Showing papers on "Comb generator published in 1985"
TL;DR: In this article, the first measurements of the semiconductor laser linewidth broadening factor α using a recently proposed CHP (chirp-halfwidth product) method are reported.
Abstract: First measurements of the semiconductor laser linewidth broadening factor α using a recently proposed CHP (chirp-halfwidth product) method are reported. Gain-switched optical pulses have been generated by sinusoidal RF and comb generator drive. The simultaneous recording of streak-camera and monochromator traces provides the required data for determination of α. The values of α between 6 and 7.5 are obtained for a 1.3 μm mesa laser. Computer simulations predict that the CHP formula should provide an estimate of α within ±15% for either comb generator or hard sinusoidal drive.
19 citations
TL;DR: In this article, the spacings of the pass and stop bands of the comb filters are at a multiple of the frequency by which the frequency shifter shifts that of its input signal.
Abstract: A loudspeaking telephone instrument comprises a transmit path comprising a microphone (1) and comb filter (2); a receive path comprising a comb filter (3), a frequency shifter (4) and a loudspeaker (5); and a hydrid circuit (6). The frequency shifter (4) shifts the frequency of a signal applied to its input by a fixed amount and the comb filters (2,3) are arranged so that the frequency shifted signal falls in their stop bands. This increases the available gain in the loudspeaking telephone instrument before instability occurs. The spacings of the pass and stop bands of the comb filters (2,3) are at a multiple of the frequency by which the frequency shifter shifts that of its input signal.
14 citations
TL;DR: In this article, an experimental study of chirping in 1.55 μm VPTDFB lasers under the demanding situation of high-speed modulation with high pulse on/off ratios was conducted.
Abstract: VPTDFB semiconductor lasers have been shown to exhibit particularly low transient frequency chirp resulting in record distances for dispersive fibre transmission at 2 to 4 Gbit/s rates. The letter reports experimental study of chirping in 1.55 μm VPTDFB lasers under the demanding situation of high-speed modulation with high pulse on/off ratios. The laser was modulated with 100 ps current pulses from a comb generator, or with high-frequency RF at 4 GHz. It is found that the laser's chirped linewidth is between 2 to 8 A for modulation on/off ratios from 4:1 to more than 20:1. We infer that at high laser pulse on/off ratios there will be significant pulse distortion at 8 to 10 Gbit/s rates for fibre distance of ≳≫60 km even with these low chirp VPTDFB lasers. However, the exact nature of this distortion and its system impact in dispersive fibre transmission may depend in detail on the specific laser parameters and system operating conditions.
7 citations
Patent•
31 Oct 1985TL;DR: In this article, a transition detector is disclosed which compares comb filtered component signals from adjacent image lines, and a control signal generator is generated in response to the relative levels of the detected signals for the given line, and the lines adjacent the given LINE.
Abstract: A transition detector is disclosed which compares comb filtered component signals from adjacent image lines. A detector detects signals in the band of frequencies normally occupied by color representative information for a given line and two adjacent lines. A control signal generator generates a control signal in response to the relative levels of the detected signals for the given line, and the lines adjacent the given line. The composition of the comb filtered component signal coupled from the comb filter to the component processing channel is altered in response to the generated control signal.
5 citations
Patent•
15 Apr 1985TL;DR: A signal generator circuit for a television receiver employed in a CAPTAIN or other videotex system or the like can be found in this article, where a reference signal oscillator (1) and a synchronising signal generator (2') for generating a horizontal synchronisation signal (P H ) synchronised with the reference signal.
Abstract: A signal generator circuit for a television receiver employed in a CAPTAIN or other videotex system or the likecom- prises a reference signal oscillator (1) for producing a reference signal and a synchronising signal generator (2') for generating a horizontal synchronisation signal (P H ) synchronised with the reference signal. A frequency divider (3) is responsive to the reference signal for producing a colour sub-carrier signal (SC). A phase-locked loop is responsive to the sub-carrier signal (SC) and includes a voltage-controlled oscillator (6). The voltage-controlled oscillator (6) produces an output signal (CLK o ) synchronised with the sub-carrier signal (SC) and having a series of rising edges. A rising edge of the sub-carrier signal (SC) periodically coincides with a rising edge of the signal (CLKo) from the voltage-controlled oscillator (6). A detector (13) detects a time when a rising edge of the sub-carrier signal (SC) coincides with a rising edge of the output signal (CLK o ) of the voltage-controlled oscillator (6), and a clock signal (CLK) is then generated by a generator (18), the clock signal (CLK) being synchronised with the output signal (CLK o ) of the voltage-controlled oscillator (6) and having a series of falling edges. The horizontal synchronisation signal generator (2') and the clock signal generator (18) are controlled so as to ensure that the rising edge of the horizontal synchronisation signal (P H ) coincides with a falling edge of the clock signal (CLK). This ensures an accurate count of the pulses for determining the horizontal position of a display by the receiver and prevents horizontal jitter in the display.