Abstract: Apparatus and methods for linearizing an optical transmitter are described. A linearized optical transmitter according to the present invention includes a modulator bias voltage supply that biases an optical modulator. The optical modulator modulates an optical signal with a payload modulation signal. A feedback circuit receives electrical distortion signals generated by the modulator and generates a control signal in response to at least one of the electrical distortion signals. The control signal changes the bias voltage generated by the modulator bias voltage supply so as to reduce the at least one electrical distortion signal.

Abstract: In addition to a pilot signal for the conventional operating point control, a second pilot signal with a different frequency is superimposed on an optical signal. Then, the modulation component of an optical signal corresponding to the second pilot signal is detected from the output of an external modulator, the phase of the modulation component of the optical signal is compared with the phase of the second pilot signal, and as a result, an amplitude is obtained. The amplitude of a signal indicating a phase difference obtained when the amplitude of the driving waveform of the external modulator is different from the V&pgr; of the external modulator is detected, using the amplitude of the signal indicating the phase difference obtained when the amplitude of the driving waveform is the same as V&pgr;, as a reference, and the amplitude of the driving waveform.

Abstract: The present invention provides a low-cost optical transmission system using a plurality of subscriber lines which is capable of efficiently utilizing an optical transmission path. A communication status observing section 116 in a transmitting device 1 classifies subscribers into a plurality of groups based on a communication status at each subscriber end, and outputs constellation level information and level information which are different for each group. For each constant cycle, a modulation control section 117 and a gain control section 118 respectively set a QAM constellation level and a signal level which are different for each group and used in a basic modulating section 103.

Abstract: A wavelength-division multiplex optical transmission system is provided with: preliminary optical modulators 111 to 11n for outputting optical signals having different wavelengths from each other after being modulated by communications signals 11 to 1n that are signals to be supplied to specific optical receiving parts; an optical fiber 510 for transmitting the multiplexed optical signal; a subsequent optical modulator 210 for collectively modulating the transmitted optical signal so as to collectively modulate the optical signals being multiplexed by a broadcast signal 20 that is to be supplied equally to all optical receiving parts; and an optical fiber 520 for transmitting the modulated optical signal. A frequency band for the broadcast signal 20 is set not to overlap with any of those of the communications signals 11 to 1n.

Abstract: Because the phase comparison of the light signal data row and the light clock signal, and the coding of the light signal by the light signal, are simultaneously conducted, the influence of the phase variation in the signal path is not affected in principle, and the optimum phase condition is automatically established/maintained, and thereby, the present invention operates as an all-light type light receiver by which the light data and light clock are reproduced. Further, because the electric signal used herein exists in the range from the DC to the frequency of the difference between the light signal data row and the light clock signal, problems peculiar to the high speed electric signal can be avoided.

Abstract: The optical transmitter includes a semiconductor laser device, and an optical modulator region optically connected to the semiconductor laser device and having the function of modulating the output light from the semiconductor laser device. The operating temperature of the optical modulator region is changed without changing the oscillation wavelength of the semiconductor laser device.

Abstract: An optical transmission controller includes a semiconductor-laser, a semiconductor laser driver, a monitor photoreceptor, a waveform detector and a phase relation adjuster. The semiconductor laser driver allows the semiconductor laser to output an optical signal. The monitor photoreceptor monitors the optical signal output. The waveform detector detects a fall state of the optical signal output. The phase relation adjuster adjusts a phase relation between a fall timing of an input current and a variation timing of a relaxation oscillation of the optical signal output in accordance with a detection result of the waveform detector.

Abstract: A distortion monitor for a non-linear device is provided. The control circuit includes an input coupleable to receive a signal from the non-linear device and a first frequency monitor coupled to the input. The frequency monitor monitors the level of one of even and odd order distortion at a first frequency and creates a first signal indicative of the level of the distortion without the use of a pilot tone.

Abstract: The present invention alms at providing a low cost optical transmitter capable of controlling, with a high precision, fluctuations in optical output characteristic of a semiconductor light emitting device such as due to a temperature change.

