Tunable Optical Notch Filter Research Articles

Design of tunable notch filter based on plasmonic and InGaAsP waveguide

A highly efficient compact tunable optical notch filter is proposed and analyzed using the 2D Finite Element Method (FEM). The proposed structure consists of a slanted stub plasmonic resonator, Metal–Insulator–Metal (MIM) waveguide, and InGaAsP as a third-order non-linear optical material. By altering the pumping state of the InGaAsP, the filtered wavelengths may be easily controlled continuously over 200 nm a range. The suggested notch filter can remove four narrow bands of wavelengths, each around 50 nm wide, and a transmission of about − 17 dB. The proposed filter’s key advantages are its high transmission coefficient and fabrication simplicity with compact size. For future integrated plasmonic devices such as outdoor visible light communications and optical imaging, the proposed filter can be manufactured using an oblique angle shadow evaporation technique.

Continuously Tunable Optical Notch Filter With Functions of a Mirror and a Beam Splitter

The objective of this study was to develop continuously tunable optical notch filters by combining four left- and right-handed circular cholesteric liquid crystal (CLC) cells without subsidiary optical components. By rotating each filter, the photonic band position could be continuously blue shifted over 100-nm spectral range. Using four notch filter sets with four different chiral dopant concentrations, spectral range from 440 to 870 nm could be covered. Since each CLC cell has only one chiral dopant concentration, it could be stable for a long time. Each filter is independent of polarization in the spectral range. Filter performance was highly enhanced by introducing an anti-reflection layer on the filter device. There was no light leakage inside the photonic band. Outside the band, transmittance was about 70%-100%. In addition, these filters had stable operation under extremely high laser intensity (~124 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of CW 532-nm diode laser and ~4.43 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of Nd: YAG pulse laser operation for 2 h) without showing damage. Such filters also have functions as a mirror and a beam splitter. Depending on CLC materials, this simple and easy strategy could be used to prepare filters for applications in VIS and NIR spectral range devices.

Continuously tunable optical notch filter and band-pass filter systems that cover the visible to near-infrared spectral ranges.

Spatially continuous tunable optical notch and band-pass filter systems that cover the visible (VIS) and near-infrared (NIR) spectral ranges from ∼460 nm to ∼1,000 nm are realized by combining left- and right-handed circular cholesteric liquid crystal (CLC) wedge cells with continuous pitch gradient. The notch filter system is polarization independent in all of the spectral ranges. The band-pass filter system, when the left- and right-handed CLCs are arranged in a row, is polarization independent, while when they are arranged at right angles, they are polarization dependent; furthermore, the full-width at half-maximum of the band-pass filter can be changed reversibly from the original bandwidth of 36nm to 16nm. Depending on the CLC materials, this strategy could be applied to the UV, VIS, and IR spectral ranges. Due to the high performance in the broad spectral range, cost-effective facile fabrication process, simple mechanical control, and small size, it is expected that our optical tunable filter strategies could become one of the key parts of laser-based Raman spectroscopy, fluorescence, life science devices, optical communication systems, astronomical telescopes, and so forth.

Independently tunable optical notch filter based on double ring resonator structure

A novel technique of designing optical notch filter is proposed from digital filter perspective for Mach–Zehnder interferometer with double ring resonator coupled structure. It is based on Z-transform method. The key advantage of this structure is that it removes phase shifters, which is usually used in existing notch filter with ring resonator structure. So the proposed notch filter has high stability and good reliability. The proposed design method to obtain the structural parameters of the notch filter is not only effective and simple, but also can be used to implement the optical notch filter with arbitrary notch frequency, 3dB rejection bandwidth and notch point number. One design example of notch filter with two notch frequencies and different 3dB rejection bandwidth is presented in the paper in detail. The change of the intensity response of the design example is also investigated for each design parameters deviating from ideal value. The results show that the notch frequency and 3dB rejection bandwidth of each notch point can be tuned independently.

Dynamic control of a phase-shifted FBG through acousto-optic modulation

When an acoustic wave excites a phase-shifted fiber Bragg grating (PSFBG) several properties of the transmission/reflection spectrum, such as transmission notch depth and spectral bandwidth are influenced. In this work, a study on the effect of acoustic waves in PSFBGs is presented. The results are supported by theoretical simulation and experimental work. The technique can be used for different applications, such as in a fast tunable optical notch filter.

Tunable Optical Notch Filter Realized by Shifting the Photonic Bandgap in a Silicon Photonic Crystal Line-Defect Waveguide

A tunable optical notch filter was realized by thermally shifting the TM-like (the light's electric field perpendicular to the substrate) bandgap of a silicon photonic crystal slab W1 line-defect waveguide with silica cladding. This device is compact-its footprint is 340times16 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , excluding the electrode pads. The 3-dB bandwidth of the device was about 5 nm, and the extinction ratio at the center wavelength was as high as 40 dB. A maximum center wavelength shift of 17.9 nm was attained at a heating power of 0.7W, with a tuning efficiency of 25.5 nm/W. The tuning response time was less than 100 mus

Demonstration of tunable optical notch filter using 1-D opto-VLSI processor

An opto-very-large-scale-integrated (opto-VLSI)-based tunable optical filter structure is demonstrated. Filter tunability is achieved by reconfiguring the holographic diffraction grating of an opto-VLSI processor, allowing virtually any type of filter response to be synthesized. A proof-of-concept tunable notch filter with wavelength span of 7 nm is experimentally verified

Synthesis of Rejection Band Profile in Ultrasonically Induced Long-Period Optical Fiber Gratings

An ultrasonically induced long-period fiber grating functions as a tunable optical notch filter, since the pitch of refractive index modulation is changed according to the driving frequency of the ultrasonic vibration propagating along a fiber. In this study, two methods of synthesizing the band profile are investigated experimentally. The first method is to add two signals with different frequencies to excite the ultrasonic vibration, while the other is to switch two signals by frequency shift keying modulation. For both methods, the tunability of the rejection band profile is evaluated with respect to the difference in the two frequencies and the amplitude ratio of the two ultrasonic signals.

Narrowband optical filter, with a variable transmission spectrum, using stimulated Brillouin scattering in optical fiber

A novel shape-adjustable narrowband optical filter utilizing stimulated Brillouin scattering in an optical fiber is proposed and demonstrated. In this scheme, binary-phase-shift-keying modulation is applied to the pump wave to broaden and shape the Brillouin gain spectrum. By choosing an appropriate modulation data pattern, we realized a flat-top steep-cutoff optical bandpass filter with a 3-dB bandwidth of 1.5 GHz and a 10-dB bandwidth of 2 GHz is realized. In addition, a tunable optical notch filter is also realized by deamplification of the anti-Stokes wave.

Four-channel tunable optical notch filter using InGaAsP/InP reflection gratings

A new tunable optical notch filter for use in wavelength division multiplexing (WDM) transmission system has been fabricated in the InGaAsP/InP material system for use at 1.55 /spl mu/m. The device uses tunable reflection gratings in a waveguide to control the channels (4 in this case). Crosstalk levels between 9 dB and 20 dB have been measured, depending on the channel. System experiments at 150 Mb/s show less than 1 dB crosstalk penalty at 10/sup /spl minus/9/ bit-error rate. >