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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 13 — Jun. 23, 2008
  • pp: 9513–9518
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Full mapping of optical noise in photonic devices: an evaluation by near-field scanning microscopy

Jean-Marie Moison, Izo Abram, and Marcel Bensoussan  »View Author Affiliations


Optics Express, Vol. 16, Issue 13, pp. 9513-9518 (2008)
http://dx.doi.org/10.1364/OE.16.009513


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Abstract

We demonstrate the possibility of mapping the transverse spatial distribution of optical noise at the output of photonic devices. Maps of local low-frequency noise are obtained by using statistics on multiple-sampling data from near-field scanning optical microscopy (NSOM). On selected laser diodes, the signatures of basic types of transverse mode instabilities (relative phase and amplitude of modes) are unambiguously obtained. On more complex systems, the types of mode instability can be identified and their intensity can be monitored. Such noise mapping opens a new path for analyzing noise origins and for optimizing device design.

© 2008 Optical Society of America

1. Introduction

2. Experimental

Our purpose can be accomplished by many imaging devices, provided that signal and noise components of the power emitted by each point in the source are determined with the very high spatial resolution required by the small size of modern devices. For the sake of demonstrating the principle and potentialities of noise mapping, we use here near-field scanning optical microscopy (NSOM) which directly probes the local emission with sub-λ resolution. NSOM imaging involves scanning a small scattering object across the light source. Recording the scattered power during the scan generates the signal map, proportional to the map of the source intensity. The ultra resolution is obtained when both the size of the object and its distance to the source are in the sub-wavelength range. All data shown in the following have been obtained with a conventional NSOM setup using the tip of uncoated pulled fibers both as scattering object and as collector of scattered light; the resolution obtained is <300nm [11

11. S. Bourzeix, J. M. Moison, F. Mignard, F. Barthe, A. C. Boccara, C. Licoppe, B. Mersali, M. Allovon, and A. Bruno, “Near-field optical imaging of light propagation in semiconductor waveguide structures,” Appl. Phys. Lett. 73, 1035–1037 (1998). [CrossRef]

]. The signal map records the average output of the photodetector connected to the other end of the fiber (Fig. 1). The global power captured by the tip over the map is the integral S of the signal map and can be converted to actual emitted power P through calibration.

Fig. 1. Schematics of the experimental setup.

Detecting noise in this signal can be accomplished by several means, including spectrum analyzers, auto-correlators or balanced homodyne setups. For the sake of demonstration, we use here a simple multiple-sampling procedure. The scattered power is repeatedly sampled at time intervals τ, up to a large number of samples M, and the average and standard deviation of the data set are stored as signal and noise maps. Under standard assumptions of stochasticity and ergodicity, the deviation measures the noise within the [1/2Mτ-1/2 τ] frequency band [12

12. N. G. Van Kampen, Stochastic Processes in Physics and Chemistry (North Holland, Amsterdam1981).

]. With τ~100µs and M~100, this band Δf [50-5000Hz] involves the LF (usually 1/f) tail of the optoelectronic noise. The noise intensity is measured by the ratio of the integrals of the noise and signal maps N/S, the reciprocal of the usual S/N ratio, or by the relative intensity noise defined as RIN*=(N/S)2/Δf, in analogy with the classical RIN definition [4

4. K. Peterman, Laser diode modulation and noise (Klüwer, Dordrecht1991).

,13

13. I. Joindot, “Measurement of relative intensity noise (RIN) in semiconductor lasers,” J. Phys. III France 2, 1591–1603 (1992). [CrossRef]

]. RIN* is expected to be larger than the RIN measured on the global power, since it involves in addition noise patterns which conserve this global power, such as partition noise.

3. Basic mode instabilities

We exemplify the noise analysis procedure on sources which display a rich variety of noise behaviors, namely a preliminary batch of cascade lasers [14

14. F. Dross, F. Van Dijk, O. Parillaud, B. Vinter, and N. Vodjdani, “Single-transverse-mode InGaAsP/InP edge-emitting bipolar cascade laser,” IEEE J. Quantum Electron. 41, 1356–1360 (2005). [CrossRef]

,15

15. F. Dross, F. van Dijk, and Ph. Gallion, “Discussion on the improvement of opto-RF link properties by using a bipolar cascade laser source,” IET Optoelectronics 1, 9–15 (2007). [CrossRef]

] involving two active layers separated by a tunnel junction, emitting around 1.55µm. We first focus on two lasers which display particularly simple behaviors, since those are basic blocks for analyzing complex cases. Their signal map (Fig. 2(a) and (c)) involves two stripes, in agreement with the calculated main mode of the structure with two stripes centered on the active layers. For laser #1 above threshold (Fig. 2(b)), the noise map involves four stripes, with nodes located at the signal antinodes; for laser #2 below threshold (Fig. 2(d)) it features five stripes, two of which are centered on the signal nodes.

