Change In Optical Power Research Articles

Feedback Coupling Module of Optical Transceiver Using Projection Core Fiber

We propose a unique type optical transceiver with a lens position feedback control system to preserve a high optical coupling efficiency between a laser diode and a single-mode fiber (SMF). In this method, accurate alignment or welding is eliminated in the assembly of optical components. This system is also free from a long-term optical power change caused by optical component displacement with environmental variation in temperature and oscillation. In this study, we investigated an optical coupling system, where the position of an optical axis is tuned by active feedback control detecting the optical diffractive pattern from a projecting core fiber (PrCF). By this method, the optical transceiver enabled a lens position control of less than 0.3 µm in a noise environment of 100 Hz–0.25G (G-forces), and was able to maintain optical transmission.

Submersion Sensor Using Bending-Sensitive Fiber

A sensor using bending sensitive fiber (BSF) was studied for real-time long-distance sensing of submersion. The structure of the submersion sensor effectively used the relationship between buoyant force and bending loss of the BSF. A three-dimensional finite-difference beam propagation method (3D FD-BPM) was used to select the bending dimension of the proposed submersion sensor. The operation of the submersion sensor utilizing the BSF was also investigated using 3D FD-BPM. As results of experiments, the submersion sensor fabricated showed a change of optical power from -17 to -1 dB at 1550 nm when the selected sensing region was submerged. In addition, the BSF was easily connected to a single mode fiber (SMF) by fusionsplicing. The BSF exhibited a -1 dB loss when connected to a SMF at both ends.

Luminescence degradation of InGaN/GaN violet LEDs

The changes of optical output power and electrical property of InGaN/GaN violet light-emitting diodes (LEDs) with different indium compositions have been investigated, under injection current densities of 26.5 and 79.5 A/cm 2. When injection current density was 26.5 A/cm 2, output power of LEDs with low indium composition (2%) degraded more rapidly than the ones of 10% indium inside. At a large injection level of 79.5 A/cm 2, the difference in optical power degradation between LEDs of 10% and 2% indium composition became small. A discussion based on the results of current–voltage curves , L– I curves, as well as optical power degradation with stress time indicates that LEDs with 10% indium composition have better performance than LEDs with 2% indium composition. It is believed that the indium enhancement of radiative recombination helps preventing defect generation during electrical stress.

Refractive Change Induced by the LASIK Flap in a Biomechanical Finite Element Model

To study the effect of varying four parameters on the refractive change induced by the LASIK flap. Using a variety of patient-specific data such as topography, pachymetry, and axial length, a finite element model is built. The model is used in a non-linear finite element analysis to determine the response and change in optical power of the cornea as a function of a material property of the cornea (corneal elasticity), flap diameter and thickness, and intraocular pressure. The central flattening or hyperopic shift occurred atop the flap in all four of the simulated eyes tested with the creation of the LASIK flap. Of the four parameters tested, modulus of elasticity (Young's modulus) had the most profound effect on the results of hyperopic shift, varying from <0.5 diopters (D) in the least elastic (stiffest) cornea to >2.0 D of hyperopic shift in the most elastic cornea. The depth of the lenticular cut was the second-most significant parameter tested varying from 0.24 D at 100 microns to 1.25 D at 275 microns of depth. Varying intraocular pressure demonstrated less difference, and varying corneal flap diameter demonstrated the least difference in induced refractive change on the model. The hyperopic shift was noted to be greater in hyperopic than in myopic eyes (simulated) tested. Three-dimensional finite element analysis modeling of actual patient data could lead to a better understanding of the biomechanical response of corneal tissue to the lenticular flap creation and potentially for ablation patterns produced by the excimer laser. Understanding these biomechanical responses may lead to greater predictability and improvement of visual outcomes.

Microstructure fibers for gas detection

The paper deals with experimental investigation of capabilities of microstructure fibers (MSFs) for evanescent-wave chemical sensing. It presents results on the sensitivity of MSFs of a “grapefruit” type to gaseous toluene in mixtures with nitrogen which flow through the fiber holes. The sensitivity is determined on the basis of changes of the output optical power from the fiber caused by refractive-index changes of the fiber cladding induced by toluene and determined at 670 nm. Specific changes of spectral absorbance due to C–H overtones of toluene in a range of 1600–1800 nm are also utilized. Results obtained both with unmodified fibers and with fibers modified by the application of methyltriethoxysilane-based xerogel layers onto the hole walls are presented. The results show that fibers modified by the xerogel layers are sensitive to gaseous toluene in the cladding holes. Changes of the output power can also be determined with fibers unmodified by the xerogel layers, namely for saturated toluene mixtures. The presence of toluene in the detection layers was proved by spectral measurements.

