Optical Taps Research Articles

2-Dimensional integrated optical power measurement of multiple single-mode optical fibers in wide wavelength range of O to L-band using Fresnel reflection-based optical taps with infrared image sensors

We perform optical power measurements at wavelengths of 1260 nm to 1630 nm for nine single-mode optical fibers integrated in a two-dimensional array with pitch of 500 μm. We employ two optical taps with Fresnel reflection to split parts of the lights from the optical fibers, and two infrared image sensors to measure the optical power of the split lights. We clarify the variation in the optical powers from the output data of the image sensors. The measurable range was −15 dBm to −50 dBm; the mean square error was 0.37 dB. No polarization dependency was observed while changing the polarization condition of the lights in the optical fibers. The measurements were performed while changing the wavelength of the lights in the optical fibers from 1260 nm to 1630 nm and the resulting mean square error was 0.50 dB. The performance of the prototype is sufficient for practical use in the management of optical network facilities in data centers.

P4Tune: Enabling Programmability in Non-Programmable Networks

Data plane programmability has attracted significant attention, permitting network operators to run customized packet processing functions. Unfortunately, networks today are still largely dominated by proprietary fixed-function devices. It is challenging for operators to completely migrate to programmable data planes (PDPs) due to the economical costs of replacing equipment and limited expertise in maintaining and operating programmable networks. This article introduces P4Tune, a cost-efficient architecture that uses passive PDPs coupled with optical taps. P4Tune runs customized packet processing functions operating at line rate and collects network information with nanosecond resolution. This visibility enables intelligent algorithms residing in the control plane to construct configuration rules and apply them on the legacy devices, thus creating a closed control loop. P4Tune brings the benefits of processing traffic at line rate to legacy networks. Additionally, by using PDPs passively, the architecture can be safely deployed without disrupting current network operations, fostering incremental use of PDPs (i.e., no need to deploy complex code at once). The article demonstrates three applications of the proposed architecture related to Quality of Service (QoS) and cybersecurity.

Non-invasive Delay State Calibration of Silicon Optical Switching Delay Line

Silicon optical switching delay line (OSDL) chip, which composed of optical switches cascaded with optical waveguides of different lengths, has the merits of broadband true time delay and high delay accuracy, and is one of the key components in microwave photonic beamforming system. Due to the inevitable manufacturing errors of silicon photonic chips, the driving voltages of the “through” and “cross” states of each optical switch in OSDL need to be calibrated separately to ensure properly switching among different delay states. In general, additional optical power monitor taps or variable optical attenuators (VOAs) can be added into OSDL to achieve the switching voltage calibration processes of all the optical switches. However, adding additional optical power monitor taps after each optical switch will increase the extra loss of the delay line, also the I/O ports will be greatly increased. Introducing silicon VOAs based on carrier injection in each delay stage of the silicon OSDL will increase the manufacturing cost and control complexity. Therefore, a simple and non-invasive calibration technique for all the optical switches in OSDL chip is greatly needed. Here, based on the interferograms induced by the cascade unbalanced Mach-Zehnder interferences formed in OSDL, we propose a simple and effective calibration method for silicon OSDL chip without introducing additional components. As a proof of concept, we calibrated and measured all the delay states of a 5-Bit silicon OSDL chip, and the measured results agree well with those obtained with optical power monitor taps.

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.

Femtosecond laser inscription of asymmetric directional couplers for in-fiber optical taps and fiber cladding photonics.

Precise alignment of femtosecond laser tracks in standard single mode optical fiber is shown to enable controllable optical tapping of the fiber core waveguide light with fiber cladding photonic circuits. Asymmetric directional couplers are presented with tunable coupling ratios up to 62% and bandwidths up to 300 nm at telecommunication wavelengths. Real-time fiber monitoring during laser writing permitted a means of controlling the coupler length to compensate for micron-scale alignment errors and to facilitate tailored design of coupling ratio, spectral bandwidth and polarization properties. Laser induced waveguide birefringence was harnessed for polarization dependent coupling that led to the formation of in-fiber polarization-selective taps with 32 dB extinction ratio. This technology enables the interconnection of light propagating in pre-existing waveguides with laser-formed devices, thereby opening a new practical direction for the three-dimensional integration of optical devices in the cladding of optical fibers and planar lightwave circuits.

