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Showing papers on "Pulse-position modulation published in 1995"


Journal ArticleDOI
TL;DR: Direct-detection optical synchronous code-division multiple-access systems with M-ary pulse-position modulation (PPM) signaling are investigated and it is shown that under average power and bit error rate constraints, there always exists a pulse position multiplicity that permit all the subscribers to communicate simultaneously.
Abstract: Direct-detection optical synchronous code-division multiple-access (CDMA) systems with M-ary pulse-position modulation (PPM) signaling are investigated. Optical orthogonal codes are used as the signature sequences of our system. A union upper bound on the bit error rate is derived taking into account the effect of the background noise, multiple-user interference, and receiver shot noise. The performance characteristics are then discussed for a variety of system parameters. Another upper bound on the probability of error is also obtained (based on Chernoff inequality). This bound is utilized to derive achievable expressions for both the maximum number of users that can communicate simultaneously with asymptotically zero error rate and the channel capacity. Our results show that under average power and bit error rate constraints, there always exists a pulse position multiplicity that permit all the subscribers to communicate simultaneously. >

130 citations


Proceedings ArticleDOI
25 Jul 1995
TL;DR: Computer simulation confirms that the proposed system can achieve higher bit rate transmission with higher quality in both flat Rayleigh and frequency selective fading environments.
Abstract: This paper proposes a symbol rate and modulation level controlled adaptive modulation/TDMA/TDD for future personal communication systems. To achieve wide dynamic range for the modulation parameter control as well as to improve delay spread immunity, the proposed system controls both modulation level and symbol rate according to the channel conditions. Moreover, the proposed system also applies a novel channel condition monitor based on the instantaneous delay profile measurement for the modulation parameter control. Computer simulation confirms that the proposed system can achieve higher bit rate transmission with higher quality in both flat Rayleigh and frequency selective fading environments.

115 citations


Proceedings ArticleDOI
25 Jul 1995
TL;DR: The authors show that the successive IC scheme for higher modulation together with mixed modulation or parallel channels give a considerable increase in performance and flexibility compared to single modulation systems employing a conventional detector.
Abstract: Analyses a successive interference cancellation (IC) scheme for M-ary QAM modulation in direct sequence code division multiple access (DS/CDMA) systems. The performance under Rayleigh fading is analysed for single modulation systems and systems employing either of two different methods, mixed modulation or parallel channels, for handling multiple data rates. The authors show that the successive IC scheme for higher modulation together with mixed modulation or parallel channels give a considerable increase in performance and flexibility compared to single modulation systems employing a conventional detector.

53 citations


Patent
Bar-David Israel1
23 Aug 1995
TL;DR: In this paper, a spread spectrum code pulse position modulated communication system is presented, where the frequency spectrum of a transmitted signal is spread by encoding bits with a predefined spectrum-spreading codeword (420,440) which is in accordance with regulatory requirements or other standardization decisions.
Abstract: In a spread spectrum code pulse position modulated communication system the frequency spectrum of a transmitted signal is spread by encoding bits with a predefined spectrum-spreading codeword (420,440) which is in accordance with regulatory requirements or other standardization decisions. When the predefined spread spectrum codeword is passed through a filter matched to the characteristics of the codeword, a peak is detected in the main lobe. A positive main lobe can indicate a binary value of "0" and a negative main lobe, associated with the inverse of the predefined codeword, can represent a binary value of "1". Additional information is conveyed by modulating the position of the center of the codeword within the symbol duration. In one embodiment, the position of the center of the codeword is varied (410) among eight positions. Thus, eight signal states are available, and three additional bits may thereby be conveyed. Two differently and independently time-shifted spread spectrum codewords (420,440) may be modulated (455), each with one of two orthogonal carrier signals, such as a sine and a cosine wave, thereby conveying a total of eight bits per symbol duration. Here, a symbol duration is the duration of a codeword.

38 citations


Patent
02 May 1995
TL;DR: In this article, a correlation is established between a set of symbols and the corresponding signal position/signal characteristic combinations, where each symbol has a corresponding pulse position and a corresponding signal characteristic.
Abstract: A method and apparatus for transmitting information over a wireless connection are provided. A correlation is established between a set of symbols and a set of pulse position/signal characteristic combinations. Thus, each symbol has a corresponding pulse position and a corresponding signal characteristic. The signal characteristic may be, for example, a particular frequency, amplitude or phase. To communicate a symbol, a device generates a signal in which a tone burst is sent during the pulse position that corresponds to the symbol. In addition, at least some portion of the signal reflects the signal characteristic that corresponds to the symbol. A receiving device determines the pulse position in which the tone burst was sent and determines the signal characteristic reflected in the signal. The receiving device then determines the symbol based on the pulse position and the signal characteristic. Synchronization is improved by generating synchronization tone bursts before each pulse position modulation frame. Inter-symbol interference is minimized by placing guard bands on each side of the synchronization pulse and/or between pulse windows in each pulse position modulation frame.

