JP2012015577A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust a wavelength of a tunable laser (TLD) to a transmission wavelength of an arrayed waveguide grating (AWG) for wavelength-demultiplexing.SOLUTION: An AWG 14 multiplexes a down-link light on an L-band from optical transmitter and receiver devices 12-1 to 12-n, demultiplexes an up-link light wavelength-multiplexed on a C-band from an optical transmission path 40 and conveys the multiplexed down-link light and the demultiplexed up-link light to the optical transmitter and receiver devices 12-1 to 12-n. A control device 34 sweeps an emission wavelength of a TLD 24 within the L-band. The output light of the TLD 24 is incident on the AWG 14 via an optical coupler 26 and a WDM coupler 28. The output light of the TLD 24 is incident on a reflector 44 and is partially reflected when its wavelength is in the transmission range of the AWG 14. A reflected light is incident on an optical receiver 32 through the optical coupler 26. A control device 34 adjusts the output wavelength of the TLD 24 so that the output signal level of the optical receiver 32 becomes more than a predetermined value.

Description

  The present invention relates to an optical transmission system that uses wavelength division multiplexing, such as a WDM-PON (Wavelength Division Multiplexing Passive Optical Network) system.

  In the field of optical access such as FTTH (Fiber To The Home), WDM-PON has attracted attention as a future high-speed transmission technology accompanying an increase in transmission traffic capacity. In WDM-PON, communication is performed by assigning different optical wavelengths to each user in uplink communication, downlink communication, or both, so that each user can occupy a communication band.

  Patent Document 1 describes a WDM-PON system as a wavelength division multiplexing optical transmission system in which wavelength multiplexing / demultiplexing elements, for example, arrayed waveguide gratings (AWG) are arranged on both sides of an optical fiber transmission line. When AWG is used as a wavelength multiplexing / demultiplexing element, optical transceivers located on both sides of the optical transmission line (in the case of PON, an OLT (Optical Line Terminal) arranged at the center station and arranged at each user's home) The signal light source of ONU (Optical Network Unit) needs to be adjusted to a wavelength that can be multiplexed and separated by AWG.

  Considering the aging of the transmission wavelength of the AWG and the versatility of the ONU for replacement, the so-called colorless capability, a variable wavelength laser diode (TLD: Tunable Laser Diode) is used as the signal light source installed in each ONU. Preferably, the wavelength can be set or adjusted. Patent Documents 2 and 3 describe techniques for adjusting the wavelength by using a wavelength tunable laser diode as a signal light source.

  In Non-Patent Document 1, the ONU outputs light while changing the wavelength of the TLD, monitors the return light reception power due to Rayleigh scattering that occurs during optical fiber transmission through the AWG, and detects the maximum light reception level. Is set as a transmission channel.

U.S. Pat. No. 7,327,771 JP-A-2005-277686 JP 2010-041444 A

OFC2010, OWG7, 2010

  In the technique described in Patent Document 2, it is necessary to dispose an LED that emits light when the TLD outputs light having a wavelength that can be appropriately separated by the wavelength demultiplexing element in the multiplexer device on the optical transmission line. The cost is increased, and maintenance labor and cost are increased.

  In the technique described in Patent Document 3, when one optical transmission / reception device can receive signal light from the other optical transmission / reception device, it is necessary to notify the wavelength to the other optical transmission / reception device. There is a problem that it takes time to determine the optical wavelength.

  In the technique described in Non-Patent Document 1, the return light due to Rayleigh scattering is monitored. Usually, the scattered light level due to Rayleigh scattering is very small, and the effect depends on the transmission path conditions. is not. When downstream signal light is present, the ONU needs to be provided with an optical filter to distinguish downstream signal light and Rayleigh scattered light, resulting in an increase in apparatus cost.

  An object of the present invention is to provide an optical transmission system that can appropriately adjust or set the wavelength of a signal light source with an inexpensive configuration.

