WO2015001421A2 - Wavelength tunable transmitter for twdm-pon and onu - Google Patents

Wavelength tunable transmitter for twdm-pon and onu Download PDF

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Publication number
WO2015001421A2
WO2015001421A2 PCT/IB2014/001526 IB2014001526W WO2015001421A2 WO 2015001421 A2 WO2015001421 A2 WO 2015001421A2 IB 2014001526 W IB2014001526 W IB 2014001526W WO 2015001421 A2 WO2015001421 A2 WO 2015001421A2
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WO
WIPO (PCT)
Prior art keywords
optical signal
micro
transmitter
wavelength
ring resonator
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PCT/IB2014/001526
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French (fr)
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WO2015001421A3 (en
Inventor
Zhensen GAO
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Alcatel Lucent
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Publication of WO2015001421A2 publication Critical patent/WO2015001421A2/en
Publication of WO2015001421A3 publication Critical patent/WO2015001421A3/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/506—Multiwavelength transmitters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1028—Coupling to elements in the cavity, e.g. coupling to waveguides adjacent the active region, e.g. forward coupled [DFC] structures
    • H01S5/1032—Coupling to elements comprising an optical axis that is not aligned with the optical axis of the active region
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/572—Wavelength control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
    • H01S5/0612—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by temperature
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems

Definitions

  • the present disclosure relates to the field of optical network technology, and particularly, to a wavelength tunable transmitter for bandwidth symmetric TWDM-PON and an ONU including such a wavelength tunable transmitter.
  • TWDM-PON hybrid time and wavelength division multiplexing passive optical access network
  • the conventional XG-PON system provides a downstream rate of 10 Gb/s and an upstream rate of 2.5 Gb/s and the TWDM-PON system usually uses four pairs of wavelength and thus can provide a downstream rate of 40 Gb/s and an upstream rate of 10 Gb/s.
  • the optical line terminal OLT in such a TWDM-PON system usually generates four downstream wavelengths by four continuous-wave lasers.
  • a wavelength tunable transmitter is required to be equipped in the ONU to generate any one of the four wavelengths.
  • such a laser includes tunable DFB laser, external injection locked laser and self-seeding injection locked laser.
  • the tunable wavelength of a tunable DFB laser is achieved by temperature controlling and the tunable wavelength range is limited, thus the modulation rate is usually less than 10 Gb/s; the other two types of lasers also have its own drawbacks and the modulation speed is also less than 10 Gb/s. Therefore, the uplink speed of the conventional ONU is limited and it is not desired for the exponentially growing data amount.
  • a first aspect of the invention proposes a wavelength tunable transmitter for bandwidth symmetric TWDM-PON, comprising:
  • a multi-mode transmitter for outputting an optical signal containing a plurality of longitudinal modes
  • an optical circulator including a first port for receiving the optical signal from the multi-mode transmitter, a second port for outputting the optical signal and a third port;
  • a first micro-ring resonator including a first input for receiving the optical signal from the second port, a first output for outputting a first component of the resonant portion of the optical signal and a second output for outputting a second component of the resonant portion of the optical signal, wherein the second output is connected to the third port of the optical circulator.
  • the transmitter according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal containing the plurality of longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the plurality of longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.
  • the first component is smaller than the second component, such that the majority of the second component is feedback into the optical circulator to suppress the optical signal with other wavelengths.
  • the transmitter further comprises:
  • a second micro-ring resonator for modulating the first component of the resonant portion of the optical signal at a first modulation speed.
  • the optical signal selected by the first micro-ring resonator could be modulated.
  • the first modulation speed is at least 10 Gb/s.
  • the modulation speed of 10 Gb/s or even more could be achieved and thus the communication speed requirements of the next generation optical network (NG-PON) could be satisfied.
  • the transmitter further comprises a second control means for controlling the second micro-ring resonator, and wherein the second control means adjusts the second micro-ring resonator by using thermal-heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator.
  • the temperature adjustment and the corresponding parameter of the electro-optic effect could be controlled by the second control means and thus the second micro-ring resonator could modulate the optical signal with a first wavelength.
  • the multi-mode transmitter is an FP-LD for generating an optical signal containing at least four different longitudinal modes.
  • the multi-mode transmitter includes many types and FP-LD multi-mode transmitter is one type of them which is cost effective, namely the manufacture cost of the wavelength tunable transmitter is further reduced in such a manner and thus it is benefit for scale applications.
