Low-loss passive alignment of single-mode fibers in low-temperature cofired ceramics using CO2 laser fabricated U-grooves

We report a step toward optoelectronic integration on low-temperature cofired ceramics substrates in the form of fiber alignment U-grooves. The precision of the CO2 laser machining of green state ceramic for this purpose is investigated. The groove-writing process with a speed of 1 mm/s was carried out in air at room temperature and ambient pressure. The process is to a large extent self-cleaning without any gas jet assist. By analysis of groove profiles after firing of a near-zero shrinkage green tape formulation, it is shown that the cutting accuracy is approximately 2 microm, which is at the fundamental limit set by the particle size (1-5 microm). We demonstrate low-loss butt coupling of <1 dB for single-mode fibers using the laser written U-grooves. The technique exhibits a potential for fabrication of low-cost fiber ribbon and fiber array connectors.     

Laser direct writing polymeric single-mode waveguide devices with a rib structure

A focused argon-ion laser beam is used on a spin-coated polymeric thin-film deposited upon a SiO2/Si substrate to polymerize the core for fabrication of Gaussian profile optical channel waveguides. A rib structure that allows only the fundamental mode to propagate even with its higher dimension and high-index contrast between the core and the cladding was fabricated. When the thickness of the core-index region outside the rib section decreases, the waveguide produces higher-order modes at the output. The waveguide reported here has cross-sectional dimensions and numerical apertures that match the single-mode fibers for efficient coupling. I used a mixture of two intermiscible acrylate monomers for the cladding and the core of the waveguides. The polymerization process and its dependent dwell time or scan speed and the laser power intensity are shown. I present the operational characteristics of directional couplers using a rib waveguide structure with a core-cladding index difference.     

Slot optical waveguide usage in forming passive optical devices

We have reviewed the work on SOI slot optical waveguides followed by our work. In a slot waveguide structure, light can be confined in a low index slot guarded by high index slabs. Slot structures are being used in forming complex structures; such as ring resonator circuits. The increased round trip in ring resonator circuits signifies the importance of dispersion calculations. We did analytical and numerical investigations of slot structures' dispersion characteristics. Our dispersion tuned slot structures can help in reducing the dispersion effects on optical signal, which will in turn improve the efficiency of light-on-chip circuits. Since the advent of slot optical waveguides, SOI based slot optical waveguides have been under consideration. It has been found that glass based slot optical waveguide structures with relatively low refractive index contrast ratio can also play an important role in forming complex nano-size optical devices. We made use of power confined inside low index slot regions for a double slot structure. Opto-mechanical sensors have been proposed based upon: (a) variation in power confined inside low index slot region due to the movement of central high index slab under the action of external force (temperature, pressure, humidity, etc). vide Chinese Patent No. ZL 200710176770.1, 2007 (b) variation in power confined inside low refractive index slot regions due to movement of both slots under the action of external force (temperature, pressure, humidity, etc).     

Model-based far-field alignment algorithm for Gaussian beamlike single-mode optical devices

Single-mode device-to-fiber alignment automation is usually achieved with a classical mathematical optimization approach. We present a different approach, which is based on the identification of particular intrinsic characteristics of the coupled optical power and on estimating residual axial, transverse, and angular misalignments in the far field. Such a model-based approach is based on the physical nature of the optical coupling phenomenon and can replace or be complementary to already known automated alignment methods. An alignment algorithm is described and validated experimentally using two single-mode fibers as Gaussian beam emitter and receiver.     

Polarization state fixer composed of passive optical devices

We investigate a polarization state fixer that produces light with an arbitrary desired polarization state and constant power from an arbitrary elliptically polarized input light whose principal polarization axis fluctuates randomly. An example of such a device composed of a quarter-wave plate and a polarizer is proposed, and its characteristics at wavelengths of 633 nm and 1550 nm are demonstrated. We conclude that we cannot obtain a passive device that produces fixed-axis, linearly polarized light with a constant power level from an elliptically polarized light with a varying elliptical parameter.     

Some characteristics of an extremely-short-external-cavity laser diode realized by butt coupling a Fabry-Perot laser diode to a single-mode optical fiber

When butt coupling a Fabry-Perot laser diode to an extremely closely spaced waveguide (separation less than or equal to a few times the Rayleigh range of the laser beam), there is a trade-off between the optimal power coupling and the variation of the coupled laser diode's operational characteristics. Changes in the butt-coupling configuration parameters influence the coupling efficiency, as well as the strength of the feedback into the laser diode. Using a previously reported phenomenological model that treats the butt-coupled laser diode as an extremely short external-cavity (ESEC) device, we quantitatively describe how the butt-coupling parameters can be used to control the output power, threshold current, wavelength, and relative intensity noise of the ESEC laser diode. Our analyses are supported by experimental results. The importance of choosing the correct coordinate plane for evaluation of the overlap integrals that are used in the model is also discussed.     

Long-period grating fabricated by periodically tapering standard single-mode fiber

We fabricated an asymmetric long-period grating (LPG) by periodically tapering a section of standard single-mode fiber using a resistive filament heating. The LPG exhibits large peak transmission attenuation of -30.31 dB with only 22 periods in a 1.0 cm long optical fiber and possesses unique characteristics for sensing applications. The bending and strain sensitivities are 1.74 nm m and 1.11 pm/mu epsilon, respectively. The polarization dependent loss is large, up to 11.65 dB, which is caused by an asymmetric index profile in the cross section of the tapered LPG.     

