Squeezed photon-number noise and sub-Poissonian electrical partition noise in a semiconductor laser

Abstract

Amplitude noise on the light from a semiconductor laser produced a photocurrent fluctuation spectrum that was a maximum of 85/o ( -8.3 dB) below the shot-noise limit. Squeezing in semiconductor lasers is not limited by the overall quantum, or current transfer, efticiency from the laser injection current to the detector photocurrent. Current leakage away from the lasing junction does not introduce Poissonian partition noise. PACS numbers: 42.50.Dv Photon-number eigenstates or Fock states of the electromagnetic field appear to be ideal for optical communication' and for a variety of high-precision measurements.It has been shown theoretically" that the amplitude fluctuation on the field from a pump-noisesuppressed laser can be reduced to below the standard quantum limit (SQL). In the case of a semiconductor laser, the pump noise is suppressed by a high-impedance constant-current source. Light from constant-currentdriven semiconductor lasers featuring squeezed amplitude fluctuation has been demonstrated. ' However, the modest degree of squeezing observed was ascribed to various deficiencies associated with the measurement system. In this experiment, we were able to reduce the eff'ects of optical feedback from the measurement system, and increase the light collection efficiency by direct "face-to-face" coupling of the laser and detector. Consequently we improved the noise reduction and further elucidated the basic physical processes that acct the noise properties of the device. The spectrum of photocurrent fluctuation was measured to be 85 -+7% below the shotnoise limit (SNL). Given that the detection quantum efficiency was approximately 89%, this corresponds to a squeezed amplitude fluctuation (at the front facet) of 96% ( -14 dB) below the SQL. This is by far the largest quantum noise reduction observed in any experiment; and it represents the closest approach so far to a number state. Apparently, amplitude squeezing in semiconductor lasers is not limited by the overall quantum efficiency but only by the optical output coupling efficiency. An explanation of this unexpected result is that current division does not introduce Poissonian partition noise, in contrast to the Poissonian partition noise associated with optical field division.Quadrature fluctuations of a number state, =~z =(2n+1)/4, are larger than the vacuum noise floor. This is in contrast to a quadrature squeezed state, which is a minimum-uncertainty state, where the fluctuation in the quadrature with reduced noise (A'i for example) is below that of the vacuum (~i~-, ' ). The field from a semiconductor laser is not in a minimum-V+ LED T LASER +A1 ZS D2 o RF oDC we, Rs V 50( 1K FIG. 1. The principal elements of the experimental ap-paratus that were inside the cryostat. The power spectrum of the amplified photocurrent is displayed on a spectrum analyzer (not shown), and the average detector current is monitored at the output labeled dc. uncertainty state; more importantly, the photon-number fluctuation may approach that of a number state. Removal of the re...

Observation of anticorrelated modal noise in a quasi-single-mode laser diode with a Michelson interferometer

“…2(a)] the fringe patterns of all the different modes are in phase (white fringe), so the noise compensation between the modes is as effective as it would be in the directly detected laser light. For vanishing armlength difference, phase-noise effects, which are proportional to (l a /c) 2 , are also absent (cf. below and Appen- Fig.…”

Wide-band suppression of photon-number fluctuations in a high-speed light-emitting diode driven by a constant-current source

“…This is, to our best knowledge, the widest bandwidth for the intensity squeezing ever reported with LEDs, rather closer to the bandwidth observed with laser diodes. 2 Another significance lies in the bias current density, ϳ38 A/cm 2 , which is obviously two orders of magnitude lower than the typical threshold current densities for the onset of lasing. The third important point is, needless to say, the room-temperature operation of the LED.…”

Generation of amplitude-squeezed light from 1550 nm distributed feedback semiconductor laser under wavelength selective optical feedback conditions

“…Among other methods, Richardson and co-workers showed that the amplitude squeezing, the intensity noise reduction below the shot noise limit, could be achieved in constant-current-driven semiconductor lasers. 1 But in almost all these experiments, the amount of squeezing measured at room temperature from a free-running laser is less than expected. Moreover, the generation of amplitude-squeezed light from distributed feedback semiconductor laser ͑DFB͒, although single mode, has been up to now considerably less successful than that from Fabry-Perot devices.…”

“…The electronic delay present in one arm of the receiver causes a periodic frequency-dependent phase shift between the two signals entering the hybrid junction with the result that the output current noise power from the receiver varies, as a function of frequency, between the actual laser noise and the shot noise level ͑SNL͒. 2 The quantum Langevin analysis indicates that the pump amplitude fluctuation is the thermal current noise generated by the driven source resistance R. 1 It becomes smaller than the SNL when R is higher than the dipole's differential resistance (R d ) of the laser. Figure 1 presents the noise level measured with the delay line balanced receiver where r is the pumping rate.…”