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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 12 — Jun. 17, 2013
  • pp: 14512–14529
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Injection locking-based pump recovery for phase-sensitive amplified links

Samuel L. I. Olsson, Bill Corcoran, Carl Lundström, Ekawit Tipsuwannakul, Stylianos Sygletos, Andrew D. Ellis, Zhi Tong, Magnus Karlsson, and Peter A. Andrekson  »View Author Affiliations


Optics Express, Vol. 21, Issue 12, pp. 14512-14529 (2013)
http://dx.doi.org/10.1364/OE.21.014512


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Abstract

An injection locking-based pump recovery system for phase-sensitive amplified links, capable of handling 40 dB effective span loss, is demonstrated. Measurements with 10 GBd DQPSK signals show penalty-free recovery of a pump wave, phase modulated with two sinusoidal RF-tones at 0.1 GHz and 0.3 GHz, with 64 dB amplification. The operating power limit for the pump recovery system is experimentally investigated and is governed by the noise transfer and phase modulation transfer characteristics of the injection-locked laser. The corresponding link penalties are explained and quantified. This system enables, for the first time, WDM compatible phase-sensitive amplified links over significant lengths.

© 2013 OSA

1. Introduction

Phase-sensitive amplifiers (PSAs), e.g. fiber optic parametric amplifiers (FOPAs) in phase-sensitive (PS)-mode, are in theory capable of noiseless amplification, i.e. a 0 dB noise figure (NF) [1

1. C. M. Caves, “Quantum limits on noise in linear amplifiers,” Phys. Rev. D 26, 1817–1839 (1982) [CrossRef] .

]. This should be compared with phase-insensitive amplifiers (PIAs) such as erbium-doped fiber amplifiers (EDFAs) having a 3 dB quantum-limited NF at high gain [2

2. E. Desurvire, Erbium-doped Fiber Amplifiers (John Wiley & Sons, 1994).

]. Low NF PSAs have been realized in both FOPAs [3

3. W. Imajuku, A. Takada, and Y. Yamabayashi, “Low-noise amplification under the 3dB noise figure in high-gain phase-sensitive fibre amplifier,” Electron. Lett 35, 1954–1955 (1999) [CrossRef] .

], and nonlinear crystals [4

4. D. J. Lovering, J. A Levenson, P. Vidakovic, J. Webjörn, and P. St. J. Russell, “Noiseless optical amplification in quasi-phase-matched bulk lithium niobate,” Opt. Lett. 21, 1439–1441 (1996) [CrossRef] [PubMed] .

], with FOPA-based implementations showing significantly higher gain. A high-gain optical amplifier with close to 0 dB NF would have major impact on areas such as sensing and spectroscopy as well as fiber optical communication systems [5

5. Z. Tong, C. Lundström, P. A. Andrekson, C. J. McKinstrie, M. Karlsson, D. J. Blessing, E. Tipsuwannakul, B. J. Puttnam, H. Toda, and L. Grüner-Nielsen, “Towards ultrasensitive optical links enabled by low-noise phase-sensitive amplifiers,” Nat. Photonics 5, 430–436 (2011) [CrossRef] .

].

FOPA PSAs require in their simplest configuration three frequency- and phase-locked waves at the input, commonly referred to as pump, signal, and idler, and can be implemented in frequency-degenerate and frequency-nondegenerate configurations. Frequency-degenerate PSAs can only amplify one specific wavelength channel for a given pump configuration and are difficult to implement with high gain due to the quadratic dependence of the gain on the pump power [6

6. J. Hansryd, P. A. Andrekson, M. Westlund, J. Li, and P. O. Hedekvist, “Fiber-based optical parametric amplifiers and their applications,” IEEE J. Sel. Topics Quantum Electron. 8, 506–520 (2002) [CrossRef] .

]. Frequency-nondegenerate PSAs on the other hand support simultaneous amplification of many independent signals and can provide high gain, growing exponentially with pump power [7

7. J. Kakande, C. Lundström, P. A. Andrekson, Z. Tong, M. Karlsson, P. Petropoulos, F. Parmigiani, and D. J. Richardson, “Detailed characterization of a fiber-optic parametric amplifier in phase-sensitive and phase-insensitive operation,” Opt. Express 18, 4130–4137 (2010) [CrossRef] [PubMed] .

].

Fig. 1 Schematic illustration of a phase-sensitive amplified (PSA) transmission link based on the copier-PSA scheme.

Pump recovery can be accomplished using optical injection locking (IL). There have been several demonstrations of pump wave generation, using IL, for subsequent use in PSAs. However, not in the context of frequency-nondegenerate PSA-amplified transmission links. IL has been used for phase-locking a semiconductor ring laser to a pulsed signal that was used as pump in an in-line frequency-degenerate PSA [18

18. A. Takada and W. Imajuku, “Optical phase-sensitive amplifier with pump laser phase-locked to input signal light,” in Proceedings of European Conference and Exhibition on Optical Communication (ECOC), (Optical Society of America, 1997), 98–101.

]. An all-optical regenerator has been demonstrated where IL was used for narrowband filtering of a generated carrier wave and the injection-locked wave later used as pump in a saturated PSA [19

19. R. Slavík, F. Parmigiani, J. Kakande, C. Lundström, M. Sjödin, P. A. Andrekson, R. Weerasuriya, S. Sygletos, A. D. Ellis, L. Grüner-Nielsen, D. Jakobsen, S. Herstrøm, R. Phelan, J. OGorman, A. Bogris, D. Syvridis, S. Dasgupta, P. Petropoulos, and D. J. Richardson, “All-optical phase and amplitude regenerator for next-generation telecommunications systems,” Nat. Photonics 4, 690–695 (2010) [CrossRef] .

]. Two schemes, both using IL, have been demonstrated for generating phase-locked pump waves for use in in-line “black-box” frequency-nondegenerate PSAs [20

20. S. Sygletos, R. Weerasuriya, S. K. Ibrahim, F. Gunning, R. Phelan, J. O’Gorman, J. O’Carrol, B. Kelly, A. Bogris, D. Syvridis, C. Lundström, P. Andrekson, F. Parmigiani, D. J. Richardson, and A. D. Ellis, “Phase locking and carrier extraction schemes for phase sensitive amplification,” in Conference on Transparent Optical Networks (ICTON), 2010 12th International, Technical Digest (CD) (Optical Society of America, 2010), paper Mo.C1.3 [CrossRef] .

].