  An optical transmission system according to the present invention includes an optical transmission line, a plurality of first optical transmission / reception devices that use different upstream and downstream wavelengths, and a plurality of second optical communication devices that communicate with the plurality of first optical transmission / reception devices. And the downstream light output from the plurality of first optical transmission / reception devices are wavelength-multiplexed, and the upstream light multiplexed from the optical transmission path is directed to each of the plurality of first transmission / reception devices. First wavelength demultiplexing means for wavelength-separating light, and the optical transmission line wavelength-multiplexes upstream light output from the plurality of second optical transmission / reception devices, and the first wavelength demultiplexing means A second wavelength multiplexing / separating unit for wavelength-separating the downstream light multiplexed in step 1 into downstream light directed to each of the plurality of second transmission / reception devices, the first wavelength multiplexing / separating unit, and the second wavelength A reflector disposed between the demultiplexing means and The first optical transmission / reception device demultiplexes all downstream wavelengths used by the plurality of first optical transmission / reception devices and all upstream wavelengths used by the plurality of first optical transmission / reception devices. The first WDM coupler, the first transmission device including the first tunable light source serving as the signal light source, the first reception device, and the reflection of the downstream light output from the first transmission device. A first light receiver that receives the first reflected light from the transmitter and the downstream light output from the first transmitter is supplied to the first WDM coupler, and the first WDM coupler receives the first light from the first WDM coupler. The level of the first reflected light is predetermined according to the first optical coupler that supplies the first reflected light to the first light receiver and the level of the reflected light received by the first light receiver. 1st control which controls the wavelength of the said 1st wavelength variable light source so that it may become more than a value Characterized by comprising a location.

  According to the present invention, by providing a reflector that reflects the light that has passed through the wavelength demultiplexing means, it is possible to easily adjust the wavelength of the wavelength variable light source serving as the signal light source to a wavelength that is transmitted through the wavelength demultiplexing means. it can. In addition, the wavelength can be adjusted while executing data transmission.

It is a schematic block diagram of one Example of this invention. It is an example of the transmission characteristic of input / output port # 1 of AWG of a present Example. It is an example of the transmission characteristic of AWG of a present Example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of the present invention. In the WDM-PON system shown in FIG. 1, an OLT (Optical Line Terminal) 10 disposed in a center station is optically connected to n ONUs (Optical Network Units) 50-1 to 50-n via an optical transmission line 40. Connect.

  The OLT 10 wavelength multiplexes optical transmission / reception devices 12-1 to 12-n communicating with different ONUs 50-1 to 50-n, and optical transmission / reception devices 12-1 to 12-n, and optical transmission lines. An AWG (Arrayed Waveguide Grating) 14 is provided as a wavelength demultiplexing means for separating the optical signal from the optical transmission line 40 into individual wavelength lights. The optical transceivers 12-1 to 12-n have the same configuration, but the upstream signal light wavelength and the downstream signal light wavelength are different.

  The AWG 14 multiplexes the input light of the n input / output ports # 1 to #n according to the wavelength and outputs the multiplexed light from the multiplexed light input / output port #M. And is output from the input / output ports # 1 to #n and has a periodic wavelength transmission characteristic as is well known. 2 shows an example of transmission characteristics between one input / output port #i of the AWG 14 and the multiplexed optical input / output port #M. FIG. 3 shows input / output ports # 1 to #n of the AWG 14 and the multiplexed optical input / output port #M. The example of the transmission characteristic between M is shown. 2 and 3, the horizontal axis indicates the wavelength, and the vertical axis indicates the transmission loss.

Although details will be described later, the optical transceiver 12-i of the OLT 10 communicates with the ONU 50-i using the downstream signal light wavelength λd _i and the upstream signal light wavelength λu _i . However, i = 1 to n. Downstream signal light wavelength λd ₁ ~λd _n are different from each other, the upstream signal wavelength λu ₁ ~λu _n are different from each other, and, different from any downstream signal light wavelength λd ₁ ~λd _n.

The AWG 14 multiplexes downstream signal lights (wavelengths λd _{1 to} λd _n ) from the optical transmission / reception apparatuses 12-1 to 12 -n to the ONUs 50-1 to 50 -n, respectively, and transmits and receives optical signals from the ONUs 50-1 to 50 -n. The upstream signal light (wavelengths λu _{1 to} λu _n ) to the devices 12-1 to 12-n is separated. Downstream signal light wavelength λd ₁ ~λd _n and an uplink signal wavelength λu ₁ ~λu _n are located in a different band of AWG14. For example, the downstream signal wavelength λd ₁ ~λd _n belong to the L-band of AWG14, upstream signal wavelength λu ₁ ~λu _n belongs to C-band of AWG14.

