Vertical Directional Coupler Research Articles

Design of SiON-based grating-assisted vertical directional couplers

In this paper, we present the design of a SiON-based grating-assisted codirectional coupler for dissimilar waveguides, based on an accurate numerical method. All the design parameters, including coupling length and coupling efficiency, have been calculated at the free-space optical wavelength of lambda=1.54 mum for both TE and TM polarisations as a function of grating height, thickness of the coupled slabs, gap thickness between the two coupled planar waveguides. It is shown that efficient (up to 70%) and polarisation independent vertical couplers can be realised.

편광에 관계없이 매우 높은 소멸비와 짧은 길이를 가지는 수직 방향성 결합기 스위치

We propose a novel vertical directional coupler switch using a vertical directional coupler with polarization independent coupling lengths employing the doublesided deep-ridge waveguide structure. This switch is composed of a switching operation induced section with symmetric structures and an extinction ratio enhanced section with asymmetric structures. We present design methods and examples for this switch with very short lengths and very high extinction ratios larger than 30 dB for both TE and TM modes in cases of both cross and bar states.

Double-Sided Deep-Ridge 도파관 구조 수직 방향성 결합기의 날개구조부 폭과 두께가 편광 특성에 미치는 영향

Double-Sided Deep-Ridge(DSDR) 수직 방향성 결합기의 날개구조부 폭과 두께가 편광에 따른 결합길이에 미치는 영향에 관하여 연구하였다. 날개구조부가 존재하지 않는 DSDR 수직 방향성 결합기는 편광에 무관한 결합길이를 가질 수 없음을 볼 수 있었다. 일정한 날개구조부 두께에 대하여 날개구조부 폭이 특정 길이 이상이 되면 TE 모드와 TM 모드의 결합길이의 변화는 거의 없으며 또한 두 모드의 결합길이의 차이도 거의 발생하지 않음을 볼 수 있었다. 따라서 편광에 무관한 결합길이를 가지는 DSDR 수직 방향성 결합기를 구현하기 위한 최소 날개구조부 폭이 존재함을 볼 수 있었다. 이러한 최소 날개구조부 폭은-같은 코어 두께에 대해서는 날개구조부 두께가 증가할수록, 같은 날개구조부 두께에 대해서는 코어 두께가 감소할수록-증가함을 볼 수 있었다. 또한 최소 날개구조부 두께는 코어의 두께에 의하여 결정됨을 볼 수 있었고 코어의 두께가 증가할수록 최소 날개구조부 두께는 감소함을 볼 수 있었다. We investigate the effect of the wing width and thickness of a Double-Sided Deep-Ridge(DSDR) vertical directional coupler on the coupling length dependent on the polarization, We have found that the DSDR vertical directional coupler without a wing does not have polarization independent coupling lengths. The variation of the coupling length of TE and TM modes and the difference between the coupling lengths of the two modes are negligible as the wing width increases beyond the specific wing width for the same wing thickness. Thus, we can see that a DSDR vertical directional coupler has a wing width larger than the minimum wing width to obtain the polarization independent coupling length. The minimum wing width increases as the wing thickness increases for the same core thickness and as the core thickness decreases for the same wing width. Also, we have found that the minimum wing thickness is determined by the core thickness and the minimum wing thickness decreases as the core thickness increases.