Sidelobe Suppression Enhancement of Radiofrequency Photonic Filters via Time-to-frequency Mapping

We present a multi-tap microwave photonic filter with high selectivity through applying time-to-frequency mapping and optical frequency comb shaping techniques. When arranged in the time-to-frequency mapping stage, by a Fourier transform, the deviation of the optical taps to the target profile is significantly reduced while maintaining the apodization profile, resulting in high sidelobe suppression in the filters. By applying a simple time-to-frequency mapping stage to the conventional optical frequency combs, we demonstrate a substantially enhanced (>10dB) sidelobe suppression, resulting in filter lineshapes exhibiting a significantly high (>40dB) main lobe to sidelobe suppression ratio. These results highlight the potential of the technique for implementation in various passband filters with high sidelobe suppression.

Continuously Tunable Microwave Photonic Filter Using a Multiwavelength Fiber Laser

A tunable microwave photonic filter is demonstrated by employing a stable multiwavelength erbium-doped fiber laser and a dispersive medium. The specific configuration of the multiwavelength laser allows for adjustment of the number of laser lines, i.e., the optical taps of the filter and their spectral spacing. The transfer function of the filter is continuously tunable, exhibiting transmitted bands of less than 1-GHz bandwidth and sidelobe suppression of -17 dB in the 10-30 GHz frequency range.

Non-intrusive measurement of In-Band OSNR of high bitrate polarization-multiplexed signals

The In-Band OSNR of polarization-multiplexed signals in deployed networks may be determined non-intrusively with a novel modulation-format-agnostic approach suitable for implementation in field-portable optical spectrum analyzers. This approach advantageously makes use of available optical taps in the network for simultaneous measurement of all the channels of a high-bandwidth DWDM system. We have confirmed the validity of this approach using measurements acquired on polarization-multiplexed signals in representative high-bandwidth network testbeds.

Optical waveguide tap with low polarization dependence and flattened wavelength using a Mach–Zehnder directional coupler

The coupling length of a directional coupler is strongly polarization dependent, especially for use in waveguide tap monitoring applications. To avoid severe polarization and maximize the wavelength flatness of optical waveguide taps, a 12 μm thick silicon-on-insulator (SOI) platform and Mach–Zehnder directional couplers implemented with the bending effect illustrated low coupling loss to a SMF-28 fiber, low polarization dependence, and insensitive wavelength on the tap port for monitoring applications. Our results demonstrated that the optical waveguide tap, which carries a portion of the light signal, showed a 0.077 coupling ratio and 0.2 dB for the polarization-dependent loss. The wavelength variation for the coupling ratio was less than 4% across the entire C-band. A 0.26 dB per interface coupling loss was also achieved between the 12 μm thick SOI waveguide and the SMF-28 fiber.

Microwave frequency measurement using a finite impulse response system that incorporates Lorentzian profile-weighted optical taps

We propose an advanced photonic microwave processing scheme useful for the accurate measurement of incoming microwave signal frequency over a wide frequency bandwidth. Our scheme is based on a finite impulse response system using Lorentzian profile-weighted multiple optical wavelength taps. Unlike the conventional schemes based on two optical taps, our scheme allows for well-defined, linear mapping of the incoming microwave frequency onto the output electrical power utilizing a log scale. In order to verify the principle, an experimental demonstration was carried out by using a multiwavelength channel beam, which was produced by the combination of a broadband, continuous wave supercontinuum and a digital micromirror device-based spatial light modulator. An excellent frequency measuring performance over a range of 1–9 GHz was achieved.

Continuously Tunable Microwave Photonic Filter With Negative Coefficients Using Cross-Phase Modulation in an SOA-MZ Interferometer

A notch filter with negative tap is proposed based on exploiting cross-phase modulation in a semiconductor optical amplifier Mach-Zehnder interferometer. This configuration shows a high operation bandwidth and reduces the chirp of the modulated signal compared to prior proposed configurations based on cross-gain modulation. We compare the operation of the structure when optic delay lines or dispersive fibers are used to generate the optical taps. Moreover, a continuous free-spectral range tuning is shown.