32 citations


01 Jan 1995
TL;DR: Different modulation schemes supporting multiple data rates in a Direct Sequence Code DivisionMultiple Access (DS/CDMA) system are studied and it is shown that the multi processing-gain scheme and the multi-channel scheme have almost the same performance.
Abstract: Different modulation schemes supporting multiple data rates in a Direct Sequence Code DivisionMultiple Access (DS/CDMA) system are studied. Both AWGN and multipath Rayleigh fadingchannels are considered. It is shown that the multi processing-gain scheme and the multi-channelscheme have almost the same performance. However, the multi-channel scheme may have someadvantages due to near-far resistance, easier code design and multi-user receiver construction.The drawback though, is the need for linear amplifiers also in mobile terminals. A multi-modula-tion scheme is also possible, but the performance for the users with the high data rates are signifi-cantly worse than for the other schemes. Furthermore multi chip-rate, parallel combinatory spreadspectrum (PC/SS) and pulse position modulation (PPM) are discussed briefly.Keywords: DS/CDMA, Spread spectrum, multi-rate schemes, PCS, multi-channel, multi chip-rate, multi processing-gain and multi-modulation schemes, Parallel Combinatory Spread Spec-trum (PC/SS), parallel channels, Amplitude Modulation (AM), Quadrature Amplitude Modula-tion (QAM).

25 citations


Proceedings ArticleDOI
06 Nov 1995
TL;DR: In this article, an adaptive modulation system with a punctured convolutional code for land mobile communications is proposed to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments.
Abstract: This paper proposes an adaptive modulation system with a punctured convolutional code for land mobile communications to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments. The proposed system adaptively controls the coding rate of the punctured convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. The performance in fading environments is evaluated theoretically and by computer simulation. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

24 citations


Journal ArticleDOI
TL;DR: This paper presents a digital implementation of a Multi-Carrier Modulation scheme without spectral overlapping between sub-carriers, which uses aQAM modulation and a square root Nyquist pulse shaping function and guarantees orthogonality betweenSub-carrier signals even after transmission over a dispersive fading channel.
Abstract: This paper presents a digital implementation of a Multi-Carrier Modulation scheme without spectral overlapping between sub-carriers. This scheme uses aQAM modulation and a square root Nyquist pulse shaping function. It guarantees orthogonality between sub-carrier signals even after transmission over a dispersive fading channel. The modulator and the demodulator use aK-pointDFT and a set of polyphase filters. Therefore all single-carrier equalization and detection techniques can be used in this Multi-Carrier Modulation system.

21 citations


Journal ArticleDOI
01 Feb 1995
TL;DR: In this article, an original scheme for the utilisation of Optically Preamplified (EDFA) PPM receivers in inter-satellite laser communications is presented, in order to facilitate high bit rate operation an analysis is presented for a PPM system employing threshold detection.
Abstract: An original scheme for the utilisation of optically preamplified (EDFA) PPM receivers in intersatellite laser communications is presented. In order to facilitate high bit rate operation an analysis is presented for a PPM system employing threshold detection. When operating at the STM-1 bit rate of 155 Mbit/s and using conservative parameters the authors' model demonstrates a possible receiver sensitivity of 13.5 photons/bit (at a BER of 10/sup -6/) in the presence of background noise, thus indicating the impressive potential of the proposed receiver formation for use in satellite communications. The authors further demonstrate that their threshold detection PPM scheme can obtain receiver sensitivities up to 12.3 dB-better than an equivalent EDFA OOK NRZ satellite receiver, for which new results are also presented. Furthermore the results indicate that the PPM system may perform at sensitivities beyond the fundamental optically preamplified OOK NRZ limit of 27.3 photons/bit. >

