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Reflection-modeopticalinjectionlocking
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Reflection-mode optical injection locking
Weijian Yang,1 Peng Guo,1,2 Devang Parekh,1 and Connie J. Chang-Hasnain1,*
1
Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720,
USA
2
State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Electronics
Engineering and Computer Science, Peking University, Beijing 100871, China
*cch@eecs.berkeley.edu
Abstract: A novel model including the interference effect of master laser
reflection is established for reflection-mode optical injection locking. This
model sheds insight on the physical origin of some rather distinct but
unexplained modulation characteristics of optical injection-locked verticalcavity surface-emitting lasers (VCSELs), including data pattern inversion in
on-off keying modulation, a large RF gain at low frequency, and an
anomalous DC-suppression under small signal modulation, in specific
locking conditions. Excellent agreement is obtained between the simulation
and experiment results.
©2010 Optical Society of America
OCIS codes: (140.3520) Lasers, injection-locked; (250.7260) Vertical cavity surface emitting
lasers; (260.3160) Interference.
References and links
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14.
E. K. Lau, X. Zhao, H. K. Sung, D. Parekh, C. Chang-Hasnain, and M. C. Wu, “Strong optical injection-locked
semiconductor lasers demonstrating > 100-GHz resonance frequencies and 80-GHz intrinsic bandwidths,” Opt.
Express 16(9), 6609–6618 (2008).
X. Zhao, B. Zhang, L. Christen, D. Parekh, W. Hofmann, M. C. Amann, F. Koyama, A. E. Willner, and C. J.
Chang-Hasnain, “Greatly increased fiber transmission distance with an optically injection-locked vertical-cavity
surface-emitting laser,” Opt. Express 17(16), 13785–13791 (2009).
D. Parekh, B. Zhang, X. Zhao, Y. Yue, W. Hofmann, M. C. Amann, A. E. Willner, and C. J. Chang-Hasnain,
“90-km single-mode fiber transmission of 10-Gb/s multimode VCSELs under optical injection locking,” in
Optical Fiber Communication Conference, OSA Technical Digest (CD) (Optical Society of America, 2009),
paper OTuK7.
L. Chrostowski, X. Zhao, and C. J. Chang-Hasnain, “Microwave performance of optically injection-locked
VCSELs,” IEEE Trans. Microw. Theory Tech. 54(2), 788–796 (2006).
X. Zhao, and C. J. Chang-Hasnain, “A new amplifier model for resonance enhancement of optically injectionlocked lasers,” IEEE Photon. Technol. Lett. 20(6), 395–397 (2008).
E. K. Lau, H. Sung, and M. C. Wu, “Frequency response enhancement of optical injection-locked lasers,” IEEE
J. Quantum Electron. 44(1), 90–99 (2008).
A. Murakami, K. Kawashima, and K. Atsuki, “Cavity resonance shift and bandwidth enhancement in
semiconductor lasers with strong light injection,” IEEE J. Quantum Electron. 39(10), 1196–1204 (2003).
T. B. Simpson, J. M. Liu, and A. Gavrielides, “Bandwidth enhancement and broadband noise reduction in
injection-locked semiconductor lasers,” IEEE Photon. Technol. Lett. 7(7), 709–711 (1995).
F. Mogensen, H. Olesen, and G. Jacobsen, “Locking conditions and stability properties for a semiconductor laser
with external light injection,” IEEE J. Quantum Electron. 21(7), 784–793 (1985).
R. Lang, “Injection locking properties of a semiconductor laser,” IEEE J. Quantum Electron. 18(6), 976–983
(1982).
W. Yang, P. Guo, D. Parekh, W. Hofmann, M. C. Amann, and C. J. Chang-Hasnain, “Physical origin of data
pattern inversion in optical injection-locked VCSELs,” in Frontiers in Optics, OSA Technical Digest (CD)
(Optical Society of America, 2009), paper FTuW2.