IL has also proved to be an extremely useful technique in a number of areas and has been thoroughly investigated for applications such as FM spectroscopy [21

21. S. Kasapi, S. Lathi, and Y. Yamamoto, “Amplitude-squeezed, frequency-modulated, tunable, diode-laser-based source for sub-shot-noise FM spectroscopy,” Opt. Lett. 22, 478–480 (1997) [CrossRef] [PubMed] .

], and modulation bandwidth enhancement [22

22. E. K. Lau, L. J. Wong, X. Zhao, Y. K. Chen, C. J. Chang-Hasnain, and M. C. Wu, “Bandwidth enhancement by master modulation of optical injection-locked lasers,” J. Lightw. Technol. 26, 2584–2593 (2008) [CrossRef] .

]. There has also been a number of theoretical and experimental investigations dedicated to amplitude modulation (AM) and frequency modulation (FM) transfer for various operating regimes and slave laser (SL) driving conditions [23

23. A. Fragkos, A. Bogris, D. Syvridis, and R. Phelan, “Amplitude noise limiting amplifier for phase encoded signals using injection locking in semiconductor lasers,” J. Lightw. Technol. 30, 764–771 (2012) [CrossRef] .

25

25. M. Vainio, M. Merimaa, and K. Nyholm, “Modulation transfer characteristics of injection-locked diode lasers,” Opt. Commun. 267, 455–463 (2006) [CrossRef] .

]. However, to the best of our knowledge, no detailed investigation of amplified spontaneous emission (ASE) noise transfer through an injection-locked distributed feedback (DFB) laser has previously been published, with only power spectral density measurements performed of the output of a semiconductor laser injection-locked to an ASE degraded signal [23

23. A. Fragkos, A. Bogris, D. Syvridis, and R. Phelan, “Amplitude noise limiting amplifier for phase encoded signals using injection locking in semiconductor lasers,” J. Lightw. Technol. 30, 764–771 (2012) [CrossRef] .

].

2. The pump recovery scheme and demonstration

2.1. Experimental setup

The experimental setup is shown in Fig. 2. A signal wave at 1545.2 nm was encoded with a 10 GBd DQPSK 215 − 1 pseudorandom bit sequence (PRBS). The signal was combined, using a wavelength division multiplexer (WDM), with a high-power pump wave at 1553.7 nm, phase modulated with two sinusoidal radio frequency (RF)-tones at 0.1 GHz and 0.3 GHz (giving 0.8 GHz bandwidth) for suppression of SBS in the FOPAs.

Fig. 2 Experimental setup used for demonstration and bit error ratio characterization of an injection locking-based pump recovery system in a phase-sensitive amplified link. DQPSK: differential quadrature phase-shift keyed, PRBS: pseudorandom bit sequence, RF: radio frequency, PC: polarization controller, WDM: wavelength division multiplexer, HNLF: highly nonlinear fiber, VOA: variable optical attenuator, EDFA: erbium-doped fiber amplifier, IL: injection locking, PZT: piezoelectric transducer, PSA: phase-sensitive amplifier, PIA: phase-insensitive amplifier, BER: bit error ratio, PLL: phase-locked loop.

After recombining the pump with the signal/idler pair they were again separated and the signal/idler pair was passed through a polarization controller (PC) while the pump was passed through the pump recovery system. The pump OSNR at the input of the pump recovery system was > 60 dB. The signal/idler pair was attenuated by more than 20 dB between the copier and the PSA/PIA preamplifier for all measurements which should be enough to decorrelate the signal/idler noise added in the copier.

The PSA/PIA preamplifier was implemented with two cascaded spools of stretched Ge-doped HNLF with an isolator in between for SBS suppression [31

31. C. Lundström, R. Malik, L. Grüner-Nielsen, B. Corcoran, S. L. I. Olsson, M. Karlsson, and P. A. Andrekson, “Fiber optic parametric amplifier With 10-dB net gain without pump dithering,” IEEE Photon. Technol. Lett. 25, 234–237 (2013) [CrossRef] .

]. The gain was 20 dB both in the PSA- and PIA-case and was tuned by varying the output power from EDFA3. For the PSA-case the signal and idler powers launched into the preamplifier were equal. The FOPA preamplifiers were compared against an EDFA preamplifier with 3.8 dB NF, also with 20 dB gain. PCs were used to align the SOP of the waves before the FOPAs.

For the BER measurements the received signal power was measured at point B and varied using the OP. The preamplifier output was passed through a 2.0 nm bandpass filter and then into the differential receiver, comprising of a 1-bit delay interferometer and an amplified balanced receiver. Although only one branch of the DQPSK signal was demodulated and used for BER measurement, it has been previously shown that for copier-PSA schemes both tributaries perform similarly [15

15. Z. Tong, C. Lundström, E. Tipsuwannakul, M. Karlsson, and P. A. Andrekson, “Phase-Sensitive Amplified DWDM DQPSK Signals Using Free-Running Lasers with 6-dB Link SNR Improvement over EDFA-based Systems,” in European Conference and Exhibition on Optical Communication (ECOC), Technical Digest (CD) (Optical Society of America, 2010), paper PDP1.3 [CrossRef] .

]. Part of the filtered signal was diverted and used as a feedback signal for the PLL.

2.2. Measurement results

Measurement results showing BER versus received signal power, i.e. signal power measured at point B, are presented in Fig. 3. For each of our three preamplifier configurations, with or without IL in the pump recovery system, we compare operation at different pump OSNR at point A.

Fig. 3 Measured bit error ratio (BER) versus received signal power (signal power at point B) comparing a phase-insensitive amplifier (PIA) and a phase-sensitive amplifier (PSA) amplified receiver with and without injection locking (IL) in the pump recovery system with an erbium-doped fiber amplifier (EDFA) amplified receiver. The measurements were done at various pump optical signal-to-noise ratio (OSNR) at point A, as given by the legend. The straight lines are linear fittings to the measurement points.

At high pump OSNR (56 dB), we observe all systems operating as expected, with a 4.8 dB sensitivity increase comparing the PIA- and PSA-amplified cases. This is close to the ideal 6 dB improvement expected through the lower NF of the PSA [16

16. Z. Tong, C. Lundström, P. A. Andrekson, M. Karlsson, and A. Bogris, “Ultralow noise, broadband phase-sensitive optical amplifiers, and their applications,” IEEE J. Sel. Topics Quantum Electron. 18, 1016–1032 (2012) [CrossRef] .

].

When lowering pump OSNR from 56 dB to 37 dB, both the PIA- and PSA-amplified systems show a large sensitivity penalty when IL is not used in the pump recovery system. With IL in place, both the PIA- and PSA-amplified systems show much improved performance. However, significant penalty is observed when the pump OSNR is degraded to 11 dB.

