Tunable Lasers and Related Devices with Liquid Crystal Enabled Functionalities for DWDM Optical Communication

Transcription

1 Tunable Lasers and Related Devices with Liquid Crystal Enabled Functionalities for DWDM Optical Communication Ci-Ling Pan Department of Electrophysics, Institute of Electro-Optical Engineering National Chiao Tung University, 1001 Ta Hsueh Road Hsinchu, Taiwan 30010, ROC

2 Motivation and Objectives Tunable Lasers for DWDM Optical Communication that are 1. Compact 2. Allow Channel switching 3. Wavelength according to the ITU Grid 4. Power equalization 5. Multiple Wavelengths Other Generic Devices w/lc-enabled functionality: 1. Demux 2. Tunable Filter

3 Part (I): Tunable Lasers for DWDM Optical Communication

4 Basic Design Concept Patented Folded Telescopic Grating-loaded External Cavity (US 5,524,012 and pending) Use the LCPM (Liquid Crystal Pixel Mirror), a reflection-type liquid crystal spatial light modulator, for digital tuning and selection of the laser wavelength

5 Conventional Grating-tuned External Cavity Laser Diode Littrow Grating LD Obj. Lens Grazing-incidence Grating Obj. Lens LD Obj. Lens HR AR o/p AR o/p Mirror Littrow -type ECL Littman-type ECL

6 Folded Grating-Lens-Stripe-Mirror External Cavity Laser Diode Grazing-incidence Grating Objective Lens Laser Diode Intra-cavity dispersion compensation Si Substrate Au Lens Multi-λ co-axial output Spatial Mode Control λ 1 λ 2 V-Shape Stripe Mirror Single Stripe Mirror

7 λ - Tuning Mechanism Grating incident light θ i Lens mλ = a(sinθ + sinθ ) Where m : diffraction orders a : groove spacing θi : incident angle θr : diffractive angle f : focus length i r ( ) λ 2 θ r ( ) θ r λ 1 diffracted light λ 2 λ 1 x For m=1, dλ = a cosθr dθ r x = f tanθ λ = a cosθr x r 1 f f θ r

8 Multi-λ -ECL w/lcpm Grating Objective Lens Laser Diode Lens incident light λ 1 λ 2 LCPM

9 Liquid Crystal Pixel Mirror Patterned ITO W/SA NLC ITO W/SA Incident laser beam Au-coated silicon substrate (mirror) Polarizer Glass

10 Fabrication of the LCPM ITO-coated glass Photoresist Patterning and Developing Etching SA polarizer Packaging ITO Glass NLC Patterned ITO Glass Au-coated Si External Circuit incident light LC Alignment layer (SA) LCPM

11 Liquid Crystal Pixel Mirror or Liquid Crystal Spatial Light Modulator The LC-SLM pixel pitch/width = 83.3/79.3 µm or 125/100 µm Pixel number=96;the thickness~ 8 µm

12 Transmittance of the LCPM /w.o. Au Mirror 80 Transmittance (%) voltage up voltage down V rms (Volt)

13 Digitally tuning the ECL (1550nm) in 100 GHz step (ITU grid) 100 GHz Output power(dbm) Wavelength(nm) SMSR (db) wavelength (nm) Tuning range ~ 60 nm, SMSR > 30 db

14 Max. Tuning Range (I = 1.54 I th ) nm Relative optical power (dbm) Wavelength(nm) Relative Amplitude nm Wavelength(nm) Relative optical power(dbm) Scan Time Linewidth < 20 MHz (Instrument-limited) 2

15 Multi-wavelength Operation -30 Optical power(dbm) nm 0.74nm Optical power(dbm) nm 1.48nm Optical power(dbm) Wavelength(nm) 1.50nm 1.98nm Optical power(dbm) nm Wavelength(nm) 1.28nm Wavelength(nm) Wavelength(nm)

16 Multi-wavelengths Operation Optical power(dbm) nm 0.76nm 2.00nm Wavelength(nm) Optical power(dbm) nm 0.76nm Wavelength(nm) 3.98nm

17 Multi-wavelength Mode-locked MOPA w/intra-cavity dispersion compensation Optical power (dbm) λ Master Laser: Up to 20 λ demonstrated Master Laser Optical Power (dbm) wavelength (nm) MOPA (w/injection): P av > 150 mw, τ = 25 ps MOPA w.o./injection MOPA: P avg > 150 mw τ = 25 ps -75 The LCPM wavelength (nm)

18 MODE-HOP-FREE FINE TUNING OF AN EXTERNAL-CAVITY DIODE LASER WITH AN INTRACAVITY LIQUID CRYSTAL CELL HR -30 Laser Diode AR Obj. Lens Mirror NLC cell Grating Output Transmitted Intensity (a.u.) Vrms (V) Mode-hop-free tuning range : 19.2 GHz -40 Power (dbm) Sat. Abs. Intensity (a.u.) Rb D 2 -line nm 85B 87B Wavelength (nm) I LD = λ L β L 2 2 ; β= λ/ I LD Scan Voltage (mv) Application:High-Res. Spectroscopy

