OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 22 — Nov. 4, 2013
  • pp: 26983–26989
« Show journal navigation

Transverse mode discrimination in long-wavelength wafer-fused vertical-cavity surface-emitting lasers by intra-cavity patterning

Nicolas Volet, Tomasz Czyszanowski, Jaroslaw Walczak, Lukas Mutter, Benjamin Dwir, Zlatko Micković, Pascal Gallo, Andrei Caliman, Alexei Sirbu, Alexandru Mereuta, Vladimir Iakovlev, and Eli Kapon  »View Author Affiliations


Optics Express, Vol. 21, Issue 22, pp. 26983-26989 (2013)
http://dx.doi.org/10.1364/OE.21.026983


View Full Text Article

Acrobat PDF (7246 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Transverse mode discrimination is demonstrated in long-wavelength wafer-fused vertical-cavity surface-emitting lasers using ring-shaped air gap patterns at the fused interface between the cavity and the top distributed Bragg reflector. A significant number of devices with varying pattern dimensions was investigated by on-wafer mapping, allowing in particular the identification of a design that reproducibly increases the maximal single-mode emitted power by about 30 %. Numerical simulations support these observations and allow specifying optimized ring dimensions for which higher-order transverse modes are localized out of the optical aperture. These simulations predict further enhancement of the single-mode properties of the devices with negligible penalty on threshold current and emitted power.

© 2013 OSA

1. Introduction

Current developments in optical fiber communication networks require ever increasing bandwidths and drastic reduction in power consumption of the optical modules involved. Vertical-cavity surface-emitting lasers (VCSELs) offer considerable advantages in these applications over traditional edge-emitting lasers, owing to their easier wavelength setting, inherent low-power consumption, circular beams and low manufacturing costs [1

1. R. Michalzik, ed., VCSELs: Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers (Springer, 2013).

]. Until recently, the single-mode (SM) performance of long-wavelength (1.3–1.6 μm) VCSELs lagged behind their short-wavelength (< 1 μm) counterparts, because of the totally different device technologies and the lower performance of the gain material at longer wavelengths. The most successful long-wavelength VCSEL technologies employ strained AlGaInAs quantum wells (QWs) for the active region and a buried tunnel junction (TJ) for current and optical confinements [2

2. E. Kapon and A. Sirbu, “Long-wavelength VCSELs: Power-efficient answer,” Nat. Photonics 3, 27–29 (2009). [CrossRef]

]. This approach has led to room-temperature single-mode (SM) emission powers with record values of 5.4 mW and 8.2 mW, respectively at 1320 nm [3

3. A. Mircea, A. Caliman, V. Iakovlev, A. Mereuta, G. Suruceanu, C.-A. Berseth, P. Royo, A. Syrbu, and E. Kapon, “Cavity mode—Gain peak tradeoff for 1320-nm wafer-fused VCSELs with 3-mW single-mode emission power and 10-Gb/s modulation speed up to 70 °C,” IEEE Photonics Technol. Lett. 19, 121–123 (2007). [CrossRef]

] and 1550 nm [4

4. T. Gründl, P. Debernardi, M. Müller, C. Grasse, P. Ebert, K. Geiger, M. Ortsiefer, G. Böhm, R. Meyer, and M.-C. Amann, “Record single-mode, high-power VCSELs by inhibition of spatial hole burning,” IEEE J. Sel. Top. Quantum Electron. 19, 1700913 (2013). [CrossRef]

] wavelengths. To our knowledge, these record values far exceed those obtained in a manufacturing environment, where other performance parameters (e.g., current versus voltage characteristics, high-speed modulation, polarization, exact emission wavelength, device yield) need to be met as well. Therefore, new reliable techniques for increasing the SM power are still needed.

Wafer-fused long-wavelength VCSELs are well-positioned for real applications, having already been reported to fulfill the Telcordia reliability requirements [5

5. A. Sirbu, G. Suruceanu, V. Iakovlev, A. Mereuta, Z. Mickovic, A. Caliman, and E. Kapon, “Reliability of 1310 nm wafer fused VCSELs,” IEEE Photonics Technol. Lett. 25, 1555–1558 (2013). [CrossRef]

]. Moreover, with this technology that provides access to the core of the optical microcavity, the interfaces of the cavity are exposed before fusion. This permits surface patterning that can introduce additional optical confinement [6

6. A. Sirbu, V. Iakovlev, A. Mereuta, A. Caliman, G. Suruceanu, and E. Kapon, “Wafer-fused heterostructures: Application to vertical cavity surface-emitting lasers emitting in the 1310 nm band,” Semicond. Sci. Technol. 26, 014016 (2011). [CrossRef]

, 7

7. T. Czyszanowski, R. P. Sarzala, M. Dems, J. Walczak, M. Wasiak, W. Nakwaski, V. Iakovlev, N. Volet, and E. Kapon, “Spatial-mode discrimination in guided and antiguided arrays of long-wavelength VCSELs,” IEEE J. Sel. Top. Quantum Electron. 19, 1702010 (2013).