  • the transmitter further comprises a first control means for controlling the first micro-ring resonator, and wherein the first control means adjusts the first micro-ring resonator by using thermal-heating or electro-optic effect, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, wherein the first wavelength is the resonant wavelength of the first micro-ring resonator.
  • the controlling method of the first control means here is similar with the controlling method of the second control means mentioned above.
  • the first micro-ring resonator could select an optical signal with a first wavelength and thus the wavelength tuning capability according to the present invention could be achieved.
  • the free spectral ranges of the multi-mode transmitter and the first micro-ring resonator are FS i and FSR 2 respectively, FSRI and FSR2 satisfy the following relationship:
  • FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
  • the first micro-ring resonator will only select an optical signal with one kind of wavelength but not select more than one optical signal within the free spectral range of the first micro-ring resonator and thus the transmitter according to the present invention could exactly select the required optical signal from the multi-mode transmitter.
  • a second aspect of the invention proposes an optical network unit for bandwidth symmetric TWDM-PON, the optical network unit comprises a wavelength tunable transmitter according to the first aspect of the invention.
  • the optical network unit according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal with multiple longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the multiple longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.
  • Fig. l illustrates the schematic structural diagram 100 of the wavelength tunable transmitter according to the present invention
  • Figs.2(a)-2(c) illustrate the schematic diagram of the entire process for selecting the wavelength ⁇ by using the wavelength tunable transmitter according to the present invention
  • Figs.2(d)-2(f) illustrate the schematic diagram of the entire process for selecting the wavelength ⁇ 3 by using the wavelength tunable transmitter according to the present invention
  • Fig.2(g) illustrates the relationship between the FS s of the multi-mode transmitter and the first micro-ring resonator
  • Fig.3(a) illustrates the schematic diagram of the relationship between the two components of the first micro-ring resonator
  • Fig.3(b) illustrates the schematic diagram of the relationship between the two components of the second micro-ring resonator
  • Fig.4(a) illustrates the relationship between the frequency detuning and the temperature change
  • Fig.4(b) illustrates the relationship between frequency detuning change under different temperature changes
  • Fig.5 illustrates a working procedure flowchart 300 of the wavelength tunable transmitter for bandwidth symmetric TWDM-PON and the optical network unit including such a wavelength tunable transmitter.
  • a first aspect of the invention proposes a wavelength tunable transmitter 100 for bandwidth symmetric TWDM-PON, comprising:
  • a multi-mode transmitter 110 for outputting an optical signal containing a plurality of longitudinal modes
  • an optical circulator 120 including a first port 121 for receiving the optical signal from the multi-mode transmitter 110, a second port 122 for outputting the optical signal and a third port 123;
  • a first micro-ring resonator 130 including a first input 131 for receiving the optical signal from the second port 122, a first output 132 for outputting a first component of the resonant portion of the optical signal and a second output 133 for outputting a second component of the resonant portion of the optical signal, wherein the second output 133 is connected to the third port of the optical circulator 123.
  • the transmitter according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal with multiple longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the plurality of longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.
  • the first component is smaller than the second component, such that the majority of the second component is feedback into the optical circulator to suppress the optical signal with other wavelengths.
  • the transmitter further comprises:
  • a second micro-ring resonator 140 for modulating the first component of the resonant portion of the optical signal at a first modulation speed.
  • the optical signal selected by the first micro-ring resonator could be modulated.
  • the first modulation speed is at least 10 Gb/s.
  • the transmitter further comprises a second control means for controlling the second micro-ring resonator, and wherein the second control means adjusts the second micro-ring resonator by using thermal-heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator.
  • the temperature adjustment and the corresponding parameter of the electrical-optical effect could be controlled by the second control means and thus the second micro-ring resonator could modulate the optical signal with a first wavelength.
  • the multi-mode transmitter is an FP-LD for generating an optical signal containing at least four different longitudinal modes.
  • the multi-mode transmitter includes many types and FP-LD multi-mode transmitter is one type of them which is cost effective, namely the manufacture cost of the wavelength tunable transmitter is further reduced in such a manner and thus it is benefit for scale applications.
  • the transmitter further comprises a first control means for controlling the first micro-ring resonator, and the first control means adjusts the first micro-ring resonator by using thermal-heating or electro-optic effect, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, wherein the first wavelength is the resonant wavelength of the first micro-ring resonator.
