JP3643281B2 - Optical signal processing circuit and optical signal processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical signal processing circuit and an optical signal processing method, and more particularly to an optical serial-parallel conversion circuit that converts a high-speed optical signal into a plurality of lower-speed optical signals and a processing method therefor.
[0002]
[Prior art]
With the development of optical signal transmission technology and optical signal processing technology, it has become necessary to handle higher speed optical signals. However, when the signal speed is increased, there is a problem that electrical processing becomes extremely difficult when performing signal processing. For this reason, it is necessary to convert a high-speed optical signal into an optical serial-parallel signal and reduce it to a low signal speed that can be electrically processed.
[0003]
However, as a conventional optical serial-parallel conversion processing method, a method using surface emission second harmonic generation (Shih-Chen Wang et al., J. Lightwave Technol. Vol. 14, No. 12, p. 2736 ( 1996)), a method using an excitonic giant nonlinear effect (K.Ema et al.Appl.Phys.Lett.Vol.59 No.25 p.2799 (1991)), and a hologram. A method (PCSun et al., Opt. Lett. Vol. 20, No. 16, p1728 (1995)) exists.
[0004]
[Problems to be solved by the invention]
However, since the first method uses the surface nonlinear effect, there is a problem that the efficiency is extremely poor and the loss is very large. Further, the second method has a problem that the nonlinear medium needs to be cooled to the liquid helium temperature in order to obtain a large nonlinear effect, and probe light is required. Furthermore, since the third method uses a diffraction effect, there are problems such as extremely large loss and the need for probe light. Therefore, all of the above-described methods require extreme running costs, are inefficient, and have a problem that it is very difficult to maintain stable performance over a long period of time.
[0005]
The present invention has been made in view of such problems, and an object of the present invention is to provide a stable and simple optical signal processing circuit and optical signal processing method that have little loss and do not require probe light. There is.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an optical signal processing circuit for converting a high-speed optical signal into a plurality of lower-speed optical signals. A time for distributing incident signal light to the plurality of optical paths, and converting time-series signal light into spatial signal light on the emission surface of the plurality of optical paths; Spatial conversion means and first Fourier transform / imaging that spatially Fourier transforms and images the spatial signal light output from the time-space conversion means and spatially expands the temporal spectrum of the incident signal. means and, arranged in the vicinity of the focal plane of the Fourier transform and imaging means of the first, with respect to the temporal spectrum spatially deployed, each Fourier phase component of each fixed time only Fourier phase time so as to maintain a constant To the phase modulator array for modulating, output from the phase modulator array, the spatial signal light Fourier phase was kept constant by receiving time modulation, the second to the spatial Fourier transform and imaging again A Fourier transform / imaging means is provided.
[0007]
According to a second aspect of the present invention, in the first aspect of the present invention, the time-space conversion means is composed of an arrayed waveguide, and the first and second imaging means are Fourier-transformed spatial signal light. It is characterized by comprising a slab waveguide having a function.
[0008]
According to a third aspect of the present invention, in the optical signal processing method for converting a high-speed optical signal into a plurality of lower-speed optical signals, a plurality of optical paths provided so as to give a certain time delay between adjacent optical paths are provided. A step of distributing incident signal light to the plurality of optical paths and converting time-series signal light into spatial signal light on an emission surface of the plurality of optical paths; and spatially Fourier transforming and imaging the spatial signal light. The time-frequency spectrum of the time-series signal light is developed as a spatial distribution, and the temporal change of the Fourier phase after the Fourier transform is modulated by temporal modulation for each time-frequency component. The step of keeping the phase term of the frequency spectrum constant over time and the Fourier transform image that keeps the Fourier phase constant are spatially Fourier transformed to serial-parallel transform the time-series signal light. It is characterized in that a step of generating a plurality of time-series optical signal of the low time density.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment of an optical signal processing circuit according to the present invention. In FIG. 1, reference numeral 101 denotes an input waveguide, reference numeral 102 denotes a slab waveguide, and the light from the input waveguide 101 is sent to the array waveguide 103. It has the function to distribute to. The arrayed waveguide 103 has a function of time-space converting incident signal light. Reference numeral 104 denotes a slab waveguide having a function of Fourier transforming each output light from the arrayed waveguide 103. That is, the frequency component of the input optical signal is spatially developed on the end face (focal plane) opposite to the end face connected to the arrayed waveguide 103 of the slab waveguide 104, and the spatial axis and the frequency axis are linear. They are proportional to each other through dispersion. A circuit configuration including the input waveguide 101, the slab waveguide 102, the arrayed waveguide 103, and the slab waveguide 104 is generally called an arrayed waveguide grating.