]. In particular, this intra-cavity pattern can be designed to enhance the confinement of the fundamental mode (FM) with respect to that of higher-order transverse modes (HOTMs).

The purpose of this paper is to demonstrate that intra-cavity patterns in long-wavelength wafer-fused VCSELs represent a suitable solution for transverse mode discrimination, compatible with industrial fabrication. We show an increase of more than 0.45 mW in SM power for a specifically designed cavity pattern. Numerical simulations of the patterned VCSEL structures confirm the experimental results, allow interpretation of the impact of patterning on mode confinement and provide essential information for further optimization of the SM performance.

2. Patterned-cavity VCSEL design

Fig. 1 (a) Schematic cross-section of the patterned VCSEL, refractive index along the cavity (in green) and calculated normalized electric field (in blue). Red dashed lines show the position of the fused interfaces. (b) SEM micrographs of a vertical cross-section at the center of the device. Inset shows an enlargement of the area delimited by the yellow rectangle.

Such patterned VCSELs were structurally studied by cross-sectional focused ion beam (FIB) etching combined with scanning electron microscopy (SEM) to characterize the intra-cavity ring pattern after fusion. The device was cleaved from the wafer and placed in the chamber of a Zeiss NVision 40 microscope equipped with a FIB module, where SEM images were automatically acquired every 85 nm etching increment of the cleaved surface. This enabled a three-dimensional reconstruction of the patterned cavity, which confirmed its ring shape, and revealed a good etched-wall verticality and low surface roughness. One of these images is displayed in Fig. 1(b) and shows the central cross-section of the patterned cavity and the TJ mesa. From such images, we measured for this particular pattern design L ≅ 70 nm, w ≅ 1.1 μm, dP ≅ 8.7 μm and dTJ ≅ 6 μm, in close agreement with the target parameters.

3. Lasing characteristics

Several hundreds of devices with different pattern dimensions were tested on-wafer, enabling statistical analysis of the impact of the cavity pattern on the threshold current, emitted power and lasing spectra in current and temperature ranges. We selected the most typical device of each family of pattern parameters for further higher-resolution spectral measurements and spectrally-resolved near-field (NF) imaging.

Figure 2(a) presents the optical spectra at different currents of three typical VCSELs: the reference device without pattern and two patterned devices labeled π1 (w = 1.5 μm, dP = 9 μm) and π2 (w = 1.0 μm, dP = 8 μm). These spectra show that HOTMs are affected by the cavity patterning. Figure 2(b) displays these spectra at 12 mA, rigidly blueshifted so that the emission wavelengths of the FMs LP01 coincide. The spectral power of the FM of both patterned devices is not deteriorated. Conversely, the HOTMs (LP11, LP21) are suppressed for patterned devices. This reduction is larger for pattern π2. We also notice a systematic blueshift of the emission wavelengths of the HOTMs as compared to the FM for the patterned devices. This blueshift further increases with the order of the mode and for reduced dP, like in the case of pattern π2. Indeed, since the mode fields extend more into the region of lower effective index introduced by the etched ring, they acquire a lower effective mode index and thereby a shorter resonance wavelength as compared to the corresponding modes of the device without pattern.

Fig. 2 Characteristics of patterned-cavity and non-patterned VCSELs at 20°C. (a) Optical spectra versus current and (b) at 12 mA. (c) SMSR and emitted power for the device without pattern (black), with pattern π1 (red) and with pattern π2 (green).

The top part of Fig. 2(c) presents the difference of spectral power between LP01 and LP11, or side-mode suppression ratio (SMSR), for these devices versus current. The current ISM above which the emission becomes multi-mode, i.e. with a SMSR smaller than 30 dB, depends on the pattern dimensions. For the reference device, we measured ISM ≅ 7.7 mA and it emits in SM over a wavelength range ΔλSM ≅ 2.8 nm scanned during the current ramping up to ISM. For pattern π1, ISM is reduced, while for pattern π2, ISM ≅ 12.3 mA and ΔλSM ≅ 4.9 nm. This continuous wavelength tuning range thus shows an increase of 2.1 nm, which is very valuable for applications such as tunable diode laser absorption spectroscopy (TDLAS) [10

10. A. Larsson, “Advances in VCSELs for communication and sensing,” IEEE J. Sel. Top. Quantum Electron. 17, 1552–1567 (2011). [CrossRef]

].

