KR100990264B1 - Light source apparatus and optical communication system including ring resonator - Google Patents

Abstract

Disclosed are an optical communication system including a light source device for outputting a plurality of light spectrums having a predetermined line width, an optical filter for filtering a plurality of light spectrums with a constant channel spacing, and an optical transmitter and receiver for receiving the filtered light. The line width of the light spectrum is not greater than the channel spacing. The light source device includes a pumping light providing unit that provides pumping light, a gain medium that receives the pumping light and outputs light of a first wavelength band, and receives a plurality of resonances within the first wavelength band by receiving light of the first wavelength band. A ring resonator for outputting a plurality of light spectrums having a constant line width at a wavelength, a first optical coupler for outputting a part of the light input from the ring resonator and returning the rest to a gain medium, and being fed back through the first optical coupler from the ring resonator And a second optical coupler for coupling the light and the pumped light to output the gain medium. A light source having a light line width smaller than the pass band of each channel of the optical filter can be made. Accordingly, the intensity noise noise (RIN) generated when the light source does not pass the pass band and the optical signal is cut may reduce the transmission speed and the transmission distance.

Wavelength Locked, Wavelength Independent, Optical Transmitter, External Injection Light

Description

LIGHT SOURCE APPARATUS AND OPTICAL COMMUNICATION SYSTEM INCLUDING RING RESONATOR}

The present invention relates to an optical communication device, and more particularly, to a light source device and an optical communication system having a ring resonator.

Wavelength Division Multiplexing (WDM) is a method of transmitting and receiving light of different wavelengths output from a plurality of optical transceivers through one optical fiber. The wavelength division multiplexing method can transmit a large amount of data at a time to increase the bandwidth between transmission intervals, and the cost of leasing the optical path by transmitting data using one optical fiber instead of using multiple optical fibers And there is an advantage that can save the maintenance cost.

In the conventional wavelength division multiplexing method, the output of an optical transceiver having a wavelength determined for each channel is input to a wavelength division and multiplexing device having an optical thin film filter (TFF) or an arrayed waveguide grating (AWG). do. That is, the conventional wavelength division multiplexing system requires a plurality of optical transceivers for each channel, so the system operator has a disadvantage of having a predetermined quantity of optical transmitters for each channel in advance for maintenance.

In order to solve this problem, Korean Patent Registration No. 10-0325687 and "Optical signal transmitter" entitled "Optical Signal Transmitter" are named "Light source for wavelength-division multiplex optical communication using a Fabry-Perot laser diode immersed in injected coherent light." Patent Publication No. 20030007207 proposes a wavelength independent (colorless or colorfree) wavelength division multiplexing method for automatically determining an output wavelength of an optical transceiver at a wavelength assigned to a connection port between an optical transceiver and a wavelength division multiplexing device. According to this proposal, non-coherent broadband light is passed through an optical thin film filter or an arrayed waveguide diffraction grating, and then to a Fabric-Perot Laser Diode (FP-LD), Semiconductor Optical Amplifier (SOA) or Reflective Semiconductor Optical Amplifier (RSAA). Injection is performed to selectively output light of a specific wavelength desired (wavelength locked light).

Wavelength Independent When the output light of a broadband light source (BLS) located in an optical line termination device of a wavelength division optical communication system passes through an optical thin film filter or an arrayed waveguide diffraction grating placed at a remote node, it is allocated per channel. Only optical signals of bandwidth magnitude pass. When the broadband light that is passed through each channel is injected into FP LD or RSOA, wavelength locking occurs according to the corresponding channel wavelength, and it is more flexible than the method of using a specific wavelength optical transceiver. By using the wavelength division multiplex optical communication system can be implemented.

However, since the spectrum of the output light of the broadband light source passes through the diffraction grating with the optical thin film filter or the arrayed waveguide, the Relative Intensity Noise (RIN) is optically generated. As a result, the quality of the light output signal of the wavelength independent optical transceiver is lower than the quality of the light output signal of the general optical transceiver, thereby limiting the transmission speed and distance.

