We used a system that exploits the Mach–Zehnder interferometer structure and Young’s double-pinhole interference principle to measure the three-dimensional topographies of small objects at high precision. Next, we performed phase profilometry to measure small objects and achieve a height measurement within a 10 × 10-cm area. The accuracy of the measurement system improved by 44.1%, and the measurement time was reduced by 63.2%.
Polarization sensitivity is an important factor that affects the interrogation of ultrasmall arrayed waveguide grating (AWG) for fiber Bragg grating (FBG) sensor. An ultrasmall 1 × 8 silicon-on-insulator (SoI) AWG with a core size of less than 530 μm × 480 μm is proposed in this study. This ultrasmall SoI AWG exhibits good transmission spectra and high polarization sensitivity. The increased channel numbers and tight structure increase the polarization sensitivity of AWG. Temperature interrogation experiments show that the FBG sensor interrogation is drastically affected when the effect of polarization sensitivity on the ultrasmall AWG is sufficiently large.
An electrically tunable grating coupler is designed and numerically demonstrated. With a lateral p-i-n diode embedded, the optical spectrum of coupling efficiency can be tuned with the applied voltage. To simulate the coupling spectra response with bias voltage, the optical simulation and electrical simulation are carried out with the commercial software Lumerical Finite-Difference Time-Domain Solutions and Synopsys Sentaurus TCAD. Due to the dual effect of spectrum shift and optical loss, the coupling efficiency spectrum can be greatly modulated. With a bias voltage of 2 V, the resulting spectrum shift is 47.5 nm and the peak coupling efficiency at the designed wavelength center can be modulated from 52% to 10%. In addition, the electrical tuning can be used for compensation of postassembly spectrum shift. The effects of the incident angle error and epoxy curing process are discussed. According to our simulation results, tuning voltages of 1 and 2 V are enough to compensate for the incident angle error of 2.5 deg and 3.5 deg, respectively. For the spectrum shift caused by epoxy bonding, the required tuning voltage is as low as 0.82 V. Though it brings additional optical loss, the tuning technique shows interesting prospects in postassembly coupling optimization or channel equalization.
A multipoint fiber optic sensor based on two cascaded multimode interferometer (MMI) and fiber Bragg grating (FBG) structures is proposed and demonstrated for simultaneous measurement of refractive index (RI) and temperature. The MMI is fabricated by splicing a section of no-core fiber (NCF) with two single-mode fibers. The suitable NCF lengths of 19.1 and 38.8 mm are selected by simulations to achieve wavelength division multiplexing. The two MMIs are sensitive to RI and temperature with the maximal RI sensitivities of 429.42228 and 399.20718 nm/RIU in the range of 1.333 to 1.419 and the temperature sensitivities of 10.05 and 10.22 pm/°C in the range of 26.4°C to 100°C, respectively. However, the FBGs are only sensitive to the latter with the sensitivities of 10.4 and 10.73 pm/°C. Therefore, dual-parameter measurement is obtained and cross-sensitivity issue can be solved. The distance between the two sensing heads is up to 12 km, which demonstrates the feasibility of long-distance measurement. During measurement, there is no mutual interference to each sensing head. The experimental results show that the average errors of RI are 7.61×10−4 RIU and 6.81×10−4 RIU and the average errors of temperature are 0.017°C and 0.012°C, respectively. This sensor exhibits the advantages of high RI sensitivity, dual-parameter and long-distance measurement, low cost, and easy and repeatable fabrication.
A sensor head consisting of an all single-mode fiber (SMF) in-line Mach–Zehnder interferometer (MZI) with an embedded fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature. It is fabricated by cascading two bulge-taper fusion structures in a section of SMF including an FBG. The MZI is sensitive to fiber bending and ambient temperature with a sensitivity of −16.59 nm/m−1 in the range of 1.05 to 4.05 m−1 and 58 pm/°C in the range of 30°C to 100°C, respectively. However, the FBG is only sensitive to the latter with a sensitivity of 13 pm/°C. Simultaneous measurement of curvature and temperature is obtained and the cross-sensitivity issue can be solved. The experimental results show that the average relative error of the curvature is 0.38%, which is about 18 times better than that without temperature compensating. The average error of temperature is only 0.21°C.
