Optical Fiber Amplifier with Multi-slot Configuration for Analogue Video Distribution Kyosuke Takemoto, Noriaki Shimada, Takuya Aizawa, Tetsuya Sakai and Hideyuki Hosoya High-quality and/or multi-channel analogue video distribution services have been widely deployed recently. This trend is increasing the necessity of optical fiber amplifiers. We have developed an optical fiber amplifier - Fujikura optical amplifier model (FOAM) - for analogue video distribution services having a multi-slot chassis for up to 9 EDFA (Erbium Doped Fiber Amplifier) units, dual power-source units, multiple fan units, and an SNMP (Simple Network Management Protocol) control unit. Hot swapping is possible with all the units for easy maintenance. This amplifier was carefully designed to have low distortion, low noise figure, and wide operating wavelength. The outer dimension of 19 in. width with 3 U height was chosen to meet the EIA (Electronic Industries Alliance) standards. To our knowledge as of now, this chassis is the smallest in size with the highest number of EDFA units. In a relatively small system application or so, the one EDFA unit with just 1U height is adequate. We have also developed a unit for such an application. In this report, we describe the characteristics of FOAM Series in detail. 1. Introduction Recently, over 100 channels of conventional terrestrial broadcasting, satellite broadcasting, and movie programs are in commercial service with the overwhelming prevalence of broadband networks. Demands for high-quality analogue transmission using optical fiber are increasing in order to achieve such services. Figure 1 illustrates the video distribution system using optical fibers. In this system, branching optical fibers in different locations are essential in order to provide video signals to many subscribers at a low cost. Optical fiber amplifiers are required to compensate Central Office Satellite broadcasting Terrestrial broadcasting for the optical power loss due to the optical splitters used for branching 1). In this paper, we report the development of the optical fiber amplifier which can be loaded up to 9 EDFA units 2), together with the optical fiber amplifier, for small-scale applications. 2. Product Outline Figure 2 shows the multi-slot type optical fiber amplifier 'FOAM-U12', which consists of the 19-in. rack mountable chassis with EIA: 3U height (3Uchassis) and various functional units that can be mounted into the chassis. The chassis can be loaded with up to 2 power-source units, 3 fan units, an SNMP unit, and 9 EDFA units, all of which are hot swappable. Multiple power-source and fan units were selected for redundancy. VTR program 9 EDFA Units HEADEND Optical Optical Amplifier Splitter Fig. 1. Block Diagram of Video Distribution System Using Optical Amplifier. 6 2 Power-Source Units SNMP Unit 3 Fan Units Fig. 2. Appearance of Multi-Slot Type Optical Amplifier System FOAM-U12. We also developed a 19-in. rack mountable chassis with EIA: 1U height (1U-chassis) for smaller systems. Figure 3 illustrates the 1U-chassis optical amplifier, which can be loaded up to 2 power-source units and 3 fan units, an SNMP unit, and an EDFA unit. The EDFA unit and the SNMP unit are exactly the same as the ones used in 3U-chassis. All the units are hot swappable as in the case of 3U-chassis. We have also developed an optical coupler unit and an optical switch unit, which will hereafter be described in detail. The former unit is used to branch the output signal from the amplifier and the latter unit is used to switch optical path for the amplifier from main line to maintenance line when there is a problem with the main line. Moreover, we developed a switch-coupler unit 3 Fan Units(rear side) 2 Power-Source Units EDFA Unit SNMP Unit Fig. 3. Appearance of 1U Type Optical Amplifier System FOAM-M01. Optical-Switch Unit Optical Switch-Coupler Unit EDFA Coupler Unit Optical Coupler Units (1x4, 1x8, 1x16) Fig. 4. Appearance of Application of FOAM-U12's Option Units. and an EDFA-coupler unit by combining the two units mentioned above. These option units have compatibility with the EDFA unit, and can be mounted in 3U-chassis as shown in Fig. 4, which enables users to save space. 