Water sensor using macrobending-sensitive fiber for real-time submersion monitoring

A fast reusable water sensor for long-distance real-time submersion monitoring was fabricated using a macrobending-sensitive fiber (MSF). The proposed water sensor consists of floating matter, periodic macrobending deformers, and a MSF. In this structure, the floating matter moves up and down according to the buoyant force of water, thereby controlling the bending loss of the MSF and allowing the proposed sensor to detect submersion. A basic bending experiment was conducted using a MSF and macrobending deformer, and the results used to fabricate an efficient water sensor. In contrast to existing sensors where the optical loss increases in the case of submersion, the optical loss of the fabricated sensor decreases due to the buoyant force when the selected area is submerged. As such, the fabricated sensor is able to transmit submersion information further than sensors that detect submersion by increasing the optical loss, and it is unaffected by environmental factors, such as humidity and pollutants in the water. The proposed sensor detects submersion by monitoring a 16dB optical power change of 1550nm, and the change in the optical power of the fabricated sensor is only affected by the buoyant force. In addition, the proposed water sensor quickly returns to its initial state when the water disappears, and the insertion loss when it is connected to a single-mode fiber (SMF) at both ends using a connector is only −1.2dB at 1550nm.

Temperature-insensitive fiber Bragg grating liquid-level sensor based on bending cantilever beam

A temperature insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflection optical power change with the liquid level and they are insensitive to spatially uniform temperature variations. For a liquid level variation of 500 mm and a temperature range from 0/spl deg/C to 80/spl deg/C, the measured liquid level fluctuates less than 2% without any temperature compensation. By optical power detection via a pin photodiode, the liquid-level sensor avoids complex demodulation process and potentially costs low.

All silica S-band double-pass erbium-doped fiber amplifier

Double-pass (DP) and single-pass (SP) erbium-doped depressed cladding fiber amplifiers designed for S-band operation are evaluated under changes of the input optical power, pumping power, and fiber bending radius. The DP configuration employs the usual combination of a circulator and a Faraday rotator mirror while the SP is based on the copropagating scheme. The amplifiers were characterized in terms of gain and noise figure. It is demonstrated that the DP topology shows much improved gain performance compared to the SP configuration although the noise figure is slightly degraded by counterpropagating amplified spontaneous emission.

Intensity-modulating characteristics of a laser diode subjected to optical injection

We have found that the optical power of a laser diode (LD) does not change with the injected light intensity that is modulated when its injection current is at some specific values. The amplitude of optical power change of the LD varies periodically with the increase of the injection current. It is made clear through theoretical analysis that these phenomena are caused by gain compression and interband carrier absorption of the LD that depend on longitudinal mode competition, bandgap-shrinkage effects, thermal conduction, and so on. Our experimental results make it easy to eliminate optical power change of LDs. We only need to choose a proper value of the injection current.

Corneal power, thickness, and stiffness: Results of a prospective randomized controlled trial of PRK and LASIK for myopia

To compare the short-, medium-, and long-term changes in corneal optical power and corneal aberrations, central corneal thickness, and corneal "stiffness" assessed by pneumotonometry readings in patients having laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) for myopia. Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark. One eye of each of 45 patients with myopia ranging from -6.00 to -8.00 diopters (D) (spherical equivalent spectacle refraction [SER]) was randomized to LASIK (n=25; mean SER -7.12 D +/- 0.57 [SD]) or PRK (n=20; mean SER -6.91 +/- 0.57 D). Data were collected prospectively before and 1, 3, 6, 12, and 36 months after surgery. Measurements included corneal topography (TMS-1, Tomey), corneal thickness (ultrasound pachymetry), and apparent intraocular pressure (IOP) (pneumotonometry). Retreatments were not performed during the first year, and retreated eyes were excluded from the 3-year follow-up. Changes in corneal power and aberrations, thickness, and apparent IOP were calculated in a pair-wise manner for 3 time periods: short term (preoperative to 1 month after surgery), medium term (1 to 12 months after surgery), and long term (1 to 3 years after surgery). In the short term, corneal power decreased equally in LASIK and PRK eyes. Spherical aberrations and coma-like aberrations increased equally, while corneal thickness decreased significantly less in LASIK eyes than in PRK eyes. The apparent IOP decreased more in LASIK eyes than in PRK eyes. In the medium term, corneal power increased significantly in both groups. Spherical aberrations decreased significantly in PRK eyes but not in LASIK eyes. From 1 to 12 months, corneal thickness increased more in PRK eyes than in LASIK eyes. During this period, the apparent IOP increased significantly in LASIK eyes. In the long term, corneal power and corneal aberrations did not change significantly in either group. Corneal thickness increased slightly but significantly in both groups. The apparent IOP increased significantly more in PRK eyes. Differences between LASIK and PRK related to time-dependent events affecting corneal shape and structural integrity were present. Peripheral changes in flap hydration in LASIK eyes and epithelial and/or stromal thickening in PRK eyes appeared to be the most important factors in optical power changes in the first year after treatment. The changes in apparent IOP suggest that some interlamellar healing occurred during the first year after LASIK. After LASIK and PRK, corneal bending stiffness seemed permanently decreased, although some restiffening may occur in PRK eyes in the long term.

