Pilot-tone based self-homodyne detection using

Pilot-tone based self-homodyne detection using optical nonlinear wave mixing YINWEN CAO,1,* MORTEZA ZIYADI,1 AHMED ALMAIMAN,1 AMIRHOSSEIN MOHAJERIN-ARIAEI,1 PEICHENG LIAO,1 CHANGJING BAO,1 FATEMEH ALISHAHI,1 AHMAD FALLAHPOUR,1 BISHARA SHAMEE,1 ASHER J. WILLNER,1 YOUICHI AKASAKA,2 TADASHI IKEUCHI,2 STEVEN WILKINSON,3 CARSTEN LANGROCK,4 MARTIN M. FEJER,4 JOSEPH TOUCH,5 MOSHE TUR,6 AND ALAN E. WILLNER1 1

Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA Fujitsu Laboratories of America, 2801 Telecom Parkway, Richardson, TX 75082, USA 3 Raytheon Company, El Segundo, CA 92195, USA 4 Edward L. Ginzton Laboratory, 348 Via Pueblo Mall, Stanford University, Stanford, CA 94305, USA 5 Information Sciences Institute, University of Southern California, Marina del Rey, CA 90292, USA 6 School of Electrical Engineering, Tel Aviv University, Ramat Aviv 69978, Israel *Corresponding author: [email protected] 2

Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX

An all-optical pilot-tone based self-homodyne detection scheme using nonlinear wave mixing is experimentally demonstrated. Two scenarios are investigated using (i) multiple WDM channels with sufficient power of pilot tones, (ii) a single channel with a low-power pilot tone. The eye-diagram and bit-error-rate (BER) of the system are studied by tuning various parameters, such as pump power, relative phase, and pilot-to-signal ratio (PSR). OCIS codes: (060.2920) Homodyning; (060.2360) Fiber optics links and subsystems; (060.4370) Nonlinear optics, fibers. http://dx.doi.org/10.1364/OL.99.099999

Optical coherent detection is of importance in optical communication systems, especially for the recovery of sensitive phase-encoded data signals [1-3]. A coherent detection system notably requires phase and frequency locking between the incoming signal and the local oscillator (LO). Approaches to achieving a stable locking include the use of an optical phaselocked loop (OPLL) [4-6] or digital carrier recovery [7-10]. Self-homodyne detection (SHD) is another approach which can potentially simplify receiver signal processing [11] and relax the requirement for narrow linewidth lasers [12]. One common approach to realizing SHD relies on transmitting a pilot tone along with the data channel on another frequency or an orthogonal polarization. At the receiver, the pilot tone is extracted and processed in a different path that allows it to later beat with the data channel as an LO laser [11-14]. That approach requires

sufficient pilot-to-signal ratio (PSR) to ensure system performance [15,16] and it is typically accomplished by (i) transmitting a pilot tone with sufficient power, which reduces the effective data signal power that can be accommodated for transmission; or (ii) amplifying/regenerating a low-power co-transmitted pilot tone in a separate path at the receiver, which might require a phaselocked loop [13]. Recently, there has been another SHD method proposed using two stages of optical nonlinear wave mixing without sending a pilot tone [17]. By generating the delayed version of the incoming signal conjugate which is later mixed with the original signal, that approach can automatically lock a “local” pump to the signal without requiring a feedback loop controller. However, that approach (i) alters the original data encoding from quadraturephase-shift-keying (QPSK) to differential QPSK by using an optical differentiator, and (ii) might be difficult to extend to a multichannel wavelength-division-multiplexed (WDM) system. In this paper, we demonstrate SHD that combines the use of the co-transmitted pilot tone and optical nonlinear wave mixing at the receiver. Our method is as follows: (i) at the transmitter, a pilot tone is placed at an adjacent frequency to a data channel; and (ii) at the receiver, phase-locked optical frequency comb lines are employed to convert the pilot tone to the center of the data channel spectrum [18,19]. This approach uses only a single nonlinear mixing stage to achieve automatic phase-locking for SHD without path separation or altering the data encoding. We demonstrate it with multiple WDM channels, each with its own pilot tone. In an experiment, two 20-Gbaud QPSK channels are recovered using a single periodically poled lithium niobate (PPLN)

