Ultranarrow band and high-quantum-efficiency photodetector with waveguide-grating structure and inclined top mirror

A new type of one-mirror inclined waveguide-grating photodetector, which combines a waveguide-grating filter and an inclined top mirror is proposed. Greatly improved spectral response is achieved by the integration of waveguide-grating into classical thin-film homogeneous layers. Comparison between the grating filter and Fabry-Perot filter demonstrates that this structure has two advantages over other photodetector devices. First, the inclined mirror can decouple the quantum efficiency from response speed and spectral response linewidth. Second, comparing the traditional photodetector with Fabry-Perot filter, this type of photodetector with the same materials requires significantly fewer layers while maintaining the same linewidth response, high peak efficiency and remarkably low sideband reflectivity. Thus, this type of photodetector device represents basic new optical features with a significant potential for practical applications.     

Narrow-linewidth bandpass filters with diffractive thin-film layers

Bandpass filters based on guided-mode resonance effects in waveguide-grating structures are obtained by use of a genetic algorithm search-and-optimization routine. Calculated examples show that narrow linewidths, high peaks, and low sideband transmittances can be achieved in thin-film diffractive devices with few layers. A filter with a linewidth of 0.2 nm at a central wavelength of 0.55 microm is demonstrated in a two-layer-two-grating structure. At 10.6-microm wavelength, a filter consisting of a single binary grating is obtained that has a linewidth of 12.7 nm and extended, low sideband transmittance. A three-layer device with a surface relief Si grating and two underlying homogeneous layers of SiO(2) and Si yields a high-efficiency filter centered at 1.55 microm with a linewidth of 0.1 nm.     

Increasing the angular tolerance of resonant grating filters with doubly periodic structures

One can increase the angular tolerance of resonant grating filters without modifying the spectral bandwidth by adding a second grating component parallel to the first one. The angular tolerance and the filter linewidth can be controlled by the designer in an independent way. Numerical results show that this property permits the use of waveguide-grating filters with standard collimated beams.     

High-efficiency guided-mode resonance filter

A high-efficiency guided-mode resonance reflection filter is reported. The device consists of a surface-relief photoresist grating and an underlying HfO (2) waveguide layer deposited on a fused-silica substrate. The spectral response measured with a dye-laser beam at normal incidence exhibited a peak reflectance of 98% at a wavelength of 860 nm with sideband reflectance below ~5% extending over the wavelength range provided by the dye (800-900 nm). At normal incidence the filter linewidth was 2.2 nm. High-efficiency double-peak resonances occurred at nonnormal incidence, with the spectral locations of the maxima vayring with the incidence angle. The filter response at various angles of incidence agreed well with the theoretically calculated reflectance curves.     

Autocollimation reflection of light from the surface of corrugated waveguides with leaky modes

The diffraction of light at the corrugated surface of a layer structure was studied. We show that the excitation of the waveguide modes in a layer structure causes a significant change in the diffraction efficiency of the corrugated structure. It is found that the diffraction efficiency of a grating in the autocollimation regime may be as much as 100% with reasonable depths of the grating. The efficiency of a waveguide-grating mirror in dye lasers is experimentally demonstrated.     

Design of single-material guided-mode resonance filter

In this letter, a guided-mode resonance （GMR） filter with the same material for both the grating layer and the waveguide layer is designed, and its optical properties are investigated. The GMR filter owns almost 100% reflection at the resonance wavelength of 800 nm with the full-width at half-maximum （FWHM） of 20 nm, and its sideband reflection from 700 to 1000 nm is less than 5%. As the resonance wavelength is influenced by more than one parameter during the fabrication process, GMR filter with the same resonance wavelength can be obtained by adjusting other parameters or even one parameter to deviate from the design value.     

Color filters featuring high transmission efficiency and broad bandwidth based on resonant waveguide-metallic grating

A one-dimensional transmission color filter based on a resonant waveguide-metallic subwavelength grating was numerically investigated by employing rigorous coupled-wave analysis (RCWA) and genetic algorithm (GA). The hybrid numerical method is used to determine the optimal parameters (the grating period, filling factor, grating thickness, and waveguide thickness) of two waveguide-grating structures, namely a double-layer resonant waveguide-metallic grating and a triple-layer resonant waveguide-metallic grating. The optical responses of these structures are evaluated and compared in terms of the ideal transmission efficiency aiming at the central wavelengths of 645 nm, 546 nm, and 455 nm of red (R), green (G), and blue (B) lights, respectively, over the visible region (380–780 nm). The results show that the optical performance of the double-layer with silver grating achieves the highest transmission efficiency of 82% (R), 81% (G), and 66% (B); and the largest bandwidth of about 125 nm (R), 118 nm (G), and 85 nm (B). Compared with existing color filters, the proposed device not only obtains a higher transmission and broader bandwidth, but it also suppresses redundant spectral peaks and transmission sidebands.     