The optical transmission line 40 includes a single mode optical fiber 42, a reflector 44, an AWG 46, and branch optical fibers 48-1 to 48-n. An optical fiber 42 connects the OLT 10 and the multiplexed light input / output port #M of the AWG 46, and a reflector 44 on the optical fiber 42 is disposed. The branch optical fibers 48-1 to 48-n connect the input / output ports # 1 to #n of the AWG 46 to the ONUs 50-1 to 50-n, respectively. The reflector 44 and the AWG 46 are so-called remote nodes. In this embodiment, the reflector 44, the wavelength λd ₁ ~λd _n, the λu ₁ ~λu _n, about 4% (- 14 dB equivalent), preferably reflected by the reflective index of about 1-10%. The reflector 44 may be disposed between the optical fiber 42 and the OLT 10.

  The reflector 44 may be formed, for example, by intentionally processing the ferrule part shape of the optical connector part that connects the optical fiber 42 and the AWG. When there is no need to adjust the wavelength of the signal light source on the OLT side, the reflector 44 reflects the upstream signal light from the ONUs 50-1 to 50-n and does not reflect the downstream signal light from the OLT 10. It is good also as a structure which permeate | transmits. Such a reflector 44, for example, uses a 1: 2 branching optical coupler, divides the upstream signal light from the AWG 46 toward the OLT 10 into two parts, inputs one into the optical fiber 42, and enters the other into the optical mirror. It can be realized by reflecting the reflected light and returning the reflected light to the AWG 46.

The AWG 46 has the same wavelength demultiplexing characteristics as the AWG 14. However, it is only necessary that the transmission wavelengths (center wavelengths) of the input / output ports # 1 to #n coincide with each other, and the characteristic curves of the transmission wavelength characteristics of the individual input / output ports # 1 to #n need not be the same. . In other words, there are generally two types of wavelength transmission characteristics of each input / output port of the AWG: a flat top type and a Gaussian type. The AWG 14 (or 46) is a flat top type and the AWG 46 (or 14) is a Gaussian type. Also good. The AWG 46 wavelength-separates the wavelength-multiplexed downstream signal light from the OLT 10 into downstream signal lights (wavelengths λd _{1 to} λd _n ) to the ONUs 50-1 to 50 -n, and upstream signals from the ONUs 50-1 to 50 -n. Light (wavelengths λu _{1 to} λu _n ) is wavelength-multiplexed.

The configuration and basic signal flow of the optical transceiver 12-1 will be described. The transmission device 22 of the optical transmission / reception device 12-1 includes a TLD (Tunable Laser Diode) 24 as a signal light source. The TLD 24 can output laser light having an arbitrary wavelength in the L band, and the control device 34 adjusts the wavelength of the TLD 24 to the downstream signal light wavelength λd ₁ which is the transmission wavelength of the port # 1 of the AWG 14 by a method described later. To do. As a method for changing the wavelength of the laser diode, there are a method for controlling the temperature of the laser diode, a method for controlling the injection current, a method for changing the reflection wavelength characteristic of the reflector constituting the laser resonator, and the like.

The optical coupler 26 supplies the output light of the transmitter 22 to a wavelength division multiplexing (WDM) coupler 28. The WDM coupler 28 is an optical element that multiplexes and separates C-band light and L-band light, and supplies the L-band light from the optical coupler 26 to the port # 1 of the AWG 14. The WDM coupler 28 also receives C-band light (signal light of wavelength λu ₁ ) and L-band light (reflected light of wavelength λd ₁ , which will be described later) from port # 1 of the AWG _14. The former is supplied to the receiving device 30 and the latter is supplied to the optical coupler 26. Receiving device 30, the signal light of the wavelength Ramudau ₁ photoelectrically converts and outputs the demodulated data Du _1.

The optical coupler 26 supplies the light from the WDM coupler 28, that is, the L-band light from the port # 1 of the AWG 14 (which will be described later, reflected light having the wavelength λd ₁ ) to the light receiver 32. If a problem occurs when a part of the light from the WDM coupler 28 enters the TLD 24, an optical isolator may be disposed between the optical coupler 26 and the TLD 24. From such a function, it is obvious that the optical coupler 26 can be replaced by an optical circulator.