Figg. 1. Conceptual diagram d of propo osed self-homody yne detection (SH HD) system. The scheme is compo osed of (i) Brillou uin amplification to selectively am mplify the pilot to ones if pilot-to-sig gnal ratio (PSR) is low, and (ii) ph hase-preserving w wavelength conve version using optiical frequency comb lines. The folllowing two expe eriments demonsstrate SHD for diifferent scenarioss: (i) WDM chann nels with sufficieent PSR (withoutt Brillouin amplifi fication); (ii) a sin ngle channel with h low PSR (with Brillouin B amplificaation). PPLN: perriodically poled liithium niobate; H HNLF: highly non nlinear fiber.

waaveguide. To address a the power p issue off the pilot ton ne, naarrowband Brilllouin amplificatiion (BA) is addeed at the receiv ver for in-line selectiv ve amplification n of the pilot to one. This achiev ves SH HD for the chaannel with an ultra-low-poweer pilot tone. We W exxperimentally demonstrate thiss scheme in a single channel of 10 0/20-Gbaud BPSK and 10-Gbaud QPSK signals. Systeem peerformance can be b maintained with w a PSR as low w as -30dB. The concept off the proposed SHD S system is shown in Fig. 1. At th he transmitter, two data chan nnels (S1 and S2) are sent wiith different pilot ton nes (P1 and P2). At A the receiver, if the power of P1 nd P2 are low (lo ow PSR), a stagee of BA is emplo oyed to selectiveely an am mplify the pilot tone by a gain coefficient of g without needin ng paath separation [2 20,21]. In the neext stage, the datta channels (S1, S2) an nd the amplified d pilot tones (g gP1, gP2) are coupled with fo our ph hase-locked opttical frequency y comb lines to o achieve phasseprreserving wavele ength conversion n in a genetic nonlinear n elemen nt, wh hich could be a PPLN or a highlly nonlinear fibeer (HNLF) [22]. By B ch hoosing approp priate frequen ncy difference (the frequen ncy difference betweeen Si and Pi, i=1, i 2) and rellative phase (Δ Δθ) beetween the comb b lines, the pilot tones are conveerted to the centter off the data chann nel. Both I and Q components can be recovered ussing direct detecction.

Figg. 2. (a) Experim mental setup of SHD S for WDM ch hannels with higghpo ower pilot tones without the mid ddle part (Brillouiin amplification) of Figg. 1; (b) correspo onding spectra att each node; (c) eye e diagrams of the t tw wo detected 20-G Gbaud QPSK chan nnels; (d) BER meeasurements. ML LL: mode-locked laser;; DLI: delay line in nterferometer; IL LL: injection-lock ked lasser; SLM: spatial light l modulator.

In th he first experim ment, the powerr of pilot tone iis sufficiently high th hat BA can be byypassed. In Fig. 2 2, a mode-locked d laser (MLL) with a 10GHz repettition rate is injected into a delay line interferrometer (DLI) fo ollowed by a 450 0m HNLF to gen nerate optical frequen ncy comb lines w with broad specctrum, as shown n in Fig. 2(b1). A clockk synchronizer iis employed to maintain the reepetition rate with a 1 10G clock refereence. The transm mitter and receivver share the comb liines, which are decorrelated b by a 30km single mode fiber (SMF). In a spatial ligh ht modulator (SL LM) filter at thee transmitter, two coomb lines are sselected to be ssent to an IQ m modulator to generatte 20-Gbaud QP PSK signals. On n the other portt of the SLM filter, tw wo other comb llines are selecteed as the corresp ponding pilot tones oof the modulatted signals. Byy sending thesee tones into injectioon locked lasers (ILL), they are amplified at thee transmitter. The reaason to use ILL is to make the scenario that th he pilot tones have su ufficient power aat the transmittter side whereass the purpose of this experiment is tto focus on the feasibility demonstration of SHD foor multi-channell system. For ch hannel decorrelaation, each of the sign nals with its ow wn pilot tone is sent through d different fiber paths aand later combin ned, with spectru um shown in Figg. 2(b2). At th he receiver, the signals with piilot tones are aamplified and sent intto a PPLN with a quasi-phase m matching (QPM)) wavelength of ~15 550.5nm along with the receivver’s frequencyy comb lines. Inside tthe PPLN waveeguide, the pilott tones are convverted to the center of each of the data channels aas shown in Figg. 2(b3). The desired d signal is then fi filtered and sentt to a PD for deteection. Due to the patth separation b between the pilot tone and ssignal at the transm mitter side, offlin ne digital signal stabilization is employed to compen nsate the resulltant phase varriation based on a decision directed approach [23]. Because our aavailable experim mental setup has acccess to only a sin ngle PPLN (in co ontrast to the co oncept shown in Fig. 1), the two ou utput paths (I aand Q) of Fig. 1 have to be measurred separately, each followingg proper adjusttment of Δθ betweeen the comb lin nes using SLM fiilter-2 as shown n in Fig. 2(a). Figure 2(c) shows thee eye diagrams ffor the two 20--Gbaud QPSK channeels. The BER meeasurement is sh hown in Fig. 2(d d). Compared to sim multaneous mu ulti-channel deetection, separrate channel detectioon could achievve a 1.8dB OSNR improvementt at a BER of 1e-3. Th he extra penaltyy might arise from the cross-talk k in the PPLN, which iis expected to in ncrease if this ap pproach is exten nded to larger numbeer of channels. How to effectivvely suppress th he cross-talk requirees further researrch in the future.

