OPTI510R: Photonics. Khanh Kieu College of Optical Sciences, University of Arizona Meinel building R.626

Transcription

1 OPTI510R: Photonics Khanh Kieu College of Optical Sciences, University of Arizona Meinel building R.626

2 Important announcements Homework #1 is due. Homework #2 is assigned, due Feb. 12 TA out of town this week Travel to NSF Feb 26-27, pre-record lecture Mid-term exam on Feb 28 (open books/notes) Final exam on May 2 (tentative)

3 How to measure ultrashort optical pulses? How to measure the duration of fs or ps pulses? Autocorrelation trace Corner cube Delay line 1ps Input pulse train Corner cube 50/50 Beam-splitter Focusing lens BBO crystal Oscilloscope Silicon photodetector

4 How to measure ultrashort optical pulses? Experimental data

5 Interference and Devices Interference Interferometers (Michelson, Mach-Zehnder, Sagnac) Mach-Zehnder Modulators Fabry-Perot Sagnac interferometer (Rotation sensor)

6 Interference Colored patterns produced by soap bubbles Credit: J. Wyant

7 Interference Soap bubble Thin film of oil Tiger beetle Why do we see interference effect only from thin films? Credit: J. Wyant

8 Interference Multilayer thin film (made by Dave Cushing ) as viewed from two different angles Credit: J. Wyant

9 Interference Two plane waves (solutions of the wave equation) interference:,(still a solution of the wave equation) We detect the intensity instead of the amplitude:

10 Interference

11 Interference Since the oscillation is very fast, the time average becomes: Interference pattern generated by two monochromatic plane waves

12 Interference The fringes will move if 1 2 Heterodyne detection The interference fringes contain information about the relative phase of the interfering waves. We can use them to do measurements with very high precision. 2 phase shift corresponds to a displacement of

13 Michelson Interferometer Can be used to measure the coherent length of the light source. White light source Michelson interferometers

14 LIGO Laser Interferometer Gravitational-Wave Observatory

15 LIGO

16 LIGO

17 LIGO

18 LIGO

19 LIGO

20 Phase shifting interferometry Source: Wikipedia

21 Phase shifting interferometry Brake pad composed of sintered metal, ceramics, and carbon fibers, 640μm x 480μm FOV. Micro-gear WYKO NT9100 Laser textured steel, 0.9mm x 1.2mm FOV

22 Michelson Interferometer Fourier-transform spectrometer A high-resolution spectrum of CO 2 in the near-ir was obtained using a Fourier-transform spectrometer (laserfocusworld.org)

23 Fourier-transform spectrometer d/2 Monochromatic light interferogram

24 Fourier-transform spectrometer Schematic representation of an interferogram produced by bi-chromatic light

25 Fourier-transform spectrometer Schematic illustration of the formation of a broad-spectrum interferogram. Broad spectrum gives narrow response.

26 Fourier-transform spectrometer Mathematically speaking, the sum of the monochromatic interferograms simply turns into an integral:,this is the cosine Fourier transform The inverse cosine Fourier transform is simply expressed by:

27 Fourier-transform spectrometer Measurement of the infra-red absorption spectrum of a sample

28 Optical coherent tomography Schematic diagram of a time-domain OCT system Non-invasive Non-contact No radiation Painless Fast Reliable and sensitive

29 Optical coherent tomography No moving parts! Schematic diagram of a spectral-domain OCT system

30 Optical coherent tomography Axial resolution: Fujitomo s lab

31 Mach-Zehnder Interferometer Schematic diagram of a Mach-Zehnder interferometer Source: Wikipedia

32 Mach-Zehnder Modulator Schematic diagram of a MZ intensity modulator. The operating speed can be very high > 40GHz. Current research is aimed at increasing the operating speed, reducing the loss, the driving voltage, and the cost.

33 Mach-Zehnder Modulator

34 Mach-Zehnder Modulator State-of-the-art intensity modulator

35 Fabry-Perot Resonator

36 Fabry-Perot Resonator

37 Fabry-Perot Resonator

38 Fabry-Perot Resonator (α = 0, normal incident)

39 Fabry-Perot Resonator Spectrum analyzer Laser cavity Tunable filter Dispersion compensation Field enhancement

40 Fabry-Perot Resonator Reflection Microsphere Scattering Reflection HR mirrors Transmission Input Taper Transmission Microsphere resonator Fabry-Perot resonator

41 Sagnac Interferometer The sagnac sensor has the best sensitivity compared to other type of sensors.

42 Fiber Optics Gyroscope

43 Laser Gyroscope We can easily measure f beat with <1Hz precision. What would be the smallest rotation rate that we can measure using a ring Resonator with 1m radius?

44 The smallest Laser Gyroscope? Basic elements: 100 mm Microring laser Fiber taper Near field tip

45 There are many other interferometers Michelson Mach-Zehnder Sagnac Fabry-Perot Fizeau Twyman-Green Newton Nomarski

46 Question for thoughts Can you come up with a new type of interferometer? Can we explain interference by a different mechanism other than waves? New modulator design for optical communication? What is the sharpest resonance that we can make? Can you build a gyroscope that can measure the rotation of the earth and would still cost <$100? Can you build a company and then sell it for $100M?