19 Possible MOEM Implementation of the Laser LC element for fine tuning Berger et al, OFC2001, Paper TuJ2 (Iolon)

20 Tunable Laser with LC-enabled fine-tuning function Grating o/p LCPM NLC cell Objective Lens Lens λ 2 λ 1 Laser Diode AR-coated LD (Opto Speed RSOA1550CRI- R077) diffraction grating (Agilent 1100 lines/mm) o 80 Incident angle = 80 lens ( f = 25.7cm) Pixel width = 100µm ECDL cavity 100µm length=65 cm Thickness of NLC (E7) cell=52.3 µm

21 i Mode-hop-free tuning of a tunable ECDL with an intracavity LC tuning element 140 Voltage of LC = 1.00 Vrms 8 Relative Frequency Shift(GHz) Y Axis T tle Y Axis Title X Axis Title 0.63 GHz Voltage of LC =1.36 Vrms X Axis Title Voltage of LC =1.86 Vrms 1.27 GHz 8 Driving Voltage(mV) Y Axis Title NLC voltage: (1.00 Vrms to 4.56 Vrms). Theoretical predictions = GHz Experimental tuning range ~ 1.89 GHz X Axis Title 1.89 GHz Voltage of LC =4.56 Vrms Y Axis Title X Axis Title

22 Mode-hop-free tuning using the LCPM s Bias voltage=4.70 Vrms Y Axis Title Relative Frequency Shift (GHz) Driving Voltage(Vrms) LCPM voltage: 4.70 Vrms to 6.00 Vrms Tuning range ~ 1.13 GHz Y Axi Title Y Axis Title Y Axis Title X Axis Title 0.23 GHz Bias voltage=4.10 Vrms X Axis Title 0.51 GHz Bias voltage=5.40 Vrms X Axis Title 0.86 GHz Bias voltage=5.70 Vrms X Axis Title 1.13 GHz Bias voltage=6.00 Vrms Y Axis Title X Axis Title

23 Summary (I) A novel digitally tunable laser diode (λ = 1550 nm) using liquid crystal technology is demonstrated. Laser wavelength can be locked to ITU grid. Multi-wavelength operation demonstrated Mode-hop-free fine tuning demonstrated. Wavelength switching response is ~ 100 ms

24 Part (II): Functional Liquid-Crystal-Based Devices for DWDM Applications

25 Vmux: Variable Optical Demultiplexer

26 Output Power (dbm) Tunable Demultiplexer : Channels Fixed to ITU grid (100 GHz) P-polarized S-polarized channel Wavelength (nm) ITU grid (nm) Experi ment (nm) ITU- Experim ent

27 Tunable Vmux : Power Equalization -55 Blue - pixel on Green- equalized Red - pixel off Output Power (dbm) Power equalized to < 0.5 db Wavelength (nm)

28 Tunable Vmux : Output characteristics oudtput Power(dBm) Cross talk: - 30 db Extinction ratio: 13.5 db 1dB/3dB Passbands: 12.5/22.4 GHz wavelength (nm)

29 Dynamic Characteristics: Channel Switching Results λ= nm λ= nm Rise /Fall time=~12/88 ms

30 Summary (II) A 16-channel liquid-crystal-based tunable optical demultiplexer with channel spacing of 100 GHz is demonstrated. The channel crosstalk is less than 30 db and the average 1dB and 3dB passbands of 12.5 and 22.5 GHz, respectively. Insertion Loss ~ 12 db. The average extinction ratio is 13.5 db (higher if laser source is used). Power equalized to within 0.5 db. Different channels can be switched with a rise and fall time of tens of millisecond.

31 Liquid-Crystal-Based Tunable Optical Filter/Equalizer θ i =46 0 d=1100 lines/mm f 1 =51.5 mm L2: 10X objective lens

32 Tunable Filter w/lc-slm : Channels Fixed to ITU grid (100 GHz) -30 power (dbm) Light source : TLS (Tunable laser source) LC ITU grid wavelength (nm) TLS TLS power (dbm) power (dbm) th channel extinction ratio 24.7dB pixel on pixel off wavelength (nm) Extinction ratio=24.7 db Channel number = 15 Channel spacing = 0.79 nm Average extinction ratio =18.2 db

33 Tunable Filter/Equalizer nm P peak =17.9 db P peak = 0.3 db nm -50 power (dbm) wavelength (nm)

34 Summary (III) A new type of liquid-crystal-based tunable filter/demultiplexer has been developed. As a first demonstration, two channels (on 100 GHz ITU Grid) are selected with a peak-power difference of 17.9 db are equalized to within 0.3 db.

35 Acknowledgements Support by NSC, MOE, Lee-MTI Center/NCTU, and Radiatech Corp. Co-workers:.Prof. Ru-Pin Chao, Mingjay Huang, Yu-Ping Lan, Chia-Rong Sheu, and Iefan Lai