Semiconductor Optical Amplifier

Peak Wavelength(nm) From:– All –880915970101510401050128513001310149015251550 To:– All –880915970101510401050128513001310149015251550	Category	Typical Gain(dB) From:– All –1013141516181920222526282930To – All –1013141516181920222526282930	Typcial Psat(dBm) From – All –345678910111214151617 To – All –345678910111214151617	Typical Spectral Width(nm) From:– All –2532404550556080 To:– All –2532404550556080	Max. Noise Figure (dB) From:– All –77.5899.510 To – All –77.5899.510	Typical Current(mA)– All –100120150200250300350400500600700 To: – All –100120150200250300350400500600700	Polarization Dependent or Independent	Package	Part Number
Peak Wavelength(nm)	Category	Typical Gain(dB)	Typcial Psat(dBm)	Typical Spectral Width(nm)	Max. Noise Figure(dB)	Typical Current(mA)	Polarization Dependent or Independent	Package	Part Number
880	In-Line	20	10	40	8	150	Dependent	Butterfly	IPSAD0801
1015	In-Line	20	11	80	8	250	Dependent	Butterfly	IPSAD1002
1040	In-Line	25	10	55	8	250	Dependent	Butterfly	IPSAD1003
1050	In-Line	25	10	45	10	300	Dependent	Butterfly	IPSAD1001
1285	In-Line	30	17	60	7.5	700	Dependent	Butterfly	IPSAD1201
1300	In-Line	30	15	60	7	700	Dependent	Butterfly	IPSAD1305
1300	In-Line	19	7	80	7.5	300	Dependent	Butterfly	IPSAD1306
1310	Booster	10	11	40	7.5	300	Independent	Butterfly	IPSAD1307
1310	Booster	22	10	45	7.5	250	Independent	Butterfly	IPSAD1301
1310	In-Line	19	7	50	7.5	250	Independent	Butterfly	IPSAD1303
1310	In-Line	29	9	40	7.5	200	Independent	Butterfly	IPSAD1308
1310	Pre-amplifier	16	10	55	7	250	Independent	Butterfly	IPSAD1304
1310	Pre-amplifier	15	7	45	7.5	250	Independent	8-Pin	IPSAD1309
1310	Switch	18	6	40	9	100	Dependent	Butterfly	IPRAD1301
1310	Switch	10	4	50	7.5	100	Independent	Butterfly	IPSAD1302
1490	Pre-amplifier	16	11	55	8	300	Independent	Butterfly	IPSAD1402
1490	Pre-amplifier	26	9	40	8	400	Independent	Butterfly	IPSAD1401
1525	In-Line	19	7	50	8	300	Dependent	Butterfly	IPSAD1506
1550	Booster	13	14	55	9	500	Independent	Butterfly	IPSAD1505
1550	Booster	20	10	45	9	350	Independent	Butterfly	IPSAD1501
1550	Booster	15	10	55	9	350	Independent	Butterfly	IPSAD1504
1550	Booster	14	16	60	9	700	Dependent	Butterfly	IPSAD1507
1550	Booster	25	12	60	9	500	Dependent	Butterfly	IPSAD1509
1550	Booster	10	12	40	9	300	Independent	Butterfly	IPSAD1510
1550	In-Line	16	5	50	9	350	Independent	Butterfly	IPSAD1503
1550	In-Line	28	8	45	9	350	Dependent	Butterfly	IPSAD1508
1550	Switch	10	3	50	10	120	Independent	Butterfly	IPSAD1502
1550	Switch	18	6	40	9	100	Independent	Butterfly	IPRAD1501
1550	Switch	22	8	60	9.5	600	Dependent	Butterfly	IPSAD1511
1550	Switch	13	12	60	9.5	400	Independent	Butterfly	IPSAD1512
1550	Switch	22	13	60	9.5	600	Independent	Butterfly	IPSAD1513
1550	Switch	25	13	40	9.5	600	Dependent	Butterfly	IPSAD1514
1550	Booster	20	20	40	8.0	1000	Dependent	Butterfly	IPSAD1515
1600	Booster	20	9	50	10.0	400	Independent	Butterfly	IPSAD1601
1650	Booster	25	13	40	9.5	600	Dependent	Butterfly	IPSAD1602

A Semiconductor Optical Amplifier (SOA) is an optoelectronic device that can amplify an input optical signal under appropriate operating conditions. A schematic diagram of a basic SOA is presented in Fig.1 (below).