  The light receiver 32 converts the light input from the optical coupler 26 into an electrical signal. The controller 34 controls the wavelength of the TLD 24 according to the output signal of the light receiver 32 so that the output signal amplitude of the light receiver 32 is increased.

The ONUs 50-1 to 50-n have the same configuration, and FIG. 1 illustrates the configuration of the ONU 50-1 in detail. The configuration of the ONU 50-1 and the basic signal flow will be described. The transmission device 52 includes a TLD 54 as a signal light source. The TLD 54 can output a laser beam having an arbitrary wavelength in the C band, and the control device 64 sets the wavelength of the TLD 54 to the upstream signal light wavelength that is the transmission wavelength of the port # 1 of the AWG 46 (and 14) by a method described later. adjusted to λu _1. The optical coupler 56 supplies the output light of the transmission device 52 to the WDM coupler 58. The WDM coupler 58 is an optical element that multiplexes and separates C-band light and L-band light, and supplies the C-band light from the optical coupler 56 to the port # 1 of the AWG 46 via the branch optical fiber 48-1. To do. The WDM coupler 58 also receives L-band light (signal light of wavelength λd ₁ ) and C-band light (described later, reflected light of wavelength λu ₁ ) from the port # 1 of the AWG 46 via the branch optical fiber 48-1. ) Is incident, and the WDM coupler 58 supplies the former to the receiver 60 and the latter to the optical coupler 56. Receiving apparatus 60, the signal light of the wavelength .lambda.d ₁ photoelectrically converts and outputs the demodulated data Dd _1.

The optical coupler 56 supplies light from the WDM coupler 58, that is, C-band light from the input / output port # 1 of the AWG 46 (which will be described later, reflected light having a wavelength λu ₁ ) to the light receiver 62. If a problem occurs when a part of the light from the WDM coupler 58 enters the TLD 54, an optical isolator may be disposed between the optical coupler 56 and the TLD 54. From such a function, it is obvious that the optical coupler 56 can be replaced by an optical circulator.

  The light receiver 62 converts the light input from the optical coupler 56 into an electrical signal. The control device 64 controls the wavelength of the TLD 54 so that the output signal amplitude of the light receiver 62 increases in accordance with the output signal of the light receiver 62.

  First, the wavelength adjustment operation of the TLD 24 will be described. The control device 34 sweeps the emission wavelength of the TLD 24 continuously or discretely from one end (for example, the long wavelength side) to the other end (for example, the short wavelength side) of the L band. As described above, the output light of the TLD 24 enters the port # 1 of the AWG 14 via the optical coupler 26 and the WDM coupler 28. While the wavelength of the output light of the TLD 24 does not fall within the transmission range of the port # 1 of the AWG 14, no reflection by the reflector 44 occurs. Therefore, the light reflected by the reflector 44 does not enter the light receiver 32, and the output level of the light receiver 32 remains low.

When the output wavelength of the TLD 24 enters the transmission range of the port # 1 of the AWG 14, the output light of the TLD 24 passes through the AWG 14 while being attenuated according to the transmission characteristics of the port # 1 of the AWG 14, and passes through the optical fiber 42. The reflector 44 is reached, and a part thereof is reflected by the reflector 44. The reflected light from the reflector 44 propagates through the optical fiber 42 and enters the multiplexed light input / output port #M of the AWG 14. The AWG 14 outputs the reflected light incident on the multiplexed light input / output port #M to the WDM coupler 28 from the input / output port # 1. The WDM coupler 28 supplies the reflected light to the optical coupler 26, and the optical coupler 26 enters the reflected light from the WDM coupler 28 into the light receiver 32. As a result, the output signal level of the light receiver 32 increases by an amount corresponding to the intensity of the reflected light incident on the light receiver 32. The control device 34 can know that the output wavelength of the TLD 24 has approached the transmission wavelength λd ₁ of the input / output port # 1 of the AWG 14 by increasing the output signal level of the light receiver 32.

