Quantum Noise Effects in Single-Mode Injection Lasers

Andrea Eschmann, Crispin W. Gardiner

The master-equation theory for multimode semiconductor lasers [A. Eschmann and C. W. Gardiner, Phys. Rev. A 54, 760 (1996)] is adapted to treat the case of an injection-locked laser. Both the intensity noise and the phase noise of the system are examined. A decrease in the total intensity noise and in the inten- sity noises of the individual modes is found for increasing injection power, provided the injection signal does not dominate the entire system. A regime is found in which a reduction of the intensity noise below the shot noise level is obtained which is not single-mode squeezing, but which is due to anticorrelations between the individual modes, and a further regime in which true single-mode squeezing exists is also found. The phase noise is found to decrease with increasing injection strength, in other words as phase locking occurs. \textcopyright{} 1996 The American Physical Society.

M. Lax, W. H. Louisell

J. P. Woerdman, Martin P. van Exter, N. J. van Druten

T -C Zhang, J.-Ph. Poizat, Philippe Grelu +7 more

We have investigated the intensity and phase noise of single-mode laser diodes, either free-running or using different types of line narrowing techniques at room temperature, namely feedback from an external grating and injection locking. We have measured an intensity squeezing of 1.2 dB in the first case, and 1.4 dB in the second case (respectively, 1.6 dB and 2.3 dB inferred at the laser output). We have observed that the intensity noise of a free-running 'single-mode' laser diode actually results from a cancellation effect between large anticorrelated fluctuations of the main mode and of weak longitudinal side modes. It is also shown that free-running diodes exhibit very large excess phase noise. Typically more than 80 dB above shot noise at 10 MHz, which can be significantly reduced by the above-mentioned techniques.

Helmut Ritsch, P. Zoller

Christoph Becher, Klaus J. Boller

Summary form only given.Laser diodes with pump noise suppression are reliable sources for the generation of amplitude-squeezed light. Recently, it was shown that this amplitude squeezing is not always a single mode effect but can result from a cancellation among anticorrelated fluctuations between the main mode and competing side modes. To obtain more details on this correlation effect, we performed spectrally resolved intensity noise measurements with a pump noise suppressed SDL 5410-C (810 nm) diode laser in different configurations: free-running, injection-locked, and with an external Littrow grating feedback.