  • the controlling method of the first control means here is similar with the controlling method of the second control means mentioned above.
  • the first micro-ring resonator could select an optical signal with a first wavelength and thus the wavelength tuning capability according to the present invention could be achieved.
  • the free spectral ranges of the multi-mode transmitter and the first micro-ring resonator are FS i and FSR 2 respectively, FSRI and FSR2 satisfy the following relationship:
  • FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
  • the first micro-ring resonator will only select an optical signal with one kind of wavelength but not select more than one optical signal within the free spectral range of the first micro-ring resonator and thus the transmitter according to the present invention could exactly select the required optical signal from the multi-mode transmitter.
  • Fig.2 illustrates the principle of selecting one wavelength from the four different optical signals transmitted by the FP-LD multi-mode transmitter; the four different wavelengths are ⁇ 1 ; ⁇ 2 , ⁇ 3 , ⁇ 4 .
  • the Fig.2(a) of Fig.2 illustrates FP-LD output spectrum spacing 200 GHz and Fig.2(b) illustrates the transmitting spectrum of the first micro-ring resonator spacing 212 GHz.
  • the transmitting spectra of the FP-LD and the first micro-ring resonator are so configured because it must be ensured that only one optical signal with one wavelength will be selected within the FP-LD output spectrum.
  • the selected wavelength in Fig.2(c) is ⁇
  • Figs.2(d)-2(f) illustrate the schematic diagram of the entire process for selecting the wavelength ⁇ 3 by using the wavelength tunable transmitter according to the present invention
  • Fig.2(g) illustrates the relationship between the FSRs of the multi-mode transmitter and the first micro-ring resonator, namely FSR2>FSR1 *FWHM/(FWHM+FSR1) or FSR2 ⁇ FSR1 *FWHM/(FWHM-FSR1), wherein FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
  • a first control means for controlling the first micro-ring resonator (not shown in the figure) utilizes thermal-heating or electro-optic effect to adjust the first micro-ring resonator, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, the specific procedure is shown in Fig.2, the first wavelength is the resonant wavelength of the first micro-ring resonator.
  • the first component of the resonant portion enters into the second micro-ring resonator for the succeed processing via the port 132, while the other component namely the second component of the resonant portion enters back into the FP-LD multi-mode transmitter 110 via the optical circulator 120 and it is further used for suppressing the optical signal with other wavelengths, and finally an optical signal with the required wavelength and stable strength is generated at the port 132.
  • the first component is not bigger than the second component and thus it is benefit for suppressing signals with other wavelengths, so as to output a stable outputting signal.
  • the second micro-ring resonator 140 further modulates the optical signal obtained from the first micro-ring resonator and transmits the modulated signal via the port 143.
  • the second micro-ring resonator is configured to have a second control means and the second control means is configured to adjust the second micro-ring resonator by using thermal-heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator, for example, the first component is 20% and the second component is 80%.
  • the configuration of the power component percentage could be achieved by changing the coupling coefficient of the first micro-ring resonator. Those skilled in the art should understand that the percentage here is only illustrative but not for limiting the protection scope of the present invention.
  • Fig.3(a) illustrates the schematic diagram of the relationship between the two components of the first micro-ring resonator.
  • the solid line represents the second component and the dashed line represents the first component.
  • the first component and the second component compensate with each other and the sum of the first component and the second component is the entire optical signal.
  • the first component is fast 100% at the non-resonant frequency while the second component is fast 0%.
  • the first component is 20% at the resonant frequency while the second component is 80%.
  • the configuration of the power component percentage could be achieved by changing the coupling coefficient of the first micro-ring resonator.
  • Fig.3(b) illustrates the schematic diagram of the relationship between the two components of the second micro-ring resonator.
  • figure 3(a) The difference between figure 3(a) and figure 3(b) is that fast all the optical signal will be outputted by the second micro-ring resonator at the resonant frequency while fast all the optical signal will not be outputted at the non-resonant frequency, namely the outputted signal of the entire transmitter 100 will be zero.
  • Fig.4(a) illustrates the relationship between the frequency detuning and the temperature change.
  • the relationship between the frequency detuning and temperature change is fast linear and the linear characteristic is benefit for controlling the frequency detuning.
  • the wavelength sensitivity is fast 10.8GHz/°C.
  • fast a range of 20°C could achieve the scanning of the whole free spectral range FSR.
