Miniature temperature-insensitive Fabry-Pe/spl acute/rot fiber-optic pressure sensor

We present a miniature fiber-optic pressure sensor with a diameter of only 125 /spl mu/m. The sensor works as an extrinsic Fabry-Pe/spl acute/rot interferometer and the cavity length can be controlled with a resolution of about several nanometers. Also the sensor sensitivity can be easily adjusted by controlling the sensor gauge length. A passive temperature compensation scheme was used to reduce most of the sensor's temperature dependence. Since the sensor is composed entirely of fused silica, it is reliable, biocompatible, corrosion resistant, and immune to electromagnetic interference and has high-temperature capability.     

Enhanced linear dynamic range property of Franz-Keldysh effectwaveguide modulator

The spurious-free dynamic range (SFDR) of an InGaAsP-InP Franz-Keldysh effect (FKE) waveguide modulator is studied. Low-biasing the FKE modulator is shown to enhance the SFDR by 22 dB with a 3-dB optical power penalty. Polarization-independent RF operation is also obtained with low bias. At 2 mA photocurrent, the simulated narrowband and broadband SFDR are, respectively, 127 dB and 104 dB in a 1-Hz bandwidth. The measured result projects a narrowband SFDR of 129 dB-Hz ^4/5 at this photocurrent     

Short multiwavelength fiber laser made of a large-band distributed Fabry-Pe/spl acute/rot structure

Multiwavelength fiber lasers are obtained by writing two superimposed chirped fiber Bragg gratings in a photosensitive Er/sup 3+/--Yb/sup 3+/ codoped optical fiber. The chirped gratings create a distributed Fabry-Pe/spl acute/rot structure in which the resonating fields of the different laser lines are spatially separated, thus, reducing cross-gain modulation. We demonstrate multiwavelength lasers emitting simultaneously over 8 and 16 lines spaced by 50 GHz. The active structure is very compact having a total active length of 8 cm. We discuss how the properties of the device are governed by the parameters of the chirped gratings giving high flexibility in the laser design.     

5-GHz pulsed fiber Fabry-Pe/spl acute/rot laser mode-locked using carbon nanotubes

We demonstrate passive mode-locking of a short-cavity (/spl sim/2 cm) fiber Fabry-Pe/spl acute/rot laser by incorporating a carbon-nanotube-based saturable absorber. Stable pulses are generated with a pulsewidth as short as 0.68 ps at a repetition rate as high as 5.18 GHz. This is the smallest femtosecond fiber pulsed laser ever demonstrated to date.     

Modeling and experimental demonstration of ultracompact multiwavelength distributed Fabry-Pe/spl acute/rot fiber lasers

This work presents a complete model for the design and optimization of multiwavelength distributed Fabry-Pe/spl acute/rot (DFP) fiber lasers that are made by superimposing two chirped fiber Bragg gratings in a photosensitive codoped erbium-ytterbium (Er-Yb) fiber. The model is based on a matrix formulation of coupled-mode equations taking into account the chirped grating superstructure and including a spectrally resolved gain medium. The performed analysis reveals that the signal power of each channel is strongly localized near a minimum of the superstructured-grating envelope. As a consequence, the overlap between the power distributions in neighboring cavities is small, thus reducing the effect of cross-gain saturation and allowing a high number of channels in a short piece of fiber. The simulations also show how the saturation of the cross-relaxation mechanism between ytterbium and erbium leads to flat output spectra without the need for an additional equalization scheme such as a complex grating apodization profile. Furthermore, to validate the theoretical model, we present the experimental realization and characterization of a multiwavelength laser emitting in a single-mode and single-polarization over 16 wavelengths spaced by 50 GHz and with a total output power of 52 mW.     

Broad-band light source using mutually injected Fabry-Pe/spl acute/rot laser diodes for WDM-PON

We propose and demonstrate a new broad-band light source (BLS) for a wavelength division multiplexing-passive optical network (WDM-PON) based on the wavelength locked Fabry-Pe/spl acute/rot laser diodes (F-P LDs). By mutual injection between two antireflection-coated F-P LDs, we realized a broad-band light with a low relative intensity noise. By using the proposed BLS for wavelength locking of the F-P LD, we achieve color-free operation of the optical network termination with Manchester coded data. We also demonstrate a WDM-PON based on the proposed BLS.     