Optical fiber relative-humidity sensor with polyvinyl alcohol film.

We describe a fiber-optic relative-humidity (RH) sensor comprising a moisture-sensitive overlay on a single-mode side-polished fiber. The hygroscopic polymeric material deposited was polyvinyl alcohol (PVA), which proved to have good adherence and stability. The film reached a fast equilibrium with atmospheric moisture (in less than 1 min), inducing changes in the output optical power of approximately 10 dB for the 70%-90% RH range. To yield a low-cost device, single-mode standard communication fibers were used; therefore all the components of the sensor can be commercial, mass-produced telecommunication devices. The experimental results obtained are consistent with the expected behavior of the system; the output power decreases because of losses in the polished region of the fiber as the refractive index of its external medium approaches the fiber core value. Because the external medium is PVA film, its refractive index changes in response to its water content.

Faraday효과를 이용한 클램프형 광-전류 변류기의 특성 및 분석

FD10 유리를 이용한 클램프형 광전류 센서를 제작하였다. 대칭형 구조로 이루어진 2조각의 FD10유리를 이용하여 제작하였으며, 센서헤드 내부에서 반사시에 위상차가 발생하는 것을 방지하기 위해 정확히 임계각으로 광이 진행하도록 구조를 설계하였다. 제작한 광-전류 변류기 헤드를 이용하여, 0-1,000 AT 까지의 전류를 측정하고, 빛의 입사각에 따른 광의 손실, 입사광의 편광회전에 따른 광출력변화, 온도에 따른 출력의 변화 및 장시간 전류 측정 등에 대한 실험결과를 제시하고 이에 대한 분석을 통해 제작된 광전류 변류기 헤드의 전류계로서의 가능성을 입증하였다. We manufactured a clamp-type optical current transformer (COCT) head using FD10 glass. It was manufactured of two parts of FD10 glass with symmetrical structure and was designed so that light propagates along the critical angle in order to avoid a phase difference with the light within the sensor head at reflection. Also, we measured and analyzed the current of conductor from 0 to 1,000 AT, change of optical power with incidence angle of light, temperature and polarization of light, long-term current measurement using COCT head, and demonstrated the feasibility of manufactured COCT through those experiments.

Detection of aromatic hydrocarbons in air and water by using xerogel layers coated on PCS fibers excited by an inclined collimated beam

This paper deals with experimental results on the sensitivity of silica optical fibers coated with detection xerogel membranes to benzene and toluene both in gaseous mixtures and in aqueous solutions. For this purpose thin polysiloxane and methyl-group-doped polysiloxane xerogel membranes are applied on straight segments of PCS fibers. The interaction of these membranes with hydrocarbons is investigated on the basis of changes of the output optical power from the fibers excited by an inclined collimated beam. The results obtained show that the hydrophobic methyl-group-doped xerogel layers exhibit higher sensitivity to hydrocarbons both in the gaseous phase and in solutions. The detection limits are about 230ppmvol. for toluene in air and about 9mg/l for toluene in water. Both the membranes show lower sensitivity to benzene than to toluene.

Athermalizing Refractive Optics with Fluid Lenses

ABSTRACTAstronomical optics may encounter a wide range of nighttime temperatures (∼−10°C to +20°C) at mountaintop observatories. Complex refractive optics used in high‐performance spectrographs and focal reducers may perform poorly at temperature extremes unless special care is taken in their design. Refocusing will not always restore image quality, and thermally induced focal length changes may introduce troublesome image motion. We describe the techniques that we have used to predict the thermal behavior of the Binospec Spectrograph, an instrument under development for the converted Multiple Mirror Telescope. This thermal analysis must account for (1) the change in optical power due to thermal expansion of the optical elements, (2) thermal variations in the refractive indices of the optical elements, and (3) element respacings due to the interplay between the thermal expansions of the optical elements and cell materials. Binospec’s multiplets are fluid coupled to reduce the reflection losses that would occur at glass‐air surfaces; to athermalize the Binospec optics, we form weak lenses in the optical coupling fluid within multiplets. The large variation of the coupling fluid’s refractive index with temperature allows these weak fluid lenses to correct thermal changes in the optical elements and cell. This athermalization technique is attractive because it introduces no additional mechanical complexity.