P. Guo, W. Yang, D. Parekh, W. Hofmann, M. C. Amann, and C. J. Chang-Hasnain, “Anomalous modulation
characteristics of optical injection-locked VCSELs,” in Asia Communications and Photonics Conference and
Exhibition, Technical Digest (CD) (Optical Society of America, 2009), paper TuD6.
C. H. Henry, N. A. Olsson, and N. K. Dutta, “Locking range and stability of injection locked 1.54 µm InGaAsP
semiconductor lasers,” IEEE J. Quantum Electron. 21(8), 1152–1156 (1985).
W. Hofmann, N. H. Zhu, M. Ortsiefer, G. Böhm, Y. Liu, “High speed (>11 GHz) modulation of BCB-passivated
1.55 µm InGaAlAs-InP VCSELs,” Electron. Lett. 42, 976–977 (2006).
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15. X. Wang, B. Faraji, W. Hofmann, M.-C. Amann, and L. Chrostowski, “Interference effects on the frequency
response of injection-locked VCSELs,” in The 22nd IEEE International Semiconductor Laser Conference
(Institute of Electrical and Electronics Engineers, New Jersey, 2010), poster P11.
1. Introduction
Optical injection locking (OIL) has been shown to greatly enhance the performance of a
directly-modulated laser [1–8]. Resonance frequency greater than 100 GHz and an intrinsic 3
dB bandwidth up to 80 GHz have been demonstrated for directly modulated vertical-cavity
surface-emitting laser (VCSEL) under strong OIL [1]. In this regard, similar behavior is found
between injection locking of a VCSEL and an edge-emitting distributed feedback (DFB) laser
[1]. Recently, we reported an interesting data pattern inversion and the corresponding chirp
polarity inversion in both single transverse mode and multi-transverse mode OIL-VCSELs.
This leads to a ten-fold and ninety-fold increased single-mode fiber transmission distance
respectively [2,3]. This never-predicted-before phenomenon has only been observed in
VCSELs. In addition, there are two other anomalies in small-signal modulation characteristics
(S21) of OIL-VCSELs that cannot be explained by standard OIL rate equations [6–10]. First,
a large 20 dB RF gain at low frequency can be obtained for OIL-VCSEL at certain detuning
values (wavelength difference between the master and the free-running slave laser) [4].
Second, under certain other detuning values, a dip or “zero” occurs at very low frequency,
herein referred as DC-suppression.
In this paper, we establish a novel model [11,12] which includes the interference effect of
the master laser reflection for the first time. This interference was completely ignored in all
the prior analyses of the modulation characteristic of reflection-mode OIL-lasers. With the
inclusion of this interference, the distinct modulation features of OIL-VCSELs can be fully
explained and excellent agreements are obtained with experimental results. The model
established in this paper will be suitable for all reflection-mode OIL-lasers including VCSELs
and some edge-emitting lasers. The reflection not only differentiates the reflection-mode OILlasers from the transmission-mode OIL-lasers, but can be leveraged for further performance
improvements, which is also discussed here.
2. Theoretical modeling and simulation
Figure 1 shows the schematic of an OIL-VCSEL. The master laser field Em impinges onto the
front facet of the slave VCSEL and is divided into transmission and reflection. The
transmission interacts with the VCSEL cavity, described by the standard rate equations [6–
10]. A steady state is reached inside the cavity and its output Es is phase coherent with Em,
with a phase shift φs ranging from −0.5π to cot−1α [6,9], where α is the linewidth enhancement
factor. φs is determined by the detuning ∆λ = λm - λs, where λm and λs are the wavelength of the
master laser and the free-running slave VCSEL respectively.
The total output field Etotal is the sum of Es and the reflection of the master laser Emr,
where r is the reflectivity of the top facet of the VCSEL, with a phase shift φr depending on
VCSEL’s top DBR structure and λm. φr is around π in general. In previous models, only
transmitted light was considered and, hence, the interference between Es and Emr was ignored.