18 citations


Proceedings ArticleDOI
18 Jun 1995
TL;DR: R Reed-Solomon codes are shown to be more effective to reduce an asymptotic floor to the error probability of the system with large M, while CCs with soft-decision Viterbi decoding is more effective for theSystem with small M.
Abstract: We analyze the effects of an optical hard-limiter and error correction coding on the performance of direct-detection optical synchronous CDMA systems with, pulse position modulation (PPM) signaling; Reed-Solomon (RS) codes and convolutional codes (CCs) with soft-decision Viterbi decoding are employed. We analyze the upper bound on the performance under the assumption of Poisson shot noise model for the receiver photodetector and the noise due to the detector dark currents is considered. We analyze the performance under average power and bit rate constraints. Our results show that the upper bound on the performance of the system with the optical hard-limiter becomes tighter as M is increased. Moreover, RS codes are shown to be more effective to reduce an asymptotic floor to the error probability of the system with large M, while CCs with soft-decision Viterbi decoding is more effective for the system with small M.

18 citations


Patent
11 Sep 1995
TL;DR: In this article, a tri-graph encoding process is used to convert the raw input data into encoded input data, which are then encoded on the navigation signal using a PPM technique.
Abstract: A method and apparatus for encoding and decoding data on navigation signal pulse pairs utilizes pulse position modulation (PPM). The pulse interval between a first pulse and a second pulse of the pulse pair is varied depending on whether the logic value of the data to be encoded is a logic "0" or a logic "1". A tri-graph encoding process converts the raw input data into encoded input data. Each input data bit is encoded into three bits with each bit having the same logical value as the input data bit. The encoded input data is then encoded on the navigation signal using a pulse position modulation (PPM) technique. A decoder recovers the encoded data and provides an error correction process for high data integrity that corrects certain bit errors that may occur during the transmission and reception of the data on the navigation signal. The error correction process detects and corrects errors such as a missing bit, an extra bit or a bit error.

Proceedings ArticleDOI
18 Jun 1995
TL;DR: It is demonstrated that there exists an optimum PPM order, at a given number of users, that maximises the achievable bit rate and the optimum system operating parameters that minimise these errors are specified.
Abstract: A new hybrid based on pulse position modulation code division multiple access (PPM CDMA) is proposed and studied in the context of the indoor infrared LAN. The utilisation of optical orthogonal codes (OOC) as signature sequences is investigated. Original results are presented illustrating the improvement in bit rate achieved by utilising PPM CDMA rather than on-off keying (OOK) CDMA. It is demonstrated that there exists an optimum PPM order, at a given number of users, that maximises the achievable bit rate. Original results are presented for the false alarm errors due to the OOC cross-correlations while the optimum system operating parameters that minimise these errors are specified.

Patent
06 Jun 1995
TL;DR: In this paper, a pulse position modulation detector divides a timing window into a plurality of pulse position windows, determines the peak magnitude of a signal level received during each pulse position window, and compares the peak magnitudes of the signal detected during each position window to determine during which position window the greatest peak magnitude is detected.
Abstract: A pulse position modulation detector divides a timing window into a plurality of pulse position windows, determines the peak magnitude of a signal level received during each pulse position window, compares the peak magnitudes of the signal detected during each pulse position window to determine during which pulse position window the greatest peak magnitude is detected, and generates a bit sequence corresponding to the pulse position window wherein the greatest peak magnitude was detected within the current timing window.

Journal ArticleDOI
TL;DR: A modulation scheme that uses pulse-position modulation of a high-frequency binary grating to increase the diffraction efficiency of the elements is presented and experimental results show that diffraction efficiencies of >80% are attainable.
Abstract: A modulation scheme that uses pulse-position modulation of a high-frequency binary grating to increase the diffraction efficiency of the elements is presented. These elements are designed and fabricated with both one- and two-dimensional signals for operation in transmission or reflection modes in the visible and the infrared regions of the spectrum. A direct electron-beam lithography fabrication process capable of realizing features of ~280 nm with a resolution of 15 nm is described in detail. Experimental results show that diffraction efficiencies of >80% are attainable.

