Precise Wavelength Research Articles

High precision measurement technology for beat length of birefringence optical fiber

We propose a precision and flexible measurement method for the beat length of birefringence optical fiber (BOF) with a hybrid Sagnac interferometer formed with a single mode fiber directional coupler and BOFs. The measurement error equation was obtained based on error estimation theory and it was found that there is an optimum length for certain BOF under test. The measurement error can be less than 0.001 mm with 1 pm wavelength precision and 0.1 mm fiber length precision. With a high performance wavelength interrogator technology and a special designed fiber length measurement method, a beat length measurement setup was built and the measurement standard deviation of 3.08 × 10−4 mm was achieved with 250 measurement samples for solid core polarization maintaining photonic crystal fibers (PM-PCFs). The beat length stability of two PM-PCFs with different structure sizes has been measured and compared. The result demonstrated that the birefringence temperature characteristic of the PM-PCFs may be dependent on structure sizes.

Emission wavelength of multilayer distributed feedback dye lasers

Precise emission wavelength modeling is essential for understanding and optimization of distributed feedback (DFB) lasers. An analytical approach for determining the emission wavelength based on setting the propagation constant of the Bragg condition and solving for the resulting slab waveguide mode is reported. The method is advantageous to established methods as it predicts the wavelength precisely with reduced complexity. Four-layered hybrid polymer-TiO2 first order DFB dye lasers with different TiO2 layer thicknesses are studied. Varying the TiO2 thickness from 0 nm to 30 nm changes the emission wavelength by 7 nm with compelling agreement of modeling results to experimental measurements.

Optical Filter Design Using Background Wavelength Processing Techniques

Amorphous SiC tandem heterostructures are used to filter a specific band, in the visible range. Experimental and simulated results are compared to validate the use of SiC multilayered structures in applications where gain compensation is needed or to attenuate unwanted wavelengths. Spectral response data acquired under different frequencies, optical wavelength control and side irradiations are analyzed. Transfer function characteristics are discussed. Color pulsed communication channels are transmitted together and the output signal analyzed under different background conditions. Results show that under controlled wavelength backgrounds, the device sensitivity is enhanced in a precise wavelength range and quenched in the others, tuning or suppressing a specific band. Depending on the background wavelength and irradiation side, the device acts either as a long-, a short-, or a band-rejection pass filter. An optoelectronic model supports the experimental results and gives insight on the physics of the device.

Single Mode, Extreme Precision Doppler Spectrographs

AbstractThe ‘holy grail’ of exoplanet research today is the detection of an earth-like planet: a rocky planet in the habitable zone around a main-sequence star. Extremely precise Doppler spectroscopy is an indispensable tool to find and characterize earth-like planets; however, to find these planets around solar-type stars, we need nearly one order of magnitude better radial velocity (RV) precision than the best current spectrographs provide. Recent developments in astrophotonics (Bland-Hawthorn & Horton 2006, Bland-Hawthorn et al. 2010) and adaptive optics (AO) enable single mode fiber (SMF) fed, high resolution spectrographs, which can realize the next step in precision. SMF feeds have intrinsic advantages over multimode fiber or slit coupled spectrographs: The intensity distribution at the fiber exit is extremely stable, and as a result the line spread function of a well-designed spectrograph is fully decoupled from input coupling conditions, like guiding or seeing variations (Ihle et al. 2010). Modal noise, a limiting factor in current multimode fiber fed instruments (Baudrand & Walker 2001), can be eliminated by proper design, and the diffraction limited input to the spectrograph allows for very compact instrument designs, which provide excellent optomechanical stability. A SMF is the ideal interface for new, very precise wavelength calibrators, like laser frequency combs (Steinmetz et al. 2008, Osterman et al. 2012), or SMF based Fabry-Perot Etalons (Halverson et al. 2013). At near infrared wavelengths, these technologies are ready to be implemented in on-sky instruments, or already in use. We discuss a novel concept for such a spectrograph.

Habitable Zone Super-Earths with Non-Stabilised Spectrographs

AbstractDetecting the small velocity amplitudes (≤ 10 m/s) produced by habitable zone rocky planets around M Dwarfs requires radial velocity precisions of a few m s−1. However, an iodine absorption cell, commonly used as a high precision wavelength reference on non-stabilised spectrographs, is not efficient for very red and faint objects like M Dwarfs. Instead, arc lamps have to be used. With the exception of the ultra-stabilised HARPS spectrograph, achieving ~m s−1 calibration with arc lamps has not been possible because typical spectrographs experience drifts of several hundred m s−1 due to local atmospheric changes in pressure and temperature. We outline and present results from an innovative differential wavelength calibration method that enables ~m s−1 precision from non-stabilised, high-resolution spectrographs. This technique allows the detection of rocky planets with radial velocity amplitudes of a few m s−1.

Precision and fast wavelength tuning of a dynamically phase-locked widely-tunable laser

We report a precision and fast wavelength tuning technique demonstrated for a digital-supermode distributed Bragg reflector laser. The laser was dynamically offset-locked to a frequency-stabilized master laser using an optical phase-locked loop, enabling precision fast tuning to and from any frequencies within a ~40-GHz tuning range. The offset frequency noise was suppressed to the statically offset-locked level in less than ~40 μs upon each frequency switch, allowing the laser to retain the absolute frequency stability of the master laser. This technique satisfies stringent requirements for gas sensing lidars and enables other applications that require such well-controlled precision fast tuning.

Post-Growth Fabrication of Multiple Wavelength DFB Laser Arrays With Precise Wavelength Spacing

The design and experimental characterization of sidewall-etched gratings in III-V material fabricated with a post-growth technique are presented. The successful demonstration of an array of sidewall-etched distributed feedback lasers shows that this technology allows for a very accurate control of the wavelength spacing and a sidemode suppression ratio up to 60 dB.

Ultrahigh Resolution Multiplexed Fiber Bragg Grating Sensor for Crustal Strain Monitoring

We demonstrated a multiplexed fiber Bragg grating (FBG) sensor with static strain resolution of 10 nanostrain (nε) for crustal strain monitoring. Each sensor unit consists of a pair of identical FBGs for strain sensing and reference, respectively. A narrow linewidth tunable laser is used to interrogate the FBGs, and a cross-correlation algorithm is incorporated to demodulate the wavelength difference induced by strain. When no strain is applied, an ultrahigh wavelength precision corresponding to strain resolution of 3.3 nε was obtained, indicating the ultimate resolution of the sensor system. With a variable strain applied by a piezo-stage, strain resolution of 17.6 nε was demonstrated. When the sensor is adopted for the in situ monitoring of crustal deformation, the strain induced by oceanic tide is clearly recorded with a resolution of 10 nε, providing a potential tool for the geophysical measurements.

Design and Construction of Absorption Cells for Precision Radial Velocities in the K Band Using Methane Isotopologues

ABSTRACTWe present a method to optimize absorption cells for precise wavelength calibration in the near-infrared. We apply it to design and optimize methane isotopologue cells for precision radial velocity measurements in the K band. We also describe the construction and installation of two such cells for the CSHELL spectrograph at NASA’s IRTF. We have obtained their high-resolution laboratory spectra, which we can then use in precision radial velocity measurements and which can also have other applications. In terms of obtainable RV precision, methane should outperform other proposed cells, such as the ammonia cell () recently demonstrated on CRIRES/VLT. The laboratory spectra of the ammonia and methane cells show strong absorption features in the H band that could also be exploited for precision Doppler measurements. We present spectra and preliminary radial velocity measurements obtained during our first-light run. These initial results show that a precision down to can be obtained using a wavelength interval of only 5 nm in the K band and S/N ∼ 150. This supports the prediction that a precision down to a few meters per second can be achieved on late-M dwarfs using the new generation of NIR spectrographs, thus enabling the detection of terrestrial planets in their habitable zones. Doppler measurements in the NIR can also be used to mitigate the radial velocity jitter due to stellar activity, enabling more efficient surveys on young active stars.

Modulating and driving system for the application of microelectromechanical system infrared source array

A problem demanding to be solved in the development of microelectromechanical system (MEMS) IR source array has been the driving circuit and system. A method that can achieve the requirements of high driving power, high output efficiency, high voltage precision, voltage compensation, and deep frequency modulation for driving and modulating a MEMS IR source array was proposed. A liner DC steady voltage integrated circuit ADP3336 is used to drive the source array directly with a programmable compensation module ensuring the precision of radiation peak wavelength. And a FPGA as the control core of the system modulates the frequency and width of the driving pulse to control the array coding pattern. The engineering value of the system would be increased with the application of the MEMS IR source.

SIMULTANEOUS SPECTROPHOTOMETRIC ESTIMATION OF THIOCOLCHICOSIDE AND DEXKETOPROFEN TROMETAMOL IN PHARMACEUTICAL DOSAGE FORM

The present manuscript describes simple, sensitive, rapid, accurate, precise and economic dual wavelength spectrophotometric method for simultaneous determination of Thiocolchicoside and Dexketoprofen trometemol in combined tablet dosage form. The utility of dual wavelength data processing program is its ability to calculate unknown concentration of components of interest in a mixture containing an interfering component. The method was based on property of additivity of absorbances. The two wavelengths on UV spectrum of Thiocolchicoside were found out where it showed same absorbance, which were 368 nm and 284.60 nm. At 368 nm Thiocolchicoside showed some absorbance whereas Dexketoprofen trometemol showed zero absorbance. Both the drugs gave absorbance at 284.60 nm. The method involved solving of an equation based on measurement of absorbances at two wavelengths 284.6 and 368 nm. The two drugs follow Beer-Lambert’s law over the concentration range of 2-24 µg/ml. The method was successfully applied to pharmaceutical dosage form because no interference from the tablet excipients was found. The results of analysis have been validated statistically and by recovery studies.

PRECISE INFRARED RADIAL VELOCITIES FROM KECK/NIRSPEC AND THE SEARCH FOR YOUNG PLANETS

We present a high-precision infrared radial velocity study of late-type stars using spectra obtained with NIRSPEC at the W. M. Keck Observatory. Radial velocity precisions of 50 m/s are achieved for old field mid-M dwarfs using telluric features for precise wavelength calibration. Using this technique, 20 young stars in the {\beta} Pic (age ~12 Myr) and TW Hya (age ~8 Myr) Associations were monitored over several years to search for low mass companions; we also included the chromospherically active field star GJ 873 (EV Lac) in this survey. Based on comparisons with previous optical observations of these young active stars, radial velocity measurements at infrared wavelengths mitigate the radial velocity noise caused by star spots by a factor of ~3. Nevertheless, star spot noise is still the dominant source of measurement error for young stars at 2.3 {\mu}m, and limits the precision to ~77 m/s for the slowest rotating stars (v sin i < 6 km/s), increasing to ~168 m/s for rapidly rotating stars (v sin i > 12 km/s). The observations reveal both GJ 3305 and TWA 23 to be single-lined spectroscopic binaries; in the case of GJ 3305, the motion is likely caused by its 0.09" companion, identified after this survey began. The large amplitude, short-timescale variations of TWA 13A are indicative of a hot Jupiter-like companion, but the available data are insufficient to confirm this. We label it as a candidate radial velocity variable. For the remainder of the sample, these observations exclude the presence of any 'hot' (P < 3 days) companions more massive than 8 MJup, and any 'warm' (P < 30 days) companions more massive than 17 MJup, on average. Assuming an edge-on orbit for the edge-on disk system AU Mic, these observations exclude the presence of any hot Jupiters more massive than 1.8 MJup or warm Jupiters more massive than 3.9 MJup.

Laser frequency comb techniques for precise astronomical spectroscopy

Precise astronomical spectroscopic analyses routinely assume that individual pixels in charge-coupled devices (CCDs) have uniform sensitivity to photons. Intra-pixel sensitivity (IPS) variations may already cause small systematic errors in, for example, studies of extra-solar planets via stellar radial velocities and cosmological variability in fundamental constants via quasar spectroscopy, but future experiments requiring velocity precisions approaching ~1 cm/s will be more strongly affected. Laser frequency combs have been shown to provide highly precise wavelength calibration for astronomical spectrographs, but here we show that they can also be used to measure IPS variations in astronomical CCDs in situ. We successfully tested a laser frequency comb system on the Ultra-High Resolution Facility spectrograph at the Anglo-Australian Telescope. By modelling the 2-dimensional comb signal recorded in a single CCD exposure, we find that the average IPS deviates by <8 per cent if it is assumed to vary symmetrically about the pixel centre. We also demonstrate that series of comb exposures with absolutely known offsets between them can yield tighter constraints on symmetric IPS variations from ~100 pixels. We discuss measurement of asymmetric IPS variations and absolute wavelength calibration of astronomical spectrographs and CCDs using frequency combs.

Modeling Silicon-Based Periodic Waveguides for Optical Interconnects

ABSTRACTTo assist the precision and stability of wavelength at 1550 nm and 1300 nm in planar optical waveguides, hybrid semiconductor-metal corrugated gratings with nanometer period are integrated into silicon-based optical interconnects. This work utilizes multi-parametric optical waveguide models to compute the mode-coupling coefficients in the silicon photonic devices. For such a semiconductor-metal hybrid structure, a proper photonic technique needs to be utilized to solve this computational complexity. The optical method and the photonic method are used to compute coupling coefficients. Both methods have close numerical values shown in figures. Numerical results demonstrate how the normalized corrugation amplitudes of metal gratings can affect the coupling coefficients. Further physical interpretation and discussion can support and explain the above results. The modeling results can help engineers decide the values of parameters used in the design and fabrication of optical waveguides.

Wavelength Trimming of Micro-Machined VCSELs

We demonstrate the wavelength trimming of MEMS VCSELs by etching a cantilever-shaped top mirror using FIB etching. The proposed technique can be used for the post-process precise wavelength allocation of athermal MEMS VCSELs. The modeling and experimental results on 850nm MEMS VCSELs are presented. The results show a possibility of realizing both red-shift and blue-shift wavelength changes by choosing the etching area of the cantilever.

Spectral interferometry-based chromatic dispersion measurement of fibre including the zero-dispersion wavelength

We report on a simple spectral interferometric technique for chromatic dispersion measurement of a short length optical fibre including the zero-dispersion wavelength. The method utilizes a supercontinuum source, a dispersion balanced Mach-Zehnder interferometer and a fibre under test of known length inserted in one of the interferometer arms and the other arm with adjustable path length. The method is based on resolving one spectral interferogram (spectral fringes) by a low-resolution NIR spectrometer. The fringe order versus the precise wavelength position of the interference extreme in the recorded spectral signal is fitted to the approximate function from which the chromatic dispersion is obtained. We verify the applicability of the method by measuring the chromatic dispersion of two polarization modes in a birefringent holey fibre. The measurement results are compared with those obtained by a broad spectral range (500–1600 nm) measurement method, and good agreement is confirmed.

High-Q optical sensors for chemical and biological analysis.

High-Q optical sensors for chemical and biological analysis.

Single Sampling Point Detection of Frequency Modulated Terahertz Waves

We present single sampling point detection of the amplitude and phase of frequency modulated continuous wave terahertz radiation. Employing a conventional photomixing setup with a precise wavelength control allows for rapid scan rates in the kHz regime. Two application examples demonstrate the potential of this approach for real time monitoring of samples’ thicknesses and transmittances.

Wavelength Trimming of Vertical-Cavity Surface-Emitting Lasers with High-Contrast Subwavelength Grating

We proposed a trimming technology for the precise control of the lasing wavelength and lasing performance of high-contrast subwavelength grating (HCG) loaded vertical-cavity surface-emitting lasers (VCSELs). The trimming is based on the postprocess surface etching of HCG. Our result obtained using rigorous coupled wave analysis (RCWA) shows a possible precise wavelength tuning range of 3 nm for GaAs-based HCG-VCSELs. Our preliminary experiment reveals an expected smallest wavelength trimming of 0.07 nm.

Energy Dispersive Spectrometry at Wavelength Precision

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.