WO2012119391A1

WO2012119391A1 - Adjustable laser device, optical module and passive optical network system

Info

Publication number: WO2012119391A1
Application number: PCT/CN2011/078440
Authority: WO
Inventors: 周小平; 王峰
Original assignee: 华为技术有限公司
Priority date: 2011-08-16
Filing date: 2011-08-16
Publication date: 2012-09-13
Also published as: CN102349204A

Abstract

Disclosed are an adjustable laser device (100), and an optical module (200) and a passive optical network (800) using the adjustable laser device (100). The adjustable laser device (100) comprises a stop-band filter module (120), a gain medium (110) and a wavelength adjusting module (130). The stop-band filter module (120) has multiple stop-bands spaced from each other. Emitted light of the gain medium (110) has multiple longitudinal modes, and one of the longitudinal modes overlaps the stop-band of the stop-band filter module (120). The wavelength adjusting module (130) is used for adjusting the location of the longitudinal mode of the emitted light of the gain medium (110) when the adjustable laser device (100) adjusts the wavelength, so that the longitudinal mode of the emitted light is shifted to be aligned with another stop-band corresponding to a target wavelength in the stop-band filter module (120).

Description

Tunable laser, optical module and passive optical network system

TECHNICAL FIELD The present application relates generally to optical communication technologies, and in particular, to a wavelength tunable laser (ie, tunable laser:) and an optical module, and the present application also relates to a passive optical network using the tunable laser. (Passive Optical Network, PON) system.

BACKGROUND OF THE INVENTION With the increasing demand for bandwidth by users, traditional copper broadband access systems are increasingly facing bandwidth bottlenecks. At the same time, fiber-optic communication technologies with huge bandwidth capacity are becoming more mature and application costs are declining year by year. Fiber access networks, such as Passive Optical Network (PON), are gradually becoming strong competitors for next-generation broadband access networks. At present, in many fiber access network solutions, WDM PON systems based on Wavelength Division Multiplexing (WDM) technology have the advantages of large bandwidth capacity and peer-to-peer communication to ensure information security. Has received much attention. Since the WDM PON system requires each user to enjoy a single wavelength, multiple lasers with different emission wavelengths are required for both the user terminal and the optical transceiver module at the central office. If a fixed-wavelength laser (ie, a color laser) is used, as the number of users increases, the number of lasers will increase, which will bring great storage problems to operators. To this end, optical transmitters of current WDM PON systems typically employ tunable lasers to achieve colorless illumination of the source such that the WDM PON The system does not need to prepare lasers of specific wavelengths for different wavelength channels, thereby solving the storage problem and greatly reducing the operation and maintenance costs and network deployment costs. Distributed Feedback (DFB) thermal tuning laser is a common tunable laser. The main structure of the DFB thermal tuning laser is to set the thermoelectric cooling thermoelectric cooler (TEC) under the DFB die for temperature control. Modules, and the wavelength of the DFB die is adjusted by the TEC module. As the temperature increases, the corresponding wavelength of the PFB grating gradually increases, and the wavelength of the DFB grating directly determines the emission wavelength of the DFB thermal modulation laser, so that the emission wavelength of the laser can be changed by temperature adjustment. However, the DFB grating of the DFB thermal-tuning laser is usually made of InGaAsP, and the wavelength drift is generally 0.1 nm/Κ, that is, the temperature needs to be changed by 10 degrees, and the wavelength will change by 1 nm. This greatly limits the wavelength adjustment range of the DFB thermal modulation laser.

SUMMARY OF THE INVENTION The present application provides a tunable laser and optical module having a larger wavelength adjustment range. Meanwhile, the present application also provides a passive optical network system using the tunable laser. A tunable laser comprising: a stop band filter module having a plurality of mutually spaced stop bands; a gain medium coupled to the stop band filter module, the gain medium having a plurality of longitudinal modes, wherein one longitudinal a mode overlaps with a stop band of the stop band filter module; a wavelength adjustment module configured to adjust a longitudinal mode position of the emitted light of the gain medium when the tunable laser performs wavelength adjustment, so that the longitudinal mode of the emitted light Offset to correspond to the target wavelength in the stopband filter module The other stopband is relatively accurate.