[0010]
Reference numeral 105 denotes a waveguide-type phase modulator array that can modulate the Fourier phase of the spectrum developed on the focal plane of the slab waveguide 104 temporally and independently for each spectral component. Reference numeral 106 denotes a slab waveguide, which has a function of converting the spectrum modulated by the phase modulator array 105 into a spatial waveform again. Reference numeral 107 denotes an output waveguide.
[0011]
The waveguides constituting the arrayed waveguide grating in FIG. 1 are deposited on a single crystal silicon substrate as a glass fine particle film in the order of a lower cladding layer and a core layer by the flame hydrolysis volume method (FHD method), and then annealed. It is heated to a high temperature in a furnace to form a transparent glass film covering the silicon substrate. Then, after patterning the waveguide, using dry etching to remove the unnecessary core layer, the upper cladding layer is deposited again using the FHD method, and heated to a high temperature to make the upper cladding layer transparent. Let
[0012]
As a core layer on a semiconductor layer such as InP, a semiconductor having a refractive index higher than that of a clad such as InGaAsP is epitaxially grown, and a semiconductor waveguide structure or core produced by patterning and etching is used for deuterated PMMA, and the clad is used for ultraviolet light. It is clear that a waveguide structure made of a polymer such as a curable resin has a similar function. In this case, it is desirable that the material is sufficiently transparent in the wavelength range to be used.
[0013]
The waveguide type phase modulator array 105 is an element that can apply an electric field to an electrode provided on a waveguide made on a lithium niobate substrate and change the phase by the electro-optic effect. It goes without saying that the same effect can be obtained even if the electro-optic effect of the semiconductor waveguide is used.
[0014]
The operating speed is slower than that of phase modulators using lithium niobate and semiconductor electro-optic effects, but well-known liquid crystal phase modulators and phase modulators using the thermo-optic effect of silica waveguides. A phase modulator array having a modulation speed of about several kHz can be manufactured using a phase modulator using micromachine technology.
[0015]
The reason why the optical serial-parallel conversion circuit can be realized by the optical signal processing circuit shown in FIG. 1 will be described with reference to FIGS. Although the number of output ports is four here, the number is not limited to this number. The time waveform incident on the incident waveguide 101 of FIG. 1 is distributed almost uniformly to each waveguide of the arrayed waveguide 103 by the slab waveguide 102. The arrayed waveguide is designed to give a certain time delay between adjacent waveguides, and the time waveform is developed as a spatial waveform on the exit surface.
[0016]
However, the developed spatial waveform shows a temporal transition as shown in FIG. In FIG. 2A, T is the maximum time delay difference of the arrayed waveguide. At this time, on the focal plane of the slab waveguide 104, the shape of the spectrum intensity hardly changes with time, but the phase of the spectrum is spatially inclined, and the inclination changes greatly with time. If this state is illustrated with the solid line and the dotted line as the intensity and phase of the spectrum, respectively, it is as shown in FIG.