Journal ArticleDOI
TL;DR: The theoretical analysis and computer simulation of transmission performances of radio QPSK and QAM signals clarify that the proposed system is superior to the fiber-optic radio communication system using conventional coherent analog optical links.
Abstract: In this system a radio signal is converted into an optical signal with the same modulation format coherently transmitted through a wide-band optical fiber without any baseband demodulation and modulation. The theoretical analysis and computer simulation of transmission performances of radio QPSK and QAM signals clarify that the proposed system is superior to the fiber-optic radio communication system using conventional coherent analog optical links. >

Proceedings ArticleDOI
18 Jun 1995
TL;DR: In this paper, the performance of optical synchronous code-division multiple access (CDMA) with on-off keying (OOK) signaling and CDMA with M-ary pulse position modulation (PPM)/CDMA systems using prime sequence codes as signature codes is analyzed under the assumption of Poisson shot noise model for the photodetector.
Abstract: The performance of optical synchronous code-division multiple-access (CDMA) with on-off keying (OOK) signaling (OOK/CDMA) and CDMA with M-ary pulse position modulation (PPM) signaling (PPM/CDMA) systems using prime sequence codes as signature codes is analyzed under the assumption of Poisson shot noise model for the photodetector. The bit error probability of OOK/CDMA is evaluated, and the upper bound on the bit error probability of PPM/CDMA is derived. Further, the performance is compared for some values of the average signal count per second, the length of prime sequences, and the number of simultaneous users under the constraint on throughput. It is found that PPM/CDMA performs better than OOK/CDMA by the pulse position multiplicity. It is also found that as the number of slots per frame of PPM increases, the bit error probability performance is improved. Moreover, it is found that CDMA with longer prime sequence codes has better performance. Therefore, we show that in order to achieve the low bit error probability and many simultaneous users, we should employ PPM/CDMA with larger number of slots and longer prime sequence codes.

Journal ArticleDOI
TL;DR: A novel digital pulse time modulation technique called digital pulse interval modulation (DPIM) is presented, in which the input signal information is transmitted by the time intervals between two succeeding pulses.
Abstract: A novel digital pulse time modulation (PTM) technique called digital pulse interval modulation (DPIM) is presented, in which the input signal information is transmitted by the time intervals between two succeeding pulses. DPIM has simplicity of circuit configuration combined with other attractive features of digital pulse position modulation (DPPM) for optical-fiber communications. This article derives theoretical expressions for transmission capacity, code characteristics, and power spectral density (PSD), and the analytical results are compared with experimental data.

Journal ArticleDOI
TL;DR: In this paper, an original hybrid pulse position modulation code division multiple access (PPM-CDMA) scheme was proposed and studied in the context of the indoor infrared communication network.
Abstract: An original hybrid pulse position modulation code division multiple access (PPM-CDMA) scheme is proposed and studied in the context of the indoor infrared communication network. The use of optical orthogonal codes (OOC) is proposed and original results are presented illustrating the improvement in bit rate achieved by utilizing PPM-CDMA rather than on/off keying (OOK) CDMA. Results are presented for the maximum number of users that can communicate over the network at a given bit rate and it is shown that there exists an optimum PPM order, at a given number of users, that maximizes the achievable bit rate. Original results are presented for the false-alarm errors due to the OOC cross correlations, and the optimum system operating parameters that minimize these errors are specified.

Journal ArticleDOI
TL;DR: The results demonstrate that the number-state system requires less than half the energy consumed by the coherent-state one in order to attain the same performance.
Abstract: The performance of optical code-division multiple-access (CDMA) communication systems utilizing number-state light field is evaluated. Lossy direct-detection optical channels are assumed. Both on-off keying (OOK) and pulse-position modulation (PPM) schemes are investigated. For OOK, the exact bit error rate is evaluated taking into account the effect of both multiple-user interference and transmission loss. Upper and lower bounds on the bit error probability for PPM-CDMA systems are derived under the above considerations. The effect of both background and thermal noise is neglected in our analysis. Performance comparison between the number-state and coherent-state OOK/PPM-CDMA networks is also presented. Our results demonstrate that the number-state system requires less than half the energy consumed by the coherent-state one in order to attain the same performance. Lower bounds on the maximum number of simultaneous users are derived for both number- and coherent-state PPM-CDMA systems with asymptotically zero error rate. >

Journal ArticleDOI
TL;DR: It appears that moderate data rates (tens of Mb/s) are feasible with networks of about 5-20 stations even with low-link SNR, while the PE can be either crosstalk or power-limited.
Abstract: There is interest in space-based wireless optical networks with nonsynchronous multiple access capability. Since space links are usually power-limited, pulsing is necessary to accomplish the multiple accessing and data transmission. In this paper, a nonsynchronous pulsed multiple-access optical-space system using code sequences for identifying stations is considered. Both OOK and PPM data encoding is considered and the link data rates and bit error probabilities (PE) are examined. It is shown that the achievable data rates are limited by the multiple access coding and the link SNR, while the PE can be either crosstalk or power-limited. It appears that moderate data rates (tens of Mb/s) are feasible with networks of about 5-20 stations even with low-link SNR. >