100km Link

Brillouin Amplific cation for Pilot Tone Left Pilot Tone

10G/20G PRBS 215-1 AWG

10MHz Reference

I

Slave Laser

Q

10.810GH Hz ~ -∆λ

+∆λ

-∆λ

Intensity Modulattor

~

40GHz

λ~1550.7nm

IQ Modulator

DCF SMF ~80km ~20km

1

2

SMF~500m

Detector

4

10dB/D

10dB/D

A ATT Slave laser locked

Comb Source

SLM Filter

1550.96 1550.97 1550.98 1550.9 99 1550.96 1550.97 1550.98 15 550.99 Phase-Preserving g Wavelength (nm) Wavelength (nm)

3

P

s gP 2 comb lines

S P

10dB/D

P

gP

Wavelength Conversio on

4 S+ηgP

10dB/D

2

S

10dB/D

10dB/D

(b b) 1

3

HNLF~450m

Slave laser not locked

S

Rayleigh 1550 1550.5

1551

1551 1.5 1550 1550.5 1551 1551.5 1550

Wavelength (nm)

Wavelength (nm)

1552

155 54

Wavelength (nm)

1550

1552

15 554

Wavelength (nm)

Figg. 3. (a) Experim mental setup of SH HD for a single channel c with -30d dB PSSR and the spectrra when the slav ve laser for Brillou uin amplification n is freequency locked or unlocked to t the incomin ng pilot tone; (b) ( co orresponding spectra measured att each node.

In the presencee of a low-powerr co-transmitted d pilot tone, the BA B staage is included to t boost power before b the nonlin near wave mixin ng. Th he experimentall setup of a sing gle channel SHD D with low PSR R is sh hown in Fig. 3(a)). At the transmiitter, the data is generated usingg a higgh-speed arbittrary waveform m generator (A AWG), and thee I co omponent is ad dded with a lo ow-power sinu usoidal pilot tone geenerated by a 40 0GHz clock syntthesizer. The clo ock in the AWG G is freequency locked with the pilot tone t clock by a 10MHz referencce. Th hen, the data signal s modulatees a laser at th he wavelength of 15 550.7nm in an IQ modulator. The T spectrum of o the signal wiith pillot tone is show wn in Fig. 3 (b1), where the launcch power is 3dB Bm an nd the PSR is -30 0dB. The signal with w the pilot ton ne is sent to eith her (i)) the proposed SHD S structure diirectly for B2B evaluation, e or (ii)) a 10 00-km link comp promising an 80 0km SMF and a 20km dispersio on co ompensated fibeer (DCF) with a total loss of 30.7d dB. At the receiver,, the incoming siignal with pilot tone t is sent to tw wo paaths. In the up pper path, the left pilot tone is selected by y a naarrowband opttical filter and sent to a slaave laser that is freequency-locked to the input pilot p tone. Com mpared to [24,25], wh hich require a phase p locking of ILL, the slave lasser is used as a BA B pu ump so that phaase locking is no ot required. Thee temperature an nd cu urrent of the slaave laser need to o be tuned for frequency f lockin ng. Th he output is theen modulated by y a 10.810GHz sinusoidal s tone in an n intensity mod dulator biased at a the null poin nt. The generatted low wer sideband (h higher frequenccy) continuous waveform w (CW) is seelected and ampllified to act as th he BA pump, as shown s in Fig. 3(a). Affterwards, the BA B pump propag gates in the opp posite direction to th he incoming sign nal in a 500m SM MF, in which onlly the pilot tonee is am mplified by ~40dB with the narrrowband Brillouin interaction, as sh hown in Fig. 3(b2). The signal with w pilot tone iss then amplified in an n EDFA and sen nt into a narrow wband optical fiilter, in which the th Raayleigh back-scaattering compo onent is suppreessed. In the neext staage, the same co omb source in Fig. F 2(b1) are seent to a SLM filtter an nd two comb lines with a 40GHz 4 frequenccy difference are a seelected with app propriate phase adjustment. Th hen, the two com mb lin nes are amplifieed before sendiing them to a 450m 4 HNLF. Th he co omplete spectra before and afterr the HNLF are shown s in Fig. 3(b b3) an nd Fig. 3(b4), in which w the ampliified pilot tone is converted to the th