The transmission distance of the light output signal of the wavelength independent optical transceiver is determined by the intensity of the injected light. In the conventional wavelength division multiplex optical communication system, a broadband light source device using ASE (Amplified Spontaneous Emission) of EDFA (Erbium Doped Fiber Amplifier) having a high output in a wide wavelength band, a broadband light source device using SLED (Superluminescent Light Emitting Diode), etc. This is necessary. However, the wavelength band actually used is only a wavelength band passing through the diffraction grating with an optical thin film filter or an arrayed waveguide, and other wavelength bands that do not pass through are wasted. In addition, as the transmission distance increases, the output capacity of expensive pump LDs (980 nm / 1480 nm) or SLED LDs must also increase. When the light output is over a certain level, the light output of the pump LD or SLED LD should be increased by more than 3 dB to compensate for the line loss according to the light transmission distance by 3 dB. There are problems associated with the cost, size, and heat of broadband light source devices.

Provided is an optical communication system capable of reducing waste of a light source output from a broadband light source device and reducing an output capacity of a pump laser diode required for an increase in a transmission distance.

In one embodiment, a light source device for optical communication includes: a pumping light providing unit configured to provide pumping light; A gain medium receiving the pumped light and outputting light of a first wavelength band; A ring resonator configured to receive light in the first wavelength band and output a plurality of light spectrums having a predetermined line width at a predetermined plurality of resonant wavelengths in the first wavelength band; A first optical coupler for outputting a part of the light input from the ring resonator and returning the rest to the gain medium; And a second optical coupler for coupling the pumped light and the light returned from the ring resonator through the first optical coupler to be output to the gain medium.

An optical communication system according to an embodiment includes a light source device for outputting a plurality of light spectrums having a predetermined line width; An optical filter having a constant channel spacing and filtering the plurality of optical spectra; And an optical transceiver for receiving the filtered light, wherein a line width of the optical spectrum is not greater than the channel spacing.

By combining only the characteristics of the transmission to the ring resonator output port and the characteristics of the broadband light source device using the ASE of EDFA, it is possible to form broadband light having a line width smaller than the bandwidth of the optical thin film filter or the array waveguide diffraction grating. Unlike conventional broadband light that forms an optical signal in a wavelength band that is discarded outside the pass band while passing through the diffraction grating with an optical thin film filter or an arrayed waveguide, it is possible to prevent waste of the light source as a light source having a small line width.

In addition, when the same capacity of the pump LD and the same length of the EDF can be obtained higher light output than the conventional high output, low cost, it is possible to miniaturize. In addition, it is possible to solve the heat problem accompanying to make a high power broadband light source.

Optical thin-film filters or arrayed waveguides can produce a light source with an optical line width that is smaller than the pass-by-channel passband of the diffraction grating, reducing the intensity noise noise (RIN) that occurs when the light source does not pass the passband and the optical signal is truncated. The speed can be improved, and the transmission distance can be increased to enable long distance transmission of 20 km or more.

The optical communication system according to the present invention can be applied to a backhaul, a metro network, etc. of a wireless communication network as well as a wired subscriber network for applying a passive optical network (PON).

A light source device and an optical communication system having a ring resonator according to one embodiment of the present invention are described. As an example of an optical communication system, a wavelength independent optical communication system is described. However, the optical communication system of the present invention is not limited to the wavelength independent optical communication system.

In the embodiments of the present invention described below, "wavelength independent" means that the optical transceiver itself does not have only a specific wavelength of output, but is optically connected to any channel port of an optical thin film filter or array waveguide grating for wavelength division and multiplexing. The output wavelength of the transceiver is automatically determined by the wavelength assigned to the channel port to which it is connected and has a constant light output.

A wavelength independent multiplexing system is an optical line termination device (OLT) located in a telephone station, an optical network termination device having a function of converting light into an electrical signal and converting an electrical signal into an optical signal in a subscriber's home or dense area. (ONT: Optical Network Terminal) or Optical Network Unit (ONU / ONU) and Optical Line Terminator (OLT) and Optical Network Terminator or Optical Network Unit (ONT / ONU) It consists of an optical distribution network (ODN). The optical distribution network (ODN) includes a remote node (RN) at which an optical thin film filter or an arrayed waveguide diffraction grating is positioned for wavelength division and multiplexing. In order to implement a passive optical network, a remote point (RN) does not need a power supply, and uses an optical passive device capable of determining a wavelength for each channel and enabling wavelength division and multiplexing. Optical network terminators require wavelength independent optical transceivers, and optical line terminators (OLTs) require broadband light sources.

