Optical Lattice Filters Research Articles

Reconfigurable Rectangular Filter With Continuously Tunable Bandwidth and Wavelength

We propose and demonstrate a rectangular optical lattice filter with reconfigurable bandwidth and wavelength. The proposed reconfigurable rectangular lattice filter consists of three-stage cascaded ring-assisted Mach-Zehnder interferometers (RAMZIs), and each RAMZI unit serves as an approximate optical elliptical filter with optimized shape factor. The scheme and design principle are presented with the method of zero-pole theory. As a proof of concept, the proposed structure is fabricated on the Si $_3$ N $_4$ waveguide platform. In the experiment, the 3-dB bandwidth of the proposed filter can be continuously tuned from 14.1 GHz to 4.1 GHz, maintaining a rectangular transmission response, and the wavelength can also be continuously tuned. This reconfigurable rectangular optical lattice filter shows the potential in many practical applications for reconfigurable optical signal processing due to flexibility and reconfigurability.

CMOS Compatible Reconfigurable Silicon Photonic Lattice Filters Using Cascaded Unit Cells for RF-Photonic Processing

This paper presents an overview of a complementary metal-oxide-semiconductor-compatible, programmable, analog optical lattice filter based on silicon unit cells arrayed in large-scale photonic integrated circuits. The unit cell employs a combination of a ring resonator and a Mach-Zehnder interferometer with tunable phase elements in both of the paths. Each proposed unit cell contributes a separately controllable pole and zero pair. Under various configurations, we experimentally achieved >60-dB two-tone spurious-free dynamic range. For more sophisticated signal processing, we experimentally demonstrated an optical lattice filter with four cascaded unit cells capable of dynamically reconfiguring between a bandpass filter and a notch filter. The reconfiguration of the unit-cell and four-cell silicon lattice filter is based on a recursive algorithm, which brings new possibilities to RF photonic processing and a wide range of applications with design scalability to a large number of poles and zeros. The experimental results and the recursive algorithms show potentials for scaling to higher order filter designs.

CMOS-compatible temperature-independent tunable silicon optical lattice filters

We present a CMOS-compatible athermal tunable silicon optical lattice filter composed of 10 cascaded 2 × 2 asymmetric Mach-Zehnder interferometers. Active tuning experiments show that the filter central wavelength can be red-/blue-shifted by 13.1/21.3 nm with power consumption of 77/96 mW on top/bottom arms. Temperature shift measurements show that the thermal-sensitivity of the filter central wavelength before active tuning is as low as -1.465 pm/°C. The thermal-sensitivity is varied within 26.5 pm/°C to -27.1 pm/°C when the filter central wavelength is tuned in the wavelength range of 1534 nm to 1551 nm. We use the transfer matrix method to theoretically model the lattice filter and its thermal-sensitivity before and after tuning is analyzed and discussed.

Analysis of a Polynomial System Arising in the Design of an Optical Lattice Filter Useful in Channelization

In this work, we consider design questions for an active optical lattice filter, which is being manufactured at the University of Texas at Dallas, and which has proven to be useful in the signal processing task of RF channelization. The filter can be described by a linear, discrete time state space model. The controlling agents, the gains, are embedded in the matrices intervening in this state space model. Consequently, techniques from linear feedback control theory do not apply. We concentrate on the question of finding real valued gains so that the A matrix of the state space model has a prescribed characteristic polynomial. We find that three of the coefficients can be arbitrarily picked, but that the remaining are constrained by these and the other system parameters. Our techniques use methods from constructive algebraic geometry.

Demonstration of a fast-reconfigurable silicon CMOS optical lattice filter

We demonstrate a fully-reconfigurable fourth-order optical lattice filter built by cascading identical unit cells consisting of a Mach-Zehnder interferometer (MZI) and a ring resonator. The filter is fabricated using a commercial silicon complementary metal oxide semiconductor (CMOS) process and reconfigured by current injection into p-i-n diodes with a reconfiguration time of less than 10 ns. The experimental results show full control over the single unit cell pole and zero, switching the unit cell transfer function between a notch filter and a bandpass filter, narrowing the notch width down to 400 MHz, and tuning the center wavelength over the full free spectral range (FSR) of 10 GHz. Theoretical and experimental results show tuning dynamics and associated optical losses in the reconfigurable filters. The full-control of each of the four cascaded single unit cells resulted in demonstrations of a number of fourth-order transfer functions. The multimedia experimental data show live tuning and reconfiguration of optical lattice filters.