[0017]
Thus, the fact that the phase of the spectrum (Fourier phase) changes its inclination with time is due to the fact that the waveform emitted from the arrayed waveguide 104 has changed with time. As shown in FIG. 2 (c), if the phase change that just cancels out the change in the temporal slope of the Fourier phase during time T can be given to each spectral component as shown in FIG. The spectrum is again subjected to Fourier transform and returned to a spatial waveform, whereby the incident time waveform can be fixed on the output surface of the slab waveguide 106 only for the time T, as shown in FIG.
[0018]
In order to perform such processing, if the phase modulator array is # 1, # 2, # 3, and # 4 in order, the phase modulation waveform to be added is as shown in FIG. The four phase modulators used in this example are driven with a sawtooth waveform having a repetition time T, and the modulation phase amplitude is 2π for the outer two (# 1 and # 4) and two for the inner ( # 2 and # 3) are π, and the time phases in the drive waveforms of the phase modulation of # 1, # 2 and # 3, # 4 are inverted. Thereby, it is possible to fix the time change of the phase of the spectrum of the incident signal only during the time T. The waveform applied to the phase modulator array is not necessarily a sawtooth wave, but in this case, the waveguide pitch of the output waveguide 107 needs to be unequal. Moreover, the change of the waveform in input / output is as shown in FIG. 4A and FIG.
[0019]
When a 4-bit signal is stored in time T as shown in FIG. 4 (a), 1, 2, 4 ′, 2 ′, 3 ′, 4 ′,. Outputs of signals extending in the width of each time T in # 2, # 3, and # 4 (port numbers correspond to the above-described phase modulator numbers) are obtained.
[0020]
Actually, the optical signal processing circuit of the present invention was fabricated using a silica waveguide for the waveguide portion and a lithium niobate waveguide for the phase modulator array portion. The optical signal processing circuit shown in FIG. 1 excluding the phase modulator array 105 is hybrid-mounted on a silicon substrate, and the phase modulator array 105 is fabricated on a lithium niobate substrate. The design center wavelength of the arrayed waveguide portion used in this example is 1552 nm, the number of arrayed waveguides is 378, and the diffraction order (the value obtained by dividing the optical path length difference between adjacent waveguides by the wavelength) is 53. . The linear dispersion at the focal plane of the slab waveguide 104 is 1.25 GHz / μm, and the frequency resolution is about 12.7 GHz. The number of phase modulator arrays and output waveguides was four.
[0021]
FIG. 5 is an experimental circuit configuration diagram of the optical serial-parallel conversion processing performed in this embodiment. A waveguide-type intensity modulator 112 made of lithium niobate in which the output of a mode-locked laser diode 111 having a repetition rate of 40 GHz, a pulse width of 2 ps, and a center wavelength of 1552 nm is driven using a 40 Gbit / s RZ (return-to-zero) data format. The RZ optical signal having a 40 Gbit / s pulse width of 20 ps was generated by entering the circuit 114. When the four outputs are observed by the sampling oscilloscope 116 through the optical path selector 115 and the error is evaluated by the error detector 116, a clear RZ waveform output of 10 Gbit / s is obtained for each channel. It was. The error rate was ^10-12 or less, and error-free operation was confirmed.
[0022]
【The invention's effect】
As described above, according to the present invention, a plurality of optical paths are provided so as to give a certain time delay between adjacent optical paths, and incident signal light is distributed to the plurality of optical paths, and is emitted from the plurality of optical paths. The time-space conversion means for converting the time-series signal light into the spatial signal light on the surface, and the spatial signal light output from the time-space conversion means is spatially Fourier transformed and imaged to temporally convert the incident signal A first Fourier transform / imaging means for spatially expanding the spectrum, and a temporal spectrum that is arranged in the vicinity of the focal plane of the first Fourier transform / imaging means and is spatially expanded; For each Fourier phase component of , the phase modulator array that modulates in time to keep the Fourier phase constant for a certain period of time, and the Fourier phase that is output from the phase modulator array is constant after receiving the time modulation kept space Since the second Fourier transform / imaging means for spatially transforming and imaging the light again is provided, a plurality of high-speed time waveforms can be obtained by combining an arrayed waveguide grating and a phase modulator array. Can be converted into a low-speed time waveform, and optical serial-parallel conversion processing, which has been difficult in the past, can be performed.