The total output power Ptotal of the steady state can be written as,
1
1
1
2
2
2
Etotal = Es + Em r 2 + Es ⋅ Em r cos (φs − φr ) .
(1)
2
2
2
Figure 2a shows the output power in the locking map for a transmission-mode OIL-laser
[6], while Fig. 2b shows the output power for a reflection-mode OIL-laser where the
interference effect of master laser reflection is taken into account. The total output power
increases with injection ratio (defined as 20log10(|Em|/|Efr|), where Efr is the electric field of
the free-running slave laser light), which is the same in both cases. In the reflection-mode
OIL, however, Ptotal decreases with detuning, opposite to the case of the transmission-mode
Ptotal =
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Received 22 Jun 2010; revised 1 Sep 2010; accepted 12 Sep 2010; published 12 Oct 2010
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OIL [6,13]. This is because φs increases from −0.5π to cot−1α, leading to a more destructive
interference and thus a lower total output power.
Fig. 1. OIL-VCSEL model with the interference effect. Total output field Etotal = Es + Er.
Fig. 2. The total output power for (a) transmission-mode OIL and (b) reflection-mode OIL.
Small signal analysis is then performed based on the rate equations [6,7,9,10] with the
reflection model. Both |Es|2 and phase φs have a response under the small-signal modulation,
written as ∆|Es|2 and ∆φs respectively, which are superimposed on the steady state solution.
Based on Eq. (1), the total output power is written as,
(
)
1
2
2
Etotal + ∆ Etotal
2
(2)
1
1
2
2
2
2
2
1
=  Es + ∆ Es  + Em r 2 + Es + ∆ Es Em r cos (φs + ∆φs − φr ) .
2
2
 2
With the main simulation parameters listed in Table 1 in Appendix, the typical frequency
response of ∆Ptotal is simulated for different detuning values under a strong injection ratio. The
results are shown in Fig. 3, where the amplitude response |∆Ptotal|2 (the square converts optical
domain into electrical domain, known as S21) is normalized to the free-running case. It is
clearly seen that there is a DC-suppression in the amplitude response as the detuning increases
from blue (∆λ<0) to red (∆λ>0). This DC-suppression corresponds to a π phase change in the
phase response (phase of ∆Ptotal). It is the destructive interference between the OIL-VCSEL
internal output field Es and the master laser reflection light Emr that leads to this DCsuppression and phase change. We will show later that this corresponds to the transition point
for data pattern inversion in large signal modulation. As the detuning value increases further,
the DC-dip disappears and a very large RF gain is obtained, again due to the interference
effect.
Ptotal + ∆Ptotal =
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Fig. 3. Simulation results for OIL-VCSEL small-signal frequency response (S21) with different
detuning values under a strong injection ratio of 16.15 dB. (a) Normalized amplitude response;
(b) Phase response. The arrow on (b) indicates a π phase change as the detuning increases from
blue to red. From blue detuning to red detuning, the detuning values for the curves are
−0.602 nm, 0.199 nm, 0.822 nm, 1.500 nm, 1.883 nm; corresponding to the phase shift φs
−0.490π, −0.4486π, −0.400π, −0.300π, −0.165π, respectively.
Data pattern under on-off keying (OOK) large-signal modulation is simulated by fourthorder Runge-Kutta method. Extinction ratio re is defined as 10log10(P1/P2), where P1 and P2
are the OIL-VCSEL output powers corresponding to the high and low level of the modulation
current. Thus a negative extinction ratio indicates data pattern inversion. Figure 4 shows the
typical 1 Gb/s data patterns for different detuning values, with a fixed injection ratio. The
average total output power decreases with detuning, as predicted by Fig. 2b. With increasing
detuning, the data pattern changes from normal to transition state, and then to inverted.
