Optical Power Variation Research Articles

Switching time in optically bistable injection-locked semiconductor lasers

Switching between states in a dispersive bistable injection-locked slave laser has been theoretically investigated. We show that the switching can be achieved by relatively small and short (≈10-50 ps) variation of the master laser injection power or frequency, which, besides the variation of the slave laser optical power, leads to significant variation of its photon phase (≈5π/6). By using an analytical model, we calculate the switching time dependence on the magnitude of the injection power and the frequency detuning variation.

Modeling and Analysis of a Wavelet Network-Based Optical Sensor for Vibration Monitoring

In this paper, we present a wavelet network (WN)-based optical position sensor for vibration monitoring using a quad-cell photodetector array. The proposed system uses a He-Ne laser source whose Gaussian beam impinges on the photodetector array. The optical power distribution from the photodetectors is acquired and fed to a position detection system, which maps the power distribution to the x-y position of the laser beam center. The position detection system uses a WN for function approximation to yield the correct mapping. The advantage of the WN is its generalization property. The network can be trained using a small size lookup table and, when properly trained, can provide a correct estimate of the laser position even if the power readings were not included in the training set. An accurate theoretical model of the system was derived to simulate the optical power variation as the beam scans the photodetector array. An experimental setup was next developed to validate the theoretical model. The results obtained show the effectiveness of WNs to estimate the laser beam position for the purpose of vibration monitoring.

Adaptive Interrogation for Fast Optical Sensing Based on Cascaded Micro-Ring Resonators

An adaptive interrogation technique that employs integrated semiconductor micro-ring resonators (MRR) for fast-response sensing applications is proposed and numerically studied. The basic sensing scheme consists of two MRRs in an add/drop signal configuration; the first MRR plays the role of the measuring sensor, while the second one acts as a reference optical filter that converts any frequency shift induced in the spectral characteristics of the measuring sensor into optical power variations. The proposed photonic sensor has the potential to adjust its transfer function dynamically, due to the varying response of the MMRs to different operating conditions, exhibiting either an ultra-low resolution operation capable of detecting extremely small refractive index changes, or an operation with a wide dynamic range. Finally, we propose a more sophisticated approach for simultaneous interrogation that incorporates multiple MRR sensors, based on thermal heaters that modulate the response of each MRR sensor with different modulation frequencies. In contrast to the conventional interrogation techniques, the proposed configurations enable ultra-high sampling rates crucial for studying fast biochemical reactions, such as enzyme kinetics.

태양광 활용을 위한 효율적 LED 조명기구 설계 방안

LED is expected as an environmentally friendly next generation light source with its good reliability and long lifetime. The light sources for illumination have a variety of applications in the indoor and outdoor, and the variation of optical power and color rendering of the light source limits their applications. Therefore, it is necessary to research the LED lamp and its luminaire to minimize the variation of dynamic characteristics and to improve the color rendering due to that illuminating environment. Daylight is very good light source to human and can be used as primary or a secondary light source with benefits of energy, productivity and health.This paper presents the design method of LED lighting system to improve poor property in terms of CR(color redering) characteristic to use daylight effectively.

Influence of transmitter chirp and receiver imperfections on RF gain in short‐range ROMMF systems

AbstractTwo important effects that can lead to extensive detrimental effects in short‐range radio‐over‐multimode‐fiber systems are presented. The theoretical and experimental work shows transmitter chirp and receiver imperfections determining the degree of both RF gain variations as well as optical power variations. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:822–824, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25862

A Second-Order Feedforward Optical Power Control Scheme for Automotive VCSEL Drivers

This letter presents a feedforward optical power control scheme for automotive 150-Mb/s vertical-cavity surface-emitting laser (VCSEL) transmitters. The bias current exhibits a second-order dependence upon temperature, while the modulation current is provided with a piecewise linear compensation of temperature variations. The resulting VCSEL modulation performance was analyzed in detail and experimentally validated. Over the harsh automotive temperature range from -40°C to 105°C, a high extinction ratio was maintained despite very tight tolerances on pulsewidth distortion (PWD); the variation of the emitted optical power was measured to be less than 1.2 dB, while maintaining an extinction ratio better than 12 dB and a PWD less than ±2%.

