JPH01105591A - Wavelength selecting amplifier - Google Patents

Abstract

PURPOSE:To set a selecting wavelength to one, and to broaden the width of a variable wavelength by providing a phase displacing unit of pi in a diffraction grating, and providing a plurality of electrodes for supplying a current to an active region. CONSTITUTION:The phase circulation of pi/2 is generated in the phase of a light by a phase displacing unit 6 of pi provided in a diffraction grating 1b. Thus, since the variation in the phase of the light reflected by the left and right diffraction gratings 1b is given by 4Neq.pi.Leff (L/lambda-1/lambdaB). where the lambdaB is Bragg's wavelength, Neq is equivalent refractive index, and Leff is the effective length of a distributed feedback structure. Accordingly, the wavelength lambdam for satisfying the phase matching condition is given by lambdaB+ or -mlambdaB<2>/(4 Neq.Leff), and in case of m=0, the phase matching condition in the wavelength lambdaB is satisfied. Thus, when a threshold current flows to one of the electrodes 2 and a wavelength selecting current I1 equal to the threshold current flows to the other, the selecting amplification in Bragg's wavelength can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wavelength selective amplifier that selects and amplifies one wavelength from wavelength-multiplexed signal light.

[Conventional technology]

Figure 6 is a schematic configuration diagram of a conventional wavelength selective amplifier shown in IEICE Technical Report 0QE86-132. In the figure, 1 is a wavelength selective amplifier, 1a is a waveguide layer that guides signal light, and 1b is a waveguide layer. 1a is a diffraction grating provided around the circumference, IC is a substrate, 1d is an active layer, le is a cladding layer, 2 is an electrode, 3 is a conduction path for the wavelength selection current I- injected into the electrode 2, 4 is a wavelength selection amplifier 1
5 is the output light from the wavelength selective amplifier l, 12 is a stabilizing coil, and 13 is a DC power source.

In the wavelength selective amplifier 1 using a DFB laser, the reflectance increases rapidly near the Bragg wavelength λa'ZNeqΔ (first-order Bragg diffraction) determined by the equipolarized refractive index Neq of the waveguide layer 1a of the diffraction grating 1b. Figure 7 (a
). However, in a normal DFB laser, there is a phase change that occurs when light with wavelength λ is reflected by a diffraction grating.
) and the wavelength of the light must satisfy the phase matching condition.

λ two! λm#λB±□ (H+m) (114Neq
Leff Now, when a wavelength selective current l; is injected into the electrode 2, the total gain in the active layer ld becomes equal to αH-min of Fig. 7 (al), and oscillation is possible at the wavelength λ.1°. "By the way, in a laser diode amplifier, there is a difference between the electric field amplitude Ain of input light j and its electric field amplitude A10 in the resonator.
2) There is a relationship shown in the formula.

In equation (2), ■ is the wavelength selection current, and 1th is the wavelength selection current at the oscillation dark value. From equation <1), when the wavelength selection current I is set near the oscillation dark value, the amplification factor within the resonator becomes maximum, and therefore the transmission amplification factor also becomes maximum. In Fig. 7(b), the wavelength selection current I is set near the dark value, and the total gain is αH-min.
The wavelength characteristics of the transmission amplification factor of the output light 5 with respect to the input light 4 are shown for the case where the wavelength is close to .

The horizontal axis of the figure shows the deviation between the input light 4 and the Bragg wavelength in the vicinity of chain length λ=1.3 μm. In the figure, there are two peaks where the amplification factor is maximum, and the line width Δf of these peaks approaches zero as the wavelength selection current r,t approaches the dark value, and increases as it moves away from the dark value. In this way, strong wavelength selectivity occurs near the dark value.

Further, when the wavelength selection current I is changed to change the injected carrier density, the total gain changes as described above, and therefore the equipolarized refractive index also changes. Therefore, the Bragg wavelength and phase matching condition change, and the wavelength that satisfies the phase matching condition is expressed by the following equation.

− λ, ′ λm°・λIIl+Δλ± □ (%+m)4 (
Neq+Δn) ・Leff Focusing on one peak in Figure 7 (C), I = 0.99
1th.

It shows the change in wavelength of the peak value when (2) = 0.951th and I = 0.901th.

In the figure, 8 indicates that the wavelength shift in Figure 7 (C) is 2.
This is the height of the next peak value that exists near 60 GHz.

Here, in order to obtain an S/N of 20 dB or more, the wavelength selection current I needs to be 0.950 h or more, and the variable selection wavelength width at this time is about 14 Gtlz at most.

(The point that the invention is trying to solve) Since the conventional wavelength selective amplifier was configured as described above, the wavelength characteristic of the transmission amplification factor was bimodal, making it difficult to select a single wavelength. Also, by injecting a wavelength selection current, it was not possible to change the selection wavelength while keeping the gain near the dark value, so the variable selection wavelength width was 14GIIz.
There were problems in that the transmission amplification factor changed depending on the selected wavelength.