  • Fig.4(b) further illustrates the relationship between frequency detuning changes under different temperature changes. As can be seen from Fig.4(b), fast each 5°C of the temperature change could achieve 1/4 frequency detuning of the whole free spectral range FSR.
  • Fig.5 illustrates a working procedure flowchart 300 of the wavelength tunable transmitter for bandwidth symmetric TWDM-PON and the optical network unit including such a wavelength tunable transmitter.
  • the method begins at step 510, and then in step 511 the FP-LD generates an optical signal containing a plurality of longitudinal modes and send it to the optical circulator; in step 512 the first micro-ring resonator of Fig.
  • step 513 the target longitudinal mode is filtered and the optical signal of the target longitudinal mode is reflected, wherein the first micro-ring resonator 130 has a different free spectral range in comparison view of the FP-LD; in step 514 the optical signal with the resonant wavelength selected by the first micro-ring resonator 130 is feedback into the FP-LD via an optical circulator 120 to suppress signals with other wavelengths; in step 515 a gain cavity is generated between the FP-LD and a first micro-ring resonator to generate a stable signal at the resonant wavelength; then in step 516 the optical signal generated in step 515 will be transmitted to the second micro-ring resonator 140; in step 517 it is determined whether a detuning is required, if not the upstream data will be modulated at a high rate in step 518 and a bandwidth symmetric TWDM-PON is applied to the second micro-ring re
  • a second aspect of the invention proposes an optical network unit for bandwidth symmetric TWDM-PON, the optical network unit comprises a wavelength tunable transmitter according to the first aspect of the invention.
  • the optical network unit according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal with multiple longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the multiple longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.

Abstract

The invention relates to a wavelength tunable transmitter (100) for bandwidth symmetric TWDM-PON, comprising: multi-mode transmitter (110) for outputting an optical signal containing a plurality of longitudinal modes; optical circulator (120) including a first port for receiving the optical signal from the multi-mode, a second port for outputting the optical signal and a third port; and a first micro-ring resonator (130) including a first input for receiving the optical signal from the second port, a first output for outputting a first component of the resonant portion of the optical signal and a second output for outputting a second component of the resonant portion of the optical signal, wherein the second output is connected to the third port of the optical circulator (120).

Description

Wavelength Tunable Transmitter for TWDM-PON and ONU
Field of the invention
The present disclosure relates to the field of optical network technology, and particularly, to a wavelength tunable transmitter for bandwidth symmetric TWDM-PON and an ONU including such a wavelength tunable transmitter.
Background of the invention
Recently, hybrid time and wavelength division multiplexing passive optical access network (TWDM-PON) was selected as the primary solution for NGPON2 by the FSAN community in the April 2012 meeting. Due to its unique features of high system capacity, flexible bandwidth allocation, improved power efficiency by dynamic load balancing and low capital expenditure when comparing with the other candidate solutions, the TWDM-PON has attracted the majority support from global vendors and it is expected that TWDM-PON will be applied more and more.
The conventional XG-PON system provides a downstream rate of 10 Gb/s and an upstream rate of 2.5 Gb/s and the TWDM-PON system usually uses four pairs of wavelength and thus can provide a downstream rate of 40 Gb/s and an upstream rate of 10 Gb/s. However, the optical line terminal OLT in such a TWDM-PON system usually generates four downstream wavelengths by four continuous-wave lasers. A wavelength tunable transmitter is required to be equipped in the ONU to generate any one of the four wavelengths. Currently, such a laser includes tunable DFB laser, external injection locked laser and self-seeding injection locked laser. The tunable wavelength of a tunable DFB laser is achieved by temperature controlling and the tunable wavelength range is limited, thus the modulation rate is usually less than 10 Gb/s; the other two types of lasers also have its own drawbacks and the modulation speed is also less than 10 Gb/s. Therefore, the uplink speed of the conventional ONU is limited and it is not desired for the exponentially growing data amount.
Summary of the invention
In view of the prior art and the technical problem thereof identified as above, it is desirable to provide a wavelength tunable transmitter with low cost and high speed and an optical network unit including such a transmitter.
A first aspect of the invention proposes a wavelength tunable transmitter for bandwidth symmetric TWDM-PON, comprising:
a multi-mode transmitter for outputting an optical signal containing a plurality of longitudinal modes;
an optical circulator including a first port for receiving the optical signal from the multi-mode transmitter, a second port for outputting the optical signal and a third port; and
a first micro-ring resonator including a first input for receiving the optical signal from the second port, a first output for outputting a first component of the resonant portion of the optical signal and a second output for outputting a second component of the resonant portion of the optical signal, wherein the second output is connected to the third port of the optical circulator.
