Phase Noise Of Laser Diode Research Articles

Randomness evaluation of LD phase noise for use as a continuous-variable random-number generator

Binary random numbers with an occurrence ratio of p:(1-p) (0 < p < 1) are needed in some applications. They are obtainable if the phase noise of a laser diode (LD) is used as a continuous-variable random-number generator. The problem is the existence of extra noise in the measuring system. However, most of this noise can be removed by taking the difference between consecutively measured values. This report confirms this by evaluating the randomness of the phase noise of an LD as a continuous quantity. Our findings show that we can easily obtain spontaneous-emission-based continuous-variable random numbers that allow one to set any p.

Linewidth Reduction by Feedforward Locking a Laser Diode to a Femtosecond Comb Line

We propose and demonstrate a novel method to narrow the linewidth of a laser diode at 1550 nm by an electronics-assisted feedforward path and weak locking to a femtosecond comb line simultaneously. By using a femtosecond comb as an ideal ultranarrow-linewidth optical reference, the laser diode is down converted, and its phase noise is “recorded” by the resulted intermediate frequency tone, which is filtered by a 40-MHz electronic filter. The consequentially introduced electronic delay is designed to match the optical delay, which is experienced by the same laser diode for upconversion. The delay match ensures that the phase noise of laser diode can be counteracted by its former “record” in upconversion and realizes linewidth reduction. As a result, the 20-dB linewidth of final radiation has been measured as 26 kHz, which is 1/35 of that of the laser diode.

Experimental study on close-in to microwave carrier phase noise of laser diode with external feedback

The residual phase noise at close-in to carrier offset frequency is studied for optical links using a laser diode with an external optical feedback. Since the measured FM noise degradation of the modulating signal was found to be insignificantly higher than the expected 20log (n) in dB, the residual phase noise of the laser diode was measured to quantify the expected carrier signal FM noise floor level. The measured residual phase noise of a InGaAsP laser diode at 1 KHz offset carrier signal of 5.08 GHz is measured to be -100 and -90 dBc/Hz with and without a 3-cm-long free-space external cavity, respectively. The close-in to carrier phase noise results of this laser at the external cavity resonance frequency of /spl ap/5 GHz is explained for the first time in terms of laser diode nonlinearity and FM noise theory of injection locked microwave oscillators. A good match between the predicted and measured results was observed. >

Effect of laser diode characteristics on the performance of an SCM–OFDM direct detection system

This paper describes the application of the microwave subcarrier multiplexing technique (SCM) in an optical frequency division multiplexing (OFDM) system which employs an optical FM direct detection scheme. Direct frequency modulation of a laser diode offers the advantages of compact optical spectrum and simple driving circuit; it also permits a more effective utilisation of optical channel capacity. The carrier-to-noise ratio performance of each subcarrier channel is evaluated. The effect of laser diode phase noise and relative intensity noise as well as the intermodulation product of subcarrier channels on the overall system performance is analysed and the results presented.

Multichannel image-rejection coherent detection system

An analysis is made of and data is presented from a prototype of an image channel rejection systems for the coherent detection of densely packed wavelength division multiplexed (WDM) channels. The system can simultaneously process a number of channels with a single-local laser diode and can extract the feedback control signals required to adjust critical system parameters. Although the system operates most simply for frequency shift keying (FSK) and phase-shift keying (PSK), it also operates for all the usual modulation schemes with minor adjustments. The control system aspects of the system are not affected by laser-diode phase noise.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>