middlee of the data sp pectrum. In thee experiment, th he frequency spacingg between the ssignal and pilott tone is manuaally tuned to align w with the frequenccy spacing betw ween the two comb lines. For the praactical implemen ntation in which the transmitterr and receiver are at different locaations, a simplle digital frequ uency offset estimattion and compeensation [26] wo ould be required d. Finally, the data ch hannel is filtered d and sent to a P PD for real-time eye-diagram capturee and BER meassurement. For tthe BER measurrement of an IQ mod dulation formatt such as QPSK K, the reported d BER is the averagee of the separatee measurementss for I and Q com mponents. The narrowband ch haracteristic of the BA is illusttrated in Fig. 4(a). Th he frequency offfset denotes thee frequency drifft away from the opttimal Brillouin frrequency shift in n the SMF of thee experiment, measurred as 10.810G GHz. The BA gaain drops to zerro when the frequen ncy offset is ~4 45MHz. Figure 4 4(b) shows thee relationship betweeen Brillouin pum mp power and d BA gain, wherre a 150mw pump produces a ~4 40dB gain on th the pilot tone w with -34dBm power at the input of th he 500m SMF.

(a)

(b)

45 40 35 30 25 20 15 10 5 0

45

Gain (dB)

Transmitter

Gain (dB)

( (a)

35 25 15 5

0

5

10 15 20 25 30 35 40 45 Frequency offse et (MHz)

2 25

75

125

175

225

Pump Powe er (mW)

Fig. 4. ((a) Bandwidth o of Brillion ampliification; (b) gain n variation of Brillouin n amplification fo or the pilot tone b by changing the p pump power.

Fig. 5. ((a) The detected eye diagram of B BPSK varies with h Δθ between two com mb lines; (b) deteected eye diagram ms for a 10-Gbaud d system with differen nt modulation forrmats.

Systeem performancce is evaluated using 10-Gbau ud BPSK and QPSK cchannels, each w with -30 dB PSR R. Figure 5(a) sh hows that the eye-diaagram opens an nd closes with Δθ between th he two comb lines in n Fig. 3(b3). Fiigure 5(b) pressents the eye-d diagrams for differen nt modulation fo formats. As a baaseline for comp parison, a 10Gbaud BPSK signal w with a residual ccarrier in the center is sent directlyy to the PD. Com mpared to the baaseline system, tthe proposed SHD haas a relatively h higher noise leveel which is attriibuted to the extra sp pontaneous Brilllouin noise duriing pilot tone bo oosting by BA. After a 100km transm mission, the sign nal quality degrades a little furtherr, which mightt be caused b by the residuaal chromatic disperssion of the link. By adjusting Δθ θ, the I and Q co omponents of the QPSSK signal are obttained, as shown n in Fig. 5(b).