Photonic mm-Wave Generation Using a Double Passband Fiber Bragg Grating Filter

We report a simplified version of a mm-wave generator employing the sideband filtering technique which uses a single optical sideband filter. Instead of using a Mach-Zehnder-like fiber network to select a pair of sidebands, we employ a single Fabry-Perot fiber Bragg grating with a pair of passbands separated by the mm-wave frequency. Using a single filter eliminated the need for polarization control and pathlength matching that was required by the former interferometer-like arrangement. We describe a 30 GHz generator design and present its mm-wave signal spectrum showing an instrument-limited linewidth of ~20 Hz. The generation of such an extremely narrow signal spectrum from a laser with a 1 MHz linewidth demonstrates the remarkable laser frequency noise cancellation property of the sideband filtering technique.     

Wave Localization of Doubly Periodic Guided-mode Resonant Grating Filters

It is known that a doubly periodic guided-mode resonant grating (GMRG) filter has a broad angular selectivity with a narrow spectral bandwidth. This means that the doubly periodic GMRG filter operates for small beam diameter and grating area. This report describes the wave localization in the doubly periodic GMRG filter. We investigated the spread area of light waves in the waveguide layer and the accumulation of field energy by numerical simulation using the finite differential time domain (FDTD) method. Simulation results showed that, in the case of a doubly periodic GMRG filter with a Q factor of 600, the field energy is spread over an area 5 um in width, which corresponds to the expected value from the angular tolerance. And the magnitude of the field energy in the waveguide layer was Q factor times greater than the incident energy. On the other hand, a singly periodic GMRG filter with the same Q factor spread the field energy over an area 72 urn in width. This filter does not work for a small size structure or a small diameter light beam.     

All-optical generation of 40 Gb/s single sideband signals using a fiber Bragg grating

In this work, we demonstrate a reliable all-optical technique for performing optical double sideband (ODSB) to single sideband (OSSB) format conversion of a 40 Gb/s non-return-to-zero signal. It is based on the optimization of a detuned optical filter, which was implemented on a fiber Bragg grating (FBG) with a complex apodization profile. An OSSB signal with negligible distortion was obtained, as the FBG presented a nearly ideal frequency response. Higher tolerance to chromatic dispersion enabled by the OSSB signal in comparison to the ODSB signal was demonstrated on both simulation and experimental results.     

Design of guided-mode resonance filters with an antireflective surface at oblique incidence

A design approach of guided-mode resonance filter (GMRF) with an antireflective surface at oblique incidence is presented. For a given incident angle or grating filling factor, the required grating filling factor or incident angle can be expressed by the analytical forms of the quadratic equations at quarter-wavelength thickness. Long-range, low sidebands are obtainable for a single-layer GMRF under the TM mode wave illumination at oblique incidence. The reflection properties such as the symmetry of the lineshape and the sideband level in the logarithm scale can be further improved by slightly varying both the grating period and the grating thickness. Magnetic field enhancement occurs in these structures due to the coupling between the evanescent diffracted order and the waveguide mode.     

阵列波导光栅梳状带通滤波器的传输效率

在光波导模场分布高斯近似条件下,根据星形光波导耦合器的耦合特性,推导出了基于累加运算和卷积运算近似表达的阵列波导光栅梳状带通滤波器光谱响应效率的函数表达式。给出了阵列波导光栅梳状带通滤波器光谱响应效率曲线的半最大值全宽度和阵列波导光栅梳状带通滤波器的通道中心波长的光谱响应度与器件参数的关系。在输入信号光谱分布高斯近似条件下,给出了阵列波导光栅梳状带通滤波器信号通道传输效率的计算表达式和输入信号光谱宽度对阵列波导光栅梳状带通滤波器信号通道输出特性的影响。给出了物理意义明确的函数表达式,它们可为快速分析阵列波导光栅梳状带通滤波器的特性提供理论基础。     

Design and characterization of guided mode resonance filters with the improved structure for facile fabrication

In this study, a guided mode resonance filter with the improved structure for facile fabrication is designed; the properties of the designed filters are simulated by rigorous coupled wave analysis. It is found that the resonance wavelength and spectral linewidth are slightly increased with the increasing of the grating thickness, and seldom changed with the thickness of the grating filling factor, as the parameter error of the grating thickness and the grating filling factor are deviated from the designed value by ±10%, respectively, which are very favorable for simplifying preparation process of the GMR filter.     

