JP3178781B2 - Array waveguide diffraction grating optical multiplexer / demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wavelength division multiplexing (WD).
M) In a communication system, the present invention relates to an arrayed waveguide grating optical multiplexer / demultiplexer used for a wavelength monitoring circuit that monitors each wavelength of wavelength multiplexed light.

[0002]

2. Description of the Related Art A wavelength monitoring circuit using an arrayed waveguide grating optical multiplexer / demultiplexer utilizes the periodic band-pass transmission characteristics of an arrayed waveguide grating optical multiplexer / demultiplexer to output light of an adjacent port. By taking the level ratio, a wavelength discrimination characteristic which does not depend on the incident light intensity fluctuation can be obtained.

FIG. 6 shows a configuration of a wavelength monitoring circuit using a conventional arrayed waveguide diffraction grating optical multiplexer / demultiplexer. In the figure, an arrayed waveguide grating optical multiplexer / demultiplexer includes, on a substrate 10, a waveguide array 12 composed of N input waveguides 11 and M waveguides sequentially elongated by a predetermined waveguide length difference. , N
The output waveguide 13, the input-side sector-shaped slab waveguide 14 for connecting the input waveguide 11 and the waveguide array 12, and the output-side sector-shaped slab waveguide 15 for connecting the waveguide array 12 and the output waveguide 13. Are formed. FIG. 7 shows the transmission loss characteristics of each port of the output waveguide 13 when wavelength-multiplexed light (λ ₁ , λ ₂ ,..., Λ _n ) is incident on one of the input waveguides 11. The cross wavelength of the transmission loss characteristic of the adjacent port corresponds to the center wavelength (set wavelength) of each channel of the wavelength multiplexed light. FIG. 8 shows a transmission loss difference between adjacent ports near the cross wavelength. The wavelength at which the transmission loss difference is zero corresponds to each cross wavelength.

[0004] To adjacent ports of the output waveguide 13, photodetectors 31, 32 and a logarithmic amplifier 33 for obtaining an output ratio thereof are connected, respectively. The output of the logarithmic amplifier 33 becomes zero at the cross wavelength as shown in FIG. That is, the relative wavelength error between the input wavelength and the cross wavelength (set wavelength) can be detected according to the polarity and level of the error signal output from the logarithmic amplifier 33. In this way, each wavelength of the wavelength multiplexed light can be monitored by taking the ratio of the output light of the adjacent port.

[0005]

In the wavelength division multiplexing communication system in which the channel intervals are equal, there is a problem that four-wave mixing causes crosstalk between the wavelength division multiplexed signal lights. Here, four-wave mixing refers to optical frequencies f _i , f _j , f
_The three light waves of _k (k ≠ i, j) interact via the third-order nonlinear susceptibility χ ⁽³⁾ of the optical fiber, and the optical frequency f _F =
is a nonlinear process which generates a light wave f _i + f _j -f _k. In a wavelength division multiplexed signal light in which wavelengths are arranged at equal intervals, 4
A new lightwave generated by lightwave mixing will overlap other signal wavelengths and cause crosstalk. Therefore, in order to suppress crosstalk due to four-wave mixing, it is necessary to make the wavelength intervals of optical signals unequal, and accordingly, it is necessary to make the wavelength characteristics of the optical multiplexer / demultiplexer also unequal. there were.

As an optical multiplexer / demultiplexer used in a wavelength division multiplexing communication system with unequal channel intervals, there is Japanese Patent Application No. 7-18237 “Array grating type optical multiplexer / demultiplexer”. In this method, at least one of the input waveguide interval and the output waveguide interval is made unequal, thereby obtaining transmission loss characteristics with unequal channel intervals. FIG. 9 shows the transmission loss characteristics. If the channel spacing is unequal as shown here, there may be no intersection of transmission loss characteristics between adjacent ports, and the above-described cross-discrimination method of detecting a loss difference between adjacent ports and performing wavelength monitoring. Cannot be applied as it is.

An object of the present invention is to provide an arrayed waveguide grating optical multiplexer / demultiplexer used for a wavelength monitoring circuit for monitoring each wavelength of wavelength multiplexed signal light having unequal channel intervals.