An optical module includes a transmitting submodule and a receiving submodule; the transmitting submodule is configured to convert a data signal into an optical signal and output, and the receiving submodule is configured to receive the input light and convert it into a corresponding electrical signal The transmitting sub-module includes a laser and a laser driver for providing a modulation current to the laser to modulate the data signal to output light of the laser, the laser comprising: a stop band filter module, a plurality of mutually spaced stop bands; a gain medium coupled to the stop band filter module, the light of the gain medium having a plurality of longitudinal modes, wherein one longitudinal mode overlaps with a stop band of the stop band filter module.

A passive optical network system comprising an optical line terminal and a plurality of optical network units, the optical line terminals being connected to the plurality of optical network units through an optical distribution network; wherein the optical line terminals and/or optical networks The unit includes a tunable laser as described above.

In the technical solution provided by the present application, the tunable laser can shift the longitudinal mode to be opposite to the stop band corresponding to the target wavelength in the stopband filter module by adjusting the longitudinal mode position of the emitted light of the gain medium. Precise, thus achieving wavelength adjustment. Since the emitted light of the gain medium has a plurality of longitudinal modes spaced apart from each other and the stop band filter has a plurality of mutually spaced stop bands, a plurality of longitudinal modes of light emitted by the gain medium and the stop band filter The vernier effect between the plurality of stop bands of the device, when the wavelength of the tunable laser is adjusted, the longitudinal mode of the light emitted by the gain medium only needs to move at least a range of not less than one stop band interval, so that it can be realized at a certain level There is a large range of wavelength adjustment within the temperature adjustment range. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an embodiment of a tunable laser provided by the present application.

Fig. 2 is a view schematically showing the relationship between the output light of the gain medium and the stop band of the FBG module in the tunable laser shown in Fig. 1.

3 is a schematic structural view of an embodiment of an FBG module in the tunable laser of FIG. 1. 4 is a schematic diagram of an embodiment of an optical module provided by the present application.

FIG. 5 is a schematic structural diagram of a passive optical network system to which the tunable laser provided by the present application can be applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The tunable laser, optical transceiver module, and passive optical network system and device provided by the present application are described in detail below with reference to specific embodiments.

In order to solve the problem that the wavelength adjustment range of the tunable laser is small, the present application firstly provides a tunable laser having an FBG module, the FBG module including a plurality of mutually spaced stop bands, and the tunable laser utilizes temperature adjustment One of the longitudinal modes of the emitted light of the gain medium is moved to a corresponding resistance of the FBG module to the target wavelength to achieve wavelength tunable lasing. The tunable laser provided by the gain medium can realize a large wavelength within a certain temperature adjustment range by using a vernier effect between a plurality of longitudinal modes of the light-transmitting medium and a plurality of stop bands of the FBG module. Adjust the range to avoid the need to achieve wavelengths through large temperature changes as in the prior art Adjustment.

Please refer to FIG. 1 , which is a schematic diagram of an embodiment of a tunable laser provided by the present application. The tunable laser 100 includes a gain medium 110, a Fiber Bragg Grating (FBG) module 120, and a wavelength adjustment module 130.

The gain medium 110 may be an indium phosphide (InP) material having a core layer of indium gallium arsenide (InGaAsP), which may be used to provide emitted light having a plurality of longitudinal modes spaced apart from each other. For example, in one embodiment, the wavelengths of the longitudinal modes of the emitted light of the gain medium 110 are different, and the wavelength difference between adjacent longitudinal modes is the same, that is, the plurality of longitudinal modes have In other alternative embodiments, the plurality of longitudinal modes may also be aperiodic.