  As the controller 34 further sweeps the output wavelength of the TLD 24, the output signal level of the light receiver 32 increases and then decreases. At that time, the control device 34 can know that it is passing through the transmission band of the input / output port # 1 of the AWG 14. The control device 34 adjusts the output wavelength of the TLD 24 to the wavelength at which the output signal level of the light receiver 32 is maximized from the change in the output signal level of the light receiver 32 obtained by the sweep. Thereafter, the control device 34 outputs the output of the TLD 24 within the range of the transmission bandwidth of the input / output port # 1 of the AWG 14 so that the output signal level of the light receiver 32 becomes equal to or higher than a certain value or keeps the peak value. Vary the wavelength. Such fine tuning of the wavelength can be performed even during data transmission. Thereby, the wavelength of the TLD 24 can be maintained at a wavelength that can pass through the input / output port # 1 of the AWG 14 regardless of the change in wavelength due to the drive signal vs. wavelength characteristics of the TLD 24 and the ambient temperature, and the change in transmission characteristics of the AWG 14 over time.

  As a method of initially adjusting the output wavelength of the TLD 24, first, the output wavelength of the TLD 24 is swept by a step width about half the transmission bandwidth of the input / output port # 1 of the AWG 14, and the reflected light from the reflector 44 is received by the light receiver. When the light enters the beam 32, the output wavelength of the TLD 24 may be swept in smaller steps. In other words, the wavelength of the TLD 24 is roughly adjusted, and the wavelength is finely adjusted when entering or approaching the transmission band. Compared with the method of sweeping the wavelength in fine steps from the beginning to the end or the method of sweeping the wavelength continuously, the time required to determine the wavelength can be shortened.

  When the transmission characteristic of the AWG 14 is a Gaussian type, the wavelength of the maximum transmittance (minimum transmission loss) can be approximately determined from the reflected light levels of three wavelengths separated by a predetermined interval. In this case, the control device 34 discretely sweeps the wavelength of the TLD 24 at such a wavelength interval that the three wavelengths are included in the transmission characteristic Gaussian waveform, and determines the reflected light levels of the adjacent three wavelengths obtained by the wavelength sweep. Just calculate.

  When the transmission characteristic of the AWG 14 is a flat top type as shown in FIGS. 2 and 3, the center wavelength can be determined by detecting the short wavelength side edge and the long wavelength side edge of the transmission characteristic. In this case, it is necessary to sweep the wavelength of the TLD 24 so finely or continuously that these edges can be detected. A method of detecting one edge and shifting the wavelength corresponding to half of the transmission wavelength width may be used.

  When comparing the intensity of the reflected light received by the light receiver 32, it is assumed that the output light power of the TLD 24 is controlled to be constant. For example, even when the output light power of the TLD 24 fluctuates, the reflected light intensity can be compared by normalizing the reflected light intensity based on the monitor result of the output power of the TLD 24. Therefore, the transmission wavelength of the WAWG 14 can be detected.

  The wavelength adjustment method of the TLD 54 which is the signal light source of the ONUs 50-1 to 50-n is basically the same as that of the TLD 24. The wavelength adjustment operation of the TLD 54 of the ONU 50-1 will be described.

  The control device 64 sweeps the emission wavelength of the TLD 54 from one end (for example, the long wavelength side) of the C band to the other end (for example, the short wavelength side). As described above, the output light of the TLD 54 enters the port # 1 of the AWG 46 via the optical coupler 56 and the WDM coupler 58. While the wavelength of the output light of the TLD 54 does not fall within the transmission range of the port # 1 of the AWG 46, reflection by the reflector 44 does not occur. Therefore, the light reflected by the reflector 44 does not enter the light receiver 62, and the output level of the light receiver 62 remains low.

When the output wavelength of the TLD 54 enters the transmission range of the port # 1 of the AWG 46, the output light of the TLD 54 passes through the AWG 46 and enters the reflector 44 while being attenuated according to the transmission characteristics of the port # 1 of the AWG 46. A part of the light is reflected by the reflector 44. The light reflected by the reflector 44 enters the light receiver 62 via the multiplexed light input / output port #M and input / output port # 1 of the AWG 46, the WDM coupler 58, and the optical coupler 56. As a result, the output signal level of the light receiver 62 increases by an amount corresponding to the intensity of the reflected light incident on the light receiver 62. The control device 64 can know that the output wavelength of the TLD 54 has approached the transmission wavelength λu ₁ of the input / output port # 1 of the AWG 46 by increasing the output signal level of the light receiver 62.

