Abstract: In this paper, we present a method for combined fiber parameter estimation from digital filter coefficients of a polarization diverse coherent receiver. All deterministic linear optical channel parameters like residual chromatic dispersion (CD), polarization-mode dispersion (PMD), and polarization-dependent loss (PDL) are continuously monitored by analysis of the filter impulse response of the adaptive equalizer. After deriving the according equations from the theoretical linear fiber channel model, we demonstrate robust estimation for a joint combination of all impairments.

Abstract: We present a fully tunable multistage narrowband optical pole-zero notch filter that is fabricated in a silicon complementary metal oxide semiconductor (CMOS) foundry. The filter allows for the reconfigurable and independent tuning of the center frequency, null depth, and bandwidth for one or more notches simultaneously. It is constructed using a Mach-Zehnder interferometer (MZI) with cascaded tunable all-pass filter (APF) ring resonators in its arms. Measured filter nulling response exhibits ultranarrow notch 3 dB BW of 0.6350 GHz, and nulling depth of 33 dB. This filter is compact and integrated in an area of 1.75 mm2. Using this device, a novel method to cancel undesired bands of 3 dB bandwidth of < 910 MHz in microwave-photonic systems is demonstrated. The ultranarrow filter response properties have been realized based on our developed low-propagation loss silicon channel waveguide and tunable ring-resonator designs. Experimentally, they yielded a loss of 0.25 dB/cm and 0.18 dB/round trip, respectively.

Abstract: We have proposed a new design for temperature-independent silicon optical filters utilizing a combination of wide and narrow waveguides. The waveguide structure was optimized to minimize the spectral shift of the filter owing to the environmental temperature change. Based on this new waveguide design, we fabricated Mach-Zehnder interferometer optical filters on silicon-on-insulator substrates. The measured spectrum showed substantially small temperature dependence being in good agreement with the theoretical estimation.

Abstract: In this paper, we propose and demonstrate an approach to optically generating chirped microwave pulses with tunable chirp profile based on optical spectral shaping using a Sagnac loop filter incorporating a chirped fiber Bragg grating (CFBG) and linear wavelength-to-time mapping in a dispersive element. In the proposed approach, the optical power spectrum of an ultrashort optical pulse is shaped by a CFBG-incorporated Sagnac loop mirror that has a reflection spectral response with a linearly increasing or decreasing free spectral range. The spectrum-shaped optical pulse is then sent to a dispersive element to perform the linear wavelength-to-time mapping. A chirped microwave pulse with the pulse shape identical to that of the shaped spectrum is obtained at the output of a high-speed photodector. The central frequency and the chirp profile of the generated chirped microwave pulse can be controlled by simply tuning the time delay in the Sagnac loop mirror. A simple mathematical model to describe the chirped microwave pulse generation is developed. Numerical simulations and a proof-of-principle experiment are implemented to verify the proposed approach.

Abstract: Over recent years it has become experimentally possible to study the coupling of optical and mechanical modes by means of cavity-enhanced radiation pressure[1] which might enable ground state-cooling of macroscopic mechanical oscillators. For achieving this major goal in the field of cavity-optomechanics and for applications such as low-loss, narrowband ‘photonic clocks’ a combination of high optical finesse and high mechanical quality factors at mechanical oscillation frequencies exceeding the optical cavity's linewidth[1] is desirable. It has, however, so far not been possible to combine mechanical Q-factors comparable to those achieved in the field of nano- and microelectromechanical systems (e.g. [2]) with state-of-the-art values of optical finesse[3]. Here we show independent control over both optical and mechanical degrees of freedom in the same microscale optomechanical resonator[4].

Abstract: A single-photon avalanche diode-based pixel array for the analysis of fluorescence phenomena is presented. Each 180 times 150 - mum2 pixel integrates a single photon detector combined with an active quenching circuit and a 17-bit digital events counter. On-chip master logic provides the digital control phases required by the pixel array with a full programmability of the main timing synchronisms. The pixel exhibits an average dark count rate of 3 kcps and a dynamic range of over 120-dB in time uncorrelated operation. A complete characterization of the single photon avalanche diode characteristics is reported. Time-resolved fluorescence measurements have been demonstrated by detecting the fluorescence decay of quantum-dot samples without the aid of any optical filters for excitation laser light cutoff.

Abstract: We present a modified conventional camera that is able to collect multimodal images in a single exposure. Utilizing a light field architecture in conjunction with multiple filters placed in the pupil plane of a main lens, we are able to digitally reconstruct synthetic images containing specific spectral, polarimetric, and other optically filtered data. The ease with which these filters can be exchanged and reconfigured provides a high degree of flexibility in the type of information that can be collected with each image. This paper explores the various tradeoffs involved in implementing a pinhole array in parallel with a pupil-plane filter array to measure multi-dimensional optical data from a scene. It also examines the design space of a pupil-plane filter array layout. Images are shown from different multimodal filter layouts, and techniques to maximize resolution and minimize error in the synthetic images are proposed.