The real-time BER B of a 10-Gbau ud channel is meeasured, as show wn in Fig. 6(a). The reeceived power iss measured afterr the attenuator in he detector part of Fig. 3(a). Com mpared to the id deal case, the B2 2B th BP PSK has a similar BER curve. After the 100k km link, a pow wer peenalty of ~0.5dB B is observed at the t FEC limit (BER =3.8e-3). Forr a QP PSK signal, a pow wer penalty of 4dB 4 is observed at the FEC limitt. A BE ER comparison with w a 20-Gbaud d BPSK signal iss shown in Fig. 6(b) 6 to demonstrate th he tunability of the t scheme. Com mpared to the 202 Gb baud BPSK baseeline, a power penalty p of ~0.5d dB is observed at th he FEC limit. Recceived power co ould also be measured before the th BA A stage (after th he 100km link). However, sincee the signal wou uld exxperience degrad dation after two o stages of SHD, the t same received po ower would yielld a higher BER.. The result wou uld be that, exceept for the baseline cu urve, the curves would have shiffted to the right.

BPSK (w. residual carrier) B B BPSK Q QPSK B BPSK (100km)

2

FEC

3 4 5 6 7 8 -11

( 1 (b)

-Log10(BER)

-Log Log10(BER)

(a a) 1

BPSK (w. residual carrier)) BPSK

2

FEC

3 4 5 6 7 8

-9

-7 -5 -3 -1 Received Power (dBm)

1

-11

-9

-7 -5 -3 Receiv ved Power (dBm)

-1

Figg. 6. BER for (a) 10-Gbaud 1 BPSK/Q QPSK, and (b) 20-Gbaud BPSK.

Figg. 7. (a) BER measurements m fo or different levells of PSR and the t co orresponding Brillouin pump pow wer with -8.4dBm m received poweer; (b b) eye diagram of 10-Gbaud Nyquiist BPSK signal.

B2B system peerformance is alsso investigated for f different PSR Rs, wh hile the receiveed power is kep pt at -8.4dBm. Figure F 7(a) show ws th hat as PSR decreaases, the power of the Brillouin pump needs to be b increased to main ntain the same ou utput power of the t amplified pillot o PSR rem mains the same, which w producess a tone. Therefore, output reelatively constan nt BER. The prop posed scheme caan even work wiith aP PSR as low as -4 40dB. When thee PSR further deecreases to -45d dB, th he slave laser faills to lock to the faint f input pilot tone, and the BE ER drramatically increeases. The proposed scheme is also verified wiith Nyyquist pulse shaaping of 0.01 ro olling off factor,, as shown in Fig. F 7((b). This schemee could potentiaally be extended d to WDM systeem wiith low PSR, wh hich requires mu ultiple BA pump ps to be generatted acccordingly [27]. It is noted thatt the pilot tone is i separated fro om th he data channell by a 40GHz gap. g For WDM applications, th his plaacement may affect a the spectrrum efficiency. Moving the pillot tone closer to th he data spectrum m would alleviiate this problem. Ho owever, the resu ultant interferen nce from the datta spectrum cou uld deegrade the quallity of the pilott tone. Thereforre, optimizing the th loccation of the pilo ot tone requires further investiggation. In this paper, BPSK/QPSK B aree employed onlly to demonstraate th he concept of thee proposed SHD D system, which is based on higgh-

speed ooptical nonlineaar wave mixingg. Compared to conventional differen ntial detection [28] and digittal phase track king [29] for BPSK/Q QPSK, the SHD complexity migght be higher. However, SHD is expeected to relax eencoder and decoder design reestrictions in deferen ntial detection sschemes for MP PSK signals [30 0]. Also, SHD could b be important forr high order QAM M with increased d data rate, in which h high-speed digittal processing fo or phase trackin ng might be a challen nge [12]. In addiition, the abilityy of this approacch to support multiplle-channel SHD rrealization could d be of interest iin the future. ng. Center for In ntegrated Accesss Networks (CIAN); Fujitsu Fundin Laboraatories of Americca (FLA); Nation nal Science Foun ndation (NSF)

