A metal-clad optical waveguide with a semiconductor microcavity structure is proposed to increase the coupling efficiency of spontaneous emission into a lasing mode (spontaneous emission coefficient P) and to increase a total spontaneous emission rate simultaneously. Such a microcavity semiconductor laser with enhanced spontaneous emission has novel characteristics, including high quantum efficiency, low threshold pump rate, broad modulation bandwidth, and intensity noise reduced to below the shot-noise limit (amplitude squeezing).

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Electromagnetic fields with photon-number fluctuation reduced below the standard quantum limit have been generated in a constant-currentdriven semiconductor laser. The generation is based on a new principle of high-impedance suppression for pump-amplitude fluctuation in a highly saturated laser oscillator. The observed noise level is 7.3% (31% after correction for detection quantum efficiency) in power below the standard quantum limit in the entire frequency range between 350 and 450 MHz. PACS numbers: 42.50.Dv, 03.65.Bz, 42.65.Bp A number-phase minimum-uncertainty state of the electromagnetic field is mathematically defined as an eigenstate of the operator e n+ie 5, where n is the number operator, 5 the sine operator, and Z a squeezingparameter. ' When I is greater than ln(2(n)) ', the photon-number noise becomes smaller than the standard quantum limit (SQL), (An ) & (n), and the sine-operator (phase) noise becomes larger than the SQL, (AS )/(C) & 1/4(n), while the minimum-uncertainty relationship, (An )(AS ) =(C) /4, is still preserved. Here C is the cosine operator. This "nonclassical state" is analogous to a squeezed state, which is an eigenstate of the operator e a~+ie a2. It features reduced quantum noise in one quadrature, (Aa i ) & -, ', and enhanced quantuin noise in the other quadrature, (Aa2) & 4, while the minimum-uncertainty relationship,(Aai )(Aa2) = -, ', , is still preserved. Here a~and a2 are the two quadrature phase amplitudes. In order to reduce one quadrature noise finally to zero in a squeezed state, an electromagnetic mode must have an infinite photon number. This is because the enhanced quadrature noise consumes the mode energy. This trade-off relationship between quantum noise reduction and required photon number places a limit on the signal-to-noise ratio improvement achievable by a squeezed state. On the other hand, photon-number noise can be reduced to zero without the requirement of an infinite photon number in a number-phase minimumuncertainty state because enhanced phase noise does not consume energy at all. This nonclassical state approaches a photon-number state (or Fock state) as E increases. This generation of a number-phase minimumuncertainty state as well as a squeezed state is of potential importance for information transmission, precision measurement, and atomic spectroscopy. A photonnumber state, specifically, achieves the maximum chan-nel capacity in optical communication, and it also improves the performance of an interferometric gravitywave detector. The observation of quadrature phase squeezing, which is an unmistakable mark for squeezed-state generation, was first reported by Slusher et al. This landmark has been followed by three experimental groups.We have proposed three schemes for generating a number-phase minimum-uncertainty state. These are self-phase modulation in a Kerr medium incorporated with an interferometer, quantum nondemolition measurement incorporated with feedback, ' and pump-amplitude fluctuation suppression in a highly saturated laser oscillator. '' A...

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We report the photon-number squeezing of optical solitons. 2.7 ps pulses were launched as solitons down a 1.5 km optical fiber. For energies slightly above that of fundamental solitons, they broadened spectrally due to self-phase modulation caused by x ͑3͒ nonlinearities. Filtering away outlying components of the broadened spectra squeezed the soliton's photon-number fluctuations to 2.3 dB (41%) below the shot-noise limit. Accounting for losses, this corresponds to 3.7 dB (57%) photon-number squeezing. A quantum field-theoretic model shows that the outlying spectral components have large energy fluctuations, so that their removal causes squeezing.[S0031-9007 (96)01512-8] PACS numbers: 42.50.Dv, 42.50.Ar, 42.65.Tg, 42.81.DpAn optical soliton in an optical fiber acts as a "particle" of light, according to classical electrodynamics, and can propagate long distances without changing shape or losing energy. Its particlelike nature is robust-a soliton is insensitive to perturbations and undistorted by collisions with other solitons. This, understandably, has practical implications and soliton-based telecommunication technologies are actively being pursued [1].A classical electrodynamical description of soliton propagation is inadequate if a soliton's quantum mechanical properties are of interest. Quantum mechanical descriptions not only better describe a soliton's noise properties, but also predict the existence of unique quantum mechanical soliton effects [2][3][4][5][6][7][8][9]. Most of the desirable properties of classical optical solitons, including their particlelike nature, are retained by such quantum mechanical descriptions [2-4].The first quantum mechanical soliton effect to be observed experimentally was quadrature-amplitude squeezing, predicted by Carter et al. [5,6]. For such squeezing, soliton amplitudes can fluctuate with magnitudes either smaller or greater than the standard quantum limit (SQL) of coherent light pulses, depending on the measured phase [5]. The "entanglement" of two solitons makes quantum nondemolition measurements possible, and was the second quantum mechanical soliton effect to be observed [7]. As described by Haus et al., two solitons with different velocities become quantum mechanically entangled when they collide [8]. A measurement of the phase of one soliton then allows the photon number of the other soliton to be determined without introducing losses or photonnumber noise.Recently, we have observed an unanticipated new quantum mechanical soliton effect-soliton photon-number squeezing [9]. By removing a soliton's outlying spectral components with a spectral bandpass filter, we were able to reduce its photon-number fluctuations to as much as 2.3 dB (41%) below the SQL. (For photon-number squeezing, the SQL is the usual shot-noise limit for coherent pulses of light.) Accounting for measurement losses and imperfect detector efficiencies, this implies a total photon-number squeezing of 3.7 dB (57%). Only squeezed light generation using a cw semiconductor laser at 66 K has produced phot...

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