To analyze how this sensitivity penalty evolves in our different systems, we plot the Q-factor penalty versus pump OSNR at point A. The Q-factor was calculated from measured BER using: Q=20log10[2erf1(2BER)]. For the PSA-case, the penalty was taken with respect to the performance at −42 dBm received signal power at 56 dB pump OSNR giving a BER of about 10−8. For the PIA-case the penalty was taken with respect to the performance at −37 dBm received signal power at 56 dB pump OSNR also giving a BER of about 10−8. The measurements were done with the pump recovery system optimized for each measurement point.

The Q-factor penalty versus pump OSNR at point A (bottom axis) and pump power at the pump recovery system input (top axis) is plotted in Fig. 4. As the pump OSNR is decreased, we see the Q-factor penalty increases, while showing the systems without IL penalized more heavily, as in Fig. 3. For the systems without IL, this penalty becomes apparent at a pump OSNR of about 50 dB, corresponding to roughly 0 dBm pump power at the input of the pump recovery system. For the systems with IL, penalty-free operation is observed down to a pump OSNR of 20 dB, corresponding to about −30 dBm pump power at the input of the pump recovery system.

Fig. 4 Q-factor penalty calculated from measured bit error ratio versus pump optical signal-to-noise ratio (OSNR) at point A (bottom axis) and pump power at the pump recovery system input (top axis) comparing a phase-insensitive amplifier (PIA) and phase-sensitive amplifier (PSA) amplified receiver with and without injection locking (IL) in the pump recovery system.

3. Investigation of pump recovery system operation limits

Also the transfer of phase modulation through the pump recovery system will depend on the power into the pump recovery system. The phase transfer through the IL is dependent on the field injected into the SL. Increased injection of ASE noise into the SL can therefore impact and degrade the phase transfer. An obvious consequence of degraded phase transfer is reduced pump SBS suppression in the PSA/PIA which in turn can lead to a Q-factor penalty through pump noise transfer if the pump SBS becomes significant. For the PSA we also expect a degraded phase transfer to impact the PSA operation through misalignment of the phase-matching condition. If we denote the pump phase modulation at the pump recovery system input by θin and at the output by θout then the phase-matching condition in the PSA can be expressed as: 2θpθsθi = π/2 where θp = θ′p + θout and θi = 2(θ′p + θin) − θsπ/2. We see that if θoutθin, the phase-matching will be disturbed. A deviation from the phase-matching would translate into gain fluctuations which in turn would affect the output signal and cause a Q-factor penalty.

The discussion above implies that an understanding of the transfer characteristics of IL is crucial for explaining the performance of the pump recovery system. The transfer characteristics of an injection-locked DFB laser are highly dependent on parameters such as the injection ratio, defined as the ratio between the injected power and the SL output power, the frequency offset between the injected wave and the free running SL, and the SL driving current. Therefore, in order to identify the limiting factors in our pump recovery system, with our specific operating conditions, we need to measure the noise generation in the pump recovery system (and ASE noise transfer through the SL) as well as the phase modulation transfer through the pump recovery system.

3.1. Amplitude noise and phase noise generation

The noise generation in the pump recovery system was investigated using homodyne coherent detection and constellation analysis. The experimental setup is shown in Fig. 5. A wave at 1553.7 nm was split up into two branches; a signal branch and a local oscillator branch. The local oscillator branch was frequency shifted by 27 MHz using an acousto-optic modulator (AOM) and then passed into a 90° optical hybrid. The frequency was shifted in order to obtain a detectable beat tone between the local oscillator and the signal in the optical hybrid. The signal branch was passed through VOA1 for attenuation to vary the OSNR after EDFA1, i.e. at point C, and then into the pump recovery system.

Fig. 5 Homodyne coherent detection setup used for characterizing noise generation in the pump recovery system and ASE noise transfer through the slave laser. VOA: variable optical attenuator, EDFA: erbium-doped fiber amplifier, PC: polarization controller, AOM: acousto-optic modulator, IL: injection locking.

Apart from removing the last EDFA, the pump recovery system was identical to the system used for the demonstration in section 2. We assumed that the last EDFA would not affect the noise properties of the recovered pump due to the high input power (20 dBm) to the EDFA from the SL. Both the case with and without IL in the pump recovery system was investigated, as indicated in Fig. 5. As for the demonstration measurements the SL driving current was seven times the lasing threshold value and the wavelength was tuned so that the frequency difference between the SL and the incoming wave was minimized. The SOP into the SL was tuned using PC1 so that phase transfer of an incoming phase modulated wave was maximized. The SL input power was kept constant at a high value (−7.3 dBm, corresponding to an injection ratio of −27.3 dB) using VOA2 in order to reduce the effect of filtering in the SL, facilitating the measurement of broadband ASE noise transfer. At injected powers above −5 dBm the SL got over-modulated and spurious tones appeared, this regime was therefore avoided.

After the pump recovery system the wave was injected into the 90° optical hybrid. The hybrid output was detected using four 11 GHz bandwidth detectors and then sent to a real-time oscilloscope (16 GHz bandwidth) for sampling. The data was post-processed offline and amplitude noise and phase noise was extracted. The amplitude noise σ a was defined as the standard deviation of the normalized amplitude and the phase noise σp was defined as the standard deviation of the phase.

Measured amplitude noise (right axis) and phase noise (left axis) at the output of the pump recovery system versus pump OSNR at point C (bottom axis) and pump power at the pump recovery system input (top axis) is presented in Fig. 6. For the case without IL both the amplitude noise and the phase noise increase with reduced pump OSNR, due to broadband ASE noise added by EDFA1. The noise floor reached at high pump OSNR was set by the sensitivity of the measurement system.

Fig. 6 Measured amplitude noise (right axis) and phase noise (left axis) after the pump recovery system with and without injection locking (IL) in the pump recovery system versus pump optical signal-to-noise ratio (OSNR) at point C (bottom axis) and pump power at the pump recovery system input (top axis). For the case with IL the slave laser input power was kept constant at −7.3 dBm, corresponding to an injection ratio of −27.3 dB.

With IL the phase noise increases with decreased pump OSNR in a similar fashion as for the case without IL. It has been shown experimentally [25

25. M. Vainio, M. Merimaa, and K. Nyholm, “Modulation transfer characteristics of injection-locked diode lasers,” Opt. Commun. 267, 455–463 (2006) [CrossRef] .

