Method and optical network component for signal processing in an optical network and communication system

[0001] The invention relates to a method and to an optical network component for data processing in an optical network and to a communication system comprising such optical network component.

[0002] A passive optical network (PON) is a promising approach regarding fiber-to-the-home (FTTH), fiber-to-the-business (FTTB) and fiber-to-the-curb (FTTC) scenarios, in particular as it overcomes the economic limitations of traditional point-to-point solutions.

[0003] The PON has been standardized and it is currently being deptoyed by network service providers worldwide. Conventional PONS distribute downstream traffic from the optical line terminal (OLT) to optical network units (ONUs) in a broadcast manner while the ONUs send upstream data packets multiplexed in time to the OLT. Hence, communication among the ONUs needs to be conveyed through the OLT involving electronic processing such as buffering and/or scheduling, which results in latency and degrades the throughput of the network.

[0004] In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one strand of fiber.

[0005] WDM systems are divided into different wavelength patterns, conventional or coarse and dense WDM. WDM systems provide, e.g., up to 16 channels in the 3rd transmission window (Cband) of silica fibers around 1550 nm. Dense WDM uses the same transmission window but with denser channel spacing. Channel plans vary, but a typical system may use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing. Some technologies are capable of 25 GHz spacing. Amplification options enable the extension of the usable wavelengths to the L-band, more or less doubling these numbers.

[0006] Optical access networks, e.g., a coherent Ultra-Dense Wavelength Division Multiplex (UDWDM) network, are deemed to be the future data access technology.

[0007] Within the UDWDM concept, potentially all wavelengths are routed to each ONU. The respective wavelength is selected by the tuning of the local oscillator (LO) laser at the ONU. Other wavelengths also arriving at the ONT result in an optical offset and increase the noise of the signal to be detected. A sufficiently strong LO renders the contributions of such other wavelengths minor compared to the signal itself.

[0008] The problem to be solved is to overcome the disadvantages as described above and in particular to allow for an efficient optical signal processing.

[0009] This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims.

[0010] In order to overcome this problem, a method for signal processing in an optical network is provided,

• • [0011] receiving a first optical signal in form of a data signal by a tunable filter and
  • [0012] providing a selected first optical signal having a required wavelength;
  • [0013] providing an allocated second optical signal as a local oscillator signal generated by a laser; determining a wavelength of the second optical signal by the tunable filter as a component of the laser and directly adjusting the laser, and
  • [0014] tuning said selecting first optical signal and tuning said second optical signal simultaneously by setting said tunable filter.

[0015] In a next embodiment, the tunable filter is reflecting the selected first optical signal and reflecting the second optical signal being a component of the laser.

[0016] In a further embodiment, the selected first optical signal is passing the tunable filter and the second optical signal is passing the tunable filter being a component of the laser.

[0017] In another embodiment, the tunable filter is a dielectric filter.

[0018] Hence, contributions of the other wavelengths arriving at an optical network element, e.g., an ONU or an OLT, could be efficiently suppressed thereby increasing both the receiver's sensitivity and the signal-to-noise ratio.

[0019] In another embodiment, the tunable filter is an angle-tunable filter.

[0020] The tunable filter may in particular be a mechanical and/or electrical component influencing the first signal and the second signal via a single adjustment.

[0021] Pursuant to another embodiment, the first signal and the second signal are conveyed via waveguides, wherein said waveguides are offset to each other.

[0022] In case the waveguides are arranged offset to one another, e.g., crosstalk can be efficiently reduced or avoided.

[0023] According to an embodiment, said tunable element provides a mechanical and/or an electrical coupling for tuning the selected first optical signal and the second optical signal.

[0024] In particular, a single adjustment of the tunable element has an impact on the first signal and on the second signal.

[0025] According to another embodiment, said method is processed in an optical network element, in particular in an ONU and/or in an OLT.

[0026] Another embodiment comprises combining the selected first optical signal with the second optical signal for coherent demodulation.

[0027] This efficiently allows coherent reception in particular within an OLT or an ONU.

[0028] The problem stated above is also solved by an optical network component comprising

• • [0029] a tunable filter receiving a first optical signal in form of a data signal and providing a selected first optical signal having a required wavelength;
  • [0030] an adjustable laser providing an allocated second optical signal as a local oscillator signal;
  • [0031] the laser comprising a gain element and also said tunable filter as a laser component determining a wavelength of the second optical signal; and
  • [0032] the tunable filter being configured for tuning simultaneously said selected first optical signal and said second optical signal.

[0033] According to an embodiment, wherein said tunable filter is configured to tune simultaneously the first optical signal and the second optical signal via mechanical and/or electrical coupling.