The present invention was made to solve the above problems, and an object of the present invention is to provide a wavelength selective amplifier that selects only one wavelength and can have a wide variable wavelength range.

[Means for solving problems]

The wavelength selective amplifier according to the present invention is characterized in that the diffraction grating 1b is provided with a phase shift portion 6 of π, and both electrodes 2 are provided with a plurality of electrodes 2 through which a current flows through the active region.

C Effect] The phase shift portion 6 of π provided in the diffraction grating 1b causes a phase rotation of π/2 in the phase of the light. Here, if a current with a value near the dark value is passed through one of the plurality of electrodes 2, and a current with a predetermined value is passed through the other electrodes, a unimodal wavelength selection characteristic can be obtained.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.

Note that, for convenience, the number of electrode divisions was set to two. In FIG. 1, reference numeral 6 indicates a phase shift portion of π provided in the diffraction grating lb in order to select a single wavelength, and 7 indicates a phase shift portion of π provided in the diffraction grating lb in order to select a single wavelength. , is a conduction path through which a dark value setting current ``Y'' is injected into one of the two divided electrodes in order to set the total gain near the dark value.Other parts are the same as a wavelength selective amplifier using a conventional DFB laser. It is.

In the λ/4 shift DFB laser, the reflector loss is the same as in the conventional DFB laser, as shown in Figure 2(a), but
The mist phase shift portion 6 provided in the diffraction grating causes a phase rotation of π/2 in the phase of the light.

Therefore, the phase change φ of the light reflected by the left and right diffraction gratings sandwiching the λ/4 shift section is 4 Neq・π・Leff
Since it is given by (1/λ-1/λ8), the wavelength λm (λ/4) that satisfies the phase matching condition is given by equation (4).

, λ,' λm (λ/4) - λ, ±□・m 4 Neq - Leff (m is an integer) (4) From equation (4), when m = 0, the phase matching condition at Bragg wavelength λ1 is satisfied. I understand that.

Therefore, if the wavelength selection current upper = is L 1 and the threshold setting current - is I2, then under the condition of 11 = 1□, the total gain is
When set to a value near αH-win shown in Figure (a), selective amplification at the Bragg wavelength becomes possible.

Figure 2 (bl shows the wavelength characteristics of the transmission amplification factor of the output light 5 with respect to the human-powered light 4. In the figure, the horizontal axis is the wavelength λ = 1
．． It shows a deviation from the Bragg wavelength at 3 μm. Next, the effect of changing the values of the wavelength selection current II and the threshold setting current 1b will be explained. For convenience of explanation, wavelength selection current 1. The region into which the current flows is region I, and the threshold setting current ■4
The wavelength characteristics of the reflector loss in each region and the reflector loss in the entire region are schematically shown in Figure 3 T, with the region where the flow is defined as region ■.
Shown in a). In FIG. 3(a), 9a is the wavelength characteristic of the reflector loss in the region (2), 9b is the wavelength characteristic of the reflector loss in the region (2), and 9C is the wavelength characteristic of the reflector loss in the entire region.

Moreover, λ□ is the equipolarized refractive index Neq of the region ■.

The Bragg wavelength in the region ■, determined by λ. is the Bragg wavelength in region ■ determined by the equipolarized refractive index Neqz of region ■, and λ, T are λ□ and λ8. The Bragg wavelength in the entire region expressed as the average value of 11 is the minimum value of the reflector loss in the entire region. Figure 3 (bl is the injection current 11 in region I and region ■
Figure 3 shows a case where the current difference in the injection current I2 is larger than in the case of al and the wavelength difference between λ□ and λ8□ has widened. Figure 2 (a) shows λBl=λ8□=λ, This is the case when A=λ8°.

1. and I2 as shown in Figure 2 (a) and Figure 3 (al).
As the difference becomes larger? The minimum value of reflector loss αEw
in becomes large, and the reflector loss changes gradually with respect to wavelength. Furthermore, ■ to the extent shown in Figure 3(b)
, and I2 widens, the minimum value of the reflector loss is no longer one and is no longer λ8T. Note that the wavelength λ3 that satisfies the phase matching condition is expressed by the following equation using the equipolarized refractive index Neq of the region (2) and the equipolarized refractive index Neq2 of the region H.

Neqtleff++Neq21eft Neq,
1eff++Neqzleffz (k is an integer) (6) Here, 1eff,, 1effz are areas 1. Indicates the effective length of II.

In the above equation (6), 1eff, = 1eff, =
1eff.

Assuming that the lengths of the two divided electrodes are equal as 21eff=Leff, and indeed =0, the wavelength that satisfies the phase matching condition is expressed by equation (7), which is equal to the Bragg wavelength λ87 in the entire region.

λI11+ λam λo = (Neq++Neq=) A= -, λIIT
(7) In other words, the reflector loss at λIT is the minimum value αH
-min, a single wavelength can be amplified with 23 lenses.

Let the currents 11 and I2 shown in FIG. 2(a) be I, =1. .

The Bragg wavelength when set to -1° is λ. , the equipolarized refractive index is Neqo, I In I z ■. Letting the deviations from ΔII and Δ■2, λ8T can be expressed by the following formula.

