JPH0653591A - Element for converting optical frequency - Google Patents

Abstract

PURPOSE:To make it possible to sweep the wavelength of conversion light over a wide range by forming diffraction gratings partially or totally on the inactive waveguide layers on the front and rear sides, and by forming each of the diffraction gratings by repeating in different cycles the provision of the area in which the pitches vary continuously. CONSTITUTION:An element for converting the optical frequency having a semiconductor laser structure of a distributional reflectance comprises an active waveguide layer 2, an inactive waveguide layer 3, a cladding layer 4, a capping layer 5, current block layers 6 and 7, an n type electrode 8 and a p type electrode 9 on an n type InP base board 1. On both sides of the active area formed by a gain region 101, and a saturable absorption region 102, the areas 103 and 104 for a distributional reflectors are arranged on the front and rear sides. At the same time, adjacent to the area 104 for the distributional reflector, a phase adjustment area 105 is arranged. In this case, it is assumed that diffraction gratings 11a and 11b are formed partially or totally on the inactive waveguide layer 3. Each of the diffraction gratings is formed by repeating at first and second cycles the provision of the area in which the pitches vary continuously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency conversion element used for optical switching and optical information processing.

[0002]

2. Description of the Related Art Conventional optical frequency conversion elements intended for use in the fields of optical switching and optical information processing are described in H. Kawa.
guchi et al.'s report (IEEE Journal of Quantum Electronic
s, vol.24, pp.2153-2159, 1988) and a multi-electrode distributed feedback laser structure with a saturable absorption region, and a report by Nobehara et al.
4, c-160).

[0003]

However, in the conventional optical frequency conversion element, since the pitch of the diffraction grating formed in the inactive waveguide region is uniform, λ = 2Λneq (Λ:
The sweep width of the converted light wavelength in the vicinity of the Bragg wavelength λ, which is determined by the pitch of the diffraction grating, neq: equivalent refractive index, is the electrical equivalent refractive index change Δneq of the equivalent refractive index neq of the inactive waveguide region.
Was decided by. Therefore, the maximum refractive index change Δn / n of the semiconductor due to the normal current injection is about 1%, and thus the wavelength sweep width of the optical frequency conversion element of the above-mentioned conventional example is theoretically 1%.
It stayed at about 0 nm, and in the element actually reported, the converted light wavelength sweep width was about 3 nm. In consideration of applications to optical wavelength division multiplexing communication systems, optical switching, etc., it is necessary to further expand the conversion light wavelength sweep width.

In view of the above-mentioned problems, an object of the present invention is to provide the same amount of change in the equivalent refractive index of the non-active waveguide region as the conventional one,
An object of the present invention is to provide an optical frequency conversion device capable of sweeping a wavelength of a wideband conversion light over the gain bandwidth of the active waveguide region.

[0005]

In order to achieve the above object, according to claim 1 of the present invention, a diffraction grating is formed in a part or all of the front and rear inactive waveguide regions,
In the diffraction grating formed in the inactive waveguide region on the front side, a region in which the pitch continuously or intermittently changes from Λa to Λb is repeatedly formed with a period Mf (where Mf> Λa, Λb). In the diffraction grating formed in the non-active waveguide region on the side, the region where the pitch changes continuously or intermittently from Λa ′ to Λb ′ has a period Mr (where Mr>
Λa ′, Λb ′) are repeatedly formed, and the refractive indices of the front and rear inactive waveguide regions are electrically independently controlled to change the oscillation wavelength. According to claim 2, in the optical frequency conversion element according to claim 1,
Between the active region and the diffraction grating optical waveguide region, there is a phase adjustment region that is a non-active waveguide in which no diffraction grating is formed, and by adjusting the current value flowing through the electrode provided in the phase adjustment region, , The fine adjustment of the converted light wavelength was made possible.

[0006]

According to claim 1 of the present invention, in the distributed reflector region on the front side, as shown in FIG. 2, a region in which the pitch of the diffraction grating continuously changes from Λa to Λb is repeatedly formed with a period Mf. Therefore, the reflection characteristic of the distributed reflector region is, as shown in FIG. 3 (a), the wavelength interval Δλf = λo ² between the wavelength λa = 2Λaneq and the wavelength λb = 2Λbneq.
/ 2neqMf (λo = neq (Λa + Λb)) has a characteristic having a periodic reflection peak. Therefore, for convenience, the wavelengths of the reflection peak points are set to λ1 to λn. Similarly, the reflection characteristic of the distributed reflector on the rear side has a wavelength interval Δλ between the wavelength λa ′ = 2Λa′neq and the wavelength λb ′ = 2neqΛb ′.
r = λo ² / 2neq Mr with periodic reflection peaks λ1′˜
The characteristic has λk ′. Here, the pitch modulation periods Mf and Mr of the diffraction grating in the front and rear distributed reflection regions are formed in different periods.

Therefore, if the refractive indices of the front and rear distributed reflector regions are electrically controlled independently, λ1
Λ1 ′ to λ for one wavelength λi (i = 1 to n) of
One of k'can be tuned to oscillate only near its λi. Figure 3 (b) shows λ1 and λ2
2 shows an example of oscillation of i.e., i is 1 and 2. As shown in the figure, λ1 = λ1 ′ or λ2 = λ2
By adjusting the equivalent refractive index of the front and rear distributed reflector regions so as to be ', laser oscillation can be performed only in the vicinity of λ1 or λ2.

By setting λ1 to λn and λ1 'to λk' to such an extent that the gain band of the semiconductor can be covered, it is possible to control the wavelength of the converted light that covers the gain band and obtain a wide band converted wavelength sweep.

Further, by controlling the refractive index of the phase adjusting region in which the diffraction grating is not formed in the non-active region waveguide layer independently of the above-mentioned distributed reflector region, in the vicinity of the above-mentioned wavelength λi. The oscillation wavelength can be continuously swept, so that the converted light wavelength can be set in the wavelength range of λ1 to λ2.

[0010]

1 is a structural diagram of an embodiment of an optical frequency conversion device having a distributed Bragg reflector semiconductor laser structure according to the present invention. In FIG. 1, 1 is an n-type InP substrate, 2 is an InGaAsP active waveguide layer having a bandgap wavelength of 1.55 μm, 3
Is an InGaAsP inactive waveguide layer having a bandgap wavelength of 1.3 μm, 4 is a p-type InP cladding layer, 5 is a p + -type InGaAsP cap layer, 6 is a p-type InP current blocking layer, 7 is an n-type current blocking layer, 8 Is an n-type electrode, 9 is p
The pattern electrode 10a is a portion in which a diffraction grating region whose pitch continuously changes from Λa to Λb is repeatedly formed with a period Mf, and 10b is a diffraction grating region whose pitch continuously changes from Λa 'to Λb'. A portion which is repeatedly formed with a period Mr, 11 is a coupling portion between an active waveguide layer and an inactive waveguide layer, 101 is a gain region, 102 is a saturable absorption region, 10
3 and 104 are front and rear distributed reflector regions, and 105 is a phase adjustment region.

A method of manufacturing the optical frequency conversion element having the distributed Bragg reflector laser structure of the above embodiment will be briefly described. First, n-type InP is formed by using a metalorganic vapor phase epitaxial growth method.
The active waveguide layer 2 and the inactive waveguide layer 3 are formed on the substrate 1. After that, the pattern of the diffraction grating whose pitch is modulated is transferred to the resist applied on the surface of the inactive waveguide layer 3 by the electron beam exposure method, and the transferred pattern is used as a mask to perform the diffraction of the portions 10a and 10b by etching. Form a grid. Then, the waveguide is processed into a stripe shape to control the transverse mode, and the p-type InP current block layer 6, the n-type current block layer 7, and the p-type InP clad layer 4 are again formed by using the metalorganic vapor phase epitaxial growth method. , And p + type InGaAsP cap layer 5 are sequentially manufactured. Then, a p-type electrode 9 and an n-type electrode 8 are formed, and a distributed reflector region having a gain region 101 including the active waveguide layer 2, a saturable absorption region 102, and portions 10a and 10b in which a diffraction grating is formed. In order to electrically isolate 103 and 104 and the phase adjusting region 105 having the non-active waveguide layer 3 in which the diffraction grating is not formed from each other, the p-type electrodes 9 and p above their coupling portions are provided.
The + type InGsAsP cap layer 5 is removed.

In the diffraction grating of the optical frequency conversion element having the distributed Bragg reflector semiconductor laser structure of the present embodiment, in the portion 10a, regions in which the pitch continuously changes from 245.9 nm to 238.9 nm are repeatedly formed with a cycle of 75 μm. In the portion 10b, the pitch is from 235.4 nm to 23.
67.5μ period is a region that continuously changes to 8.5nm
It is repeatedly formed by m.

In the optical frequency conversion element having the distributed Bragg reflector semiconductor laser structure having the above-described structure, the hysteresis characteristics shown in FIG. 4 are obtained by injecting current into the gain region 101 and the saturable absorption region 102 at a predetermined ratio. obtain. When the present element is biased in the state A of FIG. 4 and the signal light 21 is input from the end surface of the distributed reflector region 104 on the rear side as shown in FIG. 5, the saturable absorption region 102 is excited and the device oscillates (state B). , Converted light 22 from the end surface of the front distributed reflector region 103
Is output. The wavelength of the converted light is changed by independently flowing a current or applying a voltage to the distributed reflector regions 103 and 104 and the phase adjustment region 105. The converted light wavelength when the current of the distributed reflector region 104 is changed in a state where a constant current is passed through the active region 101 and the saturable absorption region 102 and no current is passed through the distributed reflector region 103 and the phase adjustment region 105. FIG. 6 shows the state of the change of. As shown in FIG. 6, in the optical frequency conversion element having the distributed Bragg reflector semiconductor laser structure of the present embodiment, the converted light wavelength is changed from 1.575 μm to 1.75 by passing a current through the distributed reflector region 104.
A wavelength sweep of up to 45 nm is obtained, changing up to 530 μm about every 5 nm. Further, by controlling the currents flowing through the distributed reflector region 103 and the phase adjusting region 105, respectively, the converted light wavelength can be changed over the entire range of 45 nm.

In the above embodiment, the active waveguide layer,
Also, the case where the inactive waveguide layer is composed of a single semiconductor layer has been described, but the present invention can be applied to a structure in which a plurality of semiconductor layers having different compositions are laminated, such as a multiple quantum well structure. Is applicable. Further, the p-type InP current blocking layer 5 and the n-type InP in the above-described embodiment
This embodiment can be applied even to a structure using an Fe-doped InP current blocking layer instead of the current blocking layer 7.

[0015]

As described above, according to the present invention, it is possible to obtain an optical frequency conversion element having a distributed Bragg reflector semiconductor laser structure capable of sweeping a converted light wavelength in a wide band over the gain bandwidth of the active waveguide layer. .

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment of an optical frequency conversion device having a distributed Bragg reflector semiconductor laser structure according to the present invention.

FIG. 2 is a conceptual diagram of a diffraction grating formed in a distributed reflector region in the optical frequency conversion element of the present invention.

FIG. 3 is a diagram showing a method of setting a converted light wavelength by the frequency conversion element of the present invention.

FIG. 4 is a diagram showing hysteresis characteristics of the distributed reflection type semiconductor laser structure optical frequency conversion element of the present invention.

FIG. 5 is a diagram simply showing an optical frequency conversion operation of the optical frequency conversion element according to the present invention.

FIG. 6 is a diagram showing how the oscillation wavelength changes in an example according to the present invention.

[Explanation of symbols]

1 ... n-type InP substrate, 2 ... InGaAsP active waveguide layer, 3 ... InGaAsP inactive waveguide layer, 4 ... p-type In
P clad layer, 5 ... p + type InGaAsP cap layer,
6 ... p-type InP current blocking layer, 7 ... n-type InP current blocking layer, 8 ... n-type electrode, 9 ... p-type electrode, 10a ... regions in which the pitch changes from Λa to Λb are repeatedly formed with a cycle Mf. Diffraction grating part, 10b ... Pitch is Λ
A portion of the diffraction grating in which a region varying from a ′ to Λb ′ is repeatedly formed with a period Mr, 11 ... A coupling portion between an active waveguide layer and an inactive waveguide layer, 101 ... An active region, 102
... saturable absorption region, 103 ... front distributed reflector region, 10
4 ... Rear distributed reflector region, 21 ... Signal light, 22 ... Converted light.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yuzo Yoshikuni 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. An optical frequency conversion device having a distributed reflection type semiconductor laser structure having a diffraction grating optical waveguide region optically coupled to an active region on both sides of an active region consisting of a gain region and a saturable absorption region, wherein A diffraction grating is formed in a part or all of the rear inactive waveguide region, and the diffraction grating formed in the front inactive waveguide region changes in pitch continuously or intermittently from Λa to Λb. Region is repeatedly formed with a period Mf (where Mf> Λa, Λb), and the diffraction grating formed in the inactive waveguide region on the rear side is continuous or intermittent with a pitch from Λa 'to Λb'. The region that changes to is the period Mr (where Mr> Λa ′, Λb ′)
It is characterized in that the converted light wavelength is changed by controlling the refractive index of the front and rear inactive waveguide regions independently by injecting current or applying voltage. Optical frequency conversion element. 2. A phase adjustment region, which is a non-active waveguide in which no diffraction grating is formed, is provided between the active region and the diffraction grating optical waveguide region, and a current value flowing through an electrode provided in the phase adjustment region. 2. The optical frequency conversion element according to claim 1, wherein the wavelength of the converted light can be finely adjusted by adjusting.