Signal Peak Power Research Articles

Novel all-optical AND and NOR gates based on semiconductor fiber ring laser

A new scheme for all-optical AND gate and NOR gate based on simultaneous four-wave mixing (FWM) and cross-gain modulation (XGM) in a semiconductor fiber ring laser (SFRL) is proposed, and a comprehensive broad-band dynamic model of this kind of all-optical logic gates is presented. By numerical simulation, the effects of the input signal peak power and the coupling of the couplers in SFRL on the output performances of the logic gates are analyzed.

Performance of IM/DD Optical Communication System in the Presence of Residual Laser Radiation

In this paper we determine the performance of intensity-modulation/direct-detection optical communication system for various values of laser extinction ratio and bit rate. The bit error probability dependencies on optical signal peak power are given for optimally chosen threshold. We determine the numerical values of required peak average optical signal power in order to reach the bit error probability 10 -9 , and present the exact penalties due to finite extinction ratio. The receiver with PIN photodiode is observed in the analysis.

Resonant Cavity Time-Division-Multiplexed Fiber Bragg Grating Sensor Interrogator

The first resonant-cavity time-division-multiplexed (TDM) fiber Bragg grating sensor interrogation system is reported. This novel design uses a pulsed semiconductor optical amplifier in a cyclic manner to function as the optical source, amplifier, and modulator. Compatible with a range of standard wavelength detection techniques, this optically gated TDM system allows interrogation of low reflectivity "commodity" sensors spaced just 2 m apart, using a single active component. Results demonstrate an exceptional optical signal-to-noise ratio of 36 dB, a peak signal power of over +7 dBm, and no measurable crosstalk between sensors. Temperature tuning shows that the system is fully stable with a highly linear response.

Tolerance to In-Band Coherent Crosstalk of Differential Phase-Shift-Keyed Signal With Balanced Detection and FEC

It is found experimentally that the differential phase-shift-keyed (DPSK) signal with balanced detection has /spl sim/6 dB higher tolerance to in-band coherent crosstalk than on-off-keyed (OOK) signal. We attribute the improved crosstalk tolerance of the DPSK signal to its 6-dB lowered peak signal power as compared to the OOK signal for equal bit-error rate in optical signal-to-noise-ratio-limited systems. The impact of signal coherence on the crosstalk tolerance in a 10-Gb/s DPSK system adopting a standard Reed-Solomon forward-error correction is also investigated.

Intracavity optical parametric oscillator at 1572-nm wavelength pumped by passively Q-switched diode-pumped Nd:YAG laser

An intracavity optical parametric oscillator (IOPO) based on bulk KTP crystal was constructed with a Nd:YAG slab as an active medium pumped by a 300-W diode array and Cr:YAG as a passive Q-switch. A signal pulse of 1.9-mJ energy at 1572-nm wavelength was demonstrated. In the cavity, optimized with respect to single-pulse energy, a five-fold shortening of signal-pulse duration with respect to 1064-nm pump radiation was observed. A twice as large level of signal peak power of 650 kW, compared to the pump laser in the same cavity without the IOPO, was achieved. A conversion efficiency of 44% with respect to the 1064-nm pump beam and 3.8% with respect to diode pump energy was demonstrated.

Comparison of interchannel pulses four-wave mixing in SMF, NZDSF and HNLF

We systematically analyze the interchannel ultrashort pulses four-wave mixing (FWM) in dense wavelength division multiplexing (DWDM) systems with single-mode fiber (SMF), nonzero dispersion-shifted fiber (NZDSF), and highly nonlinear fiber (HNLF). We investigate the FWM conversion efficiency as functions of channel spacing, fiber length, and signal power. We show that the FWM in DWDM system with HNLF is almost 40 times larger than with NZDSF and 400 times larger than with SMF. We obtain the minima of WDM channel spacings limited by FWM for SMF, NZDSF, and HNLF. The FWM conversion efficiency approaches to a constant as the propagation length increases and is approximately an exponential function of the peak power of incident signals.

Experimental investigation of a 25-MW microwave (3-cm range) compressor prototype

An experimental study of a resonance microwave (3-cm-range) compressor with gas insulation and energy output through a superdimensional coaxial interference switch is reported. The rated parameters of the compressor are output signal power ∼25 MW, signal duration 2 ns, gain 26 dB, and efficiency ∼57%. A gain of 20 dB was achieved at a peak output signal power of 12 MW, signal duration of 2 ns, efficiency of ∼24%, and traveling wave power of 24 MW.