Fig.1-SOA simplified diagram.

An electric current externally applied to the Semiconductor Optical Amplifier excites electrons in the active region of forward biased pn-junction. When photons travel through the active area they can cause these electrons to lose some of their extra energy and generate more photons that match the wavelength of the initial ones, so called stimulated photon emission.The embedded waveguide is used to confine the propagating signal wave to the active area. Therefore, an optical signal passing through the active region is amplified and is said to have experienced optical gain.

Inphenix’s SOAs come in different form factors starting as small as a 6-pin mini butterfly that can be mounted in a CFP/CFP2 transceiver to a desktop that can be integrated with drivers and custom ordered passive components.

Inphenix SOA’s have been tested to meet Telcordia GR-468-CORE for extremely high reliability, as well as the RoHS directive.

SOA Amplification Characteristics

Inphenix’s semiconductor optical amplifiers have proven to be versatile and multifunctional devices that are key building blocks for optical networks.There are five main parameters used to characterize a Semiconductor Optical Amplifier (SOA):

• Small Signal Gain (Gs); up to 22 dB at -25dBm input power;
• Gain Bandwidth; up to 80 nm at 3 dB
• Saturation Output Power (Psat) up to 17 dBm;
• Noise Figure (NF) 7.0-8.0 dB;
• Polarization Dependent Gain (PDG)< 1 dB or up to 10 dB

A Semiconductor Optical Amplifier should have the highest gain appropriate to the application. A wide optical bandwidth is also desirable so that the SOA can amplify a wide range of signal wavelengths. Gain saturation effects introduce undesirable distortion to the output so an ideal SOA should have very high saturation output power to achieve good linearity and to maximize its dynamic range with minimum distortion. An ideal SOA should also have a very low noise figure (the physical limit is 3dB) to minimize the amplified spontaneous emission (ASE) power at the output. Finally, an ideal SOA should have very low polarization sensitivity to minimize the gain difference between the transverse-electric (TE) and transverse-magnetic (TM) polarization states. However, an ideal SOA is impossible to realize because of the physical limitations of the various processes taking place within it.

Fig. 2- SOA interrelated parameters.

SOA parameters are strongly interrelated, and in order to achieve the best value of one parameter, the other specification(s) should be compromised and/or spectral operation area should be controlled, as it is schematically shown on Fig.2.

Types of SOAs

Depending on the role SOAs play in the customer’s system, they can be classified into four categories: in-line,booster; switch SOA and preamplifier;

• In-line: higher gain, moderate Psat; lower NF and lower PDG, usually polarization independent SOA;
• Booster: higher Psat, lower gain, usually polarization dependent;
• Switch: higher Extinction Ratio and faster rise/fall time;
• Pre-amplifier: good for longer transmission distance, lower NF and higher gain.

In addition, PDG can determine polarity of an SOA.  For instance, if the PDG is less than 1.5dB, the SOA is Polar Independent (P-I) and if the PDG is up to 10 dB, the SOA is Polar Dependent (P-D).

Applications of SOA

Traditional applications

Amplification is a basic principle application of SOAs in optical communication system. SOAsarea highly versatile component that can be used for various amplifications and routing functions in telecommunications. Commercialized SOAs are now widely available in the market and are fast-becoming a cost-effective solution to optical amplification in advanced optical systems for core, metro, and ultimately access applications. SOA can be employed in any optical communication network to regenerate signals at various points in the link by operating either as a booster amplifier (post-amplifier), in-line amplifier.

Telecoms

SOAs are in use by a wide variety of industries.  One of the most important industries is telecoms, where they are valued for routing and switching.  In addition, SOAs are used to boost or amplify signal output for long-distance fiber-optic communications.  In this application, telecom firms employ fiber-optic lines from headquarters to the data centers.  These transmission lines can exceed 10km or more, requiring the use of SOAs to boost/amplify the signal from the usual light sources.

Fig. 3-SOAs in photonic carriers (top) can be used in Photonic Integrated Circuit (PIC) (bottom-left).

Functional applications

SOAs can also be used to perform functions that are, and will be, useful in future optically transparent networks. These all-optical functions can help to overcome the so called ‘electronic bottleneck’ which is presently a major limiting factor in the deployment of high-speed optical communication networks, like, for example, optical wavelength converter. Invariably, SOA functional applications are based on SOA nonlinearities. These nonlinearities are principally caused by carrier density changes induced by the amplifier input signals. The four main types of nonlinearity commonly exploited in SOAs arecross-gain modulation (XGM), cross-phase modulation (XPM), self-phase modulation (SPM) and four-wave mixing (FWM).