Simple Reconfigurable Photonic Microwave Filter Using an Arrayed Waveguide Grating and Fiber Bragg Gratings

We demonstrate a photonic microwave finite impulse response filter with reconfiguration and tuning capabilities. The filter is based on spectral slicing of a broadband source and optical fiber as a wideband dispersive medium. An arrayed waveguide grating and fiber Bragg gratings are used to select and vary the weight of the optical taps to achieve reconfiguration and tuning

Continuous tuning of photonic transversal filter based on the modification of tapped weights

We propose and experimentally demonstrate a novel technique to tune the microwave photonic filter which is based on the sinusoidal modulation superimposed to the envelope of the filter coefficients. This configuration overcomes the use of tunable optical sources and optical dispersive devices. To the best of our knowledge, these are the first experimental results where the resonances of the cited filters are shifted by changing the weight of the optical taps

Tunable radio-frequency photonic filter based on an actively mode-locked fiber laser

We propose the use of an actively mode-locked fiber laser as a multitap optical source for a microwave photonic filter. The fiber laser provides multiple optical taps with an optical frequency separation equal to the external driving radio-frequency signal of the laser that governs its repetition rate. All the optical taps show equal polarization and an overall Gaussian apodization, which reduces the sidelobes. We demonstrate continuous tunability of the filter by changing the external driving radio-frequency signal of the laser, which shows good fine tunability in the operating range of the laser from 5 to 10 GHz.

Photonic processing of microwave signals

In this paper, recent advances in the implementation of photonic tuneable transversal filters for RF signal processing developed by the Optical Communications Group are described. After a brief introduction to the field and the basic concepts, limiting factors and application of these filters are described in the field. This is based on a distinction between filters based on wavelength tuneable optical taps and others based on the tuneability of the dispersive elements that provide the time delay between samples. Recently developed approaches have also been discussed.

Advanced Optical Processing of Microwave Signals

The authors present a review on the recent approaches proposed to implement transversal RF filters. Different tunable transversal filters consisting of wavelength tunable optical taps and those employing the tunability of dispersive devices are presented showing their high-performance characteristics. A comprehensive review of the fundamentals and a discussion on the main limitation of these structures are also included.

Three-dimensional mems photonic cross-connect switch design and performance

Photonic cross-connects (PXC) play a key role in all-optical transparent networks. In this paper, the optical design and modeling of a three-dimensional microelectromechanical system (3-D MEMS) based optical switch are discussed. Basic design rules and considerations are reviewed and used to determine the optimum configuration for free-space optical switches with more than 300 ports. The optical performance of a 256 /spl times/ 256 PXC system, including a 347 /spl times/ 347 nonblocking core switch and auxiliary 2 /spl times/ 2 optical switches for 1:1 protection and optical taps for power monitoring, is presented. The core switch has 1.4-dB median insertion loss, 1.5-dB wavelength dependent loss across a broadband of 1260-1625 nm, and a typical polarization dependent loss of 0.1 dB. Environmental tests including temperature and vibration are described.

Microwave photonic filtering using Gaussian-profiled superstructured fibre Bragg grating and dispersive fibre

Microwave photonic filtering is realised using a superstructured fibre Bragg grating. The time delay of the optical taps is precisely controlled by the grating characteristics and fibre dispersion. A bandpass response with a rejection level of >45 dB is achieved.

Cascaded Amplifying Quantum Optical Taps: A Robust Noiseless Optical Bus

Two identical amplifying quantum optical taps, based on noiseless optical parametric amplification and twin beam quantum correlation, have been implemented in a series configuration and experimentally investigated. The result is an optical bus which we have shown to be robust with respect to downstream losses. {copyright} {ital 1996} {ital The American Physical Society}

Analogue transmisson characteristics of optical taps using fibre Bragg gratings for WDM multi-drop systems

Analogue transmission characteristics of fibre-Bragg-grating-based optical taps have been examined, for the first time, and considered for use in WDM multi-drop systems. A properly-fabricated fibre grating with low chromatic dispersion exhibits sufficiently low signal distortion.