Center Wavelength Shift Research Articles

Flexible all fiber Fabry-Perot filters based on superimposed chirped fiber Bragg gratings with continuous FSR tunability and its application to a multiwavelength fiber laser

We proposed and experimentally demonstrate a simple and flexible scheme of all-fiber Fabry-Perot filter with continuous free spectral range tunability exploiting a superimposed chirped fiber Bragg grating. Then, we apply the proposed continuously tunable multichannel filter to a multiwavelength SOA ring laser at room temperature. The specially designed apparatus can induce the symmetrical strain gradient and modify the chirp ratio along the superimposed chirped fiber Bragg grating attached onto a flexible cantilever beam. Then the free spectral range of the all-fiber Fabry-Perot filter can be continuously controlled by the variation of reflection chirp bandwidth of the superimposed chirped fiber Bragg grating without center wavelength shift, which depends on the moving direction of translation stage. The proposed scheme can provide the effective multichannel filter with continuous free spectral range tunability. We successfully achieve the stable operation of a multiwavelength SOA laser with eleven lasing channels based on the proposed flexibly tunable multichannel filter at room temperature.

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

Wavelength-spacing-tunable multichannel filter incorporating a sampled chirped fiber Bragg grating based on a symmetrical chirp-tuning technique without center wavelength shift

We propose and experimentally demonstrate a simple and flexible scheme for a wavelength-spacing-tunable multichannel filter exploiting a sampled chirped fiber Bragg grating based on a symmetrical modification of the chirp ratio. Symmetrical bending along a sampled chirped fiber Bragg grating attached to a flexible cantilever beam induces a variation of the chirp ratio and a reflection chirp bandwidth of the grating without a center wavelength shift. Accordingly, the wavelength spacing of a sampled chirped fiber Bragg grating is continuously controlled by the reflection chirp bandwidth variation of the grating corresponding to the bending direction, which allows for realization of an effective wavelength-spacing-tunable multichannel filter. Based on the proposed technique, we achieve the continuous tunability of the wavelength spacing in a range from 1.51 to 6.11 nm, depending on the bending direction of the cantilever beam.

Terra MODIS on-orbit spectral characterization and performance

The Moderate Resolution Imaging Spectroradiometer (MODIS) protoflight model onboard the National Aeronautics and Space Administration's Earth Observing System Terra spacecraft has been in operation for over five years since its launch in December 1999. It makes measurements using 36 spectral bands with wavelengths from 0.41 to 14.5 mum. Bands 1-19 and 26 with wavelengths below 2.2 mum, the reflective solar bands (RSBs), collect daytime reflected solar radiance at three nadir spatial resolutions: 0.25 km (bands 1-2), 0.5 km (bands 3-7), and 1 km (bands 8-19 and 26). Bands 20-25 and 27-36, the thermal emissive bands, collect both daytime and nighttime thermal emissions, at 1-km nadir spatial resolution. The MODIS spectral characterization was performed prelaunch at the system level. One of the MODIS onboard calibrators, the Spectroradiometric Calibration Assembly (SRCA), was designed to perform on-orbit spectral characterization of the MODIS RSB. This paper provides a brief overview of MODIS prelaunch spectral characterization, but focuses primarily on the algorithms and results of using the SRCA for on-orbit spectral characterization. Discussions are provided on the RSB center wavelength measurements and their relative spectral response retrievals, comparisons of on-orbit results with those from prelaunch measurements, and the dependence of center wavelength shifts on instrument temperature. For Terra MODIS, the center wavelength shifts over the past five years are less than 0.5 nm for most RSBs, indicating excellent stability of the instrument's spectral characteristics. Similar spectral performance has also been obtained from the Aqua MODIS (launched in May 2002) SRCA measurements

Simultaneous measurement of stress and temperature with a fiber Bragg grating based on a loop thin-wall section beam

We designed and demonstrated what we believe to be a novel sensor for simultaneous measurement of stress and temperature. A fiber Bragg grating is flatly adhered to the surface of a loop thin-wall section beam. The theoretical analyses and the experimental results show that both the central wavelength shift and the chirped bandwidth of the grating reflection spectrum have a linear relationship with the stress and the temperature, respectively, and the slopes of them are different. Therefore, the temperature and stress can be discriminated by interrogating the chirped fiber grating. Moreover, we also investigated the strain of the loop thin-wall section beam, and the results show that the strain is cosine proportional to the double positional angle.

Continuously tunable photonic microwave true-time delay based on tunable chirped fibre Bragg grating

A simple scheme for the photonic microwave true-time delay with high tunability based on a tunable chirped fibre Bragg grating without centre wavelength shift is experimentally demonstrated. A large dynamic range of true-time delay from 20 to 200 ps was achieved for a microwave signal carried over an optical signal.

Center wavelength adjustment of silica-based arrayed waveguide gratings by glass densification

We propose and demonstrate a new method for adjusting the center wavelength of a silica-based planar lightwave circuit interferometer via the densification of silica glass. We applied the proposed method to an arrayed waveguide grating multiplexer using a hot isostatic press, and observed a large center wavelength shift of more than 1 nm. We confirmed that the wavelength shift was stable for more than 100 h at 120/spl deg/C and 90% RH.