The transmitter according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal containing the plurality of longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the plurality of longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.
In one embodiment of the present invention, the first component is smaller than the second component, such that the majority of the second component is feedback into the optical circulator to suppress the optical signal with other wavelengths.
In one embodiment of the present invention, the transmitter further comprises:
a second micro-ring resonator for modulating the first component of the resonant portion of the optical signal at a first modulation speed.
In such a manner, the optical signal selected by the first micro-ring resonator could be modulated.
In one embodiment of the present invention, the first modulation speed is at least 10 Gb/s.
In such a manner, the modulation speed of 10 Gb/s or even more could be achieved and thus the communication speed requirements of the next generation optical network (NG-PON) could be satisfied.
In one embodiment of the present invention, the transmitter further comprises a second control means for controlling the second micro-ring resonator, and wherein the second control means adjusts the second micro-ring resonator by using thermal-heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator.
In such a manner, the temperature adjustment and the corresponding parameter of the electro-optic effect could be controlled by the second control means and thus the second micro-ring resonator could modulate the optical signal with a first wavelength.
In one embodiment of the present invention, the multi-mode transmitter is an FP-LD for generating an optical signal containing at least four different longitudinal modes.
Those skilled in the art should understand that the multi-mode transmitter includes many types and FP-LD multi-mode transmitter is one type of them which is cost effective, namely the manufacture cost of the wavelength tunable transmitter is further reduced in such a manner and thus it is benefit for scale applications.
In one embodiment of the present invention, the transmitter further comprises a first control means for controlling the first micro-ring resonator, and wherein the first control means adjusts the first micro-ring resonator by using thermal-heating or electro-optic effect, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, wherein the first wavelength is the resonant wavelength of the first micro-ring resonator.
The controlling method of the first control means here is similar with the controlling method of the second control means mentioned above. In such a manner the first micro-ring resonator could select an optical signal with a first wavelength and thus the wavelength tuning capability according to the present invention could be achieved.
In one embodiment of the present invention, the free spectral ranges of the multi-mode transmitter and the first micro-ring resonator are FS i and FSR2 respectively, FSRI and FSR2 satisfy the following relationship:
FSR2>FSR1 *FWHM/(FWHM+FSR1) or
FSRKFSR1 *FWHM/(FWHM-FSR1), wherein
FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
In such a manner, it is ensured that the first micro-ring resonator will only select an optical signal with one kind of wavelength but not select more than one optical signal within the free spectral range of the first micro-ring resonator and thus the transmitter according to the present invention could exactly select the required optical signal from the multi-mode transmitter.
Furthermore, a second aspect of the invention proposes an optical network unit for bandwidth symmetric TWDM-PON, the optical network unit comprises a wavelength tunable transmitter according to the first aspect of the invention. The optical network unit according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal with multiple longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the multiple longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.
Brief description of drawings
Other features, objects and advantages of the invention will become more apparent upon review of the following detailed description of non-limiting embodiments taken with reference to the drawings in which:
Fig. l illustrates the schematic structural diagram 100 of the wavelength tunable transmitter according to the present invention;
Figs.2(a)-2(c) illustrate the schematic diagram of the entire process for selecting the wavelength λι by using the wavelength tunable transmitter according to the present invention;
Figs.2(d)-2(f) illustrate the schematic diagram of the entire process for selecting the wavelength λ3 by using the wavelength tunable transmitter according to the present invention;
Fig.2(g) illustrates the relationship between the FS s of the multi-mode transmitter and the first micro-ring resonator;
Fig.3(a) illustrates the schematic diagram of the relationship between the two components of the first micro-ring resonator;
Fig.3(b) illustrates the schematic diagram of the relationship between the two components of the second micro-ring resonator;
Fig.4(a) illustrates the relationship between the frequency detuning and the temperature change;
Fig.4(b) illustrates the relationship between frequency detuning change under different temperature changes; and
Fig.5 illustrates a working procedure flowchart 300 of the wavelength tunable transmitter for bandwidth symmetric TWDM-PON and the optical network unit including such a wavelength tunable transmitter.
Identical or similar devices (modules) or steps will be denoted by identical or similar reference numerals throughout the drawings.
