Introduction to Optoelectronics Optical communication 3 Optical components

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Introduction to Optoelectronics Optical communication (3) Optical components Prof. Katsuaki Sato

Introduction to Optoelectronics Optical communication (3) Optical components Prof. Katsuaki Sato

Optical components • Previous lectures • (1) Optical fibers – Transmission of light by

Optical components • Previous lectures • (1) Optical fibers – Transmission of light by total reflection • (2) Laser diodes – The pn-junction is forward biased – Above threshold current lasing occurs – High density of carriers and photons are confined in thin active layer (DH structure)

Component (3) Optical detectors • Using photodiode • Very fast response required • pin

Component (3) Optical detectors • Using photodiode • Very fast response required • pin photodiode or Schottky junction photodiode are used • As material for photodiode In. Ga. As semiconductors are used

Photodiode Optical signal Photocurrent Incident photon Reverse bias Electric signal Load resistance Bias voltage

Photodiode Optical signal Photocurrent Incident photon Reverse bias Electric signal Load resistance Bias voltage p Deplet ion layer Structure and band diagram of photo-diode 佐藤勝昭編著「応用物性」p. 152 n

Photodetection • Pin-PD • Schottky PD • Response is determined by capacitance of depletion

Photodetection • Pin-PD • Schottky PD • Response is determined by capacitance of depletion layer where photocarrier flows • Thinning of depletion layer and reduction of junction area is necessary pin photodiode Schottky diode Andrew Davidson, Focused Research Inc. and Kathy Li Dessau, New Focus Inc.

Fundamentals of photodiode • Illuminate the pn junction • Electrons and holes are generated

Fundamentals of photodiode • Illuminate the pn junction • Electrons and holes are generated by an excitation across the gap • Generated electrons and holes are separated and drift to electrodes by diffusion potential p-type - + + n-type Depletion layer

Component 4 Fiber amplifier • Light signal traveling in optical fiber for 100 km

Component 4 Fiber amplifier • Light signal traveling in optical fiber for 100 km suffers 20 d. B (1/100)attenuation. Therefore the light intensity should be recovered. Optical fiber amplifier is used for this purpose. • Optical amplifier consists of an erbium doped fiber (EDF) and a pumping laser. By introducing the strong pumping light to EDF the signal light can be amplified by stimulated emission from Er ion. Optical isolator Asahi Glass Company HPhttp: //www. agc. co. jp/news/2 000/0620. htmlより EDF Light input Composer Pumping laser Band pass filter

Amplification by Er ion • EDF absorbs light with wavelength of 980 nm or

Amplification by Er ion • EDF absorbs light with wavelength of 980 nm or 1480 nm and emits infrared light with wavelength of 1530 nm. Optical amplification is possible utilizing stimulated emission of the 1530 -nm luminescence. • Inputting pumping laser light into EDF, Er ion become excited by absorbing the laser light and the signal light stimulate to make a transition to the ground level emitting the light with wavelength around 1530 nm, which is close to the signal light wavelength. Thus the incident light is amplified utilizing the emitted light. • Luminescent intensity and spectrum width differ from sample to sample according to the concentration of doped Er-ion. The broader the bandwidth of the emission band the broader the bandwidth of communication. From the Web-site of Asahi Glass Inc. HPhttp: //www. agc. co. jp/news/2000/0620. html

Component 5 Optical isolator • Optical isolator is an optical component that makes the

Component 5 Optical isolator • Optical isolator is an optical component that makes the light direction oneway. • Operation of laser diodes (LD) and optical amplifiers (EDFA) become unstable and generate noise when returned light enters. • Optical isolator utilize Faraday effect to cut off the returned beam and stabilize the operation of lasers and amplifiers. Shinkosha http: //www. shinkosha. com /products/optical/

Polarization-dependent isolator Magnetic field polarizer Incident light analyzer Faraday rotator Returned beam Forward direction

Polarization-dependent isolator Magnetic field polarizer Incident light analyzer Faraday rotator Returned beam Forward direction Reversed direction

Polarization-independent isolator Faraday rotator F ½ waveplate C Birefringent plate B 2 Birefringent plate

Polarization-independent isolator Faraday rotator F ½ waveplate C Birefringent plate B 2 Birefringent plate B 1 Fiber 2 Forward direction B 1 F C B 2 Fiber 1 Fiber 2 Reverse direction

Component 6 WDM=wavelength division multiplexing • WDM technique can increase communication capacity by transmitting

Component 6 WDM=wavelength division multiplexing • WDM technique can increase communication capacity by transmitting many different light signal of different wavelength simultaneously. • Fiber cables can utilize wavelength region from 1450 to 1650 nm since the transmission loss is very low (less than 0. 3 d. B/km) in this region.

Optical add-drop • Optical add-drop can separately drop desired wavelength from multiplexed-signal network or

Optical add-drop • Optical add-drop can separately drop desired wavelength from multiplexed-signal network or can add a particular wavelength to the network Grating optical fiber Optical circulator

Optoelectronic integrated circuits (OEIC) • Integration of optical and electronic semiconductor devices • Two

Optoelectronic integrated circuits (OEIC) • Integration of optical and electronic semiconductor devices • Two types of OEIC exist – One is integration of light emitting devices (example: LD) and driving FET circuits – The other is integration of optical detection device like PD and electronic circuits for amplification and signal processing • Compound semiconductors such as Ga. As-based and In. P-based alloy semiconductors are used. http: //www 2. nsknet. or. jp/~azuma/o/o 0028. htm

Magneto-optical circulator Prism polarizer A Faraday rotator Reflection prism Port 1 Port 3 Half

Magneto-optical circulator Prism polarizer A Faraday rotator Reflection prism Port 1 Port 3 Half wave plate Port 2 Port 4 Prism polarizer B