Fig. 2. 11×5.5µm NSOM maps of test laser diodes. Top: laser #1 above threshold, (a) signal, (b) noise. Bottom: laser #2 below threshold, (c) signal, (d) noise. In all cases, the tip vibration is horizontal. Contour lines of the signal map are superimposed on noise maps.

Within this basic two-mode scheme, the above results can be analyzed quantitatively on the basis of the vertical sections of the maps. From the main mode U2, we deduce in succession the phase instability map |UV| through formulas fit for all Gauss-Hermite modes with waist w such as |UV|=|y/w.U2-w/4.dU2/dy2|, V2, and the amplitude instability |U2-V2|.

Fig. 3. Model noise maps for phase or amplitude instabilities between the generic rectangularsymmetry transverse mode (00) or (01) and its next higher-order model. Lateral waist is here twice the vertical one.

The good agreement between experimental and calculated sections (Fig. 4), obtained without adjustable parameter except for the vertical scale, shows that noise originates mostly from phase instability with ρΔcosφ~4% for laser #1, and amplitude instability with Δρ2~2% for laser #2. It may be noted that, while the dominant mode completely masks the weak mode in the signal map, clear signatures in the noise map can be obtained even for small instabilities.

Fig. 4. Vertical sections of signal (green dots) and noise (red dots) maps for lasers #1 (bottom) and #2 (top). Red lines indicate the prediction of noise sections for phase (bottom) and amplitude (top) instabilities. Please note that predictions (red lines) appear noisier than experimental data because their calculation involves second derivatives of the signal sections.

4. Monitoring complex behaviors

Fig. 5. Evolution of signal and noise maps (left) and RIN* and global power (right) with injection current in laser #3.

This may prove to be important on the system level, for instance upon coupling to downstream sections. The transverse partition mode noise of the test lasers (RIN*>-60dB/Hz) is very high, but will not appear on global power measurements. However, under coupling to a single-mode waveguide matched to their main mode, the overall source will display a high RIN due to mode filtering of the higher-order mode (intensity instability) or pointing instability (phase instability). Evaluation from the formulas for reduction of the transmission with coupling mismatch shows that, for instance, this value rises up to ~-70dB/Hz for laser #3 above threshold. Considering the NSOM information, the coupler can be redesigned to a compromise between coupling efficiency and insertion noise, basically by enlarging the coupler in the direction of mode instability, an oblique one in the present case, to encompass the additional mode.

5. Present sensitivity limit

For this first study, we have chosen rather noisy devices purposefully. Moving to low-noise devices requires an evaluation of the limits of our approach. Possible sources of extra noise generated by the instrument involve noise in the power-detecting chain like in global noise analysis, but also terms due to the relative movements of source and imaging device. Here the tip vibration imposed for shear-force control or spurious displacements generate extra pointing noises that we evaluate on the end of a long single-mode fiber (w~4.5µm) illuminated by a stable 1.55µm laser, assumed to be a noise-free source. A modified NSOM controller allows for noise measurement within long periods during which the vibration is activated and the distance feedback is operative (Fig. 6 (center)), and short periods during which the vibration is stopped and the feedback is locked (Fig. 6 (right)). This separates the contribution of the imposed tip vibration from the other terms.

Fig. 6. 20×20µm NSOM images of an SMF mode: (left) signal map (center) noise map in vibrating-tip mode with horizontal inline displacement, (right) noise map in static-tip mode.

Since displacements are not synchronized with sampling events, pointing noise maps are given by derivatives of the signal map while N/S is ~Δd/w where Δd is the standard deviation of the displacement. Indeed the noise map in the vibrating-tip mode can be very well fit by the derivative of the signal map along the vibration direction with Δd=20±5nm. The tip vibration is therefore the dominant source of extra noise. Similar maps and values of Δd are obtained on a stable laser with w~1.1µm, showing that the analysis stands for all common source sizes.

In the static-tip mode, this term is cancelled and the noise map is fairly well fitted assuming a random isotropic displacement with Δd~2nm corresponding to spurious vibrations. It may be stressed that the measurement of pointing noise, which involves the analysis of the whole noise map, is limited only by the sensitivity of local intensity measurements and not by the tip resolution which is much larger. Finally, for instance, on sources with w=2µm the smallest RIN* we can detect at present is ~-100dB/Hz in the LF range, a fair basis for the analysis of common lasers diodes.