Trace-gas sensor based on mid-IR difference-frequency generation in PPLN with saturated output power

The development and characterization of a compact pulsed mid-IR laser source for sensitive on-line trace-gas analyses in the 3–4 μm wavelength range is reported. The source is based on an advantageous difference-frequency mixing configuration in periodically poled LiNbO 3 (PPLN) with a cw external-cavity diode laser (ECDL; 810–830 nm) for broad and accurate tunability and a diode-pumped passively Q-switched Nd:YAG laser (1064 nm) for high mid-IR peak power. With 5 mW cw pump and 4.7 kW signal peak power incident on a 19 mm long PPLN crystal, a maximum of 360 μW mid-IR peak power was generated. The narrowband (∼150 MHz) radiation was saturated by a factor of 15 compared with the nonsaturated case due to depletion of the pump laser radiation. This results in a very high amplitude stability of the generated mid-IR power and thus in a high detection sensitivity. A minimum detectable absorption coefficient of 2.8×10 −8 cm −1 was achieved in combination with a 36.2 m multipass cell in an averaging time of 20 s, as demonstrated by on-line analyses of formaldehyde traces near 3.53 μm.

System design and optimization of optically amplified WDM-TDM hybrid polarization-insensitive fiber-optic Michelson interferometric sensor

We investigate the optically amplified time-division-multiplexed (TDM) polarization-insensitive fiber-optic Michelson interferometric sensor (PIFOMIS) system using erbium-doped fiber amplifier (EDFA). The EDFA was named preamplifier, in-line amplifier or postamplifier; by the position it was located. We find that the preamplifier EDFA has limited usefulness because of its unstable amplification of the optical pulse trains. Both post- and in-line cases can work successfully in the TDM-PIFOMIS system. The amplitudes of the optical pulse trains are stable after amplified by the in-line EDFA, this is a significantly advantage of the optically amplified TDM-PIFOMIS system. The MPDS of the unamplified TDM-PIPOMIS system with an extinction ratio (ER) of 33 dB of the output pulse of the optical guide wave (OGW) modulator was 2.4/spl times/10/sup -5/ rad/(Hz)/sup 1/2/ at 1 kHz. For maintaining MPDS better than 3.4/spl times/10/sup -5/ rad/(Hz)/sup 1/2/ at 1 kHz, the allowable worst ER for the post- and in-line amplified system are 20 and 17.8 dB, respectively, and the corresponding input signal peak power should be larger than -20 and -25 dBm. While employing such two post- and two in-line EDFAs in the TDM-PIFOMIS system, the allowable loss of the sensor array is 47 dB. We analyze the phase-induced intensity noise (PIIN) of the optically amplified TDM-PIFOMIS system in detail and propose methods to reduce the PIIN. The output optical pulse of an intensity modulator with high ER is a key issue to minimize the PIIN and sensor crosstalk in the system. In order to reduce the system PIIN, complexity and cost, we suggest an optimum optically amplified WDM (wavelength-division multiplexing)-TDM hybrid PIFOMIS system with four wavelengths and four eight-sensor subarrays.

Improvement of sensitivity in optical samplingsystem

The eye diagram of a high bit rate, low-power optical signal has been successfully measured using a periodically poled lithium niobate crystal. The system has a signal-to-noise ratio of 20 dB at a signal peak power of 0.3 mW.

Equatorial spread F effects on an HF path: Doppier spread, spatial coherence, and frequency coherence