3. Features of the Units 3.1 EDFA Unit (Model: FOAM-U12AU/AC) Table 1 shows specifications of EDFA units, which have high output power, wide operating wavelength, low noise, and low distortion. This EDFA unit has eye-safe function. (1) High output power New EDFA units of 22 dBm output have been developed in addition to the previously developed 17/19 dBm output EDFA units in order to enable large-number distribution or long transmission. 22dBm output can increase the number of branches double compared with 19dBm output. We also developed EDFA coupler units by combining an EDFA and an optical coupler (1 × 2, 1 × 4 and 1 × 8) as shown in Fig. 4. (2) Wideband, low noise, low distortion Figure 5 shows noise figure (NF) characteristics of the EDFA unit, which promises high-quality transmission due to low NF of below 5.5 dB with respect to the wavelength range of 1,530 - 1,560 nm. This NF value is low enough for practical application and the wavelength range almost covers the operational range of EDFA. Figures 6 and 7 show the measurement set-up and the measured carrier-to-noise ratio (CNR) respectively, when EDFA units are multi-cascaded. In Fig. 7, only minor CNR degradations are observed even Table 1. Specifications of EDFA Unit Item EDFA Unit EDFA Coupler Unit FOAM-U12AC Type Name FOAM-U12AU2 Operating temperature 0 - 40 °C 0 - 40 °C Storage temperature −20 - 70 °C −20 - 70 °C Operating/storage humidity Non-condensing,10 - 90% Non-condensing,10 - 90% Wavelength range of input signal 1,530 - 1,560 nm 1,530 - 1,560nm Input signal power (Pin) −3 - +10 dBm −3 - +10 dBm Output signal power (Pout) 17dBm / 19dBm / 22dBm 17dBm / 19dBm / 22dBm (before branched signal) Noise figure (NF) (@Pin=0 dBm, λ=1,550 nm) 5.0 dB 5.0 dB Output stability 0.5 dB 0.5 dB Polarization dependence 0.3 dB 0.3 dB Optical connector SC/APC (angled PC) SC/APC (angled PC) Adaptable fiber SM10/125, 1. 31µm zero dispersion SM10/125, 1. 31µm zero dispersion Occupied slot 1 2 Number of output ports 1 2, 4, 8 Fujikura Technical Review, 2005 7 after multi-stage cascading and still maintaining 6dB margin against 42 dB CNR, which is believed to be enough in standard video systems. In the case of SPC connector disconnection, however, the reflection loss decreases because Fresnel reflection appears. We can detect these two kinds of fiber disconnection by applying two thresholds onto the measured values of reflection losses. (3) Eye-safe system We employed 'eye-safe system' as shown in Fig. 8. Output power is automatically shut down to prevent an operator from being exposed to high-power output light when output connector is pulled off accidentally without turning off the light, which may hurt his eye. This works when not only the output connector of EDFA units but also that of transmission fiber is disconnected. We assume the case that Angled Physical Contact (APC) connectors are used at the output of EDFA and Super Physical Contact (SPC) connectors at the output of transmission fiber. 52 CNR (dB) 50 48 46 44 42 1 0 Operational mechanisms are as follows. In the case of APC connector disconnection, reflection loss increases because Rayleigh back scattering from the transmission fiber vanishes. 2 3 4 5 6 7 Stage of Cascade EDFA Units Fig. 7. CNR Characteristic of Video Distribution System of Multi Stage Cascade EDFA Units. 6.5 Input power (Pin) = 0dBm Output power (Pout) = +17dBm NF (dB) 6.0 EDFA Unit 5.5 Increase reflection loss Decrease reflection loss Optical fiber for transmission 5.0 4.5 1,520 1,530 1,540 1,550 1,560 SPC-connector 1,570 Wavelength λ (nm) APC-connector Fig. 5. Noise Figure Characteristic of FOAM-U12AU. Fig. 8. Available Points of Eye-Safe Function. Antenna H/A P/G V/G P/G H/A V/G E/O 32SPL ATT V-ONU E/O Spectrum analyzer Modulator Degree of modulation 4.2% SMF 25km 1 25km 2 ATT Condition of EDFA Unit : 1,550nm : +2dBm Pin Pout : +17dBm 25km 3 ATT : Pilot Generator : Head-End Amplifier : Video Pattern Generator : Optical Converter : 1x32 Splitter : Optical Attenuator : Video Optical Network Unit 4 ATT 5 ATT 32SPL V-ONU Input signal power to V-ONU is -3dBm 6 ATT 7 ATT Demodulator Spectrum Analyzer Fig. 6. Block Diagram of CNR Measurement Using Multi Stage Cascade EDFA Units. 