6. Conclusion

Acknowledgments

We are grateful to S. Lovisa, A. Lestra, N. Bouché, S. Delepine from Alcatel, F. VanDijk, F. Dross, and N. Vodjdani from Thales for lending us laser sources, and F. Barthe and M.N. Mérat-Combes for technical help. This work was supported in part by the “Région Ile de France”, through SESAME project n°1377, and by the “Conseil Général de l’Essonne”.

References and links

1.

J.Ph. Poizat, T. Chang, and Ph. Grangier, “Quantum intensity noise of laser diodes and nonorthogonal spatial eigenmodes,” Phys. Rev. A 61, 043807–11 (2000). [CrossRef]

2.

B. Schmidt, N. Lichtenstein, B. Sverdlov, N. Matuschek, S. Mohrdiek, T. Pliska, J. Mueller, S. Pawlik, S. Arlt, H. U. Pfeiffer, A. Fily, and C. Harder, “Further development of high-power pump laser diodes,” Proc. SPIE 5248, 42–54 (2003). [CrossRef]

3.

J. P. Wilde, A. A. Tselikov, G. R. Gray, Y. Zhang, and S. Gangopadhyay, “Magneto-optical disk drive technology using multiple fiber-coupled flying optical heads. Part II. Laser noise considerations,” Appl. Opt. 41, 884–894 (2002). [CrossRef] [PubMed]

4.

K. Peterman, Laser diode modulation and noise (Klüwer, Dordrecht1991).

5.

F. Wölfl, J. F. Ryan, A. M. Fox, A. D. Ashmore, D. J. Mowbray, M. S. Skolnick, M. Hopkinson, and G. Hill, “Intensity noise in quantum-dot laser diodes,” Appl. Phys. Lett. 78, 3577–3579 (2001). [CrossRef]

6.

K. Haneda, M. Yoshida, M. Nakazawa, H. Yokohama, and Y. Ogawa, “Linewidth and relative intensity noise measurements of longitudinal modes in ultrahigh-speed mode-locked laser diodes,” Opt.Lett. 30, 1000–1002 (2005). [CrossRef] [PubMed]

7.

J. Ph. Poizat, T. Chang, O. Ripoll, and Ph. Grangier, “Spatial quantum noise of laser diodes,” J. Opt. Soc. Am. B 15, 1757–1761 (1998). [CrossRef]

8.

A. Bramati, J. P. Hermier, A. Z. Khoury, E. Giacobino, P. Schnitzer, R. Michalzik, K. J. Ebeling, J.Ph. Poizat, and Ph. Grangier, “Spatial distribution of the intensity noise of a vertical-cavity surface-emitting semiconductor laser,” Opt. Lett. 24, 893–895 (1999). [CrossRef]

9.

C. L. Garrido Alzar, S. M. de Paula, M. Martinelli, R. J. Horowicz, A. Z. Khoury, and G. A. Barbosa, “Transverse Fourier analysis of squeezed light in diode lasers,” J. Opt. Soc. Am. B 18, 1189–1195 (2001). [CrossRef]

10.

P. Kappe, J. Kaiser, and W. Elssäser, “Spatially correlated light emission from a resonant-cavity light-emitting diode,” Opt. Lett. 28, 49–51 (2003). [CrossRef] [PubMed]

11.

S. Bourzeix, J. M. Moison, F. Mignard, F. Barthe, A. C. Boccara, C. Licoppe, B. Mersali, M. Allovon, and A. Bruno, “Near-field optical imaging of light propagation in semiconductor waveguide structures,” Appl. Phys. Lett. 73, 1035–1037 (1998). [CrossRef]

12.

N. G. Van Kampen, Stochastic Processes in Physics and Chemistry (North Holland, Amsterdam1981).

13.

I. Joindot, “Measurement of relative intensity noise (RIN) in semiconductor lasers,” J. Phys. III France 2, 1591–1603 (1992). [CrossRef]

14.

F. Dross, F. Van Dijk, O. Parillaud, B. Vinter, and N. Vodjdani, “Single-transverse-mode InGaAsP/InP edge-emitting bipolar cascade laser,” IEEE J. Quantum Electron. 41, 1356–1360 (2005). [CrossRef]

15.

F. Dross, F. van Dijk, and Ph. Gallion, “Discussion on the improvement of opto-RF link properties by using a bipolar cascade laser source,” IET Optoelectronics 1, 9–15 (2007). [CrossRef]

16.

