In this paper, a novel measurement of FM-noise is shown. We present both experimental and simulation results by considering the external RF phase modulation, with good agreement. The results show for the first time, the influence of the phase modulation index, modulation frequency, in the conversion of FM-noise to intensity noise in an optical link by considering all effects on RF modulated light emitted by a 1550 nm DFB laser.
Wireless access systems are attractive because of their potential high data rate transmissions. For example, frequency bands in the range from 3.1 GHz up to 10.6 GHz are allocated to Ultra Wide Band IEEE 802.15.3a standards for future Wireless Personal Access Networks (WPAN).
The frequency conversion of wireless signals in the optical domain is interesting since it benefits from the huge optical bandwidth for generation and distribution of up-converted sub-bands.
This papers explores different techniques for photonics generation of microwave mixing with digital modulation of the microwave sub-carriers, at 1550 nm. The solutions exploit the non-linearity of different devices such as laser diodes, electro-optic modulators, dispersive fiber generating frequency-to-intensity modulation conversion. Comparisons are made regarding their potential applications to low-cost and broadband radio-over fiber systems like Ultra Wide Band over fiber. The mixing conversion gain, available bandwidth, complexity of the system, its applicability to broadband radio over fiber networks, are elements of comparison that are discussed in this paper.
An unbalanced Mach Zehnder interferometer (UMZ) is used here for up-conversion of a microwave subcarrier, with IQ modulation at 30 and 200 Msymb/s. Both QPSK and QAM-16 are investigated, and a low BER of 10-9 is demonstrated after detection of the up-converted microwave subcarrier for an optical power of -1dBm delivered by a directly modulated laser diode.
In this paper, we propose and demonstrate a new and original model for theoretical calculation of the noise power spectral density (NPSD) in phase-modulated optical links. The phase modulation is operated in the RF frequency range by an external phase modulator. The NPSD is derived for the first time in interferometric systems, by considering all effects such as the 1/f FM noise of the laser, and white noise applied to light from a 1550 nm DFB laser, with phase modulation. The results show for the first time the influence of the phase modulation index, modulation frequency, and interferometric delay in the phase-to-intensity noise conversion. Theoretical calculations and experimental results of conversion of FM-noise to intensity noise in an optical link are shown with good agreement.
In this paper we describe an application of Holographic CDMA technique for indoors infrared (Optical) wireless (Free- Space) communication system. A holographic CDMA technique is a multiple access technique by which each pair of users communicate by imprinting their information on a spatial code which is recognizable or known by that pair's receiver only. We will describe the two-dimensional imaging techniques, namely user's code transmission, and highlight the basic parameters and components that need to be optimized. Then we will describe the receiver's processing module, which is comprised of a Fourier transform lens and a holographic matched-filter to decode the desired user's code successfully. Free-space optical Holographic CDMA indoor Communications processing gain can in principle be as high as 1-6-108, which results in reduction of other user's interfering effects on the desired receiver's signal. Furthermore, each user can have different modulating signals (Analog or Digital), or different information rate with any signal shape which is highly desirable for the above application.
We present a new technique for remote upconversion by inserting a passive all-optical device in the microwave (MW) fiber-optic link. Using a semiconductor laser directly modulated by two MW signals and an unbalanced Mach-Zehnder interferometer (UMZ) to convert optical frequency modulation into intensity modulation, mixing is achieved after photodetection. Experiments with a UMZ integrated on glass- substrate have demonstrated the feasibility of this optical method for MW mixing with a low cost device of easy fabrication. Temperature control of the device allows optimized mixing performance and stable response. This method permits to overcome the effect of chromatic dispersion in standard singlemode fiber systems operating in the 1.55 micrometers wavelength window. Due to the presence of high-frequency fundamental components in the optical field, the received power is considerably degraded during transmission and direct detection in conventional systems, using either direct or external modulation in the MW band. With the proposed technique, lower frequency components of the field can be transmitted. The insertion of the simple UMZ generates high frequency only at detection side, therefore the available fiber length is extended. As it is shown by simulation results, this method can be used for the upconversion of MW subcarriers carrying digital signals.
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