The FBG module 120 can be coupled to the gain medium 110 by an optical fiber, which can act as a periodic stop band filter having a plurality of spaced apart and periodically distributed stop bands. The stop band of the FBG module 120 can meet the International Telecommunications Union (ITU) wavelength standard (ITU grid). In a specific embodiment, the transmission of the gain medium 110 can be made by a suitable design. Only one longitudinal mode of light overlaps the stop band of the FBG module 120, as shown in FIG. If the plurality of longitudinal dies of the light of the gain medium 110 have periodic characteristics, to ensure that only one longitudinal mode of the emitted light overlaps with the stop band of the FBG module, the period of the stop band of the FBG module 120 It should be different from the period of the plurality of longitudinal modes such that the longitudinal mode spacing of the emitted light of the gain medium has a certain deviation from the stop band spacing of the FBG module 120. Moreover, the FBG module 120 has a partial reflection characteristic for an optical signal whose wavelength overlaps with the stop band, that is, the FBG module 120 can light having a predetermined wavelength among the emitted light of the gain medium 110. At least a portion of the signal (ie, the longitudinal mode that overlaps the stop band of the FBG module 120) is reflected back to the gain medium 110 and amplified by the gain medium 110 for the stimulated radiation, such that it is reciprocated a plurality of times, such that A Fabri-Perrot (FP) resonant cavity is formed between the FBG module 120 and the gain medium 110, and finally the lasing light having a wavelength corresponding to the stop band is outputted by the resonant cavity. Since the other longitudinal modes of the emitted light of the gain medium 110 do not overlap with the stop band of the FBG module 120, other longitudinal modes cannot form reflections in the FBG module 120 and return to the gain medium 110 for injection. Zooming in, so other longitudinal modes cannot form lasing. Therefore, the tunable laser 100 is lasing only with a stable wavelength, which is the emission wavelength of the tunable laser 100. In a specific embodiment, the FBG module 120 may be a single FBG according to the needs of the wavelength adjustment range, or may be formed by connecting a plurality of FBGs having different stop bands in series (as shown in FIG. 3). The number of stop bands can be consistent with the number of wavelengths that the tunable laser 100 needs to select. For example, on a single-mode fiber SMF-28, m consecutive FBGs are connected in series, each

The FBGs respectively have n center wavelengths, and the center wavelengths of the different FBGs are different, thereby realizing mxn wavelength channels. In addition, the FBG module 120 can adopt a negative temperature compensation package to avoid temperature drift caused by temperature changes. Specifically, the negative temperature compensation package can ensure that the m FBGs connected in series are between 25 ° C and 85 ° C. The maximum drift of the wavelength in the range does not exceed 0.2 nm. In addition, the package of the FBG module 120 can also be strain-isolated at the same time to prevent the wavelength of the FBG from being affected by external strain. In addition, in an embodiment, to further improve the resonance effect of the tunable laser 100, the front end surface of the gain medium 110 (the end surface adjacent to the FBG module 120 side) and the rear end surface (ie, away from the The FBG module 120 - the end surface of the side) may be provided with an anti-reflection film 111 and a high reflection film 112, respectively. The anti-reflection film 111 can be used to reduce the reflectance of the reflected light reflected back by the FBG module 120 on the front end surface of the gain medium 110, thereby improving the reflected light returned from the FBG module 120. The high-reflection film 112 can be used to reduce the emitted light at the rear end of the gain medium 110, thereby improving the stimulated radiation effect of the gain medium 110. The wavelength adjustment module 130 can be a temperature control module. It is used to implement temperature adjustment of the gain medium 110, and according to the actual wavelength adjustment requirement of the tunable laser 100, the longitudinal mode of the emitted light of the gain medium 110 is controlled to be shifted by temperature adjustment, so that the emission The longitudinal mode of the light is aligned with the other stop band of the FBG module 120 to form and output lasing light of another wavelength to effect wavelength adjustment.

In particular, the wavelength adjustment module 130 can include a temperature control circuit 132 and a temperature adjustment unit 133. The temperature adjustment unit 133 may be disposed under the gain medium 110, and the temperature control circuit 132 may be connected to the temperature adjustment unit 133.

In a specific embodiment, the temperature adjustment unit 133 may include a Thermoelectric Cooler (TEC) component that adjusts the gain medium by a thermoelectric cooling effect according to a temperature control signal provided by the temperature control circuit 132. 110 temperature, thus adjusting the place The longitudinal mode position of the emitted light of the gain medium 100 is such that the longitudinal mode of the emitted light of the gain medium 110 is offset to another stop band in the FBG module 120 corresponding to the target wavelength. The temperature control circuit 132 can be configured to provide a temperature control signal to the temperature adjustment unit 133 to control the temperature adjustment unit 133 to perform corresponding temperature adjustment for the gain medium 110 according to a specific wavelength adjustment requirement.