Sensing

Sensing is another important industry utilizing SOAs in many applications.  One important use of SOAs in sensors is the Fiber-Bragg Interrogators.  In this setup, either an SLD or DFB is used as the input light-source.  An SOA boosts the optical signal to a fiber-Bragg grating (FBG), often through a circulator to control direction of the optical signals.  Changes in temperature or strain change the wavelength or timing of the optical signals to a PD/sensor.  This can alert the user to possible malfunctions.

Fig. 4- Fiber-Bragg Grating with SOA in-line amplifier

Another important use of SOAs in sensing is with Light Detection and Ranging (LiDAR).   LiDAR devices can be small, for only Doppler-ranging or appear as an array capable for mapping.An example of LiDAR application uses Frequency Modulated Continuous Wave (FMCW) to detect the Doppler effect of movement, such as with autonomous cars and drones.  In addition, FMCW can be used for cartography and inspection.  SOAs used in narrowband, usually with DFBs, can have high output power >20mW, for longer range.

Fig. 5- LiDAR chip with integrated SOAs. An array of these chips gives a wide-area scan.

Fig.6- Frequency Modulated Continuous Wave (FMCW) LiDAR. SOAs in green.

CWDM

The previously highlighted features of small size, good integration capability and high potential for cost reduction through scaled manufacturing processes will continue to ensure that the SOA plays an increasingly important role in future advanced optical networks. Coarse wavelength division multiplexing (CWDM) is an economic route for giving connection flexibility and increased throughput for metro and enterprise network layers. Extending the capacity and distance of CWDM systems (>100 km) requires a low cost optical amplifier operating across the entire optical bandwidth (from 1260 nm to 1620 nm). The SOA is the only viable technology available today that can be deployed to meet these expanding applications.

WDM-PON

An expanded role for SOAs in telecoms is in their use in Wavelength Division Multiplexing-Passive Optical Networks (WDM-PON).  Cable companies utilizing fiber-optic lines from the home office to the customer receiving the data, often have nodes, or distribution centers, to assist in switching and routing data.  This setup allows the efficient distribution of data to a large customer base.  SOAs are an early application of WDM-PON but may see growth in the future.

There are several other attractive applications of SOA, such as intensity and phase modulation, SOA logic for the use of optical signal processing, SOA add/drop multiplexer for optical time division multiplexed network, SOA pulse generator to generate pulse easily at high frequencies (> 10 GHz), SOA clock recovery required in optical receivers and 3R generators, SOA dispersion compensator to overcome the chromatic dispersion which limits the transmission distance, and SOA detector to detect optical signal. SOAs can also be used for gating optical signals, i.e. signals can be either amplified or absorbed by SOAs. The blocking properties of SOAs at low bias currents are extremely useful because they enable channel routing functions, such as reconfigurable add/drop multiplexers (ROADM), to be produced with off channel isolation better than 50 dB.

Advantages of SOAs

1. The optical gain provided by SOAs within a bandwidth is relatively independent of the wavelength of the incident optical signal.
2. The injection electric current serves as the pump signal for amplification instead of optical pumping.
3. Due to their compact size, SOAs can be integrated with several waveguide photonic devices on a single planar substrate.
4. They use the same technology as diode lasers.
5. SOAs have the ability to operate at communication spectral bands of 1300 nm and 1550 nm with wider bandwidth (up to 100 nm).
6. They can be configured and integrated to function as pre-amplifiers at the optical receiver end.
7. SOAs can function as simple logic gates in WDM optical networks.

Limitations of SOAs

1. SOAs can deliver output optical power up to a few tens of milliwatts (mW) only which is usually sufficient for single channel operation in a fiber–optic communication link. However, a WDM system may require up to a few mW of power per channel.
2. Since the coupling of the input optical fiber into and out of the SOA integrated chip tends to induce signal loss, SOA must provide additional optical gain in order to minimize the impact of this loss on the input/output facets of the active region.
3. SOAs are highly sensitive to the polarization of the input optical signal.
4. They generate higher noise levels in the active medium than optical fiber amplifiers.
5. In case multiple optical channels are amplified as required in WDM applications, SOAs can produce severe crosstalk.

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