Optical delay interferometer based on phase shifted fiber Bragg grating with optically controllable phase shifter

We propose a novel optical delay interferometer (ODI) with an optically controllable phase shifter. The proposed interferometer is implemented by using a phase shifted fiber Bragg grating and an Yb(3+)/Al(3+) co-doped optical fiber. The phase of the delayed optical signal is linearly controlled by adjusting the induced pumping power of a laser diode at 976 nm. Polarization dependent loss, polarization dependent center wavelength shift and temperature induced center wavelength shift of the ODI are 0.044 dB, 6 pm, and 9.8 pm/ degrees C, respectively.

Compact Arrayed-Waveguide Grating on Silicon-on-Insulator withIntegrated Waveguide Turning Mirrors

A compact arrayed-waveguide grating (AWG) on thesilicon-on-insulator material is designed and fabricated withemployment of waveguide-integrated turning mirrors (WITMs). By properlysetting the incident angle with the value of 45°, the effectivearea of the WITM AWG is only 1.15 cm×1.15 cm with the arrayedwaveguide area of 0.6 cm×0.6 cm. The crosstalk of the fabricated1×6 AWG is better than -19 dB. The on-chip insertion loss isabout -8.8 dB and the output nonuniformity is less than 0.6 dB. Thepolarization-dependent central wavelength shift is about 0.048 nm andthe polarization dependent loss is neglectable.

Tunable optical fiber filters with magnetic fluids

This letter presents a tunable optical fiber filter based on a long-period grating (LPG) by applying a magnetic field on a magnetic nanoparticle fluid. The movement of the magnetic fluid jacket surrounding the fiber cladding controlled by an applied magnetic field results in a variation of the external index between that of the magnetic fluid and air. As a result, the attenuation band of the LPG is shifted. The observed center wavelength shift of the attenuation band is as large as 7 nm, which can cover eight dense wavelength division multiplexing channels (100 GHz channel spacing). Repeatable transport of a magnetic fluid at a switching rate of 1 Hz is demonstrated.

Stresses and Temperature Stability of Dense Wavelength Division Multiplexing Filters Prepared by Reactive Ion-Assisted E-Gun Evaporation

In this paper, we report the in situ measurement of the temperature stability of narrow-band-pass filters on different types of substrate, for dense wavelength division multiplexing (DWDM) filters in optical-fiber transmission systems. The DWDM filters were designed as all-dielectric Fabry–Perot filters and fabricated by reactive ion-assisted deposition. Ta2O5 and SiO2 were used as high- and low-refractive-index layers, respectively, for constructing the DWDM filters. The accuracy and stability of the coating process were evaluated for fabricating the DWDM filters for the temperature stability of the center wavelength. The center wavelength shift was determined to be greatly dependent on the coefficient of thermal expansion of the substrate on which the filter is deposited.

Optical antenna design for indoor optical wireless communication systems

AbstractIn the present paper, the design of the non‐imaging totally internally reflecting concentrator family denominated optical antennas (OAs) is discussed, and its use for indoor optical wireless communication systems is explained. The lenses presented here can be designed to provide a prescribed angular response in order to limit the central wavelength shift in thin‐film optical filters. They can also be designed for any specific field‐of‐view (FOV), which allows greater rejection of unwanted background radiation and higher gains. The use of a variety of optical filters to achieve a high signal‐to‐noise ratio at the receiver is described. Design methods and properties of different Optical Antennas are explained. Comparisons of size and performance of total internal reflection based concentrators with those based on dielectric hemispheres and compound parabolic concentrators (CPCs) are carried out. Finally different experimental results are presented. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Silicon-on-insulator-based optical demultiplexer employing turning-mirror-integrated arrayed-waveguide grating

In this letter, we demonstrate an optical demultiplexer on the silicon-on-insulator material employing the turning-mirror-integrated arrayed-waveguide grating (AWG). We substitute the bent waveguide array in the traditional AWG configuration by adopting the structure of the turning-mirror-integrated straight waveguides. Description of the design procedure is provided. The crosstalk of the fabricated 1/spl times/4 AWG is better than -23.1 dB. The typical on-chip insertion loss is about -8 dB and the output nonuniformity is less than 0.4 dB. The polarization-dependent central wavelength shift is about 0.068 nm.

Tunable dispersion using linearly chirped polymer optical fiber Bragg gratings with fixed center wavelength

We propose a new scheme for tunable dispersion using linearly chirped polymer optical fiber Bragg gratings made in fiber tapers. The simple tension and uniform heating to the fiber gratings act as the adjustment and control process. Dispersion is tuned by the applied tensile strain. Owing to the unusually large and negative thermooptic coefficient of polymer fiber, the center wavelength shift induced by the applied strain will be offset by the effect of the uniform heating, leading to the fixed center wavelength. Our simulation demonstrates a very large dispersion tuning range, say from 2400 to 110 ps/nm.

