single, fast acquisition over a large bandwidth. As the reference arm of the optical vector network analyzer must approximately match the length of the measured fiber, additional fiber must be introduced when measuring longer fibers. This results in the polarization of the reference arm varying with wavelength over the sweep range employed in the measurement. The resulting fading of the recorded interference signal produces severe distortions of the measurement and hence must be compensated for. This work introduces a simple equalization technique to compensate for this fading, based on introducing a polarizer in the reference path and recording a fraction of the polarized reference as a correction signal. Applying the inverse of the correction signal to the recorded signal, the impact of the polarization fading is almost entirely removed, as are the corresponding measurement distortions. The proposed technique is validated in the measurement of a 39-core few-mode multi-core fiber, significantly improving measurement of wavelength dependent insertion loss.

Enhanced Modal Dispersion Estimation Enabled by Chromatic Dispersion Compensation in Optical Vector Network Analysis

Component characterization is fundamental for understanding the limits of optical devices, sub-systems, and transmission systems. With the introduction of space division multiplexing in optical fiber transmission systems, new impairments, such as mode dependent loss and differential mode dispersion arise. Spatially-diverse optical vector network analyzers are capable of measuring these characteristics in a fast single sweep over a very large bandwidth. As a result of this large bandwidth, these analyzers are sensitive to differential chromatic dispersion within the interferometric measurement setup. This study discusses the influence and compensation of differential chromatic dispersion in such systems. Partial chromatic dispersion compensation is demonstrated to improve the representation and accuracy of impulse response measurements obtained from optical vector network analyzers for fibers and components with large differential chromatic dispersion. Analysis of a 39-core few-mode multi-core fiber is discussed, reporting variances of -2.9-0.1 ps/nm, and 0.6-6.9 ps/nm for the two mode groups, respectively, between the few-mode cores. A correlation with the total impulse response is observed. Furthermore, a maximum propagation skew of 20 ns between cores is observed after 13.6 km.

Accurate optical vector network analyzer based on optical double-sideband suppressed carrier modulation

A high-accuracy optical vector network analysis (OVNA) based on optical suppressed carrier double-sideband (DSB) modulation and the Pound Drever Hall (PDH) technique is proposed and demonstrated. The accurate and stable frequency responses can be achieved by transmitting the optical carrier suppressed DSB modulation signals through the DUT, and then detecting the reflected signals. Compared with the traditional DSB-based OVNA, the measurement accuracy is improved by eliminating the errors caused by the even-order sidebands. Furthermore, the stability of the OVNA system can be kept by using the PDH feedback loop. An experiment is accomplished. The frequency responses of the FP interferometer are achieved with little measurement error induced by high-order sidebands, and no repeated frequency response appears even when the test time reaches up to 30 min. This novel method is simple and accurate, and would be used for charactering the symmetric ultra-high Q optical devices.

Accuracy-Enhanced Wideband Optical Vector Network Analyzer Based on Double-Sideband Modulation

We report a method to significantly improve the accuracy of an optical vector network analyzer (OVNA) with double-sideband (DSB) modulation. The measurement errors of the DSB-OVNA mainly derive from optical carrier uncertainty and the beating between higher order optical sidebands. We propose a three-step measurement method and an accuracy-enhanced algorithm to eliminate these measurement errors perfectly. A theoretical model is built to analyze the potential measurement errors as well as to find a way to remove them. Excellent accuracy improvement of the OVNA is confirmed by a proof-of-concept experiment. The OVNA shows an ultrahigh resolution of 667 kHz over a wideband measurement range of 80 GHz.

Wideband optical vector network analyzer based on polarization modulation

We propose a polarization modulator (PolM) -based optical vector network analyzer (OVNA) with extended measurement bandwidth. The combined use of the PolM, a polarization controller (PC) and a polarizer performs phase-and-intensity hybrid modulation of optical signal with double-sideband (DSB) modulation. The ratio between phase and intensity modulations is controlled by the PC, leading to different modulation formats. The frequency response of a device-under-test (DUT) can be obtained by processing the results of two measurements under two arbitrarily different modulation formats. The significance of this work lies in that the measurement of a DUT with bandpass response can be simply achieved, which is a huge challenge for the conventional single-sideband (SSB)-based OVNAs. In addition, the measurement bandwidth is doubled compared with the conventional SSB-based OVNA. Moreover, the PolM-based OVNA can avoid the bias drifting problem using conventional Mach–Zehnder modulator (MZM)-based scheme. The proposed method is theoretically and experimentally demonstrated. A proof-of-concept experiment is carried out and a DUT with bandpass response is successfully measured using the proposed scheme.

Long-term measurement of high Q optical resonators based on optical vector network analysis with Pound Drever Hall technique.