T. Gensty, W. Elsäßer, and C. Mann, “Intensity noise properties of quantum cascade lasers,” Opt. Express 13, 2032–2039 (2005), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-6-2032. [CrossRef] [PubMed]

OCIS Codes
(140.2020) Lasers and laser optics : Diode lasers
(270.2500) Quantum optics : Fluctuations, relaxations, and noise

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: January 22, 2008
Revised Manuscript: March 1, 2008
Manuscript Accepted: March 20, 2008
Published: June 13, 2008

Citation
Jean-Marie Moison, Izo Abram, and Marcel Bensoussan, "Full mapping of optical noise in photonic devices: an evaluation by near-field scanning microscopy," Opt. Express 16, 9513-9518 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-13-9513


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References

  1. J. Ph. Poizat, T. Chang, and Ph. Grangier, "Quantum intensity noise of laser diodes and nonorthogonal spatial eigenmodes," Phys. Rev. A 61, 043807-11 (2000). [CrossRef]
  2. B. Schmidt, N. Lichtenstein, B. Sverdlov, N. Matuschek, S. Mohrdiek, T. Pliska, J. Mueller, S. Pawlik, S. Arlt, H. U. Pfeiffer, A. Fily, and C. Harder, " Further development of high-power pump laser diodes," Proc. SPIE 5248, 42-54 (2003). [CrossRef]
  3. J. P. Wilde, A. A. Tselikov, G. R. Gray, Y. Zhang, and S. Gangopadhyay, "Magneto-optical disk drive technology using multiple fiber-coupled flying optical heads. Part II. Laser noise considerations," Appl. Opt. 41, 884-894 (2002). [CrossRef] [PubMed]
  4. K. Peterman, Laser diode modulation and noise (Klüwer, Dordrecht 1991).
  5. F. Wölfl, J. F. Ryan, A. M. Fox, A. D. Ashmore, D. J. Mowbray, M. S. Skolnick, M. Hopkinson, and G. Hill, "Intensity noise in quantum-dot laser diodes," Appl. Phys. Lett. 78, 3577-3579 (2001). [CrossRef]
  6. K. Haneda, M. Yoshida, M. Nakazawa, H. Yokohama, and Y. Ogawa, "Linewidth and relative intensity noise measurements of longitudinal modes in ultrahigh-speed mode-locked laser diodes," Opt.Lett. 30, 1000-1002 (2005). [CrossRef] [PubMed]
  7. J. Ph. Poizat, T. Chang, O. Ripoll, and Ph. Grangier, "Spatial quantum noise of laser diodes," J. Opt. Soc. Am. B 15, 1757-1761 (1998). [CrossRef]
  8. A. Bramati, J. P. Hermier, A. Z. Khoury, E. Giacobino, P. Schnitzer, R. Michalzik, K. J. Ebeling, J.Ph. Poizat, and Ph. Grangier, "Spatial distribution of the intensity noise of a vertical-cavity surface-emitting semiconductor laser," Opt. Lett. 24, 893-895 (1999). [CrossRef]
  9. C. L. Garrido Alzar, S. M. de Paula, M. Martinelli, R. J. Horowicz, A. Z. Khoury, and G. A. Barbosa, "Transverse Fourier analysis of squeezed light in diode lasers," J. Opt. Soc. Am. B 18, 1189-1195 (2001). [CrossRef]
  10. P. Kappe, J. Kaiser, and W. Elssäser, "Spatially correlated light emission from a resonant-cavity light-emitting diode," Opt. Lett. 28, 49-51 (2003). [CrossRef] [PubMed]
  11. S. Bourzeix, J. M. Moison, F. Mignard, F. Barthe, A. C. Boccara, C. Licoppe, B. Mersali, M. Allovon, and A. Bruno, "Near-field optical imaging of light propagation in semiconductor waveguide structures," Appl. Phys. Lett. 73, 1035-1037 (1998). [CrossRef]
  12. N. G. Van Kampen, Stochastic Processes in Physics and Chemistry (North Holland, Amsterdam 1981).
  13. I. Joindot, "Measurement of relative intensity noise (RIN) in semiconductor lasers," J. Phys. III France 2, 1591-1603 (1992). [CrossRef]
  14. F. Dross, F. Van Dijk, O. Parillaud, B. Vinter, and N. Vodjdani, "Single-transverse-mode InGaAsP/InP edge-emitting bipolar cascade laser," IEEE J. Quantum Electron. 41, 1356-1360 (2005); [CrossRef]
  15. F. Dross, F. van Dijk and Ph. Gallion, "Discussion on the improvement of opto-RF link properties by using a bipolar cascade laser source," IET Optoelectronics 1, 9-15 (2007). [CrossRef]
  16. T. Gensty, W. Elsä??er, and C. Mann, "Intensity noise properties of quantum cascade lasers," Opt. Express 13, 2032-2039 (2005), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-6-2032. [CrossRef] [PubMed]

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