In August 1990 we participated in the Equatorial Ionospheric Studies sounding rocket campaign near Kwajalein Atoll in the equatorial Pacific region. The campaign included measurements of plasma density using rocket probes and coherent and incoherent scatter radar. During the campaign we fielded high‐frequency ionospheric sounders over a bistatic path between Maloelap Atoll and Bikini Atoll in the Marshall Islands. The distance between the transmitters and receivers was 700 km; the ionospheric‐reflection region was at 10.18°N, 168.40°E, near the magnetic equator. We made three types of measurements: Doppler spread and spatial coherence for a single‐frequency CW path; frequency coherence of multiple CW paths; and Doppler spread and time‐delay spread for a 60‐kHz bandwidth path. We obtained such data over a period of 2 weeks for approximately 2 hours each evening; during this period spread F was common. Fifty percent of the evenings showed Doppler spread of greater than 6 Hz at the −10 dB level (relative to the peak signal power) and greater than 15 Hz at the −30 dB level. Forty percent of the evenings showed spatial coherence distance of less than 180 m in the direction normal to the bistatic path; 40% of the evenings showed spatial coherence of less than 75 m in the direction parallel to the path. Seventy‐five percent of the evenings showed coherence bandwidths of less than 1.5 kHz.

Experimental investigation of an optically amplified time-division-multiplexed polarization-insensitive fiber-optic Michelson interferometric sensor system

We experimentally investigate optically amplified time-division-multiplexed polarization-insensitive fiber-optic Michelson interferometric (PIFOMI) sensor systems, using an erbium-doped fiber amplifier (EDFA) and a phase-generated carrier (PGC) demodulation technique. The influence of the EDFA on the extinction ratio (ER) of the light pulse and on the minimum phase-detection sensitivity (MPDS) is examined. We find that the EDFA acting as a preamplifier has limited usefulness because the highly amplified spontaneous emission (ASE) noise generated by the EDFA degrades the ER and the MPDS. However, both postamplifiers and in-line EDFA's can work successfully. The MPDS of the unamplified time-division-multiplexed PIFOMI system with an ER of 33 dB was 2.4 x 10(-5) rad/(Hz)(1/2) at ~1 kHz. For maintaining a MPDS of better than 3.4 x 10(-5) rad/(Hz)(1/2) at ~1 kHz, the worst ER's for the postamplified and in-line amplified systems were 20 and 17.8 dB, respectively. The corresponding input signal peak power should be larger than -20 and -25 dBm for the postamplifiers and in-line amplifiers, respectively. When two postamplifiers and two in-line amplifiers are used, an allowable sensor system loss of 47 dB and a link length of the input-output lead fiber of 108 km can be realized for this system with a 32-sensor array. Implementation of optically amplified time-division-multiplexed and wavelength-division multiplexed-time-division multiplexed PIFOMI subarray sensor systems are also addressed.

Highly sensitive optical sampling system using timing-jitter-reducedgain-switched optical pulse

To measure the eye diagram of a high bit rate optical signal, the authors have generated a sampling pulse by gain switching, and have reduced the timing jitter by using CW light injection. The system jitter was 0.7 ps, and the signal-to-noise ratio was 20 dB at a signal peak power of 2.3 mW.

100 Gbit/s optical signal eye-diagram measurementwith optical sampling using organic nonlinear optical crystal

The eye diagram of a 100 Gbit/s optical signal has been successfully measured using sum-frequency-generation optical sampling, which uses an organic crystal (AANP: 2-adamantylamino-5-nitropyridine) with high optical nonlinearity to improve the signal-to-noise ratio of the measured waveform. Using this method, a signal-to-noise ratio > 17 dB is obtained at a signal peak power of 270 mW.

Optimum signals having specified frequency spectra

A common requirement in active acoustic measurements is to generate a periodic signal having a specified frequency spectrum and maximum average power. The signal amplitude is usually limited by a constraint on the peak signal power. A new algorithm for designing such signals is presented. An initial constant amplitude periodic chirp with approximately the desired spectrum is refined by alternate‐frequency and time‐domain operations until the process converges. The resulting signals are commonly within 0.1 dB of the theoretically optimum signals.