An optical vector network analysis (OVNA) based on double sidebands (DSB) modulation and the Pound Drever Hall (PDH) technique is proposed and demonstrated. The frequency responses measurement of the high Q optical device with high stability are achieved by transmitting the DSB modulation signals through the device. The high stability can be realized by using the PDH feedback loop. Compared with the conventional DSB-based OVNA, the proposed scheme with only one step measurement avoids the complex post-processing. Moreover, the long-term measurement with high stability can also be realized. A proof-of-concept experiment is carried out, which achieves the magnitude and phase responses of the Fabry-Perot interferometer, and there is no frequency response shift even though the test time is up to 90 minutes. The proposed method is simple and stable, which can be potentially applied in characterization and fabrication of high Q optical devices.

Optical vector network analysis of ultranarrow transitions in 166Er3+ : 7LiYF4 crystal.

We present optical vector network analysis (OVNA) of an isotopically purified Er1663+:LiYF47 crystal. The OVNA method is based on generation and detection of a modulated optical sideband by using a radio-frequency vector network analyzer. This technique is widely used in the field of microwave photonics for the characterization of optical responses of optical devices such as filters and high-Q resonators. However, dense solid-state atomic ensembles induce a large phase shift on one of the optical sidebands that results in the appearance of extra features on the measured transmission response. We present a simple theoretical model that accurately describes the observed spectra and helps to reconstruct the absorption profile of a solid-state atomic ensemble as well as corresponding change of the refractive index in the vicinity of atomic resonances.

Optical vector network analyzer based on double-sideband modulation.

We report an optical vector network analyzer (OVNA) based on double-sideband (DSB) modulation using a dual-parallel Mach-Zehnder modulator. The device under test (DUT) is measured twice with different modulation schemes. By post-processing the measurement results, the response of the DUT can be obtained accurately. Since DSB modulation is used in our approach, the measurement range is doubled compared with conventional single-sideband (SSB) modulation-based OVNA. Moreover, the measurement accuracy is improved by eliminating the even-order sidebands. The key advantage of the proposed scheme is that the measurement of a DUT with bandpass response can also be simply realized, which is a big challenge for the SSB-based OVNA. The proposed method is theoretically and experimentally demonstrated.

Few-mode fiber, splice and SDM component characterization by spatially-diverse optical vector network analysis.

This paper discusses spatially diverse optical vector network analysis for space division multiplexing (SDM) component and system characterization, which is becoming essential as SDM is widely considered to increase the capacity of optical communication systems. Characterization of a 108-channel photonic lantern spatial multiplexer, coupled to a 36-core 3-mode fiber, is experimentally demonstrated, extracting the full impulse response and complex transfer function matrices as well as insertion loss (IL) and mode-dependent loss (MDL) data. Moreover, the mode-mixing behavior of fiber splices in the few-mode multi-core fiber and their impact on system IL and MDL are analyzed, finding splices to cause significant mode-mixing and to be non-negligible in system capacity analysis.

Optical Vector Network Analyzer with an Improved Dynamic Range Based on a Polarization Multiplexing Electro-Optic Modulator**Supported by the National Natural Science Foundation of China under Grant Nos 61377070, 61090391 and 61675196, and the National High-Technology Research and Development Program of China under Grant No 2013AA014203.

We present a new method to achieve an optical vector network analyzer (OVNA) based on a polarization multiplexing electro-optic modulator (PM-EOM) without an optical bandpass filter. Optical single sideband (OSSB) modulated signals with a tunable optical carrier-sideband ratio (OCSR) are obtained at the output of the PM-EOM. The OCSR can be flexibly tuned by controlling bias voltages of the PM-EOM. The dynamic range of the OVNA is expanded by taking the improvement of the OCSR into account. The transmission response of an optical device under test (ODUT) is measured based on one-to-one mapping from optical domain to electrical domain. By optimizing the OCSR of the OSSB modulated signals, the dynamic range of the OVNA can be effectively improved with 3.7 dB. An analytical model is derived to describe the transfer function of the ODUT. The magnitude and phase responses of a fiber Bragg grating are characterized with a large dynamic range.

Fully characterization of an active optical filter based on an equivalent-phase-shifted DFB-SOA

A fully characterization of an active optical filter based on an equivalent-phase-shifted DFB-SOA has been theoretically analyzed and experimentally demonstrated in this paper. By employing an optical vector network analyzer (OVNA), transmission characteristics of the equivalent-phase-shifted DFB-SOA are obtained. The influences of driven current on transmission characteristics of the equivalent-phase-shifted DFB-SOA are also investigated. In addition to the advantage of integration, the proposed equivalent-phase-shifted DFB-SOA also shows significant application in design of photonic devices for all-optical signal processing and computing.

Optical vector network analyzer with improved accuracy based on polarization modulation and polarization pulling.

We report a novel optical vector network analyzer (OVNA) with improved accuracy based on polarization modulation and stimulated Brillouin scattering (SBS) assisted polarization pulling. The beating between adjacent higher-order optical sidebands which are generated because of the nonlinearity of an electro-optic modulator (EOM) introduces considerable error to the OVNA. In our scheme, the measurement error is significantly reduced by removing the even-order optical sidebands using polarization discrimination. The proposed approach is theoretically analyzed and experimentally verified. The experimental results show that the accuracy of the OVNA is greatly improved compared to a conventional OVNA.