Abstract: An approach to the measurement of a microwave frequency based on optical power monitoring using a complementary optical filter pair is proposed and investigated. In the proposed system, a microwave signal is applied to a Mach-Zehnder modulator, which is biased at the minimum transmission point to suppress the optical carrier. The carrier-suppressed optical signal is then sent to the complementary optical filter pair, with the powers from the complementary filters measured by two optical power meters. A mathematical expression that relates the microwave frequency and the optical powers is developed. Experiments are performed to verify the effectiveness of the proposed approach. The performance of the proposed system in terms of the frequency measurement range, operation stability, and robustness to noise is also investigated.

Abstract: A compound eye camera module comprises a lens array including at least two lenses, an imaging element including two imaging areas corresponding to the two lenses, a light shielding block in which a light shielding wall for separating the optical path of light transmitted through the two lenses is provided, an optical filter for transmitting light in a specific wavelength band out of the light transmitted through the two lenses therethrough, and a substrate having an opening larger than the optical filter. The imaging areas and the optical filter are located in a position corresponding to the opening. The imaging element is fixed to a face of the substrate on the side opposite to the lens array side. The imaging element is in contact with a face of the optical filter facing the imaging element. The light shielding block is fixed to a face of the optical filter facing the light shielding block. In the direction in which two optical axes of the two lenses are connected, the optical filter includes portions that protrude outside both ends of the imaging element, and the light-shielding block is fixed to the protruding portions of the optical filter.

Abstract: We present a hybrid optical filter design that combines interference and absorbing components for enhanced fluorescence detection in miniaturized highly-integrated lab-on-a-chip devices. The filter is designed in such a way that the advantages of each technology are used to offset the disadvantages of the other. The filter is fabricated with microfabrication compatible processes and materials for monolithic integration with microelectronics and microfluidics devices. The particular embodiment of the filter described herein is designed to discriminate fluorescence emission at 650 nm from excitation at 532 nm. The 9-layer interference filter component is fabricated with alternating TiO2 and SiO2 thin-film layers and has an attenuation of −12.6 dB at 532 nm and −0.76 dB at 650 nm. The absorbing filter component is fabricated using a dyed photopolymer (KMPR + Orasol Red) having an attenuation of −32.6 dB at 532 nm and −1.28 dB at 650 nm. The total rejection ratio of the hybrid filter is 43 dB. The filter exhibits very low autofluorescence and performs equally well at off-axis incidence angles.

Abstract: A continuously tunable microwave photonic notch filter at around 30 GHz is experimentally demonstrated and 100% fractional tuning over 360deg range is achieved without changing the shape of the spectral response. The tuning mechanism is based on the use of slow and fast light effects in semiconductor optical amplifiers assisted by optical filtering.

Abstract: Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report and review here nanophotonic devices based on stacked semiconductor NMs that were built on Si, glass and flexible PET substrates. Photonic-crystal Fano resonance based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Such a low temperature NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics.

Abstract: We propose what we believe to be a novel method to generate optical millimeter-wave signals with frequency quadrupling using two cascaded Mach–Zehnder modulators (MZMs). Both theoretical analysis and experimental demonstration are presented. By symmetrically biasing the MZMs, without any optical filters or electrical devices, a high-quality millimeter wave at 40 GHz with an optical harmonic distortion suppression ratio of more than 25 dB is obtained. Furthermore, it is also proved to be valid that the proposed scheme is insensitive to the MZM bias drift, which demonstrates a relatively higher stability.

Abstract: A novel system of a simultaneous short-wave and millimeter-wave generation using a soliton pulse within a nano-waveguide is proposed, whereas the broad spectrum of optical output can be generated. By using the suitable parameters, for instance, input soliton power, coupling coefficients, and ring radii, the short-wave and millimeter-wave output signals can be simultaneously generated and filtered in a single system. Such a system consists of two microring resonators and a nanoring resonator that can be integrated to be a single system. Initially, the large bandwidth signal is generated by using a soliton pulse within a Kerr-type nonlinear medium, whereas the signals with broad bandwidth or wavelength can be generated. Results obtained have shown the potential of using the technique for a broad light spectra generation, where the required filtering signals are allowed to form the simultaneous up-link and down-link conversion using two different frequency (wavelength) carriers within a single system.