Reconfigurable Integrated Optoelectronics

Integrated optics today is based upon chips of Si and InP. The future of this chip industry is probably contained in the thrust towards optoelectronic integrated circuits (OEICs) and photonic integrated circuits (PICs) manufactured in a high-volume foundry. We believe that reconfigurable OEICs and PICs, known as ROEICs and RPICs, constitute the ultimate embodiment of integrated photonics. This paper shows that any ROEIC-on-a-chip can be decomposed into photonic modules, some of them fixed and some of them changeable in function. Reconfiguration is provided by electrical control signals to the electro-optical building blocks. We illustrate these modules in detail and discuss 3D ROEIC chips for the highest-performance signal processing. We present examples of our module theory for RPIC optical lattice filters already constructed, and we propose new ROEICs for directed optical logic, large-scale matrix switching, and 2D beamsteering of a phased-array microwave antenna. In general, large-scale-integrated ROEICs will enable significant applications in computing, quantum computing, communications, learning, imaging, telepresence, sensing, RF/microwave photonics, information storage, cryptography, and data mining.

Extended active optical lattice filters: filter synthesis

In this paper, we study the synthesis of asymptotically stable filters from a unit cell of a two-dimensional tunable lattice filter architecture consisting of four four-port couplers and four waveguides containing semiconductor optical amplifiers. Upper bounds on the number of gains that will produce a filter with a priori prescribed poles, for a specific system, are obtained. We also provide sufficient conditions on the reflection-type coefficients, characterizing each four-port coupler, which ensure that real-valued gains, taking values in [0,1], exist so that the filter is asymptotically stable. Finally, we motivate the notion of a transmission zero of a filter and discuss the possibility of simultaneously placing both poles and transmission zeros for the unit cell.

Programmable Photonic Lattice Filters in InGaAsP–InP

A novel monolithic programmable optical lattice filter consisting of unit cell building blocks is proposed. Single unit cells incorporating a ring resonator in one arm of a Mach-Zehnder are fabricated in an InGaAsP-InP material system. Programmable poles and zeros are demonstrated and monolithically cascaded unit cells are used to synthesize a flat passband.

Extended active tunable optical lattice filters enabled by four-dimensional couplers: systems modeling

A system theoretic model of a unit cell of a two-dimensional tunable lattice filter architecture consisting of four 4-port couplers and four waveguides containing semiconductor optical amplifiers is provided. It is shown that such multiple input-multiple output devices can be modeled in state space and by transfer function matrices. This modeling can also be extended to devices constructed by concatenations of the basic building block, the unit cell.

Study of PMD and PDL Equalization Via a Nonunitary FIR Lattice Filter

We study a novel configuration and synthesis algorithm for equalization of polarization-mode dispersion (PMD) alone and combined with polarization-dependent loss (PDL) using a nonunitary optical lattice filter (NU-OLF). The NU-OLF is a generalization of a previously studied unitary lattice filter (U-OLF) for PMD equalization. Comparison of the improvement in the noise loaded PMD/PDL-induced eye closure, for typical optical signal-to-noise ratio values, shows that a NU-OLF is always superior to a U-OLF of the same order and it offers a significant advantage over a U-OLF with the same number of degrees of freedom in the equalization of PMD in the presence of PDL.

Design Algorithm for Multichannel Interleave Filters

A one-input M-output (1timesM) circuit configuration and design algorithm for an interleave filter with M output ports (Mges2) are presented. The circuit configuration is composed of a 1timesM optical lattice filter with a delay time of MDeltatau (Deltatau: unit delay time), an MtimesM diagonal delay matrix circuit, and an MtimesM modified inverse discrete Fourier transform matrix circuit. The proposed circuit with M=2 corresponds to a conventional interleave filter. The proposed synthesis algorithm is based on polyphase decomposition and yields circuit parameters ensuring that every output characteristic has an Mth-band property. A five-channel interleave filter is presented as an example of the design procedure.

