We propose a method of stabilizing the center wavelength of a semiconductor laser using the wavelength-dependent frequency shift of Stokes wave induced by stimulated Brillouin scattering in fiber. Due to the nonlinear behavior of fiber to a strong input power, Stokes wave is generated and its frequency varies in inversely proportional to the input wavelength over a small wavelength range of <1 nm. Therefore, we can obtain the size of the frequency change in Stokes shift due to the variation from the initial wavelength as an error signal. The wavelength can be stabilized by adjusting the current or temperature of the semiconductor laser to compensate for the error signal. In our experiment, 1-pm wavelength stability was achieved together with a long-term wavelength drift (>4 h) of 10 pm.
KEYWORDS: Light emitting diodes, Lamps, Received signal strength, Time division multiplexing, Telecommunications, Sensors, Receivers, Optical engineering, Modulation, Systems modeling
We propose and demonstrate an indoor location awareness method for an autonomous robot vehicle using light-emitting diodes (LEDs). The location is estimated by measuring received signal strength ratio (RSSR), which is the relative ratio of optical powers detected between each LED and optical receiver. In this method, multiple LED lamps on the indoor ceiling are used, which can radiate light only during the individual time slot assigned to each of them. Using the RSSRs, circle or straight line equations are obtained and the crossing point among those equations determines the location of the object. In the experiment, four LED lamps are identified by time-division multiplexing with room dimensions of 1.0×1.0×1.3 m 3 , and the results show that the mean of the location error is 3.24 cm in the entire floor area.
We propose and demonstrate a long-reach wavelength division multiplexed-passive optical networks (WDM-PON) based on reflective semiconductor optical amplifiers (RSOAs) with easy maintenance of the optical source. Unlike previous studies the proposed WDM-PON uses two RSOAs: one for wavelength-selected light generation to provide a constant seed light to the second RSOA, the other for active external modulation. This method is free from intensity-fluctuated power penalties inherent to directly modulated single-RSOA sources, making long-reach transmission possible. Also, the wavelength of the modulated signal can easily be changed for the same RSOA by replacing the external feedback reflector, such as a fiber Bragg grating, or via thermal tuning. The seed light has a high-side-mode suppression ratio (SMSR) of 45 dB, and the bit error rate (BER) curve reveals that the upstream 1.25-Gb/s nonreturn-to-zero (NRZ) signal with a pseudo-random binary sequence (PRBS) of length of 215−1 has power penalties of 0.22 and 0.69 dB at BERs of 10−9 after 55-km and 110-km transmission due to fiber dispersion, respectively.
Dynamic analyses of vibrational motion in cell membranes provide a lot of information on the complex dynamic motilities of a red blood cell (RBC). Here, we present the correlation properties of membrane fluctuation in discocyte and spherocyte RBCs by using quantitative phase microscopy (QPM). Since QPM can provide nanometer sensitivity in thickness measurement within a millisecond time scale, we were able to observe the membrane flicking of an RBC in nanometer resolution up to the bandwidth of 50 Hz. The correlation properties of the vibrational motion were analyzed with the detrended fluctuation analysis (DFA) method. Fractal scaling exponent α in the DFA method was calculated for the vibrational motion of a cell surface at various surface points for normal discocyte and abnormal spherocyte RBCs. Measured α values for normal RBCs are distributed between 0.7 and 1.0, whereas those for abnormal spherocyte RBCs are within a range from 0.85 to 1.2. We have also verified that the vibrational motion of background fluid outside of a cell has an α value close to 0.5, which is a typical property of an uncorrelated white noise.
Fiber Bragg grating (FBG) sensor networks have been intensively researched in optical sensor area and it developed in
wavelength division multiplexing (WDM) and time division multiplexing (TDM) technologies which was adopted for its
interrogating many optical sensors. In particular, WDM technology can be easily employed to interrogate FBG sensor
however, the number of FBG sensors is limited. On the other hand, the TDM technique can extremely expand the
number of sensor because the FBG sensors have same center wavelength. However, it suffers from a reduced sensor
output power due to low reflectivity of FBG sensor. In this paper, we proposed and demonstrated the FBG sensor
network based on code division multiple access (CDMA) with a rapid response and wide spectral dynamic range. The
reflected semiconductor optical amplifier (RSOA) as a light source was directly modulated by the generated
pseudorandom binary sequence (PRBS) code and the modulated signal is amplified and goes through FBG sensors via
circulator. When the modulated optical signal experienced FBG sensor array, the optical signal which was consistent with
center wavelength of FBGs is reflected and added from each sensors. The added signal goes into dispersion
compensating fiber (DCF) as a dispersion medium. After through the DCF, the optical signal is converted into electrical
signal by using photodetector (PD). For separate individual reflected sensor signal, the sliding correlation method was
used. The proposed method improves the code interference and it also has advantages such as a large number of sensors,
continuously measuring individual sensors, and decreasing the complexity of the sensor network.