[0008]

SUMMARY OF THE INVENTION An arrayed waveguide grating optical multiplexer / demultiplexer according to the present invention has N input waveguides for signal as well as N for monitoring wavelengths into which signal light is branched and input. The input waveguides are arranged at positions deviated from the signal input waveguides , and the wavelength monitoring is further performed on both sides of the N output waveguides.
For light of a predetermined wavelength incident from the input waveguide for viewing
Slightly inside or outside of the position where the two diffracted lights occur
An output waveguide for monitoring the wavelength is arranged at the position thus set.

[0009]

FIG. 1 shows an embodiment of an arrayed waveguide grating optical multiplexer / demultiplexer according to the present invention. In the figure, N (= 8) input waveguides 11 for signals are provided on a substrate 10,
A waveguide array 12 composed of N (= 8) input waveguides 21 for wavelength monitoring, M waveguides sequentially elongated by a predetermined waveguide length difference ΔL, and N (= 8) output waveguides Wave path 13,
Wavelength monitoring output waveguides 22 and 23, one input side fan-shaped slab waveguide 14 connecting the input waveguides 11 and 21 and the waveguide array 12, one on each side of the output waveguide 13, and the waveguide array 12 An output-side fan-shaped slab waveguide 15 that connects the output waveguides 13, 22, and 23 is formed.

FIG. 2A is an enlarged view of the boundary between the input waveguides 11 and 21 and the input-side fan-shaped slab waveguide 14. FIG. 2A shows the output-side fan-shaped slab waveguide 15 and the output waveguides 13 and 2.
FIG. 2 (b) is an enlarged view of the boundary between 2 and 23. As shown, a signal input waveguide 11 and an output waveguide 13
Are arranged at unequal intervals at the center position of the fan-shaped slab waveguide, and their transmission loss characteristics become unequal intervals as shown in FIG.

The wavelength monitoring input waveguide 21 is set at the same unequal interval as the signal input waveguide 11, and is arranged at a position where the input waveguide 11 is shifted laterally as it is. As described above, the input waveguide 21 for monitoring the wavelength is arranged at a position deviated from the center line of the input-side fan-shaped slab waveguide 14. Produces light of two diffraction orders.

The output waveguides 22 and 23 for wavelength monitoring are arranged slightly inside (they may be outside, but in the following description, inside) the positions where these two diffracted lights are generated. Accordingly, when incident FIG 2 i-th from the left of the input waveguide 21 for wavelength monitoring _{(a) (m in = i} ) port of the wavelength-multiplexed optical signal (channel setting i wavelength lambda (i)), the output FIGS. 3 (a) and 3 (b) show the light focusing characteristics of the side sector slab waveguide 15.
become that way. That is, when the input wavelength λ is λ = λ (i), the outputs of the wavelength monitoring output waveguides 22 and 23 become equal, and when λ <λ (i), the wavelength monitoring output waveguide 23 is output. Becomes large, and when λ> λ (i), the output of the wavelength monitoring output waveguide 22 becomes large.

[0013]

EXAMPLE An example in which an arrayed waveguide diffraction grating optical multiplexer / demultiplexer according to the present invention is manufactured using a silica-based optical waveguide will be described. First, Si
A SiO ₂ lower cladding layer is deposited on the substrate (10) by a flame deposition method, and then S ₂ doped with GeO ₂ as a dopant.
After depositing a core layer of SiO ₂ glass, it was vitrified in an electric furnace. Next, the core layer was etched using the patterns shown in FIGS. 1 and 2 to produce an optical waveguide portion.

Refractive index difference Δ = 0.7% of waveguide, core width 2a
= 7 µm and core thickness 2t = 7 µm. The radius of curvature R of the input side sector slab waveguide 14 and the output side sector slab waveguide 15 is 9.356 mm, and the waveguide length difference Δ of the arrayed waveguide 12.
L = 61.6 μm and the number M = 120. In FIG. 2, the center distance between the waveguides of the signal input waveguide 11 is from the left.
40 μm, 55 μm, 50 μm, 35 μm, 30 μm, 45 μm, 25
μm. The same applies to the waveguide spacing between the wavelength monitoring input waveguide 21 and the signal output waveguide 13. However,
In the output waveguide 13, the distance is from the right.

The distance between the center of the right end waveguide of the wavelength monitoring input waveguide 21 and the center of the left end waveguide of the signal input waveguide 11 was 65 μm. Further, the distance between the center of the right end waveguide of the signal output waveguide 13 and the wavelength monitoring output waveguide 22 is 181.2 μm, and the center of the left end waveguide of the signal output waveguide 13 and the wavelength monitoring The distance from the output waveguide 23 was 186.5 μm. Finally, again SiO ₂
An upper cladding layer was deposited.