Detailed description of embodiments
The following particular description of preferred embodiments will be given with reference to the drawings constituting a part of the invention. The drawings exemplarily illustrate particular embodiments, in which the invention can be practiced. The exemplary embodiments are not intended to exhaust all the embodiments of the invention. As can be appreciated, other embodiments can be possible or structural or logical modifications can be made without departing from the scope of the invention. Thus the following detailed description is not intended to be limiting, and the scope of the invention will be defined as in the appended claims.
A first aspect of the invention proposes a wavelength tunable transmitter 100 for bandwidth symmetric TWDM-PON, comprising:
a multi-mode transmitter 110 for outputting an optical signal containing a plurality of longitudinal modes;
an optical circulator 120 including a first port 121 for receiving the optical signal from the multi-mode transmitter 110, a second port 122 for outputting the optical signal and a third port 123; and
a first micro-ring resonator 130 including a first input 131 for receiving the optical signal from the second port 122, a first output 132 for outputting a first component of the resonant portion of the optical signal and a second output 133 for outputting a second component of the resonant portion of the optical signal, wherein the second output 133 is connected to the third port of the optical circulator 123.
The transmitter according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal with multiple longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the plurality of longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention.
In one embodiment of the present invention, the first component is smaller than the second component, such that the majority of the second component is feedback into the optical circulator to suppress the optical signal with other wavelengths.
In one embodiment of the present invention, the transmitter further comprises:
a second micro-ring resonator 140 for modulating the first component of the resonant portion of the optical signal at a first modulation speed.
In such a manner, the optical signal selected by the first micro-ring resonator could be modulated.
In one embodiment of the present invention, the first modulation speed is at least 10 Gb/s.
In such a manner, the modulation speed of 10 Gb/s or even more could be achieved and thus the communication speed requirements of the next generation optical network could be satisfied.
In one embodiment of the present invention, the transmitter further comprises a second control means for controlling the second micro-ring resonator, and wherein the second control means adjusts the second micro-ring resonator by using thermal-heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator.
In such a manner, the temperature adjustment and the corresponding parameter of the electrical-optical effect could be controlled by the second control means and thus the second micro-ring resonator could modulate the optical signal with a first wavelength.
In one embodiment of the present invention, the multi-mode transmitter is an FP-LD for generating an optical signal containing at least four different longitudinal modes.
Those skilled in the art should understand that the multi-mode transmitter includes many types and FP-LD multi-mode transmitter is one type of them which is cost effective, namely the manufacture cost of the wavelength tunable transmitter is further reduced in such a manner and thus it is benefit for scale applications.
In one embodiment of the present invention, the transmitter further comprises a first control means for controlling the first micro-ring resonator, and the first control means adjusts the first micro-ring resonator by using thermal-heating or electro-optic effect, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, wherein the first wavelength is the resonant wavelength of the first micro-ring resonator.
The controlling method of the first control means here is similar with the controlling method of the second control means mentioned above. In such a manner the first micro-ring resonator could select an optical signal with a first wavelength and thus the wavelength tuning capability according to the present invention could be achieved.
In one embodiment of the present invention, the free spectral ranges of the multi-mode transmitter and the first micro-ring resonator are FS i and FSR2 respectively, FSRI and FSR2 satisfy the following relationship:
FSR2>FSR1 *FWHM/(FWHM+FSR1) or
FSRKFSR1 *FWHM/(FWHM-FSR1), wherein
FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
In such a manner, it is ensured that the first micro-ring resonator will only select an optical signal with one kind of wavelength but not select more than one optical signal within the free spectral range of the first micro-ring resonator and thus the transmitter according to the present invention could exactly select the required optical signal from the multi-mode transmitter.