The emitted power versus current (LI) characteristics presented in the bottom part of Fig. 2(c) show that the maximal total emitted power of the patterned devices is generally reduced. With the pattern π2, this reduction is of about 15 % (from 2.45 mW to 2.08 mW). However, the maximal SM emitted power LSM is in fact increased for this specific patterned-cavity device, from 1.51 mW, to 1.97 mW. This is an increase of about 0.46 mW, or 30 %, of SM power at 20°C. LI characteristics at higher temperatures are reported in Fig. 3(a). At 50°C and 80°C, LSM respectively decreases to 1.47 mW and 1.05 mW for the reference device, whereas we measured 1.57 mW and 1.07 mW with the pattern π2. The ring intra-cavity patterns can therefore enhance the SM emission power and SM tunability of long-wavelength VCSELs.

Fig. 3 (a) SMSR and emitted power at 50°C (left) and at 80°C (right), for the typical device without pattern (black) and with pattern π2 (green). (b) Distribution of maximal SM emitted power LSM at 20°C for all the lasing devices without pattern (top) and with pattern π2 (bottom). Solid and dashed red lines indicate respectively the median value and the median absolute deviation.

Figure 3(b) presents the distribution of maximal SM emitted power at 20°C for all the measured lasing devices of the reference unpatterned design (top graph) and for the pattern π2 (bottom graph). The median value, as indicated by a solid red line, is larger for this specific pattern. The most typical devices reported in the present letter were selected with the criterion of having their LSM closest to the median value of the statistical distribution, and this over the whole range of studied temperatures (20–80°C). The performances of these typical devices thus represent the characteristic behavior of their specific design.

The spectrally-resolved NF distributions shown in Fig. 4(a) were acquired at 12 mA by measuring the power of the different modes with a scanning fiber probe in the image plane of the emitted beam and they were compiled by numerical interpolation. Horizontal and vertical directions are respectively parallel to [011] and [01̄1] crystal axis of the VCSEL wafer. The positioning of the TJ mesa in these data is based on the NF distribution measured at a current below threshold (amplified spontaneous emission), which was acquired in an alternate way with the NF distributions at 12 mA at each point. The normalization is such that the maximum intensity of LP01 of the reference device is set to 1.

Fig. 4 (a) Measured spectrally-resolved NF distributions of LP01 (left) and LP11 (right) for the reference device at 20°C and 12 mA. The calculated position of the TJ (dTJ = 6 μm) is indicated by a solid white circle. (b) Radial NF distributions of LP01 (solid lines) and LP11 (dashed lines) along the direction defined by the straight line between the respective maxima of these modes [see the white crosses in (a)], for the device without pattern (black), with pattern π1 (red) and π2 (green). The position of these patterns is indicated by arrows.

The radial distributions of Fig. 4(b) show that the maximum intensity of LP01 is increased for patterned devices, which indicates that the pattern leads to an enhancement of the FM. By contrast, it reduces the intensity of LP11. This effect is stronger with a pattern of smaller inner diameter like π2, where the maximal intensity of LP11 is reduced by a factor larger than 20. The distance between the maximum and the half-maximum of LP01 typically lies within a radius between 1.5 μm and 2.0 μm. In addition, for the patterns we investigated, we observe that the distance between the respective maxima of LP01 and LP11, which are indicated with crosses in Fig. 4, increases from 1.9 μm to 2.2 μm.

4. Numerical simulations of pattern effects

Fig. 5 (a) Calculated modal gain of HE11 (left) and HE21 (right) as a function of the width w and inner diameter dP of the ring pattern. (b) Radial distributions of HE11 (solid lines) and HE21 (dashed lines) without pattern (black), with pattern π2 (green) and π′ (blue), in the plane of the active region. The position of these patterns is indicated by arrows.

Patterns with w and dP values respectively larger and smaller than those shown in Fig. 5(a) can further suppress HE21, but to the detriment of the mode volume of HE11. Deeper patterns further confine HE11 and suppress HE21, and an upper limit of the pattern depth is found at about 200 nm, beyond which its electrical resistance drastically deteriorates the electrical injection. The model also predicts that the transition for HE21 to become unconfined occurs at w and dP values that do not vary significantly when the TJ diameter is increased.

5. Conclusion

References and links

1.

R. Michalzik, ed., VCSELs: Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers (Springer, 2013).

2.

E. Kapon and A. Sirbu, “Long-wavelength VCSELs: Power-efficient answer,” Nat. Photonics 3, 27–29 (2009). [CrossRef]

3.