], and theoretically [24

24. E. K. Lau and M. C. Wu, “Amplitude and frequency modulation of the master laser in injection-locked laser systems,” in Proceedings of International Topical Meeting on Microwave Photonics , (2004), 142–145.

], that high FM-to-FM conversion should be expected up to several GHz under locking conditions similar to ours. However, since the ASE noise injected into the SL is broadband we expect some filtering through the SL, which is also what we see as reduced noise compared to the case without IL. The phase noise contribution from AM-to-FM conversion is expected to be negligible compared to the contribution from FM-to-FM transfer [23

23. A. Fragkos, A. Bogris, D. Syvridis, and R. Phelan, “Amplitude noise limiting amplifier for phase encoded signals using injection locking in semiconductor lasers,” J. Lightw. Technol. 30, 764–771 (2012) [CrossRef] .

].

Based on our phase noise and amplitude noise measurements we can conclude that the performance improvement seen in Fig. 3 and Fig. 4 for the hybrid IL/EDFA pump recovery system compared to the EDFA-based system comes from the squeezing and filtering of amplitude noise and filtering of phase noise through the SL.

3.2. Phase modulation transfer degradation

The phase modulation transfer was investigated using an experimental setup similar to the one used for the noise measurements. The setup is shown in Fig. 7. In this case a phase modulator was placed before the pump recovery system and either one or two sinusoidal RF-tones were applied for transfer characterization. For the one tone case the frequency RF1 was swept from 0.10 GHz to 2.30 GHz and the phase swing at the pump recovery system input Δϕin was π. In the dual tone case the applied modulation was either {RF1 = 0.10 GHz, RF2 = 0.32 GHz} or {RF1 = 0.30 GHz, RF2 = 0.91 GHz}. In this case the phase swing Δϕin was 2π, each RF-tone contributing with π swing. The tone frequencies and amplitudes in the dual tone case were selected to produce a flat-top spectrum, since this is desirable for efficient SBS suppression [29

29. S. K. Korotky, P. B. Hansen, L. Eskildsen, and J. J. Veselka, “Efficient phase modulation scheme for suppressing stimulated Brillouin scattering,” in Proc. Technol. Dig. Conf. Integr. Opt. Fiber Commun. , (1995), 110–111.

]. The pump recovery system was tuned in the same way as for the noise measurements with the exception that also the SL input power was varied.

Fig. 7 Homodyne coherent detection setup used for characterizing phase transfer through the pump recovery system. VOA: variable optical attenuator, EDFA: erbium-doped fiber amplifier, PC: polarization controller, AOM: acousto-optic modulator, RF: radio frequency, IL: injection locking.

To determine the phase modulation transfer the sampled signal was filtered by 20 MHz bandpass filter(s) centered at the tone(s) center frequency in order to remove the noise contribution to the constellation. The phase modulation transfer ratio (MTR) was then calculated as the modulation depth at the output of the pump recovery system to that of the input
PhaseMTR=ΔϕoutΔϕin
(1)
where Δϕin = π for the one tone case and Δϕin = 2π for the two tone case.

We measured phase MTR versus pump OSNR at point C and phase MTR versus SL input power, i.e. power at point D. The measurement versus pump OSNR was done with high SL input power (−7.3 dBm, corresponding to an injection ratio of −27.3 dB) in order to minimize the transfer degradation due to the SL when studying the OSNR dependence. For the same reason the measurement versus SL input power was done with high pump OSNR (42 dB) at point C. Due to over-modulation and appearance of spurious tones the power injected into the SL was kept below −5 dBm.

Measured phase MTR versus pump OSNR at point C (bottom axis) and pump power at the pump recovery system input (top axis) is presented in Fig. 8. We see that the single tone phase MTR decrease with increased tone frequency. This is expected from the bandwidth of the FM-to-FM transfer in the SL [24

24. E. K. Lau and M. C. Wu, “Amplitude and frequency modulation of the master laser in injection-locked laser systems,” in Proceedings of International Topical Meeting on Microwave Photonics , (2004), 142–145.

]. We also see that for a fixed tone frequency the phase MTR decrease with decreased pump OSNR. This is due to the ASE noise injected into the SL. The inset show the dual tone data together with the single tone data. We note that the curves for the dual tone cases are located between the curves for the corresponding single tones. This is what to expect if the dual tone transfer is treated as independent transfer of the two single frequency tones. In particular we note that the dual tone case with {RF1 = 0.10 GHz, RF2 = 0.32 GHz} is located between the curve for the single tone RF1 = 0.10 GHz and the single tone RF1 = 0.30 GHz.

Fig. 8 Measured phase modulation transfer ratio (MTR) versus pump optical signal-to-noise ratio (OSNR) at point C (bottom axis) and pump power at the pump recovery system input (top axis) for various modulation frequencies, as given by the legend. The inset show the dual tone data together with the single tone data. The slave laser input power (power at point D) was kept at −7.6 dBm, corresponding to an injection ratio of −27.3 dB. RF: radio frequency.

Measured phase MTR versus SL input power is shown in Fig. 9. In Fig. 9, the single tone phase MTR decrease with increased tone frequency is again very clear. The phase MTR also decrease with reduced power into the SL. The reason for this is the decrease in FM-to-FM transfer bandwidth in the SL with reduced input power. The dual tone cases are located between the curves for the corresponding single tones. For the dual tone transfer, the tone with higher frequency will suffer more from the limited transfer bandwidth and thus the combined reduction in swing will be between the corresponding single tone cases.

Fig. 9 Measured phase modulation transfer ratio (MTR) versus slave laser input power (power at point D) for various frequencies as given by the legends. The pump optical signal-to-noise ratio (OSNR) at point C was kept at 42 dB. RF: radio frequency.

Our measurements have shown that phase MTR is reduced, over all measured frequencies, both with reduced pump OSNR and reduced SL input power. The impact of reducing the SL input power was stronger than reducing the pump OSNR. They have also indicated that, from the perspective of phase MTR, dual tone transfer can be treated as independent transfer of two single tone components.

4. Characterization of pump recovery induced link penalty

The Q-factor penalty, extracted from measured BER, versus SL input power for various pump OSNR values is presented in Fig. 10. For the PSA-case the Q-factor penalty was taken with respect to the BER at −42 dBm received signal power, with high pump OSNR at point A (42 dB) and high SL input power (−5 dBm). For the PIA-case the penalty was taken with respect to the BER at −37.5 dBm received signal power, also with high pump OSNR at point A (42 dB) and high SL input power (−5 dBm).