We present the real-time quantitative analysis of Vibrio vulnificus-infected host cells using quantitative phase microscopy (QPM) based on interferometric techniques. This provides the ability to retrieve the phase or optical path-length distribution over the cell with nanometer path-length sensitivity from a single interferogram image. We have used QPM to study dynamic cell morphologic changes and to noninvasively quantify the cell volumes of rat basophilic leukemia RBL-2H3 cells infected with V. vulnificus strains: wild type (MO6-24/O) and RtxA1 toxin mutant (CMM770). During the process of V. vulnificus infection in RBL-2H3 cells, the dynamic changes of quantitative phase images, cell volumes, and areas were observed in real time using QPM. In contrast, dramatic changes were not detected in RBL-2H3 cells infected with the noncytotoxic RtxA1 toxin mutant. The results showed good correlation between QPM analysis and biochemical assays, such as lactate dehydrogenase assay or β-hexosaminidase release assay. We suggest that QPM is a powerful quantitative method to study the dynamic process of host cells infected with pathogens in a noninvasive manner.
We present the study of the correlation properties of RBC flickering using double-path interferometric quantitative
phase microscopy (QPM) using detrended fluctuation analysis (DFA). For DFA of RBC membrane fluctuations, we
have measured time series thickness variations of a normal RBC for 20 seconds. The amplitude of membrane
fluctuations in RBC have showed significantly larger than the background noise level without a RBC. We have
demonstrated a practical DFA application for QPM by studying the correlation property of RBC membrane fluctuations
in a noninvasive manner. By measuring the fractal scaling exponents of the time series RBC thickness variations
obtained from QPM, we have analyzed the correlation properties of RBC membrane fluctuations and the background
noise without a sample. The exponents for a normal RBC revealed the long-range correlation property in time series
during 20 seconds. However, the averaged exponent for background noise outside a cell was close to the exponent of
white noise.
We propose and demonstrate a novel technique to generate a stable multiwavelength Raman fiber laser (RFL) based on an asymmetrical all-fiber Raman laser cavity by using a wideband chirped fiber Bragg grating (CFBG). The wideband CFBG as an input reflector has a high reflectivity covering the spectral range from 1402 to 1463 nm. Output couplers are composed of three discrete fiber Bragg gratings (FBGs), which generate a multiwavelength laser with center wavelengths of 1415, 1430, and 1445 nm. The output power variations from detuning the center wavelengths of the in-out reflectors are compared experimentally and theoretically in symmetrical and asymmetrical cavities. It is shown that the RFL output with an asymmetric cavity is more stable than that of a symmetric cavity.
We experimentally and theoretically demonstrated a novel technique to generate a stable multi-wavelength Raman fibre
laser (RFL) based on an asymmetrical all-fibre Raman laser cavity by using a broadband chirped fibre Bragg grating
(CFBG). The output power variations from detuning the center wavelength of in/out reflectors are studied with
symmetrical and asymmetrical RFL cavities. The RFL output with asymmetrical cavity is more stable than that of
symmetrical cavity.
A low-cost Raman fibre laser for multiple wavelengths at 14xx nm has been proposed and demonstrated. Using
asymmetric cavities, the Raman fibre laser provides flexible and easy complete solution of the desired multiple
wavelengths output.
We report an integrated all-fiber variable optical attenuator (VOA) for dynamic control of a device by achieving optimized taper and axial compression of an index-guiding holey fiber. We experimentally demonstrate a VOA device with dynamic ranges of 18 dB over the spectral range from 1450 to 1650 nm and a low insertion loss of 0.5 dB.
Tunable OTDR based on self-locked RSOA for in-line monitoring of WDM-PON is proposed and demonstrated. The
characteristics of self-locked RSOA were experimentally studied. The tunable OTDR was successfully demonstrated for
a range of 25 nm, having a dynamic range of about 15 dB. Under in-service state of 2.5-Gb/s data, the power penalty
induced by the line monitoring channel was about 0.1 dB at BER of 10-9. The proposed tunable OTDR is cost-effective
and useful to monitor the status of WDM-PON.
We developed the primary components applicable to HPCF links for short reach (SR) and very short reach (VSR)
data communication systems. We fabricated 4x4 HPCF fused taper splitter, HPCF pigtailed VCSEL and PIN
photodiode for high speed short reach communications and characterized back to back transmission performance of the
link composed of these components by measuring eye diagrams and jitters.
Adapting the fusion-tapering technique for glass optical fiber, we successfully fabricated a 4x4 HPCF fused taper
coupler. The HPCF with a core diameter of 200μm and an outer diameter of 230μm had step refractive index of 1.45
and 1.40 for the core and the clad. The optimized fusion length and tapering waist which make minimum insertion loss
of about 7dB and uniform output power splitting ratio with less than 0.5dB are 13mm and 150µm, respectively.