Abstract: A demultiplex unit demultiplexes the optical output of a Mach-Zehnder optical modulator and inputs the demultiplexed optical output to a wavelength detection unit. The wavelength detection unit detects the wavelength deviations in the ascending or descending part of the optical signal and inputs the wavelength deviations to a detection unit. The detection unit detects the sign and magnitude of chirping in the magnitude of wavelength deviation and inputs the sign and magnitude of chirping to a driving voltage control unit. The driving voltage control unit compares the detected sign and amount of chirping with the target sign and magnitude of chirping, and a driving voltage generation circuit provides the Mach-Zehnder optical modulator with a suitable driving voltage.

Abstract: A method and system are disclosed for robustly (using first order effects) controlling the bias point and radio frequency (RF) amplitude level of a modulator for an optical transmitter. The method comprises the steps of extracting an output dither signal component of a digital optical output signal from the optical transmitter to drive a feedback loop; measuring the output dither signal component in the feedback loop for comparison to an input dither signal to the modulator; comparing the output dither signal to the input dither signal to determine their difference; and, based on the difference between them, maintaining the bias point and the RF amplitude level at an optimum value by varying an input voltage to the modulator via the feedback loop.

Abstract: A method and apparatus for introducing a monitoring signal on an optical information signal for maintaining the correct bias condition of an interferometric modulator. A dither signal is introduced into the optical signal that is output from the modulator. This composite signal is detected by tapping off a portion of the modulated light, and monitored in the output of an optical receiver that receives the tapped light. By suitable processing of the detected portion of the signal output from the modulator the information required to determine whether the bias is correct, and how to alter the bias voltage if it is not, is obtained and used to control the bias voltage.

Abstract: A light source with a broadband frequency-periodic output spectrum for digital spectrally coded data, whereby the light source consists of a solid state laser that is frequency-modulated or phase-modulated within one bit period.

Abstract: An optical transmitter is capable of constantly operating at an optimal operating point, even when a polarization angle varies, which is realized by an operation processing device controlling such that a predetermined range of an input-and-output characteristic of a modulator is scanned in order to obtain a bias voltage point that gives an optimal operation range, and an operation point controlling circuit controlling the operation range by a feedback control with the detected bias voltage point as a starting point.

Abstract: The present invention relates to an optical communication apparatus for detecting the intensity of light in an optical modulator or the intensity of a modulation signal and for controlling the operating point of the optical modulator based on the result of detection. In the optical communication apparatus having such a configuration, the operating point of the optical modulator can be kept stable even when the input light or the modulation signal is temporarily non-existent in the optical communication apparatus.

Abstract: In the method and apparatus for controlling the power level of a laser signal in free space communication, a communication terminal transmits an output laser beam into free space and also receives information, through a channel that is not free space laser based, about the power of the output laser beam measured at a distance and at different times. The terminal determines whether a drop in the power of the output laser beam measured at the distance is due to atmospheric effects based on the received information. The terminal increases the power level of the output laser beam to a desired level if the power drop is determined to be due to atmospheric effects. On the other hand, the terminal lowers the power of the output laser beam to a predetermined level if the power drop is determined to be due to blockage thus avoiding harm to accidental observers that might intrude into the path of the laser beams.

Abstract: In an optical transmitter, continuous wave light from a laser passes through a data modulator (DM) for non-return-to-zero (NRZ) encoding of a data stream and through a pulse modulator to add return-to-zero encoding to the modulated optical signal. A modulator controller monitors the output optical signal power, optimizes the bias setting for the DM and the PM, and optimizes the phase relationship between the pulse and data components of the modulated optical signal. For each optimization, a low amplitude and low frequency dither signal is injected at appropriate points in the modulator. A single photo detector and electrical receiver are used in a multiplexed fashion to monitor the optical output signal and derive separate feedback signals. Remaining control circuitry forces a null in a respective residual dither component in the optical output signal to maintain the desired bias level or phase alignment.

Abstract: The invention relates to an optoelectronic communication system having a data source (1) and a data sink (2), a transmitting unit (3) and a receiving unit (4) being present for data transmission from the data source (1) to the data sink (2). According to the invention it is proposed that the transmitting unit (3) and the receiving unit (4) are respectively structured as part of the data sink (2), a controllable modulation unit (5) being arranged in the data source (1), and the controllable modulation unit (5) altering the transmitted signal (6.1) of the transmitting unit (3) such that the signal (6.2) reflected from the modulation unit (5) to the receiving unit (4) includes the data information of the data source (1).