As described above, in the tunable laser 100 provided in this embodiment, when the wavelength adjustment is performed, the temperature adjustment unit 133 only needs to adjust one of the longitudinal modes of the emitted light of the gain medium 110 by temperature adjustment to Another stopband corresponding to the target wavelength in the FBG module 120 can be aligned. Therefore, the range of wavelength adjustment of the tunable laser 100 provided by this embodiment mainly depends on the number of stop bands of the FBG module 120 and the spacing between the stop bands, since the emitted light of the gain medium 110 has a plurality of mutually spaced intervals. a longitudinal mode, and the FBG module 120 has a plurality of mutually spaced stop bands. In the tunable laser 100 wavelength adjustment provided in this embodiment, the longitudinal mode of the light emitted by the gain medium 110 only needs to be moved by no more than one The range of the stop band interval, by the above-mentioned cursor effect, the tunable laser 100 can achieve a large wavelength adjustment range within a certain temperature adjustment range, avoiding the need to achieve a large temperature change as in the prior art. Wavelength adjustment. On the other hand, in order to achieve wavelength locking after the tunable laser 100 is adjusted after the wavelength adjustment, the wavelength adjustment module 130 may further include an optical power detecting unit 131. The optical power detecting module 131 may be a monitor photodiode (MPD) disposed at a rear end of the gain medium 110 for detecting an exit from the rear end of the gain medium 110. The optical power of the optical signal (i.e., the backward optical power of the gain medium is detected), and the detected optical power is converted into a current proportionally and output to the temperature control circuit 132.

It should be understood that even if the rear end surface of the gain medium 110 is provided with the high reflection film 112, a small amount of light is output from the rear end surface due to the high reflection film instead of the 100% total reflection film, The power detection module 131 detects. The optical power detecting module 131 converts the backward optical power of the gain medium into a current proportionally, and by detecting the magnitude of the output current, the backward optical power of the gain medium 110 can be obtained; and the optical power The backward optical power received by the detecting module 131 and the forward transmit power of the gain medium 110 generally have a fixed proportional relationship. Therefore, the backward power received by the optical power detecting module 131 can be used to calculate the The current forward transmit power of the gain medium 110, ie the current output optical power of the gain medium 110.

If the temperature adjustment unit 133 is under the control of the temperature control circuit 132, the temperature adjustment of the gain medium 110 may be such that one of the longitudinal modes of the gain medium 110 and the target wavelength of the FBG module 120 When the corresponding stop band is relatively punctual, since a stable resonance is generated, at this time, the optical power detected by the optical power detecting unit 131 can reach a maximum value, and the output current thereof also reaches a maximum value; if there is no alignment, then The output current of the optical power detecting unit 131 does not reach the maximum value. Therefore, in a specific embodiment, the temperature control circuit 132 can determine whether one of the longitudinal modes of the gain medium 110 and the target of the FBG are determined by determining whether the output current of the optical power detecting unit 131 reaches a maximum value. The stop band corresponding to the wavelength has been aligned, and determines whether to control the temperature adjustment unit 133 to stop the gain medium 110 temperature adjustment.