Abstract: We propose a new system of the dark-bright solitons conversion using a micro- and nanoring resonators incorporating an optical add/drop filter, where the add/drop filter can be used to convert the dark soliton to a bright soliton. The key advantage of the system is that the detection of the dark soliton pulse is normally difficult due to the low level of input power. First, a dark soliton pulse is input into a microring resonator and then propagated into smaller micro- and nanoring resonators, respectively. Second, the add/drop filter is applied (connected) into the ring system, where the bright and dark solitons are obtained via the drop and through (or throughput) ports of the add/drop filter, respectively. The results obtained have shown that the detected soliton power can be controlled by the input soliton power and the ring resonator coupling coefficient, which is enough power to use in the transmission link. Thus, significant conversion-amplified signals can be achieved.

Abstract: The optical gain of reflective optical network units (ONUs) may produce a critical amplifying feedback on the single-fiber transmission impairments. In this paper, its influence on the passive optical networks transmission with reflective-ONU is theoretically analyzed and experimentally confirmed. Analytical expressions for the optical crosstalk-to-signal ratio and the Q-parameter in presence of Rayleigh backscattering, reflection interferences and ASE noise are given. As a resulting design guideline, the ONU gain should be adjusted to about 3 dB below the total link loss; in addition, component return loss at the drop section must be higher than 30 dB. Experimental results with two basic types of reflective-ONUs, namely a loop structure formed by a Mach-Zehnder modulator and an optical amplifier, and another one employing a reflective-SOA, are in agreement with the theoretical approach.

Abstract: Microring resonator filters, which are made of dielectric-loaded surface plasmon polariton waveguides and operate in the telecom spectral range, are thoroughly analyzed by means of vectorial three dimensional (3D) finite element method (FEM) simulations. The filters’ functional characteristics, such as the resonant frequencies where the transmission minima occur, the free spectral range, the extinction ratio, and the minima linewidth associated with the quality factor of the resonances, are investigated for different values of the key structural parameters, namely, the ring radius and the gap separating the bus waveguide from the ring. The rigorous 3D-FEM simulations are qualitatively complemented by a simplified model. Apart from the harmonic propagation simulations, the uncoupled microring is treated as an eigenvalue problem, and the frequencies of the resonances are compared with those of the transmission minima. Furthermore, the possibility of exploiting the thermally tuned microring resonator filter ...

Abstract: A complete theory describing the transmission of atomic vapor Faraday filters is developed. The dependence of the filter transmission on atomic density and external magnetic field strength, as well as the frequency dependence of transmission, are explained in physical terms. As examples, applications of the computed results to ongoing research to suppress sky background, thus allowing Na lidar operation under sunlit conditions, and to enable measurement of the density of mesospheric oxygen atoms are briefly discussed.

Abstract: Full-duplex bidirectional transmission at 10 Gb/s is demonstrated for extended wavelength division multiplexed passive optical network (WDM-PON) applications, achieving transmission distances up to 25 km of standard single mode fiber (SSMF) when using a low-bandwidth (approximately 1.2 GHz) reflective semiconductor optical amplifier (RSOA) for signal re-modulation at the optical network unit (ONU). The system is assisted by optimum offset filtering at the optical line terminal (OLT)-receiver and the performance is further improved with the use of decision-feedback equalization (DFE). Chromatic dispersion (CD) and Rayleigh Backscattering (RB) effects are considered and analyzed.

Abstract: We propose an optical approach to generating chirped microwave pulses using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response. If a chirp-free broadband microwave pulse is inputted into the filter, a chirped microwave pulse is generated thanks to the quadratic phase response of the filter. To design a PMDLF with a quadratic phase response, complex tap coefficients are required, which is hard to implement in the optical domain. In this letter, a PMDLF with equivalent complex coefficients implemented based on a nonuniformly spaced delay-line structure is demonstrated. Since only positive coefficients are required, the filter is easy to implement. A design example is provided. A five-tap PMDLF to generate a chirped microwave pulse with a chirp rate of 13.2 GHz/ns is then experimentally demonstrated.

Abstract: We investigate the performance of OFDM-modulated signals in spectrum-sliced elastic optical path network. We analyze the filtering characteristics and the guard band for multi-node transmission. The architecture increases spectral efficiency over the current WDM systems.

Abstract: Externally amplified spontaneous emission (ASE) injection-locking characteristics and optical data transmission performances of a TO-56 can-packaged Fabry-Perot laser diode (FPLD) with 1% front-facet reflectivity are investigated using a wavelength-division-multiplexing passive-optical network (WDM-PON) system configured by an array-waveguide grating (AWG) based MUX/DMUX filters with channel spacing of 200 GHz. Quasi-single-mode output of such a nearly color-free weak-resonant-cavity FPLD with highest side-mode suppressing ratio of 31 dB is achieved with ASE injection-locking, providing a bit-error-rate (BER) of < 10-13 at receiving power of -31 dBm and a power penalty of 0.5 dB after 20-km transmission in single-mode fiber with a bit rate up to 1.25 Gbit/s.