Optimization of VCSELs for Self-Mixing Sensing

We have simulated the variations in optical output power from a vertical-cavity surface-emitting laser (VCSEL) subject to self-mixing feedback, which is very important for applications in sensing. In order to maximize the self-mixing signal for a given feedback we have optimized the epitaxial design of the VCSEL. The most important parameters are the number of quantum wells (gain), the number of Bragg mirrors (reflection), and the detector position.

Optical Signal Channel Power Stability in a Transparent Optical Network Using Large-Scale Photonic Cross Connects and Automatic Gain Control EDFAs

We discuss the change in the number of optical signal channels transmitted through wavelength division multiplexing links in a transparent optical network and report detailed measurement results of optical signal channel power variation in an experimental setup configured with realistic large-scale photonic cross-connect (PXC) switches fabricated using three-dimensional microelectromechanical system (3D MEMS) technology. The scale of the PXC-based network ranges from 100 to 300 km to simulate a realistic long-haul optical network using 100-km-long dispersion-shifted fibers and L-band erbium-doped fiber amplifiers with a high-speed automatic gain control circuit. The measurement results demonstrate the feasibility of stable operation of a transparent optical network by using these state-of-the-art technologies with proper parameter settings.

FABRICATION OF MACH-ZEHNDER INTERFEROMETOR BASED ON PLANAR WAVEGUIDE FOR THE APPLICATION OF BIOSENSORS

In this paper, designed and simulated Power Splitter (PS) integrated Mach-Zehnder interferometer (MZI) based planar waveguide devices (which is called here a PS-MZI). Moreover, we fabricated optical waveguide based on the PS-MZI for application to the biosensor. The integrated optical structure is sensitive to refractive index change induced due to the interaction of the evanescent field with an immobilized biological sample placed on one of the two arms of the interferometer. The PS-MZI sensor was preceded by a Y -junction, which splits the input power between the sensor and a reference branch to minimize the effect of optical power variations. The waveguide were optimized at a wavelength of 1550 nm and fabricated according to the design rule of 0.45 delta%, which is the difference of refractive index between the core and clad. The fabrication of PS-MZI optical waveguides was performed by a conventional planar lightwave circuit (PLC) fabrication process. The PS-MZI optical waveguides were measured of the optical characteristics for the application of biosensors.

Optical generation of microwave signal for FMCW radar applications

AbstractAn optically shifted oscillator has been designed in integrated technology and tested in order to use as a signal generator for frequency modulated continuous wave radar applications. Simulation and measurement results demonstrate a 200 MHz microwave frequency tuning range when the applied optical power varies from 0 to 100 mW at a wavelength of 800 nm. Illumination is applied on a photoconductive switch inserted within the circuit to achieve a quasi‐linear oscillation frequency shift with a linear variation of optical power. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 690–693, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24146

Locking bandwidth of optically injected Fabry–Perot semiconductor lasers for high injection strengths

The authors compare simulated results using a commercial software program with solutions of the rate equation (RE) and Fabry-Perot (FP) models of an optically injected FP semiconductor laser for high injection strengths (with injection ratios between the master and slave lasers above 0 dB). For linewidth enhancement factors (α-factors) of 0 and 3, the locking bandwidth is compared with the RE model and in the case of an α-factor of 0, the results are also compared with the FP model. It is found that the RE model for high injection strengths does not describe the locking bandwidth very well, whereas the FP model gives good agreement with our simulated results. Additionally, the longitudinal variation of optical power and electron concentration are shown for different injection strengths and different detuning values. For an α-factor of 3, the spatial variations of these properties become asymmetrical for higher injection strengths and with an increase in detuning, they are found to exhibit decreased fluctuations when the lower locking boundary is approached through the locking region. Therefore it is important to take spatial variation into account for high injection strengths. © 2008 The Institution of Engineering and Technology.

Wavelength Tuning of Vertical-Cavity Surface-Emitting Lasers by an Internal Device Heater

We have fabricated thermal-induced wavelength- tunable vertical-cavity surface-emitting lasers with a 780-nm emission wavelength that is tunable by using an internal device heater. A 5.36-nm tuning range was achieved by means of a 70-mA tuning current and a 3.5-mA driving current while maintaining continuous single-mode operation and the optical power variation is less than 2.5 dB in the tuning range. In addition, a multimode tuning range of 9.1 nm was achieved with a 90-mA tuning current and a 7-mA driving current.

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.

Control and Stabilization of bit-wise phase correlation in 160 (4 x 40) Gbit/s OTDM signal and its impact on transmission

Detail of control technique of bit-wise phase correlation in 160 (4 x 40) Gbit/s optical time division multiplexing (OTDM) signal using a phase-correlation monitor based on 1-bit delay asymmetric interferometers (AIFs) is described. The 1-bit delay AIF transforms a bit-by-bit optical phase discontinuity to an optical power variation, so that it enables to quantify the phase-jump between adjacent bits. By use of this unique technique, we experimentally demonstrated stable generation of bitwisely phase-controlled 160 Gbit/s periodical alternate-phase return-to-Zero (APRZ) signal in addition to other different modulation formats such as conventional RZ, carrier suppressed RZ (CS-RZ), pair-wise alternate-phase CSRZ (PAP-CSRZ) and pi/2-APRZ. And long term stability was observed with CS-RZ signal. Also, we show some experimental results of 120 km un-repeatered transmission using standard single mode fiber (SSMF) and then discuss the impact of bit-wise phase change on 160 Gbit/s OTDM transmission performance.

Nonlinear Polarization Rotation in Semiconductor Optical Amplifiers With Linear Polarization Maintenance

We propose a geometrical model based on the concept of dynamic eigenstates of polarization to describe the behavior of nonlinear polarization rotation (NPR) arising in semiconductor optical amplifiers (SOAs). The rotation axis with respect to either the bias current or the optical power variation is demonstrated on the Poincare sphere (PS), meanwhile a procedure to find the rotation axis is presented. Thus, the SOA-based NPR with linear polarization maintenance (zero polarization ellipticity angle) can be achieved experimentally. The rotation of polarization azimuth on the PS with respect to the bias current, the probe signal power, and the pump signal power variation is measured experimentally. The 180deg phase difference between the transverse electric and the transverse magnetic modes can be all achieved with linear polarization maintenance.

Fabrication of an Electro-Optical Temperature Sensor Based on Silicon Oxynitride Films Deposited by PECVD

We present the fabrication and characterization of an electro-optical temperature sensor based on silicon oxynitride dielectric films deposited by Plasma Enhanced Chemical Vapor Deposition at low temperatures (~300oC). The temperature sensor is basically a Mach-Zehnder interferometer such that a temperature difference between its arms produces a phase difference between the electromagnetic waves traveling through each arm thus originating a variation in the output optical power. In order to analyze the feasibility of this sensor, a temperature difference is imposed by applying a heating element in one of the arms. The results show that it is possible to control the optical device output through the adequate control of the heating element. Furthermore, the influence of heat propagation, multimode noise and methods to obtain monomode optical waveguides and self-sustained Mach- Zehnder structures are discussed in this work.

Feedback control and characterization of a microcantilever using optical radiation pressure

The authors describe a simple method for feedback regulation of the response of a microcantilever using the radiation pressure of a laser. A modified fiber-optic interferometer uses one laser to read out the position of the cantilever and another laser of a different wavelength to apply a force that is a phase-shifted function of that position. The method does not require a high-finesse cavity, and the feedback force is due solely to the momentum of the photons in the second laser. The feedback phase can be adjusted to increase or decrease the microcantilever’s effective quality factor Qeff and effective temperature Teff. The authors demonstrate a reduction of both Qeff and Teff of a silicon nitride microcantilever by more than a factor of 15 using a root-mean-square optical power variation of ∼2μW. Additionally, the authors suggest a method for determination of the spring constant of a cantilever using the known force exerted on it by radiation pressure.