편광에 관계없이 매우 짧은 결합길이를 가지는 Double-Sided Deep-Ridge 도파관 구조 수직 방향성 결합기의 소멸비 향상

편광에 관계없이 매우 짧은 결합 길이를 가지는 Double-Sided Deep-Ridge (DSDR) 도파관 구조를 가지는 수직 방향성 결합기의 두 코어 굴절율에 약간의 비대칭성을 줌으로써 편광에 관계없이 소멸비가 크게 향상됨을 보였다. 내부 클래딩의 두께와 두 코어의 두께가 감소할수록 두 코어는 강하게 결합되기 때문에 최대 소멸비를 보이는 두 코어 사이의 굴절율의 비대칭값과 30 ㏈ 이상의 소멸비를 보이는 코어 굴절율의 공차는 증가한다. 또한 내부 클래딩의 두께와 두 코어의 두께가 감소할수록 두 코어사이의 결합이 강하게 되어 결합기 길이와 30 ㏈ 이상의 소멸비를 가지는 결합길이의 공차는 감소한다. 편광에 관계없이 100 <TEX>$\mu\textrm{m}$</TEX> 이하의 매우 짧은 소자길이를 가지며 30 ㏈ 이상의 매우 높은 소멸비를 가지는 DSDR수직 방향성 결합기를 구현할 수 있음을 보였다. We show that the extinction ratio is improved using slight asymmetry in two core refractive indices of polarization independent very short vertical directional couplers with the double-sided deep-ridge (DSDR) waveguide structure. The optimum asymmetry with the maximum extinction ratio and the tolerance of the refractive index of core with the extinction ratio larger 1ha]1 30 ㏈ increase as the thickness of inner cladding layer and the two cores decrease due to the increase of the coupling strength between the two cores. Also, the device length and the tolerance of the device length with the extinction ratio larger than 30 ㏈ decrease as the thickness of the inner cladding layer and the two cores decrease due to the increase of the coupling strength between the two cores. We show that polarization independent vertical directional couplers with the DSDR waveguide structure with the device length less than 100 <TEX>${\mu}{\textrm}{m}$</TEX> and the extinction ratio larger than 30 ㏈ could be implemented.

편광에 무관한 매우 짧은 결합 길이를 가지는 새로운 수직 방향성 결합기

편광에 따른 성능 변화가 작은 deep-ridge 도파관 구조에 제작이 용이한 double-sided 프로세스를 이용하여 구현할 수 있는 편광에 무관한 매우 짧은 결합 길이를 가지는 double-sided deep-ridge 도파관 구조를 가지는 새로운 수직 방향성 결합기를 제안하고 여러 가지 구조 파라미터들이 결합길이에 미치는 영향에 대하여 연구하였다. 도파관 폭의 변화에 대한 결합길이의 변화는 코어 두께의 변화에 대한 결합길이의 변화보다 작게 나타나는 것을 볼 수 있었다. 내부 클래딩 영역의 두께가 감소할수록, 코어 두께가 감소할수록 결합 길이가 감소함을 볼 수 있었다. 또한 같은 코어 두께에 대해서는 내부 클래딩 영역의 두께가 감소할수록, 같은 내부 클래딩 영역의 두께에 대해서는 코어 두께가 감소할수록 편광에 관계없이 결합 길이가 같아지는 도파관 폭이 작아짐을 볼 수 있었다. We propose a novel vertical directional coupler with polarization independent very short coupling lengths using the double-sided deep-ridge waveguide structure which could be implemented using double-sided process to polarization insensitive deep-ridge waveguide structures and investigate the effect of various structure parameters on the coupling length. Variation of coupling length for the variation of the waveguide width is smaller than that for the variation of the core thickness. Coupling length decreases as the inner cladding layer thickness and the core thickness decrease. The waveguide width with the polarization independent coupling length decreases as the inner cladding layer thickness decreases for the same core thickness and the core thickness decreases for the same inner cladding layer thickness.

Vertical optical directional coupler

A method for fabricating optical directional couplers by combining thermal and field assisted ion exchange processes is presented. Modeling, design, fabrication, and test methods are discussed. Thi...

A novel vertical directional coupler switch with switching-operation-induced section and extinction-ratio-enhanced section

A novel vertical directional coupler switch with a switching-operation-induced section and an extinction-ratio-enhanced section is proposed. Switching operation is achieved by changing the refractive indexes of both cores in the switching-operation-induced section, and an improvement of extinction ratios larger than 30 dB for both cross and bar states is achieved by controlling the asymmetry of the refractive indexes of two cores in the extinction-ratio-enhanced section without changing the refractive index of the inner-cladding layer between the two waveguides. The required refractive indexes for the cores in the switching-operation-induced and extinction-ratio-enhanced sections are calculated for various thickness of the inner-cladding layer.