An efficient and high-performance binary blazed grating coupler was designed based on silicon-on-insulator (SOI) used for silicon-based hybrid photodetector integration in an arrayed waveguide grating demodulation integrated microsystem. A relatively high coupling efficiency was obtained to optimize mode matching by the finite-difference time-domain method by choosing appropriate grating parameters, including period, etching depth, and fill factor. Coupling efficiency output at 1550 nm for the TE mode reached 68%. This value was >60% in the wavelength range of 1450 to 1600 nm, specifically 71.4% around 1478 nm. An InP/InGaAs photodetector and SOI wafer were integrated by using benzocyclobutene (BCB) bonding. When the thickness of the BCB bonding layer was 440 nm, power absorption efficiency at 1550 nm for the TE mode reached 78.5%, whereas efficiency reached ∼81.8% around 1475 nm.
A highly efficient polarization-independent output grating coupler was optimized and designed based on silicon-on-insulator used for silica-based hybrid photodetector integration in an arrayed waveguide grating demodulation-integrated microsystem. The finite-difference time-domain (FDTD) method optimizes coupling efficiency by enabling the design of the grating period, duty cycle, etch depth, grating length, and polarization-dependent loss (PDL). The output coupling efficiencies of both the transverse electric (TE) and transverse magnetic (TM) modes are higher than 60% at 1517 to 1605 nm and ∼67% at around 1550 nm. The designed grating exhibits the desired property at the 3-dB bandwidth of 200 nm from 1450 to 1650 nm and a PDL <0.5 dB of 110 nm from 1513 to 1623 nm. The power absorption efficiency at 1550 nm for TE and TM modes reaches 78% and 70%, respectively. Both the power absorption efficiency of TE mode and that of TM mode are over 70% in a broad band of 1491 to 1550 nm.
This article was originally published in Vol. 52, No. 6 of Optical Engineering on 19 June 2013 with an incorrect citation identifier (CID) of 064603. The paper was removed and republished online with a correct CID of 064003 on 21 June 2013.
The typical structure of the six-digit CID for OE uses the first two digits to indicate the volume number, and the middle two digits to indicate the section category. This paper was originally published under the heading “Integrated Optics” (section code 46), but has been republished under the category “Optical Components, Detectors, and Displays,” which uses section code 40.
Compact 2×2 couplers based on silicon nanowires are fabricated and tested. They include a directional (X) coupler, a cross-gap coupler (CGC), and a multimode interference (MMI) coupler. The length of the X coupler’s parallel film waveguide is 1 μm. The theoretical minimum excess loss of the X coupler is 0.73 dB, whereas its experimental value is 1.0817 dB. CGC has a coupling region length of 24 μm. The minimum excess loss of CGC, which is 0.6 dB in theory, is experimentally determined to be 0.6737 dB. Taper waveguides are used as input/output waveguides for the MMI coupler. The footprint of the MMI region is only 6×57 μm 2 . The excess loss of the MMI coupler is theoretically 0.46 dB, but its experimental value is 0.5423 dB. The experimental nonuniformity of the MMI coupler is 0.0063 dB when the center wavelength is 1.55 μm. The maximum excess loss of the MMI coupler is 0.8233 dB in the wavelength range of 1.52 to 1.58 μm. The simulated and experimental results show that a small 2×2 MMI coupler that is suitable for optoelectronic integration exhibits lower excess loss, wider bandwidth, and better uniformity.
We have designed, fabricated, and characterized a 1×8 ultra-small compact arrayed-waveguide grating (AWG) on silicon-on-insulator (SOI) in a fiber grating demodulation integration microsystem. The miniature AWG, consisting of Si photonic wire waveguides, was designed using the complete modeling simulation in the beam propagation method. The device was fabricated on an SOI substrate and evaluated in the wavelength range around 1.55 μm, with an effective area of 230×160 μm . Clear demultiplexing characteristics were observed with a channel spacing of 1.91 nm. The influence of the waveguide widths on crosstalk defined by adjacent channel crosstalk and phase error is discussed. Insertion loss, crosstalk, and nonuniformity of loss were measured to be −3.18 , −23.1 , and −1.35 dB , respectively. Thus, the AWG design is the best choice for a fiber Bragg grating demodulation microsystem.
The integration of fiber grating demodulation system is a research emphasis in the study of demodulation systems. On-chip arrayed waveguide grating (AWG) demodulation integration makes integration possible in a demodulation system. A 1×8 silicon nanowire AWG for on-chip AWG demodulation integration microsystem is proposed and designed. The center wavelength is 1550.918 nm, the waveguide width is 350 nm, the waveguide thickness is 220 nm, and the effective area is 267×259 μm2. The single-mode waveguide cross-section structure is designed according to the refractive index of the silicon-on-insulator material. The mask layout territory of the 1×8 AWG is designed and optimized using the beam propagation method. A cone-shaped mold spots converter is proposed in the design process. Furthermore, the wavelength-division-multiplexing-phasar simulation system is established to simulate the stable output optical propagation characteristics of the designed AWG. The simulation result shows that the insert loss of the AWG is 10.658 dB, and the crosstalk is 3.037 dB, which is lower under the same waveguide, thickness, and size. This condition makes the AWG design the best choice for a fiber Bragg grating demodulation microsystem.