A. Mircea, A. Caliman, V. Iakovlev, A. Mereuta, G. Suruceanu, C.-A. Berseth, P. Royo, A. Syrbu, and E. Kapon, “Cavity mode—Gain peak tradeoff for 1320-nm wafer-fused VCSELs with 3-mW single-mode emission power and 10-Gb/s modulation speed up to 70 °C,” IEEE Photonics Technol. Lett. 19, 121–123 (2007). [CrossRef]

4.

T. Gründl, P. Debernardi, M. Müller, C. Grasse, P. Ebert, K. Geiger, M. Ortsiefer, G. Böhm, R. Meyer, and M.-C. Amann, “Record single-mode, high-power VCSELs by inhibition of spatial hole burning,” IEEE J. Sel. Top. Quantum Electron. 19, 1700913 (2013). [CrossRef]

5.

A. Sirbu, G. Suruceanu, V. Iakovlev, A. Mereuta, Z. Mickovic, A. Caliman, and E. Kapon, “Reliability of 1310 nm wafer fused VCSELs,” IEEE Photonics Technol. Lett. 25, 1555–1558 (2013). [CrossRef]

6.

A. Sirbu, V. Iakovlev, A. Mereuta, A. Caliman, G. Suruceanu, and E. Kapon, “Wafer-fused heterostructures: Application to vertical cavity surface-emitting lasers emitting in the 1310 nm band,” Semicond. Sci. Technol. 26, 014016 (2011). [CrossRef]

7.

T. Czyszanowski, R. P. Sarzala, M. Dems, J. Walczak, M. Wasiak, W. Nakwaski, V. Iakovlev, N. Volet, and E. Kapon, “Spatial-mode discrimination in guided and antiguided arrays of long-wavelength VCSELs,” IEEE J. Sel. Top. Quantum Electron. 19, 1702010 (2013).

8.

A. Mereuta, A. Syrbu, V. Iakovlev, A. Rudra, A. Caliman, G. Suruceanu, C.-A. Berseth, E. Deichsel, and E. Kapon, “1.5 μ m VCSEL structure optimization for high-power and high-temperature operation,” J. Cryst. Growth 272, 520–525 (2004). [CrossRef]

9.

A. Syrbu, A. Mircea, A. Mereuta, A. Caliman, C.-A. Berseth, G. Suruceanu, V. Iakovlev, M. Achtenhagen, A. Rudra, and E. Kapon, “1.5-mW single-mode operation of wafer-fused 1550-nm VCSELs,” IEEE Photon. Technol. Lett. 16, 1230–1232 (2004). [CrossRef]

10.

A. Larsson, “Advances in VCSELs for communication and sensing,” IEEE J. Sel. Top. Quantum Electron. 17, 1552–1567 (2011). [CrossRef]

11.

R. P. Sarzala and W. Nakwaski, “Optimization of 1.3 μm GaAs-based oxide-confined (GaIn)(NAs) vertical-cavity surface-emitting lasers for low-threshold room-temperature operation,” J. Phys. Condens. Matter 16, S3121–S3140 (2004). [CrossRef]

12.

M. Dems, R. Kotynski, and K. Panajotov, “Plane wave admittance method—A novel approach for determining the electromagnetic modes in photonic structures,” Opt. Express 13, 3196–3207 (2005). [CrossRef] [PubMed]

13.

L. Frasunkiewicz, T. Czyszanowski, M. Wasiak, M. Dems, R. P. Sarzala, W. Nakwaski, and K. Panajotov, “Optimisation of single-mode photonic-crystal results in limited improvement of emitted power and unexpected broad range of tuning,” IEEE J. Lightwave Technol. 31, 1360–1366 (2013). [CrossRef]

14.

M. Müller, P. Debernardi, C. Grasse, T. Gründl, and M.-C. Amann, “Tweaking the modal properties of 1.3-μm short-cavity VCSEL—Simulation and experiment,” IEEE Photonics Technol. Lett. 25, 140–143 (2013). [CrossRef]

OCIS Codes
(100.6950) Image processing : Tomographic image processing
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.3430) Lasers and laser optics : Laser theory
(140.3570) Lasers and laser optics : Lasers, single-mode
(140.3600) Lasers and laser optics : Lasers, tunable
(160.4236) Materials : Nanomaterials
(140.7260) Lasers and laser optics : Vertical cavity surface emitting lasers

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: September 30, 2013
Revised Manuscript: October 21, 2013
Manuscript Accepted: October 21, 2013
Published: October 31, 2013