Abstract: A differential absorption lidar (DIAL) instrument for automated profiling of water vapor in the lower troposphere has been designed, tested, and is in routine operation at Montana State University. The laser transmitter for the DIAL instrument uses a widely tunable external cavity diode laser (ECDL) to injection seed two cascaded semiconductor optical amplifiers (SOAs) to produce a laser transmitter that accesses the 824‐841-nm spectral range. The DIAL receiver utilizes a 28-cm-diameter Schmidt‐Cassegrain telescope; an avalanche photodiode (APD) detector; and a narrowband optical filter to collect, discriminate, and measure the scattered light. A technique of correcting for the wavelength-dependent incident angle upon the narrowband optical filter as a function of range has been developed to allow accurate water vapor profiles to be measured down to 225 m above the surface. Data comparisons using the DIAL instrument and collocated radiosonde measurements are presented demonstrating the capabilities of the DIAL instrument.

Abstract: We present a new intensity-modulated analog optical link architecture in which a pulsed optical carrier replaces the standard low-noise continuous-wave laser. Through a time-domain analysis of the sampled link architecture, we show that the link performance metrics reduce to those of a conventional analog optical link in the absence of photodiode nonlinearity. Experimental measurements of the link gain and third-order nonlinearity are presented, emphasizing the link performance as a function of received photocurrent. The work presented here demonstrates that the performance of sampled analog optical links rivals that of the conventional architecture, even in the presence of significant photodiode nonlinearity.

Abstract: A new all-fiber sensor capable of simultaneous measurement of strain and temperature is presented. The sensor system is formed by a fiber Bragg grating and two sections of multimode fibers (MMFs). One section of the MMF is isolated from strain and acts as a temperature-dependent edge filter, while the other is isolated from both strain and temperature changes. By monitoring the optical power changes, it is feasible to obtain information that permits simultaneous measurement of strain and temperature with a low-cost and simple structure.

Abstract: Thermochromic liquid crystal filters are fabricated by providing two polarizers oriented at offset polarity with respect to each other; providing alignment structures adjacent the inner surfaces of the polarizers; placing a plurality of spacers between the polarizers; and filling a space created by the spacers with a thermotropic liquid crystal that acts as a wave block in an isotropic state and acts as a depolarizer in a nematic state. Alternatively, the filters can be created by encapsulating a thermochromic liquid crystal with a polymer material to form a flexible film and orienting the thermochromic liquid crystal in the polymer material to create a structure that functions as a thermochromic optical filter. Such filters can control the flow of light and radiant heat through selective reflection, transmission, absorption, and/or re-emission. The filters have particular application in passive or active light-regulating and temperature-regulating films, materials, and devices, and particularly as construction materials.

Abstract: Chirped microwave pulse compression using a photonic microwave filter with nonlinear phase response to implement matched filtering is proposed and investigated. The photonic microwave filter with the required phase response is realized based on optical phase to microwave phase conversion through single-sideband modulation and heterodyne detection. A detailed theoretical analysis on the photonic microwave filter design and the linearly chirped microwave pulse compression is developed. A photonic microwave filter having a quadratic phase response with a bandwidth of 3 GHz is implemented. An application of the photonic microwave filter for linearly chirped microwave pulse compression is investigated.

Abstract: A bandwidth-tunable filter has been demonstrated based on a micro-electro-mechanical-system (MEMS) actuated single-crystalline silicon microtoroidal resonator. Bandwidth is tuned from 2.8to78.4 GHz by voltage control, the largest bandwidth tuning range reported to date to our knowledge in resonator-based filters. A 21.8 dB extinction ratio is attained as a dynamic add-drop filter.

Abstract: We report angular and polarization dependent transmission properties of Fano resonance optical filters with transferred silicon nanomembrane on glass substrate. The transmission spectra of the filters can have either weak or strong polarization and angular dependence, depending on properties of individual Fano resonance modal dispersion. Measurement results agree very well with simulations based on a rigorous coupled-wave analysis for the transmission spectra, on planewave expansion wave-vector technique for the dispersion property analysis, and on a three-dimensional finite-difference time-domain technique for the propagating modal study. These results will provide importance guidance for the design of a new class of ultra-compact surface-normal frequency selective components with preferred polarization and angular properties. These components are highly desirable for silicon photonic integration.