λ, T-λ,. +(Δn+(Δ■υ+Δnz(Δ■2)
)ΔHere, Δn+(ΔI, ), Δnz(ΔIJ is ΔI
The equipolarized refractive index shows a deviation from Neq by l+Δtz. In addition, as shown in Fig. 3(a) and Fig. 3(bl), λ
, T is the case where the total gain in the entire region due to the currents 1'+ and [2 is equal to the minimum mirror loss αH-min 11.

ctH-min(Δrll+Δnz)”c(to+Δ1
．． ．． 1. +Δb) where G(I.+Δ[+, I'o+Δ
It) indicates the total gain over the entire range. Figure 4 (al~4th
Figure (f) shows the coupling constant K of the diffraction grating, 66.7 cm-i, λ/4 shift DFB laser length L = 300 μm, λ
/4 Wavelength selection current when the shift position is placed at the center of the laser! 1 is changed from 0.961o to 1.4io and the threshold supporting current I2 is adjusted using equation (9) to maintain the dark value. Also, Fig. 5 shows the Bragg wavelength λII of the entire range for the wavelength selection current ■? and the value of the dark value potential current 2 which sets the total gain at that time near the dark value.

In Figure 5, (ρ) is ll-10, and (q) is I t -1.
, 321°. As can be seen from FIGS. 4B to 4E, 1 is I, -I. (p) and 11shi 1.321 o
(If it is between ql, the transmission amplification factor of the wavelength selective amplifier l is maintained at least 20 dB higher than that of other wavelengths for the selected wavelength. In other words, 27.5 as shown in Figure 5)
It is possible to select a single wavelength while ensuring S/N=20 da in the wavelength range of A (~490 Gb). This is the conventional D
It has a wavelength selection variable width that is approximately 35 times larger than that using an FB laser.

Although the above embodiment was explained using a two-divided electrode, it is also easy to obtain the same function by adjusting the current given to each divided electrode using a multi-divided electrode. improves.

〔Effect of the invention〕

As described above, according to the present invention, the diffraction grating is provided with a phase shift portion of π and a plurality of electrodes for passing current through the active region, so that the transmission amplification characteristic of the wavelength selective amplifier can be made unimodal and the injection This has the effect of making the selective wavelength variable range by current about 35 times wider than that of the conventional method.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a structure showing an embodiment of the present invention;
Figure (al is a characteristic diagram showing the wavelength dependence of reflector loss of λ/4 shift DFB laser, Figure 2) is λ/4 shift) DF
Characteristic diagrams showing the wavelength dependence of the amplification factor of a wavelength selective amplifier using a B laser, Figure 3 (a) and in Figure 3) show the reflection mirror loss when different injection currents are applied to the two divided electrodes. Characteristic diagrams of wavelength dependence, Figures 4 (a) to 4 (f) are characteristic diagrams showing the wavelength dependence of transmission amplification factor when different currents are injected into two divided electrodes, and Figure 5 is FIG. 3 is a characteristic diagram showing a change in a transmission amplification wavelength with respect to a wavelength selection current value and a calculation result of a dark value setting current value at that time. Fig. 6 is a schematic diagram of the structure of a conventional wavelength selective amplifier, Fig. 7(a) is a characteristic diagram showing the wavelength dependence of reflector loss of a normal DFB laser, and Fig. 7(b) is a diagram of the conventional wavelength selective amplifier. FIG. 7C is a characteristic diagram showing the wavelength dependence of the transmission amplification factor of the selective amplifier. FIG. 7C is a characteristic diagram showing the change in the transmission amplification wavelength due to the wavelength selection current of the conventional wavelength selective amplifier. In the figure, 1a is a waveguide layer, 1b is a diffraction grating, IC is a substrate, ld is an active layer, 1e is a cladding layer, 2 is an electrode,
is a wavelength selection current, 4 is an input light, 5 is an output light, 6 is a phase shift part of π, and 1 is a dark value setting current, respectively. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa (and 2 others) 1st) Ko 1a; 4; Yoshikata, Ib; times-rfr4-+, 1c: Reizaka, 1c+;; t・bl, 1e: Kura, 712;
Kiwami, commonly known as 3sho, 4:X, but 5;≦power. 61 几 no l upper phase Cre (shi 4 biton, 7; (μAI池! ta. 12; Ujin lshi filli shi 13; L pull U, name 20 (a) χ80' namyo name 21 sword (b) Fu”... 2° hole from t (GHz) Fig. 4 (a
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L procedural amendment (Jijo Showa year 8)

Claims (1)

[Claims] Wavelength-multiplexed signal light is guided to the waveguide layer, and a signal with a specific wavelength is selected and amplified by using the reflection of the diffraction grating provided around the waveguide layer and by changing the current flowing through the active region. What is claimed is: 1. A wavelength selective amplifier characterized in that the diffraction grating is provided with a phase shift portion of π and a plurality of electrodes for flowing a current through the active region are provided.