Referring to FIG. 1, the non-coherent broadband light source (BLS) 10 of the optical line terminator OLT of the present invention outputs broadband spectral light at a predetermined interval. The output light of the light source (BLS) 10 passes through an optical waveguide diffraction grating or an optical thin film filter (AWG / TFF) 40 that performs a filter function through an optical circulator 20 and an optical fiber 30. To pass. Preferably, the output light of the BLS 10 is composed of a plurality of spectra distributed over a predetermined band. The line width of each of the spectra is no wider than the channel spacing of the AWG / TFF 40. That is, the line width of each spectrum may be equal to or narrower than the channel spacing of the AWG / TFF 40. The BLS 10 and the AWG / TFF 40 determine the wavelength of each channel of the wavelength independent optical transceiver. A light source with a narrower linewidth than the bandwidth allocated for each channel passes through the AWG / TFF 40 and has optically low intensity noise noise (RIN). Amplifier 50).

The broadband light source (BLS) 10 may be configured by combining an Erbium Doped Fiber Amplifier (EDFA) and a ring resonator. Referring to FIG. 2, the light output (pumped light) of 980 nm or 1480 nm output from the pump laser diode (LD) 11 of the broadband light source 10A device for implementing the wavelength independent wavelength division multiplexing method is the first. It is input to the gain medium Erbium Doped Fiber (EDF) 13 via an optical coupler 12. The pumping light output from the pump LD 11 excites the electrons of the EDF. That is, when pumped light of 980 nm or 1480 nm output from the pump LD 11 is injected into the EDF 13, electrons of the EDF are excited and spontaneously discharged to naturally emit light (ASE: Amplified) in a wide band (first wavelength band). Spontaneous Emission) is obtained. The ASE output from the EDF 13 is input to an input port of the ring resonator 14. The ring resonator 14 outputs light having a resonance wavelength determined through a drop port according to the size and refractive index of the ring. Optical signals corresponding to the resonance wavelength from the ring resonator 14 are periodically output in the wavelength band (first wavelength band) of the natural emission light and have the same free spectral range (FSR). That is, a large number of spectrums having an interval of FSR are periodically output in the wavelength band of natural emission light. The second optical coupler 15 outputs a portion of the ring resonator 14 output and the rest is returned to the EDF 13. The first optical coupler 12 combines the light output of the pump LD 11 with the output of the returned ring resonator 14. As such, the output optical signal of the ring resonator 14 is partially output through the second optical combiner 15 and the rest is again outputted together with the optical output of the pump LD 11 through the first optical combiner 12. It is input to the EDF 13 and is again input to the ring resonator 14 through an excitation and emission process. As a result of repeating this process, only signals corresponding to the resonant wavelength of the ring resonator 14 are amplified and output to the drop port of the ring resonator 14 and the through port of the ring resonator 14. Only part of the light signal outputted to the power supply is lost, thereby reducing the waste of the light source.

When Erbium-doped optical fiber is used as a gain medium for receiving pumped light and emitting light in a first wavelength band, as shown in FIG. 3, the BLS 10B is directed against the input of the EDF 13. The optical isolator 16 may be further included to increase the signal gain efficiency without being affected by the reflection of the ASE. In addition, a gain flattening filter (GFF) 17 may be further included to flatten the optical signal output through the drop port of the ring resonator 14.

In addition, as shown in FIG. 4, the BLS 10C prevents the optical signal output through the ring resonator 14 from being reflected and input to the ring resonator 14, thereby preventing the ring resonator 14 and the second optical coupler ( 15 may further include an optical isolator 18. The position and quantity of the optical isolator 16, 18, the gain flattening filter 17, etc., the position of the pump LD, and the pumping direction are not limited to the examples shown in FIGS. 2 to 4, and various modifications are possible. Such changes may also be another embodiment without departing from the scope of the present invention.

The free spectral range (FSR) of the resonant wavelength output from the ring resonator is determined by the speed "C" of the light, the refractive index "n" of the ring resonator waveguide, and the length "L" of the ring resonator, as shown in Equation 1 below. .

Free Spectral Range (FSR) = C / 2nL

The FSR is determined by Equation 1 to match the channel spacing determined by the optical thin film filter or the array waveguide diffraction grating, which is essential for implementing the wavelength independent multiplexed passive optical network. On the other hand, the line width and the resonance wavelength of the light output from the ring resonator may also be affected by the coupling strength of the waveguides, the size and the number of rings.