Refereences 1. P. J. W Winzer, IEEE Comm m. Mag. 48, 26 (20110). 2. E. Ip, A A. Lau, D. Barros, aand J. Kahn, Opt. Exxp. 16, 753 (2008). 3. M. G. Taylor, Photon. Teechnol. Lett. 16, 6774 (2004). 4. L. Kazoovsky, J. Lightw. Teechnol. 2, 182 (19886). 5. S. Risttic, A. Bhardwaj, M M. J. Rodwell, L. A A. Coldren and L. A A. Johansson, J. Lighttw. Technol. 28, 5226 (2010). 6. M. Luu, H. Park, E. Blocch, A. Sivananthan n, A. Bhardwaj, ZZ. Griffith, L. A. Johannsson, M. J. Rodweell, and L. A. Coldreen, Opt. Exp. 20, 97736 (2012). 7. X. Zhoou, Photon. Technool. Lett. 22, 1051 (22010). 8. A. Viteerbi, IEEE Trans. Inffo. Theory 29, 543 (1983). 9. I. Fataadin, D. Ives and S. J. Savory, Photon. Technol. Lett. 22, 631 (2010). 10. T. Pfa fau, S. Hoffmann, aand R. Noé, J. Lightw w. Technol. 27, 989 (2009). 11. Z. V Vujičić, R. S. Luís, J. Mendinueta, A A. Shahpari, N. B. Pavlović, B. J. Puttnnam, Y. Kamio, M M. Nakamura, N. Wada, and A. Teeixeira, Photon. Technol. Lett. 27, 2226 (2015). 12. M. N Nakamura, Y. Kamioo, and T. Miyazaki,, Opt. Exp. 16, 10611 (2008). 13. A. Chhiuchiarelli, M. Ficce, E. Ciaramella, aand A. Seeds, Opt. Exp. 19, 1707 (20111). 14. K. Kaasai, S. Beppu, Y. W Wang, and M. Nakaazawa, Proc. OFC, W W1E.4 (2015). 15. T. Koobayashi, A. Sano, A A. Matsuura, Y. Miyamoto and K. Ish hihara, J. Lightw. Technol. 30, 3805 (2012). 16. T. Huuynh, L. Nguyen, V V. Vujicic and L. Baarry, J. Opt. Comm m. Netw. 6, 152 (20144). 17. M. CChitgarha, A. Moohajerin-Ariaei, Y. Cao, M. Ziyadi, SS. Khaleghi, A. Almaaiman, J. Touch, C C. Langrock, M. FFejer, and A. Willlner, J. Lightw. Technol. 33, 1344 (2015). 18. M. ZZiyadi, A. Mohajerrin Ariaei, M. Chittgarha, Y. Cao, A. Almaiman, Y. Akasaaka, J. Yang, G. Xiee, P. Liao, M. Sekiyaa, J. Touch, M. Tur, C. Langrock, M. Fejerr and A. Willner, Prroc. CLEO, STh1O.66 (2015). 19. Y. Caao, A. Almaiman, M M. Ziyadi, P. Liao, A A. Mohajerin Ariaeei, F. Alishah, C. Bao, A. Fallahpour, B B. Shamee, A. Willner, A. Youichi, T. Ikeuchi, S. Wilkiinson, J. Touch, M.. Tur, and A. Willneer, Proc. OFC, M2A A.6 (2016). 20. N. A.. Olsson and J. van der Ziel, Appl. Phyys. Lett. 48, 1329 (11986). 21. L. Baanchi, M. Presi, R R. Proietti, and E. Ciaramella, Opt. EExp. 18, 12702 (20100). 22. G. Luu, T. Bo, T. Sakamooto, N. Yamamoto, and C. Chan, Opt. Exp. 24, 22573 (20166). 23. X. Zhhou and J. Yu, J. Ligghtw. Technol., 27, 3641 (2009). 24. A. A Albores-Mejia, T. Kaneko, E. Banno, K. Uesaka, H. Shoji, and H. Kuwaatsuka, Proc. ECOC C, Tu.3.1.4 (2014). 25. K. Kaasai, Y. Wang, S. Beeppu, M. Yoshida,, and M. Nakazawaa, Opt. Exp. 23, 291774 (2015). 26. A. Leeven, N. Kaneda, U U. V. Kco, and Y. K.. Chen, Photon. Teechnol. Lett. 19, 366 ((2007). 27. A. Loorences-Riesgo, M.. Mazur, T. Eriksson n, P. Andrekson, an nd M. Karlsson, Opt. Exp. 24, 29714 (20016). r, Proc. OFC, 2002, paper WX6. 28. R. Grriffin and A. Carter, 29. R. Nooé, J. Lightw. Technnol. 23, 802 (2005)). 30. T. M Miyazaki, Photon. Teechnol. Lett. 18, 3888 (2006).