Gain measurements of Fabry-Pe/spl acute/rot semiconductor lasers using a nonlinear least-squares fitting method

A method for the measurement of the gain-reflectance product of Fabry-Pe/spl acute/rot (F-P) semiconductor lasers is proposed and compared to other techniques. The method is based on a nonlinear, least-squares fitting of the F-P modes to an Airy function. A separate fitting is performed over each mode, as measured with an optical spectrum analyzer (OSA), so that the gain-reflectance parameters are extracted. The influence of the OSAs response function is considered by convolution of the Airy function with the response function of the OSA. By comparing with the Hakki-Paoli method, the mode sum/min method, and the Fourier series expansion method, we find that the nonlinear fitting method is the least sensitive to noise. However, owing to a broadening of the F-P modes of the semiconductor laser, the mode sum/min method combined with a deconvolution technique gives the least underestimated gain above threshold.     

Multiwavelength erbium-doped fiber Fabry-Pe/spl acute/rot laser and its uniform spectral lines power operation

Multiwavelength erbium-doped fiber laser by means of phase modulation in a linear cavity configuration is presented. Stable multiwavelength lasing is achieved by applying any one of the waveforms of sine, square, sawtoothed, and triangular at a suitable frequency between 500 Hz to a few tens of kilohertz to the phase modulator. The output spectral lines power equalization is performed by adjusting the frequency to drive the all-fiber phase modulator and the polarization controller or dc offset voltage of a LiNbO/sub 3/ amplitude modulator, which is incorporated in a polarization-maintaining fiber Lyot-Sagnac filter.     

Electrooptic temperature sensor based on a Fabry-Pe/spl acute/rot resonator with a liquid crystal film

An electrooptic (EO) temperature sensor based on a Fabry-Pe/spl acute/rot (FP) resonator with a nematic liquid crystal (NLC) film is proposed. A novel compensation scheme of the EO effect allows for precise determination of temperature by monitoring the resonant wavelength of the NLC FP sensor. The proposed EO temperature sensor provides good stability, high resolution, self-calibration capability, and low driving voltage.     

Injection-locked Fabry-Pe/spl acute/rot laser with electronic feedback for clock recovery from high-speed OTDM signals

We demonstrate the use of an injection-locked Fabry-Pe/spl acute/rot laser diode with electronic feedback for base-rate clock recovery in N/spl times/10 Gb/s optical time-division-multiplexing (OTDM) systems. Injection-locking enhances the resonance frequency of the laser and the electrical feedback achieves strong resonance at the base-rate frequency of the injected data streams, enabling ultrastable electrical clock signal generation at the base rate of 10 GHz. Experimental demonstrations for clock recovery at 10 GHz from 40-Gb/s OTDM data streams and 4-1 demultiplexing of the data using the extracted clock after fiber transmission is presented. The timing jitter measured in the recovered electrical clock is less than 0.25 ps.     

Resonator-based multi-stage /spl Sigma//spl Delta/ modulator for wideband applications with improved dynamic range

A new design methodology for wideband, multi-stage, multi-bit /spl Sigma//spl Delta/ modulators (/spl Sigma//spl Delta/Ms) with improved dynamic range, is presented. The key to improving dynamic range is to have the first stage oscillated, then the coarse quantisation noise vanishes and hence circuit non-linearities do not cause a leakage quantisation noise problem. Based on the proposed methodology, a fourth-order four-bit /spl Sigma//spl Delta/M can achieve the dynamic range of 80 dB at the OSR of 8 without using additional calibration techniques.     