A Novel Vertical Directional Coupler Switch with Switching Operation-Induced, Extinction Ratio-Adjusted, and Extinction Ratio-Enhanced Sections

We propose a novel very short (< 300 µm) vertical directional coupler switch with high extinction ratios larger than 30 dB. The device consists of a switching operation induced section (SOIS), an extinction ratio adjusted section (ERAS), and an extinction ratio enhanced section (ERES). These are achieved by changing the refractive index of one core. The switching operation is induced by changing the refractive index of one core in the SOIS. The improvement of extinction ratios larger than 30 dB for both the cross and bar states is made by controlling the asymmetry of the refractive indices of both cores in the ERES. Through the ERAS, different extinction ratios between the cross and bar states at the end of the SOIS are changed to the same value. For this reason, the optimum asymmetry of the refractive indices of the cores for the maximum extinction ratios and the lengths of ERES are the same for cross and bar states. Design guidelines for high extinction ratios with large tolerances are presented.

Interface of directly bonded InP wafers for vertical couplers

Vertical directional couplers fabricated using direct wafer bonding have demonstrated a very short coupling length and a small excess optical loss introduced by the bonded interface layer. The structure of the interface of directly bonded InP wafers is investigated. Dislocations at the interface are found to accommodate the tilt misorientation between the two wafers without introducing extra misfit. Body-centered-tetragonal In inclusions of a size of few nanometers are identified at the interface. The excess optical loss of the coupler based on directly bonded InP wafers due to the formation of these inclusions may be eliminated by using lower temperature and a phosphor atmosphere for direct bonding.

BPM Analysis of an Integrated Optical Switch using Polymeric Optical Waveguides and SSFLC at 1.55 µm

An optical switch using polymeric waveguides and ferroelectric liquid crystals (FLC) has been modelled by using a 3D vectorial beam propagation method (BPM) at the wavelength of 1.55 µm used in optical communications. The switch structure is a vertical directional coupler consisting of a surface stabilised FLC (SSFLC) embedded between two polymeric optical waveguides and ITO layers as electrodes. A polymeric buffer layer has been introduced to reduce losses due to ITO absorption. Polymeric waveguides and buffers used in our analysis can be obtained by different compositions of P(PFS-GMA) (poly(pentafluorostyrene-co-glycidyl methacrylate)). Several devices have been modelled with different values of the refractive indexes of the individual layers. Simulations show the benefits in terms of loss reduction due to the presence of the buffer. An optimised device presents an extinction ratio of more than 50 dB and losses lower than 1 dB with a coupling length of only 174 µm.

Ultra Short Two-Section Vertical Directional Coupler Switches with High Extinction Ratios

We show that both cross and bar states with high extinction ratios larger than 30 dB can be achieved at the same end of ultra short fused vertical directional coupler switches (FVCSs) with two sections by changing the refractive indices of cores and inner cladding layer less than 1%. The improvement of extinction ratios for various combinations of the refractive indices in a two-section FVCS is studied using the improved coupled theory and beam propagation method. Design guidelines to achieve high extinction ratios with large tolerances are presented.

Improved Extinction Ratios for Both Cross and Bar States Using Two-Section Ultra Short Vertical Directional Couplers

We show that both cross and bar states with high extinction ratios larger than 30 dB can be achieved in ultra short vertical directional couplers with two sections. Various combinations of the refractive indices in the two sections are studied using the improved coupled mode theory and the beam propagation method. Design guidelines to achieve high extinction ratios with large tolerances are presented.

