JPH07168216A - Wavelength selecting optical switch - Google Patents

Abstract

PURPOSE:To enable tuning to a wide band by providing gratings with periodic discrete structures and varying the discrete periods of the discrete gratings from each other in internal two regions. CONSTITUTION:The gratings 13 are constituted of the periodic discrete structures and, therefore, overall spectra in a reverse direction are periodic peaks. The waveguide mode propagating in the first waveguide 11 is subjected to reverse directional coupling by these discrete gratings and is converted to a waveguide mode 2 propagating the second waveguide 12 with reverse directional coupling efficiency. The periods of such discrete grating arrays are slightly varied to ZL, ZR in the two regions in the element, by which the peak intervals of the reverse directional coupling spectra in the right and left regions are varied in the two regions. The refractive indices of the first and/or the second waveguides 11, 12 are changed, by which the independent shifting of the reverse directional coupling peaks of the right and left two regions by a method of current implantation, etc., is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength selective optical switch for dropping / adding an arbitrary signal in an optical wavelength division multiplexing system.

[0002]

2. Description of the Related Art In optical fiber communication, a wavelength division multiplexing system (hereinafter referred to as WDM system) has been actively developed as a method capable of effectively utilizing a wide wavelength band and expecting a dramatic increase in transmission capacity. There is. WDM like this
In a system, a wavelength selective optical switch that can spatially separate or combine arbitrary wavelength signal lights and that can tune the wavelength over a wide range plays an important role, and its high performance is expected. There is. Conventionally, a wavelength-selective optical switch has been composed of an acousto-optic TE / TM mode converter and a polarization mode splitter, as described in the proceedings of the Autumn Meeting of the Institute of Electronics, Information and Communication Engineers B-599 (1991). . Alternatively, it was composed of a combination of a Fabry-Perot filter and an optical circulator, as described in Proceedings of IEICE Autumn Meeting SB-7-3 (1992).

[0003]

However, all of them require optical alignment of a plurality of parts, which causes a problem that the device becomes large. And in the acousto-optic type,
Although the tuning range is wide, it is difficult to increase the wavelength multiplicity because the selected wavelength interval is wide. In the Fabry-Perot type, on the contrary, the tuning range is FSR (free spectral ra).
nge; free spectrum interval), and it was difficult to increase the wavelength multiplicity in both cases.

[0004]

According to the present invention, in a wavelength selective high switch comprising a waveguide structure having two waveguide modes coupled to each other through a grating, the grating has a periodic discrete structure. In addition, by realizing a wavelength selective high switch characterized in that the discrete periods of the discrete grating are different from each other in two internal regions, wideband tuning is possible and high-density wavelength multiplexing is possible. A possible wavelength selective switch can be realized compactly with a single element.

[0005]

【Example】

(Embodiment 1) FIGS. 1 and 2 show a first embodiment of the present invention. FIG. 1 conceptually shows a cross-sectional structure of a wavelength selective optical switch according to the present invention. In the figure, 11 is a first waveguide through which transmitted light is guided, and 12 is for branching / adding selective wavelength light. Is a second waveguide for Since the grating 13 is composed of a periodic discrete structure, the backward coupling spectrum has a periodic peak as shown in FIG.
This grating arrangement is used as a sampled grating by Applied Physics Letters Vol. 60,
P. 2322 (1992). In the present invention, as shown in FIG. 1, the waveguide mode 1 propagating in the first waveguide is subjected to the backward coupling by the discrete grating, and the second waveguide is provided with the backward coupling efficiency as shown in FIG. Is converted to the guided mode 2 which propagates the wave. At this time, the grating period is Λ, the mode refractive index of each guided mode is n ₁ ,
Given n ₂ , the selected central wavelength λ _c is expressed as:

Λ _c = (n ₁ + n ₂ ) Λ (1) When the wavelength λ _c is the center of the backward coupling peak sequence and the backward coupling peak interval is Δλ, the following expression is obtained.

Δλ = λ _c ² / (n _g1 + n _g2 ) Ζ ₀ (2) where Ζ ₀ is the discrete period of the grating array, n _g1 , n
_g2 is the group mode refractive index of the two guided modes. The mode refractive index _ng is, when n _c (λ) is the mode refractive index at the wavelength λ,

[0008]

[Outer 1] It is represented by. By making the period of such a discrete grating sequence slightly different from Ζ _L and Ζ _R in the two regions in the device as shown in Fig. 1, the peak interval Δλ of the backward coupling spectrum is 2 in the left and right regions. Different in the area. In the present embodiment, Δλ for Ζ _L = 60 μm
Is about 50Å, and Δλ is about 60Å for Ζ _R = 50μ. In the present invention, by changing the refractive index of the first and / or the second waveguide, the backward coupling peaks in the two left and right regions are independently shifted by a method such as current injection from the electrode 1415. I do. By this control, the wavelengths at which the backward coupling peaks from the left and right grating rows match can be freely selected. Of the light incident from the first waveguide, only the light of the selected wavelength is resonated between the two waveguides and emitted from the second waveguide. If the resonator has an optical amplification effect, the selected wavelength is further emphasized, so that the crosstalk suppression ratio with the non-selected wavelength can be improved. Optical amplification is performed by providing an optical amplification area in the intermediate area between the left and right grating rows, or by providing the grating area with an optical amplification effect. First of the light emitted from the second waveguide
The spatial separation from the waveguide is due to, for example, the construction of a radiating grating or a bent waveguide.