  When the control device 64 further sweeps the output wavelength of the TLD 54, the output signal level of the light receiver 62 increases and then decreases. At that time, the control device 64 can know that the transmission band of the input / output port # 1 of the AWG 46 is passing. The control device 64 adjusts the output wavelength of the TLD 54 to a wavelength that maximizes the output signal level of the light receiver 62 from the change in the output signal level of the light receiver 62 obtained by the sweep. Thereafter, the control device 64 outputs the output of the TLD 54 within the range of the transmission bandwidth of the input / output port # 1 of the AWG 46 so that the output signal level of the light receiver 62 becomes a certain level or higher or keeps the peak value. Vary the wavelength. Such fine tuning of the wavelength can be performed even during data transmission. Accordingly, the wavelength of the TLD 54 can be maintained at a wavelength that can pass through the input / output port # 1 of the AWG 46 regardless of the change in wavelength due to the drive signal versus wavelength characteristics of the TLD 54 and the ambient temperature, and the change in the transmission characteristics of the AWG 46 over time.

  As a method of initially adjusting the output wavelength of the TLD 54, first, the output wavelength of the TLD 54 is swept with a step width about half the transmission bandwidth of the input / output port # 1 of the AWG 46, and the reflected light from the reflector 44 is received by the light receiver. When the light enters the light source 62, the output wavelength of the TLD 54 may be swept in smaller steps. In other words, the wavelength of the TLD 54 is roughly adjusted, and the wavelength is finely adjusted when entering or approaching the transmission band. Compared with the method of sweeping the wavelength from the beginning to the end in fine steps, the time required to determine the wavelength can be shortened.

  Thus, when the wavelengths of the TLDs 24 of the optical transceivers 12-1 to 12-n of the OLT 10 and the TLDs 54 of the ONUs 50-1 to 50-n are adjusted, the optical transceivers 12-1 to 12-n corresponding to each other are adjusted. Communication between the ONUs 50-1 to 50-n.

An operation of downlink data transmission from the optical transceiver 12-1 to the ONU 50-1 will be briefly described. The transmission device 22 of the optical transmission / reception device 12-1 uses the TLD 24 to generate downlink signal light (wavelength λd ₁ ) that carries the downlink data Dd ₁ and outputs it to the optical coupler 26. Downstream signal light (wavelength λd ₁ ) passes through the optical coupler 26, the WDM coupler 28, the AWG 14, and the optical fiber 42, and enters the reflector 44. The reflector 44 transmits most of the incoming downstream signal light (wavelength λd ₁ ) and reflects a small part thereof. As described above, the component reflected by the reflector 44 is used to adjust the wavelength of the TLD 24 of the optical transceiver 12-1.

Downstream signal light (wavelength λd ₁ ) transmitted through the reflector 44 enters the multiplexed optical input / output port #M of the AWG 46, is output from the input / output port # 1 to the branch optical fiber 48-1, and is transmitted to the ONU 50-1. Incident. In the ONU 50-1, the WDM coupler 58 supplies the downstream signal light (wavelength λd ₁ ) from the optical fiber 48-1 to the receiving device 60. The receiving device 60 photoelectrically converts the downstream signal light (wavelength λd ₁ ) from the WDM coupler 58, demodulates and outputs the data Dd ₁ . In this way, the downlink data Dd ₁ is transmitted from the OLT 10 to the ONU 50-1.

The operation of uplink data transmission from the ONU 50-1 to the optical transceiver 12-1 will be briefly described. The transmission device 52 of the ONU 50-1 uses the TLD 54 to generate upstream signal light (wavelength λu ₁ ) that carries upstream data Du ₁ and outputs it to the optical coupler 56. The upstream signal light (wavelength λu ₁ ) passes through the optical coupler 56, the WDM coupler 58, the branch optical fiber 48-1, the input / output port # 1 and the multiplexed optical input / output port #M of the AWG 46, and enters the reflector 44. Incident. The reflector 44 transmits most of the incoming upstream signal light (wavelength λu ₁ ) and reflects a small part thereof. As described above, the component reflected by the reflector 44 is used to adjust the wavelength of the TLD 54 of the ONU 50-1.