References (Long Format) 1. P. J. Winzer, "Beyond 100G Ethernet," in IEEE Communications Magazine, vol. 48, no. 7, pp. 26-30, 2010. 2. Ezra Ip, Alan Pak Tao Lau, Daniel J. F. Barros, and Joseph M. Kahn, "Coherent detection in optical fiber systems," in Optics Express, vol. 16, no. 2, pp. 753-791, 2008. 3. M. G. Taylor, "Coherent detection method using DSP for demodulation of signal and subsequent equalization of propagation impairments," in Photonics Technology Letters, vol. 16, no. 2, pp. 674-676, 2004. 4. L. Kazovsky, "Balanced phase-locked loops for optical homodyne receivers: Performance analysis, design considerations, and laser linewidth requirements," in Journal of Lightwave Technology, vol. 4, no. 2, pp. 182195, 1986. 5. S. Ristic, A. Bhardwaj, M. J. Rodwell, L. A. Coldren and L. A. Johansson, "An Optical Phase-Locked Loop Photonic Integrated Circuit," in Journal of Lightwave Technology, vol. 28, no. 4, pp. 526-538, 2010. 6. M. Lu, H. Park, E. Bloch, A. Sivananthan, A. Bhardwaj, Z. Griffith, L. Johansson, M. Rodwell, and L. Coldren, "Highly integrated optical heterodyne phase-locked loop with phase/frequency detection," in Optics Express, vol. 20, no. 9, pp. 9736-9741, 2012. 7. X. Zhou, “An improved feed-forward carrier recovery algorithm for coherent receivers with M-QAM modulation format,” in Photonics Technology Letters, IEEE, vol. 22, no. 14, pp. 1051 –1053, 2010. 8. A. Viterbi, “Nonlinear estimation of PSK-modulated carrier phase with application to burst digital transmission,” in Information Theory, IEEE Transactions on, vol. 29, no. 4, pp. 543–551, 1983. 9. I. Fatadin, D. Ives and S. J. Savory, "Laser Linewidth Tolerance for 16-QAM Coherent Optical Systems Using QPSK Partitioning," in Photonics Technology Letters, vol. 22, no. 9, pp. 631-633, 2010. 10. T. Pfau, S. Hoffmann, and R. Noé, "Hardware-Efficient Coherent Digital Receiver Concept with Feedforward Carrier Recovery for M-QAM Constellations," in Journal of Lightwave Technology, vol. 27, no. 8, pp. 989-999, 2009. 11. Z. Vujičić, R. S. Luís, J. Mendinueta, A. Shahpari, N. B. Pavlović, B. J. Puttnam, Y. Kamio, M. Nakamura, N. Wada, and A. Teixeira, "SelfHomodyne Detection-Based Fully Coherent Reflective PON Using RSOA and Simplified DSP," in Photonics Technology Letters, vol. 27, no. 21, pp. 2226-2229, 2015. 12. M. Nakamura, Y. Kamio, and T. Miyazaki, "Linewidth-tolerant 10-Gbit/s 16-QAM transmission using a pilot-carrier based phase-noise cancelling technique," in Optics Express, vol. 16, no. 14, pp. 10611-10616, 2008. 13. A. Chiuchiarelli, M. J. Fice, E. Ciaramella, and A. J. Seeds, "Effective homodyne optical phase locking to PSK signal by means of 8b10b line coding," in Optics Express, vol. 19, no. 3, pp. 1707-1712, 2011. 14. K. Kasai, S. Beppu, Y. Wang, and M. Nakazawa, "256 QAM (Polarizationmultiplexed, 5 Gsymbol/s) Coherent Transmission with an Injectionlocked Homodyne Detection Technique," in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2015), paper W1E.4. 15. T. Kobayashi, A. Sano, A. Matsuura, Y. Miyamoto and K. Ishihara, "Nonlinear Tolerant Spectrally-Efficient Transmission Using PDM 64-QAM Single Carrier FDM With Digital Pilot-Tone," in Journal of Lightwave Technology, vol. 30, no. 24, pp. 3805-3815, 2012. 16. T. N. Huynh, L. Nguyen, V. Vujicic and L. P. Barry, "Pilot-tone-aided transmission of high-order QAM for optical packet switched networks," in IEEE/OSA Journal of Optical Communications and Networking, vol. 6, no. 2, pp. 152-158, 2014. 17. M. R. Chitgarha, A. Mohajerin-Ariaei, Y. Cao, M. Ziyadi, S. Khaleghi, A. Almaiman, J. Touch, C. Langrock, M. Fejer, and A. Willner, "Tunable Homodyne Detection of an Incoming QPSK Data Signal Using Two Fixed Pump Lasers," in Journal of Lightwave Technology, vol. 33, no. 7, pp. 1344-1350, 2015. 18. M. Ziyadi, A. Mohajerin Ariaei, M. R. Chitgarha, Y. Cao, A. Almaiman, Y. Akasaka, J. Y. Yang, G. Xie, P. Liao, M. Sekiya, J. Touch, M. Tur, C. Langrock,