For example, the temperature control circuit 132 may be pre-set with a current theoretical maximum value, after adjusting the longitudinal mode of the emitted light of the gain medium 110 to a vicinity of the stop band corresponding to the target wavelength according to the wavelength adjustment, when When the output current of the optical power detecting unit 131 reaches the theoretical maximum value, the temperature control circuit 132 can control the temperature adjusting unit 133 to stop the temperature adjustment, and then the emission wavelength of the tunable laser 100 can be locked. At the target wavelength. Based on the tunable laser 100 described above, the present application further provides an optical module using the tunable laser 100. Please refer to FIG. 4 , which is a schematic structural diagram of an embodiment of an optical module provided by the present application. The optical module 200 includes a sending submodule 210 and a receiving submodule 220. The transmitting sub-module 210 is configured to convert a data signal into an optical signal and transmit the data signal. In a specific embodiment, the transmitting sub-module 210 may include a Laser Diode Device (LDD) 211 and a laser (Laser Diode, LD). ) 212. The laser 212 can be the tunable laser 100 provided by the present application. For the specific structure and working process, refer to the description of the foregoing embodiment. The laser driver 211 is configured to provide a modulation current to the laser 212 to modulate the data signal at the output light of the laser 212 to effect data transmission. The receiving sub-module 220 is configured to receive input light from an external device and perform photoelectric conversion to form a corresponding electrical signal. The embodiment of the present invention further provides a passive optical network system, which may be a wavelength division multiplexed passive optical network (WDM PON) system as shown in FIG. 5. The WDM The PON system 800 includes an optical line terminal 810 at a central office (CO) and a plurality of optical network units 820 on the user side, wherein the optical line terminal 810 is connected through an Optical Distribution Network (ODN) 830. To the plurality of optical network units 820. The optical distribution network 830 can include a backbone optical fiber 831, a wavelength division multiplexing/demultiplexing 832, and a plurality of branching fibers 833, wherein the backbone optical fiber 831 is connected to the optical line terminal 810 and passes the wave A sub-multiplexer/demultiplexer 832 is connected to the plurality of branch fibers 833, which are respectively connected to the optical network unit 820. The wavelength division multiplexing/demultiplexing device 832 may be an Array Waveguide Grating (AWG) disposed at a remote node (RN), that is, a remote AWG (RN-AWG).

The optical line terminal 810 includes a plurality of central office optical modules 811, and the plurality of first optical modules (ie, central office optical modules: ) 811 pass through another wavelength division multiplexing/demultiplexing device 812 located at the central office. For example, a central AWG is coupled to the backbone fiber 831. Each optical network unit 820 includes a second optical module (ie, a user-side optical module: 821). The second optical module 821 corresponds to __ between the first optical module 811, and each pair of the first optical module 811 and the second optical module 821 respectively perform similar point-to-point communication using different communication wavelengths.

The first optical module 811 and the second optical module 812 can respectively adopt the optical module 200 provided by the foregoing embodiment. Specifically, the first optical module 811 and the second optical module 812 are respectively used. The laser is used as the light source, and the laser can be the tunable laser 100 provided in the above embodiments of the present application. For the specific structure and working process, refer to the description of the above embodiment. The above is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or within the technical scope of the present disclosure. Alternatives are intended to be covered by the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

Rights request

A tunable laser characterized by comprising:

a stop band filter module having a plurality of spaced-apart stop bands;

a gain medium connected to the stopband filter module, the light of the gain medium having a plurality of longitudinal modes, wherein a longitudinal mode overlaps with a stop band of the stop band filter module;

a wavelength adjustment module, configured to adjust a longitudinal mode position of the emitted light of the gain medium when the tunable laser performs wavelength adjustment, to shift a longitudinal mode of the emitted light to a target and a target in the stopband filter module The other stop band corresponding to the wavelength is aligned.

2. The tunable laser of claim 1 wherein the stopband filter module is a periodic stopband filter module having a plurality of spaced apart and periodically distributed stop bands.

3. The tunable laser of claim 2, wherein the plurality of stop bands of the periodic stop band filter module meet the International Telecommunication Union ITU wavelength standard.

4. The tunable laser of claim 2, wherein a spacing between the plurality of stop bands of the periodic stop band filter module and a plurality of longitudinal modes of the light of the gain medium The spacing is different.

4. The tunable laser of claim 3 wherein the plurality of longitudinal dies of the transmitted light of the gain medium have periodic characteristics and the wavelength differences between adjacent longitudinal modes are the same.

The tunable laser of any of claims 1 to 4, wherein the periodic filtering module is a fiber Bragg grating module comprising at least one fiber Bragg grating.

6. The tunable laser of claim 5, wherein the fiber Bragg grating module comprises a plurality of fiber Bragg gratings connected in series with each other, each fiber Bragg grating having a plurality of center wavelengths and different fiber Bragg gratings The center wavelengths vary.

7. The tunable laser of claim 1 wherein said stopband filtering module is coupled to when said one of said longitudinal modes of said gain medium overlaps said stopband filter module Forming a Fabry-Perot cavity between the gain media, wherein the stop band filter module reflects a portion of the optical signal having a wavelength corresponding to the stop band back to the gain medium for stimulated radiation to The Fabry-Perot cavity is caused to output lasing light having a wavelength corresponding to the stop band.