Tunable dispersion compensator based on uniform fiber Bragg grating and its application to tunable pulse repetition-rate multiplication

A new technique to control the chromatic dispersion of a uniform fiber Bragg grating based on the symmetrical bending is proposed and experimentally demonstrated. The specially designed two translation stages with gears and a sawtooth wheel can simultaneously induce the tension and compression strain corresponding to the bending direction. The tension and compression strain can effectively control the chirp ratio along the fiber grating attached on a flexible cantilever beam and consequently the dispersion value without the center wavelength shift. We successfully achieve the wide tuning range of chromatic dispersion without the center wavelength shift, which is less than 0.02 nm. We also reduce the group delay ripple as low as ~+/-5 ps. And we also demonstrate the application of the proposed tunable dispersion compensation technique to the tunable pulse repetition-rate multiplication and obtain high-quality pulses at repetition rates of 20 ~ 40 GHz.

Characteristics of polymer waveguide notch filters using thermooptic long-period gratings

We demonstrate experimentally the feasibility of a polymer waveguide notch filter using a thermooptic long-period grating. This notch filter consists of a channel waveguide, a cladding surrounding the channel, and buffer layers sandwiching the cladding. Periodic heaters formed on the upper buffer layer induce a long-period grating thermooptically. Thus, they generate temporarily a resonance band of notch type in the transmission spectrum of the filter. Using thermocurable polymers, we have fabricated notch filters 1 and 2 that have different cladding thicknesses. Experimental results demonstrate two features of the notch filters. One feature is dynamical controllability of the attenuation of a resonance band. For TE mode, the maximum attenuation of notch filters 1 and 2 increases from 0 to 27 dB as the power applied to notch filters 1 and 2 increases from 0 to 851 and 1170 mW, respectively. The other feature is controllability of the direction and magnitude of the center wavelength shift occurring when the attenuation is tuned. The shift property depends on the cladding thickness. The measured characteristics of notch filters 1 and 2 are qualitatively in good agreement with our theoretical analysis. Using this feature, we may implement the notch filter whose attenuation is adjustable without center wavelength shift. This polymer waveguide notch filter may be used to implement a compact filter whose spectrum is dynamically tailored.

Simultaneous measurement of load and position with an embedded chirped sampled fibre grating

In this paper we present the use of a chirped sampled grating for distributed sensing of pressure over a small area (e.g. a few centimetres). The grating is embedded in fibre-reinforced composite. It is found that the shift in the central wavelength of each sub-grating in the chirped sampled grating increases monotonically with an increase in the applied force. The central wavelength of the sub-grating gives the location of the applied pressure. When a surface comes into contact with the sensor, the distribution of the pressure determines the shift in central wavelength of the various sub-gratings. The sub-grating that experiences the maximum pressure will show maximum wavelength shift whereas adjacent sub-gratings will show less shift. This method gives the location and magnitude of the load even when the load is not directly applied to any of the sub-gratings. The sensor design comprises of a sampled chirped grating embedded in unidirectional fibre-reinforced composite prepreg. The prepreg enhances the mechanical strength and the unidirectional embedding reduces birefringence. The number of layers in the prepreg stack varies the sensitivity.

Derivation of the center-wavelength shift of narrow-bandpass filters under temperature change

We derive a simple equation to predict the center-wavelength shift of a Fabry-Perot type narrow-bandpass filter by using the conventional characteristic matrix method and the elastic strain model as the temperature varies. We determine the thermal expansion coefficient of substrate from the zero-shift condition of the center wavelength of the filter. The calculated shifts are in a good agreement with the experimental ones, in which the narrow-bandpass filters are prepared by plasma ion-assisted deposition on four substrates with different thermal expansion coefficients.

Tuning sampled nonlinearly chirped fiber Bragg gratings with adjustable chirp and fixed center wavelength

AbstractA simple method for tuning a sampled nonlinearly chirped fiber Bragg grating (SNCFBG) without a center‐wavelength shift is demonstrated experimentally. A uniform sampled fiber Bragg grating (SFBG) is adhered on a bent plastic plate along a precalculated curve. The nonlinear chirp among the SFBG channels is tuned when a displacement is applied to the free end of the plastic plate and the central wavelength of the grating is fixed. The dispersion varies from −996.3 to −117.9 ps/nm in the center channel and the center‐wavelength shift is as small as 0.06 nm in the tuning process. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 432–434, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20493

Tunable dispersion compensation with fixed center wavelength and bandwidth using a side-polished linearly chirped fiber Bragg grating

We propose a new method for tuning the dispersion of a linearly chirped fiber Bragg grating with fixed center wavelength and bandwidth. We polished one side of the grating and attached it to a cantilever metal beam. By contacting an index matching block to the polished face of the grating, we could shorten the effective grating length through which light can propagate in the core of fiber. Decrease of grating length results in reflection bandwidth narrowing. However, by bending the grating attached on the cantilever beam, we could restore the bandwidth. Because the grating is shortened without bandwidth narrowing, the amount of dispersion is decreased. By using this method, we tuned chromatic dispersion of the linearly chirped fiber Bragg grating from −687.24 to − 256.11 ps / nm for 0.75 nm fixed bandwidth without center wavelength shift.