Fig.2 illustrates the principle of selecting one wavelength from the four different optical signals transmitted by the FP-LD multi-mode transmitter; the four different wavelengths are λ1 ; λ2, λ3, λ4. The Fig.2(a) of Fig.2 illustrates FP-LD output spectrum spacing 200 GHz and Fig.2(b) illustrates the transmitting spectrum of the first micro-ring resonator spacing 212 GHz. The transmitting spectra of the FP-LD and the first micro-ring resonator are so configured because it must be ensured that only one optical signal with one wavelength will be selected within the FP-LD output spectrum. For example, the selected wavelength in Fig.2(c) is λχ , and Figs.2(d)-2(f) illustrate the schematic diagram of the entire process for selecting the wavelength λ3 by using the wavelength tunable transmitter according to the present invention. Fig.2(g) illustrates the relationship between the FSRs of the multi-mode transmitter and the first micro-ring resonator, namely FSR2>FSR1 *FWHM/(FWHM+FSR1) or FSR2<FSR1 *FWHM/(FWHM-FSR1), wherein FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
Referring to Fig.1 , the working principle of the first resonator and the second resonator is illustrated. A first control means for controlling the first micro-ring resonator (not shown in the figure) utilizes thermal-heating or electro-optic effect to adjust the first micro-ring resonator, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, the specific procedure is shown in Fig.2, the first wavelength is the resonant wavelength of the first micro-ring resonator. The first component of the resonant portion enters into the second micro-ring resonator for the succeed processing via the port 132, while the other component namely the second component of the resonant portion enters back into the FP-LD multi-mode transmitter 110 via the optical circulator 120 and it is further used for suppressing the optical signal with other wavelengths, and finally an optical signal with the required wavelength and stable strength is generated at the port 132. Generally, the first component is not bigger than the second component and thus it is benefit for suppressing signals with other wavelengths, so as to output a stable outputting signal. The second micro-ring resonator 140 further modulates the optical signal obtained from the first micro-ring resonator and transmits the modulated signal via the port 143. The second micro-ring resonator is configured to have a second control means and the second control means is configured to adjust the second micro-ring resonator by using thermal-heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator, for example, the first component is 20% and the second component is 80%. The configuration of the power component percentage could be achieved by changing the coupling coefficient of the first micro-ring resonator. Those skilled in the art should understand that the percentage here is only illustrative but not for limiting the protection scope of the present invention.
Fig.3(a) illustrates the schematic diagram of the relationship between the two components of the first micro-ring resonator. As can be seen from the figure, the solid line represents the second component and the dashed line represents the first component. The first component and the second component compensate with each other and the sum of the first component and the second component is the entire optical signal. The first component is fast 100% at the non-resonant frequency while the second component is fast 0%. The first component is 20% at the resonant frequency while the second component is 80%. The configuration of the power component percentage could be achieved by changing the coupling coefficient of the first micro-ring resonator. Fig.3(b) illustrates the schematic diagram of the relationship between the two components of the second micro-ring resonator. The difference between figure 3(a) and figure 3(b) is that fast all the optical signal will be outputted by the second micro-ring resonator at the resonant frequency while fast all the optical signal will not be outputted at the non-resonant frequency, namely the outputted signal of the entire transmitter 100 will be zero.
Fig.4(a) illustrates the relationship between the frequency detuning and the temperature change. As can be seen from this figure, the relationship between the frequency detuning and temperature change is fast linear and the linear characteristic is benefit for controlling the frequency detuning. As can be seen from this figure, the wavelength sensitivity is fast 10.8GHz/°C. Thus, fast a range of 20°C could achieve the scanning of the whole free spectral range FSR. Fig.4(b) further illustrates the relationship between frequency detuning changes under different temperature changes. As can be seen from Fig.4(b), fast each 5°C of the temperature change could achieve 1/4 frequency detuning of the whole free spectral range FSR. Therefore, it is easy to achieve the frequency detuning illustrated in Figs.2(a)-2(f). Since the resonant frequency of the first and the second resonator is periodical, it is not needed to change the temperature continuously within 4FSR to adjust the wavelength from λι to λ4, in contrary, the present invention only needs to make adjustment in one FSR and thus the temperature resonant range is smaller and the resonant speed is more quick.
Fig.5 illustrates a working procedure flowchart 300 of the wavelength tunable transmitter for bandwidth symmetric TWDM-PON and the optical network unit including such a wavelength tunable transmitter. As can be seen from Fig.5, the method begins at step 510, and then in step 511 the FP-LD generates an optical signal containing a plurality of longitudinal modes and send it to the optical circulator; in step 512 the first micro-ring resonator of Fig. l aligns its resonant wavelength with the required to be selected target longitudinal mode and select it out; in step 513 the target longitudinal mode is filtered and the optical signal of the target longitudinal mode is reflected, wherein the first micro-ring resonator 130 has a different free spectral range in comparison view of the FP-LD; in step 514 the optical signal with the resonant wavelength selected by the first micro-ring resonator 130 is feedback into the FP-LD via an optical circulator 120 to suppress signals with other wavelengths; in step 515 a gain cavity is generated between the FP-LD and a first micro-ring resonator to generate a stable signal at the resonant wavelength; then in step 516 the optical signal generated in step 515 will be transmitted to the second micro-ring resonator 140; in step 517 it is determined whether a detuning is required, if not the upstream data will be modulated at a high rate in step 518 and a bandwidth symmetric TWDM-PON is applied to the second micro-ring resonator and then the method ends in step 520; in contrast if a detuning is required then the resonant wavelength of the second micro-ring resonator is adjusted to the required upstream wavelength in step 519 and then the method enters into 518 and implements as mentioned above.