The upstream signal light (wavelength λu ₁ ) transmitted through the reflector 44 enters the WDM coupler 28 via the optical fiber 42, the multiplexed light input / output port #M and the input / output port # 1 of the AWG 14. The WDM coupler 28 supplies the upstream signal light (wavelength λu ₁ ) from the input / output port # 1 of the AWG ₁₄ to the reception device 30. The receiving device 30 photoelectrically converts the upstream signal light (wavelength λu ₁ ) from the WDM coupler 28, demodulates and outputs data Du ₁ . In this way, the upstream data Du ₁ is transmitted from the ONU 50-1 to the OLT ₁₀ .

  In the case of the TLD 54 of the ONUs 50-1 to 50-n, the wavelength channels of the AWGs 14 and 46 used in the individual ONUs 50-1 to 50-n may be set with a dip switch or the like. For example, a user or an ONU installation worker sets a wavelength channel designated in advance with the dip switch. The control device 64 performs the above-described wavelength adjustment with the wavelength channel set by the DIP switch as a target.

  The above embodiment is more generally a WDM optical transmission system, in which case the ONUs 50-1 to 50-n can be referred to as so-called optical transmission / reception devices, and the optical transmission / reception devices 12-1 to 12-n, respectively. 1-to-1 communication.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

10: OLT
12-1 to 12-n: Optical transceiver 14: AWG
22: Transmitter 24: TLD
26: Optical coupler 28: WDM coupler 30: Receiver 32: Light receiver 34: Controller 40: Optical transmission line 42: Single mode optical fiber 44: Reflector 46: AWG
48-1 to 48-n: Branched optical fibers 50-1 to 50-n: ONU
52: Transmitter 54: TLD
56: Optical coupler 58: WDM coupler 60: Receiver 62: Light receiver 64: Controller

Claims (2)

An optical transmission line (40);
A plurality of first optical transceivers (12-1 to 12-n) that use different upstream and downstream wavelengths;
A plurality of second optical transceivers (50-1 to 50-n) communicating with the plurality of first optical transceivers;
First, the downstream light output from the plurality of first optical transmission / reception devices is wavelength-multiplexed, and the multiplexed upstream light from the optical transmission path is wavelength-separated into upstream light directed to each of the plurality of first transmission / reception devices. 1 wavelength demultiplexing means (14)
And
The optical transmission line is
Downlink light that wavelength-multiplexes upstream light output from the plurality of second optical transmission / reception devices, and that transmits the downstream light multiplexed by the first wavelength demultiplexing means to each of the plurality of second transmission / reception devices. Second wavelength demultiplexing means (40) for wavelength separation into
Reflector (44) disposed between the first wavelength demultiplexing means and the second wavelength demultiplexing means
And
The first optical transmission / reception device demultiplexes all the downstream wavelengths used by the plurality of first optical transmission / reception devices and all the upstream wavelengths used by the plurality of first optical transmission / reception devices. WDM coupler (28), a first transmission device (22) including a first variable wavelength light source (24) serving as a signal light source, a first reception device (30), and the first transmission device The downstream light output from the first transmitter (22) and the first light receiver (32) that receives the first reflected light from the reflector (44) of the downstream light output from (22). A first optical coupler (supplied to the first WDM coupler (28) and supplying the first reflected light from the first WDM coupler (28) to the first light receiver (32). 26) and the level of the reflected light received by the first light receiver (32), An optical transmission system, wherein a level of the reflected light of said 1 comprises a first control unit (34) and controlling the wavelength of the first wavelength-tunable light source to be equal to or greater than the predetermined value.   A second optical transceiver that demultiplexes all downstream wavelengths used by the plurality of first optical transceivers and all upstream wavelengths used by the plurality of first optical transceivers; A second transmitter (52) including a WDM coupler (58), a second wavelength tunable light source (54) serving as a signal light source, a second receiver (60), and the second transmitter ( 52), the second light receiver (62) that receives the second reflected light from the reflector (44) and the upstream light output from the second transmitter (52). A second optical coupler (56) that supplies the second reflected light from the second WDM coupler (58) to the second light receiver (62) and supplies the second reflected light to the second WDM coupler (58). ) And the level of the second reflected light received by the second light receiver (62) And a second control device (64) for controlling the wavelength of the second wavelength tunable light source so that the level of the second reflected light is equal to or higher than a predetermined value. The optical transmission system described.

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