As a light source for VSR networks, we chose a vertical cavity surface emitting laser (VCSEL) and developed a
package with a HPCF pigtail. After positioning VCSEL and HPCF that made a minimum coupling loss, we glued the
HPCF inside ceramic ferrule housing. In HPCF-PIN PD packaging, we added a micro polymer lens tip onto the HPCF
ends to match the mode field area to the sensitive area of GaAs or InGaAs PIN PD. Coupling between a PIN PD chip
and the lensed HPCF was optimized with the radius of curvature of 156µm with a low coupling loss of 0.3dB, which is
compatible to conventional MMF-PD packaging. For 1.25 Gbps data rate, the eyes adequate to eye mask in gigabit
Ethernet were wide open after all HPCF transmission link and no significant power penalty was observed.
We report a three-wavelength Raman fiber laser (RFL) with the equal spaced wavelengths based on partially-degenerated four-wave mixing (PD-FWM) in a highly Ge-doped fiber. The FWM processes in cascaded RFLs reduce the threshold power and improve the slope efficiency for two configurations of three-wavelength RFLs. We show a comparison between two configurations of RFLs characterized by their slope efficiency and their threshold.
A novel photonic microwave notch filter with both negative and positive coefficients is proposed and demonstrated using a single optical source as a probe beam. Due to the change in birefringence induced by another modulated pump beam, both non-inverted and inverted signals are generated in a highly nonlinear fiber. These are separated by using a polarization beam splitter and recombined with optical time delay given to one of them. From the generation of both coefficients and the orthogonal property between them, no resonance peaks were observed at baseband and the optical coherence could be avoided independently of the source coherence length. The experimental results show a stable transfer response with the free spectral range of 65 MHz and 1.32 GHz when the optical path difference is given to 3.19 m and 0.19 m, respectively.
We discuss a phenomenon of upstream bandwidth waste in a conventional dynamic bandwidth allocation scheme and propose a novel upstream bandwidth allocation scheme to enhance upstream bandwidth efficiency in Ethernet PON, and evaluate performance of the proposed scheme in terms of upstream channel throughput, mean queueing delay, and mean queue length of ONUs.
A monitoring technique for multiple power splitter-passive optical networks (PS-PON) is presented. The technique is based on the remote sensing of fiber Bragg grating (FBG) using a tunable OTDR. To monitor the multiple PS-PON, the FBG can be used for a wavelength dependent reflective reference on each branch end of the PS. The FBG helps discern an individual event of the multiple PS-PON for the monitoring in collaborate with information of Rayleigh backscattered power. The multiple PS-PON can be analyzed by the monitoring method at the central office under 10-Gbit/s in-service.
A two-user, 10-Gbits/s optical code-division multiple-access system implemented by using cascaded long-period fiber gratings formed in a dispersion-compensating fiber (DCF) is demonstrated. Our results show that the sensitivity of cladding modes to the refractive index change on the cladding surface is greatly reduced by utilizing the inner-cladding mode of the DCF. Two pairs of encoder/decoder are constructed and the performance is evaluated by measuring bit error rate (BER). With an interferer, a BER of 1.5×10–12 is measured at a received optical power of –6 dBm.
A clock and data recovery circuit using the clock jitter reduction technique is proposed for a 622-Mbit/s burst-mode data stream. The clock jitter reduction is achieved by controlling the clock duty cycle with the phase information of the recovered clock. The proposed clock recovery circuit, based on the gated oscillator, recovers a low-jitter output clock with up to 4090 consecutive zeros.
We present an upstream transmission method independent of temperature characteristics of the remote node (RN) in a WDM-PON. This method employs a self-injection locked Fabry-Perot laser diode (F-P LD) for upstream transmission in the optical network unit (ONU). Using this method, the sidemodes of the F-P LD are suppressed, and the F-P LD is matched to the center wavelength of the wavelength distributor/combiner placed at the RN. The experimental results confirm that bidirectional error-free transmission at 1.25/10 Gbit/s could be achieved.
A surveillance technique for passive optical networks (PON) is presented. The technique is based on the remote sensing of fiber Bragg grating using a tunable OTDR. Hybrid architecture of WDM and passive splitter-PON can be analyzed by the surveillance method at the central office under in-service state of PON.
In this paper, we introduce a structural model for WDM (wavelength division multiplexing)-based LT (line termination) systems containing the fundamental functions recommended by ITU-T, and we describe how to configure the supervisory system and data communication channels to be adaptable to the WDM- based transmission systems considering compatibility with the SDH-based supervisory systems. Also we propose that two new reference points (N2 and N3) be added to the MCF (message communication function) like N and P from the view point of the telecommunication management network.
Two types of fiber optic reflectively tapped delay line matched filters are produced for use as photonic packet address detectors in an optical ring network. Dielectric films evaporated on cleaved fiber ends function as light taps for the filters. Experimental results and theoretical calculation on photonic packet address detectors with 1 Gbps address code of (101) are reported.
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