Citation
Nicolas Volet, Tomasz Czyszanowski, Jaroslaw Walczak, Lukas Mutter, Benjamin Dwir, Zlatko Micković, Pascal Gallo, Andrei Caliman, Alexei Sirbu, Alexandru Mereuta, Vladimir Iakovlev, and Eli Kapon, "Transverse mode discrimination in long-wavelength wafer-fused vertical-cavity surface-emitting lasers by intra-cavity patterning," Opt. Express 21, 26983-26989 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-22-26983


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. R. Michalzik, ed., VCSELs: Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers (Springer, 2013).
  2. E. Kapon and A. Sirbu, “Long-wavelength VCSELs: Power-efficient answer,” Nat. Photonics3, 27–29 (2009). [CrossRef]
  3. A. Mircea, A. Caliman, V. Iakovlev, A. Mereuta, G. Suruceanu, C.-A. Berseth, P. Royo, A. Syrbu, and E. Kapon, “Cavity mode—Gain peak tradeoff for 1320-nm wafer-fused VCSELs with 3-mW single-mode emission power and 10-Gb/s modulation speed up to 70 °C,” IEEE Photonics Technol. Lett.19, 121–123 (2007). [CrossRef]
  4. T. Gründl, P. Debernardi, M. Müller, C. Grasse, P. Ebert, K. Geiger, M. Ortsiefer, G. Böhm, R. Meyer, and M.-C. Amann, “Record single-mode, high-power VCSELs by inhibition of spatial hole burning,” IEEE J. Sel. Top. Quantum Electron.19, 1700913 (2013). [CrossRef]
  5. A. Sirbu, G. Suruceanu, V. Iakovlev, A. Mereuta, Z. Mickovic, A. Caliman, and E. Kapon, “Reliability of 1310 nm wafer fused VCSELs,” IEEE Photonics Technol. Lett.25, 1555–1558 (2013). [CrossRef]
  6. A. Sirbu, V. Iakovlev, A. Mereuta, A. Caliman, G. Suruceanu, and E. Kapon, “Wafer-fused heterostructures: Application to vertical cavity surface-emitting lasers emitting in the 1310 nm band,” Semicond. Sci. Technol.26, 014016 (2011). [CrossRef]
  7. T. Czyszanowski, R. P. Sarzala, M. Dems, J. Walczak, M. Wasiak, W. Nakwaski, V. Iakovlev, N. Volet, and E. Kapon, “Spatial-mode discrimination in guided and antiguided arrays of long-wavelength VCSELs,” IEEE J. Sel. Top. Quantum Electron.19, 1702010 (2013).
  8. A. Mereuta, A. Syrbu, V. Iakovlev, A. Rudra, A. Caliman, G. Suruceanu, C.-A. Berseth, E. Deichsel, and E. Kapon, “1.5 μ m VCSEL structure optimization for high-power and high-temperature operation,” J. Cryst. Growth272, 520–525 (2004). [CrossRef]
  9. A. Syrbu, A. Mircea, A. Mereuta, A. Caliman, C.-A. Berseth, G. Suruceanu, V. Iakovlev, M. Achtenhagen, A. Rudra, and E. Kapon, “1.5-mW single-mode operation of wafer-fused 1550-nm VCSELs,” IEEE Photon. Technol. Lett.16, 1230–1232 (2004). [CrossRef]
  10. A. Larsson, “Advances in VCSELs for communication and sensing,” IEEE J. Sel. Top. Quantum Electron.17, 1552–1567 (2011). [CrossRef]
  11. R. P. Sarzala and W. Nakwaski, “Optimization of 1.3 μm GaAs-based oxide-confined (GaIn)(NAs) vertical-cavity surface-emitting lasers for low-threshold room-temperature operation,” J. Phys. Condens. Matter16, S3121–S3140 (2004). [CrossRef]
  12. M. Dems, R. Kotynski, and K. Panajotov, “Plane wave admittance method—A novel approach for determining the electromagnetic modes in photonic structures,” Opt. Express13, 3196–3207 (2005). [CrossRef] [PubMed]
  13. L. Frasunkiewicz, T. Czyszanowski, M. Wasiak, M. Dems, R. P. Sarzala, W. Nakwaski, and K. Panajotov, “Optimisation of single-mode photonic-crystal results in limited improvement of emitted power and unexpected broad range of tuning,” IEEE J. Lightwave Technol.31, 1360–1366 (2013). [CrossRef]
  14. M. Müller, P. Debernardi, C. Grasse, T. Gründl, and M.-C. Amann, “Tweaking the modal properties of 1.3-μm short-cavity VCSEL—Simulation and experiment,” IEEE Photonics Technol. Lett.25, 140–143 (2013). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4 Fig. 5
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited