Fabry-Perot type semiconductor laser with bulk optic feedback system – 4 GHz Detection Bandwidth

The experimental setup, shown in Fig. 1, consists of a multiple quantum well 830 nm semiconductor laser (APL 830-40) which has a free-running room temperature threshold of 48.2 mA. The output beam is collimated with an 8 mm focal length aspheric lens. The beam then passes through a 50:50 cube beamsplitter and an acousto-optic modulator (G&H 23080) before being reflected from an external mirror (R = 99%). It is the zeroth order beam from the acousto-optic modulator (AOM) which is coupled back to the semiconductor laser as the delayed optical feedback. The beam splitter directs half of the output beam to a 22 GHz photodiode. The photodiode signal was recorded for 1 µs (20 kpts) on a digital oscilloscope (Agilent Infiniium 54854A DSO) with a 4 GHz real-time bandwidth at a sampling rate of 20 GSa/s to constitute a single time series for subsequent analysis. The external cavity established by the external reflector has a round trip length of 135 cm (4.5 ns round trip period).

Fig. 1. Semiconductor laser with optical feedback setup
Fig. 1. Semiconductor laser with optical feedback setup

A high density data set of experimental output power time series was generated that could then be analyzed using a number of different analysis tools to generate high resolution maps. These quantify different aspects of the nonlinear dynamics at any point in the parameter space. The parameter space was injection current and the fraction of delayed optical feedback. The injection current was swept from 45 mA to 70 mA in steps of 0.1 mA and the optical feedback level was varied by adjusting the 0th order transmission of the AOM from 75.5% to 6.5% (in 351 non-uniform steps sizes), giving a total of 88,101 time series covering the operating region of interest. The transmission of the AOM is used as the variable which is proportional to the optical feedback level in the maps that are presented.

Fig. 2. Dynamics maps of (a) RMS amplitude (b) permutation entropy (D = 5, τ = 2) and (c) permutation entropy (D = 5, τ = 90) as a function of optical feedback level and laser injection current. The white curve shows the laser threshold injection decreasing with increasing optical feedback [1].
Fig. 2. Dynamics maps of (a) RMS amplitude (b) permutation entropy (D = 5, τ = 2) and (c) permutation entropy (D = 5, τ = 90) as a function of optical feedback level and laser injection current. The white curve shows the laser threshold injection decreasing with increasing optical feedback [1].

Figure 2 shows detailed maps of the (a) RMS amplitude and (b) normalized permutation entropy for the laser system over the range of the injection-feedback parameter space which shows complex dynamics. The RMS amplitude map identifies where the laser displays fluctuations in the output power, the bulk of which occur in the coherence collapse region bounded by distinct upper and lower boundaries. Areas of low amplitude correspond to CW operation or the laser operating below threshold, indicated by the solid white curves in Fig. 2.

The maps of permutation entropy in Fig. 2(b) and 2(c) provides a relative quantitative measure of the complexity (on different time scales) of the output power fluctuations in the time series. Permutation entropy was calculated for ordinal pattern length D = 5 and delay of τ = 2 points (Fig. 2(b)) and τ = 90 points (fig. 2(c)). Typical time series and associated RF spectra for different parts of the map marked as (i), (ii) and (iii) in Fig. 2(b) are shown in Fig. 3.

Fig. 3. Time series and corresponding FFT spectra for different regions of the parameter space as marked in Fig. 2. (i) Iinj = 68.7 mA, TAOM = 0.644, (ii) Iinj = 58.5 mA, TAOM = 0.194, (iii) Iinj = 68.2 mA, TAOM = 0.09.
Fig. 3. Time series and corresponding FFT spectra for different regions of the parameter space as marked in Fig. 2. (i) Iinj = 68.7 mA, TAOM = 0.644, (ii) Iinj = 58.5 mA, TAOM = 0.194, (iii) Iinj = 68.2 mA, TAOM = 0.09.

View more detailed discussion of this system.

 

References

[1] J. P. Toomey and D. M. Kane, “Mapping the dynamic complexity of a semiconductor laser with optical feedback using permutation entropy,” Optics Express 22 (2), 1713-1725 (2014).

 

 

Information about the data available

Download here

This data is being provided to be used in the context of the SIEF project “Big Data Knowledge Discovery”

Any use of this data should cite the following reference:
J. P. Toomey and D. M. Kane, “Mapping the dynamic complexity of a semiconductor laser with optical feedback using permutation entropy,” Optics Express 22 (2), 1713-1725 (2014).

Source:

Dr Joshua P Toomey
MQ Photonics Research Centre
Department of Physics and Astronomy
Macquarie University
josh.toomey@mq.edu.au

Prof Deborah M Kane
MQ Photonics Research Centre
Department of Physics and Astronomy
Macquarie University
deb.kane@mq.edu.au

Data Set Information:
This data set was recorded from an experimental semiconductor laser subject to optical feedback on 13/08/12.
Laser wavelength ~ 830nm. External cavity round trip time 4.5ns.

During the experiment, 2 system parameters were varied: the optical feedback level and laser injection current.

  • Optical feedback was varied by changing the RF power to an acousto-optic modulator (AOM) which varies the amount of laser power transmitted in the 0th order beam. A voltage between 0V-1V corresponds to maximum transmission (0V) and minimum transmission (1V). The actual power transmitted by the AOM is not a linear relationship with voltage. Relative feedback level can be approximated from the reduction in laser threshold.
  • Laser injection is controlled by directly varying the current supply to the device (Profile ITC510 Laser Diode Combi-controller). Laser was held at a constant 25C.

The dataset contains 88,101 files containing output power time series recorded from the laser using a fast photodiode (Discovery Semiconductors DCS30S 22GHz) and 4GHz realtime oscilloscope (Agilent 54854A) for different settings of:

  • Injection (251 values = 45mA to 70mA in 0.1mA steps)
  • Feedback (351 values from 0.45V to 0.8V in 0.001V steps)

The filenames consist of the AOM and INJ values at which the data was recorded:
e.g. AOM_0.642V_INJ_45.2mA.h5 : feedback = 0.642 V, injection = 45 mA

These values are also recorded in the file attributes as ‘var1’ and ‘var2’.

Each hdf5 file consist of a single dataset called ‘TimeSeries’. This contains a time series of amplitude values measured as the voltage across the 50ohm oscilloscope input.

Time series were sampled at 20GSamples/s (50ps per data point) and contain 20,000pts for a total record length of 1microsecond.