Fig. 10 Q-factor penalty calculated from measured bit error ratio versus slave laser input power (power at point D). The measurements were done at various pump optical signal-to-noise ratio (OSNR) at point C, as given by the legend. The phase-insensitive amplifier (PIA) gain and phase-sensitive amplifier (PSA) gain was kept at 20 dB.

For the PIA-case there is a large Q-factor penalty at the combination of low pump OSNR and high SL input power. The penalty is reduced both with increased pump OSNR and reduced SL input power. The penalty reduction with increased pump OSNR is explained by the reduction of phase noise and amplitude noise generated in the pump recovery system, as shown in Fig. 6. The penalty reduction with reduced SL input power can be understood as follows. As the SL input power is reduced also the bandwidth of the FM-to-FM transfer is decreased, as seen in Fig. 9. In practice the SL will work as a phase bandpass filter centered at the pump frequency, with the bandwidth set by the FM-to-FM transfer bandwidth. Therefore, as the power into the SL is reduced more noise is filtered out and the penalty decrease. With reduced power into the SL (and reduced pump OSNR) the phase MTR is also reduced. Below about −20 dBm SL input power this lead to a sharp penalty onset due to pump SBS (not shown in Fig. 10).

In the PSA-case the Q-factor penalty curve is V-shaped at low pump OSNR (11 dB and 22 dB). In this case there are two effects influencing the penalty. The phase noise filtering in the SL is still an important effect but also the phase MTR is important, since that will impact the phase-matching in the PSA. The combined effect of these two factors, with phase noise giving penalty at high SL input powers (> −13 dBm for the 21 dB pump OSNR case) and phase-matching misalignment giving penalty at low SL input powers (< −13 dBm for the 21 dB pump OSNR case), give the V-shape. The measurement at 11 dB pump OSNR show higher penalty, both at low and high SL input powers, than the measurement at 22 dB pump OSNR since lower pump OSNR both introduce more noise and degrade the phase MTR, as seen in Fig. 6 and Fig. 8, respectively. For high pump OSNR (32 dB and 42 dB) there is no penalty at high SL input powers, i.e. there is no penalty due to phase noise. There is only a penalty at low SL input power (< −13 dBm) due to imperfect phase-matching in the PSA.

Finally, in Fig. 11 we show the Q-factor penalty versus pump OSNR at point C (bottom axis) and pump power at the pump recovery system input (top axis) for various SL input powers. The Q-factor penalty for the PSA-case was taken with respect to the BER at −42 dBm received signal power and for the PIA-case with respect to the BER at −37.5 dBm received signal power. In both cases with high pump OSNR at point A (45 dB) and high SL input power (−5 dBm). Measurements penalized by SBS, occurring at combined low pump OSNR and low SL input power, were removed from Fig. 11.

Fig. 11 Q-factor penalty calculated from measured bit error ratio versus pump optical signal-to-noise ratio (OSNR) at point C (bottom axis) and pump power at the pump recovery system input (top axis). The measurements were done at various slave laser input powers, as given by the legend. The phase-insensitive amplifier (PIA) gain and phase-sensitive amplifier (PSA) gain was kept at 20 dB.

In Fig. 11 the impact of phase noise filtering through the SL is again very clear, when comparing curves at difference SL input power. The effect of imperfect phase-matching in the PSA is not clearly visible since the lowest SL input power presented is at −15 dBm, just marginally below the −13 dBm where we started to see the effect in Fig. 10. An interesting feature that is clearly visible is that the PSA-case show less Q-factor penalty than the PIA-case, i.e. the PSA is less sensitive to noise on the recovered pump than the PIA. The reason for this difference between the PSA-case and the PIA-case, also seen in Fig. 10, is not clear.

Based on the results shown in Fig. 10 we can deduce how large phase MTR is needed for penalty-free pump recovery operation in the PSA-amplified link. For high pump OSNR (32 dB and 42 dB) we saw a penalty onset due to low phase MTR at −13 dB SL input power. Referring to Fig. 9, that show phase MTR versus SL input power at 42 dB pump OSNR, we can relate the SL input power to a phase MTR value. In Fig. 9 we can read out that at a SL input power of 13 dBm the phase MTR is approximately 97% for the dual tone case or approximately 98% for the single RF1 = 0.10 GHz tone and approximately 96% for the single RF1 = 0.30 GHz tone.

We can also deduce how much noise that can be tolerated for penalty-free pump recovery operation in the PSA- and PIA-amplified link. In Fig. 11 we see that the penalty onset is at about 25 dB pump OSNR for the PSA-case with −7.6 dBm SL input power. The corresponding value for the PIA-case is about 30 dB. In Fig. 6, showing the phase noise and amplitude noise versus pump OSNR at −7.3 dBm SL input power, we can read the corresponding phase noise and amplitude noise values. At 25 dB pump OSNR (the PSA-case penalty onset) the phase noise is 2.0 degrees and the amplitude noise is 0.03. At 30 dB pump OSNR (the PIA-case penalty onset) the phase noise is 1.4 degrees and the amplitude noise 0.03.

The penalty-free operating range for the pump recovery system could, for both the PSA-and PIA-amplified links, be extended to include lower pump OSNR values if lower bandwidth pump phase modulation was used. For the PIA-case this would mean that the SL input power could be reduced without introducing penalty from SBS, thus allowing for better noise filtering. For the PSA-case the effect would be that the penalty onset due to imperfect phase modulation transfer would move to lower SL input power which in turn would allow for lower SL input power and better noise filtering through the SL.

We can now explain the Q-factor penalty difference between the PIA- and PSA-case with IL seen at low pump OSNR values in Fig. 4. For the PIA system the penalty originate from SBS and for the PSA system the penalty is due to the combined effect of noise on the pump and imperfect phase-matching in the PSA.

Alternative SBS suppression techniques, not based on pump phase modulation, would improve the operating limits both in the PSA- and PIA-case since that would allow for lower bandwidth phase modulation of the pump or in the extreme case no pump phase modulation. In the case of no pump phase modulation we expect both the PSA and PIA system to be limited by in-band pump noise and the practical problem of keeping the frequency difference between the incoming pump and the SL within the IL locking bandwidth. However, we have not observed any penalty from in-band noise in the measurements we have presented here.

5. Conclusions

Measurements, based on homodyne coherent detection and constellation analysis, show that amplitude squeezing, amplitude noise filtering, and phase noise filtering through the SL can explain the superior performance of the hybrid IL/EDFA-based pump recovery system compared to a simple EDFA-based system. The measurements also showed that the phase MTR for the pump recovery system is reduced both with reduced SL input power, strong dependence, and with reduced pump OSNR, weaker dependence, and indicated that dual tone transfer can be treated as independent transfer of two single tones.