Temperature-insensitive multipoint strain-sensing system based on fiber Bragg gratings and optical power detection scheme

This work presents a new temperature-insensitive multipoint strain sensor based on fiber Bragg gratings. A divider circuit at the post detection port compensates for optical power variation and thermal instability induced by the nonflatness of the source spectrum. Experimental results show a measurement resolution of /spl plusmn/0.35 /spl mu/S and a temperature stability of /spl plusmn/0.005% for no strain (/spl plusmn/0.48% for a strain of <400 /spl mu/S) in an example with two sensing points. A measurement linearity of /spl plusmn/0.17% is estimated in the range 0 to 350 /spl mu/S with no crosstalk.

Non-linear transmission effects in duobinary and dicode optical systems

This paper presents optical duobinary and dicode signalling, as alternatives to the binary format, in order to improve the transmission performance in the presense of non-linear effects in a dense wavelength division multiplex (WDM) optical system. Duobinary signalling is applied to an optical system to explore the reduction of stimulated Brillouin scattering (SBS) effects. Duobinary signalling suppresses the SBS effects, and an eye-opening improvement of 0.25 to 1.2 dB is achieved relative to binary transmission over a range of input power levels. An experimental study demonstrates that duobinary modulation suppresses the four wave mixing (FWM) products of a dense WDM system by a maximum of 3 dB. The suppression is maintained over a range of channel spacings. An investigation of the impact of fibre dispersion on FWM products under binary, duobinary and dicode modulation in a dense WDM system is then performed, with interchannel spacing and optical power variation. This leads to the development of a set of guidelines for the application areas, in which it is appropriate to use duobinary or dicode modulation in WDM systems as a means of mitigating the impact of FWM.

저 전류 및 고 효율로 동작하는 양자 우물 매립형 butt-coupled sampled grating distributed bragg reflector laser diode 설계 및 제작

본 논문에서는 저 전류 및 고 효율로 동작하는 planar buried heterostructure(PBH) 구조로 sampled grating(SG) distributed bragg reflector(DBR) laser diode(LD)를 처음으로 설계하고 제작하였다. 특히 활성층과 도파로층의 높은 결합 효율을 얻기 위해 건식 식각과 습식 식각을 같이 사용하여 결함이 거의 없는 butt-coupling(BT) 계면을 형성하였다. 제작된 파장 가변레이저의 평균 발진 임계전류는 약 12 mA로 ridged waveguide(RWG)와 buried ridge stripe(BRS) 구조로 제작된 결과 보다 두 배 정도 낮게 나타났으며, 광 출력은 200 mA에서 약 20 mW 정도로 RWG 와 BRS 보다 각각 9 mW, 13 mW 더 우수하게 나타났다. 그리고 파장 가변 영역을 측정한 결과 44 nm로 설계결과와 일치하였으며, 최대 파장 가변 영역 안에서 출력 변화 폭이 5 dB 이내로서 RWG 구조의 9 dB보다 출력변화 폭이 4 dB 적게 나타났다. 전체 파장 가변 영역에서 SMSR이 35 dB 이상으로 나타났다. We have fabricated and designed wavelength-tunable sampled grating distributed Bragg reflector laser diodes(SGDBR-LD) by using, for the first time, planar buried heterostructures(PBH). The diodes have low threshold current values and high-performance of laser operation. Growth condition using metal organic chemical vapor deposition(MOCVD) was optimized for the formation of a good butt-coupling at the interface. A maximum output power of the fabricated device was 20 mW under 200 mA continuous wave(CW) operation at <TEX>$25^{\circ}C$</TEX>. Average threshold current and voltage were 12 mA and 0.8 V, approximately. This output power is higher than those of ridge waveguide(RWG) and buried ridge stripe(BRS) structures by amounts of 9 mW and 13 mW, respectively. We obtained a tuning range of 44.4nm which is well matched with the target value of our design. The side mode suppression ratio of more than 35 dB was obtained for the whole tuning range. Optical output power variation was less than 5 dB, which is 4 dB smaller than that of RWG structures.