Furthermore, a second aspect of the invention proposes an optical network unit for bandwidth symmetric TWDM-PON, the optical network unit comprises a wavelength tunable transmitter according to the first aspect of the invention. The optical network unit according to the present invention could achieve the wavelength tuning capability, namely an optical signal with a longitudinal mode is selected from the optical signal with multiple longitudinal modes transmitted by the multi-mode transmitter, so as to avoid to design a plurality of transmitting elements for the multiple longitudinal modes, and thus the manufacture cost and the complexity of the system structure of the wavelength tunable transmitter is reduced and it is benefit for the application of the wavelength tunable transmitter according to the present invention. Those skilled in the art shall appreciate that the invention apparently will not be limited to the foregoing exemplary embodiments and can be embodied in other specific forms without departing from the spirit or essence of the invention. Accordingly the embodiments shall be construed anyway to be exemplary and non-limiting. Moreover apparently the term "comprising" will not preclude another element(s) or step(s), and the term "a" or "an" will not preclude plural. A plurality of elements stated in an apparatus claim can alternatively be embodied as a single element. The terms "first", "second", etc., are intended to designate a name but not to suggest any specific order.

Claims

1. A wavelength tunable transmitter (100) for bandwidth symmetric TWDM-PON, comprising:
a multi-mode transmitter (110) for outputting an optical signal containing a plurality of longitudinal modes;
an optical circulator (120) including a first port for receiving the optical signal from the multi-mode transmitter, a second port for outputting the optical signal and a third port; and
a first micro-ring resonator (130) including a first input for receiving the optical signal from the second port, a first output for outputting a first component of the resonant portion of the optical signal and a second output for outputting a second component of the resonant portion of the optical signal, wherein the second output is connected to the third port of the optical circulator (120).
2. The transmitter according to claim 1 , wherein the first component is smaller than the second component.
3. The transmitter according to claim 1 , wherein the transmitter further comprises:
a second micro-ring resonator (140) for modulating the first component of the resonant portion of the optical signal at a first modulation speed.
4. The transmitter according to claim 3, wherein the first modulation speed is at least 10 Gb/s.
5. The transmitter according to claim 3, wherein the transmitter further comprises a second control means for controlling the second micro-ring resonator (140), and the second control means adjusts the second micro-ring resonator (140) by using thermal -heating or electro-optic effect, so as to modulate an optical signal with a first wavelength, wherein the first wavelength is the resonant wavelength of the second micro-ring resonator (140).
6. The transmitter according to claim 1 , wherein the multi-mode transmitter is an FP-LD for generating an optical signal containing at least four different longitudinal modes.
7. The transmitter according to claim 1 , wherein the transmitter further comprises a first control means for controlling the first micro-ring resonator (130), and wherein the first control means adjusts the first micro-ring resonator (130) by using thermal -heating or electro-optic effect, so as to select an optical signal with a first wavelength from the optical signal containing the plurality of longitudinal modes, wherein the first wavelength is the resonant wavelength of the first micro-ring resonator (130).
8. The transmitter according to claim 1 , wherein the free spectral ranges of the multi-mode transmitter and the first micro-ring resonator are FSRi and FS 2 respectively, FSR^ and FSR2 satisfying the following relationship:
FSR2>FSR1*FWHM/(FWHM+FSR1) or
F SR2<F SRj *F WHM/(F WHM-F SRj),
wherein FWHM is the half maximum of full bandwidth of the spectrum of the multi-mode transmitter.
9. An optical network unit for bandwidth symmetric T WDM-PON, characterized in that the optical network unit comprises a wavelength tunable transmitter according to any of claims 1 to 8.
PCT/IB2014/001526 2013-06-25 2014-06-19 Wavelength tunable transmitter for twdm-pon and onu WO2015001421A2 (en)

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