This work was supported by the European Research Council Advanced Grant PSOPA (291618), by the Knut and Alice Wallenberg Foundation, and by the Swedish Research Council. The authors would like to thank OFS Fitel Denmark for providing the HNLFs.

References and links

1.

C. M. Caves, “Quantum limits on noise in linear amplifiers,” Phys. Rev. D 26, 1817–1839 (1982) [CrossRef] .

2.

E. Desurvire, Erbium-doped Fiber Amplifiers (John Wiley & Sons, 1994).

3.

W. Imajuku, A. Takada, and Y. Yamabayashi, “Low-noise amplification under the 3dB noise figure in high-gain phase-sensitive fibre amplifier,” Electron. Lett 35, 1954–1955 (1999) [CrossRef] .

4.

D. J. Lovering, J. A Levenson, P. Vidakovic, J. Webjörn, and P. St. J. Russell, “Noiseless optical amplification in quasi-phase-matched bulk lithium niobate,” Opt. Lett. 21, 1439–1441 (1996) [CrossRef] [PubMed] .

5.

Z. Tong, C. Lundström, P. A. Andrekson, C. J. McKinstrie, M. Karlsson, D. J. Blessing, E. Tipsuwannakul, B. J. Puttnam, H. Toda, and L. Grüner-Nielsen, “Towards ultrasensitive optical links enabled by low-noise phase-sensitive amplifiers,” Nat. Photonics 5, 430–436 (2011) [CrossRef] .

6.

J. Hansryd, P. A. Andrekson, M. Westlund, J. Li, and P. O. Hedekvist, “Fiber-based optical parametric amplifiers and their applications,” IEEE J. Sel. Topics Quantum Electron. 8, 506–520 (2002) [CrossRef] .

7.

J. Kakande, C. Lundström, P. A. Andrekson, Z. Tong, M. Karlsson, P. Petropoulos, F. Parmigiani, and D. J. Richardson, “Detailed characterization of a fiber-optic parametric amplifier in phase-sensitive and phase-insensitive operation,” Opt. Express 18, 4130–4137 (2010) [CrossRef] [PubMed] .

8.

M. Vasilyev, “Distributed phase-sensitive amplification,” Opt. Express 13, 7563–7571 (2005) [CrossRef] [PubMed] .

9.

R. Tang, P. Devgan, V. S. Grigoryan, and P. Kumar, “Inline frequency-non-degenerate phase-sensitive fibre parametric amplifier for fibre-optic communication,” Electron. Lett 41, 1072–1074 (2005) [CrossRef] .

10.

R. Tang, P. Devgan, P. L. Voss, V. S. Grigoryan, and P. Kumar, “In-line frequency-nondegenerate phase-sensitive fiber-optical parametric amplifier,” IEEE Photon. Technol. Lett. 17, 1845–1847 (2005) [CrossRef] .

11.

O. K. Lim, V. Grigoryan, M. Shin, and P. Kumar, “Ultra-low-noise inline fiber-optic phase-sensitive amplifier for analog optical signals,” in Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC), Technical Digest (CD) (Optical Society of America, 2008), paper OML3.

12.

R. Tang, J. Lasri, P. S. Devgan, V. Grigoryan, P. Kumar, and M. Vasilyev, “Gain characteristics of a frequency nondegenerate phase-sensitive fiber-optic parametric amplifier with phase self-stabilized input,” Opt. Express 13, 10483–10493 (2005) [CrossRef] [PubMed] .

13.

Z. Tong, C. J. McKinstrie, C. Lundström, M. Karlsson, and P. A. Andrekson, “Noise performance of optical fiber transmission links that use non-degenerate cascaded phase-sensitive amplifiers,” Opt. Express 18, 15426–15439 (2010) [CrossRef] [PubMed] .

14.

C. J. McKinstrie, M. Karlsson, and Z. Tong, “Field-quadrature and photon-number correlations produced by parametric processes,” Opt. Express 18, 19792–19823 (2010) [CrossRef] [PubMed] .

15.

Z. Tong, C. Lundström, E. Tipsuwannakul, M. Karlsson, and P. A. Andrekson, “Phase-Sensitive Amplified DWDM DQPSK Signals Using Free-Running Lasers with 6-dB Link SNR Improvement over EDFA-based Systems,” in European Conference and Exhibition on Optical Communication (ECOC), Technical Digest (CD) (Optical Society of America, 2010), paper PDP1.3 [CrossRef] .

16.

Z. Tong, C. Lundström, P. A. Andrekson, M. Karlsson, and A. Bogris, “Ultralow noise, broadband phase-sensitive optical amplifiers, and their applications,” IEEE J. Sel. Topics Quantum Electron. 18, 1016–1032 (2012) [CrossRef] .

17.

Z. Tong, A. Bogris, C. Lundström, C. J. McKinstrie, M. Vasilyev, M. Karlsson, and P. A. Andrekson, “Modeling and measurement of the noise figure of a cascaded non-degenerate phase-sensitive parametric amplifier,” Opt. Express 18, 14820–14835 (2010) [CrossRef] [PubMed] .

18.

A. Takada and W. Imajuku, “Optical phase-sensitive amplifier with pump laser phase-locked to input signal light,” in Proceedings of European Conference and Exhibition on Optical Communication (ECOC), (Optical Society of America, 1997), 98–101.

19.

R. Slavík, F. Parmigiani, J. Kakande, C. Lundström, M. Sjödin, P. A. Andrekson, R. Weerasuriya, S. Sygletos, A. D. Ellis, L. Grüner-Nielsen, D. Jakobsen, S. Herstrøm, R. Phelan, J. OGorman, A. Bogris, D. Syvridis, S. Dasgupta, P. Petropoulos, and D. J. Richardson, “All-optical phase and amplitude regenerator for next-generation telecommunications systems,” Nat. Photonics 4, 690–695 (2010) [CrossRef] .

20.

S. Sygletos, R. Weerasuriya, S. K. Ibrahim, F. Gunning, R. Phelan, J. O’Gorman, J. O’Carrol, B. Kelly, A. Bogris, D. Syvridis, C. Lundström, P. Andrekson, F. Parmigiani, D. J. Richardson, and A. D. Ellis, “Phase locking and carrier extraction schemes for phase sensitive amplification,” in Conference on Transparent Optical Networks (ICTON), 2010 12th International, Technical Digest (CD) (Optical Society of America, 2010), paper Mo.C1.3 [CrossRef] .

21.