Gaussian-like spectra equalization with linear-phase lattice filters

We present a design scheme to achieve equalization of Gaussian-like spectra by using linear-phase optical lattice filters. The proposed scheme separates the design of the phase response from the amplitude response of the equalization filter by introducing a symmetrically folded lattice structure. With the proposed structure, the linear-phase characteristic of the equalization filter is guaranteed regardless of the other design parameters. Then the amplitude response of the equalization filter is designed through a constrained optimization problem solved by using an efficient recursive algorithm. In addition to theoretical analysis, the effectiveness of the proposed design scheme is demonstrated by simulations and experiments through the equalization of a super-luminescence light-emitting diode as an illustrative example.

Linear-phase fiber lattice equalizer for Gaussian-like spectra

We present an all-fiber linear-phase equalizer for equalizing Gaussian-like spectra. The equalizer uses an optical lattice filter in a symmetric folded structure. Compared to existing solutions to linear phase equalization, the proposed equalizer has guaranteed linear phase responses and lower power attenuation. As an illustrative example, the effectiveness of the proposed equalizer is demonstrated with the flattening of the output spectrum of a superluminescent light emitting diode.

Equalization of Gaussian-like spectra with optical lattice filters

We present a filter design scheme in which we use an all-fiber lattice filter to equalize Gaussian-like spectra. With a two-step design strategy, the designed equalization filter can flatten the Gaussian-like spectra in the maximally flat sense, and the spectrum ripples can be assessed quantitatively. The equalization performance is analyzed theoretically. It is also shown that the equalization performance can be improved only with an increased odd order of the lattice filter. As an illustrative example, the proposed scheme is applied to the design of an all-fiber equalization filter to flatten the output spectrum of a superluminescence light-emitting diode. Simulation and experimental results verify the theoretical analysis.

Active Optical Lattice Filters

Optical lattice filter structures including gains are introduced and analyzed. The photonic realization of the active, adaptive lattice filter is described. The algorithms which map between gains space and filter coefficients space are presented and studied. The sensitivities of filter parameters with respect to gains are derived and calculated. An example which is relevant to adaptive signal processing is also provided.

Optical Lattice-Type Add–Drop Multiplexing Filters and Their Use in WDM Networks

This paper examines the use of optical lattice filters as wavelength add/drop devices in WDM ring or bus networks. Various filter design methodologies are investigated, including methods to produce passband-flattened low sidelobe filters. The effects of cascading such devices are examined from the viewpoint of net transmission bandwidth and coherent or “in-band” crosstalk and are compared with the use of pairs of 1:nwavelength multiplexer/demultiplexers to perform the add/drop function. We find that the use of optical lattice-type add/drop filters results in a much broader net transmission bandwidth than even the use of pairs of passband-flattened 1:nwavelength multiplexer/demultiplexers. The use of passband-flattened optical lattice filters with correspondingly broad stopbands helps to significantly broaden the coherent crosstalk-limited bandwidth. The characteristics of a four-channel add/drop filter fabricated using silica waveguide technology and the performance of a three-node 3×2.5 Gbps WDM ring network built using a number of these devices are reported.

High-speed discrete-time optical filtering

We demonstrate very-high-speed discrete-time filtering using optical lattice filters. We generate 667 GHz bursts of 250 fs optical pulses whose leading edges have step and ramp shaped envelopes, and convolve them with designed lattice filter system responses to produce discrete-time signals with ramp and quadratic shaped envelopes. These filters thus act as precise digital integrators. >

Analysis and design of optical lattice filters in the presence of imperfections

We analyze the operation of optical lattice filters in the presence of such practical imperfections as losses, and finite mirror reflectivity specification. Our test case of interest is the class of multi-mirror structures which transform a single short pulse into a very high frequency burst of short pulses. In addition to understanding the effects of these losses, we show how to redesign these multi-mirror structures to achieve locally optimal performance in the presence of losses. The effects of phase errors on pulse train shape are also studied.

Optical lattice filters from the wave field of laser radiation

Optical lattice filters from the wave field of laser radiation