Proceedings ArticleDOI
18 Jun 1995
TL;DR: Results show that when MLSD is employed, 16-PPM provides the best average-power efficiency among the modulation techniques considered, and these techniques are compared to on-off keying.
Abstract: Examines the performance of pulse-position modulation (PPM) on indoor infrared channels with multipath-induced intersymbol interference (ISI). The authors review maximum-likelihood sequence detection (MLSD) for PPM over ISI channels in additive white Gaussian noise. They evaluate the performance of PPM links other 46 actual measured indoor infrared channels. Detailed performance results are presented for 2-, 4-, 8-, and 16-PPM at bit rates of 10 Mb/s and 30 Mb/s, and these techniques are compared to on-off keying. They results show that when MLSD is employed, 16-PPM provides the best average-power efficiency among the modulation techniques considered.

Journal ArticleDOI
TL;DR: The high SNR rules have a performance nearly equal to that of the ML rules, but provide a significant performance improvement over the simple correlation rules and are virtually as simple to implement for a wide range of signal energies.
Abstract: We investigate frame synchronization algorithms for direct detection multi-pulse pulse position modulation (MPPM) optical communication systems. The optimal rules (in a maximum likelihood sense) are derived, approximations to them that are computationally easier to implement are identified, and upper bounds on the synchronization probability are obtained. It is seen that the high SNR rules have a performance nearly equal to that of the ML rules, but provide a significant performance improvement over the simple correlation rules and are virtually as simple to implement for a wide range of signal energies. We also address the problem of designing periodic MPPM synchronization sequences with good autocorrelation properties, based on a maximum, worst case, peak-to-sidelobe distance criterion. Upper bounds on the peak-to-sidelobe distance for such sequences are derived, and a few sequences, generated by computer simulations, for different synchronization sequence lengths are given. >

Patent
Mark Devon1
17 Mar 1995
TL;DR: In this article, a method and apparatus for detecting and indicating a collision on a wireless channel are provided, where data is transmitted over the wireless channel using pulse position modulation, and a transceiver is disclosed for connecting a device to a wire-based network via a wireless connection.
Abstract: A method and apparatus for detecting and indicating a collision on a wireless channel are provided. According to the method, data is transmitted over the wireless channel using pulse position modulation. The channel is monitored during each pulse position modulation frame to determine whether a pulse occurs during more than one pulse window of the pulse position modulation frame. If a pulse occurs during more than one pulse window of a pulse position modulation frame, then the devices on the wireless channel determine that a collision has occurred. A transceiver is disclosed for connecting a device to a wire-based network via a wireless connection. The device and transceiver communicate over the wireless connection using pulse position modulation. If a collision occurs on the wire-based network, then the transceiver transmits to the device a signal in which pulses are asserted during more than one pulse window of a pulse position modulation frame. The signal, which violates standard pulse position modulation rules, indicates to the device that a collision occurred.

Proceedings ArticleDOI
14 Nov 1995
TL;DR: The results indicate that TCM is a very promising coding technique for L-PPM on high-speed non-directed infrared channels.
Abstract: We examine the performance of high-speed non-directed infrared links using pulse-position modulation (PPM) with trellis-coded modulation (TCM) to mitigate the effects of multipath-induced intersymbol interference (ISI) on such links. Using the measured characteristics of multipath indoor infrared channels, we calculate BER curves and ISI power penalties for maximum-likelihood sequence detection of 8-PPM links using rate-2/3 trellis codes operating at 10 and 30 Mb/s. Our results indicate that TCM is a very promising coding technique for L-PPM on high-speed non-directed infrared channels.

Patent
22 Dec 1995
TL;DR: In this article, a PLL-mode radio frequency module is provided with a CPU, which functions to vary a waveform of a PPM signal fed from a transmitter body so as to permit a pulse duty ratio of the PPM signals to be about 50%.
Abstract: A PLL-mode radiofrequency module capable of being connected to a transmitter of any kind The PLL-mode module is provided therein with a CPU, which functions to vary a waveform of a PPM signal fed thereto from a transmitter body so as to permit a pulse duty ratio of the PPM signal to be about 50% The PPM signal thus varied is fed to a modulation circuit and then subjected to FSK modulation, so that a PLL oscillator constituted by a PLL circuit and a modulation circuit or voltage control oscillator generates a frequency as indicated by a rotary switch A carrier frequency controller thus constructed is arranged on a side of the PLL-mode radiofrequency module rather than the transmitter body, so that the PLL-mode radiofrequency module may be connected to a transmitter of any kind