Investigation of a periodically segmented waveguide Fabry-Pe/spl acute/rot interferometer for use as a chemical/biosensor

We present a periodically segmented waveguide Fabry-Pe/spl acute/rot interferometer (PSW-FPI) intended to be used for tagless real-time chemical/ biological sensing through bulk-material interaction. The differential sensor detects changes in the refractive index (RI) of a sample regardless of its absolute RI value. Experiments with a series of sucrose solutions of various concentrations are compared with theoretical results, and a very good match is found between the two. The theoretical sensitivity limit for a 50-dB-signal-to-noise-ratio (SNR) measurement system is estimated as /spl delta/n=3/spl middot/10/sup -7/. For a 29-dB-SNR measurement system, a measured sensitivity limit of /spl delta/n=4/spl middot/10/sup -5/ is comparable with the previously reported sensitivities of label-free real-time optical biosensors (2/spl middot/10/sup -5/-5/spl middot/10/sup -5/). However, the total required sensing length (720 /spl mu/m) of our PSW-FPI sensor is much shorter than that of the previously reported devices (9-20 mm).     

A theoretical model of a wavelength-locked Fabry-Pe/spl acute/rot laser diode to the externally injected narrow-band ASE

We propose a theoretical model of the wavelength-locked Fabry-Pe/spl acute/rot laser diode (F-P LD) to the externally injected narrow-band amplified spontaneous emission. The model explains the dynamics of the wavelength-locked F-P LD. The simulation results with the proposed model show good agreement with the experimental results.     

Multiplexing of millimeter-wave signals for fiber-radio links by direct modulation of a two-mode locked Fabry-Pe/spl acute/rot laser

In this paper, we introduce generation of multiplexed signals on the millimeter-wave bands for fiber-radio systems where an optical millimeter-wave generator is based on a two-mode locked Fabry-Pe/spl acute/rot (FP) slave laser, whose injection current is directly modulated by a signal source. We qualitatively consider the distortion of the millimeter-wave signals from the FP slave laser. The distortion components on the millimeter-wave bands are induced from the simultaneous modulation of the locked modes and the nonlinear modulation response of the FP laser. Two-tone modulation of the locked FP laser is examined to evaluate the dynamic range of the millimeter-wave signals against the second- and third-order distortion components. We also perform fiber transmission of three 156-Mb/s-BPSK signals on the 60-GHz band to demonstrate fiber-radio down-link systems. The total capacity of the down-link system is discussed. In addition, two methods for multicarrier generation on the millimeter-wave bands are proposed. Multicarrier generators supported by these methods can be used as local signals for up-link millimeter-wave signals. The first method is based on multitone modulation of the FP slave laser. We attempt the down-conversion of a 52-Mb/s ASK signal on the 60-GHz band by using the millimeter-wave local signals. The second method depends on the distorted modulation of the FP slave laser by using a single continuous wave signal where the DC-bias level of the FP laser's injection current is partly under the threshold value. We confirm that five carriers on the 60-GHz band are effectively generated by using the second method. Furthermore, the influences of the chromatic dispersion effects on the millimeter-wave local signals are investigated for both methods.     

Generation of wavelength-tunable optical pulses using a linear-cavity fiber laser scheme with a Fabry-Pe/spl acute/rot laser diode

A wavelength-tunable mode-locked linear-cavity fiber laser was demonstrated using a Fabry-Pe/spl acute/rot laser diode. By adding a tunable bandpass filter within the linear cavity, the wavelength-tunable fiber laser was easy to be tuned dynamically. This linear-cavity fiber laser output exhibited a good performance having the optical sidemode suppression ratio over 30 dB and the wavelength-tuning range up to 27 nm. Furthermore, this fiber laser generated pulses with pulsewidth between 53.2 and 80.4 ps at a repetition frequency of 908.39 MHz.     

Rational harmonic mode-locking of erbium-doped fiber laser at 40 GHz using a loss-modulated Fabry-Pe/spl acute/rot laser diode

Rational harmonic mode-locking of an Erbium-doped fiber ring laser (EDFL) at repetition frequency of 40 GHz is demonstrated by using a purely loss-modulated Fabry-Pe/spl acute/rot laser diode (FPLD) at 1 GHz. The FPLD is neither lasing nor gain-switching, which requires a threshold modulation power of 18 dBm to initiate harmonic mode-locking of the EDFL. After chirp compensation, the nearly transform-limited pulsewidth and spectral linewidth of 3 ps and 1.3 nm are obtained at repetition frequency of 40 GHz, which corresponds to a time-bandwidth product of 0.31. The EDFL gradually evolves from harmonic mode-locking to injection-locking mode as the FPLD changes from loss-modulation to gain-switching mode by increasing its dc driving current.     