S. Kasapi, S. Lathi, and Y. Yamamoto, “Amplitude-squeezed, frequency-modulated, tunable, diode-laser-based source for sub-shot-noise FM spectroscopy,” Opt. Lett. 22, 478–480 (1997) [CrossRef] [PubMed] .

22.

E. K. Lau, L. J. Wong, X. Zhao, Y. K. Chen, C. J. Chang-Hasnain, and M. C. Wu, “Bandwidth enhancement by master modulation of optical injection-locked lasers,” J. Lightw. Technol. 26, 2584–2593 (2008) [CrossRef] .

23.

A. Fragkos, A. Bogris, D. Syvridis, and R. Phelan, “Amplitude noise limiting amplifier for phase encoded signals using injection locking in semiconductor lasers,” J. Lightw. Technol. 30, 764–771 (2012) [CrossRef] .

24.

E. K. Lau and M. C. Wu, “Amplitude and frequency modulation of the master laser in injection-locked laser systems,” in Proceedings of International Topical Meeting on Microwave Photonics , (2004), 142–145.

25.

M. Vainio, M. Merimaa, and K. Nyholm, “Modulation transfer characteristics of injection-locked diode lasers,” Opt. Commun. 267, 455–463 (2006) [CrossRef] .

26.

S. L. I. Olsson, B. Corcoran, C. Lundström, E. Tipsuwannakul, S. Sygletos, A. D. Ellis, Z. Tong, M. Karlsson, and P. A. Andrekson, “Optical injection-locking-based pump recovery for phase-sensitively amplified links,” in Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC), Technical Digest (CD) (Optical Society of America, 2012), paper OW3C.3.

27.

B. Corcoran, S. L. I. Olsson, C. Lundström, M. Karlsson, and P. Andrekson, “Phase-sensitive optical pre-amplifier implemented in an 80km DQPSK link,” in Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC), Technical Digest (CD) (Optical Society of America, 2012), paper PDP5A.4 [CrossRef] .

28.

S. L. I. Olsson, B. Corcoran, C. Lundström, M. Sjödin, M. Karlsson, and P. A. Andrekson, “Phase-sensitive amplified optical link operating in the nonlinear transmission regime,” in European Conference and Exhibition on Optical Communication (ECOC), Technical Digest (CD) (Optical Society of America, 2012), paper Th.2.F.1 [CrossRef] .

29.

S. K. Korotky, P. B. Hansen, L. Eskildsen, and J. J. Veselka, “Efficient phase modulation scheme for suppressing stimulated Brillouin scattering,” in Proc. Technol. Dig. Conf. Integr. Opt. Fiber Commun. , (1995), 110–111.

30.

A. Furusawa, “Amplitude squeezing of a semiconductor laser with light injection,” Opt. Lett. 21, 2014–2016 (1996) [CrossRef] [PubMed] .

31.

C. Lundström, R. Malik, L. Grüner-Nielsen, B. Corcoran, S. L. I. Olsson, M. Karlsson, and P. A. Andrekson, “Fiber optic parametric amplifier With 10-dB net gain without pump dithering,” IEEE Photon. Technol. Lett. 25, 234–237 (2013) [CrossRef] .

OCIS Codes
(060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
(140.3520) Lasers and laser optics : Lasers, injection-locked

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: April 4, 2013
Revised Manuscript: May 30, 2013
Manuscript Accepted: June 5, 2013
Published: June 11, 2013

Citation
Samuel L. I. Olsson, Bill Corcoran, Carl Lundström, Ekawit Tipsuwannakul, Stylianos Sygletos, Andrew D. Ellis, Zhi Tong, Magnus Karlsson, and Peter A. Andrekson, "Injection locking-based pump recovery for phase-sensitive amplified links," Opt. Express 21, 14512-14529 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-12-14512