Heart sound includes a lot of physiological and pathological information of heart and blood vessel. Heart sound detecting
is an important method to gain the heart status, and has important significance to early diagnoses of cardiopathy. In order
to improve sensitivity and reduce noise, a heart sound measurement method based on fiber Bragg grating was
researched. By the vibration principle of plane round diaphragm, a heart sound sensor structure of fiber Bragg grating
was designed and a heart sound sensing mathematical model was established. A formula of heart sound sensitivity was
deduced and the theoretical sensitivity of the designed sensor is 957.11pm/KPa. Based on matched grating method, the
experiment system was built, by which the excursion of reflected wavelength of the sensing grating was detected and the
information of heart sound was obtained. Experiments show that the designed sensor can detect the heart sound and the
reflected wavelength variety range is about 70pm. When the sampling frequency is 1 KHz, the extracted heart sound
waveform by using the db4 wavelet has the same characteristics with a standard heart sound sensor.
KEYWORDS: Fiber Bragg gratings, Heart, Signal detection, Signal processing, Sensors, Body temperature, Integrated circuits, Digital signal processing, Intelligent sensors, Temperature metrology
A human physiological parameters intelligent clothing is researched with FBG sensor technology. In this paper, the
principles and methods of measuring human physiological parameters including body temperature and heart rate in
intelligent clothing with distributed FBG are studied, the mathematical models of human physiological parameters
measurement are built; the processing method of body temperature and heart rate detection signals is presented; human
physiological parameters detection module is designed, the interference signals are filtered out, and the measurement
accuracy is improved; the integration of the intelligent clothing is given. The intelligent clothing can implement real-time
measurement, processing, storage and output of body temperature and heart rate. It has accurate measurement,
portability, low cost, real-time monitoring, and other advantages. The intelligent clothing can realize the non-contact
monitoring between doctors and patients, timely find the diseases such as cancer and infectious diseases, and make
patients get timely treatment. It has great significance and value for ensuring the health of the elders and the children
with language dysfunction.
Based on optical fiber grating sensing technology, the signal processing system of smart clothes was designed. The
clothes embedded in fiber Bragg gratings (FBGs) sensor can measure the body physiological parameters, such as
temperature, and detect the healthy condition of wearer. The paper presented FBG wavelength detection and signal
processing methods with wearable characteristics, designed optical scheme and demodulated circuit in terms of tunable
F-P filer wavelength demodulation theory. The numerical arithmetic of processing wavelength data was researched and
realized in ARM. By testing, the measuring scope of wavelength is from 1520.5 to 1562nm, and the resolution of
wavelength can arrive at 2pm. By selecting appropriate center wavelength of sensing gratings and referenced gratings,
the relative error of wavelength can less than 0.001%. The signal processing system can adjust the excursion of F-P
cavity timely, and has characters of portability, wireless data transmission.
KEYWORDS: Computer aided design, Transistors, Device simulation, Signal to noise ratio, Resistors, Modeling and simulation, Radio frequency circuits, Analog electronics, Capacitors, Interference (communication)
High-level RF design based on behaviorally described models allows the evaluation of the performance of the architecture and system at an early stage. It also serves as the top-down design methodology in a familiar circuit design environment. VHDL-AMS supports the time and frequency domain modeling and noise modeling which make the RF circuit and system modeling in VHDL-AMS possible. In this paper we represent a methodology to design and optimize RF LNA in VHDL-AMS to get a RF LNA model with flexible specification input and high fidelity to noise and nonlinearity issues. Some of the challenges encountered in the behavioral modeling and simulation of RF LNA will be discussed. Typical RF LNA characteristics, such as noise figure and nonlinearity are addressed.
KEYWORDS: Resistance, Temperature metrology, Diodes, Bistability, Logic, Field effect transistors, Digital electronics, Lithium, Data transmission, Microwave radiation
We have measured the I-V characteristics of the Resonant tunneling diode (RTD) fabricated by ourselves. Basing on the measured results, several questions have been analyzed and discussed: (1) Temperature effects on I-V characteristics; (2) “The Apparent positive resistance phenomena” in negative resistance region. The analysis and discussion on above questions are very useful and helpful for design and fabrication of RTD.
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