[0034] According to an embodiment, wherein the selected first optical signal is reflected by the tunable filter and the second optical signal is reflected by the tunable filter as a component of the laser.

[0035] According to another embodiment, wherein the selected first optical signal is passing the tunable filter and the second optical signal is passing the tunable filter being a component of the laser.

[0036] Both versions, mirror or bandpass, of the tunable optical filter are possible.

[0037] According to another embodiment, said tunable filter is an angle-tunable dielectric filter.

[0038] According to another embodiment, the optical component is configured as a component of an optical network unit or of an optical line terminal.

[0039] The problem stated supra is further solved by a communication system comprising the optical network component as described herein.

[0040] Embodiments of the invention are shown and illustrated in the following figures:

[0043] The approach provided herein enables a tunable element of an optical component to be used for filtering purposes.

[0044] Said tunable element may in particular be or comprise a dielectric filter that determines the wavelength of a local oscillator (LO).

[0045] FIG. 1 shows an optical gain element 106 (e.g., a laser active medium) providing an optical signal via a waveguide 105 and a lens 104 to a filter 103, which is in particular an angle-tunable dielectric filter. The combination of said filter 103 and the optical gain element 106 comprising a mirror 107 constitutes a tunable laser 108, i.e. the tunable laser 108 can be adjusted via said filter 103.

[0046] On the other hand, a data signal is conveyed via a waveguide 101 to a circulator 102, which feeds the data signal towards the filter 103 and the reflection or signal provided by the filter 103 to a splitter 109. The splitter 109 supplies its input signal to a modulator 111 and further via a fiber (not shown) to a remote receiver as well as to a local receiver 110 for further processing purposes.

[0047] Hence the filter 103 has an impact on the data signal conveyed via the circulator 102 as well as on the signal provided by the optical gain element 106.

[0048] The filter 103 may serve as a mirror for the laser 106 and the back side of the filter 103 may serve as a mirror for the data signal.

[0049] The filter 103 may provide a physical impact due to its positioning to both, the LO signal as well as the data signal.

[0050] Hence, the filter 103 can be used for selecting and/or adjusting the wavelength of the LO as well as it can be used for filtering the incoming data signal. In particular, the signal wavelength required (including, e.g., some (few) neighboring channels) is reflected by said filter 103.

[0051] In case the tunable laser 108 is adjusted by moving the angle of the filter 103, the data signal as well as the LO signal provided by the tunable laser 108 are adjusted accordingly, i.e. dependent on such movement or position of the filter 103.

[0052] Advantageously, the wavelength of the data signal and the wavelength of the laser signal (LO signal) can be automatically aligned by said filter without any need for additional elements or components.

[0053] In case the incoming data signal is too strong and the wavelength passing the filter 103 may have an impact on the optical gain element 106, the signal waveguide 101 and the laser waveguide 105 could be arranged in a slightly offset way to avoid such effect. In addition, cross-talk could be reduced or avoided by such offset arrangement of the waveguides 101 and 105.

[0054] It is a further advantage that an integrated photonic circuit can be used thus gaining receiver sensitivity.

[0055] The arrangement shown in FIG. 1 can be provided with an optical network component, e.g., with an OLT or an ONU.

[0056] FIG. 2 shows an exemplary arrangement as how an incoming and an outgoing signal may be influenced by a single tunable element, e.g., a filter.

[0057] An optical gain element 201 comprises a Semiconductor Optical Amplifier (SOA) 205 via which a signal is being conveyed towards a filter 203 and reflected by a mirror (or reflector) 204 back to the optical gain element 201. Hence, the filter 203 can be used to adjust a wavelength of a laser. The optical gain element 201 comprises a mirror 202 that is used to reflect the incoming signal from the filter 203 to be modulated by a modulator 209 and provided as an output signal “Signal Out” 207.

[0058] It is noted that the optical gain element may be a laser diode comprising an anti-reflection coating.

[0059] In addition, an input signal (data signal, “Signal In” 210) can be fed via the filter 203 to a photodiode 208.

[0060] The filter 203 may be realized as a mechanical component comprising a rotational axis 206 such that the impact to the signal generated by the laser 201 and the input signal corresponds to the positioning or movement of said filter.

[0061] The filter 203 can be adjusted by a piezo-electric actuator, e.g. a motor or the like.

[0062] Furthermore, the signal conveyed from the optical gain element 201 towards the mirror 204 may in addition be utilized and/or combined with the input signal “Signal In” 210 to allow for a coherent reception.

• [0063] OLT Optical Line Terminal
• [0064] ONU Optical Network Unit
• [0065] PD Photo Diode
• [0066] PON Passive Optical Network
• [0067] SOA Semiconductor Optical Amplifier
• [0068] UDWDM Ultra Dense WDM
• [0069] WDM Wavelength Division Multiplex