8. The tunable laser of claim 1, wherein the wavelength adjustment module is a temperature control module, and the temperature control module adjusts a temperature of the gain medium when the tunable laser performs wavelength adjustment The longitudinal mode of the emitted light of the gain medium is shifted.

9. The tunable laser of claim 8, wherein the temperature control module comprises a temperature control circuit and a temperature adjustment unit, the temperature control circuit providing the temperature adjustment unit according to the wavelength adjustment requirement a temperature control signal, the temperature adjustment unit adjusting a temperature of the gain medium according to the temperature control signal to offset a longitudinal mode of the emitted light of the gain medium to correspond to a target wavelength in the stopband filter module The stop band is relatively accurate.

10. The tunable laser of claim 9 wherein said temperature regulating unit comprises a thermoelectric cooling TEC assembly.

11. The tunable laser of claim 9 wherein said temperature control mode The block further includes an optical power detecting unit configured to detect a backward optical power of the gain medium, and the temperature control circuit is further configured to detect a backward optical power at the optical power detecting unit The temperature adjustment unit is controlled to stop temperature adjustment at a maximum time to lock the wavelength of the emitted light of the gain medium at the target wavelength.

12. An optical module, comprising: a transmitting submodule and a receiving submodule; the transmitting submodule for converting a data signal into an optical signal and outputting, the receiving submodule for receiving input light and Converted to the corresponding electrical signal;

The transmitting sub-module includes a laser and a laser driver for providing a modulation current to the laser to modulate the data signal at an output of the laser, the laser comprising:

a stop band filter module having a plurality of spaced-apart stop bands;

A gain medium is coupled to the stopband filter module, the light of the gain medium having a plurality of longitudinal modes, wherein a longitudinal mode overlaps with a stop band of the stop band filter module.

The optical module of claim 12, wherein the stop band filter module is a periodic stop band filter module having a plurality of stop bands that are spaced apart from each other and are periodically distributed.

The optical module according to claim 13, wherein a spacing between a plurality of stop bands of the periodic stop band filter module and a plurality of longitudinal modes of the emitted light of the gain medium different.

The optical module according to any one of claims 12 to 14, wherein The periodic filtering module is a fiber Bragg grating module that includes at least one fiber Bragg grating.

16. The optical module of claim 15 wherein said fiber Bragg grating module comprises a plurality of fiber Bragg gratings connected in series with each other, each fiber Bragg grating having a plurality of center wavelengths and different fiber Bragg gratings The center wavelengths are different.

17. The optical module of claim 12, wherein the laser further comprises: a wavelength adjustment module for adjusting a longitudinal mode position of the emitted light of the gain medium when the tunable laser performs wavelength adjustment And shifting the longitudinal mode of the emitted light to be aligned with another stop band corresponding to the target wavelength in the stop band filter module.

The optical module according to claim 17, wherein the wavelength adjustment module is a temperature control module, and the temperature control module adjusts a temperature of the gain medium by adjusting a temperature of the tunable laser. The longitudinal mode of the emitted light of the gain medium is offset.

19. The optical module of claim 18, wherein the temperature control module comprises a temperature control circuit and a temperature adjustment unit, the temperature control circuit providing a temperature to the temperature adjustment unit according to the wavelength adjustment required a control signal, the temperature adjustment unit adjusting a temperature of the gain medium according to the temperature control signal to shift a longitudinal mode of the emitted light of the gain medium to a target wavelength corresponding to the target wavelength in the stopband filter module The stop band is relatively accurate.

The optical module according to claim 19, wherein the temperature control module further comprises an optical power detecting unit, wherein the optical power detecting unit is configured to detect a backward optical power of the gain medium, and The temperature control circuit is further configured to detect the backward direction of the optical power detecting unit The temperature adjustment unit is controlled to stop temperature adjustment when the optical power is maximum to lock the wavelength of the emitted light of the gain medium to the target wavelength.

A passive optical network system, comprising: an optical line terminal and a plurality of optical network units, wherein the optical line terminal is connected to the plurality of optical network units through an optical distribution network; wherein the light The line termination and/or optical network unit comprises a tunable laser as claimed in any one of claims 1 to 11.