Fig. 4. Simulation results for OIL-VCSEL 1 Gb/s OOK data pattern with different detuning
values under a fixed injection ratio of 12.0 dB. As the detuning changes from blue to red, the
data pattern changes from normal to transition state, and then to inverted. From blue detuning
to red detuning, the detuning values for the curves are −0.115 nm, 0.321 nm, 1.178 nm, 1.662
nm; corresponding to the phase shift φs −0.470π, −0.430π, −0.300π, −0.125π, respectively.
Next, we compare simulation results for small- and large- signal modulation response by
sweeping the parameter space of injection ratio and detuning value. Figure 5 shows the RF
response at 1 GHz and the extinction ratio of the 1 Gb/s data pattern on the same locking map.
The locking range of the large-signal modulation is slightly smaller than that of the smallsignal modulation, due to the larger perturbation to the system in the large-signal modulation.
It is interesting to note that the DC-suppression in Fig. 5a is at the same parameter space with
the transition state at which the extinction ratio is zero in Fig. 5b, confirming a strong
correlation between them. For a certain injection ratio at the red detuning side, the
interference effect makes P1 into a very small value, resulting in a very large (in magnitude),
and desirable extinction ratio with data pattern inverted. This is indeed the regime of interests
for greatly increased fiber transmission distance [2,3].
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Fig. 5. Simulation results for the RF response of the small-signal analysis at 1 GHz and the
extinction ratio re of the 1 Gb/s OOK large-signal modulation of OIL-VCSEL on the same
locking map. The negative re indicates data pattern inversion. The dashed line on (b) indicates
the conditions where re = 0.
3. Experiment
Detailed experiments on 1.55 µm buried-tunnel-junction (BTJ) VCSELs [14] were performed
to verify the simulation results and, in particular, the correlation between small- and largesignal modulation.
The VCSEL and experimental setup were similar to that reported elsewhere [1]. The
VCSEL was biased at 4 mA, 2.5 times threshold current, with −3 dBm free-running output
power. The small-signal modulation response of the OIL-VCSEL was measured at a fixed
injection ratio of 20 dB for different detuning values, shown in Fig. 6. At blue detuning (e.g.
∆λ = −0.759 nm), a high resonance frequency of 100 GHz was attained, similar to what was
reported [1]. The large damping at lower frequencies is due to the parasitic RC of the VCSEL.
Increasing the detuning to 0.149 nm, a large DC-dip was seen, which was not reported before.
Further detuning to the red side, the DC-dip disappeared and a large RF gain 12.5 dB at low
frequency was obtained. Similar observation with >20 dB gain was reported in Ref. 4.
Fig. 6. RF response of the small-signal modulation of the OIL-VCSEL for different detuning
values (−0.759 nm, 0.149 nm, 0.395 nm and 1.165 nm), at a fixed injection ratio of 20 dB. FR:
free running.
Figure 7 shows experimental results of OIL-VCSEL under 1 Gb/s OOK modulation at
different detuning values, with the injection ratio optimized at 12.9 dB for good extinction
ratios. With increasing detuning, the data pattern changes from normal, transition state, to
inversion. The typical top DBR mirror field reflectivity of the VCSEL is higher than 99%,
resulting in a strong reflection and interference effect of the master laser light. Extinction ratio
as high as 12 dB with a 3.6 dB signal amplification compared to the free-running case was
achieved with the 1.036 nm detuning.
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Fig. 7. Data pattern of the 1Gb/s OOK large-signal modulation of OIL-VCSEL for different
detuning values (−0.230 nm, 0.134 nm, 0.630 nm and 1.036 nm), at a fixed injection ratio of
12.9 dB. FR: free running.
The RF response at 1 GHz and the extinction ratio of the 1 Gb/s data pattern were
measured at different points in the same parameter space for another VCSEL (5 mA bias
current which is 3 times threshold current, −0.7 dBm free-running output power), with the
results shown in Fig. 8. The strong correlation between the DC-suppression in small-signal
modulation and transition state in large-signal modulation is clearly seen. All these results
agree very well with the simulation.