[0023]
Also, using multiple optical paths provided so as to give a certain time delay between adjacent optical paths, the incident signal light is distributed to the multiple optical paths, and the time-series signal light is spatially signaled on the exit surfaces of the multiple optical paths. The step of converting into light, the step of spatially transforming and imaging the spatial signal light, developing the time-frequency spectrum of the time-series signal light as a spatial distribution, and the temporal change of the Fourier phase after the Fourier transform, A step of keeping the phase term of the frequency spectrum constant for a certain period of time by applying temporal modulation for each time frequency component, and spatially Fourier transforming a Fourier transform image that keeps the Fourier phase constant. The time-series signal light is serial-parallel converted to generate a plurality of time-series optical signals with lower time density. Similarly, a high-speed time waveform is converted into a plurality of low-speed time waveforms. It is possible to convert.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of an embodiment of an optical serial-parallel conversion circuit according to the present invention.
2 is a conceptual diagram illustrating the principle of an optical signal processing circuit in the conversion circuit of FIG. 1;
3 is a conceptual diagram illustrating a phase modulation method of an optical signal processing method in the conversion circuit of FIG. 1;
4 is a conceptual diagram showing an input / output waveform state of the optical signal processing method in the conversion circuit of FIG. 1;
FIG. 5 is a configuration diagram showing an embodiment of an optical serial-parallel conversion system according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 Input waveguide 102 Slab waveguide 103 Array waveguide 104 Slab waveguide 105 Waveguide type phase modulator array 106 Slab waveguide 107 Output waveguide 111 Mode-locked laser diode 112 Waveguide type intensity modulator 113 made of lithium niobate 113 Light Filter 114 Main circuit 115 Optical path selector 116 Sampling oscilloscope

Claims (3)

In an optical signal processing circuit that converts a high-speed optical signal into a plurality of lower-speed optical signals,
Provided with a plurality of optical paths provided so as to give a certain time delay between the adjacent optical paths, distributes the incident signal light to the plurality of optical paths, and the time-series signal light on the emission surface of the plurality of optical paths as a spatial signal A time-space conversion means for converting to light;
A first Fourier transform / imaging means that spatially transforms and images the spatial signal light output from the time-space transform means and spatially expands the temporal spectrum of the incident signal;
Is disposed in the vicinity of the focal plane of the Fourier transform and imaging means of the first, with respect to the spatially expanded the temporal spectrum, each Fourier phase component of each, the Fourier phase constant for a certain time A phase modulator array that modulates in time to maintain ,
And a second Fourier transform / imaging means for spatially transforming and imaging the spatial signal light output from the phase modulator array and subjected to time modulation to keep the Fourier phase constant . An optical signal processing circuit.   2. The time-space conversion means is constituted by an arrayed waveguide, and the first and second imaging means are constituted by slab waveguides having a function of Fourier transforming spatial signal light. An optical signal processing circuit according to 1. In an optical signal processing method for converting a high-speed optical signal into a plurality of lower-speed optical signals,
Using a plurality of optical paths provided so as to give a certain time delay between adjacent optical paths, the incident signal light is distributed to the plurality of optical paths, and the time-series signal light is spatially signaled on the emission surface of the plurality of optical paths. Converting to light;
Spatially Fourier transforming and imaging the spatial signal light, and developing a time-frequency spectrum of the time-series signal light as a spatial distribution;
A step of keeping the phase term of the frequency spectrum constant for a fixed time by temporally modulating the temporal change of the Fourier phase after the Fourier transform for each time frequency component;
A step of spatially Fourier transforming a Fourier transform image maintaining a constant Fourier phase to serial-parallel convert time series signal light to generate a plurality of time series optical signals having lower time density. An optical signal processing method.

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