The embodiment will be described with reference to FIG. The device is composed of the InP substrate 31 and the InP lower clad layer 32.
To a thickness of 1.5 μm and InGaAsP (λ _g = 1.3
After the first waveguide 33 made of (.mu.m) is grown to a thickness of 0.2 .mu.m, the upper portion of the first waveguide 33 is etched as a grating. In the grating, first, a region in which the grating is not formed is patterned in a stripe pattern with a first resist, and then a second resist is applied, and then a grating pattern is written by a laser interference exposure method. Etch the grating by reactive ion beam etching. Since the portion covered with the first resist is not etched, discrete grating rows as shown in FIG. 1 are formed. The grating period is 0.25 μm, and the periods of the discrete grating rows are 60 μm and 50 μm on the left and right, respectively, and the region where the grating exists is 10 μm. Then, In
The P intermediate layer clad 34 is formed to a thickness of 1.4 μm with InGa
Second waveguide 35 made of AsP (λ _g = 1.57 μm)
To a thickness of 0.3 μm, and the InP upper clad 36 is 1.
Grow 5 μm. The waveguide is

[0010]

[Outside 2] The first waveguide is formed by etching in a letter shape and filling the side surface with the InP clad 37.

[0011]

[Outside 3] In a letter shape, the second waveguide

[0012]

[Outside 4] It is shaped like a letter. On the input side, only a part of the second waveguide layer is removed, the input side is limited to the first waveguide as shown in the figure, and on the output side, the first and second waveguides are

[0013]

[Outside 5] Letter,

[0014]

[Outside 6] In the first waveguide, the light is formed in the shape of a letter, the light travels straight because of its straightness, and in the second waveguide, the light travels straight.

[0015]

[Outside 7] Since the light travels in a letter shape, the respective output lights are spatially separated. The electrodes are formed corresponding to the left and right grating regions. The light from the external cavity type wavelength tunable laser was input to the first waveguide, and the output light spectrum from the second waveguide was measured. By controlling the amount of current injection into the two electrodes, the wavelength of the backward directional coupling resonance was changed, and the peak wavelength of the output light spectrum was changed. As a result, a wavelength change was confirmed from 1.52 μm to 1.58 μm while being discontinuous. When all wavelengths are not selected, the wavelength in which the backward directional resonance is generated is removed from the transmission wavelength range, so that the output from the second waveguide is transmitted and the light is transmitted through the first waveguide. By design, it is possible not to output all of the selected wavelength light from the second waveguide, but to output only a part of the selected wavelength light from the second waveguide and the rest from the first waveguide together with the non-selected wavelength light.

(Embodiment 2) This embodiment will be described with reference to FIG. The difference from the above embodiment is that the phase between the gratings forming the left and right grating regions is shifted by a half wavelength, that is, (2m + 1) Λ between the peaks of the grating.
This is a point configured to shift by / 2 (m: integer). Specifically, the peaks and valleys of the grating are reversed in the left and right regions. The grating inversion structure can be manufactured by using a resist for interference exposure as a positive type resist and a negative type resist in the left and right regions, respectively. Alternatively, if electron beam direct exposure is used, the period of the grating may be shifted by a half period at the boundary. The other manufacturing procedure is the same as that of the above-mentioned embodiment. By providing the grating phase shift, the wavelength at which the backward directional coupling resonance is stable becomes stable, and the operation of the wavelength selective optical switch becomes stable.

(Embodiment 3) FIG. 5 is a diagram for explaining a third embodiment of the present invention. Two regions are provided between the grating regions, one has a role of controlling the phase, and the other one has a role of controlling the optical gain. First, the InP lower clad 52 was formed to a thickness of 1.5 μm, and the first waveguide 53 made of InGaAsP (λ _g = 1.3 μm) was formed to a thickness of 0.15 μm on the InP intermediate layer on the InP substrate 51. The cladding 54 has a thickness of 1.4 μm and is made of InGaAsP (λ
_g = 1.52 μm) with a second waveguide 55 of 0.3 μm
to a thickness of 0.05 μm and an active layer 56 of InGaAsP (λ _g = 1.57 μm).
A grating layer 57 made of sP (λ _g = 1.45 μm) is grown to a thickness of 0.1 μm. After etching the optical gain region 59 to the grating layer and the phase control region 58 to the active layer, the grating regions 501 and 502 are etched.
Is etched as a grating. The manufacturing method of the discrete grating of the grating regions 501 and 502 is the same as that of the first embodiment. Then, a grating coupler 503 for radiating and outputting light of a selected wavelength is produced outside the discrete grating region 502 in the same manner. This grating period is 0.4 so that the second-order diffracted light is not generated and the first-order diffracted light is emitted away from the waveguide.
It is set to 5 μm. Furthermore, the grating 503 may be a blazed grating so as to emit light only in the upward direction. The output grating 503 is not discrete, and a length of several hundreds μm is sufficient. After forming all the gratings, the InP upper clad 504 is grown to a total thickness of 1.5 μm. Furthermore, the side surface of the waveguide is In
It is filled with P. Only a part of the second waveguide layer is removed, and the input side is limited to the first waveguide as shown. The light of the selected wavelength and the light of the other wavelengths are spatially separated by the grating radiator formed in the second waveguide. The electrodes consist of two electrodes corresponding to the left and right grating regions and two electrodes corresponding to the phase control region and the optical gain region, for a total of four electrodes. In this embodiment, current is injected into the optical gain region to obtain a gain, and current is injected into the phase control region to change the refractive index to control the phase. The optical spectrum was measured by the same evaluation as in the first example. By controlling the amount of current injection into the four electrodes, the wavelength at which the backward directional resonance occurs was changed, and the peak wavelength of the output light spectrum could be changed while keeping the output light gain constant.