Resolution performance of Wiener filters

To improve the resolution of seismic events, one often designs a Wiener inverse filter that optimally (in the least‐squares sense) transforms a measured source signature into a spike. When this filter is applied to seismic data, the bandwidth of any noise which is present increases along with the bandwidth of the signal. Thus the signal‐to‐noise ratio is degraded. To reduce signal ambiguity it is common practice to prewhiten the Wiener filter. Prewhitening the filter improves the output signal‐to‐ambient noise ratio, but at the same time it reduces resolution. The ability to resolve the temporal separation between events is determined by the resolution time constant which we define as the ratio of signal energy to peak signal power from the filter. For unfiltered wavelets the resolution time constant becomes the reciprocal of resolving power recently described by Widess (1982). For matched filter signals the resolution time constant can be regarded as the inverse of the frequency span of the signal. Although it is satisfying that the resolution time constant definition agrees with other measures of resolution, this more general definition has two major advantages. First, it incorporates the effect of filtering; second, it is easily generalized to incorporate the effects of noise by assuming that the filter is a Wiener filter. For a given amount of noise the Wiener filter is a generalization of the matched filter. Marine seismic wavelets demonstrate how reducing the noise level improves the resolution of a Wiener filter relative to a matched filter. For these wavelets a point of diminishing return is reached, such that, to realize a further small increase in resolution, a large increase in input signal‐to‐noise ratio is required to maintain interpretable information at the output.

Pure single-mode LiNdP_4O_12 solid-state laser transmitter for 13-μm fiber-optic communications

A pure single-mode high-bit-rate solid-state laser transmitter was fabricated using a GaAlAs laser-pumped LiNdP(4)O(12) laser oscillator, a YIG isolator, and a LiNbO(3) traveling-wave directional-coupler waveguide modulator. Signal peak power of 0.17 mW coupled to an output single-mode fiber was obtained at 1.317-microm wavelength. Half-wavelength voltage was 6.0 V and 3-dB bandwidth was 2.8 GHz.

Mixing of N2 laser and dye laser pulses in ADP to generate difference frequency tunable from 0.68 to 1.1 μm

This paper reports the first direct application of a nitrogen laser as a frequency mixing component in a parametric experiment. Tunable infrared radiation from 0.68 to 1.1 μm is generated by mixing N2 laser and dye laser pulses in ADP. The experimental tuning curve is in good agreement with theory. A peak signal power of 1 W is obtained over an interaction length of 1.1 cm with 7 kW of N2 laser and 5 kW of dye laser power. The signal bandwidth is consistent with those of the input beams. Possible extensions of the tuning range are discussed.

A Nonadaptive Processing of Radar Pulse Trains for Clutter Rejection

The problem of detecting coherent pulse trains with uniform amplitude in a clutter-plus-noise environment is considered. A radar processor for detecting targets moving radially with respect to the clutter is proposed. The minimum interpulse spacing of the transmitted signal is assumed long enough that returns are not received simultaneously from different ranges within a region of extended clutter, and the central frequency of the clutter power spectrum is postulated to be known. The processor is singled out as the linear filter, orthogonal to the clutter central frequency component, which yields the maximum ratio of peak signal power to average noise power. The filter can be implemented by slightly modifying the structure of the conventional matched filter. The performance of such a filter is compared with that achievable if full a priori knowledge of the input interference were available and with that of the conventional matched filter. This comparison is made on a signal-to-interference power ratio basis after assuming a transmitted signal consisting of equally spaced pulses and an interference characterized by an exponential covariance matrix.

Optimum radar signal processing in clutter

This paper considers the joint optimization of a class of radar signals and filters in a number of clutter-pins-noise environments. The radar signal processor in this case will be optimum in the sense that its output at the time of target detection yields the maximum ratio of peak signal power to total interference power. If the interference at the input to this signal processor is a Gaussian random process, this processor also yields the maximum probability of detection for a given value of false-alarm probability. The signals used are pulse trains and the filters are tapped delay lines. The purpose of signal design is to determine the optimum complex weighting for each pulse of the pulse train. Filter design yields the optimum complex weighting for the output taps of the delay line. Filter design for a specified signal is considered first. This is followed by combined signal and filter design and matched filter design. Constrained signal and filter design is investigated last. It should be emphasized that the optimizations require a knowledge of the clutter time-frequency distribution. For practical situations, when the clutter distribution is unknown, an adaptive filter is proposed that automatically provides the optimum filter weights for a given transmitted signal. When the clutter has a range-time extent less than the equivalent range-time extent of the signal, filter design alone yields nearly optimum performance. As the clutter becomes extended in range-time, it is necessary to consider jointly the design of signal and filter to obtain an optimum radar signal processor. In this report it is suggested that the signal be designed under the assumption of the clutter being extended over a broad range of Dopplers and that the signal processor consist of a bank of adaptive filters. Then each filter output yields the maximum ratio of peak signal to total interference power for this signal design.