M. Fejer and A. E. Willner, "Demonstration of tunable and automatic frequency/phase locking for multiple-wavelength QPSK and 16-QAM homodyne receivers using a single nonlinear element," in 2015 Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, 2015, pp. 12. 19. Y. Cao, A. Almaiman, M. Ziyadi, P. Liao, A. Mohajerin Ariaei, F. Alishah, C. Bao, A. Fallahpour, B. Shamee, A. Willner, A. Youichi, T. Ikeuchi, S. Wilkinson, J. Touch, M. Tur, and A. Willner, "Demonstration of Automatically Phase-Locked Self-Homodyne Detection with a Low-Power Pilot Tone based on Brillouin Amplification and Optical Frequency Combs," in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2016), paper M2A.6. 20. N. A. Olsson and J. van der Ziel, “Cancellation of fiber loss by semiconductor laser pumped Brillouin amplification at 1.5 μm,” in Applied Physics Letters, vol. 48, pp. 1329-1330, 1986. 21. L. Banchi, M. Presi, R. Proietti, and E. Ciaramella, "System feasibility of using stimulated Brillouin scattering in self coherent detection schemes," in Optics Express, vol. 18, no. 12, pp. 12702-12707, 2010. 22. G. Lu, T. Bo, T. Sakamoto, N. Yamamoto, and C. Chan, "Flexible and scalable wavelength multicast of coherent optical OFDM with tolerance against pump phase-noise using reconfigurable coherent multi-carrier pumping," in Optics Express, vol. 24, no. 20, pp. 22573-22580, 2016. 23. X. Zhou and J. Yu, "Multi-Level, Multi-Dimensional Coding for High-Speed and High-Spectral-Efficiency Optical Transmission," in Journal of Lightwave Technology, vol. 27, no. 16, pp. 3641–3653, 2009. 24. A. Albores-Mejia, T. Kaneko, E. Banno, K. Uesaka, H. Shoji, and H. Kuwatsuka, “Hardware efficient QAM16 all-optical carrier recovery using a single optically-stabilized injection-locked semiconductor laser,” in Proceedings of the Euro. Conf. on Optical Communication (ECOC), Cannes, 2014, Tu.3.1.4. 25. K. Kasai, Y. Wang, S. Beppu, M. Yoshida, and M. Nakazawa, “80 Gbit/s, 256 QAM coherent transmission over 150 km with an injection-locked homodyne receiver,” in Optics Express, vol. 23, no. 22, pp. 29174–29183, 2015. 26. A. Leven, N. Kaneda, U. V. Kco, and Y. K. Chen, “Frequency estimation in intradyne reception,” in Photonics Technology Letters, vol. 19, no. 6, pp. 366–368, 2007. 27. A. Lorences-Riesgo, M. Mazur, T. Eriksson, P. Andrekson, and M. Karlsson, "Self-homodyne 24×32-QAM superchannel receiver enabled by all-optical comb regeneration using brillouin amplification," in Optics Express, vol. 24, no. 26, pp. 29714-29723, 2016. 28. R. Griffin and A. Carter, “Optical differential quadrature phase-shift key (oDQPSK) for high capacity optical transmission,” in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2002), paper WX6. 29. R. Noé, “Phase noise tolerant synchronous QPSK/BPSK baseband type intradyne receiver concept with feedforward carrier recovery,” in Journal of Lightwave Technology, vol. 23, no. 2, pp. 802–808, 2005. 30. T. Miyazaki, "Linewidth-tolerant QPSK homodyne transmission using a polarization-multiplexed pilot carrier," in Photonics Technology Letters, vol. 18, no. 2, pp. 388-390, 2006.