(Embodiment 4) FIG. 6 shows an example in which the wavelength selective optical switch of the present invention is used in a bus type communication network. 6 in the figure
1 is a bus line, 62 and 63 are optical repeaters, and 64 and 6
5, 66, 67 are optical nodes, 68, 69, 601, 60
Reference numeral 2 is a terminal including an OE and EO converter. The optical node includes the wavelength selective optical switch according to the present invention.
Further, the optical node may include an OE / EO conversion unit. The optical repeater is provided to compensate for transmission loss and branch loss. Of course, in the optical node, for example, there is a configuration in which a wavelength selective optical switch compensates for the above loss. By tuning the wavelength selective optical switch to the desired wavelength channel of the signal / data passing through the transmission line, only the desired light is branched and transmitted to the terminal. On the contrary, when a signal / data is sent from the terminal, by tuning the wavelength selective optical switch to the wavelength, the signal can be placed on the transmission line without giving branch loss to the transmission line.

(Embodiment 5) FIG. 7 is an example in which the optical switch of the present invention is used in a loop network. 71 in the figure
Are optical transmission lines, 72 to 77 are optical nodes, and 78 and 79 are optical nodes for transmission outside the loop. 701-7
Reference numeral 06 is a terminal. The optical nodes 72-77 include wavelength selective optical switches according to the present invention. The optical node or terminal includes an OE / EO conversion unit. In this embodiment, the wavelength selective optical switch in the optical node compensates the transmission loss. The role of the wavelength selective optical switch in transmitting and receiving the wavelength signal from the terminal is the same as that in the above-mentioned embodiment.

[0020]

As described above, by forming a directional coupling type wavelength selective optical switch with a grating having a discrete structure, a very small element size,
It is possible to realize a wideband wavelength selective optical switch that is compatible with a high-density wavelength division multiplexing system.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a wavelength selective switch according to the present invention.

FIG. 2 is a diagram showing a backward coupling efficiency of a discrete structure grating used in the present invention.

FIG. 3 is a perspective view of the wavelength selective switch according to the first embodiment.

FIG. 4 is a sectional view of a wavelength selective switch according to a second embodiment.

FIG. 5 is a sectional view of a wavelength selective switch according to a third embodiment.

FIG. 6 is a diagram showing a configuration of an optical bus system according to a fourth embodiment.

FIG. 7 is a diagram showing a configuration of an optical loop system according to a fifth embodiment.

[Explanation of symbols]

11, 33, 53 First waveguide 12, 35, 55 Second waveguide 13, 57 Discrete grating 14, 15, 58, 59, 501, 502 Electrode 32, 34, 36, 37, 52, 54, 504 Clad 31, 51 Substrate 503 Emission Grating 56 Active Layer 61, 71 Optical Transmission Line 64, 65, 66, 67, 72, 73, 74, 75, 7
6, 77, 78, 79 optical nodes 68, 69, 601, 602, 701, 702, 70
3, 704, 705, 706 Terminal 62, 63 Optical repeater

Claims (7)

[Claims] 1. A wavelength selective optical switch comprising a waveguide structure having two waveguide modes, which are backward-coupled through a grating, wherein the grating has a periodic discrete structure, and the discrete structure is provided. A wavelength selective optical switch characterized in that the discrete period of the grating is different in the two internal regions. 2. An electrode is provided corresponding to each of the two regions having different discrete periods, and the refractive index of the waveguide in each of the two regions can be independently controlled. The wavelength selective optical switch described. 3. The optical gain region according to claim 1, further comprising:
The wavelength selective switch described. 4. The wavelength selective optical switch according to claim 1, wherein a phase shift structure for compensating the phase of the resonance wavelength is formed between the two regions having different discrete periods. 5. The wavelength selective optical switch according to claim 1, wherein a phase control region and an optical gain region are formed between the two regions having different discrete periods. 6. A part of one waveguide is refracted as a means for extracting selected light.
5. The wavelength selective optical switch described in 5 above. 7. The wavelength selective optical switch according to claim 1, wherein a grating radiator that selectively emits one guided mode is formed as a means for extracting the selected light.