8 ATT SN Meter Figure 9 shows the reflection loss versus transmission fiber length connected to the EDFA output. The reflection loss ranges between threshold 1 and 2 when the connector is properly connected. If SPCconnector is disconnected at the output of the transmission fiber, reflection loss decreases below the threshold 1. On the other hand, if the APC-connector at the EDFA output is disconnected, the reflection loss increases and becomes greater than the threshold 2. We can adjust each threshold value according to the system requirement. 3.2 Chassis and Power Source Table 2 shows the dimension and electrical specifications of the chassis for FOAM series. Slots for the EDFA unit and that for the SNMP unit are hot swappable; it is possible to exchange the EDFA units and the SNMP unit while other units are running. Two types of chassis mentioned below have a redundancy of power-source units and fan units, which realizes highly reliable operation. We will explain the two types of chassis in detail hereafter. Reflection loss (dB) 60 APC-connector disconnected 50 Thresholds 2 40 Proper connection Thresholds 1 30 20 SPC-connector disconnected 10 0 2 4 6 8 10 12 Distance of transmission (km) (2) 1U type chassis (FOAM-M01PF) Temperature of LD case TLD (°C) (1) Multi slot chassis (FOAM-U12PF) This chassis has a height of EIA: 3U, which is the smallest to our knowledge as the chassis which can be loaded with up to 9 EDFA units. We set cooling fans on the rear side of the chassis and many blow- holes on the front side of it. This structure is available to suppress the chassis height, because it is not necessary for cooling structure such as fan and blowholes to be put on/under the chassis. Moreover, thermal dissipation of pumping laser diodes (LDs) must be considered carefully because performance and reliability of LDs strongly depends on their operating case temperature. Therefore, the design of chassis structure is very important to obtain both compactness and high reliability. We optimized the layout of components inside the chassis through simulation. Figure 10 shows the simulated temperatures of LDs and measured temperatures at an ambient temperature of 40°C. Horizontal axis indicates the slot number of EDFA counted from left; solid line and broken line indicate simulated result of 19 dBm output EDFA and that of 22 dBm output EDFA, respectively. EDFAs of 17 dBm and 19 dBm output have one LD whose operating temperature should be below 75°C, while EDFA of 22 dBm output has a 1.48 µm LD additionally whose operating temperature should be below 70°C. From this figure, we can see that LD temperature is well below 70°C, and that measured results coincide well with the simulated result. 14 65 60 +22dBm 1.48 µm LD 55 +22dBm 0.98 µm LD 50 45 40 +19dBm 0.98 µm LD At 40 °C atmosphere with 9 EDFA Units install 1 2 3 4 5 6 7 8 Slot number of 3U rack mount chassis 9 Fig. 10. Comparison of a Calculation Value and an Actual Measurement of LD-case Temperature. Fig. 9. Relation between Reflection Loss and Distance of Transmission at Connector Pulled Out. Table 2. Specifications of Optical Amplifier Chassis Item EIA : 3U multi slot chassis EIA : 1U single-slot chassis Model FOAM-U12 FOAM-M01 Voltage AC : 100V ±10%, 50/60Hz DC : 48V ±10% AC : 100V ±10%, 50/60Hz DC : 48V ±10% Operating temperature 0 – 40 °C 0 – 40 °C Storage temperature −20 – 70 °C −20 – 70 °C Operating/Storage humidity Non-condensing, 10 - 90% Non-condensing, 10 - 90% Dimension (W × D × H) 482.0 × 399 × 132.4mm3 482.0 × 400 × 43.6 mm3 Power consumption 290 W(with EDFA-Unit full installed) 100 W(with EDFA-Unit full installed) Number of EDFA slot 9 1 Fujikura Technical Review, 2005 9 Table 3. Specifications of Optical Coupler Unit Number of split 2 4 8 16 Model FOAM-U12CP-1 × 2 FOAM-U12CP-1×4 FOAM-U12CP-1 × 8 FOAM-U12CP-1 × 16 Wavelength(nm) 1,290 - 1,330 nm, 1,530 - 1,560 nm Insertion loss(dB) 4.7 8.4 12.0 15.5 Loss uniformity(dB) 1.4 2.0 1.5 2.0 Return loss (dB) 50 50 50 Slot occupation Fiber 50 1 2 SM10/125 Connector SC/APC Operating condition 0 - 40 °C, 10 - 90%RH EDFA Unit 1 2 EDFA Unit 1x8 Optical Coupler Unit 3 4 5 6 7 Fig. 12. Application of Optical Coupler Unit for 1 × 8 Splitter. We developed 1U-chassis, which can be loaded with only 1 unit of EDFA for space saving in the system that requires only one amplifier. It is of 19 