Transmission guided-mode resonance filters based on high reflection multilayer stacks

The transmission guided-mode resonance filters are implemented by integration of diffraction grating into classical thin films to produce high efficiency in the central wavelength and arbitrarily low sideband response over a quite large spectral range. Transmission guided-mode resonance filters require considerable fewer thin films to acquire narrow line width and high peak transmission in the central wavelength compared with classical multilayer high-reflectance coatings with a stack of quarter-wave thickness. The properties of transmission filters with single/double waveguide grating in the different layers of high refection stacks are compared each other. It is demonstrated that the narrow line width transmission filters can be abstained with only two different materials.     

Fiber Grating Based Optical Recirculating Filter with an Optimized Response

A novel optical recirculating filter for RF applications is described, which exploits a specially designed fiber grating with a ramped spectral profile to enable optimization of the filter response. The design overcomes the limitations imposed by loss in conventional fiber recirculating filters. Additionally, a tunable free spectral range is demonstrated by using the device in a grating array. Both theoretical and experimental results are presented and discussed.     

Fiber Grating Based Optical Recirculating Filter with an Optimized Response

A novel optical recirculating filter for RF applications is described, which exploits a specially designed fiber grating with a ramped spectral profile to enable optimization of the filter response. The design overcomes the limitations imposed by loss in conventional fiber recirculating filters. Additionally, a tunable free spectral range is demonstrated by using the device in a grating array. Both theoretical and experimental results are presented and discussed.     

High-reflectivity fiber-optic bandpass filter designed by use of the iterative solution to the Gel'fand-Levitan-Marchenko equations

A fiber Bragg grating bandpass filter has been investigated. The profile of the 3.1-cm-long grating was synthesized for high reflectivity and low dispersion by use of the iterative solution to the Gel'fand-Levitan-Marchenko equations. A grating designed according to this synthesis was written into a boron-codoped germanosilica fiber. The measured spectral response was in good agreement with simulations. The achieved in-band reflection was 97%, and the passband ripple was only 0.06 dB.     

Spectral Analysis of Transmission Echelon Grating Filters for Photonic Networks

This paper describes a method of analyzing spectral behavior that allows transmission echelon grating filters to be designed for use in constructing photonic networks. These networks include dense wavelength division multiplexing systems and other such applications. First, the configuration and principle of this filter are described. Then, the transmittance spectrum of the transmission echelon grating filter is considered for incident lights with rectangular, Gaussian, and sinc electric field distributions. Next, a more realistic spectral response is considered by taking reasonable fabrication errors into account. Finally, the group delay and the transmittance of linearly chirped echelon grating filters are analyzed to access their potential for use as a wavelength dispersion equalizer. These analytical results make it possible to design practical echelon grating filters.     

Surface corrugation Bragg gratings on optical fiber tapers created via plasma etch postprocessing

We describe a reflection-based fiber filter fabricated by plasma etching a surface corrugation Bragg grating on a tapered single-mode fiber. The taper waist with the grating forms the functional part of the filter, and the adiabatic taper transition removes unwanted higher-order modes. The spectral response is controlled by varying the taper diameter while maintaining a constant grating period. Reflection spectra have been investigated theoretically and experimentally and found to be in good agreement.     

Highly selective terahertz optical frequency comb generator

Using a 10.5-GHz resonant electro-optic modulator placed inside a resonant optical cavity, we generated an optical frequency comb with a span wider than 3 THz. The optical resonator consists of three mirrors, with the output coupler being a thin Fabry-Perot cavity with a free spectral range of 2 THz and a finesse of 400. Tuning this filter cavity onto resonance with a particular high-order sideband permits efficient output coupling of the desired sideband power from the comb generator, while keeping all other sidebands inside for continued comb generation. This spectrally pure output light was then heterodyne detected by another laser with a frequency offset of the order of 1 THz.