The change in the refractive index of the waveguide of the ring resonator according to the external environment can be stably maintained through temperature control using a TEC (Thermo Electric Cooler). That is, in order to prevent the resonance wavelength of the ring resonator from changing due to the change in refractive index due to the temperature change, TEC may be used to compensate for the temperature change of the ring resonator due to the external temperature change. In addition, by designing a thermal (temperature insensitive) waveguide using materials having different refractive index temperature coefficients, a ring resonator having a constant resonant wavelength can be designed by reducing a change in refractive index of the ring resonator due to an external temperature change. .

As shown in FIG. 5, the ring resonator 14A may be implemented as a single ring, or as shown in FIG. 6, the ring resonator 14B may be implemented as multiple rings. The ring resonators 14A and 14B include an input port P1 through which an optical signal is input, a first linear waveguide L1 through which the input optical signal passes, a second linear waveguide L2, and a ring waveguide RO and RO. ₁ , RO ₂ , RO ₃ , RO ₄ ), an output port P2 of the second linear waveguide L2, and a through port P3 of the first linear waveguide L1. do.

The ring resonators 14A and 14B are wavelengths of light satisfying phase matching between the first linear waveguide L1, the second linear waveguide L2, and the ring waveguides RO, RO ₁ , RO ₂ , RO ₃ , and RO ₄ . That is, only the resonant wavelength is output to the output port P2, and the pass port P3 passes only the remaining optical signal transmitted to the output port P2 among the optical signals input from the input port P1. Of the resonant wavelength transmitted to the output port P2 according to the coupling strength between the linear waveguides L1 and L2 of the ring resonators 14A and 14B and the ring waveguides RO, RO ₁ , RO ₂ , RO ₃ , and RO ₄ . Line width changes. In general, as the light coupling intensity increases, the line width becomes larger, and as the light coupling intensity becomes smaller, the line width becomes smaller. In addition, the use of multiple rings compared to a single ring increases the effective resonance length and decreases the bandwidth, thereby narrowing the line width of the output optical signal and improving the frequency chirp characteristics. For more details on ring resonators, see BE Little et al, "Microring resonator channel dropping filters", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 15, NO.6, JUNE 1997.

Single or multiple ring resonators (RO, RO ₁ , RO ₂ , RO ₃ , RO ₄ ) can be implemented by forming the optical coupling structure of the ring waveguide in a horizontal structure and a vertical structure using a Planar Lightwave Circuit (PLC) technology. The broadband light source device using the ring resonator of the present invention and the broadband light source using the ring resonator in the optical communication system using the same can be implemented by doping Erbium to the linear waveguide of the ring resonator using PLC technology. Therefore, it is not necessary to use a separate EDF, and the smallest broadband light source can be made through the erbium-doped ring resonator and the pump LD.

Figure 7a shows the output light spectrum (Ch # 1 ~ Ch # N) for each channel of the BLS (10, 10A, 10B, 10C) according to an embodiment of the present invention, Figure 7b shows a conventional wavelength independent wavelength division multiplexing method Shows the spectrum of the output light of the broadband light source that was used for the optical line termination to implement. As shown in FIG. 7B, a conventional broadband light source provides a wide band light source including all channels of an optical thin film filter or an arrayed waveguide diffraction grating, whereas the BLS 10, 10A, 10B, and 10C of the present invention are optical as shown in FIG. 7A. Thin-film filters or arrayed waveguides output spectra with line widths no greater than the channel spacing of the diffraction grating.

FIG. 8A illustrates a state in which output light of BLSs 10, 10A, 10B, and 10C passes through the AWG / TFF 40 according to an embodiment of the present invention, and FIG. 8B illustrates output light of a conventional broadband light source (dotted line display). The state which passed this AWG / TFF 40 is shown. 9 illustrates an eye mask 92 in which a channel-specific output spectrum 91 of a broadband light source and a channel-specific light source are wavelength-locked in an F-P LD or an RSOA according to an embodiment of the present invention. From the comparison of Figs. 8A and 8B, the BLSs 10, 10A, 10B, and 10C of the present invention output the spectrums of the linewidth not wider than the channel spacing of the AWG / TFF 40, thereby increasing the intensity noise noise (RIN) characteristics. The better the thinner the '1' level signal, the better the signal characteristics.