Tunable single-mode operation of a pulsed optical parametric oscillator pumped by a multimode laser

High-quality single-longitudinal-mode (SLM) tunable signal radiation is generated by a pulsed optical parametric oscillator (OPO) pumped by a compact, inexpensive multimode laser. The OPO is based on periodically poled lithium niobate (PPLN) in a ring cavity that is injection seeded at its resonated signal wavelength by a single-mode tunable diode laser. Accurate control of the OPO cavity length and crystal temperature ensures a continuously tunable SLM signal output frequency range of >7.5 THz (>250 cm(-1)); the corresponding idler output remains multimode. High-resolution molecular spectra are recorded to verify OPO performance at wavelengths of ~1.55 mum. The observed signal optical bandwidth of 相似文献   

Homogenous concept for the coupling of active and passive single-mode devices by utilizing planar gradient-index lenses and silicon-V grooves

A new concept for a common interface between passive and active single-mode devices is proposed. The submicrometer alignment accuracy necessary for efficient coupling of single-mode devices is extended to the range of some 10 mum by beam expansion with planar gradient-index microlenses; the increased angular sensitivity is satisfied by the use of planar surfaces. The imaging system is used off axis, resulting in a suppression of backreflections in the range >60 dB. Of many possible variations of components (fibers, waveguides, optoelectronic integrated circuits, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodiodes), the coupling of fibers and waveguides is examined in detail. Expected coupling efficiency and sensitivity to lateral misalignment are calculated by use of a modified beam-propagation method. In this way, the overall performance of the connector can be compared with existing connector concepts, and the feasibility of the concept is proven. Experimental results for the fiber-fiber connector are given.     

Ultrafast nonlinear optical effect in CdTe-doped glasses fabricated by the laser evaporation method

The laser evaporation method is an attractive technology to synthesize composite materials. We tried to apply the laser evaporation method on fabrication of CdTe-doped glasses for the first time. CdTe microcrystallites embedded in SiO₂ films were confirmed by transmission electron microscope images. The third-order nonlinear susceptibility χ⁽³⁾ and the decay time τ of CdTe-doped glasses were measured by three-beam forward type degenerate four-wave mixing. The maximum value of χ⁽³⁾ was estimated 4.2 x 10^-7 esu when the absorption coefficient was 6000 cm^-1. From the limitation of pulse duration of 5 ps, τ was not exactly measured but imagined to be shorter than 10 ps, which was much faster than the other semiconductor-doped glasses ever reported. The figure of merit defined as χ^(3)/τ is probably larger than 7.     

Highly efficient wideband continuum generation in a single-mode optical fiber by powerful broadband laser pumping

By pumping a single-mode optical fiber with a powerful broadband nonselective dye laser, we obtain a high-efficiency wideband continuum (530-930 nm) with nonlinear conversion efficiency exceeding 90%. Experimental conditions for a coherent regime of broadband stimulated Raman scattering are created, which in combination with the broadband self-phase modulation and the four-photon parametric processes leads to a spectral broadening and to the continuum formation. The influence of the pump laser spectral linewidth on the nonlinear conversion efficiency is analyzed and investigated by comparative experiments at narrow-band and broadband laser excitations.     

一种微型转子的激光加工和光致旋转

利用单束强聚焦激光产生的光学力可以驱动微型器件,具有无机械接触和无需导线等优点,为微型机电系统提供了一种新型的驱动方式。在自行研制的飞秒激光微细加工系统中,采用一种新型的丙烯酸酯紫外光固化树脂,通过双光子聚合加工出直径6μm的万字形微转子。利用光镊装置实现了微转子的俘获,并在激光功率50mW时实现了转速为200rpm的光致旋转。微型转子的光致旋转为实现微机械马达提供了一种有效手段。     

Mode-field diameter of single-mode optical fiber by far-field scanning

I use the direct far-field method to measure the mode-field diameter of a single-mode fiber with an expanded uncertainty of 30 nm, with a coverage factor of 2. For a step-index fiber with a mode-field diameter of approximately 9 mum, the major sources of uncertainty are nonlinearity in the electronics, angular errors and scattered light in the apparatus, and the polarization and noncircularity of the mode of the fiber. The paper concludes by showing an inconsistency in the derivation of the far-field expression for mode-field diameter.     

Large-mode-area leaky optical fiber fabricated by MCVD

A large-mode-area single-mode optical fiber based on leaky-mode filtering was prepared by a modified chemical vapor deposition (MCVD) technique. The fiber has a leaky cladding that discriminates the fundamental mode from higher-order modes. A preliminary version has a 25 μm core diameter and 0.11 numerical aperture. A Gaussian-like mode with 22 μm mode field diameter was observed after 3 m propagation, in agreement with modeling.     

Multiwell laser heterostructures fabricated by liquid-phase epitaxy

A methodology has been developed for growing InGaAsP/InP multiwell laser heterostructures by liquid-phase epitaxy. Depth profiling using a secondary ion mass spectrometer was used to investigate the distribution profiles of the composition of multiwell laser heterostructures. Liquid-phase epitaxy was used to fabricate InGaAsP/InP multiwell laser heterostructures with active regions having emission wavelengths of 1.3 and 1.55 μm and their radiative characteristics were studied. Pis’ma Zh. Tekh. Fiz. 24, 61–67 (November 12, 1998)