Chaotic self-pulsation and cross-modulation in a wavelength-selective external-cavity laser diode

Chaotic self-pulsation in a single wavelength external-cavity laser diode is observed. It is shown that the self-pulsation is caused by interdependencies between the optical output power and the compound cavity losses through the refractive index of the laser diode material. Refractive index changes result in a detuning between the externally selected wavelength and the weak internal-mode structure of the anti-reflection coated laser diode. This detuning is directly related to the compound cavity losses. On the one hand, a change in optical output power results in a change of the refractive index via the carrier density. On the other hand, it results in a change of refractive index via temperature changes. Compared to the carrier induced refractive index change, the temperature induced refractive index change is opposite in sign, a factor of /spl sim/10/sup 2/ smaller and slower. The switch-on and switch-off time of the self-pulsation is governed by the carrier life time. The repetition rate of the self-pulsation is governed by the thermal time constant and is in the megahertz region. Cross-modulation resulting from the thermal induced refractive index change is demonstrated. In a two-wavelength double external-cavity laser diode, optical power at one wavelength effects the optical power at the other wavelength. This cross-modulation is shown to be related to previous experiments on a laser neural network. A novel technique is introduced to measure the thermal impedance of a laser diode that is based on the cross-modulation.

RF response of analog optical links employing optical phase conjugation

The RF transfer function of analog optical links employing optical phase conjugation (OPC) for the compensation of the carrier suppression effect is investigated theoretically. It is well known that the ultimate performance of the OPC technique depends on several system parameters such as fiber span lengths, dispersion characteristics, input optical powers, or optical transmitter chirp. The influence of these parameters on the RF system response is studied by means of simulation, showing that the main degradation of the equalized response is due to the joint action of nonlinear effects and asymmetric optical power change along the fiber spans.

Domain structure in the ferroelastic langbeinite K2Cd1.6Mn0.4 (SO4)3

The ferroelastic phase transition in K2Cd1.6Mn0.4 (SO4)3 solution was investigated by optical microscopy method. The existence of the permissible domain structure in those compounds in whole temperature region below 23F222 second order phase transition was found. It was shown that in the crystals which belong to the isolated point, the domain walls are permissible due to enantiomorphic twinning. The determined orientation of domain walls is {110}. The investigation of the topography of the optical activity shows the change of optical rotary power in some regions in 23 phase of K2Cd0.4Mn1.6 (SO4)3 crystals. Obtained results are discussed on the base of thermodynamic potential and prototype phase with point group symmetry 43m.

Spatial beam switching and bistability in a diode ring laser

We report bistable switching of the output direction in certain triangular diode ring lasers. These lasers operate unidirectionally at large drive currents, with up to 98% of the output power emerging from either the clockwise or the counterclockwise direction. The preferred direction can switch back and forth, with a large hysteresis loop, as the drive current is varied. Up to 20 mW of optical power changes direction at each switch. We propose an explanation based on the theory of two-mode competition via gain saturation.

Indirect optically injection-locked oscillator for millimeter-wave communication system

A millimeter-wave optically injection-locked oscillator has been designed and fabricated. It represents the first millimeter-wave hybrid transistor oscillator locked to a long-wavelength optical signal. The oscillator could be used as a photoreceiver in remote base stations in future picocellular communication systems employing fiber-optic backbones; its high gain (output relative to input locking signal) and relative flatness in output power may make it attractive compared to simple millimeter-wave amplifier configurations. Measurement results show the output signal exhibits little variation (less than 0.7 dB) with input optical power changes of 6 dB. A locking bandwidth of 2.6 MHz has also been achieved.

Effect of Doping Silica Gel Layers with TiOTi-Chains and Cu2+-Ephedrine on the Sensitivity of the Layers to Gases

In this paper the interaction of polysiloxane and TiOTi-doped polysiloxane gel layers containing Cu2+-ephedrine (CuEP) with carbon dioxide, nitrogen and water is investigated. This interaction is studied through changes of the output optical power from an optical fiber coated with the investigated gel layer. The layers are prepared with sols based on tetraethoxysilane and titanium isopropoxide, isopropanol, acetylacetone and Cu2+-ephedrine by the repeated dip-coating method. The applied gel layers are dried at 70°C.