In the present invention, a broadband light source structure using EDFA's ASE and a ring resonator are used to make a broadband light source having a line width smaller than the bandwidth of an optical thin film filter or an arrayed waveguide diffraction grating. Can be implemented.

It is to be understood that the above described embodiments are merely illustrative of some of the various embodiments employing the principles of the present invention. It will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the invention.

1 is a schematic diagram of a wavelength independent wavelength division multiple communication system according to an embodiment of the present invention;

2 to 4 is a schematic view showing the configuration of a broadband light source device according to an embodiment of the present invention.

5 is a schematic view showing an example of the configuration of a single ring waveguide.

6 is a schematic view showing a configuration example of a multiple ring waveguide.

7A is an output light spectrum of a broadband light source according to an embodiment of the present invention.

7B is an output light spectrum of a conventional broadband light source.

8A is a light spectrum after output light of a broadband light source according to an embodiment of the present invention passes through AWG / TFF.

8B is a light spectrum after output light of a conventional broadband light source passes through AWG / TFF.

9 is an eye mask in which the output spectrum for each channel and the light source for each channel of the broadband light source according to the embodiment of the present invention are wavelength-locked.

Claims (19)

A light source device for optical communication, A pumping light providing unit providing a pumping light; A gain medium receiving the pumped light and outputting light of a first wavelength band; A ring resonator configured to receive light in the first wavelength band and output a plurality of light spectrums having a predetermined line width at a predetermined plurality of resonant wavelengths in the first wavelength band; A first optical coupler for outputting a part of the light input from the ring resonator and returning the rest to the gain medium; And And a second optical coupler for coupling the pumped light and the light returned from the ring resonator through the first optical coupler to output the gain medium. A light source device for amplifying only the signals corresponding to the resonant wavelength of the ring resonator through a feedback process, and outputs a light source having a line width narrower than the pass band for each channel of the optical filter. The method of claim 1, The pumping light providing unit is a pump laser diode (Pump LD), the light source device. The method of claim 1, The gain medium is EDF (Erbium Doped Fiber), light source device. The method of claim 3, And the EDF outputs natural emission light of the first wavelength band. The method of claim 1, And the ring resonator comprises at least one ring. The method of claim 5, And a first isolator between the ring resonator and the first optical coupler. The method according to claim 5 or 6, And a second isolator between the second optical coupler and the gain medium. The method of claim 7, wherein And a gain flattening filter coupled to the first optical coupler for flattening the gain of output light. As an optical communication system, A light source device for outputting a plurality of light spectrums having a predetermined line width; An optical filter having a constant channel spacing and filtering the plurality of optical spectra; Including an optical transmitter for receiving the filtered light, The light source device outputs a light source having a line width narrower than a pass band for each channel of the optical filter by extracting, returning, and amplifying the light source at a predetermined wavelength interval from the broadband light source through a feedback process using a resonance wavelength of a ring resonator. Optical communication system. 10. The method of claim 9, The light source device, A pumping light providing unit for providing pumping light; A gain medium receiving the pumped light and outputting light of a first wavelength band; The ring resonator configured to receive light in the first wavelength band and output a plurality of light spectrums having a predetermined line width at a predetermined plurality of resonant wavelengths in the first wavelength band; A first optical coupler for outputting a part of the light input from the ring resonator and returning the rest to the optical amplifier; And And a second optical coupler for coupling the pumped light and the light returned from the ring resonator through the first optical coupler to output the gain medium. 10. The method of claim 9, The optical filter is an arrayed waveguide diffraction grating or an optical thin film filter. 10. The method of claim 9, The optical transceiver is an optical communication system, a FP-LD (Fabry-Perot Laser Diode) or RSOA (Reflective Semiconductor Optical Amplifier). The method of claim 10, The pumping light providing unit is a pump laser diode (Pump LD), optical communication system. The method of claim 10, The gain medium is Erbium Doped Fiber (EDF). The method of claim 14, And the EDF outputs natural emission light of the first wavelength band. The method of claim 10, And the ring resonator comprises at least one ring. The method of claim 16, And a first isolator between the ring resonator and the first optical coupler. The method according to claim 16 or 17, And a second isolator between the second optical coupler and the gain medium. The method of claim 18, And a gain flattening filter coupled to the first optical coupler for flattening the gain of output light.

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