Journal ArticleDOI
TL;DR: An original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format is presented and the conditions required to achieve and optimize both slot and frame synchronization are predicted.
Abstract: Digital pulse position modulation (PPM) has been shown to be attractive for implementation over the optical fibre channel when the laser transmitters are average power limited and the channel bandwidth is abundant. The synchronization requirements for optical fibre PPM however have not yet been addressed. We present an original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format. Further we predict the conditions required to achieve and optimize both slot and frame synchronization. The major system parameters including the modulation index, data probability distribution and pulse shape are catered for and used in the analysis. A novel technique, capable of coping with the different PPM word sizes, is presented and used to achieve frame phase extraction directly from the PPM stream. Appropriate mathematical models are developed and used to predict the spectral properties at the output of the frame phase synchronizer. Original practical results measured on a PPM system are presented and shown to agree with the theoretical models and predictions to within 1 dB. >

Proceedings ArticleDOI
TL;DR: In this paper, a new form of pulse time modulation, termed digital pulse interval modulation (DPIM), is introduced, exhibiting improved performance and relaxed timing constraints compared to digital pulse position modulation.
Abstract: A new form of pulse time modulation, termed digital pulse interval modulation (DPIM) is introduced in this paper, exhibiting improved performance and relaxed timing constraints compared to digital pulse position modulation (DPPM). Theoretical expressions are presented for transmission capacity, code characteristics and power spectral density, along with measurements from a simple experimental prototype, illustrating the advantages of the new scheme.

Patent
29 Dec 1995
TL;DR: In this paper, a relaxation oscillation subcarrier on-off keying scheme was proposed to improve the signal-to-noise ratio of a receiver receiving the modulated optical signals and the data rate of the optical signal.
Abstract: An optical communications system for transmission of optical signals using relaxation oscillation subcarrier, on-off keying modulation of the optical signals. Relaxation oscillation subcarrier on-off keying improves the signal-to-noise ratio of a receiver receiving the modulated optical signals and the data rate of the optical signal. A modulation device generates relaxation oscillations by pulsing a driving current for a transmitter between a first level below a threshold current and a second level above the threshold current. The optical communication system can further include a fiber optic link between the transmitter and the receiver. The optical communications system can further incorporate multiple frequency shift keying. The modulation device and modulation scheme can be used in all digital optical communications systems using a pulsed laser diode.

Patent
24 Nov 1995
TL;DR: In this paper, a system for transmission on an optical link by modulating an optical carrier suitable for video-communication cable networks, includes devices for increasing the modulation of the optical carrier, such as increasing the intensity modulation.
Abstract: A system for transmission on an optical link by modulating an optical carrier suitable for video-communication cable networks, includes devices for increasing the modulation of the optical carrier, such as increasing the intensity modulation. The system is particularly suited for the case in which a high input optical power is coupled into the optical link. Also, the modulation can be increased from a null value if the modulation is other than intensity modulation, in order to prevent or to reduce phenomena degrading transmission quality associated with the Brillouin effect.

Proceedings ArticleDOI
20 Apr 1995
TL;DR: In this paper, the authors demonstrated that gain-switch operation is preferable to Q-switching operation to control and to obtain a good pulse width and amplitude reproducibility for Mars-Earth spatial communications.
Abstract: The CNES (Centre National d'Etudes Spatiales, French space agency) established the laser system characteristics for Mars-Earth spatial communications using the Pulse Position Modulation technique. Today, diode-pumped solid-state lasers are under intense research and development. Indeed, in comparison with flash-lamp pumped laser, they offer significant advantages in terms of efficiency, compactness, lifetime and high beam quality. We have demonstrated that gain-switch operation is preferable to Q-switching technique to control and to obtain a good pulse width and amplitude reproducibility. The pulse width requirement and the laser-diode pumping scheme lead to a preferred configuration based on a microchip laser oscillator coupled to an amplifier. Best results were performed with a Nd:YVO4 microchip longitudinally-pumped by fiber-coupled laser-diode bar. Diffraction limited beam, 15 ns pulse width and 100 kHz repetition rate were achieved. The output beam was actually also single frequency and linearly polarized. A transversally-diode-pumped 7-pass amplifier is also demonstrated.