An all-optical 2R regenerator using a compact self-seeded Fabry-Pe/spl acute/rot laser diode incorporated in a bidirectional EDFA

An all-optical 2R regenerator, based on a compact self-seeded Fabry-Pe/spl acute/rot laser diode with a 10-mm-long embedded fiber Bragg grating cavity, and a bidirectional erbium-doped fiber amplifier, is proposed and experimentally demonstrated to execute all-optical 2R regeneration at 10 Gb/s. Compared with the conventional 1R regeneration, the proposed scheme has achieved significant 6.4-dB improvement of power penalty at bit-error ratio =10/sup -9/ in the transmission experiment over 100-km standard single-mode fiber.     

Time-frequency analysis of multiple fringe and nonsinusoidal signals obtained from a fiber-optic vibration sensor using an extrinsic Fabry-Pe/spl acute/rot interferometer

In the case of multiple fringes and complex frequency measurements, the frequency of the output signal changes rapidly when the vibration changes and frequency breakdown takes place at the turning point. For a particular vibration signature containing many frequency components at different time intervals, it is often difficult to trace the direction of the vibration as well as individual frequency peaks. In such cases, advanced signal-processing scheme is necessary to decode the vibration signature. This paper investigates the data interrogation technique for multifrequency and complex signals of surface vibration obtained from an extrinsic Fabry-Pe/spl acute/rot interferometric sensor. In this paper, wavelet transform (WT)-based signal processing methodology has been employed to count of optical fringes with special reference to signals having subfringes. A WT-based tool has also been developed for unambiguous identification of frequency components from a nonsinusoidal vibration. The results of such WT-based analyses are presented, and merits as well as demerits of the proposed methods are discussed.     

Highly linear 2.5-V CMOS /spl Sigma//spl Delta/ modulator for ADSL+

We present a 90-dB spurious-free dynamic range sigma-delta modulator (/spl Sigma//spl Delta/M) for asymmetric digital subscriber line applications (both ADSL and ADSL+), with up to a 4.4-MS/s digital output rate. It uses a cascade (MASH) multibit architecture and has been implemented in a 2.5-V supply, 0.25-/spl mu/m CMOS process with metal-insulator-metal capacitors. The prototypes feature 78-dB dynamic range (DR) in the 30-kHz to 2.2-MHz band (ADSL+) and 85-dB DR in the 30-kHz to 1.1-MHz band (ADSL). Integral and differential nonlinearity are within /spl plusmn/0.85 and /spl plusmn/0.80 LSB/sub 14 b/, respectively. The /spl Sigma//spl Delta/ modulator and its auxiliary blocks (clock phase and reference voltage generators, and I/O buffers) dissipate 65.8 mW. Only 55 mW are dissipated in the /spl Sigma//spl Delta/ modulator.     

A 3.3-mW /spl Sigma//spl Delta/ modulator for UMTS in 0.18-/spl mu/m CMOS with 70-dB dynamic range in 2-MHz bandwidth

A quadrature fourth-order, continuous-time, /spl Sigma//spl Delta/ modulator with 1.5-b quantizer and feedback digital-to-analog converter (DAC) for a universal mobile telecommunication system (UMTS) receiver chain is presented. It achieves a dynamic range of 70 dB in a 2-MHz bandwidth and the total harmonic distortion is -74 dB at full-scale input. When used in an integrated receiver for UMTS, the dynamic range of the modulator substantially reduces the need for analog automatic gain control and its tolerance of large out-of-band interference also permits the use of only first-order prefiltering. An IC including an I and Q /spl Sigma//spl Delta/ modulator, phase-locked loop, oscillator, and bandgap dissipates 11.5 mW at 1.8 V. The active area is 0.41 mm/sup 2/ in a 0.18-/spl mu/m 1-poly 5-metal CMOS technology.