In the wavelength monitoring circuit using the arrayed waveguide grating optical multiplexer / demultiplexer manufactured as described above, the ports of the wavelength monitoring input waveguide 21 for receiving the wavelength multiplexed signal light are sequentially switched, and the wavelength monitoring is performed. By taking the level ratio of the output light from the output waveguides 22 and 23 for wavelength, wavelength discrimination characteristics for each channel corresponding to the input port can be obtained. That is, the wavelength can be monitored without being affected by the unequal channel interval.

[0017] Here, the first from the left of the input waveguide _{21 (m in = 1),} 4 th (m _in = 4), 8 th (m _in =
FIG. 4 shows the measurement results of the transmission loss characteristics of the output waveguides 22 and 23 when the wavelength multiplexed signal light is incident on the port 8). The cross wavelength of each transmission loss characteristic corresponds to the center wavelength (set wavelength) of the channel corresponding to the input port. FIG. 5 shows the transmission loss difference between the output waveguides 22 and 23 near the cross wavelength. The wavelength at which the transmission loss difference is zero corresponds to each cross wavelength. Therefore, each wavelength of the wavelength multiplexed signal light can be monitored by detecting the relative wavelength error between the input wavelength and the cross wavelength (set wavelength) for each channel.

[0018]

As described above, by using the arrayed waveguide grating optical multiplexer / demultiplexer of the present invention, it is possible to monitor each wavelength of the wavelength division multiplexed signal light at unequal channel intervals. If the waveguide spacing of the wavelength monitoring input waveguides is made equal, it is possible to monitor each wavelength of the wavelength multiplexed signal light having the same channel spacing.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an arrayed waveguide grating optical multiplexer / demultiplexer according to the present invention.

FIG. 2 is an enlarged view of a boundary between input waveguides 11 and 21 and an input-side fan-shaped slab waveguide 14, and a boundary between output-side fan-shaped slab waveguide 15 and output waveguides 13, 22, and 23;

FIG. 3 is a diagram showing light focusing characteristics of an output fan-shaped slab waveguide 15;

FIG. 4 is a diagram showing transmission loss characteristics of output waveguides 22 and 23 for wavelength monitoring.

FIG. 5 is a diagram illustrating a transmission loss difference between output waveguides 22 and 23 in the vicinity of a cross wavelength.

FIG. 6 is a diagram showing a configuration of a wavelength monitoring circuit using a conventional arrayed waveguide grating optical multiplexer / demultiplexer.

FIG. 7 is a diagram showing transmission loss characteristics of each port of the output waveguide 13;

FIG. 8 is a diagram showing a transmission loss difference between adjacent ports in the vicinity of a cross wavelength.

FIG. 9 is a diagram showing transmission loss characteristics of an arrayed waveguide grating optical multiplexer / demultiplexer with unequal channel spacing.

[Explanation of symbols]

 Reference Signs List 11 input waveguide (for signal) 12 waveguide array 13 output waveguide (for signal) 14 input-side fan-shaped slab waveguide 15 output-side fan-shaped slab waveguide 21 input waveguide (for wavelength monitoring) 22, 23 output waveguide ( 31, 32 Photodetector 33 Logarithmic amplifier

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/14 G02B 6/28-6/293

Claims (1)

(57) [Claims] 1. A substrate having N (N is an integer), N output waveguides, and M (M is an integer of 2 or more) sequentially elongated by a predetermined waveguide length difference on a substrate. A waveguide array comprising: a waveguide; an input-side fan-shaped slab waveguide for connecting the input waveguide to the waveguide array; and an output-side fan-shaped slab waveguide for connecting the waveguide array to the output waveguide. In the arrayed waveguide grating optical multiplexer / demultiplexer formed with the above, in addition to the N input waveguides for signal, N input waveguides for monitoring the wavelength into which the signal light is branched and inputted are used for the signal. input waveguides arranged in a position shifted from the waveguide, each further one on each side of said N output waveguides, the wave
To the light of the specified wavelength that has entered from the input waveguide for monitoring the length.
Slightly inside or outside of the position where the two diffracted lights occur
An array waveguide diffraction grating optical multiplexer / demultiplexer, wherein an output waveguide for wavelength monitoring is arranged at a position shifted from the above .