Design of an Ultrashort Directional Coupler With an SSFLC Coupling Layer

A design of a vertical directional coupler, operating at the wavelength λ= 632.8 nm, is presented. The coupler consists of a layer of the Hoechst ferroelectric liquid crystal mixture FELIX-M4851–025, homogeneously aligned and sandwiched between two single mode ion-exchanged BK7 glass waveguides. The design of the directional coupler was carried out by using the beam propagation method, taking into account also teflon alignment layer and ITO electrode contributions. Given the FLC mixture refractive indices, n o =1.611 and n o = 1.466 at λ= 632.8 nm and T= 25°C, calculations show that less than 60 μm coupling length, with an extinction ratio higher than 21 dB can be obtained by using single mode waveguides with a refractive index change at the surface Δn= 0.013, an FLC layer 2 μm thick, and cone axis tilted by about 19° from the propagation direction of the lightwave.

Fused vertical couplers

A vertical directional coupler fabricated using wafer fusion is demonstrated with a very short coupling length of 62 μm. The optical propagation loss introduced by the fused layer is investigated. An excess loss of 1.1 dB/cm at 1.55 μm was measured for waveguides which incorporate a fused junction near the core region. Fused vertical couplers make it possible to realize three-dimensional waveguide structures and compact switching arrays and they solve some of the topology problems of large switch arrays.

Wafer-fused optoelectronics for switching

Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 /spl mu/m and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 /spl mu/m wavelength. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 /spl mu/m gap layer exhibit a coupling length of 62 /spl mu/m and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed.

Ultrashort low-loss optical multiquantum-well GaAs/GaAlAsvertical directional coupler switch

An optical GaAs/GaAlAs multiquantum-well vertical directional coupler switch with a device length of 85 µm is presented. At a wavelength of 854 nm the voltage necessary for switching was 5 V, associated with a transmission loss of only 2 dB in the switched state and an extinction ratio of greater than 10 dB. The device parameters were chosen so as to enable monolithic integration.

Low-voltage vertical directional coupler switch with suppressed electroabsorption

We have studied the performance of a vertical directional coupler in which a multiple quantum well and a bulk semiconductor material act as the cores of the two guides in two arms. The power output of the device is expected to be unaffected by the electroabsorption effect in a directional coupler based on quantum confined Stark effect even when operated very close to the excitonic absorption edge. The above principle is utilized in realizing low-voltage switching and almost equal power in bar and cross states in a multiple-quantum-well (MQW) vertical directional coupler. Our calculation for a vertical coupler composed of InGaAsP bulk and InGaAsP-InP MQWs show switching voltages comparable to that of a similar coupler composed of a more complex barrier reservoir and quantum well electron transfer (BRAQWET) structure, with a slightly lower value of power output.

Improved vertical directional coupler for optimum edge coupling to an embedded photodetector

An improved vertical coupling structure, consisting of a graded-index planar buried waveguide in glass and a dielectric overlayer, is designed and realized to provide an optimum edge coupling to a modeled GaAs photodetector. Calculations of the attenuation coefficient and coupling efficiency show an optimum absorption behavior. Normal-mode measurements and beam-propagation calculations of the coupling length and power transfer ratio are compared.

A novel vertical Δκ directional coupler switch using liquid crystals

To decrease the switching length of the directional coupler switch and to use the advantages of the electro-optic properties of (LC's), we propose a novel vertical /spl Delta//spl kappa/ directional coupler switch using LC's and present the calculated results relevant to the design considerations. Because of the large birefringence of LC's, a very short switching length less than 60 /spl mu/m is possible. Besides, a N/spl times/N switch is also proposed for practical applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

SSFLC optical directional coupler switch with a short device length: a proposal

A novel vertical directional coupler waveguide switch composed of ferroelectric liquid crystal (FLC) is proposed and analyzed. The surface stabilized ferroelectric liquid crystal break (SSFLC) is used as an active separation layer between passive waveguides. To decrease the switching length, the waveguide switch is based on the power crossing the separation layer rather than coupling between waveguides. The calculated results relevant to the switch parameters such as the switching length, switching time, capacitance, and extinction ratio are presented. Because of the large birefringence of FLC, a very short switching length, less than 60 /spl mu/m, is possible.