Fig. 8. RF response of the small-signal modulation at 1 GHz and extinction ratio re of the 1
Gb/s OOK large-signal modulation of OIL-VCSEL on the same locking map. The crosses
show in which conditions the data were taken in the experiment, and the dashed line on (b)
indicates the conditions where re = 0.
4. Application
The reflection-mode OIL model would find its great application in optical communication and
optical data processing. It predicts the conditions of data pattern inversion and the
corresponding chirp polarity inversion, which is exactly the region where the greatly increased
single-mode fiber transmission distance was achieved in the OIL-VCSELs [2,3]. Furthermore,
since the OIL-VCSEL can operate either in normal data state or inverted data state, it is
possible to develop some optical switching applications. For example, a frequency-modulated
master laser can be used to modulate the detuning value of the OIL-VCSEL, and thus the
switching can occur between the normal data state and inverted date state. Alternatively, an
intensity-modulated master laser can be used to control the injection power and thus the
switching. However, as seen in Fig. 5 and Fig. 8, the transition line is very flat with respect to
the injection ratio, making this switching difficult. On the other hand, by adjusting the
VCSEL’s front DBR reflectivity and phase, it is possible to tilt the transition line. Figure 9
shows the same simulations as Fig. 5, except that the front DBR’s field reflectivity is changed
from 0.9968 to 0.9962 while the reflection phase from 1.000π to 0.970π at 1550 nm. The
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transition line is tilted, and the output of the VCSEL can switch between normal state and
inverted state by different injection powers from the master laser. Reference [11] shows the
initial experimental switching results, and this may be possibly further developed into an
optical logic gate.
Fig. 9. Simulation results for the extinction ratio re of the 1 Gb/s OOK large-signal modulation
of the OIL-VCSEL on the locking map. (Simulation parameters are listed in Table 1 in
Appendix, except that the field reflectivity of the VCSEL’s front DBR is changed from 0.9968
to 0.9962 while the reflection phase from 1.000π to 0.970π at 1550 nm.) The dashed line
indicates the conditions where re = 0. The output of the VCSEL can switch between normal
state and inverted state by different injection powers from the master laser, shown by the
double head arrow line.
5. Conclusion
The proposed model incorporates the interference effect of the master laser reflection into the
total output of the reflection-mode OIL-lasers. This reflection, which once was considered
detrimental for practical applications, is shown to be a key to explain the rather distinct
modulation characteristics of OIL-VCSELs. The small-signal RF response is strongly
correlated to the data patterns in large-signal modulation. The distinct DC-suppression reflects
itself into the transition state in large-signal modulation. The large RF gain at low frequency is
both seen in simulation and experiment. This model will not only be useful to optimize the
conditions for OIL-VCSEL-based optical communication, but also expand OIL-VCSELs
applications into multi-level modulation, photonic switching and logic gates.
Appendix
Simulation parameters of the slave VCSEL are listed in the following table.
Table 1. Simulation Parameters of the Slave VCSEL
Central wavelength
Top DBR field reflectivity
Bottom mirror field reflectivity
Cavity length
Differential gain
Transparency carrier density
Cavity distributed material loss
1.55 µm
0.9968
1
2.87 µm
5.5 × 10−20 m2
2.0 × 1024 m−3
3.8 × 103 m−1
Mode confinement factor
Linewidth enhancement factor
Photon life time
Carrier life time
Gain saturation coefficient
Laser active region volume
Cavity effective refractive index
0.048
8
2.2 × 10−12 s
8.3 × 10−10 s
2.7 × 10−23 m3
1.0 × 10−18 m3
3.24
Acknowledgements
The authors thank M. C. Amann and W. Hofmann for providing the 1.55 µm VCSELs, and
the support from National Security Science and Engineering Faculty Fellowship. The authors
were made aware of an independent work [15] with relevant similarities after the submission
of this manuscript.
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Received 22 Jun 2010; revised 1 Sep 2010; accepted 12 Sep 2010; published 12 Oct 2010
27 September 2010 / Vol. 18, No. 20 / OPTICS EXPRESS 20893