Wavelength Selective Element Research Articles

In-line fiber-optic components using Langmuir–Blodgett films

Langmuir-Blodgett (LB) films of omega-tricosenoic acid are deposited onto side-polished optical fibers, resulting in wavelength-selective elements. The wavelength response is shown to be strongly dependent on film thickness, giving a shift in central wavelength with film thickness of Deltalambda(0)/Deltad = 2.4, in agreement with a simple phasematching model. It is demonstrated that an alternative polishing technique, requiring no substrates or epoxy, allows more repeatable LB deposition and produces devices with similar characteristics. This is the only technique that will allow deposition of more complex electro-optic LB film-forming molecules.

A novel miniature spectrometer using an integrated acousto-optic tunable filter

In this paper, a novel miniature spectrometer is described which employs an integrated-optic acousto-optic tunable filter (IAOTF) as the monochromatic wavelength selective element. The performance of the system is highlighted by measuring the absorption spectra of two samples in the region of 1400 to 1600 nm. In the experiment, a light emitting diode (LED) centered at a wavelength of 1530 nm, is used as the light source and spectral filtering is achieved using an IAOTF that is tunable over more than 260 nm. The device exhibits a FWHM resolution of 1.2 nm, measures 25×3×1 mm3, weighs under 1 g and requires less than 70 mW of rf drive power. This miniature spectrometer offers several attractive design features that have utilities in a variety of applications, particularly for portable analysis and operation in harsh environments.

Generation of electrically wavelength tunable (Δλ= 40 nm) singlemodelaser pulses from a 1.3 µm Fabry-Perot laser by self-seedingin a fibre-optic configuration

A novel wavelength tunable self-seeding configuration without classical wavelength selective elements is presented. A multimode gain-switched Fabry-Perot laser shows singlemode emission in this configuration. The extremely simple setup consists only of the laser diode, a fibre coupler and 1 km of dispersion shifted fibre. The lasing wavelength is controlled by varying the repetition frequency. A sidemode suppression ratio better than 20 dB over a 40 nm tuning range is achieved.

Design considerations for Rowland circle gratings used in photonic integrated devices for WDM applications

Design issues of photonic integrated devices for WDM applications based on Rowland circle gratings have been studied. Effects of grating period, diffraction order, grating aperture (size), and Rowland circle size on device performance are discussed. The point spread function of a typical Rowland circle grating is evaluated numerically which yields an optical image (spot) size of several microns in diameter. Our study shows that there is a tradeoff between channel dispersion and feedback efficiency in choosing the grating period when a Rowland circle grating is used as the wavelength-selective element for a parallel-waveguide-type wavelength division multiplexing device. >

Output coupling induced wavelength shifts in erbium-doped fiber lasers

Experimental results of shifting the operating wavelength of erbium fiber lasers by varying the wavelength independent output coupling are presented. No wavelength selective elements are incorporated in the laser cavity. The results are in agreement with the simplified theory of A.O. Nielsen et al. (Electron. Lett., vol.27, no.18, p.1644-5, 1991). >

Error rate degradation due to switch crosstalk in large modular switched optical networks

A theoretical model of an optical network incorporating wavelength selective elements, amplifiers, couplers and switches is presented. The model is used to evaluate a large modular switch optical network that provides the capability of adapting easily to changes in network traffic requirements. The network dimensions are shown to be limited by the optical crosstalk in the switch matrices and by the polarization dependent loss in the optical components.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Novel acoustically tuned fibre laser

A polarisation diverse, dual output, linear travelling wave fibre laser has been designed and tested and found to be tunable over a continuous spectrum of nearly 18nm using a single-stage tunable acousto-optic filter as the wavelength selective element.

Wavelength selective optical logic and interconnects

A wavelength selective optical logic (WSOL) element that uses monolithically integrated wavelength selective optical input and output elements is described. Input optical signals are detected by photothyristors situated in an optical cavity which provides a highly selective response of a wavelength determined by the fabrication process. Output signals are generated by vertical cavity surface emitting lasers, whose lasing wavelengths can also be specified during the fabrication process. A vertical integration of these input and output elements that is suitable for wavelength selective optical logic and wavelength selective optical interconnect applications is proposed. The proposed circuitry is easily cascadable so that arbitrarily complex optical logic functions can be performed by WSOL devices in series. Several of the possible logic functions are described, including OR and AND gates, an adder, and a flip-flop. >

Optimization of X-ray emission from a laser-produced plasma in a narrow wavelength band

The X-ray emission from laser-produced plasmas at an X-ray wavelength of approximately 10.4 nm was measured for Al and Gd target materials. The laser power density on the target surface was varied between 1.5 × 1010 and 3 × 1012 W/cm2 to obtain different electron temperatures. The output from the plasma was measured using an X-ray reflecting Pd-C multilayer coating as a wavelength-selective element and a diamond photoconductive detector. The emission at 10.4 nm is strongest at the low end of the power density range investigated. A strong increase is found for Al targets due to a contribution of line radiation, which is not present in the Gd plasmas. The measured conversion efficiency for Al plasmas was (4.5 ± 1)% in a 3% bandwidth at an X-ray wavelength of 10.4 nm.

Intracavity doubling of CW diode-pumped Nd:YAG lasers with KTP

Intracavity-doubled lasers exhibit amplitude fluctuations driven by a combination of two nonlinearities: sum generation and spatial hole burning. Optimizing the cavity polarizations to minimize sum generation does not consistently eliminate the oscillations. Elimination of spatial hole burning prevents oscillations over a much larger range of operating conditions. The system is still bistable however, and can suffer abrupt changes in power due to mode hops. This can be eliminated with an etalon or other wavelength selective element.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mirror-folded polarization-independent wavelength filter

A 1.55- mu m polarization-independent optical bandpass filter with a 3-dB bandwidth of 6 AA and a tuning range of at least 100 AA is demonstrated. The photonic circuit of the filter consists of a waveguide TE-TM mode splitter, two parallel electrooptic TE-to-TM, TM-to-TE mode converters as the wavelength selective element, and a reflective mirror at the far end of the crystal. The circuit can be viewed as a mirror-folded version of the polarization-independent filter. It is shown that by passing the light two times through the narrowband mode converters, the filter bandwidth can be reduced by about a factor of two compared to a conventional single-pass filter of the same length. A novel tunable mode converter structure is also demonstrated that allows coherent in-phase mode conversion during the two passes through the mirror-folded filter. >

Widely tunable optical‐fiber ring laser using high‐performance traveling wave amplifier

AbstractA widely tunable optical‐fiber ring laser is fabricated using a traveling wave amplifier (TWA) and an optical‐fiber loop as the gain medium and the external cavity. The wavelength tuning in the wide range of more than 100 nm is obtained using a high‐performance TWA and a low‐loss external cavity.The TWA is made by anti‐reflection (AR) coated on both facets of a VIPS (V‐grooved inner stripe laser on p‐substrate) laser with residual reflectivity less than 10−4∼ 10−6. The length of the TWA is optimized to obtain high gain peak. The gain distribution of more than 16 dB in the wavelength range of 100 nm and the high gain peak of 30 dB are achieved. As the external cavity structure, the use of a diffraction grating and a bandpass filter, as the wavelength selective elements, are investigated and compared with each other.Hence, it is found that when the filter is used, the wavelength tuning range is about 10 nm wider than that of the grating and the fiber output power over 14 mW is achieved. The laser exhibits a very narrow linewidth of 15 kHz (longitudinal mode) and is believed to be a very useful source in optical communications if it is made to become a single‐mode one.

An electronically tunable fiber laser with a liquid-crystal etalon filter as the wavelength-tuning element

Wavelength-tunable lasers in the near infrared have a wide range of applications for fiber-based lightwave systems. A description is given of a tunable erbium-doped fiber laser using a liquid-crystal etalon filter (LCF) as the wavelength-selective element. The laser is continuously tunable over a range of 45 nm (1523-1568 nm) with a voltage of 2.1-3.3 V applied to the LCF, and operates single-mode with a very narrow linewidth (<100 kHz). The experiment demonstrates the potential of the laser as compact laser source that can be tuned over a very large wavelength range with an IC-compatible voltage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multibranch frequency-selective reflectors and application to tunable single-mode semiconductor lasers

Multibranch reflectors (MBRs) are proposed as a flexible wavelength-selective element for optical integrated circuits generally and for tunable single-mode lasers specifically. The undesired recurring peaks of reflectivity obtained with two-branch MBRs are spread out in the spectrum by using three or more branches. Design relations are given for the lengths of an arbitrary number of branches, for the selectivity near the peak response, for the wavelength interval to the nearest undesired peak, and for tuning changes in the various branches. It is shown that an MBR is not sensitive to amplitude differences of the order of 20% between the branches, but requires phase control in order to achieve tuning to a specific wavelength. The effects of semiconductor gain variation with wavelength are obtained from a rate-equation solution including MBR. By changing the semiconductor temperature (gain peak) at the same time as the MBR is tuned, a broad range of tuning without jumps is achievable.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

InGaAsP Y-branch grating demultiplexer

We report on the fabrication of a passive Y-branch wavelength-division demultiplexer with InGaAsP/InP rib waveguides. The wavelength-selective elements are Bragg reflection gratings on top of the two output ribs of the branch. A channel spacing of 13.5 nm in the 1.5?m region and a crosstalk attenuation of more than 18 dB for TE-polarised light were achieved.

Optically pumped tunable mode-locked Si-doped GaAs laser

Mode-locked operation of Si-doped bulk GaAs in external cavity was achieved by synchronous pumping with a Kr+ laser at 647.1 nm. High beam quality and peak powers of up to 3.3 W are unique features of this laser. The spontaneous spectrum is narrower than those of dyes, allowing a stabilized single-frequency operation with fewer wavelength selective elements, while tunability over a range of 300 Å was achieved by varying the temperature.

Cavity configuration in a dye laser for dispersion on the two output beams

A novel and simple laser cavity configuration is proposed in which the two output beams of the active medium are dispersed by only one wavelength selective element. This configuration permits complete elimination of background superluminescene reinjection in active medium, additional linewidth narrowing and extention of the spectral tuning range. An experimental check on the example of the second harmonic of a YAG:Nd 3+ pumped dye laser is reported.

Wavelength-selective Beam Splitters with Minimum Polarizing Effects for Wavelength-division Multiplexing in Optical Communication Systems

A new method of designing dielectric edge filters for wavelength-selective optical tapping elements based on the beam splitter concept relies on the analysis of the envelope of the reflectance for the beam components oscillating normal and parallel to the plane of incidence in the passband of the filter. Despite the 45° angle of incidence of the beam, the strong polarizing effects usually encountered are almost entirely avoided for the two wavelengths that are to be demultiplexed. A number of multilayer stack designs of the type S(H/2 L H/2) k S are described in which the ideal reflectance Rs = Rp = 0 is realized for the s and p components at the wavelength to be passed, while the desired value Rs≈Rp≈1 is realized for the wavelength to be rejected.

Frequency-locking of a CW dye laser to absorption lines of neon by a Faraday filter

Single-mode CW oscillations at absorption lines of neon from the 1s states to the 2p states were achieved by inserting a Faraday filter in an argon-laser-pumped dye laser cavity without any other wavelength selective elements. The oscillations at absorption lines were selected by choosing adequate values of the filling pressure of a neon discharge tube and a magnetic field strength. The oscillation frequency shifted with the increase of the magnetic field strength toward higher frequency in the center region and toward lower frequency on the wing of the absorption line, which was found to be due to the isotope effect. Good agreement was found between the experimental results and the theoretically calculated feature of the Faraday filter.

Competition between selected and nonselected modes in a multi-mode laser

Utilizing a simple previously introduced model for a laser emitting a broad homogeneous line, which takes account of mechanisms giving rise to mode coexistence, mode competition is studied for the case of one mode (or a small group of modes) being selected, by means of a wavelength selective element, out of the whole spectrum of a cw laser. It is shown that a critical value for the loss of the privileged mode ĝh 1 exists, in the sense that for ĝh 1 ⩾ η 1 the privileged mode completely quenches the remaining modes, while for ĝh 1 < η 1 the latter grow up and, hence, influence the privileged mode by mode competition. As a consequence, the slope in the intensity of the selected mode, as a function of its loss η 1, exhibits a distinct jump at the critical point. As will be shown in detail, from a measurement of this jump the effective strength of mechanisms responsible for mode coexistence, can be determined directly.