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References

  1. C. M. Caves, “Quantum limits on noise in linear amplifiers,” Phys. Rev. D26, 1817–1839 (1982). [CrossRef]
  2. E. Desurvire, Erbium-doped Fiber Amplifiers (John Wiley & Sons, 1994).
  3. W. Imajuku, A. Takada, and Y. Yamabayashi, “Low-noise amplification under the 3dB noise figure in high-gain phase-sensitive fibre amplifier,” Electron. Lett35, 1954–1955 (1999). [CrossRef]
  4. D. J. Lovering, J. A Levenson, P. Vidakovic, J. Webjörn, and P. St. J. Russell, “Noiseless optical amplification in quasi-phase-matched bulk lithium niobate,” Opt. Lett.21, 1439–1441 (1996). [CrossRef] [PubMed]
  5. Z. Tong, C. Lundström, P. A. Andrekson, C. J. McKinstrie, M. Karlsson, D. J. Blessing, E. Tipsuwannakul, B. J. Puttnam, H. Toda, and L. Grüner-Nielsen, “Towards ultrasensitive optical links enabled by low-noise phase-sensitive amplifiers,” Nat. Photonics5, 430–436 (2011). [CrossRef]
  6. J. Hansryd, P. A. Andrekson, M. Westlund, J. Li, and P. O. Hedekvist, “Fiber-based optical parametric amplifiers and their applications,” IEEE J. Sel. Topics Quantum Electron.8, 506–520 (2002). [CrossRef]
  7. J. Kakande, C. Lundström, P. A. Andrekson, Z. Tong, M. Karlsson, P. Petropoulos, F. Parmigiani, and D. J. Richardson, “Detailed characterization of a fiber-optic parametric amplifier in phase-sensitive and phase-insensitive operation,” Opt. Express18, 4130–4137 (2010). [CrossRef] [PubMed]
  8. M. Vasilyev, “Distributed phase-sensitive amplification,” Opt. Express13, 7563–7571 (2005). [CrossRef] [PubMed]
  9. R. Tang, P. Devgan, V. S. Grigoryan, and P. Kumar, “Inline frequency-non-degenerate phase-sensitive fibre parametric amplifier for fibre-optic communication,” Electron. Lett41, 1072–1074 (2005). [CrossRef]
  10. R. Tang, P. Devgan, P. L. Voss, V. S. Grigoryan, and P. Kumar, “In-line frequency-nondegenerate phase-sensitive fiber-optical parametric amplifier,” IEEE Photon. Technol. Lett.17, 1845–1847 (2005). [CrossRef]
  11. O. K. Lim, V. Grigoryan, M. Shin, and P. Kumar, “Ultra-low-noise inline fiber-optic phase-sensitive amplifier for analog optical signals,” in Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC), Technical Digest (CD) (Optical Society of America, 2008), paper OML3.
  12. R. Tang, J. Lasri, P. S. Devgan, V. Grigoryan, P. Kumar, and M. Vasilyev, “Gain characteristics of a frequency nondegenerate phase-sensitive fiber-optic parametric amplifier with phase self-stabilized input,” Opt. Express13, 10483–10493 (2005). [CrossRef] [PubMed]
  13. Z. Tong, C. J. McKinstrie, C. Lundström, M. Karlsson, and P. A. Andrekson, “Noise performance of optical fiber transmission links that use non-degenerate cascaded phase-sensitive amplifiers,” Opt. Express18, 15426–15439 (2010). [CrossRef] [PubMed]
  14. C. J. McKinstrie, M. Karlsson, and Z. Tong, “Field-quadrature and photon-number correlations produced by parametric processes,” Opt. Express18, 19792–19823 (2010). [CrossRef] [PubMed]
  15. Z. Tong, C. Lundström, E. Tipsuwannakul, M. Karlsson, and P. A. Andrekson, “Phase-Sensitive Amplified DWDM DQPSK Signals Using Free-Running Lasers with 6-dB Link SNR Improvement over EDFA-based Systems,” in European Conference and Exhibition on Optical Communication (ECOC), Technical Digest (CD) (Optical Society of America, 2010), paper PDP1.3. [CrossRef]
  16. Z. Tong, C. Lundström, P. A. Andrekson, M. Karlsson, and A. Bogris, “Ultralow noise, broadband phase-sensitive optical amplifiers, and their applications,” IEEE J. Sel. Topics Quantum Electron.18, 1016–1032 (2012). [CrossRef]
  17. Z. Tong, A. Bogris, C. Lundström, C. J. McKinstrie, M. Vasilyev, M. Karlsson, and P. A. Andrekson, “Modeling and measurement of the noise figure of a cascaded non-degenerate phase-sensitive parametric amplifier,” Opt. Express18, 14820–14835 (2010). [CrossRef] [PubMed]
  18. A. Takada and W. Imajuku, “Optical phase-sensitive amplifier with pump laser phase-locked to input signal light,” in Proceedings of European Conference and Exhibition on Optical Communication (ECOC), (Optical Society of America, 1997), 98–101.
  19. R. Slavík, F. Parmigiani, J. Kakande, C. Lundström, M. Sjödin, P. A. Andrekson, R. Weerasuriya, S. Sygletos, A. D. Ellis, L. Grüner-Nielsen, D. Jakobsen, S. Herstrøm, R. Phelan, J. OGorman, A. Bogris, D. Syvridis, S. Dasgupta, P. Petropoulos, and D. J. Richardson, “All-optical phase and amplitude regenerator for next-generation telecommunications systems,” Nat. Photonics4, 690–695 (2010). [CrossRef]
  20. S. Sygletos, R. Weerasuriya, S. K. Ibrahim, F. Gunning, R. Phelan, J. O’Gorman, J. O’Carrol, B. Kelly, A. Bogris, D. Syvridis, C. Lundström, P. Andrekson, F. Parmigiani, D. J. Richardson, and A. D. Ellis, “Phase locking and carrier extraction schemes for phase sensitive amplification,” in Conference on Transparent Optical Networks (ICTON), 2010 12th International, Technical Digest (CD) (Optical Society of America, 2010), paper Mo.C1.3. [CrossRef]
  21. S. Kasapi, S. Lathi, and Y. Yamamoto, “Amplitude-squeezed, frequency-modulated, tunable, diode-laser-based source for sub-shot-noise FM spectroscopy,” Opt. Lett.22, 478–480 (1997). [CrossRef] [PubMed]
  22. E. K. Lau, L. J. Wong, X. Zhao, Y. K. Chen, C. J. Chang-Hasnain, and M. C. Wu, “Bandwidth enhancement by master modulation of optical injection-locked lasers,” J. Lightw. Technol.26, 2584–2593 (2008). [CrossRef]
  23. A. Fragkos, A. Bogris, D. Syvridis, and R. Phelan, “Amplitude noise limiting amplifier for phase encoded signals using injection locking in semiconductor lasers,” J. Lightw. Technol.30, 764–771 (2012). [CrossRef]
  24. E. K. Lau and M. C. Wu, “Amplitude and frequency modulation of the master laser in injection-locked laser systems,” in Proceedings of International Topical Meeting on Microwave Photonics, (2004), 142–145.
  25. M. Vainio, M. Merimaa, and K. Nyholm, “Modulation transfer characteristics of injection-locked diode lasers,” Opt. Commun.267, 455–463 (2006). [CrossRef]
  26. S. L. I. Olsson, B. Corcoran, C. Lundström, E. Tipsuwannakul, S. Sygletos, A. D. Ellis, Z. Tong, M. Karlsson, and P. A. Andrekson, “Optical injection-locking-based pump recovery for phase-sensitively amplified links,” in Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC), Technical Digest (CD) (Optical Society of America, 2012), paper OW3C.3.
  27. B. Corcoran, S. L. I. Olsson, C. Lundström, M. Karlsson, and P. Andrekson, “Phase-sensitive optical pre-amplifier implemented in an 80km DQPSK link,” in Optical Fiber Communication Conference and Exposition (OFC) and National Fiber Optic Engineers Conference (NFOEC), Technical Digest (CD) (Optical Society of America, 2012), paper PDP5A.4. [CrossRef]
  28. S. L. I. Olsson, B. Corcoran, C. Lundström, M. Sjödin, M. Karlsson, and P. A. Andrekson, “Phase-sensitive amplified optical link operating in the nonlinear transmission regime,” in European Conference and Exhibition on Optical Communication (ECOC), Technical Digest (CD) (Optical Society of America, 2012), paper Th.2.F.1. [CrossRef]
  29. S. K. Korotky, P. B. Hansen, L. Eskildsen, and J. J. Veselka, “Efficient phase modulation scheme for suppressing stimulated Brillouin scattering,” in Proc. Technol. Dig. Conf. Integr. Opt. Fiber Commun., (1995), 110–111.
  30. A. Furusawa, “Amplitude squeezing of a semiconductor laser with light injection,” Opt. Lett.21, 2014–2016 (1996). [CrossRef] [PubMed]
  31. C. Lundström, R. Malik, L. Grüner-Nielsen, B. Corcoran, S. L. I. Olsson, M. Karlsson, and P. A. Andrekson, “Fiber optic parametric amplifier With 10-dB net gain without pump dithering,” IEEE Photon. Technol. Lett.25, 234–237 (2013). [CrossRef]

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