in. rack size with 1U height, and slots have compatibility with 3U-chassis as with the EDFA unit and the SNMP unit. This unit selects one line out of two lines, a main line and a maintenance line, according to their status. When there is optical power down in a main line, this unit detects it and automatically selects a maintenance line for system redundancy in automaticswitching mode. 3.3 SNMP Unit This unit maintains state of the switch even if the power supply is shut down because it uses self-holding device. We also developed a switch-coupler unit by combining the optical switch and the optical coupler, which is suitable to construct redundant systems. Figures 13 and 14 show the redundant configuration with the optical switch unit. Figure 13 shows a block diagram of a distribution network system for repeater, in which the signal reaches the optical switch through redundant path and is divided into four ports of 19dBm output. Figure 14 is a block diagram of the distribution network near the subscribers in which the signal is divided into eight ports for relatively close subscribers and 16 ports for relatively distant subscribers. An SNMP unit enables monitoring and controlling of the various units through RS-232C port and Ethernet port. Figure 11 shows the display image of manager software that supports Graphical User Interface (GUI ) . 3.4 Optical Coupler Unit (FOAM-U12CP) An optical coupler unit divides the optical video signal into 2, 4, 8 and 16 ports, whose specification is summarized in Table 3. When the number of branches is rather high like 816, branched signal will be guided to another amplifier for amplification as shown in Fig. 12. On the other hand, when the number of branches is rather small, branched signal will be guided directly to subscribers or to another amplifier after being transmitted over a certain distance. 3.5 Optical Switch Unit (FOAM-U12SW) Table 4 shows specifications of optical switch units. 10 8 Fig. 11. Display Image of EDFA Manager Software -FOAMAN-. 4. Conclusion We have developed an optical fiber amplifier for video distribution. This amplifier has two types of chassis, which can Table 4. Specifications of Optical Switch Unit Item Optical Switch Unit Optical Switch-coupler Unit Model FOAM-U12SW-1 × 2A FOAM-U12SW-1 × 2 FOAM-U12SC-1 × 2A FOAM-U12SC-1 × 2 Optical switch I/O port 1×2 1×2 1×2 1×2 Optical coupler I/O port - - 1×2 1×2 Wavelength(nm) 1,290 - 1,320, 1,530 - 1,560 Optical switch insertion loss(dB) 2.0 1.2 2.0 1.2 Return loss(dB) 50 50 50 50 Cross talk(dB) −50 −50 −50 −50 Switching time(msec) 10 10 10 10 Optical switch type Self holding Self holding Self holding Self holding Auto switching Available - Available - Optical coupler insertion loss(dB) - - 4.7 4.7 Optical coupler insertion loss uniformity(dB) - - 1.4 1.4 Fiber SM 10/125 Connector SC/APC Operating condition 0 - 40 °C, 10 - 90% RH Switch-coupler Unit Main line EDFA Unit (+17dBm) EDFA-coupler Unit 1x4 Optical +22dBm Coupler Optical Switch EDFA-coupler Unit 1x2 Maintenance Optical line Coupler 1x2 EDFA Optical (+22dBm) Coupler Main line +17dBm EDFA Unit Transmit to subscribers 1x2 EDFA Optical (+22dBm) Coupler Optical Switch Unit Maintenance line 1x4 Optical Coupler Unit 1x4 Optical +22dBm Coupler Long distance for subscribers 1x8 Optical +22dBm Coupler Fig. 13. Application of Optical Switch Unit 1 : for Repeater. meet system requirement. We have described the feature and function of the EDFA unit, the optical coupler unit, the optical switch unit, and the SNMP unit, which can be installed and shared by two types of chassis. Using these units for loss compensation, distribution, and assurance of redundancy, video distribution systems can be constructed. We believe these optical fiber amplifiers fulfill the needs in the field. References 1) H. Ishio, et al.: Optical amplifiers and their applications, pp. 1x8 Optical +22dBm Coupler Short distance for subscribers Fig. 14. Application of Optical Switch Unit 2: Distributor for Subscribers. 2) K. Takemoto, et al.: Development of high-density-mounting erbium doped fiber amplifier for fiber to the home, Proc. of the 2004 IEICE General Conf., C-3-118, p. 292, 2004 (in Japanese). 203-206, Ohm-sya, 1992 (in Japanese). Fujikura Technical Review, 2005 11